O. Kanhere and T. S. Rappaport, “Position Location for Futuristic Cellular Communications - 5G and Beyond,” in IEEE Communications Magazine, vol. 59, no. 1, pp. 70-75, January 2021. Position Location for Futuristic Cellular Communications - 5G and Beyond Ojas Kanhere and Theodore S. Rappaport NYU WIRELESS NYU Tandon School of Engineering Brooklyn, NY 11201 {ojask, tsr}@nyu.edu Abstract—With vast mmWave spectrum and narrow of geo-tagged Wi-Fi hotspots have been used by beam antenna technology, precise position location is companies such as Apple and Google. The UE now possible in 5G and future mobile communication may be localized using the known positions of all systems. In this article, we describe how centimeter- level localization accuracy can be achieved, particularly Wi-Fi hotspots that the UE can hear, where the through the use of map-based techniques. We show how UE position estimate is formed from the weighted data fusion of parallel information streams, machine average of the received signal strengths, providing learning, and cooperative localization techniques further an accuracy of tens of meters. Although FCC improve positioning accuracy. requirements specify a horizontal localization error of less than 50 m for 80 percent of enhanced I. INTRODUCTION 911 (E911) callers, a localization error less than Precise position location (also called position- 3 m will be required for positioning applications ing or localization) is a key application for the of the future. Additionally, FCC requires a vertical fifth generation (5G) of mobile communications localization error less than 3 m for 80 percent of and beyond, wherein the position of objects is E911 callers by April 2021, to identify the caller’s determined to within centimeters. With the rapid floor level, which is achievable using barometric adoption of Internet of Things (IoT) devices, a pressure sensors present in modern cell phones (see variety of new applications that require centimeter- FCC’s Fifth Report and Order PS Docket 07-114.). level precise positioning shall emerge, such as In addition to infrastructure-based positioning automated factories that require precise knowledge systems, other sensor-based technologies such as of machinery and product locations to within cen- vision-based localization using cameras (commonly timeters. Geofencing is the creation of a virtual utilized by drones [1]) can provide accurate posi- geographic boundary surrounding a region of in- tioning capabilities when fused with inertial sen- terest to monitor people, objects, or vehicles, and sors. However, in low-visibility environments, lo- by using sensors on a moving object, the location calization systems at cellular frequencies work bet- of the object may be continually and adaptively ter since they are not blocked when visibility is “geofenced” to trigger a software notification im- hampered. Ultrasound indoor positioning systems mediately when the object enters or leaves the such as Forkbeard are able to achieve a preci- virtual geographic boundary. Position location to sion level of 10 cm within an office environment. arXiv:2102.12074v1 [cs.IT] 24 Feb 2021 within 1-2 m will enable accurate geofencing, such Autonomous vehicles utilize light detection and that users entering/leaving a room or equipment and ranging (LIDAR) to estimate the relative distances people may be tracked in hospitals, factories, within to other vehicles with sub-millimeter accuracy [2], and outside buildings. while factory-based systems using infrared have Today’s fourth generation (4G) cellular networks shown good accuracy [3]. rely on LTE signaling and the global positioning Position location solutions are being developed system (GPS) (which is accurate to within 5 m). using other media such as ultra wideband (UWB), However, in indoor obstructed environments, or in RFID, visible light, and Bluetooth. UWB signals, in underground parking areas and urban canyons, GPS the 3.1-10.6 GHz band, have a bandwidth of more signals are attenuated and reflected such that user than 500 MHz. Rapid strides in utilizing UWB equipment (UE) cannot be accurately localized. for localization are expected, with the iPhone 11 To further refine the positioning capabilities of currently carrying UWB chips that are typically GPS indoors and in urban canyons, SnapTrack capable of achieving a ranging accuracy on the “wireless assisted GPS” (WAG) improved the sen- order of centimeters [4]. sitivity of GPS receivers. Additionally, databases The advent of millimeter-wave (mmWave) com- munications enables a paradigm shift in localization capabilities by allowing joint communication and position location, utilizing the same infrastructure. As shown in this article, the massive bandwidths, coupled with the high gain directional, steerable Δ = − multiple-input multiple-output (MIMO) antennas 2 1 hyperbola at mmWave frequencies, enable unprecedented lo- calization accuracy in smartphones of the future. circle BS 1 We demonstrate how the utilization