Abstract:
The present invention provides for a modulation control device and method that can be implemented economically in existing communication networks or new networks to increase capacity. A modulation control device in accordance with the present invention allows for possibly more than one call to simultaneously utilize the same frequency channel for AMPS systems or the same frequency during the same timeslot for TDMA systems. A modulation control device in accordance with the present invention evaluates the transmission quality of a frequency channel and if acceptable, the modulation control device phase divides the frequency channel. The modulation control device assigns phase adjustment values to a call preferably which remain independent of the information encoding modulation techniques utilized. A call then can be modulated by the assigned phase adjustment value during transmission, and the call may be identified by the assigned phase adjustment value during reception. The present invention further provides a methodology for modulating calls by varying phase to increase capacity in wireless communication networks.

Description:
FIELD OF THE INVENTION 
   The present invention generally relates to wireless communication networks, and more particularly to increasing the capacity of wireless communication networks. 
   BACKGROUND OF THE INVENTION 
   In recent years, the popularity and growth of wireless communication networks has increased in dramatic fashion. In fact, wireless networks are continually pressed to keep up with the demands for increased capacity while maintaining reliable and acceptable service. Steps are continuously being taken to increase capacity in existing networks, but the demand for more capacity remains because of the tremendous growth in wireless communications. 
   Traditional wireless communication networks are partitioned into service areas known as cells wherein mobile units within a cell communicate via radio links with a base station that services that cell. The base station is coupled to the public switch telephone network: for access to the land network. A pool of available frequency channels is assigned to each cell in such a way that the same frequency channels can be reused in other cells that are sufficiently separated by enough distance to prevent unacceptable co-channel interference. These frequency channel re-use patterns can be implemented with assumptions that include equal-sized, regularly spaced cells with uniformly distributed traffic loads. The re-use patterns can also be adjusted to increase capacity based on real world considerations such as usage patterns and topography to increase capacity. The design and operation of a typical wireless communication network is described in an article titled “Advanced Mobile Phone Service” by Belcher, IEEE Transactions on Vehicular Technology, Vol. VT29, No. 2, May 1980, pp. 238–244. 
   Attempts at further increasing capacity for digital wireless networks have included using a Code Division Multiple Access (CDMA) architecture based on the IS-95 digital wireless standard. IS-95 refers to the standard set by the Electronics Industries Association (EIA) and the Telecommunications Industries Association (TIA) for the implementation of a CDMA architecture. In CDMA systems, a unique code is allocated to each mobile unit and all calls are communicated simultaneously over a broad band of frequency, i.e., 1.25 MHz for IS-95, thus spreading the energy of the calls over a large bandwidth. The calls are decoded by using the knowledge of the unique code of a mobile unit to retrieve a particular call. 
   Further attempts to increase capacity for wireless communication networks have been implemented by using a Time Division Multiple Access (TDMA) architecture. TDMA is an implementation that allows multiple calls to use a shared frequency channel by using different time slots. Standards have been set by the Electronics Industries Association (EIA) and the Telecommunications Industries Association (TIA) for the implementation of a TDMA architecture following EIA/TIA documents IS-54/IS-136. The European digital wireless network, referred to as Global System for Mobile Communications (GSM), also uses a TDMA architecture. The frequency channel is divided into timeslots with each mobile unit being assigned at least one timeslot during which it can communicate with the base station. For IS-54/IS-136 each frequency channel is allocated 30 kHz of bandwidth which is divided into six timeslots. For full rate operation, each mobile unit is assigned two of the six timeslots of the frequency channel. For half rate operation, each mobile unit is assigned only one timeslot. 
   A technique to increase capacity over traditional TDMA is called Enhanced Time Division Multiple Access (E-TDMA) which dynamically allocates timeslots to mobile units thereby taking advantage of the dead space that results from one-way alternating conversations and the redundant nature of human speech. Accordingly, mobile units are not assigned permanent timeslots for the call duration but receive timeslots for communicating only when needed. However, E-TDMA is complex in design, and therefore, difficult if not impractical to implement. The cost of an E-TDMA system is yet another impediment to its acceptance. 
