UWB Wake-Up Radio: Concept & Benefits in IEEE 802.15.4ab

Introduction : In previous UWB generations (802.15.4a/z), a receiver often had to wake up its main radio periodically to check for incoming messages. Since the main UWB radio requires significant power (due to high-speed sampling and PLLs), this “sniffing” drained batteries quickly.

How UWB Wake-Up Radio works

The Wake-Up Radio (WUB) introduces a dedicated, ultra-low-power receiver mode that operates independently of the main UWB radio.

• WU-RXDEV (Receiver): Remains in a deep sleep state with only a tiny fraction of power consumption, listening for a specific “Wake-Up Signal.”
• WU-TXDEV (Transmitter): Sends a specialized burst pattern to trigger the receiver.

Once the Wake-Up Receiver detects this specific signal, it triggers the main, power-hungry UWB radio to turn on and process the high-speed data.

Protocol

The wake-up mechanism uses a simplified signal structure to ensure it is easy to detect without complex processing:

• Signal Structure: The wake-up message consists of millisecond-spaced bursts of pulses (approx. 8 µs duration) transmitted at a PRF of 62.4 MHz.
• Modulation (Burst Position): Information is encoded by the position of the burst.
  • Binary 1: Represented by a burst in the first position.
  • Binary 0: Represented by a burst in the second position (24 µs later).
• Sequence:
  • SYNC: A repetition of binary 1s to alert the receiver.
  • Delimiter: A single binary 0.
  • Device ID: A 16-bit ID to ensure only the specific target device wakes up (preventing false wake-ups).
• Timing: The receiver turns on briefly every 10.25 ms to 102.5 ms (configurable) to check for a SYNC burst.

Key Significance & Benefits of Wake-Up Radio (WUB)

Following are some of the key advantages of Wake-Up Radio in UWB.

1. By keeping the main UWB radio off until absolutely needed, devices can run on coin cell batteries for years.
2. Without WUB, low power devices usually sleep for long intervals (e.g. 1 second) to save power. If a user tries to unlock a door during that sleep window, there is a lag. With WUB, the door lock can sleep deeply but still respond almost instantly when the “Wake-Up” signal is sent.
3. It offers targeted activation. Because the Wake-Up packet includes a 16-bit Device ID, a transmitter can wake up a single specific tag in a room full of tags. This prevents wasting energy on devices that are not involved in the current transaction.
4. It simplifies receiver architecture. The WUB signal is designed for non-coherent detection. This means the receiver does not need complex, energy-intensive Carrier Frequency synchronization circuits (PLLs) just to detect the wake-up call, further lowering the standby power floor.

Summary: The Wake Up Radio is arguably the most commercially significant feature of the 802.15.4ab standard. By decoupling the listening function from the power hungry main radio, manufacturers can finally deploy UWB tags with multi year battery lives comparable to Bluetooth LE. This innovation opens the door to a new generation of “install and forget” smart home sensors and industrial trackers that are efficient, responsive and maintenance free.