Ico Services Limited

International Mobile Satellite Organization

Inmarsat Limited

Dennis Roy Mullins

Mark Grayson

Patrick Chomet

Samuel G Munoz-Garcia

Peter Poskett

Shinichi Nomoto

Richard Wyrwas

Stephane Gosselin

Ben Hutchinson

Keith Norman Guy Hungerford

Shimichi Nomoto

In a satellite mobile telecommunications system based on the GSM standard, and using a TDMA frame structure, discontinuous transmission (DTX) mode is used to take advantage of the substantial silences which occur during normal speech. In this mode, traffic channel (TCH) data is not sent, but control of the link between a ground station and a user terminal is maintained by sending control channel data bursts (SACCH) together with silence descriptor (SID) frames. To avoid high peak to mean values of transmission power at the satellite, the emission time of the bursts is controlled so as to be uniform over the available sending opportunities. Conventional techniques for doing this cannot be used in a system which includes diversity operation. Therefore, the burst transmission time at the ground station is set in dependence on a reference provided by the user terminal which is a modified version of the reference generated for contention resolution of random access requests.

Data multiplexing for diversity operation

A mobile communication system has a plurality of satellites and mobile stations. A mobile station is capable of communicating with more than one satellite. A satellite transmits a set of neighboring cell data to one of the mobile stations. The data set comprises first and second portions related to communication with a first and a second satellite of the plurality of satellites, respectively. When the data set is received the first time by the mobile station, it decodes both first and second data portions to establish a neighboring cell list, which is stored within the mobile station. When the mobile station receives subsequent transmissions of neighboring cell data, it need only decode either the first data portion or the second data portion based on the presence or absence of an alert message.

Neighboring cell list generation in a mobile satellite communication system

In a cellular satellite mobile telecommunication system, cell reception measurements for cell broadcast channels (BCCH) at a user terminal (UT ) are made in an idle mode when no call is being made. At the commencement of a call, the measurement information ( , FIG. ) relating to the measurement made in the idle mode is encoded onto a slow control channel (SACCH ) associated with a speech channel (TCH) for speech communication from the user terminal to a remote ground station (SAN ) via a satellite ( ), and the power of the speech channel transmitted to the user terminal from the satellite, and from the UT to the satellite, for the call, is set in dependence upon the report. The reported data can also be used to determine whether to make a cell or satellite handover.

Idle mode measurement

A method and apparatus are disclosed for a system where a user terminal can communicate with satellites A-C, the satellites A-C can communicate with earth stations A-E which in turn can communicate with the terrestrial telephone system . The user terminal can register with one of the earth stations C which has an associated mobile satellite switching center C which acts as a gateway into the terrestrial system . When attempting to contact the user terminal from the terrestrial system the mobile satellite switching center C of visitor registration, if it cannot make the contact itself, instructs other earth stations , in turn, according to different methods of alternative earth station selection, until contact is made, and then routes all voice messages through itself C to retain the single and original gateway into the terrestrial system

Satellite communications gateway management system

In a satellite mobile telecommunication system, TDMF traffic is transmitted from a SAN via a satellite to a mobile user terminal UT , over a duplex link . The SAN instructs the satellite to transmit signals over link to UT at a power level dependent upon the quality of signal received by UT , so as to adaptively control the power to an efficient level. Similarly, the power level of signals transmitted by UT to the satellite is controlled depending on the error rate. The power level required is computed as a function of the average of easured areas determined during a given measurement period together with a margin which is computed as an adaptive function of a deviation of the errors bout the average value.

Transmission quality reporting

A communication station for generating or receiving an angularly dispersed array of radiation beams, comprising an array of radiating elements ( ) defining an array antenna ( ); and a beam former ( ), the beam former comprising a passive network having a first side (X) carrying a plurality of beam ports for electrical signals corresponding to the beams and a second side (Y) carrying a plurality of antenna ports corresponding to the radiating elements, each beam port being connected to a plurality of antenna ports via a network ( ) of power divider ( ) and phase shifter ( ) components, the phase shifts of which are in integer multiples of a predetermined constant, so as to generate the array of beams; in which the array antenna ( ) has triangular or hexagonal symmetry and the array of beams has triangular or hexagonal symmetry.

