A demod-remod coherent tracking loop for QPSK and SQPSK is described and analyzed. This type of receiver is attractive since all of the available signal power is despread and used to generate the tracking error signal when the pulses reaching the nonlinearities are rectangular. The same demod-remod circuit is widely used for bandlimited pulses, for which less than full power is converted to the carrier phase error signal. All system parameters pertinent to system performance are enumerated. The effects of the IF and arm filters on the statistics of the noise are determined. With respect to the signal, the filters are considered only insofar as they reduce the delivered signal power. It is demonstrated how a tracking phase error converts some of the signal power into additional noise power. The results of performance computation are presented.

A demod-remod coherent tracking loop for QPSK and SQPSK is described and analyzed in [1]. Those results are used to obtain the power spectral density of the equivalent noise of the tracking loop and the probability density function of the steady-state phase error, The effects of the IF and arm filters on the statistics of the noise and QPSK signal are developed. The results of performance computations are presented.

The spread spectrum acquisition and tracking performance for the ShuttleS-band andKu-band communication links are analyzed and compared to test results. TheS-band link requirements are more severe than those of theKu-band links, hence, different despreader designs were developed for the two systems. TheS-band despreader acquires pseudonoise code lock by examining all possible code phases in half chip steps while theKu-band despreader acquires pseudonoise code lock by continuously sweeping a tau-jitter loop. Both despreaders employ a tau-jitter loop for code tracking. The code tracking performance is computed for the tau-jitter loop and compared to that of the more complex delay lock loop.

The performance of a class of pulse Doppler radars with a digitally implemented signal processing unit is investigated. TheKuband rendezvous radar onboard the Shuttle Orbiter is a pulse Doppler radar which is in this class. The detection capability is first presented. A unified analysis of digital radar tracking loops is presented which employs logarithmic discriminants. The results are applied to angle, range, and range rate tracking loops. Numerical results of the amplitude monopulse angle tracking loop are presented for theKu-band rendezvous radar of the Space Shuttle.

Unbalanced quadriphase-shift-keying (QPSK) is an attractive means for transmitting two digital data streams which in general have different average powers, data rates, and data formats. Previous analyses of the tracking performance of Costas loop demodulators of unbalanced QPSK have accounted only for the filtering effect produced by the loop's two arm filters on the equivalent additive noise perturbing the loop. When the bandwidth of these filters is selected on the order of the data rate, as is typical of optimum Costas loop design, the filtering degradations of the data modulations themselves and the crossmodulation noise produced by their multiplication in the loop often cannot be neglected. The purpose of this paper is to incorporate these additional filtering effects into the analysis. Many of the results obtained herein are in the form of closed-form expressions which can easily be evaluated numerically for design and performance prediction purposes.