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Lecture 1. 1. ORGANIZATION AND STRUCTURE OF AVIATION TELECOMMUNICATION
Terminology: • АFS – Aeronautical Fixed service (авіаційна фіксована служба) • АМS – Aeronautical Mobile Service (авіаційна рухома служба) • AMSS – Aeronautical Mobile Satellite Service (авіаційна рухома супутникова служба) • ATN – Aeronautical Telecommunication Network (мережа авіаційного електрозв’язку) • ATS – Air Traffic Service (обслуговування повітряного руху) • CNS/ATN – Communication, Navigation & Surveillance/Air Traffic Management (концепція зв’язку, навігації і спостереження для цілей організації повітряного руху)
The Organisation and Structure of Aviation Telecommunication • The organisation of aviation telecommunication is carried out according to requirements of the current legislation of Ukraine, regulatory legal acts which regulate activity of civil aviation of Ukraine, rules of the Convention on the international civil aviation (ICAO).
Basic purposes of aviation telecommunication: - An exchange of messages between bodies of Air Traffic Service (ATS) and the aircrafts during flight; - Interaction of ATS bodies during planning of air space use; - Interaction between services of the enterprises and organisations of civil aviation during transmission (receiving) of the administrative and industrial information; - The automated data exchange with the aircraft and ground users who provide flights; - Transmission (receiving) of messages which contain the operative meteorological information; - Interaction with subsections of corresponding bodies of the Ministry of Defense of Ukraine, the Ministry of Extreme Situations of Ukraine, the Ministry of Internal Affairs of Ukraine and other central enforcement authorities.
Basic requirements for aviation telecommunications: • timeliness of the organization of networks for aviation telecommunication, • speed of an exchange of messages, • reliability and truthfulness of an information transmission, • efficiency and profitability of communication.
Organizational structure of aviation telecommunications • • The aviation fixed service (АFS); Aviation mobile service (АМS); Service of aviation broadcasting; Aviation mobile satellite service (АМSS).
Aviation ground telecommunication and aviation air telecommunication are parts of aviation telecommunication. Aviation ground telecommunication is the basic resource for interaction of ATS bodies, civil aviation enterprises in the course of industrial activity. It is organised according to: - accepted ATS structure in Ukraine and structure of industrial-technological activity of each enterprise, organisation and ATS bodies, - and also taking into account of Rules of aviation telecommunication in civil aviation of Ukraine (2003).
• Aviation ground telecommunication is subdivided into: - Aviation telephone telecommunication; - Aviation cable (telegraph) telecommunication; - Aviation telecommunication of the automated data exchange.
Aviation air telecommunication is: - the basic communication facility of ATS bodies with airplane crews (bilateral telecommunication "air-earth") and between airplane crews which are in flight, - and also means of signals receiving from radio beacons and disaster places.
Aviation air telecommunication in civil aviation of Ukraine is appointed for such kinds of service: - Regional ATS dispatching; - Dispatching service of the approaching; - Aerodrome dispatching service of air traffic; - Flight-information service; - For saving and search and rescue works; - For the automated data exchange; - For industrial-commercial activity.
For bilateral telecommunication "air-earth" of ATS bodies with airplane crews radio telephone communication and (or) the automated exchange by digital data is used. Aviation air telecommunication is carried out by means of an aviation radio communication in very high frequencies (VHF) range. The list of channels of aviation air telecommunication, their radio data and operating modes are given in manuals of the aero navigation information.
Means of aviation air telecommunication ATS dispatching should provide: - Direct, operative, continuous and free from radio interference bilateral telecommunication "air-earth"; - Constant availability for service without searches and frequency tuning; - Possibility of circular message transmission; - High quality of telecommunication. It is possible also to use a selective call of the airplane.
Requirements to reliability of aviation air telecommunication: The aviation radio communication with the airplane is considered lost if throughout 5 minutes the crew (dispatcher) does not answer a call of all possible channels of aviation air radio telephone communication after numerous calls on each of them.
