Telecommunications
The term telecommunications traditionally indicates the set of techniques and procedures for the remote communication of sounds (voice, music), images, texts, etc., which today are referred to as signals, quantities varying over time and of an electromagnetic nature, acoustic or other, now almost always represented in numerical form (or, more widely, digital). The signals are able to convey the information to be transmitted, which is generated by a sender and sent to one or more recipients (point-to-point, mono or bi-directional telecommunications, or point-to-multipoint) or broadcasted ( broadcasting) to an unlimited number of recipients (as in common radio and television broadcasting services). This is increasingly accompanied by the acquisition, at a distance, of information on external situations, such as the natural environment (and its changes due to human intervention) and the traffic of mobile means (air, sea, land). The disciplines classified under the name of telecommunications can therefore be divided into two groups: telecommunications in the classical meaning mentioned above, or in the strict sense, and detection which is characterized by the generation of information content by means of signals that interact with the surrounding environment, o are generated by itself, and which includes the areas of remote sensing, surveillance and recognition (with classification / identification of objects of interest).
In the two broad sectors, the methodologies and theories (in particular those relating to the synthesis, analysis and processing of one- and multidimensional signals and the statistical decision) are similar and, at times, coincident, even if the applications are different.
This also happens in a third sector of growing application relevance, that of radio navigation, which allows a user to govern his own path thanks to the radioelectric signals emitted by fixed infrastructures or in orbit around the Earth (in the second case the term satellite navigation is used sometimes followed by the global adjective).
An example of functional coexistence of telecommunications in the strict sense with sensing and navigation is present in air traffic management. The air traffic control systems (ATC, Air traffic control) have the purpose of guaranteeing the safety of the flight without compromising the economy and speed. The growth of air traffic (about 6% per year with double-digit values in the East) requires a continuous improvement of safety in terms of accidents per flight hour (currently, of the order of one unit for ten million hours) including the various phases: taxiing, take-off, ascent, airway flight, descent, landing. The necessary minimum separations (longitudinal, lateral, vertical) between pairs of aircraft are maintained through cooperation between pilots and air traffic controllers, constantly in radio contact. The former use the on-board navigation system, based on terrestrial and satellite radio aids and inertial navigators; the latter use airspace surveillance systems (primary and secondary radars, multilateration, automatic dependent surveillance). The necessary connection between pilot and controller is evolving from traditional radio telephony in amplitude modulation (which has the considerable operational advantage of allowing all pilots tuned to the frequency locally used to listen) to numerical techniques for the transmission of both data and voice . In addition, a fixed telecommunications network connects the various ATC centers under whose responsibility the aircraft gradually passes on its path. based on terrestrial and satellite radio aids and inertial navigators; the latter use airspace surveillance systems (primary and secondary radars, multilateration, automatic dependent surveillance). The necessary connection between pilot and controller is evolving from traditional radio telephony in amplitude modulation (which has the considerable operational advantage of allowing all pilots tuned to the frequency locally used to listen to) to numerical techniques for the transmission of both data and voice . Furthermore, a fixed telecommunications network connects the various ATC centers under whose responsibility the aircraft gradually passes on its path. based on terrestrial and satellite radio aids and inertial navigators; the latter use airspace surveillance systems (primary and secondary radars, multilateration, automatic dependent surveillance). The necessary connection between pilot and controller is evolving from traditional radio telephony in amplitude modulation (which has the considerable operational advantage of allowing all pilots tuned to the frequency locally used to listen to) to numerical techniques for the transmission of both data and voice . Furthermore, a fixed telecommunications network connects the various ATC centers under whose responsibility the aircraft gradually passes on its path. the latter use airspace surveillance systems (primary and secondary radars, multilateration, automatic dependent surveillance). The necessary connection between pilot and controller is evolving from traditional radio telephony in amplitude modulation (which has the considerable operational advantage of allowing all pilots tuned to the frequency locally used to listen) to numerical techniques for the transmission of both data and voice . Furthermore, a fixed telecommunications network connects the various ATC centers under whose responsibility the aircraft gradually passes on its path. the latter use airspace surveillance systems (primary and secondary radar, multilateration, automatic dependent surveillance). The necessary connection between pilot and controller is evolving from traditional radio telephony in amplitude modulation (which has the considerable operational advantage of allowing all pilots tuned to the frequency locally used to listen to) to numerical techniques for the transmission of both data and voice . Furthermore, a fixed telecommunications network connects the various ATC centers under whose responsibility the aircraft gradually passes on its path. The necessary connection between pilot and controller is evolving from traditional radio telephony in amplitude modulation (which has the considerable operational advantage of allowing all pilots tuned to the frequency locally used to listen to) to numerical techniques for the transmission of both data and voice . Furthermore, a fixed telecommunications network connects the various ATC centers under whose responsibility the aircraft gradually passes on its path. The necessary connection between pilot and controller is evolving from traditional radio telephony in amplitude modulation (which has the considerable operational advantage of allowing all pilots tuned to the frequency locally used to listen) to numerical techniques for the transmission of both data and voice . In addition, a fixed telecommunications network connects the various ATC centers under whose responsibility the aircraft gradually passes on its path.
