Patent Publication Number: US-9431701-B1

Title: Dual antenna transfer switch system, method and apparatus

Description:
This application claims priority and benefit as a continuation of U.S. application Ser. No. 13/245,691, filed on Sep. 26, 2011. 
    
    
     BACKGROUND 
     Wireless communication systems, such as very small aperture terminal (“VSAT”) systems typically include one or more antennas at each ground terminal. Typically, dual antenna systems are employed for moving vessels, vehicles, or crafts that require a capability for continuous communication, which requires a continuous line of sight to a satellite, hub, or other communication terminal or node. For example, commercial ships may use a dual VSAT system for receiving an internet connection, telephone connections, television broadcast, etc. A dual VSAT system includes two steerable antennas, which compliment each other by switching the communication connection between the two antennas when one antenna is in a blockage zone where the antenna does not have satellite visibility. The antennas may enter a blockage zone caused by, for example, a mast on the ship which impedes satellite visibility. When one antenna is entering a blockage zone, the communication connection may be switched to the other antenna. The antennas are generally placed on a ship so that both antennas are not simultaneously in a blockage zone caused by shipboard structures or equipment. However, situations causing an antenna to unexpectedly lose satellite visibility remain a problem. For example, any type of signal interference or noise, blockages from other ships, cranes, mountains, weather conditions, antenna drift, and/or various equipment problems may cause communication failures or interruptions. Any unexpected signal degradation may be problematic. Accordingly, the dual antenna communications systems of the prior art may be improved as presently disclosed. 
     SUMMARY 
     The present disclosure provides a new and innovative system, methods, and apparatus for dual antenna transfer switching. In an example embodiment, a dual antenna system includes antennas, antenna control units, a transfer switch, and one or two modems. For example, the transfer switch may transfer a connection from one antenna to the other based on a change in satellite visibility due to entering a preprogrammed blockage zone or an unexpected loss of satellite visibility. The transfer switch may receive GPS data from an external GPS unit and/or the antenna control units and buffer the GPS data to the one or two modems. The transfer switch may provide a modem receive-lock signal to retarget a line of sight in response to an antenna drift. The transfer switch may transfer the connection between the antennas based on a satellite visibility value based on signal reception quality and/or a modem receive-lock status. The transfer switch may determine the uplink transmission power levels of the antennas and set an attenuation level for one of the antennas based on a difference in the uplink transmission power levels by attenuating the higher power antenna to be balanced with the lower power antenna. 
     Additional features and advantages of the disclosed system, methods, and apparatus are described in, and will be apparent from, the following Detailed Description and the Figures. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a high level block diagram of an example dual antenna communications system, according to an example embodiment of the present invention. 
         FIG. 2  is a detailed block diagram of an example transfer switch, according to an example embodiment of the present invention. 
         FIG. 3  includes a flowchart illustrating an example process for dual antenna transfer switching, according to an example embodiment of the present invention. 
         FIG. 4  includes a flowchart illustrating an example process for dual antenna transfer switching, according to an example embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS 
     The present disclosure relates in general to a wireless communications system, and in particular, a system for dual antenna transfer switching. Briefly, in an example embodiment, a dual antenna system is provided with a transfer switch that provides improved switching of a communication connection between the antennas. For example a transfer switch may transfer a connection based on reception quality or modem receive-lock status. For example, the transfer switch may provide for a modem receive-lock signal to retarget a line of sight based on antenna drift. For example, the transfer switch may power balance the uplink transmission power levels of the antennas. For example, the transfer switch may buffer GPS data from an external GPS unit to a modem. For example, the transfer switch may optimally determine whether to transfer or maintain a connection when both antennas are experiencing a loss of satellite visibility. For example a transfer switch may transfer a connection based on an in network or out of network status. Further, for example, a solid state transfer switch may seamlessly perform a connection transfer very quickly, for example, in twenty nanoseconds. 
