Source: https://patents.justia.com/patent/20180376393
Timestamp: 2020-02-28 15:25:11
Document Index: 710113321

Matched Legal Cases: ['Application No. 62', 'arth 640', 'arth 640', 'arth 640', 'arth 640', 'arth 640', 'arth 640']

US Patent Application for METHOD AND APPARATUS FOR MULTIPLEXING HYBRID SATELLITE CONSTELLATIONS Patent Application (Application #20180376393 issued December 27, 2018) - Justia Patents Search
Justia Patents US Patent Application for METHOD AND APPARATUS FOR MULTIPLEXING HYBRID SATELLITE CONSTELLATIONS Patent Application (Application #20180376393)
A method and apparatus for operating a satellite system including different satellites that may belong to different types of satellite constellations. In some implementations, the satellite system may include a LEO satellite constellation and one or more non-LEO satellite constellations that can be used to increase the forward link capacity of the LEO satellite constellation, for example, by allowing an LEO satellite to offload at least some of its forward link traffic to one of the non-LEO satellites. The user terminals can dynamically switch forward link communications between a LEO satellite and a non-LEO satellite while maintaining a return link connection with the LEO satellite.
This Patent Application claims priority under 35 U.S.C. 119(e) to commonly-owned U.S. Provisional Patent Application No. 62/523,250 entitled “Method and Apparatus for Multiplexing Hybrid Satellite Constellations” filed on Jun. 21, 2017, the entirety of which is incorporated by reference herein.
Various aspects described herein relate to satellite communications, and more particularly to improving the reception of weak signals transmitted from ground-based devices.
Geosynchronous satellites have long been used for communications. A geosynchronous satellite is stationary relative to a given location on the Earth, and thus there is little timing shift and frequency shift in radio signal propagation between a communication transceiver on the Earth and the geosynchronous satellite. However, because geosynchronous satellites are limited to a geosynchronous orbit (GSO), the number of satellites that may be placed in the GSO is limited. As alternatives to geosynchronous satellites, communication systems which utilize a constellation of satellites in non-geosynchronous orbits (NGSO), such as low-earth orbits (LEO) and medium-earth orbits (MEO), have been devised to provide communication coverage to the entire Earth or at least large parts of the Earth.
A constellation of NGSO satellites may provide coverage for greater portions of Earth than a constellation of GSO satellites, for example, because the orbital planes of NGSO satellites are not limited to geosynchronous orbits. LEO satellites typically employ orbits between approximately 160 km and 2,000 km above the surface of the Earth, and MEO satellites typically employ orbits between approximately 2,000 km and 35,000 km above the surface of the Earth. MEO satellites are visible to observers on Earth for much longer periods of time than LEO satellites, and typically have a larger coverage area (such as a wider footprint) on Earth than LEO satellites. The longer durations of visibility and wider footprints of MEO satellites means that fewer satellites are needed in an MEO constellation than in an LEO constellation to provide similar coverage on Earth. However, because MEO satellites orbit the Earth at much greater altitudes than LEO satellites, MEO satellites have much longer signal propagation delays than LEO satellites, and may require greater transmission power levels than LEO satellites.
GSO satellites typically employ larger antennas than LEO satellites, and may therefore offer greater bandwidth and better signal-to-noise ratios (SNRs) than LEO satellites. MEO satellites also may employ larger antennas than LEO satellites, and therefore also may offer greater bandwidth and SNRs than LEO satellites. However, LEO satellites are typically less complex, less expensive, and easier to put into orbit that MEO satellites and GSO satellites.
It may be desirable for a satellite system to include multiple types of satellite constellations, for example, to leverage the advantages of different types of satellite constellations. Integrating multiple types of satellite constellations into a single satellite system that offers uninterrupted service while ensuring user satisfaction can be challenging. These challenges may be compounded when user terminals configured for communications with one type of satellite constellation are to be deployed in a satellite system which includes different types of satellite constellations.
One innovative aspect of the subject matter described in this disclosure can be implemented as a method for switching forward link communications of a user terminal between a first satellite and a second satellite. The first and second satellites can be different types of satellites, and can belong to different satellite constellations. In some aspects, the first satellite is a low-earth orbit (LEO) satellite, and the second satellite is one of a medium-earth orbit (MEO) satellite or a geosynchronous orbit (GSO) satellite. In other aspects, the first satellite is a first LEO satellite, and the second satellite is a second LEO satellite. The method can be performed by a user terminal, and can include receiving first data on a forward link of the first satellite, and receiving time-division multiplexing (TDM) configuration information on the forward link of the first satellite, the TDM configuration information specifying a TDM transmission pattern for forward link communications to the user terminal from at least the first and second satellites.
The method can also include switching forward link communications of the user terminal from the first satellite to the second satellite during a handover operation, receiving second data on a forward link of the second satellite after the handover operation and transmitting one or more control or data messages to a network controller on a return link of the first satellite after the handover operation. In some implementations, the one or more control or data messages can include an acknowledgement of the second data received by the user terminal. In addition, or in the alternative, the one or more control or data messages can include information pertaining to the handover operation from the first satellite to the second satellite.
In some implementations, switching the forward link communications from the first satellite to the second satellite can be triggered by a radio controller circuit (RRC) message transmitted to the user terminal using the forward link of the first satellite. In some aspects, the second data can be transmitted using a concatenated code including a turbo code as an inner code and including a Bose-Chaudhuri-Hocquenghem (BCH) code as an outer code.
Another innovative aspect of the subject matter described in this disclosure can be implemented in a user terminal to switch its forward link communications between first and second satellites. In some implementations, the user terminal can include one or more processors and a memory. The memory can store instructions that, when executed by the one or more processors, cause the user terminal to receive first data on a forward link of the first satellite; receive time-division multiplexing (TDM) configuration information on the forward link of the first satellite, the TDM configuration information specifying a TDM transmission pattern for forward link communications to the user terminal from at least the first and second satellites; switch forward link communications of the user terminal from the first satellite to the second satellite during a handover operation;receive second data on a forward link of the second satellite after the handover operation; and transmit one or more control or data messages to a network controller on a return link of the first satellite after the handover operation.
Another innovative aspect of the subject matter described in this disclosure can be implemented in a non-transitory computer-readable medium. The non-transitory computer-readable medium can store instructions that, when executed by one or more processors of a user terminal, cause the user terminal to switch its forward link communications terminal between first and second satellites by performing a number of operations. In some implementations, the number of operations can include receiving first data on a forward link of the first satellite; receiving time-division multiplexing (TDM) configuration information on the forward link of the first satellite, the TDM configuration information specifying a TDM transmission pattern for forward link communications to the user terminal from at least the first and second satellites; switching forward link communications of the user terminal from the first satellite to the second satellite during a handover operation; receiving second data on a forward link of the second satellite after the handover operation; and transmitting one or more control or data messages to a network controller on a return link of the first satellite after the handover operation.
Another innovative aspect of the subject matter described in this disclosure can be implemented in an apparatus to switch its forward link communications between first and second satellites. In some implementations, the apparatus can include means for receiving first data on a forward link of the first satellite; means for receiving time-division multiplexing (TDM) configuration information on the forward link of the first satellite, the TDM configuration information specifying a TDM transmission pattern for forward link communications to the user terminal from at least the first and second satellites; means for switching forward link communications of the user terminal from the first satellite to the second satellite during a handover operation; means for receiving second data on a forward link of the second satellite after the handover operation; and means for transmitting one or more control or data messages to a network controller on a return link of the first satellite after the handover operation.
FIG. 6 shows a diagram depicting an example satellite system.
FIG. 7 shows a block diagram of an example user terminal.
FIG. 8 shows a block diagram depicting a UT communicating with a first satellite and a second satellite that may belong to different satellite constellations.
FIG. 9 shows an example timing diagram depicting an asymmetric distribution of forward link and return link subframes for a given communication frame.
FIG. 10A shows a timing diagram depicting an example handover operation from a first LEO satellite to a second LEO satellite without switching forward link communications between non-LEO satellites.
FIG. 10B shows a timing diagram depicting an example handover operation from a first LEO satellite to a second LEO satellite aligned with a handover operation between non-LEO satellites.
FIG. 11 shows a block diagram of an example controller.
FIG. 12 shows an illustrative flow chart depicting an example satellite handover operation.
FIG. 13 shows an illustrative flow chart depicting another example satellite handover operation.
The example implementations described herein may allow a user terminal to transmit and receive data using a satellite system including different types of satellites that may belong to different types of satellite constellations. In some implementations, the satellite system may include a constellation of LEO satellites and one or more non-LEO satellite constellations. The one or more non-LEO satellite constellations may be used to increase the forward link capacity of the LEO satellite constellation, for example, by allowing an LEO satellite to offload at least some of its forward link traffic to one of the non-LEO satellites. In some aspects, the non-LEO satellites may not provide return link resources for user terminals to request data re-transmissions, to send channel quality information (CQI) to a satellite controller, and to report data reception errors. Thus, in accordance with aspects of the present disclosure, the user terminals may dynamically switch forward link communications between a LEO satellite and a non-LEO satellite (or between two different non-LEO satellites) while maintaining a return link connection with the LEO satellite. In some aspects, the user terminal includes a single antenna and is configured to dynamically switch communications between different types of satellites (such as between LEO satellites, MEO satellites, and GSO satellites) using time-division multiplexing (TDM)-based transmission patterns. In this manner, forward link resources of the satellite system may be dynamically switched between different satellites to increase overall data throughput of the satellite system while allowing the user terminals to use the return link resources of the LEO satellite to request data re-transmissions, to send channel quality information to the satellite controller, to report data reception errors to the satellite controller, and to send other information (such as control data, user data, acknowledgements, HTTP get, hybrid automatic repeat requests (HARQs), channel quality information (CQI) reports, configuration information, and so on) to the satellite controller.
As used herein, the terms “ephemeris” and “ephemeris data” refer to satellite orbital information that contains positions of one or more satellites for a number of given times (e.g., in the future). A satellite's position may be expressed using a 3-dimensional coordinate system such as a spherical coordinate system. For example, in a spherical coordinate system, a satellite's position relative to a fixed point on Earth may be represented as a line extending from the fixed point on Earth to the satellite. The line may be expressed as a vector including three numbers: the radial distance of the satellite from the fixed point, the elevation angle, and the azimuth (or azimuth angle). The elevation angle, which may also be referred to as the inclination angle or the polar angle, is the angle between the line and a reference plane parallel to the surface of the Earth. Thus, as used herein, the terms “elevation angle,” “inclination angle,” and “polar angle” may be interchangeable. The reference plane may be referred to herein as the “azimuth plane,” and thus the terms “reference plane” and “azimuth plane” may be interchangeable. The azimuth is the angle between a reference direction and the orthogonal projection of the line onto the azimuth plane. For purposes of discussion herein, the reference direction may correspond to the direction of true North, and may hereinafter be referred to as the reference azimuth. Thus, as used herein, the terms “reference azimuth” and “reference direction” may be interchangeable, and for at some implementations may refer to a direction of true North.
