Е. В. Тихонова английский язык для самостоятельной работы студентов учебное пособие Омск
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I. Read the text and find answers to the questions:
II. Match the definitions:
III. Choose the statement, which expresses the main idea of the text.
XII. Complete the sentences: Ecology is one of those words which does not have strict academic … The fate of future generations on our planet resembles … It is sometimes difficult to argue about … We must not ignore our future well-being for … The idea of “home” includes … Mankind is rapidly driving many species to extinction by … We can’t halt … The harm caused by nuclear tests, atom bombs and accidents at the atomic power stations is … XIII. Write an outline of the text. XIV. Summarize the text according to the outline. Make use of the connectives:
IX. Try to memorize the words and word-groups: wireless networks – беспроводныесети to convey complex messages – передаватьсложныесообщения analog signals – аналоговыесигналы digital signals – цифровыесигналы a continuous bit stream – непрерывныйпотокбитов a packet radio – пакетноерадио via radio transmission – порадиосвязи to establish a bidirectional communications link – установитьдвунаправленнуюсвязь adhос wirelessnetworks – произвольные беспроводные сети next – generationcellularservices – сотовыеслужбыследующегопоколения. I. Study text A. Try to understand all details. Use a dictionary if necessary: TEXT A HISTORY OF WIRELESS COMMUNICATIONS The first wireless networks were developed in the Pre-industrial age. These systems transmitted information over line-of-sight distances (later extended by telescopes) using smoke signals, torch signaling, flashing mirrors, signal flares, or semaphore flags. An elaborate set of signal combinations was developed to convey complex messages with these rudimentary signals. Observation stations were built on hilltops and along roads to relay these messages over large distances. These early communication networks were, replaced first, by the telegraph network (invented by Samuel Morse in 1838) and later by the telephone. In 1895, a few decades after the telephone was invented, Marconi demonstrated the first radio transmission from the Isle of Wight to a tugboat 18 miles away, and radio communications was born. Radio technology advanced, rapidly to enable transmissions over larger distances with better quality, less power, and smaller, cheaper devices, thereby enabling public and private radio communications, television, and wireless networking. Early radio systems transmitted analog signals. Today most radio systems transmit digital signals composed of binary bits, where the bits are obtained directly from a data signal or by digitizing an analog voice or music signal. A digital radio can transmit a continuous bit stream or it can group the bits into packets. The latter type of radio is called a packet radio and is characterized by bursty transmissions: the radio is idle except when it transmits a packet. The first network based on packet radio. ALOHANET, was developed at the University of Hawaii in 1971. This network enabled computer sites at seven campuses spread out over four islands to communicate with a central computer on Oahu via radio transmission. The network architecture used a star topology with the central computer at its hub. Any two computers could establish a bi-directional communications link between them by going through the central hub. ALOHANET incorporated the first set of protocols for channel access and routing in packet, radio systems, and many of the underlying principles in these protocols are still in use today. The U.S. military was extremely interested in the combination of packet data and broadcast radio inherent to ALOHANET. Throughout the 70's and early 80's the Defense Advanced Research Projects Agency (DARPA) invested significant resources to develop networks using packet radios for tactical communications in the battlefield. The nodes in these ad hoc wireless networks had the ability to self-configure (or reconfigure) into a network without the aid of any established infrastructure. DARPA's investment in ad hoc networks peaked in the mid 1980's, but the resulting networks fell far short of expectations in terms of speed and performance. DARPA has continued work on ad hoc wireless network research for military use, but many technical challenges in terms of performance and robustness remain. Packet radio networks have also found commercial application in supporting wide-area wireless data services. These services, first introduced in the early l990's, enable wireless data access (including email, file transfer, and web browsing) at fairly low speeds, on the order of 20 Kbps. The market for these wide-area wireless data services is relatively flat, due mainly to their low data rates, high cost, and lack of «killer applications». Next-generation cellular services are slated to provide wireless data in addition to voice, which will provide stiff competition to these data-only services. II. Say whether the following statements are true or false: 1. The first wireless networks were developed in the Post-industrial age. 2. The early communication networks were replaced first by the telephone. 3. Early radio systems transmitted analog signals. 4. A digital radio can transmit a continuous bit stream or it can group the bits into packets. III. Answer the following questions 1. How did the first wireless networks transmit information? 2. Where were observation stations built? 3. Where did Marconi demonstrate the first radio transmission from? 4. What is a packet radio characterized by? 5. What is the name of the first network based on packet radio? 6. What did the network architecture use? 7. What was the U.S. military interested in? 8. What was the ability of the nodes in ad hoc wireless networks? 9. What is the commercial application of packet radio networks? 