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Abstract

Содержание

Introduction

Recently, in the developed countries of the world, intensive work has been carried out to create fresh SRD (Short Range Devices) super–technological radio devices, which are used in all kinds of data transmission devices, detection, security and security systems, telemetry information collection systems, and a large number of devices of different purposes.

Wireless SRDs use the unlicensed frequency spectrum 2,4 GHz, which already operates all sorts of radio engineering instruments in industry, science and medicine. The systematic increase in the density of radio electronic means (avionics) in the limited frequency spectrum leads to a sharp increase in the value of the interference caused by them. The issue of interference is quite acute where RECs are obliged to be located in a limited space. As a rule, their number can be measured in dozens, and the distance between them varies from meters to centimeters.

In order to obtain high noise immunity in such an environment, SRD [3] technologies have taken various measures, for example, Frequency Hop Spread Spectrum (FHSS) signals according to pseudo–random law are used. Apart from the fact that transmitted packets have every chance to be protected with support of noise–immune coding, in other ways, in which transmission of lost packets is repeated automatically.

All wireless communication standards and technologies can be classified according to a number of different parameters. Table 3.1 provides a brief classification of the most current wireless communication standards.

1. Theme urgency

The relevance of the topic The relevance of the selected topic is due to the fact that the number of users of wireless transmission systems is constantly increasing and resources of wireless connection technology are limited. The simultaneous increase in the load on wireless communications and the lack of global capabilities to expand the resources of wireless communication channels requires an increase in the information efficiency of the wireless transmission system.

802.11 standards are modern wireless communication standards, provide faster data transfer, meet the requirements of all modern services and applications.

2. Goal and tasks of the research

The aim of the study is to improve the information efficiency of 802.11 using the signal – code design change algorithm.

Main objectives of a research:

  1. Analysis of parameters affecting information efficiency in modern wireless networks;
  2. Build a simulation model to investigate the signal – code design switching algorithm in 802.11 standards;
  3. Based on research data, make suggestions to improve information efficiency in 802.11 standards.

Research Subject: IEEE 802.11 Wireless Networks

Research subject: information efficiency of 802.11 wireless communication.

3. Analysis of Bluetooth, WiFi, and ZigBee communication technologies

All wireless data standards and technologies can be classified according to a number of formal parameters. Table 3.1 provides a general classification of the most current wireless data standards.[1]

Table 3.1 – General Classification of Basic Wireless Communication Standards

Classification parameters ZigBee Bluetooth Wi–Fi
Data transmission speed, kbps 250 721 11000/54000
Communication range, m 200 class 1 – 100;
class 2 – 10;
class 3 – 1		 100
Consumption of current, active мА/sleep mkA 30/1 70/20 450
Modulation DSSS FHSS DSSS
Topology peer to peer,
star,
tree		 peer to peer,
star,
tree		 peer to peer,
star,
Frequencies, MHz 2400–2483 2400–2483 2412–2484

There are three technical parameters that most often determine the scope of a particular standard in a particular user application: power consumption (or current consumption), communication range, and data rate. The following leaders can be conditionally distinguished by the value of these parameters:

3.1 Bluetooth

The Bluetooth standard is a compromise in terms of economy/range/speed ratio. It has the largest number of intersections with other Short Range RF group standards in terms of its functionality and application in various applications. So letʼs start by looking at it.

The main idea of Bluetooth was to create a universal, reliable and very cheap wireless radio interface. Bluetooth technology allows interfacing with various professional and consumer equipment in voice, data and multimedia modes, while ensuring its electromagnetic compatibility with other home or office equipment. As stated in the table, there are only three classes of Bluetooth devices if you grade them by radiated power: first – Up to 100  meters (up to 100  мW); second – Up to 10 meters (up to 2,5 mW); third – Up to 1 meters (up to 1 mW).

Pluses and minuses

After analyzing the current state of Bluetooth technology, you can identify the advantages and disadvantages. The advantages of the standard include:

Main shortcomings:

Scopes

Based on the characteristic features of Bluetooth modules, their fields of application have been formed in Russia and abroad:

3.2 Wi–Fi

Wi–Fi Wireless Data Standard was created specifically to combine multiple computers into a single LAN. Conventional wire networks require multiple cables to be laid through walls, ceilings, and indoor partitions. There are also certain restrictions on the location of devices in space. Wi–Fi wireless networks do not have these disadvantages: you can add computers and other wireless devices with minimal physical, time, and material costs. Wi–Fi wireless devices use radio waves from the frequency spectrum defined by the IEEE 802.11 standard to transmit information. There are four variations of the Wi–Fi standard (Table 4). 802.11n supports two frequency bands simultaneously to four antennas. The total data rate is 150–600 Mbps

Table 3.2 Variations of Wi–Fi

Standard 802.11b 802.11g 802.11a 802.11n
Number of non–overlapping radio channels used 3 3 3 11
Frequency range, GHz 2,4 2,4 5 2,4/5
Maximum data rate in radio channel, Mbps 11 54 54 150–600

Pluses and minuses

We will formulate some key features of Wi–Fi standard. Its advantages include:

Main shortcomings:

Scopes

The characteristics of the Wi–Fi standard dictate the main areas of its application. It:

3.3 ZigBee

In cases where the line–of–sight radio range is not sufficiently long and there is a need to increase it while keeping power consumption low, it is advisable to pay attention to the ZigBee wireless standard. The characteristics of this standard allow:

The ZigBee–library was among themselves developed for simplification of process of development and ensuring the maximum compatibility of ZigBee devices of different producers; clusters (ZigBee Cluster Library, ZCL). This document introduces the concept of standard device types, standard commands for these devices, sets of standard attributes, ranges of values for these attributes, data types for setting attribute values, etc. ZCL groups clusters by general purpose; For working with sensors; For lighting, ventilation, etc. Using standard message forwarding clusters is a requirement for all new ZigBee specifications since 2007.

