Haitao Liu

A low-complexity LMMSE channel estimation method for OFDM-based cooperative diversity systems with multiple amplify-and-forward relays

Orthogonal frequency division multiplexing- (OFDM-) based amplify-and-forward (AF) cooperative communication is an effective way for single-antenna systems to exploit the spatial diversity gains in frequency-selective fading channels, but the receiver usually requires the knowledge of the channel state information to recover the transmitted signals. In this paper, a training-sequences-aided linear minimum mean square error (LMMSE) channel estimation method is proposed for OFDM-based cooperative diversity systems with multiple AF relays over frequency-selective fading channels. The mean square error (MSE) bound on the proposed method is derived and the optimal training scheme with respect to this bound is also given. By exploiting the optimal training scheme, an optimal low-rank LMMSE channel estimator is introduced to reduce the computational complexity of the proposed method via singular value decomposition. Furthermore, the Chu sequence is employed as the training sequence to implement the optimal training scheme with easy realization at the source terminal and reduced computational complexity at the relay terminals. The performance of the proposed low-complexity channel estimation method and the superiority of the derived optimal training scheme are verified through simulation results.

Outage Probability of Selection Cooperation With MRC in Nakagami-

Selection cooperation has been shown to be an effective way to implement cooperative diversity in wireless networks. In this letter, we investigate the outage performance of decode-and-forward selection cooperation with optimal maximal ratio combining (MRC) receiver at the destination to combine the signal replicas available from the source and the selected relay in Nakagami-/mbim fading channels with arbitrary real-valued/mbim. In particular, an exact closed-form expression for the outage probability is derived for integer values of fading severity parameter/mbim and an infinite summation expression for the noninteger situation. Our analysis extends previous results pertaining to selection combining (SC) receiver at the destination. Simulation and numerical results are presented to show the validity of the analytical results, as well as the effect of the two hops unbalanced fading conditions on the performance gain of MRC with respect to SC.

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This paper presents a simple single-carrier (SC) distributed space-time block coded transmission scheme for asynchronous cooperative communications over frequency-selective channels. The cyclic prefix (CP) at the source node and relay nodes is used to combat inter-symbol interference from multi-path fading and the timing errors from the relay nodes. In this scheme, the relay nodes only implement very simple operations on their received signals to construct distributed space-time block code, and decoding, DFT and IDFT operations are only needed at the destination node. The low complexity SC zero-forcing frequency domain equalization (ZF-FDE) is applied at the destination node to recover the transmitted signals. The analysis and simulation results demonstrate that this simple SC scheme can achieve order-two spatial diversity gain for amplify-and-forward based cooperative communication over frequency-selective channels in the presence of asynchronization between relay nodes.This paper proposes a simple orthogonal frequency -division multiplexing (OFDM) transmission scheme for asynchronous cooperative communications over frequency-selective fading channels. In this scheme, the relay nodes only implement very simple operations on their received signals, and no decoding, DFT or IDFT operation is needed. With our proposal, the received signals have the Alamouti code structure on each subcarrier, and thus, it has the fast symbol-wise ML decoding. The analysis and simulation results demonstrate that our simple scheme can achieve order-two spatial diversity gain for amplify-and-forward based cooperative communications over frequency-selective fading channels in the presence of asynchronization between relay nodes.