FIG. 1 illustrates an example of a satellite communication system 100 which includes a plurality of satellites (although only one satellite 300 is shown for simplicity) in a number of non-geosynchronous orbits, for example, low-earth orbits (LEO) and medium-earth orbits (MEO), a satellite access network (SAN) 150 in communication with the satellite 300, a plurality of user terminals (UTs) 400 and 401 in communication with the satellite 300, and a plurality of user equipment (UE) 500 and 501 in communication with the UTs 400 and 401, respectively. Each UE 500 or 501 may be a user device such as a mobile device, a telephone, a smartphone, a tablet, a laptop computer, a computer, a wearable device, a smart watch, an audiovisual device, or any device including the capability to communicate with a UT. Additionally, the UE 500 and/or UE 501 may be a device (e.g., access point, small cell, etc.) that is used to communicate to one or more end user devices. In the example illustrated in FIG. 1, the UT 400 and the UE 500 communicate with each other via a bidirectional access link (having a forward access link and return access link), and similarly, the UT 401 and the UE 501 communicate with each other via another bidirectional access link. In another implementation, one or more additional UEs (not shown) may be configured to receive only and therefore communicate with a UT only using a forward access link. In another implementation, one or more additional UEs (not shown) may also communicate with UT 400 or UT 401. Alternatively, a UT and a corresponding UE may be integral parts of a single physical device, such as a mobile telephone with an integral satellite transceiver and an antenna for communicating directly with a satellite, for example.
The UT 400 may include a satellite handover circuit 425 that may allow the UT 400 to dynamically switch communications from a first satellite to a second satellite. In example implementations, the satellite handover circuit 425 may perform satellite handover operations by switching communications with the SAN 150 from the first satellite to the second satellite. In some aspects, the first and second satellites may be part of the same satellite constellation (such as a LEO constellation). In other aspects, the first and second satellites may be part of different satellite constellations (such as a LEO constellation and a MEO constellation, a MEO constellation and a GSO constellation, or a LEO constellation and a GSO constellation). Although not shown in FIG. 1 for simplicity, the UT 401 may also include a satellite handover circuit 425 that may allow the UT 401 to dynamically switch communications from a first satellite to a second satellite, for example, in a manner similar to that of the UT 400.
The SAN 150 may include gateways 200 and 201, infrastructure 106, and additional components (not shown for simplicity) for communicating with the satellite 300. The gateway 200 may have access to the Internet 108 or one or more other types of public, semiprivate or private networks. In the example illustrated in FIG. 1, the gateway 200 is in communication with infrastructure 106, which is capable of accessing the Internet 108 or one or more other types of public, semiprivate or private networks. The gateway 200 may also be coupled to various types of communication backhaul, including, for example, landline networks such as optical fiber networks or public switched telephone networks (PSTN) 110. Further, in alternative implementations, the gateway 200 may interface to the Internet 108, PSTN 110, or one or more other types of public, semiprivate or private networks without using infrastructure 106. Still further, gateway 200 may communicate with other gateways, such as gateway 201 through the infrastructure 106 or alternatively may be configured to communicate to gateway 201 without using infrastructure 106. Infrastructure 106 may include, in whole or part, a network control center (NCC), a satellite control center (SCC), a wired and/or wireless core network and/or any other components or systems used to facilitate operation of and/or communication with the satellite communication system 100.
The SAN 150 may include a satellite handover controller 152 that allows the SAN 150 to coordinate or otherwise facilitate switching communications with a user terminal (e.g., UT 400 and/or UT 401) from a first satellite to a second satellite. In some implementations, the first satellite may be part of (or associated with) a first constellation of satellites, and the second satellite may be part of (or associated with) a second constellation of satellites that is different than the first constellation of satellites. In some aspects, the first satellite may be an LEO satellite and the second satellite may be an MEO satellite. In other aspects, the first satellite may be an LEO satellite and the second satellite may be an GSO satellite. In still other aspects, the first satellite may be an MEO satellite and the second satellite may be an GSO satellite. In other implementations, the first and second satellites may be part of (or associated with) the same constellation of satellites (such as a constellation of NGSO satellites).
RF subsystem 210, which may include a number of RF transceivers 212, an RF controller 214, and an antenna controller 216, may transmit communication signals to satellite 300 via a forward feeder link 301F, and may receive communication signals from satellite 300 via a return feeder link 301R. Although not shown for simplicity, each of the RF transceivers 212 may include a transmit chain and a receive chain. Each receive chain may include a low noise amplifier (LNA) and a down-converter (e.g., a mixer) to amplify and down-convert, respectively, received communication signals in a well-known manner In addition, each receive chain may include an analog-to-digital converter (ADC) to convert the received communication signals from analog signals to digital signals (e.g., for processing by digital subsystem 220). Each transmit chain may include an up-converter (e.g., a mixer) and a power amplifier (PA) to up-convert and amplify, respectively, communication signals to be transmitted to satellite 300 in a well-known manner In addition, each transmit chain may include a digital-to-analog converter (DAC) to convert the digital signals received from digital subsystem 220 to analog signals to be transmitted to satellite 300.
The control processor 228 may also control the generation and power of pilot, synchronization, and paging channel signals and their coupling to the transmit power controller (not shown for simplicity). The pilot channel is a signal that is not modulated by data, and may use a repetitive unchanging pattern or non-varying frame structure type (pattern) or tone type input. For example, the orthogonal function used to form the channel for the pilot signal generally has a constant value, such as all 13 s or 0's, or a well-known repetitive pattern, such as a structured pattern of interspersed 1's and 0's.
The UT 400 may include a satellite handover circuit 425 that may allow the UT 400 to dynamically switch communications from a first satellite to a second satellite. In example implementations, the satellite handover circuit 425 may perform satellite handover operations by switching communications with the SAN 150 from the first satellite to the second satellite. In some aspects, the first and second satellites may be part of the same satellite constellation (such as a LEO constellation). In other aspects, the first and second satellites may be part of different satellite constellations (such as a LEO constellation and a MEO constellation, a MEO constellation and a GSO constellation, or a LEO constellation and a GSO constellation).
In the example illustrated in FIG. 4, the UT 400 also includes an optional local time, frequency and/or position references 434 (e.g., an SPS receiver), which may provide local time, frequency and/or position information to the control processor 420 for various applications, including, for example, time and frequency synchronization for the UT 400.
Digital data receivers 416A-416N and searcher receiver 418 are configured with signal correlation elements to demodulate and track specific signals. Searcher receiver 418 is used to search for pilot signals, or other relatively fixed pattern strong signals, while digital data receivers 416A-416N are used to demodulate other signals associated with detected pilot signals. However, a digital data receiver 416 can be assigned to track the pilot signal after acquisition to accurately determine the ratio of signal chip energies to signal noise, and to formulate pilot signal strength. Therefore, the outputs of these units can be monitored to determine the energy in, or frequency of, the pilot signal or other signals. These receivers also employ frequency tracking elements that can be monitored to provide current frequency and timing information to control processor 420 for signals being demodulated.
As mentioned above, GSO satellites are deployed in geostationary orbits at approximately 35,000 km above the earth's surface, and revolve around the Earth in an equatorial orbit at the earth's own angular velocity, for example, such that GSO satellites appear motionless in the sky to a stationary observer on Earth. In contrast, NGSO satellites such as LEO and MEO satellites are deployed in non-geostationary orbits and revolve around the earth above various paths of the earth's surface at relatively low altitudes and relatively fast speeds (e.g., as compared with GSO satellites). For example, LEO satellites typically employ orbits between approximately 160 km and 2,000 km above the surface of the Earth, and MEO satellites typically employ orbits between approximately 2,000 km and 35,000 km above the surface of the Earth. MEO satellites are visible to observers on Earth for much longer periods of time than LEO satellites, and typically have a larger coverage area (such as a wider footprint) on Earth than LEO satellites. The longer durations of visibility and wider footprints of MEO satellites means that fewer satellites are needed in an MEO constellation than in an LEO constellation to provide similar coverage areas on Earth. However, because MEO satellites orbit the Earth at much greater altitudes than LEO satellites, MEO satellites have much longer signal propagation delays than LEO satellites.
In some implementations, a satellite system may include a number of different satellite constellations to provide coverage area on Earth for user terminals (such as the UT 400 of FIG. 4). In some aspects, the satellite system may include a constellation of LEO satellites and a constellation of MEO satellites. In other aspects, the satellite system may include a constellation of LEO satellites and a constellation of GSO satellites. In still other aspects, the satellite system may include a constellation of LEO satellites, a constellation of MEO satellites, and a constellation of GSO satellites. In addition, or in the alternative, the satellite system may include more than one constellation of LEO satellites, more than one constellation of MEO satellites, more than one constellation of GSO satellites, or any combination thereof.
FIG. 6 shows an example satellite system 600 deployed in orbit around Earth 640. The example satellite system 600 is shown to include an LEO satellite constellation 610, an MEO satellite constellation 620, and a GSO constellation 630. The LEO satellite constellation 610 is shown to include a plurality of LEO satellites 611A-611H, the MEO satellite constellation 620 is shown to include a plurality of MEO satellites 621A-621C, and the GSO satellite constellation 630 is shown to include a plurality of GSO satellites 631A-631D. In some aspects, each of LEO satellites 611A-611H may be one example of the satellite 300 of FIGS. 1 and 3. In addition, or in the alternative, each of the MEO satellites 621A-621C may be one example of the satellite 300 of FIGS. 1 and 3, or each of the GSO satellites 631A-631D may be one example of the satellite 300 of FIGS. 1 and 3 (or both). Although the LEO constellation 610 is shown in FIG. 6 as including only eight satellites 611A-611H for simplicity, the LEO constellation 610 may include any suitable number of satellites 611, for example, to provide world-wide satellite coverage. Similarly, although the MEO constellation 620 is shown in FIG. 6 as including only three satellites 621A-621C for simplicity, the MEO constellation 620 may include any suitable number of satellites 621, for example, to provide world-wide satellite coverage. Likewise, although the GSO constellation 630 is shown in FIG. 6 as including only four satellites 631A-631D for simplicity, the GSO constellation 630 may include any suitable number of satellites 631. As used herein, the “LEO satellite 611” may refer to any one (or more) of the LEO satellites 611A-611H of FIG. 6, the “MEO satellite 621” may refer to any one (or more) of the MEO satellites 621A-621C of FIG. 6, and the “GSO satellite 631” may refer to any one (or more) of the GSO satellites 631A-631D of FIG. 6.
The LEO satellites 611A-611H may orbit the Earth 640 in any suitable number of non-geosynchronous orbital planes (not shown for simplicity), and each of the orbital planes may include a plurality of the LEO satellites. Similarly, the MEO satellites 621A-621C may orbit the Earth 640 in any suitable number of non-geosynchronous orbital planes (not shown for simplicity), and each of the orbital planes may include a plurality of the MEO satellites. The non-geosynchronous orbital planes may include, for example, polar orbital patterns and/or Walker orbital patterns. To a stationary observer on Earth 640, the LEO satellites 611A-611H and the MEO satellites 621A-621C appear to move quickly across the sky in a plurality of different paths across the Earth's surface. In contrast, the GSO satellites 631A-631D may appear, to a stationary observer on Earth 640, motionless in a fixed position in the sky located above the earth's equator 641. It is noted that for a given point on the surface of Earth 640, there may be an arc of positions in the sky along which the GSO satellites 631A-631D may be located. This arc of GSO satellite positions may be referred to herein as the GSO arc 650.
