| Authors: | |
| Raghun | |
| An M. Rao | |
| Harpreet S. Dhillon | |
| Vuk Marojevic | |
| Jeffrey H. Reed |
One Sentence Summary:
consider an underlay radar- to receive and transmit beamforming capabilities of the radar massive MIMO spectrum sharing scenario in which massive and BS, respectively
Abstract:
-In this paper, we consider an underlay radar- to receive and transmit beamforming capabilities of the radar massive MIMO spectrum sharing scenario in which massive and BS, respectively. Therefore, it is important to understand MIMO base stations (BSs) with elevation beamforming capa- the worst-case interference at the radar as a function of key cbeilnittieersedareataltlhoewerdadtaor.opMeroadteelionugtstihdee aloccairtciounlasr oefxctlhuesiomnaszsoinvee deployment parameters in such scenarios. MIMO BSs as a homogeneous Poisson point process (PPP), we Related Work: Multi-antenna techniques have been wellderive an analytical expression for a tight upper bound on the explored in the radar-communications coexistence literature. average interference at the radar due to cellular transmissions. In the case of coordination between the primary and secondary The challenge lies in bounding the worst-case elevation angle for users, MIMO techniques have been investigated in the context ebaacshedmoanssivtheeMcIiMrcOumBrSa,dfiourswdhiiscthriwbuetdioenvisoefaanotvyepliccaolnsPtrouiscstoionn- of spectrum sharing between a MIMO radar and the MUVoronoi (PV) cell. While these worst-case elevation angles are MIMO downlink [2], MIMO radar and full-duplex cellular correlated for neighboring BSs due to the structure of the PV systems [3], and MIMO radar and a MIMO communication tessellation, it does not explicitly appear in our analysis because of system [4], under performance and power constraints. Even our focus on the average interference. We also provide an estimate though secondary user interference mitigation is possible using aofs tahecinroclme inwaitlhavaerreaageeqinutaelrfteoretnhcee abvyeraapgperoaxreimaaotfintgheeatcyhpiccealll multi-antenna radars in uncoordinated scenarios [5], its feasicell. Using these results, we demonstrate that the gap between bility in the presence of a large multi-cell network of massive the two results remains approximately constant with respect to MIMO BSs is limited to scenarios of sparse deployments the exclusion zone radius. Our analysis reveals useful trends and/or large exclusion zone radii. in average interference power, as a function of key deployment Owing to its tractability, tools from stochastic geometry eplaermaemnettserpsersurcahdaasr/rBaSd,arB/SBSdaennsteitnyn,aanhdeigehxctslu,nsiuomnbzeornoefraandtieunsn.a have been used recently to analyze spectrum sharing systems [6], [7]. Authors in [8] considered a radar-WiFi spectrum Index Terms-Stochastic geometry, radar-massive MIMO sharing scenario, where WiFi access points (APs) were modcoexistence, 3D beamforming, Rician channels, exclusion zones, average interference. eled as a homogeneous PPP. The exclusion zone radius was computed for different scenarios based on side-information available at the APs. In [9], the authors evaluated the mean agI. INTRODUCTION gregate interference from Wi-Fi APs to radar using tools from Spectrum sharing and massive MIMO are two key spectral stochastic geometry. However, these works consider azimuthefficiency enhancing techniques that have been included in only beamforming, and do not model the impact of elevation the Third Generation Partnership Project (3GPP) Release 15 beamforming, which is a prominent feature introduced in specifications. While massive MIMO enhances spectral effi- 5G NR. While [10], [11] considered the elevation angle, the ciency by increasing the dimension of spatial multiplexing focus of these works is on antenna height optimization and by an order of magnitude, spectrum sharing improves it by interference mitigation in cellular networks. sharing spectrum between different wireless technologies in Contributions: In this work, we develop a novel and the spatial and temporal dimensions. Spectrum sharing is tractable analytical framework to analyze the average inparticularly attractive in the sub-6 GHz frequency bands, terference power in radar-massive MIMO spectrum sharing where spectrum is under-utilized due to conservative policies scenarios, which is a key metric that has been used in drafting [1]. Among the various incumbents, radars are the biggest spectrum sharing policies in recent years [12]. Incorporating consumer of spectrum in the sub-6 GHz bands. In underlay elevation beamforming into the stochastic geometry frameradar-cellular spectrum sharing scenarios where the estab- work is challenging, since Voronoi cells of the BSs can lishment of an exclusion zone limits cellular interference to be arbitrarily large. To overcome this, we devise a novel the radar, coordination is often impossible due to security formulation based on the circumradius distribution of the concerns, or unfeasible due to practical limitations. The lack Voronoi cell [13]. In addition, the presence of sidelobes result of coordination can potentially exacerbate the interference due in a beamforming gain that is a non-monotonic function of the elevation angle. We derive an upper bound on the beamforming DeRpa.rMtm.eRntaoo,fHE.CSE.,DVhiilrlgoinniaanTdeJc.hH,.BRlaecekdsbaurreg,wVitAh,W2i4re0l6e1s,s@UVSAT, (Ber-amdaleily: gain that monotonically decreases with the elevation angle, {raghumr,hdhillon,reedjh}@vt.edu). V. Marojevic is with the Department of which is crucial to deriving the upper bound on the average ECE at Mississippi State University, Mississippi State, MS, 39762, USA (e- interference. We also derive the nominal average interference CmNaiSl:-1v5u6k4.m14a8ro,jeCvNicS@-1e6c4e2.m87ss3t,ataen.edduE).CTChSe-1s7u3p1p7o1rt1oifsthgeraUte.fSu.llNySaFckGnroawntls- power by modeling each Voronoi cell as a circle of area equal edged. to the average area of a typical cell. Finally, we provide