D.J. van Wyk

Turbo-coded/multi-antenna diversity combining scheme for DS/CDMA systems

In this paper the performance of a combined turbo coded and antenna diversity scheme to synchronous direct-sequence code-division multiple-access (DS/CDMA) communication over fading mobile radio channels is considered. Turbo codes have a built in structure that is suitable for diversity techniques to improve the quality of communications. The binary input data to a rate 1/(M+1) multiple turbo encoder produces M+1 coded bits, which, in turn, are assigned through suitable puncturing patterns to M different antennas and transmitted from each antenna simultaneously. The novelty of the transmission scheme, is that the original single-antenna rate-1/2 turbo coded system is transformed into a more powerful rate-1/(M+1) turbo code. The bit error rate performance of the proposed combined antenna and turbo coding diversity combining scheme is studied by means of simulation for a quadrature phase-shift keying (QPSK) DS/CDMA system on a non-frequency selective Rayleigh fading channel. Employing the turbo-coded/multi-antenna diversity combining scheme it is shown that lower bit error rate performance can be achieved, compared to a conventional single antenna scheme employing the same coding strategy.

A synchronous Q/sup 2/PSK DS-CDMA system: system conceptualisation, implementation and performance analysis

This paper describes the implementation of a spectrally efficient 4-dimensional Q/sup 2/PSK (quadrature-quadrature phase shift keying) DSSS modulation strategy. By using Q/sup 2/PSK, combinations of four, two or one data streams can be modulated in parallel in the same bandwidth as normally occupied by a QPSK system. This allows for even greater flexibility in terms of data throughput rate and reliability in accordance with the prevailing channel conditions. The disadvantages of the Q/sup 2/PSK modulation strategy, such as its inherent sensitivity to phase distortion, can be effectively mitigated by employing the multidimensional spreading technique proposed in this paper. Finally, the efficiency of the proposed Q/sup 2/PSK DS-SSMA system is assessed and demonstrated in a multi-user interference (MUI) environment by means of computer simulation. Very promising results is demonstrated with relatively short sequences used in the simulation studies.

Application of a burst-error-correction Viterbi algorithm to Q/sup 2/PSK on Rician fading channels

This paper deals with the design and implementation of a random-burst-error-correcting soft-decision adaptive Viterbi decoder (AVD) for four-dimensional (4D) quadrature-quadrature phase-shift keying (Q/sup 2/PSK) when operating on Rician fading channels. The characteristics of the Rician fading channels are examined and analysed in terms of the probability distributions of amplitude and burst errors. Having the background knowledge of the burst error distribution, an adaptive random-burst-error-correcting Viterbi decoding strategy is designed for incorporation into a digital Q/sup 2/PSK communication system. Performance results are presented to illustrate the efficiency of the adaptive Viterbi decoder under typical Rician channel conditions.

Performance of Q/sup 2/PSK employing multiple trellis coded modulation on Rician fading channels

In this paper the design and evaluation of 4-state multiple trellis-coded modulation (MTCM) codes for application to quadrature-quadrature phase-shift keying (Q/sup 2/PSK) are presented. Computer simulations are used to evaluate the performance of these code designs in a non-frequency selective Rician fading propagation environment. Coherent detection, and the benefits of the use of channel state information (CSI) in conjunction with MTCM are also considered. The paper has particular relevance to land mobile satellite radio.

On the Wigner distribution of a class of complex spreading sequences

In this paper the time-frequency (TF) characteristics, e.g. time-varying spectrum instantaneous frequency and time spread or multipath (MP), of a class of complex perfect-squares minimum-phase (PS-MP) constant-amplitude-zero-autocorrelation (CAZAC) sequences are investigated by means of variants of the quadratic time/frequency Wigner distribution (WD), with specific emphasis on the so called pseudo Wigner distribution (PWD). An appropriate discrete PWD (DPWD) algorithm is then employed to extract characteristic channel parameters (e.g. time spread or MP and frequency spread or Doppler) of typical simulated multipath channels, from the complex probing sequences. Simulation results are presented to illustrate the advantages of the DPWD approach.<<ETX>>

