How to Calculate the Average RSSI for an 802.11

Written by steve mcdonnell Google
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How to Calculate the Average RSSI for an 802.11
RSSI indicates the strength of a wireless networking signal. (wireless image by Szymon Apanowicz from

Received signal strength indication (RSSI) is a relative measurement of the strength of a radio signal's energy as measured by a wireless network interface card (NIC). RSSI is used by a wireless NIC to determine if other devices are transmitting on the channel or if it is "clear to send" (CTS). It is also used to determine when a wireless signal decreases enough that the device should attempt to roam to a new device, called the "roaming threshold." The RSSI scale is different for each NIC vendor because the vendor defines its own RSSI maximum, called RSSI_Max, which is less than or equal to 255. Use a free wireless network monitoring tool to measure or calculate RSSI at regular intervals, sum the values and divide by the number of observations to compute an average RSSI. If RSSI is not reported directly, you can calculate it by dividing the signal-to-noise ratio (SNR) by the RSSI_Max.

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  1. 1

    Download a free wireless networking tool that will enable you to measure SNR or RSSI. Install and run the wireless networking tool.

  2. 2

    Locate the wireless router from which you want to measure average RSSI from within the wireless networking tool. Find the signal strength indicator and determine if it is reported as SNR, measured in dBm, or in arbitrary RSSI units. Identify the frequency at which the utility reports signal strength.

  3. 3

    Determine the amount of time you will use for the average RSSI calculation; for example, five seconds. Collect the SNR or RSSI values at each interval; for example, once per second for five seconds.

  4. 4

    Determine the RSSI_Max for the vendor of your NIC by visiting the vendor's website if the wireless utility only provides SNR. Sample RSSI_Max values used by NIC vendors are 60 for Atheros, 100 for Cisco and 60 for Symbol.

  5. 5

    Convert SNR to RSSI if you collected SNR measurements. Divide SNR by RSSI_Max and multiply by 100 to get a percentage for each observation. For example, if SNR is 40 dBm and RSSI_Max is 100, the RSSI value will be 40/100 * 100 = 40 per cent.

  6. 6

    Sum the RSSI values for each observation and divide by the total number of observations to get an average RSSI. For example, if the RSSI values were 40, 52, 43, 44 and 45, the average RSSI would be (40 + 52 + 43 + 44 + 45)/5 = 44.8 per cent.

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