Research On Uplink Channel Accessing Mechanism Of MU-MIMO WLANs

The demand of mobile communication increases significantly with the rapid development of intelligent equipments and the wide adoption of multi-media applications.In order to further improve the performance of wireless local access network(i.e.WLAN),multiple-user multiple-input-multiple-output(i.e.MU-MIMO)technology has been brought into IEEE 802.11ac standard.Due to its capability of improving system capacity via spatial resuse,MU-MIMO WLANs have attracted more and more attentions.Specifically,channel accessing mechanisms of MU-MIMO WLANs that allow multiple users to concurrently communicate with one access point,have become a research hotspot and are of great theoretical and practical significance.In existing uplink channel accessing mechanisms of MU-MIMO WLANs,transmission collisions can only be detected at the end of transmissions.And these fail transmissions caused by collisions consumed a lot of time and spectrum resource.In mass user scenarios,system performance will decrease significantly due to frequent collisions.Therefore,it is necessary and challenging to design channel accessing mechanisms,which can stop current transmission immediately when collision occurs and decrease resource wasting caused by fail transmissions for MU-MIMO WLANs.This thesis focuses on this challenge and it has the following contributions.1.A periodically-sensing-based random channel accessing mechanism is proposed.By allowing the first accessing user sensing channel periodically and suspending transmission in time,the proposed mechanism can detect collisions and stop on-going transmissions as soon as possible.In this way the resource wasted by fail transmissions can be decreased greatly and the performance of MU-MIMO WLANs can be improved obviously.Moreover,system model is built for the proposed mechanism,and saturation throughput and average delay of MU-MIMO WLANs are obtained through numerical analysis.Simulation results show that the proposed mechanism can improve the performance of MU-MIMO WLANs efficiently especially in mass user conditions.For example,when the number of users reaches 50,saturation throughput of the proposed mechanism is 78.57%much more than the existing CSMA/CA-based channel accessing mechanism,and average delay of the proposed mechanism is 33.34%less than the existing CSMA/CA-based channel accessing mechanism.2.A periodically-sensing-based RTS/CTS channel accessing mechanism is proposed.By allowing transmitting users sensing channel periodically and suspending transmission in time,the proposed mechanism can detect collisions and stop on-going transmissions as soon as possible.Through this way the resource wasted by fail transmissions can be decreased greatly and the performance of the MU-MIMO WLANs can be prompted obviously.Moreover,system model is built for the proposed mechanism,and saturation throughput and average delay of MU-MIMO WLANs are obtained through numerical analysis.Simulation results show that the proposed mechanism can improve the performance of MU-MIMO WLANs efficiently.Specifically,in less user conditions the proposed mechanism performs much better than the existing CB-CSMA/CA-based channel accessing mechanism and performs a little worse than the proposed periodically-sensing-based random channel accessing mechanism.In mass user conditions the proposed mechanism performs much better than both the existing CB-CSMA/CA-based channel accessing mechanism and the proposed periodically-sensing-based random channel accessing mechanism.For example,when the number of users reaches 50,saturation throughput of the proposed mechanism is 76.67%much more than the existing CB-CSMA/CA-based channel accessing mechanism and is 9.82%much more than the proposed periodically-sensing-based random channel accessing mechanism,and average delay of the proposed mechanism is 43.34%less than the existing CB-CSMA/CA-based channel accessing mechanism and is 13.58%less than the proposed periodically-sensing-based random channel accessing mechanism.3.A hybrid channel accessing mechanism is proposed for MU-MIMO WLANs to make full use of the proposed two mechanisms according to different network conditions.By choosing a better one from the proposed mechanisms,the hybrid channel accessing mechanism can maintain high system performance.4.Practical applications of the proposed system models are studied,and a user satisfaction-based WLAN offloading algorithm is proposed for heterogeneous wireless network,where user satisfaction is evaluated by both saturation throughput and network expense.Experimental results prove that the proposed algorithm has much higher user satisfaction than both the existing cellular-first offloading algorithm and the wlan-first offloading algorithm.Aiming at decreasing the resource wasted by fail transmissions,a periodically-sensing-based random channel accessing mechanism and a periodically-sensing-based RTS/CTS channel accessing mechanism are proposed.Both mechanisms can decrease the time wasted by fail transmissions and improve the performance of MU-MIMO WLANs.Moreover,a hybrid channel accessing mechanism is proposed to make full use of the proposed channel accessing mechanisms,and a user satisfaction-based WLAN offloading algorithm is proposed for heterogeneous wireless network to achieve higher user satisfaction.Therefore,this thesis is of certain significance in both theoretical research and practical application.It provides new ideas for uplink channel accessing mechanism of MU-MIMO WLANs,and can be used in heterogeneous network for WLAN offloading problem.