Publications

Modulation / Coding

On Differentially Demodulated CPFSK

Anthony Griffin and Desmond P. Taylor

Abstract - This paper develops a differential encoder for differentially demodulated continuous phase frequency shift keying (CPFSK). CPFSK schemes with modulation index h = K/P, where K and P are relatively prime positive integers, can be represented by a decomposed model consisting of a continuous phase encoder (CPE) and a memoryless modulator (MM). The differential encoder is shown to fit well with the CPE and form a decomposed model of differentially encoded CPFSK (DCPFSK). A basic receiver structure for differentially demodulating DCPFSK is presented along with simulation results. An exact formula for the minimum squared Euclidean distance (MSED) of differentially demodulated DCPFSK is also given.

This paper was presented at the 1996 IEEE International Conference on Communications
Copyright © by the Institute of Electrical and Electronics Engineers, Inc

Asymptotic Performance of Product Codes

D.M. Rankin and T.A. Gulliver

Abstract - This paper presents the asymptotic performance of Hamming and extended Hamming product codes for the binary symmetric channel and the additive white Gaussian Noise(AWGN) channel. Simulation results for very low complexity high dimensional single parity check product codes on the AWGN channel are also given.

This paper was presented at the 1999 IEEE International Conference on Communications
Copyright © by the Institute of Electrical and Electronics Engineers, Inc

Randomly Interleaved Single Parity Check Product Codes

D.M. Rankin and T.A. Gulliver

Abstract - This paper considers single parity check (SPC) product codes which are randomly interleaved between the dimensions of the code. The aim of the random interleaving is to reduce the number of codewords at minimum distance and potentially improve the minimum distance of the code. The performance is significantly improved with a three or more dimensional interleaved SPC product code.

This paper was presented at the 1999 IEEE Pacitif Rim Conference on Communications, Computers and Signal Processing

Copyright © by the Institute of Electrical and Electronics Engineers, Inc

Randomly Interleaved SPC Product Codes

D.M. Rankin and T.A. Gulliver

Abstract - This paper considers single parity check (SPC) product codes which are randomly interleaved between the encoding of each dimension. Using random interleaving reduces the number of low weight codewords and so improves performance.

This paper has been accepted for the 2000 IEEE International Symposium on Information Theory
Copyright © by the Institute of Electrical and Electronics Engineers, Inc

Lattice Codes and Generalized Minimum Distance Decoding for OFDM Systems

Alan Clark and Desmond P. Taylor

Abstract - Lattice coding of orthogonal frequency division multiplexing (OFDM) systems is considered. Mapping of multilevel construction lattices to OFDM blocks is shown, and a methodology for probabilistic analysis of multistage generalized minimum distance (GMD) decoding of the received OFDM blocks is derived. As a case study transmission of points from a 128-dimensional Barnes-Wall lattice is considered. Tight approximations to the system error rate are obtained and verified by simulation. It appears that GMD decoding of lattice encoded OFDM provides high coding gain at low complexity.

Receiver Design for the Fading Channel

MLSE Receiver for the Dispersive Rayleigh Fading Channel

Wing Seng Leon and Desmond P. Taylor

Abstract - A maximum likelihood sequence estimator for the dispersive Rayleigh fading channel is developed. Following [1, 2], the MLSE uses a Kalman based channel estimator to acquire the channel parameters necessary to formulate the maximum likelihood metric. However, unlike the MLSE receiver presented in [1, 2], the proposed receiver uses the f-power series channel model [3, 4] to formulate the ML metric and the state space representation of the channel and the received samples. For channels with small delay spreads, this approach is advantageous because only a small number of parameters are required to be estimated by the Kalman channel estimator. Simulation results are presented for various channel parameters.

This paper was presented at the 1997 IEEE International Conference on Communications
Copyright © by the Institute of Electrical and Electronics Engineers, Inc

Equalization of Linearly Frequency-Selective Fading Channels

W.S. Leon, U. Mengali and D.P. Taylor

Abstract - A simple technique for removing intersymbol interference (ISI) introduced by "linearly frequency-selective" fading channels is presented. The technique involves the optimization of the overall impulse response of the transmit and receive filters and effectively reduces the channel to one which is flat fading. Computer simulation results show that this equalization method works for channels with small delays.

