TIMING ADJUSTMENT CONTROL FOR EFFICIENT TIME DIVISION DUPLEX COMMUNICATION

Abstract: A system for time division duplex communication over a single frequency band wherein guard time overhead is reduced by active adjustment of reverse link transmission timing as a function of round trip propagation delay. Responding to a polling message from the base station, a user station seeking to establish communication transmits a reply message. The base station using a propagation delay calculator (812) calculates the distance of the user station by measuring the propagation delay with respect to receipt of the reply message and a timing control unit (806) and transmitter (807) for sending a timing adjustment command to the user station instructing it to advance or retard its timing. Thereafter, the base station monitors the user station transmissions and periodically commands it to adjust its timing in a like manner. The user station transmits a control preamble at the start of each time slot to allow the base station to perform round trip timing calculations and adjustment of the user station's power or antenna selection.

Description: DESCRIPTION Timing Adjustment Control for Efficient Time Division Duplex Communication 5 Background of the Invention Field of the Invention The field of the present invention pertains to communications and, more particularly, to an air interface 10 structure and protocol suitable for use in a cellular communication environment. Description of Related Art A growing demand for flexible, mobile communication has 15 led to development of a variety of techniques for allocating available communication bandwidth among a steadily increasing number of users of cellular services. Two conventional techniques for allocating communication bandwidth between a cellular base station and a set of cellular user stations 20 (also called "mobile stations") are frequency division duplex (FDD) and time division duplex (TDD) . As used herein, FDD refers to a technique for establishing full duplex communications having both forward and reverse links separated in frequency, and TDD refers to a 25 technique for establishing full duplex communications having both forward and reverse links occurring on the same frequency but separated in time to avoid collisions. Other techniques for communication are time division multiple access (TDMA) , wherein transmissions by a plurality of users are separated in 30 time to avoid conflicts, frequency division multiple access (FDMA) , wherein transmissions by a plurality of users are separated in frequency to avoid conflicts, and time division ' multiplex (TDM), wherein multiple data streams are time multiplexed together over a single carrier. Various * 35 combinations of FDD, TDD, FDMA, and TDMA may also be utilized. In a particular FDD technique, a base station is allocated a set of frequencies over which it may transmit, using a different frequency slot for each user station, and each user station is allocated a different frequency over which it may transmit to the base station. For each new user in contact with a base station, a new pair of frequencies is required to support the communication link between the base station and the new user station. The number of users that can be supported by a single base station is therefore limited by the number of available frequency slots. In a particular TDD technique, the same frequency is used for all user stations in communication with a particular base station. Interference between user stations is avoided by requiring that user stations transmit at different times from one another and from the base station. This is accomplished by dividing a time period into a plurality of time frames, and each time frame into a plurality of time slots. Typically, the base station communicates with only one user station during a time slot, and communicates with all the user stations sequentially during different time slots over a single time frame. Thus, the base station communicates with a particular user station once during each time frame. In one version of the described system, the base station is allocated a first portion of each time slot during which the base station transmits to a particular user station, and the user station is allocated a second portion of the time slot during which the user station responds to the base station. Thus, the base station may transmit to a first user station, await a response, and, after receiving a response from the first user station, transmit to a second user station, and so on, until the base station has communicated with all user stations sequentially over a particular time frame. Time division duplex has an advantage over FDD and FDMA of requiring use of only a single frequency bandwidth. However, a drawback of many conventional TDD or TDMA systems is that their efficiency suffers as cell size increases. The reduction in efficiency stems from the relatively unpredictable nature of propagation delay times of transmissions from the base station over air channels to the user stations, and from the user stations over air channels back to the base station. Because user stations are often mobile and can move anywhere within the radius of the cell covered by a base station, the base station generally does not know in advance how long the propagation delay will be for communicating with a particular user station. In order to plan for the worst case, conventional TDD systems typically provide a round-trip guard time to ensure that communication will be completed with the first user station before initiating communication with the second user station. Because the round-trip guard time is present in each time slot regardless of how near or far a user station is, the required round-trip guard time can add substantial overhead, particularly in large cells. The extra overhead limits the number of users, and hence the efficiency, of TDD systems. Figure 1 is an illustration of the basic round trip timing for a TDD system from a base station perspective. A polling loop 101, or time frame, for a base station is divided into a plurality of time slots 103. Each time slot 103 is used for communication from the base station to a particular user station. Thus, each time slot comprises a base transmission 105, a user transmission 107, and a delay period 106 during which the base transmission 105 propagates to the user station, the user station processes and generates a responsive user transmission 107, and the user transmission 107 propagates to the base station. If the user station is located right next to the base station, then the base station can expect to hear from the user station immediately after finishing its transmission and switching to a receive mode. As the distance between the user station and the base station grows, the time spent by the base station waiting for a response grows as well. The base station will not hear from the user station immediately but will have to wait for signals to propagate to the user station and back. As shown in Fig. 1, in a first time slot 110 the user transmission 107 arrives at the base station at a time approximately equidistant between the end of the base transmission 105 and the start of the user transmission 107, indicating that the user station is about half a cell radius from the base station. In a second time slot 111, the user transmission 107 appears very close to the end of the base transmission 105, indicating that the user station is very close to the base station. In a third time slot 112, the user transmission 107 appears at the very end of the time slot 112, indicating that the user station is near or at the cell boundary. Because the third time slot 112 corresponds to a user station at the maximum communication distance for a particular base station, the delay 106 shown in the third time slot 112 represents the maximum round-trip propagation time and, hence, the maximum round-trip guard time. In addition to propagation delay times, there also may be delays in switching between receive and transmit mode in the user station, base station, or both, which are not depicted in Fig. 1 for simplicity. Typical transmit/receive switching times are about two microseconds, but additional allocations may be made to account for channel ringing effects associated with multipath. As cell size increases, TDD guard time must increase to account for longer propagation times. In such a case, guard time consumes an increasingly large portion of the available time slot, particularly for shorter round trip frame dura- tions. The percentage increase in time spent for overhead is due to the fact that TDD guard time is a fixed length, determined by cell radius, while the actual round trip frame duration varies according to the distance of the user station. Consequently, as cells get larger, an increasing amount of time is spent on overhead in the form of guard times rather than actual information transfer between user stations and the base station. One conventional TDD system is the Digital European Cordless Telecommunications (DECT) system developed by the European Telecommunications Standards Institute (ETSI) . In the DECT system, a base station transmits a long burst of data segmented into time slots, with each time slot having data associated with a particular user station. After a guard time, user stations respond in a designated group of consecutive time slots, in the same order as the base station sent data to the user stations. Another system in current use is the Global System for Mobile communications ("GSM") . Figure 4 illustrates a timing pattern according to certain existing GSM standards. According to these standards, communication between a base station and user stations is divided into eight burst periods 402. Up to eight different user stations can communicate with a base station, one in each burst period 402. GSM standards require two separate frequency bands. The base station transmits over a first frequency F A , while the user stations transmit over a second frequency F B . After a user station receives a base transmission 405 on the first frequency F A during a particular burst period 402, the user station shifts in frequency by 45 MHz to the second frequency F B and transmits a user transmission 406 in response to the base transmission 405 approximately three burst periods 402 later. The three burst period delay is assumed to be large enough to account for propagation time between the base station and the user station. It is important in the GSM system that the user transmissions 406 received at the base station fit into the appropriate burst periods 402. Otherwise, the user transmissions 406 from user stations using adjacent burst periods 402 could overlap, resulting in poor transmission quality or even loss of communication due to interference between user stations. Accordingly, each burst period 402 is surrounded by a guard times 407 to account for uncertain signal propagation delays between the base station and the user station. By comparing the time of the signal actually received from the user station 302 to the expected receive time, the base station may command the user station to advance or retard its transmission timing in order to fall within the proper burst period 402, a feature known as adaptive frame alignment. A specification relating to adaptive frame alignment for the GSM system is TS GSM 05.10. A drawback of the described GSM system is that it requires two separate frequency bands. It also has a relatively rigid structure, which may limit its flexibility or adaptability to certain cellular environments. Another system in presence use is known as Wide Area Coverage System (WACS) , a narrowband system employing aspects of both FDMA and TDMA. Under WACS, as in GSM, two distinct frequency bands are used. One frequency band is used for user station transmissions, and the other frequency band is used for base station transmissions. The user station transmissions are offset by one-half of a time slot from the corresponding base station transmissions, in order to allow for propagation time between the base station and the user station. Standard WACS does not support spread spectrum communication (a known type of communication wherein the bandwidth of the transmitted signal exceeds the bandwidth of the data to be transmitted) , and has an overall structure that may be characterized as relatively rigid. In a number of systems, the channel structure is such that a user station may have to transmit a response to a base station while receiving information on another channel. The capability for simultaneous transmission and reception generally requires the use of a diplexer, which is a relatively expensive component for a mobile handset. It would be advantageous to provide a flexible system having the benefits of time division duplex communication, particularly in large cells, but without having an overhead of a full round-trip guard time in every time slot. It would further be advantageous to provide such a system requiring only a single frequency band for communication. It would further be advantageous to provide a TDMA or combination TDMA/FDMA system wherein user stations are not required to be fitted with a diplexer. It would further be advantageous to provide a time frame structure readily adaptable to single or multiple frequency bands, and for use in either a variety of communication environments. Summary of the Invention The present invention in one aspect provides an efficient means for carrying out time division multiplexed communication, particularly in large cell environments. In one embodiment, in a first portion of a time frame, a base station issues consecutive base transmissions directed to each of the communicating user stations. A single collective guard time is allocated while the base station awaits a response from the first user station. The user stations then respond, one by one, in allocated time slots on the same frequency as the base station, with only minimal guard times between each reception. In order to prevent interference among the user transmissions, the base station commands the user stations to advance or retard their transmission timing. To initiate communication between a base station and a user station, each base transmission may have a header indicating whether or not the slot pair is unoccupied. If a slot pair is free, the user station responds with a brief message in its designated portion of the slot pair. The user portion of the slot pair includes a full round-trip guard time allowance to account for the uncertain distance between the base station and the user station upon initial communication. The base station compares the actual time of receiving the user transmission with the expected time of reception, and determines how far away the user station is. In subsequent time frames, the base station may command the user station to advance or retard its timing as necessary so that full information messages may thereafter be sent without interference among user stations. In another aspect of the invention, base transmissions are alternated with user transmissions over the same frequency band. The base station and user stations may precede their main data transmissions with a preamble, such as, for example, where desired for synchronization of spread spectrum communication signals or for conducting power control. The preamble may be transmitted at a designated time interval between two data transmissions. The base station may command the user station to advance or retard its timing based on a calculated round-trip propagation time. In other embodiments of the invention, multiple frequency bands are utilized. For example, one frequency band may be used for base station transmissions, and another frequency band may be used for user station transmissions. Reverse-link user station transmissions are offset from the base station transmissions by a predetermined amount. A base station and user stations may transmit a preamble prior to a time slot designated for a main data transmission, and may interleave the preamble in a designated time interval between two time other time slots. The preamble may consist of multiple bursts, one burst from each a different antenna, to allow channel sounding at the target. The base station may command the user station to advance or retard its timing based on a calculation of round-trip propagation delay time. In another aspect of the present invention, a universal frame structure is provided for use in a TDMA or TDMA/FDMA system. A suitable frame structure employing ranging capability may be constructed from timing elements which may include provision for data transmissions, preambles, guard times, and the like. A frame structure may be constructed suitable for operation in various embodiments in either a high tier or a low tier environment, by selecting an appropriate combination of the generic timing elements. A dual-mode base station structure is also provided capable of multiple frequency band operation. The base station takes advantage of a low IF digital correlator design. Further variations, adaptations, details and refinements of the embodiments generally described above are also disclosed in herein. Brief Description of the Drawings The various objects, features and advantages of the present invention may be better understood by examining the Detailed Description of the Preferred Embodiments found below, together with the appended figures, wherein: Figure 1 is an illustration of the basic round trip timing for a prior art TDD system, from a base station perspective. Figure 2 is a graph of round-trip guard time as a percentage of the actual round trip frame duration in the prior art TDD system of Fig. 1. Figures 3A and 3B are diagrams of cellular environments for communication. Figure 4 is an illustration of a timing pattern according to existing GSM standards. Figure 5A is an illustration of the basic round trip timing of a TDD/TDM/TDMA system, from a base station perspective, in accordance with one embodiment of the present invention. Figure 5B is a timing diagram showing an initial communication link-up between a base station 304 and a user station 302. Figure 5C is a timing diagram showing a variation of the TDD/TDM/TDMA system of Fig. 5A using an interleaved symbol transmission format. Figure 5D is a chart comparing performance of the system of Fig. 5A, without forward error correction, and the system of Fig. 5C, with forward error correction. Figure 6 is a graph of round-trip guard time as a percentage of the actual round trip frame duration in the embodiment of Fig. 5A. Figure 7 is an illustration of an alternative timing protocol for reducing total round trip guard time. Figure 8A is a hardware block diagram of a base station in accordance with an embodiment of the invention. Figure 8B is a hardware block diagram of an alternative embodiment of a base station. Figure 9 is a hardware block diagram of a user station in accordance with an embodiment of the present invention. Figure 10A is a diagram of timing sub-elements in accordance with another embodiment of the present invention, and Figures 10B through 10E are diagrams of time frame structures expressed in terms of the timing sub-elements of Fig. 10A. Figure IIA is a diagram of timing sub-elements in accordance with another embodiment of the present invention, and Figures 11B through 11D are diagrams of time frame structures expressed in terms of the timing sub-elements of Fig. 10A. Figures 12A-C are tables of a preferred message formats for base station and user station transmissions. Figures 13A-B are diagrams showing the construction of concatenated preambles, and Figure 13C is a chart comparing preamble performance. Figures 13D-E are graphs comparing preamble performance using matched and mismatched filters. Figures 14-17 are charts comparing various performance aspects of high tier and low tier air interfaces incorporating selected features of the embodiments described herein. Figure 18 is a block diagram of a low IF digital correlator. Figure 19A is a block diagram of a dual-mode base station capable of operating over multiple frequencies and having both spread spectrum and narrowband communication capabilities, and Fig. 19B is a chart showing selected frequencies and other parameters for use in the dual-mode base station of Fig. 19A. Detailed Description of the Preferred Embodiments The present invention provides in one aspect an efficient means for carrying out time division duplex communication, and is well suited for a large cell environment. Embodiments of the invention may take advantage of spread spectrum communication techniques, such as, for example, code division multiple access (CDMA) techniques in which communication signals are encoded using a pseudo-random coding sequence, or may be used in conjunction with frequency division multiple access (FDMA) techniques in which communication signals are multiplexed over different frequencies, or may be used in conjunction with a combination of CDMA, FDMA or other communication techniques. Figure 3A is a diagram of a cellular environment for a communication system having base stations and user stations. In Fig. 3A, a communication system 301 for communication among a plurality of user stations 302 includes a plurality of cells 303, each with a base station 304, typically located at the center of the cell 303. Each station (both the base stations 304 and the user stations 302) generally comprises a receiver and a transmitter. The user stations 302 and base stations 304 may communicate using time division duplex or any of the other communication techniques disclosed herein. Figure 3B is a diagram of a cellular environment in which the invention may operate. As shown in Fig. 3B, a geographical region 309 is divided into a plurality of cells 303. Associated with each cell 303 is an assigned frequency Fl, F2 or F3 and an assigned spread spectrum code or code set Cl through C7. In order to minimize interference between adjacent cells 303, in a preferred embodiment three different frequencies Fl, F2 and F3 are assigned in such a manner that no two adjacent cells 303 have the same assigned frequency Fl, F2 or F3. To further reduce the possibility of intercell interference, different orthogonal spread spectrum codes or code sets Cl through C7 are assigned as shown in adjacent clusters 310. Although seven spread spectrum codes or code sets Cl through C7, which are convenient to form a 7-cell repeated pattern, are shown in Fig. 3B, the number of spread spectrum codes or code sets may vary depending upon the particular application. Further information regarding a particular cellular communication environment may be found in U.S. Application Serial No. 07/682,050 entitled "Three Cell Wireless Communication System" filed on April 8, 1991 in the name of Robert C. Dixon, and in U.S. Application Serial No. 08/284,053 entitled "PCS Pocket Phone/Microcell Communication Over-Air Protocol" filed on August 1, 1994 in the name of Gary B. Anderson et al. , each of which is hereby incorporated by reference as if fully set forth herein. While the use of spread spectrum for carrier modulation is not a requirement for practicing the invention, its use in the cellular environment of Fig. 3B may permit a very efficient frequency reuse factor of N = 3 for allocating different carrier frequencies Fl, F2 and F3 to adjacent cells 303. Interference between cells 303 using the same carrier frequency Fl, F2 or F3 is reduced by the propagation loss due to the distance separating the cells 303 (no two cells 303 using the same frequency Fl, F2 or F3 are less than two cells 303 in distance away from one another) , and also by the spread spectrum processing gain of cells 103 using the same carrier frequencies Fl, F2 or F3. Additional interference isolation is provided through CDMA code separation. TDD or TDMA communication techniques may also be used in conjunction with the cellular architecture of Fig. 3B. In a preferred embodiment of the invention using time division duplex, the same frequency Fl, F2 or F3 is used for all user stations 302 in communication with a particular base station 304. Interference between user stations 302 is avoided by requiring that different user stations 302 do not transmit at the same time, or at the same time as the base station 304. The base station 304 is allocated a first portion of a time slot during which the base station 304 transmits to a particular user station, and each user station 302 is allocated a second portion of the time slot during which it responds. Thus, the base station 304 may transmit to a first user station 302, await a response, and, after receiving a response from the first user station 302, transmit to a second user station 302, and so on. As noted previously with respect to Fig. 1, the mobility of user stations 302 leads to unpredictability in the propagation delay times of transmissions from the base station 304 over air channels to the user stations 302, and from the switch once from transmit to receive mode and back again in a given time frame 501. Also unlike the Fig. 1 system, in which the base station must wait in each time slot 103 for the user station to switch from receive to transmit mode, only the first user station 302 responding in the time frame 501 of the Fig. 5A embodiment potentially adds a receive/transmit switching delay to the system. In the Fig. 5A embodiment, the timing structure is preferably organized such that user-to-base messages from the user stations 302 arriving at the base station 304 during the receiving portion 504 do not overlap. If each user station 302 were to begin reverse link transmissions at a fixed offset from the time of forward link data reception according to its time slot number, overlapping messages and resulting interference would occasionally be seen by the base station 304. To prevent such interference of incoming user transmissions, each user station 302 biases its transmission start timing as a function its own two-way propagation time to the base station 304, as further explained below. Reverse link messages thus arrive in the receiving portion 504 of the time frame 501 at the base station 304 in sequence and without overlap. In order to allow for timing errors and channel ringing, abbreviated guard bands 512 are provided between each pair of receive time slots 511. These abbreviated guard bands 512 are significantly shorter than the maximum round trip guard time 106 as described with respect to Fig. 1. To bias its transmission start timing, in a preferred embodiment the base station 304 is provided with means for determining round trip propagation delay to each user station 302. A round trip timing (RTT) measurement is preferably accomplished as a cooperative effort between the base station 304 and the user station 302 and therefore comprises a communication transaction between the base station 304 and the user station 302. An RTT transaction may be done upon initial establishment of communication between a base station 304 and a user station 302, and periodically thereafter as necessary. The measured round-trip time from the RTT transaction may also be averaged over time. In an RTT transaction, the base station 304 sends an RTT command message instructing the user station 302 to return a short RTT reply message a predetermined delay period ΔT after reception. The predetermined delay period ΔT may be sent as part of the RTT command message, or may be pre-programmed as a system parameter. The base station 304 measures the time at which it receives the RTT reply message. The base station 304 then computes the propagation delay to the user station 302 based on the time of sending the RTT command message, the predetermined delay period ΔT, and the time of receiving the short RTT reply message. Once the base station 304 has computed the propagation delay to the user station 302, the base station 304 then sends a bias time message to the user station 302 either informing the user station 302 of the propagation delay measured in the RTT transaction, or providing a specific timing adjustment command. The user station 302 thereafter times its transmissions based on the information contained in the bias time message. Once timing has been established in such a manner, the base station 304 may periodically command the user station 302 to advance or retard its transmission timing to keep reverse link TDMA time slots aligned. The mechanics of adjusting the timing responsive to the timing adjustment commands may be similar to the techniques conventionally employed in the GSM system generally described elsewhere herein. Timing adjustment command control may be carried out, for example, according to the techniques described in GSM specification TS GSM 05.10, which is incorporated by reference as if set forth fully herein. After a response from the user stati n 302 is received at the base station 304, the base station 304 may maintain closed loop control over the timing of the user station 302 by adjusting timing of the user station transmission as often as each time frame 501 if necessary. that the corresponding time slot pair 510, 511 is available or unoccupied, the user station 302 attempts to respond with a reply message. The header 550 may contain bits which define a delay time ΔT and indicate to the responding user station 302 a predetermined delay time before it should transmit in reply. The delay time ΔT may by measured with respect to a variety of references, but is preferably measured relative to the start of the corresponding receive time slot 511. The user station 302 preferably comprises means (such ' as timers and/or counters) for keeping track of the relative position and timing of the time slots 510 and 511 in order to respond accurately. In the example of Fig. 5B, the delay time ΔT represents a relative delay time measured from the start of the appropriate receive time slot 511. An exploded view of the receive time slot 511 is shown in Fig. 5B. At the appropriate receive time slot 511, the user station 302 delays for a delay time ΔT before sending a reply message 562. The delay time ΔT may be used by the user station 302 for error processing or other internal housekeeping tasks. As Fig. 5B is illustrated from the perspective of the base station 304 awaiting receipt of the reply message 562, the base station 304 will perceive a propagation delay 561 from the time the user station 302 transmits the reply message 362 until the time of actual receipt of the reply