Object of research: signal in wireless networks. Objective: to study the behaviour of electromagnetic waves in a wireless network in the event of a collision with a physical obstacle. Research methods: system approach, comparison methods, index method, structural analysis, correlation-regression analysis. The behaviour of electromagnetic waves and physical obstacles is analysed in the paper. Problem solving options at the user level are suggested. A local wireless network has been created as a mean of studying the signal level. The practical significance of the research is to study and analyse local networks and physical obstacles in the signal path in order to use these results in wireless networks designing. The results of these studies can be used to improve radio communication. Application scope - modern telecommunication systems of Ukraine.
It is necessary to list the general logic of propagation of electromagnetic waves. The higher the frequency, the more the obstacles affect a signal. Low-frequency radio waves from the AM bands easily penetrate into a house, which allows you to use only one indoor antenna. A higher frequency television signal usually requires an external antenna. Infrared and visible light do not pass through the walls, limiting transmission to the line of sight (LOS). The higher the frequency, the faster the signal energy decreases with increasing distance to the source. When electromagnetic waves propagate in a free space (without reflections), the attenuation of the signal power is proportional to the square of the distance from the signal source and the square of the signal frequency. Low frequencies (up to 2 MHz) propagate on the Earth’s surface. Therefore, AM radio signals can be transmitted over a distance of hundreds of kilometres.
Signals with a frequency of 2 to 30 MHz are reflected by the Earth’s ionosphere, so they can propagate to even greater distances - several thousand kilometres (with sufficient transmission power). Signals in the range above 30 MHz propagate only in a straight line, i.e. they are signals of direct visibility. At frequencies above
can cause a sharp deterioration in the transmission quality of microwave systems. To successfully use the
microwave range, it is also necessary to take into account additional problems associated with the behaviour
of signals that propagate within line of sight and encounter obstacles in their path [
When the signal encounters an obstacle that is partially transparent to a given wavelength and at the same time the size of which is much larger than the wavelength, part of the signal energy is reflected from such an obstacle. The waves of the microwave range are several centimetres long, so they are partially reflected from the walls of houses when the signals are transmitted in a city. If the signal encounters an obstacle (for example, a metal plate) much larger than the wavelength, then there is diffraction - the signal seems to bypass the obstacle, so such a signal can be received without even being in the line of sight. Finally, when encountering an obstacle whose dimensions are commensurate with the wavelength, the signal is scattered, propagating at
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different angles [
by special coding methods that distribute signal energy over a wide range of frequencies. In addition, signal transmitters (and receivers, if possible) are to be preferably placed on high towers to avoid multiple reflections.
Reflection of electromagnetic waves. Not only the power of the transmitting station and the sensitivity of
the receiver, but also the location of the antennas significantly affect a reliable connection between the
transmitting and receiving antennas. This principle became the basis for both cellular communication [
Diffraction of electromagnetic waves. When providing long-distance radio communication in the design
of wireless computers in accordance with the WiMAX standard, it is necessary to take into account the impact
on the propagation of electromagnetic waves from the Earth’s surface, its topography and the atmospheric
conditions. It is known from the theory of wave processes that the phenomenon of diffraction has a significant
effect on the propagation of waves in space, the essence of which is to avoid a wave of obstructions if the size
of an obstacle is close to the wavelength [
electromagnetic waves, they move in an electric field. If the frequency of the wave is equal to the natural frequency of oscillations of the particles, there is a resonance, accompanied by significant absorption.
oscillations are called forced oscillations. Usually this oscillation will have the same frequency and direction
as the electric field strength of the incident wave. However, its amplitude will be much smaller than in the case
of resonance. In addition, the phase of forced oscillations differs from the phase of the incident wave, because
the speed of photons decreases when penetrating a denser medium above [
Absorption of electromagnetic waves. Due to the absorption, the intensity of the incident electromagnetic wave decreases as it passes through the medium. The absorption of the medium is defined as the ratio between the absorbed and the intensity of the falling substance. Absorption is the result of the partial conversion of light energy into thermal motion or oscillations of absorbing molecules. A completely transparent medium does not absorb light, i.e. the total energy of light coming in and out of the specified medium is the same. Among biological tissues, the cornea and lens of the eye can be considered almost transparent to visible light. The terms ‘transparent’ and ‘opaque’ are relative, as they certainly depend on the wavelength. For example, the cornea and lens consist mainly of water, which strongly absorbs in the infrared region of the spectrum.
of physical obstructions on the operation of wireless networks. The following tasks were set: physical obstacles and the phenomena they cause, as well as a description of their models. Study of particular physical obstacles with Wi-Fi Scanner v.21.03.
