Research On High-Rate Transmission Technologies In MIMO-OFDM Wireless Communication System

Many technologies have been proposed, and communication system has also been developed from one to another generation so far, but the motivation of this development is quite simple, which is the requirement for higher data rate and higher reliability. Now we are in 3G age and the convenience brought by code division multiple access (CDMA) shocks everyone. However, a new communication revolution is abuliding in both fields of research and industry, which will lead us into the next generation system with orthogonal frequency division multiplexing (OFDM) as its key technique. In 3GPP long term evolution (LTE) standard, OFDM and single-carrier frequency domain equalization (SC-FDE) are chosen as the physical-layer transmission modes in the form of orthogonal frequency division multiple access (OFDMA) in downlink and single-carrier frequency division multiple access (SC-FDMA) in uplink, and multiple antennas are also agreed to be employed on the base-stations and mobile devices to make multiple-input-multiple-output (MIMO) technology realized. All of them indicate that OFDM, SC-FDE and MIMO have been confirmed as the key technologies in the next generation communication system. In this thesis, these technologies are considered, and some transmission schemes and corresponding equalization algorithms are proposed with the aim of much higher data rate.High transmission rate and spectrum efficiency can be achieved by OFDM, because of the parallel transmission structure. With the cyclic prefix (CP), the multi-path interference can be removed, and the simple frequency-domain equalization can also be employed to compensate distortions and recover the data. The structure of SC-FDE is very similar to OFDM, and both of them are CP-aided transmission systems. Therefore, the advantages of OFDM mentioned above are also possessed by SC-FDE. However, there is no additional information in the CP, so the use of CP reduces both spectrum efficiency and power efficiency of system. Both OFDM and SC-FDE systems without CP are investigated in this thesis, and turbo equalization algorithms are proposed for them to reduce the effect of interference and noise with the consideration of their own characters. In their receivers, one-tap equalizers based on minimum mean square error (MMSE) criterion are derived, the computation method of soft information is improved, and some simplification is employed to reduce the processing complexity. Compared with current equalization algorithms, our proposed algorithms can achieve better error performance at the price of complexity increase.Then the OFDM system without CP is considered to be combined with spatial multiplexing and diversity techniques. In particular, both H-BLAST OFDM and space frequency block code (SFBC) OFDM systems without CP are investigated. Co-antenna interference or inter-layer interference is inevitable in spatial multiplexing system. Besides that, inter-block interference and inter-carrier interference of each layer can also make an impact on other layers in the H-BLAST OFDM system without CP. While in the SFBC-OFDM system without CP, intra-SFBC interference will appear when the system works under serious frequency-selective channel. Against such serious interference, a frequency-domain combiner based on signal to interference plus noise ratio (SINR) maximization and a one-tap frequency domain equalizer based on MMSE criterion are proposed for the H-BLAST OFDM and SFBC-OFDM systems without CP respectively in this thesis. The principle of turbo equalization is introduced in their receiving processes. Specifically, interference cancellation, equalization and soft channel decoding are performed iteratively to improve the error performance of system. Some simplification is also employed here to reduce the complexity of algorithms. Simulation results show that, with our proposed algorithms, interference can be suppressed efficiently, and good performance can be achieved. With multiple transmit antennas and appropriate spatial code structure, transmit diversity gains can be achieved by spatial diversity technique, e.g. Alamouti scheme. However, the transmission rate can not be boosted even if the number of transmit antenna increases. Aiming at this problem, a high-rate transmit diversity scheme or a syncretic scheme of spatial multiplexing and diversity gains is proposed. Because it is based on SFBC, the proposed scheme is named SFBC-SM in this thesis. Keeping the spatial diversity gains, SFBC-SM can help MIMO system reach higher transmission rate. Compared with other schemes as double SFBC system, no additional transmit antennas are required in SFBC-SM system. For SFBC-SM OFDM system, a two-step iterative equalization algorithm is proposed. At first, the initial estimates of symbols are obtained by MMSE equalization. And then coupled with SFBC decoding, successive interference cancellation is employed to suppress co-antenna interference and improve these estimates. After that, the SFBC-SM scheme is combined with SC-FDE, and a simply time-domain method is proposed for the transmitter to construct signals. At the receiver, a turbo equalization with parallel interference cancellation is proposed. Simulation results of both systems show that, the error performance of SFBC-SM system approaches the SFBC system, while the data rate is the same as the H-BLAST system...