Resource Allocation In Wireless Relaying Networks

With the increase of requirements for communication anywhere and anytime, novel communication technologies develop successively. Relaying technology, as a new archi-tecture, enlarges communication coverage, enhances the quality of the communication link, and reduces the transmission power at a relatively lower cost. Thus, it has received significant attention from both the academic and industrial fields. The resource allocation plays an important role for improving system performance (like transmission rate) in the traditional one-hop wireless network with a limited amount of resource. However, while the introduction of relaying technology brought some benefits, it complicated resource al-location at the same time. As such, the problem concerning the relaying technique must be reconsidered due to the property of the two-hop link. As there has been little work done in this area, this dissertation will focus on resource allocation in the relay-based network as the research direction.First, the design of existing resource allocation schemes are always based on some ideal assumptions. For example, it is assumed that the length of time slot for the source and relay nodes is equal; and that the relay node is reliable anytime. Although these simplified models make the design and analysis much easier, they also incur inevitable deviations from those in realistic scenarios. Secondly, the problem of inter-cell interfer-ence caused by the universal frequency reuse factor is becoming increasingly significant. The influence of inter-cell interference on resource allocation is a problem awaiting res-olution-the impact of the inter-cell interference on the joint mode/route selection and power allocation, for example. Finally, the influence of mobility on resource allocation still remains to be explored for better understanding. Examples of issues that need to be addressed include means of reducing the influence of mobility on inter-relay handover and methods of maximizing benefits by means of mobility utilization.The asymmetry time slot allocation based transmission route selection problem is formulated as a convex optimization problem and analyzed in the aspect of performance gain. In this model, a joint time slot allocation and transmission route selection scheme is provided. Through simulations, it is verified that transmission rate can be improved greatly. Subsequently, this dissertation formulates the trust-based relay selection problem as a restless bandit problem, where the trust of a relay node is considered. The optimiza-tion problem is solved by applying the dual decomposition method. To facilitate practical implementation, the priority-index heuristic method is employed for this problem. Sim-ulations are conducted to demonstrate the effectiveness of the proposed trust-based relay selection scheme.Secondly, this dissertation investigates the resource allocation scheme in the pres-ence of the inter-cell interference. Based on the defined transmission range and interfer-ence range, a transmission route selection and power allocation is offered in the multi-cell environment. The transmission link with the maximum capacity is chosen for each cell. An interference table is established based on the chosen link in each cell. According to the interference table, the transmit power is reduced to mitigate the interference by using minimum power allocation or adaptive power allocation. Next, considering accumula-tion of the multi-cell interference, a two-step resource allocation method is proposed to combine the transmission mode/route selection and power allocation problem, where the transmission mode/route is selected based on the channel state and inter-cell interference; given the selected transmission mode/route, the power allocation problem is formulated and solved by using geometry programming. In order to further reduce the overhead a-mong cells, a heuristic and distributed resource allocation scheme is provided based on the asymptotic analysis of the system transmission rate for easy implementation. A num-ber of simulations demonstrate that the proposed method could evidently improve the system performance.The influence of user mobility on resource allocation cannot be ignored. The hand-off decision caused by the movement of the user is formulated as a semi-Markov decision process for maximizing the transmission rate while reducing the handoff overhead. Based on the relationship between signal-plus-noise ratio (SNR) and speed, the state transition matrix of the SNR of the transmission channel in semi-Markov decision process is derived theoretically as a function of the moving speeds of the user. In terms of the definition of the overhead, the inter-cell and intra-cell overhead is incorporated into the reward func-tion of the Markov model. The optimal strategy is then obtained using the value iteration algorithm. The implementation issue is discussed based on this algorithm. By simulation, the best transmission rate can be attained with a little overhead cost. Next, an adaptive carry-store forward (ACSF) scheme is proposed to select an idle user as a relay in this dissertation for reducing the communication outage time of a target user. To keep the target and the relaying node having continuous communications in the uncovered areas, the relay should carry and store, in advance, a sufficient amount of data that are destined to the target node, and the moving speed of the target node can be adaptively changed according to the relay. The optimum moving speeds of the target node are formulated as a convex optimization problem. When multiple candidate nodes are available, the one with the minimum communication outage time is selected as the relay. Numerical re-sults demonstrate that the proposed ACSF scheme can greatly reduce the communication outage time.