Lookup Table-based Digital Pre-distortion Method And System Simulation

The third generation mobile communication(3G)has already integrated with people's life in European,which is also just been around the corner in China.The third generation mobile communication system which could support massive different kinds of services, and provide person-to-person communication service to anybody, in any place, any time needs good network architecture support. Therefore, The information transmission technology of modern communication system is developing rapidly in the direction of multi-carrier, multi-level, broad band and high Peak-Average-Ratio(PAR). New broad band digital transmission techniques(such as OFDM,WCDMA) and high spectrum efficiency modulation techniques(such as QPSK, M-QAM) are extensive used. These high efficient multi-carrier&multi-channel digital modulation transmission techniques, which are based on non-constant envelope,request high linearity of radio frequency power amplifiers(RF RAs).When signal is amplified by RF PAs, intermodulation distortion is generated, which results in spectral regrowth, then leads to adjacent channel interference.We usually adopt linear approach to correct the distortion-signal. Among the linear approach, digital predistortion is one the best approach due to its high precision, adaptability and capability that relatively simple to achieve. This paper focuses on the algorithm and the implementation of the DPD system. Then we demonstrate the effectiveness of the novel method we have proposed by means of simulation. major work including: 1 We make fully analysis of the nonlinear systems and discuss the problems of communication system arising from the nonlinear distortion theoretically. Then, we make comparison of various commonly used linearization technique and analyse several commonly used mathematical model of the power amplifier and give a framework for a variety of model plans. The analysis of algorithm which is the core of adaptive digital predistortion technology is our research goal. The method based on Polynomial and look up table is our concern. We commit ourselves to analyse the LMS, RLS and Newton algorithm in order to solve the nonlinear problem that bring from PA.2 We simulate the predistortion system which is base on our proposed LUT method with Agilent's software ADS.The transistor we apply is Motorola's MRF21125 which power amplifier operating frequency is 2.14Ghz..3 We simulate the proposed predistorttion LUT method using 16-QAM and 64-QAM modulate signal under software MATLAB, then make the simulation with WCDMA signal further and make comparison with absent predistotor and other people's method.4 We simulate the proposed lookup table method based on OFDM system which carrier numbers is 128, 20dB SNR and length of FFT is 128. we analyse and make comparison of our proposed predistortion system with constellation. Results obviously verify the practicability and advantage of our proposed method. During the test, we have been using the QAM mapping.