Advanced Modulation Techniques for V.Fast

An overview is provided of the modulation techniques that are being considered for a new voiceband modem Recommendation, nicknamed V.fast. These techniques include adaptive bandwidth operation for automatically selecting the transmission band, multi-dimensional trollis coded modulation for higher coding gain, constellation shaping for higher shaping gain, precoding and pre-emphasis for advanced equalization, and warping for resistance against signal-dependent impairments. Simulation results are presented to illustrate performance. By adaptively selecting an appropriate combination of these modulation techniques based on line conditions, V.fast modems are expected to double the maximum data rate of standard modems.

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