WO2015139146A1

WO2015139146A1 - System and method for satellite network capacity boost by frequency cross-strapping

Info

Publication number: WO2015139146A1
Application number: PCT/CA2015/050222
Authority: WO
Inventors: Dave WENDLING; Ken SKUBLICS; Victor GOODING; Surinder PAL SINGH; Andre E. Bigras
Original assignee: Telesat Canada
Priority date: 2014-03-21
Filing date: 2015-03-23
Publication date: 2015-09-24
Also published as: CA2847314A1

Abstract

The present invention relates to satellite systems and more particularly, to the provision of a satellite system and method which provides a smooth transition for legacy systems to exploit higher communication frequencies. The improved system and methods described herein are novel in that they separate the standard gateway frequency bands from the user frequency bands, and they incorporate a switch that provides the capability to switch between two frequency bands on the gateway side, while keeping the same uplink and downlink frequencies of operation for the user side. This ability for in-orbit switching of the gateway frequencies of operation offers major benefits in terms of a boost in throughput capacity and flexibility in satellite replacement transition logistics, while maintaining system performance.

Description

System and Method for Satellite Network Capacity Boost by Frequency Cross- Strapping

FIELD OF INVENTION

[0001] The present invention relates to satellite systems and more particularly, to the provision of a satellite system and method which provides a smooth transition for legacy systems to exploit higher communication frequencies.

BACKGROUND OF THE INVENTION

[0002] The demand for broadband satellite services such as Internet access, data, voice, video and other services has been growing steadily over the years. As a result there is a need to provide additional communication bandwidth, and a need to transition existing lower- frequency systems to higher frequencies.

[0003] Operating a given satellite to provide the needed broadband services in a specific geographic area requires an optimum combination of available orbital slot, frequency band of operation, and corresponding landing rights for the slot and the area. Typical Fixed Service Satellite (FSS) broadband networks operate in a single spectrum band with its associated uplink and downlink frequencies, such as in the V-band (50 to 75 GHz), Ka-band (26.5 to 40 GHz), Ku-band (12 to 18 GHz) and the C-band (4 to 8 GHz). With the continued upward trend in demand for more capacity and lower service costs, more and more satellites are being designed to operate in the higher bands which offer more frequency spectrum, with more total throughput and the associated cost reductions through economies of scale. However, in many cases, operators have legacy systems operating at lower frequencies with extensive installed user infrastructure, making the complete transition to a higher frequency band an expensive operational and logistical challenge. Furthermore, for areas with high rain fade attenuation, service delivery at a higher frequency may result in degradation of link availability due to higher fade attenuation, or equivalently, a reduction in the bandwidth efficiency (i.e., Mbps/ Hz) in order to maintain performance levels. [0004] Such barriers preventing legacy lower frequency network operators and users from taking advantage of the benefits of higher frequency bands are a direct consequence of the normal satellite system implementations with the combinations of uplink and downlink frequencies that are pre-defined on a standard frequency band basis. Most existing satellite communication systems are designed to operate in a specific frequency band that can only be changed at great expense and inconvenience, for example, by purchasing, installing and commissioning new equipment and infrastructure.

[0005] Suppose for example, that a satellite operator has a single Ku-band satellite system 100 as shown in Figure 1, where a single gateway 102 communicates with a Ku-band satellite 104 via an uplink channel 106 and the Ku-band satellite 104 communicates with multiple user terminals 108 via a downlink channel 110. The satellite operator may encounter the following situation:

1. The Ku-band satellite 104 is nearing end-of-life, and has to be replaced soon to provide continuity of service. The satellite operator is faced with the following dilemma: a) replacement with another single-band Ku satellite that does not allow for the inevitable network growth over the new satellite's lifetime, or b) replacement with a single-band Ka satellite that would provide more capacity for growth, but would also involve the daunting task of transitioning all of the user terminals to Ka-band. That is, all of the user terminals 108 would have to switch to new hardware which operates in the Ka-band; or

2. The Ku-band satellite is at mid-life, but is already fully utilized with additional demand being unsatisfied due to lack of capacity. The decision is either to: a) wait for end-of-life and risk loss of market, or b) launch a new satellite now, with the dilemma given in item 1 above.

[0006] Clearly, none of these options are desirable. There is therefore a need for an improved satellite system and method, and there is particularly a need for a satellite system and method which provides for a smooth transition of legacy systems to a higher communication frequency.

SUMMARY OF THE INVENTION

[0007] It is an object of the invention to provide an improved satellite system and method which mitigates upon the problems described above and in particular, provides for a smooth transition of legacy systems to a higher communication frequency.

[0008] As noted above, barriers preventing legacy lower frequency network operators and users from taking advantage of the benefits of higher frequency bands are a direct consequence of the normal satellite system implementations with the combinations of uplink and downlink frequencies that are pre-defined on a standard frequency band basis. The improved system and methods described herein are novel in that they separate the standard gateway frequency bands from the user frequency bands, and they incorporate a switch that provides an in-orbit capability to switch between two frequency bands on the gateway side, while keeping the same uplink and downlink frequencies of operation for the user side. This ability for in-orbit switching of the gateway frequencies of operation offers major benefits in terms of a boost in throughput capacity and flexibility in satellite replacement transition logistics, while maintaining system performance.

