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An Overview of Ultra-WideBand (UWB) Standards and Organizations (IEEE 802.15.4, FiRa, Apple): Interoperability Aspects and Future Research Directions

Dieter Coppens, Adnan Shahid, Sam Lemey, Ben Van Herbruggen Chris Marshall, Eli De Poorter

arXiv:2202.02190v2eess.SPcs.IT

TL;DR

The paper addresses how growing UWB deployment and multiple radio chips affect interoperability across standards and configuration choices. It surveys chips, standards, organizations, and compatibility across protocol layers, finding that PHY interoperability is possible with matching settings while MAC, localization, and discovery remain more dependent on proprietary or differing procedures.

  • Problem

    Growing UWB deployment and multiple radio chips make the standards and configuration factors affecting compatibility increasingly important.

  • Method

    The paper surveys UWB radio chips, standards, organizations, and compatibility implications across the PHY, MAC, localization, device-discovery, and upper layers.

  • Results

    PHY compatibility is possible with correct settings, but MAC access schemes and localization techniques are mostly proprietary, while FiRa and Apple discovery procedures are incompatible.

  • Takeaways & Limitations

    Interoperability requires aligned PHY configuration and compatible MAC, localization, and discovery procedures across devices.

Abstract

from arXiv · show

The increasing popularity of ultra-wideband (UWB) technology for location-based services, such as access control and real-time indoor track&tracing, as well as UWB support in new consumer devices such as smartphones, has resulted in the availability of multiple new UWB radio chips. However, due to this increase in UWB device availability, the question of which (industry) standards and configuration factors impact UWB interoperability and compatibility becomes increasingly important. In this paper, the fundamentals of UWB compatibility are investigated by first giving an overview of different UWB radio chips on the market. After that, an overview of UWB standards and organizations is given. Next, this overview is used to discuss the focus of these different standards and to identify the differences between them. We describe compatibility issues and associated interoperability aspects related to physical (PHY), medium-access-control (MAC) and upper layers. For the PHY layer, compatibility is possible for all UWB radio chips if the correct settings are configured. For the MAC layer, the implementation of the multiple access scheme as well as the localization technique is mostly proprietary. For the device discovery, several standards are currently being drafted. Finally, future challenges related to UWB interoperability are discussed.

I. INTRODUCTION

UWB’s growing use in consumer devices and location-based services makes compatibility increasingly important. This paper reviews prior work and addresses interoperability across the PHY, MAC, and upper layers.

  • UWB fundamentals: UWB uses very short pulses and high bandwidth to support high channel capacity, low transmission power, multipath robustness, and precise timing.Timing precision enables ranging techniques including ToF, TDoA, and TWR; reported ranging error can be as low as 58 mm.
  • Motivation: Commercial adoption spans smartphones, digital keys, indoor positioning, contact tracing, and vehicle access control, increasing the need for compatible systems.Examples include Samsung Nearby Share, Apple spatial awareness, contact tracing, and hands-free vehicle access.
  • Contributions: The paper contributes an overview of prominent standards, IEEE 802.15.4 and 802.15.4z PHY differences, multilayer hardware compatibility implications, and related research challenges.Its structure covers standards, radio chips, PHY and MAC compatibility, localization, device discovery, and future directions.
  • Related work: Prior research largely emphasizes PHY standards, while fewer studies examine MAC protocols, localization, and upper-layer interoperability.Existing work reviews PHY specifications, MAC protocols, ranging technologies, and security, but these areas are not commonly treated together.
  • Research gap: The identified research gap is a lack of studies covering the full UWB protocol stack while analyzing compatibility among defined standards.The paper links this gap to the increasing deployment of UWB systems.
  • Research focus: The paper investigates compatibility between UWB radio chips that support different standards or standard versions, including communication and ranging consequences.It also considers compatibility at the MAC and upper layers.

III. OVERVIEW OF UWB STANDARDS

UWB standardization is distributed across organizations and OSI layers, with standards serving different purposes. IEEE defines core PHY and MAC layers, while FiRa, Apple, and CCC specify higher-layer or application-oriented solutions.

