Design And Model Optimization Of Distributed MAC Protocols For CSMA-based Long-distance Wireless Networks

Nowadays, medium access control(MAC) protocols based on carrier sense multiple access with collision avoidance(CSMA/CA) mechanism having been widely deployed in short distance communication networks. As the most widely used CSMA/CA protocol, IEEE 802.11 DCF introduces binary exponential backoff(BEB) procedure to reduce the transmission collisions, and resolves the hidden terminal problems through RTS/CTS handshake. Due to the characteristics of easy deployment, high reliability and survivability, DCF protocols have been widely used in the aera of WLAN Mesh networks, wireless sensor networks, and so on.With the development of wireless network technologies, researchers are devoting to adopting DCF protocol into long distance networks. In civil applications, DCF protocol is used to construct long distance Wi Fi networks or UAV WiFi networks to provide internet service for underdeveloped areas. Also, in military applications, CSMA/CA meschnism has been used in aeronautical data link system, eg, the high-speed data link ACR-740, which is used by Israeli army to provide information sharing among AWACS and fighters. However, DCF is initialed for short distance communications, and gains poor performace in networking efficiency and network throughput when it is used in long distance communications. Why this comes about and how to design MAC protocols based on CSMA/CA to meet the requirements of long distance communications remains a great challenge. In this paper, our research is exactly focused on the challenges mentioned above and our contributions can be summarized as follows:(1) In short distance wireless networks, the basic slot duration of CSMA/CA protocols is usually set to be larger than the maximum propagation delay. The purpouse is to guarantee that the signal from one node can be sensed by any other node in the carrier sense range of that node. Unfortunately, in long distance applications, the propagation delay is much longer. If the duration of the basic slot is still set to be the maximum propagation delay, the throughput performace will decreases significantly. This paper reverses the relationship between network throughput and the basic slot duration through Markov chain model. Based on analytical modeling, we analyze the strategies to optimize network throughput via adjusting the basic slot duration under different network scales, which can be used to guide the design of CSMA MAC protocols for long distance wireless networks.(2) According to the modeling and analyzing of the saturation throughput of DCF protocol in long distance wireless networks, this paper designs a new CSMA/CA MAC protocol, which is based on the competitive node aware and the contention window optimization scheme. Every node competes to be the central management node in distributed manner. The central management node is responsible for discovering all the copmpetitive nodes and notifying other nodes. All nodes start sending packets periodically after sensing the number of competitive nodes. Contention window value changes dynamically according to the number of competitive nodes. In order to improve overall throughput, this paper use a Markov chain model to accurately calculate the optical contention window value, which can maximize the saturation throughput. The simulation results obtained by the EXata simulator validate this model. Compared with DCF, the protocol can obtain better throughput in long distance wireless networks.