Abstract:
Systems and methods for single-point to fixed-multipoint communication. The invention dynamically allocates bandwidth based on traffic demands, thus providing efficient bandwidth utilization, particularly with bursty or time sensitive data traffic. A system includes a Base Station and a plurality of Remote Stations. The Base Station transmits information to the Remote Stations via a Forward Channel and the Remote Stations transmit information via a Reverse Channel. Before transmitting on the Reverse Channel, each of the Remote Stations listens (monitors) the Reverse Channel to ascertain whether any other Remote Station is transmitting. Remote Stations transmit data only when a Remote Station determines that the channel is clear. The Remote Stations listen in sequential order, eliminating the probability of collisions caused by simultaneous transmissions from Remote Stations. The data traffic is accordingly aggregated, thus providing efficient bandwidth utilization.

Description:
The present application claims priority under 35 U.S.C. § 119(e) to provisional application 60/118,662 filed on Jan. 14, 1999, the entirety of which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to data communication, and more particularly, to a method and system for single-point to fixed-multipoint communication. 
     BACKGROUND OF THE INVENTION 
     In a conventional single-point to fixed-multipoint data communication system, a base station transmits to fixed remote stations and each of the fixed remote stations, in turn, transmits to the base station. Such systems typically use one or more predetermined and typically internationally adopted communication protocols. These protocols tend to be optimized for particular applications and industries. For example, protocols used for wireless communication tend to be developed and influenced by the telecommunication industry. However, since many of these conventional systems that have communication media interconnecting the base station to the fixed remote stations are terrestrial (e.g., copper or optical fiber medium) the data communication protocols tend to be developed and/or heavily influenced by the computer industry. 
     A fixed wireless system is generally characterized by a point to multipoint topology where remote stations are fixed at specific locations. Wireless in the Local Loop (WLL) is an example of a point to multipoint topology. Most WLL solutions use a variant one of the major wireless telecommunication protocols such as Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), or Code Division Multiple Access (CDMA). Systems using these protocols assign and reserve bandwidth for the communication between the remote stations and the base station. 
     A FDMA-based system assigns a separate channel in an available channel band to each remote station. For instance, in cellular systems these channels are assigned by the base station upon receiving a request for channel from a cellular phone (radio). There is a common channel used for control information that is passed back and forth between the base and remote. A TDMA-based system breaks a channel into time slots. Each remote station is assigned a time slot. If there is no data to be transmitted when the time slot becomes available, the bandwidth is wasted since it is not reallocated to another remote radio. In general, a CDMA-based system uses a non-correlating coding sequence to allow multiple radios to transmit and receive in the same frequency range. In cellular CDMA, a base station assigns a code based on a request from a cell phone. There is a practical limit to the number of codes in use in a sector, thus limiting the number of active channels. 
     Conventional wireless telecommunication protocols tend to be efficient where there is a continuous flow of information. However, Internet data traffic and modern voice digitizing technology is by its nature bursty in its use of bandwidth. Accordingly, systems using these conventional protocols do not make efficient use of the available channel bandwidth with the bursty data traffic, largely because the assigned channels remain idle whenever their assigned stations are not bursting. 
     Another drawback associated with existing wireless telecommunications protocols is that they require a base station to communicate and broker bandwidth among the remote stations which causes significant delays. Additionally, these conventional protocols fail to accommodate the various demands of different remote stations at different times because of their inability to dynamically allocate bandwidth based on traffic demand. 
     Conventional computer-based data communication protocols are typically designed and used for multipoint to multipoint communication. Such protocol are optimized to handle bursty data traffic. Examples of such protocols include Carrier Sense Multiple Access (CSMA) and Carrier Sense Multiple Access/Collision Detection (CSMA/CD) protocols. When optimized, these protocols can make efficient use of the bandwidth. The optimization, however, assumes the multipoint-to-multipoint underlying topology. In addition, because of the lack of channel reservations and due to the inconsistency of burstiness of data traffic, these protocols fail to adequately support time sensitive data traffic, such as digitized voice, at high utilization rate of their bandwidth. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to systems and methods for efficient single-point to fixed-multipoint data (data and/or digitized voice) communication. The invention overcomes the drawbacks of conventional systems and protocols, particularly with respect to applications with bursty or time sensitive data traffic, by dynamically allocating bandwidth based on traffic demands. 
