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DEVELOPMENT OF OPTICAL VlDEOlAUDlO SIGNAL DISTRIBUTION NETWORK OF FUJI TELEVISION’S NEW BROADCAST CENTER

T. Shiozawa’, H. Makita’, M. Murakami’, N. Shimosaka‘, T. Tan-no’, K. Ueno’, C. Kamise2, and S. Ando2

NEC Corporation, Japan and *Fuji Television Network Inc., Japan 1

ABSTRACT

Fuji Television’s new broadcast center facilities have recently been installed and are now in fully operational, starting in March 1997. The new broadcast center employs a newly developed optical videolaudio signal distribution network. This paper describes the system structure and performance of the optical network. A Wavelength-Division and Time Division hybrid multiplexed (WD/TD) optical network has been applied to the broadcast center. This type of optical network is attractive for a broadcast center application, because of its large capacity, multiple format handling, and flexible operation capabilities. The optical network utilizes 16- channel Wavelength-Division Multiplexing (WDM) technology and 16-channel Time Division Multiplexing (TDM) technology for 143Mb/s NTSC composite video signals (TDM high-way speed: 2.29Gb/s). By using these technologies, the optical network distributes about 150 digital NTSC composite video combined with , audio signals, together with about 15 HDTV signals (1.5Gb/s), to 20 studios and control rooms. This new system of operation has drastically reduced the operator work load in the signal distribution center.

INTRODUCTION

Today’s TV broadcast centers require large capacity and flexible routing networks for handling uncompressed serial digital video signals, whose speed is in the hundreds of Mb/s. In this regard, optical technologies have been shown to offer great promise for increasing both capacity and flexibility of networks(l)(Z). The development and installation of facilities of Fuji Television’s new broadcast center have recently been completed, and the facilities are now in fully operational, starting in March 1997. The new broadcast center employs optical videolaudio signal distribution network. A Wavelength-Division and Time Division hybrid multiplexed (WD/TD) optical network(3)-(6) has been applied to the broadcast center. To the authors’ knowledge, this is the world first practical implementation of an optical network to a broadcast center. This paper describes the design concept of the new broadcast center and performance of the developed optical network.

THE BASIC DESIGN CONCEPT OF DlSTRlBUTlON/TRANSMlSSION SYSTEMS FOR THE NEW BROADCAST STATION

The following characteristics would be required for the video/audio signal distribution network in a broadcast center.

1) High bandwidth for treating uncompressed serial digital video signals, whose speed is in the hundreds of Mb/s. Multiple-format capability; Even at present, there are many broadcasting formats in Japan, such as Standard Definition TV (SDTV, NTSC), Enhanced Definition TV (EDTV), and High Definition TV (HDTV). In future, new kinds of format including compression format such as MPEG, would be added. Flexibility is required especially for distribution networks for application of these broadcasting formats and the future all-HDTV studios. This is because, the distribution/transmission system is the most important basic infrastructure in broadcast stations.

Large capacity and gradual expandability.

2)

3) Flexibility in operation. 4)

The following performances are required for the video/audio signal distribution network in the new broadcast center.

1 Video signal formats SDTV (NTSC Composite SMPTE259M,

1 43 M b/s)

1.485GbIs). HDTV (SMPTE292M/BTA S-O04A,

.The number of video sources SDTV: 150 (future >200) H DTV: 15 (future > 20)

International Broadcasting Convention, 12-16 September 1997 Conference Publication No. 447, 0 IEE, 1997

236

=The number of destinations (studios or control rooms): 20 (future >50)

Optical networks are very attractive, while, using conventional switching systems, a huge distribution system would be required to satisfy these requirements.

Generally, optical networks have the following features (1)-(4);

Good performance is available in long distance transmission of high speed serial digital signals. An optical fiber is lightweight and flexible for wiring. The optical network has immunity against electromagnetic induction (EMI).

In addition, to satisfy the requirements described above, an optical network structure has been optimally designed. Figure 1 shows the structure of the optical network introduced in the new broadcast center. This structure uses two sets of Wavelength-Division and Time-Division hybrid multiplexed (WD/TD) optical network, together with 2x1 photonic switch matrices(7). Serial digital video signals, combined with audio signals, are Time- Division Multiplexed (TDM) into high speed signals at the signal distribution center. Each individual TDM signal is applied to an optical transmitter, which has its unique wavelength. The TDM optical signals with unique wavelengths are Wavelength-Division Multiplexed (WDM) using a star coupler to form WD and TD hybrid multiplexed signals. Two sets of WDRD hybrid multiplexed optical signal are distributed to receiver units located studios or control rooms, by using two optical fiber cables. In each receiver unit, desired video signals can be selected by using tunable wavelength filters and TD-selectors,

after selecting one star coupler system out of two by using 2x1 photonic switches.