Each the LEO satellites 611A-611H may include a number of directional antennas to provide high-speed forward links (e.g., downlinks) with user terminals such as UT 400 of FIG. 1 and/or with gateways such as gateway 200 of FIG. 1, while each of the GSO satellites 631A-631D may include a number of omni-directional antennas to provide satellite coverage over large portions of the Earth's surface. In some implementations, each the MEO satellites 621A-621C may include a number of directional antennas to provide high-speed forward links (e.g., downlinks) with user terminals such as UT 400 of FIG. 1 and/or with gateways such as gateway 200 of FIG. 1. A high-gain directional antenna achieves higher data rates and is less susceptible to interference than an omni-directional antenna by focusing radiation into a relatively narrow beam width (as compared to the relatively wide beam width associated with an omni-directional antenna). For example, as depicted in FIG. 6, the coverage area 613A provided by a beam 612A transmitted from LEO satellite 611A is relatively small compared to the coverage area 633A provided by a beam 632A transmitted from GSO satellite 631A. Accordingly, although not shown in FIG. 6 for simplicity, the footprint of each of the LEO satellites 611A-611H may be significantly smaller than the footprint of each of the GSO satellites 631A-631D.
The UT 400 may include or be associated with one or more directional antennas to provide high-speed return links (e.g., uplinks) to LEO satellites 611A-611H, to MEO satellites 621A-621C, and/or to GSO satellites 631A-631D. For example, a beam 460 transmitted from UT 400 may also have a relatively narrow beam width (e.g., as compared to the relatively wide beam width of an omni-directional antenna typically associated with a GSO earth station, not shown for simplicity). The relatively narrow beam widths associated with UT 400 may create challenges when switching communications from a first satellite to a second satellite, particularly when the first and second satellites are part of (or belong to) different satellite constellations (and therefore may have different orbital patterns, different propagation delays, different carrier signals, different modulation and coding schemes (MCSs), and so on).
FIG. 7 shows a block diagram of an example user terminal (UT) 700. The UT 700 may be one implementation of any of the UTs 400 and/or 401 of FIG. 4. The UT 700 includes a transceiver 710, a processor 720, a memory 730, a signal processing system 740, an antenna 750, and an antenna switching circuit 760. The transceiver 710 may be used to transmit signals to and receive signals from satellites, UEs, and/or other suitable wireless devices. In some implementations, the transceiver 710 may employ a single modem, for example, to minimize cost and complexity of the UT 700 (although using a single modem to communicate with satellites which may belong to different constellations and which may transmit at different frequencies and/or using different modulation schemes may be challenging).
The transceiver 710 may employ various types of coding (encoding and decoding) schemes including, for example, block coding, convolutional or turbo coding, or any combination thereof. In some implementations, the transceiver 710 may use concatenating coding in which an outer code is used with an inner code to decode data received from a satellite and to encode data to be transmitted to a satellite. For example, in some aspects, a satellite may use a Bose-Chaudhuri-Hocquenghem (BCH) code as an outer code and use a turbo code as an inner code to encode data for transmission to the UT 700 on a forward link, and the UT 700 may use the BCH code as the outer code and use the turbo code as the inner code to decode the data received from the satellite. In other implementations, the transceiver 710 may use interleaving, which may be considered to be part of the coding scheme. In addition, a Cyclic Redundancy Check (CRC) may be generated from information bits in a data structure and appended thereto for error control.
The transceiver 710 also may translate data symbols (e.g., bits) of a block into channel symbols. For example, every B bits in a block may be grouped together, and each of the blocks may be mapped to a point in a modulation constellation, for example, so that a signal containing the blocks can be mapped to as many as 2B constellation points. The combination of modulation and coding schemes used by the UT 700 and a corresponding satellite may be represented by a Modulation and Coding Index (MCI) value.
In some implementations, the UT 700 may employ blind detection and error control in which the MCI for the block being decoding is not transmitted along with the block. Regardless of whether the MCIs are transmitted or not, different modulation and coding schemes may be employed for different blocks. In this manner, multiple modulation and coding schemes (MCSs) may be used to transmit, within the same slot, multiple blocks destined for one or more UTs. The various satellite communication links may utilize various medium access schemes such as, for example, single carrier TDMA. The signal constellation space may represent any one of a number of well-known modulation techniques including, for example, Phase Shift Keying (PSK), Quadrature Phase Shift Keying (QPSK), or Quadrature Amplitude Modulation (QAM). The QAM transmission schemes may include 16-QAM, 64-QAM, 128-QAM, 256-QAM, and so on.
The antenna 750 is coupled to the transceiver 710, and may be any suitable high-gain directional antenna. In some implementations, the antenna 750 may be configured for transmitting or receiving (or both) right-hand polarized electromagnetic radiation or left-hand polarized electromagnetic radiation, and may include multiple elements or components (such as for beam steering). In some aspects, the antenna 750 may include a transmission antenna configured for right-hand or left-hand polarization, and may include a receive antenna configured for right-hand or left-hand polarization. In other aspects, the antenna 750 may include a transmission antenna configured for one of right-hand or left-hand polarization, and may include a receive antenna configured for the other of right-hand or left-hand polarization (such as to provide isolation between FL communications and RL communications of the UT 700). In other implementations, the antenna 750 may be configured to transmit and receive other wireless signals or communications). In some aspects, the antenna 750 may be configured to have a transmit bandwidth suitable for transmitting signals to LEO satellites (such as LEO satellites 611A-611H), and configured to have a receive bandwidth suitable for receiving signals from LEO satellites 611A-611H, from MEO satellites (such as MEO satellites 621A-621C), and from GSO satellites (such as GSO satellites 631A-631D). In addition, or in the alternative, the antenna 750 may include separate apertures (such as one aperture for transmission and another aperture for reception).
The antenna 750 may facilitate a satellite link 755 between the UT 700 and a selected one (or more) of a number of satellites belonging to different types of satellite constellations using a single transceiver 710 provided in the UT 700. For example, referring also to FIG. 6, the antenna 750 may establish and receive data on a FL of one of the LEO satellites 611A-611H during a first time period, may establish and receive data on a FL of one of the MEO satellites 621A-621C during a second time period, and may establish and receive data on a FL of one of the GSO satellites 631A-631D during a third time period. In some implementations, the MEO satellites 621A-621C and the GSO satellites 631A-631D may not provide a return link upon which the UT 700 may transmit control information or messages to the gateway 200 (e.g., to the SAN 150). As explained below, the UT 700 may use the return link provided by LEO satellites 611A-611H to transmit control information or messages to the SAN 150, irrespective of which satellite or satellite constellation is providing forward link data to the UT 700.
The memory 730 includes a transmit (TX) data store 731 and a receive (RX) data store 732. The TX data store 731 may store outgoing data to be transmitted on a forward link of a satellite beam. In some implementations, the TX data store 731 may store FL data associated with ongoing HARQ processes maintained by one or more of the schedulers for forward-link communications received from a network controller. The RX data store 732 may store incoming data received on a return link of a satellite beam. In some implementations, the RX data store 732 may store RL data associated with ongoing HARQ processes maintained by one or more of the schedulers for return-link communications sent to the network controller.
The memory 730 may also include a non-transitory computer-readable medium (e.g., one or more nonvolatile memory elements, such as EPROM, EEPROM, Flash memory, a hard drive, etc.) that may store at least the following software (SW) modules:
a forward-link (FL) communication SW module 733 to preserve and/or maintain ongoing forward link communications during inter-satellite handover operations (and during inter-beam handover operations), for example, as described for one or more operations of FIG. 12;
a return-link (RL) communication SW module 734 to preserve and/or maintain ongoing return link communications during inter-satellite handover operations (and during inter-beam handover operations), for example, as described for one or more operations of FIG. 12;
a satellite handover SW module 735 to facilitate and control satellite handover operations, for example, as described for one or more operations of FIG. 12; and
an antenna switching SW module 736 to dynamically adjust or switch the antenna 750 between different satellites, for example, as described for one or more operations of FIG. 12.
Each software module includes instructions that, when executed by the processor 720, cause the user terminal 700 to perform the corresponding functions. The non-transitory computer-readable medium of memory 730 thus includes instructions for performing all or a portion of the operations of FIG. 12.
The processor 720 may be any suitable one or more processors capable of executing scripts or instructions of one or more software programs stored in the UT 700 (e.g., within the memory 730). The processor 720 may execute the FL communication SW module 733 to preserve and/or maintain ongoing forward link communications during inter-satellite handover operations, for example, by communicating FL feedback messages and related HARQ information received from a serving satellite to a target satellite. The processor 720 may also execute the FL communication SW module 733 to preserve and/or maintain ongoing forward link communications during inter-beam handover operations, for example, by communicating an FL feedback message received by a scheduler for the serving beam (and related HARQ information) to a scheduler for the target beam.
The processor 720 may execute the RL communication SW module 734 to preserve and/or maintain an ongoing return link connection with an LEO satellite during inter-satellite handover operations, for example, so that the UT 700 can communicate control information or messages to the SAN 150 using the return link of the LEO satellite. In some aspects, the control information or messages may include (but not limited to) one or more of control data, user data, acknowledgements (such as RLC ack and TCP ack), HTTP get, HARQs, CQI reports, RRC configuration information, and so on). In some implementations, execution of the FL communication SW module 733 and the RL communication SW module 734 may be used to switch communications between beams of different satellites in the same satellite constellation (such as switching communications from a serving beam of LEO satellite 611A to a target beam of LEO satellite 611B). In addition, or in the alternative, execution of the FL communication SW module 733 and the RL communication SW module 734 may be used to switch communications between beams of different satellites belonging to different satellite constellations (such as switching communications from a serving beam of LEO satellite 611A to a target beam of MEO satellite 621B, switching communications from a serving beam of LEO satellite 611A to a target beam of GSO satellite 631B, or switching communications from a serving beam of MEO satellite 621A to a target beam of MEO satellite 621B).
The processor 720 may also execute the RL communication SW module 734 to preserve and/or maintain ongoing return link communications during inter-beam and inter-satellite handover operations, for example, by communicating RL data received by a scheduler for the serving beam (and related HARQ information) to a scheduler for the target beam. In some implementations, execution of the FL communication SW module 733 and the RL communication SW module 734 may be used to switch communications between different beams of the same satellite.
The processor 720 may execute the satellite handover SW module 735 to facilitate and control satellite handover operations. In some implementations, the processor 720 may execute the satellite handover SW module 735 to acquire, track, and lock a target satellite (such as a satellite with which the UT 700 does not yet have a communications link). The processor 720 may also execute the satellite handover SW module 735 to concurrently communicate with a serving satellite and a target satellite using a suitable time-division multiplexing (TDM) based transmission pattern.
