#1 Nov. 17, 2017 16:08:21

mkirk
Registered: 2016-03-09
Posts: 50
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CSMA-CA power threshold on Siflex R2

We think we are experiencing high RF noise in one of our setups. We use source routed packets that use CCA mode, with security and retry ACKs. Sometimes the packets are not received - even at higher Tx power levels. Simple short packets with Security but without CCA or retry ACKs seem to work OK

Reviewing the AT86RF212B Datasheet, there are two CCA_MODE methods:
CSMA-CA and LBT (listen before talk)

For CSMA-CA, there are 4 modes:
1) Mode 1 - Energy (ED) above threshold: P_THRESH = -98dBm + 2.07dB*CCA_ED_THRES
Default is -84.5dBm Lowest is -98 dBm, highest is -67dBm
2) Mode 2 - Carrier Sense only (default 0x07 and 0x0F = empty channel)
3/4) Modes 3a/3b - Carrier sense OR/AND energy above threshold (P_THRESH)

There also is a LBT (listen before talk) mode set in XAH_CTRL_1 register.

Which mode is used in LSR Siflex R2 - CSMA-CA or LBT?

If CSMA-CA is used, is the CCA_ED_THRESH value modified over time to compensate for RF conditions? Or is it left at the default setting?

Thanks,
Mike

Edited mkirk (Nov. 20, 2017 18:30:00)

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#2 Dec. 4, 2017 17:22:31

mkirk
Registered: 2016-03-09
Posts: 50
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CSMA-CA power threshold on Siflex R2

LSR responded via tech support email. For the benefit of others who may have same question.

LSR Siflex02 with ModFlex protocol uses CSMA-CA mode 1 - energy above threshold
CCA_ED_THRESH is set to maximum 15 (0xF)

For OQPSK, this give a threshold of -67dBm minus any gain in the front end Rx preamp (if SiFlex02 has one).

No dynamic adjustments are made to CCA_ED_THRESH, it is set at boot time.

LSR/Laird - please feel free to revise with any corrections.


Edited mkirk (Dec. 4, 2017 21:23:27)

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