The Resource Allocation In Heterogeneous Wireless Networks

Along with the explosively increasing of mobile terminals, traditional cel-lular networks based on macro base stations (BSs) cannot fully satisfy users’traffic demands. Heterogeneous networks (HetNets) are emerging as a flexi-ble and economical infrastructure to meet various users’ requirements and pro-vide higher transmission rate and better quality of service (QoS). In HetNets,different types of BSs, such as the macro BS, the pico BS and the femto BS,vary in size, maximum transmission power and cost. They are deployed at different places according to different wireless traffic demands and different coverage area so as to improve the users’ experience. Besides, the device-to-device (D2D) communication is emerging as a promising technique to satisfy the communication of users in the proximity of each other. Since the D2D user can communicate with the target user using the same channel with the BS’s, the D2D communication can improve the overall throughput, enhance the spec-tral efficiency and reduce the power consumption in the wireless network. The potential D2D users can choose the D2D mode in which they communicate to the target directly, or the cellular mode in which they communicate to the device with the help of the small BS when the quality of the D2D communica-tion is low. However, as small BSs and D2D communications are introduced into the wireless communication system, the interference environment becomes increasingly complicated. The complex interference may degrade the perfor-mance of the system if the resources (such as wireless channels, transmission power and so on) cannot be allocated appropriately.Based on this situation, the thesis studies the resource allocation problem in a HetNet composed of the macro BS and pico BSs firstly. Then the resource allocation problem in the D2D-enabled HetNet is investigated further. The main innovations and contributions of the paper are as follows.1) To improve the energy efficiency (EE) of users, a user association and power control scheme is proposed for uplink wireless communication in a two-tier HetNet. In order to preserve fairness to some extent, the log function is adopted to define the uplink EE utility for each user. It is noted that the log utility has intrinsic fairness due to its monotonous increasing and diminishing marginal income. Then the optimization problem is formulated and a two-step iterative optimization algorithm is proposed to solve the problem with the con-vex optimization theory and Newton’s method.2) In order to improve the uplink EE of secondary users (SUs), the user as-sociation and power control scheme during uplink transmission in the HetNet containing primary users (PUs) and SUs is investigated. Ordinary cellular users are characterized as PUs, while SUs are the unlicensed users, sensors or some other Internet of Things (IoT) equipments. The PUs occupy all the channels in the HetNet and SUs try to reuse the channels of PUs. We consider two transmis-sion modes for SUs, i.e., the SU can associate with the BS directly or through the help of its cooperative relay. Considering the users’ rate requirement and the power constraint, we investigate the optimization of sum EE of SUs. Then the original problem is decomposed into several subproblems which are solved separately.3) To improve the uplink capacity of D2D-enabled femtocells, ajoint chan-nel allocation, mode selection and power control scheme is proposed for cellu-lar users and D2D users in femtocells during uplink wireless communication.Considering the rate constrained QoS requirement for users in femtocells and the interference limit for users served by the macro BS, we formulate the prob-lem as the users’ capacity maximization problem in femtocells. The original optimization problem is transformed into a convex form and solved with the Lagrangian dual decomposition method.4) To study the joint optimization of EE and spectrum efficiency (SE) of D2D users and cellular users during uplink transmission in the D2D-enabled HetNet, a power control and channel allocation scheme is proposed in this pa-per. The utility which reflects the tradeoff between EE and SE is defined firstly.Then the problem is formulated as the tradeoff utility maximization problem with channel allocation and power control. After that, the problem is decom-posed into several subproblems which can be solved efficiently with the convex optimization theory and the bipartite maximum weight matching algorithm.