[0009] In one embodiment of the invention there is provided a satellite system comprising: a satellite; at least one gateway in communication with the satellite; at least one user in communication with the satellite; the at least one gateway being operable to transmit a command to the satellite directing it to transition gateway-to-satellite communication from a current frequency band, to a higher frequency band; and the satellite being operable to receive the command to transition to a higher frequency band, and in response to receiving the command to transition to the higher frequency band, to switch communication with the at least one gateway to the higher frequency band, cross-strapping the communications to the at least one user in the current frequency band. [0010] In another embodiment of the invention there is provided a method of operation for a satellite system satellite system comprising: providing a satellite communications system including: a satellite; at least one gateway in communication with the satellite in a current frequency band; and at least one user in communication with the satellite in the current frequency band; the at least one gateway transmitting a command to the satellite directing it to transition gateway-to-satellite communication from the current frequency band, to a higher frequency band; and the satellite receiving the command to transition to a higher frequency band, and responding to receiving the command to transition to the higher frequency band, by switching communication with the at least one gateway to the higher frequency band, cross- strapping the communications to the at least one user in the current frequency band.

[0011] In a further embodiment of the invention there is provided a satellite gateway comprising: communication means for transmitting and receiving signals to and from a satellite, and means for transmitting a command to the satellite directing it to transition gateway-to-satellite communications from a current frequency band, to a higher frequency band.

[0012] In a still further embodiment of the invention there is provided a satellite comprising: communication means for transmitting and receiving signals to and from a base station; flight control means; and means responsive to a command to transition to a higher frequency band, by switching communication with a gateway to the higher frequency band, cross-strapping the communications to at least one user in a current frequency band.

[0013] Other systems, methods, features and advantages of the invention will be, or will become, apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description, be within the scope of the invention, and be protected by the following claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] These and other features of the invention will become more apparent from the following description in which reference is made to the appended drawings wherein:

Figure 1 presents a block diagram of an exemplary satellite communications system as known in the art;

Figures 2 A and 2B present a block diagram of an exemplary satellite communications system where the gateway is located within the user coverage area, and a corresponding frequency schedule;

Figures 3A and 3B present a block diagram of an exemplary satellite communications cross- strapping system where the gateway is located within the user coverage area, and a corresponding frequency schedule;

Figure 4A presents a block diagram of an exemplary satellite communications cross- strapping system where the gateway is located outside the user coverage area, while Figures 4B to 4E set out corresponding frequency schedules for three communication bands of the system;

Figure 5 presents an exemplary block diagram for a gateway in an embodiment of the invention;

Figures 6A and 6B present exemplary block diagrams for a satellite in an embodiment of the invention, Figure 6A presenting the general operational components, and Figure 6B presenting the communication components; and

Figure 7 presents a flow chart of an exemplary method of implementing the invention.

[0015] Similar reference numerals have been used in different figures to denote similar components. DETAILED DESCRIPTION

[0016] As noted above, there is a need for a satellite system and method which overcomes some of the difficulties inherent in the use of prior art systems. In particular, it is desirable that the improved satellite system and method provide for a smooth transition of legacy systems to a higher communication frequency.

[0017] The invention proposes a novel satellite payload system that provides multiple benefits to the service provider and the users, including boosting the capacity of the existing network while allowing users to keep their existing user infrastructure. The system allows gateways to transition the frequency they use to communicate with satellites smoothly to a higher frequency, while providing continuous services to their users (i.e. the users continue to communicate with the satellite at the same frequency as before). The benefits are derived from a satellite with a flexible, on-board, switchable cross-strapping capability that enables the operating gateway frequency band to be changed when required. Cross-strapping refers to a signal being uploaded in one frequency and being downloaded in another. In the cross- strapping examples described herein, signals are uploaded from the gateway to the satellite in the higher frequency Ka-band, and are downloaded to user terminals in the lower frequency Ku-band, though of course, other frequency bands may also be used.

[0018] The system includes a satellite that incorporates a dual -band communication payload with in-orbit capability to change its operational frequency band via an integrated on-board switch. In general, the invention may be applied to any two different frequency bands with the specifics of the application depending on the satellite operator's requirements. In one embodiment of the invention which offers distinct and significant advantages, gateway operation is switched from a lower frequency band to a higher frequency band. More specifically, consider an operational single band Ku-band network with a number of gateways and a large number of user terminals in service. As explained above, suppose that the satellite operator has a Ku-band satellite that is nearing end-of-life, and has to be replaced soon to provide continuity of service. The satellite operator has two options: replace the satellite with another single-band Ku satellite that does not allow for the inevitable network growth over the new satellite's lifetime, or replace the satellite with a single-band Ka satellite that would provide more capacity for growth, but would also involve the daunting task of transitioning all of the user terminals to Ka-band. If the satellite operator has a Ku-band satellite that is at mid-life, but is already fully utilized with demand being unsatisfied due to lack of capacity, the satellite operator has two options: wait for end-of-life and risk loss of market in the meantime, or launch a new satellite now, which puts the operator in the same dilemma as the operator who must decide whether to launch a new Ku satellite with less capacity than required, or launch a Ka satellite that his customers cannot access without significant investment and inconvenience.

