Other Parts Discussed in Thread: MSP430F2274, CC1101, CC2530
Hey everybody,
I have a question about the LQI values I read out from the appended bytes. While the RSSI values seem to be absolutely reasonable, the LQI values are appearing to me almost with no correlation to their intention.The data sheet says that a low LQI value means a good and a high value means a bad link quality.
For approx 4000 packets I recorded the RSSI and LQI values for 3 output power settings (-34.2 dBm/0.3dBm/7.2dBm). Apart from that my setup (see 'Test setup' below) remained completely the same during recording.
I know that of course more power doesn't necessarily mean a better link quality but is it really common that almost all values are represented, especially the worst one ('127') very often for such a harmless setup.
Here is e.g. a typical LQI value line ...26 127 72 77 49 71 34 57 56 93 58 84 77 60 127 57 53 69 33 25 127 75 100 81 47 44 38 54 114 88 60 64 26 31 42 73 76 46 35 45 127 53 100 47... having a line-of-sight, 7.2dBm output power and 3 feet (1m) distance setup.
I also made a histogram..
As one can see concerning the LQIs there is almost no difference between the 3 output power setups...why is that!? And even worse they all have a lot of 127s.
Is there something wrong with my interpretation?
Any help is appreciated.
best regards, FT
Test setup: I'm using the provided code examples from TI in combination with 2 modules talking with 500kBaud to each other. Each module has a MSP430F2274 and CC1101. The distance between them is in the range of 3 feet (1m) - LoS, pointing to each other. I enabled Fixed Packet Length, FEC, DC filter, Preamble is 16 bytes ...
[Update 2011-12-14]
Another strange behaviour I can not explain is that when I set the output power to a very low level (let's say -30dBm) then the receiving module is almost out of range with the current distance. The RSSI values are between -90 and -100dBm and if the distance between them gets slightly more then almost all sent packets go lost. But right before I reach this limit the LQI values drop down and reach constant 0 while it seems that still all packets are getting received at this point.
The second I get closer to the sender the LQI values become again immediately random values between 20 and 127 and every move I do away from the sender leads immediately to the loss of all packets.
