Do you trust your GPS? Would you be prepared to follow it blindly? Though we rarely think of it as such, a position reading from the Global Navigation Satellite Systems (GNSS) receiver in our smartphone or our car is a statistical quantity. It tells you that with a given probability – say 50% – you are within a defined distance – say 1 meter – from the indicated position. Ultimately, how you relate to the information provided depends on how much faith you are willing to place in the output your device delivers.
Global Navigation Satellite Systems (GNSS)
GNSS has long been the unique source for accurate position estimates for user devices. But as applications become more widespread, diverse, and safety-critical, understanding how to quantify the reliability of readings and having alternative sources of input to fall back to when GNSS is unavailable have become paramount to their success.
GNSS is, of course, not the only available source of position information. Devices featuring a cellular modem can determine their approximate position using cellular signals. Key players in the market, such as u-blox, have long offered cellular signal-based and hybrid positioning solutions in their cellular communication modules, the latter combining GNSS and cellular signals, to expand the coverage of location services.
Now, 5G positioning, an often overlooked component of the 5G technology construct, is being developed and standardized by the industry-driven 3GPP (Third-Generation Partnership Project). This body, which brings together seven organizations dedicated to developing telecommunications standards and hundreds of corporate members, is pushing the development of 5G positioning as a component of next-generation cellular communication technology, with the needs of diverse industry verticals in mind.
A Brief Look Back
Positioning has played an important role in enabling cellular communication since its very inception. Initially, it was a mere side product: to route incoming calls to the recipient’s end device, mobile network operators needed to know which specific cellular base station end-users were connected to at any given time.
That changed in 1999, when US regulatory authorities put in place requirements for high accuracy position estimates to enable emergency services, which led to the first generation of dedicated location services based on cellular technology.1 The EU followed the US example in 2002.2 Since then, the range of location services has expanded with each successive generation of cellular technology, driven primarily by industry demands and standardized by the 3GPP.
As a result, today’s 4G LTE networks offer mobile network operators a broad range of approaches to determine each user’s location with varying degrees of accuracy. These approaches take advantage of varying combinations of fixed and mobile network infrastructure, as well as external sources, such as positioning satellites.
The following table outlines the main 4G LTE location services.3
Table 1. The Main 4G LTE Location Services
New Use Cases and Demands
While the main driver for location-based services has been demands from regulatory authorities, today, several public and private companies including hardware and equipment manufacturers, space agencies, and mobile network operators are pushing for the delivery of higher accuracy and precision by cellular location services to enable a new generation of commercially motivated location-based services.
These applications are broadly categorized as UE-Assisted, in which the network and external application obtain the position in order to track the whereabouts of the object, and UE-based, in which the UE computes its own position for the purpose of navigation and guidance.4
At the same time, the penetration of the Internet of Things (IoT) into every facet of our economy and social lives is increasing expectations on the coverage and reliability of positioning technology. Whereas today, we expect to have access to high-speed Internet just about everywhere, the same will likely become true of high accuracy positioning.
As a result, the 3GPP and other standardization bodies are taking a fresh look at the application space and performance requirements for cellular positioning in their upcoming releases. Use cases that stand to benefit from improved high precision positioning services are broad-ranging, including industry, asset tracking, automotive, traffic management, smart cities, shared bikes, hospitals, UAVs, public services, Augmented Reality (AR), and consumer and professional wearables.
Overall, 5G technology aims to offer a variety of cellular-based and hybrid positioning services delivering both absolute and relative positioning, depending on the needs of each specific use case. Crucially position information should be delivered with a measure of the confidence that can be placed on the reading. Key requirements that have yet to be fully defined and agreed are horizontal and vertical accuracy, relative accuracy (between nearby devices), time-to-first-fix, velocity accuracy, power consumption, latencies, as well as operational and security-related properties.5
In the following, we’ll take a look at the demands imposed by three use cases in particular in the vertical industries: (i) UAV missions and operations, (ii) IIoT tracking applications, and (iii) autonomous vehicle navigation. The values cited for the first two use cases are drawn from the 3GPP TR 22.872 technical report.6 Those for the automotive use case, which comprises a broad range of specific applications, are drawn from additional references.7,8
Figure 1. Requirements for emerging 5G positioning use cases in three selected verticals.
How the New Generation of GNSS Receivers is Changing Positioning
Over the past years, satellite-based positioning has been undergoing rapid development. In the early days of satellite navigation, GNSS receivers had to rely on a single constellation of orbiting satellites, either the US GPS or Russian GLONASS systems, to determine their position. Now there are more operational systems with the European Galileo and Chinese Beidou systems and several regional augmentation systems added to the original two. Today, multi-constellation GNSS receivers that can concurrently receive signals from all orbiting GNSS constellations, such as the u-blox F9 generation of receivers, are becoming the norm. As a result, receivers are able to “see” a greater number of satellites, even when large portions of the sky are obstructed, such as in urban (or actual) canyons, improving accuracy and reducing the time to achieve a position fix.
