Tx interval in MKW41Z SMAC Connectivity test item PER

[leochao]

Hi,

Why the value of Tx interval or the inner frame spacing should be larger than 5ms?

And how did we determine this value?

In our test case, there are 68% samples will failed in receiver sensitivity PER (≤30.8%) under input signal level -90dbm and TX interval 5ms.

But they pass if the TX interval set to 7ms as the user guide as below.

Is this value a standard protocol or not?

Thanks,

Leo

[santiago_lopez · Accepted solution]

Hi Leo,

This interval is defined by the application and depends on the size of the packet. This time is required to process the received packet and it changes depending on the payload size. For example, a payload of 116 bytes requires the message interval to be higher than 8 mS

In a custom application you would need to measure what is the minimum time required before you can send another packet.

Saludos

Santiago López

[leochao]

Hi Lopez,

Thanks for the answer. That's useful.

I have another question about this topic.

Is this value a standard protocol? How about the limitation on KW41Z if the transmitter is another 802.15.4 device?

They don't know the requirement(For example, a payload of 116 bytes requires the message interval to be higher than 8 mS) for KW41Z as a receiver.

Thanks,

Leo 

[santiago_lopez]

It is not a standard value. It will depend on the time it takes to the message to reach the receiver and the time it takes to the receiver to process that packet and prepare for a new reception. As you mention, if other device does not know this and tries to send another packet immediately, this packet will be lost. That's why protocols like MAC over 802.15.4 implements message acknowledge. This way, a new message is not sent until an acknowledge from the previous message is received. This prevents messages to get lost by the receiver.

Hope this helps.

Santiago

[leochao]

Hi Lopez,

Thanks for your kind reply in detail.

It’s clear to me now.

cheers!

Leo