wifi sensitivity issue

Dear All:

I have a question about wifi sensitivity caliculation.

Our TIS sensitivity test result is -85dbm and I want to roughly caliculation by equation.



SG(Pt=-30dBm)---TXANT(Gt=3dB) ---- AIR(Ploss=-50dB)----RXANT(Gr=5dB) ----DUT(Pr)


By equation the sensitivity before RXANT is -83dbm,how is the totally sensitivity?

ex: real sensitivity=-83dbm

real sensitivity=-83dbm+5=-78dbm

real sensitivity=-83dbm-5=-88dbm

which one is correct?



Thanks,

Sensitivity is also function of wanted signal-to-noise ratio.You can also say for that as EVM,BER etc.
That's why calculation only doesn't make sense much.It mostly depends on the modulation,bit rate which you intend to use.
You calculated signal level at the RX antenna and it has little meaning in terms of sensitivity.

Dear BigBoss,
Thanks for your feedback.
Please ignore modulation, BER,EVM.
Because I want to know should we need add or subtract RX antenna or ignore antenna gain.
Do you know which solution is correct?

Thanks,
Best regards

The received power at RX side is given by:

Prx=Ptx+Gatx-Lctx-PL+Garx-Lctx

where:

Prx is the received power, in dBm
Ptx is the transmitted power in dBm
Gatx is the gain of the TX antenna, in dBi
Lctx is the loss of the cable from TX to antenna, in dB
PL is the pathloss, in dB
Garx is the gain of the RX antenna, in dBi
Lcrx is the loss from the antenna to the receiver, in dB

So in your case (with no cable losses) we have:

Prx = -30 + 3 - 0 - 50 + 5 - 0 = -72 dBm

Then if in that setup you reached the sensitivity when Ptx=-30 dBm, then at the input of your receiver the power was -72 dBm.

I don't understand where the -83 dBm comes from (possibly you subctract the gain of the TX antenna).

Dear Albgg:
I took a mistake. The sensitivity before RX antenna is -30+3-50=-77dbm not -83dbm.
In my case our TIS measurement result is -85dBm, but antenna engineer told me
dut receiver is -77-5=-82 not -77+5=-72. it confused me.
It seems he is wrong.

Thanks,

Unless your receiving antenna has a negative gain (that is Garx=-5 dBi) the correct calculation gives -72 dBm.
A gain of 5 dBi means the signal is increased of 5 dB with respect to a isotropic radiator (the "i" of dBi) that has a gain of 0 dBi.