HK1249970B - Apparatus and methods for efficient data transmission in half-duplex communication systems - Google Patents

Description

Method and device for efficient data transmission in half-duplex communication system

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application claims priority to U.S. Provisional Application No. 62/188,317, filed on July 2, 2015, entitled “METHOD AND APPARATUS FOREFFICIENT DATA TRANSMISSIONS IN HALF-DUPLEX COMMUNICATION SYSTEMS WITH LARGEPROPAGATION DELAYS,” which has been assigned to the assignee of the present application and is hereby expressly incorporated herein by reference in its entirety.

Background Art

Generally speaking, various aspects described herein relate to communication systems, and more particularly, to data transmission in a half-duplex communication system with large propagation delay.

Traditional satellite-based communication systems include a gateway and one or more satellites for relaying communication signals between the gateway and one or more user terminals. A gateway is an earth station with an antenna for sending and receiving signals to and from a communication satellite. The gateway uses satellites to provide a communication link connecting one user terminal to other user terminals or users of other communication systems, such as the public switched telephone network, the Internet, and various public and/or private networks. Satellites are orbiting receivers and transponders used to relay information.

Satellites can receive and transmit signals to user terminals, assuming the user terminals are within the satellite's "orbit." A satellite's orbit is the geographic area on the Earth's surface within the satellite's signal range. This orbit is typically divided geographically into "beams" through the use of beamforming antennas. Each beam covers a specific geographic area within the orbit. Beams can be steered so that more than one beam from the same satellite covers the same specific geographic area.

Geosynchronous satellites have been used for communications for a long time. Geosynchronous satellites are fixed relative to a given location on Earth, and therefore there is minimal timing and Doppler frequency shift in the propagation of wireless signals between communication transceivers on Earth and on the geosynchronous satellite. However, because geosynchronous satellites are confined to a geosynchronous orbit (GSO), which is a circle with a radius of approximately 42,164 km from the center of the Earth directly above the Earth's equator, the number of satellites in the GSO is limited. As an alternative to geosynchronous satellites, communication systems using constellations of satellites in non-geosynchronous orbits, such as low Earth orbit (LEO), have been designed to provide communication coverage for the entire Earth, or at least a large portion of the Earth.

Satellite communication systems typically experience significant propagation delays between satellites and ground stations (including user terminals (UTs) and gateways) due to the distance between the satellites and ground stations. Some satellite communication systems employ frequency division duplexing (FDD), which theoretically allows a ground station's transceivers to simultaneously receive and transmit on different radio frequencies if they are sufficiently spaced apart. However, in some FDD satellite communication systems, the frequency separation between the receive and transmit bands of a given ground station's FDD transceiver can be very small due to the premium placed on frequency bands. In some instances, the receive and transmit frequencies of a given ground station may be too close for a duplexer to handle simultaneous reception and transmission of wireless signals without interfering with each other.

In typical FDD communication systems where the receive and transmit frequency bands are close to each other, a half-duplex receive and transmit scheme is used, with a guard time between receive and transmit to avoid interference between the receive and transmit signals. At a given ground station, a half-duplex transceiver can be implemented to both receive and transmit wireless signals, but not at the same time. For example, a UT in a satellite communication network can receive a forward link (FL) signal from a satellite in a designated time slot or subframe of a given half-duplex (HD) frame and transmit a return link (RL) signal to the satellite, with a specified amount of guard time between the FL subframe and the RL subframe.

In traditional half-duplex systems, a substantial guard time is typically provided to ensure ample time between reception and transmission. Because no information-carrying signals are received or transmitted during this guard time, the large guard time in each HD frame results in wasted overhead and inefficiency. Therefore, it would be desirable to reduce this guard time overhead and improve efficiency in half-duplex communication systems.

Summary of the Invention

Aspects of the present disclosure are directed to apparatus and methods for efficient data transmission in a half-duplex communication system with large propagation delay.

In one aspect, a method for determining a time lag of a return link time reference relative to a forward link time reference in a satellite communication system is provided. The method comprises: determining a minimum round-trip propagation delay of a signal between a ground station and a satellite; determining a transition time for a half-duplex transceiver of the ground station to switch between a transmit mode and a receive mode; determining a system parameter based on the transition time for the half-duplex transceiver to switch between the transmit mode and the receive mode; and determining the time lag of the return link time reference relative to the forward link time reference based on the minimum round-trip propagation delay and the system parameter.

In another aspect, an apparatus is provided for determining a time lag of a return link time reference relative to a forward link time reference in a satellite communication system. The apparatus includes at least one processor; and at least one memory coupled to the at least one processor, the at least one processor and the at least one memory configured to: determine a minimum round-trip propagation delay of a signal between a ground station and a satellite; determine a transition time for a half-duplex transceiver of the ground station to switch between a transmit mode and a receive mode; determine a system parameter based on the transition time for the half-duplex transceiver to switch between the transmit mode and the receive mode; and determine the time lag of the return link time reference relative to the forward link time reference based on the minimum round-trip propagation delay and the system parameter.

In another aspect, an apparatus configured to determine a time lag of a return link time reference relative to a forward link time reference in a satellite communication system is provided. The apparatus includes: means for determining a minimum round-trip propagation delay of a signal between a ground station and a satellite; means for determining a transition time for a half-duplex transceiver of the ground station to switch between a transmit mode and a receive mode; means for determining a system parameter based on the transition time for the half-duplex transceiver to switch between the transmit mode and the receive mode; and means for determining the time lag of the return link time reference relative to the forward link time reference based on the minimum round-trip propagation delay and the system parameter.

In another aspect, a computer-readable medium is provided that includes at least one instruction for causing a computer or processor to perform a method for determining a time lag of a return link time reference relative to a forward link time reference in a satellite communication system. The at least one instruction includes instructions for: determining a minimum round-trip propagation delay of a signal between a ground station and a satellite; determining a transition time for a half-duplex transceiver of the ground station to switch between a transmit mode and a receive mode; determining a system parameter based on the transition time for the half-duplex transceiver to switch between the transmit mode and the receive mode; and determining the time lag of the return link time reference relative to the forward link time reference based on the minimum round-trip propagation delay and the system parameter.

In another aspect, a method for determining a guard time between transmission and reception of a half-duplex transceiver is provided. The method includes determining a maximum round-trip propagation delay of a signal between the half-duplex transceiver and a satellite; determining a minimum round-trip propagation delay of a signal between the half-duplex transceiver and the satellite; determining a maximum differential round-trip propagation delay based on the maximum round-trip propagation delay and the minimum round-trip propagation delay; determining a transition time for the half-duplex transceiver to switch between a transmit mode and a receive mode; and determining the guard time based on the maximum differential round-trip propagation delay and the transition time for the half-duplex transceiver to switch between the transmit mode and the receive mode.

In another aspect, an apparatus configured to determine a guard time between reception and transmission of a half-duplex transceiver is provided. The apparatus includes at least one processor; and at least one memory coupled to the at least one processor, the at least one processor and the at least one memory configured to: determine a maximum round-trip propagation delay of a signal between the half-duplex transceiver and a satellite; determine a minimum round-trip propagation delay of a signal between the half-duplex transceiver and the satellite; determine a maximum differential round-trip propagation delay based on the maximum round-trip propagation delay and the minimum round-trip propagation delay; determine a transition time for the half-duplex transceiver to switch between a transmit mode and a receive mode; and determine the guard time based on the maximum differential round-trip propagation delay and the transition time for the half-duplex transceiver to switch between the transmit mode and the receive mode.

In another aspect, an apparatus for determining a guard time between transmission and reception of a half-duplex transceiver is provided. The apparatus includes: means for determining a maximum round-trip propagation delay of a signal between the half-duplex transceiver and a satellite; means for determining a minimum round-trip propagation delay of a signal between the half-duplex transceiver and the satellite; means for determining a maximum differential round-trip propagation delay based on the maximum round-trip propagation delay and the minimum round-trip propagation delay; means for determining a transition time for the half-duplex transceiver to switch between a transmit mode and a receive mode; and means for determining the guard time based on the maximum differential round-trip propagation delay and the transition time for the half-duplex transceiver to switch between the transmit mode and the receive mode.

In another aspect, a computer-readable medium is provided that includes at least one instruction for causing a computer or processor to perform a method for determining a guard time between reception and transmission of a half-duplex transceiver. The at least one instruction includes instructions for: determining a maximum round-trip propagation delay of a signal between the half-duplex transceiver and a satellite; determining a minimum round-trip propagation delay of a signal between the half-duplex transceiver and the satellite; determining a maximum differential round-trip propagation delay based on the maximum round-trip propagation delay and the minimum round-trip propagation delay; determining a transition time for the half-duplex transceiver to switch between a transmit mode and a receive mode; and determining the guard time based on the maximum differential round-trip propagation delay and the transition time for the half-duplex transceiver to switch between the transmit mode and the receive mode.

In another aspect, a method for determining a forward link time duration and a guard time duration in a half-duplex frame in a satellite communication system is provided. The method includes allocating a forward link time segment in a special subframe of the half-duplex frame; allocating a guard time segment in the special subframe; determining the forward link time duration in the half-duplex frame based on the forward two-way segment in the special subframe; and determining the guard time duration in the half-duplex frame based on the guard time segment in the special subframe.

In another aspect, an apparatus configured to determine a forward link time duration and a guard time duration in a half-duplex frame in a satellite communication system is provided. The apparatus includes: at least one processor; and at least one memory coupled to the at least one processor, the at least one processor and the at least one memory configured to: allocate a forward link time segment in a special subframe of the half-duplex frame; allocate a guard time segment in the special subframe; determine the forward link time duration in the half-duplex frame based on the forward two-way segment in the special subframe; and determine the guard time duration in the half-duplex frame based on the guard time segment in the special subframe.

In another aspect, an apparatus for determining a forward link time duration and a guard time duration in a half-duplex frame in a satellite communication system is provided. The apparatus includes: means for allocating a forward link time segment in a special subframe of the half-duplex frame; means for allocating a guard time segment in the special subframe; means for determining the forward link time duration in the half-duplex frame based on the forward two-way segment in the special subframe; and means for determining the guard time duration in the half-duplex frame based on the guard time segment in the special subframe.

In another aspect, a computer-readable medium is provided that includes at least one instruction for causing a computer or processor to perform a method for determining a forward link time duration and a guard time duration in a half-duplex frame in a satellite communication system. The at least one instruction includes instructions for: allocating a forward link time segment in a special subframe of the half-duplex frame; allocating a guard time segment in the special subframe; determining the forward link time duration in the half-duplex frame based on the forward two-way segment in the special subframe; and determining the guard time duration in the half-duplex frame based on the guard time segment in the special subframe.

