Understanding Wireless Networks: Attenuation Units dB and dBm, RSSI Values, and Signal Strength

Hi, recently I started to study in depth the topic of wireless networks.
I am having trouble understanding the units of attenuation i.e. dB and signal strength dBm.

Let's assume that the RSSI is -20 dBm (the receiver is located right next to the router) and theoretically I would like to put a wall between the transmitter and receiver with an attenuation of 7 dB, how much RSSI will come out if I take into account the attenuation of this wall?

I read somewhere that an attenuation of 3 dB results in a signal drop of 50%. So what purely theoretical, if my signal in a given room is -50 dBM, and then a wall with an attenuation of 3 dB appears then the signal will drop to -75 dBM?

Another question, the router should be operating at 100 mW which is 20 dBm why then right next to the router the signal power is around -15 dBm instead of those theoretical 20 dBm?

Thank you in advance for your time.

The simplest explanation is here. Read it carefully 2-3 times and it will be clear.

Decybele n...ościej.pdf Download (120.85 kB) Decybele n...udniej.pdf Download (1.37 MB) Decybele ..we.pdf Download (1.11 MB) .

Unfortunately, but I had already familiarized myself with these materials and yet all these questions mentioned above were born. I thought that with a practical approach I would be able to understand the issue. Would anyone be willing to answer me the aforementioned questions?

MrPiotras wrote:

I am having trouble understanding the units of attenuation i.e. dB

Suggest you read https://ep.com.pl/files/4169.pdf - decibel is just an easier to use measure of signal attenuation or gain multiplication. In HF technology we usually use the multiplication factor of attenuation or power gain.
In the above article is table 4:



Instead of writing "The cable between the antenna and the receiver is long and introduces 100 times the signal attenuation" we can write "introduces 20dB attenuation".

MrPiotras wrote:

signal power dBm

This letter "m" indicates what the reference level is, in this case 1mW. Hence, below you write:

MrPiotras wrote:

work at 100 mW or 20 dBm

because 20dB in multiples is 100 times - 100*1mW=100mW.

MrPiotras wrote:

Another question, the router should be operating at 100mW which is 20 dBm why then right next to the router the signal power is about -15 dBm instead of those theoretical 20 dBm?

Because the output of the transmitter is not connected to the input of the receiver by a perfect wire - between one and the other there are still antennas with a rather omnidirectional characteristic....

Well then, if the signal power is, let's say, -50dBm and we attenuate it with a wall of 7 dB, how do I calculate how much output signal will come out? How do I know if 7dB is a lot or a little?

MrPiotras wrote:

if the signal strength is, let's say, -50dBm and we attenuate it with a 7 dB wall, how do I calculate how much output signal will come out?

-57dBm.

MrPiotras wrote:

How do I know if 7dB is a lot or a little?

Calculate for yourself on a "multiplication" measure. -7dB is about 5 times the power attenuation.

https://www.softpedia.com/get/Science-CAD/mini-dB-Calculator.shtml
A useful program just for playing with decibels volts watts etc.

MrPiotras wrote:

Another question, the router should be operating at 100 mW or 20 dBm so why is the signal strength right next to the router around -15 dBm instead of those theoretical 20 dBm?

Because the signal strength depends on the distance from the source. The information "so why then next to router" is completely inaccurate.