| Recently, Network coding has been proved to be the breakthrough in the research field of network and communication. It is an effective technique to increase network capacity and improve the robustness and reliability of networks. It allows intermediate nodes to perform processing operations on the incoming packets, in addition to just forwarding them. The broadcast character of wireless link is very appropriate for the application of network coding technique. Currently, the combination of wireless network and network coding has gained significant interest domestic and overseas. This thesis investigates the application of network coding in wireless network. In order to improve the reliability and the throughput of wireless network, we do extensive research on network coding incorporated with the multicast communication in WLAN, the routing optimization in multi-hop network and the retransmission efficiency for wireless broadcast system, and focus on the protocol design and the theory for the performance analysis. The main inventive works and conclusions of the thesis are listed as follows.Firstly,we review the recent development in theory and application of network coding technique. The conception and basic theory of the network coding are introduced. The construction and optimization of network coding schemes are classified and analyzed in detail. Furthermore, we summarize the state of arts in application of network coding in wireless networks and propose the key technologies, the open issues and challenges of network coding referring to both theory and application in near future.Secondly, we propose a multicast MAC protocol called MPNC (Multicast Protocol based on Network Coding) based on network coding to solve the problem of the unreliable multicast service provided by IEEE 802.11 for the wireless local area network (WLAN). MPNC takes use of the network coding group to transmit multicast data frames. In multicast source node, the data frames are combined with random linear codes for transmission. In receiving nodes, the data frames are decoded after receiving enough combined frames. According to the 802.11 DCF exponential backoff mechanisms, we build the 2-dim Markov chain model for the channel contention of the multicast terminal and multiple unicast terminals. Analytic solutions are derived for the saturation throughput of MPNC under the error-prone channels. Simulation result validates the conclusion of the theory analysis, and shows that the MPNC scheme can effectively reduce the number of transmission for multicast frames and improve the bandwidth efficiency. Thirdly, we propose a rate adaptive multicast MAC protocol based on network coding called RAMPNC (Rate Adaptive Multicast Protocol based on Network Coding) to solve the problem that the proposed multicast MAC protocols for WLAN can not adapt the quick channel variations. The proposed protocol has two key characters. In on aspect, RAMPNC takes use of the network coding group to transmit multicast data frames. The transmission times are reduced and the bandwidth efficiency is improved because of the information mixing character of the network coding. In the other aspect, the channel state information is obtained through RTS-CTS signal exchange. The RAMPNC can adjust the physical sending rate in accordance with the estimated SNR from multicast nodes. Simulation shows that RAMPNC can respond to channel variations quickly and achieve better performance than existing protocols in terms of multicast throughput, average frame transmission delay and frame delivery rate, etc.Fourthly, we investigate the network coding transmission scheme for multiple unicast flows in wireless multihop networks. By integrating the advantage of both network coding and opportunistic routing, we propose a network coding-aware opportunistic routing protocol called NCAOR (Network Coding-Aware Opportunistic Routing). The expected transmission count (ETX) is selected as the opportunistic routing metric. For each hop, the node chooses multiple neighbors to form an opportunistic node set for forwarding, which is composed of nodes satisfied special conditions. And each opportunistic node computes the gain of the forwarding packet by the utility function, which considered both the distance to destination and the network coding gain. According to the computation result, each opportunistic node can set the forwarding time for receipted packet intelligently. By choosing the average transmission time of data packet as the metric, we analyze the transmission performance of the NCAOR for the scenarios of both one-hop relay with bi-directional unicast flows and multi-hop relays with bi-directional unicast flows. We discuss the influence of different parameters, such as the delivery probability of the wireless link, the number of opportunistic nodes and the average path length. Simulation results show that the proposed NCAOR can get better improvement on performance such as throughput, energy and network coding chances, when compared to the COPE(Complete Opportunity Encoding) using the traditional routing protocol.Fifthly, we do some research on the improving the retransmission performance for wireless broadcast system with network coding. A broadcast retransmission scheme called RNC-ARQ (Random Network Coding-Automatic Repeat Request) based on the random network coding is put forward for the wireless broadcast system. The scheme transmits broadcast data packets in a batch processing mode and retransmits lost packets in a per-batch way. In accordance with the packet reception feedback matrix, the source combines all lost packets in a batch with random linear codes for retransmission. And all receiver nodes can recover the lost data packets by solving the linear equation system. Based on the Gilbert-Elliott channel model, a multi-state Markov model is generated by uniting the channel state with the reception mode of received nodes. Based on this model, the closed-form expressions are derived for the throughput of RNC-ARQ. Simulation result validates the theory analysis, and shows that the proposed RNC-ARQ scheme is better than the SR-ARQ(Selective Repeat-Automatic Repeat Request) and XOR-ARQ (XOR network coding-Automatic Repeat Request) scheme in terms of the throughput under the same channel conditions.
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