Technologies For Ditiatal Communication System Based On Low Precision Quantization

Digital signal processing(DSP) is the core technology for modern digital communications. The digital receiver is more precision, greater flexibility and stability than the analog receivers. Therefore, digital receiver is widely used in communication systems. However, with the development of communication technology, digital to analog converter becomes a bottleneck for the digital communication systems. ADCs with high rate and high precision are rare. Meanwhile, the high speed and high precision ADCs require great power consumption, which is not suitable for wireless communication devices. Low precision quantization is an effective solution. Low precision quantify, especially 1 bit quantization, has widely used in the ultra-wideband communication systems while there is little research on other communication systems.In this thesis, the impact of large quantization error which caused by low precision quantization such as 2-4 bits on QPSK modulated system is discussed. Automatic gain control and carrier phase recovery are also studied.In 2nd chapter, the performance loss caused by the slow fading channel, phase bias and symbol timing synchronization error is analyzed. The result shows that low precision quantization can be acceptable for the practical applications if the quantizer is proper.The 3rd chapter focuses on carrier phase estimation of QPSK receiver with low precision quantization. Different algorithms are discussed with the low information bits. A new useful phase estimator is proposed in this part.Automatic gain control is another important part in the digital receivers. Different kind of automatic gain control and algorithm of signal amplitude estimate is discussed first, and an automatic gain control with 1order filter is proposed. The frequency response of the automatic gain control is analyzed as well as estimate error. This automatic gain control scheme is robust for the slow changing channel.Dither is a useful technology in many field, in analog-to-digital converter it can improve the effect bits under certain conditions. The effect of dither in ADC is discussed as well as in phase estimate algorithm.