WO2001097409A1 - Attribution du spectre radioelectrique - Google Patents

Attribution du spectre radioelectrique Download PDF

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Publication number
WO2001097409A1
WO2001097409A1 PCT/GB2000/002339 GB0002339W WO0197409A1 WO 2001097409 A1 WO2001097409 A1 WO 2001097409A1 GB 0002339 W GB0002339 W GB 0002339W WO 0197409 A1 WO0197409 A1 WO 0197409A1
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WO
WIPO (PCT)
Prior art keywords
spectrum
zones
allocation
reuse
areas
Prior art date
Application number
PCT/GB2000/002339
Other languages
English (en)
Inventor
Philip Hon Nghia Quan
Samuel G. Munoz-Garcia
Tor Wisloff
Original Assignee
Ico Services Ltd.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Ico Services Ltd. filed Critical Ico Services Ltd.
Priority to PCT/GB2000/002339 priority Critical patent/WO2001097409A1/fr
Publication of WO2001097409A1 publication Critical patent/WO2001097409A1/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/14—Relay systems
    • H04B7/15—Active relay systems
    • H04B7/185—Space-based or airborne stations; Stations for satellite systems
    • H04B7/1853—Satellite systems for providing telephony service to a mobile station, i.e. mobile satellite service
    • H04B7/18563—Arrangements for interconnecting multiple systems
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/14—Relay systems
    • H04B7/15—Active relay systems
    • H04B7/204—Multiple access
    • H04B7/2041—Spot beam multiple access
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W72/00—Local resource management
    • H04W72/04—Wireless resource allocation
    • H04W72/044—Wireless resource allocation based on the type of the allocated resource
    • H04W72/0453—Resources in frequency domain, e.g. a carrier in FDMA
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W84/00—Network topologies
    • H04W84/02—Hierarchically pre-organised networks, e.g. paging networks, cellular networks, WLAN [Wireless Local Area Network] or WLL [Wireless Local Loop]
    • H04W84/04—Large scale networks; Deep hierarchical networks
    • H04W84/06—Airborne or Satellite Networks

Definitions

  • the present invention relates to allocating radio frequency spectrum and has particular application to a cellular telecommunications system such as a satellite telecommunications network.
  • Terrestrial mobile telecommunications systems are well known and a number of different systems have developed which operate according to different standards.
  • These public land mobile networks may operate according to analog or digital standards.
  • GSM Global System Mobile
  • AMPS Advanced Mobile Phone Service
  • DAMPS Digital American Mobile Phone System
  • PDC Personal Digital Communication
  • GSM Global System Mobile
  • AMPS Advanced Mobile Phone Service
  • PHS Personal Handiphone System
  • PDC Personal Digital Communication
  • IRIDIUMTM satellite cellular system A number of different mobile telecommunication systems have been proposed that use satellite communication links to the mobile user terminals.
  • One network known as the IRIDIUMTM satellite cellular system is described in for example EP-A- 0365885 and US Patent No. 5 394 561 (Motorola), which makes use of a constellation of so-called low earth orbit (LEO) satellites, that have an orbital radius of 780 km.
  • LEO low earth orbit
  • Mobile user terminals such as telephone handsets are configured to establish a link to an overhead orbiting satellite, from which a call can be directed to another satellite in the constellation and then typically to a ground station which is connected to conventional land-based networks.
  • MEO medium earth orbit
  • IEO intermediate earth orbits
  • the ICOTM satellite cellular system described for example in GB-A-2 295 296 includes a constellation of MEO satellites. Communication does not occur between adjacent satellites and instead, a signal from a mobile user terminal such as a mobile handset is directed firstly to the satellite and then directed to a ground station or satellite access node (SAN), connected to a land-based telephone network.
  • GSM digital terrestrial cellular technology
  • Radio coverage is cellular, similar to GSM.
  • cells are served by spot beams, using highly directional antennas placed on orbiting satellites.
  • the ICOTM system there are 10 satellites, divided into two orthogonal planes, each satellite having 163 highly directional antennas.
  • the satellite-based system differs from the ground- based GSM system in that spot beams move across the earth and the cells they define are larger. Furthermore, spot beams from different satellites can overlap and such overlap is time varying.
  • the spot beams carry two-way call traffic comprising data, sent in bursts at specific time intervals and allotted frequencies. It is known to use CDMA, FDMA and
  • each call takes up a portion of spectrum. As more calls are carried over the radio link, more bandwidth is used.
