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What is RSSI?

Eswaran Rathinam12
Intellectual 350 points
Other Parts Discussed in Thread: CC1200

Hello ,

           im confused about the term RSSI.I Suppose it is the strength of the received power at the receiver end.I did a basic experiment.i have a cc1200module connected to trxeb board.i connected the two boards antenna out through a SMA Cables.The datasheet quotes that the transmitter sends out signal at 14Dbm.But when i run the PER Test code at boards,i got a RSSI of  -9Dbm even when the boards are connected through SMA cables.Im sure that the cables wont be having a loss of ''23Db''.So i connected the antenna and run the same code,i got a RSSI of -6Db,when the boards are pretty close at same orientation.(4cm away).So what is actually RSSI?And why im getting a loss of more than 23dbm when i connect through cables.Please reply..Thank you..

  • 0
    TI__Mastermind 39860 points
    RSSI is the received signal strength, i.e the power level at the antenna. Please refer to the middle left plot on page 17 in the CC1200 data sheet. This shows the RSSI versus input power level. What you see from this figure is that the RSSI reading saturates at approx -10 dBm, i.e any input power level above this will give a reading of approx -10 dBm. Below the saturation point the RSSI increases linearly with input power level.

    Note also that the absolute maximum rating for the input power is +10 dBm. Thus, do not apply +14 dBm as you did in your testing. This can permanently damage the chip.
  • 0 in reply to Sverre
    Intellectual 350 points
    ok,i understand..but the link margin displayed on the LCD is calculated as Received power-Sensitivity right??or it is RSSI- Sensitivity??Because when i give an input of 0 OR 5Dbm,the RSSI Is same -9Dbm which is as mentioned in datasheet.But what about Link margin??Even that is same as 111Dbm.So is the link margin calculated as RSSI -Sensitivity??
  • 0 in reply to Eswaran Rathinam12
    TI__Mastermind 39860 points
    On the LCD the link margin or or guard band is calculated as the difference between the RSSI and the sensitivity of the receiver. Since the RSSI saturates at approx -10 dBm you get the same calculated link margin on the LCD for 0 and 5 dBm input power level.

    In reality the link margin will 5 dB higher for the latter since the actual received signal power (not estimated RSSI) determines the link margin.

    In any case, if the link margin is 100 dB or 105 dB is really no concern. The link margin (guard band) is relevant for low input power levels.
  • 0 in reply to Sverre
    Intellectual 350 points
    But ,what is RSSI Units in graph given in datasheet.Because if my input power is around -10 Dbm,the RSSI Value should be 70 Dbm(according to the datasheet),but im getting -11Dbm.What does the RSSI units in datasheet?and when i run the PER Test on the board at -10 Dbm,i get a RSSI of -11Dbm which is good but when i run using SMART RF studio with easy mode at TX Powe of -24Dbm,i get -23Dbm at receiver.So there is a gain of 1Dbm.I dont know why?Please help...Thank you..
  • 0 in reply to Eswaran Rathinam12
    TI__Guru**** 317180 points
    The graph in the datasheet shows the RSSI read from the RSSI register. The value read from the register has an offset (given by SmartRF Studio) compared to the real value. When using SmartRF Studio the offset is accounted for.

    For you test, how do you know that the Tx power actually is -24 dBm?
  • 0 in reply to TER
    Intellectual 350 points
    Ok Thanks...I have Set it to transmit -24Dbm im Smart RF Studio..