WO2011009027A1 - Système et procédé pour communications de données utilisant des liaisons de transpondeurs de télémétrie - Google Patents

Système et procédé pour communications de données utilisant des liaisons de transpondeurs de télémétrie Download PDF

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Publication number
WO2011009027A1
WO2011009027A1 PCT/US2010/042232 US2010042232W WO2011009027A1 WO 2011009027 A1 WO2011009027 A1 WO 2011009027A1 US 2010042232 W US2010042232 W US 2010042232W WO 2011009027 A1 WO2011009027 A1 WO 2011009027A1
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dme
signal
transponder
interrogator
transponders
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Ryan Haoyun Wu
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Saab Sensis Corp
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Sensis Corp
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
    • G01S13/74—Systems using reradiation of radio waves, e.g. secondary radar systems; Analogous systems
    • G01S13/76—Systems using reradiation of radio waves, e.g. secondary radar systems; Analogous systems wherein pulse-type signals are transmitted
    • G01S13/78—Systems using reradiation of radio waves, e.g. secondary radar systems; Analogous systems wherein pulse-type signals are transmitted discriminating between different kinds of targets, e.g. IFF-radar, i.e. identification of friend or foe
    • G01S13/785—Distance Measuring Equipment [DME] systems
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems

Definitions

  • the present invention relates to systems and methods to implement new digital communication capabilities on Distance Measuring Equipment (DME) uplinks and downlinks, without causing any perceivable interference with or performance degradation of existing DME operations.
  • DME Distance Measuring Equipment
  • DME is a ground-based navigation system which consists of a network of ground transponders and airborne interrogating units (interrogators).
  • an interrogator transmits DME pulse pair signals to be received by an intended ground transponder on a predetermined downlink frequency within the DME frequency band of 962 MHz to 1150 MHz.
  • the ground transponder determines whether the received signal is a valid interrogation signal by checking the spacing between the two pulses in the DME pulse pair signal. If a valid interrogation is detected, ground transponder transmits a reply signal on a predetermined uplink frequency after a preset delay of
  • the reply signal consists of a pulse pair with a fixed spacing that is transmitted on a different predetermined uplink frequency within the DME frequency band.
  • the specific pairing of interrogation and replying frequencies and the spacing between the pulses in the interrogation and replying pulse pair signals defines the DME channel/mode of DME operations.
  • Each channel consists of an interrogation frequency band and a replying frequency band that are separated from adjacent bands by IMHz.
  • the purpose of defining DME channels and modes is to minimize the co-channel interference between adjacent DME transponders. It is important that adjacent DME transponders operate either on a different frequency or use different modes when operating on the same uplink or down link frequency.
  • the DME frequency range includes the uplink and downlink secondary surveillance radar (SSR) frequency bands
  • the DME channels that are within these SSR frequency bands need to be reserved from usage by DME ground transponders whose operating coverage area overlap with the coverage area of an operating SSR.
  • the FAA Next Generation (NextGen) Automatic Dependent Surveillance - Broadcast (ADS-B) surveillance system which is partially built upon SSR uplink and downlink frequencies, includes DME channels that overlap the SSR frequencies and these overlapping DME channels cannot be assigned to any DME operations.
  • a DME interrogator e.g., aircraft
  • a DME transponder e.g., ground transponder
  • Fig. 1 illustrates the operating principles of legacy DME equipment using the interrogation and reply method of operation.
  • An interrogation message consists of pseudo-randomly spaced DME pulse pairs. Upon receiving a DME pulse pair the DME transponder reply with a pulse pair after a constant time delay. The interrogation and reply pulses are modulated at different frequencies to minimize interference.
  • An interrogation signal containing pseudo-randomly spaced DME pulse pairs are transmitted by the DME interrogator on a DME downlink frequency to the DME transponder, as shown in Fig. 1.
  • the DME transponder determines whether the pulse pair of the interrogation signal is valid and when the received interrogation signal is valid the DME transponder replies with a reply signal containing an identical DME pulse pair to the interrogator on a DME uplink frequency after a fixed transponder delay.
  • the DME interrogator receives the reply signal and correlates the received pulse pair in the reply signal with the known pulse pair transmitted in the interrogation signal to determine the total delay time.
  • the DME interrogator determines the range from the DME interrogator to the DME transponder.
  • the pseudo-randomly spaced sequence of pulse pairs are known only to the DME interrogator so that when the DME interrogator receives a reply signal, the DME interrogator performs a correlation between the transmitted DME interrogation signal and the received DME reply signal to determine if the correct pseudo-randomly spaced DME pulse pairs can be identified in the received reply signal.
  • An example of the pseudo-randomly spaced sequence of pulse pairs for a DME interrogation signal and the DME reply signal are shown in Fig. 1.
