Propagation from a geostationary satellite to terminals inside buildings

As part of a study of the likely performance of the Inmarsat D service, BT performed some in-building reception trials from a geostationary orbit (GSO) satellite at its laboratories based at Martlesham Heath. A test Inmarsat D signal was broadcast from the Atlantic Ocean Region East (AORE) satellite in the land mobile satellite system band (1510-1559 MHz). This one-way service is aimed at hand-portable terminals with compact antennas. The user bit-rate is just under 10 bits/s which means that the link operates with a large margin (about 16 dB) from a global beam transponder to a small antenna. The signal from the satellite is circularly polarised and, since the service was originally designed to operate under reflected signal and in-building conditions where the polarisation is uncertain, a linearly polarised patch is the most likely candidate terminal antenna. The original intention of the trials was to assess the quality of service that could be guaranteed inside buildings. During these trials, a fading pattern was discovered that depends on the room height above ground. The paper describes the likely performance of the D service within rooms, followed by a description of a fading pattern that was encountered. It goes on to prove that the pattern movement is caused by the satellite inclination, to illustrate its dependence on the room height above ground and to indicate possible countermeasures. It also addresses the implications on hand-held terminals operating with intermediate circular orbit satellites.