Researches Of MIMO Wireless Communication Technology

With the rapid development of wireless communication services, the conflict between the finite frequency spectrum and communication capacity has been getting more and more serious. In this condition, how to increase the spectrum efficiency farthest has been a pepsi topic. MIMO technology breaks through the Shannon capacity limit. In fading channel, MIMO technology can elevate the channel capacity manifoldly without additional bandwidth and transmitting power consumptions. The incremental channel capacity can be utilized to improve the transmission rate as well as the communication reliability. MIMO technology has been considered as the revolutionary technology for the next generation wideband wireless communications.Currently, antenna design is still one of the important factors that make MIMO technology difficult to apply in mobile communications and 3G systems. Considering the fact of wireless communications, the author investigates the antenna issues of MIMO systems. Two schemes are listed in the dissertation. One scheme is to design wideband compact antennas to decrease antennas size. Another is to utilize multimode antennas or multi-polarized antennas to decrease the number of antennas, in which one antenna can work acting as multiple antennas. The author depicts multiple wideband compact microstrip antennas and several designs of wideband dual-polarized microstrip antennas. In this dissertation, two antennas, biconical multibeam antenna and self-complementary, archimedian, four-arm spiral antenna, are discussed to introduce the applications of multimode antennas in MIMO systems. One of the important researches of this dissertation is the applications of polarization diversity in MIMO systems. The author analyzes the factors that affect the MIMO channel correlation and capacity when polarization diversity is used in outdoor and indoor MIMO wireless systems, and points out what should be considered in antenna designs.In the precious researches, attaining the maximum diversity gain or maximum spatial multiplexing gain is the objective of space-time code. The author analyzes the relationship of the tow types of gains and derives the trade-off between them. The trade-off indicates that if appropriate space-time code is adopted, tow types of gains can be achieved simultaneously while the values of them are restricted by an optimal trade-off performance.In the researches of MIMO-OFDM technology, the author derives the channel capacity of MIMO-OFDM systems in view of the deficiency of previous researches. The effects of the number of sub-carriers, delay spread, angle spread and antenna spacing on the channel capacity are investigated. It is shown that the spectrum efficiency increases by nearly twice when combining OFDM technology. Accordingly, a higher channel capacity can be achieved at a lower cost of antennas and hardware. Additionally, the delay spread is a positive factor for the channel capacity of MIMO-OFDM systems, which provides another diversity resource. Furthermore, the author discusses the STF code and GSTF code that can take full advantage of this diversity resource.