Characterisation and synchronisation of a netted software defined radio radar

The present work intends to characterise the combination of two netted software defined radios (SDR) and different radio frequency (RF) front-ends installed in them, together with a two-stratum time dissemination and synchronisation system. A modified implementation of the Network Time Protocol is used as coarse event synchronisation for either SDR back-end. The White rabbit light embedded node implementation of the commonly known white rabbit synchronisation system (IEEE 1588 PTP-2019) or arbitrary wave form generators are used as fine time dissemination system for either SDR. The resulting netted transceiver system is intended to compose a demonstrator for proof-of-concept experiments. The findings presented in this article show that the chosen combination of hardware and software is suitable for radar applications operating within L-, S- and C-bands. A channel coherency throughout the network with a relative modified Allan deviation of less than 80 fs for averaging intervals of 1 s, a phase noise better than −118 dBc/Hz at 10 Hz frequency offset and a fractional frequency lower than $\pm 2.5\cdot 10^{-13}$ was measured. Within a single transceiver node, a fractional frequency lower than $\pm 2\cdot 10^{-13}$ and phase noise of −124 dBc/Hz at 10 Hz frequency offset were measured as well. Multistatic radar systems exploit wide spatial diversity to enhance target detection and tracking, albeit with increased complexity when compared to a monostatic configuration. To exploit these benefits, all participating transceiver nodes within the netted radar need to synchronise to a common time base $\left(t_0\right)$. The achieved synchronisation level increases the accuracy with which the chain of timed events at the transmitter and at the receiver side occur, intending to maximise the signal-to-noise ratio available at the receiver. The Universal software radio peripheral model X310 with two different daughterboard models as RF front-end was used as SDR on either radar node. A network combining data and synchronisation purposes allowed the radar nodes under test to operate synchronously. The two-stratum synchronisation system used glass fibres between 2 m and 5 km of length or coaxial cables with 2 m in length for network traffic, time and frequency dissemination purposes. The multiple RF front-ends were stimulated by means of arbitrary waveform generators with calibrated traceability. Up-chirp and sinusoid waveforms were used as stimuli for measuring the offset of either channel with regards of $t_0$ to ultimately estimate the achievable coherency limits of the system under test. Both analogue and digital evaluation methods were considered.