Jitter Floor Elimination for Blind Feedforward/Feedback Symbol-Timing Recovery Exploiting the Extended Zero-Crossing Property

Carrier-blind and non-data-aided recovery of the symbol timing is of paramount importance in digital receivers, that is, detailed knowledge about carrier frequency and phase or any pilot sequence is not necessary for proper operation. In this context, feedforward algorithms are particularly helpful in packet-oriented systems, where rapid and stable acquisition of the major transmission parameters is essential for subsequent processing stages. On the other hand, feedback algorithms are typically used to track small deviations from the stable equilibrium point. In the current paper, we propose a new approach for blind feedforward and feedback recovery of the symbol timing, which needs just one or two samples per symbol. The method is characterized by a second filter operated in parallel to the receiver-matched filter. Under Nyquist conditions, exemplified by baseband pulses having a square-root raised cosine spectrum, this filter exhibits an impulse response satisfying the extended zero-crossing property, that is, it vanishes for all integer multiples of the symbol period including the origin. Using this idea for symbol-timing recovery, it is shown that the annoying jitter floor – typical for most timing recovery schemes and caused by inter-symbol interference – can be avoided irrespective of the selected modulation scheme