The processor 720 may execute the antenna switching SW module 736 to dynamically adjust or switch the antenna 750 between different satellites (such as by tuning the transceiver 710 and calibrating the antenna 750 to the transmission frequency and timing used by the target satellite). In some aspects, one or more functions performed by execution of the antenna switching SW module 736 may be performed or implemented by the antenna switching circuit 760.
The signal processing system 740 may implement one or more protocol stacks. In some implementations, the one or more protocol stacks may operate in accordance with the Open Systems Interconnection (OSI) model (or another suitable protocol stack model). The OSI model is a seven-layer model developed by the International Standardization Organization (ISO) that describes how to interconnect any combination of network devices in terms of seven functional layers organized in a hierarchy. The higher in hierarchy an OSI layer is, the closer it is to an end user; the lower in hierarchy an OSI layer is, the closer it is to a physical channel From highest level of the hierarchy to lowest level of the hierarchy, the OSI Model includes the Application layer, the Presentation Layer, the Session Layer, the Transport Layer, the Network Layer, the Data-Link Layer, and the Physical Layer (not shown for simplicity). The Data-Link Layer is divided into logical link control (LLC) layer and the media access control (MAC) layer.
The PHY defines the relationship between the UT 700 and communication medium (such as the satellite link 755), and is responsible for modulating signals to be transmitted from the UT 700 and for demodulating signals received by the UT 700. The MAC layer may provide framing, encoding, and decoding, and is responsible for controlling access to the communication medium. In some aspects, the PHY and the MAC may provide block coding, convolutional coding, turbo coding, and outer coding for data received by the UT 700.
In some implementations, hybrid automatic repeat request (HARQ) processes are performed by the PHY and managed by the MAC layer of the UT 700. HARQ may be used by the UT 700 to request retransmission of data that was received in error. More specifically, HARQ allows the UT 700 to buffer and combine incorrectly received data (such as packets, frames, PDUs, MPDUs, and so on) to potentially reduce the number of retransmissions needed to properly reconstruct a particular unit of data. For example, if the UT 700 receives an incorrect unit of data from a network controller such as the SAN 150, the UT 700 may request retransmission of that particular unit of data. Rather than discard the incorrect unit of data, the UT 700 may store the incorrect unit of data (e.g., in a HARQ buffer) so that it can be combined with the retransmitted data, for example, thereby allowing the UT 700 to more quickly recover the correct unit of data.
For example, if both the original unit of data and the retransmitted data have errors, the UT 700 may combine the error-free portions of the original unit of data and the error-free portions of the retransmitted data to reconstruct the correct unit of data. The UT 700 may use return links provided by the LEO satellites 611A-611H to send HARQ feedback information to the network controller or the SAN 150. The HARQ feedback information may include an acknowledgement (ACK) to indicate that a corresponding unit or group of FL data was received correctly, or may include a negative acknowledgement (NACK) of FL data to indicate that the corresponding unit or group of FL data was received incorrectly (or not received at all).
The data-link layer is responsible for identifying network layer protocols, encapsulating packets, error checking, and frame synchronization. The network layer provides the functional and procedural means of transferring variable length data sequences such as datagrams or packets. The presentation, session, and transport layers may provide a communication plane for providing VoIP, web surfing, and other communication functionalities. The application layer may interact with software applications that implement or facilitate communications between devices.
In some implementations, one or more of the functions of the signal processing system 740 may be performed by executing software programs or instructions using the processor 720. In addition, or in the alternative, one or more of the functions of the signal processing system 740 may be performed by hardware under control of firmware, or may be performed by special purpose hardware such as application specific integrated circuits (ASIC), or field programmable gate arrays (FPGA). For example, in some implementations, one or more functions of the PHY of the signal processing system 740 may be implemented or performed by the transceiver 710.
FIG. 8 shows a block diagram 800 depicting a user terminal (UT) 700 communicating with a first satellite 810 and a second satellite 820. As shown in FIG. 8, the UT 700 (see also FIG. 7) may communicate with the UE 500 using any suitable communication protocol including, for example, cellular, Wi-Fi, Wi-Max, and Ethernet communications. The UT 700 may communicate with the gateway 200 via at least one of the first satellite 810 and the second satellite 820, and the gateway 200 may communicate with one or more other networks (such as the Internet, for example, as depicted in FIG. 1).
The first satellite 810 and the second satellite 820 may belong to different satellite constellations. In some implementations, the first satellite 810 may be one of the LEO satellites 611A-611H of FIG. 6, and the second satellite 820 may be one of the MEO satellites 621A-621C of FIG. 6. In other implementations, the first satellite 810 may be one of the LEO satellites 611A-611H of FIG. 6, and the second satellite 820 may be one of the GSO satellites 631A-631D of FIG. 6. In some other implementations, the first satellite 810 may be one of the MEO satellites 621A-621C of FIG. 6, and the second satellite 820 may be one of the GSO satellites 631A-631D of FIG. 6. In some other implementations, the first satellite 810 may be one of the LEO satellites 611A-611H of FIG. 6, and the second satellite 820 may an LEO satellite which belongs to another satellite constellation (such as different than the LEO satellite constellation 610 depicted in FIG. 6).
The first satellite 810 communicates with gateway 200 via a first feeder link 811, and communicates with the UT 700 via a first service link 812. The second satellite 820 communicates with gateway 200 via a second feeder link 821, and communicates with the UT 700 via a second service link 822. In some implementations, the first feeder link 811 and the first service link 812 associated with the first satellite 810 each include forward links and return links, and the second feeder link 821 and the second service link 822 associated with the second satellite 820 each include only forward links. For such implementations, the UT 700 may receive forward link communications from gateway 200 via either the first satellite 810 or the second satellite 820 (or both), and may transmit data to the gateway 200 using only the first satellite 810. In this manner, the second satellite 820 may provide additional forward link bandwidth for the satellite system, for example, to supplement the forward link capacity of the first satellite 810. In some aspects, the first satellite 810 and the second satellite 820 each have independent PHY cell IDs, for example, so that the UT 700 can direct transmissions to either the first satellite 810 or the second satellite 820 (and so that the first satellite 810 and the second satellite 820 can each determine whether it is the intended recipient of data transmitted from the UT 700).
The first satellite 810 provides a return link for transmissions from the UT 700 to the gateway 200, for example, that may be used by the UT 700 to transmit control information or messages that may include one or more of control data, user data, acknowledgements (such as RLC ack and TCP ack), HTTP get, HARQs, CQI reports, and RRC configuration information to the SAN 150. For example, if the UT 700 receives data in error from the first satellite 810, the UT 700 may use a HARQ process to request retransmission of the data received in error by transmitting a HARQ to the gateway 200 on the return link provided by the first satellite 810.
The second satellite 820 may not provide a return link for transmissions from the UT 700 to the gateway 200, and therefore may not facilitate HARQ processes or other error correction techniques for the UT 700. The lack of return link capabilities of the second satellite 820 may present challenges when the UT 700 receives data in error, particularly from the second satellite 820. In addition, because any ongoing HARQ processes with the first satellite 810 may be reset during a satellite handover operation from the first satellite 810 to the second satellite 820 (which may undesirably cause an increase in the number of retransmissions and thereby reduce the overall throughput of communications in the satellite system), switching communications of the UT 700 from the first satellite 810 to the second satellite 820 also may present challenges. For example, the lack of return link capabilities of the second satellite 820 may not afford the UT 700 an opportunity to transmit control information and messages (such as control data, user data, acknowledgements, HTTP get, and so on) to the SAN 150 via the second satellite 820).
In accordance with aspects of the present disclosure, the first satellite 810 (which may be one of the LEO satellites 611A-611H) may provide the anchor carrier signals for the satellite system, and the second satellite 820 (which may be one of the MEO satellites 621A-621C or one of the GSO satellites 631A-631D) may provide secondary carrier signals for the satellite system. In some implementations, the anchor carrier signals provided by the first satellite 810 may support both FL and RL transmissions to and from the UT 700, while the secondary carrier signals provided by the second satellite 820 may support only FL transmissions to the UT 700. The UT 700 transmits control information or messages to the SAN 150 using the RL anchor carrier signals of the first satellite 810. In some aspects, the control information or messages may include (but not limited to) one or more of control data, user data, acknowledgements (such as RLC ack and TCP ack), HTTP get, HARQs, CQI reports, RRC configuration information, and so on).
In some implementations, the UT 700 performs acquisition, access, registration, and paging operations with the first satellite 810 using the anchor carrier signals. Once the UT 700 establishes a connection with the SAN 150 via one or more serving beams of the first satellite 810, the SAN 150 may provide the UT 700 with ephemeris data and the PHY cell ID for the second satellite 820. In some aspects, the SAN 150 may also provide the UT 700 with ephemeris data and the PHY cell IDs for one or more of the LEO satellites 611A-611H, the MEO satellites 621A-621C, and the GSO satellites 631A-631D.
In some implementations, the UT 700 includes a single antenna 750 for communicating with both the first satellite 810 and the second satellite 820, and the bandwidth of the antenna 750 may include transmission frequencies used by both the first satellite 810 and the second satellite 820. In some aspects, the UT 700 may be configured to quickly re-position, re-orient, and/or tune its antenna 750 during handover operations between different types of satellites or between satellites belonging to different satellite constellations. In implementations for which the UT 700 includes only one transceiver 710, the transceiver 710 may be configured to decode modulated data received from either the first satellite 810 or the second satellite 820.
In some implementations, the satellite system may ensure that the UT 700 can receive and decode data received on the forward link from the second satellite 820 by specifying that traffic transmitted to the UT 700 on the forward link of the second satellite 820 has a target block error rate (BLER) greater than or equal to a threshold error rate (THerror) for at least the first transmission. By initially transmitting forward link traffic to the UT 700 using a BLER greater than or equal to THerror, the second satellite 820 may minimize or eliminate data reception errors at the UT 700, which in turn may reduce the frequency with which the UT 700 transmits data reception error messages (such as HARQ messages, radio-link controller (RLC) acknowledgements, HTTP Get messages, and so on) to the SAN 150 using RL resources of the first satellite 810. In some aspects, subsequent forward link traffic may be transmitted from the second satellite 820 to the UT 700 using a target BLER less than THerror. In some aspects, the value of THerror may be approximately equal to 10−6. In other aspects, other suitable values may be used for THerror.
In some implementations, the satellite system disclosed herein may employ outer codes when transmitting data on the forward links of the MEO satellites 621A-621C and the GSO satellites 631A-631D to avoid the error floor of turbo codes. In some aspects, the outer codes may be used on top of the turbo codes for forward link data transmissions to the UT 700 from the MEO satellites 621A-621C and the GSO satellites 631A-631D. For example, data transmissions having a target BLER on the order of 10−6 may have a target BLER that is less than the error floor of the turbo code, which is undesirable. To mitigate this problem, a satellite such as one of the MEO satellites 621A-621C or one of the GSO satellites 631A-631D may use concatenated coding in which a turbo code is used as an inner code and a BCH code is used as an outer code, for example, such that the resulting concatenated code has an error floor less than the value of THerror (such as less than approximately 10−6).