In another aspect, a method for scheduling time offsets for a plurality of user terminals within a beam coverage of a satellite in a satellite communication system is provided. The method comprises: determining a number of time offsets based on a number of active user terminals within the beam coverage; assigning equally spaced time offsets based on the number of time offsets; determining whether an aggregation pattern of the active user terminals within the beam coverage has random offsets; and distributing approximately equal traffic loads across time for the active user terminals.

In another aspect, an apparatus configured to schedule time offsets for a plurality of user terminals within a beam coverage of a satellite in a satellite communication system is provided. The apparatus includes: at least one processor; and at least one memory coupled to the at least one processor, the at least one processor and the at least one memory configured to: determine a number of time offsets based on a number of active user terminals within the beam coverage; assign equally spaced time offsets based on the number of time offsets; determine whether an aggregation pattern of the active user terminals within the beam coverage has random offsets; and distribute approximately equal traffic loads across time for the active user terminals.

In another aspect, an apparatus for scheduling time offsets for a plurality of user terminals within a beam coverage of a satellite in a satellite communication system is provided. The apparatus includes: means for determining a number of time offsets based on a number of active user terminals within the beam coverage; means for assigning equally spaced time offsets based on the number of time offsets; means for determining whether an aggregation pattern of the active user terminals within the beam coverage has random offsets; and means for distributing approximately equal traffic loads over time for the active user terminals.

In another aspect, a computer-readable medium is provided that includes at least one instruction for causing a computer or processor to perform a method for scheduling time offsets for a plurality of user terminals within a beam coverage of a satellite in a satellite communication system. The at least one instruction includes instructions for: determining a number of time offsets based on a number of active user terminals within the beam coverage; assigning equally spaced time offsets based on the number of time offsets; determining whether an aggregation pattern of the active user terminals within the beam coverage has random offsets; and distributing approximately equal traffic loads across time for the active user terminals.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are presented to aid in the description of aspects of the present disclosure and are presented solely for purposes of illustration of the various aspects and not limitation thereof.

FIG1 is a block diagram of an example of a communication system.

FIG. 2 is a block diagram of an example of the gateway of FIG. 1 .

FIG3 is a block diagram of an example of the satellite of FIG1.

FIG. 4 is a block diagram of an example of a user terminal of FIG. 1 .

FIG5 is a block diagram of an example of the user equipment of FIG1.

FIG6 is a diagram illustrating an example of a half-duplex (HD) frame.

FIG. 7 is a diagram illustrating an example of a special subframe (SSF) in the HD frame of FIG. 6 .

8 is a diagram illustrating an example of a hybrid automatic requery (HARQ) timeline with a feeder link delay of approximately 9.2 ms.

FIG9 is a diagram illustrating an example of a HARQ timeline having approximately 4 ms.

10 is a block diagram illustrating an example of modules for determining an amount of guard time in an HD frame.

11 is a block diagram illustrating an example of means for offsetting a time reference of a return link relative to a time reference of a forward link.

12 is a block diagram illustrating an example of modules for determining a half-duplex transmit/receive mode at a user terminal.

13 is a block diagram illustrating an example of a random offset scheduler.

14 is a block diagram illustrating an example of an adaptive SSF scheduler.

15 is a flow chart depicting a method for determining a time lag of a return link time reference relative to a forward link time reference in a satellite communication system.

16 is a flow chart depicting a method for determining a guard time between reception and transmission in a half-duplex transceiver.

17 is a flow chart depicting a method for determining a forward link time duration and a guard time duration in a half-duplex frame in a satellite communication system.

18 is a flow chart depicting time offsets for scheduling multiple user terminals within the beam coverage of a satellite in a satellite communication system.

DETAILED DESCRIPTION

Various aspects of the present disclosure relate to methods and apparatus for synchronizing the time or frequency of wireless signals transmitted by a user terminal (UT) communicating with a gateway via a satellite in a non-geostationary satellite communication system (e.g., a low earth orbit (LEO) satellite communication system used for data, voice, or video communications). In one aspect, the transmission time of wireless signals from the user terminal can be adjusted so that the signals arrive at the gateway at the same time or with a time difference of arrival within a specified tolerance. In another aspect, the carrier frequency of wireless signals transmitted from the user terminal can be adjusted so that frequency offset differences (including but not limited to Doppler shift differences) at the gateway are eliminated or at least reduced to an amount within a specified tolerance. In one aspect, open-loop pre-correction is provided to generate pre-correction values for the time or frequency, which can be applied to adjust the transmission time to compensate for propagation delay or adjust the carrier frequency to eliminate or reduce frequency offset differences. In another aspect, closed-loop pre-correction is provided in addition to the open-loop pre-correction to provide more accurate correction values for the time or frequency. In yet another aspect, a satellite communication system can have a large number of active user terminals present in the coverage of a beam. A random time offset may be applied by the scheduler in order to distribute approximately equal traffic load at the time offset.Various other aspects of the present disclosure will also be described in more detail below.

Aspects of the present disclosure are described below in the description and related drawings for specific examples. Alternative examples can be designed without departing from the scope of the present disclosure. In addition, well-known elements will not be described in detail or will be omitted to avoid blurring the relevant details of the present disclosure.

The word "exemplary" is used in this application to mean "serving as an example, instance, or illustration." Any aspect described in this application as "exemplary" is not necessarily to be construed as preferred or advantageous over other aspects. Likewise, the term "aspects" does not require that all aspects include the discussed feature, advantage, or mode of operation.

The terms used in this application are only for the purpose of describing specific aspects and are not intended to limit the aspects. As used in this application, unless the context clearly indicates otherwise, the singular forms "a", "an" and "the" are intended to also include the plural forms. It should also be understood that the terms "comprises", "comprising", "includes" or "including" when used in this application indicate the occurrence of a stated attribute, integer, step, operation, unit or component, but do not hinder the occurrence or addition of one or more other attributes, integers, steps, operations, units, components or their sets. In addition, it should be understood that the word "or" has the same meaning as the Boolean operator "OR", that is, unless explicitly stated, it includes the possibility of "any one" and "both" and is not limited to "exclusive or" ("XOR"). It should also be understood that unless explicitly stated, the symbol "/" between two adjacent words has the same meaning as "or". In addition, unless explicitly stated, phrases such as "connected to", "coupled to" or "communicating with..." are not limited to direct connections.

In addition, many aspects are described in the form of a sequence of actions to be performed by, for example, a unit of a computing device. It should be appreciated that the various actions described in this application can be performed by a dedicated circuit (e.g., a central processing unit (CPU), a graphics processing unit (GPU), a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field programmable gate array (FPGA), or various other types of general-purpose or dedicated processors or circuits), by program instructions executed by one or more processors, or by a combination of the two. In addition, these action sequences described in this application can be considered to be all implemented in any form of computer-readable storage medium having stored therein a corresponding set of computer instructions, which, when executed, cause the associated processor to perform the functions described in this application. Therefore, various aspects of the present disclosure can be implemented in a variety of different forms, all of which are expected to be within the scope of the claimed subject matter. In addition, for each aspect described in this application, the corresponding form of any of these aspects can be described in this application as, for example, "logic configured to..." that performs the described actions.

FIG1 illustrates an example of a satellite communication system 100, which includes a plurality of satellites in non-geosynchronous orbits (e.g., low Earth orbit (LEO)) (although only one satellite 300 is shown for clarity of illustration), a gateway 200 in communication with satellite 300, a plurality of user terminals (UTs) 400 and 401 in communication with satellite 300, and a plurality of user equipment (UEs) 500 and 501 in communication with UTs 400 and 401, respectively. In one aspect, gateway 200 includes a scheduler 202, which may be, for example, an adaptive special subframe (SSF) scheduler and/or a random offset scheduler. Details regarding scheduler 202 and related functionality are provided in subsequent sections and figures. In the example shown in FIG1 , UT 400 and UE 500 communicate with each other via a bidirectional access link (having a forward access link and a return access link), and similarly, UT 401 and 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 the UT using only a forward access link. In another implementation, one or more additional UEs (not shown) may also communicate with UT 400 or UT 401. Alternatively, the UT and the corresponding UE may be part of a single physical device (such as a mobile phone with an internal satellite transceiver and an antenna for communicating directly with a satellite). Each UE 500 or 501 may be a user device such as a mobile device, phone, smartphone, tablet, laptop, computer, wearable device, smartwatch, audio-visual device, or any device that includes the ability to communicate with a UT. Additionally, UE 500 and/or UE 501 may be a device (e.g., an access point, a small cell, etc.) for communicating to one or more end-user devices.

The gateway 200 can access the Internet 108 or one or more other types of public, semi-private or private networks. In the example shown in Figure 1, the gateway 200 communicates with the infrastructure 106, which can access the Internet 108 or one or more other types of public, semi-private or private networks. The gateway 200 can also be coupled to various types of communication backhauls, including landline networks such as fiber optic networks or public switched telephone networks (PSTN) 110. In addition, in other implementations, the gateway 200 can be interfaced to the Internet 108, PSTN 110 or one or more other types of public, semi-private or private networks without using the infrastructure 106. Further, the gateway 200 can communicate with other gateways (such as gateway 201) through the infrastructure 106, or can be configured to communicate with the gateway 201 without using the infrastructure 106. The infrastructure 106 can include, in whole or in 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 for assisting the operation of the satellite communication system 100 and/or communicating therewith.

The communication between satellite 300 and gateway 200 in both directions is called a feeder link, while the communication between the satellite and one of UTs 400 and 410 in both directions can be called a service link. The signal path from satellite 300 to a ground station (which can be gateway 200 or one of UTs 400 and 401) can generally be called a downlink. The signal path from a ground station to satellite 300 can generally be called an uplink. In addition, as shown in the figure, the signal can have general directionality, such as a forward link and a return link or reverse link. Therefore, the communication link in the direction of terminating at UT 400 by satellite 300 initiated from gateway 200 is called a forward link, while the communication link in the direction of terminating at gateway 200 by satellite 300 initiated from UT 400 is called a return link or reverse link. Similarly, in Figure 1, the signal path from gateway 200 to satellite 300 is labeled "forward link (FL)", and the signal path from satellite 300 to gateway 200 is labeled "return link (RL)". In a similar manner, the signal path from each UT 400 or 401 to the satellite 300 is labeled "Return Link (RL)" in FIG. 1, while the signal path from the satellite 300 to each UT 400 or 401 is labeled "Forward Link (FL)."

