Abstract:
A split gateway hub for a bent-leg communication system is disclosed. The gateway hub includes: a modulator to modulate a bit stream into a signal to be transmitted to a remote terminal via a radio frequency (RF) signal; a Time Synchronization Application (TSA), geographically co-located with the modulator, to provide timing reference and synchronization to the remote terminal; a network access component to provide traffic for the bit stream; and an Inroute Group Manager (IGM) to manage the traffic to and from the remote terminal. In the split gateway hub, the IGM is disposed geographically remote from either the TSA or from the network access component, and the bent-leg communication system uses a satellite or a High Attitude Platform (HAP) for relaying the RF signal.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims the benefit of U.S. Provisional Application No. 62/168,865, filed May 31, 2015, which is incorporated in its entirety by reference for all purposes as if fully set forth herein. 
     
    
     FIELD 
       [0002]    The present disclosure relates to a method and a system for providing synchronization timing for a split hub type operation. In particular, the present disclosure provides synchronization timing when the transmission equipment is distant from traffic/internet access equipment; for example, when the transmission equipment is on an aircraft, but the traffic/internet access equipment is on the ground. 
       SUMMARY 
       [0003]    This Summary is provided to introduce a selection of concepts in a simplified form that is further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. 
         [0004]    A split gateway hub for a bent-leg communication system is disclosed. The gateway hub includes: a modulator to modulate a bit stream into a signal to be transmitted to a remote terminal via a radio frequency (RF) signal; a Time Synchronization Application (TSA), geographically co-located with the modulator, to provide timing reference and synchronization to the remote terminal; a network access component to provide traffic for the bit stream; and an Inroute Group Manager (IGM) to manage the traffic to and from the remote terminal. In the split gateway hub, the IGM is disposed geographically remote from either the TSA or from the network access component, and the bent-leg communication system uses a satellite or a High Attitude Platform (HAP) for relaying the RF signal. 
         [0005]    Additional features will be set forth in the description that follows, and in part will be apparent from the description, or may be learned by practice of what is described. 
     
    
     
       DRAWINGS 
         [0006]    In order to describe the manner in which the above-recited and other advantages and features may be obtained, a more particular description is provided below and will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments and are not therefore to be considered to be limiting of its scope, implementations will be described and explained with additional specificity and detail through the use of the accompanying drawings. 
           [0007]      FIG. 1  illustrates a logical view of an exemplary satellite/High Altitude Platform (HAP) split hub communication system, according to various embodiments. 
           [0008]      FIG. 2  illustrates a logical view of an exemplary geographically diverse hub communication system, according to various embodiments. 
           [0009]      FIG. 3  illustrates synchronization timing for a bent-pipe communications system according to various embodiments. 
           [0010]      FIG. 4  is a logical diagram of an exemplary system that may be implemented on a split location hub for an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]    Embodiments are discussed in detail below. While specific implementations are discussed, it should be understood that this is done for illustration purposes only. A person skilled in the relevant art will recognize that other components and configurations may be used without parting from the spirit and scope of the subject matter of this disclosure. 
         [0012]    The terminology used herein is for describing particular embodiments only and is not intended to be limiting of the present disclosure. As used herein, the singular forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. Furthermore, the use of the terms a, an, etc. does not denote a limitation of quantity, but rather denotes the presence of at least one of the referenced items. The use of the terms “first,” “second,” and the like does not imply any particular order, but they are included to either identify individual elements or to distinguish one element from another. It will be further understood that the terms “comprises” and/or “comprising”, or “includes” and/or “including” when used in this specification, specify the presence of stated features, regions, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components, and/or groups thereof Although some features may be described with respect to individual exemplary embodiments, aspects need not be limited thereto such that features from one or more exemplary embodiments may be combinable with other features from one or more exemplary embodiments. 
         [0013]    A star topology communication system can include a gateway hub at the center of the star and remote terminals at the points of the star. In exemplary embodiments, the hub sends a continuous Digital Video Broadcasting—Satellite—Second Generation (DVB-S2) Time Division Multiplexing (TDM) data stream to a satellite for broadcast to all the remote terminals in the coverage region. The remote terminals use Time Division Multiplexing Access (TDMA) to access shared inroute channels for transmissions through the satellite to the hub. In TDMA, each remote terminal transmits its data bursts to the satellite for relay to the hub such that the bursts arrive within a narrow window of time, the aperture, within a specified burst of a particular frame at the hub. Such star-topology relay communication systems are also known as a bent pipe transmission as the satellite provides the bend in the bent pipe. Typically, the timing reference and synchronization in the bent-pipe system is maintained at the gateway hub. 
