Abstract: In an aspect of the invention, a method is performed in a transceiver for adaptive power amplifier linearization in time division duplex communication systems. The method comprises, in response to a first condition, performing, using a feedback signal generated by receiving subsystem circuitry, adaptive power amplifier linearization on a signal to be transmitted. The method additionally comprises, in response to a second condition, performing operations in order to determine receive data from a received radio frequency (RF) signal. The operations use at least the receiving subsystem circuitry. In a further aspect of the present invention, a transceiver is disclosed.

Abstract: A composite code is made for example by exclusive-OR'ing each real element of a first constituent code A with each element of a second constituent code B to obtain a basic composite code. To suppress autocorrelation, differing numbers of doping code elements are inserted between code segments made from combining each element of code A with an element of code B. A matched filter first stage removes from its input the A code and any doping code added to it, summing the elements of code A. A matched filter second stage removes from its input the B code and any doping code added at the second level. The summed elements of code B are the input to the first stage. Optionally, the summed elements of the doping code at any level may be delayed and summed with the elements of the A code in the first stage.

Abstract: A matched filter decorrelator is described for efficiently performing a carrier frequency search while despreading a P/N long code constructed from two or more constituent codes such as codes A, B, C. The received signal is phase rotated into a frequency bin and partially despread, preferably over all but one of the constituent codes. To despread the final constituent code, the partially despread signal is input in parallel into frequency bins, where a phase rotator sets each input to a different bin. The frequency bins are then despread in parallel over the final constituent code, and an energy peak in one accumulator indicates which bin is the carrier frequency. Alternatively, a Fourier transform could be used over each of the frequency bins. By partially despreading prior to division into carrier frequency bins, hardware and computational burden are reduced as compared to prior art decorrelators. The present invention is particularly apt for use with an acquisition burst in a secure network.

Abstract: A method is presented for estimating a phase error for first (rI) and second (rQ) orthogonal signal components spread respectively by different first cI and second cQ spreading codes. A cross-despread value IdQ and/or QdI is determined by despreading one signal component with the spreading codes associated with the other signal component (rI with cQ or rQ with cI). In parallel, the same signal component is also despread with its associated spreading code to determine an estimated data symbol for that component. An interference of Q into I or I into Q is calculated and multiplied by the estimated data symbol, and subtracted from the cross-despread value to achieve an estimate of phase error. Preferably, both cross-despread values are obtained, normalized to a common data rate, scaled to maximize signal to noise ratio, and combined into one phase error estimate. A phase error detector includes despreaders, multipliers, and adders to determine the cross-despread value and subtract the interference from it.

Abstract: A PN code hopping method for mitigating cross-correlation interference is provided. The method includes the steps of providing a memory device and storing a plurality of PN codes, where each PN code is associated with a useful life cycle. The PN codes are pseudo-randomly accessed and used to spread a modulated signal for their respective useful life cycle before another PN code is pseudo-randomly retrieved.

Abstract: A communications system employs the use of both synchronous CDMA and FDMA to provide a variable bandwidth waveform with multiple bonded transmitters and receivers that are agile in both frequency and PN code to permit a variable bandwidth and variable rate multiple access system. In a first aspect the teachings provide the use of both CDMA and FDMA together to enable an improved concentration efficiency by making a larger pool of bandwidth available to each user. In a second aspect these teachings enable channel bonding across both code space and frequency space, thus making the system capable of operating within a variable (not necessarily contiguous) bandwidth and at a finely variable rate.

Abstract: A method is disclosed for obtaining a spreading code set for a code division multiple access (CDMA) communications system. The method includes (a) generating a P?×P? spreading code set where P?=P/N, where P is the spreading gain in chips/symbol and where N is an integer multiple of 2; and (b) replicating chips in each spreading code by N to produce a P?×P spreading code set. The step of generating may include randomizing the spreading code set by performing at least one or row or column permutation. The P?×P spreading code set is subsequently loaded into system hardware for operating the system hardware with a bandwidth that is less than the bandwidth that would be required to operate with the P?×P? Hadamard spreading code set. The CDMA system may be a synchronous, direct sequence code division multiple access communications system.

