WWVB time signal broadcast: an enhanced broadcast format and multi-mode receiver

WWVB is a broadcast station, operated by the National Institute of Standards and Technology, which has been broadcasting time information to radio-controlled clocks (RCC) throughout the continental US since 1965. The transmitted information includes the year (excluding the century), day, hour, minute, and notifications for leap seconds and for daylight saving time (DST) transitions. By receiving this information from WWVB, RCCs can acquire and maintain accurate timing and automatically adjust for DST transitions and leap seconds. The legacy amplitude modulation (AM)-based broadcast format, introduced in the 1960s, while allowing for a simple implementation of a receiver with the technology of that era, exhibits low efficiency. Consequently, RCCs based on it often fail to receive reliably, particularly in locations that are distant from the station, such as on the East Coast. To improve the station's coverage, an enhanced broadcast format, based on the addition of phase modulation (PM), was deployed in 2012. This article presents an overview of this new broadcast format and its enhanced features, including its modulation scheme, information encoding, channel coding, and transmission modes. These features enable more reliable receiver performance and greater time-keeping accuracy at reduced power consumption. Additionally, various challenges and considerations associated with the design of receivers for the new broadcast format are presented.