1. Introduction

This document is the result of more that one year of studies, meetings and engineering projecting process in which a number of Representatives from Administrations, Service Providers and end users has being involved. The idea of the proposal to our Distinguised Collegues of adjacent FIRs to begin studies regarding the improvement of the ground-to-ground communication was developed during the AFI/7 RAN meeting, held in Abuja (Nigeria) in may 1997.

The AFI/7 RAN Meeting itself introduced a recommendation requesting the States to assume VSAT networks as a way-out to the communication problems.

The SAT Group, due to the importance of this subject, request the creation of a task force to undertake work which objective should be the establishment of a VSAT network within the EUR/SAM corridor.

The 2nd. Task meeting which will be held in Casablanca in october will reach a conclusion to be submitted to the SAT group in the next SAT/7, planed to meet in Sal at the end of 1998. This document is writen as the result of the coordination of such works, and will be discussed deeply.

This document sumarized all aspects to take into account when such a VSAT network is being projected. We will show what is considered as the best state-of-the art solution available today. Some considerations have being made: The network must comply with the ICAO recommedations about ATS/DS circuits and AFTN links.

Direct Speech Circuits means a non-HUB direct link with a very high level of availability. We do have PSTN lines between ATC Centers but the reliability, quality and costs of those lines are out-of-date and have to be improved in this oceanic area.

As it was allready mentioned, this study is the result of the collaboration of many experts, who did work and still are trying to give to this project their bit of knowledge and work. Let us express here our deepest gratitude to them all.

2. The VSAT communication network between adjacent FIRs

2.1. Introduction

The ICAO AFI/7 RAN Meeting aproved the Recommendation 9/2 (AFI/7 WP/129), that strongly support the use of VSAT technology to improve the ATS/DS circuits and AFTN links between adjacent FIRs in the AFI Region. Such Recommendation has being produced also by other Regions, and there are several Task Forces working on the subject.

The document presented here makes references to two different Regions; the EUR/SAM corridor, for which this Task Force was created and the SAM Region. In the last GREPECAS COM/SG/8, held in Caracas in august, the ICAO SAM Regional Office recognized the efforts made by this task force and invited it to bring this study to the next SAM Digital Network Meeting (REDDIG).

The actual direct links between FIRs in the EUR/SAM corridor are based in leased PSTN circuits. Those circuits are expensive and their quality and reliability are in most cases unappropiate. This problem was postponed until some of the States began to work or install their VSAT networks.

Those networks solve the related troubles and it's the intention of this document to give the Meeting the most efficient and cost-efective solution found with the current technology available.

2.2. Area to be covered

The FIRs involved in this study are those where are included in the EUR/SAM corridor. This corridor is formed by the FIRs of Lisbon, Santa Maria, Sevilla, Casablanca, Sal, Dakar and Recife.

Being an oceanic airspace, the distances only give the chance to think about Satellite communication, once we have discharged optical fiber or earth-microwave links, because costs and/or access to remote areas.

2.3. Satellites

The theory of the use of communication satellite as repeaters is simple. Earth stations transmit to the satellite the information (uplink segment) and the repeater module in the repeater spread the information to any receiver sntonized in that frequency.

Distance and remoteness are then solved. The questions that arised now is to find the satellite provider that covers the area concerned. And not only cover but with what capacity and power.

The satellite providers use three frequency bands. Each band has its own coverage footprint and characteristics. The bands are: Ku and Hemispheric & global C Band.

Ku-Band (12-14 GHz.) is the best reliable band of frequency to be used. The EIRP (Espectral Isotrope Radiance Power) is the highest possible (max. 50 dbW) but the footprint is very focused. Normally, due to commercial interest of the providers, this coverages are lightning the northern hemisphere; North America and Europe, where the demand of service is much bigger. There is no Ku-band coverage in the Atlantic Ocean Region (AOR) that could cover the entire EUR/SAM corridor.

The C-band (4-6 GHz) is quite shorter in retransmition power but the coverage is hemispherical. That means the footprints cover a contour of Europa & Africa (Eastern Hemi. (EH)) and America (Western Hemi (WH)). The question that arised here was:

  1. To find the satellite who also could be seen by the oceanic islands involved; Azores, Cape Verde, Canarias and Madeira.
  2. The power supplied by this C-band footprint had to be the biggest available.

The C-band has another footprint type, name global, that gives lower power but a total coverage of the area seen by the satellite. Later, when a little comment about the Brazilian connection is given, we will be able to take the global coverage under consideration.

In april 1998, INTELSAT, who is nowadays the only provider that gives this coverage required, launch a new satellite, named IS-801 and situated on geostationary position at 328,5ºE, that doubled the power given by its inmediate antecesor., reaching 34,5 dbW in the 2 dB contour for their first time. This project that were in the calculation process, moves inmediatly to the new values because the earth station costs were dramatically reduced, and taking into account that the space segment lease were at the same cost. The earth stations, as is will be shown later in this document, are based on VSAT equipments (very small aperture terminals) and were reduced in antenna and HPA power in the transition to the IS-801.

The footprint of the INTELSAT IS-801, in a equatorial geosinchronous space orbit at 328,5ºE, is given in the figure 2.1. The C-band hemispheric coverage is shown in light blue.

It will be explained later the interconection of both beams, but as it is shown in the figure, all nodes have full coverage except Recife (Brazil). The solution found, discussed later in this document, recommends the instalation of the node in Brasilia, and a switching process to Recife with an earth link. In this way, the link Dakar-Recife will be granted without further delays and the Brasilia node could have the capability to comply with the REDDIG network of the SAM Region.

2.4. Types of satellite services provided by INTELSAT

INTELSAT offers two different types of service; IBS and INTELNET. The Intelsat business service (IBS), supports a full range of digital business communications. It's provided on a carrier basis and can be used in simplex or full duplex mode, for either point-to-point or point-to-multipoint applications. INTELSAT standard earth station have to be used with this service. IBS carriers are sized by information data rate, overhead and FEC rate and Open Network operation transmission characteristics have been defined by INTELSAT in order to facilitate the design and interoperability of different manufacture's modem/framing unit equipments. The rates of the space segment depends on the transmission carrier bandwith and on the antenna's diameter of the receivers of this bandwith. Therefore in a network working with IBS service, if the antennas are of the same size, the costs decrease substantially.

The INTELNET lease service, which also supports a full range of business communication applications, is provided on a transponder leases basis in capacity allotments from 100 Khz to 72 Mhz in 100 Khz increments.