MIMO and OFDM technology is the core technology of 4G network, and have great development prospects. The main drawback of MIMO-OFDM system is the high PAPR. This paper is based on Cross-antenna rotation and inversion and Active Constellation Extension. The paper proposed the joint algorithm to reduce PAPR in STBC MIMO-OFDM system. It makes use of time, space and frequency freedom to improve the PAPR performance. The simulation results show that the joint algorithm can effectively reduce the PAPR value and do not increase the bit error rate in STBC MIMO-OFDM system.

The fourth generation mobile communication system is a high-speed broadband wireless communication system, it needs MIMO and OFDM technology which have high spectral efficiency and suitable for a multi-path fading channel. Because the MIMO-OFDM system is still an multi-carrier modulation system, the main drawback is the high PAPR value. This paper proposed an improved algorithm based on optimized PTS to reduce PAPR in STBC MIMO-OFDM system. The simulation results show that the improved algorithm can effectively reduce the PAPR value and do not increase the amount of computation in STBC MIMO-OFDM system.