FIG2 is an example block diagram of a gateway 200, which may also be applied to gateway 201 in FIG1 . Gateway 200 is shown to include several antennas 205, an RF subsystem 210, a digital subsystem 220, a public switched telephone network (PSTN) interface 230, a local area network (LAN) interface 240, a gateway interface 245, and a gateway controller 250. RF subsystem 210 is coupled to antenna 205 and digital subsystem 220. Digital subsystem 220 is coupled to PSTN interface 230, LAN interface 240, and gateway interface 245. Gateway controller 250 is coupled to RF subsystem 210, digital subsystem 220, PSTN interface 230, LAN interface 240, and gateway interface 245.

The RF subsystem 210, which may include several RF transceivers 212, an RF controller 214, and an antenna controller 216, can transmit communication signals to the satellite 300 via a forward link (FL) 301F and receive communication signals from the satellite 300 via a return link (RL) 301R. Although not shown for simplicity, each RF transceiver 212 may include a transmit chain and a receive chain. Each receive chain may include a low-noise amplifier (LNA) and a downconverter (e.g., a mixer) for amplifying and downconverting received communication signals, respectively, in a known manner. Furthermore, each receive chain may include an analog-to-digital converter (ADC) for converting received communication signals from analog to digital (e.g., for processing by the digital subsystem 220). Each transmit chain may include an upconverter (e.g., a mixer) and a power amplifier (PA) for upconverting and amplifying communication signals, respectively, for transmission to the satellite 300, in a known manner. Furthermore, each transmit chain may include a digital-to-analog converter (DAC) for converting digital signals received from the digital subsystem 220 into analog signals for transmission to the satellite 300.

The RF controller 214 may be used to control various aspects of the RF transceiver 212 (e.g., carrier frequency selection, frequency and phase calibration, gain settings, etc.). The antenna controller 216 may control various aspects of the antenna 205 (e.g., beamforming, beam steering, gain settings, frequency tuning, etc.).

The digital subsystem 220 may include a number of digital receiver modules 222, a number of digital transmitter modules 224, a baseband (BB) processor 226, and a control (CTRL) processor 228. The digital subsystem 220 may process communication signals received from the RF subsystem 210 and forward the processed communication signals to the PSTN interface 230 and/or the LAN interface 240, and may also process communication signals received from the PSTN interface 230 and/or the LAN interface 240 and forward the processed communication signals to the RF subsystem 210.

Each digital receiver module 222 may correspond to a signal processing element for managing communications between the gateway 200 and the UT 400. One of the receive chains of the RF transceiver 212 may provide input signals to multiple digital receiver modules 222. Several digital receiver modules 222 may be used to accommodate all satellite beams and possible diversity mode signals being processed at any given time. Although not shown for simplicity, each digital receiver module 222 may include one or more digital data receivers, a search receiver, and a diversity combiner and decoder module. The search receiver may be used to search for an appropriate diversity pattern of a carrier signal and may be used to search for a pilot signal (or other relatively fixed pattern strong signal).

The digital transmitter modules 224 may process signals to be transmitted to the UT 400 via the satellite 300. Although not shown for simplicity, each digital transmitter module 224 may include a transmit modulator that modulates data for transmission. The transmit power of each transmit modulator may be controlled by a corresponding digital transmit power controller (not shown for simplicity), which may (1) apply a minimum power level for interference reduction and resource allocation purposes, and (2) apply an appropriate level of power as needed to compensate for attenuation and other path transfer characteristics in the transmission path and other paths.

A control (CTRL) processor 228, coupled to the digital receiver module 222, the digital transmitter module 224, and the BB 226, may provide command and control signals for enabling functions such as, but not limited to, signal processing, timing signal generation, power control, switching control, diversity combining, and system connectivity.

The CTRL processor 228 can also control the generation and power of pilot, synchronization, and paging channel signals, as well as their coupling to a transmit power controller (not shown for simplicity). The pilot channel is a signal that is not modulated with data and can use a repeating, unchanging pattern or a constant frame structure type (pattern) or frequency modulation type input. For example, the orthogonal function used to form the channel of the pilot signal generally has a constant value, such as all 1s or 0s, or a well-known repeating pattern, such as a structured pattern of interleaved 1s and 0s.

The baseband (BB) processor 226 is well known in the art and is therefore not described in detail in this application. For example, the BB 226 may include various known elements such as (but not limited to) encoders, data modems, and digital data switching and storage components.

The PSTN interface 230 can provide and receive communication signals to and from the external PSTN, either directly or through additional infrastructure 106, as shown in FIG1 . The PSTN interface 230 is well known in the art and is therefore not described in detail herein. For other implementations, the PSTN interface 230 can be omitted or replaced with any other suitable interface that connects the system 200 to a terrestrial network (e.g., the Internet 108).

The LAN interface 240 can provide communication signals to or receive communication signals from an external LAN. For example, the LAN interface 240 can be coupled to the Internet 108 directly or through additional infrastructure 106 as shown in FIG1 . The LAN interface 240 is well known in the art and is therefore not described in detail in this application.

The gateway interface 245 can provide communication signals to and receive communication signals from one or more other gateways associated with the satellite communication system 100 of FIG. 1 (and/or to/from gateways associated with other satellite communication systems, not shown for simplicity). For some implementations, the gateway interface 245 can communicate with the other gateways via one or more dedicated communication lines or channels (not shown for simplicity). For other implementations, the gateway interface 245 can communicate with the other gateways using the PSTN 110 and/or other networks, such as the Internet 108 (see also FIG. 1 ). For at least one implementation, the gateway interface 245 can communicate with the other gateways via the infrastructure 106.

Overall gateway control may be provided by a gateway controller 250. The gateway controller 250 may plan and control the use of satellite 300 resources by the gateway 200. For example, the gateway controller 250 may analyze trends, generate service plans, allocate satellite resources, monitor (or track) satellite positioning, and monitor the performance of the gateway 200 and/or satellite 300. The gateway controller 250 may also be coupled to a ground-based satellite controller (not shown for simplicity) that maintains and monitors the orbits of the satellites 300, relays satellite usage messages to the gateway 200, tracks the positioning of the satellites 300, and/or adjusts various channel settings of the satellites 300.

In the example implementation shown in FIG2 , the gateway controller 250 includes a scheduler 202, which can be an adaptive special subframe (SSF) scheduler and/or a random offset scheduler. Details about the scheduler and related functions are provided in subsequent paragraphs and figures (e.g., see FIG13 and 14 ). The scheduler 202 can provide information to the RF subsystem 210, the digital subsystem 220, and/or the interfaces 230, 240, and 245. In one aspect, this information can be used in a satellite communication system with a large number of active user terminals in a beam coverage. The random time offset is applied to distribute approximately equal traffic load on the time offset to assist, for example, communication between the gateway 200 and UTs 400 and 401.

2 , the gateway controller 250 may optionally include a local time, frequency, and positioning reference 251 that can provide local time and frequency information to the RF subsystem 210, the digital subsystem 220, and/or the interfaces 230, 240, and 245. This time and frequency information can be used to synchronize the various components of the gateway 200 with each other and/or with the satellite 300. The local time, frequency, and positioning reference 251 can also provide positioning information (e.g., satellite orbit data) of the satellite 300 to the various components of the gateway 200. Furthermore, while depicted in FIG2 as being included in the gateway controller 250, for other implementations, the local time, frequency, and positioning reference 251 can be a separate subsystem coupled to the gateway controller 250 (and/or one or more of the digital subsystem 220 and the RF subsystem 210).

2 for simplicity, the gateway controller 250 may also be coupled to a network control center (NCC) and/or a satellite control center (SCC). For example, the gateway controller 250 may allow the SCC to communicate directly with the satellite 300, for example, to retrieve satellite orbit data from the satellite 300. The gateway controller 250 may also receive processed information (e.g., from the SCC and/or the NCC) that allows the gateway controller 250 to properly aim its antenna 205 (e.g., toward the satellite 300), schedule beam transmissions, coordinate handoffs, and perform various other well-known functions.

3 is an example block diagram of a satellite 300 for illustration purposes only. It should be understood that the specific satellite configuration may vary significantly and may or may not include onboard processing. In addition, although shown as a single satellite, two or more satellites using inter-satellite communications may provide a functional connection between the gateway 200 and the UT 400. It should be understood that the present disclosure is not limited to any particular satellite configuration, but rather any satellite or combination of satellites capable of providing a functional connection between the gateway 200 and the UT 400 may be considered within the scope of the present disclosure. In one example, the satellite 300 is shown as including a forward repeater 310, a return repeater 320, an oscillator 330, a controller 340, forward link antennas 352(1)-352(N), and return link antennas 361(1)-361(N). The forward repeater 310 can process communication signals in a corresponding channel or frequency band and can include a corresponding one of first bandpass filters 311(1)-311(N), a corresponding one of first LNAs 312(1)-312(N), a corresponding one of frequency converters 313(1)-313(N), a corresponding one of second LNAs 314(1)-314(N), a corresponding one of second bandpass filters 315(1)-315(N), and a corresponding one of PAs 316(1)-316(N). Each of the PAs 316(1)-316(N) is coupled to a corresponding one of the antennas 352(1)-352(N).

In each of the corresponding forward paths FP(1)-FP(N), a first bandpass filter 311(1) passes signal components having frequencies within the channel or frequency band of the corresponding forward path FP(1)-FP(N) and filters signal components having frequencies outside the channel or frequency band of the corresponding forward path FP(1)-FP(N). Thus, the passband of the first bandpass filter 311(1) corresponds to the width of the channel associated with the corresponding forward path FP(1)-FP(N). A first LNA 312(1) amplifies the received communication signal to a level suitable for processing by a frequency converter 313(1). The frequency converter 313(1) converts the frequency of the communication signal in the corresponding forward path FP(1)-FP(N) (e.g., to a frequency suitable for transmission from the satellite 300 to the UT 400). A second LNA 314(1) amplifies the frequency-converted communication signal, and a second bandpass filter 315(1) filters signal components having frequencies outside the width of the associated channel. PA 316(1) amplifies the filtered signal to a power level suitable for transmission via corresponding antennas 352(1)-352(N) to UT 400. Return repeater 320, including a number N of return paths RP(1)-RP(N), receives communication signals from UT 400 along return link (RL) 301R via antennas 361(1)-361(N) and transmits communication signals along RL 301R to gateway 200 via one or more antennas 362. Each of the return paths RP(1)-RP(N) may process communication signals within a corresponding channel or frequency band, may be coupled to a corresponding one of the antennas 361(1)-361(N), and may include a corresponding one of the first bandpass filters 321(1)-321(N), a corresponding one of the first LNAs 322(1)-322(N), a corresponding one of the frequency converters 323(1)-323(N), a corresponding one of the second LNAs 324(1)-324(N), and a corresponding one of the second bandpass filters 325(1)-325(N).

