The Research On PAPR Reduction In MIMO-OFDM System

The combination of Multiple-Input Multiple-Output (MIMO) and Orthogonal Frequency Division Multiplexing (OFDM), which is regarded as the most effective measure to improve spectral efficiency and system throughput, is the key technology of the physical layer in the 4G wireless mobile communications. The PAPR reduction algorithm of the MIMO-OFDM system is studied in the thesis and some theoretical and practical results are gained.Selective mapping (SLM) is one of the probability techniques often adopted to reduce PAPR in the OFDM system. It can be used to decrease the PAPR effectively, but there is a shortcoming of large computational complexity. Based on the individual SLM (ISLM) scheme, the multiple antennas concurrent selective mapping (CSLM) is investigated and the side information is lessened greatly as a result. Meanwhile, the CSLM scheme is improved by utilizing the orthogonal characteristic of space-time block coding and consequently, the computational complexity is cut down enormously. Moreover, the various phase sequences used in CSLM are considered emphatically and it is also proposed to lower the PAPR of the MIMO-OFDM system by using chaotic sequence as phase sequence.A new PAPR reduction scheme, called as Cross-Antenna Rotation and Inversion (CARI), is researched in the MIMO-OFDM system. In this method, according to the characteristics of the multiple transmit antennas in the MIMO-OFDM system, the dates from different transmit antennas are partitioned into the sub-blocks with equal sizes and then these sub-blocks are made to rotate and inverse across all antennas. So, an amount of the permutated sequence sets are obtained and then, a set with the best PAPR property is chosen for transmission to reduce the PAPR of the MIMO-OFDM system effectively. Furthermore, in view of the partition thought of the CARI scheme, a distinct computational scheme is put forward. In the new computational scheme, the CARI algorithm is made better by using the linear property of IFFT transform and therefore, the computational complexity is decreased greatly and there is no influence on the PAPR reduction effect. Compared with the CSLM scheme, both the PAPR resisting effect and the computational complexity reduction of the CARI algorithm with the new computational scheme are prior to that of the former.