Receiver Design of Radio-Controlled Clocks Based on the New WWVB Broadcast Format

Abstract

The architecture and algorithms for the first alldigital radio-controlled clock receiver for the new WWVB broadcast format are proposed. To address the potentially low signal-to-noise ratio conditions and the relatively large frequency offsets experienced in the receiver, two alternative timing synchronization approaches are investigated, i.e., one based on a maximum-likelihood (ML) criterion and the other based on correlation. We show that the correlation-based synchronization technique reduces the implementation complexity by over 50%, while its performance is only less than 1 dB inferior to that of the ML-based technique. Decision and detection algorithms are proposed for two operating regimes in the receiver: tracking and acquisition. In tracking, the proposed decision strategies reduce the timing mean squared error by as much as 63% compared with what the synchronizer produces without any additional processing. In acquisition, the proposed joint synchronization and decoding technique significantly improves the robustness by exploiting the channel code in the data. Compared with receivers based on the legacy broadcast, over 15 dB performance gains are achieved by the modulation and algorithms proposed for the tracking and acquisition operations. In addition to reception performance analyses, energy consumption tradeoffs are also presented.

Sequential Frame Synchronization Based on Hypothesis Testing With Unknown Channel State Information

“…It is concluded that hypothesis testing has a clear performance advantage over point estimation only if the sync word is relatively short with respect to frame length (less than 20%). Future work will take into account the large and time-varying frequency offset at the receiver, such as that experienced in RCC receivers [16], [19]. Potential interference should also be considered in designing the synchronization framework.…”

“…Substituting (22) into (19), changing the variable from ν 1−η and − ν 1+η to ν, and using the identity [24] ∞ 0…”

“…into (19) if c i+n = −c i , and substituting (22) into (19) if c i+n = c i . Similarly, due to independence of noise samples, the characteristic function of V is:…”

“…For example, after making bit decisions for BPSK modulated signals, the channel is effectively modeled as a Binary Symmetric Channel (BSC) for synchronization purposes, and hence the channel gain does not affect the synchronization performance [18]. However, for receivers operating in low SNR conditions, such as a radio-controlled clock (RCC) for the WWVB broadcast [16], [19], accurate bit decisions cannot be made before the synchronization. Since the synchronization process exploits the entire known sequence representing the sync word, it has higher effective output SNR than the SNR per bit.…”