of cooperative BS 2 (x1,y1) (x2,y2) d2 ,2 localization, machine learning, user tracking, and d 1 ,3 multipath enables precise centimeter-level position 1 location. d3 Δ 1 − 3 UE (x,y) BS 3 II. FUNDAMENTAL LOCALIZATION (x3,y3) TECHNIQUES Fig. 1. The UE may be localized based on ToA (black circles), Today’s localization solutions primarily focus on TDoA (red hyperbola), or AoA (black dotted lines) localization geometric localization with augmented assistance, techniques [5]. wherein the position of the base station (BS) is known and the UE location is determined based on geometric constraints such as the BS-UE distances The short wavelength in the mmWave frequency and physical angular orientations between BS and band allows electrically large (but physically small) UE. antenna arrays to be deployed at both the UE and In angle of arrival (AoA) localization technique, BS. MmWave BS antenna arrays with 256 antenna the UE estimates the angle of the strongest re- elements and 32-element mobile antenna arrays ceived signal. AoA positioning was conceived for are already commercially available. The frequency- E911 in the early days of cellular [5]. In time independent half-power beamwidth (HPBW) of a of arrival (ToA) (or time difference of arrival, uniform rectangular array (URA) antenna with TDoA) localization techniques, the UE estimates half-wavelength element spacing is approximately the distance (or difference in distance) from the (102/N)°, where N is the number of antenna ele- BS by estimating travel time (or differences in ments in each linear dimension of the planar array travel time) of the reference signal from the BS. [8], as seen in Fig. 2. The UE may then be localized to the point where Narrower HPBWs of antenna arrays allow the the circles (or hyperbolas) corresponding to the AoA of received signals to be estimated precisely, BS-UE distances intersect. A spatial resolution of and further signal processing provides better accu- up to 2.44 m and 4.88 m is achievable with 5G racy. For example, the sum-and-difference for an New Radio (NR) waveforms for ToA and TDoA infrared system technique achieved sub-degree an- measurements, respectively [6]. In addition to uti- gular resolution with two overlapping and slightly lizing GPS for UE localization, 4G (and future 5G) offset antenna arrays [3], showing it is possible to networks implement TDoA localization and utilize very accurately detect precise AoA at UEs or BSs. the barometric pressure sensors in UE for altitude Although mmWave frequencies suffer from estimation [1]. The operation of AoA, ToA, and higher path loss in the first meter of propagation TDoA localization techniques is illustrated in Fig. and experience greater blockage losses compared 1 and is well understood. to lower frequencies, the greater gain provided by the directional antennas coupled with smaller A. Accurate Localization in 5G Networks with Di- serving cells (100-200 m radius) compensates for rectional Antenna Arrays and Wide Bandwidths the additional path loss. Indeed, recent research [9] In the 5G era, it is now possible to achieve very demonstrates the feasibility of using mmWave for accurate localization performance with highly di- outdoor localization. rectional antenna arrays having narrow beamwidths Utilization of mmWave frequency bands will and wide bandwidths [7]. The frequency range (FR) enable unprecedented positioning accuracy due to 2 of 5G NR covers mmWave frequencies ranging the ultra-wide bandwidths available, since the larger from 24.25 GHz to 52.6 GHz. Additionally, the bandwidths allow finer time resolution of multipath IEEE 802.11 ad standard supports the use of the signals transmitted from the BS to the UE, on the 60 GHz mmWave band indoors, from 57 GHz to order of a nanosecond, where a 1 ns time resolution 71 GHz. implies a spatial resolution of 30 cm before addi- more than 5° when the UE was moved by 5 cm, the signal was assumed to correspond to an NLoS path and thus discarded from use in estimating position. By suppressing NLoS multipath and only using the LoS path, a median localization accuracy of 23 cm was achieved with six 2.4 GHz WiFi access points [11]. Estimating the BS-UE distance, a critical step for ToA localization, may additionally be utilized to determine whether the BS-UE link is in NLoS. The running variance of the BS-UE distance estimates Fig. 2. The normalized antenna gain (with respect to boresight - 2 the axis of maximum gain) of URAs with 8×8, 16×16, 32×32, and (σ ) in NLoS is greater than LoS; hence, NLoS BS- 64×64 array elements. Note the half power beamwidths (HPBWs) UE links may be identified based on the running are 12.76°, 6.34°, 3.17°, and 1.55° respectively. variance observed in real time. The UE can accu- rately be assumed to be in NLoS (and the UE-BS link is not used for localization) when σ2 is greater tional processing that can further improve accuracy. than a calibrated threshold γ [12]. The variance of distance estimates is greater for a mobile user B.