  • the radio frequency spectrum is finite and its division and national regulatory bodies govern allocation. Thus, only a restricted range of frequencies is available for use by the satellite system.
  • the present invention seeks to solve this problem.
  • non-reuse areas are defined corresponding to a group of cells wherein spectrum cannot be used more than once concurrently, and are considered in relation to a plurality of zones, within the area of coverage of the network.
  • the non-reuse areas each overlie a respective one of said zones and partially overlap zones adjacent to the overlaid zone.
  • Spectrum is allocated to the non-reuse areas for allocating spectrum to their respective overlaid zones.
  • a determination is made of the spectrum used in zones that are partially overlapped by the non-reuse areas as a result of the allocation of spectrum to the non-reuse areas. This allows the allocation of spectrum to the zones to be optimised individually.
  • An offered traffic spectrum is defined corresponding to the spectrum to be consumed by call traffic in the zones individually and the allocation of spectrum to the non-reuse areas may be carried so as to optimise allocation of spectrum to the zones individually in relation to their offered spectrum.
  • a maximum available spectrum may be defined for the zones individually and the spectrum allocated to the zones individually to optimise the allocation in relation to their offered spectrum and their maximum available spectrum and to maximise the system's capacity to handle the offered traffic spectrum for all of the zones.
  • An iterative technique may be used to allocate the amount of spectrum to the non re-use areas.
  • the non-reuse areas reduce the scale of the computation required to allocate spectrum, thereby improving the speed of the allocation process
  • the invention also includes a processor configured to perform the method and a telecommunications network that includes the processor, together with a computer program product for the processor.
  • Figure 1 is a schematic diagram of a satellite mobile communications network
  • Figure 2 is a schematic diagram showing communication circuits of a satellite
  • Figure 3 is a schematic diagram of the footprint of the satellite divided into spot- beams
  • Figure 4 is a schematic diagram illustrating the assignment of four frequencies amongst an array of spot-beams
  • Figure 5 is a diagram of a constellation of satellites in the same orbital plane indicating leading and trailing edges their respective footprints
  • Figure 6 is a schematic of an array of spot-beams with frequency re-use, modified to take account of the overlap between the leading and trailing edge of two satellites;
  • Figure 7 is a schematic diagram of traffic demand in different regions of the earth, in which the area of the circle in each region is proportional to the demand;
  • Figure 8 is a diagram showing a circle encompassing the worst non re-use area
  • Figure 9 a schematic diagram showing spectrum in adjacent regions is consumed for a single test point
  • Figure 10 is a schematic diagram similar to Figure 9 using two and three test points
  • Figure 11 is a schematic block diagram of processing steps performed at NMC 21 to compute spectrum allocation and control call distribution to comply with the spectrum allocation
  • Figure 12 is a schematic block diagram of a process for updating the spectrum allocation.
  • FIG. 1 a schematic block diagram of a satellite mobile telecommunication network is shown corresponding to the ICOTM network.
  • a first mobile user terminal la in the form of a mobile telephone handset can communicate on a radio channel over a communication path 2, 3 via an earth orbiting satellite 4a with a first land-based satellite access node (SAN) 5a.
  • the first SAN 5a is provided with an antenna configuration 6 that can track the orbiting satellite 4a.
  • the antenna configuration 6 may include five dish antennae for tracking individual ones of the satellites 4.
  • a number of the SANs 5a, 5b, 5c, etc are connected together to form a backbone network 7, which is connected through a number of gateways (GW) 8a, 8b, 8c, etc to conventional land-based telephone networks.
  • the first GW 8a is connected to a land-based public switch telephone network (PSTN) 9, which permits connection to be made to a conventional telephone set 10.
  • PSTN public switch telephone network
  • the first GW 8a is additionally connected to a public switch data network (PSDN) 11 and a public land mobile network (PLMN) 12.
  • PSDN public switch data network
  • PLMN public land mobile network
  • Each GW 8a, 8b, 8c may comprise existing International Switching Centres or mobile switching centres (MSCs) of the type used in GSM mobile networks.
  • the gateway functions may be performed within each SAN, or externally of the SANs as shown schematically in Figure 1.
  • the user terminal la can also communicate with the conventional land-based mobile network PLMN 12, which is shown schematically to include a transceiver station 13 that establishes a duplex link 14 with the user terminal la.
