Файл: Учебнометодическое пособие по английскому языку для специалистов и бакалавров 2 курса института ртс. Москва 2019.docx

Cellular Radio Telephones

Cellular radio telephones, or cell phones, combine their portable radio capability with the wired, or wireline, telephone network to provide mobile users with access to the rest of the public telephone system used by non-mobile callers. Modern cellular telephones use a network of several short-range antennas that connect to the telephone system. Because the antennas have a shorter range, frequencies can be reused a short distance away without interference.
Satellite Communications

Satellite communications services connect users directly to the telephone network from almost anywhere in the world. Special telephones are available to consumers that communicate directly with communications satellites orbiting the earth. The satellites transmit these signals to ground stations that are connected to the telephone system. These satellite services, while more expensive than cellular or other wireless services, give users access to the telephone network in areas of the world where no telephone service exists.

The number of companies offering wireless communications services has grown steadily in recent years. In 1988 about 500 companies offered cellular radio telephone (cell phone) services. By 1995 that number had grown to over 1500 companies serving millions of subscribers. Wireless communication is becoming increasingly popular because of the convenience and mobility it affords, the expanded availability of radio frequencies for transmitting, and improvements in technology.

Refraction is important at long ranges (tens to hundreds of kilometers) due to gradients in moisture content and temperature in the atmosphere. In urban, mountainous, or indoor environments, obstruction by intervening obstacles and reflection from nearby surfaces are very common, and contribute to multipath distortion: that is, reflected and delayed replicates of the transmitted signal are combined at the receiver. Signals from different paths can add constructively or destructively: such variations in amplitude are known as fading. The dependence of signal strength on position of transmitter and receiver becomes complex and often non-monotonic, making single-receiver estimates of position inaccurate and unreliable. Multilateration, using many receivers, is often combined with calibration measurements ("fingerprinting") to improve accuracy.

Task 1. Read and translate text B.

Task 2. Find the sentence which expresses the main idea of each paragraph of text B. Entitle each paragraph.

Task 3. Answer the following questions.

1. Which device uses radio waves to transmit and receive signals?

2. What is the main function of the transmitter?

3. What do wireless communications systems involve?

4. Can you describe the modes of wireless communications?

5. What are the basic principles of cellular radio telephones and satellite communications?

Task 4. Make up and write the scheme of text B using titles of each paragraph.

Task 5. Write the summary of text B.

Task 6. Give the Russian equivalents of the following expressions:

wireless telecommunications system, fixed location, wireless technologies, wire-based services, short-range communication, one-way transmission, the encoded signal triggers.

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Text C

Radiolocation
Radiolocating is the process of finding the location of something through the use of radio waves. It generally refers to passive uses, particularly radar - as well as detecting buried cables, water mains, and other public utilities. It is similar to radionavigation, but radiolocation usually refers to passively finding a distant object rather than actively one's own position. Both are types of radiodetermination. Radiolocation is also used in real-time locating systems (RTLS) for tracking valuable assets.

Basic principles

An object can be located by measuring the characteristics of received radio waves. The radio waves may be transmitted by the object to be located, or they may be backscattered waves (as in radar or passive RFID). A stud finder uses radiolocation when it uses radio waves rather than ultrasound.

One technique measures a distance by using the difference in the power of the received signal strength (RSSI) as compared to the originating signal strength. Another technique uses the time of arrival (TOA), when the time of transmission and speed of propagation are known. Combining TOA data from several receivers at different known locations (time difference of arrival, TDOA) can provide an estimate of position even in the absence of knowledge of the time of transmission. The angle of arrival (AOA) at a receiving station can be determined by the use of a directional antenna, or by differential time of arrival at an array of antennas with known location. AOA information may be combined with distance estimates from the techniques previously described to establish the location of a transmitter or backscatterer. Alternatively, the AOA at two receiving stations of known location establishes the position of the transmitter. The use of multiple receivers to locate a transmitter is known as multilateration.

Use of RSSI to locate a transmitter from a single receiver requires that both the transmitted (or backscattered) power from the object to be located are known, and that the propagation characteristics of the intervening region are known. In empty space, signal strength decreases as the inverse square of the distance for distances large compared to a wavelength and compared to the object to be located, but in most real environments, a number of impairments can occur: absorption, refraction, shadowing, and reflection. Absorption is negligible for radio propagation in air at frequencies less than about 10 GHz, but becomes important at multi-GHz frequencies where rotational molecular states can be excited.

