Digital Synchronization of Software-Defined Radios in a Wireless Distributed Radar Network

Abstract

Precise synchronization of time, frequency, and phase is crucial for coherent processing in distributed radar systems, especially at higher frequencies where timing errors rapidly degrade performance. To enable distributed radar operations, such as coherent transmit beamforming, distributed radar systems must achieve time synchronization on the order of tens of picoseconds, requiring extraordinarily robust techniques to correct timing errors. The gr-harmonia out-of-tree module implements a synchronization algorithm to achieve time, frequency, and phase alignment across distributed radar networks using Universal Software Radio Peripheral (USRP) Hardware Driver (UHD)-compatible software-defined radio (SDR) systems. The algorithm is realized entirely in digital signal processing and thus requires no additional hardware, allowing it to be implemented in networks of unmodified SDRs. Because the synchronization approach is decentralized, it scales efficiently with an arbitrary number of nodes to be synchronized. The module operates exclusively through the GNU Radio message passing interface, converting pulsed data into a protocol data unit (PDU) to reduce buffering-induced latency. The module utilizes UHD burst mode with metadata flags to schedule pulses with accurate timing. It comprises blocks for waveform generation, transmission, and reception, as well as frequency and time peak estimation, clock drift estimation, clock bias, and phase estimation. In this paper, the synchronization framework and functionality of each block are discussed, and the results of the synchronization process are shown for data collected from an open-air test with three Ettus X310s using gr-harmonia.