Equalization Techniques for Distributed Space-Time Block Codes With Amplify-and-Forward Relaying

In this paper, we investigate equalization methods for cooperative diversity schemes over frequency-selective fading channels. Specifically, we consider three equalization schemes proposed originally for conventional space-time block codes (STBC) and extend them to distributed STBC in a cooperative transmission scenario with amplify-and-forward relaying. The distributed STBC equalization schemes are named after their original counterparts as distributed time-reversal (D-TR) STBC, distributed single-carrier (D-SC) STBC, and distributed orthogonal frequency division multiplexed (D-OFDM) STBC. The underlying orthogonality of distributed STBC results in decoupled data streams at the receiver side allowing low-complexity implementations. Without loss of generality, we consider a single-relay scenario where the source-to-relay SrarrR, relay-to-destination RrarrD, and source-to-destination SrarrD links experience possibly different channel delay spreads. Under the assumption of perfect power control for the relay terminal and high signal-to-noise ratio (SNR) for the underlying links, our performance analysis demonstrates that D-TR-STBC, D-SC-STBC, and coded D-OFDM-STBC schemes are able to achieve a maximum diversity order of min(L
₁
,L
₃
)+L
₂
+2 where L
₁
, L
₂
, and L
₃
are the channel memory lengths for SrarrR, SrarrD, and RrarrD links, respectively. This illustrates that the minimum of the multipath diversity orders experienced in SrarrR and RrarrD links becomes the performance bottleneck for the relaying path. For the case of a nonfading relaying path where line-of-sight propagation is possible in either one of these underlying links, we demonstrate that diversity orders of L
₁
+L
₂
+2 and L
₃
+L
₂
+2 are achievable assuming nonfading SrarrR and RrarrD links, respectively. An extensive Monte Carlo simulation study is presented to corroborate the analytical results and to provide detailed performance comparisons among the three candidate equalization schemes