SUMMARY
1. Telecommunications in the strict sense. 2. Detection and radio navigation.
1. TELECOMMUNICATIONS IN THE STRICT SENSE
In telecommunications in the strict sense, the methods and modalities with which information are encoded, transferred to destination, interpreted and managed are defined.
A distinction is made between a transmission function, in which the information, conveyed by a suitable signal, is transferred from one point to another, and a switching function, in which it is routed to the recipient. Modern telecommunications are essentially numerical; the information source, often of the analog type (voice, video, etc.), is coded in numerical form, generating sequences of signals representing information units or bits. To allow forwarding on the transmission channel (copper cable, optical fiber, radio channel or ether) the signals are modulated, for example by varying their central frequency (frequency modulation, called wavelength modulation in the case of optical fibers) . This also makes it possible to transmit information from different sources on the same transmission medium (fig. 2 ).
The first applications of coding and modulation date back to radio communications (Morse code) which increased the safety of maritime transport and, subsequently, of air transport.
To allow the use of the same transmission channel to multiple sources and / or multiple recipients, it is necessary to resort to separation techniques in the domains that characterize the signal (frequency band, channel usage times, transmission code). Multiplexing in frequency division is flanked by time division (in which each source occupies the channel for an assigned interval of time) and code division (in which each source is characterized by its own code). In the access of multiple users to the same transmission channel, therefore, there are FDMA (Frequency division multiple access), TDMA (Time division multiple access) and CDMA (Code division multiple access) or combinations of them. Multiplexing on several levels allowed long distance telephony,
The telephone network (PSTN, Public switched telephone network) is a network made up of intermediate nodes (called exchanges) and transmission lines. The connection between the user and a control unit is a line formed by two copper wires, with a diameter of approx. 0,6 mm and length up to a few km, called twisted pair , while the lines that connect the exchanges together are called junctions. The user lines are connected to a local exchange, while a transit exchange is connected only to other exchanges. Switching during the call formation phase consists in configuring the contacts inside the control units in order to put the two users in physical communication. Once the connection between the two users has been established, the dedicated circuit remains at their complete disposal.
The creation of the inter-subscriber path used in plain old telephone service (POTS) is called circuit switching, as it establishes a physical connection between the two subscribers for the duration of the conversation. The same type of switching, but with numerical signals, is used in the ISDN (Integrated services digital network), introduced in the late 1980s and capable of providing the user in the basic configuration with two 64 Kbit / s B channels (currently the DSL techniques, Digital subscriber line, allow much greater capacities). With X.25 and Frame Relay technologies, networks evolve (late eighties, early nineties) towards more efficient packet switching, where the information to be transmitted is divided into groups or packets of information to which a header is added. (header ) that allows you to recognize them; the packets are sent separately, and the original message is reconstructed at their destination, rearranging them in the right order.
Strong changes in the world of telecommunications are due to the introduction of data networks for telecommunications, mainly the global communication network Internet. In the evolution of telecommunications we distinguish a pre-era and a post-era era. In the first, telecommunications were mostly analog and broadcast (eg, radio and television) and networks were mostly based on circuit switching with analog signals. The introduction of packet networks and then the Internet has led to a new vision of telecommunications, which are becoming numerical and more efficient. In this case it is possible to make packages follow different paths; it is also possible to send packets from different senders on the same line, making the network efficient and flexible, saving time and costs. Broadcasting communication is also transformed from analog to digital with the new digital satellite channels, with digital terrestrial television, with digital radio broadcasting, and finally integration with cellular telephony.
In modern telecommunications any type of information (text, data, music, audio, video, image) is digitized and encoded according to a standard (source coding, such as MPEG for video or MP3 for audio) which allows the synthetic representation of the information to be transmitted by eliminating the redundancies present in the source data and then transferred through different methods and different means of communication (cable, radio waves, optical fiber), regardless of the content; a further processing, called channel coding, makes the information suitable to be transferred on the chosen medium without degradation by adding error control codes. The evolution of encodings allows a considerable saving on the volume of data to be transmitted and, at the same time,
From the user's point of view, the possibilities of accessing information are many: ( a ) TV and broadcasting; ( b ) twisted pair, both for traditional telephony and for data communication; ( c ) wireless networks; ( d ) optical fiber; ( e ) mobile telephony.
Thanks to the standardization of the representation of the contents (source coding) and of the protocols (methods with which the network subsystems communicate to exchange data), we are now moving towards a seamless communication , independent of the access method used. In this regard, we can mention Voice over IP in which common telephone calls pass through the Internet, the use of TV on demand through the Internet or webTV, and completely new services such as video sharing (the case is emblematic YouTube).
Data networks and the Internet
A first subdivision of telecommunications networks can be made between access networks and transport networks. The former allow user access, the latter allow the transmission of large amounts of data over long distances.
From a geographical and extension point of view, the networks in turn can be divided into local type networks (LAN, Local area network), metropolitan type networks (MAN) and geographic or extended type networks (WAN). Finally, personal networks or PANs (Personal area networks) extend around the user for a few meters.
