Research Of Fast Algorithms In Mobile Communication

With the rapid development of mobile communications and dramatic increase of the numbers of mobile users, it is expected that the new generation mobile communication systems should provide higher date rate, more reliable communication and faster mobile terminals. In order to achieve these fantastic features, it is required to overcome the technical challenge facing by the mobile communication systems. With the fast growing volume of data transmission by the mobile users, it is critical to manage different types of data information more quickly, effectively and reliably so as to satisfy the real-time demand of the signal processing by the mobile communications system. Hence, fast algorithms have a high theoretical and practical value to the research and application of mobile communications. In this dissertation, it has conducted in-depth research study on the key technology of code-division multiple-access (CDMA) and orthogonal frequency division multiplexing (OFDM) systems with respect to the computational complexity and system performance. Moreover, it has proposed several fast and effective computational methods.On the basis of analysis of the fundamental CDMA theory, we propose a series of practical solutions for the power control and multiuser detection techniques to improve the shortcomings of existing method. Through the simulation analysis, it demonstrates that our solutions can achieve a good performance and high feasibility to be implemented in practice.We first propose a new multiuser detector based on an iterative method of symmetric successive over-relaxation preconditioned conjugate gradient (SSOR-CG). It rides on the iterative process but without necessary to calculate the matrix inverse. It can achieve comparable bit error rate performance as the conventional decorrelating detector and linear minimum mean square error (LMMSE) detector with reduction in computational complexity. Exploiting the properties of discrete digital signals, a hybrid multiuser detector is proposed on the basis of SSOR-CG multiuser. It can improve the bit error rate performance with reduced computational complexity.Regarding the power control technique of CDMA system, we first propose to leverage on the SSOR preconditioned iterative method to tackle the power control problem. It can efficiently increase the convergence speed of the power control problem. However, its disadvantage is the heavy burden on the signaling for the link gain information exchange, which hinders its practical implementation. To tackle this problem, we further propose a block SSOR iterative power control method which can improve the speed of convergence while reducing the signaling requirement. Hence, it is suitable for practical system with varying numbers of users in reality. Besides, we propose a new call admission control method which can decide the admission action (accept/reject) of the new request in a less number of iterations. Moreover, it is free from any admission error.OFDM is receiving growing attention as the core technology for the beyond 3G and 4G mobile communication systems. In this dissertation, we focus on a major problem of OFDM technique: high peak to average power ratio (PAPR). First, we propose a low complexity partial transmit sequence (PTS) method by utilizing the characteristics of discrete digital signals. By selecting the parameter, it can tradeoff the PAPR performance and the computational complexity. Then, we propose a pre-calculated radius sphere decoding (SD) method to obtain the PAPR performance of the optimum PTS method. Compared with traditional brute force method, our proposed method can greatly reduce the computational complexity. With the pre-calculation of a smaller radius for the spherical decoding, our method can guarantee zero decoding failure.