Abstract
We consider relay channels in which the source-destination and relay-destination signals are assumed to be orthogonal and thus have to be recombined at the destination. Assuming memoryless signals at the destination and relay, we propose a low-complexity quantize-and-forward (QF) relaying scheme, which exploits the knowledge of the SNRs of the source-relay and relay-destination channels. Both in static and quasistatic channels, the quantization noise introduced by the relay is shown to be significant in certain scenarios. We therefore propose amaximum likelihood (ML) combiner at the destination, which is shown to compensate for these degradations and to provide significant performance gains. The proposed association, which comprises the QF protocol and ML detector, can be seen, in particular, as a solution for implementing a simple relaying protocol in a digital relay in contrast with the amplify-and-forward protocol which is an analog solution.
Highlights
The channels under investigation in this paper are quasistatic orthogonal relay channels for which orthogonality is defined to [1]
Several observations can be made: (a) from information-theoretic studies like [1, 2], it appears that the best choice of the relaying scheme depends on the source-relay channel signal-tonoise ratio (SNR) and that of the relay-destination channel; (b) there are not many works dedicated to the design of practical EF schemes the EF protocol has the potential to perform well for a wide range of relay receive SNRs; (c) the AF protocol is generally chosen for its simplicity but implementation-related issues are often ignored
Many simulations showed us the following trend: in quasistatic channels, the receiver performs quite no matter which relaying protocol (AF, clipped AF, or optimum QF) is used, provided that the preferred combining scheme is employed
Summary
The channels under investigation in this paper are quasistatic orthogonal relay channels for which orthogonality is defined to [1]. One of the motivations for the work presented in the paper is precisely to propose low-complexity relaying schemes (comparable to the AF protocol complexity) that can be implemented in a digital relay transceiver (in contrast with the AF protocol) and use the knowledge of the SNRs of the forward and backward channels in order for the relay to optimally adapt to the forward and backward channel conditions To achieve these goals, the main solution proposed is a quantize-and-forward (QF) protocol for which forwarding is done on a symbol-by-symbol basis and aims to minimize the mean square error (MSE) between the source signal and its reconstructed version at the output of the dequantizer at the destination.
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