Generalized distributed network coding based on nonbinary linear block codes for multi-user cooperative communications

Abstract

In this work, we propose and analyze a generalized construction of distributed network codes for a network consisting of M users sending different information to a common base station through independent block fading channels. The aim is to increase the diversity order of the system without reducing its code rate. The proposed scheme, called generalized dynamicnetwork codes (GDNC), is a generalization of the dynamicnetwork codes (DNC) recently proposed by Xiao and Skoglund. The design of the network codes that maximizes the diversity order is recognized as equivalent to the design of linear block codes over a nonbinary finite field under the Hamming metric. The proposed scheme offers a much better tradeoff between rate and diversity order. An outage probability analysis showing the improved performance is carried out, and computer simulations results are shown to agree with the analytical results.

Flexible Network Codes Design for Cooperative Diversity

“…Upon reception of y S 1 R 1 , y S 1 R 2 , y S 2 R 1 , and y S 2 R 2 , the relays R 1 and R 2 attempt to decode the symbols transmitted by S 1 and S 2 in a similar fashion as in a Decode-and-Forward (DF) cooperative protocol (Scaglione et al, 2006). Unlike other solutions available in the literature for network code design for cooperative networks (Xiao & Skoglund, 2009a) (Xiao & Skoglund, 2009b), (Rebelatto et al, 2010a), (Rebelatto et al, 2010b), we do not rely on powerful (i.e., Shannon-like) channel codes at the physical layer, which allow each relay to detect correct and wrong packets, and enable them to forward only the former ones. We consider a very simple implementation in which the relays demodulate-network-code-and-forward (D-NC-F) each received symbol without checking whether the symbol is correct or wrong.…”

“…As a matter of fact, the application of NC to a wireless context needs to take into account that the wireless medium is highly unpredictable and inhospitable for adopting the existing NC algorithms, which have mostly been designed by assuming wired (i.e., error-free) out that max-diversity-achieving network codes can be obtained by resorting to the theory of non-binary linear block codes. For example, as far as the canonical two-source two-relay cooperative network is concerned, the methods proposed in (Xiao & Skoglund, 2009a), (Xiao & Skoglund, 2009b), (Rebelatto et al, 2010a), (Rebelatto et al, 2010b) can achieve full-diversity, when, instead, XOR-based binary NC (Katti et al, 2008a) cannot. The solution proposed by all these papers to overcome the limitation in the achievable diversity is based on using network codes in a non-binary Galois field.…”

“…Also, longer decoding delays are, in general, required to design full-diversity-achieving network codes (Rebelatto et al, 2010b). Furthermore, the solutions available in (Xiao & Skoglund, 2009a), (Xiao & Skoglund, 2009b), Rebelatto et al (2010a), (Rebelatto et al, 2010b) aim at guaranteeing the same diversity gain for all the active sources of the network, which, in general, leads to an inflexible network code design as multiple sources might have different Quality-of-Service (QoS) requirements, and, so, might need different diversity gains. In conclusion, the solutions available so far seem to be still inflexible to accommodate the needs of the multi-source multi-relay scenario, as well as to keep the computational complexity of the relay nodes at a low level.…”

An Improved Energy Balance Routing Protocol based on LEACH Protocol

“…Literature [9][10] use time delay mechanism to choose the cluster head, by setting a smaller waiting time for a larger energy node, so that the nodes with more residual energy have higher probability to become cluster heads. However, Literature [9] has not studied the number of cluster heads produced in each round, if the number of cluster heads is not stable, cluster head energy consumption is too large, and then affect the overall performance of the network.…”

“…However, Literature [9] has not studied the number of cluster heads produced in each round, if the number of cluster heads is not stable, cluster head energy consumption is too large, and then affect the overall performance of the network. Literature [10] proposed algorithm, although the number of cluster heads is fixed, but the cluster head position is not good designed, so the network survival time is not effectively extended. In literature [11] the cluster head selection method of LEACH was improved, the method of single hop and multi hop is used to improve the energy efficiency of the system.…”