   The growth of existing wireless communication networks is threatened by the capacity restraints of the networks. The use of more cells is costly because of the additional base stations needed and the problems of securing additional base station sites. Also, many existing wireless communication providers are already heavily invested in equipment for specific architectures so converting to another architecture is not a commercially viable option. Therefore, it would be desirable to be able to further increase capacity efficiently, economically, and without degrading service of existing wireless communication networks. It is also desirable to give new wireless communication providers a broader array of choices when equipment and capacity concerns are addressed. 
   SUMMARY OF THE INVENTION 
   The present invention provides for modulation control devices and methods that can be implemented economically in existing and new wireless communication networks to increase capacity. A modulation control device in accordance with the present invention evaluates the transmission quality of a frequency channel and if acceptable, the modulation control device phase divides the frequency channel. For example, a modulation control device in accordance with the present invention allows for possibly more than one call to simultaneously utilize the same frequency channel for AMPS networks or the same frequency during the same timeslot for TDMA networks via phase modulation. 
   The modulation control device assigns phase adjustment values to a call preferably which remain independent of the information encoding modulation techniques utilized. A call then can be modulated by the assigned phase adjustment value during transmission, and the call may be identified by the assigned phase adjustment value during reception. The present invention further provides methodologies for modulating calls by varying phase to increase capacity in wireless communication networks. 
   In accordance with an aspect of the present invention, a system for assigning a call to one of a plurality of wireless frequency channels in a wireless communication network comprises a wireless transceiver and a modulation control device that identifies a frequency channel for the call to utilize. The modulation control device then transfers at least one assignment modulation parameter, at least including phase, to the transceiver for assigning the call to the frequency channel. When the modulation control device transfers modulation parameters including frequency channel and phase to the transceiver, then the wireless communication network can include advanced mobile phone system (AMPS) wireless networks. When the modulation control device transfers modulation parameters including timeslot and frequency as well as phase to the transceiver, then the wireless communication networks can include time division multiple access (TDMA) wireless networks including personal communications system (PCS) networks or global system for mobile communications (GSM) networks. 
   A modulation control device in accordance with the present invention can include a threshold detector that measures a transmission quality of frequency channels and a modulation control mechanism that selects available frequency channels based on the transmission quality measurements. The threshold detector may be configured to measure transmission quality of a frequency channel during the different timeslots. The modulation control mechanism may also include logic to select phase adjustment values or to retain predetermined phase adjustment values. The modulation control mechanism may include logic that can select the phase adjustment values so as to maximize the phase separation between calls on the frequency channel. Additionally, the modulation control mechanism may include logic that selects phase adjustment values that provide a unique resultant phase value for the calls. 
   The present invention also provides for mobile units capable of receiving calls that have been transmitted using phase adjustment values. These mobile units may each include a mobile modulation control device that uses a phase adjustment value received from the base station to receive calls from the base station and to transmit calls to the base station. 
   The present invention also calls for and can be conceptualized as methods for use in a wireless communication network for assigning calls to frequency channels. In one embodiment of this methodology a step of assigning a frequency channel and a phase adjustment value to a call is included. The phase adjustment value is then communicated to the mobile unit that is associated with the call so that the mobile unit can use the phase adjustment value for transmitting the call and reference the phase adjustment value for receiving the call. A variation of this methodology includes the step of measuring the transmission quality of the frequency channels individually before a frequency channel is assigned to a call. If the transmission quality of a frequency channel exceeds a predetermined value, then the call can be assigned to that frequency channel as above. 
   The present invention also calls for and can be conceptualized as methods for allocating calls in a wireless communication network that uses TDMA technology. For example, a transmission quality of the frequency channels can be individually measured during each timeslot. If the transmission quality of a frequency channel during a timeslot exceeds a predetermined value, then the call can be assigned to the frequency channel for that timeslot and assigned a phase adjustment value in accordance with an embodiment of the invention. This phase adjustment value is communicated to the mobile unit that is associated with the call. Likewise, the base station associates the phase adjustment value with the call so that the phase adjustment value can be used for transmitting the call to the mobile unit and referenced for receiving the call from the mobile unit. 