         [0014]    The present teachings a gateway hub and VSAT network where the gateway hub components are split between the hub and a distant location, for example, a satellite, a low altitude aircraft. The present teachings are also applicable where a modulator/demodulator is geographically split from an internet traffic source. This configuration would be desired when the feeder link bandwidth resource between hub and the distant location is limited, or when a geographically diverse hub is desired. Such a configuration is termed split hub, and timing synchronization becomes a problem in a split hub VSAT network. 
         [0015]    In exemplary embodiments, a gateway is where a Timing Synchronization Application (TSA) and the modulators reside. In exemplary embodiments, a hub is where a traffic sink or source resides. 
       Embodiment 1 for a Split Hub 
       [0016]      FIG. 1  illustrates a logical view of an exemplary split hub communication system, according to various embodiments. 
         [0017]    In an exemplary split hub system  100 , a traffic/network access component  110  and an Inroute Group Manager (IGM)  112  resides on the ground, and a transmission component resides on a relay  140 . In exemplary embodiments, the IGM  112  and the network access  110  are geographically co-located. In exemplary embodiments, the network access  110  may be a traffic sink and source. 
         [0018]    In exemplary embodiments, the relay  140  can include an aircraft, a satellite, a High Altitude Platform, or the like. The transmission component, for example, a modulator  122 , a demodulator  124  and a Timing Synchronization Application (TSA)  126 , reside on the relay  140  that is transmitting and receiving to/from a remote terminal (not shown), for example, a VSAT terminal. 
         [0019]    The standard DVB-S2 Outroute does not have any time marker that a remote terminal can use to synchronize its time reference with the relay  140 . However, the remote terminal must establish a time reference that is within tens of microseconds of the relay  140 &#39;s time reference so that the remote terminal can transmit bursts that arrive at the relay  140  in the assigned frames at the assigned times (i.e., within the right aperture). 
         [0020]    According to various embodiments, the relay  140 &#39;s TSA  126  provides a time reference by transmitting a Superframe Numbering Packet (SFNP) on the Outroute once every Superframe marker (for example, every 360 milliseconds). For the remote terminal to determine exactly when the Superframe marker occurred at the TSA  126  disposed in the relay  140 , the remote terminal needs to subtract the total SFNP delay from the time when it received the SFNP. In exemplary embodiments, the SFNP delay is equal to two separate delays: a relay delay and a transmission time from the relay  140  to the specific remote terminal. 
         [0021]    In exemplary embodiments, the transmission time from the relay  140  to the specific remote terminal can be determined during “Ranging”. The ranging value can drift slightly due to movement of the relay  140 . To adjust the ranging value, an estimated closed loop timing algorithm may estimate the remote terminal to relay delay. In exemplary embodiments, the estimated closed loop timing algorithm may be implemented at the inroute group manager  112 , for example, in a bandwidth allocator  114 . This estimated range delay may be repeatedly sent to the remote terminals in the SFNP packet via an outroute transmitter  116 . The estimated range delay may include a delay of transmission from when the packet is scheduled for transmission to when it is actually transmitted. 
       Embodiment 2 for a Split Hub: 
       [0022]      FIG. 2  illustrates a logical view of an exemplary geographically diverse hub communication system, according to various embodiments. 
         [0023]    In a split hub system  200 , a traffic/internet access component  210  resides on the ground but a far distance from transmission equipment. According to various embodiments, a far distance can include distances greater than 5 miles, 10 miles, 20 miles, 50 miles, 100 miles, 1000 miles, 5000 miles, 10000 miles or the like. In exemplary embodiments, the transmission components including a modulator  222 , a demodulator  224  and a timing synchronization application (TSA)  226 , that reside at a site that is diverse from the transmitting and receiving to/from a remote terminal (not shown), for example, a VSAT terminal. 
         [0024]    The standard DVB-S2 Outroute does not have any time marker that a remote terminal can use to synchronize its time reference with the a relay  240 . However, the remote terminal must establish a time reference that is within tens of microseconds of the relay  240 &#39;s time reference so that the remote terminal can transmit bursts that arrive at the relay  240  in the assigned frames at the assigned times (i.e., within the right aperture). 
         [0025]    According to various embodiments, the relay  240 &#39;s TSA  226  provides a time reference by transmitting a Superframe Numbering Packet (SFNP) on the Outroute once every Superframe marker (for example, every 360 milliseconds). For the remote terminal to determine exactly when the Superframe marker occurred at the relay  240 , the remote terminal needs to subtract the total SFNP delay from the time when it received the SFNP. The SFNP delay is equal to two separate delays: a relay delay and a transmission time from the relay  240  to the specific remote terminal. 