     Accordingly, the presently disclosed transfer switch may provide for seamless connection transfers, improved reception quality, reduced transmission uplink errors, saving transmission power, and decreased modem downtime. In a non-limiting example embodiment, certain features disclosed in the present patent application may be commercially embodied in the Transfer Switch  3000 , and/or other products and services as offered by MTN Satellite Communications, the assignee of the present application. 
     The present system may be readily realized in a dual antenna communications system  100 . A high level block diagram of an example dual antenna communications system  100  is illustrated in  FIG. 1 . The illustrated system  100  includes two antennas  102   a  and  102   b , each having an associated antenna control unit  104   a  and  104   b , respectively. The antennas  102   a ,  102   b  may transmit and receive signals to and from a satellite  101 . A transfer switch  106  is operatively coupled with the antennas  102   a ,  102   b  and the antenna control units  104   a ,  104   b . An external GPS device  108  may be coupled to the transfer switch  106 . The transfer switch is coupled to an active modem  110 . The transfer switch may also be coupled to a monitor modem  112 . The active modem  110  and monitor modem  112  may be coupled to a network router  114 , which may in turn be coupled to a network switch  116 . In an example embodiment, the system  100  is a VSAT system. The system  100  may be located, for example, on a commercial ship, a luxury yacht, an aircraft, a hovercraft, an oil platform, or the like. In an example embodiment, the satellite  101  may be a geosynchronous satellite or a geostationary satellite. 
     For example, the system  100  may be located on a cruise ship, which needs to maintain television, telephone, and internet connections for its guests. The antennas  102   a ,  102   b  may be located towards opposite sides of the ship, so that shipboard structures and equipment which may create a blockage for antenna  102   a  will not create a blockage for antenna  102   b . As the ship moves and/or as the satellite  101  moves, the antennas  102   a ,  102   b  track the location of the satellite  101  to maintain satellite visibility. If the antenna  102   a  begins to drift off the proper line of sight, communication will eventually be lost after a certain degree of drift occurs. Accordingly, the antenna control units  104   a ,  104   b  may maintain the antennas  102   a ,  102   b  line of sight with the satellite  101 . It should be appreciated that the process of satellite tracking as performed by antenna control units  104   a ,  104   b  and antennas  102   a ,  102   b  is well known in the art. Further, antenna control units  104   a ,  104   b  may be programmed to identify blockage zones which the antenna  102   a ,  102   b  will enter as the antenna  102   a ,  102   b  moves to track a satellite  101 . As discussed above, known blockage zones are typically caused by known structures or equipment which may enter the line of sight of the antenna  102   a ,  102   b . For example, a blockage zone may typically be ten or twenty degrees wide in azimuth. When the antenna  102   a  is approaching a preprogrammed blockage zone, the antenna control unit  102   a  may send a signal to the transfer switch  106  to transfer a communication connection with the satellite  101  to the other antenna  102   b.    
     It should be appreciated that an antenna  102   a ,  102   b  often includes an internal GPS unit, which provides GPS data to the ACU, which may format the data for use by the active modem  110 , and the monitor modem  112 . Accordingly, an external GPS device  108  may not be required in many cases, however, when an antenna  102   a ,  102   b  is not providing GPS data, an external GPS feed may be required by the active modem  110  and the monitor modem  112  to maintain communication with the satellite  101 . Accordingly, the transfer switch  106  may be configurable to allow for the external GPS device  108 , as either the sole source of GPS data, as a backup source of GPS data, or the like. For example, an antenna  102   a ,  102   b  that has an internal GPS unit may experience a failure, in which case, a backup external GPS device  108  may be put into use, or may be installed as a quick remedy without replacing or repairing the antenna  102   a ,  102   b.    
     The active modem  110  passes a primary connection, with substantive data being passed between the satellite  101  and the network router  114 , such as a television broadcast, radio broadcast, internet connection, or the like between. For example, antenna  102   a  may be the default antenna to receive the primary connection. The primary connection is processed by active modem  110 , which passes the data connection between the satellite  101  and network router  114 . The primary connection is also used to determine satellite visibility, for example, by measuring downlink reception quality as seen by the active modem  112  and/or ensuring modem receive-lock. 