  • the randomness of the interrogation pulse pair sequence varies from DME transponder to DME transponder. For simplicity, DME transponders often use a random pick of a set of preselected spacing between two pairs of pulses to "stagger" the
  • the DME transponder While the main purpose of the DME transponder is to reply to the interrogation signals from aircraft, the DME transponder also broadcasts its identity periodically. In accordance with international standards, approximately every 40 seconds, each transponder broadcasts its station ID using International Morse code in a time period not exceeding 10 seconds. To transmit the station ID, the DME transponder transmits a Morse code dot as a 0.1 to 0.16 second period consisting of pulse pair signals with a fixed rate of 1350 pp/s and a Morse code dash has a period that is three times longer than the Morse code dot.
  • a DME transponder When there are either no interrogations or very few interrogations, a DME transponder maintains a minimum pulse pair transmission rate of 700 pp/s by randomly transmitting pulse pairs that are not replies to an interrogation. When there are too many interrogations the DME transponder omits some of the interrogations and maintains a maximum transmission rate of between 2610 and
  • the DME transponder After receiving a DME interrogation signal containing pseudo-randomly spaced DME pulse pairs that the DME transponder determines is valid, the DME transponder will not respond to any new interrogation signals for up to 60 ⁇ s.
  • the DME transponder will not reply to a second DME interrogation signal if the second DME interrogation signal arrives within 60 ⁇ s of the arrival time of the first DME interrogation signal that the DME transponder determines is valid.
  • the purpose of this "transponder dead time” is to suppress unwanted DME interrogations caused by echo or multipath signals.
  • the result of this "transponder dead time” is that no two DME reply signals will be transmitted closer than 60 ⁇ s on the DME reply signal frequency due to the
  • the main purpose of DME operation is to allow aircraft to identify and obtain a range to a ground transponder.
  • the DME interrogation pulses do not carry any information other than the unique randomness that is only meaningful to the interrogator.
  • a system for providing data communications on a DME uplink comprising a plurality of DME transponders and at least one DME interrogator, wherein a DME uplink comprising a plurality of channels each defined by a frequency and a mode, a DME downlink comprising a plurality of channels each defined by a frequency and a mode, and the DME uplink and DME downlink are on the same frequency with different pulse spacings.
  • the at least one DME interrogator transmits an
  • interrogation signal comprising a random pulse pair on the DME downlink
  • DME transponder receives the interrogation signal transmitted by the at least one DME interrogator, determines the interrogation signal is valid and transmits a reply signal on the DME uplink, the reply signal comprising the received random pulse pair and a modulated signal that includes at least data, and the modulated signal is transmitted within a dead-time window of the DME transponder.
  • the modulated signal is modulated using direct sequence spread spectrum techniques and is transmitted at a power at least 3dB below that of the random pulse pair of the interrogation signal. In other embodiments, the modulated signal is transmitted at a power at least 1OdB below that of the random pulse pair of the interrogation signal.
  • the modulated signal is modulated using orthogonal frequency division multiplexing techniques and is transmitted at a power at least 3dB below that of the random pulse pair of the interrogation signal. In other embodiments, the modulated signal is transmitted at a power at least 1OdB below that of the interrogation signal.
  • the modulated signal is modulated using higher order modulation techniques, such as PAM, and is transmitted at a power at least 3dB below that of the interrogation signal. In other embodiments, the modulated signal is transmitted at a power at least 1OdB below that of the random pulse pair of the interrogation signal.
  • each DME transponder of the plurality of DME transponders transmits modulated signals to at least two DME interrogators using code division multiple access techniques, each modulated signal comprises one or more packets of data, and each packet of data is transmitted at a power at least 3dB below that of the random pulse pair of the interrogation signal.
  • the modulated signal is transmitted at a power at least 1OdB below that of the random pulse pair of the interrogation signal.
  • the modulated signal is transmitted immediately after the received random pulse pair within the dead-time window of the DME transponder. In other embodiments, the modulated signal is transmitted after a predetermined delay after the received random pulse pair within the dead-time window of the DME transponder.
  • a system for providing data communications on a DME uplink comprising a plurality of DME transponders and at least one DME interrogator, wherein the DME uplink comprising a channel defined by a frequency and a mode, the DME downlink comprising a channel defined by a frequency and a mode, and the DME uplink and DMW downlink are on different frequencies.
  • the at least one DME interrogator transmits an interrogation signal comprising a random pulse pair on the DME downlink and the DME transponder receives the interrogation signal transmitted by the at least one DME interrogator, determines the interrogation signal is valid and transmits a reply signal on the DME uplink, the reply signal comprising the same random pulse pair received on the DME downlink and a modulated signal, wherein the modulated signal is transmitted within a dead-time window of the DME transponder.
