Abstract: In a cellular mobile telephone system, a mobile station (4d, 4e) requests allocation of a traffic channel by sending a request in a random access channel. Where there is a significant path length difference between locations in a cell and a network antenna, for instance on a satellite (3), not all of the available TDMA slots are used for random access signals. Instead, gaps of one to three time slots are left between valid random access time slots (103, 104) to avoid collision between random access bursts arriving at the network antenna along paths of different lengths.

Abstract: In a satellie 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.

Abstract: A mobile station (4) in a satellite mobile telephone system predicts when it will move into another cell on the basis of one set of broadcast information thereby reducing the overall processing burden. The mobile station (4) can predict with a useful degree of certainty which broadcast control channel (BCCH) frequencies it should listen on when it wakes up on the basis of a stored map of the relative positions of cells. The broadcast information includes information about the current cell's (40) shape (V1, V2, V3, V4, V5, V6) and translational (T) and rotational (R) motion.

Abstract: 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.

Abstract: 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.

Abstract: In a satellite communications system, where a user terminal 10, on the surface of the earth 12, can be in diversity communication to an earth station 18 via two orbiting satellites 14, 16 at once, and there is a need, at some time, when one of the two satellites 14, 16 orbits our of range, to engage another satellite 22 in its place, the user terminal 10 is operative to suppress TDMA timeslots in its communications with the two satellites 14, 16 to listen and report on broadcast messages from another satellite 22, the suppressed timeslots being based on an assessment of which of the two satellites has the largest path attenuation.

Abstract: A satellite communications system and method, where a satellite 10 can pass messages between a user terminal 44 and an earth station 38, as the satellite moves in an orbit 12 12′ as indicated by arrow 46, comprises means for measuring the position of the user terminal 44, on the surface of the earth 14, relative to the nadir 50, by means of doppler shift measurements and propagation delay measurements between the satellite 10 and the user terminal 44. Where more than one satellite 10 is visible to the user terminal 44, combination means are employed using propagation delays to plural satellites 10, and/or recordal of the receipt times, by the user terminal 44, of timed broadcasts from one or more satellites 10 to determine the propagation delay between the one or more satellites 10 and the user terminal 44.

Abstract: In a cellular satellite mobile telecommunication system, cell reception measurements for cell broadcast channels (BCCH) at a user terminal (UT 1) are made in an idle mode when no call is being made. At the commencement of a call, the measurement information (31, FIG. 8) relating to the measurement made in the idle mode is encoded onto a slow control channel (SACCH up) associated with a speech channel (TCH) for speech communication from the user terminal to a remote ground station (SAN 1) via a satellite (3a), 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.

Abstract: In a satellite communications system, where a user terminal 34 may wish to page more than one satellite 10 or more than one spot beam 30, and where the definition of a timeslot 38 for a paging channel 48 occurs a predetermined period after the sending of a broadcast burst 42, the possibility of sustained temporal collision between paging channels 48 between adjacent satellites 10 or adjacent spot beams 30 is avoided by periodically, progressively, and cyclically, moving the predetermined period.

Abstract: In a satellite mobile telecommunication system, TDMF traffic is transmitted from a SAN 1 via a satellite 3 to a mobile user terminal UT1, over a duplex link 1, 2. The SAN 1 instructs the satellite 3a to transmit signals over link 1 to UT 1 at a power level dependent upon the quality of signal received by UT 1, so as to adaptively control the power to an efficient level. Similarly, the power level of signals transmitted by UT 1 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.

Abstract: A satellite mobile telecommunications system includes mobile terminals 2a, 2b which can communicate with one another using end-to end encryption and decryption techniques. When secure end-to-end communication is required, each terminal uses a common encryption code (RAND) to encode data and decode data transmitted between the terminals. The encryption code is transmitted in a secure manner from a remote database station (15) to the terminals. Each terminal stores a terminal key (Ka, Kb) on its SIM card and the keys are also held in the remote station (15). Partial keys (Kpa, Kb) comprising the pseudo random number (RAND) and the keys Ka, Kb stored at the station (15) are produced at the station (15) by an exclusive OR process in order to mask the keys and the random number. The partial key Kpa=Ka+(RAND) is sent to terminal 2a. At the terminal 2a, the partial key Kpa is exclusive OR-ed with the locally stored terminal key Ka on the SIM card, so as to recover (RAND).

Abstract: A multi user communications terminal apparatus providing simultaneous access for a plurality of users to a communications network in which the geographical locations of each user are registered and periodically updated, the terminal apparatus comprising a plurality of user terminals (320) each including electroacoustic transducers (34,36); and a common RF unit (304) comprising a shared RF amplifier (342) for coupling to a shared antenna system (302), in which the terminal apparatus comprises means (348) for transmitting common location updating signals, and is arranged not to transmit separate location update signals for every one of said users.