     The system  100  may always pass the primary connection through the active modem  110 , while the monitor modem  112  only has a secondary connection. For example, the monitor modem  112  may be receiving the same downlink data signals as the active modem  110 , to allow for measurement of reception quality and ensure modem receive-lock, and may provide data accordingly to the transfer switch  106  and antenna control unit  104   b . However, antenna  102   b  may only be transmitting limited data to maintain the connection, such as keep-alive signals. The transfer switch  106  may compare the satellite visibility of the antenna  102   a  to predefined thresholds and/or to the satellite visibility of the other antenna  102   b . For example, if the satellite visibility of antenna  102   a  has diminished, then the transfer switch may automatically and seamlessly transfer the primary connection to the other antenna  102   b . Similarly, for example, an antenna  102   a  may lose modem receive-lock if the antenna  102   a  drifts from the proper line of sight and the antenna  102   a  starts receiving a nearby satellite  101  with a higher transmission power on the same frequency. The active modem  110  or the monitor modem  112  may determine, for example, that the data received by antenna  102   a  is not from the proper satellite  101 , and may trigger an interrupt changing the modem receive-lock status. Accordingly, the antenna control unit  102   a  may receive this indication (e.g., via a binary interrupt line), and then retarget the antenna  102   a  to track the proper satellite  101 . If the antenna  102   a  had the primary connection, the transfer switch  106  may transfer the connection to the other antenna  102   b  while the retargeting occurs so the connection is seamlessly maintained for the user. Accordingly, users of the connection, for example, watching a television program, surfing the internet, etc., do not have any interruption in the connection. 
     Accordingly, the primary connection may be maintained through either antenna  102   a ,  102   b , when the satellite visibility is good. However, when satellite visibility decreases or some other problem with one of the two antenna connections occurs, the transfer switch may transfer the connection which is passed through to the network router  114 , and to the network switch  116 . The network switch  116  may then communicate the data connection with any suitable network (e.g., a local area network on a ship). It should be appreciated that the monitor modem  112  may communicate with the network router  114  and/or the network switch similarly to the active modem, even though monitor modem is not providing a substantive data connection (e.g., keep alive messages, networking data, addressing data). 
     It should be appreciated that the data communicated through the system  100  may be performed in many different ways, for example, using different carrier frequencies, different modulation schemes, etc. For example, baseband data is transmitted to and from the modem, which may be modulated using an intermediate frequency (e.g., 70 MHz, 140 MHz), which may be modulated to the radio frequency used for transmission between the antenna  102   a ,  102   b  and the satellite  101  (e.g., a range of 3 to 30 GHz, the K u  band, the band, the K a  band, or the X band). 
     In an example embodiment, the active modem  110  and monitor modem  112  may employ quadrature phase shift keying (“QPSK”) modulation. In an example embodiment, the active modem  110  and monitor modem  112  may employ time division multiple access (“TDMA”) for uplink transmit and single channel per carrier (“SCPC”) for downlink receive. In an example embodiment, spread spectrum and/or frequency hopping is used. Also, in an example embodiment, the system  100  only includes the active modem  110  and not the monitor modem  112 . In this set up, the antenna  102   a ,  102   b  which the primary connection is not being transmitted and received on may not be able to provide any satellite visibility value, signal reception quality, modem receive-lock status, etc., because the monitor modem  112  cannot measure or determine such information. In this case, the status of satellite that is providing the primary connection may simply be analyzed against an expect status of the other satellite. Accordingly, for example, if a connection transfer occurs from antenna  102   a  to  102   b , and the satellite visibility value of antenna  102   b  is lower than the antenna  102   a  which was previously being used, the connection may be transferred back to the original antenna  102   a.    