  • Standards landscape: Different organizations define UWB standards at different OSI layers, and their differing purposes can complicate compatibility.Figure 1 positions prominent standards within the OSI stack and shows multiple standards at some layers.
  • IEEE: IEEE 802.15.4 defines the UWB PHY and MAC layers, while its 802.15.4a amendment introduced IR-UWB for low-data-rate communication and precision ranging.The amendment was incorporated into the main standard in 2011.
  • IEEE: IEEE 802.15.4 includes HRP and LRP modes that transmit different numbers and strengths of pulses under the same maximum mean PSD.HRP transmits more but weaker pulses, whereas LRP transmits fewer but stronger pulses.
  • IEEE: IEEE 802.15.4z enhances the UWB PHY to improve ranging integrity and accuracy through additional coding, preamble options, and modulation improvements.The enhancement was released in 2020 and became IEEE 802.15.4z-2020.
  • FiRa: FiRa develops profiles above IEEE protocol layers, including a Common Service Management Layer intended to support interoperability among FiRa devices and service applications.Its setup procedure uses out-of-band discovery, capability exchange, parameter negotiation, and UWB ranging initiation.
  • Apple and CCC: Apple specifies a protocol for accessories interacting with Apple UWB chips, while CCC Digital Key 3.0 supports secure, location-aware smartphone-to-car access.Apple interoperability requires participation in the Made-For-iPhone program and adherence to its protocol.

E. OMLOX

Omlox is an open RTLS standard that standardizes location-data interfaces across diverse localization technologies and interactions for UWB-based RTLS systems. Its core currently supports reverse TDoA and ToF, enabling networking across UWB products regardless of manufacturer.

  • Standard availability: Omlox was developed through an industry collaboration involving more than 60 companies, and its interfaces are freely available for use.
  • Omlox: Omlox provides standardized interfaces for retrieving location information from UWB, RFID, 5G, BLE, Wi-Fi, and GPS systems.The interfaces use standardized data representations and web-service-based instructions for discovering providers, retrieving locations, and advertising new locations.
  • Omlox core: The omlox core specifies standardized interactions for UWB-based RTLS systems, currently supporting reverse TDoA and ToF but not TDoA or TWR.
  • Interoperability: Omlox core output can feed the omlox hub, enabling networking across UWB products regardless of manufacturer.

A. HRP UWB PHY COMPATIBILITY

HRP UWB compatibility depends on matching configured channels, frame and coding parameters, while standard compliance alone does not guarantee identical pulse behavior. IEEE 802.15.4-only and IEEE 802.15.4z devices can communicate using shared legacy settings, but enhanced security and accuracy features may be unavailable.

  • Channel compatibility: Compatible radios must use the same center frequency and bandwidth, but chips do not necessarily support every standardized HRP channel.The HRP PHY defines 16 channels, with a minimum bandwidth of 499.2 MHz; channel support varies across chips.
  • Pulse shape: Standard-compliant HRP pulses may still differ in shape, and a pulse-width difference can cause more than 0.5 ns timing error and more than 15 cm ranging-distance error.The paper states that calibrating antenna-delay parameters resolves this ranging problem.
  • Frame structure: IEEE 802.15.4-only and IEEE 802.15.4z radios must use the same frame structure, and legacy radios cannot use STS-based structures.The STS is an optional IEEE 802.15.4z field used in three of the four defined HRP frame structures.
  • Synchronization and payload decoding: Matching preamble codes, SFDs, modulation, PRF, and data rate is required for communication and ranging.The mandatory ternary preamble code of length 127 enables cross-standard connection, while incompatible or newer codes can provide accuracy benefits unavailable to legacy connections.
  • PHR and payload: Cross-standard connections support only the mandatory IEEE 802.15.4 PHR format, limiting the maximum payload to 128 bytes.IEEE 802.15.4z adds an optional format for increased payload length, but it cannot be used by an IEEE 802.15.4-only counterpart.
  • Security: STS-based security requires shared keys and cryptographic parameters, and IEEE 802.15.4-only chips cannot support this field.The paper identifies the Qorvo DW1000 as the only reviewed chip unsuitable for use cases requiring the added STS security.

