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The invention refers to a satellite communications system with a mobile user terminal. In order to provide a satellite communications system which enables communication with a mobile user terminal via conventional communication satellites on any area of interest on earth, a quasi-geostationary satel

The invention refers to a satellite communications system with a mobile user terminal. In order to provide a satellite communications system which enables communication with a mobile user terminal via conventional communication satellites on any area of interest on earth, a quasi-geostationary satellite is operated in an inclined orbit and sends a spread downlink signal s' (t) to said area of interest on earth to be received and despreaded by a mobile user terminal.

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What is claimed: 1. Method for sending a downlink signal to a mobile antenna with a low directivity within an area of interest on earth, comprising the steps of: operating a satellite as a quasi-geostationary satellite in an inclined orbit having an inclination outside the typical specification of

What is claimed: 1. Method for sending a downlink signal to a mobile antenna with a low directivity within an area of interest on earth, comprising the steps of: operating a satellite as a quasi-geostationary satellite in an inclined orbit having an inclination outside the typical specification of ±0.05° in latitude with regard to the zero inclination of the station-keeping window, and sending a spread downlink signal from said quasi-geostationary satellite to said area of interest on earth, wherein the spread downlink signal permits communication from the quasi-geostationary satellite, due to the high signal-to-noise ratio of spread spectrum modulation, that is not possible with a high bandwidth transmission used in a geostationary orbit. 2. Method according to claim 1, wherein said spread downlink signal has a frequency of above 10 GHz. 3. Method according to claim 1, farther comprising the steps of modulating an uplink signal by spread spectrum modulation with a certain spreading ratio to generate a spread uplink signal, transmitting said spread uplink signal to said quasi-geostationary satellite, and converting said spread uplink signal to said spread downlink signal. 4. Method according to claim 1, comprising the steps of transmitting an uplink signal to said quasi-geostationary satellite, on-board processing in said quasi-geostationary satellite the uplink signal by spread spectrum modulation with a certain spreading ratio to generate said spread downlink signal. 5. Method according to claim 1, wherein the station keeping control of said satellite is restricted to longitude drift corrections and eccentricity corrections. 6. Method according to claim 1, wherein additional satellites are operated in co-location with said quasi-geostationary satellite forming a satellite cluster. 7. Method according to claim 6, wherein each satellite in said satellite cluster sends a separate spread downlink signal. 8. Method according to claim 7, wherein each spread downlink signal is given its own spreading sequence with low pair-wise cross-correlation for code-division multiple access (CDMA). 9. Method according to claim 6, wherein at least two satellites of said satellite cluster send a reference signal, wherein each reference signal comprises a reference time information and a reference orbit information with regard to the sending satellite. 10. Method according to claim 1, wherein the spread downlink signal has a spreading ratio which is adjusted in combination with a channel coding such that the error probability of the despread and decoded downlink signal will be sufficiently low under the assumption of a given antenna gain of the adaptive phase array antenna. 11. Method according to claim 10, wherein the error probability to be achieved is in the order of 10-8. 12. Mobile user terminal, comprising: a mobile antenna with a low directivity, adapted to receive a spread downlink signal which is emitted by a satellite operating as a quasi-geostationary satellite in an inclined orbit having an inclination outside the typical specification of ±0.05° in latitude with regard to the zero inclination of the station-keeping window, and a processing unit for demodulating said spread downlink signal by spread spectrum demodulation, wherein the spread downlink signal permits communication from the quasi-geostationary satellite, due to the high signal-to-noise ratio of spread spectrum modulation, that is not possible with a high bandwidth transmission used in a geostationary orbit. 13. Mobile user terminal according to claim 12, wherein the mobile antenna is adapted to receive signals with a frequency of above 10 GHz. 14. Mobile user terminal according to claim 12, wherein the mobile antenna with a low directivity is a non-directional flat antenna. 15. Mobile user terminal according to claim 12, wherein the mobile antenna with a low directivity is an adaptive phase array antenna based on a planar technology and capable of adaptive beam forming. 16. Mobile user terminal according to claim 12, wherein the mobile antenna is adapted to receive reference signals sent from the quasi-geostationary satellite and at least another satellite operated in co-location with the quasi-geostationary satellite, wherein each reference signal comprises a reference time information and a reference orbit information with regard to the sending satellite and wherein the processing unit comprises a location processor for determining the coordinates of the mobile user terminal on the basis of the reference signals.