5G-Compliant Integrated Sensing and Communication at Sub-6 GHz: Experiments with SDRs and OpenAirInterface

Inhalt:
Integrated Sensing and Communication (ISAC) is attracting significant interest, with numerous studies highlighting its potential in 5G and beyond. Unfortunately, due to the inherent difficulty in integrating ISAC into non-proprietary hardware and software platforms, experimental works remain few and mainly focused on the use of 5G NR-like waveforms (often within simulated environments), lacking a 5G-compliant protocol stack enabling an end-to-end network connectivity. In this work, we present an experimental testbed for monostatic ISAC based on Software Defined Radios (SDRs) and OpenAirInterface (OAI), an open-source 5G framework adhering to the 3GPP standard. In addition to a description of the main implementation details, we present a fully digital signal processing pipeline which utilizes downlink slots of a 5G OFDM-based communication in the sub-6 GHz n77 band to enable ISAC capabilities at the 5G Node B. In the first phase, processing steps include temporal alignment of the TX and RX I/Q samples, compensating for the processing delays introduced by the OAI framework and SDR platforms. Then, after dealing with the lack of TX–RX isolation and associated Self-Interference (SI) through fully digital mitigation techniques, the digitized signals are processed using either a Matched Filter or Channel Estimation-like scheme. Experimental evaluations conducted in a cluttered indoor environment under controlled target conditions show promising capabilities in estimating both range and velocity of targets, also highlighting notable tradeoffs arising from the presence of side-lobes in the range-Doppler maps, linked to residual SI and use of 5G communication signals.