[0019] A replacement satellite mission based on the subject invention, consisting of a satellite designed with communication payload hardware for both Ku-band and Ka-band gateway operation, and with selection of the operational gateway frequencies via a switch, offers an attractive solution for both scenarios, with the following specific advantages over a replacement single band system. In the following discussion, a single polarization is assumed for simplicity, without loss of generality:

First Scenario: Ku-band Gateway is Located Within the User Coverage Area

[0020] If the Ku-band gateway 205 is located within the user coverage area 210 as shown in FIG. 2A, the available 500 MHz of Ku-band spectrum in a legacy system must be shared between the forward and return links, e.g., 250 MHz in either direction. This is clear from the exemplary frequency schedule of FIG. 2B which sets out nine gateway channels Gl (T01, T02, T03, T07, T08, T09, T13, T14, T15) and seven user channels Ul (T04, T05, T06, T10, Ti l, T12, T16). Of course, other schedules and assignments may be used, including different numbers of channels and transponders.

[0021] In contrast, a replacement satellite 305 with the switchable Ka-band/Ku-band option of the invention (see the layout shown in FIG. 3A) serving the same coverage area 210 would have access to up to 1.5 GHz of Ka-band spectrum for gateway operation, allowing the addition of a new Ka Gateway G2 310 to complement an existing Ku Gateway Gl 205. This additional spectrum for gateway operations would allow the full 500 MHz of Ku-band spectrum to be used for forward links and return links on the user side. In effect, a switch to Ka-band operation on the gateway side would provide a capacity boost of 100%, allowing the service provider to respond in a timely and cost-effective fashion to demand growth in terms of number of user terminals, speed and service tiers.

[0022] The exemplary frequency schedule of FIG. 3B sets out sixteen channels for each of the Ka-band and the Ku-band, organized into three banks: Bank 1, Bank 2 and Bank 3. Bank 1 serves User 1 (channels T01 - T06), Bank 2 serves User 2 (channels T07 - T12) and Bank 3 serves User 3 (channels T13 - T16). Cross-strapping is enabled for Bank 1 and Bank 3, so signals are uploaded from Gateway G2 in the Ka-band, and are downloaded to User terminals 1 and 3 in the Ku-band. Cross-strapping is not enabled in Bank 2, so uploading is done from Gateway Gl in the Ku-band and downloading to User U2 is also done in the Ku-band. In this embodiment there is a one-to-one correspondence on the occupied bandwidth, that is, 36 MHz at Ku is translated to 36 MHz of Ka and vice versa. If on-board processing and converting to packets is done, one can demodulate and remodulate using different error correction. The different efficiencies achieved in the Ku and Ka bands may lead to having many more user channels per the equivalent bandwidth at Ka. Again, other schedules and assignments may be used, including different numbers of channels and transponders.

Second Scenario: Ku-band Gateway is Located Outside the User Coverage

[0023] If the Ku-band gateway is located outside of the user coverage area, the Ku-band spectrum would not have to be shared between the forward and return links, thus providing 500 MHz of Ku-band capacity to the user terminals. If the Ku-band satellite is replaced by a dual-band satellite 305 operating with a Ka-band gateway 310, the same 500 MHz of capacity could be delivered to the user coverage area. Previously, the bandwidth could only be used for the gateway. With the gateway now in the Ka band, the user coverage area can be served by the newly available Ku spectrum. Furthermore, the Ka-band gateway 310, with access to up to 1.5 GHz of Ka-band spectrum, would be able to serve up to three such user coverage areas 405, assuming they are appropriately spatially separated to avoid Ku-band co-frequency interference (see FIG. 4A). In contrast, the prior art Ku-band system would have required three spatially separated gateways to serve the same three coverage areas. Thus, this scenario allows fewer gateways to be used.

[0024] Figure 4B presents a schedule of how the uplink and downlink frequencies are managed. In short, the Ka-band frequencies cannot overlap because a single gateway is being used in a single location. However, because the user terminals 108 are spatially separated, the Ku-band frequencies that serve them can be re-used. Thus, in cross-strapping mode the system provides both 1.5 GHz of uplink spectrum, and 1.5 GHz of downlink spectrum. Figures 4C - 4E present frequency schedules for each of the three user coverage areas 405. The uplinks are all different because there is no frequency overlapping allowed on the gateway side, but the downlink schedules may all be the same.

[0025] In both scenarios the gateways 310 and user terminals 108 rely on different frequencies when in cross-strapping mode, so the gateways 310 are independent of the user beam coverage. Placement of the new Ka-band gateway 310 is therefore more flexible, and can be tailored to the available landing rights. Furthermore, such placement may likely also benefit from easier coordination at Ka-band.

[0026] Service migration would be smooth and without interruption in both scenarios, as user services can be continued with the legacy Ku-band gateway until the new Ka-band gateway is operational or needed. Additional flexibility in transition planning to meet user needs could be provided via a switching matrix that allows selection of specific transponders as required. This approach may be particularly important to allow certain legacy networks to remain at full Ku-band operation if necessary.