TOA and AOA measurements are also subject to multipath errors, particularly when the direct path from the transmitter to receiver is blocked by an obstacle. Time of arrival measurements are also most accurate when the signal has distinct time-dependent features on the scale of interest—for example, when it is composed of short pulses of known duration—but Fourier transform theory shows that in order to change amplitude or phase on a short time scale, a signal must use a broad bandwidth. For example, to create a pulse of about 1 ns duration, roughly sufficient to identify location to within 0.3 m (1 foot), a bandwidth of roughly 1 GHz is required. In many regions of the radio spectrum, emission over such a broad bandwidth is not allowed by the relevant regulatory authorities, in order to avoid interference with other narrowband users of the spectrum. In the United States, unlicensed transmission is allowed in several bands, such as the 902-928 MHz and 2.4-2.483 GHz Industrial, Scientific, and Medical ISM bands, but high-power transmission cannot extend outside of these bands. However, several jurisdictions now allow ultrawideband transmission over GHz or multi-GHz bandwidths, with constraints on transmitted power to minimize interference with other spectrum users. UWB pulses can be very narrow in time, and often provide accurate estimates of TOA in urban or indoor environments.

Radiolocation is employed in a wide variety of industrial and military activities. Radar systems often use a combination of TOA and AOA to determine a backscattering object's position using a single receiver. In Doppler radar, the Doppler shift is also taken into account, determining velocity rather than location (though it helps determine future location). Real Time Location Systems RTLS using calibrated RTLS, and TDOA, are commercially available. The widely used Global Positioning System (GPS) is based on TOA of signals from satellites at known positions.

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Task 1. Read and translate text C.

Task 2. Give the definition of radiolocation.

Task 3. Complete the following sentences using the text.

1. The radio waves may be transmitted…

2. One technique measures a distance by using…

3. Another technique uses the time…

4. The use of multiple receivers to locate…

5. In empty space, signal strength decreases…

6. Absorption is negligible for radio propagation in air…

7. Signals from different paths can add constructively…

8. Radar systems often use a combination of TOA and AOA to…

Task 4. Write a summary of the text. Limit it to 10 sentences.

Task 5. Use a dictionary and find Russian equivalents of the following words.

the received signal, the original signal strength, the angel of arrival, multiple receivers, multilateration, the transmission characteristics, non-line-of-sight receptions, backscattered, the propagation characteristics, inverse square.

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Text D

Radar Principle
The electronic principle on which radar operates is very similar to the principle of sound-wave reflection. If you shout in the direction of a sound-reflecting object (like a rocky canyon or cave), you will hear an echo. If you know the speed of sound in air, you can then estimate the distance and general direction of the object. The time required for an echo to return can be roughly converted to distance if the speed of sound is known. The radio-frequency (rf) energy is transmitted to and reflected from the reflecting object. A small portion of the reflected energy returns to the radar set. This returned energy is called an ECHO, just as it is in sound terminology. Radar sets use the echo to determine the direction and distance of the reflecting object. The term RADAR is an acronym made up of the words: RAdio (Aim) Detecting And Ranging. The term "RADAR" was officially coined as an acronym by U.S. Navy Lieutenant Commander Samuel M. Tucker and F. R. Furth in November 1940. Under some conditions a radar system can measure the direction, height, distance, course and speed of these objects. The frequency of electromagnetic energy used for radar is unaffected by darkness and also penetrates fog and clouds. This permits radar systems to determine the position of airplanes, ships or other obstacles that are invisible to the naked eye because of distance, darkness, or weather. Modern radar can extract widely more information from a target's echo signal than its range. But the calculating of the range by measuring the delay time is one of its most important functions.

