Research On Linear Precoding Technologies In MIMO Systems

Multi-input multi-output (MIMO) is a key technology generally adopted by new mobilecommunication systems for higher spectral efficiency in demand of high-speed data service.Among the core technologies to obtain MIMO performance gain, the precoding technology hasbecome a hot topic. Moreover, the relevant algorithms of precoding may affect the efficiencyand reliability of the system directly. With the precoding technology as the entry point, the maincontents of the paper are as follows:1. The paper has done research on generalized zero-forcing precoder in rank-deficientMIMO channel. In MIMO system, the traditional zero-forcing precoder is not applicable to therank-deficient channel. A generalized zero-forcing precoder is proposed. By properlypartitioning channel matrix, the design of generalized zero-forcing precoder is transformed intothe solution of several equations. The algorithm is fit for rank-deficient channel and itscomputation complexity is decreasing with growing number of channel rank. The simulationindicates that the new scheme performance is consistent with the traditional method. Comparedwith SVD precoder, the BER performance of the proposed precoder is better with relatively lowcomputation.2. The paper has conducted research on the precoder design subject to per-antenna powerconstraints. In traditional distributed MIMO system, the transmiting power is not allowed to beshared among antennas. To deal with this problem, the capacity-optimal precoder withper-antenna power constraint is studied. Based on relaxed constraints, a sub-optimal closed-formsolution is derived. The optimization problem is solved by Lagrange dual optimizing procedures,and the relevant iterative algorithm is given. The simulation indicates that the numericalcapacity-optimal precoder enhances the channel capacity, compared with that of the sub-optimalsolution, especially when the number of transmit antennas is more than that of receive antennas,or the channel matrix is rank-deficient.3. Research has been carried out on the block transmission in frequency-selective MIMOchannel with joint transceiver design. Based on orthogonal projection, a transceiver scheme isproposed for MIMO block transmission over frequency-selective channel. By separatingmulti-path components, the selective MIMO channel is decomposed into L (the number ofmulti-path components) flat orthogonal MIMO effective channels, increasing degree of freedomof system design. The analytical expressions of BER and capacity are given, based on proposedcapacity-optimal power allocation. Simulation results show compared with the existingnon-block transmission, the capacity gain is proportional to L in high SNR regions.4．Systematical investigation has been given to the physical layer information theoreticalsecurity of MIMO by precoding. A scheme based on projection operator is proposed to guaranteethe MIMO physical layer information theoretical security in transmission. The transmitter hasmultiple antennas and is able to simultaneously transmit separately an information-bearing signalto the intended receiver and randomized interference to the eavesdropper in the projection space. An iterative algorithm of power allocation between them is given to maximize the secret channelcapacity. Analytical results show the received signal of adversary has some special statisticaldistributions, based on which the indeterminacy of its blind deconvolution is proved. Numericalresults indicate that the secret channel capacity of this scheme is enhanced with reduced bit errorrate at the target user, while the eavesdropper cannot demodulate correctly.