METHOD AND APPARATUS FOR TIMING CONTROL IN DIGITAL COMMUNICATION SYSTEMS

Abstract: The present invention provides an apparatus and method for detecting the relative time of arrival of different signals at a single receiver from different respective transmitters, and causing the different respective transmitters to alter the time that they transmit their signals so that the time of arrival of signals from different transmitters is within a predetermined period. The present invention uses either a closed loop timing control, a GPS based timing control, or an open loop based timing control, to determine the time that signals from different transmitters need to be altered in order to obtain time of arrival for different signals within the predetermined period. As a result of the arriving signals being "semi-synchronous", any detection algorithms taking advantage of time synchronism, for example multi-user detection or interference rejection, can be much more effective in signal detection for the data transmitted from multiple transmitters to a single receiver.

Description: METHOD AND APPARATUS FOR TIMING CONTROL IN DIGITAL COMMUNICATION SYSTEMS Field of the Invention The present invention relates to a method and apparatus for closed loop and open loop timing control for digital communication systems Background of the Related Art Synchronous and asynchronous packet based communications systems are well known In a synchronous packet based communication system, packet transmissions must be synchronized so that packets are received by the receiver with a time of arrival that falls within a narrow predetermined detection window If a packet is transmitted such that it is not received within the predetermined detection window , the receiver will not detect it In contrast, asynchronous packet based communications systems do not require synchronization of the time of arrival with a narrow predetermined window, but instead typically require either a much longer detection window in order to detect the incoming asynclironous communication or simply limit the number of users, or a dynamic allocation of packets to different users Each of these solutions, however, have either reduced capacity or increased complexity and are not, therefore, considered as effective in many circumstances In part due to the above considerations, conventional communications systems will use both synchronous and asynchronous communications For example, m a communication system based upon the IS-95 standard, communications in the forward link, from the base station to each of a large number of different users having a receiver, are synchronous Communications m the reverse link, from each of the different users back to the base station, however, are performed asynchronously This scheme is used since in the forward link, signals intended for different users from the base-station are by definition synchronous, as the data for multiple users are processed and transmitted synchronously Therefoie, signal detection is effective in combating interference in the forward link, where the receiver is located at the user's side The reverse link, how ever, does not provide a convenient timing reference Since the signals from the multiple users cannot be conveniently synchronized due to propagation delays, timing synchronization amongst the users has not been attempted in traditional CDMA systems Strategies such as error-correcting coding and closed loop power control are used in the reverse link of traditional CDMA systems, such as in IS-95, to insure that the detection of the signal from an intended user is not degraded bv the interference generated bv other users The timing of signal arrivals from multiple users is. therefore, not a major concern in such a traditional CDMA system because interfering signals are treated as noise at the receiver. Since timing control is not attempted in asynchronous environments, such as the reverse link of an IS-95 compliant communication system, the signals from multiple users arrive at random times and the interference rejection capabilities become reduced. Accordingly, asynchronous interference rejection is considered difficult and infeasible in an environment requiring higher capacity. SUMMARY OF THE INVENTION Accordingly, it is an object of this invention to obtain semi-synchronous communica- tions in order to improve signal detection capabilities. It is another object of the invention to implement a multi-user detection scheme that uses timing control in order to increase the overall capacity of the system. It is another object to implement an orthogonal-frequency division multiplexing scheme that allows multiple data streams to be transmitted by different users at the same time. In order to attain the above objects of the present invention, among others, the present invention provides an apparatus and method for detecting the relative time of arrival of different signals at a single receiver from different respective transmitters, and causing the different respective transmitters to alter the time that they transmit their signals so that the time of arrival of signals from different transmitters is within a predetermined period. The present invention uses either a closed loop timing control, a GPS based timing control, or an open loop based timing control, to determine the time that signals from different transmitters needs to be altered in order to obtain time of arrival for different signals within the predetermined period. As a result of the arriving signals being "semi-synchronous," any detection algorithms requiring time synchronism, for example multi-user detection, can be much more effective in interference rejection for the data transmitted from