An all-digital timing recovery scheme for voiceband data modems

The paper describes a method for recovering the baud timing in digitally implemented modem receivers when the sampling clock of the A/D converter at the receiver input is fixed. The all-digital scheme is particularly well suited for the implementation of high-speed voiceband modems on a powerful digital signal processor (DSP). It has the advantage of simplifying the analog front end (AFE) hardware and the interface between the AFE and the DSP. The scheme has been implemented in hardware as part of a 2400 bps full duplex voiceband modem. Its measured performance is equivalent to that of the standard approaches.