     In one embodiment, wireless data communication is provided in context of Internet Protocol Multiple Access (IPMA) system having a Base Station and a plurality of Remote Stations. In operation, the Base Station transmits data packets to the Remote Stations via a Forward Channel and the Remote Stations transmit data packets to the Base Station. Before transmitting on the Reverse Channel, each of the Remote Stations listens to (monitors) the Reverse Channel to ascertain whether any other Remote Station is transmitting. Remote Stations transmit data only when a Remote Station determines that the channel is clear. The Remote Stations listen in sequential order, eliminating the probability of collisions caused by simultaneous transmissions from Remote Stations. 
     The invention also efficiently and dynamically aggregates data traffic, thus allowing the entire bandwidth to be utilized. For example, when only one of Remote Stations requires bandwidth, the entire bandwidth is allocated to that Remote station. If multiple Remote Stations need bandwidth, the entire bandwidth is allocated according to the needs of those stations. No Remote Station is denied bandwidth nor is bandwidth wasted on a Remote Station that has no data to send with the teaching of the invention. Furthermore, use of the Reverse Channel is achieved without the overhead of brokering, thereby circumventing associated delays. 
     Another feature of the invention is that the order in which the Remote Stations listen to the Reverse Channel can be rotated periodically. Thus, equal access for transmission on the Reverse channel is ensured for all Remote Stations. 
     In another aspect of the invention, Remote Stations are assigned to various zones. Remote Stations in a given zone listen only to other Remote Stations in that zone. This reduces the hardware cost associated with Remote Stations since zones can be configured for those stations within a close geographical proximity of each other. Alternately, Remote Stations can be grouped in zones based on station type, data traffic type, or access rate requirements for the Reverse Channel. 
     Another advantage of the invention is that constraints on distance from the Base Station are removed. For example, embodiments of the invention allow communication over wireless distances in excess of 50 Km from a Base Station in 2 GHz bands. 
     In addition, embodiments of the invention are more efficient than CDMA. For example, if CDMA cellular system carries 30 simultaneous phone conversations in one cell sector, the invention can carry 240 simultaneous phone conversations using only one correlating code. 
     The foregoing, and other features and advantages of the invention, will be apparent from the following, more particular description of the preferred embodiments of the invention, the accompanying drawings, and the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
         FIG. 1  is a topological view of a single-point to fixed-multipoint wireless data communication system in accordance with the invention. 
         FIGS. 2A and 2B , respectively, are high level views of a half-duplex and a full-duplex system using a Forward Channel and Reverse Channel in accordance with the invention. 
         FIG. 3  is a detailed view of a Forward Channel, a Reverse Channel, and a Clear Channel Assessment phase in accordance with the invention. 
         FIG. 4  is a detailed view of a successive series of Forward Channel, Reverse Channel, and Clear Channel Assessment occurrences with Dwell Time rotation in accordance with the invention. 
         FIG. 5  is a detailed view of a successive series of Forward Channel, Reverse Channel, and Clear Channel Assessment occurrences with two-zones in accordance with the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The preferred embodiments of the invention are now described with reference to the figures where like reference numbers indicate like elements. Also in the figures, the left most digit of each reference number corresponds to the figure in which the reference number is first used. 
     These preferred embodiments are discussed in the context of a single-point to fixed-multipoint wireless data communication in an Internet Protocol Multiple Access (IPMA) system. The invention, however, can be practiced to provide information (e.g., data, digitized voice) for a wide range of Internet applications (e.g., e-mail, various Internet applications, etc.). For example, a single-point station can provide Internet connectivity services to the various fixed-multipoint stations to enable users at these multipoint stations to send and receive e-mail, connect with the World Wide Web, or establish digitized voice communications. Moreover, the invention can be practiced in other applications and embodiments as would be apparent to one skilled in the art. For example, the teachings of the invention can be used in a non-wireless communication medium, such as a copper-based or fiber optics-based communication medium. One such embodiment of the invention, can be a local area network having a single-point to fixed-multipoint topology. 
       FIG. 1  is a topological view of a single-point to fixed-multipoint wireless data communication system  100  in accordance with the invention. System  100  includes a Base Station  102 , and a plurality of Remote Stations  104 . Communication from and to Base Station  102  and each of the Remote Stations  104  is provided over a Forward Channel (FC)  106  and a Reverse Channel (RC)  108 , respectively. In this embodiment, FC  106  and RC  108  are modulated over carrier signals in the 2 GHz frequency range. As would be apparent to one skilled in the art, other types of modulation techniques and carrier signals can be readily utilized with the invention. In this embodiment, Base Station  102  provides an Internet connection and data (e.g., e-mail) can be downloaded to the Remote Stations  104 , via FC  106 , and Remote Stations  104  can upload data via RC  108 . 