This type of network has the following important features. First, the fact, that signals are transmitted on individually unique wavelengths, allows the system to handle simultaneously a variety of different video signal formats (HDTV, EDTV, SDTV, Others). Second, each receiver unit can freely and directly access all video/audio signals within the network. This allows a flexible operation control at various places and a reduction of the operator work load in the signal distribution center. The design is, then, extremely flexible in its operation. In addition, the use of WDM in combination with TDM allows the network to handle the required large number of video signals with a relatively small number of WD and TD channels, i.e. a practical system can be produced at present levels of optical technologies. The use of two sets of WD/TD network can enhance the system redundancy as well as network capacity. Some important signals may be transmitted using both of two WD/TD networks. Therefore, system reliability can be enhanced without preparing special standby systems.

The operation of the network has been designed to be controlled through a conventional Ether-net type Local Area Network (LAN). The video/audio signal information is also processed in the LAN.

OPTICAL NETWORK DESIGN

The following design considerations have been made to satisfy the requirements.

I 2x1 Photonic SwitcQ Tunable Wavelength Filter TD-Multiplexer

I Selected Digital Video

TX Card Signals

#2-16 RX Card #512

Figure 1. Network structure

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TDM System

Standardized digital video signals usually show large mark density variation. This may cause significant problems especially when the video signals are TD- multiplexed and transmitted by using AC-coupled optical transmission equipment, which are usually used in high speed trunk line systems. To overcome this problem, we have chosen to apply the scramble techni ue, based on the generation polynomial x17+x +I , to the inputloutput video signals for the TDM system. Although the Synchronous Digital Hierarchy (SDH) system is widely used in trunk line systems, it seems to be too complicated and expensive for a TV broadcast center network application. The simple bit-by-bit TDM technique is employed in this WD/TD network. For achieving frame synchronization, one of input channels for a TD multiplexer is used as the frame identifier. The frame identifier signal .is set to be complimentary to one adjacent signal in a TDM frame. This contributes also to reduction of the mark density variation. These functions can easily be realized by using integrated circuits (ICs) operated at a signal speed of 143Mbls. The TDM system described here has been proposed for ITU-R as a candidate for standardization(8).

s

WDM System and Optical Power Budget

Optical transmission systems, presently available with a reasonable cost, have a signal speed of about 2.4Gb/s. This means that the TDM highway speed should not exceed 2.4Gb/s to reduce the system cost. We have chosen to use 16: 1 TD-multiplexer /demultiplexer (MUNDMUX) to transmit 15 channels of 143Mb/s NTSC composite video signals, together with a frame identifier, by using one WD channel (TDM highway speed of 2.29Gb/s). Since signal speed of 1.485Gb/s is too high to employ a TDM technique, one WD channel is dedicated for one HDTV signal. While 32 channel WDM is possible within the Er3'- Doped Fiber Amplifier (EDFA) gain bandwidth, by employing a practical WD channel spacing of 1 nm, such a design would require WDM transmitters whose wavelengths were distributed over a significantly wide range of wavelength (about 30nm). Since these devices would be prohibitively expensive at the moment of development, we have chosen the Inm spaced 16-channel WDM system. By using the technologies, the network depicted in Fig. 1 can be used for distributing 480 channels of NTSC video signals or 32 channels of HDTV signals. The maximum throughput reaches, therefore, as high as 73Gb/s.

As depicted in Fig.1, each EDFA is inserted between optical transmitter and star coupler. This configuration allows the use of conventional and inexpensive EDFAs, which have been developed for a single channel amplification. In addition, the optical power variation among wavelength channels can be compensated for at the EDFA outputs by applying Automatic Power Control (APC) scheme to EDFAs.

TABLE 1 shows the optical power budget design for the network. As an optical transmitter, a DFB LD and an Electro-Absorption type (EA) optical modulator(8) is assumed. The tunable filter is a Fabry-Perot type and its crosstalk level (@lnm away from the transmission peak) is assumed to be less than -15dB. When the APC scheme is applied to EDFAs, optical power budget from EDFA output to optical receiver is to be considered. As can be seen from TABLE 1, system margin as large as 7dB is expected even with the worst case.