From a technological point of view, a distinction is made between wired ( wired ) with copper or fiber optic connections, and wireless networks , with radio connections. The following subdivision is outlined in the wireless framework: PAN networks that allow short distance communications (up to ten meters) on standard bluetooth technology (IEEE 802.15), local networks (LAN) limited to small areas such as buildings, public places and homes (distances up to hundreds of meters) on Wi-Fi technology (IEEE 802.11) and metropolitan networks based on WiMax technology (IEEE 802.16) with distances up to 50 km.
A wireless network or WLAN (Wireless local area network) is based on radio frequency (RF) technology and allows mobility within the coverage area, usually around tens of meters inside buildings and hundreds of meters around. 'open. The WiFi standard (commercial name of wireless local networks based on the IEEE 802.11 specifications with the 802.11b, 802.11g evolutions) allows the creation of relatively cheap and fast activation networks, operating in the (unregulated) frequency range of 2.4 GHz and allow for flexible systems. WiFi accesses are now available in airports, railway stations, internet cafes; in recent years, some provinces and municipal administrations have also started projects for the creation of civic networks with WiFi technology.
WiMax (Worldwide interoperability for microwave access) is the trade name to identify the IEEE 802.16 standard, and is a wireless technology that provides broadband and high-speed connectivity essentially for the so-called last mile, i.e. in the stretch that connects the user's home to the telecommunications center. With WiMax it is possible to obtain a high-speed wireless connection, up to a distance of 50 km, and at a speed of 72 Mbps. The frequencies used, subject to license, are different and depend on the version of the protocol used, for example in the mobile version (802.16e) they cover the bands of 2.3 GHz, 2.5 GHz, 3.3 GHz, 3.5 GHz and 5.8 GHz.
The multiplicity of digital networks of different typology, extension, technology and management has found a de facto standard in the Internet with the IP protocol (Internet protocol).
The Internet is today the largest telematic network in the world, connecting several hundred million computers. Born as the network of networks, in the space of a few decades it has become the global network. At the end of 2007 the number of Internet users - rapidly growing especially in the East - is estimated at one billion and six hundred thousand; the network carries about 70% of global data traffic. In the 1960s, the ARPANET project of the US Department of Defense allowed the development of a highly decentralized and redundant telematic network, therefore capable of providing connectivity even if partially destroyed; at the end of the Cold War, this technology was made available for civilian use, connecting the main university centers and then reaching business and domestic users, leading to the Internet.
The Internet is a worldwide network that allows the connection of each computer with access to a vast amount of information contained in the other computers connected to it and made available to users all over the world. The Internet thus acts as a means of collecting and disseminating information on a global scale. In reality, a computer is rarely connected directly to the Internet; more often it is connected to a network (eg the local company network) which is in turn connected to the Internet (of which it constitutes a subnet); in other cases the computer is connected to the Internet via the public telephone network. Therefore, the Internet is often referred to as the network of networks.
The Internet is a very complex logical network (that is, regardless of the technology used) and is supported by physical structures and connections of various types; consists of interconnected networks: private, public, corporate, university, commercial, wired or wireless. The Internet has created a communication standard, allowing the most diverse entities and agents to exchange data using a common protocol, TCP / IP (Transmission control protocol / Internet protocol), relatively independent of proprietary hardware specifications, operating systems, communication languages of equipment and means of communication. The strength of this protocol is that it is structured in successive layers independent of the previous ones, so that a data packet crosses several protocol layers that add information.
The address of each computer is called the IP address. In the version of the protocol called IPv4 this address is 32 bits long (indicated by four numbers between 0 and 255 separated by periods) and allows the addressing of about four billion computers. However, the growth of the Internet has made this number insufficient and a new version of the protocol (IPv6) has been defined which increases the address length to 128 bits (and the consequent number of computers to about 3 × 10 38 ). The transition from IPv4 to IPv6 is gradual (maintaining two-way compatibility) and will take a few years.
Once the Internet connection has been obtained, the user is able, through the use of appropriate software installed on his computer, to carry out activities such as: ( a ) consulting databases and catalogs; ( b ) viewing of documents, also in graphic form, issued by other users (including online versions of newspapers / periodicals); ( c ) the direct transfer of one's files to the mass memory of the computers of other users; ( d ) sending and receiving e-mail or instant messages; ( e ) the reception of music, films, programs from radio and television broadcasters; ( f ) the direct management of personal finance transactions ( home bankingand online trading ); ( g ) the purchase of consumer goods or services.
Among the main services and applications available on the Internet are: World Wide Web, search engines, FTP (File transfer protocol), e-mail, mailing list, newsgroup, webcast, file sharing, chat, podcast, IPTV (Internet protocol television), forum, VOIP, steaming, web radio, blog, e-commerce, e-learning, multiplayer.
Currently, traditional services are accompanied by services called Web 2.0, which place content and interaction between users at the center; data sharing capabilities transform passive consumers into authors of content made available to the community; examples of this philosophy are blogs, social networks, and podcasting.
The home user can access the Internet through Internet service providers (ISPs) that bring the network to the user's home using the available technology. The final link between the telecommunications network and the home user, the so-called last mile, still constitutes the majority of investments in telecommunications infrastructure. The most common access techniques that use the pair of copper conductors (the traditional telephone twisted pair) are the ADSL (Asymmetric digital subscriber line) and VDSL (Very high rate digital subscriber line) techniques .