message 362. By measuring the difference in time between the end of the delay time ΔT and the start of the reply message 562, the base station 304 may ascertain the propagation delay 561. The reply message 562 may therefore serve the function of the RTT reply message described earlier, in that the base station 304 ascertains the proper timing for the user station 302 by measuring the propagation delay 561 in receiving the reply message 562. Once the propagation delay 561 has been determined, the base station 304 can command the user station 302 to advance or retard its timing by a desired amount. For example, the base station 304 in the exemplary Fig. 5B system may command the user station 302 to advance its timing by an amount of time equal to the propagation delay time 561, so that the user station 302 transmits essentially at the very end of the abbreviated guard band 512. Thus, when the user station 302 is at the maximum range, the timing advance command will be set to zero (not including the delay ΔT, which is implicit in the user station transmissions) . Conversely, when the user station 302 is very close to the base station, the timing advance command will be set close to the full guard time provided (i.e., the maximum propagation delay time) . The timing advance command may be expressed as a number of bits or chips, so that the user station 302 will respond by advancing or retarding its timing by the number of bits or chips specified. Alternatively, the timing advance command may be expressed as a fractional amount of seconds (e.g., 2 microseconds) . As noted, the user station 302 may advance or retard its timing using techniques already developed and conventionally used for the GSM system described earlier, or by any other suitable means. In one embodiment, the delay time ΔT is preferably set equal to the receive/transmit switching time of the user station 302. Thus, the delay associated with a user station 302 switching from a receive mode to a transmit mode is not included in the RTT measurement. The delay time ΔT should also be selected short enough so that there will be no overlap between the reply message 562 of a particular user station 302 and the user-to-base transmissions in other receive time slots 511. If two user stations 302 attempting to establish communication transmit in the same receive time slot 511 using short reply messages 562, the reply messages 562 may or may not overlap depending on how far each user station 302 is positioned from the base station 304. In some situations the simultaneous reply messages 562 will cause jamming. Should the base station 304 receive two reply messages 562 in the same receive time slot 511, the base station 304 may select time plus the duration of a reply message 562. The maximum round trip propagation time therefore places a maximum limit on the number of time slots (and hence users) in the Fig. 5B system. The Fig. 7 system resolves this same problem by using a designated portion of the time frame 501 for initial establishment of communication. In the system of Fig. 7, in order to prevent the possibility of RTT reply message overlap or interference yet provide the capability of handling more time slots (particularly in larger cells) , initial communication link-up (including RTT transactions) are conducted during the idle time of the collective guard portion 503 between the end of transmission portion 502 of the time frame 501 up to and, if necessary, including the first receive time slot 511 of the receiving portion 504 of the time frame 501. The collective guard portion 503 is thereby utilized in the Fig. 7 system for conducting RTT measurements and to assist in establishing an initial communication link between the base station 304 and a new user station 302. In the Fig. 7 system, a transmission time slot 510 may comprise a header, similar to the header 550 shown in Fig. 5B. The header may indicate whether a particular time slot pair 510, 511 is free. If a time slot pair 510 is free, a user station 302 desiring to establish communication responds with a message indicating the desired time slot of communication. If no header is used, the user station 302 responds with a general request for access, and the base station 304 may in the following time frame 501 instruct the user station 302 to use a particular time slot pair 510, 511 for communication. The general request for access by the user station 302 may comprise a user station identifier, to allow the base station 304 to specifically address the user station 302 requesting access. The header 550 in the Fig. 7 system may include a command indicating a delay time ΔT after which a user station 302 desiring to establish communication may respond. Alternatively, such a delay time ΔT may be pre-programmed as a system parameter, such that the user station 302 delays its response until the delay time ΔT elapses. After detecting the end of the base transmission 502 and waiting for the delay time ΔT to elapse, the user station 302 transmits an RTT reply message 701 or 702. If the user station 302 is very close to the base station 304, then the RTT reply message 701 will appear to the base station 304 immediately after the end of the base transmission 502, and presumably within the collective guard portion 503. If the user station 302 is near the cell periphery, then the RTT reply message 702 will appear to the base station 304 either towards the end of the collective guard portion 503 or within the first receive time slot 511 of the receiving portion 504 of the time frame 501, depending on the particular system definition and timing. The first receive time slot 511 available for established data link communication is the first receive time slot 511 designated after the maximum round-trip propagation delay (including message length) of a reply message from a user station 302 at the maximum cell periphery. Some guard time allowance may also be added to ensure that reply messages from more distant user stations 302 will not interfere with the reverse data link transmissions from user stations 302 in established communication. In an embodiment wherein the headers 550 contain information as to the availability of time slot pairs 510, 511, the RTT reply message 701 or 702 may contain a time slot identifier indicating which available time slot the user station 302 desires to use for communication. The user station 302 may also determine time slot availability by monitoring the base transmission 502 and/or user transmissions 504 for a period of time, and thus transmit a RTT reply message 701 or 702 containing a time slot identifier indicating which available time slot pair 510, 511 the user station 302 desires to use for communication. In response, during the first transmit time slot 510 of the transmission portion 502, the base station 304 may issue a command approving the user station 302 to use the requested time slot In a variation of the Fig. 7 embodiment, only the collective guard portion 503 is used for initial communication link-up, and for receiving RTT reply messages 701. The first receive time slot 511 in this embodiment is not used for such a purpose. In this variation, the length of the collective guard portion 503 should be no less than the sum of the maximum round trip propagation time plus the duration of an RTT reply message 701. After receiving an RTT reply message 701 or 702 at the base station 304, the manner of response of the base station 304 depends on the particular system protocol. As noted, the base station 304 may transmit using headers 550, but need not; the user station 302 may respond with an RTT reply message 701 or 702, with or without a specific time slot request; and the first receive time slot 511 may or may not be used to receive RTT reply messages 701 or 702. The manner of response of the base station 304 therefore depends on the particular structure of the system, and the particular embodiments described herein are not meant to limit the possible base/user station initial communication processes falling within the scope of the invention. Where the first receive time slot 511 is being used along with the collective guard time 503 to receive RTT reply messages 701, 702, then the base station 304 may respond to an RTT reply message 701 or 702 with an initial communication response message in the first transmit time slot 510 of the transmit portion 502 of the immediately following time frame 501. The base station 304 may utilize a particular transmit time slot 510 (e.g., the first transmit time slot 510) for assisting in the initiation. If an RTT reply message 701 or 702 identifies a specific time slot pair 510, 511 which the user station 302 desires to use for communication, then the base station 304 may respond to the user station 302 in either the header 550, the data message portion 551, or both, of the designated transmit time slot 510 in the next immediate time frame 510. If two user stations 302 send RTT reply messages 701 or 702 requesting the initiation of communication in the same time slot pair 510, 511, the base station 304 may send a response in the header 550 of the designated transmit time slot 510 selecting one of the two user stations 302 and instructing the other user station 302 to use a different time slot pair 510, 511 or instruct it to backoff for a period of time, and may in the same time frame 501 transmit a data message in the data message portion 551 of the designated transmit time slot 510 intended for the selected user station 302. If two user stations 302 attempt to access the base station 304 simultaneously (that is, within the same time frame 501) , then the base station 304 may select the user station 302 with the stronger signal. Alternatively, the base station 304 may initiate a backoff procedure or otherwise resolve the conflict as appropriate for the particular application. For example, the base station 304 may issue a backoff command which causes each user station 302 to back off for a variable period based on an internal programming parameter unique to each user station 302 (e.g., such as a unique user identification number) . As another alternative, the base station 304 may instruct one or both user stations 302 to relocate to a different slot pair 510, 511. If the reply messages 701, 702 each contain a different time slot identifier (assuming that the user stations 302 had information as to which time slots were open, such as from the base station headers 550) , then the base station 304 could initiate communication simultaneously with both user stations 302 provided the reply messages 701, 702 were not corrupted by mutual interference (which may occur, for example, when the different user stations 302 are the same distance away from the base station 504) . As with the Fig. 5B embodiment, in the Fig. 7 embodiment the RTT reply message 701 or 702 may be used by the base station 304 to ascertain the proper timing for the user station 302 by measuring the propagation delay in receiving the reply message 701 or 702. A user station 302 seeking to establish communication delays for a delay time ΔT before sending a reply message 701 or 702 after receiving the base transmission 502. The base station 304 determines the propagation delay from the user station 302 to the base station 304 by measuring the round trip propagation delay from the end of the base transmission 502 to the time of actual receipt of the reply message 701 or 702, taking into account the delay time ΔT. Once the propagation delay time has been determined, the base station 304 can command the user station 302 to advance or retard its timing by a desired amount, relative to the appropriate time slot pair 510, 511 to be used for communication. For example, the base station 304 may command the user station 302 to advance its timing by an amount of time equal to the round trip propagation time, so that the user station 302 transmits essentially at the very end of the abbreviated guard band 512. The user station 302 may, for example, advance or retard its timing using techniques developed and conventionally used in the GSM system described earlier, or by any other suitable means. The time delay ΔT in Fig. 7 is preferably set equal to the larger of the transmit/receive switching time of the base station 304 and the receive/transmit switching time of the user station 302. This is to ensure that if the responding user station 302 is located extremely close to the base station 304, the delay of the user station 302 in switching from a receive mode to a transmit mode will not be included in the RTT measurement, and to allow the user station 302 adequate processing time. Once the user station 302 desiring to establish communication has detected the end of the base transmission 502, the user station 302 may commence its reply message 562 immediately after the delay time ΔT without fear of interference, as it is not physically possible for the reply message 562 to overtake the outward-radiating forward link message so as to cause interference with the forward link reception by other user stations 302. Figure 8A is an hardware block diagram of a base station 304 in accordance with an embodiment of the invention. The base station 304 of Fig. 8A comprises a data interface 805, a timing command unit 806, a transmitter 807, an antenna 808, a receiver 809, a mode control 810, a TDD state control 811, and a propagation delay calculator 812. Timing control for the system of Fig. 8A is carried out by the TDD state control 811. The TDD state control 811 comprises appropriate means, such as counters and clock circuits, for maintaining synchronous operation of the TDD system. The TDD state control 811 thereby precisely times the duration of the time frame 501 and its constituent parts, including each of the transmit time slots 510, the receive time slots 511, the abbreviated guard bands 512, and the collective guard portion 503. The TDD state control 811 may be synchronized from time to time with a system clock such as may be located in a base station controller, a cluster controller, or an associated network, so as to permit global synchronization among base stations in a zone or cluster. The mode control 810 selects between a transmit mode and a receive mode of operation. The mode control 810 reads information from the TDD state control 811 to determine the appropriate mode. For example, at the end of the transmission portion 502, as indicated by status bits in the TDD state control 811, the mode control 810 may switch modes from transmit mode to receive mode. At the end of the receiving portion 504, as indicated by status bits in the TDD state control 811, the mode control 810 may switch modes from receive mode to transmit mode. During the transmit mode, data to be transmitted is provided to the data interface 805 from a data bus 813. The data interface 805 provides the data to be transmitted to a timing command unit 806. As explained in more detail herein, the timing command unit 806 formats the data to be transmitted to include, if desired, a timing adjustment command 815. The data output by the timing command unit 806 may be in a format such as the transmission portion 502 shown in Fig. 5A, whereby data targeted for each user station 302 is properly segregated. The output of the timing command unit 806 is provided to the transmitter 807, which modulates the data for communication and transmits the data targeted for each user station 302 in the proper transmit time slot 510. The transmitter 807 obtains necessary timing information from either the mode control 810, or directly from the TDD state control 811. The transmitter 807 may comprise a spread spectrum modulator such as is known in the art . The data is transmitted by transmitter 807 from antenna 808. The user stations 302 receive the transmitted data, formulate responsive user-to-base messages, and send the user- to-base messages in return order. A structure of a user station 302, whereby receipt of the transmissions from the base station 304 and formulation of responsive messages is carried out, is shown in Fig. 9 and described further below. The messages from the user stations 302 appear at the base station 304 in the receive time slots 511. After switching from transmit mode to receive mode, the antenna 808 is used to receive data from the user stations 302. Although a single antenna 808 is shown in the Fig. 8A embodiment, different antennas may be used for transmit and receive functions, and multiple antennas may be used for purposes of achieving the benefits of antenna diversity. The antenna 808 is coupled to a receiver 809. The receiver 809 may comprise a demodulator or a spread spectrum correlator, or both. Demodulated data is provided to the data interface 805 and thereupon to the data bus 813. Demodulated data is also provided to the propagation delay calculator 812, which calculates the propagation delay time for the RTT transaction. In operation, the timing command unit 806 inserts a timing adjustment command, such as a time period T (which may or may not include the delay period ΔT used in the initial round trip timing transaction) , into the transmit time slot 510 instructing the user station 302 to delay sending its response by an amount of time equal to the time period T. The timing adjustment command may be placed at a designated position in a base-to-user message sent during the appropriate transmit time slot 510. For example, the timing adjustment command may be placed in a header 550 or a data message portion 551 of the transmit time slot 510. At initial communication link-up, the timing adjustment command is preferably set to the receive/transmit switching delay time of a user station 302, and is thereafter adjusted based on a calculated propagation delay time. The user station 302 receiving the timing adjustment command delays sending its response by an amount of time designated thereby. The responsive message sent by the user station 302 is received by the receiver 809 and provided to the propagation delay calculator 812. The propagation delay calculator 812 obtains precise timing information from the TDD state control 811, so that the propagation delay calculator 812 may accurately determine the over-air propagation delay of the responsive message sent from the user station 302. Specifically, the propagation delay may be calculated as the difference in time between the time of actual receipt of the responsive message from the user station 302, and the amount of time equal to the time T past the beginning of the appropriate receive time slot 511 (plus the delay period ΔT if such a delay is programmed into each user response) . In a preferred embodiment, the propagation delay calculator 812 then calculates a new timing adjustment command 815 for the particular user station 302. The new timing adjustment command 815 is preferably selected so that the responsive message from the user station 302 in the following time frame 501 begins at the end of the abbreviated guard band 512 and does not overlap with the responsive message from any other user station 302. For example, the new timing adjustment command 815 may be equal to the calculated round- trip propagation time for the particular user station 302. The timing adjustment command 815 may be updated as often as necessary to maintain a sufficient quality of communication between the base station 304 and all of the user stations 302. The propagation delay calculator 812 therefore preferably stores the calculated timing adjustment command 815 for each independent user station 302. As the user station 302 moves closer to the base station 304, the timing adjustment command 815 is increased, while as the user station 302 moves farther away from the base station 304, the timing adjustment command 815 is decreased. Thus, in a dynamic manner, the timing of the user stations 302 is advanced or retarded, and the ongoing communications between the base station 304 and the user stations 302 will not be interrupted by overlapping responsive user-to-base messages received from the user stations 302. Figure 8B is a hardware block diagram of an alternative embodiment of a base station 304. The Fig. 8B base station is similar to that of Fig. 8A, except that a start counter command and a stop counter command are employed as follows. At the start of a base transmission from the transmitter 807, a start counter command 830 is sent from the transmitter 807 to the TDD state control 811 for the target user station 302. When the receiver 809 receives a response from the target user station 302, the user station sends a stop counter command 831 to the TDD state control 811 for the target user station 302. The value stored in the counter for the particular user station 302 represents the round trip propagation delay time. A separate counter may be employed for each user station 302 with which the base station 304 is in contact. Figure 9 is a hardware block diagram of a user station 302 in accordance with an embodiment of the present invention. The user station 302 of Fig. 9 comprises a data interface 905, a timing command interpreter 906, a transmitter 907, an antenna 908, a receiver 909, a mode control 910, and a TDD state control 911. Timing control for the system of Fig. 9 is carried out by the TDD state control 911. The TDD state control 911 comprises appropriate means, such as counters and clock circuits, for maintaining synchronous operation of the user station 302 within the TDD system. The TDD state control 911 thereby precisely times the duration of the time frame 501 and coupled to a receiver 909. The receiver 909 may comprise a demodulator or a spread spectrum correlator, or both. Demodulated data is provided to the data interface 905 and thereupon to the data bus 913. Demodulated data is also provided to the timing command interpreter 906, which applies the timing adjustment command received from the base station 304. In operation, the timing command interpreter 906 parses the data received from the base station 304 to determine the timing adjustment command. Assuming the timing adjustment command comprises a time T equal to the calculated round-trip propagation (RTT) time, the timing command interpreter 906 may reset the clocks and/or timers in the TDD state control 911 at the appropriate instant (such as around the start of the next time frame 501) so as to achieve global re-alignment of its timing. If the timing adjustment command is an instruction to advance timing by an amount of time T, then the timing command interpreter 906 may reset the TDD state control 911 at a period of time T just prior to the elapsing of the current time frame 501. If the timing adjustment command is an instruction to retard timing by an amount of time T, then the timing command interpreter 906 may reset the TDD state control 911 at a period of time T just after the elapsing of the current time frame 501. The timing adjustment command may, as noted, be expressed in terms of a number of bits or chips by which the user station 302 should advance or retard its timing. The timing adjustment command may also be expressed in terms of a fractional timing unit (e.g., milliseconds) . Alternatively, the timing command interpreter 906 may maintain an internal timing adjustment variable, thereby utilizing a delta modulation technique. The internal timing adjustment variable is updated each time a timing adjustment command is received from the base station 304. If the timing adjustment command is an instruction to advance timing, then the timing adjustment variable is decreased by an amount T. If the timing adjustment command is an instruction to retard 589-2, ... 589-16. Each sub-message 589 preferably comprises the same number of symbols, e.g. 40 symbols. The first sub- message 589-1 is intended for the first user station 302, the second sub-message 589-2 is intended for the second user station 302, and so on, up to the last sub-message 589-16. A user station 302 reads part of its incoming message from the appropriate sub-message 589 in the first transmit time slot 574, the next part of its incoming message from the appropriate sub-message 589 of the second transmit time slot, and so on, until the last transmit time slot 574, in which the user station 302 receives the last part of its message. In each transmit time slot 574, preceding the interleaved message 578 is a preamble 577. The preamble 577 assists the user station 302 in synchronization, and may comprise a spread spectrum code. Preambles 577 appear in each transmit time slot 574 and are dispersed throughout the transmission portion 574, therefore allowing the user station 302 to support channel sounding operations useful for setting up a rake receiver (e.g., synchronization) and/or selection diversity. Because the user station 302 obtains its information over the entire transmission portion 571, the communication path is less sensitive to sudden fading or interference affecting only a relatively brief period of the transmission portion 571. Thus, if interference or fading corrupt information in a particular transmit time slot 574 (e.g., the second transmit time slot 574) , the user station 302 would still have 15 sub- messages 589 received without being subject to such interference or fading. By employing forward error correction techniques, the user station 302 can correct for one or more sub-messages 589 received in error. A preferred forward error correction technique utilizes Reed-Solomon codes, which can be generated by algorithms generally known in the art. The number of erroneous sub-messages 589 that can be corrected is given by the equation INT [ (R - K) /2] , where R = the number of symbols sent to a user station 302 over a burst period, K = the number of symbols used for traffic information (i.e., non-error correction) , and INT represents the function of rounding down to the nearest integer. Thus, for a Reed-Solomon code designated R(N, K) = R(40, 31) , up to INT [(40 - 31) /2] = 4 erroneous sub-messages 589 can be corrected. Although a particular symbol interleaving scheme is shown in Fig. 5C, other symbol interleaving techniques, such as diagonal interleaving, may also be used. The user stations 302 respond over the reverse link in generally the same manner as described with respect to Figs. 5A or 7. Thus, the user stations 302 respond with a user transmission in a designated receive time slot 575 of the receive portion 572. The receive time slot 575 comprises a preamble 579 and a user message 580. The receive time slots 575 are separated by abbreviated guard times 573, and ranging may be used to instruct the user stations 302 to advance or retard their timing as previously mentioned. Figure 5D is a chart comparing performance of a particular TDD/TDM/TDMA system in accordance with Fig. 5A, without forward error correction, and a particular system in accordance with Fig. 5C, with forward error correction. Figure 5D plots frame error probability against signal-to- noise ratio (Eb/No) , in dB. In Fig. 5D are shown separate plots for different rake diversity channels L (i.e., resolvable multipaths) of 1, 2 and 4. The solid plot lines in Fig. 5D represent the performance of the Fig. 5A system without forward error correction, while the dotted plot lines represent the performance of the Fig. 5C system with Reed- Solomon forward error correction. Figure 5D thus illustrates a substantial reduction in frame error probability over the Fig. 5A system by use of interleaved symbol transmission and forward error correction. Another embodiment of a time frame structure and associated timing components for carrying out communication between a base station and multiple user stations is shown in Figs. 10A-E. Figure 10A is a diagram of timing sub-elements having predefined formats for use in a time division duplex system. The three timing sub-elements shown in Fig. 10A may be used to construct a time division duplex frame structure, such as the frame structures shown in Figs. 10B-E. Although systems constructed in accordance with Figs. 10A-E preferably use spread spectrum for communication, spread spectrum is not required. However, the following description assumes the use of spread spectrum techniques. For the present example, a chipping rate of 5 MHz is preferred. In Fig. 10A are shown a base timing sub-element 1001, a user datalink timing sub-element 1011, and a range timing sub- element 1021. For each of these sub-elements 1001, 1011, and 1021, as explained more fully below, timing is shown from the perspective of the base station 304 with the initial range of the user station 302 at zero for range timing sub-element 1021. The base timing sub-element 1001 comprises a base preamble interval 1002, a base message interval 1003, and a transmit/receive switch interval 1004. The base preamble interval 1002 may be 56 chips in length. The base message interval 1003 may be 205 bits in length (or, equivalently, 1312 chips if using 32-ary encoding) . In a preferred 32-ary encoding technique, each sequence of five data bits is represented by a unique spread spectrum code of 32 chips in length. The number of spread spectrum codes used is 32, each the same number of chips long (e.g., 32 chips), to represent all possible combinations of five data bits. From the set of 32 spread spectrum codes, individual spread spectrum codes are selectively combined in series to form a transmission in the base message interval 1003. The base message interval 1003 comprises a total of up to 41 5-bit data sequences, for a total of 205 bits; thus, a transmission in the base message interval 1003 may comprise a series of up to 41 spread spectrum codes, each selected from the set of 32 spread spectrum codes, for a total of 1312 chips. Although the present preferred system of Figs 10A-E is described using a 32-ary spread spectrum coding technique, other spread spectrum techniques, including other M-ary encoding schemes (such as 4-ary, 16-ary, etc.) may also be used, depending on the particular system needs. The transmit/receive switch interval 1004 is preferably selected as a length of time sufficient to enable the switching of the base station 304 from a transmit mode to a receive mode or, in some embodiments, to enable the switching of a user station 302 from a receive mode to a transmit mode, and may be, for example, two microseconds in length. The user datalink timing sub-element 1011 and the range timing sub-element 1021 each generally provide for transmissions by more than one user station 302. As explained further below, each of these timing