A differential space-time code receiver using the EM-algorithm

Abstract

In this paper, we consider the detection of differential space-time block codes in static Rayleigh fading channels. Conventional diyerential detection (CDD), the most prevalent and most basic approach, suffers from a loss in performance when compared to coherent detection. As an alternative, we propose using the sequence estimate provided by space-time multiple symbol differential detection (ST-MSDD) to initialize an iterative receiver based on the expectation maximization (EM) algorithm. The EM-algorithm performs joint channel estimation and sequence detection. Employing BPSK modulation, simulation results show that the EMbased receiver outperforms standard ST-MSDD receivers afler three iterations. The results in the paper demonstrate that our EM-based coherent receiver, using a non-coherent first-pass. oflers a reasonable performance improvement over standard non-coherent receivers.

A Receiver for Differential Space-Time-Shifted BPSK Modulation Based on Scalar-MSDD and the EM Algorithm

“…In addition, these channel gains are assumed to be constant over the observation window of N symbol intervals. The static fading channel has been frequently considered when investigating systems with transmit and receive diversity [10,18,19,20,21,22,23]. On the other hand, the sequence of noise samples, {.…”

“…This algorithm performs iterative channel estimation and data detection, by passing information back and forth between the channel estimator and the data detector. At this point, we want to point out that other options for initializing the EM algorithm include using pilot symbols to acquire a channel fading estimate [19,20], or using differential detection to acquire a transmitted signal estimate [21]. Although using pilot symbols provides a reliable reference to estimate the channel gains, it results in a power loss, and even after several iterations, the performance of coherent detection may not be reached [19,20].…”

“…Although using pilot symbols provides a reliable reference to estimate the channel gains, it results in a power loss, and even after several iterations, the performance of coherent detection may not be reached [19,20]. In the case of initializing the EM algorithm with differentially detected sequence [21], it was determined that the transmitted sequence estimate reconstructed from a vector-MSDD information sequence estimate does not yield good channel estimates due to differential reencoding. Hence, there was a consistent performance loss when compared to a coherent receiver.…”

“…Immediately following the kth E-step is the kth M-step. Here the algorithm assumes the fading gain estimates in (21) are perfect and performs MRC and data detection according to…”

“…Furthermore, the estimated symbols in B (k) are then differentially decoded to obtain estimates of the information symbols. If it is desired to perform another EM iteration, the channel will be reestimated using (21), and hence another sequence estimate will be obtained using (22). The iterations cease when the sequence estimate does not change during two subsequent iterations, or after a prespecified number of iterations have occurred.…”