   The present invention also calls for and can be conceptualized as methods for use by a mobile unit for receiving calls which are transmitted with a phase adjustment value. This method includes the steps of receiving a phase adjustment value from the base station that identifies, at least in part, a call and demodulating the call through utilizing the phase adjustment value. This method may also include the step of filtering out noise if necessary. The present invention also calls for and can be conceptualized as methods for use by a mobile unit to transmit calls which have been assigned a phase adjustment value. This method includes the steps of the mobile unit receiving a phase adjustment value from the base station for a call, and the mobile unit using the phase adjustment value for transmitting the call to the base station. 
   Other features and advantages of the present invention will become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional features and advantages be included herein in the scope of the present invention, as defined by the claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram of a wireless communication network suitable for employing an embodiment of the present invention; 
       FIG. 2A  provides a dimensional representation of the operation of an Advanced Mobile Phone Service wireless communication network according to prior art; 
       FIG. 2B  provides a dimensional representation of the operation of an Advanced Mobile Phone Service wireless communication network in accordance with an embodiment of the present invention; 
       FIG. 3  is a schematic block diagram illustrating a base station for an Advanced Mobile Phone Service wireless communication network in accordance with an embodiment of the present invention; 
       FIG. 4  is a schematic block diagram illustrating a mobile unit for an Advanced Mobile Phone Service wireless communication network in accordance with an embodiment of the present invention; 
       FIG. 5A  provides a dimensional representation of the operation of a Time Division Multiple Access wireless communication network according to prior art; 
       FIG. 5B  provides a dimensional representation of the operation of a Time Division Multiple Access wireless communication network in accordance with an embodiment of the present invention; 
       FIG. 6  is a schematic block diagram illustrating a base station for a Time Division Multiple Access wireless communication network in accordance with an embodiment of the present invention; 
       FIG. 6A  is a functional diagram illustrating four level phase division for a frequency channel for a Time Division Multiple Access wireless communication network in accordance with an embodiment of the present invention; 
       FIG. 7  is a schematic block diagram illustrating a mobile unit for a Time Division Multiple Access wireless communication network in accordance with an embodiment of the present invention; 
       FIG. 8  is a flowchart of the operation of a wireless base station in accordance with an embodiment of the present invention; and 
       FIG. 9  is a flowchart of the operation of a wireless mobile unit in accordance with an embodiment of the present invention. 
   

   DESCRIPTION OF PREFERRED EMBODIMENTS 
   The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in different forms and should not be construed as limited to the embodiments as set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. The elements of the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present invention. Furthermore, like reference numbers refer to like elements throughout. This description includes a general overview of wireless communication networks, a first preferred embodiment, which is suitable for an AMPS system, and a second preferred embodiment which is suitable for IS-54/IS-136 TDMA systems. 
   With reference now to the drawings,  FIG. 1  shows a wireless communication network  12  suitable for employing the present invention. The wireless communication network  12  includes a plurality of cells  14  configured to cover a particular geographic area, as well known in the art. It should be understood that the shape and configuration of the cells  14  are merely exemplary of that which is commonly used in the industry, and does not constitute any part of the invention. The cells  14  in  FIG. 1  are configured in a seven cell repeating pattern with each cell having one-seventh of the total number of channels of the wireless communication network  12 . In today&#39;s North America wireless network, there are typically 420 channels reused in each seven cell pattern. Accordingly, each cell  14  has sixty channels allotted to it. At each cell  14  is a base station  15  that provides a radio interface with a plurality of mobile units  16 . A carrier facility  17  interconnects each base station  15  to a mobile telecommunications switching office (MTSO)  18 . Each carrier facility  17  comprises a transmission media suited for transmitting a signal from each respective base station  15  to the MTSO  18 . The MTSO  18  interconnects the wireless portion of the wireless communication network  12  to the public switch telephone network (PSTN)  20 . 
