Low-complexity symbol timing error detection for quasi-orthogonal space-time block codes

The author presents the design and analysis of low-complexity symbol timing error detectors (TEDs) for timing synchronisation in quasi-orthogonal space-time block code (QOSTBC) receivers. The estimators operate on data symbols and approximate decision variables, producing timing error measurements which are shown to be robust to channel fading. In evaluating the detector S-curve for the general form of the estimator, the author shows that the result is independent of the constellation rotation angle employed by the code. The expressions for the estimation error variance and TED signal-to-noise ratio are also obtained, with the analysis carried out under the assumptions of perfect data and channel knowledge at the receiver. Through system simulations, the effects of decision errors on the detector characteristics are examined, and the overall system performance is evaluated, where the proposed TEDs are incorporated into the receiver timing loop. Receivers with perfect channel knowledge and pilot-based channel estimation are considered. Symbol error rate results show timing synchronisation loss of less than 0.5 dB for a receiver with perfect channel information. In addition, it is shown that the receiver is able to track the timing variations two orders of magnitude faster than required by the present-day hardware oscillators.