Exploiting Smartphone Peripherals for Precise Time Synchronization Achieving precise time synchronization across a collection of smartphones poses unique challenges due to their limited hardware support, exclusively wireless networking interface, and restricted timing stack control. Given the ubiquity and popularity of smartphones in modern distributed applications, clock discrepancies often lead to degraded application performance. In this paper, we present and evaluate alternative approaches to attain precise time synchronization by leveraging the various peripherals available on modern smartphone devices. Our evaluation across Android smartphones typically attains synchronization accuracy within (i) 200xc2xb5s using audio, (ii) 3000xc2xb5s using Bluetooth Low Energy, and (iii) 1000xc2xb5s using WiFi. Under certain conditions, we show that smartphones synchronized using one peripheral can accurately timestamp and generate synchronous events over other peripherals. The provided guide and accompanying opensource implementations offer developers a means to select the appropriate time synchronization technique when building distributed applications.

IEEE 1588Based General and Precise Time Synchronization Method for Multiple Sensors * An increasing number of robotic systems contain multiple sensors, and the accurate timestamps of sensors are crucial for fusing multiple sensors information in robot applications. However, the accuracy and stability of traditional timestamp synchronization algorithms are degraded when synchronizing the timestamps of multiple sensors, due to the clock inconsistency, asynchronous trigger delay, and variable transmission delay. This paper presents a general and precise time synchronization method for multiple sensors with respect to a local clock (i.e. typically a computerxe2x80x99s internal clock). First, to reduce the software scheduling delay, an IEEE 1588based method, which combines hardware and software to obtain timestamps, is formulated to modify the masterslave timestamp acquisition location. Second, a hardware synchronization trigger method is proposed to reduce the runtime of trigger threads in the software, by introducing the microprocessor to trigger multiple sensors synchronously. Finally, a timestamp matching method is proposed to reduce the unreliability of variable communication delays by matching the trigger timestamp and the timestamp of data reception. To the best of our knowledge, this approach is the first synchronization method to combine hardware and software to obtain the timestamps of multiple sensors. Results show that the ability of our method can estimate time offset to microsecond accuracy.