Abstract: Disclosed is a method for operating a code division multiple access communications system, and a system that operates in accordance with the method. The method operates within a coverage area of a base station by assigning a set of spreading codes to individual ones of a plurality of subscriber stations and then, during transmissions within the cell, by periodically hopping amongst spreading code within the set of spreading codes such that at any given time no two subscriber stations operate with the same spreading code. The set of spreading codes may include the all one's spreading code. The step of periodically hopping preferably changes from a currently used spreading code to a next spreading code at a symbol rate or at a multiple of the symbol rate.

Abstract: A method is disclosed for operating a synchronous space division multiple access, code division multiple access communications system. The method includes steps of, within a coverage area of a base station (BS), (a) assigning the same spreading code to a plurality of subscriber stations (SSs); and (b) beamforming using an antenna array at the BS so as to maximize the signal to interference plus noise ratio for a signal transmitted from a desired SS, The beamforming operates to steer a null towards another same-code SS to minimize interference from the same-code SS. Assuming that the antenna array has M-elements (M>1), then individual ones of P orthogonal spreading codes can be reused ?M times within the coverage area, where 1/M<??1. The step of beamforming includes an initial step of despreading the signal received from the desired SS, followed by a step of spatial filtering.

Abstract: This invention provides a highly flexible multiplexing scheme for Direct Sequence CDMA systems enabling the CDMA system to flexibly allocate CDMA channel resources between packet-switched broadcast channels and fast-circuit-switched dedicated channels in order to optimize system throughput. A method and system are provided for operating a communication system. The method has steps of: flexibly allocating CDMA channel resources between packet-switched broadcast channels and fast-circuit-switched dedicated channels in order to optimize system throughput, and employing a side channel as required to send all or a part of a total amount of data, depending on the total amount of the data. A bandwidth allocation scheme allocates a set of CDMA channels for burst packet-switched channels, and data is time division multiplexed over the set of burst CDMA channels providing a wide bandwidth data pipe for packet-switched data.

Abstract: A method is disclosed for operating a synchronous space division multiple access, code division multiple access communications system. The method operates, within a coverage area of a base station (BS) or radio base unit (RBU) having a multi-element antenna array, for estimating a SSV for individual ones of a plurality of active subscriber stations (SSs) and assigns a spreading code to a subscriber station (SS) that minimizes the similarity of the determined SSVs of the SSs in a spreading code set. A metric used to measure the similarity of the spatial signature vectors of the SSs comprises the squared sum of the inner products of same code SSs' SSV with a current SS's SSV. The step of assigning includes calculating the magnitude of the squared inner product of the SSVs of all pairs of active SSs; using the calculated values for determining ?n(c) for each spreading code that is not already used some specified maximum number of times; and assigning to a SS the spreading code with a minimum ?n(c).

Abstract: A method is disclosed for operating a synchronous space division multiple access, code division multiple access communications system. The method operates, within a coverage area of a base station (BS) or radio base unit (RBU) having a multi-element antenna array, to assign spreading codes to users. The method estimates a spatial signature vector (SSV) for a current subscriber station; uses the estimated SSV as a weight vector when determining the output power that is correlated with each of a plurality of spreading code sequences and assigns a spreading code to the current subscriber station that is determined to have the minimum output power. The step of determining the output power includes steering a beamformer toward the current subscriber station by setting the weight vector equal to the SSV, and also determines the average squared value of the antenna array output that has been despread using a code i.

Abstract: A method is disclosed for operating a wireless communications system, such as a DS-CDMA communications system, by transmitting a waveform that includes a plurality of repeating frames each having x header training base symbols in a header training symbol field (TH) and y tail training base symbols in a tail training symbol field (TT). The frame is received and functions as one of a plurality of different types of frames depending on the content of at least TT. In the preferred embodiment the frame functions as one of a normal traffic frame, a termination frame, or a legacy frame providing backwards compatibility with another waveform. A given one of the frames includes four equal-size data fields separated by three equal-sized control fields, the header training symbol field (TH) and the tail training symbol field (TT).

