Low-power high-accuracy timing systems for efficient duty cycling

Abstract

Time keeping and synchronization are important services for networked and embedded systems. High quality timing information allows embedded network nodes to provide accurate time-stamping, fast localization, efficient duty cycling schedules, and other basic but essential functions -all of which are required for low power operation.In this paper we present a new type of local clock source called Crystal Compensated Crystal based Timer (XCXT) and a number of novel algorithms that effectively utilize it to achieve low power consumption in wireless sensor networks. The XCXT has timing accuracies similar to timers based on temperature compensated crystal oscillators (TCXO) but has a lower implementation cost and requires less power. Our initial 8MHz prototype unit, using the simplest algorithm, achieves an effective frequency stability of ±1.2ppm and consumes only 1.27mW. On the other hand, commercially available TCXOs with similar stability can cost over 10 times as much and consume over 20mW.In addition to the prototype, we will present algorithms that will improve the XCXT's power consumption by at least 48%, depending on application and environmental conditions. We will also show how XCXT's power efficiency can be improved even further by employing clocks at different frequency when different time granularities are required by an application.

Putting the software radio on a low-calorie diet

“…The simplest way to lower the floor on achievable duty cycle is to reduce the clock skew, which in turn requires stabilizing the crystal using a range of simple, complex, or exotic mechanisms [5,7,8,9,17,26,34,35]. We find, however, that a commercially-available temperature-compensated crystal oscillator (TCXO) like the DS32KHz [3] offers sufficient stability -on the order of ±2 ppm indoors -and draws only 2 µA, offering a lower bound on the duty cycle of just DC = 2 × r skew = 0.0004%.…”

Development of Energy Efficiency Aware Applications Using Commercial Low Power Embedded Systems

“…Further clock conversions in ESPs would cause additional power consumption. Therefore, as has been shown previously (e.g., (Schmid et al, 2010;SiLabs, 2003)), from the point of view of power consumption, using the external low-frequency clock crystal is often much more convenient than using a high-frequency internal crystal and later dividing the frequency.…”

Support for a Long Lifetime and Short End-to-End Delays with TDMA Protocols in Sensor Networks

“…To shorten guard times, reference [24] introduces sensor nodes equipped with two oscillators, reducing frequency stability to ± 1.2 ppm. Another work [25] applies the LR (linear regression) to previous drift samples and shorten guard times.…”