In each of the corresponding return paths RP(1)-RP(N), a first bandpass filter 321(1) passes signal components having frequencies within the channel or frequency band of the corresponding return path RP(1)-RP(N) and filters signal components having frequencies outside the channel or frequency band of the corresponding return path RP(1)-RP(N). Thus, the passband of the first bandpass filter 321(1) may correspond to the width of the channel associated with the corresponding return path RP(1)-RP(N) for some implementations. The first LNA 322(1) amplifies all received communication signals to a level suitable for processing by the frequency converter 323(1). The frequency converter 323(1) converts the frequency of the communication signals in the corresponding return path RP(1)-RP(N) (e.g., to a frequency suitable for transmission from the satellite 300 to the gateway 200). The second LNA 324(1) amplifies the frequency-converted communication signals, and the second bandpass filter 325(1) filters signal components having frequencies outside the associated channel width. The signals from the return paths RP(1)-RP(N) are combined and provided to one or more antennas 362 via the PA 326. The PA 326 amplifies the combined signal for transmission to the gateway 200.

Oscillator 330 may be any suitable circuit or device that generates an oscillating signal to provide a forward local oscillator signal LO(F) to frequency converters 313(1)-313(N) of forward transponder 310 and a return local oscillator signal LO(R) to frequency converters 323(1)-323(N) of return transponder 320. For example, the LO(F) signal may be used by frequency converters 313(1)-313(N) to convert communication signals from a frequency band associated with signal transmission from gateway 200 to satellite 300 to a frequency band associated with signal transmission from satellite 300 to UT 400. The LO(R) signal may be used by frequency converters 323(1)-323(N) to convert communication signals from a frequency band associated with signal transmission from UT 400 to satellite 300 to a frequency band associated with signal transmission from satellite 300 to gateway 200.

Controller 340, coupled to forward transponder 310, return transponder 320, and oscillator 330, can control various operations of satellite 300, including, but not limited to, channel allocation. In one aspect, controller 340 can include a memory coupled to a processor (not shown for simplicity). The memory can include a non-volatile computer-readable medium (e.g., one or more non-volatile memory elements such as EPROM, EEPROM, flash memory, hard drive, etc.) that stores instructions that, when executed by the processor, cause satellite 300 to perform operations including, but not limited to, those described herein.

An example of a transceiver for use in UT 400 or 401 is shown in FIG4 . In FIG4 , at least one antenna 410 is provided for receiving forward two-way communication signals (e.g., from satellite 300), which can be transferred to an analog receiver 414 where they are down-converted, amplified, and digitized. A duplexer element 412 is typically used to allow the same antenna 410 to provide both transmit and receive functions. Alternatively, the transceiver of UT 400 or 401 can employ separate antennas 410 operating at different transmit and receive frequencies.

The digital communication signals output by analog receiver 414 are transferred to at least one digital data receiver 416A-416N and at least one searcher receiver 418. Digital data receivers 416A-416N may be used to achieve a desired level of signal diversity depending on an acceptable level of transceiver complexity, as will be apparent to those skilled in the relevant art.

At least one user terminal control processor 420 is coupled to the digital data receivers 416A-416N and the searcher receiver 418. The control processor 420 provides, among other functions, basic signal processing, timing, power, and handoff control or coordination, as well as selection of frequencies for signal carriers. Another basic control function that can be performed by the control processor 420 is the selection or operation of functions to be used to process various signal waveforms. The signal processing performed by the control processor 420 can include the determination of relative signal strength and the calculation of various relevant signal parameters. These calculations of signal parameters (such as timing and frequency) can include the use of additional or separate dedicated circuitry to provide increased efficiency or speed in the measurement or improved allocation of control processing resources.

The outputs of digital data receivers 416A-416N are coupled to digital baseband circuitry 422 within UT 400. The digital baseband circuitry 422 includes processing and presentation components for transferring information to and from UE 500, such as shown in FIG1 . Referring to FIG4 , if diversity signal processing is employed, the digital baseband circuitry 422 may include a diversity combiner and decoder. Some of these components may also operate under the control of, or in communication with, the control processor 420.

When voice or other data is prepared as an outgoing message or communication signal originating from the UT 400, the digital baseband circuitry 422 is used to receive, store, process, or otherwise prepare the required data for transmission. The digital baseband circuitry 422 provides this data to a transmit modulator 426 operating under the control of the control processor 420. The output of the transmit modulator 426 is transferred to a digital transmit power controller 428, which provides output power control to an analog transmit power amplifier 430 for eventual transmission of the outgoing signal from the antenna 410 to a satellite (e.g., satellite 300).

4 , the UT transceiver also includes a memory 432 associated with the control processor 420. The memory 432 may include instructions for execution by the control processor 420 and data processed by the control processor 420. In the example depicted in FIG4 , the memory 432 may include instructions for performing time or frequency adjustments to be applied to RF signals to be transmitted by the UT 400 to the satellite 300 via the RL 301R.

In the example shown in FIG. 4 , the UT 400 also includes an optional local time, frequency, and/or positioning reference 434 (e.g., a GPS receiver) that can provide local time, frequency, and/or positioning information to the control processor 420 for various applications, including, for example, time or frequency synchronization of the UT 400.

Digital data receivers 416A-416N and searcher receiver 418 are equipped with signal correlation elements for demodulating and tracking specific signals. Searcher receiver 418 is used to search for a pilot signal, or other relatively fixed-pattern strong signal, while digital data receivers 416A-416N are used to demodulate other signals associated with the detected pilot signal. However, digital data receivers 416A-416N can be assigned to track the pilot signal after acquisition to accurately determine the signal chip energy to noise ratio and to express the pilot signal strength in a formula. Therefore, the outputs of these digital data receivers 416A-416N can be monitored to determine the energy in the pilot signal or other signals or their frequency. These digital data receivers 416A-416N also employ frequency tracking elements that can be monitored to provide the control processor 420 with current frequency and timing information for signal demodulation.

The control processor 420 can use this information to determine how much the received signal has deviated from the oscillator frequency and when to scale it to the same frequency band. This information and other information related to frequency error and frequency shift can be stored in the memory or storage 432 as needed.

The control processor 420 may also be coupled to a UE interface circuit 450 to enable communication between the UT 400 and one or more other UEs (not shown). The UE interface circuit 450 may be configured as needed to communicate with various UE configurations and, accordingly, may include various transceivers and related components based on the various communication technologies employed to communicate with the various supported UEs. For example, the UE interface circuit 450 may include one or more antennas, a wide area network (WAN) transceiver, a wireless local area network (WLAN) transceiver, a local area network (LAN) interface, a public switched telephone network (PSTN) interface (not shown), and/or other well-known communication technologies configured to communicate with one or more UEs (communicating with the UT 400).

FIG5 is a block diagram illustrating an example of a UE 500 that can also be applied to the UE 501 of FIG1 . The UE 500 as shown in FIG5 can be, for example, a mobile device, a handheld computer, a tablet computer, a wearable device, a smart watch or any type of device that can interact with a user. In addition, the UE 500 can be a network-side device that provides connections to various end-user devices and/or to various public or private networks. In the example shown in FIG5 , the UE 500 can include a LAN interface 502, one or more antennas 504, a wide area network (WAN) transceiver 506, a wireless local area network (WLAN) transceiver 508 and a satellite positioning system (SPS) receiver 510. The SPS receiver 510 can be compatible with a global positioning system (GPS), a global navigation satellite system (GLONASS) and/or any other global or regional satellite-based positioning system. In other aspects, the UE 500 may include a WLAN transceiver 508 (e.g., a Wi-Fi transceiver), with or without, for example, the LAN interface 502, the WAN transceiver 506, and/or the SPS receiver 510. Furthermore, the UE 500 may include additional transceivers (e.g., Bluetooth, ZigBee, and other well-known technologies), with or without, for example, the LAN interface 502, the WAN transceiver 506, and/or the SPS receiver 510. Therefore, the elements illustrated with respect to the UE 500 are provided merely as an example configuration and are not intended to limit the configuration of the UE according to the various aspects disclosed herein.

5 , processor 512 is connected to LAN interface 502, WAN transceiver 506, WLAN transceiver 508, and SPS receiver 510. Optionally, motion sensor 514 and other sensors may be coupled to processor 512.

Memory 516 is connected to processor 512. In one aspect, as shown in FIG1 , memory 516 may include data 519 that may be sent to and/or received from UT 400. Referring to FIG5 , memory 516 may also include, for example, stored instructions 520 to be executed by processor 512 for performing processing steps for communicating with UT 400. UE 500 may also include a user interface 522, which may include hardware and software for interacting with the input or output of processor 512 via, for example, light, sound, or tactile input or output. In the example shown in FIG5 , UE 500 includes a microphone/speaker 524, a keyboard 526, and a display 528 connected to user interface 522. Alternatively, the user's tactile input or output may be integrated with display 528 using, for example, a touchscreen display. Again, the elements shown in FIG5 are not intended to limit the configuration of the UE disclosed herein, and it should be understood that the elements included in UE 500 will vary based on the design choices of the device's end user and system engineers.

In addition, UE 500 may be, for example, a mobile device or an external network-side device that communicates with but is independent of UT 400 shown in Figure 1. In addition, UE 500 and UT 400 may be components of a single physical device.

In the example shown in FIG1 , two UTs 400 and 401 can communicate bidirectionally with satellite 300 via the RL and FL within a beam coverage. Satellite 300 can communicate with more than two UTs 400 and 401 within the beam coverage. The RL from UTs 400 and 401 to satellite 300 is therefore a many-to-one channel. Significant time delay and frequency offset differences can exist between different UTs within a beam coverage. Frequency offset differences can be due to, for example, differences in the Doppler frequency shift experienced by the UTs 400 and 401 within a beam coverage due to the relative motion of satellite 300 and UTs 400 and 401. For example, some UTs 400 and 401 may be mobile, while others may be stationary. Frequency offset differences between different UTs 400 and 401 may also be caused by other factors, such as frequency shifts caused by radio frequency (RF) components in the transmitter chains of some of the UTs 400 and 401 within the beam coverage.

In the satellite communication system 100 shown in FIG1 , multiple UTs 400 and 401 within a beam coverage can be time division multiplexed (TDM), frequency division multiplexed (FDM), or multiplexed in some other manner. Regardless of whether the multiplexing of the different UTs 400 and 401 within the beam coverage is achieved via TDM, FDM, or some other type of multiplexing, due to the distance between the satellite and the UTs, the amount of one-way propagation delay, that is, the amount of time it takes for a wireless signal to travel one way between the UT and the satellite, can be in the range of approximately 4 ms to approximately 5.2665 ms.

