Simple passive/active proximity warning system

Claim 2

A proximity warning system for an Own station, comprising: (a) means for selectively enabling the production and transmission of interrogation messages at Own station at least in part in response to the SSR environment sensed at Own station; (b) means for producing from received interrogation messages transmitted by SSRs within operational range of said Own station and received reply messages transmitted by transponder-equipped Other stations in response to said SSR interrogation messages during a predetermined period following reception of each said interrogation message at Own station, a differential time of arrival value for each of said Other stations with respect to each of said SSRs; (c) means for producing from received reply messages transmitted by said Other stations in response to said interrogation messages from Own station during a predetermined period following transmission of each said interrogation message from Own station, a direct time of arrival value for each of said Other stations with respect to Own station; (d) means for selecting from among the several most recent time of arrival values produced by means (b) if any and by means (c) if any, the largest time of arrival value associated with each of said Other stations that has been substantially duplicated a predetermined number of times; and (e) means for producing a threat alert output in response to any time of arrival value selected by means (d) that is below a predetermined value.

Claim 3

The system set forth in claim 1 further comprising: (f) means responsive to an altimeter at Own station and to said received reply messages containing altitude information for producing a differential altitude value for each said identified Other station with respect to Own station; and (g) means for preventing means (e) from producing said threat alert output in response to time of arrival values associated with any of said Other stations whose differential altitude values are greater than a predetermined amount.

Claim 4

The system set forth in claim 2 further comprising: alarm device means for producing a threat alert in response to said threat alert output.

Claim 5

The system set forth in claim 3 wherein: means (a) includes a 1030 MHz interrogator; and means (b) includes a 1030 MHz receiver and a 1090 MHz receiver.

Claim 7

The system set forth in claim 5, further comprising: means for randomly varying said time between transmissions about a nominal value within finite predetermined limits to help minimize interference to and from other ATC systems.

Claim 10

The system set forth in claim 8 wherein said nominal time is above a value of about 5 milliseconds, thereby rendering said interrogation messages from Own station easily distinguishable from interrogation messages from SSR ground stations.

Claim 11

The system set forth in claim 8 wherein the nominal interval of time between consecutive sets of interrogation messages if any is at least about four seconds, thereby helping to minimize the amount of interference attributable to interrogation messages from Own station.

Claim 12

The system set forth in claim 8 wherein the number of consecutive interrogation messages within each set is in the range of 6 to 10.

Claim 13

The system set forth in claim 8 further comprising: means for randomly varying the time between consecutive interrogation messages within each set about a nominal value within finite predetermined limits to help minimize interference to and from other ATC systems.

Claim 14

The system set forth in claim 8 further comprising: means for randomly varying the time between consecutive sets of interrogation messages about a nominal value within finite predetermined limits to help minimize interference to and from other ATC systems.

Claim 15

The system set forth in claim 2 wherein means (a) enables the production and transmission of interrogation messages in one or more sets, and interrogation messages within each said set are alternated between mode A and mode C interrogation messages.

Claim 17

A proximity warning system for an Own station, comprising: (a) means for producing from received interrogation messages transmitted by SSRs within operational range of said Own station and received reply messages transmitted by transponder-equipped Other stations in response to said SSR interrogation messages during a predetermined period following reception of each said SSR interrogation message at Own station, a differential time of arrival value for each of said Other stations with respect to each said SSR; (b) means for producing from received reply messages transmitted by said Other stations in response to interrogation messages transmitted from Own station during a predetermined period following transmission of each said interrogation message from Own station, a direct time of arrival value for each of said Other stations with respect to Own station; (c) means for selecting from among the several most recent time of arrival values produced by means (b) if any and by means (a), the largest time of arrival value associated with each said Other station that has been substantially duplicated a predetermined number of times; (d) means for producing a potential threat output in response to any time of arrival value selected by means (c) that is below a predetermined value; (e) means for producing at least one set of interrogation messages at Own station in response to said potential threat output; and (f) means for producing a threat alert output when said potential threat output is not negated on account of direct time of arrival values produced by means (b).

