Research And Application Of CSMA Mechanism In Ad Hoc Network

With the development of various network applications,ad hoc networks have been applied in lots of scenarios in the daily life.The increase of the traffic and the ever-increasing demand for quality of service(QoS)require for higher network performance.This paper mainly focuses on the media access control layer and proposes adjusted Carrier Sense Multiple Access(CSMA)mechanisms,in order to improve the transmission efficiency and reliability of the network.In the paper,the CSMA mechanism in ad hoc networks is studied in the following aspects.Wireless sensor networks(WSNs)and vehicle ad hoc networks(VANETs)are two classic ad hoc networks.In this thesis,the CSMA mechanism is investigated in these two kinds of networks.The first section in the thesis gives an overview of this research.This section reviews the history of ad hoc networks and the CSMA mechanisms.Also,it presents the state-of-the-arts of WSNs,VANETs,and multi-channel ad hoc networks.The second section introduces the work in WSNs.With the development of the Internet of Things(IoT),WSNs become more and more important.Energy efficiency,one of the crucial performance indices,is always considered for designing protocols and algorithms in WSNs.In this paper,we focus on data frame transmission under SINR(signal to interference plus noise ratio)model.An efficient mechanism,called as SINR-Q-CSMA,is proposed.We divide the transmission into two scenarios,i.e,the sink circle and the regular circle.SINR-Q-CSMA combines dual-channel method with time slotted method according to different scenarios,which can avoid the collision problem effectively.Moreover,SINR-Q-CSMA employs a solution based on queue length to solve the collision when it cannot be avoided.The simulations show that SINR-Q-CSMA can improve the success possibility and reduce the collision possibility effectively.And the average energy consumption can be saved about 45% as well.The third second details the work in VANETs.As for the VANETs,the paper focuses on how to improve the transmission reliability by CSMA mechanisms.It is a great challenge to achieve the reliable communication in VANETs,due to the high device density.The common solutions for this scenario have severe problems,because they are designed to enhance the reliability of emergency messages,without considering the status messages.In this paper,we present the cooperative Carrier Sense Multiple Access(CO-CSMA),where a specially-designed possibility-variable CSMA(pvCSMA)method is proposed to transmit the status message and a Request To Send/Clear To Send(RTS/CTS)method is employed to transmit the emergency message.Further,with a cross-layer method combining the physical(PHY)layer with the medium access control(MAC)layer,we successfully give transmitters the ability to transmit and sense simultaneously.The theoretical analysis and simulation prove the effectiveness and feasibility of the algorithms.The fourth section describes the contributions in multi-channel ad hoc networks.Achieving the maximum throughput is one of the most important issues in ad hoc networks.Many algorithms have been proposed to improve the performance of the network.However,it can be usually ignored that different packets have various gain values for the network.In this paper,we design a new CSMA protocol with game theory,i.e.Game-Theory-based CSMA for Multi-Channel(MC-GT CSMA),aiming for the high weighted throughput in multi-channel ad hoc networks.At first,we propose the distance constraint under SINR model,efficiently avoiding the interference and enhancing the success probability.In MC-GT CSMA,senders determine a specific channel and sub-slot for transmitting the packet,then use RTS/CTS message to communicate with the receivers;the senders transmit the packet with determined settings in the data slot.Moreover,gain values of different packets are considered.Specifically,packets with different weight have various probabilities of sending an RTS message,and the probabilities are calculated by game theory.Based on the analysis of theorem and simulations,it can be proved that MC-GT CSMA can achieve the high weighted throughput with game theory in multi-channel ad hoc networks.The conclusions are drawn in the last section.This section gives a review for the thesis and presents the advantages and drawbacks of the proposed methods.In addition,it also gives some future works and plans to further improve the robustness and efficiency of the proposed methods.