Precoded gaussian minimum shift keying carrier tracking loop
AssigneeThe Aerospace Corporation
InventorsTien M. Nguyen, John M. Charroux
Life of this patent
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Abstract
An improved Gaussian minimum shift keying (GMSK) carrier tracking loop operating at baseband takes advantage of the orthogonality of precoded data GMSK signals and Laurent filtering to provide a carrier phase error signal generated at baseband for carrier phase derotation of the received GMSK signal. The carrier tracking loop also provides demodulated data estimates with performance equal to that of a GMSK serial demodulator. The tracking loop uses data directed feedback to improve noise rejection, but still has fast acquisition by operating at baseband.
Claims13
A method of demodulating a received signal having a phase modulated carrier signal of a carrier signal modulated by symbols having a symbol time period, the symbols are generated from preceding an input data stream as a precoded input data stream, the method comprising the steps of,
- carrier demodulating the received signal by a carrier reference into a carrier demodulated signal,
- phase demodulating the carrier demodulated signal by a phase amount into a baseband received signal,
- converting the baseband received signal into an imaginary component and a real component,
- real filtering the real component into a real phase signal,
- imaginary filtering the imaginary component into an imaginary phase signal,
- even real sampling at even symbol time boundaries the real phase signal into a sampled even real phase signal,
- odd real sampling at odd symbol time boundaries the real phase signal into a sampled odd real phase signal,
- real hard limiting the sampled odd real phase signal into real data estimates,
- even imaginary sampling at even symbol time boundaries the imaginary phase signal into a sampled even imaginary phase signal,
- odd imaginary sampling at odd symbol time boundaries the imaginary phase signal into a sampled odd imaginary phase signal,
- imaginary hard limiting the sampled even imaginary phase signal into imaginary data estimates, the imaginary and real data estimates are alternating estimates of the input data stream,
- even phase multiplying the imaginary data estimates by the sampled even real phase signal for generating an even phase error,
- odd phase multiplying the real data estimates by the sampled odd imaginary phase signal for generating an odd phase error,
- combining the even and odd phase errors into a phase error estimate, and
- phase adjusting the phase amount by the phase error estimate for phase demodulation of the carrier demodulated signal during the phase demodulating step.
A method of generating an output data stream from a received signal having a phase modulated carrier signal of a carrier signal modulated by precoded symbols having a symbol time period, the symbols are generated from preceding an input data stream as a precoded input data stream, the method comprising the steps of,
- generating a carrier reference estimate from the received signal,
- generating a carrier phase estimate from the received signal,
- carrier demodulating the received signal by the carrier reference estimate into a carrier demodulated signal,
- phase demodulating the carrier demodulated signal by a phase amount into a baseband received signal,
- converting the baseband received signal into an imaginary component and a real component,
- real filtering the real component into a real phase signal,
- imaginary filtering the imaginary component into an imaginary phase signal,
- even real sampling at even symbol time boundaries the real phase signal into a sampled even real phase signal,
- odd real sampling at odd symbol time boundaries the real phase signal into a sampled odd real phase signal,
- real hard limiting the sampled odd real phase signal into real data estimates,
- even imaginary sampling at even symbol time boundaries the imaginary phase signal into a sampled even imaginary phase signal,
- odd imaginary sampling at odd symbol time boundaries the imaginary phase signal into a sampled odd imaginary phase signal,
- imaginary hard limiting the sampled even imaginary phase signal into imaginary data estimates, the imaginary and real data estimates are alternating estimates of the input data stream,
- even phase multiplying the imaginary data estimates by the sampled even real phase signal for generating an even phase error,
- odd phase multiplying the real data estimates by the sampled odd imaginary phase signal for generating an odd phase error,
- combining the even and odd phase errors into a phase error estimate,
- phase adjusting the phase amount by the phase error estimate for phase demodulation of the carrier demodulated signal during the phase demodulating step by adjusting the carrier phase estimate by the phase error estimate for determining the phase amount, and
- data detecting the baseband received signal into the output data stream being an estimate of the input data stream.
Dependencies are inferred from the claim text.