Multiple-access relaying with network coding: iterative network/channel decoding with imperfect CSI
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Multiple-access relaying with network coding: iterative network/channel decoding with imperfect CSI Xuan-Thang Vu* , Marco Di Renzo and Pierre Duhamel
Abstract In this paper, we study the performance of the four-node multiple-access relay channel with binary Network Coding (NC) in various Rayleigh fading scenarios. In particular, two relay protocols, decode-and-forward (DF) and demodulate-and-forward (DMF) are considered. In the first case, channel decoding is performed at the relay before NC and forwarding. In the second case, only demodulation is performed at the relay. The contributions of the paper are as follows: (1) two joint network/channel decoding (JNCD) algorithms, which take into account possible decoding error at the relay, are developed in both DF and DMF relay protocols; (2) both perfect channel state information (CSI) and imperfect CSI at receivers are studied. In addition, we propose a practical method to forward the relays error characterization to the destination (quantization of the BER). This results in a fully practical scheme. (3) We show by simulation that the number of pilot symbols only affects the coding gain but not the diversity order, and that quantization accuracy affects both coding gain and diversity order. Moreover, when compared with the recent results using DMF protocol, our proposed DF protocol algorithm shows an improvement of 4 dB in fully interleaved Rayleigh fading channels and 0.7 dB in block Rayleigh fading channels. Keywords: Network coding; Cooperative relaying; Joint network/channel decoding; Imperfect channel state information
1 Introduction In cooperative communications systems, idle nodes have the capability to relay information from other active nodes. Hence multiple copies of the same signal can reach a given destination through independent fading channels, which result in potential spatial diversity gains. However, diversity gains are usually achieved with some loss in system throughput [1,2]. Network Coding (NC) has recently been introduced as a capacity–achieving routing scheme where intermediate network nodes are allowed to combine several input packets into one output packet [3]. Recent results have shown that NC can also provide improved performance and energy efficiency compared with conventional network routing techniques [4]. However, besides the many *Correspondence: [email protected] Laboratory of Signals and Systems (LSS), French National Center for Scientific Research (CNRS) – École Supérieure d’Électricité (SUPÉLEC) – University of Paris–Sud 11, 3 rue Joliot–Curie, 91192 Gif–sur–Yvette (Paris), France
potential advantages and applications of NC over classical routing, the NC principle is not without limitations. A fundamental problem that NC needs to take into account over lossy (e.g., wireless) networks is the so-called error propagation problem: corrupted packets injected by some intermediate nodes may propagate through the network until the destination, and might render impossible to decode the original informa
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