Detection of impulse noise using unused spreading codes

Abstract

An impulse detector which can detect both low and high levels of impulse noise in a CDMA system is comprised of circuitry to calculate the background noise level in unused codes. Another circuit calculates the average noise power in the unused codes of each spreading interval to output the noise power per spreading interval. This average is continuously averaged over spreading intervals by another circuit which outputs the average background noise power. A comparator compares the noise power in the current spreading interval with the background noise power plus a programmable threshold and generates an erasure indication if the background noise power plus a discrimination threshold is exceeded.

Description

Background technique [0001] In cable modems and cellular systems and other wireless technologies that use modulated radio frequency carriers to transmit digital data from one place to another, there is always the problem of impulsive noise corrupting the transmission and creating errors. Impulse noise can arise from a variety of sources. [0002] Digital data transmission typically involves a stream of data bits that are decomposed into codewords, such as Reed-Solomon block codes, for encoding together with error detection and error correction bits (hereinafter referred to as ECC bits). The codewords thus encoded are then modulated onto one or more RF carriers and transmitted. At the receiving end, the encoded codeword is recovered and the ECC bits are used to determine if an error occurred and correct the error. The ECC bits only have a predetermined limited "range" based on the number of errors that can be detected and corrected. When impulse noise exists and is detected,...

AI Technical Summary

Problems solved by technology

[0004] However, for low power impulsive noise, the detection problem becomes much more complicated because it is difficult to distinguish what is noise from what is the real signal, and it is even more difficult to just remove the noise

This is because the power threshold is of limited use, and when it is low enough to detect low power signals, the power of uncorrupted payload data may also exceed the threshold and cause errors in generating symbols that are not corrupted by noise removal instructions for

There is a limit to how close the noise power threshold can be set to the desired power

This allows some symbols corrupted by low power noise to pass through the system and cause errors in recovering payload data and desynchronizing the CMTS tracking loop

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