[0027] Along with the opportunity for higher service speeds, the switch to Ka-band on the gateway side only, would allow user terminals to continue to operate at Ku-band and benefit from the relatively more favourable fade attenuation characteristics, compared to a full Ka- band transition. General System Considerations

[0028] The invention has been described generally in the context of a Geostationary Earth Orbit (GEO) system, but the invention is independent of the nature of the satellite system itself and can be applied to any satellite system. For example, meteorological monitoring satellites and communications satellites are usually located in GEO or Low Earth Orbit (LEO). GEO satellites appear to be motionless in the sky, providing the satellite with a continuous view of a given area on the surface of the Earth. This is done by placing the satellite directly above the Earth's equator (0° latitude), with a period equal to the Earth's rotational period, an orbital eccentricity of approximately zero and at an altitude of 35,789 km. LEO satellites are not stationary, requiring a constellation of satellites in order to provide continuous coverage in a given area, the satellites being tracked and communication being handed from one satellite to another as the satellites pass in and out of view. Such tracking and handoff is known in the art, and can be implemented independent of the invention.

[0029] Similarly, the issues of orbital control and flight dynamics are independent of the invention and are known in the art for the implementation of different satellite systems. That is, orbit-correcting adjustments required to keep the satellites in the desired orbit would be made by satellite's on-board propulsion system in the same way as those of other satellite systems. These adjustments are necessary to compensate for the Earth's oblateness, gravitational forces of the sun and moon, solar radiation pressure and the like.

[0030] The invention has been described in the context of Ku-bands transitioning to Ka- bands, but the invention can be applied to any frequency band transition. For example, standard satellite communication bands include: L- Band (1-3 GHz); X band (approximately 7 - 8 GHz); Ku-band (approximately 11 - 15 GHz), and Ka-band (approximately 17 - 31 GHz). Transitions can be made between any pairings of these. Error correction, encoding and re-transmission of lost / corrupted packets would also be used, as well as multi-beam satellite systems utilizing frequency re-use. As well, the examples are described herein as a single polarity, but of course frequency channels could be implemented in right hand circular polarization (RHCP) and left hand circular polarization (LHCP), or in other schemes. One very common scheme, for example, is "linear polarization" which is implemented as horizontal polarization and vertical polarization. Further, any communication protocol may be used including Multi-Frequency Time-Division Multiple Access (MF-TDMA), Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), Orthogonal Frequency Division Multiple Access (OFDMA), Code Division Multiple Access (CDMA), or any number of hybrid or other schemes known in the art.

Base Station Considerations

[0031] As shown in Figures 3A and 4A, the system includes one or more satellites 305 with cross-strapping communications functionality and an Earth observation, communication and/or scientific payload, and at least one gateway 310 (sometimes referred to as a hub, base station or ground station). The gateway 310 may also serve as an interface between the one or more satellites 305 and a network 505 as shown in Figure 5, configuring data and information from the network 505, so that it can be directed to the user terminals 108. It may also format data and information received from the one or more satellites 305, for delivery to the network 505. The gateway 310 also effects Telemetry, Tracking & Control (TTC) of the one or more satellites 305. TTC is well known in the art and is generally independent of the invention.

[0032] Figure 5 illustrates a simplified block diagram of an exemplary gateway system 500 for communicating with the one or more satellites 305. The communication signals between the gateway system 500 and the one or more satellites 305 may include operational / control signals and payload related signals including communication data. In the case of a scientific payload, the payload related signals may include control signals transmitted to instruments, and observation / monitoring data received from the instruments. The architecture of the gateway system 500 may be modified from what is shown, to receive and present other types of information. Additional components may also be employed, such as one or more computers, servers, networks and other related devices, depending on the application.

[0033] As shown in Figure 5, the gateway system 500 may include an antenna 510, a transceiver 515, a processing unit or system 520, and a network communications system 525. [0034] The antenna 510 is designed to receive and transmit signals at the desired communication frequencies, typically comprising a parabolic reflector with high directivity in the direction of the satellite and low directivity in other directions. In the case of a GEO system with a ' stationary' satellite a non-tracking antenna may be used. In the case of a LEO system or other system with 'moving' satellites, a tracking antenna would be employed to track the satellites across the sky. The antenna 510 may comprise a variety of alternative configurations and elements, including features such as high isolation between orthogonal polarizations, high efficiency in the operational frequency bands, and low noise. Antenna arrays or other antenna designs may be used as required by the application.

[0035] The gateway transceiver 515 consists of a receiver portion for receiving data from the satellites and preparing it for the CPU 520, and a transmission portion for processing data from the CPU 520, preparing it for transmission to the one or more satellites 305 via the antenna 510. The transmitting portion of the transceiver 515 may, for example, multiplex, encode and compress data to be transmitted to the one or more satellites 305, then modulate the data to the desired transmission frequency and amplify it for transmission. Multiple channels may be used, error correction coding, and the like. In a complementary manner, the receiver portion of the transceiver 515 demodulates received signals and performs any necessary demultiplexing, decoding, decompressing, error correction and formatting of the signals from the antenna, for use by the CPU 520. The antenna and/or transceiver may also include any other desired switches, filters, low-noise amplifiers, downconverters (for example, to an intermediate frequency), and other components.

