The TIMAC provides three parameters as part of the Data-Indication when receiving a packet:
-     LQI: Link Quality Indicator, the raw LQI of the received data frame

Anyone can help me on the CC2420 measurement data - RSSI and LQI.

1) It seems like what we read is average CORR, not LQI, based on its data range [50, 110].

How can we observe the LQI from cc2420? What about a & b used in the relation formula?

2) The correlation value one can read out from cc2420 is the average correlation value over the first 8 symbols following SFD received in a packet.

One symbol is 32-chip sequence (+1 or -1). Given the perfect condition, the CORR per symbol could be as high as 32. How can it be limited in 110, as mentioned in (1)?

For your reference, I also attach some of TI FAQs on LQI and RSSI.

http://e2e.ti.com/support/low_power_rf/f/160/t/18233.aspx

http://e2e.ti.com/support/low_power_rf/f/160/p/18255/70843.aspx#70843

Pls help me out. Thanks

Could you explain further what is the mathematical formula the cc2420 radio used to calculate the LQI? How is the correlation done?

I am also a CC1101 user, I found our prototype node has LQI value only around 50, do you know what is the maximum LQI for cc1101 radio? It seems to me it shall not be 110.

Tkashi,

A 802.15.4 symbol can be translated into a sequence of phase shifts. A symbol is 32 made up from 32 chips, giving 31 phase shifts. When trying to demodulate the incoming data the demodulator tries to match the incoming phase shifts to the known 802.15.4 symbols. If the incoming sequence matches well the correlation will be high, if it matches poorly the correlation will be low.

The correlation value one can read out from cc2430/CC2420/CC2520 is the average correlation value over the first 8 symbols received in a packet. Good SNR will give higher correlation than low SNR (This differs from RSSI which only measures the energy in the channel).

1. Correlation gives an indication of the SNR of the incoming data
2. High correlation = High SNR = low probability of errors