  • the modulated signal is modulated using direct sequence spread spectrum techniques and is transmitted at a power at least 3dB below that of the random pulse pair of the interrogation signal.
  • the modulated signal is transmitted at a power at least 1OdB below that of the random pulse pair of the interrogation signal.
  • the modulated signal is modulated using orthogonal frequency division multiplexing techniques and is transmitted at a power at least 3dB below that of the random pulse pair of the interrogation signal. In other embodiments, the modulated signal is transmitted at a power at least 1OdB below that of the random pulse pair of the interrogation signal.
  • the modulated signal is modulated using higher order modulation techniques, such as phase amplitude modulation (PAM), and is transmitted at a power at least 3dB below that of the random pulse pair of the interrogation signal. In other embodiments, the modulated signal is transmitted at a power at least 1OdB below that of the random pulse pair of the interrogation signal.
  • PAM phase amplitude modulation
  • the modulated signal comprises one or more packets of data, each packet of data is transmitted at a power at least 3dB below that of the random pulse pair of the interrogation signal. In other embodiments, the modulated signal is transmitted at a power at least 1OdB below that of the
  • the modulated signal is transmitted immediately after the received random pulse pair within the dead-time window of the DME transponder. In other embodiments, the modulated signal is transmitted after a predetermined delay after the received random pulse pair within the dead-time window of the DME transponder.
  • a system for providing a timing signal on a DME uplink comprising a plurality of DME transponders and at least one DME interrogator, wherein the plurality of DME transponders synchronously broadcast a timing signal comprising a timing message header, and the at least one DME interrogator receives the timing signal from more than one DME transponder of the plurality of DME transponders.
  • the at least one DME interrogator determines a TOA for each of the timing signals received from two or more DME transponders of the plurality of DME transponders and computes a TDOA measurement using TOAs from two DME transponders of the plurality of DME transponders. In other embodiments, the at least one DME interrogator computes its own position using two or more TDOA measurements from the determined TOAs of timing signals received from at least three DME transponders of the plurality of DME transponders.
  • a system for providing a timing signal on a DME uplink comprising a plurality of DME transponders and at least one DME interrogator, wherein the plurality of DME transponders asynchronously broadcast a timing signal comprising a timing message header and a message payload comprising at least a UTC time of message, and the at least one DME interrogator receives the timing signal from more than one DME transponder of the plurality of DME transponders.
  • the at least one DME interrogator determines a TOA for each of the timing signals received from two or more DME transponders of the plurality of DME transponders and computes a TDOA measurement using TOAs from two DME transponders of the plurality of DME transponders and the message payloads of the received timing signals. In other embodiments, the at least one DME interrogator computes its own position using two or more TDOA measurements from the determined TOAs of timing signals received from at least three DME transponders of the plurality of DME transponders and the message payloads of the received timing signals.
  • a system for providing a heartbeat signal on a DME uplink comprising a plurality of DME transponders and at least one DME interrogator, wherein the plurality of DME transponders synchronously broadcast the heartbeat signal, the heartbeat signal comprising at least a predetermined heartbeat message bit pattern header, and the at least one DME interrogator receives the heartbeat signal from more than one DME transponder of the plurality of DME transponders.
  • the heartbeat signal further comprises a message pay load of one of a plurality of predefined pulse sequences, and each pulse sequence of the plurality of predefined pulse sequences represents a sequence of one or more data bits.
  • the at least one DME interrogator determines a TOA for each of the heartbeat signals received from two or more DME transponders of the plurality of DME transponders and computes a TDOA measurement using TOAs from two DME transponders of the plurality of DME transponders.
  • the at least one DME interrogator computes its own position using two or more TDOA measurements from the determined TOAs of heartbeat signals received from at least three DME transponders of the plurality of DME transponders.
  • a method of providing data communications on a DME downlink comprising defining a number N of communications channels on the DME downlink, each channel having a predefined pseudo-random number (PRN), and a plurality of bit PRNs, each bit PRN representing a sequence of one or more data bits, providing a DME interrogator that listens to signals transmitted by each DME transponder of a plurality of DME transponders and each DME interrogator of at least one DME interrogator, identifies channel PRNs of the predefined N communications channels in use by the DME transponders and DME interrogators, selects an unused DME channel PRN of the predefined N communications channels, and transmits the unused DME channel PRN to the DME transponder.
  • the DME transponder receives the unused DME channel PRN transmitted by the DME interrogator and establishes a data communication link with the DME interrogator, wherein the
  • the channel PRN is a pulse pair spacing pattern.
  • the predefined bit PRNs comprise at least two bit pulse pair spacing patterns, one bit pulse pair spacing pattern representing a binary "0" and the other bit pulse pair spacing pattern representing a binary "1".
