Are there any reference designs, application notes and/or software examples for using the KW24D512 antenna diversity features?
Currently there is not any reference design or application note for antenna diversity at all. There might be something later this year but there is not an exact release date. There is however a post in communities about it: https://community.freescale.com/thread/331875. I hope it helps.
Thanks for your reply. As I understand it, antenna diversity improves RX performance by choosing the first antenna observed to meet pre-defined signal strength criteria during the preamble stage of an incoming transmission. Presumably in the case of back-and-forth communications with a remote node this would then result in any reply being sent using the same antenna, which would be the best choice. In the case of a router, however, the best antenna for receiving might not always be the best antenna for transmitting, as the router will be forwarding the packet on to a different node.
Is it possible to have the application control antenna selection, at a high level, to optimise TX operations? e.g. Could we keep track of the 'best antenna' for each node in software (based on previous automatic antenna selection during RX) and then use this information when transmitting?
You may see in the article that active antenna can be set manually if FAD is disabled: “ When FAD is enabled, the PhyPlmeSetANTXStateRequest() function can be used to set the starting antenna. If FAD is disabled, this function will actually set the active antenna.”
In other words, one could use PhyPlmeSetFADStateRequest(FALSE), to disable FAD, then use PhyPlmeSetANTXStateRequest( 1 / 0 ) to select the desired antenna. This will allow you to control which antenna is to be used based in your custom process at application level.
Thanks again for the reply. Is the ability to control the TX antenna at the application level a common requirement for router products that use antenna diversity? Are you aware of any successful implementations of this on the KW platform?
Just trying to get a feel for how difficult this will be to implement effectively.
Honestly, I am not aware of any similar product so far, thus I am not able to comment on this. I guess it is up to the final application to decide how to use the FAD feature. Sorry for the inconvenience.
Just wondering if you could clarify a couple of things for us regarding the FAD antenna selection logic:
- It is possible to select a starting antenna, i.e. the first antenna that will be tested during FAD. In practice does this selection make much difference, i.e. won't the two antennas be switched rapidly while waiting for the next RX preamble anyway, so it's just a matter of chance whether or not one antenna happens to be selected when the preamble starts and therefore becomes the 'first antenna' tested?
- At what point will the FAD switching resume after an RX frame has been processed?
- If a node sends an unprompted TX frame, which antenna will be used? Will it be the antenna that is currently selected by the FAD switching?
See Antenna diversity on MKW21D512 for more info on FAD implementation and performance
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