Initially, GNSS receivers used satellite signals transmitted on a single frequency band to estimate their location. One of the main sources of position error is caused when the satellite signals slow down as they traverse the charged ionosphere. Because this delay is proportional to the inverse of the squared frequency, using signals from additional frequency bands can help determine and correct for the ionospheric error. The latest generation of dual-band GNSS receivers has brought down the average position error from roughly 2.5 m to less than one meter in open sky conditions using standard code-based positioning.
The quality of GNSS positioning has long benefitted from commercial GNSS correction services. GNSS correction service providers typically monitor incoming GNSS signals using a network of base stations with precisely known positions and transmit tailored correction information to end users for a fee. For code-based positioning, these are termed differential corrections.
When using high precision carrier phase tracking RTK (Real Time Kinematic) methods, corrections obtained from a nearby reference receiver allow centimeter-level positioning to be achieved. Today, a new generation of GNSS correction services is in the making, which takes an alternative approach, broadcasting GNSS code and carrier phase correction data for an entire geographical region, e.g. a country or an entire continent, via the Internet or satellite.
The combination of multi-constellation and multi-band receivers with new GNSS correction schemes to achieve centimeter-level accuracies, all at a significantly reduced cost of ownership, is paving the way for new types of mass market applications for centimeter-level high accuracy positioning.
That said, GNSS continues to suffer from two disadvantages: Receivers need to be ideally within line of sight of the orbiting satellites to determine position. Indoors and in tunnels, the services are degraded or even unavailable. And, in the best case, it takes a GNSS receiver several seconds to unambiguously determine its position for the first time from a cold start. Powered by inertial sensors, dead reckoning solutions, primarily tailored to automotive applications, significantly extend the purview of high accuracy positioning beyond the reach of GNSS signals. Assisted GNSS (A-GNSS) speeds up time to first fix by offering a faster way to retrieve GNSS orbit and clock data than via the GNSS signals themselves.
How 5G will Bring New Improvements to Cellular-Based Positioning
5G New Radio, the next generation of cellular technology defined by the 3GPP from Release 15, is already in the making.9 End users in some regions will first get access to the non-standalone architecture that builds on 4G LTE as early as H1 2019, with Samsung and Verizon, LG and Sprint, and Huawei releasing 5G smartphones in early 2019, and Apple expected to follow in 2020.10 This will be followed by the deployment of standalone 5G.
Several mobile network operators have already publicly announced deployments of 5G networks, starting in urban centers. The US is leading the pack. AT&T started its rollouts in 2018 and will continue through 2019, with the goal of offering nationwide coverage mid-year.11 In Korea, the second country to enter the race, telcos have jointly announced plans to rollout 5G in March 2019.12 In the UK, Vodafone announced plans to begin rolling out the technology in 2020. However, high accuracy positioning services won’t become part of 3GPP 5G NR specifications until Release 16 around the end of 2019, with deployment following in 2020 earliest.
The driving forces behind 5G are diverse. New applications are bringing heightened demands to the table in terms of reliability, availability, coverage, and latency of cellular network performance. Mobile network operators are looking to 5G to build new revenue streams from industry verticals. Chipset vendors see in 5G an opportunity to boost revenue by licensing intellectual property rights. And users will get the higher data rates they have been asking for.
5G cellular communication technology addresses these diverse requirements through three key usage scenarios: eMBB, uRLLC, and mMTC, which we briefly describe below.
- eMBB (enhanced Mobile Broadband) expands the spectrum dedicated to cellular communication to much higher frequencies that transport data at faster speeds.
- URLLC (Ultra Reliable Low Latency Communications) drives new opportunities such as autonomous vehicle and vehicle-to-everything (V2X) applications.
- mMTC (massive Machine Type Communications) will continue to evolve the developments of IoT applications in low power wide area (LPWA) communications.
Enabling positioning in these scenarios requires new signals and new infrastructure that can be exploited to expand the range of techniques available,13 including larger bandwidths at higher frequencies, more antennas combined into complex antenna arrays, and denser telecommunication networks. The targets are ambitious: sub-meter position accuracy delivered with low latency below 15 milliseconds.
5G Offers Larger Bandwidths and Frequencies
3GPP is currently focusing on bringing an array of 4G LTE positioning methods into 5G. Typically, these use uplink and downlink signals to determine the position of individual end-devices to determine their position relative to mobile network antennas, which serve as anchor points. Examples are enhanced Cell-ID and TDOA-based approaches.
In enhanced Cell-ID, end devices monitor their proximity to multiple base stations, measuring signal strength and approximate propagation time to the device. By combining these observations, a better estimate of device position can be calculated than simply measuring the nearest cell center alone.
In TDOA-based approaches, the end device accurately measures the arrival times of signals from multiple base stations. Using multilateration based on the time differences between observed receive times, the device can determine its position to the observed base stations more accurately than using enhanced Cell-ID.