  • the method further comprises the DME
  • the interrogator transmitting the unused DME channel PRN at least once every 2 seconds to maintain the communication link in an active state.
  • the communication link is terminated by the DME interrogator when the DME interrogator does not transmit the channel PRN on the selected DME channel within 2 seconds.
  • the predefined bit PRNs comprise at least four bit pulse pair spacing patterns indicating a binary "00", “01”, “10” or “11". In other embodiments, the predefined bit PRNs comprise at least eight bit pulse pair spacing patterns indicating a binary "0000", "0001”, “0010”, “0011”, “0100”, “0101”, “0110”, “0111”, “1000”, “1001”, “1010”, “1011” or “1111”.
  • a data capacity for data communications on the DME downlink channel is determined using the following equation:
  • C is the data rate capacity in bits per second
  • W is the frequency bandwidth in Hz; and S/N is the signal-to-noise ratio
  • a method of providing data communications on a DME uplink channel comprising transmitting a DME interrogation signal from at least one DME transmitter on a DME downlink and receiving the interrogation signal at a DME transponder that determines whether the interrogation signal is valid, and transmits a DME reply signal on the DME uplink, said reply signal comprising the received interrogation signal and a modulated signal, that includes at least data, wherein the modulated signal is transmitted within a dead- time window of the DME transponder.
  • the method further comprises modulating data onto the modulated signal using direct sequence spread spectrum techniques and transmitting the modulated signal at a power at least 3dB below that of the random pulse pair of the interrogation signal.
  • the method further comprises modulating data onto the modulated signal using orthogonal frequency division multiplexing techniques and transmitting the modulated signal transmitted at a power at least 3dB below that of the random pulse pair of the interrogation signal.
  • the method further comprises modulating data onto the modulated signal using higher order modulation techniques and transmitting the modulated signal at a power at least 3dB below that of the random pulse pair of the interrogation signal.
  • the method further comprises each DME transponder of the plurality of DME transponders transmits modulated signals to at least the DME interrogators using code division multiple access techniques, each modulated signal comprises one or more packets of data, and transmitting each packet of data at a power at least 3dB below that of the random pulse pair of the interrogation signal.
  • a system for providing two way data communications on a DME downlink comprising a plurality of DME transponders, each DME transponder being assigned primary channels for transmitting reply pulses in response to valid received interrogation signals, wherein a group of DME transponders cover a predetermined airspace and share a common secondary channel, the common secondary channel being designated for two way communications; and at least one DME interrogator transmitting a signal containing a predetermined pulse pair sequence to at least one DME transponder of the group of DME transponders, wherein the predetermined pulse pair sequence requests two way communication on the common secondary channel.
  • the at least one DME transponder of the group of DME transponders receives the transmitted signal from the at least one DME interrogator, determines the received transmitted signal is valid, and establishes a two way communication link with at least one DME interrogator on the common secondary channel, wherein the DME interrogator transmits a signal containing a data on the common secondary channel and the DME transponder replies by transmitting a signal containing data on the common secondary channel within a dead-time window of the DME
  • the DME interrogator and the DME transponder modulate data bits onto the secondary channel using direct sequence spread spectrum techniques. In other embodiments, the DME interrogator and the DME transponder modulate data bits onto the secondary channel using orthogonal frequency division multiplexing techniques. In yet other embodiments, the DME interrogator and the DME transponder modulate data bits onto the secondary channel using higher order modulation techniques.
  • a system for providing two way data communications on a DME downlink comprising a plurality of DME transponders, each DME transponder being assigned primary channels for transmitting reply pulses in response to valid received interrogation signals, wherein each DME transponder is assigned a secondary channel designated for two way communications, and a DME interrogator transmitting a signal containing a predetermined pulse pair sequence to one DME transponder of the plurality of DME transponders, wherein the predetermined pulse pair sequence requesting two way communication on the secondary channel of the DME transponder.
  • the DME transponder of the group of DME transponders receives the transmitted signal from the at least one DME interrogator, determines the received transmitted signal is valid, and establishes a two way communication link with the DME interrogator on the secondary channel, wherein the DME interrogator transmits a signal containing data on the secondary channel and the DME transponder replies by transmitting a signal containing data on the common secondary channel within a dead-time window of the DME transponder.
  • the DME interrogator and the DME transponder modulate data bits onto the secondary channel using direct sequence spread spectrum techniques. In other embodiments, the DME interrogator and the DME transponder modulate data bits onto the secondary channel using orthogonal frequency division multiplexing techniques. In yet other embodiments, the DME interrogator and the DME transponder modulate data bits onto the secondary channel using higher order modulation techniques.