In this example, the round trip delay of signal propagation in the satellite communication system 100 can be almost 10.533 ms. If the guard time between receive and transmit cycles for a given UT is equal to the maximum round trip delay, then the receive and transmit cycles need to be much longer to reduce the guard time overhead.

In one aspect, methods and apparatus are provided for offsetting a time reference to reduce the guard time required for receive and transmit operations of a half-duplex transceiver of a separate UT. In one aspect, if the RL time reference is offset (i.e., time-lagged) by a minimum round-trip delay (RTD) of 8 ms relative to the FL time reference, the guard time required for the half-duplex transceiver is the maximum differential RTD of 2.533 ms, plus the time required for the half-duplex transceiver to switch from receive mode to transmit mode and vice versa. In contrast to other efficient half-duplex FDD operation schemes, the methods and apparatus according to various aspects of this disclosure do not require discarding any portion of a symbol, such as the cyclic prefix of an orthogonal frequency division multiplexing (OFDM) symbol.

FIG6 is a diagram illustrating an example of a receive/transmit mode of a half-duplex (HD) frame of the half-duplex UT transceiver. In this example, the HD frame has a duration of 10 ms and includes four segments or subframes, including an "F" for "FL," followed by an "S" for a special subframe (SSF), followed by a "G" for a guard time, followed by an "R" for a RL.

In one aspect, a HD frame format, such as one comprising F, S, G, and R subframes, allows for a one-to-one association between FL and RL subframes due to constraints on FL and RL hybrid automatic requery (HARQ) requests and RL scheduling grants. In this example, when HD has a duration of 10 ms, the time allocations for subframes F, S, G, and R are 3 ms, 1 ms, 2 ms, and 4 ms, respectively.

FIG7 is a diagram illustrating an example of a special subframe (SSF), that is, a subframe S in the HD frame of FIG6 . In one aspect, the SSF includes a first portion, a FL component F _SSF immediately following the RF subframe F shown in FIG6 , and a second portion, a guard time component G _SSF immediately preceding the guard subframe G shown in FIG6 . In the example SSF shown in FIG7 , the FL component F _SSF is a time segment designated for the FL, and the guard time component G _SSF is a time segment designated for the guard time.

For example, if the duration of an HD frame is 10 ms, the SSF can have a duration of approximately 1 ms, including an F _SSF having a duration of approximately 0.2 ms for the FL and a G _SSF having a duration greater than 0.8 ms for the guard time. In this example, the total guard time, which is the sum of the guard time component G _SSF in the SSF as shown in FIG. 7 and the guard time in subframe G as shown in FIG. 6 , is approximately 2.8 ms. Similarly, the total duration for the FL is the sum of the FL component F _SSF in the SSF and the duration of subframe F, which is approximately 3.2 ms in this example. In one aspect, the ratio of the FL component F _SSF relative to the guard time component G _SSF in the SSF can be dynamically adjusted as described in further detail below.

As is apparent from Figure 6, the subframe G used for guard time needs to be significantly shorter in duration than the HD frame. In one aspect, the minimum guard time required in the HD frame for the half-duplex transceiver can be the maximum differential round-trip propagation delay, which is the maximum round-trip propagation delay minus the minimum round-trip propagation delay, without accounting for delays caused by the half-duplex transceiver switching from receive mode to transmit mode and vice versa. In the example described above, the maximum round-trip propagation delay is approximately 10.533 ms and the minimum round-trip propagation delay is approximately 8 ms. Therefore, the maximum differential round-trip propagation delay would be 10.533 ms - 8 ms = 2.533 ms. In one aspect, the delay caused by the half-duplex transceiver switching from receive mode to transmit mode and vice versa is added to the maximum differential round-trip propagation delay to derive the guard time required to separate the transmission of the return link signal from the reception of the forward link signal.

In a typical half-duplex transceiver, circuit components such as a phase-locked loop (PLL) and a power amplifier (PA) have a finite amount of time to settle when the transceiver switches from transmit mode to receive mode, or vice versa. In one aspect, additional time margin can be provided in this guard time to accommodate the time required to switch from transmit mode to receive mode, and vice versa. For example, a typical half-duplex transceiver may require approximately 100 μs of transition time from transmit mode to receive mode for the PLL and PA to settle. In this typical half-duplex transceiver, the transition time from receive mode to transmit mode scheduled for the PLL and PA is also approximately 100 μs.

In one aspect, the guard time required for the half-duplex transceiver at the UT is equal to the maximum differential round-trip propagation delay, plus the transition time from receive mode to transmit mode, plus the transition time from the transmit mode to receive mode. In the example described above, the maximum differential round-trip propagation delay is approximately 2.533 ms and the transition time for each half-duplex transition between transmit mode and receive mode in either direction is approximately 100 μs. The guard time of the half-duplex transceiver at the UT should be at least 2.533 ms + 0.1 ms + 0.1 ms = 2.733 ms, which can be rounded up to 2.8 ms.

In one aspect, the time reference of the RL can be offset (i.e., time-lagged) relative to the time reference of the FL by a set amount in order to reduce the time length required for the subframe G in each HD frame. In one aspect, the time reference of the RL can be offset or time-lagged relative to the time reference of the FL by an amount approximately equal to the minimum round-trip propagation delay, i.e., two times the minimum propagation delay for one-way signal motion between the UT and the satellite, less a small adjustment based on the transmission time required for the half-duplex transceiver to switch between transmit and receive modes, as described in more detail below.

In one aspect, the RL's time reference can be offset or time-lag relative to the FL's time reference by slightly less than the minimum round-trip propagation delay. For example, if the minimum one-way propagation delay is approximately 4 ms, the RL's time reference can be offset by approximately 8 ms relative to the FL's time reference, minus a small adjustment based on system parameters for the transition time of the half-duplex transceiver switching between transmit and receive modes.

The amount by which the RL's time reference is delayed or offset relative to the FL's time reference can be set equal to the minimum round-trip propagation delay minus _TR2F , which is a system parameter based on the transition time of the half-duplex transceiver between transmit and receive modes. For example, if the transition time scheduled for transceiver components such as the PLL and PA when the half-duplex transceiver switches from transmit mode to receive mode or vice versa is approximately 100 μs, the system parameter _TR2F can be slightly larger than _TR2F to accommodate the margin for the transition time.

In the example described above regarding an HD frame having a length of 10 ms and including F, S, G, and R subframes, subframe S is a special subframe (SSF) including a FL time component, F _SSF , and a guard time component, G _SSF . As shown in Figures 6 and 7 , the lengths of the F, S, G, and R subframes are 3 ms, 1 ms, 2 ms, and 4 ms, respectively. If the FL time component, F _SSF , has a length of 0.2 ms and the guard time component, G _SSF , has a length of 0.8 ms, the total duration allocated to the FL in the HD frame can be 3 ms + 0.2 ms = 3.2 ms, the total duration allocated to the guard time is 2.8 ms, and the total duration allocated to the RL remains at 4 ms, which is the length of the R subframe. In this example, the UT can achieve a 32% FL beam occupancy and a 40% RL beam occupancy.

In one aspect, multiple random offsets can be used for half-duplex mode HD frames for multiple UTs within a beam coverage. In the example described above, ten HD frames with a length of 10 ms and a 1 ms interval between each pair of adjacent offsets (e.g., 0 ms, 2 ms, ..., 9 ms) can be provided for half-duplex mode. In one aspect, a UT's half-duplex transceiver can listen to the FL when no traffic is present. Upon arrival of FL and/or RL traffic for the UT, the UT's half-duplex mode begins at a random offset, which can be any offset from 0 ms to 9 ms. At the end of the traffic burst, the UT enters a state for FL listening. The next time FL and/or RL traffic arrives for the UT, the UT's half-duplex mode begins at another random offset, which can be different from the previous offset. For any UT within a beam coverage, the HD frame offset varies over time in a random pattern that follows the random arrival times of FL and/or RL traffic.

In a satellite communication network where a satellite beam covers a large number of UTs, at any instant in time, each active UT has a half-duplex mode with a random offset that is independent of other active UTs in the beam coverage. With a large number of UTs in the beam coverage, a set of half-duplex modes can be created with random offsets. With a large number of active UTs randomly located in the beam coverage, it can be expected that there will be approximately equal numbers of UTs per offset and that traffic will be approximately evenly distributed in time.

In the example described above, ten offsets from 0 ms to 9 ms are provided. Assuming an HD frame length of 10 ms, each offset (0 ms, 1 ms, 2 ms, ... 9 ms) can contain approximately equal numbers of UTs. If the number of active UEs in a beam coverage is relatively small, for example, less than 10 UTs in a beam coverage, several equally spaced offsets less than 10 offsets can be provided, for example, a total of five offsets with a 2 ms interval between each pair of adjacent offsets, namely, 0 ms, 2 ms, 4 ms, 6 ms, and 8 ms. Furthermore, it can be expected that approximately equal numbers of UTs will be found in each time offset.

In one aspect, a system time reference and HARQ timeline for a communication system with half-duplex transceivers are established such that these time references and HARQ timelines can be implemented by a scheduler (e.g., scheduler 202), which can be located in either a gateway or infrastructure for UTs operating with a full-duplex physical layer. In one aspect, forward link HARQ and return link HARQ acknowledgment rules can be determined in the satellite time reference for half-duplex operation. In one aspect, these forward link and return link HARQ timing rules are constraints that the half-duplex scheduler needs to adhere to.

In one aspect, satellite 300 acts as a repeater between gateway 200 and UTs 400 and 401 in one beam coverage of satellite 300 in the example shown in FIG 1. In one aspect, the time reference of the satellite RL receiver is offset or time delayed relative to the time reference of the satellite FL transmitter by an amount equal to the minimum round-trip propagation delay minus _TR2F , _which is the time of scheduled transitions of transceiver circuit components, such as PLLs and PAs, during transitions from transmit mode to receive mode or vice versa as described above.

Figures 8 and 9 are diagrams illustrating examples of HARQ timelines with feeder link delays of approximately 9.2 ms and approximately 4 ms, respectively. The propagation delay of the forward and return link signals between the satellite 300 and the gateway 200 is determined by the distance between the satellite 300 and the gateway 200. In the example shown in Figure 8 , the feeder link delay between the leading edge of subframe F of frame k of the gateway transmitter (GW TX) and the leading edge of subframe F of frame k+1 of the satellite FL transmitter (Sat FSL TX) is approximately 9.2 ms.

8 , assuming that the one-way propagation delay between the satellite 300 and the UT 400 and/or 401 at or near the center of a beam coverage is approximately 4 ms, the leading edge of subframe F of frame k at the receiver of the UT 400 and/or 401 at or near the center of the beam coverage (UT RX@center) is offset by approximately 4 ms from the leading edge of subframe F of frame k at Sat FSL TX. In contrast, the one-way propagation delay between the satellite 300 and the UT 400 and/or 401 at or near the edge of the beam coverage of the satellite 300 is approximately 5.2 ms.

