Mantracourt Electronics Limited
T24 Technical Manual
78
RSSI, CV and LQI
Packets received from remote devices have RSSI and CV bytes present at the end of the packet.
RSSI is Received Signal Strength Indication
This indicates the strength of the received signal. This approximates to dB and can be calculated from the RSSI
byte which is stored in 2's compliment format. This value also has an offset of 45.
To convert the byte value to RSSI use the following algorithm.
RSSI = RSSIBYTE
If RSSI > 127 Then RSSI = ((RSSI – 1) Xor 0xFF) * -1
RSSI = RSSI – 45
CV is Correlation Value
This indicates the quality of the signal. The value of the CV byte (0-255) needs the most significant bit masking
off (AND with &H7F) where a poor CV is around 55 and a good CV is 110.
CV = CVBYTE
CV = CV AND &H7F
LQI is Link Quality Indication
Mantracourt may also refer to
Link Quality
which is derived from the RSSI and CV values:
LQI = (((94 + RSSI) + (CV - 55)) / 2) * 3.9
Which gives an
operational
range of approximately 0 to 255.
This operational range covers the extremes of very poor to very good connection quality so we usually take a
portion of this to represent the
usable
range which gives the user a better representation of usable, real-world
quality.
The LQI range from 50 to 128 can be thought of as to represent 0-100%
usable
quality.
This reduced portion of the range represents the
usable
range and may be represented, for example, by a signal
strength indicator as found on a mobile/cell phone.
Operational
Usable
0
50
128
255
0%
100%
The charts below indicate the operational and usable combinations of RSSI and CV where black is poor and white
is good.
Operational
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
RSSI
50 55 60 65 70 75 80 85 90 95 100 105110
CV
Usable
0%
100%
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
RSSI
50 55 60 65 70 75 80 85 90 95 100105110
CV
