Telecommunications – Carrier wave repeater or relay system – Portable or mobile repeater
Reexamination Certificate
1999-02-10
2001-12-18
Bost, Dwayne (Department: 2681)
Telecommunications
Carrier wave repeater or relay system
Portable or mobile repeater
C455S427000, C455S429000
Reexamination Certificate
active
06332069
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus and method, for use in a satellite-based communications network, for minimizing blocking of communication between the network and access terminals resulting from differences in the signal propagation delays for the access terminals due to their different locations within a coverage area serviced by a spot beam generated by a satellite in the network. More particularly, the present invention relates to an apparatus and method for minimizing such communication blocking by segregating the coverage area of the spot beam into at least one coverage zone, segregating the communication carriers available for the spot beam into a number of carrier groups corresponding to the number of coverage zones, and assigning to each carrier group a specific burst offset time period in accordance with which communication bursts are transmitted over carriers in the carrier group between the network and access terminals located within the coverage zone serviced by the carrier group.
2. Description of the Related Art
A satellite communications network, such as a geosynchronous earth orbit mobile communications network, comprises at least one geosynchronous earth orbit satellite, a ground-based advanced operations center (AOC) and spacecraft operations center (SOC) associated with the satellite, at least one ground-based gateway station (GS), and at least one access terminal (AT), which is typically a hand-held or vehicle mounted mobile telephone. The satellite enables the access terminal to communicate with other access terminals, or with other telephones in the terrestrial public switched telephone network (PSTN), via the gateway stations under the control of the gateway stations. The AOC provides system-wide resource management and control functions for its respective satellite, and the SOC controls on-orbit satellite operations for its respective satellite.
To communicate with access terminals, the network controls a satellite to generate at least one spot beam, which is typically an L-band frequency signal, toward the surface of the earth. Each spot beam covers a predetermined geographic region of the earth, thus enabling access terminals within that region to communicate with the network via communications signals transmitted to the satellite over a carrier selected from a plurality of carriers assigned to the spot beam.
For example, when an access terminal places a call to another access terminal or to a terrestrial telephone, the access terminal generates and transmits a channel request message on a random access channel (RACH) at a frequency assigned to the spot beam to the satellite. Typically, a channel request message includes data representing a random number, which is used as an identifier for the access terminal sending the channel request message, as well as contention resolution and timing synchronization information.
The satellite includes a receiver which, under the control of the network, establishes time frames of a particular duration during which channel request messages are received. When a channel request message is received by the satellite during a particular time frame, and is thus received by the network, the network transmits data via the satellite to the access terminal to establish a communication link between the access terminal and network. The data includes access channel information (access grant channel information) indicating the frequencies of the carriers over which communication between the network and the access terminal is to occur during the call. Typically, a carrier of a particular frequency is assigned to service transmission of communications from the satellite to the access terminal, and a carrier of another frequency is assigned to service transmission of communications from the access terminal to the satellite. Hence, a pair of carriers service communication between the satellite and an access terminal.
Communication between the network and access terminal occurs in the form of signal bursts of a predetermined duration which are transmitted over the carrier pair designated by the access grant channel information between the access terminal and satellite. Signal bursts transmitted from the satellite to the access terminal, along with signal bursts being transmitted to other access terminals, if any, also assigned to a carrier in the carrier pair, are transmitted over the carrier in a time-division multiple access (TDMA) manner. That is, each signal burst being transmitted from the satellite to the access terminal is time-multiplexed with the signal bursts being transmitted by the satellite to the other access terminals in a TDMA frame of a particular duration, and transmitted over the carrier.
A TDMA frame includes a plurality of timeslots, which become occupied by the time-multiplexed signal bursts being transmitted. For example, a TDMA frame can include 24 timeslots, and each signal burst can be 3 timeslots long. Accordingly, a 24 timeslot TDMA frame can contain up to eight signal bursts which are being transmitted to eight respective access terminals (i.e., 8 signal bursts of 3 timeslots each), with each burst occupying three specific sequential timeslots of the TDMA frame. Naturally, a 24 timeslot TDMA frame can accommodate only four signal bursts which are each 6 timeslots in length, with each signal burst occupying six specific sequential timeslots of the TDMA frame.
Upon receiving its appropriate signal burst transmitted from the satellite, each access terminal transmits a signal burst back to the satellite in a TDMA frame over the other carrier in the carrier pair. An access terminal begins transmitting its respective signal burst at an appropriate instant in time after the instant in time at which the access terminal began receiving its respective signal burst transmitted from the satellite as described above. Because the transmitter/receiver of an access terminal is a typically a half-diplexer which permits only signal transmission or signal reception at any given time, the time period in which the access terminal transmits a signal burst can not overlap the time period in which the access terminal is receiving a signal burst.
Specifically, each access terminal begins transmitting its respective signal burst at an appropriate time after receiving a signal burst, which will properly position the signal burst in the TDMA frame so as not to overlap any other signal burst being transmitted by another access terminal, and so that the signal burst will be received at the satellite at the appropriate receive time. An access terminal determines when transmission of the signal burst should begin based on the amount of burst offset required at the satellite, which is the desired duration of time which should elapse from the start of transmission by the satellite of a signal burst to the access terminal and the subsequent start of receipt by the satellite of a signal burst transmitted from that access terminal. The access terminal also takes into account an estimated time which will elapse between the instant when a signal burst is transmitted by the access terminal and the instant when that signal burst is received by the satellite, which is known as the propagation delay.
An access terminal estimates the propagation delay for a distance measured from its location on the earth's surface to the satellite, which is orbiting at about 22,000 miles above the earth's surface. Because the distance from the surface of the earth at the equator to the satellite is less than the distance from the surface of the earth in the extreme northern and southern hemispheres to the satellite, the propagation delay for a signal burst sent from an access terminal close to the equator is less than that for a signal burst sent from an access terminal in, for example, northern Europe. An access terminal can include global positioning system (GPS) equipment, or any other suitable device, which enables it to determine its location on the earth's surface, and thus es
Arnold Steven
Noerpel Anthony
Roos Dave
Zhao Wei
Bost Dwayne
Hughes Electronics Corporation
Sales Michael W.
Trinh Sonny
Whelan John T.
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