Coherent receiver employing nonlinear coherence detection for carrier tracking

Claim 2

In a receiver channel for a time varying signal, x, characterized by x square root 2Pc sin Phi + square root 2S X cos Phi + ni, where Phi omega ot+ theta characterizes modulation due to receiver motion or the randomness of said channel, ni is a narrowband, ''''white'''' Gaussian noise process of double-sided bandwidth Wi Hz and single-sided spectral density No watts/Hz, Pc m2P represents power at the carrier frequency, S (1-m2)P represents the power remaining in the modulation sidebands, m denotes the modulation factor, X d is a biphase modulated subcarrier, and and d represent the data subcarrier and the data waveforms, respectively, which are assumed to be square waveforms, a tracking loop comprised of a voltage controlled oscillator for generating a time varying reference signal ru square root 2K1cos Phi at an output terminal thereof in response to a feedback signal at an input terminal, where said feedback signal is the sum of one or more feedback signals S1 through S7 at respective points 1 through 7 of said loop excepting a signal at point 1, 2 or 6 by itself, or a signal at point 4 by itself for low data stream signal-to-noise ratios, and excepting sums of only signals S1 and S6 or only signals S2 and S4 for low data stream signal-to-noise ratios, said loop including means responsive to said received signal and said reference signal for generating said one or more feedback signals, where said feedback signals are characterized by the following equations, neglecting double frequency terms: Epsilon u K1 ( square root Pc sin phi + square root S X cos phi + nu(t, phi )) Epsilon l K2 ( square root Pc cos phi - square root S X siN phi nl(t, phi )) where Epsilon u is the output of an inphase phase detector and Epsilon l is the output of a quadrature phase detector using the reference signal ru for inphase phase detection of said signal x and a 90* phase shifted reference signal characterized by rl square root 2 K2 sin Phi for quadrature phase detection of said signal x and X d is a biphase modulated subcarrier, and d represent the data subcarrier and the data waveforms, respectively, and and d represent the receiver''s estimates of the data subcarrier and the data waveforms, respectively;

Claim 3

The combination of claim 1 including means responsive to said received signal delayed one symbol period T, said reference signal and said reference signal shifted 90* for producing one or both of respective delayed inphase and quadrature phase detected and filtered signals S8 and S9 at respective points 8 and 9 given by S8 g1K1( Square Root Pc sin phi + nu1T) S9 g1K2( Square Root Pc cos phi + nl1T) where it is assumed that the phase-error phi is constant over the symbol period T, and the noise process nulT is orthogonal to the noise processes nu1, nu2, nu3, nl1, nl2 and nl3 when the correlation time of the noise is much less than T, and said signals at points 8 and 9 produced are added to signals produced as corresponding inphase and quadrature phase detected and filtered signals of said undelayed input signal x, where the inphase phase detected and filtered signal is said signal SS2 at point 2.

Claim 4

In a receiver channel for a time varying signal x characterized by x Square Root 2Pc sin Phi + 2 Square Root S X cos Phi + ni, where X d is a biphase modulated subcarrier, and d represent the data subcarrier and the data waveforms, respectively, which are assumed to be square waveforms, and d represent the receiver''s estimates of the data subcarrier and the data waveforms, respectively, and where Pc m2P represents power at the carrier frequency, S (1-m2)P represents the power remaining in the modulation sidebands and m denotes the modulation, a generic tracking loop, provided to exploit the principle of nonlinear coherence comprised of: a voltage controlled oscillator for generating a time varying reference signal ru Square Root 2 K1 cos Phi , where Phi is the time varying loop estimate of Phi and Phi omega ot + theta , where theta characterizes modulation due to receiver motion or the randomness of said channel; a summing junction and a smoothing filter coupling the junction to a control terminal of the oscillator; a 90* phase-shift network for providing a quadrature phase reference signal rl Square Root 2 K2 sin Phi ; two multipliers responsive to the receiver signal and the signals ru and rl for producing quadrature phase error signals epsilon u xru and epsilon l xrl; a first low-pass filter of a particular bandwidth and gain coupling the signal ru to a point 2 connected to said summing junction; a first multiplier having one terminal connected to receive the output of said first filter and the output of a second low-pass filter of a particular bandwidth and gain to provide a product signal at a point 1 connected to said summing junction; means for demodulating the phase error signal epsilon u by a phase estimate of a reference square-wave subcarrier and a third low-pass filter of a particular bandwidth and gain for filtering the demodulated signal; means for delaying this subcarrier demodulated and filtered signal a time T equal to a data symbol period; means for multiplying this first delayed signal by d(t-T) where d(t) is the time varying estimate of the data waveform; means for multiplying the output of this last multiplying means by the output of the first filter to produce a third feedback signal at point 3 connected to the summing junction; means for demodulating the phase error signal epsilon l by a phase quadrature estimate of the reference square-wave subcarrier and a fourth low-pass filter of a particular bandwidth and gain for filtering the phase quadrature demodulated signal; means for delaying this subcarrier phase quadrature demodulated and filtered signal a time T; means for multiplying this second delayed signal by d(t-T) to produce another signal at a point 6 connected to the summing junction; means for multiplying the output of this last multiplying means by the product of the multiplying means of the first delayed signal and d(t-T) to produce yet another signal at a point 5 connected to the summing junction; means for multiplying the output of the second low-pass filter and the output of the penultimate multiplying means to produce a signal at a point 7 connected to the summing means; fifth and sixth low-pass filters of particular bandwidth and gain connected to the outputs of respective third and fourth filters; and a multiplier having its output terminal connected to a point 4, one input terminal connected to the output of said sixth filter and another input terminal connected to the output of said fifth filter by an operator which provides a function approximately equal to tanh x, where x is the output of said fifth filter; wherein the gain of said filters may be selectively set to zero to effectively remove signals at points 1 through 7 to provide a desired combination of feedback signals to said summing junction.

