Wireless IEEE1588 over an Infrared Interface

Wireless communication is one of the key topics in the time of internet of things (IOT) and industry 4.0. Every sensor or actor should be smart and able to communicate over a network and in many cases a wired network is not an option. For the use in industrial and measurement and control networks, the devices have to be synchronized via the wireless link as well. There are many different wireless technologies, most of them are radio based and not deterministic (reflections, retransmission, etc.) which makes them quite challenging for implementing the Precision Time Protocol (PTP). Instead of using radio based communication also free-space optical (FSO) communication e.g. infrared can be used. Serial infrared (SIR) is a very simple, short-range, limited-bandwidth, low-power, cheap and deterministic method to transfer data via a Universal Asynchronous Receiver Transmitter (UART) like protocol between multiple infrared nodes. The combination of PTP with SIR has been studied in this paper. Especially the timestamping and encapsulation of PTP frames has been analyzed in detail. An experimental implementation based on an FPGA transceiver is outlined and synchronization accuracy measurements done with different spacing between two nodes. Experimental results are presented that show that sub-microsecond synchronization via a wireless link can be achieved and that free-space optical communication can be an equally useful approach compared to radio communication if it comes to low-bandwidth, short-range wireless communication.