In case of infringement of an aviation radio communication the crew of the airplane and ATS body should take corresponding measures for its recovery.
Classification of Radio Services in Accordance with ITU Standards The Telecommunication Standardization Sector (ITU-T) coordinates standards for telecommunications on behalf of the International Telecommunication Union (ITU) and is based in Geneva, Switzerland.
ITU has been an intergovernmental public-private partnership organization since its inception and now has a membership of 191 countries (Member States) and over 700 public and private sector companies as well as international and regional telecommunication entities, known as Sector Members and Associates, which undertake most of the work of the Sector. ITU-T has a permanent secretariat, the Telecommunication Standardization Bureau (TSB), based at the ITU HQ in Geneva, Switzerland. The elected Director of the Bureau is Mr. Malcolm Johnson of the UK. Mr. Johnson was elected by the ITU Membership to the Directorship for a 4 -year term in November 2006.
Series and Recommendations ITU-T Recommendations are the names given to telecommunications and computer protocol specification documents published by ITU-T. Many of the Recommendations that define OSI are also ISO standards. Standards for Internet protocols are typically developed in the IETF, and standards for mobile telephone systems are developed in ETSI and other forums. Series of ITU Recommendations ITU-T issues Recommendations that have names like X. 500, where X is the series and 500 is an identifying number. When a Recommendation is updated, it will (mostly) keep the same number, so the year of issue may be necessary to identify a specific version of a Recommendation. The term "X. 500" is used both to refer to the specific X. 500 Recommendation, and to the entire family of Recommendations named X. 5 xx, where the specific X. 500 Recommendation forms the introduction and overview to the set.
Radio communication systems are intended for: - bilateral information interchange between aircraft crew and ground radio stations; - bilateral information interchange between aircraft crew and others aircrafts; - for internal communication between members of crew; - for communication between crew and passengers. Into an obligatory minimum of the radio communication equipment of passenger planes enter: - microwave radio station; - HF radio station; - radio station for an emergency communication.
The VHF radio station is intended for operative communication within direct radio visibility (up to 350 km). It works in a range of 118 -137, 975 MHz, a step of frequency adjustment 25 к. Hz. As it is the basic communication system, on aircraft 2 complete sets of equipment are installed - one the basic, another reserve. Accordingly there are two antennas, one - the upper arrangement (for work with the basic complete set), another - the lower arrangement (for the work with the second complete set). The HF radio station (fig. 1. 6) is intended for a longdistance communication on distances up to 3000 km. Frequencies range of HF-communication is 2 -30 MHz, a step of adjustment is 1000 Hz (28000 channels). On aircraft usually 1 or 2 complete sets of equipment are installed.
Fig. 1. 6. HF radio station
Portable radio station for an emergency communication and giving of distress signals works on frequencies of 121, 5 and 243 MHz. In subpolar and polar areas the radio station of a range 325 -530 к. Hz is necessary still. The choice of radio station and its frequency tuning on modern aircrafts is made with the help of the same multipurpose control panel which is used for adjustment of radio navigating systems. For this purpose in transceivers receiving of a standard digital consecutive code is provided, by which the tuning frequency from multipurpose control panel is transmitted.
On many modern aircrafts the satellite communication station is installed. Communications satellites logically supplement orbital groupings of global navigating systems, allowing considerably improve characteristics of the last due to use of systems of regional increase RAS (Regional Augmentation System). Using the broadband channel of this system signals relaying of ground stations are carried out. However the satellite communication basic purpose consists in the organization of service communication and communication of passengers with the subscribers who are out of limits of direct radio visibility.