Claim 5

In a receiver channel for a time varying signal x characterized by x Square Root 2Pc sin Phi + 2 Square Root S X cos Phi + ni, where X d is a biphase modulated subcarrier, and d represent the data subcarrier and the data waveforms, respectively, which are assumed to be square waveforms, and d represent the receiver''s estimates of the data subcarrier and the data waveforms, respectively, and where Pc m2P represents power at the carrier frequency, S (1-m2)P represents the power remaining in the modulation sidebands and m denotes the modulation, a generic tracking loop, provided to exploit the principle of nonlinear coherence comprised of: a voltage controlled oscillator for generating a time varying reference signal ru Square Root 2 K1 cos Phi , where Phi is the time varying loop estimate of Phi and Phi omega ot + theta , where theta characterizes modulation due to receiver motion or the randomness of said channel; a summing junction and a smoothing filter coupling the junction to a control terminal of the oscillator; a 90* phase-shift network for providing a quadrature phase reference signal rl Square Root 2 K2 sin Phi ; two multipliers responsive to the receiver signal and the signals ru and rl for producing quadrature phase error signals epsilon u xru and epsilon l xrl; a first low-pass filter of a particular bandwidth and gain coupling the signal ru to a point 2 connected to said summing junction; a first multiplier having one terminal connected to receive the output of said first filter and the output of a second low-pass filter of a particular bandwidth and gain to provide a product signal at a point 1 connected to said summing junction; means for demodulating the phase error signal epsilon u by a phase estimate of a reference square-wave subcarrier and a third low-pass filter of a particular bandwidth and gain for filtering the demodulated signal; means for delaying this subcarrier demodulated and filtered signal a time T equal to a data symbol period; means for multiplying this first delayed signal by d(t-T) where d(t) is the time varying estimate of the data waveform; means for multiplying the output of this last multiplying means by the output of the first filter to produce a third feedback signal at point 3 connected to the summing junction; means for demodulating the phase error signal epsilon l by a phase quadrature estimate of the reference square-wave subcarrier and a fourth low-pass filter of a particular bandwidth and gain for filtering the phase quadrature demodulated signal; means for delaying this subcarrier phase quadrature demodulated and filtered signal a time T; means for multiplying this second delayed signal by d(t-T) to produce another signal at a point 6 connected to the summing junction; means for multiplying the output of this last multiplying means by the product of the multiplying means of the first delayed signal and d(t-T) to produce yet another signal at a point 5 connected to the summing junction; means for multiplying the output of the second low-pass filter and the output of the penultimate multiplying means to produce a signal at a point 7 connected to the summing means; fifth and sixth low-pass filters of particular bandwidth and gain connected to the outputs of respective third and fourth filters; and a multiplier having its output terminal connected to a point 4, one input terminal connected to the output of said sixth filter and another input terminal connected to the output of said fifth filter by an operator which provides a function approximately equal to tanh x, where x is the output of said fifth filter; wherein the gain of said filters may be selectively set to zero to effectively remove signals at points 1 through 7 to provide a desired combination of feedback signals to said summing junction.

Claim 6

The combination of claim 2 adapted to exploit sideband power in applications where phase error can be assumed to be constant over several data symbol intervals, by providing additional feedback signals at points 8 and 9 using a delay means of a delay time T coupling said receiver input signal x to two additional multipliers, one receiving the reference signals ru and the other receiving the reference rl for inphase and quadrature phase detection of the delayed input signal, and using separate low-pass filters of particular bandwidth and gain coupling the outputs of said additional multipliers to said points 8 and 9, means for connecting the filtered output of the inphase error signal thus produced at point 8 to said signal S2 at point 2, and means for connecting the filtered output of the quadrature phase error signal thus produced at point 9, wherein the gain of said separate low-pass filters may be selectively set to zero to effectively remove signals at points 8 and 9 from said tracking loop.