Data aided symbol timing system for precoded continuous phase modulated signals

Abstract

Data aided carrier phase and symbol timing synchronizers are implemented at baseband as digital modulators isolating input signal inphase and quadrature component signals fed into inphase and quadrature. Laurent transforms that function as data detector to provide odd and even data bit multiplexed output data signal while cross coupling the inphase and quadrature transformed outputs for removing data modulation in error signals to correct phase errors and timing errors in the received signal so as to provide reliable data demodulation of noisy received signals having dynamic carrier phase and symbol timing errors as found in continuous phase modulation communications systems such as Gaussian minimum shift keying communications systems.

Description

STATEMENT OF GOVERNMENT INTEREST[0001]The invention was made with Government support under contract No. F04701-93-C-0094 by the Department of the Air Force. The Government has certain rights in the invention.REFERENCE TO RELATED APPLICATION[0002]The present application is related to applicant's copending application entitled Data Aided Carrier Phase Timing Tracking System for Precoded Continuous Phase Modulated Signals, Ser. No. 09 / 694,650, filed Oct. 24, 2000, by the same inventors.FIELD OF THE INVENTION[0003]The invention relates to the field of continuous phase modulation communications systems. More particularly, the present invention relates to symbol time tracking for continues phase modulations communications systems, such as Gaussian minimum shift keying communications systems having small bandwidth time products.BACKGROUND OF THE INVENTION[0004]In synchronous digital data communication systems, the carrier phase and symbol timing of the received signal must be acquired and ...

AI Technical Summary

Benefits of technology

[0019]The present invention is directed to data aided synchronization in digital carrier phase and symbol timing synchronizers applicable to precoded continuous phase modulation (CPM) signal formats, such as in Gaussian minimum shift keying (GMSK) communications systems having, for example, a modulation index of ½ with a bandwidth time product (BT) of ⅕. The imbedded synchronizers enable simple implementations for data demodulation for CPM signals, such as GMSK signals with small BT values. Data aided tracking is applied in one form to symbol time tracking, and in another form, to carrier phase tracking. An advantage of the proposed data aided symbol timing synchronizer is the combination of both symbol timing tracking and data demodulation functions into an integrated process obviating the need for a separate data demodulator in the receiver. For example, for GMSK signals with BT values of ⅓ and larger, the data demodulation performance in the symbol timing synchronizer can provide optimum performance. An advantage of the data aided carrier phase synchronizer is the combination of both carrier phase tracking and data demodulation functions into one integrated process obviating a need for separate data demodulator in the receiver. For example, for GMSK signals with BT values of ⅓ and larger, the data demodulated performance provided by the carrier phase synchronizer can also be optimum.

[0021]These digital synchronizers are use to track the symbol timing or carrier phase of a continuous phase modulation signal received in the presence of noise with the receiver operating in a data demodulation mode. These synchronizers have a nondegraded bit error rate (BER) performance with reduced design complexity. The GMSK signal with a BT=⅕ can be used as a typical partial response CPM signal. The hardware implementation of such a GMSK receiver with both synchronizers can be modeled for providing simulated BER performance. With data precoding of the original data bit stream prior to transmission of the CPM signal, the synchronizers can function as serial demodulators that achieve absolute phase data detection. The data preceding and data aided synchronization approach for detecting symbol timing and carrier phase error is central to providing accurate symbol time and carrier phase tracking in the synchronizers with reduced design complexity. These and other advantages will become more apparent from the following detailed description of the preferred embodiment.

Problems solved by technology

The use of CPM signals in communications systems can potentially achieve significant improvement in both power and spectral efficiency over other conventional modulation techniques, at the cost of a moderate increase in receiver complexity.

Often, symbol time tracking and carrier phase tracking limit the performance of CPM systems.

These synchronizers often lose track during noisy communications.

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