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Comment by ACCount39 | Hacker News Reader

I know for sure that Qualcomm LTE/5G modems are also SDRs under the hood.

Like Wi-Fi chips, they don't use SDR mode during most of the normal operation. They have dedicated hardware units that do a lot of the decimation, conversion, modulation and demodulation efficiently. But the "SDR mode" is still there for things like factory calibration.

Makes me wonder how many other common MCUs and SoCs are just waiting for someone to unlock SDR in them.

TX is less "not possible" and more "this dev doesn't want to enable it" from what I gathered. Probably for "I don't want people using this to shit all over the spectrum" kinds of reasons. So you can get TX - it'll just require extra hacking.

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Yes they are. And they have a much wider tuning range (I have one that tunes from 240 MHz to 7 GHz). Problem of standard hardware is that every path has dedicated SAW/BAW bandpass filters that yeet anything not in uplink/downlink. And you need an unfused chip for custom Hexagon DSP stuff (so no phones).

Base stations are also SDRs by the way xD

Their DSP/SoC silicon includes a wideband transceiver? But phone chips have external bandpass filters? Interesting. Mostly I've seen baseband processor + external transceiver (wideband or not) with its own filters.

External transceiver over QLink.

I know the LTE modems had ADCs and DACs in SoC - ZIF with analog signal running straight between the tuner and the SoC. But 5G systems rolled ADC/DAC into the transceiver chip itself - with only the digital processing living in SoC.

Is the "QLink" setup they use in 5G systems now just a thin protocol running over LVDS and streaming I/Q between the transceiver and SoC DSP as digital signals?

Never actually went that far, but I did wonder if you could plug a QLink tuner chip into an FPGA to use it as a broadband SDR frontend.

There are also chips like NXP layerscape which do the sampling and hardware acceleration on a chip which streams to host (though still need another transceiver).

The motivation for this is of course beamforming, angle of arrival, spatial streaming, etc. You connect multiple antennas with different views back to the base station.

Yeah, I've worked on such chips where there is essentially a DSP with extra Wi-Fi specific hardware blocks on a shared memory bus. The DSP runs its standard assembly language and makes calls to the blocks, which are themselves configured with config registers or even a kind of microcode style assembly.

Those hardware blocks could be useful for certain applications but most importantly for triggering captures only when there are frames to process and giving you both the frame + the sample.

So for me the perfect hack would allow both normal Wi-Fi tx/rx and triggered or continuous rx sampling.

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