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We're going to check some technical terms that are present in documentation, and we'll use this little
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diagram as a support for the explanation. 
First of all, we transmit with a power Pₜ and the fraction
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of this power will arrive to the receiver.
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But along a transmission path, some noise has been added to the signal.
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So at the receiver side, we have Pᵣ, the reserved power, plus Pₙ the noise power.
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So what do we want?
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We want to have the highest possible received power.
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And of course, we also would like the noise to be as low as possible, ideally, and theoretically we would
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like the received power equal to the transmitted power and the noise power equal to zero.
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But that's obviously not possible, because that would mean that a transmission path is lossless and
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noiseless.
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Now that we have explained these three terms, we can explain almost everything.
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First of all, the first term that we will see in the documentation is a term called RSSI.
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RSSI is the abbreviation of receive signal strength indication and it's equivalent to the received power
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Pᵣ.
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Then they will speak about the sensitivity.
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Sensitivity is something that is very important for a receiver because it's the minimum power that it
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will be able to receive.
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So a power Pₜ has been emitted.
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There is an attenuation in the air because there are losses during transmission.
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And finally, there is more residual power received. 
If this residual power is high enough for the receiver
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to demodulate the signal.
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It means that this power was higher than the receiver sensitivity.
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Let's recap that one more time.
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We receive a signal with a power called RSSI.
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If the RSSI is greater than the sensitivity, then it's okay.
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If it's lower than the sensitivity, then it's not okay.
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The third term is related to the noise power.
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Indeed, we receive Pᵣ, but we also receive Pₙ and we're going to make the ratio between the two of
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them Pᵣ over Pₙ.
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And of course, we want this ratio to be as high as possible to indicate that there is more useful signal
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than noise.
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These three definitions, they have units.
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And again, we use decibels.
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So dBm for RSSI and sensitivity because in both case we speak about power and dB for signal to
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noise ratio because we speak about power ratio.
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And the beauty of the decibel representation is that we will be able to add and subtract them each other.