LQI function

Which chip are you referring to?

cc2500

eZ430-rf2500 

The LQI can be read from the LQI status register or it can be appended to the received packet in the RX FIFO. LQI is a metric of the current quality of the received signal. The LQI gives an estimate of how easily a received signal can be demodulated by accumulating the magnitude of the error between ideal constellations and the received signal over the 64 symbols immediately following the sync word. LQI is best used as a relative measurement of the link quality (a high value indicates a better link than what a low value does), since the value is dependent on the modulation format.

To simplify: If the received modulation is FSK or GFSK, the receiver will measure the frequency of each "bit" and compare it with the expected frequency based on the channel frequency and the deviation and the measured frequency offset. If other modulations are used, the error of the modulated parameter (frequency for FSK/GFSK, phase for MSK, amplitude for ASK etc) will be measured against the expected ideal value

RSSI (Received Signal Strength Indicator) is a signal strength indication. It does not care about the "quality" or "correctness" of the signal. LQI does not care about the actual signal strength, but the signal quality often is linked to signal strength. This is because a strong signal is likely to be less affected by noise and thus will be seen as "cleaner" or more "correct" by the receiver.

There are four to five "extreme cases" that can be used to illustrate how RSSI and LQI work:

1. A weak signal in the presence of noise may give low RSSI and low LQI.

2. A weak signal in "total" absence of noise may give low RSSI and high LQI.

3. Strong noise (usually coming from an interferer) may give high RSSI and low LQI.

4. A strong signal without much noise may give high RSSI and high LQI.

5. A very strong signal that causes the receiver to saturate may give high RSSI and low LQI.

Note that both RSSI and LQI are best used as relative measurements since the values are dependent on the modulation format.

BR

Siri

Is LQI calculated the same way in CC2420 (chip on a CC2420EB and LQI read through SmartRF PacketSniffer)?
 

Hi Dears,

Also, I have problem with getting LQI values, I have searched on hal_rf and basic_rf functions but I have not find anything, reading LQI in sniffer is really good (I have not checked yet but in registers will be good) but I want to use LQI values in my program.

Could you help about that issue?

Regards,

ES

My question for CC2530,

thank you for your consideration.