| Orthogonal frequency division multiplexing (OFDM, Orthogonal Frequency DivisionMultiplexing), which is one of a multicarrier modulation methods. For it allows the frequencyspectrum to overlap each other between the sub-channels, and all of the sub-carrier existsorthogonality, it is possible to maximize the use of spectrum resources and has a high spectralefficiency. It has strong anti-frequency selective fading and anti-interference ability and canfit the high-speed transmission rate, which make the OFDM technology be widely used inwireless LAN (WLAN), digital audio/video systems and so on. Foremore, it is seen as thecore technology of the next-generation mobile communication system.If the inherent peak to average power ratio of OFDM system is too high to exceed thepower dynamic range of the transmitter power amplifier (HPA, High Power Amplifier) willcause the signal distortion damage, which destroy the mutual orthogonality between thesub-channel, and also easy to make the battery life shorter. Finally, it will result in an overalldecrease in system performance.In the OFDM system, in order to avoid the system caused by the emergence of highPAPR nonlinear distortion, we must take the appropriate method to reduce PAPR to make thechange of amplitude of the OFDM signal amplifier in the affordable range. According towhether have the impact on the signal, the PAPR reduction techniques can be classified asnon-distortion methods and distortion methods. The latter method due to the introduction ofthe signal radiation and will lead to the signal distortion, which make the system bit error rate(BER, Bit Error Rate) increased and make the system performance decline. So this paperresearchs non-distortion methods to reduct PAPR, such as Partial Transmit Sequence (PTS)and Selected Mapping (SLM).Besides, based on recently literature, OFDM system cannot take advantage of themultipath diversity provided by the multipath fading channel, resulting in degradation onsystem capacity. To counteract these issues, numbers of algorithms and schemes have beenproposed, like linearly MIMO-OFDM. Many literatures focus on the space-frequency blockcoding (SFBC) and space-time block coding (STBC) applying in the OFDM system, by using the advantage of space, time or frequency diversity to improve the performance of the OFDMsystem. Moreover, since the STBC/SFBC based on Alamouti scheme has a low complexity, itis widely implemented in various communication systems. However, the high PAPR is stillthe critical issue in the STBC/SFBC OFDM system.This paper first focus on the background and development of OFDM, then analyze thecurrent popular methods of reducing PAPR, following, the STBC/SFBC-OFDM system basedon Alamouti scheme is researched to the PAPR performance. After PTS and SLM having beenput into the STBC/SFBC-OFDM system, according to the result of the simulation and thecomputation about the complexity of the systems, it is found that the SFBC-DHT-OFDMsystem has the best PAPR performance and has the least complexity.Finally, we summarize the whole paper and put forward the idea about the futureresearch. |
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