Patent ID: 6285708
Filing Date: 2001-09-04
Classification: H04L

Abstract:
A transmitting modem receiving digital data from a data source, modulating carriers to represent said digital data, and applying a resulting modulated signal to a channel connectable to a receiving modem, said channel being subject to a power spectral density mask, said transmitting modem comprising:first, second, and third signal modulators, each with an input;a signal combiner with a combined output connected to said channel;a serial-to-parallel converter connected to said data source and to each of said first, second, and third signal modulator inputs such that said digital data from said data source is converted to multiple parallel streams applied respectively to said first, second, and third signal modulators;each of said first, second, and third signal modulators having a respective output connected to said signal combiner such that a sum of output signals of said first, second, and third signal modulators is applied to said channel;a transfer characteristic of said channel being such that a first minimum power required to represent a specified minimum number of bits by modulating in a first frequency sub-band falls below said power spectral density mask and such a that a second minimum power required to represent a second specified minimum number of bits by modulating in each of second and third frequency sub-bands exceeds said power spectral density mask;said serial-to-parallel converter being programmed to feed a first bit of said digital data to said first signal modulator to represent said first bit by modulating in said first frequency sub-band at a first power level at least as high as said first minimum power;said serial-to-parallel converting being programmed to feed a second bit of said digital data to said second and third modulators to represent said second bit by coherently modulating in both said second and said third frequency sub-bands at a second power level below said first power level, whereby resulting signals applied in said second and third frequency sub-bands may be combined by said receiving modem to retrieve said second bit;said first and second minimum number of bits both being equal to one in the absence of some other specified constraint.