         [0026]    In exemplary embodiments, the transmission time from the satellite to the specific remote terminal can be determined during “Ranging”. The ranging value can drift slightly due to movement of the relay  240 . To adjust the ranging value, an estimated closed loop timing algorithm may estimate the remote terminal to relay delay. In exemplary embodiments, the estimated closed loop timing algorithm may be implemented at the Inroute Group Manager (IGM)  212 , for example, in a bandwidth allocator  214 . This estimated relay delay may be repeatedly sent to the remote terminals in the SFNP packet via an outroute transmitter  216 . The estimated satellite delay may include a delay of transmission from when the packet is scheduled for transmission to when the packet is actually transmitted. 
       Synchronization Timing for a Split Hub: 
       [0027]      FIG. 3  illustrates synchronization timing for a bent-pipe communications system according to various embodiments. 
         [0028]    A bent-pipe communication system  300  can use a relay  306  to communicate between a remote terminal (not shown) and a gateway (not shown). The relay  306  can be located remote from a gateway and can include, for example, a satellite, an aircraft, a High Altitude Platform or the like. A gateway outroute frame  302  represents frames and slots (or timeslots) out bound from the gateway to a terminal. A gateway inroute frame  304  represents frames in bound from the terminal to the gateway. A terminal inroute frame  308  represents frame in bound from the gateway to the terminal. Various delays can be added as the signal is propagated from the gateway to the terminal and back. The timing delays of the bent-pipe communication system  300  using the relay  306  are illustrated in  FIG. 3  and can be as follows:
       T HO : A gateway offset time that represents a time interval between the ideal instant of transmission of SFNP N  at the gateway and the start of reception of frame N at the gateway. This is also known as space-time offset (STO).   T HS : A propagation time from gateway to the relay  306  (satellite or aircraft) (same value as T SH )   T SR : A propagation time from the relay  306  (satellite or aircraft) to the remote terminal (same value as T RS )   T RO : A terminal offset time that represents a time between an “ideal” receipt of SFNP N  at a remote terminal and the transmit time for the start of transmission for frame N at this terminal.   T RS : A propagation time from terminal to the relay  306  (satellite or aircraft).   T SH : A propagation time from a relay  306  (satellite or aircraft) to the gateway.   SFNP N : Superframe numbering packet that marks frame N.       
 
         [0036]    When a portion of the gateway, for example, a modulator, a demodulator, a TSA and a transceiver are co-located at the relay  306 , then T HO  and T SH  are essentially 0. In exemplary embodiments, the T HS  and T SH  propagation times can be determined by ranging. 
         [0037]      FIG. 4  is a logical diagram of an exemplary system that may be implemented on a split location hub for an embodiment of the invention. 
         [0038]    A communication system  400  can include a gateway hub  402 , a remote terminal  430  and a relay  440 . The gateway hub  402  can include a network access  410 . The network access  410  can provide access to the Internet, an enterprise network, a private network or the like. In exemplary embodiments, the network  410  can provide a hub functionality of the gateway hub  402 . The hub functionality is where a traffic sink or source resides. 
         [0039]    The gateway hub  402  can include a split  420  including a modulator  422 , a demodulator  424 , a timing synchronization application (TSA)  426  and a transceiver  428 . The split  420  can provide a gateway functionality of the gateway hub  402 . The gateway functionality where a Timing Synchronization Application (TSA) and the modulators reside. 
         [0040]    In exemplary embodiments, the split  420  can be co-located with the network access  410 . As such, all components of the gateway hub  402  can be co-located. 
         [0041]    In exemplary embodiments, the split  420  can be implemented a far distance from the network access  410 . In exemplary embodiments, the split  420  of the gateway hub  402  can be implemented in or co-located with the relay  440 . 
         [0042]    According to various embodiments, the remote terminal  430  can include a transceiver  432 , a modulator  434  and a demodulator  436 . The remote terminal  430  can be located remote from the network access  410 , the split  420  and the relay  430 . 
         [0043]    The TSA  426  can determine the propagation time from the gateway hub  402  to the relay  440 , and the propagation time from the relay  440  to the remote terminal  430  (respectively, T HS  and T SR  propagation times illustrated in  FIG. 3 ). 
         [0044]    The gateway hub  402  can include an inroute group manager (IGM)  412 . In exemplary embodiments, the TSA  426  can determine the space-time offset T HO  and provide the space-time offset T HO  to the IGM  412 . The IGM  412  can utilize the propagation times determined by the TSA to perform various activities, for example, bandwidth allocation, forward error correction and the like. 
         [0045]    Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms for implementing the claims. 
         [0046]    Although the above descriptions may contain specific details, they should not be construed as limiting the claims in any way. Other configurations of the described embodiments are part of the scope of this disclosure. Further, implementations consistent with the subject matter of this disclosure may have more or fewer acts than as described, or may implement acts in a different order than as shown. Accordingly, the appended claims and their legal equivalents should only define the invention, rather than any specific examples given.