We have explained the basics for calculating the range and link budget in the last blog posts. The free space attenuation, line of sight and also the radio wave propagation on the Hata model are part of the simulation software of the following chapters.
Hot air balloons are often used in the unlicensed band to show the range of the radio signal. We will also pick up the propaganda with hot-air balloons and explain their range. With the hot air balloons, we can explain at best the free space attenuation. But real life is on the ground. We do not live in tents but in brick and cement houses. In Germany, typical applications such as energy meters for electricity and gas are usually found in the basement of buildings. Energy meters in cellars are an extreme LPWAN application. Also, the bicycle in the garage or the dog on the sofa are attenuated by the wall of the garage or the wall of the building. In the blog posts about the basics, you can read how to calculate this attenuation of the walls. The learned is now used in the simulation. As we learned in the last lesson, the molecules in the air already form an attenuation for the radio wave. The surface of the earth, the condition of the surface and/or structure of the surface form likewise an attenuation of the radio waves. In addition, there are buildings or trees.
To explain the wave propagation by using of simulation software we plan a radio tower with a height of 25 m in the middle of the North Sea. Then we plan the same radio tower in the city Neustadt am Rübenberge. The region around Neustadt is relatively flat and borders on the inland sea Steinhuder Meer. In order to hide the topography in this observation, we have placed the antenna mast with a height of 25 m in the North Sea near the island of Helgoland. Helgoland is a German island in the North Sea. The radio tower in the middle of the North Sea has the best conditions for the propagation of radio waves. This ideal example shows how far a radio wave can travel without any restrictions due to hills, vegetation or buildings.
Helgoland is 40 km away from the continent and has an area of less than two square kilometres. Until 1890 Helgoland was part of Great Britain and before that part of Denmark.
In the simulation, the water of the North Sea forms a planar surface, including the terrestrial curvature. The surface of the water has lower attenuation than, for example, the moor or the meadows in the area of Neustadt am Rübenberge. This means that the range we have achieved in the North Sea is an extreme that we cannot achieve in the real area of Neustadt. The region around Neustadt is very flat, but also no salt desert.
We stay with the values used in the chapter about the link budget. Areas with possible indoor coverage are marked in green. As soon as the maximum attenuation of 28 dB is exceeded, the software marks the area with the colour red. East of the 25 m high antenna mast in the North Sea is the island of Helgoland. The island forms a radio shadow and leads to the fact that behind the island no more reception is possible. The radio wave propagation in the simulation software is based on the Okumura Hata model.
Furthermore, the program calculates the refraction of radio waves at the tops of hills and mountains. Thus, the reception behind the hills and mountains is also visible. The cliffs of the island Helgoland show this clearly. A part of the island, already marked red, is only reached by refraction. We will come back on the refraction later in detail.
In the south of the antenna mast are the Frisian Islands. The minimal increase of the islands leads to the fact that reception is still possible in the outside area on the island. A few kilometres before the islands, the radio link departs through the earth’s curvature and the high points of the islands are just reached in this way.
In the next sections, we will explain in detail all the parameters that can be set during the simulation and the results of the simulation of the relatively simple test environment in the middle of the North Sea.
Anyone who is planning their own private LPWAN is welcome to contact us. We would be happy to explain how to use the software to simulate a wireless network in workshops or online seminars. If you don’t plan your own network and want to use an existing one and want to develop your own PCBs for this purpose, please do not hesitate to contact us. We are happy to share our experience from the numerous LPWAN projects with you. Please send your requests to harald.naumann(at)lte-modem.com