B. LRP UWB PHY COMPATIBILITY

LRP UWB compatibility between IEEE 802.15.4 and IEEE 802.15.4z is restricted to legacy mode classes. The enhanced standard's added modes, performance benefits, and standardized ranging are therefore unavailable in cross-standard communication.

  • LRP modes: LRP UWB modes combine modulation and PRF to determine a mode's data rate and characteristics.The paper organizes modes into classes including long-range, extended, base, and newer dual-frequency variants.
  • Frame structure: LRP frames contain a preamble, SFD, PHR, and payload, with the preamble and symbol structure depending on the selected mode class.IEEE 802.15.4z adds longer SFD options beyond the single length-16 SFD defined in IEEE 802.15.4.
  • PHR and ranging fields: The LRP PHR carries encoding, header-extension, SECDED, and frame-length information, while IEEE 802.15.4z uses a reserved field to signal ranging.The optional LEIP postamble is intended to enhance the ability to locate the transmitter.
  • Cross-standard compatibility: IEEE 802.15.4 and IEEE 802.15.4z LRP PHYs are compatible for communication only in the long-range, extended, or base modes.The dual-frequency and other enhanced modes cannot be used for cross-standard communication.
  • Compatibility consequences: Cross-standard LRP communication does not provide the IEEE 802.15.4z improvements in data rate, sensitivity, or power consumption, nor standardized ranging.The paper notes that 3dB access had implemented similar LRP ranging before IEEE 802.15.4z was released.

A. MAC LAYER

The IEEE 802.15.4/4z MAC frame has a standardized header, variable-length payload, and error-checking footer. Although 802.15.4z adds localization techniques, its MAC-frame changes do not create compatibility consequences.

  • The MAC frame contains a header, variable-length payload, and Frame Checking Sequence footer.The footer uses a cyclic redundancy check to detect transmission errors.
  • The frame control field is 16 bits and specifies the frame type and MAC-header components.Frame types include Beacon, Data, Acknowledgement, MAC command, Multipurpose, and Fragment.
  • MAC-header fields indicate acknowledgement requests, PAN-ID compression, destination and source addressing modes, and frame version.Addressing-mode fields specify whether addresses are present and their sizes; the frame-version field identifies standard revisions.
  • IEEE 802.15.4z does not change the MAC frame, so using the different standards creates no MAC-layer compatibility consequences.Its main MAC enhancement is adding localization techniques to the functional description.

B. MULTIPLE ACCESS SCHEMES

UWB systems can use the same MAC frame format, but they generally use proprietary multiple-access schemes because no standardized scheme has been established for UWB.

  • UWB radio chips can use the same MAC frame format, but multiple-access schemes remain proprietary.The lack of consensus on the best scheme for UWB systems has prevented definition of a standard multiple-access scheme.

VII. LOCALIZATION TECHNIQUES

UWB localization determines a tag’s location from signal timing, using a tag and multiple anchors to estimate distances or relative position.

  • Localization techniques calculate distance or relative position from UWB signal-arrival timing.The common setup uses a UWB tag and multiple UWB anchors to determine the tag’s location.

A. TOF

UWB localization uses timing-based techniques to estimate distances and positions, while compatibility depends on both devices agreeing on the technique and exchanging the required frames. FiRa coordinates discovery, capability exchange, parameter negotiation, and ranging setup through an out-of-band channel.

  • A. TOF: Time of Flight calculates tag–anchor distance from propagation time using d = c ∗ToF.The tag transmits its send time, the anchor records the receive time, and c is given as 299.8 ∗10^6 m/s.
  • B. TDOA: TDoA locates a tag by intersecting at least three hyperbolas derived from arrival-time differences at anchors.The tag does not know its own position unless that position is transmitted back.
  • C. TWR: TWR removes the need for anchor–tag synchronization by deriving ToF from round-trip time and a fixed reply time.With three anchors, TWR supports trilateration; Double-Sided TWR uses at least three messages and lets both devices calculate distance.
  • D. Compatibility: Compatibility requires sender and receiver agreement on the localization technique and transmission of the frames needed to calculate distance or location.TDoA suits asset tracking when the tag need not know its location, whereas TWR suits ad-hoc applications such as hands-free access control.
  • E. FiRa setup: FiRa discovery and ranging setup uses an out-of-band channel, typically BLE, followed by capability exchange, parameter selection, optional role and key negotiation, and ranging.FiRa capability messages report PHY and MAC versions, device roles, and supported UWB parameters.

