The True Performance of the Simplified Data Transition Tracking Loop

Abstract

The tracking performance of a simplified (no transition detector in the in-phase arm and no delay in the quadrature arm) data transition tracking loop (SDTTL) suggested in the conference literature (Chiu and Lee, 1987) a number of years ago for symbol synchronization of an NRZ data stream is presented. It is shown that, contrary to what was previously stated in Chiu and Lee, 1987, the SDTTL and the traditional DTTL have performances that are quite different, the latter always being the more superior. In fact, asymptotically for large symbol SNR, the mean-squared timing error of the SDTTL is 3 dB worse than that of the DTTL which considerably negates its implementation simplification. Even at low SNR, where neither scheme would be motivated by maximum a posteriori (MAP) estimation of symbol sync considerations, the DTTL still outperforms the SDTTL.