  • Fig. 1 illustrates the operating principles of legacy DME equipment
  • Fig. 2 summarizes the in-band lower bandwidth embodiments of the present invention
  • Fig. 3(a) illustrates the reuse of different DME channels across the NAS
  • Fig. 3(b) illustrates the distance between reused DME channels across the NAS
  • Fig. 4(a) illustrates the DME transponder Dead Time window
  • Fig. 4(b) illustrates an example of the DME transponder Dead Time window modulation in one embodiment of the present invention
  • Fig. 5(a) illustrates an example of the DME interrogator random pulse pair spacing pattern in one embodiment of the present invention
  • Fig. 5(b) illustrates an example of two orthogonal DME interrogator pseudorandom pulse pair spacing patterns in one embodiment of the present invention
  • Fig. 6 illustrates the DME uplink (UL) communication using Transponder Dead Time Modulation, DME downlink (DL) communication using PRN Pulse Staggering Coding and the Heartbeat Timing Information using Pulse Staggering Coding.
  • the disclosed embodiments of the present invention implement a new digital communication capability on DME uplinks and DME downlinks, without causing any perceivable interference or performance degradation of existing DME operations.
  • DME Distance Measuring Equipment
  • two specific inefficient features of existing Distance Measuring Equipment (DME) operations specifically (i) the randomness and lack of meaning of the interrogation pulse pair sequence in a DME interrogation signal transmitted by the aircraft (hereinafter DME interrogator) on the DME downlink and (ii) after the ground DME transponder (hereinafter DME transponder) transmits a reply signal containing the received interrogation pulse pair sequence, the dead time of approximately 60 ⁇ s on the DME uplink (i.e., ground-to-aircraft), are exploited to provide one way or two way data communications using the existing DME frequencies.
  • DME Distance Measuring Equipment
  • Each DME transponder is assigned one or more channels on which the DME transponder transmits reply signals in response to received interrogation signals and periodically broadcasts its station ID as discussed above.
  • a DME uplink includes a plurality of channels, each channel is defined by a predetermine frequency and a mode.
  • the DME frequency band includes frequencies of 962 MHz to 1150 MHz.
  • a DME downlink also includes a plurality of channels, each channel is defined by a predetermine frequency and a mode.
  • the first through fourth embodiments of the present invention provide an in-band data communication capability on existing DME uplinks and DME downlinks that exploit portions of the aforementioned inefficiencies in existing DME operations are summarized in Fig. 2. These embodiments provide a limited data communication bandwidth because they are largely subject to the existing framework of DME operations. Though these embodiments are limited in bandwidth, these embodiments implement new data communication capabilities on existing DME systems with either a minimum or no interference with existing DME operations.
  • the fifth through seventh embodiments of the present invention provide an out-of-band higher bandwidth data communication capability on common or dedicated secondary DME channels on existing DME uplinks and DME downlinks
  • the in-band lower bandwidth embodiments provide low bandwidth communication for basic data distribution capabilities across the entire NAS and the out-of-band higher bandwidth embodiments provide additional higher-bandwidth capability for distribution of larger amounts of data.
  • the in-band lower bandwidth embodiments together with out-of-band higher bandwidth embodiments form the complete framework of implementing data communications on DME links.
  • the DME interrogator transmits a predefined interrogation pulse pair sequence on an existing DME downlink that has a specific associated meaning to the DME transponder receiving the interrogation pulse pair sequence to provide the in-band air-to-ground data communication capability.
  • the first embodiment exploits the random or pseudo-random nature of existing DME interrogation pulse pair sequences.
  • the transmitted interrogation pulse pair sequence corresponds to the pulse pair spacing pattern defined by the selected channel PRN pseudo-random number (PRN) and at least one pair of the pulse pair spacing patterns defined by the Bit PRN of the selected communication channel.
  • PRN pseudo-random number
  • the process of initiating an in-band air-to-ground data communication, transmitting data using the selected channel PRN and Bit PRN, and maintain and terminating the communication channel is described in the following steps: ⁇ For each DME transponder, a number of N communication channels are predefined each with a channel pulse pair spacing pattern (channel pseudo-random-number or channel PRN) and at least a pair of pulse pair spacing patterns indicating a binary 'O 1 and T (bit PRN). In one embodiment, N is equal to 200.
  • a DME interrogator receives signals transmitted by the DME
  • transponder and identifies channel PRNs that are being used.
  • the DME interrogator selects an unused channel PRN and transmits an interrogation signal containing the pulse pair spacing pattern that defines the selected channel PRN.
  • the combination of this step and the previous step could be considered a form of Code Sense Multiple Access as the DME interrogator determines an unused or vacant PRN pulse spacing pattern "code" for establishing a data communication channel with the DME transponder before transmitting data.
  • the DME transponder receives the DME interrogation signal, detects the pulse pair spacing pattern that defines the selected channel PRN, thereby establishing the communication channel with the DME interrogator, and gets ready to receive data transmitted by the DME interrogator on the communication channel.
