Societe Europeenne Des Satellites S.a.

Ses Astra S.a.

Gerhard Bethscheider

Guy Harles

Peter Siebert

Detlef Schulz

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

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

The invention refers to an apparatus for generating a reference frequency depending on a timing information extracted from a data stream. In order to generate a carrier frequency in a user station of a satellite TDMA network at low costs which is accurate and stable and which meets stringent phase noise requirements, it is suggested to use at least one free-running oscillator. The frequency deviation with regard to the timing information extracted from the data stream is estimated by an estimation means. At least two oscillation signals are derived from the at least one oscillation means and are linked together by a linking means yielding said reference frequency. A frequency correction value is applied to at least one of the oscillation signals such that the timing information given by the reference frequency corresponds to the timing information extracted from said data stream.

Apparatus and method for generating a reference frequency

A satellite cluster and method for operating the same. A first module satellite has as a pay load component a receiver unit and/or a transmitter unit for communication with subscriber stations and/or base stations. A second module satellite has as a pay load component a signal processing unit for communication with subscriber and/or base stations. The signal processing unit is integrated in the second module satellite separately from the receiver and transmitter units of the first module satellite. Communication devices for the interaction of the pay load components are included in the module satellites. Each module satellite is controllable separately as an aerospace vehicle such that each respective module satellite is maneuverable out of the cluster and is replaceable by a new module satellite. In one module satellite, the signal processing unit may be integrated as a pay load component separately from the receiver and transmitter units.

Satellite cluster comprising a plurality of modular 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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Ayl, Germany

Gerhard Bethscheider