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Received Signal Strength Indicator (RSSI) is a measure of the received signal power at the antenna and is usually a negative number expressed in dbm for IEEE 802.11 devices.

My questions are:

  1. Does RSSI take account the power of noise? Or is it just power of the signal? If it doesn't take into account power of noise, then how can one distinguish whether there is noise or not?

  2. Does RSSI take into account the transmit and receive antenna gain?

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does RSSI take account the power of noise? or is it just power of the signal? If it doesnt take into account power of noise, then how can one distinguish whether there is noise or not?

It is simply an indication of signal strength. Noise is a separate measure and not all 802.11 devices are capable of detecting or providing this information.

Note that in 802.11, the standard does not define any relationship between RSSI and any specific value, such as mW or dBm. Vendors are free to use whichever arbitrary scale the choose to represent RSSI, although many of them have chosen to represent this in dBm.

Does RSSI take into account the transmit and receive antenna gain?

No. It is measure of the strength of the signal it receives. A higher gain antenna would simply result in a higher RSSI as the signal would be stronger.

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  • Thank you very much, this has been helpful, does the RSSI measure the power of the whole received packet from the preamble to the data field? – Tyrone Jun 8 '15 at 19:06
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    As I understand it, no. This is typically based off the preamble, as this is a relatively simple matter. Calculating based on the whole received packet would usually provide a range of values and may require more specialized hardware. The standard doesn't define how to measure RSSI, so often the manufacturers will take the easiest path. – YLearn Jun 8 '15 at 19:17
  • Thanks again. Feel free not answer my question in this comment but I was wondering is RSSI similar to RCPI (received channel power indicator)? – Tyrone Jun 8 '15 at 19:18
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    RCPI is largely defined in 802.11k and is intended as a replacement of RSSI in 802.11. Unlike RSSI, it does measure the signal over the entire preamble/frame and the standard does set out specifications for measuring and accuracy of the signal strength. – YLearn Jun 8 '15 at 19:23
  • so major different, is that one includes the power over the whole frame and RSSI doesn't? – Tyrone Jun 8 '15 at 19:27

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