multiple transmitters to a single receiver. This invention can be applied to many different types of communications systems, and has particular applicability to code division multiple access (CDMA) systems, which CDMA systems may or may not use multi-user detection schemes in which interference rejection can then be more effective. This invention can also be applied to multiple antenna systems, where the timing of signal arrivals from multiple antennas (either from a single transmitter or from multiple transmitters) is also of importance. Still further, the present invention can be applied to orthogonal frequency division multiplexing (OFDM) systems where multiple users transmit data at the same time, which require precise timing control at the receiver Furthermore, the present invention has applicability to time division multiple access (TDMA) systems that require precise timing control BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects, features, and advantages of the present invention are further described in the detailed description which follows, with reference to the drawings by way of non- mitmg exemplary embodiments of the invention, wherein like reference nume- rals represent similar parts of the present invention throughout several views and wherein Fig 1 illustrates an overview of a multi-user system according to the invention, Fig 2 illustrates the relative time of arrival of the first sample of arbitrary packets from different transmitters at a receiver prior to application of timing control according to the invention, Fig 3 illustrates the relative time of arrival of the first sample of arbitrary packets from different transmitters at a receiver after application of timing control according to the invention, Fig 4 further illustrates the definitions of delay and advance from a design point of view, Fig 5 illustrates a block diagram of a circuit for implementing closed loop timing control according to a preferred embodiment of the invention, Fig 6 illustrates a block diagram of a circuit for implementing open loop timing control according to a preferred embodiment of the invention, and Fig 7 illustrates an example of multiple base-stations each with multiple end-users DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention implements timing control so that signals from a plurality of transceivers 100-1, 100-2, 100-3 100-n have a semi-synchronous time of arrival with respect to each other at a transceiver 120, such as illustrated in Fig 1 While not limited to the specific embodiment, the following discussion will be made with reference to a CDMA system that employs multi-user detection in the reverse link One aspect of the invention will become apparent with reference to Figs 2 and 3 Pπor to implementing the timing control of the present l ention the relatn e time of arrival of arbitrary packets from different transmitters at a receiver is asynchronous. As illustrated in Fig. 2, from a reference timing point 210, signal 100-1 lags by about 7 samples, signal 100-2 lags by about 10 samples, signal 100-3 is advanced by about 8 samples, and signal 100-4 lags by about 5 samples. Packets, which contain data and/or control information relating to the communications, from each of these users, are assumed to repeat at relatively consistent intervals so that each user can continue to communicate during a communication session. It should be noted that consistent interval is not intended to mean synchronous or asynchronous, but only a repetition of consecutive packets such that communications can continue within the system. The present invention manipulates the time that these signals are transmitted, so that their time of arrival at the receiver becomes semi-synchronous. Thus, as illustrated in Fig. 3, by advancing signal 100-1 by 7 samples, advancing signal 100-2 by 10 samples, delaying signal 100-3 by 8 samples, and advancing signal 100-4 by 5 samples, signals 100-1 to 100-4 become semi-synchronous with respect to the reference timing point 210. To further describe one implementation of an advance or a delay of time, Fig. 4 illustrates the sequence of events as a function of time. Assume that at time Tl , transmitter 100-i starts the computation in preparation for the transmission of the next packet. At time T2, the computation is completed and transmission starts. The time between T2 and Tl is called the computation latency. The delay and advance can be implemented by a delay line buffer, which holds the data to be transmitted in an array of pipeline registers. If the reference time is to be in between T2 and T3, as illustrated in Fig. 4, the buffer is about half deep, which means that the transmitted data would be delayed by (T3-T2V2 seconds. When the base station informs this transmitter to either delay or advance the transmission of the next packet, the depth of the delay line buffer is adjusted accordingly. The number of the pipeline registers that implement the delay line buffer is bounded by the maximum propagation delay between all the end-user transceivers to the base station. It should be understood that other manners of implementing the advance or delay could be used. Fig. 5 illustrates a block diagram of a circuit 500 for implementing timing control according to a preferred embodiment of the present invention. As w ill be apparent, this Figure illustrates those circuits within the end-user transceiver (such as l OO-i), as well as within a base station transceiver 120 that are needed to implement the present invention. Other parts of receivers, transmitters or transceivers can be made using conventional techniques and methods, and will therefore not be further discussed. As illustrated, at the base station