     A detailed block diagram of an example transfer switch  106  is illustrated in  FIG. 2 . In this example embodiment, a motherboard  202  may include one or more processors  204  operationally coupled to one or more memory devices  206 , and one or more interface circuits. For example, the motherboard may be linked to a power supply  208 , Rx board  210 , Tx board  212 , serial board  214 , XPort® board  216 , and LCD panel  218 . The processor  204  may be any suitable processor, such as the Microchip PIC32® microcontroller or a microprocessor from the INTEL PENTIUM® family of microprocessors. Also, for example, an Atmel® processor or an ARM® processor may be similarly employed. In an example embodiment, the motherboard  202  and one or more processors  204  are all solid state devices. The memory  206  preferably includes volatile memory and non-volatile memory. Preferably, the memory  206  stores a software program that interacts with the other devices in the system  100  as described below. This program may be executed by the processor  204  in any suitable manner. The transfer switch  106  is illustrated with various connections from the motherboard  202  to the power supply  208 , Rx board  210 , Tx board  212 , serial board  214 , XPort® board  216 , and LCD panel  218 . It should be appreciated that these connection types are merely for purposes of example, and that the transfer switch  106  may include a wide variety of different designs, components, layouts, etc. 
     The Rx board  210  and the Tx board  212  couple the transfer switch  106 , for example, to antennas  102   a ,  102   b , the active modem  110 , and the monitor modem  112 , to transmit and receive the communication signals. In an example embodiment, the Rx board  210  and the Tx board  212  may be manufactured by Honeywell, although it should be appreciated that other suitable devices may be used. For example, the Rx board  210  and the Tx board  212  may be rated for 75 ohms and capable of passing a signal ranging approximately from DC to 2.5 GHz. The transfer switch may maintain a primary communication connection with the satellite  101  (e.g., internet connection through antenna  102   a ) to the active modem  110 , while maintaining a secondary connection (e.g., keep-alive signals through antenna  102   b ) with monitor modem  112 . In an example embodiment, the Rx board  210  and the Tx board  212  may have coaxial cable couplings, or any other suitable coupling for transmitting and receiving data to and from the antennas  102   a ,  102   b , the active modem  110 , and the monitor modem  112  (e.g., a C band RF signal). 
     The serial board  214  may couple the transfer switch  106 , for example, to antenna control units  104   a ,  104   b , an external GPS unit  108 , the active modem  110 , and the monitor modem  112 . For example, GPS data, blockage zone data, etc. may be provided from the antenna control units  104   a ,  104   b  to the transfer switch  106 . The transfer switch  106  may in turn, buffer the GPS data, from the antenna control units  104   a ,  104   b  and/or the external GPS unit  108 , to the active modem  110  and the monitor modem  112 . In an example embodiment, the serial board  214  may have RJ-45 couplings, or any other suitable coupling for transmitting and receiving data to and from the antenna control units  104   a ,  104   b  and/or the external GPS unit  108 . 
     The XPort® board  216  may include, for example, an Ethernet port and/or a USB port. In an example embodiment, the XPort® board  216  may be provided by LANTRONIX®, however, it should be appreciated that various suitable alternatives may be provided. The XPort® board  216  may allow for remote access of the transfer switch  106 . As discussed below, a user may set up the transfer switch  106  locally or remotely, as well as receive status information and the like. A display such as an LCD panel  218  with a keypad may also be connected to the motherboard  202  for local user set up. For example, the LCD panel  218  may provide a user interface, which will be described in further detail below. A user interface may include prompts for human input from a user for selecting different settings, setting various thresholds, etc. The LCD panel  218  may provide various outputs in response to the user inputs and provide status information, such as the antenna connection status, reception quality, reception power, transmission power, modem receive-lock status, network status, GPS status, modem status, input confirmations, warnings, etc. Access to a switching device  106  can be controlled by appropriate security software or security measures. For example, access to the LCD panel  218  or a remote interface can be limited to users with a login and password, or the like. 
       FIG. 3  is a flowchart of an example process  300  for dual antenna transfer switching. Although the process  300  is described with reference to the flowchart illustrated in  FIG. 3 , it will be appreciated that many other methods of performing the acts associated with the process  300  may be used. For example, the order of many of the blocks may be changed, many blocks may be intermittently repeated or continually performed, certain blocks may be combined with other blocks, and many of the blocks described are optional or may only be contingently performed. 
