Comparison between Two Algorithms of 32kb/s ADPCM using QAM Signal at 16.8kb/s

This paper studies the comparison between two algorithms of 32kb/s ADPCM systems. The first algorithm uses 4-bit quantizer with sampling rate of 8000 sample/sec, and the second algorithm uses 5-bit quantizer with sampling rate of 6400 sample/sec. The comparison is done using QAM signal at data rate of 16.8kb/s. Two models of QAM signals are used, the first model operates at symbol rate of 2400 baud with each symbol is represented by 7-bit, while, the second model operates at symbol rate of 2800 baud with each symbol is represented by 6-bit. The contribution of this paper is that sending the second model of QAM signal over ADPCM with 5-bit quantizer. Simulation results show that the performance of ADPCM with 5-bit quantizer is better than 4-bit quantizer for both models of QAM signals. Also, the performance of ADPCM using second model is better than the first model. Furthermore, the performance with circular constellation is better than rectangular one