  • the DME interrogator transmits interrogation signals containing the channel PRN pulse pair spacing pattern and at least two Bit PRN pulse pair spacing patterns predefined for the selected communication channel.
  • the predefined Bit PRN pulse pair spacing patterns correspond to the binary data bits 1 O' or T that the DME interrogator is transmitting to the DME transponder.
  • the predefined Bit PRN pulse pair spacing patterns correspond to binary bits OO 5 ' Ol 5 ' ' 10' and ' 11 ' other embodiments use predefined Bit PRN pulse pair spacing patterns corresponding to four, six and eight binary bit sequences.
  • the DME interrogator periodically, at least once every M seconds, transmits an interrogation signal containing the pulse pair spacing pattern defined by the selected channel PRN to maintain the
  • M is equal to 2 seconds. In another embodiment, M is equal to 5 seconds.
  • the DME interrogator terminates the communication link by failing to transmit an interrogation signal containing the pulse pair spacing pattern defined by the selected channel PRN for more than M seconds.
  • the DME transponder does not receive an interrogation signal containing the pulse pair spacing pattern defined by the selected channel PRN for more than M seconds, the DME transponder terminates the communication channel.
  • the DME transponder communicates with the DME interrogator by transmitting a reply signal and appending data in the dead-time window of the DME transponder, which is discussed in more detail in the third embodiment of the present invention.
  • the interrogation signal transmitted by the DME interrogator and any reply signals transmitted by the DME interrogator are transmitted in the clear without any data encryption.
  • DME reply signals are implicitly addressed to a specific DME interrogator because DME interrogators only correlate reply signals that are solicited by its own interrogation signals.
  • the communication bandwidth is determined by the number of
  • interrogation signals transmitted by the DME interrogator per second and the length of each Bit PRN sequence For example, if a DME interrogator transmits an interrogation signal at a rate of 30 pp/s and each binary bit is made up of 5 pulse pairs, the resulting data rate is 6 bits per second per communication channel.
  • communications link of first embodiment can be used for broadcasting any basic aircraft identity or status information which does not require a large bandwidth, such as Mode A/C information, or data that is static/semi-static in nature.
  • the DME interrogator also transmits a predefined
  • each Bit PRN uses pulse stagger coding to define a series of two or more bits, which increases the data communications capacity of the air-to-ground data communications link.
  • each Bit PRN has the same number of pulse pairs representing the Bit PRN, the bandwidth of the communication channel is doubled.
  • the number of bits represented by each assigned Bit PRN cannot be increased infinitely and the upper limit is governed by information theory.
  • the processing bandwidth of the receiver of the DME transponder needs to be considered.
  • the more bits each Bit PRN represents will result in a higher processing burden for the DME transponder's communication receiver as more pulse-pair sequences need to be detected and checked.
  • Channel PRN and Bit PRN sequences will enable simultaneous data communications from up to 200 aircraft to a single DME transponder.
  • the pseudo-random pulse pair sequences of the first DME interrogator is orthogonal from the pulse pair sequences of the other DME interrogators so that when the interrogation signals arrive at the transponder such that two received sequences are overlapped, the integration of the sample wise product is the lowest (i.e., zero ideally).
  • the overlap of any two Bit PRN sequences includes synchronous overlap (where the first pulse pairs overlap) and asynchronous overlap (where the first pulse pairs do not overlap).
  • the resolution of the pulse position coding is equal to the pulse width which is 3.5 ⁇ s.
  • a total of (l/30-60e-6)/3.5e-6 or 9506 possible pulse-pair spacing values can be utilized for implementing the orthogonal Channel and Bit PRN sequences. More than 9506 possible pulse pair spacing values can be utilized when resolution lower than 3.5 ⁇ s is employed.
  • the DME transponder after transmitting a reply signal the DME transponder modulates and transmits data bits in the DME transponder dead time window that are attached to the reply signal to provide a ground to air communication capability.
  • this embodiment of the present invention exploits the DME transponder dead time window. After transmitting a reply signal containing pulse pairs, a DME transponder does not transmit or receive any signals for up to a nominal 60 ⁇ s to prevent undesired echo interrogation caused by multipath, as discussed in the background section.
  • This dead time window results in the under utilization of the DME reply channel frequency because during the DME transponder dead time there are no transmissions on the DME reply channel.
  • this embodiment modulates and transmits data bits in the dead time using modern techniques with multiple access (MAC) techniques on the same frequency.
  • the MAC techniques including direct sequence spread spectrum (DSSS, as used in CDMA) and orthogonal frequency division multiplexing (OFDM, as used in WiMAX or IEEE 802.16 family), as well as higher-order modulation techniques, such as phase-amplitude modulation (PAM) can be used to modulate the data bits.
