Bluetooth 6.3 spec was released a couple of weeks back, and I finally got time yesterday to go through the changes. The most interesting one is Inline PCT Transfer. Lets discuss that today.
I had written about Channel Sounding for distance measurement in older posts. In that, 2 BLE devices exchange known radio tones and watch how the phase shifts across frequencies. That phase shift carries distance information, so it can do better than signal-strength guessing.
Now the tricky part is the oscillator error. Each device has its own local oscillator. When the reflector receives a tone, the measured phase mixes the useful air-path phase with the phase difference between the two oscillators. Earlier, the reflector reported Phase Correction Term(PCT) data back. It used I and Q values, which describe amplitude and phase. The initiator combined its own phase reading with the reflector’s data and cancelled the oscillator error digitally.
BLE 6.3 moves that correction closer to the radio itself. With Inline PCT Transfer, the reflector looks at the phase of the tone it received and uses that information to shift the phase of the tone it sends back. So instead of sending all the correction details to the initiator for later math, part of the correction is built into the returned signal.
When that signal comes back, the initiator gets a cleaner phase measurement. It effectively sees the phase change from the signal travelling to the reflector and coming back again, so the useful channel phase appears doubled. That is helpful because the initiator needs less extra PCT data over HCI, which is the interface between the Bluetooth host and controller. So what’s the use case? Less reported data means less processing, less procedure time, and potentially lower power for repeated ranging.
The other BLE 6.3 changes are useful too. PHY-specific RTT accuracy improves timing and BR/EDR RF limits are relaxed for dual-mode radio design. Overall 6.3 is a good update.
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