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The majority of cellular modules are interfaced to host microcontrollers or microprocessors using UART interface or some times USB interface (where internally it's UART).

But the data rate of UART is much less. How are we able to achieve cellular data rates with respect to UART data rates?

evildemonic
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Prashanth Kumar G N
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  • Phones and other devices that support high-bandwidth applications such as streaming video don't use the same kind of modules that you see on the market for low-bandwidth embedded applications. They have much faster interfaces. – Dave Tweed Jul 14 '20 at 14:28
  • The modem is probably receiving the data at full rate over the air and buffering buffering it. The bytes then come out of the UART interface at a slower speed. Its quite possible that you could send to much data to the modem and overflow the buffer. On the other hand, if you could send lots of data at full rate to a micro-controller, in many cases you wouldn't be able to process it fast enough, and wouldn't have enough memory to store it. – user4574 Jul 14 '20 at 14:28

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How we are able to achieve cellular data rates with respect to UART Data rates?

You are not able to.

But then, most MCU projects cannot really take advantage of mobile network data rates in the slightest. The information moves very quickly between the tower and the data modem, and then very slowly between the MCU and the modem.

A human talking on a phone isn't able to achieve the network data rate either, rather the network moves their conversation as a bunch of small bursts of audio data compressed and periodically fired off with individual on-air durations far shorter than their spoken length. They are then strung back to together and played back in real time to create seemingly continuous audio.

Modular systems which need to utilize something closer to the actual capacity of a data modem use a different interface - typically USB. That may (or may not) initially appear as a virtual serial device, but unlike a real serial device, the "baud rate" in a virtual serial device is not in effect, rather USB runs at its full 12 or 480 megabit line speed. This would be the case where the modem is still a distinct submodule - typically either soldered to the board or mounted in an mPCIe slot where it uses just the embedded USB bus and power. In something like a phone, the modem is a couple of chips rather than a distinct module and may use other interfaces - in not a few smartphone SoCs part of the modem has been a processor core on the same die as the application processor, communicating via on chip interfaces and shared memory.

On a given modem carefully wired to a suitable processor you may also be able to crank up the serial baud rate... but you haven't really stated a goal for which it would be useful. And most of the goals where it would point to needing something more like an SoC than an MCU. A key part of that is because sustained high data rates almost always end up requiring large memory buffers, and once you need to give an MCU and external memory you are likely in the territory where SoCs are cheaper.

Chris Stratton
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  • I doubt that such devices use USB internally. Much more likely to be something like SDIO or even a lane of PCIe. – Dave Tweed Jul 14 '20 at 14:32
  • The next step up from the systems the OP is asking about, and which the OP might conceivably build do tend to use USB, often in a mPCIe form factor where it is the embedded USB interface, and not the PCIe lanes which are actually connected. I'm not saying there aren't more highly integrated systems which use other things, but for people constructing modular solutions the widely available modems to mount in a slot or solder as a submodule to your board are mostly USB if you want to leverage their capability, with a UART mode if you don't. – Chris Stratton Jul 14 '20 at 14:36
  • OK, fair enough! – Dave Tweed Jul 14 '20 at 14:37
  • I think most modems for high-speed applications will either be integrated into an SoC with the system CPU and so on (like smartphones) or use PCIe (for use in laptops and such). – Joren Vaes Jul 14 '20 at 14:59
  • @JorenVaes the mPCIe form factor modems you can put in your laptop use the USB bus embedded on it. They *do not* use PCIe lanes. Regardless if connectorized or as a soldered sub-module this is pretty much "how you do it" until you are placing the chips comprising a modem directly onto your board, and not as a sub-module. These USB solutions get you well into the video realm - you find them in PC's, access points, industrial/IoT devices, etc. – Chris Stratton Jul 14 '20 at 15:03
  • @ChrisStratton should have been clearer, I was not trying to correct you or anything, but merely clarifying/adding to your comment. – Joren Vaes Jul 14 '20 at 15:07