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.
21
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.
22
LESSON 3
Memorize the following basic vocabulary and terminology to text 3A:
discrete quanta — раздельные части
active devices — активное устройство, активный элемент logic gate — логический элемент, логическая схема charge-coupled device — устройство с зарядной связью field-effect microwave power devices — полевое СВЧ-
устройство
strip line circuits — полосковая схема, полосковая линия micro-strip circuits — микрополосковая схема
Text 3A
Why Digital Transmission?
Communication is the transmission of information to a remote place or a remote time. Digital communication transmits information in discrete quanta. The increasingly complex activities of mankind have forced an exponential growth in communication to sustain them, and revolutions in hardware and in our understanding of electrical communication have decimated the cost of communication and completely changed how it occurs. The foremost innovation in communication has been the advent of digital transmission and the understanding of its importance.
All about us we see a revolution in which the older methods of analog transmission are being replaced by digital transmission.
23
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.
24
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
25