Research On Key Technologies Of Relaying For Ultra-High-Speed Millimeter Wave Wireless Communication Networks

With the rapid development of communication technology, the demands for ultra-high-speed wireless multimedia applications are increasingly stronger and stronger. However, the existing wireless communication technologies, which are working on the bands below lOGHz, and dedicated to information transmission with megabits per second data rate, is rather difficult to meet the requirements of quality of service. In addition, there are a lot of existing traffics on the current microwave frequency bands, which result in the abnormal congestion of spectrum resources, and serious co-channel interferences. Thus, the 30-300GHz millimeter-wave bands, which has not yet been of fully developed and utilized, are bound to become the most promising and ideal candidate carrier frequency for the next generation of ultra-high-speed wireless air interface. In particular,60GHz band has been widely concerned by academic and industry fields due to its feature of up to 5-7 GHz continuous license-free bandwidth. However, 60GHz radio is just among one of the atmosphere absorbing "windows", and its ability of penetrating solid objects is poor, that would severely limit the transmission distances, or could easily deteriorate the communication qualities, and even induce transmission interruptions. Fortunately, the cooperative relaying, which is based on multi-hop styles, is recognized as an efficient way to compensate the path loss of radio wave, therefore, the robust transmission technologies of 60GHz millimeter-wave wireless communication networks with cooperative relaying can achieve ultra-high-speed transmission efficiently. It’s necessary to note that cooperative relaying technologies for microwave bands below 10GHz are no longer applicable for the 60GHz wireless communication systems due to the new application scenarios and new challenges of hardware costs. As the core technologies of cooperative relaying systems, relay selection, power allocation and beamforming have become important problems to be solved.Based on the cooperative systems with styles of amplitude-and-forward and decode-and-forward, and antenna configurations of single antenna element and antenna array, this dissertation investigates the features of 60GHz millimeter-wave wireless communication systems, and study the relay selection, the power allocation and the designing of beamforming weighted vectors. The main research works and innovative achievements are as follows:(1) To enhance the performances of 60GHz millimeter-wave wireless local area networks/wireless personal area networks (WLANs/WPANs) in the scenarios of constitude of both direct transmissions and cooperative relaying transmissions, a single relaying station selection algorithm, which aims to maximize the data transmission rate, has been proposed. The algorithm can distinguish between the direct and cooperative relay links through the mechanism of channel state information reporting during the beam training phase. With different targeting data rate thresholds, both theoretical analysis and simulation are carried out to evaluate the performances of average system capacities and outage probabilities. Simulation results show that the proposed algorithm can effectively exclude candidate relaying stations which are on the non-line-of-sight (NLoS) paths, expands the channel capacity of the whole network, and enhances system robustness.(2) To satisfy the requirements of user experience of 60GHz millimeter-wave multicast traffics, a scheme which can minimize the maximum sum of power of source & relay stations in the common multicast group, under the constraints of all the outage probabilities of all the links among the multicast group, and all source-relay link transmit power constraints, is proposed, and the optimization model of joint relay selection and power allocation has been formulated. In this algorithm, the beam training protocol with function of overhearing and mechanism of 1-bit channel amplitude information feedback are designed. The influence of signal-to-noise-ratio thresholds to the system performances on both power saving and outage probabilities with different parameters were compared by simulations. Simulation results show that the proposed algorithm can effectively guarantee the fairness of a common multicast group users, and greatly improve the system performances on power saving and outage probability.(3) To overcome the shortcomings of intolerable delay of the beam training protocols suggested in IEEE 802.11ad and IEEE 802.15.3c standards, a low-latency and low-power joint transceiver beam switching optimal algorithm is proposed. The proposed method is based on cooperative relay network architecture, and the optimal beam indexes can be flexiblely found after the best sector indexes are acquired, thus, the flexibility of beam searching precision is enhanced. The iterative performance is enhanced by the way of setting effective initial values, and the number of searches is reduced by direct searching for optimal beam, which can improve the efficiency of searching, thus, the method of two-stage global optimal beam searching can be realized. Simulation results show that, compared with the beam training protocols suggested in the IEEE 802.11ad and IEEE 802.15.3c standards, the proposed algorithm can be more effective in reducing the beam search delay, computational complexity, system processing power consumption, enhancing flexibility of the algorithm, and robustness of the system.(4) To achieve high antenna gains and low cost of hardware of transceiver in 60GHz millimeter-wave WLANs/WPANs, a cooperative relay system applicable analog and digital hybrid beamforming protocol is proposed. The protocol is based on the asymmetric structures of transceivers between small mobile devices and a large fixed relay station, and iterative approach is applied to beam training, thus, the beam steering vectors of user devices and the analogical component of the hybrid beamforming of the relay station can be obtained. Thereafter, the relay station obtains the optimal analog and digital hybrid beamforming weighted vectors by further digital signal processing. The adaptivity of this proposed algorithm is greatly enhanced by online decision. Simulation results show that the proposed algorithm can achieve fast convergence, full coverage by transceiver beams, and improve the system spectrum efficiency.