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A simple model for average backscatter power from clutter is developed for indoor RF sensing applications and verified through measurements. A narrowband 28 GHz sounder used a quasi-monostatic radar arrangement with an omnidirectional transmit antenna illuminating an indoor scene and a spinning horn receive antenna less than 1 m away collecting backscattered power as a function of azimuth. Median average backscatter power was found to vary over a 12 dB range, with average power generally decreasing with increasing room size. A deterministic model of average backscattered power dependent on distance to nearest wall and clutter reflection coefficient reproduces observations with 4.0 dB RMS error. 

Outdoor-to-indoor signal propagation poses significant challenges to millimeter-wave link budgets. To gain insight into outdoor-to-indoor millimeter-wave at 28GHz, we conducted an extensive measurement campaign consisting of over 2,200 link measurements in West Harlem, New York City, covering seven highly diverse buildings. A path loss model constructed over all measured links shows an average of 30dB excess loss over free space at distances beyond 50m. We find the type of glass to be the dominant factor in outdoor-to-indoor loss, with 20dB observed difference between grouped scenarios with low- and high-loss glass. Other factors such as the presence of scaffolding, tree foliage, or elevated subway tracks, as well as difference in floor height are also found to have a 5–10dB impact. We show that for urban buildings with high-loss glass, outdoor-toindoor downlink capacity up to 400Mb/s is supported for 90% of indoor customer premises equipment by a base station up to 40m away. For buildings with low-loss glass, such as our case study covering multiple classrooms of a public school, downlink capacity over 2.8/1.4Gb/s is possible from a base station 57/133m away within line-of-sight. We expect these results to help inform the planning of millimeter-wave networks targeting outdoor-toindoor deployments in dense urban environments, as well as provide insight into the development of scheduling and beam management algorithms. Index Terms—Millimeter-wave wireless, 28 GHz measurements, path loss models, wireless network planning, 5G-andbeyond networks. 

In the US, people spend 87% of their time indoors and have an average of four connected devices per person (in 2020). As such, providing indoor coverage has always been a challenge but becomes even more difficult as carrier frequencies increase to mmWave and beyond. This paper investigates the outdoor and outdoor-indoor coverage of an urban network comparing globally standardized building penetration models and implementing models to corresponding scenarios. The glass used in windows of buildings in the grid plays a pivotal role in determining the outdoor-to-indoor propagation loss. For 28 GHz with 1 W/polarization transmit power in the urban street grid, the downlink data rates for 90% of outdoor users are estimated at over 250 Mbps. In contrast, 15% of indoor users are estimated to be in outage, with SNR < −3 dB when base stations are 400 m apart with one-fifth of the buildings imposing high penetration loss (∼ 35 dB). At 3.5 GHz, base stations may achieve over 250 Mbps for 90% indoor users if 400 MHz bandwidth with 100 W/polarization transmit power is available. The methods and models presented can be used to facilitate decisions regarding the density and transmit power required to provide high data rates to majority users in urban centers. 

Outdoor-to-indoor (OtI) signal propagation further challenges link budgets at millimeter-wave (mmWave). To gain insight into OtI mmWaveat28GHz, we conducted an extensive measurement campaign consisting of over 2,000 link measurements in West Harlem, NewYorkCity, covering seven highly diverse buildings. A path loss model constructed over all links shows an average of 30dB excess loss over free space at distances beyond 50m. We find the type of glass to be the dominant factor in OtI loss, with 20dB observed difference between clustered scenarios with low- and high-loss glass. Other factors, such as difference in floor height, are found to have an impact between 5ś10dB. We show that for urban buildings with high-loss glass, OtI data rates up to 400Mb/s are supported for 90% of indoor users by a base station (BS) up to 49m away. For buildings with low-loss glass, such as our case study covering multiple classrooms of a public school, data rates over 2.8/1.4Gb/s are possible from a BS 68/175m away when a line-of-sight path is available. We expect these results to be useful for the deployment of OtI mmWave networks in dense urban environments and the development of scheduling and beam management algorithms.