An adaptive equalizer structure based on a state space formulation and maximum likelihood sequence estimation (MLSE) is developed for a time-varying, frequency-selective channel. Differential phase shift keying (DPSK) is assumed at the transmitter and effective differential decoding is performed at the receiver. The standard models of a time-varying linear channel and the Karhunen-Loeve (KL) expansion underpin the receiver structure. Analytical and simulation results for the receiver are shown. The resulting receiver is a per-survivor structure.

This letter investigates the influence of transmit and receive filtering on the design and associated performance of wireless communication systems. Based on derivations using power-series models of time- or frequency-selective channels, we present pulse-shaping filters which can be matched to the characteristics of the channel. The choice of filter parameters allows some degree of control over the received signal. The peak-to-average-power-ratio (PAPR) requirements in the transmitter are determined. Orthogonal frequency-division multiplexing (OFDM) represents an alternative method of achieving some of the stated objectives of the pulse-shaping methods developed. Consideration is given to PAPR, bandwidth efficiency, receiver complexity, and performance in terms of error probability for the derived pulses and related forms of OFDM.

This letter extends the theory of the matched filter bound for fading dispersive channels. We generalize to arbitrary fading, as well as delay, properties of the channel. The channel model is a standard time varying linear filter and the calculation of the matched filter bound is based on a Karhunen-Loeve expansion of the received pulse spectrum when an isolated pulse is transmitted. Results are presented illustrating the various diversity effects. We conclude that in addition to the effect on probability of bit error of implicit delay diversity there is the less well known effect of implicit Doppler diversity in fast fading. The effect on probability of bit error of pulse shaping and explicit diversity is also illustrated.

In this paper, we derive pulses that yield Nyquist or near Nyquist properties when convolved with the initial terms of the series model of a slow fading dispersive channel. For the f-power series these are the so called powers of Nyquist pulses. For a Karhunen-Loeve series, model pulses are found that maximize the ratio of the mean peak-sample energy to mean residual intersymbol interference energy for a given bandwidth expansion factor. Under certain conditions, the approach significantly lessens the need for, or complexity of, equalization. Other benefits attributable to the use of the derived pulses, including those related to timing recovery, are discussed.

Decompositions of fading dispersive channels find utility in channel modeling and in the estimation of channel state information in a receiver. This letter considers decompositions based on the f-power series and Karhunen-Loeve expansions and investigates their relative ability to model selected channels. Development of such models should enable the design of reduced complexity receiver structures.