Antenna system

A method and apparatus for preventing interference between a first satellite and a second satellite which share frequencies for their up or down links is disclosed. A ground station receives downlink interference above an acceptable threshold from the first satellite if the first satellite and the second satellite are separated, relative to the ground station, by less than a minimum discrimination angle. Likewise, the first satellite receives unacceptable uplink interference from the ground station in that situation. To overcome the problem of interference, the second satellite is prevented from transmitting to or receiving from a forbidden area of the earth's surface. The forbidden area may either be determined as an area within which the first satellite and the second satellite are separated by less that the minimum discrimination angle, or as a band within which the first satellite is separated by less than the minimum discrimination angle from any point within an orbital band within which the second satellite is located. Communications to and from the forbidden area are either handed over to other areas outside the forbidden area for routing into the forbidden area through a ground network, or are handed over to another satellite.

Method and apparatus for limiting interference between satellite systems

A satellite communications system comprises satellites 9A-C, earth stations 7A-E, user terminals 11 and controlling gateways 3 in the form of mobile satellite switching centers 5A-E. Access with a user terminal 11 may be gained to a terrestrial telephone system 1 by earth stations 7A-E contacting the satellites 9A-C and by the satellites contacting the user terminals 11. The satellites 9A-C periodically broadcast messages indicative of the earth station 7A-E with which they are instantly in contact. The user terminal 11 listens to and logs these broadcasts to keep a list of the relative number of times each earth station 7A-E can be heard. When calling into the system, the user terminal pages earth stations in descending order of number of entries in the log. When in contact, the user terminal 11 sends the log to the system. When subsequently trying to contact the user terminal 11, the system uses earth stations in descending order of number of entries on the log, last received from the user terminal.

User terminal access in satellite communication systems

A terminal 44 44A 44B using standard navigational satellite 142 position determination to find its position on the surface of the earth 14, has its performance enhanced by being linked to a communications satellite system 10 38. In one variant, the communications satellite 10 broadcasts on each of a plurality of spot beams 30, each interactive with a different part of the earth, the broadcast indicating which navigational satellites 142 are accessible for a terminal within that beam 30. The terminal 44 44A 44B receives the broadcast and adjusts the navigational satellite receiver 174 to look for signals only from the nominated navigational satellites 142. In another variant, the communications satellite system 10 38 approximately measures the position of the terminal 44 44B and then informs the terminal 44 44B which navigational satellites are accessible from the terminal 44 44B, the navigational satellite receiver 174 again only looking for signals from the nominated navigational satellites 142. In both variants, the time required to establish a position is reduced by the navigational satellite receiver 174 not being required to listen for inappropriate or inaccessible navigational satellites 142.

Satellite terminal position determination

A satellite system and method comprises a satellite 10 induced to roll 46 and pitch 52 in its orbit 12 to keep antennae 34 36 pointing ever directly at the nadir 40 as the nadir moves over the surface of the earth 14. The satellite 10 has a yaw rotation 54 designed to keep the solar panels, which rotate only about one axis, ever pointing at ninety degrees to the direction of the sun 42 for maximum solar panel efficiency. The beam pattern of the antennae 34 36 is counter-rotated to oppose the yaw motion 54. Compensation for the season of the year is applied.

Satellite operating system and method

A satellite system facilitates communications between earth stations and both geostationary satellites and non-geostationary satellites in an orbit at a lower altitude than that of said the geostationary satellites by preventing the non-geostationary satellite from transmitting signals that might possibly interfere with signals transmitted by the geostationary satellites. The non-geostationary satellite includes position acquisition subsystem for determining the position, and in particular the latitude, of the non-geostationary satellite relative to the surface of the earth. A data processor determines a forbidden band of locations on the surface of the earth all possible geostationary satellites and the non-geostationary satellite, at its determined position, are separated by less than a specified minimum discrimination angle. An antenna control subsystem in the non-geostationary satellite controls transmission of signal energy from the non-geostationary satellite in accordance with the satellites position so as to prevent transmission of signal energy from the non-geostationary satellite to said locations within the forbidden band.

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London, United Kingdom

Dennis Roy Mullins