IEEE 1588 Clock Synchronization Performance over Time-Varying Wireless Channels

One of the major requirements of Ultra-Reliable Low-Latency Communications (URLLC) is a high clock synchronization performance between nodes. This is especially critical in Industrial Wireless Sensor and Actuator Networks (IWSAN), where every sensor and actuator of the network must take samples with very precise timing. In this paper, we detail the challenges of distributing a global base time in wireless communications and address some insights to achieve a very high clock synchronization performance. Besides this, Orthogonal Frequency-Division Multiplexing (OFDM) has been proposed to be used in the next generation of industrial communication standards, such as SHARP, due to their robustness in high dispersive channels. Based on these considerations, we have built an IEEE 802.11a/g modem with hardware timestamping and we have evaluated the clock synchronization over several wireless channels. The wireless channels have been run in a channel emulator and they represent four different scenarios: small office, big office, open space, and small factory. The results show that clock synchronization is quite affected by channel dispersion and channel Doppler speed, but the performance of our system is good enough to its use in industrial scenarios and comparable to Ethernet-based synchronization at channels with low and medium dispersion.