     The communication between Base Station  102  and each Remote Station  104  can be conducted with a half- or full-duplex embodiments.  FIG. 2A  is a high level view of a half-duplex embodiment  200  of the invention. In this embodiment, Base Station  102  first transmits to each Remote Station  104  via FC  106 . During this time interval, each Remote Station  104  tunes (switches) to the frequency of FC  106  and receives data packets (or data packet) transmitted by Base Station  102 . The time interval allotted for FC  106  is based, in part, on the time requirements for Base Station  102  to transmit (or burst) data and each Remote Stations  104  to receive the data. 
     Base Station  102  can dynamically communicate with Remote Stations  104  in a number of different addressing schemes. For example, for each FC  106 , a data packet can be destined for a specific Remote Station  104 , all Remote Stations  104 , or a subset (pre-assigned group) thereof. Data packets destined for a specific Remote Station are marked by a unique address that is assigned a priori to each Remote Station  104 . In such an instance, each Remote Station  104  detects FC  106 , but only the Remote Station with a matching address will process the received data and the remaining Remote Stations  104  will discard the transmitted data packets. Data packets destined to all Remote Stations  104  are marked by a broadcast address. Upon detection of FC  106 , each Remote Station  104  will recognize the broadcast address and process the received data. Data packets destined for a subset of Remote Stations  104  are marked by a special address, thereby providing a semi-broadcast type of communication. 
     The foregoing addressing scheme of the invention can be readily mapped into higher level protocols, such as the widely used Internet Protocol (IP). In such an embodiment, the address of each Remote Station  104  can correspond to the IP address of that Remote Station  104 . Alternatively, the Remote Station IP address itself can be used directly within the addressing scheme of embodiments of the invention. The advantage of this later embodiment is the elimination of added complexity of mapping and the easier interface to the Internet, or other IP networks, via the Base Station  102 . Moreover, in such IP embodiments, existing higher level networking communication software and hardware can be utilized with the invention. For instance, data packets that are meant to be sent to all Remote Stations  104  can use the default addressing broadcast scheme of IP. These types of data packets can include control data that can be used for overall system management, provisioning, control, or merely to broadcast user information to the Remote Stations  104 . Data packets that are meant to be sent to a specific Remote Station  104  will have the IP address of that specific station. Accordingly, only that specific Remote Station will unpack that data packet at its networking layer while all other Remote Stations  104  will simply discard that packet. Another advantage of using the IP protocol, as an addressing scheme, is the ability to create zones that correspond to one or more sub-networks of the IP network. Accordingly, such embodiments of the invention can be configured so that a subset of the Remote Stations  104  exist in one IP sub-network or zone. 
     Returning to  FIG. 2A , once the time allotted for FC  106  has expired, each Remote Station  104  switches to listen to the frequency of RC  108  and enters into a Clear Channel Assessment (CCA)  202  phase. During this time, each Remote Station  104  listens to RC  108  to ascertain whether other Remote Stations  104  are transmitting. If a first Remote Station, which has data packets to send to Base Station  102 , ascertains that none of the other Remote Stations  104  is transmitting, the first Remote Station transmits its data packets to Base Station  102  until the time allotted for RC  108  expires. Since each Remote Station  104  listens to all transmissions originating from any other Remote Stations  104 , each Remote Station  104  detects the transmission of the first Remote Station and refrains from transmitting. Further discussion of these features of the invention is provided below. Once the time allotted for RC  108  expires, all Remote Stations  104  switch their listening frequency again to re-tune to FC  106  and Base Station  102  begins to transmit another occurrence of FC  106  to Remote Stations  104 . 
     In accordance with the invention, each Remote Station  104  thereby determines whether or not to transmit data (by monitoring the RC  108 ). In this regard, the embodiments of the invention do not require Base Station  102  to broker or provide access to RC  108  among Remote Stations  104 . Accordingly, any propagation delay associated with the brokering is circumvented. 
     To facilitate the requisite handshaking and low error rate communication between Base Station  102  and Remote Stations  104 , these stations are synchronized. Methods for synchronizing communication systems are well known in the art and can be readily employed with the embodiments of this invention. For example, synchronization can be achieved during the initial configuration of system  100  and can be maintained by broadcast control packets transmitted from Base Station  102 . 