The UT 700 may initially access the satellite system by first acquiring the first satellite 810 (which may be one of the LEO satellites 611A-611H of FIG. 6). The UT 700 may obtain ephemeris data of the first satellite 810 in any suitable manner. In some implementations, the UT 700 may store ephemeris data of the first satellite 810 in a memory (such as memory 730 of FIG. 7). In other implementations, the UT 700 may obtain ephemeris data of the first satellite 810 from another UT, from another satellite, from the SAN 150, or from a combination thereof. In some aspects, the UT 700 may detect a satellite beam from the first satellite 810, search for a reference signal, run a frequency tracking loop, and decode satellite information blocks (SIBs) received from the first satellite 810. The SIBs may include ephemeris data for a number of the first satellites 810 (such as one or more of the LEO satellites 611A-611H).
In addition, or in the alternative, the SIBs transmitted from the first satellite 810 may include ephemeris data for a number of the second satellites 820 (such as one or more of the MEO satellites 621A-621C and/or one or more of the GSO satellites 631A-631D of FIG. 6). In some implementations, the SAN 150 may determine portions of ephemeris data for a number of the second satellites 820 (such as based on the location of the UT 700, elevation angles between the UT 700 and the second satellites 820, azimuth values between the UT 700 and the second satellites 820, and so on), and transmit the determined portions of the ephemeris data to the UT 700 via the forward link of the first satellite 810. In some aspects, the SAN 150 may send ephemeris data for a number of the second satellites 820 in the UT's field of view to the UT 700 using the forward link of the first satellite 810.
Once the UT 700 establishes a satellite link with the first satellite 810, the UT 700 may camp on the first satellite 810, may perform Idle Mode cell selection and re-selection on the first satellite 810, and may decode paging on the first satellite 810. The UT 700 may determine whether it is capable of receiving data from the second satellite 820, and may report this capability to the SAN 150, for example, using the return link of the first satellite 810. In some aspects, the UT 700 also may indicate its outer code capabilities to the SAN 150 (such as by using the return link of the first satellite 810).
Once the UT 700 has obtained or determined ephemeris data for the second satellite 820, the UT 700 may switch its forward link communications from the first satellite 810 to the second satellite 820. In this manner, the first satellite 810 may provide the anchor carrier signal for initial acquisition, access, registration, and paging operations for the UT 700, and the second satellite 820 may provide secondary carrier signals to increase the forward link capacity of the satellite system available for transmitting data to the UT 700 (and other UTs). In some implementations, the SAN 150 may determine whether (or when) to switch the forward link communications of the UT 700 from a serving beam of the first satellite 810 to a target beam of the second satellite 820.
In some implementations, the SAN 150 also may request channel information from the UT 700 and/or may request the UT 700 to measure channel quality information (CQI) of the forward links provided by one or more of the second satellites 820. The SAN 150 may transmit channel information requests or CQI measurement requests (or both) using unicast messages, multicast messages, or broadcast messages. In some aspects, the SAN 150 may identify the second satellites 820 for which the UT 700 is requested to measure CQI. In response to the request, the UT 700 may measure the CQI of the forward links (e.g., the target beam) of the identified second satellite(s) 820, and may transmit a CQI report to the SAN 150 using the return link of the first satellite 810. The SAN 150 may receive CQI reports from a number of UTs via the return links of one or more of the first satellites 810, and may selectively instruct the UT 700 to switch its forward link communications from the first satellite 810 to a selected one of the second satellites 820 based on a number of parameters (such as bandwidth and capacity information decoded from the received CQI reports, latency requirements or tolerances of data transmitted to the UT 700, the types or classifications of data transmitted to the UT 700, propagation delays associated with one or more of the satellites, and so on). In some aspects, the SAN 150 may instruct the UT 700 to switch its forward link communications by transmitting an RRC message to the UT 700 using the forward link of the first satellite 810, for example, in a manner similar to that used for providing coarse acquisition codes to the UT 700.
In some implementations, the UT 700 may concurrently communicate with the first satellite 810 and the second satellite 820 using a time-division multiplexing (TDM) based transmission pattern. To support half-duplex communication between the SAN 150 and a particular UT, transmissions on the forward service link 302F (such as from the SAN 150 to the UT) may be coordinated with transmissions on the return service link 301F (such as from the UT to the SAN 150). In some aspects, a given communications cycle (such as ˜10 ms) may be subdivided into a number of forward link transmissions and a number of return link transmissions. For example, each forward link transmission may correspond with an individual subframe (e.g., a FL subframe) of data and/or control information sent from the SAN 150 to a particular UT. Similarly, each return link transmission may correspond with an individual subframe (e.g., an RL subframe) of data and/or control information sent from the particular UT to the SAN 150. The FL subframes and the RL subframes of a given communication cycle may collectively form a communication frame (or a “radio” frame). In other implementations, the SAN 150 may select one or more TDM based transmission patterns that allow the UT 700 to receive forward link data from the first satellite 810, the second satellite 820, and a third satellite (e.g., such as from a LEO satellite 611, a MEO satellite 621, and a GSO satellite 631).
FIG. 9 shows an example timing diagram 900 depicting an asymmetric distribution of FL subframes and RL subframes for two communication frames 910(1) and 910(2). More specifically, the timing diagram 900 shows a UT switching between the forward links of an LEO satellite 611 and an MEO satellite 621 while maintaining return link communications with the LEO satellite 611. For the example depicted in FIG. 9, each of the communication frames 910(1) and 910(2) has a duration of 10 milli-seconds (ms), and may be subdivided into ten subframe slots SF0-SF9 (such that each of the subframe slots SF0-SF9 has a duration of 1 ms). Each of the subframe slots SF0-SF9 may be occupied by a FL subframe, an RL subframe, or left unassigned. In some aspects, the two communication frames 910(1) and 910(2) may correspond to a TDM transmission pattern having a period of 20 ms.
A guard period (GP) may be inserted between the first communication frame 910(1) and the second communication frame 910(2). In some aspects, the guard period may occur during transmission of the second communication frame 910(2). The guard period may be used when switching UT communications between satellites that belong to different satellite constellations (such as when switching forward link communications of a UT from the LEO satellite 611 to the MEO satellite 621, when switching forward link communications of a UT from the LEO satellite 611 to a GSO satellite 631, when switching forward link communications of a UT from the MEO satellite 621 to a GSO satellite 631, and so on). Thus, for at least some implementations, there are no data transmissions during the guard period, for example, to allow the UT time to switch between receiving forward link traffic and transmitting return link traffic. It is noted that the 2 service link delays shown in FIG. 9 are independent and asynchronous.
During the time period associated with transmission of the first communication frame 910(1), the LEO satellite 611 either transmits or receives data, and the MEO satellite 621 does not transmit data (e.g., the LEO satellite 611 is “on” and the MEO satellite 621 is “off”). For the example of FIG. 9, the LEO satellite 611 transmits data to the UT on its forward link via subframes SF0-SF3 between times t1 and t2, switches from a transmission mode to a reception mode between times t2 and t3, and receives data from the UT on its return link via subframes SF6-SF9 between times t3 and t4. The transmission period of the first communication frame 910(1) ends at time t5, which is followed by a guard period between times t5 and t6. The guard period may be used by the SAN 150 to switch forward link communications from the LEO satellite 611 to the MEO satellite 621. In some aspects, the MEO satellite 621 may prepare for transmission operations during the guard period.
At time t6, the time period associated with transmission of the second communication frame 910(2) begins, and the MEO satellite 621 transmits data to the UT on its forward link via subframes SF7-SF9 and subframes SF0-SF4 of the second communication frame 910(2) between times t6 and t7. The LEO satellite 611 may be inactive (or at least not transmitting data to the UT) between times t6 and t7. During a second guard period between times t7 and t8, the SAN 150 switches forward link communications from the MEO satellite 621 to the LEO satellite 611. Thereafter, at time t8, the LEO satellite 611 begins transmitting data to the UT on its forward link via subframes SF0-SF3 during a time period associated with transmission of a third communication frame (not shown for simplicity).
Some example TDM-based transmission patterns are shown below in Table 1, where “S1” denotes the first satellite 810 (such as the LEO satellite 611), “S2” denotes the second satellite 820 (such as the MEO satellite 621), and “S3” denotes a third satellite (such as the GSO satellite 631):
TABLE 1 TDM Pattern Periodicity S1 (LEO) S2 (MEO) S3 (GSO)
P1 10 ms 10 ms 0 ms 0 ms P2 20 ms 10 ms 10 ms 0 ms P3 30 ms 10 ms 0 ms 20 ms P4 60 ms 10 ms 20 ms 30 ms
The above examples may use 10 ms-long communication frames (e.g., transmission slots) for transmitting data to the UT 700, and may serve either a full-duplex UT or a half-duplex UT. In addition, the 10 ms-long communication frames also may allow the UT 700 to periodically transmit information (such as control data, user data, RLC acknowledgements, TCP acknowledgements, HTTP GETs, and so on) on the return link of the first satellite 810, which in turn may ensure that information provided by the UT 700 is received by the SAN 150.
As indicated in Table 1, transmission pattern P1 has a period of 10 ms, and is allocated only to the LEO satellite 611. In some implementations for which the UT 700 operates as a half-duplex device, a first portion of each period of transmission pattern P1 may be allocated for forward link transmissions from the LEO satellite 611 to the UT 700, and a second portion of the period of transmission pattern P1 may be allocated for return link transmissions from the UT 700 to the LEO satellite 611. In other implementations for which the UT 700 operates as a full-duplex device, the 10 ms allocated to the LEO satellite 611 may be used for both forward link transmissions and return link transmissions between the UT 700 and the LEO satellite 611. The return link transmissions may include information such as, for example, control data, user data, RLC acknowledgements, TCP acknowledgements, HTTP GETs, and the like.
Transmission pattern P2 has a period of 20 ms, and allocates forward link resources of the LEO satellite 611 and the MEO satellite 621 to the UT 700. More specifically, the first 10 ms of each period of transmission pattern P2 is allocated to the LEO satellite 611, and the last 10 ms of each period of transmission pattern P2 is allocated to the MEO satellite 621. In some implementations for which the UT 700 operates as a half-duplex device, a first portion of the 10 ms allocated to the LEO satellite 611 may be used for forward link transmissions from the LEO satellite 611 to the UT 700, and a second portion of the 10 ms allocated to the LEO satellite 611 may be used for return link transmissions from the UT 700 to the LEO satellite 611. In other implementations for which the UT 700 operates as a full-duplex device, the 10 ms allocated to the LEO satellite 611 may be used for both forward link transmissions and return link transmissions between the UT 700 and the LEO satellite 611. The return link transmissions may include information (such as control data, user data, RLC acknowledgements, TCP acknowledgements, HTTP GETs, and the like) pertaining to the LEO satellite 611, the MEO satellite 621, or both. In some aspects, transmission pattern P2 may correspond to the example timing diagram 900 of FIG. 9.