Basic design of a radar system (the operating principle of a primary radar set)

The radar antenna illuminates the target with a microwave signal, which is then reflected and picked up by a receiving device. The electrical signal picked up by the receiving antenna is called echo or return. The radar signal is generated by a powerful transmitter and received by a highly sensitive receiver.
The Primary Radar Basic Principle

All targets produce a diffuse reflection i.e. it is reflected in a wide number of directions. The reflected signal is also called scattering. Backscatter is the term given to reflections in the opposite direction to the incident rays. Radar signals can be displayed on the traditional plan position indicator (PPI) or other more advanced radar display systems. A PPI has a rotating vector with the radar at the origin, which indicates the pointing direction of the antenna and hence the bearing of targets.
Transmitter

The radar transmitter produces the short duration high-power rf pulses of energy that are into space by the antenna.
Duplexer

The duplexer alternately switches the antenna between the transmitter and antenna need be used. This switching is necessary because the high-power pulses of the transmitter would destroy the receiver if energy were allowed to enter the receiver.

Receiver

The receivers amplify and demodulate the received RF-signals. The receiver provides video signals on the output.

Radar Antenna

The Antenna transfers the transmitter energy to signals in space with the required distribution and efficiency. This process is applied in an identical way on reception.

Indicator

The indicator should present to the observer a continuous, easily understandable, graphic picture of the relative position of radar targets. The radar screen displays the produced from the echo signals bright blips. The longer the pulses were delayed by the runtime, the further away from the center of this radar scope they are displayed.

Task 1. Read and translate text D.

Task 2. Write the summary of text D.

Task 3. Look through the text and answer the following questions:

1. What does the term “radar” mean?

2. What is the basic design of a radar system?

3. Why do we need transmitter?

4. Explain, what is duplexer?

5. What are the main functions of receiver, antenna, indicator?

Task 4. Write and then formulate a brief description of the radar system. Your description should answer these questions:

1. What does the radar system consist of?

2. What are the components of the transmitter?

3. What does the receiver consist of?

4. Where is the signal generated?

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5. What happens to it after that?

6. If a target is hit, what happens to the reflected signal?

7. How does the receiver process the signal?

8. What happens to both signals finally?

Task 5. To help you make description of the radar system, match components and their functions.

Oscillator the signal is radiated

Power amplifier the signal is generated

Transmitting antenna the signal is amplified

Receiving antenna the signal is rectified

Radio frequency amplifier the signal is amplified

Detector both signals are displayed

Comparator a weak reflected signal is received

Indicator the received signal is compared with a reference signal from the transmitter

Task 6. Read this text. Try to retell.

Let's take a look at how the perception module finds out what's around the car:

1. Radar - a common sensor that is already used on cars with cruise mode. However, the radar is not very well aware that in front of him is a pedestrian, if he is not in a metal suit. A distinctive feature of the radar is the ability to learn the radial velocity.

2. Cameras are responsible for the overall picture on the road.

3. Lidar - a sensor that determines the distance to certain objects on the road, and also "sees" everything better than radars and cameras. But he has two minuses: price and quality. Even if the lidar is made according to all the guests, it can still quickly fail due to the constant movement, actually because f this it remains a niche technology. But in general, a lidar is an interesting invention, with the help of which is good. In order to better distinguish what is around a car, the method of segmentation can be applied by instances, where, unlike ordinary segmentation, objects do not merge into one color, but break into parts. The vision of the car can be realized using only cameras and radars- the cheapest technology. The peculiarity of this method lies in the local use of technology: base maps are loaded into the on-board computer, processed by neural networks, and then compared to the loaded maps.

Task 7. Make up your questions to the text “Multiplexer”. Ask your partner.

Multiplexer

In electronics, a multiplexer (or mux) is a device that selects between several analog or digital input signals and forwards it to a single output line. A multiplexer of 2n inputs has n select lines, which are used to select which input line to send to the output. Multiplexers are mainly used to increase the amount of data that can be sent over the network within a certain amount of time and bandwidth. A multiplexer is also called a data selector. Multiplexers can also be used to implement Boolean functions of multiple variables.

An electronic multiplexer makes it possible for several signals to share one device or resource, for example, one A/D converter or one communication line, instead of having one device per input signal.

Conversely, a demultiplexer (or demux) is a device taking a single input signal and selecting one of many data-output-lines, which is connected to the single input. A multiplexer is often used with a complementary demultiplexer on the receiving end.

An electronic multiplexer can be considered as a multiple-input, single-output switch, and a demultiplexer as a single-input, multiple-output switch. The schematic symbol for a multiplexer is an isosceles trapezoid with the longer parallel side containing the input pins and the short parallel side containing the output pin.

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