ADSL owes its name to the asymmetry of the maximum speeds that can be reached in both directions (user-network and network-user). For telecommunications services, the amount of information that the user fetches from the network is generally much greater than that which he himself sends. Over short distances (less than 2.5 km) ADSL allows a maximum bit rate of 9 Mbit / s in the direction from the network to the user ( downstream ) and 1 Mbit / s in the opposite direction ( upstream ). ADSL2 extends the capacity of ADSL in the transmission speed which can, in the best conditions, reach a downstream speed of 12 Mbit / s and 3.5 Mbit / s upstream depending on the quality of the line. Finally, ADSL2 + can reach up to 24 Mbit / s downstream and 1.5 Mbit / s upstream.
Starting from the last telephone switching center, the distribution of the signal towards the user typically occurs by means of a first length of optical fiber, and a final section in copper.
The demarcation point between the optical fiber and the copper section can be positioned more or less close to the end user. A distinction is made between FTTH (Fiber to the home) if the connection to the user is made entirely of optical fiber, FFTB (Fiber to the building) if the optical fiber reaches the basement of the user's home, FTTC (Fiber to the curb) if the distribution cabinet from which the copper section starts is positioned immediately outside the building where the user is located.
These modes with optical fiber, cable, wire (wired) are complemented by wireless modes (WiMax) and modes linked to cellular telephony (GPRS, EDGE, UMTS systems, described below); finally, there is the possibility of exploiting the electricity network (PLC services, Powerline communication).
TV and radio broadcasting
TV, like networks, has followed its own evolutionary line and other broadcasting methods have been added to diffusion ( broadcasting ) carried out with a dedicated network of television repeaters scattered throughout the territory.
Based on the transmission method used in the section of the network that reaches the user, terrestrial television is distinguished, if it uses radio transmitters placed on the surface of the Earth, satellite television, if it uses radio waves emitted by transmitters on board artificial satellites, cable television, if you use telecommunication cables. The coding standards of video images vary over time: those of current mass television broadcasting date back to the introduction of color in the 1960s and provide for transmission in the VHF and UHF ranges with the well-known PAL, SECAM and NTSC systems; in Europe the MAC (Multiplexed analogue components) standard was also developed in the 1980s for direct broadcasting from satellite.
Video information services adapt to the trend of use of digital networks, which allow greater quality, flexibility in the combination of different services, ease of encryption to protect information and access control.
In September 1993 Digital video broadcasting (DVB) was born in Europe through the signing of a Memorandum of understanding by 80 operators in the sector aimed at producing technical specifications on which to define the standards for digital television broadcasting. DVB produced standards for each transmission medium (terrestrial, satellite, cable) used by the TV. In particular: ( a ) DVB-S (S, satellite), to receive video signals with a satellite receiver connected to a generally parabolic antenna; ( b ) DVB-C (C, cable), for cable TV; ( c ) DVB-T (T, terrestrial), for digital terrestrial (in which the television signal is received through normal television antennas); (d ) DVB-H (H, Handheld), which is the standard for broadcasting to mobile terminals such as cell phones.
Finally, the most recent and still being tested DVB-SH (Digital video broadcasting-satellite services to Handhelds) is an evolution of DVB-H that allows integration with hybrid satellite / terrestrial networks. At the beginning of 2008, South Korea and Japan had 20 million mobile viewers, more than 30 times the number of users in the European Union.
High definition television (HDTV) has introduced video images of significantly higher quality than analog television standards. Unlike traditional TV, where you have the standard 4: 3 and widescreen format16: 9 for TV screen images, high definition is 16: 9 as standard. A traditional video frame in the PAL system consists of 625 lines (transmitted interlaced, 25 or 30 times per second for even lines, 25 or 30 times per second for odd lines). The horizontal resolution of the picture in traditional analog video is a function of the signal bandwidth (a quality signal suitable for transmission has a band of 5 MHz, sufficient to resolve about 400 lines). In digital TV, the sampling standard provides 720 pixels on the horizontal axis, the highest quality obtainable from a DVB broadcast or a DVD. HDTV technology comprises four video formats, which differ in both actual resolution and image scanning modes. The two best known are: (a ) the 720p format, commonly called HD READY, which has a resolution of 921,600 pixels (1280 × 720) with progressive scan, for which the entire picture is transmitted for each transmission cycle (50 or 60 Hz depending on the country) image; ( b ) the 1080p format, commonly called FULL HD, which has a resolution of 2,073,600 pixels (1920 × 1080), also in progressive scan.
In the progressive transition from analogue to digital, broadcasting transmissions also pass from the old amplitude modulation (AM) transmission and, in the VHF range (88 ÷ 108 MHz), frequency modulation (FM) to digital broadcasting. A notable example of this step is DAB (Digital audio broadcasting), developed in Europe as part of the EUREKA 147 project and currently being introduced in numerous countries including outside Europe (an important exception being the United States, which has its own protocol called IBOC, In band on channel). DAB digitally coded transmission has the same advantages as television broadcasting and can, in principle, operate on frequencies between 30 MHz and 3 GHz for mobile reception or higher frequencies in the case of fixed reception;
Finally, we speak of IPTV (Internet protocol television) to indicate a system where the television service is transmitted using the Internet protocol: the television contents are received by the user through data networks. According to some media experts, within a few years the traditional TV broadcast will be supplanted by these new technologies. For home users, IPTV is often offered together with broadband Internet services and VoIP (Voice over internet protocol). The combined commercial offer of IPTV, VoIP and Internet access is called Triple play (if you add mobility we are talking about Quadruple play).