   In addition, the MTSO  18  may include a base station controller  26  and a wireless switch  28  that are interconnected by a link  29 . The base station controller  26  essentially interfaces the wireless portion of the network  12  with the wireless switch  28 . The base station controller  26  performs the mobility management functions of the MTSO  18 , for instance, channel routing functions and handoff functions. Thus, the wireless switch  28  is kept insulated from changes in a call arising from the mobility of the customer or arising from bandwidth management (i.e., hand-offs initiated by the base station controller  26  for bandwidth utilization between cells). The wireless switch  28  interfaces with the PSTN  20  via a link  32  that may include links to a variety of long distance exchange carriers and/or a local exchange carrier, as is well known in the art. 
   In a preferred embodiment, the present invention modifies base stations  15  to increase the capacity of the wireless communication network  12 . Note, however, that the present invention may be implemented at the base stations  15  located at the cells  14  or in the MTSO  18  or in the base station controller  26  or distributed between different elements of the wireless communication network  12 . 
   I. Implementation of a Modulation Control Device According to the Present Invention for AMPS 
   Advanced Mobile Phone System (AMPS) is a well known way to implement a wireless communication network. AMPS provides multiple access by dividing a frequency block typically into 30 kHz frequency channels. Accordingly, multiple access in such a system is based upon the single dimension of frequency as illustrated in  FIG. 2A . In accordance with the present invention, access to multiple users would be governed by two dimensions (frequency and phase) as illustrated by the two dimensional system  40  in  FIG. 2B . This added dimension may allow for as many as P times more users than with mere frequency division, where P is the number of different phase adjustment values chosen to allocate the calls. While theoretically unlimited, the number of phase adjustment values possible is limited as a practical matter by the physical limits of the frequency channel (e.g., the noise of the frequency channel and the ability to recover the signals). A typical implementation might use four phase adjustment values. 
   AMPS uses frequency shift keying (FSK) for encoding information onto the carrier frequency. Therefore, the phase adjustment values can be chosen to maximize phase separation between the phase adjustment values without concerns over confusion that might result if the information was encoded by phase. 
   Now referring to  FIG. 3 , illustrated is a base station  200  in accordance with an embodiment of the present invention in which the base station  200  uses radio equipment  202  for interfacing with at least one mobile unit  204 . The base station  200  further includes a modulation control device  214  and a transceiver  216 . The modulation control device  214  is communicatively connected to the transceiver  216 . 
   The modulation control device  214  comprises a threshold detector  218  and a modulation control mechanism  220 . The threshold detector  218  is configured to measure the transmission quality (the signal quality and noise) of a plurality of frequency channels  222  and to deliver these measurements to the modulation control mechanism  220 . 
   This implementation begins with a first mobile unit  204  requesting initial service from the base station  200  for a call. The modulation control mechanism  220  compares the transmission quality measurements, taken by the threshold detector  218 , of a first frequency channel  222  with a predetermined threshold level. If the measured transmission quality of the first frequency channel  222  is greater than the predetermined threshold level, then the modulation control mechanism  220  assigns the first frequency channel  222  and a phase adjustment value to the call of the mobile unit  204 , and retains these assignment parameters (i.e., the phase adjustment value and the identity of the frequency channel to which the call was assigned). Otherwise, the modulation control mechanism  220  compares the transmission quality of a second frequency channel  222  with the predetermined threshold level. If the measured transmission quality of the second frequency channel  222  is greater than the predetermined threshold level, then the modulation control mechanism  220  assigns the second frequency channel  222  and a phase adjustment value to the call of the mobile unit  204  as shown above. If not, then the modulation control mechanism  220  will continue through the plurality of frequency channels  222  until the call can be assigned to a frequency channel  222  (i.e., until a frequency channel&#39;s quality measurement exceed the predetermined level). Once a last frequency channel  222  of the plurality of frequency channels  222  has been reached, the modulation control mechanism  220  returns to the first frequency channel  222  of the plurality of frequency channels  222  and increments the phase adjustment value to the next phase value. Once a last frequency channel  222  of the plurality of frequency channels  222  has been reached and the last phase adjustment value of a plurality of such values has been reached, the modulation control mechanism  220  returns to the first frequency channel  222  and resets the phase adjustment value to the initial phase value. 