Abstract: A method is disclosed for operating a synchronous space division multiple access, code division multiple access communications system, as is a system that operates in accordance with the method. The method operates, within a coverage area of a base station (BS), to assign the same spreading code to a plurality of subscriber stations (SSs) and to transmitting signals to, and receive signals from, the SSs using an antenna array having M elements, where M>1 and where the M elements are spaced apart by more than one-half wavelength from one another. The spacing is a function of a size of an aperture of the antenna array which is a function of a signal bandwidth to carrier frequency ratio. The antenna array aperture is preferably less than k=p/360*fc/B wavelengths, where p is a maximum acceptable phase variation over the signal bandwidth, where fc is the carrier frequency and where B is the signal bandwidth.

Abstract: Method and apparatus for maintaining synchronization in a CDMA communication system by operating closed loop timing control between a radio base unit and subscriber units, operating open loop timing control between the radio base unit and the subscriber units, and using timing information derived from the open loop to correct the closed loop. Generally the open loop is faster in response than the closed loop. The open loop timing control may be generated by using GPS data. A radio base station and a subscriber unit operating in accordance with these principles.

Abstract: A maximum likelihood (ML) detector provides improved performance in the presence of multiple user interference (MUI), particularly performance of a multiuser receiver for asynchronous CDMA. The detector can be implemented using a Viterbi algorithm, this greatly reducing system sensitivity to MUI. An approximation to the ML detector provides a sparse trellis search based on the structure of the ML detector. The resulting detector, which may be referred to as a reduced-complexity recursive detector (RCRD), has a dynamic structure that allows a trade-off between complexity and performance. Use is made of a unique metric to define the trellis-structure and the M-algorithm to reduce the number of surviving paths. The metric calculation is then repeated at decision points to provide soft-decision information for further signal processing, soft-decision decoding of an error-correction code, or iterative reception of the multiuser signal.

Abstract: A method is disclosed for obtaining a spreading code set for a code division multiple access (CDMA) communications system. The method includes (a) generating a P′×P′ spreading code set where P′=P/N, where P is the spreading gain in chips/symbol and where N is an integer multiple of 2; and (b) replicating chips in each spreading code by N to produce a P′×P spreading code set. The step of generating may include randomizing the spreading code set by performing at least one or row or column permutation. The P′×P spreading code set is subsequently loaded into system hardware for operating the system hardware with a bandwidth that is less than the bandwidth that would be required to operate with the P′×P′ Hadamard spreading code set. The CDMA system may be a synchronous, direct sequence code division multiple access communications system.

Abstract: A method is disclosed for operating a synchronous space division multiple access, code division multiple access communications system. The method operates, within a coverage area of a base station (BS) or radio base unit (RBU) having a multi-element antenna array, for estimating a SSV for individual ones of a plurality of active subscriber stations (SSs) and assigns a spreading code to a subscriber station (SS) that minimizes the similarity of the determined SSVs of the SSs in a spreading code set. A metric used to measure the similarity of the spatial signature vectors of the SSs comprises the squared sum of the inner products of same code SSs' SSV with a current SS's SSV. The step of assigning includes calculating the magnitude of the squared inner product of the SSVs of all pairs of active SSs; using the calculated values for determining &xgr;n(c) for each spreading code that is not already used some specified maximum number of times; and assigning to a SS the spreading code with a minimum &xgr;n(c).

Abstract: A method is disclosed for operating a synchronous space division multiple access, code division multiple access communications system. The method operates, within a coverage area of a base station (BS) or radio base unit (RBU) having a multi-element antenna array, to assign spreading codes to users. The method estimates a spatial signature vector (SSV) for a current subscriber station; uses the estimated SSV as a weight vector when determining the output power that is correlated with each of a plurality of spreading code sequences and assigns a spreading code to the current subscriber station that is determined to have the minimum output power. The step of determining the output power includes steering a beamformer toward the current subscriber station by setting the weight vector equal to the SSV, and also determines the average squared value of the antenna array output that has been despread using a code i.

Abstract: A method is disclosed for operating a wireless communications system, such as a DS-CDMA communications system, by transmitting a waveform that includes a plurality of repeating frames each having x header training base symbols in a header training symbol field (TH) and y tail training base symbols in a tail training symbol field (TT). The frame is received and functions as one of a plurality of different types of frames depending on the content of at least TT. In the preferred embodiment the frame functions as one of a normal traffic frame, a termination frame, or a legacy frame providing backwards compatibility with another waveform. A given one of the frames includes four equal-size data fields separated by three equal-sized control fields, the header training symbol field (TH) and the tail training symbol field (TT).