Adaptive Digital Predistortion Technology For RF Pover Aplifiers

With the rapid development of wireless communication,in order to make more efficient use of frequency spectrum and achieve greater power efficiency,the linear modulation methods and high-efficiency Radia Frequency power amplifiers are widely used.The RF amplifiers usually use power back-off to achieve the system's linearity requirement under non-constant envelope modulation.However,in order to improve output power and efficiency,power amplifiers always work in the saturated state,which will produce severe nonlinear distortion. The nonlinearity creates spectral growth (broadening) beyond the signal bandwidth, which interferes with adjacent channels. It also causes distortions within the signal bandwidth, which decreases the bit error rate at the receiver.In order to achieve high linear and reasonably efficient Power amplifier, we can use linearization techniques in general. Digital predistortion is one of the most effective ways among all linearization techniques. So the main goal of our research is that implements digital predistortion system. In order to study digital predistortion system and simulate it, we need to master and understand nonlinear characteristics and memory effects of power amplifier, and mean while, to build exact behavioral model of power amplifier. This thesis discusses and studies the following contents step by step, including PA nonlinear characteristic and distortion, PA memory effect and cancellation, PA behavioral model and digital predistortion system and simulating realization.In the section of PA nonlinear characteristic, introduces representation of nonlinear characteristic, nonlinear characteristic parameters, distortion products, nonlinear analytical methods, characteristic simulation, and so on. In the section of PA memory effects, analyzes identification of memory effects, reason causing memory effects, verifies existence of memory effects, and gives some methods canceling memory effects. In the section of PA behavioral model, analyzes and compares a few typical PA behavioral model proposed. In the section of digital predistortion system and simulating implementation, analyzes and compares a few main linearization techniques, builds and simulates digital-base band predistortion system in MATLAB circumstance, builds the system of experiments and verifies the system.The main tasks and contributions in this thesis can be summarized as follows:1. Analyzes PA nonlinear characteristics and resulting distortion, concludes that amplitude of inter modulation products will increase and output spectrum will be deteriorate when input power increases. Verifies existence of memory effects through theoretical analysis. The principles of predistorter are described. The look-up-table based predistorters are discussed in detail.2. The principles of predistortion techniques are described. A predistortion method using the ameliorative Memory-Polynomials is proposed to linearize power amplifiers.3. Uses the joint simulation of ADS and MATLAB software to evaluate the performance of this system.4. Builds the experiments system of Digital Predistortion, verifies the system of DPD to prove the advantage of the system.5. Giving the results of the experiments system of Digital Predistortion. Plan the work of future.