Spread spectrum bit allocation algorithm

• US 6,418,161 B1
• Filed: 05/25/2001
• Issued: 07/09/2002
• Est. Priority Date: 12/31/1997
• Status: Expired due to Fees

• Current Assignee: AT&T Corporation (AT&T, Inc.)
• Original Assignee: AT&T Corporation (AT&T, Inc.)
• Inventors: Sonalkar, Ranjan V., Shively, Richard Robert
• Primary Examiner(s): Ghayour, Mohammad H.
• Application Number:
  US09/864,241
• Publication Number:
  US 20020044597A1
• Time in Patent Office: 410 Days
• Field of Search: 375/222, 375/215, 375/240, 375/220, 455/522, 455/509, 455/464, 370/391, 370/358
• US Class Current: 375/222
• CPC Class Codes: H04L 5/0044 allocation of payload

Abstract

High transmission capacity in a twisted pair signal line, where power is limited by a power spectral-density mask and an aggregate signal power constraint, is obtained by: (1) allocating data to multitone sub-bands according to a lowest marginal power-cost per bit scheme and (2) in an environment where an aggregate power budget remains after all bits have been allocated to all sub-bands with sufficient margins to carry a bit, assigning additional bits to sub-bands with otherwise insufficient power margins to carry a single bit, by frequency-domain-spreading a single bit across several sub-bands at correspondingly reduced power levels, to permit the otherwise unacceptable noise levels to be reduced on average by despreading at the receiving end. Another feature of the invention, applicable in an environment in which multiple interfering channels are employed, provides increased signal throughput by (3) transmitting coherently in a number of multitone sub-bands, identical blocks of data, with the number of multitone sub-bands being equal to a number of interfering channels and multiplying the signal carried by corresponding sub-bands in the separate interfering channels by a different respective vector from an orthonormal basis set so that near-end cross-talk is eliminated upon despreading at the receiving end.

Claims

1. A transmitting modem receiving digital data from a data source, modulating carriers to represent the digital data, and applying a resulting modulated signal to a channel that is connectable to a receiving modem, the transmitting modem comprising:

a plurality of signal modulators, each signal modulator having an input;

a signal combiner having a combined output connected to the channel; and

a serial-to-parallel converter connected to the data source and to each of said the plurality of signal modulator inputs such that the digital data from data source is converted to multiple parallel streams that are respectively applied to the respective inputs of the plurality of signal modulators;

each of the plurality of signal modulators having a respective output that is connected to the signal combiner such that a sum of output signals of said the plurality of signal modulators is applied to the channel;

the serial-to-parallel converter being programmed to feed a selected bit of the digital data to said the plurality of the signal modulators to represent the selected bit by coherently modulating the selected bit in each of a plurality of frequency sub-bands, whereby resulting signals in each of the plurality of frequency sub-bands may be coherently linearly combined by the receiving modem to retrieve the selected bit and such that incoherent components and coherent, but at least partially orthogonal components of the resulting signals are attenuated and a coherent component of a modulated signal applied by said the plurality of signal modulators is amplified.

2. A method for transmitting data through a channel that is subject to a power spectral density mask limit and an aggregate power constraint, comprising steps of:

detecting a frequency-dependent transmission characteristic of the channel;

defining a plurality of sub-bands of an aggregate transmission band in response to the step of detecting the frequency dependent transmission characteristic of the channel, the aggregate power constraint, and the power spectral density mask limit; and

generating a plurality of modulated signals each having a power dynamic range permitted by the power spectral density mask limit, each modulated signal representing a selected portion of the data.