Interrogation signal processor for air traffic control communications
First Claim
1. A digital Mode S Interrogation Signal Processor for implementation in either a Mode S transponder or air collision avoidance system, comprising:
- Mode S preamble detector means for detecting a Mode S preamble of a transmitted signal and for generating a preamble detection signal;
phase-shift reversal detection means, in response to said preamble detection signal, for detecting a phase shift reversal in the transmitted signal and for generating a Mode S verification signal; and
said phase-shift reversal detection means determining that the transmitted signal is a Mode S signal when generating said Mode S verification signal;
digital differential phase-shift keyed demodulating means, in response to said Mode S verification signal, or digitally demodulating said Mode S signal to obtain useful information for air collision avoidance.
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Abstract
The present invention is directed to a Mode S uplink or interrogation signal demodulation system which can quickly recognize the Mode S signal and also filter out of noise present in the Mode S uplink or interrogation signal, thereby reducing the bit error rate. To realize this goal the present invention includes a digital differential phase-shift keyed demodulator to demodulate the differential phase-shift keyed data, thereby reducing the time needed to acquire the Mode S uplink or interrogation signal. This digital demodulator also reduces the noise present in the Mode S uplink or interrogation signal and provides an integrated system which is small in structure that can be easily implemented in an aircraft. This Mode S system also includes a preamble and sync phase reversal detection circuit to recognize if the transmitted signal is a Mode S signal. This signal also utilizes Mode A and Mode C detection devices to make the system compatible with present communication systems.
114 Citations
66 Claims
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1. A digital Mode S Interrogation Signal Processor for implementation in either a Mode S transponder or air collision avoidance system, comprising:
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Mode S preamble detector means for detecting a Mode S preamble of a transmitted signal and for generating a preamble detection signal; phase-shift reversal detection means, in response to said preamble detection signal, for detecting a phase shift reversal in the transmitted signal and for generating a Mode S verification signal; and said phase-shift reversal detection means determining that the transmitted signal is a Mode S signal when generating said Mode S verification signal; digital differential phase-shift keyed demodulating means, in response to said Mode S verification signal, or digitally demodulating said Mode S signal to obtain useful information for air collision avoidance. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
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16. A Mode S Interrogation Signal Processor for collision avoidance system, comprising:
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Mode S signal detector means for determining if a received signal is a Mode S signal; splitter means, operatively connected to said Mode S signal detector means, for splitting a transmitted Mode S signal into a quadrature signal and an in-phase signal, said quadrature signal being odd-samples of said transmitted Mode S signal and said in-phase signal being even samples of said transmitted Mode S. signal; digital Hilbert transformation means, operatively connected to said splitter means, for performing a Hilbert transformation upon said quadrature signal and said in-phase signal to produce transformed signals; delay means, operatively connected to said digital Hilbert transformation means, for delaying the transformed quadrature and in-phase signals by one clock cycle; multiplying means, operatively connected to said delay means, for multiplying the delayed transformed quadrature signal with a current transformed quadrature signal and for multiplying the delayed transformed in-phase signal by a current transformed in-phase signal; summer means, operatively connected to said multiplying means, for summing the products produced by said multiplying means; and threshold means, operatively connected to said summer means, for determining a polarity of the sum produced by said summer means. - View Dependent Claims (17, 18, 19, 20, 21, 22, 23, 24)
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25. A Mode S Interrogation Signal Processor for collision avoidance system, comprising:
