The Research Of MAC Protocol In Wireless Ad Hoc Networks

WANET is a wireless autonomous network which does not rely on pre-existing infrastructures in a distributed environment. Due to the minimal configuration and deployment requirements, Wireless ad hoc networks are increasingly widely used in various military and civilian occasions. Also, the emergence of different needs greatly promoted the research and development of wireless ad hoc network, which makes the wireless ad hoc network become one focus of the current research.Wireless nodes often carry a limited supply of energy, so there is need to consider how to reduce the energy consumption of wireless communication to extend the life of the network. Power control in MAC protocol is a way to reduce energy consumption of communication. On the one hand, power control can determine the received signal quality, transmission range, the level of interference to the remaining nodes as well as the network throughput and end-to-end delay. On the other hand, wireless signal in the dissemination process have path loss. In the free space, radio waves follow an inverse square law for power density:the power density is proportional to the inverse square of the distance. But in the real world, path loss can also be influenced by obstacles (such as walls, trees), terrain, humidity and so on. Path loss has uncertainties, which directly determines whether the signal can be correctly received or not. All of the above cases make the transmission power control very complicated.Based on the above analysis of the impact of the power control on network performance and the wireless signal propagation characteristics, two power control MAC protocols were designed-a lightweight path loss adaptive power control protocol and a power control MAC protocol based on collision resolution. In the former, M-PCM protocol maintains a running average RSSI, computed by exponential weighted averaging of each RSSI returned by destination node. Meanwhile, M-PCM changes the transmit power dynamically based on this average value. In this way, M-PCM reduced the packet loss rate, thus increasing the throughput and reducing the energy consumption. The power control strategy in M-PCM can be used in other static power control protocol based on IEEE 802.11 data transfer process. The simulation experiments show that the designed protocol performs better than PCM protocol in energy efficiency and network throughput. In the latter, all frames in the process of communication use the optimal transmit power to reduce energy consumption. Furthermore, when the collisions happen, based on whether the interferer will communicate with the interfered node, RPC protocol takes the appropriate measures to increase more concurrent transmissions and reduce the retransmission and energy consumption. The simulation experiments show that RPC protocol performs better than SHUSH protocol in network throughput and end-to-end delay.