The Optimal Transmitter Design Of MIMO System Based On Channel Statistical Information

Modern wireless communications must cope with critical performance limiting challenges that include limited availability of radio frequency spectrum and a complex time-varying wireless environment (fading and multipath). Meeting the increasing demand for higher data rates, better quality of service, higher network capacity and user coverage calls for innovative techniques that improve spectral efficiency and link reliability. The use of multiple antennas at receiver and transmitter in a wireless system, popularly known as MIMO wireless is an emerging cost-effective technology that promises significant improvement in these measures. It is believed that the wireless MIMO technology will be one of the key ones that realize the high-speed broadband wireless Internet access networks in the future and has wide application prospect in the third generation (3G) or beyond third generation (B3G) mobile communications. A growing acknowledgment of the performance gains from MIMO technology has spurred the insertion of this technology into wireless standards, notably the mobile standards such as UMTS and CDMA 2000. MIMO techniques are also under study in IEEE 802.16 and 802.11 standards for fixed and WLAN applications respectively.MIMO technology can increase data rate without increasing transmission power and bandwidth. It has been proved that the capacity of MIMO system increases as the minimum number of transmit and receive antennas when the channel state information (CSI) is perfectly known at transmitter and receiver. The capacity will degrade greatly when the CSI is not known at transmitter. But in real transmission environment, the perfect CSI can not be obtained at transmitter because of fast change of fading channel, transmission delay and channel estimation error. The channel statistical information can be taken as stationary in a long time. The channel statistical information need to be fed back to the transmitter only when it is changed. It has been proved that the channel statistical information is beneficial to capacity. The optimal design of transmitter with channel statistical information is analyzed in this paper. The main contribution of this paper is listed as follows.Shannon capacity, outage probability and system error probability are taken as performance criterion separately to study the optimal transmitter design when the channel statistical information is fed back to transmitter. When Shannon capacity is taken as the performance criterion, the optimal transmitter design with channel mean information or channel covariance information is introduced firstly. Then the optimal design is studied in detail when both of these two statistical information can be obtained simultaneously. The optimal transmission direction is derived and the optimal power allocation algorithm is given. When outage probability is taken as the performance criterion, the optimal transmitter design of MIMO system with spatial correlation at both transmitter and receiver is discussed. Finally, an upper bound of SEP is derived and the optimal precoder design is analyzed when the system error probability is taken as the performance criterion.A new precoder structure which suits to non-orthogonal STBC with covariance feedback to the transmitter is presented. STBC is often designed for i.i.d. Rayleigh fading channels, assuming no CSI at transmitter. A linear precoder functions as a multi-mode beamformer matching the channel, based on the CSI at transmitter. The precoder and STBC combination, therefore, can exploit the available CSI and is robust to channel fading at the same time. Based on the OSTBC, a new precoder design method which suits to non-orthogonal STBC with covariance information at the transmitter is presented. The optimal eigen-vectors of this precoder are proved to be related to the transmit correlation matrix and STBC, and the optimal power allocation method is also given.The effect of channel estimation error on the system performance is analyzed. For SISO system, the effects of channel estimation error on the outage capacity in Nakagami-m and Rice fading channels are discussed. The upper and lower bounds on outage capacity are derived. For MIMO system, the channel capacity is taken as the performance and the effect of channel estimation error is analyzed. The optimal transmission strategy is studied when there is channel estimation error at receiver and different channel state information can be obtained at transmitter. The effect of channel estimation error on the channel capacity is analyzed by simulation and the system performance with different transmission strategies is compared.At the last part of this dissertation, the whole work of the dissertation is outlined and the future research issues are discussed.