     The example process  300  may begin when GPS data is received from an external GPS unit and/or an antenna control unit (block  302 ). For example, a transfer switch of a VSAT system receives GPS coordinates only from an external GPS unit and not from an antenna control unit. The GPS data is buffered to at least one modem (block  304 ). For example, the external GPS coordinates are buffered through the transfer switch to two modems. In an example embodiment, the transfer switch  106  does not truncate the GPS data, so the GPS location data may be very accurate and precise. In an example embodiment, only GPS data from an external GPS device is used. In an example embodiment, only GPS data from the antennas through the antenna control units is used. In an example embodiment, GPS data from an external GPS device and GPS data from the antennas through the antenna control units are used. 
     The example process  300  may continue as a modem receive-lock signal is provided to an antenna control unit to retarget a line of sight following an antenna drift (block  306 ). For example, the modem causes an interrupt line in the antenna control unit to change from 0 to 1 after receiving improper data. For example, the modem may determine that the data is in an incorrect format, indicating the antenna has drifted and locked on to the wrong satellite. Even a slight antenna drift may cause loss of modem receive-lock. Also, it should be appreciated that modem receive-lock may be lost or not provided for a variety of other reasons, for example, such as improper unbalanced uplink transmission power level when transferring from one antenna to another. 
     Further, a satellite visibility value is determined for both antennas based on signal reception quality or modem receive-lock status (block  308 ). For example, satellite visibility values are determined for antenna A as 5.5 and for antenna B as 8. A satellite visibility value may be determined, for example, based on reception quality, modem receive-lock status, transmission power, and/or reception power. In an example embodiment, the satellite visibility values may be measured in decibels. Reception quality of data received at a modem  110 ,  112  can be measured in a variety of ways. For example, signal to noise ratio (“SNR”), carrier to noise ratio (“C/N”), carrier to noise density, and/or latency may measure reception quality. Accordingly, reception quality may be measured in decibels, bits, milliseconds, etc. It should be appreciated that different performance indicators may be used for different systems, modulation techniques, etc. For example, a C/N value may be more useful than an SNR value for determining a reception quality for a particular VSAT system. 
     A connection is transferred between the antennas based on the satellite visibility value (block  310 ). For example, the connection is transferred from antenna A to antenna B. The transfer switch may compare the determined satellite visibility value of an antenna to a threshold value, and/or may compare the determined satellite visibility value of the antennas to each other. For example, if a satellite visibility value is in dB, a user may set a threshold (e.g., 12 dB) above which the connection need not be changed, even if the satellite visibility of the other antenna is higher. If the antenna providing the primary connection has a satellite visibility value below the threshold, the differential between the antennas is determined, and if large enough (e.g., 5 dB), the transfer switch may transfer the connection. Accordingly, for example, a user may set threshold and difference triggers using a remote interface at a threshold of 7 dB and difference threshold of greater than 2 dB. It should be appreciated that the threshold and difference triggers may be set so as to not cause more switching than necessary. 
     The example process  300  may include the uplink transmission power levels for the antennas being determined (block  312 ). For example, the antenna A uplink transmission power level is slightly higher than antenna B&#39;s. Accordingly, an attenuation level is set for an antenna based on a difference in uplink transmission power levels of the antennas to balance the higher powered antenna to the other antenna (block  314 ). For example, the transfer switch attenuates the uplink power transmission of antenna A by 0.5 dB to balance the antennas. It should be appreciated that unbalanced uplink transmission power from the antennas may cause problems for the satellite receiving the uplink transmission during a transmission from one antenna to the other antenna. Typically, antennas may be very well balanced and not need any attenuation. However, for example, if one antenna is replaced so that the two antennas include one old antenna and one new antenna, even of the same exact model, the uplink transmission power levels may be different. For example, switching from an old antenna to a new antenna when entering a preprogrammed blockage zone may cause an error at the satellite if the new antenna has a hotter signal, or a higher uplink transmission power. 
