Traditional oscillators used in timing modules of CDMA and WiMAX base stations are large and expensive. Applying cheaper and smaller, albeit more inaccurate, oscillators in timing modules is an interesting research challenge. An adaptive control algorithm is presented to enhance the oscillators to meet the requirements of base stations during holdover mode. An oscillator frequency stability model is developed for the adaptive control algorithm. This model takes into account the control loop which creates the correction signal when the timing module is in locked mode. A recursive prediction error method is used to identify the system model parameters. Simulation results show that an oscillator enhanced by our adaptive control algorithm improves the oscillator performance significantly, compared with uncorrected oscillators. Our results also show the benefit of explicitly modeling the control loop. Finally, the cumulative time error upper bound of such enhanced oscillators is investigated analytically and comparison results between the analytical and simulated upper bound are provided. The results show that the analytical upper bound can serve as a practical guide for system designers.

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Journal IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control
Zhou, H. (Hui), Kunz, T, & Schwartz, H.M. (2011). Adaptive correction method for an OCXO and investigation of analytical cumulative time error upper bound. IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, 58(1), 43–50. doi:10.1109/TUFFC.2011.1772