Study On Joint Pre-coding Technologies In Coordinated Multi-point Systems

With the rapid development of wireless mobile communication technology from3G to4G, shortages of wireless network resources have become the focus of technology innovation because of demands for high-speed multimedia data service. Some new terminologies such as coordinated transition appeared in recent years. Coordinated multi-point, CoMP, as one of key technologies of long time evolution-advanced (LTE-A) has become an inevitable tendency of study and development. The basic idea of CoMP is to make the system structure of multiple-input multiple-output (MIMO) network virtual for achieving multi-point joint transmissions so as to avoid or eliminate co-frequency interference. Channel state information (CSI) and data information are shared among multi-cells by allowing the user data to be jointly processed by several interfering base stations in order to exploit interference between adjacent cells as useful information. And then the whole cooperative system is optimized to raise the utilization rate of resources, and improve receptivity of edge users. Moreover, for multi-antenna access technique in the future, distributed wireless mobile communication system is widely approved by its broad coverage area, big system capacity and high power efficiency. Therefore the technology, which combines distributed radio mobile communication network with CoMP, is better to realize the development goals of mobile communication than a single method.In distributed antenna systems with coordinated multi-point transmission mode, different pre-coding matrixes are used by distributional RAUs, which are coordinated, to process orthogonal frequency division multiplexing (OFDM) data. However, CSI that is required to pre-code is difficult to be computed accurately in a very short time because of requirements of high-rate transmission and impacts of complex communication environment. The scheme of using one pre-coding method can’t meet the communication need; therefore the joint coding has caused wide concern.On the basis of a comprehensive analysis of coordinated multi-point distributed system, the pre-coding method is introduced into system model in this paper. It is mainly focusing on the impact on overall system performance after adopting two joint coding methods that are proposed in this paper. One is based on a coordinated pre-coding scheme, the other is based on a combination of pre-coding and time space block code (STBC). The main contributions of this paper are:(1) The scheme of CoMP in distributional antenna system is studied. On the basis of discussions about characteristics(e.g., flexible resources allocation, wide distribution) of the distributed system and advantages(e.g., validity, reliability) of the collaborative transmission, a transmitted structure in coordinated multi-point distributed system at local scope is proposed in order to simplify and reduce the system complexity which is caused by sharing information within global scope. It will be considered and adopted as an implementation scheme for further development in the next generation of wireless network.(2) In distributed radio mobile communication and coordinated multi-point system, the deterioration of channel quality can seriously affect the system receptivity of edge users, and therefore the coordinated coding procession can be used to improve the quality of receiver. A coordinated transmission and joint pre-coding method is proposed in this paper. Coordinated remote antenna units (RAU) are processed jointly. According to state information of channel, different pre-coding rules are adopted by each RAU to transmit data to the same user. A Maximal-ratio combining (MRC) algorithm is used to calculate the received signals of terminals.(3) Though analysis of efficient coding gains and diversity gains about pre-coding and space time code in distributed system with coordinated multi-point transmission mode. A joint processing method is proposed in this paper so as to overcome the impact of complex communication environment and improve edge user’s receptivity. According to channel state information, some relevant RAUs (Remote Antenna Units) are chosen in distributed antenna system to form a cooperating set accommodate users. Pre-coding rules are adopted correspondingly by each RAU which come from cooperating set to preprocess users’data firstly, and then the processed data is transmitted by using STBC. A MRC (Maxima-Ratio Combining) approach is used to calculate the received space diversity and signals which are transmitted jointly by each coordinated RAUs in this system.Simulation experiment results show that the proposed method can effectively improve not only the bit error rate, but also the transmission reliability. Furthermore, it indicates a better application prospect and also provides a theoretical reference for the next generation of wireless communication technology.