Research On Code Division Multiple Access Technology Based On Ad Hoc Network

Ad Hoc network does not rely on the existing fixed network communications infrastructure, and is able to start the network quickly. Because of its dynamic network, fully distributed, Ad Hoc network is not easy to be limited by the environment, has very strong robustness and survivability, especially suitable for application on military affairs and emergency relief. Code division ad hoc network not only inherits the ad hoc network’s advantages, but also supports concurrent communication and with a very high security level because of adopting CDMA technology.However, introducing this form of network into VHF channel has brought a series of problems, such as the hidden terminal and exposed terminal, near far effect, too much short control frame and the broadcasting problem, presents a great challenge in the MAC layer protocol design.After in-depth study of the existing code division MAC layer protocol of Manet’s, and taking ultra-short wave channel characteristics into consideration, we mainly consider two mature ad hoc network MAC layer protocol :SBT-CDMA and DRC, and transplant them to the VHF channel, through simulation, obtains the performance curves. Then propose the two-way channel reservation and power control access protocol(DRC-PC CDMA), the key point of this protocol is that:(1) Eliminate the hidden terminal effect using the receive busy tone and power detection technology to reduce the rate of channel conflict.(2) Realize the dynamic assignment of spreading codes through the interaction of the control frame, at the same time to inform the other node of the current channel conditions and to eliminate the influence of near far effect by power control.(3) Reduce the number of control frames, we introduce the channel reservation technology, by using the ACK frame in the reserved bits when the data frame transmission is completed to inform other node to maintain the channel.(4) We use unique radio spread spectrum code and boardcast busy tone to implement the broadcast transmission. Through the simulation, we can see the protocol performance is better,this work provide some reference for future research.