Study On Distributed Network-Channel Coding In Wireless Sensor Networks

Distributed channel coding is an efficient coding scheme to improve the transmission reliability for cooperative communication network. Network coding is a novel approach to enhance the throughput of networks. In network coding scheme, the relay nodes are allowed to encode the data packets received from multiple source nodes and send the encoded packets instead. Coding operations enable the relay nodes to compress the information, and whenever possible, to reduce the number of transmissions and bandwidth consumption. Recently, joint design of distributed channel and network coding becomes a hot topic for wireless sensor networks (WSNs). An important realization is the adaptive network coded cooperation (ANCC) scheme, which exploits the combined network-channel coding gain for a multi-source network. In this approach, the authors proposed a distributed coding scheme to simplify the network code design problem to the problem of designing a graph code by matching a real-time network topology to a Tanner graph. This thesis focus on the techniques of distributed network coding in wireless sensor networks. Specially, we mainly investigate the application of joint design of distributed channel coding and network coding technologies in wireless communication systems. The main contribution of our work can be summarized as follows:We investigate the performance of a wireless sensor network with multiple transmission sessions, in which multiple groups of source nodes communicate with their respective destination nodes via a shared wireless relay network. A multiple transmission session model with network code division multiplexing (NCDM) scheme is proposed to remove the inter-session interference at each destination. The fundamental idea of the NCDM scheme takes advantage of the property of the low-density generator matrix (LDGM) codes, i.e., by right multiplying the transpose matrix of the parity check matrix with its corresponding generator matrix, it will obtain a matrix with all zero elements. Based on the analysis of the NCDM scheme, new code design criteria for the construction of the generator matrix is proposed. We further evaluate the wireless sensor network with multiple transmission sessions applying the proposed NCDM scheme in terms of throughput and complexity. Our evaluation demonstrates that the proposed scheme not only has a linear computational complexity, but also shows a similar error performance and a considerable throughput improvement compared with its counterpart, which is referred to as a serial session scheme.A distributed network coding (DNC) scheme based on the Raptor codes is proposed for wireless sensor networks, where a group of sensor nodes, acting as source nodes, communicate with a single sink through some other sensor nodes, serving as relay nodes, in a multi-hop fashion. At the sink, a graph-based Raptor code is formed on the fly. After receiving a sufficient number of encoded packets, the sink begins to decode. The main contributions of this paper are the derivation of a bit error rate (BER) lower bound for the LT (Luby-Transform)-based DNC scheme over Rayleigh fading channels under maximum-likelihood (ML) decoding, and the derivations of upper and lower BER bounds for the proposed Raptor-based DNC scheme on the basis of the derived BER bound of LT codes. Numerical and simulation results show that the derived upper and lower BER bounds come closer, particularly as the length of the codewords is increased with a larger expanding coefficient. The developed bounds can be used to optimize degree distributions of fountain codes over Rayleigh fading channels.An unequal error protection (UEP) DNC scheme based on fountain codes is proposed to provide arbitrary error protection (i.e., continuous protection levels) to all the source nodes in WSNs. We derive the upper and lower BER bounds for the proposed UEP DNC scheme with ML decoding over Rayleigh fading channels. Numerical results show that the derived analytical bounds are tight and our proposed UEP DNC scheme based on fountain codes has a strong UEP property.