| The rapid development of wireless communications has brought great changes in the way of communication and life. For the ever-increasing demand of wireless service, much more frequency band is needed to make sure enough transmission rates. But the frequency resource is actually limited. So, how to utilize wireless resource efficiently becomes more and more important. Nowadays multi-input multi-output (MIMO) technology is regarded as one of the most effective methods to improve the spectrum utilization.The researches have shown that the MIMO technology essentially provides spatial diversity and spatial multiplexing gain for wireless communication systems. Spatial diversity technique is a powerful technique to mitigate fading in wireless links. Spatial multiplexing can provide a linear increase in channel capacity scaled to the antenna number without additional consumption of power or bandwidth, which enlarge the frequency spectral efficiency. With the perfect channel state information (CSI), the MIMO system can reach the optimal performance by realizing directive transmission. Without any CSI, space-time coding is an effective method to improve system performance with transmit diversity gain. However, for most of MIMO systems, the transmitter can get partial CSI from the feedback of receiver. With the feedback, the transmitter may make an improved space-time coding more suitable for the channel.At present, the research emphasis has transferred from single user to multiuser MIMO system. The multiuser MIMO system can communicate with multiple users without extra time slots and frequency resources and can provide much more channel capacity compared with the single user MIMO system. In order to eliminate the interference among different users, the transmitter should precode the transmission signal based on the known CSI. Zero-forcing Beamforming (ZFBF) as a kind of precoding techniques has been researched broadly. But ZFBF has limitation in the number of users who receive service simultaneously. So the transmitter should select the optimal user subset for service effectively. At the same time, in order to ensure fairness among different users, scheduling is required to manage the users' access to the resources. On the other hand, with the employment of more antennas at transmitter, antenna selection is a low cost technique to capture many advantages of MIMO system without the limitation of RF cost.In this dissertation, single MIMO system with space-time coding and multiuser MISO system with antenna & user selection are studied. In general, the main achievements of this dissertation are listed as follows:(1) The DSTTD system as a typical single user MIMO system which has been drawn into 4G standards is researched first. An improved coding scheme is proposed with limited angle feedback at the transmitter in DSTTD system. The feedback is calculated at receiver with the criterion of maximizing the minimum postprocessing SNR. With less feedback bits, the new coding scheme can reach almost the same performance of traditional TAS scheme.(2) Two algorithms of transmit antenna and user selection in MU-MISO system based on different QoS are proposed. Both the two methods' selection criteria are maximizing the system sum-rate. One of the algorithms selects the user subset first and then select transmit antenna subset according to the selected users; the other selects the user and transmit antenna jointly. The two algorithms both reach the near-to-optimal performance and have lower complexity.Based on above analysis, space-time coding scheme based on angle feedback in DSTTD system and transmit antenna & user selection methods for multi-user MISO systems are studied in this dissertation. Finally, the problems to be solved in this research field and future research topics are summarized. |
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