Spread spectrum communication system
First Claim
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1. A frequency hopping spread spectrum communication system comprising:
- transmitter means for transmitting a radio frequency (RF) signal, said transmitter means having a first frequency hopping pattern generator means for generating a frequency hopping pattern and modulator means for modulating the frequency of transmission of the RF signal in accordance with said frequency hopping pattern; and
receiver means for receiving the RF signal of the transmitter means, said receiver means having a second frequency hopping pattern generator means for generating said frequency hopping pattern, and demodulator means for demodulating the RF signal in accordance with said frequency hopping pattern;
wherein said demodulator means comprises a phase locked loop circuit for tracking the transmitted RF signal, said second frequency hopping pattern generator means having means for generating a pattern of offset voltages in accordance with said frequency hopping pattern, and said phase locked loop circuit having a voltage controlled oscillator responsive to the offset voltage means wherein tracking breaks caused by hops in the frequency of transmission are avoided.
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Abstract
Disclosed is a spread spectrum communication system realized by using the frequency hopping coherent detection system wherein such an offset voltage pattern is predetermined by a polynomial is applied to the VCO of the PLL in the receiver thereof, so that the PLL can be operated with a narrow bandwidth because of the narrow bandwidth of the loop filter as well as a decreased loop gain while avoiding tracking break caused by narrow lock range due to the narrow bandwidth of the loop filter as well as the decreased loop gain.
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Citations
6 Claims
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1. A frequency hopping spread spectrum communication system comprising:
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transmitter means for transmitting a radio frequency (RF) signal, said transmitter means having a first frequency hopping pattern generator means for generating a frequency hopping pattern and modulator means for modulating the frequency of transmission of the RF signal in accordance with said frequency hopping pattern; and receiver means for receiving the RF signal of the transmitter means, said receiver means having a second frequency hopping pattern generator means for generating said frequency hopping pattern, and demodulator means for demodulating the RF signal in accordance with said frequency hopping pattern; wherein said demodulator means comprises a phase locked loop circuit for tracking the transmitted RF signal, said second frequency hopping pattern generator means having means for generating a pattern of offset voltages in accordance with said frequency hopping pattern, and said phase locked loop circuit having a voltage controlled oscillator responsive to the offset voltage means wherein tracking breaks caused by hops in the frequency of transmission are avoided. - View Dependent Claims (2, 3, 4)
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- 5. In a spread spectrum communication system in which modulated carriers are transmitted from a transmitter and are received by a receiver, the improvement wherein the system comprises a frequency hopping coherent detection system for coherently demodulating the carriers, said detection system comprising a phase locked loop and a frequency hopping signal reproduction circuit in the receiver, said phase locked loop having a narrow bandwith and a decreased loop gain to provide a narrow lock range, said frequency hopping signal reproduction circuit for generating a pattern of offset voltage signals in accordance with a frequency hopping pattern, said offset voltage pattern signals being applied to the phase locked loop so that tracking breaks caused by a narrow lock range of the phase locked loop are avoided.
Specification