Pulse or digital communications – Receivers – Automatic baseline or threshold adjustment
Reexamination Certificate
1998-04-30
2001-09-11
Chin, Stephen (Department: 2634)
Pulse or digital communications
Receivers
Automatic baseline or threshold adjustment
C375S222000, C375S316000, C375S329000
Reexamination Certificate
active
06289057
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the field of energy detection for detecting a valid signal in a modem, and more particularly or detecting a valid signal at a receiver of a modem for activation of a transmitter and for enabling power savings in receiver and transmitter circuits in modems.
BACKGROUND OF THE INVENTION
In communication systems a modem is used to convert (modulate) digital signals generated by a computer into analog signals suitable for transmission over telephone lines. Another modem, located at the receiving end of the transmission, converts (demodulates) the analog signals back into digital form. Transmitter and receiver circuits located in a central switching office linecard are generally maintained in a power-on state waiting for communication requests from a user. The central office linecard is also used to store system parameters such as equalizer coefficients or automatic gain control (AGC) settings in the case of a sudden drop of signal power or other interruptions. The linecard must discriminate between a desired received signal and noise or other interference signals based on the level and the occupied frequency range. in addition, on the customer side (CPE-customer premise equipment), the receiver must be able to perform a similar task.
The advantage of maintaining the central office equipment in a power-on state is that it will respond quickly to users'requests. However, this results in a significant waste of power when the receiver is inactive. Traditional simple analog energy or peak detect methods for signal detection are easily triggered by impulse noise or other radio frequency (RF) signals.
Further, in situations where the received signal disappears suddenly due to a power surge or other transmitter failure, prior art systems would start to reconverge their equalizer and timing recovery circuits on a non-QAM (quadrature amplitude modulation) signal, which led to problems when the proper QAM signal reappeared.
Consequently, there is a need for an energy detection system that permits the receiver and transmitter circuits in modems to conserve power when there is no communication requested by a user, and adapted to detect a valid user signal reliably and differentiate it from high level noise or other types of interference.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method and an apparatus for improving the detection of a valid carrier signal at a receiver of a modem.
Another object of the present invention is to provide a method and an apparatus for enabling power savings in receiver and transmitter circuits in modems.
In accordance with an aspect of the present invention there is provided an energy detection apparatus for detecting a valid signal at a receiver in a modem comprising: (a) an integrator for averaging an energy level in a prescribed number of signal samples to produce an average energy level; and (b) a first comparator for comparing the average energy level with a predetermined threshold, whereby if the average energy level is greater than the predetermined threshold then the valid signal has been detected.
In accordance with another aspect of the present invention there is provided a method of energy detection for detecting a valid signal in a modem, comprising the steps of: (a) processing a prescribed number of signal samples; (b) determining an average energy level for the prescribed number of signal samples; and (c) declaring the valid signal when the average energy level is greater than a prescribed energy level threshold.
In accordance with another aspect of the present invention there is provided a method of energy detection for detecting a valid signal in a receiver of a modem, comprising the steps of: (a) processing a prescribed number of signal samples; (b) determining an average energy level for the prescribed number of signal samples; (c) determining a gain of an amplifier based on the processed signal samples; (d) comparing the average energy level with a prescribed energy level threshold; and (e) comparing the gain of the amplifier with a prescribed amplifier gain threshold, wherein if the average energy level is greater than the prescribed energy level threshold and if the gain of the amplifier is less than the prescribed amplifier gain threshold then the valid signal has been detected.
REFERENCES:
patent: 4494240 (1985-01-01), Payton
patent: 5388127 (1995-02-01), Scarpa
patent: 5446771 (1995-08-01), Lin
patent: 5512898 (1996-04-01), Norsworthy et al.
patent: 5701332 (1997-12-01), Decrouez
patent: 5701601 (1997-12-01), Tomoe et al.
patent: 5926502 (1999-07-01), Schilling
Noel Peter
Velez Edgar
Yirga Sisay
Chin Stephen
Deppe Betsy L.
Nortel Networks Limited
Swabey Ogilvy Renault
Wood Max R.
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