8 , a two-way communication timeline is depicted between the gateway 200 and UTs 400 and/or 401 at or near the center of one beam coverage of the satellite 300 (acting as a repeater). The timeline from the leading edge of subframe F of frame k at GW TX to the leading edge of subframe F of frame k+1 at Sat FSL TX is depicted by the dashed line (F: 1 ^st TX), with a propagation time of approximately 9.2 ms, while the timeline from the leading edge of subframe F of frame k+1 at Sat FSL TX to the leading edge of subframe F of frame k+1 at UT RX@center is depicted by the dashed line ((F: 1 ^st TX)), with a propagation time of approximately 4 ms.

At UT 400 and/or 401, processing and waiting time is provided, depicted by the dashed line (F: proc&wait). In frame k+1 at UT 400 and/or 401, a guard time is provided in subframe G to separate the reception of the forward link signal at the UT in subframe F and the transmission of the return link signal at UT 400 and/or 401 in subframe R. As shown in FIG8 , the guard time in subframe G is part of the processing or waiting time to allow UT 400 and/or 401 to process the signal or data before subsequent transmission on the return link.

In the example shown in FIG8 , a timeline depicting transmissions initiated by UT 400 and/or 401 at or near the center of beam coverage is also shown as a dashed line (R: 1 st TX) from the leading edge of subframe R of frame k at the UT transmitter (UT TX@ ^center ) to the leading edge of subframe R of frame k+1 at the satellite RL receiver (Sat RSL RX). Satellite 300 relays a return link signal from UT 400 and/or 401 to the gateway along the dashed line (R: 1 ^st TX) from the leading edge of subframe R of frame k+1 at Sat RSL RX to the leading edge of subframe R of frame k+1 at the gateway receiver (GW RX). Processing and waiting time (R: proc&wait) may also be provided at gateway 200 to allow gateway 200 to process the signal or data prior to subsequent transmission on the forward link.

In the example shown in FIG8 , negative acknowledgement (NAK) signals are sent from UT 400 and/or 401 at or near the center of the beam coverage to gateway 200 via satellite 300, as indicated by the dashed lines (F: NAK) from the leading edge of subframe R of frame k+1 at UT TX @center to the leading edge of subframe R of frame k+2 at Sat RSL RX, and from the leading edge of subframe R of frame k+2 at Sat RSL RX to the leading edge of subframe R of frame k+3 at GW RX.

Likewise, another NAK signal is sent from gateway 200 to UT 400 and/or 401 via satellite 300, as shown by the dashed lines (F:NAK) from the leading edge of subframe F of frame k+3 at GWTX to the leading edge of subframe F of frame k+4 at Sat FSL TX, and from the leading edge of subframe F of frame k+4 at Sat FSL TX to the leading edge of subframe F of frame k+4 at UT RX@center. Instead of a NAK, an acknowledgment (ACK) signal may be sent by UT 400 and/or 401 in response to a received forward link signal, and similarly, an ACK signal may be sent by gateway 200 in response to a received return link signal.

8 , a minimum round-trip propagation delay of approximately 8 ms is assumed between the satellite 300 and the UTs 400 and/or 401. Thus, a time delay of approximately 8 ms-TR2F is provided between the time reference of the Sat RSL RX relative to the time reference of the Sat FSL TX, as shown in FIG8 as the time difference of 8 ms- _TR2F between the leading edge of frame k at the Sat _RSL RX and the leading edge of frame k at the Sat FSL TX.

In this example, _TR2F is a system parameter that accounts for the transition time required by a half-duplex UT transceiver when switching from receive mode to transmit mode or vice versa, e.g., 100 μs plus a small margin for this transition time. In the example shown in FIG8 , it can also be assumed that UT 400 and/or 401 requires approximately 2 ms of processing time between receiving the forward link packet and sending an ACK or NAK response. The approximately 2 ms processing time required by UT 400 and/or 401 can be illustrated by providing a time gap of approximately 2 ms between the trailing edge of subframe R of frame k+1 at Sat RSL RX and the leading edge of subframe F of frame k+2 at Sat FSL TX, e.g., as shown in FIG8 .

The receive and transmit operations and ACK/NAK responses of UTs 400 and/or 401 at or near the edge of the beam coverage (UT RX@edge and UT TX@edge) as shown in FIG8 are similar to those of UTs 400 and/or 401 at or near the center of the beam coverage (UT RX@center and UT TX@center). However, the leading edge of subframe F of frame k at UT RX@edge is delayed by approximately 5.2 ms from the leading edge of subframe F of frame k at Sat FSL TX.

In this example, for UTs 400 and/or 401 at or near the edge of the beam coverage, a time gap of approximately 2.6 ms is provided between the trailing edge of subframe R of frame k at UT TX@edge and the leading edge of subframe F of the next frame k+1 at UT TX@edge. To compensate for the approximately 2.6 ms time gap between two adjacent frames, the length of the guard time in subframe G between subframe F and subframe R in each HD frame in UTs 400 and/or 401 at or near the edge of the beam coverage is reduced. In one aspect, the guard time in a given HD frame can be dynamically adjusted by implementing an adaptive special subframe (SSF), as described in further detail below.

FIG9 is a schematic diagram illustrating an example of a HARQ timeline for a satellite communication system in which the feeder link delay between the gateway 200 and the satellite 300 is approximately 4 ms. In this example, there is a time gap of approximately 4 ms between the leading edge of subframe F of frame k+1 at the GW TX and the leading edge of subframe F of frame k+1 at the Sat FSL TX. In the example shown in FIG9 , it can also be assumed that there is a minimum round-trip propagation delay of approximately 8 ms between the satellite 300 and the UT 400 and/or 401, and that the UT 400 and/or 401 requires approximately 2 ms of processing time between receiving the forward link packet and sending the ACK or NAK response.

Similar to the example shown in FIG8 , a time delay of 8 ms- _TR2F is provided between the time reference of Sat RSL RX relative to the time reference of Sat FSL TX, as shown in FIG9 by the time difference of 8 ms-TR2F between the leading edge of frame k at Sat RSL RX and the leading edge of frame _k at Sat FSL TX, where _TR2F is the time required to accommodate the half-duplex UT transceiver when switching from receive mode to transmit mode or vice versa, plus a margin. In addition, a time gap of approximately 2 ms plus _TR2F can be provided between the trailing edge of subframe R of frame k+1 at Sat RSL RX and the leading edge of subframe F of frame k+2 at Sat FSL TX, for example, to accommodate the processing time required by UT 400 and/or 401 to process received packets and the time required for the half-duplex UT transceiver to accommodate the transition between receive and transmit modes.

Based on the examples shown in Figures 8 and 9, it will be appreciated that the half-duplex frame pattern at the gateway 200, satellite 300, and UTs 400 and/or 401 can be repeated for frames other than those shown in Figures 8 and 9, such as frames k+4, k+5, and so on. In one aspect, the satellite FL transmit time reference at Sat FSL TX can be set to a zero offset time reference. In one aspect, the timelines of the gateway transmitter and receiver and the UT transmitter and receiver can be derived based on the time delays of the corresponding frames relative to the satellite FL transmit time reference. It should be appreciated that the zero offset time reference can be set in other ways to provide the desired relative time delays at the gateway 200 and UTs 400 and/or 401.

In one aspect, an adaptive special subframe (SSF) is provided to allow the total guard time to increase or decrease with a corresponding decrease or increase in the total time allocated to the forward link in a given HD frame. In the example shown in Figures 6 and 7 and described above, the 10ms HD frame consists of subframes F, S, G, and R having lengths of 3ms, 1ms, 2ms, and 4ms, respectively, and in special subframe S, one time segment is allocated to FL F _SSF and another time segment is allocated to time G _SSF . Therefore, the total amount of time for FL in the 10ms HD frame of Figure 6 is 3ms + 0.2ms = 3.2ms, while the total guard time in the 10ms HD frame of Figure 6 is 0.8ms + 2ms = 2.8ms.

In one aspect, the allocation between the amount of time for the F _SSF and the amount of guard time G _SSF in the SSF can be dynamically changed depending on whether the UT 400 and/or 401 is at or near the center of the satellite 300's beam coverage, i.e., where the round-trip propagation delay of signals between the satellite 300 and the UT 400 and/or 401 is at or near a minimum, or at or near the edge of the satellite 300's beam coverage, i.e., where the round-trip propagation delay of signals between the satellite 300 and the UT 400 and/or 401 is at or near a maximum. In one aspect, there are successive SSF configurations between the center and edge of the beam coverage, with different allocations of time between the F _SSF and the G _SSF , but the total amount of time for the SSF remains constant at 1 ms.

In one aspect, the amount of time allocated to the F _SSF can be increased or decreased, either continuously or discontinuously, in increasing or decreasing increments, and the amount of time allocated to the G _SSF can be correspondingly decreased or increased, either continuously or discontinuously, in decreasing or increasing increments, depending on the round-trip propagation delay between the UT 400 and/or 401 and the satellite 300, which is determined by the location of the UT 400 and/or 401 in the beam coverage. For example, in a 10 ms HD frame, for a UT 400 and/or 401 at the center of the beam coverage, where the round-trip propagation delay is at a maximum, the entire length of the SSF can be allocated to the FL, effectively resulting in allocations of 4 ms, 2 ms, and 4 ms for the forward link, guard time, and return link, respectively.

On the other hand, for UTs 400 and/or 401 at the edge of the beam coverage, where the round-trip propagation delay is at a maximum, 0.2 ms of the 1 ms SSF may be allocated to the FL, while 0.8 ms of the 1 ms SSF may be allocated to the guard time, effectively resulting in an allocation of 3.2 ms for the forward link, 2.8 ms for the guard time, and 4 ms for the return link, respectively, in the HD frame.

In one aspect, a scheduler may be provided to adaptively adjust the time allocation between the F _SSF and the G _SSF in one SSF, depending on the location of the UT 400 and/or 401 in a given beam range. In one aspect, the scheduler may be implemented in a processor that is part of a gateway (e.g., gateway 200 shown in FIG. 1 ) or part of an infrastructure (e.g., infrastructure 106 shown in FIG. 1 ).

In one aspect, the scheduler can adaptively adjust the SSF configuration by scheduling the appropriate amount of forward link traffic from gateway 200 through satellite 300 to UT 400 and/or 401. In one aspect, UT 400 and/or 401 only needs to follow full-duplex frequency division duplex (FDD) timeline specifications.

