Research On User Association And Resource Allocation In Heterogeneous Wireless Networks

The rapid development of smart mobile devices and mobile internet services in recent years has generated an enormous increasing demand in data traffic under the cellular networks. Networks with multiple radio access technologies (RATs) would become the most prevalent features in next generation mobile networks. Under such backgrounds, radio resource management (RRM) study plays a key role for the collaboration and integration of heterogeneous wireless networks (HWNs).In HWNs, there are two different access modes based on whether a single radio interface or multiple radio interfaces of the user equipment (UE) can be used simultaneously for the same service, namely single radio access and multiple radio access. Different access modes will result in different effects on the integration of HWNs, especially in RRM. Due to the divergences in access modes, the corresponding radio resource allocation algorithms can be classified in two categories:algorithms using a single radio interface of each UE at any time and algorithms utilizing multiple radio interfaces of each UE simultaneously. Based on different access modes, this dissertation mainly focuses on user association and resource allocation problems in HWNs, considering different application requirements and objectives.To tackle the user association and resource allocation problems in single radio access based HWNs, this dissertation presents a proportional fairness based user association and resource allocation mechanisms in cellular and WLAN coexisted network. For computational simplicity, we assume that the WLAN uses a resource reservation protocol to avoid channel contention collisions. Hence, the resources of WLAN are modeled as time slots. Then, we mapped the resources of cellular and WLAN networks to achievable rate region. The system sum-rate maximization problem under proportional rate constraint is formulated, which is non-convex and hard to obtain the optimal solution. We decompose the problem into two sub-problems:user association and resource allocation. By relaxing the constraint and solving the problem, we get a deduction that the user association scheme is related to the user’s rate ratio between different networks. Based on this, a low complicity algorithm is proposed. For a given user association scheme, the resource allocation scheme can be derived by exploiting the structure of the problem. Simulation results show that the algorithm can guarantee the fairness among users effectively and has the flexibility to control the system resources allocation among different users.To solve the user association and resource allocation problems in multiple radio access based HWNs, this dissertation investigate the radio resource allocation problems considering minimum-rate requirement of users in cellular and WLAN coexisted network. The optimization problem is formulated considering the main features of Orthogonal Frequency Division Multiple Access (OFDMA) based cellular network and IEEE802.11distributed coordination function (DCF) based WLAN network, which is non-convex and difficult to solve directly. To make the original problem tractable, we divided it into three sub-problems:a) user association, b) subcarrier allocation, c) power allocation. Suboptimal heuristic algorithms are proposed for user association and subcarrier allocation, and the optimal power allocation solution is obtained by using Karush-Kuhn-Tucker (KKT) conditions. Simulation results show that our proposed suboptimal algorithms can achieve considerable gains over other schemes.