Pulse or digital communications – Spread spectrum – Direct sequence
Patent
1983-11-07
1987-08-25
Olms, Douglas W.
Pulse or digital communications
Spread spectrum
Direct sequence
375119, 375120, 370104, H04L 704, H03D 324, H04J 306
Patent
active
046898069
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 3 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.
REFERENCES:
patent: 3564424 (1968-05-01), Freeman et al.
patent: 4203002 (1980-05-01), Nossen
patent: 4259740 (1981-03-01), Snell et al.
patent: 4375694 (1983-03-01), Kuhn
Chin Wellington
Hughes Aircraft Company
Karambelas A. W.
Meltzer M. J.
Olms Douglas W.
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