A baseband is a really fancy specialized SDR. Most are based on arcane VLIW DSP architectures like Qualcomm’s Hexagon or Samsung Marconi - you’ll usually have several DSPs handling the different physical layer channels, and then some coordinating DSPs doing L1 channel mixing and timing (in 4G and 5G, various logical and transport channels are muxed into the same physical channels).
Then a set of higher level processor cores (usually referred to as CP, sometimes still a DSP but often a general purpose application processor like ARM) will handle the MAC and above. There will be occasional fixed function blocks for some common protocol functions, but generally it’s less “analog magic” in the way people think when they hear “radio” and more “DSP magic.”
Seems like the difficult part is doing that effectively while avoiding IP issues -- patents on software and math have entrenched Qualcomm's dominance.
Imagine if all of the IP for ML or AI were held by a single company that got the regulating body (ITU/3GPP) to require their use. Makes a mockery of FRAND terms.
The hard part is designing a good modem while also unambiguously working around all the Qualcomm patents in all the jurisdictions that have iPhone, which is all of them.
Because if you don’t do that, you’re still paying Qualcomm which defeats an important purpose of making your own modem.
[0] Fair, reasonable, and non-discriminatory. Each one of those words has a funny legal definition separate from whatever English you're thinking of.
[1] Who, incidentally, sold Apple the modem division that made the C1, because Intel is nothing but a bottomless pit of bad management decisions
As the reply below, Apple still has to pay its SEP. Given Apple has its current deal with Qualcomm until 2027 with time to extend further we likely won't know the full details. Previously it was 5% of Wholesale price for all Qualcomm patents whether they are SEP, wireless or not. With a cap or maximum $20 per smartphone meaning the Pro range don't have to pay a lot more. And rebate towards the modem Apple purchase. The reality after deducting rebate Apple was paying closer to 5%. For reference Ericsson ask for 3% on 5G SEP, previous Cory ruling suggest reality was closer to 2%.
And even CPUs (esp state of art) have to worry about radio effects, as in avoiding internally and across chipset.
It is a ridiculous amount of work and if you're new to the business, it takes a long time just to be build the lab test suite. And you need to support not just the latest and greatest protocols but also legacy ones. The operators have their own say and test labs as well and they all have slightly different setups and requirements.
> And even CPUs (esp state of art) have to worry about radio effects, as in avoiding internally and across chipset.
Radio effect are rarely an issue with regular chips. Crosstalk within a chip only happens between wires that are within hundreds of nanometers separated from each other.
Easy to believe radios would be an order of magnitude harder, what with the ancient proprietary standards and actual physical radio stuff. (The closest CPUs get is serdes and in my experience those are bought in from Synopsys et al.)
Nobody will use a phone company that doesn't work with iPhones.
If there are reports of iPhones failing to work reliably from Kansas City to Kuala Lumpur then it would be unlikely to be the operators being blamed here.
A modem, well nobody's going to help them build one of those; it'd put them out of business - ARM's business _is_ selling access to its body of work.
Same with the GPU except that was later on - it was a licensed PowerVR IP until Apple started using their own custom GPU from the A11.
It's the opposite, AArch64 was designed by ARM in order to produce their CPUs.
