Mac Layer Scheduling Strategy Based On Network Coding In Wireless Networks

Because of its very strong flexibility and mobility, the application of wireless network technology becomes more and more popular, especially in scenarios such as environmental monitoring, military operation, transportation, office and so on. The broadcast nature of wireless channel brings some changes to the design of wireless network protocol stack, particularly on MAC layer. Under the conventional transmission mode, relay node is only responsible for store-and-forwarding packets, no extra processing involved, thus wasting the potential coding gain. As a newly presented idea, network coding allowed intermediate nodes to perform coding operations on the received data; this can lead to significant throughput improvements. The existing theoretical research has proven that this technology can effectively improve network throughput and bandwidth utilization, and has better performance in energy saving.Firstly, this paper described the origin of the network coding technology and introduced the basic principle of network coding. Then, we carried out a detailed comparative analysis between inter-flow and intra-flow network coding, obtaining their applicable wireless network environment, respectively. All kinds of network coding-based applications get long-term development, and these findings show that network coding has advantages such as improving network throughput, reducing latency, enhancing reliability and so on. All these advantages promote us to conduct extensive research on it further.Next, we analyzed the mechanism of wireless network MAC layer. MAC layer protocol determines the channel access mechanism of wireless nodes. Nodes access the channel using CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) fashion, so this implements the distributed management of all involved nodes. For adapting to the demand of power saving of wireless sensor networks, some MAC variants were produced by performing some allocation strategy to the Listen/Sleep cycle. With the continuing development of network coding, its application in the MAC layer will gradually start up, and designing a MAC protocol suitable for network coding will become a new topic.Lastly, for one hop Butterfly wireless network with backlogged source nodes, we introduce network coding to the design of MAC layer and a MAC layer scheduling strategy based on network coding is proposed. This resulting strategy dynamically performs allocation to the buffer of the coding node, with every flow owning its own virtual buffer. When the difference of numbers of the packets in each virtual buffer reached the predefined threshold, MAC enlarges the contention window size of the source node, the number of buffered packets of which is more than the other. By doing so, the chance of accessing channel of the other source node is increased, thus the probability of encoding packets at coding node will increase. Results of simulations performed on Matlab have shown that compared to traditional wireless networks that were with or without network coding involved, our strategy outperforms them in terms of throughput and latency.