Spread spectrum communication system using a quasi-geostationary satellite

• US 20030181161A1
• Filed: 02/20/2003
• Published: 09/25/2003
• Est. Priority Date: 09/28/2000
• Status: Active Grant

• Current Assignee: SES ASTRA SA (SES SA)
• Original Assignee: SES ASTRA SA (SES SA)
• Inventors: Harles, Guy, Bethscheider, Gerhard
• Granted Patent: US 7,539,456 B2
• Time in Patent Office: Days
• US Class Current: 455/12.1
• CPC Class Codes: H04B 7/18569 Arrangements for system physical machines management, i.e. for construction operations control, administration, maintenance
• CPC Class Codes: H04B 7/19 Earth-synchronous stations
• CPC Class Codes: H04B 7/216 Code division or spread-spectrum multiple access [CDMA, SSMA]

Abstract

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.

Claims

1. A method for illuminating an area of interest on earth with a downlink signal, comprising the steps of:

operating a quasi-geostationary satellite in an inclined orbit, and

sending a spread downlink signal s′

(t) from said quasi-geostationary satellite to said area of interest on earth.

2. The method according to claim 1, further comprising the steps of modulating an uplink signal p(t) by spread spectrum modulation with a certain spreading ratio to generate a spread uplink signal s(t), transmitting said spread uplink signal s(t) to said quasi-geostationary satellite, and converting said spread uplink signal s(t) to said spread downlink signal s′

(t).

3. The 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 s′

(t).

4. The method according to claim 1, wherein the station keeping control of said satellite is restricted to longitude drift corrections and eccentricity corrections.

5. The method according to claims 1, wherein additional satellites are operated in co-location with said quasi-geostationary satellite forming a satellite cluster.

6. The method according to claim 5, wherein each satellite in said satellite cluster sends a separate spread downlink signal s_i′

(t).

7. The method according to claim 6, wherein each spread downlink signal s_i′

(t) is given its own spreading sequence with low pair-wise cross-correlation for code-division multiple access (CDMA).

8. The method according to claim 5, 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.

9. A mobile user terminal, comprising:

a mobile antenna with a low directivity, adapted to receive a spread downlink signal s′

(t), which is emitted by a quasi-geostationary satellite operated in an inclined orbit, and

a processing unit for demodulating said spread downlink signal s′

(t) by spread spectrum demodulation.

10. The mobile user terminal according to claim 9, wherein the mobile antenna is adapted to receive signals with a frequency of above 10 GHz.

11. The mobile user terminal according to claim 9, 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.