Low-latency RFI Nulling and Multi-User Scaling for 5G and Radio Astronomy Coexistence

5G network operators are constantly under pressure from regulatory agencies who restrict the deployment of base stations (gNBs) close to incumbent services, such as radio astronomy services (RAS), to avoid interfering with them. Recent works for coexistence with RAS employ limited channel modeling approaches and use explicit out-of-band communication between the gNB and RAS. However, the strict latency requirements of 5G make explicit communications less desirable due to their overheads. Deploying gNBs close to RAS is also not yet supported. In this paper, we propose a proactive open-loop beamforming and interference nullification technique in which a gNB nullifies its downlink signal at a nearby RAS telescope while beamforming to its users (UEs). We estimate the gNB-RAS channel using raytracing on open-source terrain maps. We formulate a problem that maximizes the minimum rate for UEs under the constraint of maximum allowable interference power at the RAS and show that its time complexity scales cubically with the number of gNB antennas. Hence, we propose a heuristic solution that achieves 4 orders better latency and 100 dBW lower interference power than the max-min rate solution with similar sum rate on users. Our proposed solution consistently achieves less than -310 dBW interference power, even when the gNB-RAS distance is less than 1 km, satisfying international regulations, and is robust against moving users that vary in location and elevation.