Mimo-ofdm Systems Papr Reducing Algorithm

The advantages of OFDM systems are high spectral efficiency and suitable for high-data-rate transmission over a multi-path fading channel. MIMO systems may be implemented in a number of different ways to obtain either a diversity gain or a capacity gain. For high-data-rate transmission, OFDM can transform such a frequency-selective MIMO channel into a set of parallel frequency-flat MIMO channels, decrease receiver complexity, and deal with the multi-path fading efficiently by combining MIMO and OFDM techniques .Therefore, MIMO-OFDM has become a promising candidate for 4G mobile wireless systems.But one of the major drawbacks of MIMO-OFDM systems is the high peak-to-average power ratio (PAPR),which makes the distortion occur duing to the nonlinearity of the high power amplifier. It will result in deteriorating the performance of the system. So this dissertation focuses on reducing the PAPR algorithms design for MIMO-OFDM systems, and the main innovations and contributions are:1. Based on cross-antenna rotation and inversion (CARI), an improved method is presented for PAPR reduction, which obtains better performance by utilizing additional degrees of freedom for multiple antennas. Firstly, The PAPR is reduced further by increasing the degrees of freedom for two antennas. Then, we have also proposed an improved scheme for more antenna system. Two sub-optimal schemes, termed Improved Successive Suboptimal CARI (Improved SS-CARI) and Improved Random Suboptimal CARI (Improved RS-CARI ) are proposed to reduce computational complexity. The performance analyses have shown that remarkable improvement of PAPR is obtained by the proposed scheme. Two suboptimal schemes are also investigated, which are easy in computation and simple in implementation.2. A method based on CARI is presented for MIMO-OFDM peak-to-average power ratio reduction. Firstly, an optimal scheme is proposed for PAPR reduction, which utilizes the degrees of freedom by employing multiple antennas. Then two sub-optimal schemes are proposed to reduce computational complexity by transforming the subblock successively and setting the threshold. The proposed suboptimal scheme, termed adaptive subblock successive transform (ASST) has shown that slight performance advantage and remarkably lower computational complexity compared to the successive suboptimal CARI (SS-CARI) scheme.