New Improved System for WWVB Broadcast
The WWVB broadcast of the time-code signal has not undergone major changes in its communications protocol and modulation scheme since its introduction in 1963. Its amplitude-modulation (AM) and pulse-width based representations of its digital symbols were designed to allow for a simple low-cost realization of a receiver based on envelope detection, resulting in poor efficiency in the modulated signal, as with AM audio broadcasting. Over a decade ago, the station's power was significantly increased, allowing the broadcast from Colorado to effectively cover most of North America. This has spurred the popularity of radio-controlled clocks and watches, more commonly known as "atomic clocks". However, electromagnetic interference (EMI) experienced in typical residential and office environments can make it difficult to receive the WWVB signal in various locations.
A new protocol and backward-compatible modulation scheme was proposed and accepted for deployment by NIST to effectively addresses these problems. This will enable greatly improved reception of the WWVB broadcast without impacting the existing devices. The backward-compatibility is achieved by maintaining the existing AM characteristics, while adding various new features through phase modulation (PM). The new modulation scheme and protocol are described and are shown to be effective in addressing these challenges, resulting in several orders of magnitude in performance improvements. Preliminary analyses, including simulated and measured results, were presented to illustrate the challenges encountered in existing receivers, at the 43rd Annual Precise Time and Time Interval (PTTI) Meeting.
Students Involved: S. Balasubramanian