From the UT's perspective, UT 400 and/or 401 may not be aware of the HD frame mode designed for half-duplex operation, but may be aware of its own half-duplex capabilities and may inform the scheduler in the network of its half-duplex capabilities via a message on the return link (e.g., a UT capability message). In one aspect, UT 400 and/or 401 listens to each subframe as a FL subframe unless it is granted an RL subframe. In one aspect, UT 400 and/or 401 follows the scheduler's grants for FL reception and RL transmission and follows the half-duplex FDD timeline specifications for HARQ and grants.

The scheduler may be implemented in the gateway 200 (e.g., scheduler 202) or the infrastructure 106. In one aspect, the half-duplex scheduler is required to follow established FL and RL HARQ timing rules. In one aspect, the scheduler may follow the half-duplex mode of the half-duplex UT, but is not required to do so.

For example, for a UT 400 and/or 401 located at or near the center of a beam coverage, that is, where the round-trip propagation delay between the UT 400 and/or 401 and the satellite 300 is at or near a maximum, a time allocation of 4 ms, 2 ms, and 4 ms is provided for forward link signal reception, guard time, and return link signal transmission, respectively, in a given HD frame. In this example, the UT 400 and/or 401 can achieve a 40% beam occupancy for the forward link and a 40% beam occupancy for the return link.

In one aspect, if multiple UTs are present within a beam coverage, the random offsets described above may be provided by the scheduler. For example, as described above, for a 10ms HD frame, if a large number of active UTs are present within a beam coverage (e.g., more than 10 UTs), 10 offsets may be provided for half-duplex mode, ranging from 0ms to 9ms in 1ms increments. If the number of active UTs within a beam coverage is relatively small, e.g., fewer than 10 UTs, 5 offsets may be provided, ranging from 0ms to 8ms in 2ms increments. Due to the expected randomness of the positions of the various UTs within a beam coverage over time, it is expected that approximately equal numbers of UTs will be found within each offset over time. In one aspect, the scheduler may implement the random offsets to ensure that the aggregated patterns of all active UEs within a beam coverage have random offsets and that approximately equal traffic load is distributed across all offsets.

FIG10 is a block diagram illustrating an example of a module for determining the amount of guard time in a half-duplex frame in block 1000. In one aspect, a minimum round-trip propagation delay for a UT within one beam coverage of a satellite is determined in block 1002, and a maximum round-trip propagation delay for the UT is determined in block 1004. In one aspect, the minimum round-trip propagation delay is the round-trip delay for signal propagation when the UT is at the center of the beam coverage. In another aspect, the maximum round-trip propagation delay is the round-trip delay for signal propagation when the UT is at the edge of the beam coverage.

10 , based on the minimum and maximum round-trip propagation delays determined in blocks 1002 and 1004, respectively, a maximum differential round-trip propagation delay is determined in block 1008. In one aspect, the maximum differential round-trip propagation delay is determined by subtracting the minimum round-trip propagation delay from the maximum round-trip propagation delay.

At block 1006, a determination is made as to the required transition time for circuit components of the half-duplex transceiver, such as a phase-locked loop (PLL) or a power amplifier (PA), when the half-duplex transceiver switches from a receive mode to a transmit mode and vice versa. In one aspect, a margin can be included in the transition time for the half-duplex transceiver to switch from a receive mode to a transmit mode and vice versa. Based on the maximum differential round-trip propagation delay and the transition time for the transceiver to switch from a receive mode to a transmit mode and vice versa, a guard time between the forward link and the return link in the half-duplex frame at the UT can be determined at block 1010. In one aspect, the guard time is determined by summing the maximum differential round-trip propagation delay with the transition time from the receive mode to the transmit mode and the transition time from the transmit mode to the receive mode.

FIG11 is a block diagram illustrating an example of a module for offsetting the time reference of the return link relative to the time reference of the forward link in block 1100. In one aspect, a minimum round-trip propagation delay is determined in block 1102, and the time required for the circuit components of the half-duplex transceiver (including, for example, a PLL or PA) to schedule a transition when the transceiver switches from transmit mode to receive mode or vice versa is determined in block 1104. As described above, in one aspect, the minimum round-trip propagation delay is the round-trip delay for a signal propagated by a UT within the beam coverage of a satellite when communicating with the satellite at the center of the beam coverage.

11 , a system parameter _TR2F is determined based on the transition time in block 1106. In one aspect, the system parameter _TR2F can be determined by adding a margin to the transition time required for a duplex transceiver to switch from transmit mode to receive mode or vice versa. Based on the minimum round-trip propagation delay and the system parameter _TR2F , an amount by which the return link time reference is offset or time-lagged relative to the forward link time reference is determined in block 1108.

In one aspect, the amount of the offset or time lag is determined by subtracting the system parameter _TR2F from the minimum round-trip propagation delay. In one aspect, the forward link time reference at the satellite forward link transmitter can be set to a zero offset time reference, and the return link time reference at the satellite return link receiver can be offset or delayed in time relative to the forward link time reference at the satellite forward link transmitter.

12 is a block diagram illustrating an example of a module for determining a half-duplex transmit/receive mode at a user terminal (UT) in block 1200. In one aspect, a forward link time segment F _SSF in a special subframe (SSF) of the HD frame is allocated in block 1202, and a guard time segment G _SSF in the SSF of the HD frame is allocated in block 1204. In one aspect described above, while the total SSF length remains constant at 1 ms in a 10 ms HD frame, the ratio of the forward link time segment F _SSF and the ratio of the guard time segment G _SSF in the SSF can be dynamically adjusted based at least in part on the total amount of guard time required in the HD frame.

As shown in Figures 6 and 7 and described above, in an HD frame, the forward link time segment F _SSF in subframe S immediately follows subframe F, and the total duration of the UT's forward link reception is the sum of the duration of subframe F and the duration of the F _SSF in subframe S. Similarly, in the HD frame, the guard time segment G _SSF in subframe S immediately precedes subframe G, and the total duration of the guard time is the sum of the duration of subframe G and the duration of the G _SSF in subframe S. In the example shown in Figure 6, the duration of subframe R for the UT's return link transmission remains constant at 4 ms. Referring to Figure 12, the forward link time, guard time, and return link time in the HD frame are allocated in block 1206.

FIG13 is a block diagram illustrating an example of a random offset scheduler 130. In one aspect, the number of offsets is determined by a module in block 1302 based on the number of active UTs found within a satellite's beam coverage. In one aspect, the offsets are assigned at equal intervals by a module in block 1304. If the number of active UTs within the beam coverage is large, e.g., greater than 10 UTs, and the HD frame length is 10 ms, then 10 offsets from 0 ms to 9 ms may be provided in 1 ms increments as described above. If there are fewer than 10 active UTs, for example, then a smaller number of offsets may be provided, e.g., 5 offsets from 0 ms to 8 ms in 2 ms increments as described above.

In one aspect, the random offset scheduler 1300 can be implemented in a gateway (such as gateway 200 shown in FIG. 1 ) or in an infrastructure (such as infrastructure 106 shown in FIG. 1 ). In one aspect, a UT within a satellite's beam coverage does not necessarily need to be aware of the presence of the random offset scheduler 1300 within the gateway 200 or infrastructure 106. The UT simply needs to apply the time offset determined for that particular UT by the random offset scheduler 1300. Referring to FIG. 13 , the random offset scheduler 1300 includes a module in block 1306 for determining whether the aggregation pattern of all active UTs within the beam coverage has a random offset. Based on the determination of the aggregation pattern, the module in block 1308 of the random offset scheduler 1300 distributes approximately equal traffic load across all offsets.

FIG14 is a block diagram illustrating an example of an adaptive special subframe (SSF) scheduler in block 1400. In one aspect, the adaptive SSF scheduler 1400 can be implemented in a gateway (such as the gateway 200 shown in FIG1 ) or in an infrastructure (such as the infrastructure 106 shown in FIG1 ). In one aspect, UTs within a satellite's beam coverage do not necessarily need to be aware of the presence of the random offset scheduler 1400 in the gateway 200 or the infrastructure 106.

14 , the modules in block 1402 of the adaptive SSF scheduler 1400 dynamically adjust the forward link time segment F _SSF based on the UT's position relative to the satellite, which determines the distance between the UT and the satellite and, therefore, the propagation delay. In one aspect, the adaptive SSF scheduler 1400 further includes modules in block 1404 for adjusting the guard time segment G _SSF in the adaptive SSF scheduler 1400 based on the UT's position within the satellite's coverage area.

In one aspect, since the total length of the adaptive SSF scheduler 1400 remains constant, an increase in the guard time segment G _SSF forces a decrease in the forward link time segment F _SSF , and vice versa. Based on the dynamic adjustment of F _SSF and G _SSF , the module in block 1406 determines the total forward link reception time and the total guard time between forward link transmission and return link transmission in the HD frame for the UT. In one aspect, the total forward link reception time is determined by adding the duration of F _SSF to the duration of the forward link subframe F in the HD frame, as shown in FIG6 , and the total guard time is determined by adding the duration of G _SSF to the duration of the guard subframe G in the HD frame, as shown in FIG6 .

The functions of the modules of Figures 10-14 can be implemented in various ways consistent with the teachings of this application. In some designs, the functions of these modules can be implemented as one or more electronic components. In some designs, the functions of these modules can be implemented as a processing system including one or more processor components. In some designs, the functions of these modules can be implemented using, for example, at least a portion of one or more integrated circuits (e.g., ASICs). As discussed in this application, an integrated circuit can include a processor, software, other related components, or some combination thereof. Therefore, the functions of different modules can be implemented as, for example, different subsets of an integrated circuit, different subsets of a set of software modules, or a combination thereof. Moreover, it should be understood that a given subset (e.g., a subset of an integrated circuit and/or a subset of a set of software modules) can provide at least a portion of the functions of more than one module. In addition, it should be understood that the modules and functions described in this application can be implemented in one or more elements of a satellite communication system (e.g., a gateway, infrastructure, satellite, and/or UT). For example, in some aspects, the functions can be shared between multiple elements of the satellite communication system (e.g., a gateway and infrastructure) that communicate with each other. Therefore, the illustrations provided in this application are merely examples.

In addition, the components and functions represented in Figures 10-14, as well as other components and functions described in this application, can be implemented using any suitable units. These units can also be implemented, at least in part, using corresponding structures as described in this application. For example, the components described above in conjunction with the "module for..." components of Figures 10-14 can also correspond to the functional bodies of the similarly designed "unit for...". Therefore, in some aspects, one or more of these units can be implemented using one or more processor components, integrated circuits, or other applicable structures described in this application.

