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RSSI-Received Signal Strength Indication

This page describes RSSI i.e. Received Signal Strength Indication. It mentions RSSI calculation in WLAN and WiMAX OFDM based systems.

The term used to measure the received signal power/strength of the input signal to RF receiver is called RSSI(Received signal strength Indication).

It is measured at the following places in the wireless receiver:
• before IF amplifier in the case of dual conversion receiver
• at baseband stage in the case of zero IF receiver after ADC using I/Q signals
• before ADC (measured as DC voltage)

At Baseband Stage it is measured using following equation:
RSSI = I2 + Q2
The calculation varies based on number of OFDM symbols as per IEEE Standard i.e. 802.11 or 802.16. It is averaged over one OFDM symbol as per requirement.

RSSI in WLAN device as per IEEE 802.11

The RSSI is measurement of RF signal energy received by the 802.11 OFDM Physical layer. RSSI is represented by 8 bits(256 levels). It is measured by the the Station(STA) during the reception of the PLCP preamble which is transmitted by Access Point(AP).

RSSI in WiMAX device as per IEEE 802.16

When RSSI measurement is desired by BS(Base Station), it will request SS to provide the same. SS upon request measure RSSI using OFDM downlink preamble. These measured mean and standard deviation of RSSI is reported back via REP-RSP message. Measured in dBm and range from -40dBm(0x53) to -123dBm(0x00).

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