Claim 18

A proximity warning system for an Own station, comprising: (a) means for producing from received interrogation messages transmitted by SSRs within operational range of said Own station and received reply messages transmitted by transponder-equipped Other stations in response to said SSR interrogation messages during a predetermined period following reception of each said SSR interrogation message at Own station, a differential time of arrival value for each of said Other stations with respect to each said SSR; (b) means for producing from received reply messages transmitted by said Other stations in response to interrogation messages transmitted from Own station during a predetermined period following transmission of each said interrogation message from Own station, a direct time of arrival value for each of said Other stations with respect to Own station; (c) means for selecting from among the several most recent time of arrival values produced by means (b) if any and by means (a), the largest time of arrival value associated with each said Other station that has been substantially duplicated a predetermined number of times; (d) means for producing a potential threat output in response to any time of arrival value selected by means (c) that is below a predetermined value; (e) means for producing at least one set of interrogation messages at Own station in response to said potential threat output; and (f) means for producing a threat alert output when said potential threat output is not negated on account of direct time of arrival values produced by means (b).

Claim 19

The system set forth in claim 16 further comprising: (g) means responsive to an altimeter at Own station and to said received reply messages containing altitude information for producing a differential altitude value for each said identified Other station with respect to Own station; and (h) means for preventing means (f) from producing said threat alert output in response to time of arrival values associated with any of said Other stations whose differential altitude values are greater than a predetermined amount.

Claim 20

A proximity warning system for an Own station, wherein the decision to transmit 1030 MHz interrogation messages is based at least in part upon passive detection of a potential threat through differential time of arrival techniques, said system comprising: (a) means for producing from received interrogation messages transmitted by SSRs within operational range of said Own station and received reply messages transmitted by transponder-equipped Other stations in response to said interrogation messages during a predetermined period following reception of each said interrogation message at Own station, differential time of arrival values for said Other stations with respect to each said SSR; (b) means for producing, from among the several most recent differential time of arrival values produced by means (a), a potential threat alert output when at least one of said Other stations appears to be, according to the largest differential time of arrival value associated therewith, within a predetermined range of Own station that defines at least in part when an Other station is deemed to be a threat; (c) control means for enabling the production and transmission of at least a plurality of 1030 MHz interrogation messages at Own station in response to said potential threat alert output; and (d) means for verifying from received reply messages transmitted by said Other stations in response to said interrogation messages from Own station whether said one of said Other stations is actually within said predetermined range, whereby the number of interrogation messages transmitted from Own station to determine whether any of said Other stations is an actual threat is minimized.

Claim 21

A proximity warning system for an Own station, wherein the decision to transmit 1030 MHz interrogation messages is based at least in part upon passive detection of a potential threat through differential time of arrival techniques, said system comprising: (a) means for producing from received interrogation messages transmitted by SSRs within operational range of said Own station and received reply messages transmitted by transponder-equipped Other stations in response to said interrogation messages during a predetermined period following reception of each said interrogation message at Own station, differential time of arrival values for said Other stations with respect to each said SSR; (b) means for producing, from among the several most recent differential time of arrival values produced by means (a), a potential threat alert output when at least one of said Other stations appears to be, according to the largest differential time of arrival value associated therewith, within a predetermined range of Own station that defines at least in part when an Other station is deemed to be a threat; (c) control means for enabling the production and transmission of at least a plurality of 1030 MHz interrogation messages at Own station in response to said potential threat alert output; and (d) means for verifying from received reply messages transmitted by said Other stations in response to said interrogation messages from Own station whether said one of said Other stations is actually within said predetermined range, whereby the number of interrogation messages transmitted from Own station to determine whether any of said Other stations is an actual threat is minimized.

Claim 22

The system set forth in claim 18, further comprising: (e) means for providing a threat alert output when said one of said Other stations is actually within said predetermined range.