Another class is the as-of-yet poorly exploited sidelink, a 4G LTE technology involving device-to-device communication that may allow devices to determine their positions relative to each other. An obvious use-case is vehicle-to-vehicle (V2V) communications.
5G’s new spectrum allocation is good news for cellular-based positioning, in particular, due to the availability of larger bandwidths that are located at higher frequencies (mmWave above 24 GHz in addition to sub 6 GHz). Larger bandwidth means that signal time can be more accurately resolved (there is an inverse relationship between time and bandwidth), so larger bandwidths offer improved ability to resolve multipath effects, the main source of error in cluttered urban and indoor settings because signals that travel different paths arrive at different times.
5G’s move to new frequencies also affects the geographical deployment of cellular base stations and the antenna technologies used, again benefitting cellular-based positioning. Because they incur higher propagation losses, shorter wavelengths have less range than longer ones, which means that MNO’s will need to deploy more base stations to maintain coverage. In addition, the introduction of antenna arrays with beamforming capabilities will help to direct signals towards end users. A higher density of directionally aware antennas will improve the resolution of multipath components by measuring delay, the angle of arrival (AoA), and the angle of departure (AoD), improving positioning performance. Additionally, it may become possible to localize devices using a single base station.
Ubiquitous High-Precision Positioning will Require Hybrid Approaches
No single approach will be able to reliably provide the accuracy required by the target use cases in all environmental conditions. As we’ve seen, while today’s GNSS-based solutions are able to reliably provide high accuracy positions, they have limitations for indoor applications. On the other hand, 5G-based positioning solutions can complement and provide accurate position estimates for both indoor and outdoor scenarios.
Hybrid solutions that optimally combine multiple cellular approaches with non-cellular ones, such as GNSS, terrestrial beacon systems (TBS), measurements based on Wi-Fi and Bluetooth, and inertial measurements (IMU), are most promising to achieve these goals. The additional redundancies allow increased fault tolerance and improved integrity of the overall solution, delivering a quantitative measure of confidence to go along with each position estimate.
Recognizing the promise of hybrid positioning solutions to enable new applications, the 3GPP study scope includes GNSS and satellite signals, as well as terrestrial signals such as Wi-Fi and Bluetooth, and more. The resulting solutions, arising from the 3GPP study item, are targeting introduction in radio specifications for Release 16 – Q1 2020.
Challenges Set for the 3GPP
The 3GPP has set itself ambitious goals, with Release 16 scheduled for H1, 2020. Implementing cellular-based positioning solutions on top of 5G’s diverse signal landscape will be a complex endeavor, as will encouraging timely deployment of infrastructure to enable sufficiently broad coverage to attract a large enough user base.
As we’ve seen, hybrid positioning approaches will be crucial in meeting the stringent needs of emerging applications, in particular as the expectation for high accuracy positioning everywhere, all the time, becomes the norm. This will inevitably require representatives from different technologies – be it GNSS, cellular, short range, satellite communications, or others – to work together to produce a result that is better than the sum of its constituent parts.
u-blox’s unique position in the industry, as a leading provider of GNSS, short-range wireless, and cellular technology, makes the advent of 5G positioning approaches, in particular, those combining technologies, particularly exciting. Hybrid positioning builds on the convergence of our core competencies, and we see huge potential for innovation, new levels of performance, and new use cases. As we contribute to expediting the coming together of these different worlds to provide a better and more comprehensive solution, we can’t help but look forward to the outcome.
This article was co-authored by David Bartlett, Senior Principal Engineer, Product Center Positioning at u-blox.
- 1) FCC 911 and E911 Services
- 2) Summaries of EU Legislation: Affordable telecommunications services - users' rights
- 3) Based on “Evolution of Positioning Techniques in Cellular Networks, from 2G to 4G,” Rafael Saraiva Campos, Hindawi, 2017
- 4) UE is short for User Equipment
- 5, 6) 3GPP TR 22.872 V16.1.0 (2018-09), Technical report, 3rd Generation Partnership Project; Technical Specification Group Services and System Aspects; Study on positioning use cases; Stage 1, (Release 16)
- 7) High precision positioning for Cooperative-ITS (HIGHTS), Project deliverable D2.1: Use cases and Application Requirements (May 1, 2015)
- 8) Report on Road User Needs and Requirements, Outcome of the European GNSS’s USER Consultation Platform, European Global Navigation Satellite Systems Agency (GSA) (October 18, 2018)
- 9) System architecture milestone of 5G Phase 1 is achieved, 3GPP, (December 21, 2017)
- 10) Top 5G phones: every 5G phone announced and still to come in 2019
- 11) AT&T Names 99 New 5G Evolution Markets
- 12) Carrier heads commit to ‘Korea 5G Day’
- 13) Whitepaper on New Localization Methods for 5G Wireless Systems and the Internet-of-Things, COST Action CA15104, IRACON ; Pedersen, Troels; Fleury, Bernard Henri
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