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#1 2018-Jul-17 02:05:58

vutran
Member
Registered: 2017-Jul-01
Posts: 35

RSSI value is not proportional to magnitude?

Hi,

I have a doubt of RSSI and magnitude of the IQ data. Currently, I want to receive a quite low power signal from a device. And I want to use the energy trigger to start the capturing the suspected packets. However, it seems that the RSSI is not correct (in WARPLAB 7.7.1). Please have a look at the following image image. From 800 - 1800, there is quite clear 1.5 cycles of low frequency signal with high magnitude. But the corresponding RSSI is very low. It causes the packets to be missed. Can you give me some explanation of the phenomenon as well as how RSSI is calculated?
Thank you.

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#2 2018-Jul-17 09:11:34

murphpo
Administrator
From: Mango Communications
Registered: 2006-Jul-03
Posts: 4924

Re: RSSI value is not proportional to magnitude?

The MAX2829 RSSI circuit is an RF power detector that integrates across bandwidth at the output of the Rx LPF (refer to the block diagram on pg 25 of the MAX2829 datasheet). The signal you highlighted is narrowband. When this narrowband signal is the only signal, the RSSI power detector will observe low power across the channel bandwidth. If you want to use RSSI for packet detection you must construct a preamble whose amplitude and bandwidth are similar to the payload, such as the 802.11 OFDM waveform where the STF and LTF are constructed with the same average power as the payload OFDM symbols.

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