Research On Compensation Of Nonlinear Distortion In Wideband Receivers

With the rapid development of the telecommunications industry in the past three decades, a large number of communication devices emerge. The transmitter and receiver as essential aspects of communication systems, play an important role in the innovation of modern communication technology. However, the nonlinear characteristics of the transmitter and receiver will greatly reduce the quality and efficiency in communication system. In the transmitter, Multi-carrier modulation technique is often used, such as QPSK, QAM and OFDM, which results in a higher PAPR and a bigger nonlinear distortion problem. The receiver front-end consist of amplifiers, ADC, the mixer and so on can also lead to nonlinear distortion on signals. Thus linearization or nonlinear compensation technique is applied to solve the matters. Combined the nonlinear system models and adaptive algorithm, this paper is studying on how to compensate nonlinear distortion caused by digital receiver front-end. The work can be summarized as follow:(1) Classify the linearity techniques and describe the advantages and disadvantages of every technique.(2) Summary the basic theory of nonlinear systems. Take the power amplifier for an example and analyze the nonlinear characteristics, intermodulation distortion and memory effect. Then describe the common memory-less nonlinear models and memory nonlinear models. Finally, some indicators were given to measure the nonlinear distortion.(3) Considered the situation that the nonlinear distortion components of strong signals may cover the weak signal in the receiver, the terminal could not demodulate the weak signal. An advanced blind nonlinear system identification and compensation technique is introduced to build to objective function and apply the adaptive algorithm to update the parameters in nonlinear memory model. Finally, under the test signals, the simulation verifies the feasibility of adaptive compensation algorithm.(4) Considered the situation that multiple signals received by the same receiver, the self-generated nonlinear distortions and inter-band modulation components have a bad effect on demodulate the desire signals. An adaptive compensation technique is applied to solve the problem. To enhance the performance of compensation, the de-embedding is employed to reconstruct the polynomial model. Simulation shows the different power spectrums, constellations and the value of EVM before and after compensation to verify the validity of this algorithm.