Transmission pattern P3 has a period of 30 ms, and allocates forward link resources of the LEO satellite 611 and the GSO satellite 631 to the UT 700. More specifically, the first 10 ms of each period of transmission pattern P3 is allocated to the LEO satellite 611, and the last 20 ms of each period of transmission pattern P3 is allocated to the GSO satellite 631. In some implementations for which the UT 700 operates as a half-duplex device, a first portion of the 10 ms allocated to the LEO satellite 611 may be used for forward link transmissions from the LEO satellite 611 to the UT 700, and a second portion of the 10 ms allocated to the LEO satellite 611 may be used for return link transmissions from the UT 700 to the LEO satellite 611. In other implementations for which the UT 700 operates as a full-duplex device, the 10 ms allocated to the LEO satellite 611 may be used for both forward link transmissions and return link transmissions between the UT 700 and the LEO satellite 611. The return link transmissions may include information (such as control data, user data, RLC acknowledgements, TCP acknowledgements, HTTP GETs, and the like) pertaining to the LEO satellite 611, the GSO satellite 631, or both.
Transmission pattern P4 has a period of 60 ms, and allocates forward link resources of the LEO satellite 611, the MEO satellite 621, and the GSO satellite 631 to the UT 700. More specifically, the first 10 ms of each period of transmission pattern P4 is allocated to the LEO satellite 611, the next 20 ms of each period of transmission pattern P4 is allocated to the MEO satellite 621, and the last 30 ms of each period of transmission pattern P4 is allocated to the GSO satellite 631. In some implementations for which the UT 700 operates as a half-duplex device, a first portion of the 10 ms allocated to the LEO satellite 611 may be used for forward link transmissions from the LEO satellite 611 to the UT 700, and a second portion of the 10 ms allocated to the LEO satellite 611 may be used for return link transmissions from the UT 700 to the LEO satellite 611. In other implementations for which the UT 700 operates as a full-duplex device, the 10 ms allocated to the LEO satellite 611 may be used for both forward link transmissions and return link transmissions between the UT 700 and the LEO satellite 611. The return link transmissions may include information (such as control data, user data, RLC acknowledgements, TCP acknowledgements, HTTP GETs, and the like) pertaining to the LEO satellite 611, the MEO satellite 621, the GSO satellite 631, or any combination thereof.
The SAN 150 (or other suitable network controller) may use any number of TDM-based transmission patterns (such as the four example TDM-based transmission patterns P1-P4 indicated above) to dynamically allocate forward link resources of satellite systems disclosed herein to the UT 700. In some implementations, the SAN 150 may select a particular TDM transmission pattern for the UT 700 based at least in part on latency requirements or tolerances of forward link traffic associated with the UT 700, the relative propagation delays of the LEO satellites 611, the MEO satellites 621, and the GSO satellites 631, or any combination thereof. As described above, MEO satellites 621 orbit the Earth at much greater altitudes than the LEO satellites 611, and may have much longer signal propagation delays than the LEO satellites 611. The GSO satellites 631 may offer greater bandwidth and better signal-to-noise ratios (SNRs) than the LEO satellites 611 or the MEO satellites 621, yet have much longer signal propagation delays than the LEO satellites 611 and the MEO satellites 621. Thus, in some aspects, the forward link resources of the LEO satellite 611 may be used for low-latency traffic, the forward link resources of the MEO satellite 621 may be used for traffic that can tolerate longer latencies, and the forward link resources of the GSO satellite 631 may be used for traffic that can tolerate even longer latencies.
For example, if a first user associated with the UT 700 is receiving low-latency voice communications, a second user associated with the UT 700 is browsing the Internet, and a third user associated with the UT 700 is receiving streaming video, then the SAN 150 may allocate 10 ms forward link transmission slots of the LEO satellite 611 to the first user, may allocate 20 ms forward link transmission slots of the MEO satellite 621 to the second user, and may allocate 30 ms forward link transmission slots of the GSO satellite 631 to the third user. In some aspects, the SAN 150 may allocate the forward link transmission slots of the LEO satellite 611 to the first user because the LEO satellite 611 has the lowest propagation delays and may therefore be most suitable for low-latency traffic (and other high-priority data); the SAN 150 may allocate the forward link transmission slots of the MEO satellite 621 to the second user because Internet browsing can tolerate longer propagation delays than real-time voice traffic; and the SAN 150 may allocate the forward link transmission slots of the GSO satellite 631 to the third user because streaming video may tolerate the longer propagation delays associated with the GSO satellite 631.
The timelines of the LEO satellites 611A-611H, the MEO satellites 621A-621C, and/or the GSO satellites 631A-631D may drift over time relative to each other. The SAN 150 can store ephemeris data for all the satellites in the satellite system and the positions of the UTs on Earth, and may determine the service link delays between the given UT and each of a selected LEO satellite, MEO satellite, and GSO satellite. In some aspects, the SAN 150 may keep track of the service link delays (as well as the relative changes between them), for example, so that the UT 700 switches forward link communications from the LEO satellite 611 to either the MEO satellite or the GSO satellite during the “off time” of the LEO satellite 611. The SAN 150 may dynamically track the relative timing slew of the selected LEO satellite, the selected MEO satellite, and the selected GSO satellite, and may schedule forward link traffic using subframes of the MEO and GSO satellites occurring during the off time of the LEO satellite (less a guard period and timing offsets toff1 and toff2 before and after the guard period, respectively). In this manner, the SAN 150 (or a scheduler associated with the SAN 150 or another suitable network controller) may schedule the transmission of forward link data from non-LEO satellites in subframes at times during the “off periods” of the LEO satellite.
In some aspects, the UT 700 can report a capability parameter (denoted herein as the timeToRepointAndReacquire) indicating an amount of time associated with repositioning its antenna 750 and re-acquiring the physical layer loops to switch its communications from one satellite to another satellite. The SAN 150 (or a scheduler associated with the SAN 150) may ensure that the durations of toff1 and toff2 are greater than the duration of the timeToRepointAndReacquire. If a UT is configured with a hybrid communication pattern, the power control system of the UT is enabled during forward link transmissions using an LEO satellite and is disabled during forward link transmissions using an MEO satellite or a GEO satellite.
The UT 700 may be served by a LEO satellite 611, a MEO satellite 621, and a GSO satellite 631 based on a TDM transmission pattern that dynamically allocates forward link resources available to the UT 700 between the LEO satellite 611, the MEO satellite 621, and the GSO satellite 631. In implementations for which the MEO satellite 621 and the GSO satellite 631 do not provide return link resources, the UT 700 may maintain the return link connection with the LEO satellite 611 even when its forward link is served by the MEO satellite 621 and/or the GSO satellite 631. In this manner, the SAN 150 may use the return link of the LEO satellite 611 to complete handover operations between non-LEO satellites. In addition, or in the alternative, the SAN 150 may use the forward link resources of the LEO satellite 611 to initiate or trigger handover operations between non-LEO satellites.
Referring also to FIG. 6, the LEO satellites 611A-611H orbit the Earth at much lower altitudes than the MEO satellites 621A-621C, and are visible to a UT 700 for much shorter time periods than the MEO satellites 621A-621C (or the GSO satellites 631A-631D). As such, handover operations between LEO satellites 611A-611H may occur much more frequently than handover operations between MEO satellites 621A-621C (or between GSO satellites 631A-631D). In some implementations, the UT 700 may switch its service link connection between LEO satellites 611A-611H a multitude of times during the service period of one of the MEO satellites 621A-621C. For example, in one implementation, the UT 700 may switch its service link connection between LEO satellites 611A-611H every 3 minutes, and may switch its forward link connection between MEO satellites 621A-621C every 35-40 minutes.
In some implementations, handover messages used during handover operations between LEO satellites 611A-611H may include a new field containing information pertaining to forward link offloading capabilities of the MEO satellites 621A-621C and GSO satellites 631A-631D. This new field may be used to ensure that forward link communications are switched between MEO satellites and/or GSO satellites at the same time as handover operations between LEO satellites. In some aspects, this new field includes the Physical cell ID and carrier frequency of the MEO and GSO satellites, for example, so that a given UT can measure the forward link channel conditions of the MEO and GSO satellites and then provide a CQI report to the SAN using the return link of the LEO satellite. In addition, or in the alternative, the given UT may measure the signal strengths and/or the SNRs of the forward links of the MEO and GSO satellites and then transmit a measurement report containing the measured signal strengths and/or SNRs to the SAN 150 using the return link of the LEO satellite.
FIG. 10A shows a timing diagram 1000A depicting an example handover operation from a first LEO satellite to a second LEO satellite without switching forward link resources between non-LEO satellites. For the example of FIG. 10A, the first and second LEO satellites may be two of the LEO satellites 611A-611H, and the non-LEO satellite may be one of the MEO satellites 621A-621C or one of the GSO satellites 631A-631D. Prior to time to, the SAN 150 transmits a handover command on the FL of the first LEO satellite. The handover command, which is received by the first LEO satellite at time to and received by the UT at time t1, may instruct the non-LEO and LEO satellites to cease transmission and reception operations. In some implementations, the handover command may contain information of the non-LEO satellite to which forward link communications are offloaded from the LEO satellites. The information may include (but is not limited to) ephemeris data of the non-LEO satellite, the physical cell ID of the non-LEO satellite, and the carrier frequency of the non-LEO satellite.
The handover operation is activated at the first LEO satellite at time t2, and is activated at the UT at time t3. In response thereto, the non-LEO and LEO satellites cease transmission and reception operations on the service links with the UT. After time t3, the UT may begin tuning its transceiver and calibrating its antenna to the transmission frequency and timing used by the second LEO satellite (e.g., to synchronize the UT with the second LEO satellite). The handover operation completes at time t4, after which the SAN 150 allows the non-LEO and LEO satellites to resume transmission and reception operations. During the satellite handover operation between times t2 and t4, the service links between the UT and the satellites may be interrupted (such that the UT does not transmit or receive data during the satellite handover interruption period). The UT completes its RRC reconfiguration at time t5, and the second LEO satellite completes its RRC reconfiguration at time t6. The non-LEO satellite transmits data on its forward link to the UT at time t7, and the UT receives the transmitted forward link data at time t8. In addition, or in the alternative, the second LEO satellite may begin transmitting data on its forward link to the UT at time t7.
In some implementations, handover operations between MEO satellites (or GSO satellites) can be aligned with handover operations between LEO satellites, which may obviate the need for independent RRC reconfiguration messages for beam releases of the MEO and GSO satellites. FIG. 10B shows a timing diagram 1000B depicting an example handover operation from a first LEO satellite to a second LEO satellite that is aligned with a handover operation between non-LEO satellites. For the example of FIG. 10B, the first and second LEO satellites may be two of the LEO satellites 611A-611H, and the non-LEO satellites may be two of the MEO satellites 621A-621C or two of the GSO satellites 631A-631D.
The handover command, which is received by the first LEO satellite at time to and received by the UT at time t1, may instruct the non-LEO and LEO satellites to cease transmission and reception operations. In some implementations, the handover command may contain information pertaining to both the LEO handover operation and the non-LEO handover operation. The information may include (but is not limited to) ephemeris data of the target non-LEO satellite, the physical cell ID of the target non-LEO satellite, and the carrier frequency of the target non-LEO satellite.
