Abstract:
Systems and methods for conveying aeronautical radio voice and signaling over a satellite IP network are described. According to disclosed embodiments, a remote very high frequency (VHF) transceiver is connected with a central location where Air Traffic Control is exercised. The system implements an end-to-end path employing satellite communications to transmit radio voice and signaling. A method is also provided that enables radio call setup and voice transport so as to allow aircraft pilots and flight controllers to communicate.

Description:
FIELD 
     The present disclosure relates generally to aeronautical communications, and more particularly, to systems and methods for conveying aeronautical radio voice and signaling over a satellite IP network. 
     BACKGROUND 
     Air Traffic Control (ATC) functions to control flights in a controlled airspace, i.e., an airspace that is continuously controlled throughout a flight so that a specific separation between aircraft, both vertically and horizontally, is achieved. ATC is provided by either an Area Control Center (ACC) when the aircraft flies within a Flight Information Region (FIR), or by the Approach (APP) or Tower (TWR) units of a controlled airport upon takeoff or landing. In order for a flight to be controlled, voice communications between the pilot of the aircraft and the flight controller have to be continuously available and the aircraft has to be monitored via radar. 
     Very High Frequency (VHF) communications are achieved by a large number of earth-based VHF transceiver stations. The interconnection of the VHF transceivers with the ATC center is implemented using a ground communication networking infrastructure. At the ATC center, a radio PBX (e.g., the Voice Communication System, or VCS) handles the signals to and from the VHF transceiver sites and routes voice communications to flight controllers. The same PBX handles the interconnection with the airports, which have their own flight controllers. 
     In areas with mountainous terrains, it is extremely difficult, if not impossible, to provide the necessary communication infrastructure so that the remote VHF transceiver station can relay voice to and from the ATC center. This poses great threats to flight safety, often forcing the authorities to close parts of the airspace. 
     The use of satellite communications offers a viable alternative to VHF transceiver stations where it is not possible to use ground means to implement the communication infrastructure. However, though satellite communications offer exceptional geographical coverage, they also induce a large amount of transmission delay. For example, for geostationary trajectories, transmission delay is equal to approximately 260 milliseconds from one point to another, if a single hop is assumed. This delay poses important problems to aeronautical communications. For example, since the reaction time of pilots and controllers to difficult situations depends on the delay of the channel that they use to communicate, the minimum allowed separation depends on that delay. In addition, radio call control is adversely affected, because if ground communication means such as leased lines are used, the delay is in the order of some microseconds. 
     SUMMARY 
     Systems and methods for conveying aeronautical radio voice and signaling over a satellite IP network are described that overcome the disadvantages described above. According to one embodiment, a system for conveying aeronautical communications is described. The system comprises a very high frequency (VHF) transceiver installed at a remote site, a first radio-over-IP gateway connected to the VHF transceiver installed at the remote site, a first satellite router connected to the first radio-over-IP gateway installed at the remote site, a second satellite router installed at a central location, a second radio-over-IP gateway connected to the second satellite router installed at the central location, and a voice communication system (VCS) connected to the second radio-over-IP gateway installed at the central location. 
     According to another embodiment, a method for conveying aeronautical communications is described. The method comprises the steps of detecting push-to-talk (PTT) signaling from a first external radio system, relaying the PTT signaling to the first external radio system, capturing voice data from the first external radio system, encoding the voice data, storing the voice data in a first transmit buffer, and initiating a call setup sequence. If the call setup sequence is successful, the method further comprises the steps of transmitting the voice data to a second external radio system, decoding the voice data, and clearing the first transmit buffer. If the call setup sequence is unsuccessful, the method further comprises the step of clearing the first transmit buffer. According to another embodiment, a computer readable medium having computer executable instructions embedded thereon for performing the acts of this method is described. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating a system for conveying aeronautical radio voice and signaling over a satellite IP network according to an embodiment. 
         FIG. 2  is a block diagram illustrating the internal components of a Radio-over-IP (RoIP) gateway of a system for conveying aeronautical radio voice and signaling over a satellite IP network according to an embodiment. 
         FIG. 3  is a flow chart illustrating a method for conveying aeronautical radio voice over a satellite IP network according to an embodiment. 
         FIG. 4  is a sequence diagram illustrating a method of reducing end-to-end delay after successful call setup according to an embodiment. 
         FIG. 5  is a sequence diagram illustrating a method of terminating an ongoing call step sequence as unsuccessful according to an embodiment. 
         FIG. 6  is a sequence diagram illustrating a method of successfully tearing down an existing voice call according to an embodiment. 
         FIG. 7  is a sequence diagram illustrating a method of aborting a call teardown sequence of an existing voice call when the communication end that has initiated the call teardown sequence decides to transmit in accordance with an embodiment. 