After reviewing the above disclosure, it should be appreciated that various aspects can support methods for performing the various functions disclosed herein. For example, FIG. 15 is a flow chart depicting a method for determining a time lag of a return link time reference relative to a forward link time reference in a satellite communication system. In block 1502, a minimum round-trip propagation delay of a signal between a ground station and a satellite is determined. In block 1504, a transition time for a half-duplex transceiver of the ground station to switch between a transmit mode and a receive mode is determined. In block 1506, a system parameter is determined based on the transition time for the half-duplex transceiver to switch between a transmit mode and a receive mode. In block 1508, a time lag of the return link time reference relative to the forward link time reference is determined based on the minimum round-trip propagation delay and the system parameter. The method can be performed in a satellite communication system 100, as depicted in FIG. The satellite communication system 100 can include a satellite 300 and at least one ground station (e.g., UT 400, UT 401) having a half-duplex transceiver within the beam coverage of the satellite 300.

In another aspect, FIG16 is a flow chart illustrating a method for determining a guard time between receiving and transmitting in a half-duplex transceiver. In block 1602, a maximum round-trip propagation delay of a signal between the half-duplex transceiver and a satellite is determined. In block 1604, a minimum round-trip propagation delay of a signal between the half-duplex transceiver and the satellite is determined. In block 1606, a maximum differential round-trip propagation delay is determined based on the maximum round-trip propagation delay and the minimum round-trip propagation delay. In block 1608, a transition time for the half-duplex transceiver to switch between transmit and receive modes is determined. In block 1610, a guard time is determined based on the maximum differential round-trip propagation delay and the transition time for the half-duplex transceiver to switch between transmit and receive modes. The method may be performed in a satellite communication system 100, as illustrated in FIG1 . The satellite communication system 100 may include a satellite 300 and at least one ground station (e.g., UT 400, UT 401) having a half-duplex transceiver within the beam coverage of the satellite 300.

In another aspect, FIG17 is a flow chart depicting a method for determining a forward link time duration and a guard time duration in a half-duplex frame in a satellite communication system. In block 1702, a forward link time segment is allocated in a special subframe of the half-duplex frame. In block 1704, a guard time segment is allocated in the special subframe. In block 1706, the forward link time duration in the half-duplex frame is determined based on the forward link time segment in the special subframe. In block 1708, the guard time duration in the half-duplex frame is determined based on the guard time segment in the special subframe. The method can be performed in a satellite communication system 100 as depicted in FIG1 . The satellite communication system 100 can include a gateway 200 having a scheduler 202, a satellite 300, and at least one ground station (e.g., UT 400, UT 401) having a half-duplex transceiver in the beam coverage of the satellite 300.

In another aspect, FIG18 is a flow chart illustrating a method for scheduling time offsets for multiple user terminals within the beam coverage of a satellite in a satellite communication system. In block 1802, a number of time offsets is determined based on the number of active user terminals within the beam coverage. In block 1804, equally spaced time offsets are assigned based on the number of time offsets. In block 1806, a determination is made as to whether the aggregation pattern of the active user terminals within the beam coverage has random offsets. In block 1808, approximately equal traffic load is distributed over time for the active user terminals. The method may be performed in a satellite communication system 100 as depicted in FIG1 . The satellite communication system 100 may include a gateway 200 having a scheduler 202, a satellite 300, and at least one ground station (e.g., UT 400, UT 401) having a half-duplex transceiver within the beam coverage of the satellite 300.

Those skilled in the art will appreciate that information and signals may be represented using any of a variety of different techniques and methods. For example, data, instructions, commands, information, signals, bits, symbols, and chips mentioned throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

In addition, it will be understood by those skilled in the art that the various exemplary logic blocks, modules, circuits, and algorithm steps described in conjunction with the disclosed aspects of the present invention can be implemented as electronic hardware, computer software, or a combination thereof. In order to clearly illustrate the interchangeability between hardware and software, the various exemplary components, blocks, modules, circuits, and steps above are generally described around their functions. Whether such functions are implemented as hardware or software depends on the specific application and the design constraints imposed on the entire system. A skilled person can implement the described functions in a flexible manner for each specific application, but such implementation decisions should not be interpreted as causing a deviation from the scope of protection of the present disclosure.

The methods, sequences, or algorithms described in conjunction with the disclosed aspects of the present invention may be implemented directly in hardware, software modules executed by a processor, or a combination thereof. The software modules may be located in RAM storage, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, a hard disk, a removable hard disk, a CD-ROM, or any other form of storage medium known in the art. An exemplary storage medium is connected to the processor, and the processor can read information from and write information to the storage medium. Alternatively, the storage medium may be integrated into the processor.

Thus, one aspect of the present disclosure may include a computer-readable medium that embodies one or more methods disclosed herein for half-duplex data transmission in a non-geostationary satellite communication system. Therefore, the present disclosure is not limited to the examples shown, and any means for performing the functions described herein are included in aspects of the present disclosure.

Although the above disclosure shows illustrative aspects, it should be noted that various changes and modifications can be made without departing from the scope of protection of the appended claims. Unless explicitly stated, the actions of the functions, steps or methods of the aspects described in this application do not need to be performed in any particular order. In addition, although elements are described or stated in singular form, plural forms are also contemplated unless explicitly stated to be limited to the singular. Therefore, the present disclosure is not limited to the examples shown, and any unit for performing the functions described in this application may be included in the aspects of the present disclosure.

Claims (8)

1. A method for determining the time lag between a return link time reference and a forward link time reference in a satellite communication system, the method comprising: Determine the minimum round-trip propagation delay of the signal between the ground station and the satellite; Determine the switching time of the half-duplex transceiver of the ground station between transmit mode and receive mode; The system parameters are determined based on the switching time of the half-duplex transceiver between the transmitting mode and the receiving mode; The time lag of the return link time reference relative to the forward link time reference is determined by offsetting the system parameters from the minimum round-trip propagation delay; and Based on the determined time lag, at least one of one or more transmission operations or one or more reception operations performed by the satellite is scheduled. The scheduling involves scheduling one or more transmission operations performed by the satellite on the first n+k frame set, and scheduling one or more reception operations performed by the satellite on the second n+k frame set, where n is greater than or equal to zero. Wherein, the leading edge of frame k in the second set of n+k frames is the time lag determined by the deviation of the leading edge of frame k in the first set of n+k frames from the satellite. Wherein, the return link time reference is the return link receiver time reference of the satellite, and The forward link time reference is the forward link transmitter time reference of the satellite. 2. The method of claim 1, further comprising determining a guard time between receiving and transmitting in the half-duplex transceiver. 3. The method of claim 2, wherein determining the guard time between receiving and transmitting in the half-duplex transceiver comprises: Determine the maximum round-trip propagation delay of the signal between the ground station and the satellite; The maximum difference round-trip propagation delay is determined based on the maximum round-trip propagation delay and the minimum round-trip propagation delay; and The protection time is determined based on the maximum difference round-trip propagation delay and the switching time of the half-duplex transceiver when switching between the transmit mode and the receive mode. 4. The method of claim 1, wherein the ground station includes a user terminal. 5. The method of claim 1, wherein the satellite comprises a non-geostationary satellite. 6. An apparatus configured to determine the time lag of a return link time reference relative to a forward link time reference in a satellite communication system, the apparatus comprising: At least one processor; and At least one memory coupled to the at least one processor, wherein the at least one processor and the at least one memory are configured as follows: Determine the minimum round-trip propagation delay of the signal between the ground station and the satellite; Determine the switching time of the half-duplex transceiver of the ground station between transmit mode and receive mode; The system parameters are determined based on the switching time of the half-duplex transceiver between the transmitting mode and the receiving mode; The time lag of the return link time reference relative to the forward link time reference is determined by offsetting the system parameters from the minimum round-trip propagation delay; and Based on the determined time lag, at least one of one or more transmission operations or one or more reception operations performed by the satellite is scheduled. Wherein, the at least one processor schedules the one or more transmission operations performed by the satellite on a first n+k frame set, and the at least one processor schedules the one or more reception operations performed by the satellite on a second n+k frame set, wherein n is greater than or equal to zero. Wherein, the leading edge of frame k in the second set of n+k frames is the time lag determined by the deviation of the leading edge of frame k in the first set of n+k frames from the satellite. Wherein, the return link time reference is the return link receiver time reference of the satellite, and The forward link time reference is the forward link transmitter time reference of the satellite. 7. An apparatus configured to determine the time lag of a return link time reference relative to a forward link time reference in a satellite communication system, the apparatus comprising: A unit used to determine the minimum round-trip propagation delay of a signal between a ground station and a satellite; A unit for determining the switching time of the half-duplex transceiver of the ground station between transmit mode and receive mode; A unit for determining system parameters based on the switching time of the half-duplex transceiver when switching between the transmit mode and the receive mode; A unit for determining the time lag of the return link time reference relative to the forward link time reference by offsetting the system parameters from the minimum round-trip propagation delay; and A unit for scheduling at least one of one or more transmission operations or one or more reception operations performed by the satellite based on a determined time lag. The scheduling unit schedules one or more transmission operations performed by the satellite on the first n+k frame set, and the scheduling unit schedules one or more reception operations performed by the satellite on the second n+k frame set, where n is greater than or equal to zero. Wherein, the leading edge of frame k in the second set of n+k frames is the time lag determined by the deviation of the leading edge of frame k in the first set of n+k frames from the satellite. Wherein, the return link time reference is the return link receiver time reference of the satellite, and The forward link time reference is the forward link transmitter time reference of the satellite. 8. A non-transitory computer-readable medium comprising at least one instruction for causing a computer or processor to perform a method for determining a time lag between a return link time reference and a forward link time reference in a satellite communication system, the at least one instruction comprising instructions for performing the following operations: Determine the minimum round-trip propagation delay of the signal between the ground station and the satellite; Determine the switching time of the half-duplex transceiver of the ground station between transmit mode and receive mode; The system parameters are determined based on the switching time of the half-duplex transceiver between the transmitting mode and the receiving mode; The time lag of the return link time reference relative to the forward link time reference is determined by offsetting the system parameters from the minimum round-trip propagation delay; and Based on the determined time lag, at least one of one or more transmission operations or one or more reception operations performed by the satellite is scheduled. The one or more transmission operations performed by the satellite are scheduled on a first set of n+k frames, and the one or more reception operations performed by the satellite are scheduled on a second set of n+k frames, where n is greater than or equal to zero. Wherein, the leading edge of frame k in the second set of n+k frames is the time lag determined by the deviation of the leading edge of frame k in the first set of n+k frames from the satellite. Wherein, the return link time reference is the return link receiver time reference of the satellite, and The forward link time reference is the forward link transmitter time reference of the satellite.