Mobile phone
Telecommunications through mobile terminals (cell phones) had a significant boost in the 1990s: a distinction is made between cordless systems, in which mobility is limited to the domestic or more urban environment, also called low-mobility systems, and large-scale mobile phones, which allow the user to travel throughout the country or even abroad. In both cases, the covered territory is divided into elementary service areas called cells. In the simplest case of the home cordless system, the cell is the user's home and it is not possible to move outside of it. In other cases it is possible to move from one cell to another adjacent cell and the transfer of the call between the two cells is called handover. If it is possible to continue to use the service even when moving within networks managed by operators other than the one with which you have subscribed, we speak of roaming .
The division into cells is necessary to be able to serve large areas and allow many users to access the service at the same time despite having a limited number of radio channels available. The same channels are then reused in cells duly distant from each other; it is therefore necessary to adopt an appropriate scheme for reusing the channels in space.
By referring to a regular grid of hexagonal cells and assuming the uniforming terminals distributed in the service area, it is possible to assign the same number of radio channels to each cell. The cells are then grouped into clusters of size N ( fig. 3 ) and all the radio channels of the system are used within each cluster.
In general, a distinction is made between first generation, analogue and frequency division access (FDMA) mobile systems, such as TACS (Total access communication system), second generation, numeric, time division access (TDMA) systems such as GSM (Global system for mobile communication), third generation, numeric, with code division access (CDMA) broadband (W-CDMA) such as UMTS (Universal mobile telecommunications system), which allow a high binary flow ( up to 2 Mbit / s), the transport capacity of 'packets', the support of multimedia services, the variability of the Quality of Service (QoS) parameters.
The launch of the new GSM mobile phone systems and UMTS made the TACS obsolete which, after allowing the rapid initial spread of mobile telephony in Italy, stopped working at the end of 2005, giving up its frequencies to GSM. The standardization of the GSM system began in 1982 and its launch in Europe took place ten years later. In mobile systems, the connection between the fixed network and the user is guaranteed in GSM by a base radio station called BTS (Base transceiver station), operating in Europe in the 900 MHz (876 ÷ 960 MHz) and 1800 MHz (1710 MHz) range. ÷ 1880 MHz). The entire territory is divided into areoles, each of which is covered by one of these stations. In addition to the telephone service, the GSM network can be used for sending data and faxes.
These services are flanked by GPRS services (General packet radio service), designed to carry out the transfer of data at medium speed, using the TDMA channels of the GSM network. A further evolution is the EDGE technology (Enhanced data rates for GSM evolution ), which allows to reach higher speeds, between 20 and 200 kbit / s, depending on the model of mobile phone / terminal used (mobile phone class), of the number of users connected per cell and finally the distance between the terminal and the nearest antenna.
Finally, the latest UMTS system, in addition to the classic voice signal transport, supports a maximum transfer rate of 1920 kbit / s. Typical applications, for example in UMTS networks in Italy, are: voice, videoconferencing and packet data transmission. Since 2004, UMTS 2 and UMTS 2+ have also been present in Italy, two extensions of the UMTS protocol, which operate on current UMTS networks and reach speeds of 1.8 and 3 Mbit / s respectively.
In the near future, the current UMTS networks will be enhanced through the HSDPA (High speed downlink packet access) access technology, with a theoretical maximum speed towards the user of 10 Mbit / s.
The frequency bands originally envisaged for the UMTS standard are 1885 ÷ 2025 MHz and 2110 ÷ 2200 MHz, respectively for transmission and reception.
Evolution of telecommunications
The evolution of telecommunications in the last decades is characterized by the integration of information transmission and processing, hence the acronym ICT (Information and communication technologies); this integration is driven by the continuous increase, at the same costs, of the computing, storage and transmission capacities, which can be estimated as doubling in less than two years. For example: ( a ) Moore's empirical law indicates the doubling time of microprocessor capacities in 18 months; ( b ) portable compact flash memories, initially of the order of 32 ÷ 64 million bytes, in a few years they have reached tens of gigabytes, i.e. billions of elementary information, while hard disks approach the capacity of one terabyte (1000 gigabytes) and in the world there are hundreds of databases with a capacity greater than one petabyte (one million gigabytes); ( c ) finally, the transmission capacity on the optical fiber transport network, thanks to photonic technologies (DWDM, Dense wavelength division multiplexing), allows the transport of a few terabits per second on a single fiber. In the whole planet (November 2007) data for 161 exabytes (ie 161 billion gigabytes) are recorded and the e-mail traffic in 2006 alone generated (excluding SPAM messages) 6 exabytes.
