Field Trial of Optical Fibre Cable-TV System Optical Fibre System for ...

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155 KURT BERGSTEN Networks Department Central Administration of Swedish Telecommunications GERHARD GOBL Public Telecommunications Division Telefonaktiebolaget LM Ericsson Conventional cable-TV Coaxial cable and broadband amplifiers are used for conventional cable-TV systems. The networks have almost exclusively a tree and branch structure, which has proved to be very economical for the distribution of television and sound radio programs from a head end to the households. A conventional cable-TV network has the following levels: Trunk network, which is the network between head ends if several such head ends are linked together. The link between the satellite ground ! station and a head end is also a part of the trunk i network. /l Primary and secondary network, comprising J the networks between the head end and the i points where the signals are delivered to the I distribution networks. I Distribution network, which is constructed in a residential area or premises. The distribution centre in a residential area at Skarpnäck about 10 km from the centre of Stockholm. The 3 km long cable is used to transmit the TV and sound radio programs which are fed in at the head end to a subcentre at Skarpnäck. The transmission is digital. In the subcentre the signals are converted back to analog form for further distribution over a conventional cable-TV system to the households in the area. The field trial has since been extended by an additional fibreoptic cable to offer the same programs as at Skarpnäck to a residential area at Enskededalen, about 4.5 km from the main centre at Farsta. Fig. 1 shows the fibre-optic network serving Skarpnäck and Enskededalen. The network may be seen as a first stage in the construction of a future broadband video, audio, data and text communication network. The figure also shows a planned extension whereby a satellite antenna on the Kaknäs Tower is connected to the Skarpnäck network. Programs received via INTELSAT and other satellites may then be distributed over the cable-TV network. Objectives The introduction of new products, e.g. transmission systems, in telecommunication networks is nearly always preceded by more or less extensive field trials aimed at detecting any weaknesses in the system in good time so that networks correspond generally to today's central antenna networks. Base network, is a common name for trunk, primary and secondary networks. The Swedish Telecommunications Administration is today constructing cable-TV networks at all these levels. The main emphasis is on base networks while distribution networks will be constructed principally in new residential areas. Broadband networks In a future service-integrated broadband network optical fibres will be used also for the subscriber lines. The networks will have a starshaped structure and every subscriber will be connected to a central point in the network where there is switching equipment for different services such as telephony, television and sound radio programs. In such a network only the programs selected by the subscriber at a particular time will be transmitted. they can be put right before the system is introduced on a wider scale. A field trial also provides valuable experience and ideas for future improvements. The aimof the field trial is to gain experience of - digitization of television and sound radio signals, comprising methods for digitization, encoding and reduction of redundancy in TV pictures - transmission engineering, comprising, modulation methods, the capacity and quality of the link, cost optimization, circuitry and choice of components - installation techniques, comprising the handling of fibre cables in base networks at branches, termination, splicing, fault tracing and repair - system engineering with network topology, integrated services, mix of distributive and interactive services, control and supervision as well as economy - operation and maintenance of fibreoptic cable-TV systems, comprising the collection, transmission and presentation of alarms. Selection of the route A residential area in Skarpnäck was chosen for the trial. In this area some 4000 flats are being built during the period 1983-1987, and also about 150 small houses. South of the area some light industries will be located. The Farsta automatic exchange about 3 km from Skarpnäck has been selected as the head end. Along the entire route between the Farsta exchange and Skarpnäck there are ducts to be shared by metallic telephony and fibre cables, resulting in major cost reductions. Along the route there are also other residential areas, e.g. Norra Sköndal and Södra Sköndal, which henceforth may receive TV and sound radio signals from the main centre by optical tapping of the fibre-optic cable. In 1984 an existing residential area in Enskededalen with some 2000 flats was included in the trial area. System structure Digital transmission The block diagram of the trial plant is shown in fig. 2. Two optical cables, each