Abstract: A control device (7) located in battery operated device or battery pack is used to control charging and discharging cycles of a pair of rechargeable batteries (6a, 6b). The device determines which of the batteries is least charged and, if not already fully discharged, allows power to be drawn from the battery until it becomes fully discharged. The device then allows the other battery to be drained. When the batteries are placed in a charger (3), the control device only allows fully discharged batteries to be charged. In this way, only full discharge and charge cycles are performed, which maximises the lifetime of the batteries.

Abstract: A mobile telephone (UT 1) is configured for dual mode operation, so as to communicate either via an earth-orbiting satellite 3a with a satellite network (SAN 1) or through a conventional land-based cellular network (PLMN 9). In order to provide interworking between the satellite network and the land, cellular network 9, an interworking function (IWF 31) provides data to the cellular network 9 concerning the location of the user terminal (UT 1) in relation to the satellite network. The data is transmitted from the satellite visitor location register (VLRSAT 1) to the home location register (HLR) of the cellular network 9. The IWF maintains a list of roaming subscribers provisioned with services which are specific to the visited network and not available in the home network. The (IWF 31) is configured to operate with local GSM, DAMPS, PHS or other local land-based networks, depending on the geographic location of the SAN.

Abstract: In a preferred satellite (3) communications environment, spread spectrum communications, under extremes of digital message readability, is established for a digital message 23 by division into smaller elements W(0)-W(C−1) which are transmitted in turn, each multiplied for logical inversion or non-inversion, by the individual, sequential digits of a preferred binary polynomial 35, being either a PN polynomial, an m-polynomial, or simply displaying alternate logical ones and zeroes. The preferred polynomial may be used convey an alternative polynomial for better reception of a subsequent digital message.

Abstract: In a satellite position fixing system, where an earth station 38 communicates with a satellite 10 which, in turn, communicates with selectable ones out of a plurality of user terminals 44 whose position, on the surface of the earth 14, is measured, the accuracy of measurement of the position of the satellite 10 is improved by using all of the user terminals 44 as further triangulation points, the improved position being incorporated in further user terminal 44 position determinations, and so on to create a cumulative improvement. Weighting is applied so that user terminals 44 with large errors in triangulation are given small significance and those with small errors are given great significance.

Abstract: In a satellite communication system where user terminals 11 communicate via satellites 9A-E with earth stations 7A-E to join with a terrestrial telephone network 1, a controller 18 at a master earth station 7A monitors all earth stations 7A-E for a request for service received from a user terminal 11, then calculates which earth station 7A-E is best placed to service the request and instructs the best placed earth station 7B to service the request. In servicing the request, the best placed earth station 7B uses that earth station 5C whereat the user terminal 11 is registered as a visitor as the gateway into the terrestrial system 1 by routing all voice grade messages thereto and therefrom via a voice link 21. If the user terminal 11 is not registered at any earth station 7A-E, the best placed earth station becomes the earth station of registration and acts as a gateway.

Abstract: A mobile satellite communications system having at least one mobile terminal (2), at least one ground station (6), at least one relay satellite (4) interconnecting said user terminal (2) and said ground station (6), and a management store (48) associated with said ground station (6), in which the user terminal (2) is configured to initiate registration signalling with said store (48). The user terminal (2) initiates registration signalling when reception conditions relating to a downlink channel relayed via said satellite (4) become unsatisfactory over a given time greater than a predetermined minimum value and then return to a satisfactory condition. Specifically, signals received in a given channel are monitored in relation to predetermined criteria, and the duration of periods when the monitored signals do not meet the criteria are timed.

Abstract: In a satellite communications system, where a satellite 10 provides a plurality of radio beams 30, and where distance and/or angle measurement from a satellite 10 or satellites 10 enables the position of the user terminal 44, on the surface of the earth 14, to be measured to within an uncertainty of being in one out of a possible plurality of positions 142, when some out of the plurality of positions fall within a single beam 30A, which one of the plurality of possible positions 142 is actually occupied by the user terminal 44 is determined by assessing the quality of signals received from those other, adjacent, overlapping beams 30B-30G which surround the beam 30A.

Abstract: In a satellite communication system, a user terminal (11) seeks response from a selected earth station (7A-E) for a request for service based analysing the signal quality of broadcasts from earth stations (7A-E). Whichever earth station (7A-E) responds calculates which earth station (7A-E) can best meet the request for service. If it is another earth station (7A-E), the user terminal (11) is intructed to redirect the request for service thereto and, once in contact, the user terminal (11) addresses all new requests directly thereto, until the best earth station (7A-E) calculates that there is a better earth station (7A-E), and instructs the user terminal (11) to address all future requests for service thereto.