       FIG. 4  is a flowchart of an example process  400  for dual antenna transfer switching. Although the process  400  is described with reference to the flowchart illustrated in  FIG. 4 , it will be appreciated that many other methods of performing the acts associated with the process  400  may be used. For example, the order of many of the blocks may be changed, many blocks may be intermittently repeated or continually performed, certain blocks may be combined with other blocks, and many of the blocks described are optional or may only be contingently performed. 
     The example process  400  may begin with determining a preprogrammed blockage zone parameter for both antennas (block  402 ). For example, the transfer switch determines that antenna A is approaching a known blockage zone and antenna B is not in or approaching a known blockage zone. Also, determine a satellite visibility value based on reception quality and/or modem receive-lock status for both antennas (block  404 ). For example, the transfer switch determines the satellite visibility of antenna A is 13 and the satellite visibility of antenna B is 6.5. Next, determine an availability parameter based on the preprogrammed blockage zone parameter and satellite visibility value for both antennas (block  406 ). For example, the transfer switch determines the availability of antenna A as NO and antenna B as YES. Even though antenna A may have better satellite visibility, because it is entering a blockage zone, it is determined to be unavailable. Then, transfer a connection between the antennas based on the availability parameters (block  408 ). For example, the connection is transferred from antenna A to antenna B. Also, in an example embodiment, when the availability parameter of both antennas is unavailable, the connection may be transferred from an antenna in a blockage zone to an antenna outside of a blockage zone. Accordingly, if the satellite visibility improves, the satellite which is not in a known blockage zone has the connection. Similarly, when the availability parameter of the antennas is either both unavailable or both available, the connection may be maintained with the current antenna. 
     Also, the example process  400  may include determining the network status of the antennas when the availability parameters are the same for both antennas (block  410 ). For example, after antenna A exits the preprogrammed blockage zone so both antennas are available, the transfer switch determines the network status of antenna A as in network and antenna B as out of network. For example, even if antenna B has high satellite visibility, good signal reception, modem receive-lock, and/or adequate reception power the satellite may not be able to properly receive the uplink transmission data. For example, if the antenna has a problem (e.g., physical fault such as bent or broken wire, disabled amplifier, insufficient buck converter), the satellite may provide a status of out of network. In this case, the connection may be transferred between the antennas based on the network status of the antennas (block  412 ). For example, the connection is transferred from antenna B to antenna A. Accordingly, even if the satellite visibility of antenna B is better than antenna A, if for example, the buck converter for antenna B is rated at a lower power than antenna A&#39;s buck converter. It should be appreciated that such a problem may arise in a case where a storm or other interference is causing a higher than normal level of power from the buck converter to be needed to establish an in network connection with the satellite. Also, in an example embodiment, when both antennas have a status of out of network, the connection may be transferred to an antenna that is not in a known blockage zone. 
     For exemplary purposes, the present disclosure discusses a various examples relating to a VSAT antenna system. However, it should be appreciated that the disclosed system, methods, and apparatus may be advantageously used in any antenna system employing at least two steerable antennas. For example, a terrestrial communication system using microwave point to point links may employ a system of steerable antennas using a transfer switch as described within the present disclosure. In an example embodiment, any mobile or immobile vehicle, vessel, craft, or platform may include a dual antenna system as presently disclosed. 
     It will be appreciated that all of the disclosed methods and procedures described herein can be implemented using one or more computer programs or components. These components may be provided as a series of computer instructions on any conventional computer-readable medium, including RAM, ROM, flash memory, magnetic or optical disks, optical memory, or other storage media. The instructions may be configured to be executed by a processor, which when executing the series of computer instructions performs or facilitates the performance of all or part of the disclosed methods and procedures. 
     It should be understood that various changes and modifications to the example embodiments described herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present subject matter and without diminishing its intended advantages. It is therefore intended that such changes and modifications be covered by the appended claims. Also, it should be appreciated that the features of the dependent claims may be embodied in the systems, methods, and apparatus of each of the independent claims.