Research And Simulation On MAC Protocol For Wireless Multimedia Sensor Networks

The growing popularity of wireless sensor network technology and multimedia applications has prompted a new generation of wireless multimedia sensor network technology(WMSNs). Design of the media access control protocol for wireless multimedia sensor network has severe challenges, such as low delay, low energy consumption, high throughput, while WMSNs provies people with rich media information and sensuality.This paper firstly introduces the research status of WMSNs, network system structure, key technology and application prospect, then analyzes the key technologies of MAC protocols for WMSNs. There are some limitations for the existing MAC protocols used in WSNs to be directly used in WMSNs, but the improvements of these MAC protocols can be applied in some application scenarios of WMSNs. MAC protocols with differentiated services, hybrid MAC protocol and the cross-layer design dependencies between MAC layer and other layers of the communication stack especially the physical layer, are the research directions of WMSNs MAC protocols.Sensor networks are application-oriented networks. Real-time-sensitive multimedia traffic and other non-real-time traffic both exist in most wireless multimedia sensor networks. contention-based MAC protocols work well when burst multimedia traffic is in a small amount.S-MAC protocol is a classic contention-based MAC protocol. This paper analyzes the strategy which S-MAC protocol used. Using periodic listen / sleep scheduling mechanism, the sensor nodes can keep a sleep state for a long time to reduce the energy consumption of the nodes. The neighboring nodes form virtual clusters group together. The nodes in same virtual cluster have the same scheduling period, which reduces the energy consumption caused by idle listening. Through adaptive monitoring mechanism, the relevant node adaptively wakes up and forward messages at the end of the data transmission time, reducing the data transmission delay in the network. The mechanism of S-MAC protocol save node energy as far as possible. But the data size of the multi-media information in wireless multimedia sensor networks is large. And the transmission and processing of multi-media information also has special requirements, such as special requirements for network quality of service.So S-MAC protocol has some limitations to be used in the wireless multimedia sensor network.According to the characteristic of WMSNs and improving the network performance, we improved S-MAC protocol. This paper puts forward the adaptive contention window adjustment mechanism(ACWA-MAC) and the adaptive duty cycle adjustment mechanism(DTD-MAC). ACWA-MAC protocol contention window size changes according to different network load. To forecast the main network data flow type, DTD-MAC makes the data packet transmission statistical failure rate, accordingly adjusting the duty ratio to adapt to the changes of the data flow types in the network. Finally, the new algorithm and the mechanism is verified by simulation on the NS2 platform under the environment of Linux.The result shows that ACWA-MAC algorithm significantly reduces the network packet loss rate and the energy consumption of the network;DTD-MAC algorithm significantly reduces the network packet loss rate and average delay, at the same time the algorithm improves network throughput.