Rep. Itu-r bt. 2025 report itu-r b
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- 2.4.1.4.4.4 Map showing locations of test points
- 2.4.1.4.4.5 Service Range
- 2.4.1.5 General conclusions
- 2.4.2 Digisat demonstration
2.4.1.4.4.3 Test points locationTABLE 2.7 Locations of the 26 test points in and around Metz
All the points are located in an area where the directional return link receiving antenna has its maximal gain. 2.4.1.4.4.4 Map showing locations of test points
MAP 2.1 [2025-map021] 2.4.1.4.4.5 Service RangeThe service range given in Fig. 2.11, for the four SFDMA transmission modes, can be calculated using Table 2.8 that includes RF figures derived from current DVB-T user-side assumptions (as antenna locations, gains, etc., in the fixed and portable modes) and propagation model assessments for rural and urban areas. 
FIGURE 2.11 [2025-0211] TABLE 2.8 RF figures for the service area determination in the four transmission modes
2.4.1.5 General conclusions– Two field trials of the SFDMA UHF return channel were set up in Rennes and in Metz (France), at real and operational high-power broadcast transmitting stations; their configurations are described above. – The experimentation using both the Metz and Rennes test platforms has shown results confirming the general feasibility of the SFDMA system as a return link access in UHF channels; furthermore: – the feasibility of the reception of infinitesimal signals (–120, –130 dBm for a 1 kHz bandwidth) at a principal UHF broadcasting site (with ERP transmitted powers in excess of a Megawatt) has been proven, – the results are consistent with the theoretical calculations made on the RF parameters and the proposed transmission power required to enable a service range compatible with the TV reception: in a rural environment and in the most secure transmission mode (QPSK with 1/2 coding rate): 1 Watt for a range up to 70 km. – The theoretical SFDMA system tolerances have been proven to be valid by an exhaustive comparison with the laboratory tests. – But important developments and trials are still ahead! In the future, further trials need to be performed in order to: – consolidate the different RF parameters, with an optimized metrology – test new transmitting configurations such as the indoor-mode – improve the system performances in the urban environment (by implementing relay stations...). Last, but not least, the integration of the SFDMA return channel into the DVB-T system (while fulfilling the system requirements) will have to be proved feasible: this is one of the aims of the 18‑month iTTi (Interactive Terrestrial Tv Integration) ACTS project which began work in March 1998. The DVB group is being kept informed of progress, and it should be noted that any future move towards standardization of the system will in due course be at the discretion of the DVB group.
At HISPASAT SCC in Arganda (Madrid), the interactive server was connected to the Master Station (HUB). When a request from a user was received by the server, the server identified which user was requesting and forwarded the addressed information to the DVB-S chain (the user received the Forward Interaction Path which was embedded into the DVB‑TS), which was received in Palexpo (Geneva) through the data output of the DVB-IRD connected to the client PC. The Forward Interaction Path was embedded into the DVB-S Transport Stream following the DVB specification for data broadcasting (see Fig. 2.12). 
FIGURE 2.12 [2025-0212] The satellite section of the interactive system was based on a CDMA satellite network for the specific implementation performed in DIGISAT, with SITs working in the Ku band (14/11‑12 GHz). The following key points define the satellite section used for the interactive system demonstration: – CDMA satellite multiple access technology. – Satellite channel access control mode based on Slotted-Aloha protocol. – Antenna sizes: 1.20 m for the HUB located at Arganda and 0.90 m for the SIT located at Geneva (see Note 1). – SIT power amplifier level: 2 W. NOTE 1 – This specific configuration was used for the Demo. In Operational conditions the SIT antenna size can be reduced to 55 cm and the amplifier power level to 0.5 W following the analysis performed in DIGISAT. Regarding the Interactive System Coaxial Section, the demonstrated prototype equipment was based on a subset of the options provided by the DVB-RC-CATV specification (ETS 300 800). The Coaxial Section Grouping Terminal and two IIMs based on PC platforms were available for transporting the visitor interactive requests to the satellite section. The interface between the satellite and coaxial section is based on RS-232 and SLIP (Serial Line IP) communication protocol between both sides as recommended in prTR 101 201. After DIGISAT Project, S3M gave an step further in the development and introduction of interactive services via satellite: S3M project (March 1998-December 1999) has developed and tested a return channel system via satellite for SMATV particularized for small SMATV installations. The project has tested and demonstrated in several public events during 1999 the technical and economical viability of a return channel via satellite where the advantage is the share of the infrastructure cost among all the users in a building. The S3M project has also cooperated in the ITU-T SG 9 in the production of the draft Recommendation J.118 (J.smatv/matv).
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