transceiver 120. the precise timing of each user (such as transceiver l OO-i) relative to a reference time point is extracted by a timing acquisition circuit 510 dedicated to that user A timing comparatoi 530 gathers the timing information from each timing acquisition circuit 510 and performs time alignment in order to determine the advance or delay of the packets to be transmitted by that user's transceiver The information on the amount of advance or delav that needs to be inserted by that particular transceiv er 100-1, which is performed separately for each individual user, is sent to that user as a timing control signal that is part of the data packet, which packet is assembled m the transceiver 120 using a conventional data packet assembler 580 This information, once receiv ed and decoded by the data packet decoder 570 associated with the transceiver 100-1 of the intended user is used to control a delay line buffer 540, which receives the data packet to be transmitted to the transceiver 120 from its own data packet assembler 550 before transmitting the next packet to the transceiver This procedure can be repeated at each packet to further refine the accuracy of the timing control This timing control proceduie can also be exercised occasionally, a predetermined intervals, or once every several packets, depending on the relative dynamics of the base-station and individual end-user transceivers. Alternatively, an updated timing control signal is retransmitted when the timing comparator 530 determines that the time- alignment has changed a predetermined amount, such that the time-alignment is no longer within a predetermined range Since the timing acquisition function at the receiver is necessary to determine the precise sampling phase of the incoming signal for signal detection, the extraction of the timing control signal from the incoming signal is relatively easily implemented by the timing extraction circuit, which extracts the timing information using conventional timing acquisition techniques, such as those proposed in H Meyr, M Moeneclaey, and S Fechtel, Chapters 5 & 10, Digital Communication Receivers, John Wiley and Sons, 1998, New York, K. H Mueller and H Muller, "Timing recovery in digital synchronous data receivers," IEEE Trans Communications, Vol COM-24, pp 516-531 , May 1976, and B Sklar. Chapter 8, Digital Communications Fundamentals and Applications, Prentice Hall, 1988, New Jersey Of conventional techniques, the delay-lock-loop technique is most commonly used for timing extraction The accuracy of closed-loop timing control implemented by the circuit 500 should preferably be within a fractional of a sample period, or at most a couple of sample periods, in order to provide for effective interference rejection in a CDMA system or concurrent multi- carrier signal detection in an OFDM system If the timing control does not align all packets from the various users to within a few sample periods, then the effectiveness that the present invention is able to ha\ e will become substantially reduced For example, the multi-user detection algorithms, such as described in Sergio Verdu, Muluusci Detection. Cambridge Uni ersitv Pi ess 1 98 w hen applied to asv nchronous channels either demand a lot more computation 01 suffer from a 1 eduction in ov erall channel capacity This invention either ιela\es the computation lequnement m performing such algorithms for asynchronous channels or increases the achiev able s stem capacity bv allowing more users to be tiansmittmg at the same time Fig 6 illustrates a block diagram of a circuit 600 for implementing open loop timing contiol accoidmg to a preferred embodiment of the present invention As will be apparent, this Figure lllustiates those circuits within the end-user transceiver (such as lOO-i) In contrast to the circuits required by the closed loop timing control of Fig 5, the present invention can be implemented by making adaptations to end-user transceivers, without significantly affecting the design and operation of the base station transceiv er 120 As in the discussion of the closed loop timing control svstem provided above, other parts of receivers, transmitters or transceivers not mentioned herein can be made using conventional techniques and methods, and w ill therefore not be further discussed As illustrated, each transceiver lOO-i to 100-n associated with each user keeps a time reference synchronized with base station transceiv er 120 This time synchronization within each transceiv er 100-1 to 100-n is maintained by either a GPS or through other means of global synchronization mechanism The timing information of the received forward link signal is extracted bv the timing acquisition circuit 610, which can be the same as the timing acquisition circuit 510 associated with a single user device as previously discussed, except the timing acquisition circuit 610 is, in this described implementation of this embodiment part of each transceiv er 100 rather than part of the base station transceiver 120 This timing information is compared with the time w hen the data should have been transmitted by transceiv er 120 using comparator 630 The time w hen the data should have been transmitted is pre-determmed and known locally using a GPS or a globally synchronized timing device 620 The difference is calculated and serves as an estimate of the propagation delay between transceiv ei 120 and tiansceiver l OO-i This propagation delay estimation is used to control the delav line butfei 640 at the transmitter and therefore align the reverse link signal that has been assembled bv the data packet assembler 650 ith those from other users as receiv ed by transceiv er 120 The delav line buffer 640 and the data packet