High Efficient Adaptive Resource Allocation And Optimization For Wireless Heterogeneous Networks

In the next generation communication networks, heterogeneous networks consisting of macro stations and low power stations, such as relay stations and pico-stations, have drawn tremendous attention due to its high capacity and extensive converge. In the past few decades, most of research has focused on improving throughput and frequency spectrum efficiency through designing different network architecture. However, the increasing data rate and ubiquitous access requirements lead to the sharp expansion of network infrastructure, which brings the huge energy consumption. Besides, the introduction of low power stations increases the more energy consumption due to the additional circuit power of stations. Therefore, the energy efficiency problem of heterogeneous networks becomes serious. How to obtain the high energy efficiency while guaranteeing the quality of service (QoS) of all users in wireless systems, is the development trend of communication technology. This dissertation researches on the radio resource allocation of downlink under the time domain, frequency domain and power domain. The dissertation optimizes the algorithms on relay selection, interference coordination, resource scheduling and allocation in order to obtain the higher the spectral efficiency or the higher energy efficiency of whole system, which can be elaborated as follows:Firstly, a dynamic resource allocation scheme in adaptive frequency reused OFDMA-relay system based on AMC technology is proposed. In this algorithm, relay nodes have two independent antennas and operate in DF and full-duplex mode. It improves the utilization of time domain resource. Moreover, this algorithm uses the characteristic of the AMC-based system, which can tolerate some interference. Then the subcarriers are reused by BS and RSs to increase the spectrum efficiency and further improve throughput. The adaptive frequency reused algorithm with two independent antennas RS improves the system throughput compared with the orthogonal frequency allocation with single-antenna model, and adaptive frequency reused algorithms with single-antenna RS.Secondly, based on a set of discrete modulation levels in AF relay system, a joint optimization of relay selection and resource allocation under rate requirement is formulated to minimize the system transmit power consumption for promoting energy efficiency. The two-step algorithm of the problem includes a simple relay selection method and resource allocation method. The two-step solutions are based on power saving and virtual direct transmission respectively. This algorithm can reduce the dimensionality and simplify the resource allocation of relay networks. Besides, the RSs with power constraint are also considered, so the subcarriers on overload RSs are adjusted according to the result of the joint optimization. Through the analysis of simulation result, it shows that the suboptimal target could be achieved, which is very close to the optimal one. Also, the proposed relay selection algorithm decreases the power consumption compared with the traditional relay selection algorithm.Thirdly, based on a fixed set of discrete modulation levels in an OFDMA relay system, a dynamic resource allocation (DRA) subject to rate constraints is combined with the idea of opportunistic network coding to minimize the total transmission power in a frame. By taking the characteristic of a half-duplex DF mode relay, a solution is proposed for the optimal problem of each subframe after separating power-aware relay selection. The power aware relay selection in the proposed solution makes more users choose relay transmission, which provides more opportunities for network coding, then can save more resources. DRA with opportunistic network coding can save more system energy consumption compared with DRA with static network coding and DRA.Fourthly, under OFDM-based frequency-selective channel of DF relay link and AF relay link, two optimal energy efficient allocation methods are proposed, respectively. Both methods prove the existence of the unique optimal solution and consider the impact of circuit power on energy efficiency. In allocation method of DF relay link, the transmit power in each hop is adaptively allocated to maximize the energy efficiency. This proposed method of DF relay link can achieve the highest energy efficiency while ensuring the high data rate. In allocation method of AF relay link, the proposal includes two steps. First, a suboptimal subcarrier matching is achieved for introducing a virtual direct link. According to the result of subcarrier matching, the allocation problem of relay network is simplified as that in traditional cellular network. Then, the optimal power allocation of virtual direct link can be obtained by one dimensional search method. This suboptimal solution of the proposed algorithm of AF relay link is very close to the optimal solution. Besides, the effects of the rate and power constraints on energy efficiency are both analyzed in the methods of DF and AF relay link.Fifthly, in order to maximize the total energy efficiency of Amplify-and-forward relay downlink system, a joint relay selection and power allocation is proposed with the circuit power of the system. Due to the precondition of reducing the computational complexity, a step-by-step suboptimal allocation scheme is provided. The virtual direct channel gains are adopted for converting relay system to the single hop system, and relay selection scheme is achieved. Then, the power allocation could be solved by convex optimization. The solution of the proposed suboptimal scheme approaches the optimal one. Besides, in order to accommodate different user distributions, a resource allocation scheme based on cell zooming is proposed, which is adaptable to different user distribution and further improves the total system energy efficiency.At last, based on low power (LP)-ABS, a joint optimization of power allocation of ABS (called dynamic LP-ABS) and resource allocation is proposed to maximize the total throughput. The proposed algorithm takes into account the power allocation of ABSs in the marco-eNB, the ABS partition and the UE association in all cells. Simulation results show that dynamic LP-ABS can effectively increase system throughput compared to the fixed LP-ABS and zero-ABS.