sub-elements 1011, 1021 provides for transmission by a first user station 302 of a data message or a ranging message in the first part of the timing sub-element 1011 or 1021, and transmission by a second user station 302 of a control pulse preamble in the latter part of the timing sub-element 1011 or 1021. The control pulse preamble, as further described below, generally allows the base station 304 to carry out certain functions (e.g., power control) with respect to the second user station 302. The user datalink timing sub-element 1011 comprises a datalink preamble interval 1012, a user message interval 1013, a guard band 1014, a transmit/receive switch interval 1015, a second preamble interval 1016, an antenna adjustment interval 1017, a second guard band 1018, and a second transmit/receive switch interval 1019. The preamble intervals 1012, 1016 may each be 56 chips in length. The user message interval 1013 may be 205 bits in length, or 1312 chips, using the 32-ary spread spectrum coding technique described above with respect to the base timing sub-element 1001. The guard bands 1014, 1018 may each be 102.5 chips in length. The transmit/receive switch intervals 1015, 1019 may each be of a duration sufficient to allow proper switching between transmit and receive modes, or between receive and transmit modes, as the case may be. The antenna adjustment interval 1017 may be of sufficient duration to allow transmission of a data symbol indicating selection of a particular antenna beam or permitting minor adjustments to the angle of a directional antenna at the base station 302, or permitting selection of one or more antennas if the base station 302 is so equipped. The range timing sub-element 1021 comprises a ranging preamble interval 1022, a user ranging message interval 1023, a ranging guard band 1024, a transmit/receive switch interval 1025, a second preamble interval 1026, an antenna adjustment interval 1027, a second guard band 1028, and a second transmit/receive switch interval 1029. The preamble intervals 1022, 1026 may each be 56 chips in length. The user ranging message interval 1023 may be 150 bits in length, or 960 chips, using the 32-ary spread spectrum coding technique described above with respect to the base timing sub-element 1001. The ranging guard band 1024 may be 454.5 chips in length. The other guard band 1028 may be 102.5 chips in length. The transmit/receive switch intervals 1025, 1029 may each be of a duration sufficient to allow proper switching between transmit and receive modes, or between receive and transmit modes, as the case may be. The antenna adjustment interval 1027 may be of sufficient duration to allow transmission of a data symbol for selecting a particular antenna beam or permitting minor adjustments to the angle of a directional antenna at the base station 302, or permitting selection of one or more antennas if the base station 302 is so equipped. The total length of the base timing sub-element 1001 may be 1400 chips. The total length of each of the user datalink timing sub-element 1011 and the range timing sub-element 1021 may be 1725 chips. For these particular exemplary values, a chipping rate of 5 MHz is assumed. Figure 10B is a timing diagram for a fixed time division duplex frame structure (or alternatively, a zero offset TDD frame structure) using the timing sub-elements depicted in Fig. 10A. The frame structure of Fig. 10B, as well as of Figs. 10C-E described below, is shown from the perspective of the base station 304. In Fig. 10B, a time frame 1040 comprises a plurality of time slots 1041. For convenience, time slots are also designated in sequential order as TSl, TS2, TS3, etc. Each time slot 1041 comprises a base timing sub-element 1001 and either a user datalink timing sub-element 1011 or a range timing sub-element 1021. While the frame structure of Fig. 10B supports range timing sub-elements 1021, it is contemplated that communication in the Fig. 10B system, which may be denoted a fixed framing structure, will ordinarily occur using user datalink timing sub-elements 1011. It may be noted that the designated starting point of the time slots TSl, TS2, TS3, etc. is to some degree arbitrary in the Fig. 10B frame structure and various of the other embodiments as are described further herein. Accordingly, the frame structure may be defined such that time slots each start at the beginning of the user timing sub-elements 1011 or 1021, or at the start of the preamble interval 1016, or at the start or end of any particular timing interval, without changing the operation of the system in a material way. In operation, the base station 304 transmits, as part of the base timing sub-element 1001 of each time slot 1041, to user stations 302 in sequence with which it has established communication. Thus, the base station 304 transmits a preamble during the preamble interval 1002 and a base-to-user message during the base message interval 1003. In the transmit/receive switch interval 1004, the base station 304 switches from a transmit mode to a receive mode. Likewise, the user station 302 during the transmit/receive switch interval 1004 switches from a receive mode to a transmit mode. In the first time slot TSl, the base-to-user message transmitted in the base message interval 1003 is directed to a first user station Ml, which may be mobile. After the transmit/receive switch interval 1004, the first user station Ml responds with a preamble during the datalink preamble interval 1012 and with a user-to-base message during the user message interval 1013. Proper timing is preferably set upon initial establishment of communication, and the transmissions from the user stations, such as the first user station Ml, may be maintained in time alignment as seen at the base station 304 by timing adjustment commands from the base station 304, such as the timing adjustment commands described with respect to Figs. 8-9 and elsewhere herein. However, a round-trip guard time must be included in each time slot 1041 so as to allow the base-to-user message to propagate to the user station 302 and the user-to-base message to propagate to the base station 304. The depiction of the exploded time slot TSl in Fig. 10B is generally shown with the assumption that the user station Ml is at zero distance from the base station 304; hence, the user-to-base messages appear in Fig. 10B directly after the transmit/receive switch interval 1004 of the base timing sub-element 1001. However, if the user station Ml is not immediately adjacent to the base station 304, then part of guard time 1014 will be consumed in the propagation of the user-to-base message to the base station 304. Thus, if the user station Ml is at the cell periphery, then the user-to- base message will appear at the base station 304 after the elapsing of a time period equal at most to the duration of guard time 1014. Timing adjustment commands from the base station 304 may allow a shorter maximum necessary guard time 1014 than would otherwise be possible. After the transmission of the user-to-base message from the first user station Ml, which may, as perceived by the base station 304, consume up to all of the user message interval 1013 and the guard band 1014, is another transmit/receive switch interval 1015. Following the transmit/receive switch interval 1015, a control pulse preamble is received from a second user station M2 during the preamble interval 1016. The function of the control pulse preamble is explained in more detail below. Following the preamble interval 1016 is an antenna adjustment interval 1017, during which the base station 304 adjusts its transmission antenna, if necessary, so as to direct it towards the second user station M2. Following the antenna adjustment interval 1017 is another guard band 1018, which accounts for the propagation time of the control pulse preamble to the base station 304. After the preamble interval is another transmit/receive switching interval 1019 A preferred power control command from the base station 304 to the user station 302 may be encoded according to the Table 10-1 below: Table 10-1 Power Control Command Adjustment Although preferred values are provided in Table 10-1, the number of power control command steps and the differential therebetween may vary depending upon the particular application and the system requirements. Further details regarding the use of a control pulse preamble (i.e., control pulse) as a power control mechanism, and other related details, may be found in copending Application Serial Nos. 08/215,306 and 08/293,671, filed March 21, 1994 and August 1, 1994, respectively, both in the name of inventors Gary B. Anderson, Ryan N. Jensen, Bryan K. Petch, and Peter 0. Peterson, both entitled "PCS Pocket Phone/Microcell Communication Over-Air Protocol," and both of which are hereby incorporated by reference as if fully set forth herein. Returning to Fig. 10B, in the following time slot TS2 after time slot TSl, the base station 304 transmits a preamble during the base preamble interval 1002 and transmits a base- to-user message during the base message interval 1003, both directed to the second user station M2. The base station 304 thereby rapidly responds to the control pulse preamble sent by the user station M2. As with the first time slot TSl, following the base message interval 1003 is a transmit/receive switch interval 1004 during which the base station 304 i shorter, allowing more time slots 1051 per time frame 1050, and therefore more user stations 302 per base station 304. The interleaved frame structure of Fig. 10D also allows efficient use of ranging transactions between the base station and the user stations, particularly upon initial link-up of communication. Because the frame structure of Fig. 10D is interleaved, the first time slot TSl' comprises a transmission from the base station 304 to the first user station Ml and a responsive transmission, not from the first user station Ml, but from the last user station MN. In operation of the Fig. 10D system, the base station 304 transmits, as part of the base timing sub-element 1001 of each time slot 1051, to user stations 302 with which it has established communication. The base station 304 thus transmits a preamble during the preamble interval 1002 and a base-to-user message during the base message interval 1003. In the transmit/receive switch interval 1004, the base station 304 switches from a transmit mode to a receive mode. In the first time slot TSl' , the base-to-user message transmitted in the base message interval 1003 is directed to a first user station Ml, which may be mobile. After the transmit/receive switch interval 1004, the last user station MN to have been sent a message from the base station in the last time slot TSN' of the prior time frame 1050 transmits a preamble during the datalink preamble interval 1012 and a user-to-base message during the user message interval 1013. The frame structure of Fig. 10D, as noted previously, is shown from a perspective of the base station 304, and the transmissions from the user stations, such as user station MN, are maintained in time alignment as seen by the base station 304 by timing adjustment commands from the base station 304, similar to the timing adjustment commands described elsewhere herein. Proper timing is preferably set upon initial establishment of communication, by use of a ranging transaction. After the transmission of the user-to-base message from the first user station Ml, which may, as perceived by the base the control pulse sent by the user station M2. As with the first time slot TSl' , following the base message interval 1003 occurs a transmit/receive switch interval 1004 during which the base station 304 switches to a receive mode. Unlike the Fig. 10B-C embodiment, in which the latter portion of the time slot TS2' is used for receiving a transmission from the second user station M2, in the Fig. 10D embodiment the latter portion of the time slot TS2' is used for receiving a transmission from the first user station Ml. While the first user station Ml is in the process of transmitting, the second user station M2 thus has the opportunity to process the data received from the base station 304 during the same time slot TS2', and to transmit a responsive transmission timed to arrive at the base station 304 in the following time slot TS3' without interfering with other transmissions from either the base station 304 or other user stations 302. Thus, in the second time slot TS2', the base station receives from the first user station Ml a preamble during the datalink preamble interval 1012 and a user-to-base message in the user message interval 1013. It is assumed in the exemplary time frame 1050 shown of Fig. 10D that there is no established communication link in the duplex channel comprising the base portion of the third time slot TS3' and the user portion of the fourth time slot TS4', and therefore that particular duplex channel is free for communication. Because no user station 302 is in established communication during the duplex channel, no control pulse preamble is transmitted during the preamble interval 1016 of the second time slot TS2' . The base station 304 may indicate that a particular duplex channel is available for communication by, for example, transmitting a general polling message during the base message interval 1003 of the duplex channel, such as during the base message interval 1003 of time slot TS3' . Should a new user station M3 desire to establish communication with the base station 304, then the new user station M3 waits until an open user portion of a time slot preferred spread spectrum code to be used by the base station 304 and the particular user station M3 in subsequent communications. Figure 10E shows a subsequent time frame 1050 after a ranging transaction has been completed with the third user station M3. In Fig. 10E, the transactions between the user stations Ml, MN and the base station 304 occurring in the first time slot TSl' are the same as for Fig. 10D. Also, the transactions between the user stations Ml, M2 and the base station 304 occurring in the second time slot TS2 are the same as for Fig. 10D. However, during the second time slot TS2' , instead of there being no transmitted control pulse preamble in the preamble interval 1016, the third user station M3 may transmit a control pulse preamble during the preamble interval 1016 of the second time slot TS2' . Alternatively, the user station M3 may wait until the base station 304 acknowledges its ranging message sent in the prior time frame 1050 before transmitting a control pulse preamble during the preamble interval 1016 of each preceding time slot TS2' . The base station 304 may use the control pulse preamble for a variety of purposes, including power control and other purposes, as previously described. In the third time slot TS3' of Fig. 10E, the base station 304 may respond by sending an acknowledgment signal to the user station M3 during the base message interval 1003. The acknowledgment signal may be sent using a spread spectrum code determined by a user identifier sent by the user station M3 as part of the ranging message. As part of the acknowledgment signal, or in addition thereto, the base station 304 preferably sends a timing adjustment command instructing the user station M3 to advance or retard its timing by a designated amount. In following time frames 1050, communication may be carried out between the base station 304 and the user station M3 in an interleaved fashion in time slots TS3' and TS4' (in addition to the receipt of the control pulse preamble in the second time slot TS2' each time frame 1050) . In each preamble interval 1016 of the second time slot TS2', the user station 59 length to the user timing sub-elements 1110, 1121 to maintain synchronicity in the dual-frequency band system described in Figs. 11A-D, wherein the base station 304 communicates over one frequency band and the user stations 302 over another frequency band. The user datalink timing sub-element 1110 and the range timing sub-element 1121 each generally provide for transmissions by more than one user station 302. As explained further below, these timing sub-elements 1110, 1121 provide for transmission by a first user station 302 of a data message or a ranging message in the first part of the timing sub- element 1110 or 1121, and transmission by a second user station 302 of a control pulse preamble in the latter part of the timing sub-element 1110 or 1121. The control pulse preamble, as further described below, generally allows the base station 304 to carry out certain functions (e.g., power control) with respect to the second user station 302. The user datalink timing sub-element 1110 comprises a datalink preamble interval 1112, a user message interval 1113, a guard band 1114, a transmit/receive switch interval 1115, a second preamble interval 1116, an antenna adjustment interval 1117, a second guard band 1118, and a second transmit/receive switch interval 1119. The preamble intervals 1112, 1116 may each be 56 chips in length. The user message interval 1113 may be 205 bits in length, or 1312 chips, using the 32-ary spread spectrum coding technique described previously herein. The length of the guard bands 1114, 1118 may vary, but should be sufficient to allow receipt of the pertinent message transmissions without interference. The transmit/receive switch intervals 1115, 1119 may each be of a duration sufficient to allow proper switching between transmit and receive modes, or between receive and transmit modes, as the case may be. The antenna adjustment interval 1117 may be of sufficient duration to allow transmission of a data symbol for selecting a particular antenna beam or permitting minor adjustments to the angle of a directional antenna at the base 61 aspects of time division multiple access. A first frequency band 1170, also referred to as a base station frequency band, is used primarily for communication from a base station 304 to user stations 302. A second frequency band 1171, also referred to as a user station frequency band, is used primarily for communication from the user stations 302 to the base station 304. The two frequency bands 1170, 1171 are preferably located 80 MHz apart. The 80 MHz frequency separation helps to minimize co-channel interference and allows easier construction of filters in the receiver for filtering out potentially interfering signals from the reverse path communication. In the frame structure of Fig. 11B, a time frame 1140 comprises a plurality of time slots 1141. For convenience, time slots are designated in sequential order as TSl", TS2", TS3", and so on. Each time slot 1141 comprises a base timing sub-element 1101 on the base station frequency band 1170, and either a user datalink timing sub-element 1110 or a range timing sub-element 1121 on the user station frequency band 1171. The time slots 1141 are shown from the perspective of the base station 304, so that the base timing sub-elements 1101 and the user timing sub-elements 1110, 1121 appear lined up in Fig. 11B. While the frame structure of Fig. 11B supports range timing sub-elements 1121 on the user station frequency band 1171, it is contemplated that communication from the user stations 302 to the base station 304 in the Fig. 11B system will ordinarily occur using user datalink timing sub-elements 1110. In operation, the base station 304 transmits, as part of the base timing sub-element 1101 of each time slot 1141, in sequence to user stations 302 with which the base station 304 has established communication. More specifically, the base station 304 transmits a preamble during the preamble interval 1102 and a base-to-user message during the base message interval 1103. After the base message interval 1103, the base station 304 transmits three short preamble bursts in the 123- preamble burst interval 1109 directed to a different user station 302. In the exemplary system of Fig. 11B, the three preamble bursts in the 123-preamble burst interval 1109 are directed to the user station 302 to which the base station 304 will be sending a main data message two time slots 1141 later. The three short preamble bursts sent in the 123-preamble burst interval 1109 may be used for forward link diversity sensing and forward link power control purposes. Each of these three preamble bursts may be transmitted on a different antenna to allow receiving user stations 302 an opportunity to make a diversity selection for an upcoming forward link data message in a subsequent time slot 1141. Following the 123-preamble burst interval 1109 is the base fill code interval 1107, during which the base station 304 transmits a fill code. Following the base code fill interval 1107 is the transmit/receive switch interval 1104, during which the base station 304 may switch from a transmit mode to a receive mode. If the base station 304 has separate transmit and receive hardware, however, then the base station need not switch modes, and may instead continue to transmit a fill code during the transmit/receive switch interval 1104. The specific communication exchanges shown in the example of Fig. 11B will now be explained in more detail. In the first time slot TSl", on the base station frequency band 1170, the base station transmits a base-to-user message in the base message interval 1103 directed to a first user station Ml. The base station 304 then transmits a 123-preamble burst during the 123-preamble burst interval 1109, directed to another user station M3. Simultaneous with the base station transmissions, the base station 304 receives, on the user station frequency band 1171, a preamble during the datalink preamble interval 1112 and a user-to-base message during the user message interval 1113 from the last user station MN with which the base station 304 is in communication. During the control pulse preamble interval 1116 of the first time slot TSl" on the user station frequency band 1171, the base station 304 receives a control pulse preamble from the user station M2 63 to which the base station 304 is to transmit in the following time slot TS2" . The functions of the control pulse preamble sent during the control pulse preamble interval 1116 are similar to those described earlier with respect to the control pulse preamble of Figs. 10A-E (e.g., power control, antenna adjustment, etc.) . Following the preamble interval 1116 is an antenna adjustment interval 1117, during which the base station 304 has an opportunity to adjust its transmission antenna, if necessary, so as to direct it towards the second user station M2 based upon information acquired from receipt of the control pulse preamble. Following the antenna adjustment interval 1117 is another guard band 1118, which accounts for the propagation time of the control pulse preamble to the base station 304. After the preamble interval is another transmit/receive switching interval 1119 to allow the base station 304 opportunity to switch from a receive mode to a transmit mode (if necessary) , and to allow the second user station M2 opportunity to switch from a transmit mode to a receive mode. In the following time slot TS2" after the first time slot TSl", the base station 304 transmits, using the base station frequency band 1170, a preamble during the base preamble interval 1102 and a base-to-user message during the base message interval 1103, both directed to the second user station M2. The base station 304 thereby rapidly responds to the control pulse preamble sent by the user station M2. It is assumed, however, in the exemplary time frame 1140 of Fig. 11B that the base station 304 is not in established communication with any user station 302 during the fourth time slot TS4" over the base station frequency band 1170. Thus, in the 123- preamble burst interval 1109 following the base message interval 1103, the base station 304 does not transmit a 123- preamble burst directed to a user station 302. Simultaneous with the base station transmissions in the second time slot TS2", the base station 304 receives, on the user station frequency band 1171, a preamble during the PCI7US96/07905 64 datalink preamble interval 1112 and a user-to-base message during the user message interval 1113 from the user station Ml with which the base station 304 communicated in the first time slot TSl". Similar to the first time slot TSl", during the control pulse preamble interval 1116 of the second time slot TS2" on the user station frequency band 1171, the base station 304 receives a control pulse preamble from the user station M3 to which the base station 304 is to transmit in the following time slot TS3" . In the third time slot TS3", the base station 304 transmits, using the base station frequency band 1170, a preamble during the base preamble interval 1102 and a base-to- user message during the base message interval 1103, both directed to the third user station M3. Following the base message interval 1103 is a 123-preamble burst interval 1109 during which the base station 304 transmits three short preamble bursts (i.e., the 123-preamble burst) directed to a different user station M5, with which the base station 304 intends to communicate two time slots 1141 later. Simultaneous with the base station transmissions, the base station 304 receives, on the user station frequency band 1171, a preamble during the datalink preamble interval 1112 and a user-to-base message during the user message interval 1113 from the user station M2 with which the base station 304 communicated in the previous time slot TS2". Because the base station 304 is not in established communication with any user station 302 during the fourth time slot TS4" over the base station frequency band 1170, the base station 304 does not receive a control pulse preamble during the control pulse preamble interval 1116 of the third time slot TS3" on the user station frequency band 1171. A similar exchange is carried out in the fourth time slot TS4", and in subsequent time slots 1141 as well. Whether or not particular user-to-base message, base-to-user messages, and preambles or control pulse preambles are transmitted depends on whether or not the base station 304 is in 65 communication with a user station 302 requiring such exchanges at the particular time. Thus, in general, to support communication between a user station 302 and base station 304 communicating during a single time slot 1141, four messages are exchanged in each time frame 1140 between the particular user station 302 and the base station 304. The base station 304 first sends a 123-preamble in a 123-preamble interval 1109 of the time slot 1141 two slots 1141 prior to which the base station 304 intends to transmit to the user station 302. In the following time slot 1141, on a different frequency band 1171, the user station 302 responds by sending a control pulse preamble, which is received at the base station 304 during the control pulse preamble interval 1116. In the following time slot 1141, after making determinations as to power adjustment and/or timing adjustment, the base station 304 transmits to the user station 304 a base-to-user message during the base message interval 1103 on the base station frequency band 1170. In the following time slot 1141, after adjusting its power and/or timing, the user station 304 responds with a user-to-base message, which is received at the base station 304 during the user message interval 1113. As noted, it is assumed in the exemplary time frame 1140 of Fig. 11B that the base station 304 is not in established communication with any user station 302 during the fourth time slot TS4" over the base station frequency band 1170. The base station 304 may indicate that a particular time slot 1141, such as time slot TS4", is available for communication by, for example, transmitting a general polling message during the base message interval 1103 of the time slot TS4". Should a user station 302 desire to establish communication with the base station 304 (such as in the fourth time slot TS4") , then, in response to the base station 304 transmitting a general polling message during the base message interval 1103 of the fourth time slot TS4", the new user station 302 may send a general polling response message during a user message interval 1113 of the following time slot TS5" 66 (not shown) . When the new user station 302 responds with a general polling response message, the base station 304 may determine the range of the user station 302 and thereby determine a required timing adjustment for subsequent transmissions by the user station 302. The base station 304 may thereafter issue periodic timing adjustment commands to maintain receipt of user-to-base transmissions at the start of each user timing interval. The base station 304 may monitor the distance of the user station 302 by looking to the time of receiving either the control pulse preamble or the user-to- base message from a user station 302. For efficiency reasons, the guard times 1114 and 1118 are preferably kept to a minimum. The smaller the guard times 1114, 1118, the more user stations 302 may be supported by the frame structure of Fig. 11B. Typically, therefore, the guard times 1114, 1118 will not be of sufficient duration to allow a full ranging transaction to occur. In particular, a ranging transaction may result in interference between the transmission of a user station 302 seeking to establish communication and the control pulse preamble of the user station 302 already in communication in the immediately following time slot 1141 with the base station 304. If the guard times are lengthened to permit ranging transactions, then fewer user stations 302 can be supported, particularly in a large cell environment. An alternative structure having improved efficiency in a large cell environment, along with the flexibility of ranging transactions, is shown in Figs. 11C and 11D and explained in more detail below. Proper timing is preferably set upon initial establishment of communication, and the transmissions from the user stations, such as the first user station Ml, may be maintained in time alignment as seen at the base station 304 by timing adjustment commands from the base station 304, similar to the timing adjustment commands described elsewhere herein. A full round-trip guard time need not be included in each time slot 1141 because the user stations 302 and base station 304 transmit on different frequency bands, preventing 67 interference between base-to-user messages and user-to-base messages. The depiction of the frame structure in Figs. 11A-B assumes that the