Figure 1. Location of DICE installations in Europe and Russia
In the early 1980s, the European Space Agency and a number of its partners in industry and academia, recognised the value of satellite communications in the growing field of video-teleconferencing. It was decided to develop and demonstrate equipment and techniques that could become the platform on which an eventual, operational European Satellite Videoconference Network could be established. A project, called Direct Inter-establishment Communications in Europe (DICE), was initiated on an experimental basis as part of the utilisation programme of ESA's Olympus satellite. The subsequent product and service development have led to the establishment of a high-quality video-conference service, using commercial satellite capacity based on European technology.
The DICE concept was driven by a number of key requirements. Firstly, the system should exploit the inherent advantages of satellite communications in comparison to terrestrial communications:
Secondly,it must be easy to use:
Development of a a viable system based onthe above requirements was undertaken. Indoor videoconference equipment suitable for use in a normal office environment was developed (by Joanneum Research, Austria) and resulted in a range of products that achieve high quality coupled with ease of operation. The Earth station and modem facilities required for the system were developed by Matra Marconi Space (UK), TRL (UK), and Newtec (B).
Following the initial experimental phases of the project, development has been concentrated in two main areas:
This second feature has, in particular, enabled the monitoring of each station's status and the control of access to the satellite to be regulated on a network-wide basis.
DICE was originally deployed in 1990 as an experimental system using the Olympus satellite. For the first three years, it was operated in the 20/30 Ghz frequency bands. Earth stations for the system were located at ESTEC in The Netherlands; Joanneum Research in Graz, Austria; Matra Marconi at Portsmouth in the United Kingdom; Newtec in Belgium; British Aerospace at Stevenage in the United Kingdom and Matra Marconi at Toulouse in France. During those three years, the experiment operated successfully and considerable experience was obtained both in the technical and operational areas.
During that experimental phase, the system was demonstrated to the public at several large international conferences: the IAF Congress in Dresden in 1990 and in Graz in 1993; TELECOM-91 in Geneva and TELECOM-92 in Budapest; and the Olympus Conference in Seville in 1993. In addition, trans-Atlantic links were made during the World Environmental Conference in 1991 to and from Rio de Janeiro via Olympus's 20/30 GHz payload.
The most spectacular applications were during the Austrian AustroMir-91 and the German Mir-92 missions to the Russian Space Station 'Mir'. The Mission Control Centre near Moscow was connected via satellite and DICE to several sites in Western Europe. Experimenters were able to monitor the conduct of space experiments and speak interactively with the astronauts on board Mir. In addition, discussions between German, Russian and Austrian high-level politicians were conducted via DICE during the missions.
Following the end of the Olympus programme in 1993, ESA leased Ku-band capacity on a Eutelsat satellite and transferred DICE operations to that capacity. The existing sites were modified to work in the Ku band 14 GHz up path/11 GHz down path and the Earth stations had to be replaced at each location.
The network was put on a more operational footing and Matra Marconi took over the system as service provider. That company was also encouraged to form a commercial alliance with Joanneum Research, whereby Matra Marconi would supply the Earth stations and the overall service provision and Joanneum would supply the indoor videoconferencing equipment.
This arrangement has worked well and there are now numerous DICE sites throughout Western Europe and in Russia (Fig. 1). The sites in Russia and Germany were established when ESA became involved in the EuroMir project with Russia (Fig. 2). To allow all the control centres associated with the mission to maintain contact with each other, DICE was selected to provide simultaneous multi-point links using video, voice and data services
In addition, discussions have recently been held with the Swedish Space Corporation, which operates a network of four video-teleconference sites in Scandinavia, concerning the possibility of joining the two systems together to make an overall European network of stations.
The whole network operation and management operation is now being made commercial. ESA will continue to provide development support to bring new products and service improvements into the system. However, the deployment of new stations and the sale of the standard service will be a task for the companies involved.
Figure 1. Location of DICE installations in Europe and Russia
Figure 2. A DICE Earth station being installed near Moscow
In a DICE teleconference, any four sites may be simultaneously linked by satellite with 'continuous presence' video, audio, computer graphics and data facilities. With 'continuous presence', all participants can see and hear each other throughout the videoconference. This helps to create an environment similar to that of a conventional round-table meeting. Notes and sketches may also be distributed using the document transmission facilities. Figure 3 shows a typical DICE conference in progress.
