Abstract—This paper presents new modified QAM modem that operates at data rate of 12kb/s to be transmitted over 32kb/s Adaptive Differential Pulse Code Modulation (ADPCM). The purpose of this modified QAM modem is to reduce the nonlinear distortion introduced by ADPCM. The performance of ADPCM is studied considering the standard QAM modem and modified QAM modem with different constellations. The simulation results show that the performance of ADPCM with modified QAM modem is better than its performance with standard QAM modem. Also, the performance with circular constellation is better than rectangular one.
Index Terms—QAM modem, 32kb/s ADPCM.
The authors are the Department of Electrical Engineering, University of Ibb, Yemen (e-mail: muhrawi@yahoo.com, muaayed@yahoo.com).
Cite: Muhanned AL-Rawi and Muaayed AL-Rawi, "Data Transmission at 12kb/s over 32kb/s ADPCM," International Journal of Information and Electronics Engineering vol. 2, no. 3, pp. 293-295, 2012.