Wideband adaptive full response multilevel transceivers and equalizers

Wong, Choong Hin (1999) Wideband adaptive full response multilevel transceivers and equalizers. University of Southampton, Doctoral Thesis.

Abstract

In this thesis, the Minimum Mean Square Error (MMSE) Decision Feedback Equalizer (DFE) was studied in the context of a wideband Adaptive Quadrature Amplitude Modulation (AQAM) in order to mitigate the impact of multi-path Rayleigh fading channels. Explicitly, the modulation modes of no transmission (NOTX), Binary Phase Shift Keying (BPSK), 4QAM, 16QAM and 64QAM were invoked by the transmitter at a constant symbol-rate depending on the prevalent channel quality. The channel quality was quantified in terms of the output SNR of the DFE, which facilitated the joint performance optimisation of the DFE and the wideband AQAM switching regime.

A wideband AQAM numerical model was introduced and optimised over a noise limited COST 207 Typical Urban (TU) channel for target BERs of 1% and 0.01%. Consequently, a throughout average channel SNR gains for approximately 1 - 3dB and 7-9dB were achieved by the wideband AQAM system for target BERs of 1% and 0.01% respectively, when compared to the individual fixed modulation modes of BPSK, 4QAM, 16QAM and 64QAM. Subsequently, a practical Time Division Duplex (TDD) wideband AQAM system was implemented which had a channel quality latency of 2.3075ms over a slowly varying channel. This resulted in a throughput SNR gain reduction of approximately 0.9dB and 1.8dB for the target BERs of 1% and 0.01% respectively, when compared to the upper bound SNR performance gain. Multi-rate turbo block and convolutional coding were then incorporated into the wideband AQAM scheme which produced throughput channel SNR gains of approximately 1.0dB and 5.0dB for target BERs of 1% and 0.1%, respectively, in comparison to the individual fixed modulation modes. Furthermore, burst-by-burst channel decoding associated with limited depth turbo interleaver was employed at the receiver, which was exploited in order to detect the modulation modes utilized on a burst-by-burst basis.

The wideband AQAM system was also investigated in a Co-Channel Interference (CCI) limited environment, where the Joint Detection MMSE Block DFE having an embedded convolutional decoder was invoked for CCI compensation. Furthermore, the AQAM switching mechanism was refined in order to cater for a noise and CCI limited environment. In both of these CCI compensation schemes considerable gains were achieved, when compared to the time-invariant modulation schemes over a slowly fading COST 207 TU channel.

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