Figure 3. A DICE videoconference in progress, using the conference-room version of the system
The audio and video system
In the standard DICE configuration, the videoconferencing equipment is housed in two compact, transportable roll-about units, one for the video and sound, and the other for the graphics. In this way, videoconferencing facilities can be easily and quickly set up in ordinary offices, meeting rooms or laboratories.Particular attention has been paid to the sound system for DICE. By using special desktop microphones, a 7 kHz bandwidth audio channel and acoustic echo suppressor, it has been possible to achieve a good sound quality that is resistant to the local environment. The system is therefore not sensitive to the type of room used and provides a relaxed atmosphere for the users. The picture quality available is consistent with the best commercially available encoders/decoders (codecs).
The picture quality is regularly upgraded to incorporate the latest codec technology available on the market. The transmission speed can be set to a wide range of bit rates, from 64 kbit/s up to 2048 kbit/s. The bit rate normally used is 384 kbit/s.
A desktop version has recently been added to the DICE range of equipment (Fig. 4). It is based on a standard, tower-type personal computer (PC) into which the video, audio and graphics equipment is integrated. The PC's video monitor is adapted to become a multimedia monitor by the addition of a small camera, dual loudspeakers and a microphone. All the equipment is integrated into a unified design. The PC's screen functions in a Windows environment and is able to provide, on one screen, single or multiple pictures from up to three remote locations as well as remote graphics. DICE's continuous presence capability is thus available with the desktop version, when required.
Figure 4. The desktop version of the DICE equipment, showing two remote sites simultaneously
Another product in the DICE equipment range, the conference room system, is designed for use in existing conference rooms. In this version, all the electronic equipment is housed in a small cabinet which can be stored in a corner of the room. The conference room's existing audio system is used to interface with the DICE system. This enables all of the room's audio facilities, such as simultaneous translation, to be used without modification. If the room does not have an audio system, radio microphones are provided for table use so that trailing wires are avoided. Video is displayed on standard monitors or via the room's existing projection system. The camera is wall-mounted and uses a remote-controlled pan/tilt head. As with all DICE equipment, the equipment is very simple to install and operate. Cabling has been minimised so that the conference room decor and atmosphere are not disturbed.
DICE uses the latest technology in video compression. The codec boards, fully compliant to the international H.320/H.261 video-conferencing standard, are integrated in a PC into which the software configuration is loaded. This allows easy adaption to special user requirements and future enhancements. Up to three codecs can be installed in each PC.
All user equipment is connected by fibre-optics cabletothe indoorequipment that ispart of the VSAT (modems). The fibre interfaces are installed in the codec. No heavy linking cables are needed, which makes the system easy and straightforward to set up and use.
The graphics system
In contrast to conventional videoconference systems in which document cameras are used, DICE has special computer graphics facilities for document transfer during a meeting. The system can be used as a high-quality fax machine to broadcast sketches, drawings or text to the remote screens or printers for reproduction. A resolution of up to 300 dpi is supported. The local mouse position is sent to the remote stations and displayed there to support interactive discussions. Documents can be scanned in or, if already available in electronically readable format, directly transferred as files. DOS and UNIX file formats are supported. A selective ARQ protocol has been implemented for efficient use of the satellite channel and error-free transmission. A 64 kbit/s data channel multiplexed with digital video and audio in the codec is used. To minimise transfer times, data compression techniques are used.
Electronic viewgraph presentations are also possible on a multi-site basis. The transparencies to be used in the presentation are transferred page by page before the meeting, stored on each remote station's local disk, and retrieved from the local disk during the presentation. Using clicks of the mouse, the presenter may flip both forward and backward through the pages, without any significant transmission delay.
The VSAT
The VSAT consists of a Radio Frequency (RF) unit, Intermediate Frequency (IF) unit and Solid State Power Amplifiers (SSPA). The RF unit is positioned at the focus of a 2.4 meter, offset-fed antenna. Together with the SSPA, this produces 8 watts of power giving an EIRP of 57.7 dBW. The RF unit also contains the LNB and, together with the antenna and feed, gives a G/T of 24.4 dB/K.
The IF unit is an up-and-down converter from 70 MHz to the L-band and vice versa. It also contains a monitor and control microprocessor that can be controlled locally or by remote control over the satellite link via the Station Supervisory Unit. Table 1 provides a summery of the VSAT parameters.