This paper was published in the 1997 IEEE Transactions on Communications, Vol. 45, pp. 1501-1503
Copyright © by the Institute of Electrical and Electronics Engineers, Inc

An Adaptive Receiver for the Time- and Frequency-Selective Fading Channel

W.S. Leon and D.P. Taylor

Abstract - An adaptive receiver is presented in this paper for the reception of linearly modulated signals transmitted over a time- and frequency-selective fading channel. The channel is modelled as a truncated power series [1] which represents the dispersive fading channel as a sum of three elementary flat-fading channels. The proposed receiver consists of a sequence estimator with a parallel channel estimator. The channel estimator recovers the instantaneous fading processes associated with each elementary channel and filters them to generate one-step predictions of each fading process. Some implementation difficulties and solutions are also discussed. Computer simulations using quadrature phase-shift keying (QPSK) and channels with moderate delay spreads and fade rates have been used to evaluate the performance of the receiver. The results show that our technique has potential in channels with delay spread of about 20%, signal-to-noise ratio (SNR) greater than 15dB, and applications requiring bit-error rates (BER's) less than 10-2.

This paper was published in the 1997 IEEE Transactions on Communications, Vol. 45, pp. 1548-1555
Copyright © by the Institute of Electrical and Electronics Engineers, Inc

DPSK Receiver with Implicit Diversity Gain for the Linearly Frequency-Selective Rayleigh Fading Channel

Wing Seng Leon and Desmond P. Taylor

Abstract - This paper presents a simple DPSK receiver for the frequency-selective fading channel. The channel is modelled as an f-power series truncated to the first two terms [1,2]. Two time invariant receiver filters are used to remove the channel induced ISI and to separate the two implicit diversity branches. The received samples from each branch are then differentially decoded and combined. Analytical and simulation results for binary DPSK show that this receiver outperforms the conventional receiver using matched filtering and a product demodulator.

This paper was presented at the 1999 IEEE Wireless Communications and Networking Conference
Copyright © by the Institute of Electrical and Electronics Engineers, Inc

Approximating the Probability Distribution of OFDM Symbol Errors

Alan Clark, Peter Smith & Desmond Taylor

Abstract - Given an N subcarrier orthogonal frequency division multiplexing (OFDM) system transmitting over a slow fading Rayleigh channel, the distribution of b, the exact number of received symbol errors, is Poisson binomial. Hence, N!/(N-b)!/b!, terms are required to calculate each probability for b=0,1,...,N. When N is large, as in most OFDM systems, the Poisson binomial distribution is often approximated by the Poisson distribution. We show that, for large N, the total variation distance between the approximation and the true distribution is lower and upper bounded by random variables with fully known probability density functions. The bounds on the total variation distance indicate that the distribution of OFDM symbol errors is well approximated by a Poisson distribution.

Copyright © 2005, University of Canterbury. This report is not to be reproduced in any form without the written consent of the Communications Research Group, University of Canterbury, Christchurch, NewZealand. Parts of this work have been submitted to the IEEE for possible publication. Copyright may be transferred without notice.

Reduced Complexity Decoding of Space Time Trellis Codes in the Frequency Selective Channel

Jeremy Turner

Abstract - In this work a new iterative approach has been suggested for decoding Space Time Trellis Codes (STTCs) in the frequency selective Multiple Input Multiple Output (MIMO) channel. The objective of this thesis has been to investigate the performance of the approach and determine what parameters affect its performance. The proposed method uses the Partitioned Viterbi Algorithm (PVA) as an equalizer for the MIMO system. The equaliser provides soft outputs which are then used by a STTC decoder to estimate the transmitted data sequence. To reduce error propagation between the two Viterbi based algorithms, an interleaver is introduced.

To further increase the performance, an iterative approach is used, where the decoded data sequence is re-encoded and used by the PVA to improve interference cancellation. This is similar in concept to turbo equalisation. Both the PVA equaliser and STTC decoder have been adapted to provide soft outputs using a Soft Output Viterbi Algorithm (SOVA).

Simulations of a NT = 2 transmit antenna, NR = 2 receive antenna MIMO system have been performed for both 4PSK and 8PSK constellations. It is shown that the iterative procedure achieves a performance within 2.0dB of Maximum Likelihood (ML) decoding, at a FER of 10-2. However, the iterative approach suffers a small diversity loss. It is also shown that the complexity of the iterative approach is far lower than ML decoding. For example, a 16 state 4PSK STTC can be decoded using the iterative approach, with equal performance and less complexity, than a 4 state 4PSK with ML decoding.

It is also shown that for a large diversity system (rNR>3), where is the rank of the STTC, that codes designed using the trace, or Euclidean distance criteria, suggested by Chen et.al. [10] are superior to the rank and determinant criteria used by Tarokh

et.al. [59] and Baro et.al. [6]. Other factors investigated that affect the performance are the choice of interleaver, number of iterations, soft information and the size of the MIMO system. The use of a PVA or similar equaliser, coupled with an outer code could be used to increase the effective user bandwidth of the MIMO channel. Standard convolutional codes could be used with the equaliser to improve performance in an iterative approach. More research is required to investigate the performance and complexity of such an approach.

Copyright © 2005, University of Canterbury