The Research Of Relay Selection Mechanism In Multi-Hop Cellular Networks

With the rapid development of mobile communication network technology, people’s demand for communication is increasing day by day. Therefore, the next wireless communication system should provide higher transmission rate, more system capacity, larger coverage area, smoother compatible performance, and the communication mode for all these users in different QoS (Quality of Service) requirement flexiblyMulti-hop cellular network is a new type of network which combines the traditional cellular network with Ad Hoc network. It retains the concept of cells in the traditional cellular network. At the same time it introduces the technology of multi-hop in the Ad Hoc network, that is, each user can directly communicate with base station or indirectly communicate with base station via relay. Therefore, it can guarantee the QoS of each user, especially the cell-edge users.In multi-hop cellular networks, relay selection is a very important research subject. How to select a best relay from many potential relays to achieve the optimal of system throughput or other performances through the effective use of system resources has became an issue of concern. Therefore, this dissertation presents deeply studies to the relay selection mechanism in multi-hop cellular networks. The main contributions of this dissertation are as follows:(1) Proposes LTE-based multi-hop cellular networks with out-of-band relaying and analyzes the effect of802.11peer link on relay selection and system capacity.In multi-hop cellular networks, the system capacity is restricted by direct link and peer link in theory. Because the transmission rate of3G system is much lower than that of802.11b, most previous research assumed that the achievable system capacity was determined only by that of cellular air interface, and the802.11air interface capacity did not constrain the capacity of the system. However, the transmission rate of LTE access technology has been greatly improved, so the system capacity of LTE-based multi-hop cellular networks with out-of-band relaying should consider both the direct link and peer link. In the model of this dissertation, the restriction of peer link is reflected in the probability of relay selection. The probability of relay selection is decided by two aspects:one is the number of idle mode users in relay area; the other is802.11channel competitions. Combined these two points, we can obtain the probability of relay selection of the outer ring users. Then we take it to the analysis of the inter-cell interference which can be divided into three types. Finally, we analyze the impact of the inner circle radius and the peer link transmission distance on the system performance through simulation.(2) Proposes a relay selection mechanism and analyzes how to minimize the battery energy loss of the nodes in the case of single-node and multi-node relay selection in multi-hop cellular networks.In many application scenarios of multi-hop cellular networks, the node energy is supplied by batteries, such as some isolated relay station far away from the power supply or peer users in multi-hop cellular networks, and so on. In these scenarios, reducing the battery energy loss of nodes can ensure the long uninterrupted data interaction in networks and reduce the supplement of batteries. Therefore we need a relay selection mechanism to ensure minimum battery energy loss during data transmission. In this dissertation, we introduce the nonlinear discharge mode of battery to the multi-hop cellular networks and obtain the relation of outage probability and transmission power through the analysis of the two-hop outage probability. Then we analyze the two-hop energy loss, and minimize the battery energy loss through the power allocation in the case of the constraint of outage probability. After that, we analyze the multi-node relay selection mechanism on this basis. We model it as a non-equilibrium assignment problem with constraint conditions and propose a minimal element adjustment method to solve the problem.(3) Proposes two mobile-based relay selection mechanisms which can increase the relay activation time and reduce the impact of relay switchings on the system performance.In multi-hop cellular networks, due to the mobility of mobile nodes, inappropriate relay selection may cause frequent relay switchings which will bring complexity measure, frequent initialization, synchronization, delay and outage problems to deteriorate the overall performance. Few of previous schemes consider mobility problem which will introduce frequent relay switchings, but pursue improvement of throughput or energy loss only. Considering the importance of this problem, this dissertation takes note of it. Firstly we analyze the conditions of relay switchings in multi-hop cellular networks, and give the expressions of the relay switching rate and the relay activation time. Then we propose two mobile-based relay selection mechanisms which can reduce the relay switching rate and increase the relay activation time. Finally, we evaluate the proposed mechanisms through simulation and analyze the effects of various parameters (e.g. inner circle radius, peer link transmission distance, speed, average service time of call, number of MNs and so on) on system performance.