| The advantages of OFDM systems are high spectral efficiency and suitable forhigh-data-rate transmission over a multi-path fading channel. MIMO systems may beimplemented in a number of different ways to obtain either a diversity gain or acapacity gain. For high-data-rate transmission， OFDM can transform such afrequency-selective MIMO channel into a set of parallel frequency-flat MIMOchannels, decrease receiver complexity and deal with the multi-path fading efficientlyby combining MIMO and OFDM techniques. Therefore，MIMO-OFDM has become apromising candidate for4G mobile wireless systems.However, it is should be noted that the MIMO-OFDM system also has inheritedthe drawback of OFDM, which is the high peak-to-average ratio (PAPR). It will createthe consequence of non-linear distortion. As a result, the harmonic will lead to mutualinterference between the sub-channels in MIMO-OFDM system. It will have a seriousimpact on the application of the MIMO-OFDM system and hinder the development oftechnology. So the paper need to deeply analysis and research the PAPR controltechnology of OFDM. Then, study how to solve the problem of MIMO-OFDM.Therefore, the main achievements of this work consist of following aspects:Firstly, the system model and basic theory of OFDM signal are introduced.Thenits advantages and disadvantages are analyzed. And also the definition and distributionof PAPR in the OFDM system is introduced.Secondly, the most popular three kinds of PAPR reducing techniques are analyzedin the theory and performance simulation. And also their respective advantages andshortcomings are analyzed in detail. Particularly, strong emphasis is cast on clipping,compression expansion, Golay coding，selective mapping (SLM) and partial transmitsequence (PTS)，TI，etc technology. They are analyzed in the theory. The results aresimulated and compared in deep. The SLM algorithm is made for further improvementspecially. The complexity of algorithm is simplified，and makes much research andsimulation analysis of improved algorithm.Finally, the basic principle of MIMO technology and space-time coding (STBC)are in-depth analyzed. After considering characteristics of the system itself, the paperhas presented a construction of MIMO-OFDM with multi-antenna collaborative mode. To reduce complexity, a simplified integrated technology that based on the PAPRof OFDM system and combined with its features is given. This combines thecompression expansion technology with symbol scrambling technology. The results ofMATLAB simulation show that the scheme not only inhibits the PAPR ofMIMO-OFDM systems, but also reduces the number of side information andtransmission complexity of sub-system. |
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