Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1998-08-12
2001-04-03
Nguyen, Lee (Department: 2683)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C435S430000, C435S012000, C370S321000
Reexamination Certificate
active
06212378
ABSTRACT:
BACKGROUND OF THE INVENTION
Mobile cellular communication systems have become of increasing importance, providing mobile users the security of being able to seek aid in case of trouble, allowing dispatching of delivery and other vehicles with little wasted time, and the like. Present cellular communication systems use terrestrial transmitters, such as towers, to define each cell of the system, so that the extent of a particular cellular communication system is limited by the region over which the towers are distributed. Many parts of the world are relatively inaccessible, or, as in the case of the ocean, do not lend themselves to location of a plurality of dispersed cellular sites.
In these regions of the world, spacecraft-based communication systems may be preferable to terrestrial-based systems. It is desirable that a spacecraft cellular communications system adhere, insofar as possible, to the standards which are common to terrestrial systems, and in particular to such systems as the GLOBAL SYSTEM FOR MOBILE COMMUNICATIONS system (GSM), which is in use in Europe.
The GSM system is a cellular communications system which communicates with user terminals by means of electromagnetic transmissions from, and receptions of such electromagnetic signals at, base stations, fixed sites or towers spaced across the countryside. The term “user terminal” for purposes of this patent application includes mobile user terminals, and also includes hand-held and fixed user terminals, but not gateways. The GSM system is described in detail in the text
The GSM System for Mobile
Communications, subtitled
A Comprehensive Overview of the European Digital Cellular System,
authored by Michel Mouly and Marie-Bernadette Pautet, and published in 1992 by the authors, at 4, rue Elisée Reclus, F-91120 Palaiseau, France. Another text describing the GSM system is
Mobile Radio Communications,
by Raymond Steele, published 1992 by Pentech Press, London, ISBN 0-7273-1406-8. Each base station of the GSM system includes transmitter and receiver arrangements, and communicates with user terminals by way of signals in a bandwidth of 50 MHz, centered on 900 Mhz., and also by way of signals having a bandwidth of 150 Mhz centered on 1800 Mhz.
A cellular communication system should provide one or more control channels for allowing a user terminal to initially synchronize to the system, and to initiate communications with the overall network. Each base station, fixed site, or tower continually transmits network synchronization information (SCH) and network-specific information (BCCH), which a user terminal uses to synchronize to the appropriate network at initial turn-on of the user terminal. The GSM system provides a channel denominated “Random Access Channel” or RACH. In GSM, the RACH channel is used for initial synchronization of the network to the user terminal.
Spacecraft cellular communication systems are desired.
SUMMARY OF THE INVENTION
A spacecraft-based cellular time-division multiple access communication system for communication among terrestrial user terminals and terrestrial gateway terminals includes a spacecraft including a receiving arrangement, a frequency-dependent routing arrangement, a transmitting arrangement, and an antenna arrangement coupled to the transmitting and receiving arrangements. The antenna arrangement forms a plurality of beams directed toward the Earth's surface, each in a different direction, so that each beam overlies a different terrestrial footprint, some of which footprints may lie closer to the nadir than to the horizon, and others of which footprints may lie closer to the horizon than to the nadir, the receiving arrangement being for at least receiving reverse control signals transmitted over the beams from at least the user terminals, and for receiving forward control signals transmitted over at least one of the beams by way of uplink frequencies. The routing arrangement is for routing the reverse control signals and the forward control signals received by the receiving arrangement to appropriate ones of the transmitting arrangements in response to the uplink frequencies. The transmitting arrangement is for transmitting the reverse control signals and the forward control signals on at least one downlink frequency carried over one of the beams, so that the spacecraft operates in a bent-pipe manner. A plurality of the reverse and forward control signals may be transmitted from the spacecraft. The communication system
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includes a plurality of first terrestrial user communication terminals. Each of the first terrestrial user communication terminals is adapted for transmitting reverse control signals to the spacecraft by way of burst transmissions on at least one of the uplink frequencies in a first beam associated with a particular one of the footprints within which the first terrestrial user communication terminals lie. The footprint of the first beam lies near the nadir. The communication system also includes a plurality of second terrestrial user communication terminals. Each of the second terrestrial user communication terminals is adapted for transmitting reverse control signals to the spacecraft by way of burst transmissions on at least one of the uplink frequencies in a second beam associated with a particular one of the footprints within which the second terrestrial user communication terminals lie. The second footprint lies near the horizon. The communication system includes a network control center coupled to the communication system, for generating forward control signals for transmission to the terrestrial user terminals, for assigning time slots for transmissions to and from the terrestrial user terminals in a time-division multiple access manner, and for receiving the reverse control signals during receive time slots, the durations of the receive time slots selected for reception of the reverse control signals from the first terrestrial user terminals being exceeded by the durations of the receive time slots selected for reception of the reverse control signals from the second terrestrial user terminals, whereby burst transmissions from terrestrial user terminals within footprints lying nearer the horizon than to the nadir, which are potentially subject to a greater range of time delays than those burst transmissions from terrestrial user terminals lying nearer to the nadir than to the horizon, are received within longer receive time slots, which longer receive time slot tends to accommodate a greater range of temporal error. In a particular embodiment of the invention, the spacecraft includes a solar panel and power supply arrangement which produces electrical power for energizing the spacecraft and for generating the energy to be transmitted over the beams, and in this embodiment the network control center generates a single control signal carrier for each of the spot beams in order to reduce to a minimum the power requirements on the solar panel and power supply arrangement. In a communication system in which communications are desired between the terrestrial user terminals and a public switched telephone network, the system further comprises at least one gateway terrestrial terminal coupled to the public switched telephone network and communicating with the spacecraft under the control of the network control center, so that information signals may be routed among the terrestrial user terminals and users of the public switched telephone network. The network control center may be physically located separate from the one gateway terrestrial terminal.
REFERENCES:
patent: 5592481 (1997-01-01), Wiedeman et al.
patent: 5644572 (1997-07-01), Olds et al.
patent: 5974315 (1999-10-01), Hudson
patent: 6014372 (2000-01-01), Kent et al.
Lockheed Martin Corp.
Meise W. H.
Nguyen Lee
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