[0036] A local user interface 530 is also shown in Figure 5, allowing an operator to monitor the system and operation, and to effect changes. One such change, of course, is to manipulate the communication frequencies of the gateway transceiver 515 and the one or more satellites 305. This is done by sending a signal to the one or more satellites 305 to switch from one frequency band to another, and then confirming that this switch has been achieved successfully. The details of how this is effected is described under the heading "Method of Implementation" below. [0037] The geographic positions of the gateways 310 may be chosen to minimize the number of gateways required, to avoid areas with poor weather conditions, or to avoid frequency overlap with user coverage areas. As a result, the gateways 310 may not be in a geographic location that is convenient for the satellite operators and/or parties receiving the payload data. Thus, the gateways 310 will typically be provided with network communication facilities 525 so that remote computers 535 may be used to access the system 500 over the Internet or similar networks 505. The network 505 may be any type of network and can include, for example: the Internet, an IP network, an intranet, an extranet, a wide-area network ("WAN"), a local-area network ("LAN"), a virtual private network (VPN), the Public Switched Telephone Network ("PSTN"), and/or any other type of network supporting data communication between devices described herein, in different embodiments. The network 505 may include both wired and wireless connections, as well as fibre optic links. The network 505 may also connect the gateway 310 with other gateways (not shown), which may also be in communication with the one or more satellites 305.

[0038] Higher communication frequencies generally result in poorer performance which the gateway 310 will have to compensate for. But the design requirements for such systems are well known in the art (i.e. forward link may require more UPC or larger antenna, gateway site diversity may be necessary for areas of high rain fade, etc.) Note that UPC refers to Uplink Power Control; the uplink can increase transmitted power based on local atmospheric conditions to maintain the link quality.

[0039] For a Ku/Ka cross-strapped system, the gateway to/from satellite link is at a higher frequency than the user to/from satellite link. The higher frequency gateway links will experience higher rain fade rates than the lower frequency user links. To accommodate this varying fade rates for the two different frequencies, Adaptive Code Modulation (ACM) technique is used by the ground equipment. During a rain fade, an ACM system is allowed to switch to a more robust code point. For the cross-strapped Ku/Ka system, due to the inherent different fade rate change, the ACM switching point has to be carefully selected to have a smooth transition during code change such that continuity of service is maintained during switch over. Satellite Considerations

[0040] Figures 6A and 6B illustrate a simplified block diagram of a cross-strapping satellite 305 which may be used in an exemplary embodiment of the invention, Figure 6A presenting the basic operational components, and Figure 6B presenting a more detailed diagram of the communication components.

[0041] As shown in Figure 6A, the satellite 305 may include a station keeping system 610, a propulsion system 615, a power system 620, a communications system 625, a computer processing system 630, a transceiver 635 and an antenna 640. Of course, other components and arrangements may be used to implement the invention, including, for example, redundant and back-up components.

[0042] The station keeping subsystem 610 is responsible for maintaining the satellite's orbit. Accordingly, the station keeping subsystem 610 may calculate and/or receive attitude and/or orbit adjustment information, and may actuate the propulsion system 615 to adjust the satellite's attitude and/or orbit. Maintaining the orbit may also include maintaining the desired nodal separations between itself and the other satellites within the satellite constellation. The propulsion system 615 may include for example, a fuel source (i.e. fuel and oxidant tanks) and liquid fuel rocket, or an ion-thruster system.

[0043] The power subsystem 620 provides electrical power to all of the satellite systems and subsystems. The power subsystem 620 may, for example, include one or more solar panels and a supporting structure, and one or more batteries.

[0044] The satellite antenna 640 is designed to accommodate the communication frequency bands and systems required. It may, for example, comprise a reflector antenna, a lens antenna, an array antenna, an active antenna, or other antenna mechanism known in the art for reception of the required communications signals. In view of the physical size and weight constraints of the satellite 305, it will be much smaller than the antenna 510 of the gateway 310. The direction of the beam of antenna 640 is controlled by mechanically steering the antenna 640 or electronically steering the antenna beam. Alternatively, the attitude of the satellite 305 may be controlled to steer the antenna 640.

[0045] Similarly, the satellite transceiver 635 is designed to be complementary to that of the gateway 310, consisting of a receiver portion for receiving data from the gateway 310 and preparing it for the CPU 630, and a transmission portion for process data from the CPU 630 or communication payload 625, preparing it for transmission to the gateway 310 via the antenna 640. The transmitting portion of the transceiver 635 may, for example, multiplex, encode and compress data to be transmitted, then modulate the data to the desired transmission frequency and amplify it for transmission. Multiple channels may be used, error correction coding, and the like. The receiver portion of the transceiver 635 demodulates received signals and performs any necessary demultiplexing, decoding, decompressing, error correction and formatting of the signals from antenna 640, for use by the satellite CPU 630 and/or communication payload 625. The antenna 640 and/or receiver may also include any other desired switches, filters, low-noise amplifiers, downconverters (for example, to an intermediate frequency and/or baseband), and other components.