  • DSSS direct sequence spread spectrum
  • OFDM orthogonal frequency division multiplexing
  • PAM phase-amplitude modulation
  • data bits are modulated on to the DME reply channel carrier frequency within the DME transponder dead time window using direct sequence spread spectrum (DSSS).
  • DSSS is a simple code spread technique that is used to encode data bits into a sequence of 0' and T DSSS "chips" with the energy is spread over the entire sequence so that the instant transmission power is lower on per sample basis.
  • a single DME pulse is used as a DSSS "chip” and each DSSS symbol contains L chips (note that a DSSS symbol is a sequence of a pseudo randomly selected binary bits where each bit is one chip), which results in the signal strength of each DSSS chip being L times lower than the signal strength of DME reply signals.
  • a total of four pulses can be accommodated within the 60 ⁇ s DME transponder dead time window.
  • a 4-chip symbol When a 4-chip symbol is used, a total of 4 sub channels are formed since the number of users is governed by the number of orthogonal codes that exist, which is equal to the number of chips in this example. If the 4 subchannels are dedicated to the same user, the data rate is 4 bits per symbol and if the interrogation is occurring at a rate of 30 pp/s, the data rate becomes 120 bits per second.
  • the maximum number of data bits that can be modulated on the DME uplink channel carrier frequency assuming a 10 dB SNR, is:
  • the maximum number of data bits per DME reply signal limit only considers receiver white noise and assumes perfect communication conditions and modulation schemes. However, the upper limit is typically not realized in the real world due to interference, multipath, and Doppler shifts among other practical degradation factors.
  • the DME transponder dead time method for transmitting data on the DME uplink is combined with the disclosed PRN pulse staggering coding method for transmitting data on the DME downlink (air-to-ground) to provide two-way data communications on DME channels.
  • the communication bandwidth or data rate of this embodiment is moderate, as discussed above.
  • another embodiment of the present invention narrows the width of the DME pulses (e.g., chip duration reduced) so that more symbols can be accommodated in the DME transponder dead time window.
  • the narrowing the DME pulses will widen the signal bandwidth (i.e. spreading the spectrum) and could cause potential interference on adjacent channels.
  • the power transmitted is lowered as the chip duration decreases and the coverage area of the DME transponder becomes smaller, reusing of adjacent-region frequency bands may make spreading of spectrum acceptable.
  • the DME transponder transmits a special pulse-pair sequence (i.e., heartbeat sequence) that is unique to each DME transponder.
  • a special pulse-pair sequence i.e., heartbeat sequence
  • DME transponders For DME transponders to communicate data to DME interrogators (i.e., aircraft) the previously discussed PRN pulse staggering coding is not suitable because the primary function of a DME transponder is to receive interrogation signals containing a pulse pair sequence, determine whether the received interrogation signal pulse pair sequence is valid and transmit a reply signal containing the received pulse pair sequence, as well as transmit its ID periodically. Deviating from existing DME operations will potentially degrade the performance of the DME system by lowering system capacity. However, the reduction of one target worth of capacity may be tolerable in existing DME systems to incorporate a new ground-to-air communication capability. The ground-to-air communication capability will offset the lost in DME system capacity by transmitting important data from the DME transponder to airborne targets (DME interrogators).
  • each DME transponder periodically transmits a heartbeat signal containing a special pulse-pair sequence unique to each DME transponder (a heartbeat signal sequence) at a predetermined time.
  • a DME interrogator receiving at least three heartbeat signals from three DME transponders can multilaterate its own position by simple receiving multiple DME transponders' heartbeat signals, correlating each received heartbeat signal with known heartbeat sequence patterns and determining the time of arrival of each heartbeat signal. Since each heartbeat signal is
  • the DME interrogator can determine its range to the DME transponder when the DME interrogator is time synchronized to UTC. If the aircraft is not time synchronized to UTC, a Time Difference of Arrival (TDOA) can be determined from the heartbeat signals of two DME transponders and a three dimensional position can be determined from at least three TDOAs determined the heartbeats received from at least four DME transponders. Note that when the altitude is known and only horizontal (two dimensional) position is to be solved, at least two ranges or two TDOAs are then required.
  • TDOA Time Difference of Arrival
  • out-of-band higher bandwidth embodiments require additional RF frequency spectrum resources to be allocated for each DME transponder, which is why these embodiments are categorized as out-of-band higher bandwidth embodiments as compared to the in-band lower bandwidth embodiments discussed in the previous sections.
  • Fig. 3(a) The current frequency reuse of available DME channels is depicted in Fig. 3(a).
  • a DME channel is being reused 13 times and a maximum of 24 times, as observed for channel#19 as shown in Fig. 3 (a).