There are standard application profiles for standard device types. The profile specification defines the parameters required for devices to work together on the same network. There are at least two main profiles:

Pluses and minuses

Based on the peculiarities of the ZigBee standard, we will formulate its advantages and disadvantages.

Advantages:

Scopes

The main applications of ZigBee technology are:

4. Features of radio propagation

The radio wave during propagation in space occupies a volume in the form of an ellipsoid of revolution with the maximum radius in the middle of the span, which is called the Fresnel zone. Natural (land, hills, trees) and artificial (buildings, poles) obstacles entering this space weaken the signal.

The concept of Fresnel zones is based on the Huygens principle, according to which each point of the medium to which the disturbance reaches itself becomes a source of secondary waves, and the field of radiation can be considered as a superposition of all secondary waves. Based on this principle, it can be shown that objects lying within concentric circles drawn around the line–of–sight of two transivers can affect quality both positively and negatively. All obstacles inside the first circle (the first Fresnel zone) have the most negative impact. You can calculate it using the formula:

\[ r=17,3\sqrt{\frac{1}{f}\frac{D_{1}D_{2}}{D_{1}+D_{2}}} \] (4.1)

Where r is the radius of the first Fresnel zone, m;

f – exchange frequency value, GHz;

D1 and D2 – distance to obstacle from transmitter and receiver, km.

For example, for a 2.4 GHz radio link at a distance between stations of 1 km, the radius of the first Fresnel zone will be 5.5 m. That is, along the line connecting the receiver and the transmitter in its middle part within a radius of 4.4 m (80%) (or at least 3.3 m – 60%) there should be no objects reflecting or scattering radio radiation. Only by providing this condition makes sense to talk about the dominance of the direct beam and the weakening associated only with the length of the radio link. For comparison: at 500 m length the radius of this zone will be only 3.9 m (80% – 3.2 m), and at 100 m distance on the basis of this principle it is necessary to unlock the zone with diameter of only 2.8 m.

A little more about the impact of vegetation. As a rule, it is not possible to avoid passing through it (for example, through foliage of tall trees) throughout the radio channel. In such a case, according to D-link experts, it is necessary to focus on the following estimates: absorption of 12–20&nbpsp;dB per tree for hardwood and up to 40 dB – for a group of one to three coniferous trees, when foliage is inside the 60% of the first zone of Fresnel. The main multipath effects caused by the presence of hardwood cover are diffraction and scattering. The presence of trees near the subscriberʼs location may cause the signal to fade due to multipath propagation. It is also noted that the effects of the latter depend heavily on wind.

Let us also specify that even in these relatively simple conditions (see below for indoor radio waves), in order to ensure the optimal functioning of the WLAN, it is necessary to carefully approach the calculation of the energy of the route. At the same time with amplification on the receiving side it is important both not to overrun (the level of interference from foreign radio facilities will increase, up to the receiver blocking), and not to lose (the potential of the radio link will be insufficient for stable operation at high speeds).

Features of radio waves propagation in the room

Conditions for the propagation of radio waves in the room are much more difficult than in free space.

First, because of the presence of walls and massive objects of the environment. Walls and floors made of wood, synthetic materials, glass have a low influence on the spread of radio waves, obstacles made of brick, concrete – medium, reinforced concrete and walls with foil insulation – high. Metal walls and floors significantly affect the range, up to the total impossibility of communication. The influence of noncapital gypsum cardboard walls – from low to very high depending on the design of the lattice at its base – is ambiguous and in some cases can fluctuate when the humidity in the room changes.

Second, the interference nature of the indoor electromagnetic field (due to multiple reflections from objects) is more pronounced. This manifests itself in reducing field intensity and changing the original plane of polarization of waves.[2]

Gif image (frame 8, cycle 7, 99 KB)

Figure 1 – Deep fading of the signal level by 20 dB or more, following at intervals of about half wavelength, the position of which in space depends on the carrier frequency of the signal and placement of objects in the room

In most of the premises it is also possible to encounter so–called "dead zones," in which the reception of the signal is very difficult. This is possible even if the transmitter and receiver are in line of sight. The formation of "dead zones" is due to the fact that the signal follows paths of different lengths, reflecting from metal objects such as steel structures, concrete walls, metal doors, windows, ceilings, etc. A "dead zone" appears if the propagation path lengths effectively diverge by an odd number of half waves (Figure 1). But "absolutely dead zones" are usually very local and can be eliminated by small movement of the receiver and/or transmitter antennas.

So, the range of operation is influenced by many physical factors: the number of walls, floors and other objects through which the signal must pass, and radio frequency noise from other devices. In addition, the level of the signal received by the antenna in or near the building will vary over time due to the movement of objects (door opening, etc.) in the path of radio waves.

Conclusion

Thus, the feasibility of examining the information efficiency of wireless communications in general and directly based on 802.11 standards, the characteristics of wireless networks giving them an advantage over wired networks, among which the main one is the possibility of rapid installation of the network without the cost of the leading structure, have been considered.

The masterʼs work has not yet been completed when writing this auto-revision. Final completion: June 2020. The full text of the work and materials on the topic can be obtained from the author after the specified date.

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