B. APPLE NEARBY INTERACTION

Apple’s Nearby Interaction setup discovers devices through a non-UWB transport, exchanges configuration data, and then starts UWB ranging using agreed parameters.

  • Apple device discovery can use LAN, cloud, or other transports rather than being limited to BLE.
  • The accessory sends configuration data containing matching major and minor versions, update-rate preferences, and UWB configuration data length.
  • The UWB configuration data is supplied by UWB middleware through a dedicated interface that the protocol specification does not further define.
  • The Apple device sends Shareable Configuration Data before UWB ranging is configured from the exchanged UWB configuration fields.

C. CAR CONNECTIVITY CONSORTIUM (CCC)

The paper identifies unresolved CCC and broader UWB interoperability challenges spanning standard availability, PHY evolution, localization methods, and emerging applications.

  • No details of CCC Digital Key Release 3.0 had been published when the paper was written.
  • Improving on IEEE 802.15.4z: IEEE 802.15.4ab targets enhanced UWB PHY, MAC, ranging, sensing, streaming, and interoperability while retaining backward compatibility with existing devices.
  • Improving on IEEE 802.15.4z: The planned amendment includes additional channels, interference mitigation, improved high-integrity ranging, native discovery, sensing, and throughput of at least 50 Mb/s.
  • Standardization of UWB AoA: AoA can estimate a tag’s location with one multi-antenna anchor, but no UWB standard currently incorporates AoA estimation.
  • UWB radar standardization: UWB radar applications such as presence detection and health monitoring remain outside current UWB standards.
  • Pulse shape: Differences in pulse shape between radio chips remain a research issue despite common pulse-shape requirements in IEEE 802.15.4 and 802.15.4z.

C. DATA LINK LAYER CHALLENGES

Data-link interoperability remains limited because MAC frame formats are standardized while exchange procedures and configuration decisions are not consistently standardized.

  • MAC frame formats are standardized, but multiple-access exchange procedures range from ALOHA-based to synchronized TDMA-based approaches.
  • No commercial localization systems are currently interoperable, requiring different user tags for each building entered.
  • FiRa and Apple use non-UWB discovery, suggesting a need to examine whether narrowband systems suit some MAC functions better than UWB.
  • Performance analysis of device discovery approaches: Comparative analysis of FiRa and Apple discovery overhead, latency, and scalability is still lacking.
  • Link configuration decision algorithm: FiRa and Apple exchange supported PHY configurations but do not define algorithms for selecting settings under channel and application conditions.
  • Link configuration decision algorithm: Proposed standardization includes capability exchange, link-state measurements, and decisions incorporating accuracy, distance, latency, energy, channel allocation, power, and interference.

D. APPLICATION LAYER CHALLENGES

Application-layer interoperability requires common representations for localization outputs and broader support for RTLS, while current standards remain focused mainly on device-to-device use cases.

  • Application developers need standardized interpretations of distances, positions, and angles produced by interoperable UWB systems.
  • Existing IoT information models and Omlox provide examples of standardized position semantics and cross-technology distance exchange.
  • Shared information models could let localization systems exchange context and help resolve positioning errors or conflicts.
  • RTLS standards: FiRa and Apple upper-layer protocols focus on device-to-device applications such as access control and do not define extensions for RTLS.
  • Outdoor UWB regulation is not globally harmonized, with permanent outdoor systems prohibited in most countries and regions.
  • PHY compatibility between IEEE 802.15.4 and 802.15.4z is possible with matching channels, codes, frame structures, and BPRF settings, but newer accuracy and security features are unavailable in compatibility mode.
  • Higher-layer interoperability requires matching MAC, ranging, and discovery procedures because these may be proprietary or selected from different standards.
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