[0046] The CPU system 630 of the satellite 305 typically receives signals used for operation of the attitude and orbit control systems. It also receives control signals for operation of the payload 625 and processes payload data for transmission to the gateway 310. It may also manage activation and deactivation of the various subsystems as the satellite 305 passes into and out of a geographic region of interest.

[0047] The satellite 305 may also have "store and forward" functionality allowing the satellite 305 to store data when communications to a gateway is not possible. The stored data can then be relayed to the gateway when communications becomes available.

[0048] Figure 6B presents a more detailed view of an exemplary communications payload 625. In general, the purpose of the communications payload 625 is to receive data signals from the gateway 310, via antenna 640, within the frequency band and specific polarization transmitted. The satellite 305 will typically do minimal processing of those data signals, other than forwarding them to the user terminals 108. But in the case of the cross-strapping mode, those data signals will need to be down-converted from the higher carrier frequency at which they are received (in Ka-band, for example), down to a lower carrier frequency that the user terminals are operable to receive (Ku band, for example). This may be implemented by receiving the higher frequency signal via a Ka transponder 645 and converting it to an intermediate frequency (IF) which is then up-converted to the Ku-band carrier frequency for transmission to the user terminals 108. Frequency up- and down-conversion is typically performed by mixing a signal with a local oscillator signal tuned to the desired frequency as known in the art. An exemplary Ka-band local oscillator signal 650 is shown in Figure 6B along with the Ka-side mixer. Up- and down-conversion on the Ku-band side would be effected in the same manner, using the Ku-band local oscillator signal 660 and the Ku-side mixer 665 shown in Figure 6B. Signals to and from the Ku-side mixer 665 are fed to and from the Ku transponders 670.

[0049] The received and transmitted signals may be coordinated in their IF form via a switching matrix 675, which is controlled by the CPU 630. The CPU 630 receives control signals from the gateway 310. That is, the gateway 310 sends signals to the satellite 305 advising it on the frequency of each incoming data signal, where it must be sent, and at what frequency. As explained above under the Second Scenario heading, the satellite 305 may operate in a multi-beam mode, transmitting a number of narrow beams each directed at a different region of the Earth, allowing for frequency re-use. With such a multibeam satellite, there may be any number of different signal switching configurations on the satellite, allowing signals from a single gateway 310 to be switched between different spot beams.

User Terminal Considerations

[0050] The service signals transmitted from the satellite 305 may be received by one or more user terminals 108, via the respective subscriber antenna. User terminals 108 are sometimes called modems, satellite modems or subscriber terminals.

[0051] There are no changes to the user terminals 108 in the basic embodiment of the invention. The user terminals 108 are configured to transmit/receive Ku-band data signals as they have in the past, using standard antenna, transceiver and down-conversion components. Each of the user terminals 108 may comprise a single user terminal, multiple terminals, or may include other components so that signals may be distributed to other computers or to a network, in which case the user terminal may be referred to as a hub or router. The various consumer premises equipment (CPE) such as computers, local area networks, Internet appliances, wireless, hard-wired and fibre optic networks are all known in the art.

Method of Implementation

[0052] Figure 7 illustrates a flowchart of an exemplary method 700 of operating the satellite system of the invention. The method begins in block 705, by launching the satellite or satellite constellation and deploying the satellite or satellites 305 into orbits having the desired orbital parameters. Satellites 305 may be launched one at a time (e.g. one satellite per launch vehicle) or with multiple satellites in the same launch vehicle. If multiple satellites are being deployed into the same orbital plane, it may be most efficient to launch all of the satellites 305 with a single launch vehicle.

[0053] Once the satellite constellation has been launched, the satellite or satellites 305 may be activated and a commissioning / testing procedure of the basic systems performed 710. This commissioning / testing procedure may include deploying antennas and rotating the satellite or satellites 305 so that the antenna 640 is pointed in the appropriate direction, deploying solar panels, energizing processors and electronic systems, booting-up software systems, and verifying operation of all basic systems and subsystems. It may also be necessary to perform trouble-shooting and/or corrective measures as part of this procedure.

[0054] Once the basic systems and subsystems have been activated and their operation verified, the satellites 305 may be transitioned into their final orbital positions. This may comprise the satellites 305 simply propelling themselves into the correct nodal separations, if they were launched into the same operational orbit. Alternatively, if the satellites 305 were launched into a parking orbit, they may be required to consume a much larger quantity of fuel to propel themselves into their operational orbit and nodal separation. [0055] With the satellites 305 now in their final orbital positions, the payloads may be activated, commissioned and tested 715. This would be done in much the same manner as the activation, testing and commissioning of the satellites' basic systems described above, i.e. deploying any necessary antennas or sensors, energizing processors and electronic systems, booting-up software systems, and verifying operation of all the payload systems and subsystems. Of course, trouble-shooting and/or corrective measures may also be performed as part of the payload commissioning procedure. The satellite or satellites 305 are now in an operational mode.