  • the average distance between the DME stations that use identical DME channel and modes is 238 NM and a minimum of 128 NM for channel 21 as shown in Fig. 3(b).
  • each existing DME station may be assigned with at least one
  • a secondary DME channel is allocated for a group of DME transponders that are proximate to each other (i.e. several DME transponders in the same region share a single secondary DME channel).
  • the DME transponders sharing a common secondary DME channel define multiple communication sub-channels on the common secondary DME channel using previously discussed code spreading techniques, and use the multiple communication sub-channels for two-way communication between DME interrogators and DME transponders in the group of DME transponders sharing the common secondary DME channel. Since the common secondary channel can be dedicated entirely for communication purposes, different modulation and MAC schemes can be implemented on the secondary DME channel.
  • the data rate per each aircraft-ground communication sub-channel is determined by the total number of sub-channels that are established within the given bandwidth of the common secondary DME channel. In this case, it is obvious that the more DME stations that share a common secondary channel the lower the data rate each communication subchannel will be allocated.
  • a dedicated secondary DME channel is assigned to each DME
  • transponder for two-way communication between DME interrogators and the DME transponder.
  • the secondary DME channel communication network is implemented similar to a cellular phone network where DME transponders are the base stations and DME interrogators are the mobile users.
  • each DME station within a region is assigned with a dedicated secondary DME channel for data communication purposes.
  • the dedicated set of secondary channels are reused by other groups of DMEs in other regions. This is the well known "tile" pattern that is used when designing frequency reuse in a cellular network.
  • the seventh embodiment of the present invention several dedicated secondary DME channels are grouped into a single wider bandwidth secondary DME channel that is shared by a group of DME transponders.
  • the advantage of this embodiment is that the single wider bandwidth secondary DME channel enables wider-bandwidth modulation schemes to be used that would not work within the 1 MHz DME channel separation.
  • Examples of wider-bandwidth modulation schemes that can be implemented on a wider DME channel include Carrier Sense Multiple Access (CSMA) and Phase shift keying (PSK) such as used on VDL Mode 2, Self- organized Time Division Multiple Access (STDMA) such as used on VDL Mode 4, a combination of TDMA and CDMA based approaches, such as Cellular 3 G, and
  • OFDM based schemes such as IEEE 802.16.

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  • Engineering & Computer Science (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Remote Sensing (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Mobile Radio Communication Systems (AREA)

Abstract

La présente invention concerne la mise en œuvre de nouvelles possibilités de communications numériques utilisant des liaisons montantes et descendantes de télémétrie, sans entrer en concurrence avec le trafic existant des communications de télémétrie. L'invention propose ainsi des mises en œuvre intrabandes, en bas de bande passante, permettant de répartir de façon basique les données sur la totalité mise en œuvre du haut hors bande NAS de la bande passante, ce qui permet d'étendre en haut de bande passante la répartition de grandes quantités de données, de façon à offrir un cadre général complet permettant la mise en œuvre de communications de données utilisant des liaisons de télémétrie.
PCT/US2010/042232 2009-07-17 2010-07-16 Système et procédé pour communications de données utilisant des liaisons de transpondeurs de télémétrie Ceased WO2011009027A1 (fr)

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CN103592645A (zh) * 2013-11-22 2014-02-19 中国电子科技集团公司第五十四研究所 一种伪随机码调相连续波雷达速度模糊解算方法
WO2015152809A1 (fr) * 2014-04-01 2015-10-08 Utvecklingsavdelningen I Sverige Ab Procédé, système, transpondeur, et appareil de détection de position pour une mesure précise d'une position
WO2015152808A1 (fr) * 2014-04-01 2015-10-08 Great Innovations Stockholm Ab Système de détection d'objet photographique et procédé, et appareil de détection de position et transpondeur s'y rapportant
CN110824981A (zh) * 2019-10-23 2020-02-21 天津七六四通信导航技术有限公司 一种精密dme距离解算数字处理单元板及解算方法

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CN103592645A (zh) * 2013-11-22 2014-02-19 中国电子科技集团公司第五十四研究所 一种伪随机码调相连续波雷达速度模糊解算方法
WO2015152809A1 (fr) * 2014-04-01 2015-10-08 Utvecklingsavdelningen I Sverige Ab Procédé, système, transpondeur, et appareil de détection de position pour une mesure précise d'une position
WO2015152808A1 (fr) * 2014-04-01 2015-10-08 Great Innovations Stockholm Ab Système de détection d'objet photographique et procédé, et appareil de détection de position et transpondeur s'y rapportant
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CN110824981A (zh) * 2019-10-23 2020-02-21 天津七六四通信导航技术有限公司 一种精密dme距离解算数字处理单元板及解算方法

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