The Stelios system will have a range of applications. It's small size and low-cost will allow it to be integrated with a range of indoor and outdoor displays. One interesting application under consideration might come in the form of 'intelligent bus shelters'. Buses or any fleet transport vehicles can be equipped with navigational aids, such as an EGNOS/Galileo receiver. Combined with a transmitter, the operator of a transport service can send departures/arrival information and updated 'real-time' connection information via the Stelios multicast system. The information would be displayed on information boards, such as flat plasma screens located in bus shelters.
Another application of this development is something called 'dynamic advertising'. The Stelios system can be used to provide updated advertisements according to: location, time of day and audience profile. Pictures or full video clips, with or without sound, can be sent via end-of-life satellites to Stelios receivers, stored in the local cache and then presented at appropriate times on advertising boards located in for instance shopping malls or outdoors.
The entire system would be of a lowcost because existing end-of-life satellites are to be used. Once in position, 35,000 km away in space, TV satellites will remain in orbit forever, but their useful life amounts to 15 years or less. Onboard thrusters must keep each satellite pointed precisely at fixed-position Earth-based receivers. Once the thrusters' propellant runs out however, the satellites drift out of correct orbit, and are left useless for TV broadcast applications. Further life can be squeezed from a low-propellant TV satellite by switching it over to services where precision position control is less important. Most thruster propellant is expended correcting satellite attitude in the north-south direction. But if station-keeping is limited to the east-west axis then satellite lifetime could be extended by some five years. The satellite position would then oscillate across the sky by a few degrees. Stelios utilizes smaller gain antennas with wide antenna receive lobes. This enables reception even when the satellite moves across the sky and without antennas which require expensive tracking devices. The smaller antenna means reception of lower data rates than normal television receivers are capable of. Signal spreading is also required for the Stelios receivers to satisfy the power density specifications defined by ETSI (European Telecommunications Standards Institute). Signal spreading has however the added benefit of mitigating interference from other neighbouring satellites which become potentially stronger due to the wider antenna lobes resulting from the low gain antennas utilised in the Stelios system.
