Ses Astra S.a.

Societe Europeenne Des Satellites S.a.

Guy Harles

Gerhard Bethscheider

Peter Siebert

Markus Gross

Georges Krier

Marc Thill

Jos Wouters

A system for estimating a spacecraft () position is disclosed. It includes receiving stations () for receiving signals transmitted from the spacecraft () and a processing station () for receiving data from the receiving stations (). Each receiving station () records, during a recording window (), the signals transmitted from the spacecraft () and transmits, to the processing station (), data representing the recorded signals during the recording window (). The recording windows () associated with each of the receiving stations () are offset and/or of different size with respect to each other. The processing station () correlates the recorded signals to estimate the distance difference between the spacecraft () and each of a plurality of receiving stations and to estimate the spacecraft () position. A method, a receiving station (), a processing station () and a computer program are also disclosed.

Spacecraft position estimating system and method

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.

Spread spectrum communication system using a quasi-geostationary satellite

A ranging system determines ranging information of a spacecraft carrying a component of a communication channel. In order to provide a ranging system for determining ranging information of a satellite carrying a transponder as well as to provide a method thereof which yield a sufficient accuracy without causing further costs when narrow spot beams by the transponder are used, a ranging system includes a plurality of receiving stations at different locations on earth, wherein each receiving station is arranged for receiving a reference signal from the component; a synchronization unit for providing a synchronized time base between the plurality of receiving stations; a calculation unit for calculating the ranging information in accordance with the propagation time of each received reference signal and with the synchronized time base; wherein at least one receiving station includes a correlation receiver for receiving the reference signal.

Ranging system for determining ranging information of a spacecraft

The invention refers to a method and an apparatus for determining characteristics of components of a communication channel. In order to simplify the intersystem coordination in a beginning of life test of a satellite communication channel and avoiding the interference of adjacent satellite systems the method according to the invention comprises the following steps: modulating a clean carrier signal f(t) by spread spectrum modulation to generate a spreaded clean carrier signal s(t); transmitting said spreaded clean carrier signal s(t) through said communication channel at a first predetermined level; receiving a receive signal s'(t) corresponding to said spreaded clean carrier signal s(t) after having traveled through said communication channel; demodulating said receive signal s&#x2032;(t) by spread spectrum demodulation to generate a despreaded carrier signal f&#x2032;(t); determining characteristics of components of the communication channel on the basis of a comparison of said clean carrier signal f(t) and said despreaded carrier signal f&#x2032;(t).

Method and apparatus for determining characteristics of components of a communication channel

In a satellite ranging system predetermined bit sequence or group of bit sequence in a transport stream, which is a digital signal are used to generate trigger signals on the basis of which the delay introduced into the transport stream by the travel path from a satellite ground station to the satellite and back or to another satellite ground station is determined allowing a calculation of the distance between the ground station(s) and the satellite. The predetermined bit sequence or group of bit sequences may be inserted into the transport stream at the uplink site, for example as a specific payload P. In order to avoid insertion of additional packets the transport stream or part of it may be used as a predetermined bit sequence.

Ranging system and method for satellites

For determining characteristics of components of a communication channel, for example of a transponder in a communication satellite, a clean carrier signal f(t) is modulated with a pseudo noise signal PN(t) and transmitted through the communication channel at a level below the level of a payload signal which is transmitted via the communication channel simultaneously. The received signal s&prime;(t) is correlated with same pseudo noise signal PN(t) to obtain a recovered carrier signal f&prime;(t). Both the clean carrier signal f(t) and the recovered carrier signal f&prime;(t) can be used to determine the desired characteristics. Since the PN modulated clean carrier signal s(t) is transmitted at a low level, it is possible to perform measurements without switching off the payload signal.

Method and apparatus for determining characteristics of components of a communication channel under load

For determining the operating point of a non-linear amplifier,of a communication channel,, for example of a transponder in a communication satellite, a first input signal I,is transmitted through the communication channel,at a power level P,which drives the non-linear amplifier,in a non-linear operation mode. In addition, a second input signal i,is transmitted through the communication channel,simultaneously with the first input signal I,. The second input signal i,is transmitted at a level below the level of the first input signal I,. If the contribution of the second input signal i,to the total input of the non-linear amplifier is small, the operating point of the non-linear amplifier is determined almost only by the first input signal. Therefore, the output power P,corresponding to the second signal i,is determined most strongly by the input power P,of the first signal I,. The operating point (I,, P,) of said non-linear amplifier (,) is determined ont he basis of an output signal (o,) of said communication channle (,) corresponding to said second signal (i,)

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Guy Harles