Spread spectrum communication system
First Claim
1. A spread spectrum RF energy receiver comprising:
- (a) an RF energy receiving means for receiving an RF signal modulated with a first and second code;
(b) a first mixer means connected to the RF energy receiving means and local oscillator frequency generating means for converting the received RF energy signal to baseband;
(c) a code acquisition and synchronizing circuit connected to the first mixer means, the code acquisition and synchronizing circuit including a charge transfer device matched filter for determining the presence of a preselected second code in the received RF energy signal and producing a synchronization pulse;
(d) a frequency generating means for producing responsively to the synchronization pulse of the code acquisition and synchronizing circuit a replica of the preselected second code;
(e) a second mixer means connected to the frequency generating means and first mixer means for converting the baseband signal to the first code signal;
(f) a frequency drift compensating circuit connected to the second mixer for producing a phase difference signal applied to the frequency generating means for automatic frequency and/or phase control; and
(g) means operatively connected to the receiver for converting the first code signal to a binary code.
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Accused Products
Abstract
An improved spread spectrum communication system having a transmitter subsystem and a receiver subsystem is disclosed. The transmitter subsystem comprises a data source of 50 bps rate which is modulo-2 added to a C/A (clear/acquisition) code of 1,023K chips/sec in an EXCLUSIVE OR gate, phase modulated on a carrier signal at about 154 fo where fo = 10.23 MHz in a phase shift keying modulator and transmitted. The receiver subsystem comprises an antenna for receiving the phase modulated signal, a plurality of filter/amplifier mixer stages for reducing the phase modulated signal to baseband, an in-phase CCD matched filter channel and a quadrature phase CCD matched filter channel for determining the presence of the C/A code and the phase of the incoming C/A code for synchronizing a replica of the C/A code with the incoming C/A code, a mixer for beating the replica C/A code signal with the C/A code signal, a Costas loop for automatic phase control, a sampler for sampling the baseband signal, an integrator for integrating the sampled signals, and a clocked comparator for comparing the integrated signals with a zero voltage at a 50Hz rate to demodulate the data code. Two embodiments of the CCD matched filter are disclosed. The first comprises a CCD having a length equal to five times the number of stages for each period of the C/A code. The second comprises a CCD transversal filter having a feedback loop for use in its transversal filter mode and in a recursive filter mode to enhance C/A code signals relative to noise.
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Citations
11 Claims
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1. A spread spectrum RF energy receiver comprising:
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(a) an RF energy receiving means for receiving an RF signal modulated with a first and second code; (b) a first mixer means connected to the RF energy receiving means and local oscillator frequency generating means for converting the received RF energy signal to baseband; (c) a code acquisition and synchronizing circuit connected to the first mixer means, the code acquisition and synchronizing circuit including a charge transfer device matched filter for determining the presence of a preselected second code in the received RF energy signal and producing a synchronization pulse; (d) a frequency generating means for producing responsively to the synchronization pulse of the code acquisition and synchronizing circuit a replica of the preselected second code; (e) a second mixer means connected to the frequency generating means and first mixer means for converting the baseband signal to the first code signal; (f) a frequency drift compensating circuit connected to the second mixer for producing a phase difference signal applied to the frequency generating means for automatic frequency and/or phase control; and (g) means operatively connected to the receiver for converting the first code signal to a binary code. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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Specification