Обучение чтению литературы на английском языке по специальности «Радиоэлектронные системы и устройства» (120

2.A typical cell phone is known to incorporate several hundred million instructions per second of processing capacity that is largely dedicated to unique cellular standards.

3.The new generation wireless technology is supposed to use both embedded (встроенный) signal-processing algorithms and reconfigurable code structures to receive and transmit new radio protocols.

4.A monthly cell service bill is considered to contain, for instance charges for leasing radio spectrum and renting cell towers.

5.The charges for leasing radio spectrum are assumed to drop dramatically when cognitive radio appears in the marketplace.

6.Wireless signals are considered to jump automatically to an available, open frequency in cognitive radio.

7.Smart radios and other new wireless devices are likely to avoid transmission bottlenecks by switching instantly to nearby frequencies that are clear.

8.The smartest antennas are considered to employ digital processors to manipulate incoming and outgoing signals.

9.These smart antennas, also called adaptive antenna arrays, are supposed to enhance reception.

10.An adaptive array is reported to contain four to twelve antennas.

11.The digital processor embedded in the antenna array is known to perform complex mathematical operations on the signal from the antenna.

12.The terahertz (THz) region of the electromagnetic spectrum is known to lie in the gap between microwaves and infrared region.

13.Much of the interest in terahertz science and technology is believed to have grown out of the natural overlap between the electronics and optics points of view.

14.The idea of using terahertz radiation for imaging and sensing is assumed to have been discussed for at least several decades.

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15.Digital TV (or DTV) is known to use electrical pulse to transmit information precisely and efficiently. Thus, DTV is sure to offer very sharp pictures and to enable new interactive features.

16.DTV proved to be able to pack enormous amounts of information in scarce (в небольшом количестве) bandwidths.

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Obvious reasons for this include the advent of new, incredibly cheap hardware and of customers with nonanalog data to transmit. A more subtle factor is the nature of communication theory, which may require a digital format in the transmissions systems that we find convenient to use.

New Hardware. Rapidly advancing electronic technology has caused a revolution in the hardware used in digital communication.

Digital circuits have been reduced to microscopic size, weight, power consumption, and cost. In addition, huge numbers of active devices can be combined into a single integrated circuit. Other types of circuits not based on logic gates have also appeared with all the above advantages, including charge-coupled devices, switched capacitor filters, and various analog integrated circuits.

Several future generations of integrated circuit technology beyond those now in commercial use exist at this writing in the development stage. These generations relate to the use of submicron structures, new semiconductor materials, fault-tolerant or self-repairing architectures and computer-aided design aids. It is a fact, however, that knowledge of how to apply these circuits, as opposed to how to construct them, lags behind appearance of the circuits.

Microwave hardware has undergone a less publicized but equally exciting development. New solid-state hardware has appeared, such as the Gunn device and field-effect microwave power devices. Strip line and micro-strip circuits have appeared, along with new methods for phase shifting and switching microwave energy. Surface acoustic wave devices have under-- gone a rapid development. These are thin film planar devices that operate over the uhf range by means of elastic waves propagating through a piezoelectric substrate. Since these waves are on the surface, they can be easily tapped, guided, and modified; as a consequence, complex signal filtering can be realized cheaply, at great speed and in a small space. Other propagating wave devices, such as magnetostatic devices, are on the horizon.

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Disadvantages of digital transmission exist. Some are notorious to the communications engineer; an example is the tendency of digital formats to consume unreasonably wide signal bandwidths.

Some more subtle short-comings exist, however. Digital equipment contains complex and recent technology known only to a few and very expensive to design. To tap the advantages of digital transmission requires the organization of large research efforts.

(2730)

Answer the following questions.

1. What caused the development of digital transmission?

2.Why is analog transmission replaced by digital transmission?

3.What are the advantages of digital circuit technology? 4. What new devices have appeared due to the development of digital circuit technology? 5. What are the disadvantages of digital transmission?

Task 1. Explain the idea why the public wants to communicate in digital manner.

Task 2. Tell about a revolution in digital communication.

Text 3B

Fidelity of Reproduction and Error Control

Digital transmission

Fidelity of Reproduction and Error Control Digital transmission may be favored by the nature of the channel. Long distance channels are for the most part of two types, terrestrial channels consisting of long chains of repeaters or of other tandem processors such as switches, and satellite transponders. In either case aspects of the channel favor digital signaling. As an example of a channel with many repeaters, consider the microwave radio channel. Microwaves propagate in a line-of-sight fashion so that

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individual links are limited to about 50 km. If 100 such links are chained to form a 5000-km channel, communications theory shows how much the signal-to-noise ratio (SNR) must be improved in each link so that the total performance is that of an original single link. For an analog system the link SNR must be improved by 20 dВ while for a digital system operating at an error rate of ~105 only 2 dB is required.

Satellite channels, on the other hand, are marked by lower power and wide bandwidth. These qualities predispose the channel to digital transmission in another way, as we shall develop.

These channels have a special character that tends to favor digital transmission, but a digital format in any communications network makes it easier to guarantee a given data error rate or fidelity of reproduction. For analog signals that have been digitized, the fidelity of reproduction is set almost entirely by the fineness of the digitizing, and it is easily controlled throughout the system. The error rate in a digital channel generally obeys a threshold rule: Beyond a certain signal power, the receiver error rate falls very rapidly so that as long as signal power exceeds this threshold, a performance level can be virtually guaranteed throughout a system, even if many links and processors are chained. If error performance is not sufficient in one link, digital error correction methods can be used to improve it; in addition, performance of this coding will improve rapidly as a threshold signal power is exceeded.

