First some background – we’ve been able to do some pretty cool stuff with the CC1101 &/or CC430 in multiple bands & are moving forward with some new revisions to our products. Sometimes our CC430 is both ends of a TX/RX pair and sometimes we are the receiver for legacy systems we have little control over, which drives me to have concerns about TX/RX frequency offset issues in FSK modes. In some cases I have short preambles to work with and so minimizing acquisition time (the time it takes the receiver to figure out all the proper AGC, frequency offset, etc. settings) while maintaining good sensitivity is critical.
One specific concern I have is about dealing with frequency offsets between a legacy transmitter and CC1101/CC430 receiver when using FSK/GFSK (or MSK). I know that there is Frequency Offset Control provided by the FOCCFG register & I have played around with these settings experimentally and have a pretty good idea of how the FOC_LIMIT setting effects ability to receive vs. frequency offset. So, here are my questions:
1) At first glance, it seems like opening up FOC_LIMIT to 3(11)=[+/- BWchan/2] is what I would always want to do to make sure I have the best shot at receiving cleanly from transmitters that have drifted with age/temp/etc. Is there any downside to this in terms of sensitivity or acquisition time or anything else? It seems like there must be a tradeoff somewhere – so I just want to know what the tradeoff is.
[It looks experimentally like there is an acquisition-time penalty for FOC_LIMIT = 3(11) vs. 2(10) or 1(01) -- if I have a long preamble in the data, this is not a problem, but for some of the legacy systems, there is a very short preamble - so it matters].
2) I have not played with the FOC_PRE_K setting – what are the issues with changing that from whatever default setting is used now? I’ve got it at 2(10)=3k loop gain now.
3) Right now I have FOC_BS_CS_GATE = 0; From what I’ve read, this may not be the best setting as it could wander in the presence of noise. What would be the expected impact on my acquisition time if I go from 0 to 1 for this setting?
Thanks in advance!
-Tom
