Research On Scheduling And Resource Allocation Algorithm In IEEE 802.11ax

The next generation WLAN standard IEEE 802.11 ax is mainly proposed to solve the communication problem in dense scenes.The traditional 802.11 Carrier Sense Multiple Access/Collision Avoidance(CSMA/CA)channel access mechanism intensifies system conflicts in dense scenarios,resulting in inefficient MAC.802.11 ax enables multi-user transmission by introducing several related technologies,such as Orthogonal Frequency Division Multiple Access(OFDMA)and Spatial Reuse(SR),at the PHY layer and the MAC layer to improve MAC efficiency and system throughput.Compared with other traditional WiFi standards,802.11 ax mainly adopts a scheduling-based working mechanism,that is,AP contends for channels and allocate resources for each STA.Therefore,the performance of the 802.11 ax system depends largely on how resources are allocated and scheduled.This thesis studies the scheduling and resource allocation algorithms in the 802.11 ax OFDMA system,while considering the inherent characteristics.The specific work is as follows:Firstly,under the premise of not distinguishing user service types,this thesis studies the MT algorithm,RR algorithm and PF algorithm in the 802.11 ax OFDMA system with the goal of maximizing system throughput,fairness between users,and taking into account throughput and fairness.Among them,The MT algorithm schedules users with the best channel conditions on each Resource Unit(RU),but the rate fairness between users is poor;The RR algorithm assigns equal size RU to each user in turn without considering the channel conditions of each user,which is simple and fair,but at the cost of low system throughput;The PF algorithm considers both the user's instantaneous rate and the historical average rate on each RU,which can balance throughput and fairness,but the algorithm is relatively complicated;Then we simulated and analyzed the performance of the three algorithms.In addition,based on the traditional PF algorithm,an improved generalized proportional fair(GPF)algorithm is introduced in the 802.11 ax OFDMA system.The algorithm considers the performance indicators such as system throughput and long-term and short-term user fairness.By setting the scale factors of different ratios,the GPF algorithm flexibly achieves different degrees of compromise between system throughput and user rate fairness,and overcomes the shortcomings of the traditional PF algorithm that can only achieve short-term rate fairness.Then,this thesis considers four different types of QoS services defined in the 802.11 e standard,and designs the scheduling and resource allocation algorithm of the 802.11 ax system based on user priority.Specifically,this thesis first defines a resource allocation framework constrained by UPS criterion according to the QoS requirements of different services.This criterion maximizes the number of satisfied users while maintaining priority based scheduling;Then the optimal scheduling algorithm based on user priority is designed according to the UPS criterion and is transformed into a mixed integer linear programming problem.Due to a high level of complexity for the optimal scheduling algorithm,this thesis proposes a low-complexity sub-optimal algorithm,which firstly prioritizes all users and then finds the solution in each priority group.The simulation results show that the sub-optimal algorithm can achieve similar system performance to the optimal algorithm in most cases.