The Research On Resource Management In Imt-Advanced Heteregeneous Wireless Networks

Recently, with the development of mobile internet and cloud computing technology, users’demand of data service has a trend of exponential growth, in which most of the service occurs indoor. The main challenge for cellular networks is the contradiction between the growth of the mobile data traffics and the scarcity of spectrum resources. To satisfy the users’demand, especially the indoor users’requirement, low power access point can be introduced to the cellular networks, which has the shorter distance with user, can enhance the coverage, reduce the coverage hole, improve the spectral efficiency and can offload the macrocell’s traffics. The low power access point, including the femtocell base station (FBS), relay station (RS) and picocell base station (PBS), together with the macrocell base station (MBS), forms the IMT-Advanced (IMT-A) wireless heterogeneous networks (HetNet). Due to the different networking mode and access method, the low power access point also introduces some problems, such as co-channel interference, the failure of mobility handovers, physical layer security etc.To deal with the problems above, we do some research on Orthogonal Frequency Division Multiple Access (OFDMA) HetNet, including the interference mitigation, resource allocation, mobility management and physical layer security. We also propose some algorithms, which aim to improve the spectrum efficiency and system performance. The main work and innovation can be summarized as follows:1. The research on interference mitigation in two-tier femtocell HetNet. We investigate the uplink resource allocation problem of femtocells in co-channel deployment with macrocells condisdering the characteristics of channel fading and cross-tier interference. We first model the uplink power and subchannel allocation in femtocells as a non-cooperative game, where inter-cell interference is taken in to account in maximizing the femtocell capacity and uplink femto-to-macro interference is alleviated by charging each femto user a price proportional to the interference that it causes to the macrocell. Based on the non-cooperative game, we then devise a semi-distributed algorithm for each femtocell to first assign subchannels to femto users and then allocate power to subchannels. Simulation results show that the proposed interference-aware femtocell uplink resource allocation algorithm is able to provide improved capacities for not only femtocells, but also the macrocell, as well as comparable or even better tiered fairness in the two-tier network, as compared with existing unpriced subchannel assignment algorithm and modified iterative water filling-based power allocation algorithm.2. The research on resource allocation in two-tier femtocell HetNet. To cope with the problem in heterogeneous QoS, we investigate the resource allocation problem in both uplink and downlink for two-tier networks comprising spectrum-sharing femtocells and macrocells. A resource allocation scheme for co-channel femtocells is proposed, aiming to maximize the capacity for both delay-sensitive users and delay-tolerant users subject to delay-sensitive users’QoS constraint and the interference constraint imposed by the macrocell. The subchannel and power allocation problem is modeled as a mixed integer programming problem, and then transformed into a convex optimization problem by relaxing subchannel sharing, and finally solved by the dual decomposition method. Subsequently, an iterative subchannel and power allocation algorithm considering heterogeneous services and cross-tier interference is proposed for the problem using the subgradient update. We also develop a practical low-complexity distributed subchannel and power allocation algorithm to reduce the computational cost. The complexity of the proposed algorithms is analyzed, and the effectiveness of the proposed algorithms is verified by simulations.3. The research on mobility management in two-tier femtocell HetNet. To deal with the traditional inaccurate handover decision schemes, a handover optimization algorithm based on the UE’s mobility state is proposed. An analytical model was presented for the handover signalling cost analysis. Numerical results are provided to compare the signalling cost of different handover management schemes. Considering the potential frequent mobility between HeNB-HeNB and HeNBeNB, HeNB mobility enhancement is proposed as one of the most important work items in3GPP LTE-Advanced. Four X2interface based HeNB mobility enhanced architectures are explicitly discussed in terms of signalling overhead evaluation. To cope with the problem of Radio Link Failures (RLFs) and Unnecessary Handover, this thesis proposes a mobility robustness optimization approach based on Ant Colony Algorithm in the femtocell networks.4. The research on secure resource allocation in two-way relay networks. In this thesis, we consider the problem of secure resource allocation in orthogonal frequency division multiple access (OFDMA) two-way relay networks considering the presence of an eavesdropper. The joint subcarrier allocation, subcarrier pairing and power allocation problem aims to maximize the secrecy capacity for legitimate sources subject to limited power budget and orthogonal subcarrier allocation constraints. The optimization problem is modeled as a mixed integer programming problem, and then solved in an asymptotically optimal manner based on the dual method. Moreover, optimizing one domain resource allocation while given the other two-domain resource allocation, a suboptimal algorithm is proposed to reduce the complexity. Simulations are conducted to evaluate the effectiveness of the proposed near optimal and suboptimal algorithms.