Multicast is an efficient way of disseminating information to a group of receivers on the Internet and other computer networks. To combat losses, transmission repetition is common in both best effort and reliable multicast protocols. In the latter, repetition is performed by an automatic repeat request (ARQ) scheme. In either case, forward error correction (FEC) coding can be used to replace repetition, which may result in remarkably improved performance in terms of user throughput. This improvement is especially significant for wireless networks where bandwidth is valuable and loss rate is high. The main goal of this research is to find efficient FEC and hybrid FEC/ARQ (known as HARQ) schemes for a class of message-based multicast protocols, which are compatible with the protocols operating in a wireless environment. / In this thesis, firstly, general multicast and error control techniques are reviewed and examined. A message-based multicast protocol P_Mul is used as a base for performance studies and protocol modifications. P_Mul is designed to handle receivers operating in responsive and silent (no feedback) operational modes. An OPNET model of the standard P_Mul error recovery scheme, originally based on ARQ, is developed. Various schemes such as an ideal (rateless) FEC, Reed-Solomon and LDPC codes are incorporated in the model and their behaviours simulated, discussed and compared with the standard P_Mul performance. / Novel message-based mathematical models are derived that allow accurate estimation of P_Mul performance in the case of finite-length message multicast. The mathematical models take into account certain scenarios and schemes, e.g. when loss is random and all receivers non-responsive or responsive with error recovery based on ARQ or its hybrid with ideal FEC. / Furthermore, the simulation model is expanded so that P_Mul can efficiently manage complex traffic with different priorities; seamlessly serve multicast groups whose members may change operational modes frequently; and adapt to the channel conditions without saturating the network with an excessive number of packets. The performance of the P_Mul model with various enhancements is progressively simulated, compared and argued, pointing to the influence of the various protocol and network parameters. / Finally, a novel method for improving the performance of short messages at high error rates is proposed and the preliminary performance analysed. The method applies erasure decoding on smaller payload portions, called packet segments, to better match with the high error rates, yet without shortening the packet to the lower layer. With some increase in processing complexity and error detection overhead, the chance of short message reception improves considerably / Thesis (PhDTelecommunications)--University of South Australia, 2005.
| Identifer | oai:union.ndltd.org:ADTP/267467 |
| Creators | Tovirac, Julija. |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | copyright under review |
Page generated in 0.0016 seconds