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I am looking for the best way to add both Bluetooth (LE, central) and ZigBee (Coordinator) to my hardware project.

There were trials to integrate BLE (peripherial) and ZigBee (End Device) into one SoC: CC26x2 and CC13x2 by Texas Instruments. They provided the DMM: https://training.ti.com/dynamic-multi-protocol-manager-overview.

However on multiple forums I have learnt that:

  1. ZB Coordinator needs the medium almost 100%, otherwise network could/will collapse
  2. BLE connection must not be interrupted, otherwise it will fail.

My first priority is the ZB Coordinator, but I sometimes also want to use the BLE (without losing the ZB network).

There are multiple scenarios, but I have no idea which is the most appropriate:

  • Finding a single SoC that handles this with one antenna.
  • Putting two SoCs on the board with the same antenna and apply/create a rocksolid synchronization between them
  • Putting two SoCs on the board with 2 separate antenna placed in good distance (at least λ/4) from each other

All has disadvantages:

  • first: does not seem there is a SoC existing
  • second: synchronization seems quite challenging if not impossible
  • third: ugly and might be totally instable (but putting a ZB Coordinator USB stick to RPi seems working together with its BT)

This might seem insane, but we have at least one common example for co-existing radio technologies on same(ish) frequency: smartphones. If you make a VoIP call with your BT headset, your phone is constantly using its Wifi and Bluetooth at the same time.

Co-existing ZB and BT seems requiring much lower bandwidth, therefore seems a reasonable goal.

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    \$\begingroup\$ Search other vendors. Nordicsemi has a Zigbee + BTLE in a single chip (with single radio) that claims Coordinator + BTLE support. I have not checked other vendors. Also: Shopping questions are off topic here! \$\endgroup\$
    – Turbo J
    Jun 22, 2020 at 11:09
  • \$\begingroup\$ Use 2 radios with a power divider. \$\endgroup\$
    – Lior Bilia
    Jun 22, 2020 at 12:29
  • \$\begingroup\$ @TurboJ: thanks for Nordic, I was not intended this question to be about shopping but more for tech-perspective. Speaking of Nordic, could you please link here the document states ZigBee Coordinator + BTLE Central support? Thanks a lot, I haven't found it. \$\endgroup\$
    – Daniel
    Jun 22, 2020 at 13:03
  • \$\begingroup\$ @LiorBilia: can you post a rough sketch of the power divider? If I use one, I don't have to deal with synchronization? It would work similar as if it was 2 independent radios with 2 antennas? \$\endgroup\$
    – Daniel
    Jun 22, 2020 at 13:05

1 Answer 1

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You can use 2 radios with a Wilkinson power divider. You will have to make sure your transmissions don't collide, and the device that is in RX has enough attenuation so its neighbour doesn't cause damage.

Alternately, you can use RF switches and implement separate RX/TX paths.

The downside is that both radios cannot transmit at the same time, but they can receive at the same time, with reduced sensitivity due to the power divider's insertion loss(3db ideal).

The brute force approach is to have 2 antennas, one for each radio. But this will require more space and physical separation of the antennas of at least 1 wavelength.

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  • \$\begingroup\$ A have contacted two suppliers, and both are saying that BLE Central functionality is not playing well together with ZigBee as Coordinator, because both stacks need the radio a lot and there will be problems, unless I disable or minimize beacon scanning. I'd interest on why is this that hard to have these 2 techs implemented on the same board? \$\endgroup\$
    – Daniel
    Jun 24, 2020 at 14:44
  • \$\begingroup\$ Especially that for beacon scanning I believe only RX is needed for BLE. \$\endgroup\$
    – Daniel
    Jun 24, 2020 at 14:45
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    \$\begingroup\$ It is hard, because you are not implementing the stacks yourself. Both BLE and ZigBee use the same band (2.4GHz) each module's stack assumes it is the only radio on board. That is the most common use case. It doesn't have to cooperate with anyone else with regard to antenna sharing or RX/TX regime. \$\endgroup\$
    – Lior Bilia
    Jun 24, 2020 at 15:26
  • \$\begingroup\$ I believe I got some ideas of the problem: if BLE is scanning (RX), and ZB transmits (TX) it will ruin the scanning results. Am I right? \$\endgroup\$
    – Daniel
    Jun 24, 2020 at 15:57
  • \$\begingroup\$ Yes, if one radio transmit while the other receives, it will saturate the receiver, especially if they share the RF path (Common antenna, LNA, PA etc) \$\endgroup\$
    – Lior Bilia
    Jun 24, 2020 at 16:36

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