Patent ID: 6859488

Claim:
A method of detecting low power impulse noise in a synchronous code division multiple access spread spectrum digital data transmission used for transmitting data between a plurality of cable modems and a cable modem termination system, comprising the steps: a) determining the background noise power by determining the noise power received on null service identifiers (SIDs) codes and/or unassigned codes over a plurality of spreading intervals of synchronous code division multiple access transmission; b) receiving the symbols transmitted using assigned spreading codes during a spreading interval of a synchronous code division multiple access frame, and determining the noise power level during said spreading interval in by determining noise power received on null SID codes and/or in null symbols of a received symbols vector which correspond to symbols of an information vector which would have had their spectrum spread in a cable modem by unassigned codes during said spreading interval had the values of said null symbols in said information vector not been set to zero, said received symbols vector resulting from matrix multiplication of a received result vector times the transpose of a code matrix which was used in said cable modems to spread the spectrum of symbols in said information vector to be transmitted to said cable modem termination system during said spreading interval; and c) comparing the noise power level in said null symbols and/or received on null SID codes of said spreading interval as determined in step b to said background noise power in the unused codes of a plurality of spreading intervals, as determined in step a, plus a predetermined discrimination threshold, and determining from said comparison if symbols received during said spreading interval have been corrupted by impulse noise to an extent such that the symbols cannot be received properly, generating an erasure indication for each such noise corrupted symbol received during said spreading interval.