TELE-X - a Satellite System for TV and Data Communication ...

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Fig. 3 A sketch of the network DAMA traffic control station Signalling channel Combined signalling and traffic channel Subscriber connected via fiber optics area is internatlly connected via an optical fibre network. The demand for small and simple stations has led to the use of the best of both old and new satellite technologies. For example, the most modern of highpower satellites is combined with the simple but effective SCPC (Single Channel Per Carrier) transmission method. With the SCPC method the transponder signal is frequency divided into a number of carriers, which form a pool used by all stations in the network according to need. Forexample, the distribution of 64 kbit/s and 2 Mbit/s carriers is dynamic, i.e. it can be adapted to the current traffic requirement by blocking or releasing 64 kbit/s channels so that the number available corresponds to the traffic load. When a station calls another station a channel is allocated, and when the transmission is finished the channel is returned to the pool. Each cannel is independent of the others and is modulated on its own carrier. This makes for flexible allocation of channels to the stations, without complicated signal processing. All stations in the system (can be thousands) therefore have full access to each other when required. This arrangement is designated DAMA (Demand Assignment Multiple Access). Fig. 3 shows a sketch of the network. SCPC/DAMA can be compared with the now very popular TDMA (Time Division Multipel Access) systems. Such a corn- Comparison between SCPC/DAMA and TDMA Full transponder TDMA With full utilization of the TDMA (Time Division Multiple Access) method all traffic in the system passes through the satellite transponder and the earth stations via one carrier. The carrier is time divided into short bursts and thus a high momentary data rate is obtained. Since only the one carrier is present it is possible to drive the earth stations as well as the satellite output stage to saturation, which gives good utilization of their high-power transmitters. Another advantage is that with TDMA all subscribers in the network have access at any instant to all exchanged information. This provides unique facilities in a large number of traffic situations because of the possibility of varying the length or periodicity of the bursts. One drawback is that the advantages of TDMA are closely connected with the fact that at any moment all earth stations handle and sort all the traffic in the network. The radio parts in the earth station must be dimensioned for the full amount of traffic in the network, and the complexity of the "sorting equipment" increases very rapidly with the number of earth stations and the number of traffic elements per earth station. Small-scale TDMA The designation TDMA is sometimes also used for rather trivial multiplex-type systems, whose network structure and capacity allocation are set during installation and cannot be adjusted afterwards to suit the traffic requirements. The relative simplicity is attractive for smallscale TDMA in which the satellite transponder signal is divided into several carriers with different frequencies, like in the SCPC (Single Channel Per Carrier) method. Each carrier is time divided, as with full TDMA, but with a lower data rate per carrier. This demands less from the individual earth station as regards data rate and power, but means a loss of connectivity between the TDMA carriers, and a limited upper data rate for each station. The method is economical in systems with a medium data rate and a fairly small number of stations in a closed user group. TDMA or SCPC system ? TDMA stations with full transponders are complicated and expensive, as the stations must handle all traffic in the network regardless of the needs of the individual station. The method is economical when the network consists of a few earth stations, each with a large amount of traffic. In order to achieve this it is often necessary to concentrate the traffic. However, it has been found that just the cost of connecting a subscriber to an earth station via a cable or radio relay link can be higher than the cost of a complete TELE-X SCPC earth station. For reasons of economy TDMA is thus not suitable for wide-mesh networks with many subscribers. The SCPC concept means that each station is dimensioned for its own traffic (not the total network traffic), and it is therefore much cheaper than a TDMA station. Small-scale TDMA with several carriers in the same transponder can make full use of the TELE-X system. This combination may be attractive for different types of company networks in which, for example, a 2 Mbit/s channel within the SCPC system is used for TDMA traffic. The TELE-X traffic control system DAMA (Demand Assignment Multiple Access) makes possible such a combination of pure SCPC and TDMA. New services, such as data and video communication, will be used fairly sparsely even in cities. The possible users of such facilities will be numbered in tens of thousands, unlike the telephone subscribers which number millions. This fact favours TELE-X SCPC, perhaps combined with small-scale TDMA.