user stations 302 are at zero distance from the base station 304, and therefore the user-to-base message appears immediately after the preamble interval 1112 or 1122. However, if the user station 302 is not immediately adjacent to the base station 304, then part of guard time 1114 shown in Fig. IIA will be consumed in the propagation of the preamble and user-to-base message to the base station 304. Thus, if the user station 302 is at the cell periphery, then the user- to-base message will appear at the base station 304 after the elapsing of a time period equal at most to the duration of guard time 1114. In order to ensure that the guard times 1114 and 1118 are kept to a minimum, timing adjustment commands are preferably transmitted from the base station 304 periodically so as to keep the user preambles and user-to-base messages arriving at the base station 304 as close to the start of the user timing sub-element 1110 as possible, without interfering with the transmissions of the previous use station 302. If a ranging transaction is supported in the Fig. 11B environment, then the portion of a time slot 1141 on the user station frequency band 1171 may comprise a range timing sub- element 1121, as described previously with respect to Fig. IIA, during which a ranging transaction is carried out between the base station 304 and a new user station 302. Thus, the user station 302 transmits a preamble during a ranging preamble interval 1122 of time slot 1141, and transmits a ranging message during the user ranging message interval 1123 of time slot 1141. The user station 302 delays transmitting the preamble and ranging message for an amount of time ΔT. The delay time ΔT may be communicated by the base station 304 as part of the general polling message, or may be a pre¬ programmed system parameter. The base station 304 determines the propagation delay from the user station 302 to the base station 304 by measuring the round trip propagation delay from the end of the previous time slot 1141 to the time of actual messages, or for only control pulse preambles. However, code division multiplexing in such a manner may not provide satisfactory isolation between the interfering signals, or may require unacceptably long time slots. In the following time frames 1140, after establishing communication with user station M3 in the manner described above, communication may be carried out between the base station 304 and the user station M3 in an interleaved fashion over several time slots 1140. As part of each transmission from the base station 304, the base station 304 may update the timing adjustment command to the user station M3. Should a user station 302 terminate communication in a time slot 1141 or be handed off to a new base station 304, then the base station 304 may begin to transmit a general polling message during the newly opened time slot 1141, indicating that the time slot 1141 is free for communication. New user stations 302 may thereby establish communication with the same base station 304. A simple means to adapt an FDD/TDMA system such as shown in Fig. 11B to emulate a TDD system is to alternately black out time slots on each of the two frequency bands 1170 and 1171. Thus, during time slot TSl", the base station 304 transmits to a user station M- L over frequency band 1170, while no transmission is conducted over frequency band 1171. During the next time slot TS2", the user station Ml responds over frequency band 1171, while no transmission is conducted over frequency band 1170. The next two time slots TS3" and TS4" are used for duplex communication between the base station 304 and the next user station M 2 , with the user slot in TS3" and the base slot in TS4" being dormant. The described frame structure generally supports fewer user stations 302 than the frame structure shown in Fig. 11B due to the dormancy of alternating time slots on each frequency band 1170 and 1171, but allows a TDD interface such as shown in Fig. 10B to be emulated with minimal modification to the base and user stations (e.g., by transmitting and receiving on different frequency bands) . If both frequency bands 1170 and 1171 are selected to be the same, then the system will be true TDD, thus allowing the same hardware to be capable of either FDD/TDMA or TDD operation simply by appropriate selection of the frequency bands and appropriate selection of the time slots (i.e., by selecting in an alternating manner) on the forward and reverse links during which to transmit. Figure 11C is a timing diagram for an offset interleaved FDD/TDMA frame structure using the timing sub-elements depicted in Fig. IIA, as shown from the perspective of the base station 304. As described further below, the offset interleaved FDD/TDMA frame structure of Fig. 11C permits larger cells by allowing time for user stations 302 to receive base station transmissions intended for them before having to reply, and may prevent the need for a costly diplexer in the user station 302. Figure 11C is a frame structure for a system using two frequency bands for communication in addition to certain aspects of time division multiple access. A first frequency band 1172, also referred to as a base station frequency band, is used primarily for communication from a base station 304 to user stations 302. A second frequency band 1173, also referred to as a user station frequency band, is used primarily for communication from the user stations 302 to the base station 304. The two frequency bands 1172, 1173 are preferably located 80 MHz apart. The 80 MHz frequency separation helps to minimize co-channel interference and allows easier construction of filters in the receiver for filtering out potentially interfering signals from the reverse path communication. In the frame structure of Fig. 11C, a time frame 1150 comprises a plurality of time slots 1151. For convenience, time slots are designated in sequential order as OTS1, OTS2, OTS3, and so on. Each time slot 1151 comprises a base timing sub-element 1101 on the base station frequency band 1170, and either a user datalink timing sub-element 1110 or a range timing sub-element 1121 on the user station frequency band 1171. The time slots 1151 are shown from the perspective of the base station 304, so that the base timing sub-elements 1101 and the user timing sub-elements 1110, 1121 appear staggered in Fig. 11C by a predetermined offset time 1160. The frame structure of Fig. 11C supports both range timing sub-elements 1121 and user datalink timing sub-elements 1110 on the user station frequency band 1171. In operation, the base station 304 transmits, as part of the base timing sub-element 1101 of each time slot 1151, in sequence to user stations 302 with which the base station 304 has established communication. Thus, the base station 304 transmits a preamble during the preamble interval 1102 and a base-to-user message during the base message interval 1103. After the base message interval 1103, the base station 304 transmits three short preamble bursts in the 123-preamble burst interval 1109 directed to a different user station 302. In the exemplary system of Fig. 11C, the three preamble bursts in the 123-preamble burst interval 1109 are directed to the user station 302 to which the base station 304 will be sending a main data message two time slots 1151 later. As with the system of Fig. 11B, the three short preamble bursts sent in the 123-preamble burst interval 1109 may be used for forward link diversity sensing and forward link power control purposes. Each of these three preamble bursts may be transmitted on a different antenna to allow receiving user stations 302 an opportunity to make a diversity selection for an upcoming forward link data message in a subsequent time slot 1151. Following the 123-preamble burst interval 1109 is the base fill code interval 1107, during which the base station 304 transmits a fill code. Following the base code fill interval 1107 is the transmit/receive switch interval 1104, during which the base station 304 may switch from a transmit mode to a receive mode. Preferably, however, the base station 304 has separate transmit and receive hardware, and therefore does not need to switch modes. Instead, the base station 304 may continue to transmit a fill code during the transmit/receive switch interval 1104. The specific communication exchanges shown in the example of Fig. 11C will now be explained in more detail. In the first time slot OTSl, on the base station frequency band 1172, the base station transmits a base-to-user message in the base message interval 1103 directed to a first user station Ml. The base station 304 then transmits a 123-preamble burst during the 123-preamble burst interval 1109, directed to another user station M3. Simultaneous with the base station transmissions, but offset therefrom by an offset time 1160, the base station 304 receives, on the user station frequency band 1173, a preamble during the datalink preamble interval 1112 and a user-to-base message during the user message interval 1113 from the last user station MN with which the base station 304 is in communication. During the control pulse preamble interval 1116 of the first time slot OTSl on the user station frequency band 1173, the base station 304 receives a control pulse preamble from the user station M2 to which the base station 304 is to transmit in the following time slot OTS2. The functions of the control pulse preamble sent during the control pulse preamble interval 1116 are similar to those described earlier with respect to the control pulse preamble of Figs. 10A-E and 11B (e.g., power control, antenna adjustment, etc.) . Following the preamble interval 1116 is an antenna adjustment interval 1117, during which the base station 304 has an opportunity to adjust its transmission antenna, if necessary, so as to direct it towards the second user station M2 based upon information acquired from receipt of the control pulse preamble. Following the antenna adjustment interval 1117 is another guard band 1118, to allow for propagation of the control pulse preamble to the base station 304. After the preamble interval is another transmit/receive switching interval 1119 to allow the base station 304 opportunity to switch from a receive mode to a transmit mode (if necessary) , and to allow the second user station M2 opportunity to switch from a transmit mode to a receive mode. 4 PCI7US96/07905 74 different user station M5, with which the base station 304 will communicate two slots 1151 later. Simultaneous with the base station transmissions but offset therefrom by an offset time 1160, the base station 304 receives, on the user station frequency band 1173, a preamble during the datalink preamble interval 1112 and a user-to-base message during the user message interval 1113 from the user station M2 with which the base station 304 communicated in the previous time slot 0TS2. Because the base station 304 is not in established communication with any user station 302 during the fourth time slot 0TS4 over the base station frequency band 1172, the base station 304 does not receive a control pulse preamble during the control pulse preamble interval 1116 of the third time slot 0TS3 on the user station frequency band 1173. A similar exchange is carried out in the fourth time slot 0TS4, and in subsequent time slots 1151 as well. Whether or not particular user-to-base message, base-to-user messages, and preambles or control pulse preambles are transmitted depends on whether or not the base station 304 is in communication with a user station 302 requiring such exchanges at the particular time. Thus, in general, to support communication between a user station 302 and base station 304 communicating during a single time slot 1151, four messages are exchanged in each time frame 1150 between the particular user station 302 and the base station 304. The base station 304 first sends a 123-preamble in a 123-preamble interval 1109 of the time slot 1151 two slots 1151 prior to which the base station 304 intends to transmit to the user station 302. In the following time slot 1151, on a different frequency band 1173 and delayed by an offset time 1160, the user station 302 responds by sending a control pulse preamble, which is received at the base station 304 during the control pulse preamble interval 1116. In the following time slot 1151, after making determinations as to power adjustment and/or timing adjustment, the base station 304 transmits to the user station 304 a base-to-user message station 304 transmit on different frequency bands, preventing interference between base-to-user messages and user-to-base messages. The depiction of the frame structure in Fig. 11C (i.e., the exploded time slots 1151) assumes that the user stations 302 are at zero distance from the base station 304. However, if the user station 302 is not immediately adjacent to the base station 304, then part of guard time 1114 (as shown in Fig. IIA) will be consumed in the propagation of the preamble and user-to-base message to the base station 304. Thus, if the user station 302 is at the cell periphery, then the user- to-base message will appear at the base station 304 after the elapsing of a time period equal at most to the duration of guard time 1114. In order to ensure that the guard times 1114 and 1118 are kept to a minimum, timing adjustment commands are preferably transmitted from the base station 304 periodically so as to keep the user preambles and user-to-base messages arriving at the base station 304 as close to the start of the user timing sub-element 1110 as possible, without interfering with the transmissions of the previous use station 302. When a user station 302 first establishes communication with the base station 304 in the Fig. 11C frame structure, a ranging transaction is carried out. The time slot 1151 on the user station frequency band 1173 during which the ranging transaction is initiated preferably comprises a range timing sub-element 1121, as described previously with respect to Fig. IIA. The user station 302 transmits a preamble during a ranging preamble interval 1122 of time slot 1151, and transmits a ranging message during the user ranging message interval 1123 of time slot 1151. The user station 302 delays transmitting the preamble and ranging message for an amount of time ΔT. The delay time ΔT may be communicated by the base station 304 as part of the general polling message, or may be a pre-programmed system parameter. The base station 304 determines the propagation delay from the user station 302 to the base station 304 by measuring the round trip propagation delay from the end of the previous time slot 1151 to the time by the user station 302. The user station 302 therefore does not need a diplexer, which can be a relatively expensive component. Operation without a diplexer is particularly beneficial where the user station 302 is embodied as a mobile handset, because it is often important to keep manufacturing costs of the handset as low as possible. Other hardware efficiency may also be achieved by not requiring simultaneous transmission and reception; for example, the user station 302 could use the same frequency synthesizer for both transmitting and receiving functions. Figure 11D shows a subsequent time frame 1150 after a ranging transaction has been completed with the third user station 3. In Fig. 11D, the transactions between the user stations Ml, MN and the base station 304 occurring in the first time slot OTSl are the same as for Fig. 11C. Also, the transactions between the user stations Ml, M2 and the base station 304 occurring in the second time slot OTS2 are the same as for Fig. 11C. However, during the second time slot OTS2, instead of there being no transmitted control pulse preamble in the preamble interval 1116, the third user station M3 may transmit a control pulse preamble during the preamble interval 1116 of the second time slot 0TS2. Alternatively, the user station M3 may wait until the base station 304 acknowledges its ranging message sent in the prior time frame 1150 before transmitting a control pulse preamble during the preamble interval 1116 of each preceding time slot 0TS2. In the following time frames 1150, after establishing communication with the third user station M3 in the manner described above, communication may be carried out between the base station 304 and the user station M3 as shown in Fig. 11D. As part of each transmission from the base station 304, the base station 304 may update the timing adjustment command to the user station M3. Should a user station 302 terminate communication in a time slot 1151 or be handed off to a new base station 304, then the base station 304 may begin to transmit a general polling message during the newly opened time slot 1151, indicating that the time slot 1151 is free for communication. New user stations 302 may thereby establish communication with the same base station 304. Figures 12A-C are tables showing preferred message formats for base station and user station transmissions. Tables 12B-1 through 12B-3 show message formats for transmissions used in handshaking or an acquisition mode. Tables 12C-1 through 12C-4 show message formats (both symmetric and asymmetric) after acquisition when in traffic mode. It should be noted that the asymmetric message formats are intended for use in the TDD based system variants, but not the FDD based systems. Tables 12A-1 through 12A-4 show the header format for each of the different message types in Tables 12B-1 through 12C-4. For example, Table 12A-1 shows a header format for a base polling transmission (general or specific) as described earlier. The header format of Table 12A-1 comprises 21 bits. The particular header format comprises 10 fields totalling 19 bits, leaving two spare bits. The fields include a B/H field of 1 bit identifying whether the transmission source is a base station or a user station; an E field of 1 bit which may be used as an extension of the B/H field; a G/S field of 1 bit indicating whether the polling message is general or specific; a P/N field of 1 bit indicating whether the transmission is in a polling or traffic message; an SA field of 1 bit used for identification checking and verification; a P R field of 3 bits used for power control; a CU field of 2 bits indicating slot utilization; an opposite link quality field of 2 bits indicating how well the sending unit is receiving the opposite sense link; a timing adjustment command of 3 bits providing a command to the user station to adjust its timing if necessary; and a header FC (frame check word) field of 4 bits used for error detection (similar to a CRC) . A header format for a base traffic transmission is shown in Table 12A-2. The header format is the same as that of Table 12A-1, except that an additional B/ grant field of 2 bits for the allocation of addition bandwidth to the user station 302 through time slot aggregation or asymmetric time slot use. The header format of Table 12A-2 utilizes 21 bits. A header format for a mobile or user polling transmission is shown in Table 12A-3. The header format is similar to that of Table 12A-1, except that it does not include a CU field or a timing command field. Also, the header format of Table 12A- 3 includes a B/ request field of 1 bit for a request of additional bandwidth or time slots. The Table 12A-3 header format includes 6 spare bits. A header format for a mobile or user traffic transmission is shown in Table 12A-4. The header format of Table 12A-4 is the same as that of Table 12A-3, except that the B/W request field is designated in place of a B/W grant field. Thus, the header formats for user stations 302 and base stations 304 are selected to be the same length in the exemplary embodiment described with respect to Figs. 12A-C, whether or not in polling or traffic mode, and whether or not the polling message is general or specific. Tables 12B-1 through 12B-3 show message formats for transmissions used in handshaking or an acquisition mode. Table 12B-1 shows a message format of 205 bits for a base general polling transmission. The message format of Table 12B-1 includes a header field of 21 bits, which comprises fields shown in Table 12A-1; a base ID field of 32 bits for identifying the base station 304 transmitting the general polling message; various network and system identification fields, such as a service provider field of 16 bits which may be used to indicate, e.g., a telephone network or other communication source, a zone field of 16 bits which may be used to identify, e.g., a paging cluster, and a facility field of 32 bits; a slot number field of 6 bits indicating the slot number of the associated general polling transmission so as to assist the user station 302 in synchronization; and a frame FCW field of 16 bits for error correction and transmission integrity verification. A message format of 150 bits for a mobile or user station response transmission is shown in Table 12B-3. The message used for an asymmetric frame structure. Similarly, Tables 12A-3 and 12A-4 are mobile or user station traffic mode message formats; the message format of Table 12A-3 is used for a symmetric frame structure, and the format of Table 12A-4 is used for an asymmetric frame structure. In a symmetric frame structure, each of the traffic mode messages is 205 bits in length. Each of the traffic mode message comprises a D-channel field (or data field) of 8 bits in length for slow data rate messaging capability, and a B- channel field (or bearer field) of 160 or 176 bits in length, depending on whether or not a frame FCW field of 16 bits is used. In an asymmetric frame structure, used only in TDD system variants, the traffic mode message from one source is a different length, usually much longer, than the traffic mode message from the other source. The asymmetric frame structure allows a much higher data bandwidth in one direction of the communication link than the other direction. Thus, one of the traffic mode messages is 45 bits in length, while the other traffic mode messages is 365 bits in length. The total length for a forward and reverse link message still totals 410 bits, as with the symmetric frame structure. Each of the traffic mode message comprises a D-channel field (or data field) of 8 bits in length for slow data rate messaging capability, and a B-channel field (or bearer field) of either 0, 16, 320 or 336 bits in length, depending on which source has the higher transmission rate, and depending on whether or not a frame FCW field of 16 bits is used. Base and user messages are preferably sent using an M-ary encoding technique. The base and user messages are preferably comprised of a concatenated sequence of data symbols, wherein each data symbol represents 5 bits. A spread spectrum code, or symbol code, is transmitted for each data symbol. Thus, a transmitted symbol code may represent a whole or a portion of a data field, or multiple data fields, or portions of more than one data field, of a base or user message. As an alternative processing mechanism, M of N detectors can be used for detection alert purposes while the full length preamble is used for detection confirmation and channel sensing/equalization purposes. Code sets may be created having preambles using different MPS28 codes exhibiting low cross-correlation. A potential limitation with this approach is that there are only two MPS28 codewords. Thus, to create an N=7 code reuse pattern, "near" MPS28 codewords may be included so as to enlarge the potential available preambles exhibiting favorable cross-correlation characteristics. The two MPS28 codewords have peak temporal sidelobe levels of - 22.9 dB, while the near MPS28 codewords have peak temporal sidelobe levels of -19.4 dB. Preamble processing may further be augmented by taking advantage of the control pulse preamble (e.g., in preamble interval 1016) and 123-preamble message transmissions described earlier herein with respect to Figs. 10A-11D. The control pulse preamble and 123-preamble transmissions generally have fixed timing with respect to the initial preamble transmissions (e.g., in preamble intervals 1002 or 1102) preceding each main user or base transmission, and can be used to aid in synchronization particularly on the reverse link where two full-length preamble transmissions are associated with each main user or base transmission. Preamble length is effectively doubled by processing both the control pulse preamble or 123-preamble, and the preambles preceding the main user or base transmission. Figures 14-17 are charts comparing various performance aspects of selected high tier and low tier air interfaces incorporating designated features of the embodiments described herein. By the term "high tier" is generally meant system coverage over a wide area and hence low capacity. Conversely, the term "low tier" is generally applied to communication services for localized high capacity and/or specialized needs. In one scheme, users are assigned to the lowest tier possible to preserve capacity in higher tiers. In general, high tier applications are characterized by relatively large cells to provide umbrella coverage and connectivity, wherein users tend to have high measured mobility factors (e.g., high speed vehicular). High tier operations may also be characterized by high transmit power at the base station, high gain receive antennas, and high elevation antenna placement. Factors such as delay spread (resulting from multiple propagation delays due to reflections) and horizontal phase center separation as applied to multipath and antenna diversity can be quite important. For example, increased antenna complexity and aperture size may weigh against the use of large numbers of diversity antennas in high tier applications. Receiver sensitivity may also be an important limiting factor. Small coherence bandwidths make spread spectrum waveforms favored in high tier applications. Low tier applications are generally characterized by smaller cells with coverage limited by physical obstructions and number of radiating centers rather than receiver sensitivity. Small delay spreads allow for higher symbol rate and favor antenna diversity techniques for overcoming multipath fading. Either spread spectrum or narrowband signals may be used, and narrowband signals may be advantageous for achieving high capacity spot coverage and dynamic channel allocation. Dynamic channel assignment algorithms are favored to provide rapid response to changing traffic requirements and to permit relatively small reuse patterns by taking advantage of physical obstructions. Low tier applications may include, for example, wireless local loop, spot coverage for "holes" in high tier coverage, localized high capacity, and wireless Centrex. While certain general characteristics of high tier and low tier applications have been described, these terms as applied herein are not meant to restrict the applicability of the principles of the present invention as set forth in its various embodiments. Categorization as high or low tier is merely intended to facilitate illustration of the exemplary embodiments described herein, and provide useful guideposts in system design. The designations of high or low tier are not necessarily exclusive of one another, nor do they necessarily encompass all possible communication systems. High tier and low tier designations may be applied to operations in either the licensed or unlicensed frequency bands. In the unlicensed isochronous band (1910-1920 MHz), FCC rules essentially require a TDD or TDMA/FDD hybrid because of the narrow available frequency range, with a maximum signal bandwidth of 1.25 MHz. "Listen before talk" capability is commonly required in order to sense and avoid the transmissions of other users prior to transmitting. Applications in the isochronous band are typically of the low tier variety, and include wireless PBX, smart badges (e.g., position determining devices and passive RF radiating devices) , home cordless, and compressed video distribution. Dynamic channel allocation and low tier structure is preferred due to the FCC requirements. Further, power limitations generally preclude large cells. In the Industrial Scientific Medical (ISM) band (2400- 2483.5 MHz), applications are similar to the unlicensed isochronous band, except that the federal regulations are somewhat less restrictive. Spread spectrum techniques are preferred to minimize transmission power (e.g., to 1 watt or less) , with a minimum of 10 dB processing gain typically required. A TDD or TDMA/FDD hybrid structure is preferred due to the small frequency range of the ISM band. Figure 14 is a summary chart comparing various air interfaces, generally grouped by high tier and low tier designations. The first column of Fig. 14 identifies the air interface type. The air interface type is identified by the chipping rate, tier, and frame structure -- either TDD (single frequency band with time division) or FDD/TDMA (multiple frequency bands with time division) , such as described earlier with respect to Figs. 10A-E and 11A-D. Thus, for example, the identifier "5.00HT" appearing in the first row of the first column of the chart of Fig. 14 identifies the air interface as having a chipping rate of 5.00 Megachips (Mcp), being high tier, and having a TDD structure. Similarly, the identifier "0.64LF" appearing in the sixth row of column one identifies the air interface as having a chipping rate of 0.64 Mcp, being low tier, and having an FDD/TDMA structure. A total of 16 different air interfaces (10 high tier, 6 low tier) are summarized in Fig. 14. The second column of the chart of Fig. 14 identifies the duplex method, which is also indicated, as described above, by the last initial of the air interface type. The third column of the chart of Fig. 14 identifies the number of time slots for each particular air interface type. For the particular described embodiments, time slots range from 8 to 32. The fourth column of the chart of Fig. 14 identifies the chipping rate (in MHz) for each particular air interface type. The fifth column of the Fig. 14 chart indicates the number of channels in each allocation, which is an approximation of the number of supportable RF channels given a particular bandwidth allocation (e.g., 30 MHz), and may vary according to a chosen modulation technique and the chipping rate. The sixth column of the Fig. 14 chart indicates the sensitivity (in dBm) measured at the antenna post. The seventh and eighth columns of the Fig. 14 chart indicate the number of base stations required in different propagation