Abstract
A new modem circuit technique is proposed for multilevel signal transmission to utilise the transmission bandwidth efficiently in bandwidth-constrained voice-band channels. Using this technique, a 16-level quadrature amplitude modulated (16-QAM ) signal is generated as a cascaded configuration of an 8-level phase-shift keying (8-PSK) and a 4-level amplitude-shift keying ( 4-ASK) using waveform mapping rules. The data detection procedure, which is based on the determination of each symbol one-by-one by inspection of their amplitude level and absolute phase information, is described.
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