The Research Of Wifi Broadcasting Based On Network Coding

Recently, with the rapid development of wireless networks, the Wireless Local Area Network (WiFi) has received much attention, because of its advantages in lower construction and operating costs, the higher transmission rate, longer transmission distance’, over other networks. With the development of mobile television and other broadcasting.business on mobile phones, the use of WiFi in broadcast scenario will be much more common. But, since each client has the different channel state to the access point,the AP has to adjust the data rate to support all customers, so WiFi lacks an efficient multicast mechanism. In traditional methods, WiFi AP’s performance deteriorated, rapidly in broadcast/multicast mode. And using the global error recovery techniques to recover lost data will easily lead to some other problems, such as, Feedback Storms, Recovery Storm, Congestion and many other problems, which are hard to solve.As a promising technology that can theoretically reach the Min-cut Max-flow capacity in theory, network coding can make effective use of frequency resources through recombining and coding the information the relay node received from different nodes and broadcasting it out, in this way, the forwarding ability of relay node is enhanced, thereby increasing the throughput of the communication system. At the same time, integrating network coding into collaborative communication can also improve the security and robustness of the system, arise the overall performance of the entire communication system.Currently, the main solutions for the problems of WiFi multicast are using appropriate error control strategies (ARQ) and transferring the multicast data stream into unicast data stream for transmission. This paper also utilize these two aspects, namely the research is jointing the Network Coding in multicast and unicast scenarios. And proposed an optimal coding scheme based on greedy algorithm and illustrate the problem as finding the largest cluster in an undirected graph. Then, we mathematical analysis and simulate the performance gain between the traditional retransmission mechanism and the retransmission with Network Coding strategy. Conclusion is drawn that our encoding algorithm can effectively improve the efficiency of WiFi multicast.The main research is as follows:(1) In a WiFi multicast network, considering a downlink-broadcast system with an AP as the transmission node and a particular set of receiving nodes; We proposed a retransmission and error correction scheme based on Network Coding. Compare with the traditional ARQ (Automatic Repeat Request) method and the scheme with Network Coding, we can get the coding performance gain in our scheme. Meanwhile, we analysis the computational complexity and delay effects to the system.(2) In a WiFi unicast downlink network, the receivers aim at different data flows from the AP, we proposed a coding scheme based on greedy algorithm, abstracted the optimal coding scheme as the problem of finding the largest cluster in an undirected graph. The simulation results proved that our algorithm can perform better and the computational complexity can also be realized.Finally, the development trend and the applications of Network Coding theory and WiFi network in the near future are proposed.