Satellite communication systems provide high-quality digital communication with high degree of reliability in any point of globe. Flight crews by means of a satellite communication get access to the information of flight support services, including to the information about meteoconditions. Crews get access to the operative information of the airports about situation on air lines. Thus messages about traffic schedule changes arrive in real time. From aircraft board to the ground data are transferred through the satellite for flight control, for example, about quantity of fuel onboard, an estimated time of arrival, the equipment indication. Using this information, ground services personnel can plan better preparation of the necessary equipment for minimization of a plane holding time. Transmitting of the spot news about emergencies, skyjack attempt, etc. has great value. The satellite communication gives the chance for passengers to speak in flight by phone and to send facsimile messages or digital computer data to any point of globe.
Satellite communication system consists of a ground communication station, satellites and an onboard communication station. The ground station carries out functions of system management and represents "airlock" (шлюз) for an input in ground communication networks. The satellites located, as a rule, in geostationary orbits, broadcast communication signals between onboard communication stations and ground stations or between ground stations. Onboard stations communicate with satellites on frequencies of a L-range (1530 -1670 MHz)
Onboard station includes a salon communication system, the satellite communication terminal, and one or several antennas (for multichannel maintenance). The salon Communication system contains the block of linking with phones, fax machines and computers of passengers, connection with the equipment of cabin communication, with the onboard equipment of communication, including interface for North American telephone system (NATS), the European telephone communication system the earth the-plane (TFTS) and system Gatelink. NATS represents cellular telephone system of the microwave range, TFTS is the European cellular telephone system of a L-range, and Gatelink – is system of linking with telecommunication services accessible through the inter-network interface. The linking block carries out the same functions, as office automatic telephone station with input and output communication. Standard aircraft communication system provides flexibility in a choice of telephone sets types, fax machines, computers and the cabin equipment.
Besides the listed onboard aircraft systems the following radio communication equipment can be placed: - radar-tracking transponder of air-traffic control; - system of a selective call; - system of address communication; - equipment of internal crew communication; - amplifier of communication with passengers.
Radar-tracking transponder of airtraffic control is intended for work with ground aerodrome and route secondary radars of ATC services. In an operative range of such radar the transponder provides automatic delivery of a co-ordinate mark of aircraft location and the information about flight heignt and aircraft number (identifier). For systems of ATC the transponder transmit also the information about the fuel rest. Operating frequency in a transmitting mode is 1090± 0, 06 MHz, in receiving mode - 1030 MHz.
The transponder contains two transceivers, each of which works on upper, lower and keel antennas, and also a control panel. The system of a selective call allows carrying out a call of the particular plane or the helicopter from ground station by a radio channel. A ground part of system contains the coder (the block which is carrying out the selective coding) and HF- or VHF- transmitter. The receiver, the decoder and the panel for aircraft code setting is installed onboard. The system of address communication uses the existing radio communication equipment for transmitting from the plane on the earth and back digital-alphabetic information in ACARS format. Existing systems of address communication work in the HF-range. The new generation of these systems will use the VHF-range.
The equipment of internal communication provides: - bilateral telecommunication between crew members; - bilateral telecommunication of crew with stewards; - bilateral telecommunication of stewards among themselves; - bilateral radio communication of crew through any of onboard radio stations; - listening by crew of identification signals of radio navigating systems and sound signals of marker radio beacons; - listening by crew of special sound and speech messages, formed by onboard systems; - sound alarm system for calling stewards.
The onboard amplifier of communication with passengers provides: - voice communication from the pilot to crew and passengers; - voice communication from the steward to passengers; - amplifying of the written down messages and music; - voice-frequency calls (a call of the steward, "not to smoke" etc. ).
Now in aviation the global telecommunication networks intended for transmitting of digital data from the earth on aircraft and from aircraft on the earth are introduced. These networks will connect in a unit all components of civil aviation - being in air and on the ground flying machines, airlines, services of an air traffic control, a weather service etc. They will provide communication, navigation, an air traffic control. The onboard equipment will be filled up by 12 telecommunication terminals, an alarm board and a router. For information transmitting from a board and receiving addressed to aircraft information will be used already available radio stations.