     The invention also provides Guard Times (GT)  204  to accommodate for delays associated with embodiments thereof and to optimize each embodiment to specifications of that embodiment (e.g., extremely low error rate, minimized synchronization time, etc.). As noted before, the invention can be practiced, with various applications, topologies, and station designs. Each embodiment will require the compensation for propagation delays associated with FC  106  and RC  108  transmissions (a function of the distance between the stations) and delays associated with the circuitry (hardware), processing, and frequency switching of the stations. It would be apparent to one skilled in the art how to calculate or measure such delay times. 
     In the present embodiment, GT  204  are placed at the beginning and end of FC  106 , RC  108  and CCA  202 . Other GT  204  arrangements, however, can be used to accommodate for aforementioned and other delays. For example, an embodiment of the invention can have GT  204  placed at the beginning and at the end of FC  106 , at the end of RC  108 , and at the end CCA  202 . 
       FIG. 2B  is a high level view of a full-duplex embodiment  206  of the invention. The main difference between this embodiment and the aforementioned half-duplex embodiment is that the transmission of FC  106  overlaps with the transmission of RC  108 . The transmission of FC  106 , however, does not occur during the CCA  202  phase of RC  108 . Accordingly, the transmission of FC  106  begins after the expiration of the time allotted for the CCA  202  phase. As illustrated in  FIG. 2B , FC  106  can last for a period that equals the time remaining for the RC transmission  108 . As with half-duplex embodiments of the invention, full-duplex embodiments can utilize GT  204  to accommodate for various delays. 
       FIG. 3  is a detailed view of FC  106 , RC  108 , and CCA  202  and illustrates the operation of a full-duplex embodiment of the invention  300 . Initially, Remote Stations  104  are tuned to listen to the frequency of FC  106 . After the time allotted for FC  106  expires, each Remote Station  104  re-tunes to the frequency of RC  108  and begins to listen to this channel. This marks the beginning of the CCA  202  phase. 
     In this embodiment, CCA  202  is divided into periods of time, Dwell Time (DT) of equal time duration. However, other embodiments of the invention can use DT of various time durations. As illustrated in  FIG. 3 , in there are “n” DT periods (e.g., DT 1    302 , DT 2    304 , and DT n    306 ). In general, each Remote Station  104  is dynamically assigned a particular DT period and listening occurs in a serial manner. Each Remote Station  104  listens to RC  108  during its designated DT and if during its DT the channel clear, that station can transmit data. More specifically, during the CCA  202  phase, each Remote Station  104  waits until its assigned DT to listen RC  108 . A first Remote Station (e.g., a Remote Station designated an identification (Id) of one) with DT 1    302  listens first to RC  108 . After the expiration of DT 1    302 , a second Remote Station (e.g., a Remote Station designated with an Id of two) listens to RC  108  for the period of DT 2    304 . Similarly, an “n th ” Remote Station waits until the beginning of DT n    306  to listen to RC  108  for that DT period. A Remote Stations that has data to send to Base Station  102  does so only when that Remote Station has listened to RC  108 , at its designed DT, and has ascertained that no other Remote Station  104  is transmitting (i.e., that a clear channel exists). In the above example, if the first Remote Station has no data to send, that station spends DT 1    302  listening to RC  108  and does no transmission (even if a clear channel exists). 
     The second Remote Station starts to listen to RC  108 , at DT 2    304 , and assesses whether or not a clear channel condition is met. In this example, the channel is clear as the preceding Remote Station (i.e., the first Remote Station) did not have any data and no other station (e.g., an “n th ” Remote Station) has had the opportunity to transmit yet. If the second Remote station does not have data to transmit it listens to RC  108  during DT 2    304  without any transmission over RC  108 , in the same fashion as the first Remote Station. If, however, the second Remote Station does have data to transmit it does so over RC  108  immediately after the station assesses that a clear channel is present. In accordance with the invention, the second Remote Station will transmit all its data during the time allotted for this occurrence of RC  108  or until the RC expires. Once DT 2    304  has expired, and during DT n    306 , the “n th ” Remote Station begins to listen to RC  108  and detects that the second Remote Station is still transmitting data. Accordingly, the “n th ” Remote Station assesses that RC  108  is not a clear channel (busy) and does not transmit any data (if it had any) during this particular RC  108  period. 
     In order to ensure that all Remote Stations  104  have equal opportunity to transmit data to Base Station  102 , the order of DT (e.g.,  302 ,  304 , and  306 ) must be changed during successive RC occurrences. Otherwise, Remote Stations  104  with a low order DT (in this example, the first and second Remote Stations) would always have a higher priority to send data than Remote Stations with a higher order DT (in this example, the “n th ” Remote Station). 
