Wireless Self-organizing Network Power Control With Collision Avoidance Mechanism

In MANET, transmission power determines transmission distance and coverage, thereby further decides network topology and spatial reusage, and ultimately affects network throughput. In addition, as nodes is limitied with the capacity of battery and charged hard, transmission energy is the main aspect of network energy consumption. Therefore, transmission power control, which optimizes network performance to some extend as well as saves network consuming energy, become a very important research area of MANET.Among the research on power control of MANET, Interference aware MAC protocols, including PCMA and PCDC, adjust transmission power of potential transmitters by Collision Avoidance Information broadcasted to avoid conflicting ongoing communications, the paper called it "collision avoidance mechanism". Interference aware MAC protocols abandon channel single access and apply channel multi access, allow parallel communications sharing the same channel, solve the hidden terminal/exposed terminal problems and enhance wireless channel utilization and network throughput.After analyzing the collision avoidance mechanism of PCMA and PCDC, I find: in PCMA, at a high network load, as the method "periodically broadcast Busy Tone signal" can not meet the needs that neighbors expects to receive updated busy tone signal, the collision rates of data packets will be significantly enhanced, as a result, the channel utilization will be reduced. Frequent RTS/CTS collision will cause frequent retransmission. While in PCDC, at a high network throughput, the collision rate of RTS/CTS packets broadcasted by the maximum transmission power is relatively high. Specially,in the process of 4 way handshaking, any packet is lost or ruined, which will cause retransmission.Against the problems found in Collision Avoidance Mechanism of PCDC and PCMA, the paper propose two measures——"periodically and timely broadcast Busy Tone signal" and "RTS/CTS collision avoidance" to improve PCDC and PCMA respectively. In order to solve the problem that Busy Tone signals can not timely updates at a high network throughput, the method "busy tone will be timely broadcasted once noise tolerance is changed" is added to original broadcasting method of busy tone signal. On RTS/CTS collision, nodes are requested to intercept RTS/CTS channel and obtain the state and active period of active neighbors, which will guide the transmission of RTS/CTS. Once, RTS/CTS collision happens, collided nodes have to wait for a random time to transmit RTS.Finally, NS2 will be uesed to simulate DCF mechanism, PCMA and improved PCMA, PCDC and improved PCDC in MANET to obtain their respective packet collision rate and network throughput. Comparing the packet collision rate and network throughput of improved protocols with that of original protocols, it is found that, "periodically and timely broadcast Busy Tone signal" can improve the performace of PCMA to a limited extent, however "RTS/CTS collision avoidance" can improve the performace of PCDC at a high network load greatly.