         FIG. 8  is a sequence diagram illustrating a method of aborting a call teardown sequence of an existing voice call when the communication end that has not initiated the call teardown sequence decides to transmit in accordance with an embodiment. 
         FIG. 9  is a schematic illustrating the structure of a packet for conveying a segment of voice in synchrony with a push-to-talk (PTT) signal that applies to that segment in accordance with an embodiment. 
         FIG. 10  is a diagrammatic representation of machine in the exemplary form of computer system within which a set of instructions causes the machine to perform any one or more of the methodologies discussed herein in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     A system and method for conveying aeronautical radio voice and signaling over a satellite IP network is described. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the exemplary embodiments. It is apparent to one skilled in the art, however, that embodiments can be practiced without these specific details or with an equivalent arrangement. In some instances, well-known structures and devices are shown in block diagram form in order to avoid unnecessarily obscuring the embodiments. 
     Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views,  FIG. 1  is a block diagram illustrating a system for conveying aeronautical radio voice and signaling over a satellite IP network according to one embodiment. The end-to-end architecture of the system comprises a very high frequency (VHF) transceiver  3  (i.e., a radio system) installed at a remote site  4 ; a remote Radio-over-IP (RoIP) gateway  6  installed at a central location  7 ; and a voice communication system (VCS)  11  (i.e., a radio system). 
     According to one embodiment, a pilot  1  contacts a VHF transceiver  3  installed at a remote site  4  via and on-board VHF radio  2 . The VHF transceiver  3  relays the voice and push-to-talk (PTT) signaling to the Radio-over-IP (RoIP) gateway  5 , installed at the remote site  4 , which then attempts to initiate a voice call with the RoIP gateway  6  installed at the central location  7 . In doing so, the satellite IP modem/router  8 , installed at the remote site  4 , initiates an IP connection with the satellite IP modem/router  9 , installed at the central location  7 , through the satellite  10 . Once the connection is successfully installed, voice and PTT signaling can be communicated from the VHF radio  2  onboard the aircraft to the RoIP gateway  6  installed at the central location  7 . The RoIP gateway  6  then relays voice and PTT signaling to the VCS  11  and the controller  12  via the headset  13 , so that the parties can communicate in a transparent manner. Although shown and described as a headset  13 , it is contemplated that flight controller  12  can communicate with RoIP gateway  16  via any suitable transmitter, receiver or transceiver. 
     According to another embodiment, a controller  12  contacts the VCS  11  installed at the central location  7  via the headset  13 . The VCS  11  relays the voice and PTT signaling to the Radio-over-IP (RoIP) gateway  6 , installed at the central location  7 , which then attempts to initiate a voice call with the RoIP gateway  5  installed at the remote site  4 . In doing so, the satellite IP modem/router  9 , installed at the central location  7 , initiates an IP connection with the satellite IP modem/router  8 , installed at the remote site  4 , through the satellite  10 . Once the connection is successfully installed, voice and PTT signaling can be communicated from the controller headset  13  to the RoIP gateway  5  installed at the remote site  4 . RoIP gateway  5  then relays voice and PTT signaling to the VHF transceiver  3  which emits it. The on-board VHF radio  2  picks it up and relays it to the pilot  1 , so that the parties can communicate in a transparent manner. 
       FIG. 2  is a block diagram illustrating the internal components of RoIP gateways  5 , 6  of  FIG. 1  according to one embodiment. In this embodiment, RoIP gateway  5  is identical to RoIP gateway  6 . An interface  21  detects PTT signaling from an external radio system  30  which is conveyed over an analog circuit, and relays PTT signaling to an external radio system  30  over another analog circuit. An interface  22  captures voice waveforms from an external radio system  30  through an analog circuit under the control of the call control function  26 , and plays back voice waveforms to an external radio system  30  through another analog circuit. 
     A voice encoder  23  compresses voice to reduce its bit rate under the control of the call control function  26 . A voice decoder  24  decompresses the voice to its original bit rate. A transmit buffer  25 , under the control of the call control function  26 , stores the voice until a call has been setup so that no information is discarded. The call control function  26  sets up and tears down voice calls between two RoIP gateways. A voice transport function  27  encapsulates compressed voice data which are output by the transmit buffer  25  on IP packets and decapsulates compressed voice data contained in IP packets which are output to the voice decoder  24  under the control of the call control function  26 . The call control function  26  and the voice transport function  27  of a RoIP gateway communicate with the respective entities within another RoIP gateway using interface  28 . 
       FIG. 3  is a flow chart illustrating a method for conveying aeronautical radio voice over a satellite IP network according to one embodiment. At step  100 , a PTT signal is detected from the radio system of the user who wishes to initiate a call, provided that no call was already ongoing. This may be either the pilot  1  (through the on-board VHF radio  2  and the VHF transceiver  3 ), or the controller  12  (through the headset  13  and the VCS  11 ). This signal is detected through interface  21 . 