   When any subsequent mobile unit  204  requests service from the base station  200  for a call, the modulation control mechanism  220  identifies a frequency channel  222  and phase adjustment value for the call in substantially the same manner as described above except that the modulation control mechanism  220  begins with the phase adjustment value of the previous assigned call and with the next frequency channel  222  after the frequency channel  222  to which the previous call was assigned. 
   Once the frequency channel  222  and the phase adjustment value has been assigned to the call of the mobile unit  204 , then the frequency channel and phase adjustment value assigned may be communicated to the mobile unit  204  over the control channel, as is well known in the art. 
   When the base station  200  is transmitting to the first mobile unit  204 , the modulation control mechanism  220  may communicate with the transceiver  216 , wherein the transceiver  216  may include a plurality of modulators/demodulators  230 . The modulation control mechanism  220  can communicate the frequency channel  222  and phase adjustment value for the first mobile unit  204  for the call to the transceiver  216  so that at least one of the plurality of modulators/demodulators  230  can modulate the call based on these assignment parameters. Let A(t)cos(2πk(frequency channel assigned(t))+phase adjustment value) represent the waveform produced by at least one of the plurality of modulators/demodulators  230  where k represents the variable to control the information encoding for FSK. The waveform illustrates the phase division of an information carrying signal on a frequency channel. Note that for each additional phase adjustment value utilized an additional modulators/demodulators may be required for each frequency channel. 
   Alternatively, the modulation control device  214  may interact with the base station controller  26  to accomplish the phase adjustment value modulation so that the mobile unit  204  can identify the transmission. Yet another alternative is that the modulation control device  214  may communicate with a modulator/demodulator that is independent of the transceiver  216  to modulate the call with the associated phase adjustment value for the mobile unit  204 . Additional modulators/demodulators to modulate the call with the associated phase adjustment value can be added to existing base stations  200  to facilitate the implementation of this embodiment of the present invention. 
   When the base station  200  receives transmissions during a call from a mobile unit  204 , the transceiver  216  may communicate with the modulation control mechanism  220  to allow identification of the mobile unit  204 . For example, after the received transmission during a call is demodulated, the modulation control mechanism  220  may compare the phase of the signal with the assigned phase adjustment value to identify the mobile unit  204  that made the transmission. 
     FIG. 4  illustrates some of the elements of a mobile unit  260  for use in accordance with an embodiment of the present invention. The mobile unit  260  includes a demodulator  262 , a filter  264 , a modulator  270 , and a mobile modulation control device  272 . When the mobile unit  260  receives the assigned frequency channel  222  and phase adjustment value from the base station  200  for the call, these values are retained by the mobile modulation control device  272  for the duration of the call of the mobile unit  204 . When the mobile unit  204  receives a transmission from the base station  200  the mobile modulation control device  272  communicates the assigned phase adjustment value to the demodulator  262 . Therefore, the call can be demodulated using the phase adjustment value. The demodulator&#39;s  262  output may then be passed to the filter  264  to remove the noise and retrieve the desired transmission from the base station  200  for the call. When the mobile unit  204  wishes to transmit, the mobile modulation control device  272  may communicate the assigned phase adjustment value and frequency channel to the modulator  270 . Accordingly, the mobile unit  260  transmits a signal with the assigned phase adjustment value which allows the base station  200  to identify which mobile unit  204  made the transmission and accordingly to which call the transmission belongs. 
   II. Implementation of a Modulation Control Device According to the Present Invention for TDMA 
   A second preferred embodiment of the present invention is for use in TDMA systems. TDMA systems, wherein a frequency channel is divided into timeslots, include systems in the cellular frequency bands, GSM frequency bands, and PCS frequency bands. The IS-54/IS-136 standard which governs TDMA cellular systems divides a 30 kHz cellular channels into six timeslots. Accordingly, calls are assigned to a frequency channel for use during certain timeslots. This two dimensional multiple access system (timeslot and frequency channel) is illustrated by the two dimensional system  60  in  FIG. 5A . In accordance with the present invention, access to multiple users would be governed by three dimensions for TDMA (frequency, timeslot, and phase) as illustrated by the three dimensional system  70  in  FIG. 5B . Accordingly, an embodiment of the present invention may require three dimensions to assign and identify a call in the network. 
