Research On User Access Control And Resource Allocation In Wireless Heterogeneous Networks

Recent years,with the rapid development of mobile communication industry,the number of terminal devices such as smart phones has shown explosive growth.Meanwhile,multimedia applications emerge in large numbers,and users'requirements for different kinds of services and contents also rise continuously.These facts raise severe challenges to the current mobile communication systems.In order to cope with the rapid growth of traffic,and support various quality of service(QoS)requirements of different services,mobile operators improve the system capacity by deploying multiple types of base stations in existing cellular networks and introducing wireless local area networks(WLAN).The network architecture composed of multiple types of base stations and multiple network protocols has been called wireless heterogeneous network.In the mobile communication network,user access control and resource allocation is the key to ensure the QoS requirements of services and to improve the system performance.With the upgrade of network architecture,traditional user access control and resource allocation mechanisms need to be further researched to adapt to the wireless heterogeneous network.Compared with the cellular network composed only of macro base stations,the wireless heterogeneous network brings many new challenges,including more serious interference,uneven load distribution,asymmetric uplink and downlink coverage,asymmetric uplink and downlink traffic demand,various types of access networks,et al.In addition,due to the emergence of diverse services,users usually have differentiated QoS requirements.In the environment of wireless heterogeneous network,how to guarantee the QoS requirements of users and to promote the system performance through efficient and reliable user access control and resource allocation mechanism has become an issue worthy of further study.Therefore,this dissertation presents systematically and deeply studies on the user access control and resource allocation mechanism in the two typical scenarios of wireless heterogeneous network,i.e.,heterogeneous cellular networks and cellular-WLAN integrated networks.The main works and contributions of this dissertation are as follows.1)This dissertation addresses the resource allocation problem for mixed traffic in heterogeneous cellular networks,designs a dynamic time division duplex(TDD)transmission protocol for heterogeneous cellular networks,and proposes a resource allocation scheme which can guarantee the QoS of users' traffic flows.The diversity of user services is reflected in the differentiated QoS requirements.In heterogeneous cellular networks,uneven load distribution and diverse services will bring asymmetric downlink and uplink traffic demand.This asymmetry is particularly evident in small cells deployed in hotspots.Dynamic TDD mode has its inherent advantages in dealing with the asymmetric downlink and uplink traffic demand,but serious cross link interference between macro cell base stations and small cell base stations will be brought in as a side effect.In order to alleviate such cross link interference,guarantee the QoS requirements of diverse services,and improve the resource utilization,this dissertation combines the design of cross link interference mitigation and the design of resource allocation for diverse traffic flows.First of all,this dissertation designs a new transmission protocol for TDD heterogeneous cellular networks as an interference mitigation mechanism,which effectively combines power control and time slots allocation.On this basis,utility functions are adopted to represent the differentiated QoS requirements of user services,and resource allocation for users'traffic flows is formulated as a network utility maximization problem.Based on the optimization theory,a two level decomposition method is proposed to solve such problem,and a solving algorithm with polynomial complexity is designed.The simulation results verify that comparing with the existing schemes,the proposed resource allocation scheme combined with cross link interference mitigation can effectively improve the throughput of downlink and uplink best effort traffic flows and reduce the outage probabilities of soft QoS traffic flows.2)This dissertation studies the user association control problem in cellular-WLAN integrated networks,proposes a user uplink cellular first association scheme.Furthermore,based on the feasible set of WLAN states,this dissertation gives the association conditions for traffic flows.With the growth of mobile communication traffic,mobile operators deploy WLANs to offload traffic from cellular networks.Cellular networks and WLAN constitute the cellular-WLAN integrated networks.In a WLAN,the access point and users access the channel in a competitive manner without difference in the priority of competing channels.Due to the inherent asymmetry in the downlink and uplink for competing channels,the main competition in WLAN comes from the transmission of uplink data flows.As the uplink traffic flows in the cellular network being offloaded into the WLAN continuously,the competition becomes more and more intense,which will significantly reduce the channel utilization of WLAN and the system throughput.In order to guarantee the throughput requirements of different services,and to reduce the competition and conflict in WLAN,this dissertation designs an association control strategy to maximize the channel utilization of WLAN and the system throughput,i.e.,user uplink cellular first access strategy.This dissertation adopts the queuing theory to model the frame transmission in WLAN,derives the average throughput of different traffic flows under given WLAN states,and the feasible set of WLAN states.Furthermore,based on the feasible set of WLAN states,the association conditions of various traffic flows in WLAN are given.Finally,the simulation results verify the accuracy of the theoretical analysis.Besides,compared with the WLAN-first access scheme,the proposed scheme can improve the channel utilization of WLAN,and the overall downlink throughput of the integrated network,without affecting the downlink throughput of the cellular network.3)This dissertation studies joint throughput and power aware user association control in cellular-WLAN integrated networks,and proposes a user association control scheme based on potential game model.In cellular-WLAN integrated networks,the performance of a user is affected by not only its achievable throughput,but also its power consumption.From the system point of view,the WLAN's channel utilization and the system throughput can be maximized by mitigating uplink traffic flows from WLAN to cellular networks.However,from the user point of view,the migration of its uplink traffic flow will increase its power consumption.Therefore,in such scenario,there exists a tradeoff relationship between system throughput and user power consumption.When migrating the user's uplink traffic flow without considering its power consumption,the user performance will be impacted.Based on the above facts,during the association process,this dissertation takes into account the impact of both the user's achievable throughput and power consumption on its performance,and proposes a throughput and power aware user association control scheme.The queuing theory is adopted to model the frame transmission in WLAN,and utility functions are introduced to characterize users' satisfaction.Furthermore,the user association control problem is formulated as a game problem,and game theory is adopted to find the solution of such problem,i.e.,Nash Equilibrium point.Finally,the effect of the proposed association control scheme on the system performance is evaluated by simulation.The simulation results verify that compared with the WLAN-first access scheme,the proposed scheme can effectively improve the downlink achievable throughput of all users.