assembler 650 correspond to the delav line buffer 540 and the data packet assemblei 550 lespectiv elv , that were prev iouslv discussed This procedure can be repeated at each packet to further refine the accuracv of the timing control The open loop timing control procedure can also be exercised occasionally, or once every several packets, depending on the relative dynamics of the base- station and indiv ldual transceivers The accuracy of open loop timing control implemented by the circuit 600 is a function of the channel multipath profile and the mobility of the users Assuming that the delay spread of the channel is relatively short compared to the required length of coherence for detection, the open loop timing control according to the invention can synchronize the incoming signals to within a fractional of one data symbol period (on the same older of the delay spread) It is noted that open loop timing control is typically not as precise as closed-loop timing control, since the uncertainty in multi-path channel is largei than the uncertainty of the timing acquisition circuit at the receiver. The uncertainty in the timing can, therefore, be viewed as a form of multipath Since a properly designed multi-user detection system should perform well in the face of multipath in the forward link, the semi-synchronous reception as enabled by the present invention allows the system to deliver similar performance m the reverse link. A specific example implementing the present invention using the system descπbed above is the use of timing control in a CDMA system that employs multi-user detection. It is known how to perform interference rejection on asynchronous channels in a reverse link, but conventional interference rejection techniques are not used on time-aligned signals The application of the present invention in such systems allows all reverse link signals to become semi-synchronous, thereby simplifying the asynchronous detection algorithm to a synchronous detection algorithm. Of the conventional interference rejection techniques, the adaptive multi-user detection technique described in M Honig, U Madhow . and S Verdu, "Blind Adaptive Multiuser Detection," IEEE Trans on Information Theon , pp 944-961, Vol. 41 , No 4, July 1995 is most preferred because it decouples the detection of any single channel from that of the other channels Another preferred implementation is the use of timing control in an OFDM system that allows multiple end-users to transmit data at the same time In a conventional OFDM system, such as disclosed m B Le Floch, M Alard, and C Berrow. "Coded Orthogonal Frequency Division Multiplex," Proceedings of IEEE, pp 982-996, Vol S3, No 6, June 1995, the input data undergoes an inv erse-fast-Fourier-transform (IFFT) before being transmitted In other words, data are encoded on multiple carrier frequencies The receiv er performs a fast-Fouπer-transform (FFT) before signal detection at each carrier frequency Since the IFFT and FFT have to be performed on all data to be transmitted or received, multiple access to multiple users has traditionally been prov ided for by w av of time-division- multiple-access ( TDMA). in whicn each user is assigned a time slot to transmit its data and -S- no two users can transmit their data at the same time The present mv ention allows multiple users m an OFDM system to transmit data at the same time because the signals transmitted from different users can be time-aligned at the receiver, as long as these users use different carrier frequencies in their transmission Since the signals from different users are time- aligned, FFT can be performed on the received signal without destroying the coherent properties of the tiansmitted data It should be noted that the present invention provides a method such that signals transmitted from the transceivers 100 typically arrive at the base station transceiver 120 within a predetermined period of time, such as a few sample periods However, the present invention can still be utilized if only substantially all, or any portion, of the signals arrive within the predetermined penod In that event, however, the overall signal detection capability may be degraded as compared to the case where all signals are time-aligned, but partially aligned systems should still perform better than those without using the present invention According to the present invention, once the incoming signals are approximately aligned, any detection scheme that takes advantage of synchronous reception, for example CDMA, multi-user detection, smart antenna, multiple antenna systems, TDMA, or multi-user OFDM, can benefit from this invention The present invention can also be applied to a communication system where multiple base-stations are deployed, such as used m the cellular phone system The relative timing information of the multiple transceivers detected by each base-station can be communicated to other base-stations The exact amount of time advance or delay that should be exercised by each transceiver can be negotiated amongst the base-stations, for the purpose of achieving the best overall system performance For example, assume that there are two base-stations with their perspectiv e end-users transceivers, as illustrated in Fig 7 Base-station 710 performs timing control to its end-users transceivers 710-1 and base-station 720 performs timing control to its end-users transceivers 720-1 Since transceiver 720-1 is closer to base- station 710 than to base-station 720. it may be more advantageous for transceiv er 720-1 to be time-aligned with the reception of base-station 710, rather than to be time aligned ith the reception of base-station 720 Since, for the above example, the transceiv er 720-1 is