Maximum-likelihood synchronization, equalization, and sequence estimation for unknown time-varying frequency-selective Rician channels

Abstract

This paper develops a receiver structure to perform jointly ML synchronisation, equalisation and detection of a linearly modulated signal transmitted over a time-varying, frequency-selective, Rician faded channel, corrupted by AWGN. The receiver is particularly suited to a fast fading channel, where other receivers that rely on estimating the channel cannot track it quickly enough. The signal mean and autocovariance are needed, and a scheme is proposed for estimating these quantities adaptively. The receiver processes the specular and diffuse components (corresponding to the signal mean and autocovariance) separately. Processing the known specular component is the classical detection problem. The unknown diffuse component is processed by predictors [11]. We show that the predictors can achieve synchronisation in a novel manner, if synchronisation is required. A union bound on the receiver's BER is derived, and it tightly bounds simulated BERs in fast fading at high SNRs.

Improved Approximate Maximum-Likelihood Receiver for Differential Space–Time Block Codes Over Rayleigh-Fading Channels

“…The PEP in (11) can be evaluated by integration of the probability density function of from zero to infinity. Therefore, similar to the result in [21] (15)…”

“…Let denote the PEP of the error event of length associated with the sequences and . Similar to [21], an upper bound on the BER can be obtained from the union bound on the number of error bits averaged over transmitted sequences and corresponding error sequences for all error events. The upper bound can be written as (10) where is the probability of transmitted sequence , is the number of error bits arising from this error event, and is the number of information bits per trellis interval.…”

“…The union bound is still reliable if the bound includes a finite number of dominant error events under certain conditions. When fading is moderately fast and SNR is high, short-length error events are dominant [21]. In this case, the union bound of bit error probability can be evaluated by including only short-length error events.…”

“…Suppose the receiver obtains the detected sequence . Then, it computes "rough" channel estimates from (21) and sends them to the next receiver stage.…”

Equalization of Time-Varying Channels

“…Yu and Pasupathy [YP95] then extended [LM90] to general signal alphabets and ARMA doubly selective channels. The latter technique was extended further to carrier-frequency-offset Rician channels by Hart and Taylor in [HT98].…”