IEEE 802.15.4ab vs 802.15.4z: UWB PHY & MAC Enhancements

Introduction : The evolution of Ultra-Wideband (UWB) has moved rapidly from simple location tracking to secure digital keys and now, to a universal sensing and connection fabric. The transition from IEEE 802.15.4z to the next generation IEEE 802.15.4ab brings massive upgrades to both the Physical (PHY) and Media Access Control (MAC) layers. This tutorial provides a detailed feature comparison, highlighting how 802.15.4ab introduces Native Sensing, Enhanced Modulation and Narrowband Assistance to overcome the limitations of its predecessor.

UWB PHY Layer

The physical layer in 4ab has been significantly broadened. While 4z focused on secure pulse placement, 4ab introduces Enhanced Modulation Devices (HRP-EMDEV) and Sensing Devices (HRP-SDEV) to tackle extreme use cases. Let us understand the same.

1. Enhanced Modulation (HRP-EMDEV)

The new modulation schemes have been added which can deliver longer range and higher speed.

• Long range mode : Introduces a very long symbol time (512 ns) and a Peak Repetition Frequency (PRF) of 249.6 MHz.
• High data rate mode : Introduces very short symbol times (16 ns and 8 ns).
• Coding : Adds optional LDPC coding for dynamic data rate adaptation.

Significance:

• The long symbol time improves link budget significantly which allows signals to pass smoothly through difficult RF environments where 802.15.4z might fail.
• Achieves data rates up to 124.8 Mbps compared to approx. 27 Mbps in previous versions.

2. Native UWB Sensing (HRP-SDEV)

In 802.15.4z, sensing (radar) was possible but not standardized. The IEEE 802.15.4ab standardizes new waveform to ensure interoperability.

• Time bounded Kaiser Window pulse shape has been introduced. This newly added pulse has near zero sidelobes.
• Frequency stitching concept has been added which allows devices to combine multiple channels to emulate wider bandwidth. This has been achieved with the help of intra packet and inter packet stitching.

Significance:

• The new pulse shape offers cleaner Channel Impulse Response (CIR), crucial for detecting breathing or small gestures. Moreover, standardization makes interoperability possible between two vendors.

3. Ultra Low Power & Wake-Up Radio

The IEEE 802.15.4ab addresses the “always-on” power consumption issue of previous UWB versions.

• Wake-Up Radio : The low power mode (OOK/BPM) designed solely to listen for “wake-up” signal.
• Low Energy UWB : Non-coherent PHY which eliminates need for carrier frequency generation without PLL requirements.

Significance: Drastically reduces the cost and power consumption of tags. A device can sleep in nano amp states and only fire up the main UWB radio when triggered.

UWB MAC Layer

The Media Access Control (MAC) layer in 4ab introduces Advanced Ranging Devices (HRP-ARDEV). The biggest shift here is how the standard handles power regulations to maximize range.

1. Multi-Millisecond (MMS) Ranging

• Instead of sending one continuous packet, MMS breaks the ranging packet into fragments (RSF and RIF) sent in consecutive millisecond time slots.

Significance: This provides free “boost” to the link budget (~ 3 dB or more). This extends range without new hardware amplifiers.

2. Narrowband (NB) Assistance

• The IEEE 802.15.4ab integrates companion “narrowband PHY” (O-QPSK, similar to ZigBee/Thread) operating in 2.4 GHz, 5 GHz or 6 GHz.

Significance:

• Offloading : Control data, synchronization and polling happen on the low power Narrowband channel.
• Efficiency : The energy hungry UWB radio is turned on only for the micro-seconds needed to measure distance (i.e. during ranging phase).

Key enhancements from 802.15.4z to 802.15.4ab

Following table mentions key enhancements due to changes in specifications from in 802.15.4ab compared to IEEE 802.15.4z version including benefits.

Summary: With PHY enhancements driving data rates up to 124.8 Mbps and MAC improvements enabling millisecond level power management, 802.15.4ab is set to power the next wave of IoT.