closer to base-station 710. if it is time-aligned with base-station 710 then the interference that it may otherwise be creating for base-station 710 can be removed Although transceiver 720-1 will not necessaπlv be time aligned w ith base station 720 although it w ill be communicating w ith it. the ov erall sv stem performance w ill oe impiov ed since the remov al of a significant mterferor with respect to base station 710 will have a greater impact than a time aligned transceiver that is distant from base station 720 The above example is provided with respect to two base stations, but the present invention contemplates that three, four or more base stations may need to be in communication with each other in order to determine the station with which the particular transceiver is time aligned Further, such time alignment may be performed for reasons other than interference removal While the present invention has been described herein w ith reference to particular embodiments thereof, a latitude of modification, various changes and substitutions are intended m the foregoing disclosure, and it will be appreciated that in some instances some features of the invention will be employed without a corresponding use of other features without departing from the spirit and scope of the invention as set forth in the appended claims

Claims: I claim: 1. A method of providing a time aligning control signal to each of a plurality of transceivers that repeatedly transmit signals to a common transceiver comprising the steps of: detecting the time of arrival at the common transceiver of one signal transmitted from each of the plurality of transceivers; determining, for each transceiver, an advance or delay of a subsequent signal to be transmitted to the common transceiver so that the subsequently transmitted signal from each of the plurality of transceivers has a time of arrival substantially within a predetermined period; and transmitting from the common transceiver to each of the plurality of transceivers a timing control signal that includes an amount of advance or delay for the respective transceiver so that the subsequently transmitted signal from substantially all of the transceivers will be advanced or delayed an amount determined by the advance or delay within the timing control signal. 2. A method according to claim 1 wherein the steps of detecting, determining and transmitting are repeated for each of the plurality of transceivers during a communication session that each transceiver has with the common transceiver. 3. A method according to claim 1 wherein the steps of detecting, determining and transmitting are repeated at predetermined intervals for each of the plurality of transceivers during a communication session that each transceiver has with the common transceiver. 4. A method according to claim 1 wherein the steps of detecting, determining and transmitting are repeated for each of the plurality of transceivers during a communication session that each transceiver has with the common transceiver when the time- alignment of the respective transceiver is no longer within a predetermined range. 5. A method according to claim 1 wherein the greatest amount of advance is less than the computational latency. 6. A method according to claim 1 wherein the step of detecting the time of arrival includes the step of extracting timing information. 7 A method according to claim 6 wherein the step of extracting timing information uses a delay-lock-loop technique 8 A method according to claim 6 wherein the step of determining includes the steps of gathering the timing information and performing time alignment 9 A method according to claim 1 further including the step of performing interference rejection at the common transceiver on at least certain subsequent signals transmitted from each of the plurality of transceivers to the common transceiv er 10 A method according to claim 1 wherein there exists a second plurality of transceivers that repeatedly transmit second signals to the common transceiver, and wherein there is not determined and advance or delay of subsequent second signals for each of the second plurality of transceivers 1 1. A method of providing a time aligning control signal to each of a plurality of transceivers that repeatedly transmit signals to a common transceiver comprising the steps of detecting the time of arrival at the common transceiver of one signal transmitted from each of the plurality of transceivers, determining, for each transceiver, an advance or delay of a subsequent signal to be transmitted to the common transceiver transmitting from the common transceiver, for each of the plurality of transceivers, a timing control signal that includes an amount of advance or delay, receiving the timing control signal at each of the plurality of transceivers, extracting the timing control signal at each of the plurality of transceivers, and using the advance or delay contained in the extracted timing control signal to correspondingly adv ance or delay a subsequently transmitted signal from each of the plurality of transceivers so that the subsequently transmitted signal from substantially all of the plurality of transceivers has a time of arriv al at the common transceiver substantially w ithin a predetermined period 12 A method according to claim 1 1 further including the steps of receiv ing the subsequently transmitted signal from each of the plurality of receiv ers that arrive at the common transceiv er substantially within the predetermined penod 13 A method according to claim 12, further including the step of performing interference rejection on at least certain ones of the subsequently transmitted signals from the plurality of tiansceivers