Nortel Networks Corporation

Northern Telecom Limited

Other

Apple Inc.

Mikhail G Bakouline

Vitali B Kreindeline

Alexandre M Chloma

Rui R Wang

Wen Tong

Yuri S Shinakov

Iouri Trofimov

Ming Jia

Yong Li

Chao Wang, Legal Representative

Peiying Zhu

Gang Li

Adnan Abu-Dayya

Philip H Thomas

Hong Zhao

Zhi Ding

Mohamed El-Tarkhuni

Philip Thomas

Alexandere M Chloma

Chao Wang

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.

Communication channel optimization systems and methods in multi-user communication systems

Space-time diversity using a plurality of transmit antennas is provided with a turbo coding arrangement comprising two recursive systematic convolutional coders, to one of which input bits are supplied directly and to the other of which the information bits are supplied after interleaving of bit groups for respective symbol intervals. Symbols produced by the coders and comprising systematic and parity information are supplied to paths to the antennas alternately in successive symbol intervals to provide the space-time diversity. Arrangements are described for 2 and 4 antennas and for various convolutional codes, and an iterative decoder is also described.

Methods and apparatus for turbo space-time trellis coding

An iterative arrangement of channel estimator (), a Kalman filter unit (), and a soft demodulator () 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 () 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.

Channel estimation in CDMA communications systems using both lower power pilot channel and higher power date channel

For each user in a multi-user detection arrangement in a CDMA communications system, a detector () provides a limiting function () responsive to a combined signal to produce a detection signal, having any of at least three possible values, for supply to a signal regenerator, regenerated signals being subtracted from a received signal in successive detection iterations of the multi-user detection arrangement. A code correlated signal is supplied via an inverse hyperbolic tangent function (), or is multiplied by a multiplier inverse to an iteration index, to produce a derived signal. The derived signal is added () to a representation of a detection result stored from a previous iteration to produce the combined signal. The limiting function can comprise a hyperbolic tangent function.

Multi-user detection in CDMA communications system

In a transmitter of a wireless communications system having M transmit antennas (), each transmit antenna is supplied with a respective combined signal comprising a respective one of M groups each of N data sub-streams, orthogonally spread by N Walsh code sequences (Wto WN). The N orthogonal code sequences used for each of the M groups comprise a respective one of M different combinations of N from Northogonal code sequences, where N&#x3e;N. M and N are integers greater than one. The combined signals can also include orthogonally spread pilot signals (WP) for channel estimation at a receiver. Orthogonality of the signals transmitted from the transmit antennas is increased, so that transmit signal power can be decreased and/or the receiver can have fewer than M receive antennas.

Transmitter for a wireless communications system using multiple codes and multiple antennas

An impulse response matrix of a received signal in a TDMA communications system is approximated using a plurality of indirect variables of a linear complex vector. The indirect variables are used for synchronizing to the received signal and for tracking and frequency offset estimation during successive samples of the received signal, the samples being equalized in dependence upon the indirect variables. A demodulated signal is derived from the equalized received signal samples. Individual synchronization and tracking units, and a single equalizer, can be provided for a two-antenna receiver. Tracking errors can be used to adapt a parameter of the equalizer to reduce interference in the received signal.

Cellular communications system receivers

An encoder for a wideband CDMA communications system comprises an outer Reed-Solomon code encoder and an inner parallel concatenated convolutional code (PCCC) or turbo code encoder. An iterative PCCC decoder, for decoding the inner code, includes summing functions in forward and feedback paths for producing extrinsic information to enhance soft decoding decisions by first and second decoders in successive decoding iterations. An outer code decoder connected following the PCCC decoder also can provide serial feedback information for enhancing iterative decisions by the PCCC decoder.

Encoding and decoding methods and apparatus

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.

Carrier recovery in communications system

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.

Timing recovery and frame synchronization in communications systems

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.

Timing tracking in communications systems

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&gt;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.

Pseudo random number sequence synchronization in communications systems

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:

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Moscow, Russia

Mikhail G Bakouline