Research On Precoding Technique In MIMO System

The Multi-input Multi-output (MIMO) communication system plays an important role in thehigh-speed wireless communication because of its unique high capacity and high reliability. Somekey technologies of MIMO systems formed gradually, which made up for some defects existing inthe system and improved the performance of MIMO communication system. Precoding technologyis one of the key technologies, which uses the channel state information (CSI) to process thetransmitting signal to make the signal adopt the channel better and get a better system performance.In this paper, according to the different known levels of CSI at the transmitter, differentprecoding schemes are researched. The main work includes the following respects:1. This paper studies the characteristics of MIMO communication system, and analyzestransmission fading, delay spread, coherence bandwidth and Doppler frequency shift of the wirelessfading channel. In addition, it studies the channel model of MIMO system and the uniqueadvantages of channel capacity, and analyzes the differences of channel capacity according to thedifferent levels of CSI known to the transmitter. At the same time, this paper studies some keytechnologies of MIMO system, such as diversity technology, the space-time coding technology,signal detection technology, etc.2. In the MIMO system, according to the different levels of CSI known to the transmitter,different coding schemes are adopted, which include the precoding of fully known CSI, theprecoding of partly known CSI and the precoding of limited feedback. According to the differentschemes described above, this paper does the introduction and corresponding research.3. In the case of the precoding of partly known CSI, we combine the OSTBC with the MIMOsystem to design the optimal precoding. For the problem that orthogonal space-time block codes(OSTBC) scheme don’t have coding gain, this paper introduces the thought of super orthogonalcodes and presents an optimal precoding design scheme based on the super orthogonal codes whichcombine the idea of super-orthogonal with the existing OSTBC. The proposed precoding schemeincreases the number of orthogonal matrix, gets coding gain and improves the performance ofMIMO precoding system. Meanwhile, our scheme does not expand signal constellation set.4. As for the limited feedback precoding based on codebook, the research focuses on the codeselection standards and codebook design. This paper introduces four different code selectionstandards, which are the biggest channel capacity criteria, the minimum singular value criteria, theminimum mean square error criteria and the minimum symbol error probability criteria. We choosethe optimal codebook by the different criteria to transmit information, and according to the different criterion we can get different optimizations of MIMO system. As for the codebook design scheme,this paper first studies the Love codebook precoding scheme in MIMO system with OSTBC, whichshows the best performance so far. On the basis of codebook construct framework, this paper putsforward the new codebook design scheme by using the new codebook design criteria. Besides, thenew codebook design scheme includes the optimum scheme and the fast choose code scheme.Simulations show that precodebooks obtained by our scheme outperform ones given in [50].Furthermore, our new codebooks have a fast encoding algorithm, which can effectively reduce theencoding complexity in the case of the performance lose is limited. Then, this paper studies DFTcodebook design scheme and new codebook design scheme in the MIMO system which does notinclude OSTBC. Through the simulation and comparison of the above two codebook designschemes in two kinds of MIMO systems, they are the MIMO system includes OSTBC and theMIMO system does not include OSTBC, we discuss the necessity of OSTBC in the precodingMIMO systems.