| With the advantage of improving the spectrum efficiency and system capacity significantly by fully exploiting the spatial resource,multi-user MIMO has become a key technology of the next generation WLAN.However,multi-user MIMO will bring co-channel interference while introducing multi-user gain.In order to reduce co-channel interference and improve system performance,it is necessary to allocate reasonably spatial resource.For the next generation WLAN based on OFDMA,the whole frequency band is divided into multiple resource units.In a certain time slot,the user only works on a resource unit.Due to serious feedback overhead and sounding latency,it is essentially impossible for the transmitter to get the perfect and instantaneous channel state information(CSI)of each user on each frequency resource unit to implement the spatial resource allocation over multiple resource units.On the contrary,statistical CSI varies at a much slower rate than the instantaneous CSI and it can be more easily and accurately obtained at the transmitter.For this reason,based on statistical CSI at the transmitter,this dissertation investigates the spatial resource allocation of the next generation WLAN.The specific research work of this paper can be summarized as follows.Firstly,the characteristics and key technologies of the next generation WLAN are introduced,followed by the analysis of the linear precoding based on instantaneous CSI and statistical precoding technology under multi-user MIMO system.After that,the necessity of the spatial resource allocation under strong correlation channel is verified by simulation.Secondly,the spatial resource allocation on multi-user multi-subchannel under zero-forcing(ZF)transmission in the next generation WLAN is studied.To solve the problem that the work bandwidth of users and access point(AP)is not equal in the next generation WLAN and that the feedback overhead and sounding delay of instantaneous CSI of each user on each frequency resource unit is serious,taking into account that statistical CSI varies at a much slower rate than the instantaneous CSI,a spatial resource allocation scheme of joint statistics and instantaneous CSI is put forward.In the proposed scheme,users are grouped based on statistical CSI firstly,and then instantaneous CSI feedback is performed for the intra-group users according to the allocation result to complete the ZF precoding.The simulation results show that the proposed spatial resource allocation algorithm can reduces the system feedback cost while ensuring the system performance.Finally,the spatial resource allocation on multi-user multi-subchannel based on statistical eigen-mode transmission in the next generation WLAN is studied.To solve the problem that there are unreasonable user pairs in the optimal solution obtained by the fast resource allocation algorithm based on statistical CSI,considering that the sum rate of user groups may be lower than the single-user transmission rate with the serious interference between users in the next generation WLAN,an improved adaptive spatial resource allocation algorithm is proposed.In the proposed algorithm,we first remove the unreasonable user pairs by the transmission mode switching criterion,and then find out the optimal user matches with the multi-user statistical eigen-mode transmission while the other unpaired users perform the single-user statistical eigen-mode transmission.Simulation results show that the improved adaptive resource allocation algorithm achieves higher system rate than other spatial resource allocation algorithms. |