In the European context, half of the productivity growth in the last twenty years is due to the use of ICT in all sectors of society as well as to their development in the companies themselves. The evolutionary trends are many, and reside in a context of transition, in the most industrialized countries, from an economy mainly of products to one mainly of services, in which the added value lies in the information provided to the user rather than in its support. physical (for example, the traditional distribution and sale of books is being accompanied by their print on demandwith a reduction in distribution and warehouse costs, a process similar to the much more widespread distribution of music via the Internet, which is replacing the previous, rich music CD market). In this context, ICT equipment and sub-assemblies, especially those of users, increasingly of oriental production (Japan, China, Korea, Taiwan and, especially for the software component, India), of low costs and standardized characteristics, are often produced for companies that are competitors on the global market, and the competition, especially in the nations with the highest per capita income, shifts to the provision of services and the production of multimedia content such as films or videos; the devices may appear free to the user (as in the case of the set-top boxes necessary to use thepay-TV ), or often provided on free loan or at a symbolic price with the clause of a minimum monthly expense. In this context, the telecommunications infrastructure that uses various technologies (eg Wi-Fi, UMTS, etc.) is in any case essential for the provision of the service and / or the management and updating of the product in its software component.
The push of technology ( technology push ) and the needs of the market ( market pull ), therefore, profoundly modify the panorama of telecommunications services with three main evolutionary lines. The first evolution is towards access to information everywhere and without interruption ( seamless, ubiquitous access) in a transparent way with respect to the technologies used, also through SDR (Software defined radio). The second, connected to it, is towards the provision of information - or access to information - which makes sense in the particular place and time in which the user is, which involves his location and the construction of his profile. (with obvious confidentiality issues). The third lies in the growing need to make coherent (synchronize, align) information residing in different physical media managed by a user or to share it among multiple users, according to a model known as peer to peer., which allows the real-time transmission of video content between users with connections with high transmission capacity, both in reception and transmission (the most shared file types are MP3s, music files and DivX containing films).
Finally, user services are flanked by new telecommunications applications in the framework of communication from / between objects. Among them, the wireless sensors networks emerge, consisting of a large number (even hundreds of thousands) of tiny elements at low cost and very low energy consumption with sensory and transmission capacity, which allow to automatically acquire parameters and environmental data of various kinds, to synthesize and assimilate information by means of local processing and make them available to a control center. In the framework of communications between objects, NFC (Near field communications) evolve as part of the European SmartTouch project, based on so-called intelligent objects that are touched with a mobile reader, integrated for example in a mobile phone, with which the user can obtain information or make a payment. SmartTouch communication is based on radio frequency identification technology (RFID,
2. SURVEY AND RADIO NAVIGATION
In addition to telecommunications in the strict sense, both from a theoretical and technical point of view, as well as in applications and integrated systems, detection (surveillance and remote sensing) and radio navigation.
The survey defines the methods and modalities with which it is possible to acquire information on objects or on the surrounding environment, which in this case are the sources of information to be made available to the user through appropriate signal and data processing.
Detection systems can be classified into two types: active and passive. In active systems, such as radar and active sonar, objects and / or the surrounding environment are stimulated by suitable signals. The signals re-emitted in response to these stresses are received and processed by the detection system itself. In passive systems, such as radiometers (operating in microwaves, infrared and visible), passive sonars and optical image sensors (e.g., photos and video cameras), the emission of objects of interest is used, due to external (Sun) or spontaneous (microwave and thermal infrared) lighting.
When a detection system is used for the remote study of the natural environment, and in particular for the measurement of parameters without direct contact, we speak of remote sensing. Information from remote sensing is used in earth sciences, resource analysis, land management and civil protection for security purposes.
In relation to the various needs, a detection system can be physically placed on various fixed or mobile supports (or platforms), of the terrestrial, air, naval or satellite type. We talk about surveillance when we foresee the detection and the location of objects such as airplanes and ships for security purposes.
In the field of traffic detection and management (both for environmental analysis and for surveillance) the most significant sensor is the radar, able to measure at least the distance ( ranging ) of objects in the surrounding environment through the emission of radio waves. Radar applications are manifold (surveillance radar, tracking radar, ultra-high resolution imaging radar, altimeter radar, weather radar). The operating principle of the monostatic pulse radar (the most common one) is very simple: at regular intervals a power transmitter emits a signal, usually with a duration much shorter than the repetition period of the signal itself, which is radiated with an antenna strongly directive ( fig. 4). The same antenna is used to receive the echo reflected by the object of interest, traditionally called the target, through a very sensitive receiver. The time taken by the impulse to hit the object and back is equal to twice the distance between the radar and the target divided by the propagation speed of the radio waves (speed of light). The combined data of the orientation of the antenna at the moment of emission of the pulse and the time of reception of the signal echo provides the position of the target in the radar coverage range. The intensity of the echo decreases very rapidly as the distance increases (in free space, the power of the echo varies in inverse ratio of the fourth power of the distance); therefore in order to detect and locate very distant targets (hundreds of km) from the radar it is necessary to transmit very high powers (in the order of hundreds of kW or MW as peak values). Conversely, in the case of relatively close targets (tens of meters, as in automotive radars) the necessary peak powers can be limited to mW.
In addition to distance and angle measurements (through antenna pointing), radars can also perform speed measurements through the Doppler effect.