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splitter means, operatively connected to said Mode S signal detector means, for splitting a transmitted Mode S signal into a quadrature signal and an in-phase signal, said quadrature signal being odd-samples of said Mode S signal and said in-phase signal being even samples of said Mode S signal; digital Hilbert transformation means, operatively connected to said splitter means, for performing a Hilbert transformation upon said quadrature signal and said in-phase signal to produce transformed signals; delay means, operatively connected to said digital Hilbert transformation means, for delaying the transformed quadrature and in-phase signals by one clock cycle; multiplying means, operatively connected to said delay means, for multiplying the delayed transformed quadrature signal with a current transformed quadrature signal and for multiplying the delayed transformed in-phase signal by a current transformed in-phase signal; weighting means, operatively connected to said multiplying means, for arithmatically weighing the products from said multiplying means such that middle samples of the transmitted signal are given greater weight; first summer means, operatively connected to said multiplying means, for summing the products produced by said multiplying means; second summer means, operatively connected to said weighting means, for summing the weighted products produced by said weighting means; switch means, operatively connected to said first and second summer means, for selecting a sum from either said first or second summer means in accordance with a type of noise and interference present in the transmitted signal; and threshold means, operatively connected to said switch means, for determining a polarity of the selected sum from said switch means. - View Dependent Claims (26, 27, 28, 29, 30, 31, 32)
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33. A digital Mode S uplink demodulator for demodulating a received Mode S signal, comprising:
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phase splitting means, for splitting the received Mode S signal into an in-phase signal and a quadrature signal; digital Hilbert transformation means, operatively connected to said phase splitting means, for performing a Hilbert transformation upon said in-phase signal and said quadrature signal to produce transformed signals; delay means, operatively connected to said digital Hilbert transformation means, for delaying the transformed quadrature and in-phase signals by one clock cycle; multiplying means, operatively connected to said delay means, for multiplying the delayed transformed quadrature signal with a current transformed quadrature signal and for multiplying the delayed transformed in-phase signal by a current transformed in-phase signal; summer means, operatively connected to said multiplying means, for summing the products produced by said multiplying means; and threshold means, operatively connected to said summer means, for determining a polarity of the sum produced by said summer means. - View Dependent Claims (34, 35, 36, 37)
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38. A digital Mode S uplink demodulator for demodulating a received Mode S signal, comprising:
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phase splitting means, for splitting the received Mode S signal into an in-phase signal and a quadrature signal; digital Hilbert transformation means, operatively connected to said phase splitting means, for performing a Hilbert transformation upon said in-phase signal and said quadrature signal to produce transformed signals; delay means, operatively connected to said digital Hilbert transformation means, for delaying the transformed quadrature and in-phase signals by one clock cycle; multiplying means, operatively connected to said delay means, for multiplying the delayed transformed quadrature signal with a current transformed quadrature signal and for multiplying the delayed transformed in-phase signal by a current transformed in-phase signal; weighting means, operatively connected to said multiplying means, for arithmatically weighing the products from said multiplying means such that middle samples are given greater weight; first summer means, operatively connected to said multiplying means, for summing the products produced by said multiplying means; second summer means, operatively connected to said weighting means, for summing the weighted products produced by said multiplying means; switch means, operatively connected to said first and second summer means, for selecting a sum from either said first or second summer means in accordance with a type of noise or interference present in the transmitted signal; and threshold means, operatively connected to said summer means, for determining a polarity of the sum produced by said summer means. - View Dependent Claims (39, 40)
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41. A method for digitally receiving a Mode S signal comprising the steps of:
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(a) detecting a preamble of a transmitted Mode S signal; (b) generating a preamble detection signal when said step (a) detects the preamble; (c) detecting a phase shift reversal in the transmitted Mode S signal when the preamble detection signal is present; (d) generating a phase reversal signal when said step (c) detects the phase shift reversal; (e) splitting the transmitted Mode S signal into a quadrature signal and an in-phase signal; (f) performing a digital Hilbert transformation upon the quadrature and in-phase signals; (g) delaying the transformed quadrature and in-phase signals for one clock cycle; (h) multiplying the delayed transformed quadrature signal by a current transformed quadrature signal; (i) multiplying the delayed transformed in-phase signal by a current transformed in-phase signal; (j) summing the products of said steps (i) and (h); (k) determining a polarity of the sum of said step (j); (l) producing data having a logic "1" when said step (k) determines the polarity to be positive; and (m) producing data having a logic "0" when said step (k) determines the polarity to be negative. - View Dependent Claims (42, 43, 44, 45, 46, 47, 48, 49, 50)
