Performance of Asynchronous Tandem Standard 32 Kb/s ADPCM Systems Using QAM Signal

摘要

This paper deals with the performance of standard 32 kb/s ADPCM. This performance is measured using signal-to-noise ratio (SNR). Here, the new contribution is related with mathematical derivation of SNR for asynchronous tandem ADPCM systems as given in section 5. Another contribution is study this performance using QAM modem signal with different constellations. A computer simulation program has been developed and a number of simulation tests have been carried out using QAM modem signal at 9.6 Kb/s with four types of constellations, rectangular,& (5,11), (4,12), (8,8) circular. The results of testing asynchronous tandem ADPCM systems show that the performance degrades with increasing the stages of ADPCM. Also, the results show that the performance with circular constellation is better than rectangular constellation.