Apparatus and method for detecting a signal in a communications system

Claims

What is claimed is:

1. A method for detecting a valid message signal, said method comprising the steps of:

setting a threshold at an initial level for qualifying a received signal;

counting from a first count to a second count, said first count and said second count defining a time interval;

determining a number of false signals that were detected during said counting step;

pausing said counting step during reception of a data packet; and

adjusting said threshold according to said number of false signals that were detected during said counting step.

2. The method of claim 1, further comprising the step of pausing said counting step during a transmission of a data packet.

3. The method of claim 1, further comprising the steps of:

generating a plurality of correlation values by correlating said received signal against a known wave form; and

adjusting said number of false signals that were detected according to a result of a comparison between each of said correlation values against said threshold.

4. The method of claim 3 further comprising the step of resetting said second level of qualification upon detecting a low correlation.

5. The method of claim 4, wherein said low correlation corresponds to said correlation value being less than half of said threshold.

6. The method of claim 4 further comprising the step of disabling said resetting step if a number of consecutive signal detect pulses are generated by said first level of qualification.

7. The method of claim 3, wherein said second level of qualification on said received signal is comprised of the steps of:

generating signal detect pulses corresponding to cycles of a pattern of a preamble according to said first level of qualification; and

determining whether at least two signal detect pulses corresponding to two of said correlation values which are non-overlapping have occurred within a second time interval.

8. The method of claim 7 further comprising the steps of: determining whether N additional signal detect pulses follow at least two signal detect pulses corresponding to two correlation values which are non-overlapping within said second time interval, wherein N is programmably pre-determined; and

indicating that said received signal is said valid message signal if N additional signal detects pulses follow said at least two signal detect pulses.

9. The method of claim 1 further comprising the step of:

setting a channel busy indicator if said received signal passes said first level of qualification.

10. The method of claim 9 further comprising the step of clearing said channel busy indicator if after a first specified time period following a first signal detect pulse by said first level of qualification, said second level of qualification does not indicate said valid message signal.

11. The method of claim 3 further comprising the step of resetting said second level of qualification upon detecting a low correlation.

12. The method of claim 11, wherein said low correlation corresponds to said correlation value being less than half of said threshold.

13. The method of claim 11 further comprising the step of disabling said resetting step if a number of consecutive signal detect pulses are generated by said first level of qualification.

14. The method of claim 1 further comprising the step of adjusting said number of false signals that were detected during said time interval if a word synchronization is not achieved following a second specified time period after detection of a first signal detect pulse generated by said first level of qualification.

15. The method of claim 1 further comprising the step of distinguishing interfering tones over said valid message signal.

16. The method of claim 15, wherein said step of distinguishing interfering tones is comprised of the steps of:

determining a larger signal and a smaller signal between an in-phase signal and a quadrature signal of said received signal;

detecting a zero crossing of said larger signal;

recording an amplitude of said smaller signal;

comparing said larger signal to the previously recorded amplitude of said smaller signal after a pre-determined period of time; and

generating an interfering tone signal indicating that said received signal is an interfering tone if said amplitude of said larger signal is within a pre-determined magnitude of said smaller signal.

17. The method of claim 1, wherein said first level of qualification and said second level of qualification are based on an energy of said received signal.

18. The method of claim 1, wherein said determining step is comprised of the steps of:

performing said first level of qualification on said received signal;

incrementing said number of false signals if said received signal passes said first level of qualification;

performing said second level of qualification on said received signal; and

decrementing said number of false signals if said received signal passes said second level of qualification.

19. The method of claim 18 further comprising the step of correlating said received signal against a known waveform to determine a correlation value, wherein said received signal passes said first level of qualification if said correlation value exceeds said threshold.

20. A method for detecting a valid message signal, said method comprising the steps of:

a) setting a threshold at an initial level for qualifying a received signal;

b) counting from a first count to a second count, said first count and said second count defining an interval of time;

c) determining a number of false signals that were detected during said counting step, wherein said determining step comprises the steps of:

i) performing a first level of qualification on said received signal;

ii) incrementing said number of false signals if said received signal passes said first level of qualification;

iii) performing a second level of qualification on said received signal;

iv) decrementing said number of false signals if said second level of qualification indicates that said received signal is said valid message signal;

d) pausing said counting step during reception of a data packet;

e) lowering said threshold if said number of false signals that were detected during said counting step is less than a first pre-determined number;

f) raising said threshold if said