Management Of WLAN Interference Based On Joint Adjusting Of Power Rate And Carrier Sensing Threshold

With the growing popularity of Wireless Local Area Network（WLAN）, theinterference among the users of the system becomes more serious and can besummarized as the following three points. Firstly, some users cannot send thesignals out, secondly, some cannot receive the signals after the sending, thirdly,they can send and receive the signals only after a long period of time. Therefore,the interference reduces the quality of communication. So the mitigation ofinterference within WLAN system and the improvement of the throughput in thesystem are very urgent problems to be solved.Majority of the researches on the interference mitigation in WLAN systemfocus on the channel selection, load balancing, and the power control. For theorthogonal channels are extremely limited, it is critical to mitigate theinterference within the same channel. To reduce the interference and improve thethroughput of the system, the work should be done from three aspects, namelythe transmission power, rate, and the carrier sensing threshold, with the conditionthat the distribution of the load in the system unchanged. Recently, researchesassociated only involve one or two aspects, which is just not enough, for theconditions of the channels are changing all the time, and the parameters shouldbe adjusted simultaneously.In this thesis, an algorithm of joint adjustment is proposed to reduce theinterference in the system which combines the node’s transmission power,transmission rate, and the carrier sensing threshold. To begin with, fordetermining the power before sending the signals, the Pathloss TransmissionPower Control（PL-TPC） algorithm is used which employs a popular networkmodel in WLAN to compute the transmission power based on the receptionthreshold and the distance between the two sides. And then, to adjust thetransmission rate of the nodes, an Enhanced Adaptive Automatic Rate FallbackCollision Detect（AARFCD） algorithm is proposed, which employs the Requestto Send（RTS）/Clear to Send（CTS） mechanism alternatively and adjusts thetransmission rate based on the case of transmission success or failure. In thisalgorithm, it raises the rate after the number of successful and continuous transmission reaches a predefined threshold, distinguishes the reasons whentransmission failed successively twice, and decreases the rate if it is too high, oradjusts the carrier sensing threshold if the reason of transmission failure iscollision. Finally, as for the adjustment of carrier sensing threshold, an EnhancedNoncooperative carrier sense update algorithm（NCUA） is proposed, whichintroduces a utility function and a price function, and updates the carrier sensingthreshold iteratively based on the Enhanced NCUA algorithm.The results obtained from the NS2simulation show that the proposedalgorithm enables the system to minimize the degree of interference and achieveamaximum throughput with respect to the existing and classical algorithms.