Technologies For Digital Communication System Based On Low Precision Quantization

The digital to analog converter(ADC) is becoming one of the key issues for the digital communications as the high data transmission rate and energy efficiency are required. Due to the low conversion speedand the large power consumption, the high-precision ADC is not applicable for mobile devices in the communication systems. However the precision limited ADC can effectively solve these problems, since plenty of research works and applications have proved its feasibility in the ultra-wideband communications. In this dissertation, we study the digital communication technology with low-precision quantization. We also analyze and propose the singal processing algorithms, including automatic gain control(AGC), phase acquisition, symbol synchronization and decoding, for communication receiver with low-precision quantization.The ADC, Dither technology which is widely used in ADC, QAM modulation and 16 QAM digital receivers are introduced firstly. The necessity of AGC and phase acquisition in 16 QAM receiver with precision-limited ADC is reinforced through analyzing the affect introduced by the phase shift and amplitude attenuation.Then we study the AGC algorithm for the 16 QAM receiver with 2~4-bit ADC. On the basis of existing AGC scheme with low-precision ADC, a novel algorithm is proposed. Simulation results show the proposed algorithm can achieve a better system bit-error-rate(BER) performance than the existing algorithms when the same length training sequenceis utilized. We also propose an AGC algorithm schme for the varying signals.Meanwhile the algorithm of phase estimation in 16 QAM receiver with low-precision ADC is studied in this dissertation. We provide a hase acquisition algorithm based on the pilot, in which the rotation channel is added to enhance the estimation accuracy. Then the rotation angle for extra quantization channel and the threshold of noise variance of the dither signal are optimized through theoretical analysis and simulation. In the phase estimation algorithm, the time-varying phase shift is also taken into account.Moreover a pilot based symbol synchronization method is proposed, where the PN sequence and the proposed structure for phase acquisition are utilized. For the same receiver structure, the demodulation-decoding scheme is proposed to improve the BER performance. Finally, the BER performance of 16 QAM receiver with low-precision ADC, where the proposed AGC and phase acquisition algorithm are considered, is analyzed both in Gaussian channel and fading channel.