The handover operation is activated at the LEO satellites and the non-LEO satellites at time t2, and is activated at the UT at time t3. In response thereto, the LEO satellites and non-LEO satellites cease transmission and reception operations on the service links with the UT. After time t3, the UT may begin tuning its transceiver and calibrating its antenna to the transmission frequency and timing used by the second LEO satellite (e.g., to synchronize the UT with the second LEO satellite). The handover operation completes at time t4, after which the SAN 150 allows the satellites to resume transmission and reception operations. During the satellite handover operation between times t2 and t4, the service links between the UT and the satellites may be interrupted (such that the UT does not transmit or receive data during the satellite handover interruption period).
The UT completes its RRC reconfiguration at time t5, and the second LEO satellite completes its RRC reconfiguration at time t6. After time t6, the UT may measure the signal strength of the target beam of the second non-LEO satellite. At time tA, the UT transmits a measurement report (on the RL of the second LEO satellite) containing the measured signal strength, which is received by the SAN 150 at time tB. In some implementations, the SAN 150 may use measured signal strength information to determine whether (or when) to switch forward link communications of the non-LEO satellite. Thereafter, the SAN 150 transmits an RRC message that activates the target beam of the second non-LEO satellite at time t7. The UT may receive the RRC message by time t8. In some implementations, the SAN 150 may transmit the RRC message using the forward link of the second LEO satellite.
By aligning handover operations between non-LEO satellites with handover operations between LEO satellites, the SAN 150 may use the return link of the serving LEO satellite to receive control messages from the UT needed to complete the non-LEO handover operation. In some implementations, the timing of handover operations between non-LEO satellites may be adjusted (e.g., delayed) to align with handover operations between LEO satellites.
FIG. 11 shows a block diagram of an example network controller 1100 in accordance with example implementations. The network controller 1100, which may be one implementation of the SAN 150 of FIG. 1, may include at least an antenna (not shown for simplicity), a transceiver 1115, a processor 1120, a memory 1130, a scheduler 1140, and a radio resource control (RRC) 1150. The transceiver 1115 may be used to transmit signals to and receive signals from a number of UTs (such as UT 400 or UT 700) via one or more satellites (such as one or more of the LEO satellites 611A-611H, one or more of the MEO satellites 621A-621C, one or more of the GSO satellites 631A-631D, or any combination thereof). Although not shown in FIG. 11 for simplicity, the transceiver 1115 may include any suitable number of transmit chains and/or may include any suitable number of receive chains.
The scheduler 1140 may schedule FL resources and RL resources of a satellite, a constellation of satellites, or a satellite system for a number of UTs. In some implementations, the scheduler 1140 may schedule, control, or otherwise manage satellite handover operations for a number of UTs. In some aspects, the scheduler 1140 may determine when a UT is to switch its FL communications from a serving satellite to a target satellite, and may control FL transmissions of the serving satellite and the target satellite. The scheduler 1140 may also schedule grants of RL resources to a UT by transmitting one or RL grants to the UT, and may select the size of the granted RL resources based on buffer status reports (BSRs) received from the UT. In some aspects, the scheduler 1140 may control or manage each beam of a satellite during inter-beam handover operations.
The RRC 1150 may transmit RRC configuration messages to a UT during inter-beam handovers, during inter-satellite handovers, or both. In some implementations, the RRC configuration messages may include timing information associated with switching the UT's forward link communications from a serving satellite to a target satellite (such as from the LEO satellite 611 to the MEO satellite 621, or from the MEO satellite 621 to the LEO satellite 611). The RRC configuration messages may also be used to reconfigure and/or reestablish communications between the SAN 150 and the UT resulting from inter-satellite handovers (as well as from inter-beam handovers).
The processor 1120 is coupled to the transceiver 1115, to the memory 1130, to the scheduler 1140, and to the RRC 1150. The processor 1120 may be any suitable one or more processors capable of executing scripts or instructions of one or more software programs stored in the network controller 1100 (such as within the memory 1130).
The memory 1130 may include a UT profile data store 1131 and an ephemeris data store 1132. The UT profile data store 1131 may store profile information for a plurality of UTs. The profile information for a particular UT may include, for example, outer code capabilities of the UT, a capability of the UT to transmit and receive data from non-LEO satellites (such as MEO satellites and GSO satellites), the transmission history of the UT, location information of the UT, and any other suitable information describing or pertaining to the operation of the UT.
The ephemeris data store 1132 may store ephemeris data for any number of satellites belonging to any number of different satellite constellations. In some implementations, the ephemeris data store 1132 may store ephemeris data for the LEO satellites 611A-611H, the MEO satellites 621A-621C, and the GSO satellites 631A-631D of FIG. 6.
The memory 1130 may also include a non-transitory computer-readable storage medium (such as one or more nonvolatile memory elements, such as EPROM, EEPROM, Flash memory, a hard drive, and so on) that may store the following software modules (SW):
a satellite handover SW module 1133 to facilitate and control satellite handover operations, for example, as described for one or more operations of FIG. 12; and
a satellite link communication SW module 1134 to preserve and/or maintain ongoing RL communications during satellite handover operations, for example, as described for one or more operations of FIG. 12.
Each software module includes instructions that, when executed by the processor 1120, cause the network controller 1100 to perform the corresponding functions. The non-transitory computer-readable medium of memory 1130 thus includes instructions for performing all or a portion of the operations of FIG. 12.
The processor 1120 may execute the satellite handover SW module 1133 to facilitate and control satellite handover operations. In some implementations, execution of the satellite handover SW module 1133 may be used to switch forward link communications of a UT between different satellites (such as switching communications from LEO satellite 611A to LEO satellite 611B). Execution of the satellite handover SW module 1133 may also be used to switch forward link communications of a UT between different beams of a satellite.
The processor 1120 may execute the satellite link communication SW module 1134 to preserve and/or maintain ongoing forward link communications during inter-satellite handover operations, for example, by receiving control messages (such as HARQ messages) and feedback messages (such as CQI reports) from UTs on the return links of one or more LEO satellites. Execution of the satellite link communication SW module 1134 may also preserve and/or maintain ongoing return link communications during satellite handover operations, for example, so that a UT can transmit control messages and feedback messages to the SAN using the return link of a LEO satellite when receiving forward link data from a non-LEO satellite or when switching its forward link communications between different satellites. In this manner, the forward link communications of a UT may be dynamically switched between different satellites while maintaining a return link connection with the SAN 150 via the LEO satellite.
FIG. 12 shows an illustrative flow chart depicting an example satellite handover operation 1200. The example operation 1200 may be performed by the SAN 150 of FIG. 1 and is described with respect to FIGS. 7-9 and 10A-10B. However, it is to be understood that the operation 1200 may be performed by suitable components of the SAN 150 or another suitable network controller. The example operation 1200, which may be used to switch forward link communications of a user terminal between different satellites that may belong to different satellite constellations, is described with respect to switching the forward link communications of UT 700 between the first satellite 810 and the second satellite 820 of FIG. 8. For purposes of discussion herein, the first satellite 810 is a LEO satellite (such as one of the LEO satellites 611A-611H of FIG. 6) and the second satellite 820 is a non-LEO satellite (such as one of the MEO satellites 621A-621C or one of the GSO satellites 631A-631D of FIG. 6). One of ordinary skill in the art will readily understand that the example operation 1200 may be used to switch forward link communications of any suitable user terminal between any number of different satellites.
The SAN 150 transmits first data to the user terminal on a forward link of the first satellite 810 (1201). In some implementations, the LEO satellite may transmit data to the user terminal using a first portion of a first communication frame (e.g., using subframes SF0-SF3 of the first communication frame 910(1) of FIG. 9). In some aspects, the return link of the LEO satellite may be inactive during transmission of forward link data to the user terminal by the LEO satellite. In addition, or in the alternative, the second satellite 820 may not provide a return link for the user terminal.
The SAN 150 transmits time-division multiplexing (TDM) configuration information to the user terminal on the forward link of the first satellite, the TDM configuration information specifying a TDM transmission pattern for forward link communications to the user terminal from at least the first and second satellites (1202). In some implementations, the specified TDM transmission pattern is based on one or more of latency requirements of data transmitted to the user terminal, a type or classification of data transmitted to the user terminal, and propagation delays of the first and second satellites. In addition, or in the alternative, the specified TDM transmission pattern may configure the user terminal to receive forward link communications from a low-earth orbit (LEO) satellite during a first portion of a TDM transmission period, to receive forward link communications from a medium-earth orbit (MEO) satellite during a second portion of a TDM transmission period, and to receive forward link communications from a geosynchronous orbit (GSO) satellite during a third portion of a TDM transmission period.
The SAN 150 switches forward link communications of the user terminal from the first satellite to the second satellite during a handover operation (1203). In some implementations, the SAN 150 may cause the user terminal to switch its forward link communications from the first satellite to the second satellite by transmitting a radio controller circuit (RRC) message to the user terminal using the forward link of the first satellite.
The SAN 150 transmits second data to the user terminal on a forward link of the second satellite 820 after the handover operation (1204). In some implementations, the non-LEO satellite may transmit data to the user terminal using a number of subframes of a second communication frame (e.g., using subframes SF7-SF9 and subframes SF0-SF4 of the second communication frame 910(2) of FIG. 9). The forward link of the first satellite 810 may be disabled during transmission of the second communication frame on the forward link of the second satellite 820. In some aspects, the non-LEO satellite may transmit the second data using a concatenated code including a turbo code as an inner code and including a Bose-Chaudhuri-Hocquenghem (BCH) code as an outer code. In addition, or in the alternative, the second data may be transmitted with a BLER greater than or equal to a value, for example, to reduce data reception errors of the second data at the user terminal.
The SAN 150 receives one or more control messages from the user terminal on the return link of the first satellite 810 after the handover operation (1205). In some implementations, the user terminal may measure a signal strength of a target beam of the second satellite (e.g., the non-LEO satellite), and may embed the measured signal strength in the one or more control or data messages transmitted to the SAN 150 using the return link of the first satellite (e.g., the LEO satellite). In addition, or in the alternative, the user terminal may transmit HARQ messages to the SAN 150 using the return link of the LEO satellite.
The SAN 150 maintains the return link between the first satellite 810 and the user terminal before and after the handover operation (1206). In this manner, the user terminal may use the return link of the LEO satellite to transmit control messages and data to the SAN 150 while the user terminal has a forward link connection with the non-LEO satellite.
FIG. 13 shows an illustrative flow chart depicting another example satellite handover operation 1300. The example operation 1300 may be performed by the user terminal (UT) 700 of FIG. 7 and is described with respect to FIGS. 7-9 and 10A-10B. However, it is to be understood that the operation 1300 may be performed by another suitable user terminal. The example operation 1300 may be used to switch forward link communications of a user terminal between a first satellite and a second satellite that may belong to different satellite constellations. For purposes of discussion herein, the first satellite 810 is a LEO satellite (such as one of the LEO satellites 611A-611H of FIG. 6) and the second satellite 820 is a non-LEO satellite (such as one of the MEO satellites 621A-621C or one of the GSO satellites 631A-631D of FIG. 6). One of ordinary skill in the art will readily understand that the example operation 1300 may be used to switch forward link communications of any suitable user terminal between any number of different satellites.