  • the PLMN 12 is a GSM network.
  • ETSI European Telecommunications Institute
  • ICOTM ICOTM
  • the satellite network is designed to provide world- wide coverage and the satellites form part of a constellation of satellites, which may be arranged in several orbits. In one example, two orbits of five satellites are used, which can be shown to provide coverage of all of the surface of the earth, in which for a 10° satellite elevation angle, one satellite can be accessed by the mobile handset all of the time and two satellites can be accessed on average for 80% of the time, thereby providing system redundancy. Additional satellites may be included in the constellation in order to provide further redundancy and diversity.
  • the satellites may be arranged in a MEO constellation, for example with an orbital radius of 10,390 km, although the invention is not restricted to a particular orbital radius.
  • satellites 4a, 4b are shown in a common orbit and the satellites are tracked by the antenna arrangement of each SAN.
  • the SANs are spaced around the earth in order to provide continuous coverage.
  • the satellites are in non-geostationary orbits and comprise generally conventional satellites such as the Hughes HS 601 and may include features disclosed in GB-A-2 288 913.
  • the satellites are controlled by means of a satellite control centre (SSC) 19 and a tracking telemetry and control station (TT&C) 20, which are connected to a network management centre (NMC) 21 through a digital network 22 that is coupled to the backbone network 7.
  • SSC 19 and the TT&C 20 control operation of the satellites 4a, 4b, e.g. for setting the transmission power levels and transponder input tuning, as directed by the NMC 21.
  • Telemetry signals for the satellites 4a, 4b are received by the TT&C 20 and processed by the SSC 19 to ensure that the satellites are functioning correctly.
  • the satellite 4a communicates with a SAN 5 via a two-way antenna 18.
  • SAN-satellite signals 3 are converted in a multiplexer/demultiplexer 19.
  • the satellite communicates with a plurality of UTs la through an antenna array 20 of 163 spot beam antennas 20.
  • An up-beam processor 21 up and a down-beam processor 21 down processes the signals accordingly, to assemble and disassemble the signals fed to and from the spot beams
  • the array of 163 spot beams from each satellite covers a footprint 21 on the earth beneath each satellite, each beam including a number of different frequency channels and time slots as described in GB-A-2 293 725.
  • the beams thus provide adjacent cellular areas that correspond to the cells of a conventional land-based mobile telephone network.
  • the number of channels that can be provided in each spot beam is adjustable and can be controlled from the earth via the SANs.
  • the beam frequencies are re-used using the radio equivalent of a four colour map.
  • four-colour map theorem any map that is subjected to any manner of division on a continuous surface, can be coloured using just four colours, such that no area of one colour abuts any other area of the same colour.
  • the array of spot beams comprises groups of four spot beams A, B, C, D, shown in Figure 4, each spot beam of the group using allocable frequencies not available to the other beams in the group.
  • this arrangement is modified to take account of the overlap of footprint of adjacent satellites in the same orbit.
  • the leading edge 22 of one footprint overlaps with the trailing edge 23 of the footprint "in-front".
  • the leading and trailing portions of each cone of radio coverage have separate sets of 4 frequencies, divided between their spot beams, thereby effectively dividing the frequencies into 8 sets.
  • the arrangement is modified still further to take account of two planes of satellites, with 8 sets of frequencies apportioned to each plane of satellites.
  • a map of the world is shown with a distribution of expected demand for calls through the satellite network.
  • the world is divided into 288 zones Z of 15 x 15 degrees of latitude and longitude.
  • a circle is shown in each zone Z, which is of a size proportional to expected traffic demand, in order to illustrate the demand graphically.
  • traffic demand over the USA is relatively high whereas demand is relatively low in areas of low population or low 'phone use, such as in the middle of the Pacific Ocean.
  • each call takes up a part of the radio frequency spectrum available through one of the satellites.
  • the expected traffic demand for the network can be analysed in terms of notional units of spectrum such that each unit of spectrum is representative of a given number of concurrent calls in a particular zone Z.
  • the number of expected calls according to the traffic demand map of Figure 7, for a particular zone Z on the map will be referred to as offered traffic o and is measured in units of radio frequency spectrum.
  • the available spectrum of the satellite network is limited and thus should be allocated to spot beams of the satellites so as to satisfy the requirements of the offered traffic as far as possible.
