Method for High Precision Clock Synchronization in Wireless Systems with Application to Radio Navigation

In this paper we present a novel approach for high precision clock synchronization in wireless systems. A concept similar to the standard FMCW (frequency-modulated continuous wave) radar principle is used to estimate the offset in time and in frequency between two wireless communication units. The novel approach allows for a synchronization of both offsets significantly below 100 ps and 10 Hz, respectively. This highly accurate synchronization is used in a prototype system to measure the distance between wireless units similar to a secondary radar. The prototype works within the 5.8 GHz ISM-band and uses a bandwidth of 150 MHz. With the setup presented we can measure the distance between two radio units with a standard deviation of 4 to 5 cm over a range of 200 m. This distance deviation implies a clock and center frequency synchronization of both communication modules significantly below 100 ps and 1 ppb, respectively. The broadband measurement principle is robust towards multi-path interference. It can be extended to other frequency bands and is well-suited for direct integration into communication channels and novel modulation principles such as OFDM (orthogonal frequency division multiplexing) or SC/FDE (single carrier transmission with frequency domain equalization), e.g. for locatable WLAN (wireless local area network) devices or wireless sensor networks