     At step  110 , the RoIP gateway which has received the PTT signal (either RoIP gateway  5  or  6 ) starts digitizing the voice through interface  22 . At step  120 , the same RoIP gateway (either RoIP gateway  5  or  6 ) starts encoding the voice signal for transmission using the voice encoder  23 . At step  130 , the voice signal is stored within the transmit buffer  25 . At step  140 , a call setup sequence is started with the called communication end (either RoIP gateway  5  or  6 ) using the call control function  26  through interface  28 . Each of steps  100  to  140  may occur subsequently to or concurrently with one another. 
     If the call setup at step  140  is successful, the calling RoIP gateway (either RoIP gateway  5  or  6 ) starts transmitting the buffered voice using the voice transport function through interface  28  at step  150 . If the call setup is unsuccessful, the stored voice is discarded according to step  160 . 
     If the transmit buffer remained operational throughout the duration of the call, the end-to-end delay would include the call setup delay. Thus, it is necessary to remove the transmit buffer  25  at a suitable point in time without losing valuable voice information by doing so. Because radio communications are inherently half-duplex, this can be done during the period that the calling end (either VHF radio  2  or headset  13 ) does not transmit voice, but rather listens to the transmissions of the called end (the other of VHF radio  2  or headset  13 ). 
       FIG. 4  illustrates a method of reducing the end-to-end delay once the call setup has been successfully completed according to an embodiment. Signal  200  depicts the sequence of PTT signals (on/off) issued by the calling end, assuming that a call was not already ongoing. Signal  210  depicts the initiation and successful completion of the call setup sequence triggered by the first PTT signal of signal  200 . Signal  220  depicts the contents of the transmit buffer  25  and the point in time when it is removed from the end-to-end path. Signal  230  depicts the voice transmitted from the calling end to the called end via interface  28 , while signal  240  depicts the voice as received by the called end after the addition of the end-to-end delay that the whole system introduces. As compared to signal  200 , it is apparent that a period of silence has been removed so as to also remove the transmit buffer  25 . Signal  250  presents the response of the called end after having heard the calling end. 
     According to the method of  FIG. 4 , no new voice data are inserted in the transmit buffer  25  when (a) the call setup has been successfully completed (i.e., at point A of  FIG. 4 ), (b) the value of the PTT signal is 0 (no PTT is present, i.e., neither pilot  1  nor controller  12  wish to talk), and (c) a minimum silence period (i.e., period of time when PTT=0) is maintained between successive transmissions from the calling end, so as for the called end to be capable of discerning the individual transmissions. 
     When all of the contents of the buffer have been transmitted (i.e., at point B of  FIG. 4 ), the transmit buffer  25  is removed and no new voice data are inserted for the duration of the call. This removes the delay of the call setup from the end-to-end delay as is apparent from  FIG. 4 . 
       FIG. 5  illustrates a method for terminating an ongoing call setup sequence as unsuccessful according to an embodiment. In this embodiment, the calling end (either RoIP gateway  5  or  6 ) initiates the call setup through PTT signaling (signal  300 ), but during the call setup sequence with the called end (signal  310 ), the called end also attempts to contact the calling end (signal  330 ). In this case, the voice is discarded from the transmit buffers  25  of both ends (signals  320  and  340 ), and the pilot  1  and/or controller  12  have to try again. 
       FIG. 6  illustrates a method for tearing down an existing call according to an embodiment. According to signal  400 , the length of the time periods for which a PTT signal is not active is measured by an idle PTT timer, renewed each time the PTT is on, and if it exceeds a certain limit (i.e., the idle PTT timeout), a call teardown sequence is initiated by the communication end which has detected this condition. Each end can initiate one such sequence. When the other end also reaches the same state (signal  420 ), the call is terminated according to signal  410 . 
     If the user at either end issues a PTT during the call teardown sequence, the call teardown is aborted and the call is kept in an ongoing state.  FIG. 7  illustrates the situation in which the user at the end which has initiated the call teardown is the one who wishes to talk (signal  500 ). According to  FIG. 7 , the call teardown is rejected according to signal  510  without any additional actions on behalf of the RoIP gateways  5  and  6 . Signal  520  represents the PTT signaling of the user at the other end. 
       FIG. 8  illustrates the situation in which the user at the other end presses the PTT button (signal  620 ). In this situation, the call teardown is also rejected (signal  610 ) and the PTT idle timer of the other end is re-initialized (signal  600 ). 
