Resource Allocation And Scheduling Strategies For Wireless Multi-Hop Relay Networks

The multi-hop relay network with the orthogonal frequency multiplexing (OFDM)/orthogonal frequency multiple access (OFDMA) and relay technologies has many advantages, such as high spectral efficiency, coverage enhancement, low energy consumption, flexiable and low cost networking, and so on. which has regarded as one of the mainstreams of the network architecture of the next generation mobile communications. Because of the superiority, it has always been viewed as the promising network architecture of the next generation mobile communications. However, this novel network architecture has to face the more complex radio environment and the serious challenges about the radio resource management in comparison with the traditional cellular networks, which focuses on two main aspects:i) the traditional resource allocation problem is derived from the traditional simple dimension such as time domain, frequency domain or space domain to multi-dimensional direction, causing the corresponding resource allocation strategies can not be directly applied to relay networks, which greatly increases the complexity of resource allocation and the signaling overhea; ii) with the rapid growth of wireless traffic volume and the deployment of the great many low power relay, the energy consumption has experienced the significant increase, which can take away more than half of the energy consumption for all equipments. Unlike the researches only focus on the throughput enhancement previously, more and more researchers begin to study how to improve system efficiency to save energy under the conditions of satisfying the basic quality of service (QoS) requirements, with the emergement and development of "green communication" notions. Therefore, by taking the system energy-saiving as the main target, this dissertation investgates the key technologies of the wireless resource management for the OFDM/OFDMA-based wireless multihop relay networks, including path selection, packet scheduling and resource allocation.Firstly, two optimal energy-efficient path selection schemes, which are used for the OFDM system with amplify and forward (AF), as well as decode and forward (DF), are proposed respectively. According to the analysis of the impact of circuit power consumption, user rate requirements, bandwidth and other factors which have the effect on system energy efficiency for the path selection, two optimal energy-efficient path selection criteria based on equivalent path loss exponent are proposed respectively for both AF-mode and DF-mode relay OFDM systems by converting the fading values of relay and direct links into the equivalent path loss values.. The analysis results show that the optimal energy-efficient transmission path is determined by the factors of data rate, channel conditions and bandwidth, and satisfies the decision criteria of the optimal energy-efficient path proposed in this dissertation, based on which the three node DF relay transmission scenario is extended to relay OFDMA cellular downlink transmission system with multile users and multiple relays. Considering the circuit power consumption and fixed user rate demand conditions, a low complexity suboptimal algorithm for joint path selection, subcarrier and power allocation is proposed to maximize energy efficiency of the system. The analysis results indicate that the proposed path selection scheme can improve system energy efficiency significantly compared to the traditional schemes.Secondly, under the constraints of the minimum rate and the total transmission power, a joint optimal energy-efficient resource allocation scheme with the subcarrier pairing and power allocation is proposed for the case with a three-node OFDM-based DF-mode relay link,. Moreover, the proposed scheme considers the effect of the circuit power consumption on the system energy efficiency. As this problem is a non-convex optimization problem, of which the complexity is too high to be soloved, a case discussion method is introduced. Thus the non-convex optimization problem can be converted to a convex optimization, where the uniqueness of the optimal solution for the system energy efficiency is proved. Then, by using Lagrange multiplier method, KKT condition, and water-filling algorithm, the optimal solution of the system energy efficiency and power allocation results can be obtained. The analysis results show that, compared with the optimal energy-efficient power allocation strategy with the fixed subcarrier pairing, the proposed scheme can further improve the achievable data rate of the relay link and the energy efficiency. In addition, by comparing with the traditional optimal water-filling algorithm of the rate maximization or power minimization, the proposed scheme can adaptively allocate resources under the constraints of the total transmission power regulated by the system and the user data rate requirements to obtain the global optimal solution with lower complexity and ensure the reliability of link transmission.Thirdly, considering a more realistic scenario with the maximum power constraints of source node and relay node, a joint optimization scheme of subcarrier pairing and power allocation is proposed. Besides, in view of the constraints of circuit power consumption and the minimum user rate requirement, a joint optimization model of the subcarrier pairing and power allocation is formulated to obtain the optimal energy efficiency of the system. By converting the non-convex optimization problem to the the convex optimization problem, a case discussion method is proposed to solve this optimization problem and obtain the optimal solution using water-filling algorithm. The analysis results show that, the proposed scheme can adaptively allocate the resources under various constraints and achieve optimal energy efficiency of the system, which can also guarantee the transmission reliability and reduce the link outage probability as well as the algorithm complexity.Fourthly, for two-hop relay cellular OFDMA downlink transmission systems, an adaptive energy-saving-related packet scheduling scheme is proposed. In order to take the comprehensive factors, such as the differences between the QoS requirements for different types of services, status of packet queues, and the energy efficiency of links, into account, a proposed scheme design a priority factor of packet scheduling. On the basis of this, an adaptive packet scheduling strategy is put forward to balance the proportion of the occupied slots between the access zone and transparent zone, and reduce the probability that the packets in the packet queues of relay users cannot be timely scheduled which results from the imbalance of the proportion of leftover slots between the access zone and transparent zone, and further improve the utilization of system slot resource. The analysis results show that, the proposed scheme can satisfy the QoS requirements of the different types of services and ensure the fairness among user. Furtherly, it can reduce the energy consumption of the system under guaranteeing the system throughput performance.Lastly, with respect to two-hop relay OFDMA cellular downlink transmission systems, a semi-distributed adaptive packet scheduling scheme is proposed, by which the QoS requirements of real-time (RT) traffic and non-real-time (NRT) traffic can be distinguished.. To guarantee the QoS requirements of RT traffic and obtain certain scheduling opportunities for NRT traffic, a modified proportional fair scheduling priority factor is designed, which can distinguish the traffic types. In order to reduce the signaling overhead of relay transmission systems, an adaptive slot reallocation triggering mechanism is proposed, in which the slot reallocation process is determined whether it could be triggered by comparing the defined satisfaction factors in BS and RS with the given priority factor in advance.. Once the time slot reallocation is triggered, the scheduler in BS will timely adjust the proportion of bandwidth allocating to BS and each RS according to the requested slot number of BS and each RS. The analysis results show that, the proposed semi-distributed packet scheduling strategy is capable of improving the system throughput, meeting the QoS requirements of users, ensuring the fairness among users, modetating the signaling overhead of the system, and effectively reducing the handover packet loss rate of the relay users.