Pulse or digital communications – Repeaters – Testing
Patent
1986-08-07
1988-05-17
Griffin, Robert L.
Pulse or digital communications
Repeaters
Testing
329 50, H04L 2722
Patent
active
047456272
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention concerns a procedure for detection of the information of a received signal, as well as an electric circuit for implementing the procedure. Preferentially, the invention will serve to estimate a binary information item in a received signal modulated by frequency shift-keying (FSK).
2. Related Art
Various circuits for the reception of signals modulated by frequency shift-keying (FSK) are already known. The traditional incoherent circuits accumulate the energy of the received signal in each case for one bit period on the two frequencies F.sub.0 and F.sub.1, which represent the two binary symbols `0` and `1.` The frequency which, in each case, has the higher signal energy, provides the estimation value of the corresponding information symbol. These classical receivercircuits are explicitely described, e.g., by John M. Wozencraft and Irwin M. Jacobs in the book Principles of Communicatons Engineering, John Wiley and Sons, New York, 1965. These known circuits are theoretically optimal; however, in their practical application, they are very susceptible to non-ideal characteristics of the oscillators and filters, as well as deviation of broadcast frequencies from their ideal values.
SUMMARY OF THE INVENTION
The problem for the present invention is to enable the detection of the information of a received signal in a relatively simple matter and with relatively minimal energy utilization, even under non-ideal conditions, particularly if the received signal has a considerable portion of undesirable interference overriding the useful signal representing the information, e.g., static and signal interference.
BRIEF DESCRIPTION OF THE DRAWINGS
In the following description, the invention is explained in greater detail by reference to the attached drawings, purely as an example.
FIG. 1 shows schematically a circuit for detecting binary information in a received signal modulated by frequency shift-keying (FSK);
FIG. 2 is a diagram representing the manner of operation of the circuit according to FIG. 1, and shows various electrical signals which depend on time.
DETAILED DESCRIPTION
The circuit represented in FIG. 1 provides a signal input 20 for the possibly preamplified high-frequency received signal U1 which is modulated by frequency shift keying (FSK) between 2 frequencies f.sub.0 and f.sub.1. the signal input 20 is connected by means of wires 21 and 22 to the input of an initial mixer 23 and input to a second mixer 24. An oscillator 25 generates a sinusoidal oscillation with a constant center frequency of: ##EQU1## and is connected by means of a wire 26 with a second input of the initial mixer 23, and by a wire 27 with a phase-displacement device 28. At the output of the phase-displacement device 28, there is a sinusoidal oscillation U3, which is phase-shifted by 90.degree. in relation to the sinusoidal oscillation U2, and has the same frequency, f.sub.c. The oscillation U3 is passed by means of a wire 29 to a second input of the second mixer 24. The two mixers 23 and 24 generate mixed products U4 and U5, which are each passed by way of wires 30 and 31, respectively, to an initial low-frequency pass filter 32, and a second low-frequency pass filter 33, respectively. At the outputs of the two low-frequency pass filters 32 and 33 are two sinusoidally-progressing quadrature signals U6 and U7, which both have the deviation frequency: ##EQU2## but which are phase-shifted by 90.degree. in relation to one another. The described transformation of the received signal U1 to a low-frequency band in a single step is known as direct conversion.
The first quadrature signal U6 is passed by means of a wire 34 to an instantaneous value-sampler 35, which is controllable by an electrical signal U8. The latter is generated by a crossover detector 36, and delivered by way of a wire 37 to a control input of the sampler 35. The second quadrature signal U7 is passed by way of a wire 38 to the input of crossover detector 36. The sampler 35 and the crossover det
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Chin Stephen
Gesellschaft zur Forderung der Industrieorientierten Forschung a
Griffin Robert L.
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