Lock detector for feedback loops
First Claim
1. A receiver employing matched filter detection of signals modulated with data symbols having a data symbol period, comprising:
- means for matched filter detection and coherent demodulation of said signal, said means comprising a phase lock loop for tracking the phase of said signal;
means for providing an estimate of the signal amplitude;
means for calculating a lock detector statistic value, said value being normalized by an estimate of the signal amplitude to reduce its sensitivity to variations in the signal amplitude;
testing means responsive to said lock detector statistic value for determining whether said loop is tracking said signal at a false frequency or time offset, said means being operable over a wide signal to noise ratio (SNR) range over the entire frequency bandwidth at the input to said matched filter detection means and over the entire data symbol period; and
means responsive to said testing means for providing an indicator that the receiver is tracking at a false frequency or time estimate.
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Accused Products
Abstract
A receiver is disclosed for acquiring and tracking a data signal in a highly stressed environment. The receiver comprises first and second I.F. sections, a mixer for translation from the first I.F. frequency to the second I.F. frequency, a 2 kHz bandpass filter at the second I.F. frequency, signal translator for synchronous translation of the signal at the second I.F. frequency to baseband, a digitizer for complex sampling operation on the baseband signal, a microprocessor for processing the digital samples, and a numerically controlled oscillator coupled to the mixer and controlled by the microprocessor. The microprocessor formulates matched digital discrete Fourier transform filters which drive frequency, phase and symbol lock loops at the symbol rate. Each of the loop filters is formed by symbol-rate recursive, first-order equations. A novel mode control system is employed to implement an orderly transition through the receiver modes, comprising (i) out-of-band noise estimation, (ii) coarse frequency and time acquisition of the data signal employing a sequential probability ratio test and a handover process, (iii) frequency and symbol synchronization with the data signal, (iv) phase and symbol synchronization with the data signal, and (v) feedback loop lock confirmation. After loss of lock, the mode controller transfers the receiver operations back to the appropriate restart operation. The receiver includes a novel lock detector system adapted to determine whether the feedback loops are properly locked to the signal. The system is operable over the range of frequency and time offsets and over a wide variation in received carrier-to-noise power densities.
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Citations
19 Claims
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1. A receiver employing matched filter detection of signals modulated with data symbols having a data symbol period, comprising:
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means for matched filter detection and coherent demodulation of said signal, said means comprising a phase lock loop for tracking the phase of said signal; means for providing an estimate of the signal amplitude; means for calculating a lock detector statistic value, said value being normalized by an estimate of the signal amplitude to reduce its sensitivity to variations in the signal amplitude; testing means responsive to said lock detector statistic value for determining whether said loop is tracking said signal at a false frequency or time offset, said means being operable over a wide signal to noise ratio (SNR) range over the entire frequency bandwidth at the input to said matched filter detection means and over the entire data symbol period; and means responsive to said testing means for providing an indicator that the receiver is tracking at a false frequency or time estimate. - View Dependent Claims (2, 3, 4, 5)
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6. In a receiver employing matched filter detection and a feedback loop for tracking a signal modulated with data symbols, a system for detecting loop out-of-lock conditions, comprising:
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(a) loop signal means adapted to generate a loop parameter representative of the loop tracking performance; and (b) processing means for providing an indicator that the loop is in an out-of-lock state; and
wherein said receiver comprises first detection means for generating a complex first detection signal represented by I+jQ and whose value is representative of the spectral energy content of a first frequency band centered at the nominal signal frequency, and wherein said loop parameter is determined in accordance with the relationship ##EQU19## where η
1 is a loop scale constant, and A represents an estimate of the amplitude of the signal energy. - View Dependent Claims (7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18)
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19. A receiver employing matched filter detection of Manchester-encoded binary phase shift keyed (BPSK) signals, comprising:
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means for matched filter detection and coherent demodulation of said signal, said means comprising a phase lock loop for tracking the phase of said signal; means for calculating a lock detector statistic value; testing means responsive to said lock detector statistic value for determining whether said loop is tracking said signal at a false frequency or time offset, said means being operable over a wide signal-to-noise ratio (SNR) range; means responsive to said testing means for providing an indicator that the receiver is tracking at a false frequency or time estimate; and means for determining whether the receiver is tracking the Manchester mid-bit transition.
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Specification