  • the amount of radio frequency spectrum allocated to the individual spot beams thus needs to be configured so as to satisfy the relatively high spectrum requirement of the offered traffic for zones Z of high usage such as over the USA and the relatively low requirement of zones of low usage such as over the Pacific Ocean.
  • no frequency can be re-used within the cells produced by the group of four spot beams A, B, C & D, in case two adjacent cells interfere.
  • the area covered by the four spot beams is referred to herein as a "non re-use area" (NRA). If call traffic is carried over all the available frequencies for this group of beams, an increase in call traffic can only be accommodated by increasing the allocated spectrum.
  • the largest NRA is found at the edge of a satellite's field-of -view of the earth, with the cells produced by spot beams at the edge of the array as shown in Figure 3.
  • the spot beams project onto a larger area of the earth than at the centre of the satellite's field of view, due to the curvature of the earth.
  • this "worst case” covers 1.7% of the surface of the earth and represents a circle encompassing two of the outermost edge beams and the two beams next immediately inward from the edge of the array.
  • This worst case NRA (WNRA) is used as an analytical tool for allocating spectrum.
  • STP spectrum test point
  • the zones Z each have an associated offered traffic o relating to the expected demand as previously explained. Also the zones Z each have an associated available spectrum s which may be set by regulatory requirements of individual geopolitical regions and/ or by the call handling capacity of the satellite network itself. For example, the zones Z over North America may have an available spectrum s limited to 30 Mhz by regulatory requirements.
  • WNRAs are used to optimise allocation of spectrum to all of the zones Z via the spot beams of the satellite, in order to match as far as possible the available spectrum s to the offered spectrum o for each zone.
  • the spectrum for signals transmitted on an uplink to the user terminal from the SAN via the satellite and a downlink from the user terminal to the SAN, can be treated individually or collectively.
  • the properties of a WNRA will now be described with reference to Figure 9.
  • WNRA 1 is shown with its STP within zone Z6 on the earth.
  • the WNRA 1 not only encompasses Z6, but also encroaches, by different amounts, on surrounding zones Zl, 2, 3, 5, 7, 9, 10 and 11.
  • the provision of one unit of spectrum to the spot beams that make up the WNRA will be considered.
  • One unit of spectrum is thus provided to zone Z6 because WNRA 1 completely overlies zone Z6.
  • the provision of one unit of spectrum to Z6 results in the amount of available spectrum being reduced for the other, surrounding zones overlapped by the WNRA. This is because the unit of spectrum by definition cannot be reused within the WNRA but can be reused outside of it.
  • the amount of spectrum consumed by WNRA 1 in the partially overlapped, surrounding zones Zl, 2, 3, 5, 7, 9, 10 and 11 is assumed to be proportional to the fraction of their zonal area covered by the WNRA 1. The rationale for this assumption is discussed in more detail hereinafter.
  • WNRA 1 overlaps 10% of the area of zone Zl, in which case, no reusable spectrum is available in overlap region 24. Conversely, the unit of spectrum is available for reuse in the remaining 90% of zone Zl, non-overlap region 25. This all-or-nothing distribution of spectral availability is averaged out across the zone Zl, yielding a mean amount of spectrum available across the whole zone, which in this example is 90% of the spectrum available.
  • WNRAs move across the surface of the earth resulting in continuously varying amounts of overlap between WNRAs and zones.
  • the spectral use of each zone is relatively static. It can therefore be deduced that the amount of spectrum consumed by WRNA 1 in the partially overlapped, surrounding zones is, for modelling purposes, approximately proportional to the fraction of their zonal area covered by the WNRA. This assumption is made in the method described hereinafter.
  • the WNRA 1 overlaps 10% of the area of zone Za and so traffic to a point in zone Za employing an adjacent group of spot beams and using the same repeated frequencies as those of WNRA 1 has, on average, only 90% of the allocable spectrum available to it, thus limiting its capacity.
  • WNRAs can be used to test traffic provision for the zones. Z individually so as to optimise the spectrum allocation taking into account the offered traffic o and the available spectrum s from zone to zone.
  • a simple example using two WNRAs for adjacent zones will now be described with reference to Figure 10.
  • WNRA 1 has its STP 1 in zone Z6 and WNRA 2 has its STP 2 in zone Z7.
  • the available spectrum s and the offered traffic o for each of zones Zl - Z12 of Fig. 10 in arbitrary units of spectrum, are set out in Table 1. Table 1
  • Row A of Table 2 the spectral capacity for each zone that has been used by WNRA 1 is shown.
