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Relationship between RSSI and Packet Error Rate

SFarzan
Prodigy 70 points

Hi,

I've performed a Packet Error Rate test between two CC1200s in a room. When there is a line of sight between the transmitter and the receiver, the sensitivity is about -107 dBm. However, when the modules are a little bit further and there is not a line of sight, the sensitivity drops to about -96 dBm (packet loss happens below -96 dBm).

I was expecting to have the same performance for the same RSSI/Sensitivity, but it seems there is another parameter also involved.


Can someone please explain what could be the problem? I would appreciate it.

  • 0
    TI__Guru**** 317180 points

    RSSI is a number indicating the energy in the channel. The energy could be the wanted signal but also noise etc. If you turn on you Rx but keep your Tx off you get an indication of the noisefloor for that position of the receiver. This will set the sensitivity. When you turn on you Tx the received signal from the wanted source has to be a few dB above the noisefloor to be able to demodulate.

    In an indoor environment you will in addition have multipath effects that will impact how easy it is to receive the signal: From wikipedia:

    "The presence of reflectors in the environment surrounding a transmitter and receiver create multiple paths that a transmitted signal can traverse. As a result, the receiver sees the superposition of multiple copies of the transmitted signal, each traversing a different path. Each signal copy will experience differences in attenuation, delay and phase shift while travelling from the source to the receiver. This can result in either constructive or destructive interference, amplifying or attenuating the signal power seen at the receiver. Strong destructive interference is frequently referred to as a deep fade and may result in temporary failure of communication due to a severe drop in the channel signal-to-noise ratio."