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.
| Identifer | oai:union.ndltd.org:GATECH/oai:smartech.gatech.edu:1853/26673 |
| Date | 27 August 2007 |
| Creators | Rahnavard, Nazanin |
| Publisher | Georgia Institute of Technology |
| Source Sets | Georgia Tech Electronic Thesis and Dissertation Archive |
| Detected Language | English |
| Type | Dissertation |
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