The user terminal 700 receives data on a forward link of the first satellite (1301). In some implementations, the LEO satellite may transmit data to the user terminal using a first portion of a first communication frame (e.g., using subframes SF0-SF3 of the first communication frame 910(1) of FIG. 9). In some aspects, the return link of the LEO satellite may be inactive during transmission of forward link data to the user terminal by the LEO satellite. In addition, or in the alternative, the second satellite does not provide a return link for the user terminal.
The user terminal 700 receives time-division multiplexing (TDM) configuration information on the forward link of the first satellite, the TDM configuration information specifying a TDM transmission pattern for forward link communications to the user terminal from at least the first and second satellites (1302). In some implementations, the specified TDM transmission pattern is based on one or more of latency requirements of data transmitted to the user terminal, a type or classification of data transmitted to the user terminal, and propagation delays of the first and second satellites. In addition, or in the alternative, the specified TDM transmission pattern may configure the user terminal to receive forward link communications from a low-earth orbit (LEO) satellite during a first portion of a TDM transmission period, to receive forward link communications from a medium-earth orbit (MEO) satellite during a second portion of a TDM transmission period, and to receive forward link communications from a geosynchronous orbit (GSO) satellite during a third portion of a TDM transmission period.
The user terminal 700 switches forward link communications from the first satellite to the second satellite during a handover operation (1303). In some implementations, the SAN 150 may cause the user terminal to switch its forward link communications from the first satellite to the second satellite by transmitting a radio controller circuit (RRC) message to the user terminal using the forward link of the first satellite.
The user terminal 700 receives second data on a forward link of the second satellite after the handover operation (1304). In some implementations, the non-LEO satellite may transmit data to the user terminal using a number of subframes of a second communication frame (e.g., using subframes SF7-SF9 and subframes SF0-SF4 of the second communication frame 910(2) of FIG. 9). The forward link of the first satellite may be disabled during transmission of the second communication frame on the forward link of the second satellite. In some aspects, the non-LEO satellite may transmit the second data using a concatenated code including a turbo code as an inner code and including a Bose-Chaudhuri-Hocquenghem (BCH) code as an outer code. In addition, or in the alternative, the second data may be transmitted with a BLER greater than or equal to a value, for example, to reduce data reception errors of the second data at the user terminal.
The user terminal 700 transmits one or more control or data messages to a network controller on a return link of the first satellite after the handover operation (1305). In some implementations, the user terminal may measure a signal strength of a target beam of the second satellite (e.g., the non-LEO satellite), and may embed the measured signal strength in the one or more control or data messages transmitted to the SAN 150 using the return link of the first satellite (e.g., the LEO satellite). In addition, or in the alternative, the user terminal may transmit HARQ messages to the SAN 150 using the return link of the LEO satellite.
The user terminal 700 maintains the return link with the first satellite before and after the handover operation (1306). In this manner, the user terminal may use the return link of the LEO satellite to transmit control messages and data to the SAN 150 while the user terminal has a forward link connection with the non-LEO satellite.
1. A method for switching forward link communications of a user terminal between first and second satellites, the method performed by the user terminal and comprising:
receiving first data on a forward link of the first satellite;
receiving time-division multiplexing (TDM) configuration information on the forward link of the first satellite, the TDM configuration information specifying a TDM transmission pattern for forward link communications to the user terminal from at least the first and second satellites;
switching forward link communications of the user terminal from the first satellite to the second satellite during a handover operation;
receiving second data on a forward link of the second satellite after the handover operation; and
transmitting one or more control or data messages to a network controller on a return link of the first satellite after the handover operation.
2. The method of claim 1, wherein the one or more control or data messages comprise an acknowledgement of the second data received by the user terminal.
3. The method of claim 1, wherein the first satellite comprises a low-earth orbit (LEO) satellite, the second satellite is one of a medium-earth orbit (MEO) satellite or a geosynchronous orbit (GSO) satellite, and the one or more control or data messages comprise information pertaining to the handover operation from the first satellite to the second satellite.
4. The method of claim 1, wherein the first satellite comprises a low-earth orbit (LEO) satellite, the second satellite is one of a medium-earth orbit (MEO) satellite or a geosynchronous orbit (GSO) satellite, and the second satellite does not provide a return link for the user terminal.
5. The method of claim 1, wherein the specified TDM transmission pattern configures the user terminal to exchange data with the first satellite using a first communication frame and to receive data from the second satellite using a second communication frame.
6. The method of claim 1, wherein the specified TDM transmission pattern is based on one or more of latency requirements of data transmitted to the user terminal, a type or classification of data transmitted to the user terminal, and propagation delays of the first and second satellites.
7. The method of claim 1, wherein the specified TDM transmission pattern configures the user terminal to receive forward link communications from a low-earth orbit (LEO) satellite during a first portion of a TDM transmission period, to receive forward link communications from a medium-earth orbit (MEO) satellite during a second portion of a TDM transmission period, and to receive forward link communications from a geosynchronous orbit (GSO) satellite during a third portion of a TDM transmission period.
8. The method of claim 1, wherein the second data is transmitted from the second satellite using a concatenated code including a turbo code as an inner code and including a Bose-Chaudhuri-Hocquenghem (BCH) code as an outer code.
9. The method of claim 1, wherein the handover operation is triggered by a radio controller circuit (RRC) message transmitted to the user terminal using the forward link of the first satellite.
10. The method of claim 9, wherein the first satellite comprises a first low-earth orbit (LEO) satellite, the second satellite is one of a medium-earth orbit (MEO) satellite or a geosynchronous orbit (GSO) satellite, and the RRC message triggers a handover operation between the first satellite and a second LEO satellite.
maintaining the return link between the first satellite and the user terminal before and after the handover operation.
12. A user terminal configured to switch forward link communications between first and second satellites, the user terminal comprising:
a memory storing instructions that, when executed by the one or more processors, cause the user terminal to: receive first data on a forward link of the first satellite; receive time-division multiplexing (TDM) configuration information on the forward link of the first satellite, the TDM configuration information specifying a TDM transmission pattern for forward link communications to the user terminal from at least the first and second satellites; switch forward link communications of the user terminal from the first satellite to the second satellite during a handover operation; receive second data on a forward link of the second satellite after the handover operation; and transmit one or more control or data messages to a network controller on a return link of the first satellite after the handover operation.
13. The user terminal of claim 12, wherein the one or more control or data messages comprise an acknowledgement of the second data received by the user terminal.
14. The user terminal of claim 12, wherein the first satellite comprises a low-earth orbit (LEO) satellite, the second satellite is one of a medium-earth orbit (MEO) satellite or a geosynchronous orbit (GSO) satellite, and the one or more control or data messages comprise information pertaining to the handover operation from the first satellite to the second satellite.
15. The user terminal of claim 12, wherein the first satellite comprises a low-earth orbit (LEO) satellite, the second satellite is one of a medium-earth orbit (MEO) satellite or a geosynchronous orbit (GSO) satellite, and the second satellite does not provide a return link for the user terminal.
16. The user terminal of claim 12, wherein the specified TDM transmission pattern configures the user terminal to exchange data with the first satellite using a first communication frame and to receive data from the second satellite using a second communication frame.
17. The user terminal of claim 12, wherein the specified TDM transmission pattern is based on one or more of latency requirements of data transmitted to the user terminal, a type or classification of data transmitted to the user terminal, and propagation delays of the first and second satellites.
18. The user terminal of claim 12, wherein the specified TDM transmission pattern configures the user terminal to receive forward link communications from a low-earth orbit (LEO) satellite during a first portion of a TDM transmission period, to receive forward link communications from a medium-earth orbit (MEO) satellite during a second portion of a TDM transmission period, and to receive forward link communications from a geosynchronous orbit (GSO) satellite during a third portion of a TDM transmission period.
19. The user terminal of claim 12, wherein the second data is transmitted from the second satellite using a concatenated code including a turbo code as an inner code and including a Bose-Chaudhuri-Hocquenghem (BCH) code as an outer code.
20. The user terminal of claim 12, wherein the handover operation is triggered by a radio controller circuit (RRC) message transmitted to the user terminal using the forward link of the first satellite.
21. The user terminal of claim 20, wherein the first satellite comprises a first low-earth orbit (LEO) satellite, the second satellite is one of a medium-earth orbit (MEO) satellite or a geosynchronous orbit (GSO) satellite, and the RRC message triggers a handover operation between the first satellite and a second LEO satellite.
22. The user terminal of claim 12, wherein execution of the instructions causes the user terminal to further:
maintain the return link between the first satellite and the user terminal before and after the handover operation.
23. A non-transitory computer-readable medium comprising instructions that, when executed by one or more processors of a user terminal, cause the user terminal to switch forward link communications between first and second satellites by performing operations including:
24. The non-transitory computer-readable medium of claim 23, wherein the specified TDM transmission pattern configures the user terminal to exchange data with the first satellite using a first communication frame and to receive data from the second satellite using a second communication frame.
25. The non-transitory computer-readable medium of claim 23, wherein the specified TDM transmission pattern is based on one or more of latency requirements of data transmitted to the user terminal, a type or classification of data transmitted to the user terminal, and propagation delays of the first and second satellites.
26. The non-transitory computer-readable medium of claim 23, wherein the specified TDM transmission pattern configures the user terminal to receive forward link communications from a low-earth orbit (LEO) satellite during a first portion of a TDM transmission period, to receive forward link communications from a medium-earth orbit (MEO) satellite during a second portion of a TDM transmission period, and to receive forward link communications from a geosynchronous orbit (GSO) satellite during a third portion of a TDM transmission period.
27. The non-transitory computer-readable medium of claim 23, wherein the handover operation is triggered by a radio controller circuit (RRC) message transmitted to the user terminal using the forward link of the first satellite.
28. The non-transitory computer-readable medium of claim 27, wherein the first satellite comprises a first low-earth orbit (LEO) satellite, the second satellite is one of a medium-earth orbit (MEO) satellite or a geosynchronous orbit (GSO) satellite, and the RRC message triggers a handover operation between the first satellite and a second LEO satellite.
29. The non-transitory computer-readable medium of claim 23, wherein execution of the instructions causes the user terminal to perform operations further comprising:
30. An apparatus configured to switch forward link communications between first and second satellites, the apparatus comprising:
means for receiving first data on a forward link of the first satellite;
means for receiving time-division multiplexing (TDM) configuration information on the forward link of the first satellite, the TDM configuration information specifying a TDM transmission pattern for forward link communications to the user terminal from at least the first and second satellites;
means for switching forward link communications of the user terminal from the first satellite to the second satellite during a handover operation;
means for receiving second data on a forward link of the second satellite after the handover operation; and
means for transmitting one or more control or data messages to a network controller on a return link of the first satellite after the handover operation.
Publication number: 20180376393
Patent Grant number: 10575229
Inventors: Qiang Wu (San Diego, CA), Peter John Black (La Jolla, CA), Ruoheng Liu (San Diego, CA)
Application Number: 16/012,639
International Classification: H04W 36/08 (20060101); H04W 36/00 (20060101); H04W 36/16 (20060101); H04W 36/36 (20060101); H04L 5/26 (20060101); H04W 72/04 (20060101); H03M 13/15 (20060101); H04L 1/00 (20060101);