Research On Key Technologies Of Cellular And Ad Hoc Hybrid Networks

The cellular networks in existence are difficult to meet the demands of fast data rate, wide services and high-speed moving of the next-generation mobile wireless networks, due to the limitations of their own network architecture. For improving the faculties of the cellular networks, Ad Hoc network is introduced into the cellular networks to construct the cellular and Ad Hoc hybrid network. In this hybrid network, the advantages of one hop or multi-hops of Ad Hoc network can develop the complementation and coexistence with cellular networks and can improve the performances of the hybrid network. As a result, the cellular and Ad Hoc hybrid network has played an important role in the next-generation wireless mobile network.In the cellular and Ad Hoc hybrid network, the terminals can communicate with each other directly, but not through the Base Station (BS). This kind of network architecture avails the advantages of short distance direct communication. This communication mode is named Device-to-Device (D2D) communication. D2D communiation between terminals (D2D User Equipments), and wireless spectrum resource of the cellular network can be used by D2D communication in the way of overlay or underlay. Therefore, the widely distributed terminals can provide the data service more adaptively and flexibly, and the system capacity can be enhanced accordingly in the hybrid network. With the characteristics of multi-hops of D2D communication, the wireless relay application can be developed. Based on that, the network structure can be refined, and the network coverage also can be expanded. Therefore, the architecture of cellular and Ad Hoc hybrid network can improve the system capacity and quality of service effectively.In this thesis, we study the key technologies of the cellular and Ad Hoc hybrid network, which include the terminal communication mode selection, the relay node selection, the power control and relay node location, and the multi-hop route selection. The main contributions of this study are described as follows:Firstly, the study of terminal communication mode targets at three types of communication mode. They are cellular communication mode, D2D communication (one hop) mode, and D2D communication with relay node mode. In this thesis, based on the analysis of outage probability, the sufficient and necessary condition of not applying one hop D2D communication and the optimal relay node selection standard are deduced. The criterion of employing D2D communication with relay node mode is proposed by comparing the sum-capacity of this mode with that of cellular communication mode on the basis of the optimal relay selection. There are two innovations in this topic.1) Derive out the interference constrained precondition for applying the mode of D2D communication with relay node based on outage probabilities analysis, and the relay node selection standard is provided.2) Derive out the interference constrained criteria of employing the mode of D2D communication with relay node. According to the criteria, the communication mode of D2D with relay node can achieve better sum-capacity performance by comparing with cellular communication mode. Secondly, in the research of relay node selection for assisting the cellular network accessing, the transmission capacities between a cellular terminal and the relay node and that between the relay node and the BS are analyzed, respectively. By constrained the interference from D2D communication to cellular communication, the rule of relay node selection is derived from the transmission capacities analysis. Then, maximizing the hybrid network capacity is summarized as the issue of maximum weight matching of bipartite graph, and the KM algorithm and the greedy algorithm as two types of relay node selection methods are applied to select different relay node for every relay-needed cellular terminal according to the relay selection rule. The innovation in this research part includes deriving the relay node selection rule based on the interference constraining, and using the maximum weight matching of bipartite graph to solve the issue of maximizing the network throughput. The sum-rate can be improved by selecting the relays according to the selection rule, and KM algorithm achieves a slightly higher sum-rate than that of greedy algorithm based on the relay node selection rule. These prove the superior by using the relay node selection rule.Thirdly, the relay node location and power control in cellular and Ad Hoc hybrid network are discussed. Relay node location and power control are the key issues in this hybrid network, which impact on the system performance. In this thesis, we deduce an ergodic capacity formula for the D2D communication users reuse the resource of one primary user in Rayleigh-fading channels, and the formula is used in terms of high signal-to-noise ratio (SNR) and high interference-to-noise ratio (INR). Then, the expressions for optimal relay node location and power control are derived from the deduced formula when the distances among cellular users and D2D communication users are known. At last, an ergodic algorithm for finding the results is given. The innovations in this part of research include that deducing out an ergodic capacity formula in Rayleigh-fading channels, which is used under the conditions of high SNR and high interference and an ergodic algorithm is provided for finding the optimal relay location and power control. Using the algorithm, when the relative distances have been known, the optimal relay location can be determined, and the power of D2D transmitter and the power of relay node also can be calculated, respectively.Lastly, in the study of the multi-hops D2D communication in cellular and Ad Hoc hybrid network, the multiops route is discussed. Considering the channel model in the hybrid network, and the interference range for D2D communication, an expression of outage probability is calculated. Then, that expression is introduced into the multi-hops D2D communication, and two types of algorithm are proposed for route selection. The innovations in this research include the expression of outage probability, and compare two kind of multi-hops route selection algorithm.