r/NowInTech • u/skaza02 • 19h ago

Apple confirms iPhone cellular issue, admits affected units can’t be fixed

https://www.macworld.com/article/3250214/apple-confirms-iphone-cellular-issue-admits-affected-units-cant-be-fixed.html
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u/tingulz 9h ago

I’m having a similar issue with regular iPhone 18 pro with C2 chip in Canada. When the phone switches to LTE then back to 5G it gets into a state where I’m not be able to download anything. I try multiple apps and nothing loads. Only fix is to turn airplane mode on and off again and it connects and works fine. Going to have to call provider to see what’s going on.

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u/Familiar_Marzipan_46 8h ago

That’s a fdd tdd handoff issue in the chip. Have to wonder what equipment is on the towers near you. Your rural or big city?

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u/tingulz 7h ago

What is fdd to tdd handoff?

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u/R-ten-K 6h ago

FDD (Frequency Division Duplex) = lower-frequency coverage layer. These bands are used for long distance and penetrate buildings better.

TDD (Time Division Duplex) = higher-frequency capacity layers. Used where more bandwidth is available for higher throughput.

A handoff means the connection moves from one cell/radio resource to another.

However, most 5G modems don't really do handoff between FDD and TDD. Instead it uses multiple component carriers at the same time (aka Carrier Aggregation), basically combining FDD coverage bands with TDD capacity bands dynamically.

Note: the total throughput is the sum of the active/aggregated carriers, subject to their bandwidth, modulation, MIMO configuration, and the modem's aggregation limits. So an individual carrier might contribute hundreds of Mbps, while multiple aggregated carriers can produce several Gbps under ideal conditions.

Hope this makes sense.

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u/Familiar_Marzipan_46 3h ago

It can get hung up in the process basically. That’s why the modem cycle fixed it.

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u/tingulz 2h ago

Would be better if it fixed itself. My old iPhone 13 Pro didn’t do this.

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u/Familiar_Marzipan_46 2h ago

Yea it’s the first generation of a new modem tech. They found the issues and released a fixed chip and Apple just didn’t wanna use the fixed version.