1、 Calterah Semiconductor September 2025(Version 1.0)Abstract Ultra-Wideband(UWB)technology has become a leading solution for fine-ranging applications such as indoor positioning,asset tracking,and secure access.However,conventional IEEE 802.15.4z-based UWB ranging1 still suffers from inherent limitat

2、ions:strict regulatory power limiting the total link budget of ranging,unstable performance in non-line-of-sight conditions,and multipath interference from environments.As a result,UWBs effective ranging distance is often restricted to a few meters,with degraded stability in real-world deployments.T

3、hese challenges are particularly serious in automotive UWB digital key use cases,where reliable passive entry demands accurate detection of users distance from the car under diverse scenarios.In practice,some typical issues of UWB digital key severely impact user experience,including:-ranging stabil

4、ity degrading sharply when digital keys are carried in back pockets or bags-complex environments such as underground parking introducing false first-path detection due to heavy multipath reflection-UWB anchors inside vehicles facing severe attenuation from metal body structures and glass To overcome

5、 these limitations,IEEE 802.15.4ab(in progress)introduces Multi-Millisecond(MMS)UWB operation2,in which MMS UWB ranging fragments exchange across multiple milliseconds,enabling accumulation of the channel impulse response(CIR)over multiple milliseconds.This significantly improves the link budget of

6、UWB ranging,extends the reliable ranging distance,and enhances multipath resilience.The standard defines three MMS UWB modes:-Narrowband-Assisted(NBA)MMS UWB2:NBA MMS UWB utilizes a narrowband O-QPSK PHY for MMS control and report phases,and the UWB channel for the MMS ranging phase,which can achiev