Claim 23

An integrated proximity warning system for an Own station, comprising: (a) an active system portion having (1) interrogation decoder means for decoding SSR interrogation messages, (2) SSR environment detector and control mode selector means for automatically selecting one of a plurality of control modes in response to the number of decoded SSR interrogation messages received per unit time, and (3) 1030 MHz interrogator means for producing one or more sets of interrogation messages at any one of a plurality of transmission rates as determined by the selected control mode; and (b) a passive system portion having (1) means for receiving SSR interrogation messages transmitted by SSRs within operational range of said Own station when said Own station is within the main beam of an SSR and also when said Own station is within a side lobe of said main beam, (2) means for receiving reply messages transmitted by transponder-equipped Other stations in response to such SSR interrogation messages during a predetermined period following reception of each SSR interrogation message at said Own station, (3) means for receiving reply messages transmitted by said Other stations in response to interrogation messages from Own station during a predetermined period following transmission of each interrogation message at Own station, (4) means for identifying each of said Other stations according to its reply messages, (5) means for determining from said received SSR interrogation messages and said reply messages in response thereto a differential time of arrival value for each said identified Other station with respect to each said SSR, (6) means for determining from said reply messages in response to interrogation messages from Own station a direct time of arrival for each of said Other stations with respect to said Own station, (7) means for selecting the largest time of arrival value related to each said identified Other station from among those identities and corresponding time of arrival values that are substantially duplicated a predetermined number of times, and (8) means for producing a threat alert output in response to any such selected time of arrival value below a predetermined value.

Claim 24

An integrated proximity warning system for an Own station, comprising: (a) an active system portion having (1) interrogation decoder means for decoding SSR interrogation messages, (2) SSR environment detector and control mode selector means for automatically selecting one of a plurality of control modes in response to the number of decoded SSR interrogation messages received per unit time, and (3) 1030 MHz interrogator means for producing one or more sets of interrogation messages at any one of a plurality of transmission rates as determined by the selected control mode; and (b) a passive system portion having (1) means for receiving SSR interrogation messages transmitted by SSRs within operational range of said Own station when said Own station is within the main beam of an SSR and also when said Own station is within a side lobe of said main beam, (2) means for receiving reply messages transmitted by transponder-equipped Other stations in response to such SSR interrogation messages during a predetermined period following reception of each SSR interrogation message at said Own station, (3) means for receiving reply messages transmitted by said Other stations in response to interrogation messages from Own station during a predetermined period following transmission of each interrogation message at Own station, (4) means for identifying each of said Other stations according to its reply messages, (5) means for determining from said received SSR interrogation messages and said reply messages in response thereto a differential time of arrival value for each said identified Other station with respect to each said SSR, (6) means for determining from said reply messages in response to interrogation messages from Own station a direct time of arrival for each of said Other stations with respect to said Own station, (7) means for selecting the largest time of arrival value related to each said identified Other station from among those identities and corresponding time of arrival values that are substantially duplicated a predetermined number of times, and (8) means for producing a threat alert output in response to any such selected time of arrival value below a predetermined value.

Claim 25

The system set forth in claim 20 wherein: means (a)(2) further includes an input means for enabling the production of interrogations upon command in at least one of said control modes, and means (b) further includes means for producing a potential threat output in response to differential time of arrival values selected by means (b)(7) below said predetermined value associated with means (b)(8), said potential threat output being fed into said input means as said command.

Claim 26

A proximity warning system for an Own station, comprising: (a) means for selectively enabling the repetitive production of interrogation messages to be transmitted from Own station to nearby transponder-equipped Other stations in response to a sensed condition at Own station at one of a plurality of nominal transmission rates, and (b) means for randomly varying any such non-zero transmission rate about its nominal value within finite limits to help minimize interference to and from other ATC systems.

Claim 27

A proximity warning system for an Own station, comprising: (a) means for selectively enabling the repetitive production of interrogation messages to be transmitted from Own station to nearby transponder-equipped Other stations in response to a sensed condition at Own station at one of a plurality of nominal transmission rates, and (b) means for randomly varying any such non-zero transmission rate about its nominal value within finite limits to help minimize interference to and from other ATC systems.

Claim 28

The system set forth in claim 22 wherein said sensed condition at Own station is the approximate number of SSRs interrogating Own station.

Claim 29

The system set forth in claim 22 wherein said sensed condition at Own station is the approximate number of transponder-equipped Other stations in Own station's airspace.

Claim 30

The system set forth in claim 1 or 16, further comprising: means for automatically and inversely varying the power with which interrogation messages are transmitted from Own station in response to at least one sensed condition at Own station.

