Clock Synchronization Accuracy of Power Line Communication Connected Devices: a Case Study

In this paper a case study of two network nodes interconnected over power line communication technology is provided. Standard ping utility was modified to generate timestamps corresponding to those used in SNTP. Experimental estimation of the round trip delay and clock offset was carried out utilizing ST8500 PLC-G3 modems from ST Microelectronics. It was found that uplink and downlink delays exhibit a jitter causing communication channel asymmetry which is detrimental for the accuracy of the SNTP clock synchronization. It is suspected that the reason of uplink and downlink delays jitter is mainly due to RTOS controlled software implementing communication stacks on both client and server sides. Nevertheless, the accuracy of clock adjustment may be improved by averaging a group of clock offset estimates. In particular, to achieve approximately 10 ms accuracy 100 SNTP transactions has to be completed and the mean offset used to adjust the client clock.