The Tech Blog

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.

It’s summertime in India and most of you must be sweating through the day. Those of you who can afford air conditioning at home are probably running it at full blast now. I recently learned that AC tech does more than just cool the air. Since this knowledge isn’t common, let’s discuss it in detail today.

A residential AC is a heat pump. In a humid place, your AC also functions as a water-removal machine. Fundamentally it does not create cold air. It moves heat from your room to the outside. A refrigerant(fluid that easily changes between liquid and gas) absorbs heat at the indoor coil. The compressor squeezes it, and the outdoor coil throws that heat outside. In humid air, the indoor coil has a second job. When warm moist air touches the cold coil, air temperature drops. If the coil is colder than the dew point (the temperature where air can no longer hold all its moisture), water vapour turns into liquid water and drains out.

This is where humid climates are hard on ACs. If the room only needs a small temperature drop but the air is wet, the system still has to make the coil cold enough to condense water. That means longer run time, lower coil temperature and more compressor work. Removing water is not free because changing vapour into liquid takes energy. You are forcing water to change phase. This moisture removal can be more than 30% of the AC load.

That is why new cooling solutions are not only about better compressors. I was reading about the Global Cooling Prize and a few approaches from companies working on this problem. There is a company called Transaera that uses advanced porous desiccants to pull moisture out before cooling. The idea is simple. If the incoming air is already drier, the AC does not have to waste as much energy forcing water out on a very cold coil. Another group Kraton, with IIT Bombay, explored a membrane that lets water vapour move out first, then uses evaporative cooling.

I am new to the domain but I think this is an important shift that newer AC tech is moving towards to heat removal and moisture removal(passively) at maybe lower power even.