[0056] Operation of the payload is determined by the nature of the payload. In the case of an Earth observation payload such a weather-monitoring system, this may comprise the operation of imaging instruments, and the transmission of observation data from the satellite 305 to the gateway 310. But in the general case of a communications satellite with cross- strapping functionality, operation of the payload will typically include:

1. tuning the system frequency of each channel to the initial Ku-band carrier;

2. synchronizing the timing of each channel to the initial Ku-band carrier;

3. synchronizing the ID and protocol for each channel to the initial Ku-band carrier; and

4. beginning communications, fine tuning as required. Many different transmission modes may be used, including TDMA, SCPC, MF-TDMA, Spread Spectrum, Carrier in Carrier, etc.

[0057] When it becomes desirable to transition the uplink or forward link (i.e. the communications from the gateway 310 to the satellite or satellites 305) to Ka-band, this will be effected by performing the following steps:

1. the gateway 310 sending instructions to retune the frequency of specified communication channel from the initial Ku-band carrier to the Ka-band carrier;

2. the satellite 305 confirming receipt of the retuning instructions and retuning the channels;

3. synchronizing the timing of each retuned Ka channel;

3. synchronizing the ID and protocol for each retuned Ka channel; and

4. beginning transmission at that Ka carrier frequency, fine tuning as required. [0058] With all of the satellite systems and payload operational, the only remaining concern is to maintain the position of the satellite 305 in the orbit of interest. This can be effected in a manner known in the art and is independent of the invention.

[0059] Optionally, certain systems and subsystems may be deactivated in the course of the satellites' orbits, for example, to conserve power. If, for example, the Ka-band components are not in use prior to the frequency transition, it may be possible to deactivate those payload systems or components until they are required. Alternatively, it may be desirable to keep all of the satellite subsystems operational at all times, so that it may continue to receive and transmit data related to its health, status and control. Such functionality is known in the art.

Options and Alternatives

[0060] In addition to the implementations described above, the system of the invention may be applied to at least the following applications:

1. the systems / approaches described herein are intended to provide a permanent solution with a single frequency transition between a gateway and a satellite. But the system could be implemented in a fully reversible manner, albeit at the potential loss of capacity. In a case of a failure to the Ka gateway, for example, a command could return the configuration to its default value, assuming that the Ku gateway is still operational;

2. although the examples described herein refer to specific frequency bands, the names and ranges of the bands are independent of the invention. That is, the frequency bands such as Ka, Ku, C and V are arbitrary ranges established in the industry. The satellites, gateways and other components described herein could exploit multiple bands, any range of frequencies, or several ranges of frequencies in an application. For example, a satellite could be operable to communicate with gateways in Ka, Ku or C bands, or any frequencies between those bands;

3. the systems and methods of the invention described herein set out a way of transitioning the gateway-side of the system from a lower frequency to a higher frequency. But of course, this system could be combined with a complementary transition system on the user side, allowing users to transition a lower frequency to a higher frequency independent of the gateway-side;

4. while the invention has been described with respect to certain examples, it is clear that aspects of the invention could be exploited with less functionality and complexity. For example, the system could be employed without a switch in the satellite per se, the satellite simply reacting to whatever communications and frequencies are received. As well, the system could be implemented in a static manner in which there is no frequency transition per se on the gateway side; the gateway(s) always communicating with the satellite at the higher frequency, while the satellite cross-straps those communications to the users at the lower frequency; and

5. the system / approach described herein could be implemented to provide coverage to an alternate Ka Gateway location by either provisioning an additional Ka horn on the satellite or by using a steerable Ka satellite antenna. The satellite could be commanded to configure the signal path to the new gateway location. This functionality to transfer to an alternate gateway could be used to provide the following:

• provide disaster recovery or business continuity in case of a failure of the main Ka Gateway;

• address a change in market demands or a change in customer preference;

• offer more favorable landing rights;

• mitigate a local interference until sources are identified and managed; or

• protect the gateway signal path from intentional jamming originated by sources within the spotbeam of the main gateway

Conclusions

[0061] One or more currently preferred embodiments have been described by way of example. It will be apparent to persons skilled in the art that a number of variations and modifications can be made without departing from the scope of the invention as defined in the claims. For example, the selection of the inclination is dependent on the tradeoffs between the required service area, the amount of fuel on the spacecraft and the launch mass of the payload. These parameters can be optimized to accommodate different priorities, without departing from the concept of the invention.

[0062] The method steps of the invention may be embodied in sets of executable machine code stored in a variety of formats such as object code or source code. Such code may be described generically as programming code, software, or a computer program for simplification. The embodiments of the invention may be executed by a computer processor or similar device programmed in the manner of method steps, or may be executed by an electronic system which is provided with means for executing these steps. Similarly, an electronic memory medium such computer diskettes, hard drives, thumb drives, CD-ROMs, Random Access Memory (RAM), Read Only Memory (ROM) or similar computer software storage media known in the art, may be programmed to execute such method steps.

[0063] All citations are hereby incorporated by reference.

