Research On The Linearization Method Of Power Amplifier

With the rapid development of wireless communication techniques, the linear modulation methods are widely used. Since the modulated signal fluctuates, there methods generate unwanted inter-modulation distortion (IMD) products in a nonlinearization high power amplifier (HPA), which lead to the adjacent channel interference (ACI) that has effect on the communication between users, so it is necessary to use linearization to reduce it. Predictor is a widely used linearization technique because of its unique advantage, and the research of predistorting linearizer is becoming the hot research field. The main studying of dissertation is about basic theory, basic method, the original work and valuable results in the dissertation are as follow.1. The nonlinearization of power amplifier and the influence to the system of communication are analyzed detailed. An overview of the common linearization techniques in existence is presented and comparison is also made among their advantages and disadvantages. These works set up the base of research.2. An improved predistorting technique based on Lookup Table (LUT) is presented, which is separated into an amplitude table and a phase table. First, initialize the LUT, then adjust the value in the LUT using adaptation method to adapt the characteristic of HPA. The computer simulation shows that the predistorting linearization can achieve 38dB IMD suppression when input signal is two tones, there is about 25dB decreased for IMD when model of HPA is adjusted. It can achieve 15dB IMD suppression when input signal is broad Band, there is about 10dB decreased for IMD when model of HPA is adjusted. Furthermore, this method can track the change of HPA characteristic in order to linearize the system exactly.3. A novel digital adaptive predistorting technique based on HPA characteristic curve area is introduced. In this method, for one thing, using polynomial in nonlinearization fitting for the HPA inverse model, for other thing, using LMS algorithms based on information of feedback adjust the coefficient of polynomial, which lead to the polynomial match the inverse model of HPA exactly. The computer simulation result shows that the method algorithm stability is high, easily realized, compensation effect well. But the computational complexity is huge. Considering the shortcoming of this algorithm, a modified RLS algorithm based polynomial predistortion algorithm is proposed. The basic principle of this polynomial predistortion method is to approximate the target function with two simpler functions instead of the conventional polynomial function. A complex function is decomposed into two simpler functions so that we can compute the RLS algorithm with much less complexity. Meantime this modified polynomial predistortion is implemented in the design of the PAS. And the simulation results show good performance in the reduction of the inter-modulation distortion. Of course, the force is limited in some extent. As the error is given and the module arrives some value, the force of module for predistortion effect goes to be stable.