Study On PAPR Reducation Algorithms For MIMO-OFDM Systems

Orthogonal Frequency Divison Multiplexing (OFDM) technique divides the high rate data into many low rate data which can be transmited onto some orthogonal subcarriers. It has high spectrum efficiency. It can also eliminate the interference among symbols and the interference of multi-path.MuIti Input Multi Output (MIMO), it means the system has many antennas both at transmitter and receiver. MIMO can enhance the channel capacity highly. Meanwhile, it can provide space diversity gain and coding gain.MIMO technique can be used in flat fading channel efficiently. But it has no benefit in frequency elective fading channel. Frequency elective fading channel can be changed into flat fading channel by OFDM. So after OFDM technique, MIMO can be used in frequency elective fading channel efficiently. MIMO-OFDM can be got by combining MIMO and OFDM techniques. MIMO-OFDM system can benefit from both MIMO and OFDM techniques. It can enhance the channel capacity and transmission rate highly, and can also deal with the multi-path fading efficiently.One of the major drawbacks of MIMO-OFDM is the high peak-to-average power ratio (PAPR) of the transmit signal as the same as OFDM systems. High PAPR means when the signal was transferred through non-linear devices, such as non-linear amplifier, the amplifier requires large linear region, or it will result in distortion. High PAPR makes many restrictions to the application of MIMO-OFDM. So it is necessary for us to research the PAPR reduction algorithoms.PAPR reduction algorithms of MIMO-OFDM system are researched on two main aspects in this thesis.First, it is how to use the properties of MIMO-OFDM to reduce the computational complexity about migrateing the existing algorithms of OFDM into MIMO-OFDM.Concurrent Partial Transmit Sequence (CPTS) algorithm is proposed, it is an effective way of migrating PTS to STBC-OFDM. In this way, compared to Individual Partial Transmit Sequences (IPTS), half of the computational complexity can be reduced. Besides, it is proved that the conjugate relationship of Weight Vector (CRWV) between datas on two antennas when using PTS in STBC-OFDM system. With the CRWV, the computational complexity of using PTS and transmission of side information can be reduced, or it can be used to check if the side information (SI) is correctly transmitted, and the correct transmission of side information (SI) is veryimportant to using PTS.Second, it is how to improve the reduction effect of PAPR reduction algorithms in MIMO-OFDM.Based on the research of the best combining rules, a most effective combined algorithm PTS-Clipping is proposed. Last, the reasonable structure of using PTS-Clipping in MIMO-OFDM is given. With this method, the PAPR of MIMO-OFDM system can be reduced effectively and efficiently.