environments, with 100% being a reference set with respect to the 5.00HT air interface. The propagation environments considered in the Fig. 14 chart include R 2 (open area) , R 4 (urban) , and R 7 (low antenna urban) , as listed. The air interface types in Fig. 14 are also broken into four general categories, including high tier, low tier, unlicensed isochronous, and ISM air interface types. High tier operation assumes antenna diversity (L ant ) using two antennas, a number of resolvable multipaths (L rake ) of two, and a 30 MHz bandwidth allocation. The number of resolvable multipaths is generally a function of receiver capability, delay spread and antenna placement. Low tier operation assumes antenna diversity using three antennas, a single resolvable communication path, and a 30 MHz bandwidth allocation. Unlicensed isochronous operation assumes antenna diversity using three antennas, a single resolvable communication path, and a 1.25 MHz channel bandwidth. ISM operation assumes antenna diversity using three antennas, a single resolvable communication path, and an 83.5 MHz bandwidth allocation. Figure 15 compares the digital range limits (in miles) for the air interfaces described in Fig. 14. Digital range depends in part upon the number of time slots employed and whether ranging (i.e., timing adjustment control) is used. The multiple columns under the heading "Ranging Used" indicate whether or not timing control is implemented in the system, and correspond in the same order to the multiple columns under the "Time Slots" heading, which indicates the number of time slots used. The multiple columns under the "Digital Range" heading correspond in the same order to the columns under the "Ranging Used" and the "Time Slots" headings. Thus, for example, with the 5.00HT air interface, there are three possible embodiments shown. A first embodiment uses 32 time slots and ranging (timing adjustment) , leading to a digital range of 8.47 miles. A second embodiment uses 32 time slots and no ranging, leading to a digital range of 1.91 miles. A third embodiment uses 25 time slots and no ranging, leading to a digital range of 10.06 miles. It may be observed from the exemplary system parameters shown in the Fig. 15 chart that digital range may be increased either by reducing the number of time slots used, increasing the chipping rate, utilizing multiple frequency bands (i.e., using FDD and TDD techniques) , or using ranging (timing adjustment) . Figure 16 is a chart describing the impact of various air interface structures on base-user initial handshaking negotiations and on time slot aggregation. The variables considered in Fig. 16 are whether the base station 304 operates in a ranging or non-ranging mode, whether the user station 302 has a diplexer, whether a forward link antenna probe signal is employed, and whether interleaved traffic streams are supported. The number of base time slots which must occur between each communication are shown under the heading "Number of Base Slots Forbidden Between." The number is different for initial acquisition transactions, which appear under the sub-heading "GP/SP Negotiations" (GP referring to general polling messages, and SP referring to specific polling messages, as explained previously herein) , and for traffic mode transactions, which appear under the heading "Same Mobile Traffic Slots." The latter number determines maximum slot aggregation, which appears in the last column (as a percentage of the total time frame) . From the Fig. 16 chart, it can be seen that supporting ranging transactions may require a system to take into consideration delays in initial acquisition transactions. Further, the ability to support ranging transactions may also impact slot aggregation potential. This impact may be mitigated or eliminated if the user station 302 is outfitted with a diplexer, allowing the user station 302 to transmit and receive signals simultaneously. Tables A-l through A-28 (pp. 103-130) set forth illustrative high tier and low tier air interface specifications in more detail. In particular, specifications are provided for the air interfaces designated as 5.00 HT, 2.80 HF, 1.60 HF, 1.40 HF, 0.64 LF, 0.56 LF, and 0.35 LF in various configurations. Figure 13C is a chart comparing preamble detection performance in high tier and low tier environments for a number of different air interfaces previously described. Longer preambles may be desired for asynchronous code separation, particularly in high tier applications. Shorter preambles may suffice for selected non-spread low tier and unlicensed isochronous environments, particularly where larger average N reuse patterns are employed. The Fig. 13C chart tabulates preamble detection performance in Rayleigh fading assuming use of three antennas and employment of antenna diversity techniques, wherein the strongest of the three antenna signals is selected for communication. For preamble detection, it is desirable to have at least a 99.9% detection probability to ensure reliable communications and to prevent the preamble from becoming a link performance limiting factor. Antenna probe detections are not required to be as reliable because they are used only in diversity processing, so a failure to detect an antenna probe signal merely leads to a power increase command for the forward link. Associated with each air interface type listed in the Fig. 13C chart is an exemplary preamble codeword length in the second column thereof, and an exemplary antenna probe codeword length (for each of three antenna probe signals in three- antenna diversity) in the fourth main column thereof. Codeword length is given in chips. The third main column and the fifth main column of the Fig. 13C chart compare detection performance for a 99.9% detection threshold and a 90% detection threshold, respectively, for the case of no sidelobe and a -7 dB peak sidelobe. As preamble codeword length decreases, relative cross-correlation power levels (i.e., the power difference between the peak autocorrelation power level and the cross-correlation power level) increase. Thus, the Fig. 13C chart shows that raising detection thresholds to reject cross-correlation sidelobes from other transmitters also leads to degraded preamble detection performance. A higher signal-to-noise ratio for the system may be necessary where preamble detection thresholds are raised. A flexible, highly adaptable air interface system has thus far been described, having application to TDD and FDD/TDMA operations wherein either spread spectrum or narrowband signal techniques, or both, are employed. Basic timing elements for ranging transactions and traffic mode exchanges, including a provision for a control pulse preamble, are used in the definition of a suitable frame structure. The basic timing elements differ slightly for TDD and FDD/TDMA frame structures, as described with respect to Figs. 10A and IIA. The basic timing elements may be used in either a fixed or interleaved format, and either zero offset format or an offset format, as previously described. The frame structures are suitable for use in high tier or low tier applications, and a single base station or user station may support more than one frame structure and more than one mode (e.g., spread spectrum or narrowband, or low or high tier) . Advantages exist with both the TDD and FDD/TDMA air interface structures. A TDD structure more readily supports asymmetric data rates between forward and reverse links by shifting a percentage of the timeline allocated to each link. A TDD structure allows for antenna diversity to be accomplished at the base station 304 for both the forward and reverse links since the propagation paths are symmetric with respect to multipath fading (but not necessarily interference) . A TDD structure also permits simpler phased array antenna designs in high-gain base station installations because separate forward and reverse link manifold structures are not needed. Further, TDD systems are more able to share frequencies with existing fixed microwave (OFS) users because fewer frequency bands are needed. An FDD/TDMA structure may reduce adjacent channel interference caused by other base or mobile transmissions. An FDD/TDMA system generally has 3 dB better sensitivity than a comparable TDD system, therefore potentially requiring fewer base stations and being less expensive to deploy. An FDD/TDMA structure may lessen sensitivity to multipath induced intersymbol interference because half the symbol rate is used as compared with TDD. Further, mobile units in an FDD/TDMA system may use less power and be cheaper to manufacture since bandwidths are halved, D/A and A/D conversion rates are halved, and RF related signal processing elements operate at half the speed. An FDD/TDMA system may require less frequency separation between adjacent high and low tier operations, and may allow base stations to operate without global synchronization, particularly when in low tier modes. Digital range may also be increased in an FDD/TDMA system because the timelines are twice as drawn out. Figure 18 is a block diagram of a particular low IF digital correlator for use in a receiver operating in conjunction with the air interface structures disclosed herein, although it should be noted that a variety of different correlators may be suitable for use in the various embodiments disclosed herein. In the Fig. 18 correlator, a received signal 1810 is provided to an analog-to-digital (A/D) converter 1811. The A/D converter 1811 preferably performs one or two bit A/D conversion and operates at roughly four times the code rate or higher. Thus, code rates of 1.023 MHz to 10.23 MHz result in sample rates for A/D converter 1811 in the range of 4 to 50 MHz. The A/D converter 1811 outputs a digitized signal 1812, which is connected to two multipliers 1815 and 1816. A carrier numerically controlled oscillator (NCO) block 1821 and a vector mapping block 1820 operate in conjunction to provide an appropriate frequency for demodulation and downconversion to a low IF frequency. The vector mapping block 1820 outputs a sine signal 1813 and a cosine signal 1814 at the selected conversion frequency. The sine signal 1813 is connected to multiplier 1815, and the cosine signal 1816 is connected to multiplier 1816, so as to generate an I IF signal 1830 and a Q IF signal 1831. The I IF signal 1830 is connected to an I multiplier 1842, and the Q IF signal 1831 is connected to a Q multiplier 1843. A code NCO block 1840 and a code mapping block 1841 operate in conjunction to provide a selected spread spectrum code 1846. The selected spread spectrum code 1846 is coupled to both the I multiplier 1842 and the Q multiplier 1843. The output of the I multiplier 1842 is connected to an I summer 1844 which counts the number of matches between the I IF signal 1030 and the selected spread spectrum code 1846. The output of the Q multiplier 1843 is connected to an Q summer 1845 which counts the number of matches between the Q IF signal 1031 and the selected spread spectrum code 1846. The I summer 1844 outputs an I correlation signal 1850, and the Q summer 1845 outputs a Q correlation signal 1851. Alternatively, a zero IF digital correlator may be used instead of a low IF digital correlator. A zero IF digital correlator performs I and Q separation prior to A/D conversion, hence requiring the use of two A/D converters instead of one. The A/D converters for the zero IF correlator may operate at the code rate, instead of at four times the code rate as is done by A/D converter 1811. Figure 19A is a block diagram of an exemplary dual-mode base station capable of operating over multiple frequencies and having both spread spectrum and narrowband communication capabilities. The base station block diagram of Fig. 19A includes a frequency plan architecture for use with a low IF digital transceiver ASIC 1920. The base station may employ an FDD technique wherein the user stations 302 transmit at the lower duplex frequency, and the base station 304 transmits at the higher duplex frequency. The base station of Fig. 19A preferably uses a direct synthesis digital CPM modulator, such as described, for example, in Kopta, "New Universal All Digital CPM Modulator, " IEEE Trans. COM (April 1987) . The Fig. 19A dual-mode base station comprises an antenna 1901, preferably capable of operating at a 2 GHz frequency range. The antenna 1901 is connected to a diplexer 1910, which allows the base station to simultaneously transmit and receive signals through the antenna 1901. The transmitted and received signals are translated to appropriate frequencies generated by multiplying or dividing a master clock frequency output from a master oscillator 1921. The master oscillator 1921 generates a master frequency (e.g., 22.4 MHz) which is provided to a clock divider circuit 1922 for dividing the master frequency by a predefined factor, e.g., 28. The master oscillator 1921 is also connected to another clock divider circuit 1926 which divides the master frequency by a programmable parameter M, determined by the physical layer with over which the base station operates. The output of clock divider circuit 1926 may be further divided down by another clock divider 1927 which divides by a programmable parameter M2, in order to support a second mode of operation over a different physical layer, if desired. Signals to be transmitted are provided by ASIC 1920 to a digital-to-analog (D/A) converter 1933, which is clocked by a signal from clock divider circuit 1926. The output of the D/A converter 1933 is connected to a low pass filter 1934 to provide smoothing of the signal envelope. The low pass filter 1934 is connected to a multiplier 1936. An output from the clock divider circuit 1922 is connected to a frequency multiplier circuit 1935 which multiplies its input by a conversion factor, such as 462. The frequency multiplier circuit 1935 is connected to a multiplier 1936, which multiplies its inputs to generate an IF transmission signal 1941. The IF transmission signal 1941 is connected to a spread spectrum bandpass filter 1937 and a narrowband bandpass filter 1938. The spread spectrum bandpass filter 1937 is a wideband filter, while the narrowband bandpass filter 1938 operates over a relatively narrow bandwidth. The bandpass filters 1937 and 1938 filter out, among other things, CPM modulator spurs from the transmitter. A multiplexer 1939 selects between an output from the spread spectrum bandpass filter 1937 and an output from the narrowband bandpass filter 1938, depending upon the mode of operation of the base station. Multiplexer 1939 is connected to a multiplier 1931. The clock divider circuit 1922 is connected to another clock divider circuit 1923, which divides its input by a factor, e.g., of 4. The output of the clock divider circuit 1923 is connected to a frequency multiplier circuit 1930, which multiplies its input by a factor of (N + 400) , where N defines the frequency of the receiving channel, as further described herein. The frequency multiplier circuit 1930 is connected to the multiplier 1931, which multiplies its inputs to generate an output signal 1942. The output signal 1942 is connected to the diplexer 1910, which allows transmission of the output signal 1942 over the antenna 1901. Signals received over the antenna 1901 pass through the diplexer 1910 and are provided to a multiplier 1951. Clock divider circuit 1923 is connected to a frequency multiplier circuit 1950, which multiplies its input by a factor of, e.g., N. The frequency multiplier circuit 1950 is connected to multiplier 1951, which combines its inputs and generates a first IF signal 1944. The first IF signal 1944 is connected to a spread spectrum bandpass filter 1952 and a narrowband bandpass filter 1953. The spread spectrum bandpass filter 1952 is a wideband filter, while the narrowband bandpass filter 1953 operates over a relatively narrow bandwidth. The bandpass filters 1952 and 1953 remove image noise and act as anti-aliasing filters. A multiplexer 1954 selects between an output from the spread spectrum bandpass filter 1952 and an output from the narrowband bandpass filter 1953. Multiplexer 1954 is connected to a multiplier 1960. An output from frequency multiplier circuit 1935 is also connected to multiplier 1960, which outputs a final IF signal 1946. The final IF signal 1946 is connected to a low pass filter 1961 and thereafter to an A/D converter 1962. The A/D converter 1962 is clocked at a rate determined by the clock divider circuit 1926. The output of the A/D converter is provided to ASIC 1920 for correlation and further processing. In particular, the received signal may be processed by the low IF correlator shown in Fig. 18 and described above, in which case A/D converter 1961 may be the same as A/D converter 1811. Typically, due to cost and equipment constraints, only one narrowband and one spread spectrum mode will be supported, although as many modes as needed can be supported by a single base station by providing similar additional hardware. Figure 19B is a chart showing selected frequencies and other parameters for use in the dual-mode base station of Fig. 19A. The Fig. 19B chart is divided according to spread spectrum and narrowband modes. The first three columns relate to different transmission rates using spread spectrum techniques, and the latter four columns relate to different transmission rates using narrowband techniques. The frequencies in each column are given in megahertz. The master oscillator frequency is designated in Fig. 19B as fO. M and M2 are programmable divide ratios for clock divider circuits 1926 and 1927. The sample rate in Fig. 19B applies to the A/D converter 1962 and D/A converter 1933. The Fs/(IB+Fch) figure represents the sampling ratio. The final IF frequency and second IF frequency are the center frequencies of the bandpass filters. Towards the bottom of Fig. 19B are sample first LO and N numbers for three different input frequencies, 1850 MHz, 1850.2 MHz, and 1930 MHz. The frequencies and other parameters appearing in the Fig. 19B chart may be selected by use of a microprocessor or other software controller, which may refer to the system timing information or clocks as necessary to coordinate the time of switching the selected frequencies and other parameters when necessary. A user station 302 may be designed in a similar fashion to the dual-mode base station of Figs. 19A-B, except that a user station 304 may not require a diplexer 1910 in air interface structures wherein the user station 302 does not need to transmit and receive simultaneously. Also, frequency multiplier circuits 1930 and 1950 would be swapped because the user station 302 transmits and receives on the opposite frequency bands from the base station 304. Alternative Embodiments While preferred embodiments are disclosed herein, many variations are possible which remain within the concept and scope of the invention, and these variations would become clear to one of ordinary skill in the art after perusal of the specification, drawings and claims herein. For example, although several embodiments have generally been described with reference to spread spectrum communication, the invention is not limited to spread spectrum communication techniques. In some narrowband applications, no preamble would be required as code synchronization is not an issue (although synchronization within a TDD or TDMA structure would still be necessary) . Moreover, while the control pulse preamble described with respect to Figs. 10A-E and 11A-D facilitates operation in some environments, these embodiments may also be implemented without the control pulse preamble. The various functions carried out by the control pulse preamble (e.g., power control, antenna selection, and the like) may be accomplished by analyzing other portions of the user transmission, or may not be necessary. In an alternative embodiment, one or more system control channels are used so as to facilitate paging of and other transactions with user stations 302 operating within a covered region. In this embodiment, the control channel or channels provide base station or system information including traffic information at neighboring base stations to assist in handoff determinations, system identification and ownership information, open time slot information, antenna scan and gain parameters, and base station loading status. The control channel or channels may also specify user station operating parameters (e.g., timer counts, or actionable thresholds for power control, handoff, and the like) , provide incoming call alerting (e.g., paging), provide time frame or other synchronization, and allocate system resources (e.g., time slots) . In heavy traffic (i.e., where a substantial portion of time slots are in use) , it may be beneficial to dedicate a fixed time slot to handling paging transactions so as to minimize user station standby time. Further, a fixed paging time slot may eliminate the need for periodically transmitting a general polling message from the base station in various time slots when open, and thereby eliminate possible interference between polling messages from the base station 304 and forward link traffic transmissions. System information is preferably broadcast over the fixed paging time slot at or near full power so as to enable user stations 302 at a variety of ranges to hear and respond to the information. This alternative embodiment may be further modified by outfitting the user stations 302 with selection diversity antennas and eliminating the user of control pulse preamble transmissions. Two preambles may be sent on the forward link, rather than using a control pulse preamble followed by a reverse link transmission followed by another forward link transmission. A comparison of such a structure with the previous described embodiments is shown in Fig. 17. In Fig. 17, the air interface type is identified in the first column as before, but with a trailing "D" indicating a user station 302 having a selection diversity antenna, and a trailing "P" indicating a user station 302 having no diversity selection antenna but employing a control pulse preamble (or "PCP") . As shown in the Fig. 17 chart, digital range is improved for the alternative embodiment employing a diversity antenna, or the number of time slots may be increased. These gains accrue because elimination of the pulse control preamble increases time available in each time frame, which may be devoted to expanding the serviceable range or increasing the number of available time slots. In another alternative embodiment, user transmissions are conducted before base transmissions. In this embodiment, no control pulse preamble may be needed as the base station 304 obtains information relating to mobile power and channel quality by analyzing the user transmission. However, in such an embodiment, there is a longer delay from when the base station 304 issues an adjustment command to the user station 302 until the user station actually effectuates the adjustment command in the following time frame, thereby increasing latency in the control loop. Whether or not the control loop latency adversely impacts performance depends on the system requirements. In addition to the above modifications, inventions described herein may be made or used in conjunction with inventions described, in whole or in part, in the following patents or co-pending applications, each of which is hereby incorporated by reference as if fully set forth herein: U.S. Patent 5,016,255, issued in the name of inventors Robert C. Dixon and Jeffrey S. Vanderpool, entitled "Asymmetric Spread Spectrum Correlator" ,* U.S. Patent 5,022,047, issued in the name of inventors Robert C. Dixon and Jeffrey S. Vanderpool, entitled "Spread Spectrum Correlator"; U.S. Patent 5,285,469, issued in the name of inventor Jeffrey S. Vanderpool, entitled "Spread Spectrum Wireless Telephone System" ,* U.S. Patent 5,291,516, issued in the name of inventors Robert C. Dixon and Jeffrey S. Vanderpool, entitled "Dual Mode Transmitter and Receiver"; U.S. Patent No. 5,402,413, issued in the name of inventor Robert C. Dixon, entitled "Three Cell Wireless Communication System" ; U.S. Patent Application Serial No. 08/161,187, filed December 3, 1993, in the name of inventor Robert C. Dixon, entitled "Method and Apparatus for Establishing Spread Spectrum Communication" ; U.S. Patent Application Serial No. 08/146,491, filed November 1, 1993, in the name of inventors Robert A. Gold and Robert C. Dixon, entitled "Despreading/Demodulating Direct Sequence Spread Spectrum Signals"; U.S. Patent Application Serial No. 08/293,671, filed August 18, 1994, in the name of inventors Robert C. Dixon, Jeffrey S. Vanderpool, and Douglas G. Smith, entitled "Multi-Mode, Multi-Band Spread Spectrum Communication System"; U.S. Patent Application Serial No. 08/293,671 filed on August 1, 1994, in the name of inventors Gary B. Anderson, Ryan N. Jensen, Bryan K. Petch, and Peter 0. Peterson, entitled "PCS Pocket Phone/Microcell Communication Over-Air Protocol"; U.S. Patent Application Serial No. 08/304,091, filed September 1, 1994, in the name of inventors Randy Durrant and Mark Burbach, entitled "Coherent and Noncoherent CPM Correlation Method and Apparatus"; U.S. Patent Application Serial No. 08/334,587, filed November 3, 1994, in the name of inventor Logan Scott, entitled "Antenna Diversity Techniques"; and U.S. Patent Application Serial No. 08/383,518, filed February 3, 1995, Lyon & Lyon Docket No. 201/081, in the name of inventor Logan Scott, entitled "Spread Spectrum Correlation Using SAW Device." It is also noted that variations in the transmission portion 502 of the time frame 501 may be employed. For example, systems employing error correction on the forward link (i.e., the base transmission) may interleave data destined for different user stations 302 across the entire burst of the transmission portion 502. Spread TDD W Link Dβαigner 3 TDD, Spread M-ary TDD, Spread M-ary TDD, Spread M-ary TDD, Spruαd M- ary FDD Setup for page 145 Operation with Email slota with Big Slots Vox Slota , Ranging Var Slots , Linked t- 5.000 Hill Chip Ratu S .000 Mill Chip Rate 5.000 Mill Chip Rαtu 5.000 MHz Chip Raio 32.0 x 0.00 kbpo 25.0 x 0.00 kbpa 32 .0 x 0.00 kbpo Os tfl Reveraa Forward Slotting B.fticiAbcyi Link Link υ 0- 2-wαy Meaaage Prime Duration (uaec) i 625.00 £25.00 Baae T/ft ' Switch Time (chlpa) i 32 32 Baae T/R Switch Time (uaeo) ■ 6.40 6.40 Mobile l->3 Tranalent Time (chlpa) i 32 32 Mobile l->2 Tranalent Time (uaeo) i 6.40 6.40 Baae R/T Switch Time (chlpa) i 32 32 Baae R/T Switch Time (uaec)i 6.40 6.40 Total switch Time (uaec) ■ 19.20 19.20 Mobile Timing Error Allowance (cnpa) i 0 0 Mobile Timing Brror Allowance (uaec) i 0.00 0.00 Max Range Bin Step Size (mi) i 0.00 0.00 To al Non Ouard Time Overhead (uaec) i 19.30 19.20 Number oC 2-way TDD Ouardei 2 2 TDD Max Cell Radiua (mi) i 1.91 1.91 C Total TDD Ouard Time Available(uaec) i 41.00 41.00 O Total TDD Ouard Time Avail, (ch pa) i 205.00 205.00 H Q) Ouard Time per TDD Ouard (chlpa) i 102.50 102.50 ■-) Total Ouard Time (uaeo) i 60.20 60.20 Λ Slot structure Blficlencyi 90.37 90.37% D of Ant Frobea to Send (Forward Link) 0 0 . Baae Antenna Probe Length (chlpa) 0 2B λntenna Switch Time (chlpa) 4 4 Total Chlpa per Antenna Word (chlpa) 4 32 PCP Sync Word Length (chlpa) 56 0 Antenna Select (aymbola) 1 0 Antenna Select (blta) 5 0 FCP Duration (chlpa) 0 sync Word Length (chlpa) 56 56 Overhead Length (Chlpa) 144 56 Deader Meeaage Length (blta) 31 21 D-channel Keaaage Length (blta) S B-Channel Maaaage Length (blta) 160 160 n-Channel Maaaage Length (bit*) 0 0 CRC Blta in Tratfiσ Hod* (bit*) 16 16 Simplex Mβaaage Length (blta) 205 205 Os slrrplex Maaaage Length (aymbola) 41 41 Simplex Maaaage Length (chlpa) 1313 1312 Total Number ot Chlpa 1456 1360 o 5 o Hr Sproαd TDD Tranumlt Slot Duration (ueoc) i 291.20 373. CO 391.30 373. CO IΛ O One Slot B-Chαnnβl Data Rate (J-pβ) i Os Aggregate B-Chαnnel D ta Rat* (lbpβ) i I'¬ 300 300 Max . of Voice Chαnnelβ per RF Channel i 35 35 e Superrramβ Duration ( aβc) i Os 30 30 CΛ Chlpa/Sloti 4000 υ Chip Duration (uaec) i 0.30 Uttuo slot Layout (mobile at zero range) i (ueoc) (chipo) (uaac) (chipo) (uooc) (chips) (uooc) (chipo) Baae Tx Preαrrble START i 0.00 0 B ae Tx Preamble BNDi 11.20 56 B ae Tx Maaaage STARTi 11.20 56 Bate Tx Mttaaøe BNDi 373.60 1368 Base Tx Antenna Maaaage STARTI 273.60 1368 Bαae Tx Antenna Maaaage BNDi 373.60 1368 Baβ* Twiddlea Thumba (FDD only) STAR i Bαae Twiddlea Thutoba (FDD only) BNDi Bαae T->R Switch STARTi 373.60 1368 Bαaβ T->R Switch BNDi 260.00 1400 O Baae Rx Preamble STARTI 380.00 1400 Baae Rx Preamble BNDi 391.30 1456 Base Rx Maaaage STAR i 291.20 1456 Ba.ee Rx Meaaαge ENDi 553.60 2768 Baeβ Rx Guard Time 1 or 3 STARTI 553.60 2768 Baae Rx Ou rd Time 1 or 3 BNDi 574.10 2870.5 Baae Rx Time Error Allowance 1 STAR i 571.10 2870.5 Baae Rx Time Error Allowance 1 BNDi 574.10 2870.5 Mobile l->2 Tranalent Time (T/R) STARTI 574.10 2870.5 Mgbile l->3 Tranalent Time (T/R) BNDi 580.50 2903.5 Bαaβ Rx PCP STARTI 580.50 3903.5 Bαae Rx PCP BNDi 598.10 3990.5 Baeβ Rx Ouαrd Time 1 STARTi ' 598.10 3990.5 Bαae Rx Guard Time 1 ENDi 618.60 3093 Baae Rx Time Error Allowance 3 STARTI 618.60 3093 Baeβ Rx Time Error Allowance 3 BNDi 618.60 3093 Mob 2->l Tr na or Bαaβ R->T βwtcb STARTi 618.60 3093 Mob 2->l Trana or Bαae R->T Swtch BNDi 625.00 3135 Leftovera (Better be £ero) i 0.00 0 Os o Os -.'proad TDD V) Data natea/RF Channeli O Os © DW per RP Channel/Chip Rate (JrJJx) VO Frequency Reuββ Factor (H) Os Minima System Bandwidth (XHx) t/l ji fl/I (dB) H Hoiβe Figure 9 290K (dB) υ Antenna Teorperature (K) Oyβ W ino. NF (dBu/Uz) Bye W inc. HF (r-M/Wli) Iπ-plimβntation Loss (dB) 1/ (3. BW) (num) M-ary NonCoher Format Bite per Symbo Required Frame Brror Rat Framo βDgth for Kb/Ho Cole, (bite) Actual Eqv. Frame Length (bi a) Antenna Divβraity Facto RaJce Diversity Facto Required Eb/No (dB) 1/Eb/lto (num) o Seneitivity l_n 3/1 (dBm) H Seneitivity,Therm Noiββ Only (dBm) S/I Induced Seneitivity oaa (dB) Required ββneitivity in S/I(mH) Max Simplex Data Rate (kbpa) Max Simplex Symbol Rate (kepa) Chlpa per Symbo Symbol Duration (uaec Chlpa per Bi Proc a using Oαin per bit (dB) S/(N*I) into A/D (dB S/N into A/D (dB Max Duplex Data Rate (lcbpa Pilot channel Overhead (kbpi Dearer Channel Duplex Rate (kbpβ Link Aeyraoβtry Factor (dB o e • •< Ό — m ft- to LΠ . . • . KQ l~, Spread FDD 12 cii ' P f PDD, Spread M-αry FDD, Spread M-αry FDD, Spread M-ary FDD, Sproad M-axγ on Vαr Slota, Ranging Vαr Slota, Linked with Small Slota with Big Slots 2.800 MUt Chip Rata 2.800 Mill Chip Ra o 2.800 Mllz Chip Rato 2.800 Mllz Chip I U 32.0 x 8.00 kbpa 32.0 x 8.00 kbpa 2Θ .0 x 8.00 kbpa Rβvβrae Forward Reverse Forward Reverse Forward Link Link Link Link Link Link (uaec) i 625.00 625.00 625.00 625 00 625.00 chlpa) i 0 32 0 0 32 (uaec) I 0.00 11.43 0.00 0.00 11.43 chlpa) i 32 0 32 32 0 (uaβα) i 11.43 0.00 11.43 11. 