Research On Key Techniques Of Multiple Co-channel Users Space-time Coding System

The wireless mobile communication system of future requires more frequency resource, and requests high efficiency of frequency spectrum. Space-time coding technique proposed in recent years is just one of techniques to realize this goal. As a kind of new technique, space-time coding attracts many investigators and has also become popular in wireless communication. Not only used in 3GPP, but also space-time coding is used in other wireless communication systems. In this paper, the attention is focused on some key techniques of space-time coding and also their application. Detecting method for the space-time coding system with multiple co-channel users are discussed. The main research works and results we have obtained in this dissertation are listed as follows:1. Proposed a new stepped compare interference cancellation method and new stepped iterative interference cancellation method.Based on the traditional two-step interference cancellation method for the space-time block coding system with two co-channel users, we propose the stepped compare interference cancellation method and the stepped iterative interference cancellation method. The first new method is the extension of the traditional two-step method, and it can be used for the space-time block coding system with more than two co-channel interference users. The stepped iterative interference cancellation method uses iterative calculation to reach the same performance compared with the stepped compare method. It can reduce the computational complexity greatly. Moreover the performance of two new methods is discussed in the paper.2. Proposed a multi-user space-time block coding system with unsymmetrical structure and its corresponding decoding method.A kind of unsymmetrical structure for space-time block coding system with multiple co-channel users is proposed in the paper. The interference cancellation and decoding method of this unsymmetrical structure system is introduced too. The unsymmetrical structure has several categories, including the users have different transmit power, the modulation modes of users are different, and the symbol rates of users are unequal. The decoding arithmetic of this system is discussed. The order of decoding can be set according the system structure. By using the new structure and the new decoding method, the computational complexity can be reduced greatly. Also a kind of simple frame structure for this unsymmetrical system is given here.3. Study on the channel estimation method in the space-time block coding system and its application.Based on the traditional MIMO channel estimation method by inserting orthogonal pilot sequences in the transmitted signals, we present the new channel estimation method by inserting the space-time block coding pilot matrix. Comparing with the traditional method, the new one has the same performance and wider pilot signal range. The new method harmonizes with the characteristic of space-time block coding system, and can be realized easily. If the channel is time varied, the estimated channel state information should be corrected real-time. Thus we introduce dynamic channel estimation method with inserted pilot matrix. Also, the adaptive LMS algorithm can be used under this situation, and it is improved by inserting pilot matrix to fast calculation convergence. At last the design rule of pilot information and decoding step of multi-usersystem receiver are dicussed.4. Proposing new differential space-time block coding rule and structure for the band-limit channel.We analyze the communication system in which the channel is band limited, and propose two type of differential space-time coding rule and construction. The new coding constructions change the relation between signal blocks or signal symbols, and form new transmit signal sets and mapping relationship. The coded signals have less phase variance between two consecutive symbols, thus the frequency spectrum of signals is more concentrated. The system adopting the new coding method will have better performance under the band-limit channel circumstance.5. Discussed differential space-time block coding system with multiple co-channel users and proposed nonsynchronous offset structure.We discuss multi-user differential space-time block coding system, and analyze the readability of differential decoding method. We can draw the conclusion that the receiver can not decoding the information of various users while the channel is unknown if multiple co-channel users in the system are synchronous. To solve this problem, a new kind of nonsynchronous offset system structure is submitted. If the multi-user system is constructed according the new offset structure, the receiver can easily cancel the interference and decode the signal by using differential method even the channel state information is unknown.