Research On Energy Efficiency Driven Wireless Local Area Networks Access Technologies

In Wireless Local Area Networks, users will opportunistically exploit thechannel with random access. And due to the time-varying property of wirelessnetworks, user can improve their transmission by probing the channel beforetransmission. As smart phones and other wireless terminals gettingincreasingly popular, the energy consumption problem of thosebattery-powered wireless devices has received more and more attention. Inthis paper, we focus on the energy efficiency of Wireless Local AreaNetworks.In the Wireless Local Area Network with Access Point, userscommunicate with each other or get access to the outside network bycontending for the transmission opportunity to Access Point. Compared with3G network, WLAN has its advantages of a higher transmission rate withlower transmission energy. However, WLAN encounters its unique problemswith energy consumption. Hence, in order to achieve the optimal energyefficiency, we design the Energy Efficiency Driven Random Access (EEDRA)strategy that specifies when to stop contention and start transmission, as wellas the power level that should be used for transmission. We apply the optimalstopping theory to maximize the energy efficiency and adopt a bisectionalgorithm to solve the maximum expected energy efficiency. We usenumerical results to show the converge speed of the algorithm. Then thetradeoff between energy efficiency and throughput is investigated among3different random access strategies. Numerical results show that comparedwith the default strategy of IEEE802.11, the EEDRA strategy we proposedhas50%gain in energy efficiency with only4%loss of the throughput. Also,we illustrate the improvement on fairness of EEDRA and evaluate its performance under different set of parameters.When investigating Wireless Ad hoc networks, there is no Access Pointor control center. In order to communicate with each other, users need toestablish their own links to transmit data. To improve the energy efficiency ofAd hoc networks with random access, we propose a multi-user random accessmethod, which takes energy efficiency as priority. The method is based on thetime-varying characteristic of channels. A multi-user random access energyconsumption model is set up. From cooperative and non-cooperativeperspective, we use game theory and optimal stopping theory to maximizeenergy efficiency in the access strategy. Then we find that the optimalscheduling scheme is a pure threshold policy. An iterative algorithm is used tofind the threshold. The convergence of the algorithm is also proved. And weinvestigate the tradeoff between energy efficiency maximization andthroughput maximization. Then, we offer a sufficient condition where energyefficiency and throughput can be maximized simultaneously. According tonumerical results, when the transmission power is relatively large comparedwith contention power and probing power, the throughput can be maximizedwithout losing too much energy efficiency. Furthermore, when selfishbehavior of users is considered, we formulate a user-centric model, in whichthe loss of energy efficiency presented to be less than10%compared with thatof network-centric case.