US 5,828,705 AGranted

Carrier tracking technique and apparatus having automatic flywheel/tracking/reacquisition control and extended signal to noise ratio

OwnerBrian W. Kroeger, Jeffrey S. Bairdinventors

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Abstract

The carrier tracking loop technique and apparatus provides smooth, accurate frequency tracking, fast reacquisition and doppler tracking over a wide dynamic range. The loop parameters of the carrier tracking loop are varied as a function of mode, i.e. flywheel, tracking or reacquisition modes. The various modes of operation are automatically detected and loop operation is enhanced by non-linear techniques. The enhancements include fourth power sample normalization to improve performance over a large dynamic range and to ease fixed point scaling. A slope limiter is included which aids in coherent detection by reducing phase noise introduced by the carrier tracking loop. Also, a predifferentiation filter further aids in coherent detection by reducing phase noise.

Claims27

Dependent claims

A carrier tracking loop comprising:

mixing means for mixing a received signal with a local oscillator signal to translate the received signal to a near baseband signal;
symbol synchronization means, coupled to said mixing means, for sampling the near baseband signal at an optimum symbol timing and outputting symbol samples;
normalization means, coupled to said symbol synchronization means, for normalizing an amplitude of the symbol samples and removing phase modulation of the symbol samples to output normalized symbol samples;
filter means, coupled to said normalization means, for selectively increasing the signal to noise ratio of the normalized symbol samples in accordance with a lock signal;
frequency discriminating means, coupled to said filter means, for estimating a frequency offset between successive filtered symbol samples and outputting an error signal indicative thereof;
loop control means, coupled to said frequency discriminating means and an externally provided reacquisition initiation signal, for a) determining a signal to noise ratio of the filtered symbol samples in accordance with the error signal and b) generating the lock signal and adjusting the gain of the carrier tracking loop in accordance with the determined signal to noise ratio and the reacquisition initiation signal;
and
oscillator means, operatively coupled to said loop control means, for generating the local oscillator signal in accordance with the gain adjusted error signal.

5 more elements

A method of tracking a carrier signal in a carrier tracking loop comprising:

a) mixing a received signal with a local oscillator signal to translate the received signal to a near baseband signal;
b) sampling the near baseband signal at an optimum symbol timing to generate symbol samples;
c) normalizing an amplitude of the symbol samples and removing phase modulation of the symbol samples to provide normalized symbol samples;
d) filtering the normalized symbol samples to selectively increase the signal to noise ratio of the normalized symbol samples in accordance with a lock signal;
e) estimating a frequency offset between successive filtered symbol samples and providing an error signal indicative thereof;
f) determining a signal to noise ratio of the filtered symbol samples in accordance with the error signal;
g) generating the lock signal and adjusting the gain of the carrier tracking loop in accordance with the determined signal to noise ratio and an externally applied reacquisition initiation signal;
and
h) generating the local oscillator signal in accordance with the gain adjusted error signal.

6 more elements

Dependencies are inferred from the claim text.