10. What do wide – aired wireless data services enable? IV. Find the information dealing with ALOHANET. Relate this information to your partner. V. Find the information dealing with the packet radio networks. Relate this information to your partner. IX. Try to memorize the words and word combinations: cellular telephone systems – сотовыетелефонныесистемы; wireless networks - беспроводныесети; cell - сота, ячейка; to provide two-way voice and data communication – обеспечитьдвухстороннююпередачуданных; to support - поддерживать; sophisticated - сложный. I. Study text A. Try to understand all details. Use a dictionary if necessary: TEXT A CELLULAR TELEPHONE SYSTEMS Cellular telephone systems, also referred to as Personal Communication Systems (PCS), are extremely popular and lucrative worldwide: these systems have sparked much of the optimism about the future of wireless networks. Cellular systems today provide two-way voice and data communication at vehicle speeds with regional or national coverage. Cellular systems were initially designed for mobile terminals inside vehicles with antennas mounted on the vehicle roof. Today these systemshave evolved to support lightweight handheld mobile terminals operating inside and outside buildings at both pedestrian and vehicle speeds. The basic premise behind cellular system design is frequency reuse, which exploits path loss to reuse the same frequency spectrum at spatially-separated locations. Specifically, the coverage area of a cellular system is divided into nonoverlappingcells where some set of channels is assigned to each cell. This same channel set is used in another cell some distance away. Operation within a cell is controlled by a centralized base station, as described in more detail below. The interference caused by users in different cells operating on the same channel set is called intercell interference. The spatial separation of cells that reuse the same channel set, the reuse distance, should be as small as possible to maximize the spectral efficiency obtained by frequency reuse. However, as the reuse distance decreases, intercell interference increases, due to the smaller propagation distance between interfering cells. Since intercell interference must remain below a given threshold for acceptable system performance, reuse distance cannot be reduced below some minimum value. In practiceit is quitedifficult to determine this minimum value since both the transmitting and interfering signals experience random power variations due to path loss, shadowing, and multipath. In order to determine the best reuse distance and base station placement, an accurate characterization of signal propagation within the cells is needed. This characterization is usually obtained using detailed analytical models, sophisticated computer-aided modeling, or empirical measurements. II. Say whether the following statements are true or false:
III. Answer the following questions: 1. Can you give another name of cellular communication systems? 2. What communication do cellular systems provide? 3. What were cellular systems initially designed for? 4. What is the basic premise behind cellular system design? 5. What is frequency reuse? 6. What is operation within a cell controlled by? 7. Does intercell interference increase and why? 8. Why is it difficult to determine the minimum value? 9. What is needed in order to determine the best reuse distance? 10. How is an accurate characterization of signal propogation usually obtained? I. Look through the list of the English words and their Russian equivalents, facilitating reading text C: replacement – замена wirelessdevices – беспроводные устройства tiny – крошечный digitaldevices – цифровые устройства cellphones – сотовые телефоны networkaccesspoints – точки доступа mainly – главным образом, в основном toprovide – снабжать, обеспечивать mode – режим toresultin – приводить к чему-либо circuit – схема, цепь todevelop – развивать, разрабатывать II. Read the following text carefully. While reading look for the answers to the given questions:
TEXT BLUETOOTH Bluetooth is a cable-replacement RF technology for short range connections between wireless devices. The Bluetooth standard is based on a tiny microchip incorporating a radio transceiver that is built into digital devices. The transceiver takes the place of a connecting cable for devices such as cell phones, laptop and palmtop computers, portable printers and projectors, and network access points. Bluetooth is mainly for short range communications, e.g. from a laptop to a nearby printer or from a cell phone to a wireless headset. Its normal range of operation is 10 m (at 1 mW transmit power), and this range can be increased to 100 m by increasing the transmit power to 100 mW. The system operates in the unregulated 2.4 GHz frequency band, hence it can be used worldwide without any licensing issues. The Bluetooth standard provides 1 asynchronous data channel at 723.2 Kbps. This mode, also known as Asynchronous Connection-Less, or ACL, there is a reverse channel with a data rate of 57.6 kbps. The specification also allows up to three synchronous channels each at a rate of 64 Kbps. This mode, also known as Synchronous Connection Oriented or SCO, is mainly used for voice applications such as headsets, but can also be used for data. These different modes result in an aggregate bit rate of approximately 1 Mbps. Routing of the asynchronous data is done via a packet switching protocol based on frequency hopping at 1600 hops per second. There is also a circuit switching protocol for the synchronous data. The Bluetooth standard was developed jointly by 3 Com, Ericsson, Intel, IBM. Lucent, Microsoft, Motorola, Nokia, and Toshiba. The standard has now been adopted by over 1300 manufacturers, and products compatible with Bluetooth are starting to appear on the market now. Specifically, the following products all use Bluetooth technology: a wireless headset for cell phones (Ericsson), a wireless USB or R.S232 connector (RTX Telecom, Adayma), wireless PCMCIA cards (IBM), and wireless set-top boxes (Eagle Wireless), to name just a few. More details on Bluetooth, including Bluetooth products currently available or under development, can be found at the website http://www.bluetooth.com. III. Say whether the following statements are true or false:
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