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

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TVT/HC Farsta p F M ii P F M Farsta automatic exchange Conference switch ET ET PfM \ /JV /J^adio UC Skarpnäck PFM © ® Demonstration room Skarpnäck Video conference room Fig. 8 Block diagram showing how the video conference and demonstration rooms are connected over optical fibres to the audio and video switching equipment at the subcentre forms part of a video network, working with analog circuits, that has been constructed in Stockholm. On fibre is used for the transmission of video and audio signals to the video conference room, the other for the transmission of the camera signal and sound in the opposite direction. For these signals, too, analog transmission with pulse frequency modulated systems is used. From the video conference room conferences can be held with every other video conference room connected to the Swedish Administration's video network or with any of the more than 20 public video conference rooms that the Swedish Administration has in operation in Sweden. The Skarpnäck TV switching unit has a capacity of 30 incoming TV and as many stereo signals. There are ten outgoing lines available, so some other locations can be connected to the switching equipment, e.g. some of the schools in the area and the library. Experience gained and further development Picture coding The selected encoding method, adaptive differential PCM (ADPCM), provides an excellent picture quality. This was confirmed in a test made by the Swedish Telecommunications Administration and Swedish Television. A subjective quality assessment was made with six program sections using the method of comparing pairs of pictures with small differences in quality. The test subjects were divided into two groups, one consisting of eight video experts and the other of 16 "ordinary" TV viewers. The expert group recorded a certain deterioration of the picture, whereas the viewer group could see no significant deterioration. The opinion was that 70 Mbit/s ADPCM encoders can very well be used for the distribution of PAL video signals. The encoder also transmits teletext signals satisfactorily. This ADPCM encoder is intended for transmission over a medium with low bit error rate (BER), e.g. optical fibre circuits, and functions well down to a BER value of c. 10~ 7 . Passive branching The installation of the passive fibre couplers was done using the same routines as employed for other cable installations. The couplers were placed in their own splicing box, furnished with stub cables, which were then spliced to the fibre cables. The difference between mode-selective and non-mode-selective
160 Fig. 10 The teleconference room at Skarpnäck couplers could be observed, especially on the first coupler which is only a few tens of metres from the transmitter. The mode-selective (fused) coupler exhibited a lower effective coupling factor measured at the end of the cable owing to the fact that mainly higher modes are coupled into the secondary fibre and these are then subjected to higher attenuation. With the non-mode-selective coupler (lens/mirror) such phenomena are avoided. Evaluation of the couplers is continuing in the field trial in order to produce reliable data for the planning of networks with passive branching. Transmission distance The transmission of 280 Mbit/s over a multimode fibre is limited mainly by the mode dispersion of the fibre, but material dispersion cannot be entirely disregarded. With wideband fibers (more than 800 MHzxkm) a repeater spacing of 7-8 km is normally attained. This is sufficient for the primary network and in most cases also for the trunk network. Most administrations today install mainly single-mode fibres in their fibre-optic networks and a single-mode version of ZAV 280/4 is also available. The dispersion limitation is thereby eliminated and the range of the system will depend almost entirely on the attenuation of the route. The single-mode version of ZAV 280/4 operates at 1300 nm and will permit repeater spacings of at least 25- 30 km. In the long distance network video transmission will take place mainly on 565 Mbit/s line systems with 8 TV channels per fibre. Operation and maintenance of the hybrid network An important task for the field trial is to evaluate the methods for operation and maintenance of cable-TV networks. At Skarpnäck alarm collection is done by an alarm collection network which transmits the alarm signals to the Swedish Administration's supervisory centre, from which the necessary measures are ordered. Referenses 1. Gobi, G. and Jacobson, S.: Optics! Fibre System for Digital Cable- iv Transmission, ZAV280/4. Ericsson Rev. 62 (1985):3, pp. 161-169. 2. Hansson, A.-K. and Jacobson, »•• Wavelength Division Multiplexing w Fibre-Optic Subscriber lines. Encsso Rev. 62(1985):3, pp. 170-174.
Page 1 and 2: ERICSSON REVIEW 4 1985 Field Trial
Page 3 and 4: Trial of Optical Fibre Cable-TV Sys
Page 5 and 6: Head end (HC] 280 Mbit/s Farsta aut
Page 7: 158 Switching equipment Fig. 7 Futu
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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