Methods, systems and computer program products for carrier drop detection using a variable threshold

• US 6,967,995 B1
• Filed: 10/29/1999
• Issued: 11/22/2005
• Est. Priority Date: 10/29/1999
• Status: Expired due to Term

• Current Assignee: Lenovo PC International Limited (Lenovo Group Ltd.)
• Original Assignee: International Business Machines Corporation
• Inventors: Schule, Robert John, Ye, Hua, Ware, Malcolm Scott, Hwang, Dongming
• Primary Examiner(s): Bocure, Tesfaldet
• Assistant Examiner(s): Kumar, Pankaj
• Application Number:
  US09/430,501
• Time in Patent Office: 2,216 Days
• Field of Search: 375/222, 375/224, 375/354, 375/356, 375/357, 375/358, 375/360, 375/316, 358/434, 358/436, 358/438, 358/439, 379/93.31, 379/93.32, 379/100.01
• US Class Current: 375/222
• CPC Class Codes: H04L 43/16 Threshold monitoring
• CPC Class Codes: H04M 11/066 Telephone sets adapted for data transmision

Abstract

Methods, systems and computer program products are provided which utilize a variable threshold for carrier drop detection. The carrier drop detection threshold is updated based on a recognized data sequence contained within the signal received by the modem. The received signal is demodulated to obtain the signal data and an updated threshold is latched when a desired data sequence is recognized in the demodulated data. Accordingly, the threshold may be updated and set as an offset from or a percentage of the carrier signal level at the time of receipt of the desired data sequence. For example, in a V.90 modem using a V.8 phase 1 sequence, receipt of the CM signal (for the answer modem) or the JM signal (for the call modem) may be used to latch an updated level for the carrier drop detection threshold, which may then be used for detecting carrier drop during the silence transmission at the end of phase 1 to allow reliable preparation of the modem for receipt of the INFO0 signal at the start of phase 2.

Claims

1. A method for modem carrier drop detection comprising the steps of:

demodulating a received signal to provide signal data;

detecting a signal strength for a portion of the received signal corresponding to a selected data pattern in the signal data;

establishing a carrier drop detection threshold at a determined level relative to the signal strength; and

detecting a carrier drop based on the carrier drop detection threshold;

wherein the modem uses a V.8 standard during startup and the step of establishing comprises the step of establishing the carrier drop detection threshold responsive to a selected data pattern in the signal data corresponding to at least one of a call menu (CM) signal and a joint menu (JM) signal.

2. A method for modem carrier drop detection comprising the steps of:

demodulating a received signal to provide signal data;

setting a flag to indicate receipt of at least one of a valid call menu (CM) signal and a valid joint menu (JM) signal;

latching an output of a signal strength detector responsive to setting of the flag, the signal strength detector being coupled to the received signal and the output of the signal strength detector corresponding to a signal strength level of the received signal;

setting a carrier drop detection threshold to a value a predetermined amount below the latched output of the signal strength detector responsive to setting of the flag; and

detecting a carrier drop based on the carrier drop detection threshold.

3. A method according to claim 2 wherein the signal strength detector is a magnitude detector.

4. A method according to claim 2 wherein the signal strength detector is an energy detector.

5. A method according to claim 4 wherein the step of setting a carrier drop detection threshold further comprises the step of setting the carrier drop detection threshold to a level about 4 dB below the latched output of the energy detector responsive to setting of the flag.

6. A method according to claim 2 wherein the detecting a carrier drop step further comprises the step of detecting a carrier drop corresponding to a silence transmission terminating a V.8 standard phase 1 and wherein the detecting a carrier drop step is followed by the step of conditioning the modem to receive a phase 2 information (INFO0) signal.

7. A method according to claim 6 wherein the conditioning step further comprises the step of starting a differential phase shift keyed (DPSK) receiver that receives the NFO0 signal.

8. A method according to claim 2 wherein the step of setting a flag further comprises setting a predetermined memory location as the flag.

9. A method according to claim 2 wherein the step of setting a flag further comprises the step of setting a latch output line to an active state.

10. A carrier drop detection system comprising:

a demodulator that demodulates a received signal to provide signal data;

a threshold circuit coupled to the demodulator that latches a carrier drop detection threshold at a level based on the received signal responsive to a selected data pattern in the signal data; and

a carrier drop detection circuit coupled to the threshold circuit that detects a carrier drop based on the carrier drop detection threshold, wherein the carrier drop detection circuit further comprises;

an energy detector having an output corresponding to an energy level of the received signal, the output of the energy detector being latched responsive to the selected data pattern in the signal data; and

a comparator coupled to the output of the energy detector and to the carrier drop detection threshold; and

wherein the threshold circuit further comprises a combiner coupled to the output of the energy detector and an offset that outputs the carrier drop detection threshold as the latched output of the energy detector reduced by the offset.

11. A carrier drop detection system according to claim 10 wherein the demodulator is a frequency shift keyed (FSK) demodulator.

12. A carrier drop detection system according to claim 10 wherein the threshold circuit further comprises a multiplier coupled to the output of the energy detector and a coefficient that outputs the carrier drop detection threshold as the latched output of the energy detector multiplied by the coefficient.

13. A carrier detection system according to claim 10 wherein the selected data pattern in the data signal is at least one of a call menu (CM) signal and a joint menu (JM) signal.