Automatic dependent surveillance: Aircraft transceiver will transmit one time per second on particular frequency information about his aircraft to another aircrafts - its identifier, coordinates, height etc. At the same time it will receive similar data from all others aircrafts. The ground centers of ATC will transmit data about those aircrafts which are not equipped by similar systems. This information will arrive in a router, and there from - in indication system on which screens the pilot can see a situation with air traffic round his aircraft.
ICAO Standards and Recommended Practices ANNEX 10 to the Convention on International Civil Aviation Aeronautical Telecommunications (Volumes I, III, IV and V) (www. scribd. com/doc/5509183/Annex 10 -ICAO) Three of the most complex and essential elements of international civil aviation are aeronautical communications, navigation and surveillance. These elements are covered by Annex 10 to the Convention. Annex 10 is divided into five volumes: Volume I — Radio Navigation Aids Volume II — Communications Procedures including those with PANS status Volume III — Communication Systems Part 1 — Digital Data Communication Systems Part 2 — Voice Communication Systems Volume IV — Surveillance Radar and Collision Avoidance Systems Volume V — Aeronautical Radio Frequency Spectrum Utilization The five volumes of this Annex contain Standards and Recommended Practices (SARPs), Procedures for Air Navigation Services (PANS) and guidance material on aeronautical communication, navigation and surveillance systems.
Requirements to an Onboard Communication Facility Parameters of modern radio stations should satisfy requirements ІСАО. Key parameters of a communication facility. Quality of an information transmitting by a communication system as a whole depends on parameters of radio station (communication facility), which form this communication system. Parameters which characterize any radio station are: - A radiation class; - Quantity of communication channels; - Stability of frequency; - Radiation power of radio station transmitter; - Sensitivity of the receiver of radio station; - Width of the receiver band; - Attenuation value of side radiations.
As a radiation class usually understand a kind of signals on an exit of transmitters or on an input of receivers. In aviation radio stations the radiation class is designated by three and more signs. The radiation class is characterized by modulation type (peak, single band, frequency, phase, pulse); character of signals which modulate carrier (analogue, discrete, digital); by a type of information which is transmitted (a telephony, telegraphy, data etc. ). For detailed radio emission classifications an obligatory three-value symbol is supplemented with two signs: feature of signals which are transmitted (types of codes, cable transmission, and television signal); a compacting kind (frequency, time, combined).
Requirements to parameters of onboard radio stations of a meter range. As a range of working frequencies usually understand area of radio frequencies in which limits the radio station can be discretely tuned. Distribution of frequencies - also is regulated by the international consent. Step of frequencies lattice defines step-type behavior of radio station tuning within a working range. ІСАО standards define both a working range, and a step frequencies lattice. Now the range of frequencies which is intended for a radio communication on meter waves (МW), makes 118. . . 137 МHz. For radio stations of meter waves range the class of radiation is accepted А 3 Е (that means peak modulation with two side bands with use of one channel for analogue signals transmitting.
Stability of frequency - parameter which defines a communication quality. Maximum deviations of frequencies are quantitatively characterized by the relation ΣΔf/f, where ∑Δf – is a total deviation of frequency Δf , which in accordance with ІСАО Standards should not exceed ± 0, 0005 % from the assigned frequency f. The quantity of the fixed frequencies within a working range of radio stations in a meter range is defined by step of frequencies lattice. ІСАО Standards allow channels separation of meter waves range 100, 50, 25 and 8, 33 KHz. But now channels separations are used on 25 KHz (old radio stations) and on 8, 33 KHz, which is defined as a result from division of 25 KHz on 3. This allows increasing quantity of channels from 760 to 2280 and in three times - resolution ability of communication in meter wave range.
Power of radio station depends on its designation and a range of working frequencies. Very often for onboard radio stations the power is restricted by impossibility: - of placing on the airplane large-sized and highly effective antennas, - of voltage increasing in output cascades of the transmitter etc. In most cases effective radiated power should be enough for creating intensity of a field in a point of receiving not less than 20 µV/m for distribution in free space on distances and heights which correspond to operating conditions of airplane.
