STARE: Real-Time Software Receiver for LTE and 5G NR Positioning and Signal Monitoring

STARE, a real-time SofTwAre REceiver for positioning with the long-term evolution (LTE) and fifth-generation (5G) new radio (NR) cellular downlink signals, is presented and demonstrated. The real-time operation is achieved by interfacing directly with the software-defined radio (SDR), therefore avoiding the requirement to store the captured signal on a drive and allowing to process signals continuously over arbitrarily long periods. STARE supports multi-channel SDRs and parallel execution of an arbitrary number of tracking channels, which independently acquire and track the desired signals. During the acquisition stage, the tracking channel applies a path selection criterion based on the signal-to-noise ratio (SNR) of the earliest path to prevent incorrect delay and phase estimation, which may occur when the channel order is overestimated. The design of the tracking stage follows a closed-loop architecture providing a continuous estimation of the delay, Doppler, phase, and SNR. The real-time operation of STARE is demonstrated by monitoring downlink signals of a commercially operated LTE base station for an uninterrupted period of one week. For this purpose, STARE is deployed on a static monitoring setup composed of a processing unit, an SDR, an omnidirectional antenna, and a high-precision Rubidium reference clock. The collected measurements are used to study the SNR and delay errors. The delay errors are estimated using the code-minus-carrier (CMC) technique and are observed to achieve a sub-meter standard deviation.