43 0.00 chlpa) i 32 0 32 • 32 0 (uaeα) i 11.43 0.00 11.43 11. 43 0.00 (uaec) i 22.86 11.43 22.86 22 .86 11.43 Mobile Timing Error Allowance (cbpa) i 0 114 59 0 114 Mobile Timing Brror Allowance (uaeα) i 0.00 40.71 21.07 Dina 0.00 40.71 Max Range Bin Step Size (oi) i 0.00 3.79 1.96 6.97 0.00 3 .79 Total Non Ouαrd Time Overhead (uaec) i 22.86 52.14 65.00 22 .86 52 .14 Number of -way TDD Ouard*i 1 1 2 2 1 O TDD Max Cell Radiue (oi) i 13 .67 -0.00 0.00 1.96 -0.00 I o Total TDD Ouαrd Time Available(uaec) i 146.79 -0.00 0.00 42 .14 -0.00 H Total TDD Guard Time Avail, (chlpa) i 411.00 -0.00 0.00 118.00 -0.00 Ouard Time per TDD Ouαrd (chlpa) i 411.00 -0.00 0.00 59 .00 -0.00 Total Ouαrd Time (uaec) i 169.64 52.14 65.00 65.00 52.14 Slot Structure Bfficiencyi 72.86% 91.66% 89.60% 89.60% 91.66% Xt t o£ Act Probβa to 8and (Forward Link) 0 3 0 0 3 . Baae Antenna Probe Length (chlpa) 56 56 56 56 56 Antenna Switch Time (chlpa) 4 4 4 4 4 Total chlpa per Antenna Kord (chlpa) 60 60 60 60 60 PCP Sync Word Length (chlpa) 112 0 112 112 0 Antenna Select (aymbola) 1 0 1 1 0 Antenna Select (bite) 5 0 5 5 0 PCP Duration (chlpa) 144 0 144 144 0 sync Kord Length (chlpa) 112 112 112 112 112 Overhead Length (Chlpa) 256 292 256 256 292 Be der Mαaaαgβ Length (blta) 21 21 21 21 21 21 D-Chαnnal Heaaαgβ Length (blta) S 0 0 D-channel Neaaαga Length (blta) 105 160 160 160 160 160 K-Channel Meaaαge Length. (blta) 0 0 0 0 0 0 rr CRC Bita is Traffic Mode (bite) 16 16 16 16 16 16 sisφlex Maaaage Length (bita) ISO 205 205 205 205 205 Sinplex Meaaαge Length (aymbola) 30 41 41 41 41 41 Simplex Heaaαge Length (chlpa) 960 1312 1312 1312 1312 1312 Total Number of Chlpa 1216 1604 1560 1604 1568 1604 O I Sy l« Spread DD Transmit Slot Duration (uaec) i 4341 .29 572 . 06 560 .00 572 . 06 560. 00 572 . 86 560 .00 572 . 06 Os One Slot S-Channel Data Rate (kbpa) i t- Aggregate B-Channel Data Rate (kbpe ) ι o Mux D of Voice Channel a per RF Channel i Superf rame Duration (msec) i CΛ H Chlpa /Slot i υ chip Duration (uaec) i Dan e slot Layout (mobile at zero range) i (uaec) (chlpa) (uaec) (chipo) (uaec) (chlpa) (uaec) (chlpa) Bαiβ Tx Preamble STARTi Baae Tx Preamble BNDi Baae Tx Maaaage STARTi Baae Tx Maaaage EMDi Base Tx Antenna Maaaage STAR i Baae Tx Antenna Maaaage BllDi llano Twiddlea Thumbs (PDD only) STARTI Base Twiddlea Thumbs (FDD only) BNDi Bαaβ T->R Switch fiTARTi O Bαae T->R Switch BNDi Baae Rx Preamble STARTi Baae Rx Preamble BNDi Base Rx Message STAR i Baae Rx Message BNDi Base Rx Guard Time 1 or 2 STAR i Base Rx Guard Time 1 or 2 ENDi Base Rx Time Error Allowance 1 STARTi Base Rx Time Error Allowance 1 BNDi Mobile l->2 Tranalent Time (T/R) OTARTi Mobile l->2 Tranalent Time (T/R) ENDi Bαae Rx PCP STAR i Bαae Rx PCP BNDi Bαae Rx Ouαrd Time 1 STARTI Bate Rx Guard Time 1 BNDi oβo Rx Time Error Allowance 2 STARTI Baae Rx Time Error Allowance 2 ENDi Hob 2->l Trana or Base R->T Swtch STARTI Mob 2->l Trana or Base R->T Swtch ENDi Leftovers (Better be Zero) i Os r O-s JO VC O o Spread FDD IΛ e O I'¬ Data Rates/RF Channel i ve BW per RF Channel/chip Rate (kflxj Os tfl Frequency Reuse rector (tt) Mlnlmim system Bandwidth (kHz) H \ 8/1 (dB) υ ' ttoiaβ , Figure 0 290K (dB) 0- Antenna Temperature ( ) Sya kT inc. HF (dBm/Hx) Sya kT inc. NP (mM/kUl) Uirpllmantαtion Loss (dB) 1/ (8. Bit) (num) M-ary NαnCohar Format Bita per Symbol Required Frame Error Rate Frama Length for Bb/No Cola, (bita) Actual Eqv. Frame Length (bita) Antenna Diversity Factor Rake Divβreity Factor Required Kb/Ho (do) o 1/Eb/NoL (num) H Sensitivity in e/I (dBm) Son-itivity,Therm Naiβe Only (dBm) 3/1 Induced Seneitivity Lose (dB) Required seneitivity in S/I(mJ») Max Simplex Data Rate (kbpa) Max Simplex Symbol Rate (kape) Chlpa per Symbol Symbol Duration (uaec) Chips per Bit Processing -tain per bit (dB) fl/(N+I) into A/D (dB) 8/N into A/D (dB) Max Duplex Data Rate (kbps)ι Pilot Channel overhead (kbpa)ι Bearer Channel Duplex Rate (kbpe)ι Link Asymmetry Factor (dB) I Os -5 ON co en o cn s si Table A- 8 *->*-- '» I ϊl'troαd FDD Link Deolgner 3 FDD. Spread H-ery FDD, Sproαd M-αry FDD, Spread M-ary FDD, Spraad M-aiy FDD Setup for page 145 Operation Ver Slota, Ranging Ver Slote, Linked with Small Slote with Dig Slotv 1.(00 Mil Chip Bete 1.600 Hilt Chip Ratu 1.600 Hill Chip Roto 1.600 Mllz Clilp lui . 11.1 x 1.00 kbpa 20.0 x 8.00 kbpa 20.0 x β.00 kbpa 16.0 x 0.00 kbpa Slotting Bf flcljon yi J -uαy lloαaagβ Prαjr-i Duration (uaec) i Deaa T/R Switch Time (chlpa) i Base T/R Switch Time (uaec) i lloblla l->3 Tranalent Time (chlpa) i Habile l->2 Tranalent Time (uaec) ι Baa- R/T Switch Time (cblpa) ι Daaa R/T Switch Tlαe (uaec) i Total Switch Tlαe (uaac) ι lloblla Timing Error λllowance (cbpa) i Mobile Timing Irror Allowance (uaec) ι Hex Range Bin Step Size (r-l) ι Tot al lion Ouαrd Tine overhead (uaec) ι lluraber of 2-way TDD Ouar a i TDD Hex Cell Radlue (ml) l Total TDD ouard Tlsβ λvallable(uaec) i Total TDD Ouard Time Avail , (chlpa) I ouαrd Time per TDD Ouard (chlpa) i Total ouard Tine (uaec) i Slot βttuctux* Btflαlancyi I oC λot Probaa to Sand (Forward Link) Baae Antenna Probe Length (chlpa) Antenna Switch Tiros (chlpa) Total Cliipe per λntennβ Hold (chlpa) PCP 6ync Hold Length (chlpa) Antenna Select (aymbola ) Antenna Select (blta ) PCP Duration (chlpa) Sync Word Length (chlpa) Overhead Length (Chlpa I Uaαdar Haaaage Length (blta) D-cbannel Heaaaga Length (blta D-Channa Haaaage Length (blta H-Cbannel Haaaage Length (blta) Os CRC Olta in Traffic Hode (blta) Slo-plex Haaaage Length (blta) slaplβx Heaaaga Length (ayαbolβ sli-plex Haaaage Length (chlpa Total I Jus-be r ot Chlp ON o Uo wr Spread FDD Transmit Slot Duration (aooc) i 725.00 920.7$ 945.00 920.75 aoo Slot B-Channol Date Rate (kbpa) i Aggregate B-Channβl Data Rate (kbps) i Max t ot Voice channels per RP Channeli Superframe Duration (msec) i Chips/Sloti Ch p Duration (uaec) i Uauo Slot Layout (mobile at zero range) i (uββc) (chips) (uooc) (chipo) (uooc) (chips) (ueoc) (chips) Base x Preamble STARTi Baae Tx Preamble BNDi Base Tx Message STARTi Base Tx Message ENDi Base Tx λntenna Message STAR i Base Tx λntenna Message BNDi Baoβ Twiddlea Thuinba (FDD only) STARTI Baoβ Twiddles Thumbs (FDD only) ENDi H Base T->R Switch STARTi H Base T->R Switch ENDi H Base Rx Preamble STARTi Base Rx Preamble BNDi Base Rx Message STARTi Base Rx Message ENDi Base Rx Ouard Time 1 or 2 STARTI Base Rx ouard Time 1 or 2 BNDi Base Rx Time Error Allowance 1 STARTI Baae Rx Time Error Allowance 1 BNDi Mobile l->2 Transient Time (T/R) STARTi Mobile l->2 Transient Time (T/R) BNDi Base Rx PCP STAR I Base Rx PCP ENDi Base Rx Ouard Time 1 STARTI Base Rx Ouard Time 1 BNDi Base Rx Time Error Allowance 2 STARTi Base Rx Time Error Allowance 2 BNDi Mob 2->l Trana or Base R->T Swtch STAR i Mob 2->l Trans or Base R->T Swtch BNDi Leftovers (Better be Zero) i Spread FDD Data Rates/RF Channel i e Ov r o- DH per RF Channel /Chip Rate (kHz) Frequency Reuse Factor (M) ve Ov Hlnlraim 3ys,tβm Bandwidth (kHz) tfl ■ 'I β/I (dB) ' Noi a e, Figure 9 290K (dB) H υ λntenna Temperature (K) sya jcT inc. NF (dBm/Uz) Sys JcT inc. HP (mW/klli) Implltαβntation Loss (dB) 1/ (3. BW) (num) M-ary Nαncohβr Format Bits per Symbo Required Frame Error Rat Fraiπo Length {or Hb/Mo Calα.(bits) Actual Bgv. Frame Length (bits) Antenna Diversity Facto Rake Diversity Facto Required Kb/Ho (dB) CN H 1/Kb/MoL (num) H Sensitivity in fl/I (dBm sensitivity,Therm Moiaβ Only (dBm) 3/1 Induced Senaitivity Loss (dB Required Sensitivity in a/I(m ) Max Simplex Data Rate (kbpa Max Simplex Symbol Rate (ksps) Chips per Symbo Symbol Duration (usec) Chips per Bi Processing Oain per bit (dB S/(t I) into λ/D (dB 3/M into λ/D (dB Max Duplex Data Rate (kbpa Pilot Channel Overhead (kbpβ Bearer Channel Duplex Rate (kbpβ Link Asytnαotry Factor (dB J H Qf ' ιe * tTe 3* peχ»ptπ * π β Bσ-» _ra BOO \∑ te-JTβ • »» P»X»ptn»H SBOS JH 6"00 X ta-ffg ->τ) sχβπu*ιτtp m jo jtKprt * nqαx lΛ*tT-rτxI->3 Mf trp»0 πoχ:)τjz-f-*oqoeg qon ιdvχj*Λθ • πroequY o-* enα sscr* jro oec i (πoqo»fj/»βι»a f j s-to-joeg o-fηcIτ)_r5oβo *aτv' 1 (PUP) TO -»ππβ->πγ errvα I (Km) -t#no,j -i πatrBJi eDs-teΛγ eevπ i (Km) jonoj q-pππtπMl -fe»; eavα 1 (POP) π-r-»o uππβqπγ etr rπiπ ■ (Mm) -tenoj qχτt*sτπ_ιχ »nvα»Λγ qerrprroi* I (Km) -tanoj q-rtπs*π-tχ v«d qoβptro** iβαox-tuT io-pjo Λq-fovdtjo H H ιeχaΛo Λqnα ii qoχs oχfSαχ; qeeptnrn W ιβχD<To Λqnα -J-pπβiit/Jtj, tjoγqτιqs eβvg i (o»βτπ) Λ»χeα βαχ-r»_ta T-rβp-rβj, XBTXJ i (sosm) Λt»χβα BαytrrBα trreprrβi eχβrt-*s '6*00 Z 3* poq:xoιj-triβ βOrroχja i EOO Vt * **i pa JxMns sC*τβχ-rs 'Cfl/IBI πj • • v»tpon.H jo e β τ-qαtoα»d ipeqαcxj-tntj »χ»σπvqo #o θΛ -teqn n T»H ' (*HH) l-t rtpt-rea *πo-)Stø poΛ-ιχ<Joa I3oqoββ βχβ πιtτo jij jo jβqarrvN ι(sdq-{) *-χtιoaχo eoχoΛ Jβd βqvn «qτ» ι(sdq ) βpoooΛ -ted e vn ββqjoΛo I (sdφO sqvij -tβpoooΛ i β τjoχq-»χτιoχBθ -TOO/Tetπ-rf OOJOΛ aai -jojis pruad FDD V) Link Dαolgnor 3 FDD, Sprαad M-ary FDD, Spread M-ary FDD, Sprood H-ary Ov I'DD, Spruαd M-aιy FDD Setup for page 145 Operation Var Slots, Ranging Var Slots, Linked w th Small Slota with Big Slo u 1.400 Mllz Chip Ratu 1.400 Mllz Chip Rate 1.400 Mllz Chip l t-u 1.400 Mil. Chip Hal.. vθ 10.5 x β.00 kbpa 16.0 x β.00 kbpα 16.0 x 8.00 kbpa 14.0 x 0.00 kbpu Ov tf H Slotting Bfficilncyi υ 2-way Moaβage Framo Duration (uaec) i Base T/R Switch Time (chlpa) i naββ T/R Switch Tlαe (usβc) i Mobile l->2 Transient Time (chlpa) i Mobile l->2 Transient Time (usec) i Baae R/T Switch Time (chlpa) i Baae R/T Switch Time (uaec) i Total Switch Time (uaβc)ι lloblla Timing Error Allowance (chpa) i Mobile Timing Brror Allowance (uaec) i Max Range Bin Step Size ( i) i Total Ouard Time Overhead (uaec) i Number of 2 -way TOD Ouardai TDD Max Cell Radiua (mi) i H Total TDD Ouard Time Available (uaec) i H Total TDD Ouard Ti o Avail, (chipe) I Guard Time per TDD Ouard (chlpa) i Total Ouard Time (uaec) i Slot Structure Btficiencyi β of λst Probea to Send (Forward Link) ■ Baae Antenna Probe Length (chlpa) Antenna Switch Time (chlpa) Total chipa per λntenna Kord (chips) PCP Sync Word Length (chips) Antenna Select (aymbola) Antenna Select (bita) PCP Duration (chipa) Syne Word Length (chlpa) Overhead Length (Chlpa) Beadar Maaaage Length (bita) D-Cbannel Maaaage Lengtb (bita) B-channel Maaaage Length (bita) R-Channel Maaaage Length (bits) CRC Bita in Traffic Mode (bita) t- Siπ-plex Massage Length (bits) JQ Sinplex Message Length (symbols Simplex Message Length (chips) O Total Number of Chip One 5 sj <? Spread FDD If) Transmit Slot Duration ( sβc) i Os Quo Slot B-Channel Data Rate (kbps) i Aggregate B-Channal Data Rate (kbps) i t * Λ Max U of Voice channels per RP Channeli tfl Supβrframβ Duration (msec) i H υ Chipa/Sloti Chip Duration (usac) i Baao Slot Layout (mobile at zero range) i (uoec) (chipo) (uooc) (chipo) (uooc) (chipo) (uooc) (chipo) Baae Tx Preamble OTARTi Base Tx Preamble BNDi Base Tx Message STλJVTi Base TX Message BNDi Base Tx Antenna Hβββage STARTi Base Tx Antenna Message ENDi Baoo Twiddlea Thumbs (FDD only) STARTI Baae Twiddles Thumbs (FDD only) BHDi Base T->R Switch ffTARTi LT) Base T->R Switch BNDi H Base Rx Preamble STARTi Base Rx Preamble BNDi Base Rx Message STARTI Base Rx Message ENDi Base Rx Ouard Time 1 or 2 START i Base Rx Ouard Time 1 or 3 BNDi Baae Rx Time Error Allowance 1 START I Baae Rx Time Error Allowance 1 EN i Mobile l->2 Transient Time (T/R) OTART i Mobile l->2 Transient Time (T/R) BNDi Baeβ Rx PCP START i Base Rx PCP ENDi Base Rx Ouard Time 1 START I Base Rx Ouard Time 1 BNDi Base Rx Time Error Allowance 2 STAR i Base Rx Time Error Allowance 3 ENDi Mob 2->l Trans or Base R->T Swtch STARTi . Mob 2->l Trans or Base R->T Swtch BNDi Leftovers (Better be Zero) i t- Os ON Spread FDD Data Rateα/RF Channel i O r- DW per RF Channel/Chip Rate (kHz) Frequency Reuse Factor (N) Os Minijium System Bandwidth (kHz) tfl 3/1 (dB) Noise'Pigurβ 0 290K (dfl) υ Antenna Temperature ( ) Sya AT inc. NF (dBα/llx) Syβ JcT inc. NF (mW/kHi) Impli βntation Loss (dB) 1/(3.DW) (num) M-ary NonCobor Format Bits per Symbol Required Frame Brror Rate Frαmo Length Cor Kb/No Calc.(bits) Actual Bqv. Frame Length (bits) Antenna Diversity Facto Rake Diversity Facto ID Required Bb/No (dB) H 1/Kb/NoL (num) H Seneitivity in 3/1 (dBm) Sonoitivity,Thβrra Noise Only (dBm) S/I Induced Sensitivity Loss (dB Required Sensitivity in β/I( M) Max Simplex Data Rate (kbps Max Simplex Symbol Rate (kspβ Chips per Symbo Symbol Duration (uβec) Chips per Bi Processing Oain per bit (dB) S/(N+I) into λ/D (dB S/N into λ/D (dB Max Duplex Data Rate (kbpβ Pilot Channel Overhead (kbps Bearer Channel Duplex Rate (kbps Link Asymmetry Factor (dB f- ve Os lo-tfs ••• » p»χβpm*π l»-)Tβ -"» peχsptt»π '•"1TB -l» βχβπτr-rqo *j-|oχ ιΛ-)-fθ-»«Sβ3 πf trpβo πoχ-tτ»zχ_-o-(oos qβ(* ids -ttΛO vππe-tUY o-j, en βao αoqDβB I (Jtoqoaø/eevu X) SJtopoerj o-fqrJtixBoeo * vι ■ (POP) π-fτ»D vαno Y e β rα I (MO*) -isnoj qfraotπijT , eOβJOAY eβvπ ■ (Mm) -tenoj q ισtr«-iχ rej oβvrj • (ι?OP) π T B 0 β ππ β qtrvf qbtrpcr β π I (MO) 3βnθd -)Tτss-rsj tDvlossi qorrptron ■ (Mm) -tenoj *»-pπoσvj -p>< qeπp-rvn I βrjoτ τj-rτΛo τ-0 ΛqjDs vo H H χOαχε qoeprrsn πoχ-|β-)s eβvα I (oerm) Λsxeα Bα-fπrβJa -uβpm- τ»r<" I (oetr ) Λeχoα Oα-fαrβ_ta otβptroj, βχOαχs ι{sdq ) -"-rro-t o βojoi αe<ϊ eqvu s-|»α I (a-t () αapoooΛ -ted β"(«rn uβriJΘΛo ι(sd {) eqvπ αepoooΛ i Bπoχ τ j χn χv εoo/T β r *"I3 ι>3T 0 Λ ααΛ »OJC * S C64 L F ^ -- llUoo/ςf η l fk, Spruαd FDD Link Designer 3 FDD, No Spread FDD, No Spread FDD, Ho Spread FDD Setup Cor page 145 Operation Var Slots, Ranging with Small Slota with Uiu 3lor.il 0.640 Mllz Chip Rate 0.640 Mill Chip Ila-u 0. S40 Mil- Ctilp Hal o 26.3 x β .00 kbpa 40.0 x β .00 kbpa 32 .0 x β .00 kbpu Reverse Forward Slottin B fici ncyi Link Link 2 -way Mesaage Frame Duration (uaec) i 500.00 500.00 Ba e T/R Switch Time (chips) i 0 β Base T/R Switch Time (uaec) i 0.00 12.50 Mobile l->2 Tranalent Time (chipa) i β 0 Mαbila l->2 Tranalent Ti me (uaec) i 12. 50 0.00 Baas R/T £vritch Time (chipa) i β 0 Bαaa R/T Switch Time (uaec) i 12 .50 0.00 Total Switch Time (uaec) i 25.00 12.50 lloblla Timing Error Allowance (chpa) ι 0 34 19 34 Mobile Timing Br or Allowance (ueec) i 0.00 53. 13 29.69 53 .13 II Bins MAX Range Bin Step Size (ml) i 0.00 4 .95 2.77 4.95 3 .89 Total Non Ouaxd Time Overhead (uβsc) i 25.00 65.63 84.38 65.63 r- Number of -way TDO Ou&rds i 1 1 H TOO Max Cell Radius (mi) i 10.77 0.00 I co Total TDO Guard Time Available (uaec) i 115.63 0.00 H Total TDO ouard Time Avail, (chipa) i 71.00 0.00 H Guard Time per TDD Ouard (chipa) ■ 74.00 0.00 Total Ouard Time (uaec) i 140.63 65.63 xi Slot Structure Bfficiencyi 71.88% 86. Θ 8 II of λnt Prαbβa to Send (Forward Link) 0 3 Baae Antenna Probe Length (chipa) 28 13 Antenna Switch Time (chips) 2 2 Total chips per λntenna Word (chipa) 30 15 FCP Sync Word Length (chipa) 28 0 Antenna Select (aymbola) 5 0 Antenna Select (bita) 5 0 PCP Duration (chipa) 33 0 Sync Word Length (chlpa) 2β 28 Overhead Length (Chipa) 61 73 Header Message Length (bits) 21 21 p-Cbannel Maaaage Length (blta) 1 a O-Cbαnnel Meaaege Length (bits) 105 160 R-Chαnnel Massage Length (bits) 0 o CRC Bits in Traffic Mode (bits) 16 16 "W f- Simplex Message Length (bits) 150 205 Ov Sinplex Message Length (aymbola) 150 205 jn Simplex Message Length (chips) 150 205 vo OV Total Number of Chlpa 211 278 0 6 0 00 0 0 OO'O 0 OO'O 0 OO'O I (θ-lt»2 •*-{ -te-jq β fl) «-»Λθ-|j»'j e ooβ OOΌSΣI Θ ot9 oo-oooτ β o»9 OOΌOOT β θ-9 OOΌOOT ΌNH ψ>vβ Λ<-U •« « U ΛO IΠJI χ<-z q°w 0 ∑6i OS'tε∑T 0 ZZ9 OS'tββ 0 ∑ε9 OS'iββ 0 tC9 OS'tββ UUYiβ HD * »nβ 1<-H B β va JO stπiJi T<-J qoH o zβL os'tε∑τ o z os'iββ ex zz9 os'tββ βτ εε9 ' os'tββ »cmj_ c •oπ-»rv-ιχχγ IOUS WΠTJ. H »svtj 0 16L OS'tε∑T 0 ∑ε9 OS'lββ O T9 Xβ'iSβ 0 CT9 Xβ'iSβ *J.HYiβ t β 3 * r»«oχχY JOJUH SOTTX IH efπ-π: 6 s zβL os'.εετ 6t ∑ε9 os'iββ o εi9 xβ'tsβ o ετ9 xβ-tsβ ions T »>»TI ι«wo ∑u "»β o εεi τε'snτ o ετ9 τβ'isβ o x9 τβ'isβ o εx9 τβ'tsβ <ΛHYis T **χι p"rø ∑H ββ vα cc εεt τε'stττ εε τ9 xβ'tsβ εε ετ9 τβ'isβ εε 9 τø'tsβ 'a aw m •«»α 0 00i Si'εδOT 0 OβS SΣ'906 O OβS Sε'906 0 08S SC'906 "XHYiS dM ∑H •™β 0 OOi Si'εβOT β OβS SΣ'906 θ OβS SΣ'906 0 OβS SC906 >πMH (H/1) mrfl qαe-f β ιτ»αj, r<-χ β χj oH o ∑6 SΣ TBOT o ∑ts st'εsβ o εis srεβo o us srεβe HHVOS (H/Λ) wrfi -jn β -fs-rs j u z<-x »XT<T°H 0 Σ69 SΣ'TβOT O ItS St'εββ 6X ItS Sr ββ O ΣiS Sf 6 *-WH τ •oσ β ΛOXXY J O -us twrri IH βββ α 0 Σ69 SΣ'TBOT 0 ΣiS St'εββ O SS 90'»90 0 CiS Si'Cββ littY--? T "treV- TY JO IH «πTi IH e β vfj 65 Σ69 SΣ'TBOT 6T US Si'εββ 0 SS 90't9β ft US Si'εββ 'OH * - { M I mfZ prono IH ββ va 0 CC9 90'6B6 0 εSS 90'V*9β 0 εSS 90'»9β 0 86t ZX'βLL tXHYiS t ∞ ! TΛ p-reno H β rrBα SOJ CC9 90'6B6 SO- εSS 90'»9β S0Σ εSS 90'»98 OST 961* H'tU i(Dra eOs β s β H IH es»α ι-3 o BΣΓ Si'β99 o eu si'εrs o βu S£'εt>s o βu Si' rs IΛHV 9 ι β »mH ∑H mm e β∑ ϋzv st'B99 βε eu srεv-s β∑ βu st'ε»s β∑ on SL'tts ON-, •xqm-βe-ia IH eβvg r-- * 0 OOf 00'SΣ9 0 OΣC OO'OOS 0 O∑ε OO'OOS O O∑ε OO'OOS ■ ϋHYXfl •Xqαnie.id' e β uα CD β oor oo's∑9 β o∑ε OOΌOS o o∑ε OOΌOS B o∑ε OOΌOS -am q->-»TΛ3 H<-I »βvα H o ∑βε os'∑τ9 o ∑τε os-tβj> o ∑τε os'tβ» o ∑τε os' nuvxs sΩ HI ∑βε os'∑T9 t-ε ∑τε os'tβr »ε ∑τε os'iβv »c ∑τε os'iβt ' a (-*.χ > aaa) s umqi βo jvι. eβva H o βt∑ βε'tεt o βi∑ βε'fεr o βt∑ βε*?εt o βtt βε'tε? liuviB (Λχuo aaa) βcfrmqi seτ τ,L ββr-α 00 5P βt∑ βε'»εr sv βi∑ βε'»εt s» βt∑ βε'r-εf s» βi∑ βε'tεr ΌNH •osβsβH »απe-*σγ ι esvα o εε∑ 9θ'»9ε o εε∑ 9θ'»9C o εε∑ 9θ'»9 o εε∑ 90-t9 iΛHΫis eoβBββH vπtjβ- > πγ x e«« a so∑ εε∑ 9θ'?9 so∑ εε∑ 9θ'»9ε soε εε∑ 9θ'»9ε so∑ εεt 9θ'»9 >αm •o«»»βH XJ. β«»a o β∑ st'ε» o β∑ srεt' o β∑ st'εt o β∑ Si' t ϋuviβ •-««« « »na BΓ. β∑ si'εt BΣ β∑ st'.εf β∑ βε si'ε» β∑ βε sfc» 'cura 4 ββvα 0 OO'O 0 OO'O 0 OO'O 0 OO'O iIHYiS •T π»e-tΛ Ii eβvα (βJTqo) (seen) (βdfT-D) (soon) (βd qo) (soon) (odTqo) (oβsn) ι(oOtre.x oαβz q-j βχγqouj) -(ΠOΛT -)oχε oσvα 1 (oasn) πoχ-)»-mα fj-rqa 1 qo B βa-qD 1 (oeara) πo-f-jτ»zn βαrβ-ijtβαnij ι eαtf β tιo -TH Λ»ϊ Bχ*ππ-»ι-fθ »oχoι\ jo a ΓBH ι(sdqχ) 9 rα » * jβα β ιβtιo-0 e-) > eejJ3Sv ι(adq ) e-juH βq»α χβατχβqo-g -)oχs eπo 3C'»ετ> C9'sτ> βε'tεf 69'6∑ε 1 (oorrn) ooχqs-mα qoχs -ιγ-mιιrB_t,ι, σαa vβj s H n Data Ratβs/RP Chαnnαli ev t- 1 ) H per RP chαnnβl/cbip Rate (kHz) ve Frequency Reuse Factor (ti) ov Hinlraim Syβpem Bandwidth (kHz) tfl • ! fl/I (dfl) rtoisβ Flrru e β 390K (dB) υ Antenna Tαπrperaturβ (K) C Sya JcT inc. HP (dBm/Hz) Sya kT Inc. MP (αH/kllz) Uj-pllroβntation Loss (dB) I/ (S.B ) (num) M-ary NαnCohβr Format Bits per Symbol Required Frame Error Rate Prune Length for Sb/No Cole, (blta) λ tual Bqv. Fratπα Length (bits) Antenna Diversity Facto Rake Diversity Facto o Required Bb/Mo (dB) SI 1/Bb/NoL (num) H Sensitivity in 3/1 (dBm) Seneitivity,Therm Noise only (dBm) S/I Induced Sensitivity Loss (dB) Required Sensitivity in S/I(m ) Max Simplex Data Rate (kbps) Max Siπvplex Symbol Rate (ksps) chips per Symbo Symbol Duration (usec) Chips per Bi Processing aain per bit (dB) 3/ (lHI) into λ/D (dB) S/H into λ/D (dB) Max Duplex Data Rate (kbpa) Pilot channel Overhead (kbps Bearer Channel Duplex Rat* (kbps) Link λsyr-toetry Factor (dB) iβqjB -(s pβxs iπiH oOσsχ-ia GOO \Z le-j-fB -,» ϊ>»τ»pπ»π βnσβ αa εoo \x ■ •*t β ".» sχβr_rtrc*o SM jo ΛβqπrrvN -n oi IA-JIOTKISO π| trpø qen ιdg jβΛθ v eqαY 0-4 en βeo-j αo-pβs 1 (-*o-)3t-/es»fI X) βαoaoes oχrrdβ3β oo orrvi 1 (POP) OfβO • »σαβ-'tιγ eβvα 1 (no) αsnoj q-r σtrsjχ SOSJSΛY eβcn < κX) 3*nθi - , χmetn*-'£ -fried eββg 1 (POP) trp»D βoue-iiiY -lerprru** 1 (jpn) -tenoj -Jxtπetrβ-ti eOβ4βΛγ qβirpuuii 1 (nm) -renOiJ -fpπsri j χrιej errp*rc|| ιβαoχ-|sχιi3χτιo Λq-ron B O H H ι»χoΛθ Λ-)txi ii qoχs βχβrj.χs qoeptron ι»χaΛo Λ-)nα -(-fiπβirβ-ti πoχ-|v-jg eβvα 1 (sesra) Λsχoα flπ-fi-rβ-ta <πβprrt>χ χτ>rκj 1 (Dββta) Λκχ*> Bαχαn»-ta nwptrei eχt5αχs i£Xβ %Z " pe-J-loddnfl aOtrβχ-tH 1 BOO Vt "I" pβ-jjod-tne eβtn»χ-ra • σπ/IGI sTf i-ies πvH jo sβsqαβojβ,* ipo-j-t-xMng sχeuuvqo »aχoΛ αβqαmj* χ»jt 1 (XΠH) R-» T«PtrBB nιβ-)*Λs p»Λoχdoα ιαoqoeB/sχerr-rτ»tτ-ι il ' j o α»q-τtv* ι(adφ|) 1 (sdφf) 1 (sd () 1 πo qτjχn-) o ε θ O/χetπmqo βofoΛ aai p»a S v '-η [ Link Designer 3 FDD, tlo Spread FDD, Uo Sproad FDD, tlo Spread PDD, IJo Sproad FDD Setup for page 145 Operation Var Slots, Ranging Var Slots, Liukad ith Small Slocu with Big Slocu 0.S60 Mill Chip Ratu 0.560 ix Chip nato 0.5G0 Mllz Chip Halu 0.5C0 I41I-- Chip l iu 13.8 n-0.00 'Jjpn 35.0 x 8.00 kbps 35.0 z 0.00 kbps 32.0 x 0.00 bpu Rβvarae Forward Slotting. Bftic£βncyι Link Link 2-wαy Maaaage .'Promo Duration (uaec) i 571. 43 Daae T/R Switch Time (chips) I 8 Daaa T/R Switch Time (uaec) i 14.29 Mobile l->2 Transient Time (chips) I 0 Mobile l->2 Transient Time (uaee) i 0.00 Baae R/T Switch Time (chipa) I 0 Daae R/T Switch Time (uaao) i 0.00 Total Switch Time (uaec) i 14.29 Mobile Timing Brror Allowance (cbpa)ι 34 Mobile Timing Brror Allowance (uaec) i 60.71 Max Range Bin Step Size (mi) I 5.66 Total Non Guard Time Overhead (uaec) i 75.00 Number of 2-way TDD Ouardai 1 C TDD Max Cell Radius (mi) I 0.00 CN Total TDD Ouard Time Available(useβ) i 0.00 Total TDD ouard Time Avail, (chipa) i 0.00 Ouαrd Time per TDD Guard (chlpa) i 0.00 Total Ouard Time (uaec) i 75.00 a Slot Structure Efficiencyi 86.88 rH X) ci 1 of Ant Frobea to Send (Forward Link) 3 E-t Baae Antenna Probe Length (chipa) 13 Antenna Switch Time (chips) 2 Total Chipa per Antenna Hord (chips) 15 PCP Sync Hord Length (chipa) 0 Antenna Select (symbols) 0 Antenna Select (bits) 0 FCP Duration (chips) 0 Sync Word Length (chips) 28 Overhead Length (Chlpa) 73 Header Maaaage Length (bite) 21 21 D-Channel Maaaage Length (blta) 8 O-Channal Maaaage Length (bita) 105 160 R-Chαnnel Maaaage Length (bits) 0 0 Ov CRC Bits in Traffic Mode (bits) 16 16 * t»- Simplex Maaaage Length (bits) ISO 205 £5 Simplex Message Length (symbols) 150 205 Simplex Message Length (chips) 150 205 Total Number ot Chips 211 278 O 0 z ^y /en IT spruad PDD Tranoinlt Slot Duration (usβc) i 376.79 496.43 47S.00 496.43 475.00 496.43 475.00 496.43 ve. One Slot B-Channβl Data. Rite (kbps) i Ov Aggregate B-Channel Ca s Kate (kbps) ■ I'¬ Mix V ot Voice Channels per RF Channeli ve Supβrframe Doration (tαβoc) ■ Ov CA Chips/Sloti H Chip Duration (uaec) i υ Dαuα Slot Layout (Habile at zero range) i (ussc) (chips) (ueoc) (chips) (usoc) (chips) (uββc) (chips) Base Tx Preamble STARTi Base Tx Preamble BNDi Base Tx Message STARTi Base Tx Message ENDi Base Tx Antenna Message STARfi Base Tx λntenna Message ENDi Base Twiddles Thumbs (FDD only) STARTI Base Twiddles Thumbs (FDD only) ENDi Base T->R Switch STAR i Base T->R Switch BNDi Base Rx Preamble STARTi CN H Base Rx Preamble BNDi Base Rx Message STARTi Base Rx Message BNDi Bass Rx Ouard Time 1 or 2 STARTi Baae Rx Ouard Time 1 or 2 ENDi Base Rx Time Brror Allowance 1 STARTI Base Rx Time Brror Allowance 1 BNDi Mobile l->2 Transient Time (T/R) STARTI Habile l->2 Transient Time (T/R) ENDi Base Rx PCP STARTI Base Rx PCP ENDi Base Rx Ouard Time 1 STARTI Baae Rx Ouard Time 1 ENDi Base Rx Time Brror Allowance 2 STARTi Base Rx Time Brror Allowance 2 BNDi Mob 2->l Trana or Base R->T Swtch STARTi Hob 2->l Trans or Base R->T Swtch BNDi Leftovers (Better be Zero) i Λtø- ϊ Spread PDD X/ (S.B») (num) M-ary NαnCohβr Format Bit* per Symbo Roquired Frame Brror Rat Frame Length for Kb/No Calc. (bite) Actual Bqv. Frame Length (bite) Antenna Divβraity Facto Rake Divβraity Facto Required Kb/No (dB) 1/Sb/ttoL (num) Seneitivity in 8/1 (dam) H Seneitivity,Therm Noiee only (dBm) S/I Induced Seneitivity Loee (dB) Required Seneitivity in B/I(mirj Max SisTplex Data Rate (kbpe) Max Simplex Symbol Rate (kapa) Chipa per Symbo Symbol Duration (uaec) Chipa per Bi Procoaoing Gain per bit (dB) 3/1H+I) into λ/D (dB) S/H into λ/D (dB Max Duplex Data Rate (kbpa Pilot Channel Overhead (kbpa Bearer channel Duplex Rate (kbpa Link λeymmotry Factor (dB (J^. Sμroαd FDD i Λ * n J c : ^ oc >/ L f/ l{> m o Ov Link Dβoignor 3 FDD, Ho Spread FDD, No Spread FDD, No Spread FDD, No Spread r~ FDD Setup for page 145 Operation Var Slota, Ranging Var Slota, Linked with Small Slota with Big slotll 0.350 Mill Chip Rate 0.350 Mil- Chip Rato 0.350 Mllz Chip Itαtu 0. 350 M1 Chip llalti VO Ov 16.4 x 8.00 kbpo 25.0 x 0.00 kbpa 25.0 x 8.00 kbpa 20.0 x 8 .00 kbpα tfl Reverae Forward Slotting Kfficiejncyi υ Link Link fi¬ --way Haaaage Frame Duration (uaβα) ι 800.00 800.00 Baae T/K Switch Time (chlpa) i 0 8 Baae T/R Switch Time (uaec) i 0.00 22.86 Mobile l->2 Tranalent Time (chipa) i β 0 Mobile l->2 Tranalent Time (uaec) i 23 . ΘS 0.00 Baaa R T Switch Time (chipa) i β 0 Baae R/T Switch Time (uaec) i 22.86 0.00 Total Switch Time (uaec) i 45.71 22. 86 Mobile Timing Brror Allowance (cbpa) ι 0 3 Mobile Timing Brror Allowance (uaec) i 0.00 8. 57 Max Range Bin Step Size (mi) i 0.00 0.80 Total HOD Ouard Time Overhead (uaec) i 45.71 31.43 Number of 3-way TDD Ouarda i 1 1 CN I TDD Max Cell Radiua (mi) i 15.17 0.00 Total TDD ouard Time Available (uaec) i 162.8S 0.00 : Total TDD Guard Time Avail, (chipa) i 57.00 0.00 e Guard Time per TDD Ouard (chipa) i 57.00 0.00 CN H Total cuard Time (uaec) i 208.57 31.43 rd Slot Structure Bfticiencyi 73.93* 96.07% in t ot λnt Frobea to Send (Forward Link) 0 3 Baaa λntenna Probe Length (chipa) 28 11 Antenna Switch Time (chipa) 2 2 Total Chipa per Antenna Kord (chlpa) 30 13 FCP Sync Hord Length (chipa) 25 0 λntenna Select (aymbola) 5 0 Antenna Select (blta) 5 0 PCP Duration (chipa) 30 0 Sync Word Length (chipa) 25 25 Overhead Length (Chipa) 55 64 Uaadar Haaaage Length (blta) 21 21 D-channel Heaaage Length (blta) β B-Channel Heaeege Length (blta) 105 160 R-Channal Meaaage Length (bita) 0 0 Ov * CRC Bita in Trattic Mode (bita) 16 16 f*- Ov Simplex Haaaage Length (blta) 150 205 S3 Sinplex Meaaage Length (aymbola) 150 205 O Simplex Meaaage Length (chlpa) 150 205 O . Total Number ot Chip* 205 269 ' Spread FDD Tranomit Slot Duration (uooc) i 505.71 768.57 742.06 760.57 742.06 760.57 742.06 768.57 One Slot B-Channol Data Hate (kbpe)ι Aggregate B-Channel Data Hate (kbps)ι Ma tt ot Voice Cbannβla per RF Channeli Supβrframe Duration (mαec) i Chips/Slo i ' Chip Duration (αeoc) i llaoo Slot Layout (πobile at loro range) i (uaec) (chips) (uooc) (chipo) (uooc) (chipu) (uooc) (chipo) Baae Tx Preamble STARTi 0.00 0 Baoe Tx Preamble EHDi 71.43 25 Baoβ Tx Meaaage STλllTi 71.43 25 Baae Tx Message BNDi 657.14 230 Baβo Tx Antenna Message STARTi 657.14 230 Base Tx λntonna Message BNDi 768.57 269 Uaoo Twiddles Tnumbβ (FDD only) STARTi 768.57 269 Base Twiddles Thumbs (FDD only) ENDi 777.14 272 Base T->R Switch OTARTi 777.14 272 Base T->R Switch EHDi 800.00 280 Baae Rx Preamble STARTI 800.00 280 Base Rx Preamble BMDi 871.43 305 Base Rx Message OTARTi 871.43 305 f- Base Rx Message KHDi 1300.00 510 Base Rx Ouard Time 1 or 2 STARTi 1300.00 510 Baae Rx Ouard Time 1 or 3 KHDi 1462.86 512 Uona Rx Time Brror Allowance 1 STAR i 1462.86 512 Baae Rx Time Brror Allowance 1 BNDi 1462.86 512 Mobile l->2 Tranalent Time (T/R) OTARTi 1462.86 512 Mobile l->2 Tranalent Time (T/R) BNDi 1485.71 520 Base Rx PCP OTARTi 1485.71 520 Baae Rx PCP BNDi 1571.43 550 Base Rx Ouard Time 1 OTARTi 1571.43 550 Baae Rx Ouard Time 1 BNDi 1571.43 552 Baoa Rx Time Brror Allowance 2 OTARTi 1571.43 552 Baae Rx Time Brror Allowance 2 BNDi 1577.14 552 Mob 2->l Trans or Base R->T Swtch STARTi 1577.14 552 Mob 2->l Trans or Base R->T Swtch ENDi 1600.00 560 Leftovers (Better be Zero) i 0.00 0 ^ Spread PDD in Data Ratea/RF Channe i © σv f- JJ per RF Channel/Chip Rate (kill) o Prβquency Reuse Factor (H) vo Ov Minimim System Bandwidth (kHz) CΛ I: fl/I (dB) • Noise'Figure 0 290K (dB) H υ λntβn a Temperature (K) Sya kT Inc. HF (dBm/liz) Sya kT inc. HF (mW/kliz) Umlimontαtion loss (dB) 1/(3.DW) (num) M-ary NonCoher Format Bits per Symbo Required Frame Brror Rate Prejia Length for Kb /No Ca c. (bits) Actual Eqv. Frame Length (bits) Antenna Diversity Facto Rake Diversity Facto Required Eb/No (dB) 1/Bb/MoL (num) 00 Seneitivity in 3/1 (dBm) Sounicivity,Therm Nsiae Only (dBm) H S/I Induced Sensitivity Loss (dB) Required Sensitivity in a/I(mW) Max βlπrplex Date Rate (kbpa) Max Sio-plβx Symbol Rate (kapa) Chips per Symbo Symbol Duration (usec) Chips per Bi Processing (Jain per bit (dB) S/(N+I) into λ/D (dB) 3/11 into λ/D (dB) Max Duplex Data Rate (kbps) Pilot Channel Overhead (kbps Bearer Channel Duplex Rate (kbps Link Aβyπtneti-y Factor (dB ••"ITS qϊ pβ-fβptrgrj βCtr»χj3 SCO Z ιeq-fS rjτ» peχep*π*] βtSav 3S BOO \X '•3Tβ *1* *χemnrq3 βU jo -trqαmt* X"βqcn iΛqfavdBO αγ α-fβo πoχqvzχjoqo»s «N ιdsχ-(eΛ0 TOπβqαy oq βnα β β orj joqoβs i (Joqses eavQ x) βjo ses 0-fφls.ιΛooo MtVI 1 (PHP) πyτ»o vrrαeqtryr orvα i (MB) 3»no& qγ βrrβjj, ββvjβΛY ββvπ i (tm) -tβnoj -r βtrvjj, -fββj eι«α t 1 (POP) πjO vπueqrrvr qeoχ>rxv*ι s i (Km) αenoj qχmβtrB.ιχ eOs sAV qerptrtH i (ftα) βnoi q-pπβrrβjx jfββj qeeprrvi* ιβπcιχq**χτi3χτo3 Λq-fo.aso ιeχoΛo A " qna ii qoχs eχ->αχB qeaptrun ιe oΛa Λ txj -pπβtrβαi πoχq«qs aβvπ i (oβeππ) Λτ*χoα βα nn»αj oreptrv , χβr<. i (DOfrtπ) Λ«χβα Dαχm»ja otβprrβT, "BOO Z "t* p β -tofdns βOr β χ j H 'GOO X q» peq j cxMns eDπvχ_ra 'oπ/ISi πj eqeepαvπ jo eOvqαβ-uo,* i βqjcκMrvs sχetπr»q;) eoχoΛ -"eqnm-. rs|.ι I (i|IH) η- T'ψπ' β α oroqβΛs peA->χ<Joα i-*oqo»s/eχβmr»qo χι jo JocfiπrvN ι(adq ) q-frojχo βoχ Λ aed e vH vqvα ι(adq ) e oαoA -tβΛ eq u pτ-eqjnΛo i [irlcru) eqtrtf -tβ o-røΛ i tπoχq- j χnoχ«o εoo Tβπw-lO ααΛ ϊojds ^h These and other variations and modifications to the communication techniques disclosed herein will become apparent to those skilled in the art, and are considered to fall within the scope and spirit of the invention and to be within the purview of the appended claims.

