How IEEE 802.15.4ab Is Set to Unlock the True Potential of UWB

Over the last decade, Ultra-Wideband (UWB) solutions based on the technology’s initial standard, IEEE 802.15.4a, have seen increased adoption within high accuracy indoor Real-Time Locating System (RTLS) applications. The introduction of the subsequent IEEE 802.15.4z amendment, published in 2020, led to additional security extensions being added to UWB. These enhancements provided UWB with the ability to deliver secure, centimeter-level accurate distance and location measurement, enabling a number of secure fine-ranging and positioning applications demanded by automotive, mobile, smart home, smart building, and other consumer, industrial, and Internet of Things (IoT) solution providers. The arrival of IEEE 802.15.4z has also led to a growing presence of UWB in smartphones, initially for automotive digital key applications and personal tracking applications, as defined by the Car Connectivity Consortium’s (CCC) Digital Key 3.0 Specification and devices such as the Apple AirTag.

However, while UWB is starting to build success, with ABI Research forecasting the technology to be one of the fastest growing wireless connectivity technologies between 2025 and 2030 (achieving a Compound Annual Growth Rate (CAGR) of 21%), the link budget limitations of 802.15.4z have caused challenges in real-world deployment scenarios, particularly for automotive digital key applications. These limitations can significantly diminish the end-user experience when it comes to reliability, power consumption, accuracy, and practical range of operation. As a result, work on the latest amendment to the IEEE 802.15.4 UWB standard began. Also known as next-generation UWB, this new amendment introduces a number of major improvements designed to enhance the secure ranging performance and accuracy over greater distances, enable a more consistent user experience, optimize efficiency, enhance scalability, and enable new use cases that existing UWB technology may struggle to support effectively.

When deploying UWB technology in real-world environments, most notably within digital key applications, several limitations of the existing IEEE 802.15.4z technology have been discovered. Key among these challenges include:

• Limited Link Budget Due to Regulatory Restrictions: The transmit power of UWB technology is heavily restricted by various other organizations to avoid interference with other technologies and incumbents. As a result, existing implementations of UWB secure ranging have a limited link budget, and the distance at which UWB can effectively perform its ranging activities is limited.
• Power Consumption: One of the challenges of using a less accurate Bluetooth® Low Energy (LE) Received Signal Strength Indicator (RSSI) solution to activate the UWB localization mode is that it can be activated prematurely. This means that the handover from Bluetooth® to UWB can happen when the user could still be significantly outside the required vehicle localization zone, resulting in prolonged activity of UWB ranging when it is not needed, unnecessarily draining battery
• Unreliable Detection of Devices: In real-world usage scenarios, such as when a car is trying to locate a UWB-enabled smartphone for keyless entry applications, a limited link budget can cause additional stability issues when users have their phones in their bags, pockets, and, in the worst-case scenario, a back pocket.
• Multipath Interference and Non-Line-of-Sight Performance: While UWB is inherently more resistant to multipath interference compared to other technologies, there are still many environments in which UWB will be deployed where signals will bounce off reflective surfaces to create multiple paths from which the UWB location needs to be derived.

IEEE 802.15.4ab seeks to address these limitations through a number of techniques. One of the enhanced ranging techniques being introduced in IEEE 802.15.4ab is Multi-Millisecond (MMS). In contrast to the conventional UWB Two-Way Ranging (TWR) distance measurement method in which devices exchange ranging information via longer ranging packets, within MMS, the UWB ranging packet can be divided into 16 smaller fragments consisting of Ranging Sequence Fragments (RSFs) and Ranging Integrity Fragments (RIFs). These are then transmitted over consecutive 1 Millisecond (ms) time slots. The receiving device is then able to accumulate information from these fragments over multiple milliseconds, significantly enhancing the combined energy compared to a single UWB ranging packet, and boosting the overall link budget. With MMS, by maintaining the average power over 1 ms, the transmission for each fragment can be boosted, while still complying with regulatory power limits. In contrast, the link budget in the conventional approach is limited by the energy utilized in this initial packet exchange.

MMS can be implemented in several ways. One approach that has demonstrated the highest link budget increase and stability to enhance the effective range and experience of IEEE 802.15.4ab is Narrowband-Assisted (NBA) MMS UWB. This utilizes a dedicated Narrowband (NB) signal to provide frequency and timing synchronization during the initialization and control phases. By decoupling the time synchronization from the UWB band into the NB, this can already provide a significant link budget improvement.

Various other improvements to the UWB PHY have also been made, including the introduction of new modulation schemes supporting data rates of up to 1.95 Megabits per Second (Mbps), specifically designed to provide a boost to signal strength and overcome challenges such as the back pocket scenario. Alongside this, IEEE 802.15.4ab also introduces optional Low-Density Parity Check (LDPC) coding, which can dynamically adjust the data rate in noisier environments to enhance reliability and robustness.

With the new features introduced in IEEE 802.15.4ab, the link budget can be improved by up to 30 Decibels (dB). This can enable secure ranging implementations that can operate over greater distances and work reliably in different environments, even in back pocket scenarios. This can also be more power efficient, potentially opening up valuable new intent-driven use cases, and reducing the infrastructure requirements of UWB technology over time.

Meanwhile, additional benefits can be found in other secure access applications, such as smart door locks in residential environments, or commercial access control readers. Not only are these typically difficult multipath environments, but they are also likely to face similar challenges from users leaving phones in their back pocket. IEEE 802.15.4ab can ensure a more consistent user experience while also enabling remote home services on approach, e.g., light activation.

In applications where intent needs to be verified at multiple stages, such as within contactless ticketing and transportation fare payments, IEEE 802.15.4ab is likely to be fundamental to the future success by reducing the cost and complexity of UWB infrastructure rollouts. Meanwhile, in other localization applications, the extended range can also help reduce the density of anchor points, reducing infrastructure costs and enabling quicker Return on Investment (ROI). 

The enhanced range provided by the new amendment can also enhance find someone/something use cases and experiences. This will enable users to more easily and precisely locate friends or family in densely populated areas, or find lost items like keys or luggage, allowing UWB to be used as an indoor Global Navigation Satellite System (GNSS)-like solution. For example, in congested car parks, users could be directed to their vehicle based on precise positioning, or at a shopping mall, family and friends could more easily be located in a large crowd.

To summarize, IEEE 802.15.4ab is directly addressing some of the major limitations in existing UWB technology, and its successful rollout will be vital in accelerating UWB market adoption beyond the nearly 1.4 billion projected device shipments by 2030.

For more information on IEEE 802.15.4ab, please see the latest ABI Research IEEE 802.15.4ab: Unlocking UWB’s true potential whitepaper in partnership with STMicroelectronics, which has committed to expanding its STM32 wireless Microcontroller Unit (MCU) family and ecosystem with upcoming support for IEEE 802.15.4ab Next-Generation UWB technology.