Performance of network coded systems supported by automatic repeat request

Abstract

Inspired by the network information theory, network coding was invented in 2000. Since then, the theory and application of network coding have received intensive research and various network coding schemes have been proposed and studied. It has been demonstrated that the packet-level network coding has the potential to outperform the traditional routing strategies in packet networks. By taking the advantages of the information carried by the packets sent to different receivers (sinks) in a packet network, packet-level network coding is capable of reducing the number of packets transmitted over the network. Therefore, the packet-level network coding employs the potential for boosting the throughput of packet networks. By contrast, the symbol-level network coding, which is also referred to as the physical-layer network coding, is capable of exploiting interference instead of avoiding it for improving the channel capacity and/or enhancing the reliability of communications. In this thesis, our focus is on the packet-level network coding.

Performance of communication systems with network coding has been widely investigated from different perspectives, mainly under the assumption that packets are reliably transmitted over networks without errors. However, in practical communication networks, transmission errors always occur and error-detection or error-correction techniques are required in order to ensure reliable communications. Therefore, in this report, we focus our attention mainly on studying the performance of the communication networks with packet-level network coding, where Automatic Retransmission reQuest (ARQ) schemes are employed for error protection. Three typical ARQ schemes are invoked in our research, which are the Stop-and-Wait ARQ (SW-ARQ), Go-Back-N ARQ (GBN-ARQ) and the Selective-Repeat ARQ (SR-ARQ). Our main concern is the impact of network coding on the throughput performance of network coding nodes or networks containing network coding nodes. Additionally, the impact of network coding on the delay performance of network coding nodes or coded networks is also addressed.

In a little more detail, in Chapter 3 of the thesis, we investigate the performance of the networks employing packet-level network coding, when assuming that transmission from one node to another is not ideal and that a certain ARQ scheme is employed for error-control. Specifically, the delay characteristics of general network coding node are first analyzed. Our studies show that, when a coding node invokes more incoming links, the average delay for successfully forming coded packets increases. Then, the delay performance of the Butterfly networks is investigated, which shows that the delay generated by a Butterfly network is dominated by the communication path containing the network coding node. Finally, the performance of the Butterfly network is investigated by simulation approaches, when the Butterfly network employs SW-ARQ, GBN-ARQ, or SR-ARQ for error-control. The achievable throughput, the average delay as well as the standard deviation of the delay are considered. Our performance results show that, when given a packet error rate Packet Error Rate (PER), the SR-ARQ scheme is capable of attaining the highest throughput and resulting in the lowest delay among these three ARQ schemes.

In Chapter 4, the steady-state throughput of general network coding nodes is investigated, when the SW-ARQ scheme is employed. We start with considering a Two-Input-Single-Output (2ISO) network coding node without queueing buffers. Expressions for computing the steady-state throughput is derived. Then, we extend our analysis to the general H-Input-Single-Output (HISO) network coding nodes without queueing buffers. Finally, our analytical approaches are further extended to the HISO network coding nodes with queueing buffers. A range of expressions for evaluating the steady-state throughput are obtained. The throughout performance of the HISO network coding nodes is investigated by both analytical and simulation approaches. Our studies in this chapter show that the throughput of a network coding node decreases, as the number of its incoming links increases. This property implies that, in a network coding system, the coding nodes may form the bottlenecks for information delivery. Furthermore, the studies show that adding buffers to the network coding node may improve the throughput performance of a network coding system.

Then, in Chapters 5 and 6, we investigate the steady-state throughput performance of the general network coding nodes, when the GBN-ARQ in Chapter 5 or the SR-ARQ in Chapter 6 is employed. Again, analytical approaches for evaluating the steady-state throughput of the general network coding nodes are concerned and a range of analytical results are obtained. Furthermore, the throughput performance of the network coding nodes supported by the GBN-ARQ or SR-ARQ is investigated by both simulations and numerical approaches.

Finally, in Chapter 7, the conclusions extracted from the research are summarized and the possible directions for future research are proposed.

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Identifiers

ORCID for Lie-Liang Yang: orcid.org/0000-0002-2032-9327

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