   The IS-54/IS-136 standard which governs TDMA 800 MHz cellular systems and 1900 MHz PCS systems uses π/4 differential quaternary phase shift keying (π/4-DQPSK), which is a modulation technique well known in the art, to encode information onto the carrier wave. This modulation technique, π/4-DQPSK, encodes information by varying the phase of the carrier wave. The present invention adjusts the phase to allow multiplexing of calls for transmission on the same frequency channel during the same timeslot. Accordingly, care should be taken in choosing the phase adjustment values to ensure that the aggregate of the information encoding phase and the phase adjustment value is unique. If the phase adjustment values are chosen poorly, then it would be possible that a call with an phase adjustment value of A and an information encoding phase of B would have the same aggregate phase as a call with an phase adjustment value of C and an information encoding phase of D when A+B equals C+D. 
   For π/4-DQPSK modulation, the information is conveyed by referencing the previous phase and the current phase; the phase of the carrier wave should be π/4 or some multiple thereof. One possible way to choose the phase adjustment values so that the aggregate phase values are unique is by the use of prime numbers. 
   Note the following example for use with π/4-DQPSK modulation. Let P represent the number of levels (different phase values chosen) of phase for assigning a call. As stated before, a typical implementation might use four levels (P=4). Let M represent the smallest prime number that is larger than P. The phase adjustment values can then be chosen with the aid of the following formula: 
         phase   ⁢           ⁢   adjustment   ⁢           ⁢     value   P       =         p   ⁡     (       2   ⁢           ⁢   π     M     )       ⁢           ⁢   where   ⁢           ⁢   p     =     1   ⁢           ⁢   to   ⁢           ⁢     P   .             
 
Accordingly, the phase adjustment values for π/4-DQPSK could be 2π/5, 4π/5, 6π/5, and 8π/5.
 
   Now referring to  FIG. 6 , illustrated is one embodiment for implementing a base station  300  in accordance with the present invention. This embodiment comprises a base station  300  which includes radio equipment  302  for interfacing with at least one mobile unit  304 . 
   The base station  300  further includes a modulation control device  314  and a transceiver  316  where the modulation control device  314  is communicatively connected to the transceiver  316 . The transceiver includes a plurality of time multiplexers  317  to implement timeslots. 
   The modulation control device  314  comprises a threshold detector  318  and a modulation control mechanism  320 . The threshold detector  318  is configured to measure the transmission quality (the signal quality and noise) of a plurality of frequency channels  322  during a plurality of timeslots and to deliver these measurements to the modulation control mechanism  320 . 
   This implementation begins with a first mobile unit  304  requesting initial service from the base station  300  for a call. The modulation control mechanism  320  compares the transmission quality measurements, taken by the threshold detector  318 , of a first frequency channel  322  during a first timeslot with a predetermined threshold level. If the measured transmission quality of the first frequency channel  322  during the first timeslot is greater than the predetermined threshold level, then the modulation control mechanism  320  assigns the frequency channel  322 , the timeslot, and a phase adjustment value to the call of the mobile unit  304 , and retains these assignment parameters (i.e., the phase adjustment value and the identity of the frequency channel  322  and timeslot to which the call was assigned). Otherwise, the modulation control mechanism  320  compares the transmission quality of a second timeslot of the first frequency channel  322  with the predetermined threshold level. If the measured transmission quality of the second timeslot of the first frequency channel  322  is greater than the predetermined threshold level, then the modulation control mechanism  320  assigns the second timeslot of the first frequency channel  322  and a phase adjustment value to the call of the mobile unit  304  as shown above. If not, then the modulation control mechanism  320  will continue through the plurality of timeslots within the plurality of frequency channels  322  until the call can be assigned to a timeslot within a frequency channel  322  (i.e., until a frequency channel&#39;s measurements during a timeslot exceed the predetermined level). 
