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Within ten years or so, terrestrial digital TV should supplant terrestrial analog TV thanks to the many advantages it offers: complete digital encoding, spectrum efficiency, enhanced data coding flexibility, lower power levels required...

Consequently, we will soon see the coexistence of analog and digital TV in neighboring or adjacent frequencies. This coexistence will entail a number of constraints that will need to be taken into account. ATDI, in partnership with Thomcast and STA, has therefore placed its expertise in radio-electric system planning at the disposal of a technical study covering the introduction of digital TV into the Principality of Andorra. ATDI took about identifying the frequencies available for digital TV within the spectrum allocated to this service, analyzing the resources that could be used in terms of the number of multiplexes, the different kinds of modulations that can be envisaged, reusing analog transmission sites, evaluating the effects of analog/digital coexistence (potential interference) and optimizing the existing TV network in order to improve analog service quality and maximize the resources available for the digital service.

Example of coverage map

For the purposes of this study, DTMs (Digital Terrain Models) and a land usage layer (20 meters) to describe built-up areas, trees, etc. as well as a 1/2500 scale raster image were used. The first stage involved auditing the stations and repeaters that formed the existing analog TV network in terms of positioning, technical parameters (power, channel, antenna diagrams, programs broadcast, etc.) and coverage areas (using ITU-R P.525 and ITU-R P.526 propagation models, diffraction with Deygout 1994).

The second stage was devoted to calculating protection areas for the existing transmitters in relation to a DVB-T transmitter broadcasting at a given frequency. This makes it possible to geographically identify the frequency resources available: for every frequency entered, a coverage map is created corresponding to the network protection area in relation to the new transmitter (the protection ratios used can be found in the CEPT Chester 97 report as well as in the ITU-R BT.1368-1 recommendation; these tables are integrated into ICS Telecom).

All of this data then serves to optimize the network and associated technologies by studying the changes to be made to the existing network in order to free up the resources necessary for digital TV. The data is also used to start determining choices of technology: if the C/N ratio of the envisaged technology is compatible with the radio-electric environment (interference on the co-channel is frequent), the choice may then be directed towards a more robust technology.

The next stage consists in drawing up an initial planning of the DVB-T network on the basis of the identified frequency resources and making the initial technological choices in order to achieve the coverage and spectrum occupation targets.

The different problems resulting from the planning stage are then analyzed, i.e., interference between the analog and digital networks, the number of multiplexes obtained, the feasibility of the investments required for the new network, etc.

At the end of the definitive planning phase for the new DVB-T network, an analysis will be performed to determine to what extent the DVB-T network is able to cover mobile receivers (using a Rayleigh profile for interference).

Since it was founded, ATDI has worked in the TV broadcasting field. For almost two years now, the R&D team has been examining certain specific aspects of the DVB-T standard and its integration into the ICS Telecom software in the form of calculation functions and deployment methodology.