Modulation depth coefficient of the transmitter should be not smaller than 0, 85 in the presence of systems for maintaining constant value of this factor. Under sensitivity usually understand a signal minimum level on a receiver input for which normal work of output cascades of the onboard receiver is provided, and the relation “signal/noise” on the detector output is more or equal to three (10 d. B). In accordance with standards the intensity of a field on a receiver input should be not smaller than 75 µV/m.
Width of a passband of the receiver depends on a spectrum of frequencies of signals which are receiving, a level of noise, a class of radiation, stability of synthesizer frequencies and speed of airplane flight. Requirements to width of a passband of onboard radio station define effective receiving band in case of a deviation from bearing frequency no more than on 8 к. Hz. The requirement for the value of side radiations suppression arises through imperfection of radio transmitters in which, except the main radiations, are generated also side radiations on harmonics (parasitic, combinational and intermodulational).
Suppression of side channels. - In case of channels separation 25 к. Hz: 50 d. B and more in case of a deviation 25 к. Hz from the assigned frequency and 40 d. B or more for a deviation 17 к. Hz; - In case of channels separation 50 к. Hz: 50 d. B and more in case of a deviation 50 к. Hz from the assigned frequency and 40 d. B or more for a deviation 35 к. Hz; - In case of channels separation 100 к. Hz: 50 d. B and more in case of a deviation 100 к. Hz from the assigned frequency.
In practice the receiver should provide effective suppression of side channels on 60 d. B and more for a deviation 25, 50 and 100 к. Hz from the assigned frequency; it concerns receivers which are intended for work in conditions channels separation 25, 50 and 100 к. Hz accordingly. Below are given ICAO requirements to radio stations in meter and decameter wave ranges.
Requirements for Parameters of Onboard Radio Stations in Decameter Wave Range In ANNEX 10 to the Convention on International Civil Aviation Aeronautical Telecommunications (Volume III) ICAO requirements for onboard high-frequency (HF) means characteristics are given. Characteristics of onboard radio stations HF range "air - earth" which are used in aviation mobile service, should answer such technical requirements. In SSB mode (Single Side Band - модуляція з однією бічною смугою) radio stations should work on any carrier frequency which is at the disposal of aviation mobile (R) services in a range of frequencies 2, 8. . . 22, 0 МHz, necessary for performance of the authorized plan of frequencies assignment for regions in which this system of a radio communication is used.
Quantity of channels in decameter waves range - is nearby 280000 with discrete frequency step of 100 Hz. So onboard equipment in decameter waves range should work with discrete lattice step of frequency 100 Hz. For transmitting (receiving) the side band is used (Fig. 1) that lays in the upper frequency half of channel relatively carrier frequency.
Fig. 1. Borders of frequency spectrum (expressed through average power) for all types of onboard transmitters in decameter waves range and transmitters of aviation stations
Frequencies band restriction on power level. For those types of onboard transmitters, stations and aviation stations transmitters which work on single side band with the use of radiations classes Н 2 В, НЗЕ, J 3 E, J 7 B or J 9 B, average power of any radiation on any discrete frequency is less than average power Рm of the transmitter: - At any frequency which is displaced relatively the assigned frequency on value from 2 to 6 к. Hz, - at least 25 d. B; - At any frequency which is displaced relatively the assigned frequency on value from 6 to 10 к. Hz, - at least 35 d. B; - At any frequency which is displaced relatively the assigned frequency on value from 10 к. Hz.
For onboard radio stations transmitters’ power levels should be the following (Fig. 1): for onboard stations - 40 d. B; for aviation stations - [43+10 lg Рm (W)] d. B. Classes of radiation J 3 E, J 7 B or J 9 B characterize single side band (SSB). Symbol J means single side band with suppressed bearing, a symbol 7 - two or more channels which transfer quantized or the digital information, a symbol 9 - complex system with one or several channels which transmits quantized or the digital information together with one or several channels of the analogue information. Third symbol B means a telegraph mode for automatic receiving.