14. A carrier drop detection system for a V.8 standard modem startup sequence, the system comprising:

a receiver circuit that receives a signal;

a detector circuit coupled to the receiver circuit that detects at least one of a call menu (CM) signal and a joint menu (JM) signal from the received signal;

a signal strength detection circuit coupled to the receiver that outputs a received signal strength for the received signal;

a threshold circuit coupled to the receiver circuit that latches a carrier drop detection threshold based on a current value of the received signal strength responsive to detection of at least one of the CM and the JM signal by the receiver circuit; and

a comparator circuit coupled to the threshold circuit and the signal strength detection circuit that compares the received signal strength to the carrier drop detection threshold to detect a carrier drop corresponding to an end of the startup sequence.

15. A carrier drop detection system comprising:

means for demodulating a received signal to provide signal data;

means for detecting a signal strength for a portion of the received signal corresponding to a selected data pattern in the signal data;

means for establishing a carrier drop detection threshold at a determined level relative to the signal strength; and

means for detecting a carrier drop based on the carrier drop detection threshold;

wherein the modem uses a V.8 standard during startup and the means for establishing comprises means for establishing the carrier drop detection threshold responsive to a selected data pattern in the signal data corresponding to at least one of a call menu (CM) signal and a joint menu (JM) signal.

16. A carrier drop detection system comprising:

means for demodulating a received signal to provide signal data;

means for setting a flag to indicate receipt of at least one of a valid call menu (CM) signal and a valid joint menu (JM) signal;

a signal strength detector coupled to the received signal and having an output corresponding to a signal strength level of the received signal;

means for latching an output of the signal strength detector responsive to setting of the flag;

means for setting a carrier drop detection threshold to a value a predetermined amount below the latched output of the signal strength detector responsive to setting of the flag; and

means for detecting a carrier drop based on the carrier drop detection threshold.

17. A system according to claim 16 wherein the signal strength detector is a magnitude detector.

18. A system according to claim 16 wherein the signal strength detector is an energy detector.

19. A system according to claim 18 wherein the means for setting further comprises means for setting the carrier drop detection threshold to a level about 4 dB below the latched output of the energy detector responsive to setting of the flag.

20. A system according to claim 16 wherein the means for detecting a carrier drop further comprises means for detecting a carrier drop corresponding to a silence transmission terminating a V.8 standard phase 1 and further comprising means for conditioning the modem to receive a phase 2 information (INFO0) signal.

21. A system according to claim 20 wherein the means for conditioning further comprises means for starting a differential phase shift keyed (DPSK) receiver that receives the INFO0 signal.

22. A system according to claim 16 wherein the means for setting a flag further comprises means for setting a predetermined memory location as the flag.

23. A system according to claim 16 wherein the means for setting a flag further comprises means for setting a latch output line to an active state.

24. A computer program product for carrier drop detection, comprising:

a computer readable storage medium having computer readable program code means embodied therein, the computer readable code means comprising;

computer readable code which demodulates a received signal to provide signal data;

computer readable code which detects a signal strength for a portion of the received signal corresponding to a selected data pattern in the signal data;

computer readable code which establishes a carrier drop detection threshold at a determined level relative to the signal strength; and

computer readable code which detects a carrier drop based on the carrier drop detection threshold; and

wherein the modem uses a V.8 standard during startup and the computer readable code which establishes a carrier drop detection threshold comprises computer readable code which establishes the carrier drop detection threshold responsive to a selected data pattern in the signal data corresponding to at least one of a call menu (CM) signal and a joint menu (JM) signal.

25. A computer program product for carrier drop detection, comprising:

a computer readable storage medium having computer readable program code means embodied therein, the computer readable code means comprising;

computer readable code which demodulates a received signal to provide signal data;

computer readable code which sets a flag to indicate receipt of at least one of a valid CM signal and a valid JM signal;

computer readable code which outputs a signal strength level of the received signal;

computer readable code which latches the output of the computer readable code which outputs a signal strength level responsive to setting of the flag;

computer readable code which sets a carrier drop detection threshold to a value a predetermined amount below the latched output responsive to setting of the flag; and

computer readable code which detects a carrier drop based on the carrier drop detection threshold.

26. A computer program product according to claim 25 wherein the computer readable code which outputs a signal strength level of the received signal outputs a magnitude.

27. A computer program product according to claim 25 wherein the computer readable code which outputs a signal strength level of the received signal outputs an energy level.

28. A computer program product according to claim 27 wherein the computer readable code which sets further comprises computer readable code which sets the carrier drop detection threshold to a level about 4 dB below the latched output responsive to setting of the flag.

29. A computer program product according to claim 25 wherein the computer readable code which detects a carrier drop further comprises computer readable code which detects a carrier drop corresponding to a silence transmission terminating a V.8 standard phase 1 and further comprising computer readable code which conditions the modem to receive a phase 2 information (INFO0) signal.

30. A computer program product according to claim 29 wherein the computer readable code which conditions further comprises computer readable code which starts a differential phase shift keyed (DPSK) receiver that receives the INFO0 signal.

31. A computer program product according to claim 25 wherein the computer readable code which sets a flag further comprises computer readable code which sets a predetermined memory location as the flag.

32. A computer program product according to claim 25 wherein the computer readable code which sets a flag further comprises computer readable code which sets a latch output line to an active state.