     The above described embodiments illustrate the importance of conveying the PTT signal in synchrony with the voice data. If the PTT signal is not conveyed in synchrony with the voice data, voice could be lost, which is unacceptable in aeronautical communications.  FIG. 9  illustrates a method of transmitting PTT signaling together with voice data so as to avoid loss of voice data according to an embodiment. The voice is transmitted in segments  710 , encapsulated into IP packets with the proper headers  700 . The encapsulation is carried out by the voice transport function  27  presented in  FIG. 2 . For each packet presented in  FIG. 9 , the PTT signal is provided by the call control function  26  and encoded using a separate bit  720 . Because each voice packet covers a specific time period while the PTT signal can vary within that period, this bit is set to 1 when the original PTT signal, captured through interface  21 , is 1 even for the minimum timing resolution of the interface. This is the safest approach, because the loss of voice data is set to zero. 
       FIG. 10  shows a diagrammatic representation of machine in the exemplary form of computer system  1000  within which a set of instructions, for causing the machine to perform any one or more of the methodologies discussed herein, may be executed. For example, computer system  1000  may represent RoIP gateways  5  and/or  6 . In alternative embodiments, the machine operates as a standalone device or may be connected (e.g., networked) to other machines. In a networked deployment, the machine may operate in the capacity of a server or a client machine in server-client network environment, as a host machine, or as a peer machine in a peer-to-peer (or distributed) network environment. The machine may be a personal computer (PC), a network router, switch or bridge, or any machine capable of executing a set of instructions (sequential or otherwise) that specify actions to be taken by that machine. Further, while only a single machine is illustrated, the term “machine” shall also be taken to include any collection of machines that individually or jointly execute a set (or multiple sets) of instructions to perform any one or more of the methodologies discussed herein. 
     According to some embodiments, computer system  1000  comprises processor  1050  (e.g., a central processing unit (CPU), a graphics processing unit (GPU) or both), main memory  1060  (e.g., read only memory (ROM), flash memory, dynamic random access memory (DRAM) such as synchronous DRAM (SDRAM) or Rambus DRAM (RDRAM), etc.) and/or static memory  1070  (e.g., flash memory, static random access memory (SRAM), etc.), which communicate with each other via bus  1095 . 
     According to some embodiments, computer system  1000  may further comprise video display unit  1010  (e.g., a liquid crystal display (LCD), a light-emitting diode display (LED), an electroluminescent display (ELD), plasma display panels (PDP), an organic light-emitting diode display (OLED), a surface-conduction electron-emitted display (SED), a nanocrystal display, a 3D display, or a cathode ray tube (CRT)). According to some embodiments, computer system  1000  also may comprise alphanumeric input device  1015  (e.g., a keyboard), cursor control device  1020  (e.g., a controller or mouse), disk drive unit  1030 , signal generation device  1040  (e.g., a speaker), and/or network interface device  1080 . In still other embodiments, video display unit  1010 , alphanumeric input device  1015  (e.g., a keyboard), cursor control device  1020  (e.g., a controller or mouse), disk drive unit  1030 , signal generation device  1040  (e.g., a speaker), and/or network interface device  1080  are optional. 
     Disk drive unit  1030  includes computer-readable medium  1034  on which is stored one or more sets of instructions (e.g., software  1036 ) embodying any one or more of the methodologies or functions described herein. Software  1036  may also reside, completely or at least partially, within main memory  1060  and/or within processor  1050  during execution thereof by computer system  1000 , main memory  1060  and processor  1050 . Processor  1050  and main memory  1060  can also constitute computer-readable media having instructions  1054  and  1064 , respectively. Software  1036  may further be transmitted or received over network  1090  via network interface device  1080 . 
     While computer-readable medium  1034  is shown in an exemplary embodiment to be a single medium, the term “computer-readable medium” should be taken to include a single medium or multiple media (e.g., a centralized or distributed database, and/or associated caches and servers) that store the one or more sets of instructions. The term “computer-readable medium” shall also be taken to include any medium that is capable of storing, encoding or carrying a set of instructions for execution by the machine and that cause the machine to perform any one or more of the methodologies of the disclosed embodiments. The term “computer-readable medium” shall accordingly be taken to include, but not be limited to, solid-state memories, and optical and magnetic media. 
     It should be understood that processes and techniques described herein are not inherently related to any particular apparatus and may be implemented by any suitable combination of components or modules. Further, various types of general purpose devices may be used in accordance with the teachings described herein. It may also prove advantageous to construct a specialized apparatus to perform the methods described herein. Those skilled in the art will appreciate that many different combinations of hardware, software, and firmware will be suitable for practicing the disclosed embodiments. 
     Embodiments have been described in relation to particular examples, which are intended in all respects to be illustrative rather than restrictive. Further, while embodiments have been described in connection with a number of examples and implementations, it is understood that various modifications and equivalent arrangements can be made to the examples while remaining within the scope of the inventive embodiments. 
     Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the embodiments disclosed herein. Various aspects and/or components of the described embodiments may be used singly or in any combination. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the disclosure being indicated by the following claims.