Bandwidth-efficient modulation for multichannel telephone carriers

This paper investigates the application of quadrature amplitude modulation to the transmission of frequency-division multiplexed, syllabically compressed telephone channels (SC/FDM/QAM). Performance calculations demonstrate that, with the proposed nonlinear mapping, this method makes transmission possible at a density of 96 4-kHz voice channels per MHz of allocated bandwidth. For carriers with 240 or more channels, the required RF carrier-to-noise ratio is 14.8 dB for full loading, and it diminishes with reduced loading.