Research On Congestion Avoidance Strategy Guaranteeing QoS Of Wireless Sensor Network

With the rapid development of Micro-Electro-Mechanical System (MEMS) and wireless communication technology, the Wireless Sensor Network (WSN) has been widely used in various real-time and remote monitoring systems. However, due to the WSN's capacity constraints, the network will lead to the network congestion when a lot of data streams aggregate in a node. This situation will result in the loss of large amounts of data packets and the deterioration of Quality-of-Service. It has been a hot topic to limit the rate of data traffic and avoid possible congestion in the WSN. In order to ensure the fairness and reliability of WSN's congestion control, the main work includes the following respects:1) This paper introduces the main components of WSN, including its main characteristics and main applications. It also analyzes the reasons for the occurrence of congestion and gives details of the existing WSN congestion control protocol pointing out their basic ideas and inherent limitations. Due to the uniqueness of WSN, this paper presents several key issues concerning the design of WSN's congestion control.2) The bit error rate will cause the loss of packets in WSN. However, the reasonable set of packet size can alleviate this loss. In order to study the relationship between the packet sizes and transmission reliability at certain bit error rate, a lot of experiments have been done in the environment of ARQ protocol with the MATLAB and NS-2 simulation tools. Experiments results show that the different bit error rate matches an optimal packets size, which can effectively balance the packets loss ratio, the packet re-transmission ratio and the link availability.3)By integrating the rate limiting method of the relaxation technology (RT) and the equitable distribution method of max-min fair (MMF) resource sharing, this paper proposes a novel adaptive rate limiting congestion control (ARLCC) algorithm to solve the congestion in WSN. ARLCC uses RT scheme to make those packets which exceed node cache delivery later within the allowed unit delay and achieve the engineering level as the sending rate of intermediate nodes under multi-limiting conditions. When the rates of multi-nodes input streams are too high and the value of EL parameter exceeds the node cache containment, it was reset to zero with the MMF scheme and then increased at a constant rate. As a result, ARLCC can limit the input streams' rates and promise that they are fairly sharing the capacity and the bandwidth of intermediate node. The experiments show that the ARLCC can significantly out-performs the use of RT scheme alone, decreasing the packets loss ratio by 53.8 percent and the average end-to-end delay by 88.8 percent, ensuring the fairness and reliability of packet transmission.4) Finally, this paper summarizes what the researches have done and points out the future research directions.