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20.02.2018

Introduction to pathloss

A transmitter generally radiates the signal which has a specific power using an antenna. This signal travels in the environment as an electromagnetic wave and suffers from a phenomenon known as pathloss. This wave isn’t aware of the exact route to the receiver and hence once transmitted propagates in the direction where the antenna directs the signal. The receiver captures a certain fraction of transmitted power depending on different factors such as distance, obstacles etc, and decodes it.

Electromagnetic wave propagates and travels further and further away. Due to this, the initial power at which the transmitter transmitted the signals spreads over a larger area. At the beginning whole transmitted power is contained in a small “bubble”. If the receiver is close to the transmitter it can capture more power. If the receiver is further away from the transmitter, the density of the power is smaller and the receiving antenna captures only small fraction of the transmitted power. The figure below depicts this phenomenon:

Signal power

 

Theoretical background

As we already know, the power of the signal reduces as the signal propagates. But what is the relation between the loss and the distance? Is the distance only variable in this equation?

Let’s take a look on following figure:

There are several parameters involved: distance, wavelength and the transmit power. Pathloss (PL) depends on distance and wavelength. The above formula confirms our observation, that greater distance means lower power. What we didn’t previously investigate is the wavelength. Attenuation is higher for shorter wavelengths. This means that high frequency signal (i.e. short wavelength) travels for a shorter distance than a low frequency signal. That is one of the reasons why 802.11ad utilizing 60GHz can be used only in a single room.

Power loss does not depend on transmitted power. If the attenuation of the path is 20dB it will affect a strong signal in the same manner as a weak signal. The difference will be visible in the received power though. If we send weak signal and it will get attenuated even more, we won’t be able to decode it.

Simulation results

In the figure below you can see the values of the pathloss for different frequencies. You can notice how different frequencies are attenuated along the traveled distance. Figure on the right presents corresponding received power. From this we can estimate the range of the system if we know required received signal power.

Pathloss and received signal

Other materials

To see other posts on network and wireless fundamentals see our explained section.

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Author

Mateusz Buczkowski

Mateusz Buczkowski received his M.Sc. degree from Poznan University of Technology in 2012. Since then he is employed at the Chair of Telecommunication Systems and Optoelectronics in the Faculty of Electronics and Telecommunications as a teaching assistant. He is pursuing his PhD in field of image processing. His research interest cover the wide spectrum of image and video processing. In particular he is interested in image quality assessment, which is his PhD topic. As a R&D engineer he took part in two FP7 EU projects, namely 5GNOW and SOLDER, where he worked on solutions that can be used in 5-th Generation wireless networks, which is to come in 2020. In Grandmetric he is involved in wireless systems research.

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