   Once a last timeslot of the plurality of timeslots for the frequency channel  322  has been reached, the modulation control mechanism  320  will evaluate the first timeslot of the next frequency channel  322  of the plurality of frequency channels  322  and will continue through the plurality of timeslots and the plurality of frequency channels  322  until the call of the mobile unit  304  can be assigned to a timeslot and a frequency channel  322 . 
   Once a last timeslot of a plurality of timeslots in a last frequency channel  322  of the plurality of frequency channels  322  has been reached, the modulation control mechanism  320  returns to the first timeslot of the first frequency channel  322  of the plurality of frequency channels  322  and increments the phase adjustment value to the next value and continues searching for an available timeslot. Once a last timeslot of a plurality of timeslots in a last frequency channel  322  of the plurality of frequency channels  322  has been reached and the last phase adjustment value of a plurality of such values has been reached, the modulation control mechanism  320  returns to the first timeslot of the first frequency channel  322  and resets the phase adjustment value to the first phase adjustment value and then continues searching for an available timeslot within a frequency channel  322 . 
   When any subsequent mobile unit  304  requests service from the base station  300 , the modulation control mechanism  320  identifies a frequency channel, timeslot, and phase adjustment value in substantially the same manner as above except that the modulation control mechanism  320  begins with the phase adjustment value of the previous assigned call and with a next timeslot of the frequency channel  322  to which the previous call was assigned. 
   Once the timeslot, the frequency channel  322 , and the phase adjustment value has been assigned to the call of the mobile unit  304 , these timeslot, frequency channel  322 , and phase adjustment value parameters may be communicated to the mobile unit  304  over the control channel, as is well known in the art. 
   When the base station  300  is transmitting to the first mobile unit  304 , he modulation control mechanism  320  may communicate with the transceiver  316 , wherein the transceiver  316  may include a plurality of modulators/demodulators  330 . The modulation control mechanism  320  may communicate the timeslot, the frequency channel, and phase adjustment value for a call of the first mobile unit  304  to the transceiver  316  so that the transceiver&#39;s modulator/demodulator  330  may modulate the call based on the phase adjustment value. 
   Let A(t)cos(2π(frequency channel assigned(t))+φ i +phase adjustment value) represent the waveform produced by at least one of the plurality of modulators/demodulators  330  where (p represents the variable to control the information encoding for π/4-DQPSK and i represents the timeslot for which the call was assigned to transmit and/or receive. The waveform illustrates the phase division of an information carrying signal on a frequency channel during a timeslot. Note that for each additional phase adjustment value utilized an additional modulators/demodulators may be required for each frequency channel. 
   As well known in the art, a traditional IS-54/IS-136 TDMA system uses a time multiplexer to create timeslots for a frequency channel thereby allowing for capacity for six calls.  FIG. 6A  illustrates the functional aspects of the phase division of a single frequency channel in a TDMA network in accordance with an embodiment of the present invention wherein four level phase division (i.e., four distinct phase adjustment values; P=4) has been chosen. Four level phase division may require additional time multiplexers  340  (illustrated is an additional time mutliplexer  340  for each phase adjustment value) to create timeslots for each phase adjustment value. As illustrated in this embodiment, a time multiplexer  340  and a modulator  345  are shown for each phase adjustment value assigned. This implementation allows for twenty-fiur calls to share a single frequency channel. Four calls, that are assigned different phase adjustment values, share the same timeslot within this single frequency channel. 
   Alternatively, the modulation control device  314  may interact with the base station controller  26  to accomplish the phase adjustment value modulation so that the mobile unit  304  can identify the transmission (i.e., the mobile unit  304  can retrieve the transmission by demodulating with the assigned phase adjustment value). Yet another alternative is that the modulation control device  314  may communicate with a modulator/demodulator that is independent of the transceiver  316  to modulate the call with the phase adjustment value for the mobile unit  304 . Additional modulators/demodulators to modulate the call with the associated phase adjustment value and additional time multiplexers can be added to existing base stations  300  to facilitate the implementation of this embodiment of the present invention. 
   When the base station  300  receives a transmission during a call from a mobile unit  304 , the transceiver  316  may communicate with the modulation control mechanism  320  to allow identification of the mobile unit  304 . After the received transmission during the call is demodulated, the modulation control mechanism  320  may compare the phase of the transmission with the assigned phase adjustment values to identify the mobile unit  304  that made the transmission. 