Requirements to accuracy of frequency tuning. Stability of the carrier frequency for maintenance of transmitting function for classes of radiations J 3 E, J 7 B or L 9 B must be so, that the difference between an actual carrier transmitting frequency and bearing (basic) frequency should not exceed: - 20 Hz for the onboard equipment; - 10 Hz for the land equipment. Short-term instability of frequency is admitted no more than 4· 10 -7. Sensitivity of the receiver is a measure of receiver ability to receive weak signals with sufficient level and quality. Sensitivity of the receiver with single side band should not exceed 0, 5 m. V (113 db/m) for the relation “signal/noise” no more than 10 d. B.
Power of radiation. The equipment of aviation stations. According to the Amendment 27 of Regulations for radio communication the maximum power Рm , that is transmitted to the antenna, for classes of radiation Н 2 В, Н 3 Е, J 3 E, J 7 В or J 9 B has not exceed the maximum value of 6 k. W. The equipment of onboard stations. The maximum power that is transmitted to the antenna, for classes of radiation Н 2 В, Н 3 Е, J 3 E, J 7 В or J 9 B does not exceed 400 W.
Ways and Kinds of the Communication Organisation The following kinds of communication are used for the organization of an aviation radio communication (Fig. 2): - Duplex communication – a kind of communication for which the information is transmitted simultaneously in both directions of a communication channel (possible half-duplex communication when communication between two stations occurs serially on independent channels in direct and return directions as at simplex communication); - Simplex communication – a kind of communication for which the information is transmitted serially in one direction of a communication channel (there exist single-channel simplex communication, namely simplex communication with use of one frequency channel in both directions);
- Circular transmission - a simultaneous information transmission which is not addressed to particular station or communication stations. Such transmission can be with acknowledgement and without acknowledgement of the information receiving; - "Blindly" transmission - an information transmission from one communication station to another in conditions when it is impossible to install a two-way communication; but it is supposed, that the station which is called, can receive the information.
Fig. 2. The scheme of the communication organization: a - simplex; b - duplex
For duplex radio communications transmission in one and in other directions is conducted usually on different carrier frequencies. It is done with the purpose that the receiver accepted signals only from the transmitter at opposite station and did not accept signals of own transmitter. Simplex communication is used, as a rule, in case of relatively small information streams. For objects with the big loading the duplex communication is characteristic.
Ways of the communication organization: a radio network and radio direction. If it is necessary to have a radio communication with a considerable quantity of objects, a radio network is arranged (Fig. 3 a). One radio station which is called as main can transfer the message both for one, and for the several subordinated objects. Its radioman keeps order in a radio network and establishes sequence of work on transmission to the subordinated stations. The last in accordance with corresponding permissions can communicate not only with the main radio station, but among them. The way of the communication organization between two correspondents is called radio direction and is used for maintenance of transmission for the big streams of messages. Duplex communication on different frequencies of receiving and transmitting (Fig. 3 b) is thus applied as usual.
Fig. 3. Types of the communication organization
Distance of communication is defined by power of transmitters and sensitivity of receivers, and also conditions of the radio-waves distribution, which are unequal for meter waves and decameter waves. It is known, that meter waves spread rectilinearly, and distance of communication in meter waves ranges is limited by range of direct visibility. Use of automatic active retranslators is the most effective way for increasing the range of communication on very high frequencies (VHF). The active single-channel retranslator is designed on the basis of two VHF radio stations (Fig. 4). The retranslator can be installed on the airplane, the helicopter or suspended on a balloon. It receives signals on one frequency and relays them on another.
Fig. 4. Organization of communication for radio direction
In a short-wave range the distance of communication is defined by distance of radio beams distribution and technical parameters of the transmitter, the receiver and the antenna-feeding device.