Can the NRF52 output an unmodulated continuous tone at a specific channel?

RE: Can the NRF52 output an unmodulated continuous tone at a specific channel?

Øyvind Karlsen — Fri, 12 Aug 2016 08:40:56 GMT

You could use a nRF52 for the CW source as well, anything the 8001 can do, the nRF52 can do as well. I am still not entirely sure why you want a full-duplex radio, the way I see it from the Ensworth paper there are no simultaneous receive and transmit operations. Please refer to the first image in this article, the difference in the article is that the backscatter node also alters the backscattered signal by a FET switch. I might very well be wrong here though, as I haven't had the time to properly research this topic.

It is very rare to use full-duplex as it requires expensive components in the antenna structure, ie. ensuring that the transmit does not self-interfere with the receive.

What is usually done is to time divide the transmit and receive and take turns, which is a form of half-duplex. I guess you are familiar with TDMA, this is the same thing.

RE: Can the NRF52 output an unmodulated continuous tone at a specific channel?

ray — Fri, 12 Aug 2016 07:32:35 GMT

Thank you! It's one part of a thesis focused on enabling applications in energy harvesting. And you are correct; a two-node solution with existing Bluetooth infrastructure (like in the Ensworth paper) would be a very desirable feature. In the worst case, my current plan is to use an NRF8001 as the CW source, and NRF52 as the receiver.

Would you know what Bluetooth chipsets are used for streaming audio? Those must be full-duplex, right?

RE: Can the NRF52 output an unmodulated continuous tone at a specific channel?

Øyvind Karlsen — Fri, 12 Aug 2016 06:19:09 GMT

Hi,

This sounds extremely interesting, really cool thesis! I have found a paper that has done what you are trying to do using a nRF51822 chip that I think you will find very helpful.

Ensworth, Joshua F., and Matthew S. Reynolds. "Every smart phone is a backscatter reader: Modulated backscatter compatibility with bluetooth 4.0 low energy (ble) devices." 2015 IEEE International Conference on RFID (RFID). IEEE, 2015.

If I'm understanding you correctly that means that you are trying to compress the method described in this paper into two nodes?

For a functional test I think all three nodes described in this text can be realized partly by a nRF5 chip. CW output from the chip should be faily straight forward. You ccould also use it to generate the output frequency for the backscatterer. Finally it is already proven as a competent BLE receviver.

RE: Can the NRF52 output an unmodulated continuous tone at a specific channel?

ray — Thu, 11 Aug 2016 17:39:17 GMT

There's recently several publications on using BLE in microwatts applications via backscattering. The idea is to incident a CW signal at a BLE beacon target, and modulate the CW signal on target-side to reduce the need to generate another carrier tone. The caveat is that the TX and RX has to be both enabled on the source-side.

RE: Can the NRF52 output an unmodulated continuous tone at a specific channel?

Øyvind Karlsen — Thu, 11 Aug 2016 10:17:34 GMT

At this price point, no. Perhaps you could elaborate a bit more on the use case, and I could suggest some alternatives.

RE: Can the NRF52 output an unmodulated continuous tone at a specific channel?

ray — Thu, 11 Aug 2016 09:21:23 GMT

That's too bad. Last question, would you know any bluetooth product that can support true full-duplexing?

RE: Can the NRF52 output an unmodulated continuous tone at a specific channel?

Øyvind Karlsen — Thu, 11 Aug 2016 06:24:21 GMT

No, it does not support full-duplex. There's no hardware to isolate the RX and TX, so they are connected in turn. If you want to use the chip this way the only way I can see it working is by using two chips.

RE: Can the NRF52 output an unmodulated continuous tone at a specific channel?

ray — Thu, 11 Aug 2016 02:14:37 GMT

Thank you! Could you confirm whether the NRF52 supports full-duplexing while the TX is a constant carrier?

I know DTM disables the stack features, but the radio test example doesn't seem to use any feature that stops the RX from operating as normal.

Regards, Ray

RE: Can the NRF52 output an unmodulated continuous tone at a specific channel?

Øyvind Karlsen — Wed, 10 Aug 2016 08:29:15 GMT

Hi,

Yes you can do this. I recommend using either the radio test example or alternately direct test mode. Both implement this already and can be found in the SDK under nRF5_SDK_11.0.0_89a8197\examples\peripheral\radio_test and nRF5_SDK_11.0.0_89a8197\examples\dtm\direct_test_mode.

Best regards,

Øyvind