that arrive at the common transceiver within the predetermined range 14 A method according to claim 13 wherein the steps of detecting, determining, transmitting, receiving, extracting, using, and receiving are repeated until a communication session between any one of the transceivers and the common transceiver ends 15 A method according to claim 14 wherein the steps of detecting, determining, transmitting, receiving, extracting, using, and receiving continue to repeat for all other transceivers when the communication session between the one of the transceivers and the common transceiver ends 16 A method according to claim 14 wherein the repeating occurs at predetermined intervals 17. A method according to claim 11 wherein the repeating occurs when the time-alignment of the respective transceiver is no longer within a predetermined range 18 A method according to claim 1 1 wherein the greatest amount of advance is less than the computational latency 19 A method according to claim 1 1 wherein the step of detecting the time of arnval includes the step of extracting timing information 20 A method according to claim 19 wherein the step of extracting timing information uses a delay-lock-loop technique 21 A method according to claim 19 wherein the step of determining includes the steps of gathering the timing information and performing time alignment 22. A method according to claim 1 1 wherein there exists a second plurality of transceivers that repeatedly transmit second signals to the common transceiver, and wherein there is not determined and advance or delay of subsequent second signals for each of the second plurality of transceivers. 23. A method of time aligning signals from each of a plurality of transceivers that repeatedly transmit reverse link signals to a common transceiver and receive transmitted forward link signals from the common transceiver comprising the steps of: receiving forward link signals at each of the plurality of transceivers transmitted from the common receiver, one forward link signal being received at each of the plurality of transceivers; detecting, at each of the plurality of transceivers, the time of arrival of the one forward link signal transmitted from the common transceiver; determining, at and for each transceiver, an advance or delay of a subsequent reverse link signal to be transmitted to the common transceiver; and transmitting the subsequent signal from each of the plurality of transceivers using the respective advance or delay so that the subsequent signal transmitted by substantially all of the plurality of transceivers has a time of arrival at the common transceiver substantially within a predetermined period. 24. A method according to claim 23 further comprising the steps of receiving each of the subsequent signals at the common transceiver; and performing interference rejection on subsequent signals received substantially within the predetermined period. 25. A method according to claim 23 wherein the steps of detecting, determining, transmitting, receiving, extracting, using, and receiving are repeated until a communication session between any one of the transceivers and the common transceiver ends. 26. A method according to claim 25 wherein the steps of detecting, determining, transmitting, receiving, extracting, using, and receiving continue to repeat for all other transceivers when the communication session between the one of the transceivers and the common transceiver ends. 27. A method according to claim 25 wherein the repeating occurs at predetermined intervals. 28 A method according to claim 23 wherein the repeating occurs when the time-alignment of the respective transceiver is no longer within a predetermined range 29 A method according to claim 23 wherein the greatest amount of advance is less than the computational latency 30 A method according to claim 23 wherein the step of detecting the time of arrival includes the step of extracting timing information. 31 A method according to claim 30 wherein the step of extracting timing information uses a delay-lock-loop technique 32 A method according to claim 30 wherein the step of determining includes the steps of gathering the timing information and performing time alignment 33. A method according to claim 23 wherein there exists a second plurality of transceivers that repeatedly transmit second signals to the common transceiver, and wherein there is not determined and advance or delay of subsequent second signals for each of the second plurality of transceivers 34 A common transceiver apparatus for providing a time aligning control signal to each of a plurality of transceivers that repeatedly transmit signals to the common transceiver comprising means for detecting the time of arrival at the common transceiver of one signal transmitted from each of the plurality of transceivers, means for determining, for each transceiver, an advance or delay of a subsequent signal to be transmitted to the common transceiver so that the subsequent signal transmitted from each of the plurality of transceivers has a time of arrival substantially within a predetermined period; and means for transmitting from the common transceiver to each of the plurality of transceivers a timing control signal that includes the advance or delay for the respective transceiver so that a subsequently transmitted signal from substantially all of the transceivers will be advanced or delayed an amount determined by the adv ance or delay within the timing control signal 35 An apparatus according to claim 34 wherein the means for transmitting includes a delay 36 An apparatus according to claim 35 wherein the greatest amount of advance in the delay line is less than the computational