Research On Restraining The Peak-to-average Power Radio Of Optical OFDM System

As an orthogonal multi-carrier modulation technique- orthogonal frequency division multiplexing(Orthogonal Frequency Division Multiplexing, OFDM), is considered to be one of the key technologies to implement the next generation mobile communication system, has been a research focus of many scholars, has been applied to many fields. Optical OFDM communication system has many advantages, and combines with RF communication system OFDM technology and optical fiber communication advantages, so it has important meaning to study the optical OFDM technology.However, the existence of high peak to average power ratio(PAPR) of optical OFDM system problem. High PAPR not only exacerbate the nonlinear effect of optical fiber itself, but also causes the optical amplifier, modulator, photoelectric detector and other optoelectronic devices over its linear limit, so reducing the PAPR of optical OFDM system is necessary. Therefore, this paper mainly studies the methods to reduce PAPR of OFDM, establish optical OFDM simulation platform, introduces in detail the companding transform method and selective mapping method to achieve a lower PAPR of optical OFDM signal. The main results are as follows:Firstly, the basic principle of OFDM system is discussed and analyzed, including the key technology of modulation and demodulation technology, the guard interval and the cyclic prefix and the orthogonal subcarriers, IFFT and FFT and other key technologies. Analyze and compare several classical methods of inhibiting OFDM PAPR.Through analysis and comparison, this paper focuses on the research of compression expansion technology(C transform) and selective mapping(SLM). For the compression expansion method, the realization is simple and the inhibition of PAPR effect is obvious but will affect the BER performance of the system, and the simulation results show that the bigger u value to reduce the peak to average has the better effect but has the worse BER performance of the system. Considering this reasons this paper selects u=2. For the selective mapping method is a linear operation and can not bring the noise to system but has rather big amount of computation, considering the option of M=4.Secondly, the two algorithms joint simulation and the result shows that for reducing the peak to average ratio effect, combined algorithm is better than the use of companding algorithm and selective mapping algorithm alone. The combined algorithm reduces about 1.8dB ratio lower than the companding algorithm, 1.2dB than the SLM algorithm in PAPR. Through the analysis it can know that the joint algorithm is less impact on the error rate, so the combined algorithm for reducing OFDM PAPR is more practical.Finally, due to the direct detection of orthogonal frequency division multiplexing(DDO-OFDM) system is simple and low cost, currently the most widely used, so this paper uses the DDO-OFDM system. Combine Optisystem and Matlab simulation software to built the simulation model of DDO-OFDM communication system, and apply the combined algorithm to the optical OFDM simulation platform. It proves that it can effectively reduce the PAPR value of the Optical OFDM system and improve the performance of the system.