Study Of Algorithm For Reducing Peak-to-Average Power Ratio In MIMO-OFDM Systems

MIMO-OFDM system can enhance the channel capacity and transmission rate highly, and can also deal with the multi-path fading efficiently, so it has become a promising candidate for 4G mobile communication system. The thesis mainly researches on the PAPR reduction algorithms of the MIMO-OFDM system. The primary contents of the thesis are as following:The individual SLM (ISLM) scheme is studied in MIMO-OFDM system. Based on that, to solve the problem that ISLM scheme doesn't benefit additional degrees of freedom provided by the use of multiple antennas scheme, an improved scheme which is SLM scheme with subblocks permutation is proposed. In this algorithm, SLM scheme in each antenna is carried out first of all, then after IFFT the gotten sequences are divided into several subblocks, and at last subblocks are permuted. The additional degrees of freedom provided by the use of multiple antennas schemecan be utilized, so that the PAPR of signals can be reduced furtherly. Simulation results show that the performance of PAPR reduction of presented method is obviously better than that of ISLM scheme.A new PAPR reduction algorithm, which is Cross-Antenna Rotation and Inversion (CARI), is researched in MIMO-OFDM system. Compared with the method based on SLM, CARI algorithm doesn't have plural multiplication and can reduce the computational complexity. Then, inevitably, optimal CARI algorithm needs a large number of iteration. Although the suboptimal scheme of CARI--successive suboptimal CARI (SS-CARI) can reduce the number of iteration, the performance of PAPR reduction is deteriorated largely. To solve this problem, a suboptimal rotation and inversion combination searching method based on sliding window is presented. By utilizing sliding windows to search for the local optimal rotation and inversion combinations, not only the whole traversal search can be avoided to reduce the complexity of CARI greatly, but also the performance of PAPR reduction based on SS-CARI can be improved. Simulation results reveal that a good tradeoff between the system complexity and the PAPR reduction capability can be obtained through using presented scheme. An algorithm which is applicable to multiple antennas permutation ( SST algorithm) is studied. Compared with CARI method which can permute between two antennas, SST algorithm is more suitable for MIMO-OFDM system. SST algorithm can fully utilize the degrees of freedom in space domain to overcome the deficiency of Cross Antenna Rotation and Inversion (CARI) algorithm, however, the degrees of freedom in frequency domain are not considered in SST algorithm. For this problem, an improved SST(ISST) algorithm is raised. Not only subblocks permuted in the same way of SST algorithm in space domain, but also subblocks on the same antenna are successively rotated in frequency domain. So it can adequately use the degrees of freedom in both space domain and frequency domain. Simulation results indicate that the effect of PAPR reduction of SST algorithm is obviously better than SST algorithm. Furthermore, as the number of subblocks being bigger this superiority is clearer.