The frequency bands that can be used by radars are still called today with letters that date back to the Second World War: L , S , C , X , K ; these have been adopted as a standard for the designation of radar bands. The frequency ranges corresponding to these designations are shown in Table 1 .L'assegnazione of frequency bands used by the radar, as well as the management of the entire electromagnetic spectrum, it is the task of the International Telecommunications Union (ITU / ITU) through a series of periodic conferences, called WARC (World Administrative Radio Conference). The complete list of radiolocation (radar) frequencies is shown intab. 2 . Note that military radars may not meet ITU standards.
Surveillance
Surveillance involves various stages some of which are mentioned below: ( a ) discovery, ie revelation and first localization of the object; ( B ) tracking, which consists in extrapolating the position of the object in successive instants so as to realize a tracking ( tracking ) with estimation of the position and speed; ( c ) identification of the object.
An appropriate surveillance function is required in air or sea traffic control and territorial air defense. The primary application for surveillance is that carried out by military radar for aerial detection and civilian radar in air traffic control (ATC). The radar systems used for surveillance have been classified into Primary surveillance radar (PSR) and Secondary surveillance radar (SSR).
To carry out the on-route control of an aircraft, a primary radar typically has a range of up to about 360 km, provides updated data every 8 ÷ 12 if it has an angular discrimination capability better than 1.5 ° and distance discrimination of 600 m. To meet these requirements, a primary radar has a large antenna that is highly directive in azimuth and not very directive in elevation (to allow aircraft to be detected at different altitudes) and a high-power transmitter (of the order of MW as peak power).
Secondary radars date back to the 1960s as ATC applications of a military friend-or-foe identification (IFF) system developed during World War II. In an SSR system, the ground station (commonly called the radar) sends standard signals to the aircraft at the central frequency of 1030 MHz, called interrogations (SSR interrogations) with appropriate coding. These signals are decoded by the transponder on board which consequently responds by sending standard signals to the ground at the central frequency of 1090 MHz, called replies.(replies, replies). The measurement of the distance and the azimuth of the aircraft are based on the same methods of the primary radar; the SSR system adds a communication channel with the aircraft, which includes the transmission to the ground of the aircraft's identifier and altitude (mode A and C interrogations and responses, respectively). An evolution of the SSR, called Mode S (where S stands for selective), reduces interference and increases the addressing and data exchange capacity; Mode S is now the standard system that replaces traditional SSR.
The new distributed localization and surveillance systems of cooperating aircraft are being added to traditional radars, which often allow better performance at lower costs. A notable distributed surveillance system is multilateration (MLAT), which uses the reception, by a certain number of ground stations, of the signals emitted by SSR transponders installed on board the aircraft for locating aircraft on the surface of the airport. , and by one or more reference transponders in known positions. Aircraft, and equipped airport service vehicles, are located by the differences in arrival times of the SSR signal emitted by them to more (at least four) receiving stations. MLAT systems allow accuracy better than 7,
A further evolution of the concept of distributed surveillance is achieved by integrating the navigation functions. L' ADS-B(Automatic dependent surveillance-broadcast) is a notable case in which aircraft (and cooperating ground vehicles) periodically transmit via data link and broadcast the estimates of their state vector (position speed etc.) in a dedicated communication channel ( Mode S, Data Link in VHF or UAT, Universal acces transponder). The state vector is derived from the aircraft's onboard navigation system. Transmission is automatic and takes place periodically; all suitably equipped and radio coverage systems can receive ADS-B reports. The users of this data are mainly ATC operators, and also the aircraft and vehicles that by filtering the data of their interest can have an image of the traffic around them.
Remote sensing
Sensors for remote sensing can exploit the emission capabilities of objects of interest and natural lighting (passive sensors) or (active sensors) use the backscatter capabilities ( backscattering) of the radiation produced by the sensor itself. Active sensors for microwave remote sensing are essentially radar; Compared to passive sensors, in the face of greater complexity and cost, they have the advantage, fundamental in regions with cloud cover, of not being appreciably affected by the masking effects caused by the cloud layers and of being able to operate during the day or at night. In remote sensing applications it is necessary to obtain very high spatial (and therefore angular) resolutions, which cannot be reached with traditional radar techniques. This is the case of the detection (and creation of maps) of the earth's surface by radars mounted on board airplanes (avionics platforms) or satellites (space platforms), the most widespread applications of remote sensing. In these cases the technique is usedSAR (Synthetic Aperture Radar), with which, thanks to the synthesis of the aperture through coherent signal processing, it is possible to obtain a high spatial resolution, independent of the wavelength and altitude. The main sensors for remote sensing (active and passive) are listed in tab. 3 .
The SAR technique, whose avionic applications with analog technologies date back to the 1950s, uses the motion of the platform to create, through signal processing, a very long virtual antenna (order of magnitude of the km in space applications) which allows to obtain a '' very high resolution in the direction of motion (azimuth or cross-range resolution ); a suitable waveform transmitted allows to obtain a resolution of the same order in the perpendicular direction ( range direction ); the image of a swath is thus obtained from space ( swath) whose typical width ranges from tens to hundreds of km, which can be increased to a few hundreds (by degrading the resolution) by means of particular techniques, one of which is SCANSAR ( spotlightSCANning SAR, SAR scanning in the direction of range). The resolution of a space SAR is typically of the order of ten meters in civil applications and can drop below one meter in the mode; in principle it does not depend on the distance or on the operating wavelength. The independence from lighting and natural emission makes SAR indispensable for remote sensing in any weather situation, at any time of day and, in the case of the use of decimetric wavelengths (L band, around 22 ÷ 24 cm; P band, around 62 ÷ 64 cm) allows the penetration of foliage and also of arid soil, for example desert, with the revelation of buried artifacts (archeology).
