Coding for wireless ad-hoc and sensor networks: unequal error protection and efficient data broadcasting
MetadataShow full item record
This thesis investigates both theoretical and practical aspects of the design and analysis of modern error-control coding schemes, namely low-density parity-check (LDPC) codes and rateless codes for unequal error protection (UEP). It also studies the application of modern error-control codes in efficient data dissemination in wireless ad-hoc and sensor networks. Two methodologies for the design and analysis of UEP-LDPC codes are proposed. For these proposed ensembles, density evolution formulas over the binary erasure channel are derived and used to optimize the degree distribution of the codes. Furthermore, for the first time, rateless codes that can provide UEP are developed. In addition to providing UEP, the proposed codes can be used in applications for which unequal recovery time is desirable, i.e., when more important parts of data are required to be recovered faster than less important parts. Asymptotic behavior of the UEP-rateless codes under the iterative decoding is investigated. In addition, the performance of the proposed codes is examined under the maximum-likelihood decoding, when the codes have short to moderate lengths. Results show that UEP-rateless codes are able to provide very low error rates for more important bits with only a subtle loss in the performance of less important bits. Moreover, it is shown that given a target bit error rate, different parts of the information symbols can be decoded after receiving different numbers of encoded symbols. This implies that information can be recovered in a progressive manner, which is of interest in many practical applications such as media-on-demand systems. This work also explores fundamental research problems related to applying error-control coding such as rateless coding to the problem of reliable and energy-efficient broadcasting in multihop wireless ad-hoc sensor networks. The proposed research touches on the four very large fields of wireless networking, coding theory, graph theory, and percolation theory. Based on the level of information that each node has about the network topology, several reliable and energy-efficient schemes are proposed, all of which are distributed and have low complexity of implementation. The first protocol does not require any information about the network topology. Another protocol, which is more energy efficient, assumes each node has local information about the network topology. In addition, this work proposes a distributed scheme for finding low-cost broadcast trees in wireless networks. This scheme takes into account various parameters such as distances between nodes and link losses. This protocol is then extended to find low-cost multicast trees. Several schemes are extensively simulated and are compared.