latency 37 An apparatus according to claim 34 wherein the means for determining includes a timing comparator 38 A transceiver that is capable of time aligning signals with other signals from other transceivers that are all repeatedly transmitting reverse link signals to a common transceiver and receive transmitted forward link signals from the common transceiver compnsing means for receiving one of the forward link signals transmitted from the common receiver, means for detecting the time of amval of the one forward link signal transmitted from the common transceiver, means for determining an advance or delay of a subsequent reverse link signal to be transmitted to the common transceiver, and means for transmitting the subsequent signal using the respective adv ance or delay so that the subsequent signal transmitted has a time of arnval at the common transceiver substantially within a predetermined penod 39 An apparatus according to claim 38 wherein the means for transmitting includes a delay 40 An apparatus according to claim 39 wherein the greatest amount of advance m the delay line is less than the computational latency 41 An apparatus according to claim 38 wherein the means for determining includes a timing comparator 42 A method of providing a time aligning control signal to each of at least first and second plurality of transceivers that repeatedly transmit signals to respectiv e at least first and second common transceiv ers compnsing the steps of detecting the time of arri al at the respective first and second common transceiver of one signal transmitted from each of the respectiv e first and second plurahtv of transceivers, determining, for each transceiver, an advance or delav of a subsequent signal to be transmitted to the common transceiver so that the subsequent signal transmitted from substantially all of the first and second plurality of transceivers has a time of arrival substantially withm a predetermined period, wherein the time of arrival for certain ones of the subsequent signals is based upon the time of arrival of the subsequent signal at the first and second common transceiver which receives the subsequent signal so that a communication session can continue and the time of arrival for at least one of the subsequent signals communicating with the first common transceiver is based upon the time of arnval of the one subsequent signal at the second common transceiver with which it is not communicating, and transmitting from the first and second common transceiver to each of the respective first and second plurality of transceivers a timing control signal that includes an amount of advance or delay for the respective transceiver so that a subsequently transmitted signal from each of the transceivers will be advanced or delayed an amount determined by the advance or delay within the timing control signal 43 A method according to claim 42 further including the step of performing interference rejection at the second common transceiv er on the one subsequent signal 44 A method according to claim 42 wherein there is included a third plurality of transceivers that repeatedly transmit signals to a third common transceiver, and herein the step of detecting detects the time of arriv al at the third common transceiver of one signal transmitted from each of the third plurahtv of transceivers, the step of determining determines, for each transceiv er, the advance or delay of a subsequent signal to be transmitted to the common transceiv er so that the subsequent signal transmitted from substantially all of the first, second and third plurahtv of transceiv ers has a time of arriv al substantially w ithm a predetermined period, wherein the time of arrival for certain ones of the subsequent signals is based upon the time of arrival of the subsequent signal at the first second and third common transceiv er which receiv es the subsequent signal so that a communication session can continue and the time of arriv al for at least one of the subsequent signals communicating with the first common transceiver is based upon the time of arrival of the one subsequent signal at the second common transceiver with which it is not communicating and the time of arnval for at least another one of the subsequent signals communicating with the first common transceiver is based upon the time of arrival of the another one subsequent signal at the third common transceiver with which it is not communicating, and the step of transmitting transmits from the first, second and third common transceiver to each of the respective first, second and third plurality of transceivers a timing control signal that includes an amount of advance or delay for the respective transceiver so that a subsequently transmitted signal from each of the transceivers will be advanced or delayed an amount determined by the advance or delay withm the timing control signal 45 A method according to claim 1 wherein the step of transmitting transmits each timing signal at a carrier frequency 46 A method according to claim 1 1 wherein each one signal and each subsequently transmitted signal are transmitted at a carrier frequency 47 A method according to claim 1 1 wherein the subsequent signal transmitted from respective transceivers are each transmitted at a earner frequency 48 An apparatus according to claim 34 wherein the means for transmitting transmits each timing signal at a carrier frequency 49 An apparatus according to claim 34 wherein the means for transmitting transmits each subsequent signal at a carrier frequency

Inventors: MENG TERESA H, MENG, TERESA, H.
Applicants: ATHEROS COMM INC, ATHEROS COMMUNICATIONS, INC.
Application year: 2000
Main classification: H04B7
IPC codes: H04B1, H04B7