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51. A method for receiving a Mode S signal comprising the steps of:
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(a) determining if a Mode S signal is being received; (b) digitally demodulating the received Mode S signal when said step (a) has determined that the received signal is Mode S; said step (b) including, (c) splitting the transmitted Mode S signal into a quadrature signal and an in-phase signal; (d) performing a digital Hilbert transformation upon the quadrature and in-phase signals; (e) delaying the transformed quadrature and in-phase signals for one clock cycle; (f) multiplying the delayed transformed quadrature signal by a current transformed quadrature signal; (g) multiplying the delayed transformed in-phase signal by a current transformed in-phase signal; (h) summing the products of said steps (f) and (g); (i) determining a polarity of the sums of said step (h); (j) producing data having a logic "1" when said step (i) determines the polarity to be positive; and (k) producing data having a logic "0" when said step (i) determines the polarity to be negative. - View Dependent Claims (52, 53, 54, 55, 56)
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57. A method for receiving a Mode S signal comprising the steps of:
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(a) determining if a Mode S signal is being received; (b) digitally demodulating the received Mode S signal when said step (a) has determined that the received signal is Mode S; said step (b) including, (c) splitting the transmitted Mode S signal into a quadrature signal and an in-phase signal; (d) performing a digital Hilbert transformation upon the quadrature and in-phase signals; (e) delaying the transformed quadrature and in-phase signals for one clock cycle; (f) multiplying the delayed transformed quadrature signal by a current transformed quadrature signal; (g) multiplying the delayed transformed in-phase signal by a current transformed in-phase signal; (h) weighting arithmatically the products of said steps (f) and (g); (i) summing the products of said steps (f) and (g); (j) summing the weight products of said step (h); (k) selecting either the sum of said step (i) or the sum of said step (j) according to a type noise or interference present in the transmitted signal; (l) determining a polarity of the selected sum of said step (k); (m) producing data having a logic "1" when said step (l) determines the polarity to be positive; and (n) producing data having a logic "0" when said step (l) determines the polarity to be negative. - View Dependent Claims (58, 59, 60)
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61. A method for digitally demodulating an uplink Mode S signal, comprising the steps of:
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(a) splitting the uplink Mode S signal into a quadrature signal and an in-phase signal; (b) performing a digital Hilbert transformation upon the quadrature and in-phase signals; (c) delaying the transformed quadrature and in-phase signals for one clock cycle; (d) multiplying the delayed transformed quadrature signal by a current transformed quadrature signal; (e) multiplying the delayed transformed in-phase signal by a current transformed in-phase signal; (f) summing the products of said steps (d) and (e); (g) determining a polarity of the sums of said step (f); (h) producing data having a logic "1" when said step (g) determines the polarity to be positive; and (i) producing data having a logic "0" when said step (g) determines the polarity to be negative. - View Dependent Claims (62, 63, 64)
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65. A method for digitally demodulating an uplink Mode S signal, comprising the steps of:
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(a) splitting the uplink Mode S signal into a quadrature signal and an in-phase signal; (b) performing a digital Hilbert transformation upon the quadrature and in-phase signals; (c) delaying the transformed quadrature and in-phase signals for one clock cycle; (d) multiplying the delayed transformed quadrature signal by a current transformed quadrature signal; (e) multiplying the delayed transformed in-phase signal by a current transformed in-phase signal; (f) weighting arithmatically the products of (d) and (e); (g) summing the products of said steps (d) and (e); (h) summing the weighted products of said step (f); (i) selecting either the sum of said step (g) or the sum of said step (h) according to a type of noise or interference present in the transmitted signal; (j) determining a polarity of the selected said step (i); (k) producing data having a logic "1" when said step (j) determines the polarity to be positive; and (l) producing data having a logic "0" when said step (j) determines the polarity to be negative. - View Dependent Claims (66)
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Specification