Abstract: An iterative arrangement of channel estimator (12), a Kalman filter unit (14), and a soft demodulator (16) is provided for producing an estimate of complex gain of a CDMA communications channel carrying data and pilot channels, and demodulated data of the data channel. An initial channel estimate is produced by the estimator (12) using only the low-power pilot channel. This later is improved by the iterative process using the data channel. The complex gains is represented by a sum of sinusoidal signals with different frequencies and randomly variable amplitude and phase.

Abstract: Systems and methods of optimizing communication channels in multi-user communication systems are provided. Coding weights are determined based on communication channel state information for communication channels between a transmitter and multiple receivers. The coding weights are applied to communication signals to be transmitted from the transmitter to the receivers. Each receiver decodes received signals using inverses of the coding weights. Embodiments of the invention support multi-user MIMO (Multiple Input Multiple Output) where each receiver has fewer antennas than the transmitter, and enhance system performance if the total number of antennas at all of the receivers exceeds the number of antennas at the transmitter.

Abstract: A differential space-time block coder produces successive space-time blocks of symbols from M-PSK symbols to be encoded, in accordance with an orthogonal matrix and a normalization factor. Differentially encoded space-time output blocks, for transmission via a plurality of transmit antennas (16, 18) of a wireless communications system, are produced by multiplying (42) each space-time block from the space-time block coder (40) by the respective previous (44) differentially encoded space-time output block. Decoding is independent of channel estimation, and the arrangement is simple, avoids error propagation, and is applicable to different numbers of transmit antennas.

Abstract: A method of carrier recovery in a wireless communications system using a known synchronization word, for example an IS-54 TDMA system, operates in two stages to produce an estimate of carrier phase. In the first stage, a complex fading factor, embodying carrier phase information, is estimated from the synchronization word in the received signal using a least square criterion. In the second stage, the carrier phase is estimated from this complex fading factor by averaging. The averaging can provide a recursive average or a moving average, or can be implemented using Kalman filtering which also provides an estimated amplitude factor and frequency shift. The method and apparatus provide a substantial improvement over phase locked loop carrier recovery.

Abstract: Timing recovery, with or without frame synchronization, in a cellular TDMA communications system is carried out by a method comprising estimating indirect variables, which embody sampling delay information, of a linear complex vector using a maximum likelihood criterion, and recovering the sampling delay from the estimated indirect variables. For recovering the sampling delay, an optimal procedure and three sub-optimal, but computationally simpler, procedures are described, along with their physical implementations. For frame synchronization, the timing recovery sampling delay is supplemented by a number of sample spacings determined by a maximum of signal amplitudes of a plurality of samples, calculated from the estimated indirect variables and the timing recovery sampling delay.

Abstract: In a TDMA cellular communications system, optimal sampling of symbols in an information sequence is maintained by a method of timing tracking in which, recursively, indirect variables of a linear complex vector are estimated from received samples and previous estimates of the indirect variables, the sampling delay, and a complex fading factor, and the complex fading factor and the sampling delay are estimated by non-linear transformations of the estimated indirect variables. The timing tracking follows a timing recovery process which produces initial estimates. An implementation of the method uses a Kalman filter having constant filter gains and a transformation of the received samples and sampling delay to a reduced time interval.

Abstract: A method is disclosed for synchronizing, in the presence of sign ambiguity, to a pseudo random maximal length sequence having a characteristic polynomial of order k with a coefficients vector A given by:A=?1 a.sub.1 a.sub.2 . . . a.sub.k-1 1!where each of the coefficients a.sub.1 to a.sub.k-1 is 1 for an intermediate tap location and otherwise is 0. A received symbol sequence is supplied to and shifted through a K=k+1 stage shift register with P intermediate taps in positions determined by a coefficients vector A.sub.in given by:A.sub.in =?1 a.sub.1 (a.sub.1 .sym.a.sub.2) (a.sub.2 .sym.a.sub.3) . . . (a.sub.k-2 .sym.a.sub.k-1) a.sub.k-1 1!where a.sub.1 and a.sub.k-1 are the inverse of a.sub.1 and a.sub.k-1 respectively and .sym. denotes a modulo-2 sum, whereby the shift register has P intermediate taps where P is a positive integer less than K. A respective correlation signal is recursively added at an input for the received symbol sequence and at each intermediate tap.

Abstract: A method of synchronizing to a pseudo random sequence, which can be generated by a linear feedback shift register having k stages and p intermediate taps, where k and p are positive integers and k>p, and a synchronization arrangement for carrying out the method are described. A received symbol sequence is supplied to a k-stage shift register with p intermediate taps in positions corresponding to the p taps of the linear feedback shift register. A respective correlation signal is recursively added at an input for the received symbol sequence and at each intermediate tap. Each correlation signal is produced by correlating at least two signals from said input, intermediate taps, and output other than the signal to which the respective correlation signal is added. The invention is particularly applicable to pilot synchronization in CDMA terminals.