EO Output ( a m ) EDFA Output (dBm)

0.0 14.5

Receiver Sencitivity (@lOYBER, dBm) -32 0 Allowable Loss (dB) 46 5

Worst Case Optical Loss (dB)

/

J

16x64 Starcoupler 20 0 Ikm Optical Fiber Cable 2 0

1x8 Optical Coupler 11 0 1x2 Photonic Swtch 1 0 Tunable Wavelength Filter 4 0

(including connectors)

1x2 Optical Coupler 1 0

EDFA Noise negligible Inter Channel Crosstalk 0 5

Power Penalty (dB)

Total @oss+Penalty, dB) 39 5

Svstem Marein (dB) 7 0

TABLE 1 - Optical power budget.

OPTICAL NETWORK DEVELOPMENT

The WD/TD network for the new TV broadcast center of Fuji Television has been developed based on the design described above. The functional diagram for the transmitter (TX) and receiver (RX) cards for NTSC video signals are shown in Fig. 2 and Fig. 3, respectively. For achieving functions of bit/frame synchronization, scramble/descramble, and TD-channel selection, two Gate-Arrays have been developed by using ECL technology. For the MUNDMUXs, GaAs ICs

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were used(5). The card measures 380" by 270". The appearance of the system rack is shown in Fig. 4. Each TX, Optical amplifier, and RX rack contains 8 cards.

The network performance has been tested by 16 channel transmission experiment using pseudo- random patterns at a rate of 2.29Gb/s. The bit error rate was measured after WD channel selection with a tunable wavelength filter. Figure

143Mbls Vid Sig

I I Figure 2. TX card diagram

- -

5 shows the optical spectrum after the filter. The crosstalk levels at the adjacent channels are as low as -18dB. The results for the bit error rate measurement are depicted in Fig. 6. The receiver sensitivities at the bit error rate of IO-' for back-to- back and after WD channel selection were - 32.0dBm and -31.8dBm, respectively. The power penalty due to 16 WD channel simultaneous operation is as small as 0.2dB.

r 1

Figure 3. RX card diagram

TX Rack 8 Cards per Rack

Optical Amplifier Rack

16x64 Star Copler 1 16x64 Starcoupler 2

8 EDFA Cards per Rack

RX Rack 8 RX Cards per Rack

Figure 4. Network equipment outlook

Figure 5. Optical spectrum

after tunable wavelength filter

1 o5

1 O6

f

-40 -35 -30 Received Power (dBm) -+

Figure 6 . Bit error measurement results

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The photograph of the operation room for the signal distribution center is depicted in Fig. 7. The system operation is performed by using terminals based on personal computers. Figure 8 shows a photograph of racks in the signal distribution center. Each of two racks on this side contains an optical transmitter unit, a star-coupler, and an optical amplifier unit. The third rack consists of optical receiver units, each of which contains 8 RX cards. Taking advantage of light weight and flexible nature of optical fiber cables comparing with coax cable, downsizing of the all facilities has been achieved in the new broadcast center.

CONCLUSION

The basic design concept of the video/audio distribution network in the Fuji Television's new broadcast center has been explained. Based on the basic design concept, the WD/TD optical network for applying the new broadcast center has been designed and developed. The network was designed to distribute about 150 channels of NTSC composite video signal as well as 15 HDTV signals. The network has already been installed in the new broadcast center and now under practical operation .

REFERENCES

1. A. Oliphant et al., SMPTE J., vol. 96, 1987. pp. 660 to 666. 2. K. J. Hood et al., J. Lightwave Techol. vol. 11, No. 5/6, 1993. pp. 680 to 687. 3. N. Shimosaka et al., ECOC/IOOC91, Sept. 1991, Paris, WeB9-3. 4. M. Misono et al., ECOC95, Sept. 1995, Brussels, Tu.B.1.6. 5. M. Fujiwara et al., IOOC95, June 1995, Hong Kong, TuA1-1. 6. C. Kamise et al., SMPTE J. ~01.106, 1997. pp. 117 to 122. 7. K. Takagi et al., JC-CNSS'94, July 1994. Taejon, Korea, pp. 367 to 372. 8. ITU-R Document 11-2/10-E Annex 1, 12 March 1996. 9. K. Komatsu et al., Optoelectronics -Device and Technologies-, vo1.9, No.2, 1994. pp. 241 to 250.

ACKNOWLEDGMENTS

The authors would like to express their gratitude to and their colleagues contributed to this work and S. Horie and M. Nagata of Fuji Television and H. Higashi, and Y. Ushiyama of NEC Corporation for their continuous encouragement.

Figure 7. Operation room of signal distribution center

Figure 8. Racks for optical transmitter, amplifier, star coupler, and optical receiver units in the signal distribution center