This project is aimed at designing, implementing and validating a mobile VSAT system at Ku-band to provide passengers of high speed trains with broadband access to the Internet.
This satellite communications system is addressed at covering the growing need from people to be always 'connected' to the Internet, even when away from home or the office, by providing continuous mobile broadband services where terrestrial infrastructures are not available.
For this purpose, the project is intended to offer a system which:
- is available along most or all of the railway track,
- is adapted to the railway environment, covering specific norms and regulations, and stringent mechanical and EMC requirements,
- has enough bandwidth to deliver video contents, e-mail and internet browsing to passengers or to provide railway operators with reliable communications in remote areas, and
- is a system able to integrate with broadband terrestrial networks whenever they are available.
The key issues to be addressed in the project will be focused on the more critical return link components, such as:
- The Mobile Terminal Station(MTS) low-profile antenna, to be allocated in a reduced space under a coach roof fulfilling train mechanical constraints.
- The stabilizer platform, to follow specific train movements reducing maximum satellite off-axis permitted EIRP.
- The CDMA VSAT base-band modem signal acquisition and synchronization algorithms adaptation for the feeder/mobile links, and review of MAC/DLC satellite protocols of to keep data traffic QoS in the severe electromagnetic wave propagation channel scenario experienced by trains.
The main benefits of the project will be to immediately deliver to the market a low profile antenna system solution able to track train movement and a mobile CDMA modem able to cope with the mayor low-profile antenna off-axis radiation constraints imposed by satellite operators. All of that, based on the Indra experience in development of either satellite antennas for vessels or CDMA modems for VSAT networks.
The starting point for this project is the existing Indra Espacio's VSAT CDMA/DAMA network, originally designed to provide personal communications for fixed and portable terminals. That system has already been upgraded and field-tested for the mobile maritime environment. However, the railway environment has constraints, in addition to mobility, e.g., multi-path and obstacles along the way, which are common in the railway environment.
The architecture of the system to be deployed is based on:
- a satellite communications network, for covering the mobile environment between terrestrial Internet Service Providers (ISP) and trainsets, and
- an on-board test-bed communications network, covered by standard COTS Wi-Fi equipment, installed to distribute Internet access through one train coach.
The satellite communications network will be able to provide asymmetric two-way IP services to trains through a combination of two different technologies: a high-rate DVB-S broadcast communication technology for the forward link, and a DAMA/CDMA technology for the return link.
The use of CDMA allows, at the same traffic rate, a reduction in the size of the antenna and HPA power needed at the VSAT. They are both quite important when integrating a mobile station onto a train, bus, ship or aircraft. On the other hand, the DVB-S standard is designed to exploit the broadcast capability of satellite in forwarding digital TV content multiplexed with internet data streams.
The satellite network topology is of multi-star type, constituted by a satellite segment, a fixed ground segment with the NMS/HUB station which is able to manage the satellite network components and provide interconnection to Internet backbones, and the mobile user segment of MTS stations that interface with internet ser
The project started at the beginning of August 2005 with a first phase to be concluded in October 2005 with the Baseline Design Review. The Critical Design Review, the first milestone of the second phase, is foreseen in January 2006. Final trials on high speed trains are planned in January-February 2006. The Final Review of the project is expected in September 2006.
In June 2006 the Mobile Terminal Station (MTS) was installed in an S-100 Alstom AVE laboratory coach (see also picture below).
The MTS consisted of:
- an outdoor unit based on antenna, radome, azimuth and elevation motors, and RF equipment, and
- an indoor unit based on CDMA/DVB modems, a switching router and ACU equipment.
The results reached during the mobility tests campaign performed on 20th of June 2006 on the route Madrid - Sevilla were of great value: the behaviour of the propagation channel in the real railway environment was measured, the antenna tracking system behaviour in curves was improved even though it became necessary to enhance the tuning further, and the behaviour of the access control and synchronization of CDMA/DVB modems was evaluated.
Since September 2006, Indra is working to integrate a newly developed multi-waveform software-radio modem with the current project. This new modem platform incorporates mobility improvements as well as the results of the real trials performed in the past. A 2nd opportunity to validate this solution in a real train environment is planned for mid of September 2007 on the RENFE laboratory coach. The project conclusion is expected by end September 2007.