Claims: Claims 1. A method of time division duplex communication between a base station and a user station over a single frequency band, comprising the steps of transmitting, over a designated frequency band, a user message from a user station directed to a base station, receiving said user message at said base station, calculating at said base station, based on the time of receiving said user message at said base station, a distance of said user station relative to said base station, and transmitting, over said designated frequency band, a base message from said base station directed to said user station, said base message comprising a timing adjustment command whereby timing of a subsequent message from said user station directed to said base station over said designated frequency band is advanced or retarded. 2. The method of claim 1 wherein at least one of said user message and said base message is transmitted using a spread spectrum technique. 3. The method of claim 1 wherein said user station maintains a timing variable, and wherein said timing adjustment command modifies said timing variable in order to advance or retard said timing. 4. The method of claim 1 wherein said user station maintains a timing parameter relative to a fixed reference, and wherein said timing adjustment command modifies said timing parameter in order to advance or retard said timing. 5. The method of claim 1 wherein said step of calculating a distance of said user station relative to said base station comprises a step of calculating a propagation delay of said base message to reach said user station and said user message to reach said base station. 6. The method of claim 1 further comprising a step of adjusting a relative timing of subsequent messages from said user station by periodically transmitting from said base station to said user station, over said designated frequency, subsequent timing adjustment commands. 7. The method of claim 1 wherein said user message is transmitted in response to a general polling message sent by said base station in an attempt to establish communication with said base station. 8. The method of claim 1 wherein said user station is in established communication with said base station, and wherein said user message comprises a control pulse preamble. 9. The method of claim 8 wherein said control pulse preamble comprises a plurality of concatenated codes. 10. The method of claim 9 wherein said control pulse preamble comprises a kronecker product of a minimum peak sidelobe code and a Barker code. 11. The method of claim 1 wherein said user station is in established communication with said base station, and wherein said user message comprises a traffic mode user-to- base message. 12. A method of time division duplex communication between a base station and a plurality of user stations over a single frequency band, wherein said base station communicates sequentially during a time frame with the user stations in established communication with said base station, and wherein said time frame is divided into a plurality of time slots of equal duration, said method comprising the steps of transmitting over a designated frequency band, during a designated time slot in a first time frame, a first base-to- user message from said base station to a user station, receiving at said base station, during said designated time slot in said first time frame and over said designated frequency band, a first user-to-base message from said user station, transmitting, during said designated time slot in a second time frame subsequent to said first time frame and over said designated frequency band, a second base-to-user message from said base station to said user station, said second base- to-user message comprising a timing adjustment command, and receiving at said base station, during said designated time slot in said second time frame and over said designated frequency band, a second user-to-base message from said user station, said second user-to-base message advanced or retarded in time in response to said timing adjustment command. 13. The method of claim 12 further comprising a step of, after receiving said first user-to-base message and before transmitting any subsequent base-to-user message from said base station, receiving at said base station a control pulse preamble from a second user station over said designated frequency band. 1 . The method of claim 13 further comprising the steps of transmitting, during a second time slot immediately following said first time slot in said first time frame, and over said designated frequency band, a third base-to-user message from said base station to said second user station, said third base-to-user message comprising a timing adjustment command, and receiving at said base station, during said second time slot and over said designated frequency band, a third user-to- base message from said second user station, said third user- to-base message advanced or retarded in time in response to said timing adjustment command. 15. The method of claim 14 wherein said control pulse preamble comprises a spread spectrum code. 16. The method of claim 14 wherein said control pulse preamble comprises a plurality of concatenated codes. 17. The method of claim 12 wherein at least one of said first user-to-base message, said second user-to-base message, said first base-to-user message, and said second base-to-user message is transmitted using a spread spectrum technique. 18. The method of claim 12 wherein said user station maintains a timing variable, and wherein said timing adjustment command modifies said timing variable in order to advance or retard the timing of said second user-to-base message. 19. The method of claim 12 wherein said user station maintains a timing parameter relative to a fixed reference, and wherein said timing adjustment command modifies said timing parameter in order to advance or retard the timing of said second user-to-base message. 20. The method of claim 12 further comprising a step of calculating a distance of said user station relative to said base station. 21. The method of claim 20 wherein said step of calculating a distance of said user station relative to said base station comprises a step of calculating a propagation delay of said first base-to-user message to reach said user station and said first user-to-base message to reach said base station. 22. The method of claim 20 further comprising a step of receiving at said base station, prior to transmitting said second user-to-base message, and over said designated frequency band, a control pulse preamble from said user station, wherein said step of calculating a distance of said user station relative to said base station comprises a step of calculating a propagation delay of said first base-to-user message to reach said user station and said control pulse preamble to reach said base station. 23. A system for carrying out time division duplex communication between a base station and a plurality of user stations over a single frequency band, said system comprising a plurality of time frames, and a plurality of time slots in each of said time frames, each of said time slots comprising a base message interval during which a base message may be sent over a predetermined frequency band by a base station to a user station in established communication with said base station, a user message interval during which a user message may be sent over said predetermined frequency band to said base station by said user station in established communication with said base station, wherein said base station periodically transmits, during said base message interval, a timing adjustment command to said user station in established communication with said base station. 24. The system of claim 23 wherein at least one of said base message and said user message is transmitted using a spread spectrum technique. 25. The system of claim 23 wherein said user station maintains a timing variable, and wherein said timing adjustment command modifies said timing variable in order to advance or retard a timing of said user station. 26. The system of claim 23 wherein said user station maintains a timing parameter relative to a fixed reference, and wherein said timing adjustment command modifies said timing parameter in order to advance or retard a timing of said user station. 27. The system of claim 23 wherein said timing adjustment command is based on a calculation of a distance of said user station relative to said base station. 28. The system of claim 27 wherein said calculation of a distance comprises a calculation of a propagation delay of said base message to reach said user station and said user message to reach said base station. 29. The method of claim 27 wherein said user station is in established communication with said base station, and wherein said user message comprises a traffic mode user-to- base message. 30. A system for carrying out time division duplex communication between a base station and a plurality of user stations over a single frequency band, wherein the base station communicates sequentially with the user stations with which the base station has established communication, said system comprising a plurality of time frames of equal duration, and a plurality of time slots in each of said time frames, each of said time slots comprising a base message interval in an initial portion of said time slot, during which either a base-to-user message may be sent by a base station to a user station in established communication with said base station during said time slot, or a general polling message may be transmitted indicating the availability of said time slot, and a user portion following said base message interval in said time slot, during which either a user-to-base message may be sent to said base station by said user station in established communication with said base station, or a reply message may be sent to said base station by a user station seeking to establish communication with said base station, said user portion and said base message interval both lying on the same frequency band, wherein said base station periodically transmits, during said base message interval, a timing adjustment command to said user station in established communication with said base station. 31. The system of claim 30 wherein said user portion comprises a preamble interval during which a control pulse preamble may be transmitted by a second user station in established communication with said base station. 32. The system of claim 31 wherein said second user station is in established communication with said base station in the time slot immediately following the time slot in which the second user station sent the control pulse preamble. 33. A method for establishing time division duplex communication between a base station and a user station over a single frequency band, wherein said base station communicates sequentially during a time frame with user stations in established communication with said base station, and wherein said time frame is divided into a plurality of time slots of equal duration, said method comprising the steps of transmitting, over a designated frequency band and during a first base interval of an available time slot in a first time frame, a general polling message, receiving, over said designated frequency band and during a user interval of said available time slot, a reply message from a user station, calculating at said base station, based on the time of receiving said reply message at said base station, a distance of said user station relative to said base station, and transmitting, over said designated frequency band and during a second base interval of said available time slot in a second time frame, a base message from said base station directed to said user station, said base message comprising a timing adjustment command whereby timing of a subsequent message from said user station directed to said base station over said designated frequency band is advanced or retarded. 34. The method of claim 33 wherein said base station and said user station communicate over said designated frequency band in said available time slot in subsequent time frames. 35. The method of claim 34 wherein said base station sends, in each of said subsequent time frames, a base-to-user message directed to said user station, and wherein said user station sends, in each of said subsequent time frames, a user- to-base message directed to said base station. 36. The method of claim 35 wherein said base-to-user message periodically comprises a new timing adjustment command. 37. The method of claim 35 wherein said user station sends, prior to each base-to-user message, a control pulse preamble over said designated frequency band and directed to said base station. 38. The method of claim 37 wherein said control pulse preamble comprises a plurality of concatenated codes. 39. The method of claim 37 wherein said control pulse preamble comprises a kronecker product of a minimum peak sidelobe code and a Barker code. 40. The method of claim 33 wherein at least one of said general polling message, reply message, and base message is transmitted using a spread spectrum technique. 41. The method of claim 33 wherein said user station maintains a timing variable, and wherein said timing adjustment command modifies said timing variable in order to advance or retard said timing. 42. The method of claim 33 wherein said user station maintains a timing parameter relative to a fixed reference, and wherein said timing adjustment command modifies said timing parameter in order to advance or retard said timing. 43. The method of claim 33 wherein said step of calculating a distance of said user station relative to said base station comprises a step of calculating a propagation delay of said general polling message to reach said user station and said reply message to reach said base station. 44. In a system for time division duplex communication wherein a base station communicates with a plurality of user stations over a single frequency band, said system comprising a plurality of periodic time frames, each time frame divided into a plurality of base time slots and a plurality of corresponding user time slots, a method including the steps of: transmitting, in a user time slot over a frequency band, a first user message from a user station to a base station, receiving, at said user station and over said frequency band, a base message from said base station, said base message comprising a timing adjustment command, and transmitting, in a user time slot over said frequency band, a second user message from said user station to said base station, said second user message advanced or retarded in relative timing with respect to the start of said user time slot, in response to said timing adjustment command. 45. A frame structure for time division duplex communication between a base station and a plurality of user stations over a single frequency band, comprising a plurality of time frames, and a plurality of time slots for each time frame, each time slot comprising a base transmission interval during which a base station may transmit over a designated frequency band a base-to-user messages to one of a plurality of user stations, and a user transmission interval during which one of said user stations may transmit a user-to-base message to said base station over said designated frequency band, wherein a first forward link transmission and a first reverse link transmission between said base station and a first user station are separated by either an intervening forward or reverse link communication with a second user station. 46. The frame structure of claim 45 wherein said first forward link transmission and said first reverse link transmission are separated by an amount of time sufficient to allow propagation of said first forward link transmission to a forward link destination and propagation of said first reverse link transmission to a reverse link destination. 47. The frame structure of claim 46 wherein said forward link destination is said first user station, and said reverse link destination is said base station. 48. The frame structure of claim 47 further comprising a preamble interval preceding said first forward link transmission, during which a control pulse preamble is received by said base station from said first user station. 49. The frame structure of claim 46 wherein said forward link destination is said base station, and said reverse link destination is said first user station. 50. The frame structure of claim 45 wherein said base- to-user messages periodically comprise a timing adjustment command whereby a relative timing of said user-to-base messages is adjusted. 51. A frame structure for time division duplex communication between a base station and a plurality of user stations over a single frequency band, comprising a plurality of time frames, and a plurality of time slots for each time frame, each time slot comprising a base transmission interval during which a base station may transmit over a designated frequency band a base-to-user messages to one of a plurality of user stations, and a user transmission interval during which one of said user stations may transmit a user-to-base message to said base station over said designated frequency band, wherein duplex communication between said base station and a first user station is carried out in a designated base interval and a designated user interval, said designated base interval and said designated user interval being separated by at least one intervening base interval or user interval. 52. The frame structure of claim 51 wherein said designated base interval and said designated user interval comprise a duplex pairing, and a time separation between said designated base interval and said designated user interval is sufficient to allow a first message to propagate over a forward link of said duplex pairing, and a second message to propagate over a reverse link of said duplex pairing. 53. The frame structure of claim 51 wherein said base- to-user message periodically comprises a timing adjustment command whereby a relative timing of said user-to-base message is adjusted. 54. A method of time division duplex communication between a base station and a plurality of user stations over a single frequency band, wherein said base station communicates during a time frame with user stations in established communication with said base station, and wherein said time frame is divided into a plurality of time slots of equal duration, said method comprising the steps of transmitting, over a designated frequency band and in a first time interval of a time frame, a first base message from a base station directed to a first user station, receiving said base message at said first user station, transmitting from a second user station, over said designated frequency band, a first user message directed to said base station, receiving said first user message at said base station in a second time interval of said time frame, transmitting, over said designated frequency band and in a third time interval of said time frame, a second base message from said base station, transmitting from said first user station, over said designated frequency band, a second user message directed to said base station, and receiving said second user message at said base station in a fourth time interval of said time frame. 55. The method of claim 54 wherein a time between transmitting said first base message and receiving said second user message is sufficient to allow said first base message to propagate from said base station to said first user station, and said second user message to propagate from said first user station to said base station. 56. The method of claim 54 wherein at least one of said first user message, said second user message, said first base message, and said second base message is transmitted using a spread spectrum technique. 57. The method of claim 54 further comprising the steps of calculating at said base station, based on a time of receiving said second user message at said base station, a distance of said first user station relative to said base station, and transmitting, over said designated frequency band, a third base message from said base station directed to said first user station, said third base message comprising a timing adjustment command whereby timing of a subsequent message from said first user station directed to said base station over said designated frequency band is advanced or retarded. 58. The method of claim 54 further comprising the step of transmitting, prior to said step of transmitting said first base message to said first user station, a control pulse preamble over said designated frequency band from said first user station to said base station. 59. A method of time duplex communication between a base station and a plurality of user stations over a single frequency band during a time frame, said time frame being divided into a plurality of time slots of equal duration, said method comprising the steps of transmitting, during a first time slot, a first base-to- user message from a base station directed to a first user station, receiving, during said first time slot, a first user-to- base message at said base station from a second user station, receiving, after said first user-to-base message, a control pulse preamble at said base station from a third user station, transmitting, during a second time slot, a second base- to-user message from said base station directed to said third user station, and receiving, during said second time slot, a second user- to-base message at said base station from said first user station. 60. The method of claim 59 further comprising the step of receiving, after said second user-to-base message, a second control pulse preamble at said base station from a fourth user station. 61. The method of claim 59 further comprising the step of calculating at said base station, based on a time of receiving said control pulse preamble at said base station, a distance of said third user station relative to said base station, wherein said second base-to-user message comprises a timing adjustment command whereby subsequent messages from said third user station directed to said base station are advanced or retarded in relative timing. 62. The method of claim 59 further comprising the steps of calculating at said base station, based on a time of receiving said second user-to-base message at said base station, a distance of said first user station relative to said base station, and transmitting, in a subsequent time frame, a third base- to-user message from said base station directed to said first user station, said third base message comprising a timing adjustment command whereby timing of a subsequent message from said first user station directed to said base station is advanced or retarded. 63. A method of interleaved time duplex communication between a base station and a plurality of user stations over a single frequency band, comprising the steps of receiving, over a designated frequency band, a first control pulse preamble at a base station from a first user station, transmitting, over said designated frequency band, a first base-to-user message from said base station to said first user station, and after a time interval of sufficient duration to receive a first user-to-base message at said base station from a second user station, transmit a second base-to-user message from said base station, and receive a second control pulse preamble at said base station from a third user station, receiving over said designated frequency band a second user-to-base message at said base station from said first user station. 64. The method of claim 63 wherein said first base-to- user message comprises a timing adjustment command. 65. The method of claim 20 wherein, in response to said timing adjustment command, subsequent messages transmitted from said first user station are advanced or retarded by an amount of time specified by said timing adjustment command. 66. The method of claim 63 wherein at least one of said first base-to-user message and said second user-to-base message is encoded using a spread spectrum technique. 67. An interleaved time division duplex frame structure wherein a base station communicates with a plurality of user stations over a single frequency band, comprising a plurality of time frames, and a plurality of time slots in each time frame, each of said time slots comprising a base message interval during which a base-to-user message may be sent over a predetermined frequency band by a base station to a first user station in established communication with said base station, a user message interval during which a user-to-base message may be received over said predetermined frequency band at said base station from a second user station in established communication with said base station, and a preamble interval during which a control pulse preamble may be received over said predetermined frequency band from a third user station in established communication with said base station, whereby said base station may respond to said third base station in an immediately following time slot. 68. The interleaved time division duplex frame structure of claim 67 wherein said base-to-user message comprises a timing adjustment command. 69. The interleaved time division duplex frame structure of claim 68 wherein, in response to said timing adjustment command, subsequent messages transmitted from said first user station are advanced or retarded by an amount of time specified by said timing adjustment command. 70. The interleaved time division duplex frame structure of claim 67 wherein at least one of said base-to-user message and said user-to-base message is encoded using a spread spectrum technique. 71. A system for carrying out time division duplex communication between a base station and a plurality of user stations over a single frequency band, comprising a plurality of time frames, and a plurality of time slots in each of said time frames, each of said time slots comprising a base interval, during which either a base-to-user message may be sent by a base station to a first user station in established communication with said base station during said time slot, or a general polling message may be transmitted by said base station indicating availability of said time slot, a user interval, during which either a user-to-base message may be received at said base station from a second user station in established communication with said base station, or a reply message may be received at said base station from a third user station seeking to establish communication with said base station, and a preamble interval during which a control pulse preamble may be received from a fourth user station in established communication with said base station, whereby said base station may respond to said fourth base station in an immediately following time slot. 72. The system of claim 71 wherein said base interval occupies an initial portion of a time slot, and said user interval a latter portion of said time slot . 73. The system of claim 71 wherein said base-to-user message comprises a timing adjustment command directed to said first user station. 74. The interleaved time division duplex frame structure of claim 73 wherein, in response to said timing adjustment command, subsequent messages transmitted from said first user station are advanced or retarded by an amount of time specified by said timing adjustment command. 75. The system of claim 71 wherein at least one of said base-to-user message and said user-to-base message is encoded using a spread spectrum technique. 76. The system of claim 71 wherein, in response to receiving said reply message at said base station from said third user station, said base station transmits a timing adjustment command directed to said third user station. 77. In a system for time division duplex communication between a base station and a plurality of user stations over a single frequency band, wherein said base station communicates during a time frame with user stations in established communication with said base station, and wherein said time frame is divided into a plurality of time slots of equal duration, a method comprising the steps of receiving at a first user station, over a designated frequency band and in a first time interval of a time frame, a first base message from a base station directed to said first user station, waiting for said base station to receive, over said designated frequency band and in a second time interval of said time frame, a first user message from a second user station directed to said base station, waiting for said base station to transmit, over said designated frequency band and in a third time interval of said time frame, a second base message from said base station, transmitting from said first user station, over said designated frequency band and in a fourth time interval of said time frame, a second user message directed to said base station. 78. A method for communicating between a base station and a plurality of user stations comprising the steps of transmitting from a base station, over a specified frequency band and during an initial portion of a time frame, a plurality of base-to-user messages directed to user stations, each of said base-to-user messages corresponding to a different base time slot, receiving at said base station from said user stations, over said specified frequency band and during a latter portion of said time frame, a plurality of user-to-base messages directed to said base station, each of said user-to-base messages corresponding to a different user time slot, and transmitting from said base station, over said specified frequency band and during a subsequent time frame, a timing adjustment command to at least one of said user stations, whereby at least one subsequent user-to-base message from said user station is advanced or retarded in time by an amount specified by said timing adjustment command. 79. The method of claim 78 wherein at least one of said base-to-user messages and said user-to-base messages is transmitted using a spread spectrum technique. 80. The method of claim 78 further comprising the steps of transmitting from said base station a signal identifying an available user time slot, receiving from a user station seeking to establish communication with said base station, over said specified frequency band and during said available user time slot, a reply message, transmitting from said base station, over said specified frequency band, a second timing adjustment command to said user station seeking to establish communication with said base station, whereby at least one subsequent user-to-base message from said user station seeking to establish communication with said base station is advanced or retarded by an amount of time specified by said second timing adjustment command. 81. The method of claim 80 wherein said reply message is transmitted from said user station seeking to establish communication with said base station in said available user time slot after a predetermined delay period. 82. The method of claim 80 wherein said reply message is transmitted using a spread spectrum technique. 