Studies On Several Key Technologies In MIMO Spatial Multiplexing System

Multiple-input Multiple-output Radio Transmission Technology(MIMO RTT), which has the potential to multiply system capacity and improve spectral eficiency without requiring extra bandwidth and power, becomes an important technical breakthrough and promises to be one of the key technologies for future wireless communication systems, and hence has attracted broad attention and research interests in recent years. MIMO Spatial multiplexing system can achieve high data rate by transmit independent data streams on different transmit Antennas. In this paper, MIMO multiplexing system is mainly researched.We present a closed-form linear precoder for a MIMO spatial multiplexing (SM) system in the presence of transmit correlation and a Ricean component. We propose a simple algorithm that adjusts the transmitted constellation through power weighting and phase shifts that can be interpreted in some extreme case as a higher order constellation design scheme. We obtain a rate-preserving MIMO multiplexing scheme that can operate smoothly at any degree of transmit correlation and any type of LOS channel component.It is known that suboptimal (equalization-based and nulling-and-cancelling) detectors for MIMO spatial multiplexing systems cannot exploit all of the available diversity. Motivated by the insight that this behavior is mainly caused by poorly conditioned channel realizations,we propose the line-search detector (LSD). It exhibits near-ML performance and has significantly lower complexity than the sphere-decoding algorithm for ML detection.We propose a technique enhancing opportunistic beamforming at the transmitter with antenna selection at each mobile receiver to overcome the limitation of large mobile user population. Significant performance improvement is achieved especially for small number of users. The simplicity and inexpensive deployment of this technique make it a highly desirable enhancement to opportunistic beamforming.In the proposed MIMO spatial multiplexing (SM) systems, mobile stations only send uplink pilots in their uplink data transmitting, do not need to estimate spatial channels. Base stations can estimate the MIMO channels by using uplink pilots. The proposed scheme uses LDPC codec to replace classical space-time coding. Furthermore, LDPC codec deployed at base station and mobile stations can cancel the co-channel interference of MIMO spatial channels. The proposed scheme is shown to allow for effective utilization of spatial spectrums.