The Research On Reducing PAPR Of MIMO-OFDM System

Multiple-input multiple-output (MIMO) technology is not only able to use multiple antenna to achieve multiple input and multiple output, making full use of space resources, but also can significantly enhance the channel capacity without increasing spectral resources and the transmit power of antenna.The advantages of Orthogonal frequency division multiplexing (OFDM) technology are high spectral efficiency and suitable for high-data-rate transmission over a multi-path fading channel. The MIMO-OFDM Systems which is combined by the two technologies can improve spectrum efficiency and improve system throughput, and it has become one of the key technologies in physical layer of the fourth-generation wireless mobile communications. However, MIMO-OFDM system also adopts multi-carrier modulation. It also has the problem of high peak average power ratio (PAPR),the same as in OFDM system.System with high PAPR value requires non-linear power amplifier with large dynamic range of devices to avoid interference between subchannels and with external radiation. The Main content of this thesis is research on PAPR reduction methods for MIMO-OFDM system, and the main innovations and contributions are as follows:(1) In the OFDM system, due to the traditional limiting method, OFDM signal has to deep sampling before the D/A conversion and the deep sample will re-update the signal peaks. Proposing a Iterative clipping algorithm based on the Traditional clipping algorithm can not only restrain the peak to re-update, but also can effectively reduce the in-band noise, filter the noise out-band, and get rid of inter-symbol interference. It can also receive the signal accurately without any additional equipment. In addition, proposed a coding method based on the traditional Selective mapping(SLM) algorithm which can reduce the auxiliary information, and play the role of correction and reducing the role of BER.(2) In the MIMO-OFDM system, basing on the individual SLM(ISLM) algorithm, improves the SLM to get the CSLM with the co-work of multiple antenna, which greatly reduce the auxiliary information. Meanwhile,the CSLM algorithm is improved by utilizing the orthogonal characteristic of space-time block coding to cut down computational complexity enormously. Based on cross-antenna rotation and inversion(CARI), an improved method is presented for PAPR reduction, which Reduce the complexity of the algorithm and supporting information.To fully exploit the additional degrees of freedom by increasing the number of transmit antenna and increasing in the frequency domain by sub-block. I proposed a new algorithm--8 degrees of freedom Space-frequency Rotation and inversion algorithm to better reduce the PAPR of MIMO-OFDM system.To reduce the computational complexity of the algorithm,appropriate improvement the algorithm to get the successive space-frequency sub-block rotation inversion algorithm.The algorithm is not only fully tap the 2 antenna rotation and inversion freedom, but also full use of the degrees of freedom on the spatial domain caused by the increasing number of antenna, and it also takes the degree of freedom frequency domain into account. It make full use of the space and the frequency domain of freedom, at the same time, it break through the restriction that the number of antenna is even, which can further upgrade the performance of PAPR of MIMO-OFDM system. The simulation result shows that successive sub-block space-frequency rotation and inversion algorithm can not only reduce the PAPR of the system, but also can reduce the complexity of the system.