83. The method of claim 80 wherein the length of said reply message is such that it will be fully received by said base station prior to the start of a second user time slot immediately following said available user time slot. 84. The method of claim 78 wherein each user time slot is separated from a following user time slot by an abbreviated guard band. 85. The method of claim 84 wherein said abbreviated guard band has a duration of less than a full round trip propagation delay time relative to a radius of a cell in which said base station is located. 86. In a communication system employing time division multiplexing, a method for establishing communication between a base station and a user station comprising the steps of transmitting from a base station, over a specified frequency band and during an initial portion of a time frame, a plurality of base-to-user messages directed to user stations with which said base station has previously established communication, said initial portion comprising a plurality of base time slots, wherein each of said base-to-user messages corresponds to a different base time slot and at least one of said base time slots is available for communication, transmitting from a user station seeking to establish communication with said base station, over said specified frequency band and during a user time slot in a user portion of said time frame, a reply message directed to said base station, said user time slot paired with said available base time slot, receiving at said base station said reply message, calculating a propagation delay at said base station based on a relative time of receiving said reply message and deriving a timing adjustment command thereby, transmitting from said base station, over said specified frequency band and during a subsequent time frame, a timing adjustment command to said user station, in response to said timing adjustment command, advancing or retarding a relative timing of subsequent user-to-base messages from said user station to said base station by an amount specified by said timing adjustment command. 87. The method of claim 86 wherein said reply message is transmitted from said user station in said user time slot after a predetermined delay period. 88. The method of claim 86 wherein one or more of said base-to-user messages and said user-to-base messages are transmitted using a spread spectrum technique. 89. The method of claim 86 wherein said reply message is transmitted using a spread spectrum technique. 90. The method of claim 86 wherein the length of said reply message is such that it will be fully received by said base station prior to the start of an immediately following user time slot. 91. A system of communication comprising a plurality of time frames of equal duration, each of said time frames comprising a base transmission portion, a collective guard portion, and a user transmission portion, said collective guard portion located between said base transmission portion and said user transmission portion, a plurality of base time slots in said base transmission portion, during each of which a base station may transmit a base-to-user message directed to one of a plurality of user stations, a plurality of user time slots in said user transmission portion, during each of which a corresponding one of said user stations may transmit a user-to-base message directed to said base station, said user time slots separated by abbreviated guard bands, wherein said base station commands at least one of said user stations to advance or retard a relative timing of its respective user-to-base message in response to a calculated propagation delay time. 92. The system of claim 91 wherein a new user station seeking to establish communication with said base station transmits a reply message to said base station during said collective guard portion. 93. The system of claim 92 wherein said base station calculates, based on a time of receiving said reply message, a new user station propagation delay for said new user station and transmits, during an available one of said base time slots, a timing adjustment command to said new user station. 94. The system of claim 92 wherein the length of said reply message is such that it will be fully received by said base station prior to the end of said collective guard portion. 95. The system of claim 91 wherein a new user station seeking to establish communication with said base station transmits a reply message to said base station during an available one of said user time slots. 96. The system of claim 95 wherein said base station calculates, based on a time of receiving said reply message, a new user station propagation delay for said new user station and transmits, during one of said base time slots corresponding to said one available user time slot, a timing adjustment command to said new user station. 97. The system of claim 95 wherein the length of said reply message is such that it will be fully received by said base station prior to the start of an immediately following user time slot. 98. The system of claim 95 wherein said available user time slot is the first user time slot. 99. The system of claim 91 wherein one or more of said base-to-user messages and said user-to-base messages are transmitted using a spread spectrum technique. 100. The system of claim 91 wherein said abbreviated guard bands have a duration of less than a full round trip propagation delay time relative to a radius of a cell in which said base station is located. 101. A method for carrying out time division multiplexed communication between a base station and a plurality of user stations over a single frequency band, comprising the steps of transmitting, during a base portion of a time frame, a base station burst over a designated frequency band, said base station burst comprising a plurality of time intervals corresponding to base time slots, wherein either a base-to- user message or a general polling message is transmitted in each of said base time slots, said base-to-user message being transmitted in the base time slots already in use for established communication with user stations, and said general polling message being transmitted in the base time slots available for communication, receiving in user time slots, during a user portion of said time frame and over said designated frequency band, a user-to-base message in the user time slots already in use for established communication with said base station, and a reply message in the user time slots in which a new user station is attempting to establish communication with said base station, and periodically transmitting from said base station, over said designated frequency band, a timing adjustment command to at least one of said user stations, whereby subsequent user- to-base messages from said user station are advanced or retarded in time by an amount specified by said timing adjustment command. 102. The method of claim 25 further comprising the step of transmitting from said base station, over said designated frequency band, an initial timing adjustment command to at least one of said user stations attempting to establish communication with said base station. 107. The system of claim 105 wherein said base time slots are interleaved. 108. The system of claim 105 wherein said base time slots are non-interleaved. 109. A method for communicating between a base station and a plurality of user stations comprising the steps of transmitting from a base station, over a specified frequency band and during a base portion of a time frame, a base station burst comprising a plurality of base-to-user messages directed to user stations, receiving at said base station from said user stations, over said specified frequency band and during a user portion of said time frame, a plurality of user-to-base messages directed to said base station, each of said user-to-base messages corresponding to a different user time slot, transmitting from said base station, over said specified frequency band and during a subsequent time frame, a timing adjustment command to at least one of said user stations, whereby subsequent user-to-base messages from said user station are advanced or retarded in time by an amount specified by said timing adjustment command. 110. The method of claim 109 wherein said base-to-user messages are interleaved. 111. The method of claim 110 wherein said base station burst comprises a plurality of blocks, each block comprising a plurality of sub-messages, and each of said base-to-user messages comprising at least one of said sub-messages from a plurality of said blocks. 112. The method of claim 111 wherein each of said base- to-user messages comprises exactly one sub-message from each of said blocks. 113. The method of claim 111 wherein at least one of said sub-messages in each of said blocks is preceded by a preamble. 114. The method of claim 113 wherein all of said sub- messages in each of said blocks are preceded by a preamble. 115. The method of claim 113 wherein said preamble comprises a spread spectrum code. 116. The method of claim 110 wherein said user stations employ forward error correction. 117. The method of claim 116 wherein said forward error correction comprises a Reed-Solomon coding technique. 118. A system for time division multiplexed communication between a base station and a plurality of user stations over a single frequency band, comprising a plurality of time frames of equal duration, a base transmission portion in each of said time frames, said base transmission portion comprising a plurality of transmit time slots, a plurality of sub-messages in each of said transmit time slots, wherein one or more sub-messages from a plurality of said transmit time slots are directed by a base station to the same user station in established communication with said base station, and a user transmission portion in each of said time frames, said user transmission portion comprising a plurality of user time slots during which user-to-base messages from user stations in established communication with said base station are received, wherein said base station periodically transmits during said base transmission portion a timing adjustment command to said user stations in established communication with said base station. 119. The system of claim 118 wherein a user station receiving said timing adjustment command advances or retards its timing by an amount specified by said timing adjustment command. 120. The system of claim 118 wherein exactly one sub- message from each of said transmit time slots is directed to the same user station. 121. The system of claim 118 wherein at least one of said sub-messages in each of said transmit time slots is preceded by a preamble. 122. The system of claim 121 wherein all of said sub- messages in each of said transmit time slots are preceded by a preamble. 123. The system of claim 121 wherein said preamble comprises a spread spectrum code. 124. The system of claim 121 wherein said user stations employ forward error correction. 125. The system of claim 121 wherein said forward error correction comprises a Reed-Solomon coding technique. 126. The system of claim 121 wherein a user station seeking to establish communication with said base station transmits an abbreviated message in an available one of said user time slots. 127. The system of claim 126 wherein said base station transmits, in response to receiving said abbreviated message, an initial timing adjustment command to said user station seeking to establish communication. 128. The system of claim 118 wherein said user time slots are separated by abbreviated guard bands. 129. A method of duplex communication between a base station and a user station over multiple frequency bands, comprising the steps of transmitting, over a first frequency band, a control pulse preamble from a user station, receiving, during a first preamble interval, said control pulse preamble at a base station, transmitting, over a second frequency band and during a base message interval, a base-to-user message from said base station to said user station, receiving said base-to-user message at said user station, transmitting, over said first frequency band, a user-to- base message from said user station, and receiving, during a user message interval, said user-to- base message at said base station. 130. The method of claim 129 further comprising the step of transmitting, prior to said step of transmitting said control pulse preamble, a plurality of preamble bursts over said second frequency band from said base station to said user station. 131. The method of claim 130 wherein said preamble bursts are three in number. 132. The method of claim 130 wherein the number of preamble bursts equals a number of antennas used by said base station, and wherein said method further comprises the steps of measuring at said user station a relative received signal quality of said preamble bursts, transmitting from said user station, as part of said user-to-base message, an indication of said relative received signal quality, and selecting at said base station, in response to said relative received signal quality, one or more of said antennas for subsequent messages to said user station. 133. The method of claim 129 wherein said base-to-user message comprises a timing adjustment command directed to said user station. 134. The method of claim 133 wherein, in response to said timing adjustment command, a subsequent message transmitted from said user station is advanced or retarded by an amount of time specified by said timing adjustment command. 135. The method of claim 129 wherein at least one of said base-to-user message and user-to-base message is encoded using a spread spectrum technique. 136. The method of claim 129 wherein said base station is capable of transmitting in either a spread spectrum or a narrowband mode. 137. The method of claim 129 wherein said control pulse preamble comprises a spread spectrum code. 138. The method of claim 129 wherein said control pulse preamble comprises a plurality of concatenated codes. 139. The method of claim 138 wherein said control pulse preamble comprises a kronecker product of a minimum peak sidelobe code and a Barker code. 140. A method of communication between a base station and a plurality of user stations over multiple frequency bands, comprising the steps of transmitting, during a first time slot and over a base transmission frequency band, a first base-to-user message from a base station to a first user station, receiving said first base-to-user message at said first user station, transmitting, over a user transmission frequency band, a control pulse preamble from a second user station to said base station, receiving, during said first time slot, said control pulse preamble at said base station, transmitting, during a second time slot and over said base transmission frequency band, a second base-to-user message from said base station to said second user station, receiving said second base-to-user message at said second user station, transmitting, over said user transmission frequency band, a user-to-base message from said first user station to said base station, and receiving, during said second time slot, said user-to- base message at said base station. 141. The method of claim 140 further comprising the steps of transmitting, over said user transmission frequency band, a second user-to-base message from said second user station to said base station, and receiving, during a third time slot, said second user-to- base message at said base station. 142. The method of claim 141 further comprising the steps of transmitting, over said user transmission frequency band, a second control pulse preamble from a third user station to said base station, receiving, during said second time slot, said second control pulse preamble at said base station, transmitting, during said third time slot and over said base transmission frequency band, a third base-to-user message from said base station to said third user station, receiving said third base-to-user message at said third user station, transmitting, over said user transmission frequency band, a third user-to-base message from said third user station to said base station, and receiving, during a fourth time slot, said third user-to- base message at said base station. 143. The method of claim 140 wherein said second base-to- user message comprises a timing adjustment command. 144. The method of claim 143 wherein, in response to said timing adjustment command, a subsequent message transmitted from said second user station to said base station is advanced or retarded by an amount of time specified by said timing adjustment command. 145. The method of claim 140 wherein at least one of said first base-to-user message, said second base-to-user message, and said user-to-base message is encoded using a spread spectrum technique. 146. The method of claim 140 further comprising the step of transmitting, prior to said step of transmitting said control pulse preamble, a plurality of preamble bursts over said base transmission frequency band from said base station to said first user station. 147. The method of claim 140 wherein said second time slot immediately follows said first time slot. 148. The method of claim 140 wherein a relative starting reference point for each time slot, including said first time slot and said second slot, is offset in time for said user transmission frequency band with respect to said base transmission frequency band. 149. The method of claim 148 wherein said offset is of sufficient duration to allow said first base-to-user message to propagate from said base station to said first user station, and said user-to-base message to propagate from said first user station to said base station. 150. The method of claim 140 wherein said base station is capable of transmitting in either a spread spectrum or a narrowband mode. 151. A frame structure for communication between a base station and a plurality of user stations over multiple frequency bands, comprising a plurality of time frames, and a plurality of time slots in each of said time frames, each of said time slots comprising a base interval, during which either a base-to-user message may be transmitted over a first frequency band by a base station to a first user station in established communication with said base station during said time slot, or a general polling message may be transmitted over said first frequency band indicating the availability of said time slot, a user interval, during which either a user-to-base message may be received over a second frequency band at said base station from a second user station in established communication with said base station, or a reply message may be received over said second frequency band at said base station from a third user station seeking to establish communication with said base station, and a preamble interval during which a control pulse preamble may be received over said second frequency band from a fourth user station in established communication with said base station, whereby said base station may respond to said fourth base station in a following time slot. 152. The frame structure of claim 151 wherein said base- to-user message comprises a timing adjustment command directed to said first user station. 153. The frame structure of claim 151 wherein at least one of said base-to-user message and said user-to-base message is encoded using a spread spectrum technique. 154. The frame structure of claim 151 wherein, in response to receiving said reply message at said base station from said third user station, said base station transmits a timing adjustment command directed to said third user station. 155. The frame structure of claim 151 wherein said user interval is offset from said base interval by a predetermined amount of time less than the duration of an entire time slot. 156. The frame structure of claim 151 wherein said user interval and said base interval are substantially overlapping. 157. The frame structure of claim 151 wherein said base station is capable of transmitting in either a spread spectrum or a narrowband mode. 158. An interleaved air interface frame structure for carrying out time division multiplexed communication between a base station and a plurality of user stations over multiple frequency bands, comprising a plurality of time frames during each of which a base station may transmit over a first designated frequency band and user stations may transmit over a second designated frequency band according to a predetermined protocol, a plurality of time slots in each of said time frames, said time slots having a base station portion corresponding to said first designated frequency band and a user station portion corresponding to said second designated frequency band, wherein said base station portion comprises a base message interval, during which said base station may transmit a first base-to-user message to a first base station in response to having received a first control pulse preamble in an immediately preceding time slot, and a base preamble interval, during which said base station may transmit at least one preamble burst directed to a second user station, whereby said second user station may respond to said at least one preamble burst in a following time slot, and wherein said user station portion comprises a user message interval, during which a third user station may transmit a user-to-base message in response to having received a second base-to-user message in an immediately preceding time slot, and a control pulse preamble interval, during which a fourth user station may transmit a control pulse preamble to said base station, whereby said base station may respond to said control pulse preamble in said following time slot. 159. The interleaved air interface frame structure of claim 158 wherein said user station portion is offset from said base station portion by a predetermined amount of time less than the duration of an entire time slot. 160. The interleaved air interface frame structure of claim 158 wherein said base-to-user message comprises a timing adjustment command directed to said first user station. 161. The interleaved air interface frame structure of claim 158 wherein at least one of said base-to-user message and user-to-base message is encoded using a spread spectrum technique. 162. The interleaved air interface frame structure of claim 158 wherein said base station is capable of transmitting in either a spread spectrum or a narrowband mode. 163. The interleaved air interface frame structure of claim 158 wherein said control pulse preamble is concatenated. 164. An interleaved frequency division duplex frame structure for communication between a base station and a plurality of user stations, comprising a plurality of time frames, and a plurality of time slots in each of said time frames, said time slots each comprising a base station portion and a user station portion, wherein a duplex pairing consists of a first base station portion in a first time slot and a first user station portion in a second time slot subsequent to said first time slot, whereby a base station transmits over a first designated frequency band a base-to-user message during said first base station portion, and said base station receives over a second designated frequency band a user-to-base message from a user station during said first user station portion, and wherein for each time slot said user station portion is offset by a predetermined amount of time from said base station portion. 165. The interleaved frequency division duplex frame structure of claim 164 wherein said predetermined amount of time is of sufficient duration to allow said base-to-user message to propagate from said base station to said first user station, and said user-to-base message to propagate from said first user station to said base station so as to be received in said first user station portion. 166. The interleaved frequency division duplex frame structure of claim 164 wherein said base-to-user message comprises a timing adjustment command directed to said user station. 167. The interleaved frequency division duplex frame structure of claim 164 wherein at least one of said base-to- user message and said user-to-base message is encoded using a spread spectrum technique. 168. The interleaved frequency division duplex frame structure of claim 164 wherein said base station is capable of transmitting in either a spread spectrum or a narrowband mode. 169. The interleaved frequency division duplex frame structure of claim 164 further comprising a preamble interval in each time slot during which said base station receives a control pulse preamble over said second designated frequency band from a user station in established communication prior to exchanging traffic messages therewith. 170. The interleaved frequency division duplex frame structure of claim 169 further comprising a plurality of preamble burst intervals in each time slot during which said base station transmits a plurality of preambles, one in each preamble burst interval, over said first designated frequency band to a user station in established communication prior to receiving said control pulse preamble. 171. The interleaved frequency division duplex frame structure of claim 170 wherein said preamble burst intervals are three in number. 172. The interleaved frequency division duplex frame structure of claim 170 wherein the number of preamble burst intervals equals a number of antennas used by said base station, and wherein said user station measures a relative received signal quality of said preamble bursts and transmits to said base station, as part of said user-to-base message, an indication of said relative received signal quality. 173. The interleaved frequency division duplex frame structure of claim 172 wherein said base station selects, in response to said relative received signal quality, one or more of said antennas for subsequent messages to said user station. 174. A frame structure for duplex communication between a base station and a plurality of user stations over multiple frequency bands, comprising a plurality of time frames, and a plurality of time slots for each time frame, each time slot comprising a base transmission interval during which a base station may transmit over a first designated frequency band a base-to-user message to a first one of a plurality of user stations in established communication with said base station, and a user transmission interval during which said base station may receive a user-to-base message over a second designated frequency band from a second one of said user stations, wherein the start of said user transmission interval in each time slot is offset by a predetermined amount of time relative to the start of said base transmission interval. 175. The frame structure of claim 174 wherein said base- to-user message to said first user station comprises a forward link transmission of a duplex pairing, and a reverse link transmission from said first user station to said base station occurs in a time slot immediately following said forward link transmission. 176. The frame structure of claim 175 wherein said forward link transmission and said reverse link transmission are separated by an amount of time sufficient to allow propagation of said forward link transmission to said first user station and propagation of said reverse link transmission to said base station, without simultaneous reception and transmission by said first user station. 177. The frame structure of claim 175 further comprising a preamble interval preceding said first forward link transmission, during which a control pulse preamble is received over said second designated frequency band by said base station from said first user station. 178. The frame structure of claim 175 wherein said base- to-user message comprises a timing adjustment command whereby a relative timing of said reverse link transmission is adjusted. 179. A method of communication between a base station and a plurality of user stations over multiple frequency bands, comprising the steps of transmitting, during a first time interval and over a base transmission frequency band, a first base-to-user message from a base station to a first user station, receiving said first base-to-user message at said first user station, transmitting, over a user transmission frequency band, a control pulse preamble from a second user station to said base station, receiving, during a second time interval, said control pulse preamble at said base station, transmitting, during a third time interval and over said base transmission frequency band, a second base-to-user message from said base station to said second user station, receiving said second base-to-user message at said second user station, transmitting, over said user transmission frequency band, a user-to-base message from said first user station to said base station, and receiving, during a fourth time interval, said user-to- base message at said base station. 180. The method of claim 179 wherein said first time interval and said second time interval occupy a first time slot, and said third time interval and said fourth time interval occupy a second time slot. 181. The method of claim 180 wherein said second time slot immediately follows said first time slot. 182. The method of claim 180 wherein said third time interval and said fourth time interval are at least partially overlapping. 183. The method of claim 179 further comprising the steps of transmitting, over said user transmission frequency band, a second user-to-base message from said second user station to said base station, and receiving, during a fifth time interval, said second user-to-base message at said base station. 184. The method of claim 179 wherein said second base-to- user message comprises a timing adjustment command. 185. The method of claim 184 wherein, in response to said timing adjustment command, a subsequent message transmitted from said second user station to said base station is advanced or retarded by an amount of time specified by said timing adjustment command. 186. A method of duplex communication between a base station and a user station over a plurality of frequency bands, comprising the steps of transmitting, over a first frequency band, a control pulse preamble from a user station to a base station, receiving at said user station, over a second frequency band, a base-to-user message from said base station, and transmitting, over said first frequency band, a user-to- base message from said user station to said base station.

Inventors: SCOTT LOGAN, SCOTT, LOGAN
Applicants: OMNIPOINT CORP, SCOTT LOGAN, OMNIPOINT CORPORATION, SCOTT, LOGAN
Application year: 1996
Main classification: H04B1
IPC codes: H04B1, H04B7, H04J3, H04J13, H04Q7