Apparatus and method for detecting a signal in a communications system
First Claim
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.
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Abstract
In a communications system, an apparatus and method for detecting a valid signal from noise. An adaptive threshold is used to qualify a received signal. The adaptive threshold is set according to the number of false detects occurring within a given time interval. The number of false detects is initially determined by a quick qualification process. This initial number is subsequently adjusted by a more accurate qualification process. The transmitted signal is modulated with a particular pattern. Upon receiving the signal, it is demodulated to retrieve that pattern. The demodulated pattern is correlated against multiple reference patterns and combined to provide a measure of peak correlation that is independent of pattern phase. Furthermore, a tone detector is used to distinguish valid signals from interfering tones. Two different types of detection methods are performed in parallel. One is based on the energy of the received signal, whereas the other is based on the correlation of the received signal.
117 Citations
65 Claims
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1. A method for detecting a valid message signal, said method comprising the steps of:
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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. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 60, 61, 62)
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20. A method for detecting a valid message signal, said method comprising the steps of:
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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 number of false signals that were detected during said counting step is greater than a second pre-determined number; and g) detecting said valid message signal based on said first level of qualification and said second level of qualification. - View Dependent Claims (21, 22, 63, 64, 65)
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23. A method for producing correlation values, said method comprising the steps of:
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modulating a carrier message signal with a particular pattern; providing at least one reference pattern; demodulating said carrier message signal to generate a demodulated pattern having a phase relative to said at least one reference pattern; correlating said demodulated pattern against said at least one reference pattern to generate coefficient values; and combining said coefficient values to provide a peak correlation value, wherein said correlating and combining steps yield a correlation value substantially independent of said phase of said demodulated pattern. - View Dependent Claims (24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49)
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50. A transceiver for qualifying a valid message signal received from a transmission source, the transceiver comprising:
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a first detector for qualifying the valid message signal by comparing a strength of a received signal to a strength threshold, wherein said received signal is indicated as being valid if said strength of said received signal exceeds said strength threshold; and a second detector for qualifying said valid message signal based on a correlation between said valid message signal and at least one reference pattern, wherein said first detector and said second detector operate in parallel. - View Dependent Claims (51, 52, 53)
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54. A data communications network comprising:
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a plurality of nodes for transmitting and receiving a plurality of message packets; means for aborting a transmission of one of said message packets if a transmission by at least one of said nodes exceeds a predetermined time interval; and means for initiating a retransmission of said one of said message packets in response to a signal generated by said at least one nodes indicating that said transmission had been previously aborted.
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55. A method for distinguishing a valid data signal from a false tone, said method comprising the steps of:
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generating an I signal and a Q signal output from a quadrature down converter, said I signal and said Q signal output corresponding to a received signal, said quadrature down converter having an I channel and a Q channel 90°
out of phase with respect to said I channel; andgenerating a signal indicating the presence of an interfering tone by comparing a phase relationship between said I signal and said Q signal. - View Dependent Claims (56, 57, 58)
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59. A method for operating a transceiver which transmits and receives message packets comprising the steps of:
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aborting a transmission by at least one of a plurality of nodes if said transmission exceeds a pre-determined time interval; and initiating a retransmission in response to a signal generated within said at least one of said plurality of nodes indicating that said transmission had been previously aborted.
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Specification