Synthesis of the model of reflection of electromagnetic waves. Geometric optical models are mainly used
to design IEEE 802.11 wireless networks within buildings according to their architecture. It is necessary to
distinguish between single-wall and multi-wall models of beam reflection. A simple single-wall reflection
model is shown in Fig. 1 [
Synthesis of electromagnetic wave diffraction model. Diffraction in the propagation of waves on the surface of the globe is not inherent in UHF and microwave frequencies, so radio communication in this frequency range can be carried out only within line of sight. In other words, the curvature of the Earth’s surface limits the possible distance between the transmitting and receiving antennas of high-frequency radio signals.
where ha, h2 are the heights of the transmitting and receiving antennas.
where the geometric parameters d1 and d2 characterize the position of the obstacle, λ0 is the wavelength. 0 = √ (5) (6) (7) (8)
receiving antennas are easy to be calculated according to the formula: where ha is the height of the antenna, hn is the height of the obstacle.
In the theory of electromagnetic wave propagation, two more important types of diffraction are considered: diffraction on a wedge-shaped obstacle and on a spherical obstacle. Signal power losses with diffraction at a wedge-shaped obstacle are determined with the geometric parameter ν and are calculated as follows: ℎ ≥ ℎ
+ 0 = ℎ ∗ √ 1 + 2 0,5 1 2 0 ≪ ℎ where h, d1, d2 are the geometric parameters of the transceiver system.
communication in computer networks. Thus, for the values of λ0=5.36 cm and λ0=12.5 cm used in Wi-Fi and
WiMAX networks, the signal attenuation parameters are very significant and almost coincide. On the contrary,
for the wavelength of the decametre range λ0=10 m the attenuation at diffraction at the obstacle is much
smaller. Another important mathematical model of radio wave diffraction, which is widely used in practice, is
diffraction on spheres [
+ ℎ2)2 − 2 where R is the radius of the sphere, h1 and h2 are the heights of the antennas, L is the range of direct visibility. The results for the height of the transmitting antenna h1=100 m and for different h2 and R parameters are shown in Fig. 4. where is the scattering coefficient. Differentiation (10) by z gives: ( ) = 0 exp(
), ( ) = 0 exp(− ), = −
, the electric field of the incident wave can be put down as:
where і is the amplitude of the incident electric field, k is the magnitude of the wave vector, and z denotes the optical axis. Intensity losses due to scattering are described by the equation (9): by one of these centres can be put down as follows:
~ . ~
, 2
due to the interference of all scattered waves, the total scattered amplitude can be put down as follows: The complex amplitude at a distance z on the optical axis consists of adding the amplitudes of all scattered spherical waves and the amplitude of the incident plane wave, i.e.: ( ) = 0( + √ ∫
2 ( ) = 0 ( + √ 2 ∫ ) ) , where 2 = 2 + 2. For this z we obtain:
, and then equation (16) will take the form: Since the wave has a finite length, scattering can be neglected. Then equation (17) takes the form: ( ) = 0 ( = √ ), and if we consider that the wavelength = 2 / , then ( ) = 0 (1 +
√ ).
According to the assumption, the scattering contribution - i.e. the second term in parentheses in equation (19) - is small compared to the initial wave (first term). Thus, they can be considered as the first two members of the decomposition into a series of the equation ( ) = 0 ( ( +
√ )). Δ = 2 ( − 1) , Thus, the phase of the incident wave changes by
√ due to scattering. The value of the phase delay: which occurs when light enters from free space into a medium with a refractive index n. Thus (12) (13) (14) (15) (16) (17) (18) (19) (20) (21)
and ( ) = exp(− ), ( ) = exp(− ′ ), = 1
, where = 0 denotes forward scattering. Within the visible range, scattering always significantly reduces when comparing green and red light.
same magnitude as the wavelength of the incident radiation, as in the case of blood cells, Rayleigh’s law cannot be applied and another type of scattering occurs, called Mie scattering (2). However, it is necessary to note two important differences between Mie scattering and Rayleigh scattering. Mie scattering shows a weaker dependence on the wavelength ~ , 0.4 ≤ ≤ 0.5 compared to Rayleigh scattering.
