FAQ ID # 36
Last Update : 2012/02/20
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Question / Issue
How does the CSQ value relate to RSSI?

Answer / Solution

The AT+CSQ command returns the Signal Quality Measure (SQM).  This is a Signal to Noise Ratio measurement that is used to ascertain the relative quality of the received cellular signal. There is no standard for this measurement, other than that all manufacturers report CSQ between 0 and 31. The scaling is unique to each cellular module model.

To convert the CSQ to a Received Signal Strength Indicator (RSSI) value, you must assume a noiseless environment. 

For the 1xMG-401 and 1xMG-401S (CDMA):

This table shows the general relationship between CSQ value and dBm in a noise free environment.

7 -104
9 -100
14 -95
16 -90
21 -85
24 -80
27 -75
31 -70

NOTE: For the CDMA LAN-Cell models, the current RSSI value can be queried directly by the AT*NETS? command.

For the GPRS-401:

0 -113 or less
1 -111
2 thru 30 -109 to -53
31 -51 or greater
99 not present or not measurable

In other words, approximate RSSI (dBm) = (-113) + (2 * CSQ)

The GPRS-401 does not provide a direct measurement of RSSI.

For the LAN-Cell 2:

RSSI values are shown directly on the HOME screen in the Cellular Interface Status area along with a relative signal strength measure (Poor, Weak, Good, Strong, Excellent).   The scale is dependent upon the specific PC-Card modem in use.  Please consult the documentation for your PC-Card modem for more information on how signal quality is measured.

Related Links
LCTN001 Cellular Antennas.pdf

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