Algorithms Design For Resource Management In LTE-A Systems

LTE-Advanced(LTE-A)system is continuously evolving for providing faster,more convenient mobile services to users.Besides a large number of user devices needs to associate with cellular networks,the ever-growing services need to be treated differently from others to reach the required quality-of-service in the future mobile networks.However,the current cellular networks are still behind market demand under the condition that the available resource in the system is limited.Therefore,LTE-A integrates a bundle of innovative solutions,such as heterogeneous cellular network,wireless backhaul,and D2D(device-to-device),etc.,in current cellular networks to improve network performance.Although these new techniques change the conventional network infrastructure,they bring new problems,such as degradation of quality-of-service caused by absurd resource block allocating,interference caused by channel reusing in a cell,spectrum partitioning caused by D2 D communications,unbalanced load caused by the different transmit powers of base stations,etc,.Current resource assignment algorithms are not suited for LTE-A systems.The network performance would be deteriorated if these problems are not well addressed.Therefore,intelligent resource management algorithms,which have been widely discussed by researchers,are suggested as an effective way to improve network performance.The primary focus of this thesis is on resource management in LTE-advanced systems and the objective is to improve network performance.The main contents include: interference mitigation,scheduling algorithm,load balancing,throughput optimizing,quality-of-service providing,spectrum partitioning and association control.With the order that research scope is from part to whole,the main contributions of this thesis are summarized as follows.First,this thesis investigates the scheduling problem on MAC layer of air interface with the objective of allocating resource blocks to services and guaranteeing QoS(quality-of-service).The current scheduling algorithms utilize head-of-line packet delay,queue length,and channel condition to determine the priority that a resource block allocates to a service.However,these algorithms cannot guarantee quality-of-service of services.Therefore,we propose a novel scheduling algorithm which differentiates service to real-time services and non-real-time services.In order to guarantee quality-of-service and control data rate,we use token bucket depth to control the amount of traffic data transmitted in each resource allocation cycle,i.e.,whether a resource block allocated to a real-time service is fully determined by quality-of-service requirement.Compared to other scheduling algorithms,the proposed algorithm improves the throughput and reduces the delay and packet loss rate.However,there is a little decrease in the throughput of non-real-time services.Second,this thesis investigates the interference problem which caused by channel reusing in device-to-device underlying cellular networks.In order to alleviate the interference between cellular communications and device-to-device communications in a cell,we propose a novel graph-coloring based channel assignment algorithm which is simple and feasible for implementation.We first construct a novel interference graph to describe the interferences between two communication links when they simultaneously reuse a channel,and then a novel graph-coloring based channel assignment algorithm is proposed to alleviate interferences by greedily assigning the best channel to a communication link according to current channel assignment status.Moreover,we convert the channel assignment problem to a robust graph color problem and search the near optimal solution as the baseline for comparisons to show the efficiency of our proposed algorithm.Numerical results indicate that the proposed algorithm not only dramatically improves the network capacity but also enhances the fairness among devices.Third,we research the network performance based on Possion point process model.Two resource allocation algorithms are proposed.In the first algorithm,we address the problem of spectrum partitioning in device-to-device underlying cellular network.We convert the throughput maximization problem into an optimal spectrum partitioning problem with signal to interference plus noise ratio constraints and solve it.Simulation results show that the proposed algorithm achieves the highest throughput.For the second algorithm,we address the time allocating problem in relay enhanced cellular networks.We take quality-of-service and capacity of backhaul link into consideration and design a flexible frame structure that base stations and relays work in TDD mode.To improve network throughput and guarantee quality-of-service for services,the algorithm assigns the appropriate time-slot to backhaul link,direct link and access link.Numerical results indicate that the proposed algorithm improves system throughput and decreases the outage probability.Forth,we propose a novel association algorithm to address the load balancing problem,which caused by unbalanced resource consumption of base stations in milti-cell scenario.We propose a novel association algorithm which combines resource consumption and channel conditions.The proposed algorithm takes the backhaul link and the TDM nature of relay into consideration and achieves load balancing among cells.The simulation results show that the proposed algorithm achieves higher system capacity and better load balancing.