Telecommunications – Carrier wave repeater or relay system – Portable or mobile repeater
Reexamination Certificate
1998-03-31
2001-04-03
Trost, William G. (Department: 2681)
Telecommunications
Carrier wave repeater or relay system
Portable or mobile repeater
C455S427000, C455S232100
Reexamination Certificate
active
06212360
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention pertains to the field of satellite communications. More particularly, the present invention relates to satellite-communication networks comprising a master earth-station and a number of remote earth-stations. In particular, this invention pertains to the control of the signal power level transmitted by the earth-stations in such networks.
2. Description of the Related Art
FIG. 1
shows a conventional very small aperture terminal (VSAT) satellite-communication network. The VSAT network comprises a master earth-station, referred to herein as a “hub”
10
, a number of remote earth-stations, referred to herein as “VSATs”
20
, and a geostationary communication satellite transponder, referred to herein as a “satellite”
30
. The hub
10
communicates with the VSATs and the VSATs
20
communicate with the hub
10
by sending transmission signals
40
through the satellite
30
.
FIGS. 2A through 2D
illustrates the operation of the conventional VSAT satellite communication network of FIG.
1
. As these figures show, the communication between the hub
10
and the VSATs
20
is accomplished through the use of an outbound transmission signal from the hub
10
to the VSATs
20
, and an inbound transmission signal from the VSATs
20
to the hub
10
.
FIGS. 2A and 2B
illustrate an outbound transmission signal from the hub
10
to a VSAT
20
. As shown in
FIG. 2A
, the outbound transmission signal first includes an outbound uplink portion
210
, passing from the hub
10
to the satellite
30
. As shown in
FIG. 2B
, the outbound transmission signal also includes an outbound downlink portion
220
, passing from the satellite
30
to the hub
10
and all VSATs
20
.
FIGS. 2C and 2D
illustrate an inbound transmission signal from a VSAT
20
to the hub
10
. As shown in
FIG. 2C
, the inbound transmission signal first includes an inbound uplink portion
230
, passing from a VSAT
20
to the satellite
30
. As shown in
FIG. 2D
, the inbound transmission signal also includes an inbound downlink portion
240
, passing from the satellite
30
to the hub
10
.
The outbound transmission signal
210
and
220
is a continuous signal sent from the hub
10
. In contrast, the inbound transmission signal
230
and
240
is sent in bursts as needed by the various VSATs
20
.
Satellite transponder resources are sold and leased in units of power and bandwidth. A VSAT network operator must carefully control both resources in order to achieve economical operation.
Code-division multiple-access (CDMA) is a multiple-access technique that forms the basis for the IS-95 digital cellular telephony standard, and has some important advantages for use in VSAT networks, particularly when it is important to be able to use small antennas at the remote terminals. The first widely-deployed VSAT networks using CDMA used the C200 product developed by Equatorial Communications Company (ECC) of Mountain View, Calif.
It is widely recognized that accurate power control is required to equalize the received power levels of signals multiplexed on a channel using the CDMA technique to maximize the operational efficiency of the network. Qualcomm, Inc. has developed a number of power control techniques for use in the CDMA cellular telephony networks that they have developed based on the IS-95 standard. Qualcomm's techniques are designed for terrestrial networks that operate without a satellite relay, and are designed to cope with the rapid fading that occurs in a mobile terrestrial microwave propagation environment.
Operational experience with the ECC C200 networks also showed the need for accurate power control of the VSAT transmitters. The C200 product was limited by the fact that the control of the VSATs' inbound (VSAT-to-hub) transmitted power levels had to be accomplished by manual intervention of an operator at the hub. Since the C200 system was primarily designed for C-Band operation, the rapid fading that occurs at higher frequencies due to rain was not a serious problem for the system. However, VSAT networks based on this product typically required periodic expert rebalancing of the inbound power levels across the network to compensate for gradual changes in the equipment or haphazard adjustments by inexperienced operators.
For VSAT networks operating at Ku-Band and higher frequencies, rain fade is a serious problem. Rain fade results from the absorption and scattering of the transmission signals
40
between the hub
10
and satellite
30
and between the VSATs
20
and the satellite
30
by water droplets or ice crystals in the atmosphere. During rain fade, changes in attenuation and hence the received signal level can occur within a few seconds. At Ku-Band and higher frequencies, rapid and automatic uplink power control becomes very important.
Uplink power control has typically been implemented only on the outbound (hub-to-VSAT) link, where the additional cost of the equipment at the hub is of minor consequence. A rain fade affecting the outbound uplink (a rain fade between the hub
10
and the satellite
30
) affects the entire network, while a rain fade on the inbound uplink (a rain fade between a VSAT
20
and the satellite
30
) only affects that VSAT
20
. Standard practice has been to operate the VSATs
20
with enough inbound (VSAT-to-hub) power to overcome most rain fades.
For CDMA VSAT operation at Ku-Band and higher frequencies, however, uplink power control on the inbound signal becomes a necessity. Uplink power control can also benefit TDMA and other modes of satellite access operation by providing the network operator the ability to control and thus reduce his transponder power requirement, by only operating the VSAT transmitter at high power levels when required to overcome rain fades.
SUMMARY OF THE INVENTION
It is an object of this invention to provide methods and apparatus for precisely and accurately controlling the power levels of both the hub earth station and the VSAT transmitters in a VSAT network.
It is another object of this invention to provide power control methods and apparatus that take into account the specific effects of the satellite transponder relay between the hub and the VSATs.
It is yet another object of this invention to provide power control mechanisms for both the outbound and the inbound links in a VSAT network that respond rapidly to changes in the atmospheric attenuation between the earth stations and the satellites.
It is still another object of this invention to provide power control mechanisms that include checks against long-term creep in the inbound power level settings of the VSATs in a VSAT network.
It is a further object of this invention to provide multiple independent means of determining whether and when the power level of an individual VSAT transmitter should be adjusted to maintain its link performance close to a setpoint.
It is a still further object of this invention to provide VSAT power control means that facilitate adjustment of the VSAT inbound link performance to take into account the requirements of different types of traffic.
It is also an object of this invention to provide VSAT power control techniques that include the ability to change the link rate to effect a change in the link performance when this cannot be accomplished by adjustments in transmitter power alone.
It is an additional object of this invention to provide power control techniques that take into account the capability of the VSAT transmitter to control its output spectrum.
Therefore, a method is presented for providing stable communication between a hub earth-station and a VSAT earth-station by regulating the power of signals transmitted via a satellite, the method comprising the steps of regulating the power an outbound signal transmitted by the hub to VSAT via the satellite, based on one of a beacon signal received from the satellite and a previous outbound signal, sending signal information from the hub to the VSAT in the outbound signal, and regulating the power of an inbound signal transmitted by th
Check William A.
Chisholm Joseph A.
Fleming, III Robert F.
Glinsman Brian J.
Kim David B.
Craver Charles
GE Capital Spacenet Services, Inc.
Jones Volentine, L.L.C.
Trost William G.
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