       FIG. 4  is a detailed view of a series of FC ( 402 ,  404 ,  406 ,  408 ), RC ( 410 ,  412 ,  414 ), and CCA ( 416 ,  418 ,  420 ) occurrences with DT rotation, in a full-duplex embodiment  400  of the invention. After FC  402  and at the beginning of RC  410 , a first Remote Station listens to the channel during DT 1    422 . Next, a second Remote Station listens during DT 2    424  and finally an “n th ” Remote Station listens during DT n    426 . The DT are then rotated in a round robin fashion for the next RC occurrence (RC  412 ). As illustrated in  FIG. 4 , during RC  412 , the Remote Station that listened last (in this example, the “n th ” Remote Station) will listen first, as its DT n    426  is shifted to the beginning of CCA  418 . The other Remote stations DT are shifted to occur later in time by a period equal to DT n . Over time of the operation the rotation provides each Remote Station  104  with an equal opportunity to transmit data. As would be apparent to one skilled in the art, assignment and the changing of DT order can readily be achieved with other algorithms other than the round robin schemes above. Equal access to the bandwidth is an important feature for those embodiments that support time sensitive traffic or require small and consistent delays. For instance, voice over IP requires not only small delays, but also consistent delay, because large variations of delay tend to cause jitter. Moreover, embodiments of the invention can be implemented with other DT structures. For example, one or more Remote Stations can be assigned a predetermined and fixed DT slot. With such embodiments, priority to certain Remote Stations can be achieved. 
     As noted above, the invention can be practiced with multiple zones.  FIG. 5  is a detailed view of a series of FC ( 502 ,  504 ,  506 ,  508 ), RC ( 510 ,  512 ,  514 ), and CCA ( 516 ,  518 ,  520 ) in a two-zone (Zone  1  and  2 ) embodiment  500  of the invention. In this embodiment, Remote Stations  104  assigned Id addresses  1  through  100  are configured in Zone  1  and Remote Stations assigned Id address  101  through  256  are configured in Zone  2 . Remote Stations, in Zone  1 , transmit at a first occurrence of a Reverse Channel (in this instance, RC  510 ). Remote Stations, in Zone  2 , transmit at a second occurrence of the Reverse Channel (in this instance, RC  512 ). Thereafter, Remote Stations, in Zone  1 , transmit again at the following occurrence of a Reverse Channel (in this instance, RC  514 ) and so forth. In this preferred embodiment, Remote Stations within a given zone only listen to the Remote Stations in their zone. 
     In this preferred embodiment, the changing of the DT order occurs independently in each zone and the rotation scheme disclosed above is utilized. Accordingly, DT associated with Remote Stations in Zone  1  (in this instance, DT 1    522  through DT 100    524 ) are rotated at each Reverse Channel in which Zone  1  Remote Stations can transmit (in this instance, RC  510  and RC  514 ). Correspondingly, DT associated with Remote Stations in Zone  2  (in this instance, DT 101    526  through DT 256    528 ) are rotated at each Reverse Channel occurrence such stations are assigned to transmit (in this instance, RC  512 ). 
     The use of zones allows for the grouping of those Remote Stations that are close in proximity to each other. The transmission hardware (e.g., antennas) of Remote Stations is thus kept at a minimum because each Remote Stations only has to listen to those Remote Station in its assigned zones. In addition, such embodiments of the invention allow the maintenance of a single Base Station in a spacious geographical area while minimizing the cost of the hardware at the Remote Stations due to their grouping in zones of smaller geographic areas. 
     Alternatively, Remote Stations can be grouped in zones that correspond to a type of service. Because the changing of DT occurs for each zones independently, those zones having fewer Remote Stations have a higher access rate for each of their Remote Stations. For instance, Zone  1  in  FIG. 5  has 100 Remote Stations while Zone  2  has 155 Remote Stations. Thus, the DT of each Remote Station in Zone  1  is rotated at a faster rate than DT of a Remote Station in Zone  2 . Accordingly, Remote Stations at Zone  1  will have a higher overall access rate than Remote Stations in Zone  2 . 
     It would be apparent to one skilled in the art that the configuration of zones and their corresponding addresses is a matter of network design, and the methods used are well known in the art. For example, a class-C IP sub-network can be assigned to a single zone with embodiments of the invention. Alternately, IP masking can be used to assign smaller or larger IP sub-networks to zones in such embodiments. 
     Although the invention has been particularly shown and described with reference to several preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined in the appended claims.