Performance of a Soft Digital-Data-Transition Tracking Loop

A report discusses the performance of a soft digital-data-transition tracking loop (DTTL) in a radio receiver that recovers digital data conveyed by binary phase-shift keying. The DTTL is used as a symbol synchronizer; it provides symbol timing to essential parts of the receiver. The DTTL includes a quadrature channel and an in-phase channel, which contains a transition detector with a hyperbolic-tangent response. The DTTL is said to be "hard" or "soft" in the special case of high or low signal-to-noise ratio (high or low SNR, respectively), for which the hyperbolic tangent can be approximated as a hard-limiting or a linear function, respectively.