Space-Time Coding for Aeronautical Telemetry: Part I—Estimators

This paper derives and analyzes the estimators required for detection and decoding of Alamouti-encoded-shaped offset QPSK version TG (SOQPSK-TG). The joint maximum likelihood (ML) estimators for the frequency offset, channel delays, and channel gains are derived and analyzed. As a complexity-reducing technique, a sequential version of the ML estimators is developed. The Cramér-Rao bound for the parameters is derived and used to analyze the performance of the estimators to determine pilot sequence length. The complexity of the frequency estimator is reduced by applying the Zoom FFT algorithm in the coarse search. The complexity of the channel delay estimator was reduced by developing a novel version of the simplex search algorithm that operated on a discrete two-dimensional grid. These estimation algorithms were implemented in a prototype demodulator that was field tested at Edwards AFB.