The Research Of Key Technologies For Cooperative Relaying Transmission In Mobile Communication Systems

With increasing demands for mobile services, mobile communication system is experiencing a significant development to support high-data-rate with very diverse quality of service requirements, broadband and low cost. The development of the 4th Generation technologies not only requires the evolution of PHY technologies, but also brings new challenges to the traditional network architecture. And the cooperative relaying network structure, which can greatly improve the system performances, provides new methods for the development of mobile communication systems.On the basis of new trends in mobile communication systems and the research of scholars in this hot area, this dissertation investigates on some key technologies for cooperative relaying in the next generation mobile networks, which include cooperative relay selection scheme, user cooperation stimulating strategy, random access scheme, load balancing algorithm and interference mitigation schemes. The main contributions of this thesis include following aspects:Based on the QoS requirments of the current users and aimed at the maximization of the system capacity, the optimal distance and transmission time from the source to relay under DF forwading mode are derived. Meanwhile, the impact of these two parameters on the system performance is analyzed. To answer the question of "to whom to perform cooperation", a hybrid cooperative relay selection algorithm (HCRSA) is then presented for relay based cellular networks. According to current user density, HCRSA will be adapted selectively between two different cooperation schemes. These are realized either between the parallel transmission between the base station and a relay node or by adopting parallel transmission between another mobile terminal and the relay node. The proposed scheme can fully utilize cooperative communication, so as to increase effectively the user capacity and as to improve system performance as well.A user cooperation stimulating strategy among rational users is proposed. The strategy is based on cooperative game theory, and enacted in the context of cooperative relaying networks. Using the pricing based mechanism, the system is modeled initially with two nodes and a Base Station (BS). Within this framework, each node is treated as a rational decision maker. To this end, each node can decide when to cooperate and how to cooperate. Cooperative Game Theory and Nash Bargaining Solution are introduced in order to present an optimal system utility as well as provide fairness among users. Under different cooperative forwarding modes, certain questions are carefully investigated, including "what is each node's best reaction to maximize its utility?" and "what is the optimal reimbursement to encourage cooperation?" The proposed strategy brings benefits to the nodes in terms of utility, and thus justifies the fairness between each user.An adaptive random access strategy is presented for multi-channel relaying networks. In the proposed scheme, Non-Real-Time (NRT) services access the Base Station (BS) by first accessing the nearest Relay Node (RN). When collision occurs, for the sake of fast and efficient access, the user will begin a frequency domain backoff rather than randomly retry in time domain. A remarkable feature of this scheme is that the RN will adaptively determine the maximum allowed frequency backoff window at each access period. This is achieved according to the new arrival rate as well as the number of available access channels. Moreover, to alleviate the interference caused by sub-channel reuse among RNs, a fractional frequency reuse scheme is also considered. The proposed algorithm improves random access procedure while making use of resource more efficiently. As for the traffic congestion issue in the cooperative relaying networks, an effective relay based load balancing scheme, employing traffic transferring and channel borrowing, is present for two-hop cellular relaying networks. In the proposed scheme, each relay station is allocated a set of real-time traffic channels so as to perform call relaying from a congested cell to another non-congested cell. Moreover, owing to the limited capacity of each relay station, dynamic channel borrowing is adopted to further facilitate load balancing between neighboring cells. With two different relay deployment scenarios considered, a multi-dimensional markov chain model is then developed to evaluate the performance of the proposed scheme. The proposed scheme achieves better performance in terms of call blocking rate, and thus improves system performance.A novel method of interference coordination for cell-edge users in cellular relaying networks is proposed. Firstly, all available frequency resource in each cell is divided into two parts. One part is allocated to users directly communicate with BS, and the other is especially reserved for users connected to BS through two-hop RNs. Furthermore, for the sake of taking system throughput as well as fairness into account, a dynamic score based scheduling strategy is designed for the two-hop users. The proposed strategy performs better on the cell throughput and the SINR of cell-edge users, and with adaptive weights, the GoS of users can also be guaranteed.A summary is given at the end, where the future research directions related to this doctoral thesis are also pointed out.