Cooperation And Optimization Of Resource Allocation For Wireless Multi-Hop Relay Networks

In the next-generation wireless communication networks, orthogonal frequency division multiplex access (OFDMA) has been the main multiple access technology for B3G and4G networks for providing high spectral efficiency through dividing the band into a number of orthogonal subcarriers. This is due to the fact that OFDMA has the ability to combat frequency-selective fading so as to avoid inter-symbol interference (ISI). Relay technology is able to provide high data rate and extend the high data rate coverage to the edge of cell. The users under unfavorable channel conditions can select a relay station (RS) for forwarding their data information to the base station (BS) to maintain the quality of service (QoS). The key technologies to support OFDMA wireless relay networks become researce hotspot in recent years. Besides, the response to the global climate change is becoming a major issue related to the national economic and social development, low carbon economy, and the energy conservation has become the focus attention of the world. The research for wireless communication technology in the past years pay little attention to the goal of energy saving, therefore, for OFDMA wireless relay networks, this dissertation investgates the cooperation and optimization of spectrum resource and power resource for the key goal of system energy saving.Firstly, in relay-enhanced OFDMA networks, the sub-carriers are not only allocated to the link from BS to MS, but also to the link from BS to relay station (RS) and from RS to MS. The spectrum needs to be reorganized to make it effectively used on the three links.The optimization goal of related work is throughput maximization according to link load and interference situation. To maximize energy-efficiency, we propose an energy-efficiency spectrum planning scheme, which considers the users’data rate requirement, the channel quality and interference situation. The energy-efficiency spectrum planning problem is formulated in OFDMA relay networks based on the discrete adaptive modulation and coding scheme (AMC) in practice system, which is solved by integer programming of optimization theory. The results of the analysis show that the proposed scheme consumes less energy than other spectrum planning scheme to transmit the same bits, and has strong adaptability to the scene with non-uniform user distribution.Secondly, for load imbalance or hotspot coverage wireless relay network, we propose an adaptive load balance based relay selection and spectrum transition joint scheme. We propose an interference capacity of the stations, which reflects the interference to the surrounding co-channel stations. The interference capacity provides a quantitative interference metric to the surrounding stations on the capacity of the system. When a user is required to access the system, the system chooses a preferred access station and an alternative access station for the user according to the channel quality. If the preferred access station is overloaded and does not have enough resources for the user, we compare the performance between accessing to the alternative station and accessing to the preferred station with spectrum transition from other stations in the same sector, and choose a better way to maintain the good system performance. The results of the analysis show that the spectrum efficiency and blocking probability of the proposed scheme in the center cell are superior to that of the independent relay selection scheme and the independent load balance based spectrum transition scheme, and the average interference capacity of the proposed scheme is the lowest, which has less impact on the performance of the surrounding stations.Thirdly, for non-full-buffer traffic, to ensure the users’quality of service, a generalized model for energy saving resource allocation issue, which dynamically allocates time-domain, frequency-domain resources and power resource, is established. Due to the strong flexibility and adaptability, the model may apply to not only the fixed time-domain allocation system, but also the non-fixed time-domain allocation system, which is sovled by using the Lagrange multiplier algorithm. Taking into account the complexity of the algorithm, a simplified resource allocation strategy is proposed by using the Hungarian method. The theory and simulation results show that the optimal algorithm can get the energy-efficiency maximization, and the energy-efficiency difference between the simplified algorithm and the optimal algorithm is less than5%, however, the complexity has been significantly reduced. Moreover, the dynamic time-domain allocation has more adaptive in uneven user distribution or link distribution than fixed time-domain allocation.Fourthly, different from allocating resources for users in recent works, before resource allocation a scheduling scheme is carried out to assign different priorities to the packets in the queue to guarantee the fairness and better system throughput. To minimize the energy consumption, the time domain, sub-carriers, bit and power resource allocation problem is formulated in OFDMA relay networks, while the optimal solution is given in this paper. However, an simplified efficient algorithm is proposed based on decomposing the original optimization problem into three subproblems. In power constraint system, when the number of users is less and the resources are sufficient, all the packets in the queue can be transmitted in a resource allocation time cycle, and the proposed energy saving resource allocation algorithm may reduce the system energy. When the number of users is lager and the resources are not sufficient, the system will serve for the packets as much as possible using the maximum transmission power, the scheduling scheme can guarantee the fairness and better system throughput with power constraint. The results of the analysis show that the energy consumption of proposed scheme is quite close to that of optimal algorithm. Because the proposed resource allocation algorithm is based on the packets queue, we also propose a novel user scheduling scheme, which considers the relay selection results and the service types. Simulation results show that the system throughput of proposed scheduling scheme is larger than that of PF, while its fairness index is close to that of PF.Lastly, this dissertation investigates the virtual MIMO pairing scheduling scheme which groups two user equipments (UEs) with individual antenna to construct a2×2VMIMO channel communicating with a base station (BS) with two receive antennas simultaneously in the uplink, and proposes a novel partly user pairing scheduling based on the SINR threshold combined with the system packet scheduling scheme, in which not all the active users are served with pairing transmission mode, as a trade-off consideration between high spectral efficiency and good quality of service, the proposed scheme determines a user whether or not using pairing transmission mode according to its SINR. The users with good channel condition can communicate with the BS using pairing transmission mode while do not decline the quality of service, while the users with poor channel condition communicate with the BS using the direct transmission mode to ensure the quality of service. The results of the analysis show that the proposed scheme combined with the Proportional Fair (PF) packet scheduling is able to reach greater system throughput. Moreover, the number of users using pairing transmission mode can be controlled by adjusting the SINR threshold, in real system, we can adjust the SINR threshold according to the usage of system resources to obtain the trade-off between the throughput and the quality of service.