Technical data for a station Antenna diameter Modulation method Frequency (Special Service Band) up link down link G/T EIRP Data rates DS/MDVS 1.8-2.5m Differentially coded OQPSK 14GHz 12GHz 19/22 dB/K 44-63 dBW 64kbit/s 2Mbit/s Maximum simultaneous channel capacity, sending/receiving Designation 64 kbit/s 2 Mbit/s 8Mbit/s 34Mbit/s DS 1/1 MDVS 1/5 1/3 FVSS - 3/3 - 1/2 TVDS 1/1 1/1 1*/1 1*/1 VROS - - - -/1 *) 8 and 34 Mbit/s cannot be transmitted simultaneously Table 2 Traffic stations for data and video communication, main types Table 1 Link parameters parison is made in a separate panel. This gives the background to an essential part in the choice of system for TELE-X. Link budget It is essential that the transmission services planned via TELE-X have a minimum of errors. A bit error rate (BER) of less than 10 -6 must be obtained for more than 99% of the time during the calendar month with the highest rainfall. In order to achieve this with the small antennas of 1.8 to 2.5 m of the low-cost earth stations, forward error correction, FEC, has been introduced for the 64kbit/s channels. The 2 Mbit/s channels have been equipped with adaptive output power at the earth stations in order to compensate for rain attenuation on the satellite uplink. Table 1 shows nominal link parameters for these two data rates for stations on the outskirts of the coverage area. The link margin to BER = 10 6 is approximately 9dB for 2.5m antennas. The same value applies for 1.8 m antennas in an inner coverage area comprising the central parts of Scandinavia, fig. 1. This gross margin is to cover attenuation and disturbance from rain, antenna align- Up link EIRP/channel (dBW) Space loss, EOC (dB) K (dBW/K) Satellite G/T, EOC (dB/K) Data rate (dBHz) Eb/No (dB) Down link EIRP/channel, EOC, (dBW) Space loss, EOC, (dB) K (dBW/K) Earth station G/T, (dB/K) Data rate (dBHz) Eb/No (dB) Total link Up link Eb/No (dB) Down link Eb/No (dB) Total Eb/No (dB) Theoretical Eb/No for BER=10~ 6 QPSK+differential coding 2 Mbit/s 64 kbit/s + 60.2 + 46.8 -207.8 -207.8 + 228.6 + 228.6 + 7.6 + 7.6 - 63.1 - 49.3* 25.5 + 39.8 -206.7 + 228.6 + 22.0 - 63.1 20.6 25.5 20.6 19.4 10.8 25.9 26.4 -206.7 + 228.6 + 22.0 - 49.3* 21.0 25.9 21.0 19.7 10.8 Gross margin (dB) 8.6 8.9 *) For the data rate modified by the error correcting code to 4/3 x 64 kbit/s ment errors, power variations, scrambling, interference, intermodulation, ageing etc. With the aid of the further 3-4dB improvement provided by FEC or adaptive output power the specified availability is obtained with a satisfactory system margin. These methods can be combined in a subsequent operating system in order to considerably reduce the satellite power for the data/video services while maintaining the same link margin. Earth stations The development within the framework of the TELE-X project comprises a station for the control of the satellite and its payload, and different types of communication stations. The latter are either user stations placed on the subscribers' premises or centrally located main stations. Data and video The main types of traffic stations, which will be included in the first ground network, are: - DS (Data Station), which is a singlechannel solid state station that cannot be extended - MDVS (Multi purpose Data/Video Station), which is a modular multi-channel station. It can be equipped as required, and is available in a stationary and a transportable version. Its range of application includes data communication, two, three or four-party video conferences, tele education and the contribution of stereo radio programs - TVDS (Transportable Video and Data Station) and FVSS (Fixed Video and Sound Station), which are modular transportable or stationary highspeed stations. Applications include data communication, video conferences, outside broadcasting, televising of events and video distribution - VROS (Video Receive Only Station), which is a specialized receiving station that cannot be extended. It can be used for, for example, video theatres and reception of videograms. Table2 gives the capacity of the different stations. Fig. 4 illustrates the technology, in the form of a block diagram of MDVS showing the signal path through a station.
Page 1: ERICSSON REVIEW Integrated Maintena
Page 5 and 6: ERICSSON REVIEW Number 1 1983 Volum
Page 7: The unique facility of a satellite
Page 11 and 12: Technical data for the feeder link
Page 13 and 14: 9 Fig. 7 Mixer and preamplifier The
Page 15 and 16: MATS ENEBORG Fibre Optics and Line
Page 17 and 18: 13 Fig. 6 The structure of system Z
Page 19 and 20: 15 Fig. 9 Part of the junction netw
Page 21 and 22: Fig. 11 Part of an urban and trunk
Page 23 and 24: 19 MATS ENEBORG BJORN JOHANSEN Depa
Page 25 and 26: Fig. 6 An example of a printout of
Page 27 and 28: Technical data for ZAN 101 Maximum
Page 29 and 30: Fig. 14 The Transmission maintenanc
Page 31 and 32: 27 BJORN LENGQUIST PER AKE WIBERG E
Page 33 and 34: 29 Supervision of the digital inter
Page 35 and 36: 31 ules can be used to successively
Page 37 and 38: BENGTJANSSON KENT JOHANSSON TOMMY O
Page 39 and 40: 35 The control individuals are divi
Page 41 and 42: 37 Fig. 10 LPB 110 used in an AXE 1
Page 43 and 44: 39 BENGT LAGERSTEDT Public Telecomm
Page 45 and 46: 41 Fig. 6 With multiplexer ZAH 1.5/
Page 47 and 48: Fig. 10 In this example of the use
Page 49 and 50: 45 HARALD BRANDT ALEKSANDER MARLEVI
Page 51 and 52: 47 Fig. 5 Stored program controlled
Page 53 and 54: 49 quency jumps and no transmission
Page 55 and 56: Hotel Communication System Robert D
Page 57 and 58: 53 Fig. 3 The answer telephones at
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55 The capacity of the hotel PABX i
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57 Fig. 7 The hotel computer, Erics
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Hardening of Telecommunication Netw
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Fig. 3 The electrical and magnetic
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63 Rise Duration time Time Fig. 7 D
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65 Component Microwave diodes Digit
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67 electrical safety regulations, a
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ERICSSON ISSN 0014-0171 Telefonakti
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