A multiple trellis coded Q/sup 2/PSK system for wireless local loop applications

The code design and performance evaluation of multiple trellis-coded modulation (MTCM) codes for application to a Q/sup 2/PSK micro-cellular wireless local loop access system are investigated. The paper formulates extended design criteria for MTCM code design based on the analysis of burst errors. Based on this criteria, the design of new 4-state codes for Q/sup 2/PSK is presented, and the bit error rate performance of these code designs, assuming coherent detection and perfect clock recovery are studied by means of simulation. It is demonstrated through computer simulation results that coding gains in excess of 13.0 dB at a bit error probability of 10/sup -5/ can be achieved with the designed MTCM coded system, relative to the uncoded system under the conditions present in a micro-cellular wireless local loop network. Furthermore, the benefits of using channel state information (CSI) in conjunction with MTCM are also considered.

A discrete pseudo Wigner distribution spread spectrum detection procedure employing complex spreading sequences

An efficient quadratic time-frequency (TF) discrete pseudo Wigner distribution (DPWD) based detection procedure is proposed for utilisation in direct sequence spread spectrum (DSSS) receivers. A class of complex generalised chirp-like (GCL) perfect-squares minimum-phase constant-amplitude-zero-autocorrelation (PS-MP CAZAC) signature or spreading sequences is employed to facilitate communications in a code division multiple access (CDMA) environment. It is shown that the new detection procedure, based on a computationally efficient DPWD algorithm, is equivalent to integrating the WD of the GCL spreading sequences along their respective lines of instantaneous frequency (IF). A simple DPWD aided frame synchronisation technique is also introduced. Simulation results of the WD scheme are presented to demonstrate the applicability and versatility of the proposed technique compared to conventional correlation-based methods.

Performance analysis of constant envelope quadriphase sequences for CDMA

This paper describes the comparison between constant envelope root-of-unity (CE-RU) and Nyquist filtered quadriphase sequences for code division multiple access (CDMA) applications. The salient feature of CE-RU filtering is the constant envelope property of the filtered sequences. The preservation of constant envelope of the sequences is desirable in fading environments. It is shown that the correlation properties of CE-RU filtered 4-phase sequences are better than those of Nyquist filtered 4-phase sequences. Preliminary results on bit error rate (BER) performance of CE-RU versus the Nyquist filtered 4-phase sequences on the additive white Gaussian noise (AWGN) channel are also presented.

An analysis of the effects of filtering on the correlation characteristics of 4-phase sequences for CDMA applications

This paper studies the construction and effects of filtering on the correlation properties of 4-phase sequences that are suitable for the use in spread spectrum multiple access communications. An introduction on the construction methods of these sequences from the set of binary sequences is presented. The effects of filtering on the correlation properties by using Nyquist and constant envelope root-of-unity (CE-LI-RU) filtering technique are also investigated. It is shown that it is possible to achieve better correlation properties by using the latter filtering method while maintaining the perfect constant envelope, which is not possible with Nyquist filtering.

A multiple trellis coded Q/sup 2/PSK system for personal communication

In this paper the performance of multiple trellis-coded modulation (MTCM) codes for application to a Q/sup 2/PSK personal communication system, are investigated. This paper considers, based on the optimum design criteria for the design of MTCM codes over fading channels, the design of new 4-state codes for Q/sup 2/PSK. The benefits in using channel state information based on fading channel estimates in conjunction with the MTCM decoder through a suitable metric weighting function are also considered. The channel estimates are obtained from sequences of known header and pilot symbols embedded in the information stream. This technique is shown to provide remarkably robust performance in the presence of fading. The bit error rate performance of the MTCM code designs (including channel side information), assuming coherent detection and perfect carrier and time synchronization, are then studied by means of simulation for cellular radio channels. It is shown that coding gains in excess of 14.0 dB at a bit error probability of 10/sup -4/ can be achieved with the MTCM coded system, relative to the uncoded system on Rayleigh fading channels.