Transmit Receive
Transmit power (EIRP) 57.5 dB/W
Figure of merit (G/T) 24.4 dB (1/K)
RF frequency range 14.0-14.5 GHz 12.5-12.75 GHz
IF frequency range 70± 18 MHz 70± 18 MHz
Tuning 1 MHz steps 1 MHz steps
Tuning in the modems 22.5 kHz steps 22.5 kHz steps
IF interface level -30 dBm + 22 dBm
Satellite modems
For a four-way conference, three satellite modems are necessary. The modems are standard IBS types with a 70 MHz interface. They are variable in rate, ranging from 64 to 2048 kbit/s, and provide QPSK half-rate forward error correction (FEC) Viterbi encoding/decoding.
Station Supervisory Unit (SSU)
The SSU is the remote controller of the VSAT. It receives commands from a Network Manage-ment and Control Centre (presently located in Portsmouth, UK) on a 9.6 kbit/s carrier which is received at the VSAT by a data receiver/ demodulator. The SSU was developed by Matra Marconi Space and has proven most successful in the field. The unit supports a number of multi-drop buses that are used to control the VSAT, the three modems and a third separate bus, which could be used to control any other customer-furnished equipment.
The status of the units connected to the SSU is monitored and passed back to the control centre, using the IBS Engineering Service Circuit (RSC) of the satellite modems. This means that a separate carrier for status monitoring is not required.
Frequency plan and link performance
The DICE network is presently using fractional transponder capacity on Channel 41 of Eutelsat II-F4 at 7° East. According to the lease arrangement, one sixteenth of the transponder bandwidth and power, corresponding to 2.25 MHz and 27.76 dBW respectively, is available to the satellite network. The transmission system has been designed such that the available transponder resources are used in a well-balanced fashion, taking into account reasonable size of the Earth-station antenna and transmit power and a satellite link margin of approximately 2 dB.
In a total bandwidth of 2.25 MHz, four carriers with an information bit rate of 384 kbit/s can be allocated, which enables one four-site or two independent point-to-point videoconferences. Each carrier is QPSK modulated with a half-rate forward error correction (FEC) and occupies a bandwidth of 536 kHz, with a 16/15 overhead rate for the engineering channel.
The required link performance (Eb/No > or = 7dB) and propagation margins of 2 dB, can be achieved with Earth-station antenna diameters of 2.4 m and a transmit power of 8 watts, which can be considered as a good compromise between Earth station investment and transponder lease cost. The satellite link performance is, to a large extent, determined by interference noise caused by other users operating on the cross-polar transponder or on adjacent channels, or even on adjacent satellites in the same frequency band.
The DICE network is fulfilling a valuable function by interconnecting numerous European establishments. However, it can only continue to be successful if it grows and accommodates more videoconference addresses. To this end, the DICE participants are actively discussing with other European satellite videoconference operators the possibility of integrating their networks with DICE so as to form a network of major proportions. Compatibility trials have already taken place and have shown that such interactivity is possible. The establishment of an overall operating organisation to run the system is now being considered.
Improvements to the connectivity to the terrestrial system, the ISDN, are also currently underway. Satellite videoconferencing can provide a powerful overlay to the terrestrial network by extending its reach to areas not presently covered. Conversely, the ISDN will greatly increase the videoconference locations accessible from DICE.
A further useful feature now being introduced, is to add automatic scheduling to the system's Network Management Control Centre (NMC). Reservations for videoconferences can then be programmed into the NMC, together with the network configuration required. At the appointed time, the NMC will automatically configure all stations participating in the conference and switch them on. At the end of the session, they will automatically be switched off.
The DICE system has been a valuable spin-off from the work carried out in ESA's Olympus utilisation programme. It is an operating system with many sites, it has a good reputation for quality of sound and video, and the level of convenience that it provides to users continues to be demonstrated daily.
As codecs continue to develop, it is foreseen that their price will fall, allowing further reductions in the cost of videoconferencing. Also, with the launch of more commercial satellites such as PanAmSat 3 and Orion, it is expected that space segment costs will also decrease. Depending on the distance between the two communicating sites, satellite time is already cheaper than time on the terrestrial-based system ISDN 2. The crossover point at present is approximately 1000 km depending on the carrier and the routing. It is forecast that the ISDN prices will also fall so it will be interesting to watch the development of future tariffs.
It is most probable that the terrestrial and the satellite-based systems will continue to co-exist, each providing service in the areas in which it offers particular advantages and with considerable interconnectivity between them.
ESA Bulletin Nr. 80.