  • Row B in Table 2 indicates the spectral capacity that remains for each zone, after deducting the effect of WNRA 1.
  • Second computation - zone Z7 optimised the capacity of zone Z7 is optimised.
  • Table 3 shows the effect of WNRA 2 on the cells that surround zone Z7 in row A. The capacity of the zones which remains after the effect of WNRA 1 is deducted, is shown in row B. The calculations are carried out in the same way as described for the first computation.
  • This method can be extended to cover all of the 288 zones Z.
  • An individual STP is located in each zone and an iterative linear programming technique is used to carry out the computations for the different combinations and compare the results so as to choose the highest total use of spectrum, to satisfy best the offered traffic o for all 288 zones. It can be shown that the STPs do not need to be located in a regular pattern for the calculation to work. Some STPs may be omitted in non-critical areas to simplify the calculation. Some of the WNRAs may be weighted by a weighting factor to increase the value of traffic to certain preselected zones.
  • the calculation thus yields an optimum allocation of spectrum for each zone Z on the map shown in Figure 7.
  • the calculation may be carried out in a processor at the NMC 21 shown in Figure 1, which instructs the SANs to control the call traffic to the individual zones Z not to exceed the allocated spectrum for each zone, as determined by the calculation.
  • step SI an initial map of the individual values of offered traffic o and available spectrum s for each individual zone Z is established. This corresponds to the reference traffic distribution shown in Figure 7.
  • the maximum available spectrum may be determined by physical constraints of the satellite system but the actual value s selected may be determined by regulatory requirements and marketing information about expected demand and achievable pricing for the satellite service, zone by zone and country by country.
  • the offered traffic o may be selected on the basis of initial marketing information concerning expected demand for the service.
  • step S2 the previously described calculation process determines the spectrum allocation, zone by zone, to determine the optimum spectral allocation for each zone Z.
  • the spectrum allocation data produced in step S2 is supplied by NMC 21 to the SANs, which use the data to limit the number of calls and hence the spectrum, so that the spectral allocation of each zone Z is not exceeded.
  • the bandwith of each satellite antenna spot beam is dynamically controllable at the SAN, permitting the spectral control to be performed for each zone individually, as the spot beams sweep over the zones, due to rotation of the satellites about the earth.
  • Figure 12 illustrates how the initial map used at step SI can be updated.
  • the traffic that is actually carried by the system during a period of actual use of the network is monitored at step S4.
  • the traffic may be monitored at the SANs and reported periodically to the NMC 21, which builds up a database of actual usage, zone by zone. This enables the offered traffic values o to be updated in the light of actual experience of running the network. Also, any changes in available spectrum 5 due to regulatory changes or other reasons are logged.
  • step S5 the initial map is updated zone by zone to, take account of the data accumulated at step S4.
  • step S5 may be carried out during the monitoring period of the actual traffic rather than as a separate step.
  • step S6 the spectrum allocation is re-calculated zone by zone, using the computation process previously described, on the basis of the updated values of the offered traffic and the available spectrum produced at step S5.
  • the call allocation of step S3 is then controlled to maintain use of the spectrum on a zone by zone basis, within the zonal allocations determined by step S6.
  • steps S5 and S6 may be performed at the NMC 21 continuously, at regular time intervals or every fixed number of calls made, to ensure that no spectral overloading is taking place in any one part of the network. Even though an individual zone Z is far from overloaded, the analysis may prove that allowing further traffic at one zone may overload the spectrum in another zone. Hence, the traffic can be curtailed through congestion control or call refusal.
  • the NMC 21 may thus instruct the MSSC 16 to prevent call set up. Alternatively, the assignment of channels may be delayed until one becomes available.
  • radio frequency spectrum can be allocated accordingly in different regions without exceeding levels set by regulatory bodies of different nations.
  • the method of determining where spectral overloading is likely to occur can be used to plan a new satellite communication system, thus ensuring the system is able to provide sufficient service when commissioned.
  • the method can be used once the satellite system is operational to predict likely conflicts whenever regulatory restrictions are proposed.
  • the iteration is computed without defining a maximum available spectrum for the zones individually and instead is carried so as to satisfy completely the spectral requirements of the offered spectrum zone-by-zone.
  • the computation thus indicates the maximum available spectrum needed to satisfy all the traffic zone-by-zone. This can be useful for designing the initial traffic handling capacity prior to commissioning the network.