Since the 1990s, there has been an increasing availability for civilian uses of technologies and products previously developed for military purposes (very high resolution images). A notable application of the recent SAR technology is found in the COSMO-SkyMed system, financed by the Italian Space Agency (ASI) and by the Italian Ministry of Defense, consisting of a constellation of 4 satellites; the first two were launched on June 8, 2007 and December 9, 2007. Each of the four satellites is equipped with a multimodal SAR in X band. The system, for dual use (civil and military), will allow constant monitoring of the territory through continuous control of coasts, agricultural and forest resources, urban environment. In the foreign context, notable developments, although not as sophisticated, are: ( a) the SAR-Lupe system (with a constellation of 5 satellites weighing 720 kg and 250 W power), intended to provide high resolution (better than one meter) SAR (X-band sensor) images to the German Ministry of Defense, with the first three satellites launched in December 2006, July 2007 and November 2007; ( b) the TerraSAR-X radar satellite, successfully launched on June 15, 2007 from the Russian Cosmodrome base in Kazakhstan, as a public-private partnership between the German aerospace agency DLR and the company EADS Astrium GmbH for the purpose (with a similar satellite that will operate in training with the former, carrying out the TanDEM-Xi mission scheduled to launch in spring 2009) to build a global, high-precision digital elevation model (DEM); the technique used, in this case, is SAR interferometry.
Radio navigation
By radio navigation we mean the process by which, through the use of radio waves, a mobile is able to navigate, that is, to reach the destination with a well-defined path through the determination of its position and guidance. Radionavigation systems (mainly aeronautical ones for civil use will be referred to) operational or in the testing phase have different architectures, functions and performances depending on the dimensionality (2D, i.e. latitude and longitude, or 3D, with the addition of the altitude ) of the determination, from the navigation conditions (speed of the mobile, visibility and distance from obstacles) and from the order of magnitude of the maximum distance within which the systems must operate, strictly related to the choice of the frequency range of the radio waves used (tab. 4 ). With radio aids placed on the surface of the Earth, distances of the order of 1000 km can be covered, provided that propagation by ground wave is used, conditioned by the use of low frequencies (in the VLF and LF ranges). Otherwise, by using direct wave propagation in visibility (in the VHF, UHF, SHF ranges), the distances - with terrestrial radio aids - are limited to approximately 50 km or 400 km, respectively for ships or aircraft; this limitation does not exist when the radio aids are placed on artificial satellites. There are therefore three classes of radio navigation systems: ( a ) long-range systems, of low precision (typically, tens of km or km), for navigation on the oceans; ( b) short-range, medium-precision systems (typically km or hundreds of meters) for coastal maritime navigation and land-based air navigation; ( c ) systems for landing, of high precision (from hundreds to tens of meters) and very high (from tens of meters to meters or even under one meter in the case of landing in the absence of visibility). With the availability of artificial satellites it was possible to have a fourth class, that of satellite systems, capable of operating with medium or high precision (and, with the help of suitable ground systems, of very high precision) over the entire surface. terrestrial and in all space surrounding the Earth. The GPS (US), GLONASS (Russian) systems and the new European Galileo system under development are well known.
Examples of long range systems are the LORAN C and the OMEGA. In LORAN C (Long range navigation C), signals are received from at least three broadcasting stations, one main and the others slave. The method used to determine the position is the hyperbolic one, ie the difference of the distances from two pairs of known points is measured; the position error varies from 300m to 15km, depending on the distances (up to 2000km). OMEGA uses a similar technique and, with proper processing, brings the position error to around 3 km.
The main short-range systems allow azimuth angle measurements, with error around 5 °, by means of a direction finder that receives the emission of an NDB (Non directional beacon) or with error around 1 ° ÷ 3 °, receiving the signal of a VOR (VHF Omni range), emitted with such modulation as to contain the azimuth information. The distances are obtained by means of the DME (Distance measuring equipment), which operates by measuring the delay with which radio wave pulses are received, emitted from the board, received and re-issued by the radio aid (responder) on the ground; there are errors of around 0.25%.
The most common radio navigation system for landing is the ILS (Instrument landing system). Thanks to particular functions of irradiation and modulation of the waves emitted by a pair of radio aids, two signals are received on board in azimuth and in elevation with respect to the direction leading to the runway; along this descent path (typically 3 ° in elevation), the distance information from the start of the runway is obtained in a discrete manner in correspondence with the passage over two or three radio beacons ( markers) located at known distances (around 0.3, 1 and 10 km). ILS are classified into categories, in relation to guaranteed benefits; in the higher ranking category (CAT IIIC) landing is allowed in complete absence of visibility. The most recent ground-based landing system is the MLS (Microwave landing system); lacking the commercial success initially expected due to the high costs of ground infrastructure and avionics, it not only allows operations in the absence of visibility, but also allows the choice of the trajectory (including curvilinear) for the aircraft
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