Cost. In cases where one can choose between digital or analog means to transmit information, digital transmission may be cheaper. This may be true because of the availability of wide bandwidth, the low cost of manufacturing digital equipment, difficulties with error control, or customer factors, like compatibility, flexibility, or need for security.

(2300)

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Text 3C

The Satellite Channel

No event has more strongly motivated digital transmission research than the communications satellite. This channel consists of a relatively linear high-power amplifier on the ground that feeds an “uplink” and a highly nonlinear low-power amplifier in the satellite that feeds a “downlink” to the ground. Microwave carrier frequencies are normal. The satellite offers an attractive star network topology; it allows communication over long distances at wide bandwidths at relatively low cost.

It appears that digital modulation will eventually predominate in this channel. Compared to other channels, the satellite transmission path is characterized by wide bandwidth, a nonlinear amplitude response, and low power, that is, by very long distances. These factors all point to digital transmission, but the most telling constraint is the low-power one.

As transmitter power drops it becomes increasingly necessary to resort to bandwidth-spreading modulations, including digital ones. Simple analog modulation has at best the same SNR as the radiofrequency channel; and for single sideband modulation, it has the same bandwidth as the information source. Once the SNR drops below 30 dB or so, transmission of telephone-quality voice, for instance, becomes impossible without a bandwidth-spreading modulation like FM. As the SNR drops into the 10–20 dB range encountered in satellite channels, the degree of bandwidth expansion must increase, and the analog transmitter and receiver components must be increasingly wideband. Eventually it becomes more efficient to convert analog signals to digital form and make use of a digital modulation method. New modulation methods will soon become available which, when combined with an efficient analog-to-digital conversion method like adaptive differential PCM, should be more efficient than analog FM over present-day commercial satellites.

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Another hallmark of the satellite channel is its nonlinearity. All rf power amplifiers must operate nonlinearly in order to be highly efficient. At the same time, dc power generation on board a satellite is a heavy contributor to launch weight. Satellites are thus compelled to operate as nonlinear amplifiers. The modulations that fare best under these conditions are constantamplitude modulations, those that have little or no envelope variation; and this narrows the choice to either analog FM or digital phase modulation. A second factor that promotes the use of constant-amplitude modulation is their apparent ability to suppress interference. Interference arises naturally in a satellite link from closely spaced adjacent channels, from the multiple carriers that appear in a multiple-access system, or from spurious carriers that sweep the satellite.

The low power and nonlinearity of the satellite channel require precisely what the channel has in abundance, bandwidth. Bandwidth reduction remains a worthwhile goal, however, since a reduction in signaling bandwidth per data symbol in any channel leads to a correspondingly higher rate of information transfer.

(2632)

Answer the following questions.

1. What does the satellite channel consist of ? 2. Why is the satellite channel used for digital transmission? 3. What are the advantages of the satellite channel? 4. What are the main features of the satellite channel?

Task 1. Find the main sentences which give the idea of each paragraph. Write down the key words to each paragraph.

Task 2. Find information from the text and tell about the role of bandwidth-spreading modulation in the satellite channel.

Task 3. Explain the importance of nonlinearity in the satellite channel.

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Grammar exercise № 3

Point out Adverbial Participle constructions and Absolute Constructions in the following sentences and translate them accordingly.

1.The basic concept of radar being relatively simple, its practical implementation is not.

2.A radar operates by radiating electromagnetic energy and detecting the echo returned from reflecting objects (targets) (отражение).

3.The nature of the echo signal provides information about the target, the range (or distance) to the target being found from the time it takes for the radiated energy to travel to the target and back.

4.Resolution being sufficiently high, a radar can discern (рассмотреть) target’s size and shape, radar resolution being obtained in range or angle, or both.

5.Radar resolution may be in range or angle, range resolution requiring large antennas.

6.Resolution in the cross — range (боковое отклонение) dimensions being not very good, it is possible to use the resolution in Doppler frequency to resole the cross — range dimensions.

7.Being not dependent on ambient radiation, radar can detect relatively small targets at near or for distances and can measure their range.

8.Though the location of a target in range and angle having been determined by radar, the echo signal also can provide information about the nature of the target.

9.Automatic detection and track (сопровождение) (ADT) being available, the operator is usually presented with the processed target track rather than raw radar detections.

10.The transmitter power being radiated into space by a directive antenna, the latter immediately concentrates the energy into a narrow beam.

11.Though deployment (развертывание) having been

delayed, 40-Gbit/s transmission will enable service providers (поставщик услуг) to deliver necessary signal bandwidth.

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12.Wireless signal being able to jump automatically to an available frequency, transmissions will be more reliable.

13.The service specific parameters having been studied, the linear system of equations can be solved.

14.The cost of a base station having been reduced due to semiconductor advances, the station could be a laptop or home computer.

15.Though conventional NRZ (non-return-to zero) modulation format being adequate for transmitting over relatively short distances, special formats may be required for longer routes.

16.Fiber with high effective mode area having been used, possible damage of the system was reduced.

17.A receiver being set to many cycles per second, you can tune the antenna circuit to any stations frequency.

18.Other transmitters interfering with your reception, your only real option will be to wait out the problem.

19.If provided with new adaptive software, nearly any wireless system will be able to locate and link to any locally available unused radio spectrum.

20.The Global Positioning System (GPS) is a space-based navigation satellite system (GNSS) that provides reliable location and time information, GPS satellites continually transmitting messages about the time the message was transmitted.

21.After many years of anticipation (ожидание) the end of conventional analog broadcasting is evident, digital broadcasts offering consumers many advantages such as crystal-clear pictures and new information services.

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