     FIG. 7  illustrates some of the elements of a mobile unit  360  for use in accordance with an embodiment of the present invention. The mobile unit  360  includes a demodulator  362 , a filter  364 , a timeslot detector/multiplexer  368  for isolating the assigned timeslot, a modulator  370 , and a mobile modulation control device  372 . When the mobile unit  360  receives the assigned frequency channel  322 , timeslot, and phase adjustment value from the base station  300  for the call, these values are retained by the mobile modulation control device  372  for the duration of the call. When the mobile unit  360  receives a transmission from the base station  300  the mobile modulation control device  372  communicates the assigned phase adjustment value to the demodulator  362 . Therefore, the transmission from the base station  300  can be demodulated using the assigned phase adjustment value. The demodulator&#39;s  362  output may then be passed to the filter  364  to remove the noise and retrieve the desired transmission from the base station  300  for the call. When the mobile unit  360  wishes to transmit, the mobile modulation control device  372  may communicate the assigned phase adjustment value, frequency channel  322 , and timeslot to the modulator  370 . Accordingly, the mobile unit  360  transmits with the assigned phase adjustment value which allows the base station  300  to identify which mobile unit  304  made the transmission and accordingly to which call the transmission belongs. 
   III. Operation of a Modulation Control Device According to the Present Invention 
   The operation of a wireless base station in accordance with an embodiment of the present invention is illustrated by  FIG. 8 . A base station in a wireless communication network begins the search for a frequency channel for a call when a mobile unit first requests service at block  400 . The transmission quality of a first frequency channel is then measured by the threshold detector at block  410 . The modulation control device then compares the transmission quality measurement of the frequency channel with a predetermined value at block  420 . The decision block  425 , if the transmission quality measurement of the frequency channel exceeds the predetermined value, then the modulation control device assigns the frequency channel and the phase adjustment value to the call, as indicated at block  430 . However, as the decision block  425  illustrates, if the transmission quality measurement of the frequency channel does not exceed the predetermined value, then the modulation control device compares the transmission quality measurement received from the threshold detector of the next frequency channel with a predetermined value at block  420 . 
   After the call has been assigned a frequency channel and a phase adjustment value, as indicated at block  430 , then the phase adjustment value is communicated to a mobile unit that is associated with the call at block  440 . The modulation control device then associates the assigned phase adjustment value with the call so that the phase adjustment value can be added during modulation for communicating with the mobile unit or referenced by the base station during reception to attribute the call to a mobile unit at block  450 . 
   Note that the operation of the modulation control device is similar for a TDMA network. In a TDMA network, the modulation control device examines each timeslot within the plurality of frequency channels. The modulation control device examines a first timeslot within the first frequency channel and if the frequency channel for that timeslot is unacceptable, the modulation control device continues searching the rest of the timeslots within the first frequency channel until an acceptable transmission quality measurement is found. The modulation control device continues to the first timeslot in a second frequency channel if no transmission quality measurement is found acceptable for any timeslot within the first frequency channel. The modulation control device will step through the timeslots in the second channel until the frequency channel has an acceptable transmission quality measurement for a timeslot. This searching continues through the plurality of timeslots in the plurality of frequency channels until a timeslot within a frequency channel is found to be acceptable. The methodology for assigning and communicating the phase adjustment value is then followed as above. 
   The operation of a wireless mobile unit in accordance with an embodiment of the present invention is illustrated by  FIG. 9 . The operation of the mobile unit begins when the mobile unit requests service from the base station, as indicated at block  500 . The mobile unit will then receive the assigned phase adjustment value from the base station preferably over the control channel, as indicated at block  510 . The mobile unit will then demodulate received transmissions and modulate the outgoing transmissions with the assigned phase adjustment value, as indicated at block  520 . The mobile unit then may filter out unwanted noise as indicated in block  530 . 
   In the drawings and specification, there have been disclosed typical preferred embodiments of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention being set forth in the following claims.