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Let's recap what's important for us.
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We understood that the received power needs to be higher than the sensitivity for successful transmission.
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Let's have a look at two cases.
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In the first case we'll consider a transmission power of 0 dBm and we'll consider a sensitivity of -100 dBm.
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In this case, between the transmitted power and the sensitivity,
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we have a difference of 100 dB and this 100 dB is our budget.
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This means that it's what we are allowed to lose in the air, in the connectors and cables and all the
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way along a transmission path.
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Now, let's take a second case: with a transmitted power of -20 dBm, and we now consider the sensitivity
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of the receiver of -120 dBm.
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The difference between the two is still 100 dBm.
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Which transmission is more interesting?
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In fact, they are exactly the same because under one hand you have the higher transmitted power but
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a bad sensitivity, and in the second case you have a lower transmitted power, but also a better sensitivity.
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Let's make an analogy of what we just said.
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We can consider that the transmitter and the receiver are on the one hand as speaker and on the other
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hand a listener.
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In the first case, the speaker use a loud voice with someone who doesn't hear very well.
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And in the second case, the speaker whispered to someone who has a very good hearing, and at the end
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of the day, it's all about your budget.
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So only the difference between the transmitted power and the sensitivity matters.
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And again, this difference is called link budget.
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There is one thing interesting in the
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second case though, it's that the transmitted
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power is lower, so it consumes less. In 4G transmission
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the budget available is around 130 dB.
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In LoRa, we have a budget of 157 dB and that result of a longer transmission distance. In LoRa, the
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world record of a transmission between a transmitter and a receiver was broken in april 2020 and it's
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832 kilometers.
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They of course complied with the European standars with a maximum transmission power of 15 dBm, which
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corresponds to 25 mW.
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This is, of course, something realized in a very specific conditions, and you will never reach this
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level of performance in the field.
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So now let's have a look at an example to recap everything.