Synthesis of the model of absorption of electromagnetic waves. The ability of a substance to absorb
electromagnetic radiation depends on certain factors, mainly on the electronic composition of its atoms and
molecules, the length of the radiation wave, the thickness of the absorbing layer and internal parameters such
as temperature or concentration of the absorption centres. [
respectively. They are usually called Lambert’s Law and Beer’s Law, and they are put down as follows: where z denotes the optical axis, (z) is the intensity at a z distance, 0 is the incident intensity, is the absorption coefficient of the medium, c is the concentration of the absorption centres, k′ depends on other internal parameters. From equation (25) we obtain:
2 ( − 1) , → − 1 = 2 2 √
If we take into account the scattering angle , we obtain a more accurate formula: ~ 14 ( )~ 1+
Measurement of signal parameters of the designed local network. The next step in wireless network research is to measure signal parameters with possible obstacles. Obstacles in this case will be such physical structures as walls and doors in the room.
To study the real network, the model of which is shown in Fig. 6, two charts will be used - of signal power (22) (23) (24) (25) (26) (27) (28)
wireless network, it is necessary to consider all the physical phenomena that affect signal quality. This section discusses possible ways to solve wireless network problems for users.
First, it should be noted that the access point is the centre of the sphere, and signals from it are sent in all directions like rays. So, the wireless network is a sphere. That is, a typical home wireless network will cover the floor where the access point is installed and the edges of the upper and lower floors. But in reality this is not the case. The Wi-Fi coverage area is a toroidal field. In shape, this field resembles a torus, the axis of which is an antenna directed in any direction. The angle of the wireless signal propagation depends on the direction of the antenna. To ensure the best propagation of electromagnetic waves in a wireless network, the antenna should be installed perpendicularly to the ground. As a result, the waves will move parallel with the ground.
around them, the best signal will be near the access point, and the farther from it, the worse.
The position of the router in the corner of the premises is not effective, as the signal no longer reaches another corner. And if you place the access point in the centre, the signal will reach all corners. That is, we can conclude that you need to place the access point as close as it is possible to the centre of the premises where the wireless network is installed. It is also effective to ensure the direct visibility of the signal. Studies performed have shown that physical obstacles attenuate the wireless signal greatly. Therefore, providing direct signal visibility will be very effective for all users on the network.
settings, we can select the modes with which the created access point will work. Wi-Fi standards b and g give a slower rate for receiving or transmitting data and a shorter range. A slightly more modern mode of operation of routers - n - is able to provide data rates up to 150 Mbps, and in ac mode, the router can transmit up to several Gbps. Of course, they also cover a greater distance. You can switch the router to a faster mode, but only if the router and other devices connected to the wireless network support high-speed standards.
Installing repeaters requires additional financial investment, but it is a great option to expand coverage. It is almost indispensable for places with a large area. It will also be useful for buildings with complex design. A special device, which may be used as a repeater and which is able to expand the coverage area of the local wireless network is not the only option. The role of such a Wi-Fi network extender can be taken over by a second router that supports WDS technology. Each option has its own characteristics. Yes, if you use a special repeater, this device connects to the access point and repeats its data. The device then creates a new access point with a different radio signal. The Wi-Fi signal will be strong and stable throughout the premises.
the speed of data exchange will decrease a couple of times. So if speed is a priority, it is better to buy a repeater.
7. Conclusions
1. In the course of this study, the design of the local wireless network, its study and analysis were performed. Problems related to physical obstacles were identified and solutions were suggested. With the help of field experiments with the designed real network, it was shown what physical obstruction may actually affect the quality of the wireless signal. In addition, we found out which material has the worst effect on the wireless network.
2. Based on the indicators of the field experiment, it was found out that the walls and floors of wood and plasterboard have a low impact on the propagation of radio waves (-64 dBm signal strength and 84% signal quality), obstacles of brick, glass, concrete - medium (values: 66 dBm and 78%), of reinforced concrete and iron - high (-71 dBm and 81%).
3. To achieve the goal of the research the following tasks were performed: Models of physical phenomena that create obstruction for wireless network signals are suggested; The parameters of wireless networks signals at different types of physical obstruction are studied; Solutions to the problems associated with the negative impact of physical obstruction on the signal of wireless networks are suggested.