Claim 31

The system set forth in claim 25 wherein said one sensed condition at Own station is the approximate number of SSRs interrogating Own station.

Claim 32

The system set forth in claim 25 wherein said one sensed condition at Own station is the approximate number of transponder-equipped Other stations in Own station's airspace.

Claim 33

A proximity warning system at Own station, comprising: (a) means for selectively enabling the production of a set of interrogations to be transmitted from Own station in response to a sensed condition at Own station, said set having a nominal pulse repetition period between consecutive interrogations; and (b) means for randomly varying the pulse repetition periods between said consecutive interrogations about their nominal value within finite predetermined limits to help minimize interference to and from other ATC systems.

Claim 34

A proximity warning system at Own station, comprising: (a) means for selectively enabling the production of a set of interrogations to be transmitted from Own station in response to a sensed condition at Own station, said set having a nominal pulse repetition period between consecutive interrogations; and (b) means for randomly varying the pulse repetition periods between said consecutive interrogations about their nominal value within finite predetermined limits to help minimize interference to and from other ATC systems.

Claim 37

In a proximity warning system at an Own station, a method of controlling when to transmit 1030 MHz interrogation messages based at least in part upon passive detection of transponder-equipped Other stations through differential time of arrival techniques, comprising the steps of: (a) producing from received interrogation messages transmitted by SSRs within operational range of said Own station and received reply messages transmitted by transponder-equipped Other stations in response to said interrogation messages during a predetermined period following reception of each said interrogation means at Own station, differential time of arrival values for said Other stations with respect to each said SSR; (b) producing, from among the several most recent differential time of arrival values produced in step (a), a potential threat alert output when at least one of said Other stations appears to be, according to the largest differential time of arrival value associated therewith, within a predetermined range of Own station that defines at least in part when an Other station is deemed to be a threat; (c) transmitting at least one 1030 MHz interrogation message at Own station in response to said potential threat alert output; and (d) verifying, from received reply messages transmitted by said Other stations in response to said interrogation message from Own station, whether said one of said Other stations is actually within said predetermined range, whereby the number of interrogation messages transmitted from Own station to determine whether any of said Other stations is an actual threat is minimized.

Claim 38

In a proximity warning system at an Own station, a method of controlling when to transmit 1030 MHz interrogation messages based at least in part upon passive detection of transponder-equipped Other stations through differential time of arrival techniques, comprising the steps of: (a) producing from received interrogation messages transmitted by SSRs within operational range of said Own station and received reply messages transmitted by transponder-equipped Other stations in response to said interrogation messages during a predetermined period following reception of each said interrogation means at Own station, differential time of arrival values for said Other stations with respect to each said SSR; (b) producing, from among the several most recent differential time of arrival values produced in step (a), a potential threat alert output when at least one of said Other stations appears to be, according to the largest differential time of arrival value associated therewith, within a predetermined range of Own station that defines at least in part when an Other station is deemed to be a threat; (c) transmitting at least one 1030 MHz interrogation message at Own station in response to said potential threat alert output; and (d) verifying, from received reply messages transmitted by said Other stations in response to said interrogation message from Own station, whether said one of said Other stations is actually within said predetermined range, whereby the number of interrogation messages transmitted from Own station to determine whether any of said Other stations is an actual threat is minimized.

Claim 39

The method set forth in claim 30, further comprising the step of: (e) providing a threat alert output when said one of said Other stations is actually within said predetermined range.

Claim 42

The method set forth in claim 29 or claim 32, further comprising the steps of: producing, in response to an altimeter output at Own station and to each said received reply message containing altitude information, a differential altitude value for each said identified Other station with respect to Own station; and preventing the production of said threat alert output in response to time of arrival values associated with any of said Other stations whose differential altitude values are greater than a predetermined amount.

Claim 49

The method set forth in claim 35 or 36 wherein said sensed condition at Own station is the approximate number of SSRs interrogating Own station.

Claim 50

The method set forth in claim 35 or 36 wherein said sensed condition at Own station is the approximate number of transponder-equipped Other stations in Own station's airspace.