Telecommunications – Carrier wave repeater or relay system – Portable or mobile repeater
Reexamination Certificate
2000-05-23
2004-03-09
Maung, Nay (Department: 2684)
Telecommunications
Carrier wave repeater or relay system
Portable or mobile repeater
C455S013100, C455S427000, C455S429000
Reexamination Certificate
active
06704543
ABSTRACT:
TECHNICAL FIELD
This invention relates to satellite communications systems using multiple spot beams from a geosynchronous earth orbit satellite to provide selective coverage of the continental United States and, more particularly, relates to a system having a satellite receiving hub in every spot beam that allows for asynchronous communications between each hub and the satellite for maximizing frequency re-use.
BACKGROUND OF THE INVENTION
The rapid growth of the Internet and the unavailability of high-speed connections from standard telephone lines and local cable providers have resulted in an intense search for an alternative high-speed mode of communications. Satellite communications (“SATCOM”) systems are a natural selection for replacing conventional land-based communications systems as a means of providing high-speed digital communications new links.
Typical SATCOM system configurations are shown in
FIGS. 1-3
.
FIG. 1
is an illustration of a SATCOM “bent-pipe” configuration for two ground terminals located within the same beam. In the bent-pipe configuration, a first ground terminal
102
transmits a signal on the uplink frequency band to a GEO satellite
108
. Upon reception of the signal, the GEO satellite shifts the frequency of the signal to a downlink frequency and retransmits the signal to the second ground terminal
104
. The “bent-pipe” configuration does not require the satellite to have on-board processing. Rather, the satellite merely acts as a relay from one ground terminal to another ground terminal. Because the satellite does not have on-board processing, the “bent-pipe” configuration is typically limited to use within a single beam
106
.
Another standard SATCOM configuration is shown in
FIG. 2
, which illustrates a SATCOM “hub” configuration. In the “hub” configuration, a series of ground terminals
202
,
204
and a single hub
206
are located within a single beam
208
. The hub acts as a two-step bent-pipe configuration, in which the uplink signal is routed from the GEO satellite
210
to an intermediate ground hub
206
. The hub acts as a local control center to assign channels and other functions associated with the network management. The intermediate stop typically adds an additional ¼-second to the signal propagation delay normally associated with the round-trip to a GEO satellite, which is unacceptable for high-quality telephony services. In order to avoid this additional delay, the hub configuration can also operate as a “bent-pipe” configuration, in which the hub is bypassed and the downlink signal is routed directly to a second ground terminal.
Additionally, ground terminals within the hub configuration may also operate in a one-way “broadcast” mode, in which a single ground terminal transmits an uplink signal to the GEO satellite, which shifts the frequency for transmission on the downlink channel. However, instead of simply transmitting the downlink signal to a single ground terminal, the satellite “broadcasts” the signal over the downlink channel to every ground terminal within the beam.
Still another standard SATCOM configuration is shown in
FIG. 3
, which is an illustration of the SES ARCS SATCOM system. The ARCS SATCOM system combines DVB technology on the downlink signal with a high-speed satellite uplink signal. The ARCS SATCOM system uses a standard Ku-Band DVB downlink
314
and a “piggyback” Ka-band payload, which routes Ka-band uplinks
316
from individual ground terminals
304
to a single hub
306
, located in Luxembourg. The ARCS SATCOM system provides eight beams
302
on the Ka-band uplink, each of which has a footprint of approximately 500 miles diameter on the earth. As a result of this high gain from the receive antenna on the satellite
308
, a dish only 75 cm in diameter with a ½W transmitter can provide 144 Kbps return channel data rate. The Ka-band uplinks from all eight of the beams are returned to the single hub in Luxembourg for processing. The DVB video data for the Ku band is broadcast on an uplink signal
312
to the satellite from the hub
306
, and is re-broadcast on the downlink signal using Ku-band DVB transponders.
Conventional SATCOM systems using geosynchronous earth orbits (“GEO”) satellites have typically provided two types of services: (a) a relay mode, in which the GEO satellite merely relays a signal from one earth terminal to another, and (b) a broadcast mode, in which the GEO satellite transmits a signal to a large number of ground terminals. In the relay mode, also known as a “bent-pipe” mode, a ground terminal transmits a signal using an uplink frequency to the GEO satellite, which retransmits the signal to a second ground terminal using a downlink frequency. This mode is illustrated in FIG.
1
. Because the transmission footprint of the GEO satellite on the earth surface is large, the power density of the signal is very low. This requires that the receiving antenna be sufficiently large, ranging from one to three meters in diameter, to achieve the requisite antenna gain. However, these large antennas are practical only for large, commercial users. Individual consumers cannot afford the space or expense of these large ground antennas. Individual consumers are willing to tolerate only small antennas, such as those used for direct broadcast satellite (DBS) transmissions, which are typically one to two feet in diameter.
Small ground antennas often operate with a “hub” service, in which the user uplink is routed from the satellite to an intermediate ground station known as the “hub.” This service is illustrated in FIG.
2
. The hub usually acts a local control center to assign channels and other functions associated with network management. This intermediate “stop” adds an additional ¼ second to the propagation delay associated with the round trip to synchronous orbit, so the total delay in one terminal transmitting to another is approximately ½ second—a delay many consider too long for viable high quality telephony today. The GEO satellite can also operate in a “mesh” configuration in which the user downlink is routed directly to the other user without the hub transmission.
In the broadcast mode, a hub or “feeder link” sends the entire spectrum of broadcast signals to the GEO satellite, which then rebroadcasts the signals to the region of interest. It is important to note that in the broadcast service all users receive the same signals, which are typically transmitted at nearly equal power levels because the ground terminals are assumed to receive the entire band of signals everywhere. The broadcast spectrum is divided up into a number of transponder bandwidths, each of which can carry a multiple of standard TV channels, high definition TV, or data. This type of transmission has become especially important in the direct broadcast satellite (“DBS”) of standard broadcast television as a competing service to cable.
Typically, GEO SATCOM systems use a single wide area coverage beam with a diameter of approximately 2,500 miles to provide complete coverage of CONUS. Therefore, in order for a ground antenna to receive adequate signal strength, the transmitter on the satellite must have sufficient power to provide an adequate power density within the single wide area coverage beam. However, this greatly increases the cost and complexity of the GEO satellite.
Another way to ensure that the ground terminal receives adequate signal strength is to use a ground station with a large diameter antenna to achieve the requisite gain. However, as the size of the antenna increases, so does the expense. Therefore, only commercial users are able to afford these antennas. Clearly, this solution is unacceptable to individual users, who demand cheaper, more aesthetically pleasing, smaller antennas.
Several attempts have been made to address this problem. One solution is to use a number of smaller spot beams instead of a single wide area coverage beam to cover the same geographical area. By decreasing the size of the spot beams while maintaining the same overall transmitted power, the power d
Hafner William R.
Howell James M.
Rigg Steven H.
Sharon Thomas E.
Taylor Thomas S.
EMS Technologies Inc.
King & Spalding LLP
Maung Nay
Orgad Edan
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