Arithmetic Research Of Restraining Phase Noise In OFDM System

As a highly efficient modulation technique, OFDM can effectively deal with the ISI introduced by the multi-path fading channel. At the same time, OFDM system having efficient spectrum, can provide a higher transfer rate. Therefore, OFDM technology is applicable to future high-speed wireless multimedia communications systems.OFDM system requires for inter-carrier with strict orthogonal, and its symbol cycle is long, so it's very sensitive of the phase noise in local oscillator. Phase noise is a random phase interferer introducted by the non-ideal factors of frequency source. It can introduce two effects of the OFDM signal demodulator: the public phase error (CPE) and the inter-carrier interference (ICI). The traditional method of the compensation is to correct the CPE, while considering ICI as a kinsmanship Gaussian noise. This approach does not always meet the system requirements, especially in the high-speed communications systems.Through analysis of the theories and the key features of OFDM technology, this papers researchs the tracking and suppression algorithm of the phase noise, and proposes improvement measures, specific design and implementation, based on the DVB-T system. The main research works are as follows:(1) Detailly analyses the modeling process of phase noise model which applicable to the DVB-T system. The Main idea is to combine the filter phase noise model and MATLAB phase noise model to simulate the phase noise. Then it is accesed to the phase of the signal after the sampling and the phase rotation.(2) Proposes a correction system of phase noise to eliminate the CPE and ICI interferences of the system, simulating and achieving. The system needs the help of the pilot information and channel estimation information of OFDM system. There are three key modules: CHE module, CPE elimination module, ICI suppression module. The algorithms of the three modules are all completed in the frequency domain, and after the completion of channel estimation and balance, eliminating the CPE interference firstly, inhibiting the ICI interference secondly.(3) The algorithm design and simulation of the CHE, CPE, ICI modules. CHE algorithm ues the LMMSE and linear interpolation in the time domain, and the Wiener filter interpolation of good performance in the frequency domain. CPE elimination algorithm is simple, but it has shortcomings. This paper improves the choice method of the continuous pilots and the average method of the phase of the CPE elimination algorithm, and achieved good results. ICI inhibition algorithm firstly uses LMS balance algorithm to determine the correction factor of the adjacent pilot carriers, and then uses the correction factor to other data carriers for ICI correction.Simulation analysis shows that the correction system of phase noise not only can reduce the phase noise interference of OFDM effectively, but also have some practical value for its not complicated achiever and small hardware spending.