Claims

WHAT IS CLAIMED IS:

1. A satellite system comprising:

a satellite;

at least one gateway in communication with said satellite;

at least one user in communication with said satellite;

said at least one gateway being operable to transmit a command to said satellite directing it to transition gateway-to-satellite communication from a current frequency band, to a higher frequency band; and

said satellite being operable to receive said command to transition to a higher frequency band, and in response to receiving said command to transition to said higher frequency band, to switch communication with said at least one gateway to said higher frequency band, cross-strapping said communications to said at least one user in said current frequency band.

2. The system of claim 1, wherein said satellite comprises a GEO (Geostationary Earth Orbit) satellite.

3. The system of either one of claims 1 and 2, wherein said current frequency band is a Ku-band and said satellite comprises a plurality of Ku-band transponders.

4. The system of any one of claims 1 to 3, wherein said higher frequency band is a Ka- band and said satellite comprises a plurality of Ka-band transponders.

5. The system of any one of claims 1 to 4, wherein said at least one user comprises multiple user terminals located in the same coverage area, whereby downlink communication frequencies may not overlap.

6. The system of any one of claims 1 to 4, wherein said at least one user comprises multiple user terminals located in different coverage areas, whereby downlink communication frequencies may be re-used.

7. The system of claim 1, wherein said satellite downconverts received signals to an intermediate frequency (IF) signal.

8. The system of claim 7, wherein said satellite routes intermediate frequency (IF) to output transponders via a switching matrix.

9. The system of any one of claims 1 to 8, wherein changes in satellite orbital perturbations are compensated for by on-board propulsion systems.

10. The system of any one of claims 1 to 9, wherein directional antennas are used for communications between the satellites and the base station.

11. The system of any one of claims 1 to 10, wherein the base station is operable to track the satellites across the sky.

12. The system of any one of claims 1 to 11, wherein the base station is operable to handoff communications between the satellites as they move across the sky.

13. The system of any one of claims 1 to 12, wherein said satellite system is a satellite communications system, the satellite including a communications payload.

14. A method of operation for a satellite system, comprising:

providing a satellite communications system including:

a satellite;

at least one gateway in communication with said satellite in a current frequency band; and

at least one user in communication with said satellite in the current frequency band;

said at least one gateway transmitting a command to said satellite directing it to transition gateway-to-satellite communication from the current frequency band, to a higher frequency band; and

said satellite receiving said command to transition to a higher frequency band, and responding to receiving said command to transition to said higher frequency band, by switching communication with said at least one gateway to said higher frequency band, cross- strapping said communications to said at least one user in said current frequency band.

15. The method of claim 14, wherein providing said satellite comprises providing a satellite in a GEO (Geostationary Earth Orbit) orbit.

16. The method of either one of claims 14 and 15, wherein said current frequency band is a Ku-band.

17. The method of any one of claims 14 to 16, wherein said higher frequency band is a Ka-band.

18. The method of any one of claims 14 to 17, wherein providing said at least one user comprises providing multiple user terminals located in the same coverage area, whereby downlink communication frequencies may not overlap.

19. The method of any one of claims 14 to 17, wherein providing said at least one user comprises providing multiple user terminals located in different coverage areas, whereby downlink communication frequencies may be re-used.

20. The method of any one of claims 14 to 19, wherein cross-strapping comprises said satellite downconverting received signals to an intermediate frequency (IF) signal.

21. The method of any one of claims 14 to 20, wherein cross-strapping comprises said satellite routes intermediate frequency (IF) signals to output transponders via a switching matrix.

22. The method of any one of claims 14 to 21, further comprising compensating for satellite orbital perturbations via on-board propulsion systems.

23. The method of any one of claims 14 to 22, wherein receiving comprises receiving via directional antennas.

24. The method of any one of claims 14 to 23, further comprising said gateway tracking the at least one satellites across the sky.

25. The method of any one of claims 14 to 24, further comprising handing off communications between the at least one satellite as they move across the sky.

26. The method of any one of claims 14 to 25, wherein said satellite system is a satellite communications system, the satellite including a communications payload.

27. A satellite gateway, comprising:

communication means for transmitting and receiving signals to and from a satellite, and

means for transmitting a command to said satellite directing it to transition gateway- to-satellite communications from a current frequency band, to a higher frequency band.

28. A satellite comprising:

communication means for transmitting and receiving signals to and from a base station;

flight control means; and

means responsive to a command to transition to a higher frequency band, by switching communication with a gateway to said higher frequency band, cross-strapping said communications to at least one user in a current frequency band.

29. A satellite system comprising:

a satellite;

at least one gateway in communication with said satellite;

at least one user in communication with said satellite;

said at least one gateway being operable to transition gateway-to-satellite communication from a current frequency band, to a higher frequency band; and

said satellite being operable to receive said communications in said higher frequency band, cross-strapping said communications to said at least one user in said current frequency band.

30. A satellite system comprising:

a satellite;

at least one gateway in communication with said satellite;

at least one user in communication with said satellite;

said at least one gateway being operable to effect gateway-to-satellite communications a higher frequency; and

said satellite being operable to receive said communications at said higher frequency, cross-strapping said communications to said at least one user at a lower frequency.