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Reading RSSI and/or LQI values from TIMAC
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Q: FAQ: Reading RSSI and/or LQI values from TIMAC by 656199
The TIMAC provides three parameters as part of the Data-Indication when receiving a packet: - mpduLinkQuality: The link quality of the received data frame - LQI: Link Quality Indicator, the raw LQI of the received data frame - RSSI: Received Signal Strenght Indicator, the raw RSSI value of the received data frameYou can check mac_radio_defs.h for more information on converting raw RSSI to LQI
Q: Re: FAQ: Reading RSSI and/or LQI values from TIMAC by 1486437
Anyone can help me on the CC2420 measurement data - RSSI and LQI.
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
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.
Pls help me out. Thanks
Q: Re: FAQ: Reading RSSI and/or LQI values from TIMAC by 1113603
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.
Q: Re: FAQ: Reading RSSI and/or LQI values from TIMAC by 611891
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
The symbol decision is made based on the correlation value for each of the 16
possible symbols. The correlation value is an average over the 8 first symbols
following the SFD, i.e. the symbol with the highest correlation
in the transmitter and receiver chains will limit the correlation values to a
maximum of ~110 (as stated in the datasheet I believe) even for a perfect communication
link. This is a result of the soft decision at the chip level. It is therefore
not possible to directly link the correlation value to a "chip error rate".
However, the correlation value will give a very good indication of the link
quality, relatively independent of the RSSI level. It will e.g. give a highly
reduced value in presents of a strong multipath fading, where the RSSI level
still indicates a high quality link.
Note that scaling the
link quality to a LQI compliant with IEEE 802.15.4 (where 0 is the lowest LQI
and 0xFF is the highest quality) must be done by software. This can be done on
basis of the RSSI value, the correlation value or a combination of
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