Research On The Key Wireless Transmission Technologies Based On Network Coding

Wireless network coding technology is widely studied because it can increase the throughput of wireless networks. However, the unreliability of wireless transmission has a lot of negative influences on the use of network coding in wireless networks. Fortunately, a lot of wireless transmission technologies have been developed to increase the reliability and efficiency. So it is necessary to jointly study the network coding and wireless transmission technologies together to further improve the reliability and efficiency of the system.In this paper, we focus on the scenario when there is one transmitter and multiple receivers (such as the broadcast phase of two way relay channel and the retransmission phase of multicast). The transmitter combines multiple messages for different receivers together using network coding, and broadcasts the coded message. The receivers use prior knowledge to recover their desired message from the coded message. For the scenario where there is one transmitter and multiple receivers, we study the network coding based adaptive modulation scheme and network coding based antenna selection algorithm in two way relay channel, and network coding based retransmission algorithm and joint network and channel decoding scheme in multicast system. The innovations for this dissertation are as follows.(1) A network coding based adaptive modulation scheme is proposed for two way relay channel in order to improve the spectral efficiency.In the broadcast phase of two way relaying, there is one transmitter (the relay node) and two receivers (the user nodes), the use of network coding constrains the relay node to broadcast at the same data rate using the modulation scheme decided by the receiver with poor channel quality. In this paper, we propose a new network coding based adaptive modulation scheme that the relay node jointly codes and modulates the messages according to both receivers’channel qualities and the receivers use subset partition technology in order to fully use both receivers’ channel gains.(2) The antenna selection algorithm for two way multi-antenna relay channel is improved and the outage performance is analyzed.In the broadcast phase of two way relay channel, in order to improve the outage performance, when the relay node can not work at network coding mode, it can switch to the store-and-forward mode. In this paper, we give the antenna selection schemes for different modes and further analyze the outage performance under proposed schemes. We also verify these analyses with simulations.(3) A novel network coding based retransmission scheme is propose for wireless reliable multicast system to improve the retransmission efficiency.In the reliable multicast system, the transmitter doesn’t retransmit as soon as it receives the NACK information from the receivers, the transmitter begins to retransmit after it transmits several data packets. The transmitter combines the lost packets from multiple receivers using network coding into one composite packet, then retransmits this composite packet, and multiple receivers can recover their lost packets from the composite packet. In this paper, a new coding principle, maximum total SNR of intended receivers is proposed for fading environment, which uses the network coding gain and the multi-user diversity gain to improve the retransmission efficiency. Since the proposed scheme is NP-complete, an efficient heuristic algorithm with very low complexity is given.(4) A joint network and channel decoding scheme for wireless reliable multicast system is proposed to improve receivers’decoding ability.In wireless environment, channel coding is always applied to the data packet before transmission. Most channel coding schemes are linear that adding two codewords will get a new codeword. The composite packet for retransmission is generated by adding multiple data packets together using XOR method, so the composite packet is a new codeword. Since each bit of the composite packet is the XORed result of the corresponding bits of the data packets, we can also treat this bit as a single parity check bit. So in this paper, a joint network and channel decoding scheme is proposed in order to help the receiver recover its lost packet in above situations. The receiver can combine the composite packet and other error packets into a single parity check product code, and decode the product code using iteration method with soft information to improve the error correction ability.