  • the calculations can be carried out at locations other than the NMC 21 in the network, for example in a distributed manner at the SANs or at a dedicated processor PI connected to the network (Fig. 1).
  • the calculation of spectrum allocation may be performed by a program on a computer readable medium such as a magnetic or optical disk Dl, inserted in the processor Pi.
  • the processor PI need not be connected to the network.
  • the processor may receive data concerning the offered traffic and the available spectrum, so as to provide a bureau service for networks.
  • the result of the calculations performed by the processor may be supplied on disk or via e-mail to the network and then used to control the SANs in order to ensure that the call traffic does not exceed the allocated spectrum, zone-by-zone.
  • the non-reuse areas may include more than the four cellular areas A, B, C, D as previously described.
  • the non-reuse area used in the computations need not be the worse case area, and the worse case area may, if used, be of a different area to the example given.
  • the non-reuse areas need not necessarily be circular and could be of other shapes.
  • the invention is not restricted to the satellite constellation described herein and can be used with LEO and other MEO constellations.
  • the invention is also applicable to geo-stationary constellations in high earth orbits, and also to systems which use balloons or other types of airborne craft instead of earth orbiting satellites.
  • signal transmission is not limited to the described TDMA configuration and other signal transmission techniques could be used, for example CDMA, FDMA or a combination thereof.

Abstract

La présente invention concerne un procédé d'attribution des ressources spectrales dans un réseau de télécommunications cellulaires mobiles, selon lequel on définit, par rapport à une pluralité de zones (Z) situées dans la zone de couverture du réseau, des zones de non réutilisation dans le cas le plus défavorable correspondant à un groupe de cellules (A,B,C,D) dans lesquelles le spectre ne peut pas être utilisé plus d'une fois simultanément. Les zones de non réutilisation recouvrent chacune une zone respective de la pluralité de zones précitées et chevauchent en partie les zones adjacentes à la zone recouverte. On définit un spectre maximum disponible (s) pour chaque zone respective, ainsi qu'un spectre de trafic offert (o) correspondant au spectre destiné à être utilisé par le trafic d'appels dans les zones individuelles. Le spectre est attribué aux zones de non réutilisation qui l'attribuent à leur tour à leurs zones recouvertes respectives. On détermine le spectre qui est utilisé dans les zones partiellement chevauchées par les zones de non réutilisation suite à l'attribution du spectre aux zones de non réutilisation. Ce procédé permet d'optimiser l'attribution du spectre aux zones individuelles par rapport au spectre offert et au spectre disponible, et il permet de maximiser la capacité du système à gérer le spectre de trafic offert pour toutes les zones.
PCT/GB2000/002339 2000-06-15 2000-06-15 Attribution du spectre radioelectrique WO2001097409A1 (fr)

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0616437A1 (fr) * 1993-03-15 1994-09-21 Motorola, Inc. Système de communication avec réutilisation de spectre sur une surface sphérique
WO1995028015A1 (fr) * 1994-04-08 1995-10-19 Ericsson Inc. Reseau pilote en phase a faisceaux a largeurs multiples
WO1996003814A1 (fr) * 1994-07-22 1996-02-08 International Mobile Satellite Organization Systeme de telecommunications mobile par satellite amrt multifaisceau
EP0876007A2 (fr) * 1997-04-26 1998-11-04 ICO Services Ltd. Mesure de la position d'un terminal par mesure de la puissance de signal d'une pluralité de sources radio
EP1011210A1 (fr) * 1998-12-15 2000-06-21 ICO Services Ltd. Allocation de spectre radio fréquence

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0616437A1 (fr) * 1993-03-15 1994-09-21 Motorola, Inc. Système de communication avec réutilisation de spectre sur une surface sphérique
WO1995028015A1 (fr) * 1994-04-08 1995-10-19 Ericsson Inc. Reseau pilote en phase a faisceaux a largeurs multiples
WO1996003814A1 (fr) * 1994-07-22 1996-02-08 International Mobile Satellite Organization Systeme de telecommunications mobile par satellite amrt multifaisceau
EP0876007A2 (fr) * 1997-04-26 1998-11-04 ICO Services Ltd. Mesure de la position d'un terminal par mesure de la puissance de signal d'une pluralité de sources radio
EP1011210A1 (fr) * 1998-12-15 2000-06-21 ICO Services Ltd. Allocation de spectre radio fréquence

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