Synchronous tracking device for direct spread spectrum receiver
First Claim
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1. A synchronous tracking device for a receiver in a direct-spread spectrum communication system in which a carrier frequency and a pseudo noise code are coherent with each other, comprising:
- first tracking means, including a shared controlled oscillator, for tracking said pseudo noise code for a predetermined time after the synchronous acquisition; and
second tracking means, including said same shared controlled oscillator, for tracking said carrier frequency after said first tracking means stops tracking, while maintaining in said same shared controlled oscillator a locking condition achieved by said first tracking means.
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Abstract
A synchronous tracking device for a receiver in a direct-spread spectrum communication system in which a carrier frequency and a pseudo noise code for spreading it are coherent. A first circuit tracks the pseudo noise code in the received signal for a predetermined time after synchronous acquisition of the pseudo noise code. A second circuit tracks the pseudo noise code after the first tracking circuit stops tracking, while maintaining a locking condition achieved by the first tracking circuit.
77 Citations
24 Claims
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1. A synchronous tracking device for a receiver in a direct-spread spectrum communication system in which a carrier frequency and a pseudo noise code are coherent with each other, comprising:
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first tracking means, including a shared controlled oscillator, for tracking said pseudo noise code for a predetermined time after the synchronous acquisition; and second tracking means, including said same shared controlled oscillator, for tracking said carrier frequency after said first tracking means stops tracking, while maintaining in said same shared controlled oscillator a locking condition achieved by said first tracking means. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A receiver tracking circuit for a direct-spread spectrum system in which a received signal derives from a transmitter carrier modulated by a data signal and spread by a coherent pseudonoise (PN) signal, comprising:
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initial tracking means for locking on the coherent PN signal in the received signal, including shared controlled oscillator means having first and second feedback inputs, for generating a local carrier, and a local PN generator synchronized to the local carrier for generating a local PN signal to be locked onto the coherent PN signal, and PN tracking error detector means for providing a first error signal coupled as a first correction signal to the first feedback input; despreading means for applying the local PN signal to the received signal to produce a despread signal; final tracking means for locking on the despread signal, including the shared controlled oscillator means, the local carrier of which is to be locked on the despread signal, and phase error detector means for providing a second correction signal to the second feedback input; and control means for holding the first correction signal at its current value and starting the final tracking means when the initial tracking means has locked on the coherent PN signal. - View Dependent Claims (8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22)
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23. A tracking circuit comprising:
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a delay locked loop having a first phase detector responsive to a received signal, a sample and hold circuit responsive to the phase detector, an adder and a shared controlled oscillator responsive to the sample and hold circuit, and a pseudonoise generator, the pseudonoise generator being responsive to said shared controlled oscillator to supply the first phase detector a local pseudonoise signal for phase comparison with the received signal; a despreader circuit responsive to the received signal and the local pseudonoise signal to produce a despread signal; a Costas loop including (i) a second phase detector responsive to the despread signal, and (ii) the adder and said shared same controlled oscillator responsive to the second phase detector; and a control circuit having a normally open controllable switch for selectively coupling the received signal to the despreader, and means for selectively triggering the sample and hold circuit.
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24. A method of tracking a received signal derived from a transmitter carrier modulated by a data signal and spread by a coherent pseudonoise (PN) signal, comprising the steps of:
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(a) providing an initial tracking circuit having a shared controlled oscillator with first and second feedback inputs, a local PN generator synchronized to the shared controlled oscillator, and a PN tracking error detector circuit; (b) initially tracking the coherent PN signal in the received signal by (i) generating a local PN signal by means of the local PN generator for locking on the coherent PN signal, (ii) generating by means of the PN tracking error detector circuit a first error signal corresponding to the phase difference between the received and local PN signals, and (iii) coupling the first error signal as a first correction signal to the first feedback input; (c) providing despreading means for applying the local PN signal to the received signal to produce a despread signal; (d) providing a final tracking circuit including the shared controlled oscillator and the phase error detector circuit; and (e) when the initial tracking circuit has locked on the coherent PN signal, finally tracking the despread signal by means of the final tracking circuit by (i) generating a second correction signal corresponding to the phase difference between the despread signal and the local carrier, (ii) providing the second correction signal to the second feedback input, and (iii) halting the initial tracking circuit by holding the first correction signal at its current value.
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Specification