Head end (HC] 280 Mbit/s Farsta automatic exchange Enskede Subcentre (UC) Skarpnäck Fig. 2 Block diagram of the digital trial plant between Farsta and Skarpnäck Fig. 3 A branching point on the optical fibre cable between Farsta and Skarpnäck containing 12 fibres, have been laid between the Farsta automatic exchange and the subcentre at Skarpnäck. The cables are of standard size. The large number of fibres was selected with future experiments in mind. The fibre-optic cable has been provided with optical taps so that other residential areas along the route can be supplied with TV and sound radio programs from the main centre. There are three optical taps in tandem, see fig. 2. A branching point is shown in fig. 3. To gain experience of the effect of different branching methods on the transmission characteristics two different types of coupler have been installed, one mode-selective (fused type) and one non-mode-selective (lens and mirror). The digital fibre-optic transmission system ZAV280/4, which is described separately, is used for the transmission. ZAV280/4 transmits 4 television channels and 16 mono sound channels over each fibre. Each video signal requires 67.2 Mbit/s and each sound channel 480 kbit/s. The gross bit rate on each fibre is 280 Mbit/s. In the subcentre at Skarpnäck the digital TV and sound radio signals are converted to analog signals and placed in their respective frequency positions in the 47-400 MHz band which is transmitted to the households on coaxial cable. The fibres are of standard multimode graded index type with the dimensions 50/125 /u.m. The bandwidth-length product is >500 MHzx km. The transmission wavelength is 850 nm. The trial plant was put into operation in October 1984 with transmission of 4 TV channels from the head end at Farsta to Skarpnäck. In February 1985 the capacity on the route was increased to comprise three 280 Mbit/s line systems and six TV encoders/decoders for 70 Mbit/s. A couple of encoders/decoders for 140 Mbit/s have also been acquired for reference purposes. In March 1985 a 280 Mbit/s line system and four TV encoders/decoders for 70 Mbit/s were installed on the route between the Farsta and Enskede automatic exchanges. The fibre-optic trunk line built up of modules comprising four television channels perfibre, which means that the plant can easily be extended for transmission of the 32 TV channels and 2* stereophonic sound channels for which the conventional cable-TV plant at Skarpnäck is designed. In the summer of 1985 the transmission capacity on the Farsta-Skarpnäck anc Farsta-Enskede routes amounted to digital TV channels and 12 digital sterec channels. Interiors from the main centre and subcentre are shown in fig. 4 and 5.
Page 1 and 2: ERICSSON REVIEW 4 1985 Field Trial
Page 3: Trial of Optical Fibre Cable-TV Sys
Page 7 and 8: 158 Switching equipment Fig. 7 Futu
Page 9 and 10: 160 Fig. 10 The teleconference room
Page 11 and 12: GERHARD GOBL Public Telecommunicati
Page 13 and 14: Fig. 5, above left Two-channel A/D
Page 15 and 16: Digital input signals Digital outpu
Page 17 and 18: Power ZAV 280/4 has individual powe
Page 19 and 20: Wavelength Division Multiplexing fo
Page 21 and 22: 172 Subscriber side BP-890 Controll
Page 23 and 24: Fig. 8 Transmission characteristics
Page 25 and 26: Most computer cabinets are 19" wide
Page 27 and 28: 178 Fig. 5 Modems in Series 7 Modem
Page 29 and 30: Computer Aided Production of Plasti
Page 31 and 32: Fig. 4 Product geometry displayed o
Page 33 and 34: Rectifier for Mobile Telephone Syst
Page 35 and 36: I OR | OFU OS I CMUP HlsHi W±±±h
Page 37 and 38: 188 Fig. 6 The rectifier with the o
Page 39 and 40: Fig. 9 Rectifier BMJ A01 001 with t
Page 41 and 42: The Renewal of the London Undergrou
Page 43 and 44: 194 Rickmansworth, and the Loughton
Page 45 and 46: 196 Fig. 5 Optical fibre cable rout
Page 47 and 48: 198 In planning the optical fibre n
Page 49 and 50: Fig. 9 The digital telephone DIAVOX
Page 51 and 52: 202 Fig. 11 Transmission equipment
Page 53 and 54: 204 Fig. 2 Automatic testing of mul
Page 55 and 56:
206 Relative occurrence for F Fig.
Page 57 and 58:
Fig. 5 Field testing of a 140 Mbit/
Page 59 and 60:
210 Fig. 7 The system down time as
Page 61 and 62:
MTBF (years) Equipment 2-5 Transmul
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