Automatic dependent surveillance system secure ADS-S

• US 7,876,259 B2
• Filed: 11/01/2007
• Issued: 01/25/2011
• Est. Priority Date: 11/06/2006
• Status: Expired due to Fees

• Current Assignee: Leonard Schuchman
• Original Assignee: Leonard Schuchman
• Inventors: Schuchman, Leonard
• Primary Examiner(s): Gregory; Bernarr E
• Application Number:
  US11/979,363
• Publication Number:
  US 20080266166A1
• Time in Patent Office: 1,181 Days
• Field of Search: 342 29- 51, 342/175, 342/195, 701/1, 701 3- 18, 701120-122, 701/200, 701/207, 701213-216, 701/300, 701/301, 709/246, 713/150, 713/168, 380/255, 380 28- 30, 380/287, 380/59, 380/277, 380 44- 47
• US Class Current: 342/37
• CPC Class Codes: G07C 5/008 communicating information to a remotely located station transmission systems for measured values G08C
• CPC Class Codes: G07C 5/085 using electronic data carriers
• CPC Class Codes: G08G 5/0013 with a ground station
• CPC Class Codes: G08G 5/0082 for monitoring traffic from a ground station radar or analogous systems specially adapted for traffic control G01S13/91

Abstract

An air traffic control automatic dependent, WAAS/GPS based, surveillance system (ADS), for operation in the TRACON airspace. The system provides encryption protection against unauthorized reading of ADS messages and unauthorized position tracking of aircraft using multilateration techniques. Each aircraft has its own encryption and long PN codes per TRACON and transmit power is controlled to protect against unauthorized ranging on the ADS-S aircraft transmission. The encryption and PN codes can be changed dynamically. Several options which account for available bandwidth, burst data rates, frequency spectrum allocations, relative cost to implement, complexity of operation, degree of protection against unauthorized users, system capacity, bits per aircraft reply message and mutual interference avoidance techniques between ADS-S, ADS-B Enroute and Mode S/ATCRBS TRACON are disclosed. ADS messages are only transmitted as replies to ATC ground terminal interrogations (no squittering). Derivative surveillance backup systems provide an anti-spoofing capability.

Claims

1. In an automatic secure dependent surveillance system (ADS-S) for protecting communications between a ground terminal connected to a terminal radar approach control (TRACON) control center and aircraft within an airspace controlled by the TRACON control center, said airspace hereinafter referred to as the TRACON, the improvement wherein:

said ground terminal is an ADS-S radio frequency (RF) ground terminal including an antenna having a data rate capability in the range of megabits per second per beam for respectively transmitting ground-to-air messages and receiving air-to-ground messages between said ground terminal and said aircraft within the TRACON, and

said ground terminal is connected to an encryption/decryption processor arranged such that each one of said ground-to-air and air-to-ground messages within the TRACON is individually encrypted by providing a unique code or code state for each aircraft to protect against unauthorized reading of the messages.

2. An ADS-S system according to claim 1, wherein aircraft within the TRACON transmit messages only in response to TRACON ground control ADS-S messages, and wherein the aircraft transmit “

automatic dependent surveillance-broadcast”

(ADS-B) messages in all other airspace, said ADS-B messages being transmitted by the aircraft in the other airspace to ground control and to all aircraft within a vicinity of the aircraft in the other airspace.

3. The AD S-S system according to claim 2, further comprising a plurality of derivative secure surveillance backup systems of which any one is achieved by:

a) using the ADS-S terminal to perform two way ranging on the ADS-S reply, estimating bearing using monopulse detection, and reading the ADS-S message for the altimetry reading;

b) utilizing a backup navigation system having aircraft reply to a ground interrogation transmitting, via an ADS-S formatted reply, the backup navigation positional information;

or

c) multilateration on an ADS-S reply to an ADS-S ground interrogation.

4. An ADS-S system according to claim 2, wherein an independent PN spread code is provided for each aircraft to place message signals under a noise floor and eliminate threats from a multilateration system which takes transmissions from aircraft within the TRACON and utilizes it to measure the range from multiple sites by unauthorized users providing them aircraft ranging and tracking information.

5. An ADS-S system according to claim 4, wherein said system ensures that the signal is under the noise floor by utilizing PN code spreading, receiver antenna gain or beam width, and aircraft radio reply power control.

6. An ADS-S system according to claim 4, wherein the system is further adapted to implement said PN codes in an FDMA structure with one aircraft link per FDMA channel.

7. An ADS-S system according to claim 4, wherein the system utilizes a base PN code which has a code chip cycle that is at least as long as the GPS P code chip cycle.

8. An ADS-S system according to claim 7, wherein the system is adapted to generate a sequence of PN code generated binary digits, over a length of the message, whose sequence of binary digits is extracted from the base PN code and whose sequence start time is randomly selected with the base PN code.

9. An ADS-S system according to claim 4, wherein the system further randomizes knowledge of code start time by having the code start time randomized for each air-to-ground link by a random reply time selected within a data bit interval.

10. An ADS-S system according to claim 4, wherein the system adds information bits to each air-to-ground encrypted message, said information bits providing the aircraft with its next PN code generator state.

11. An ADS-S system defined in claim 4, wherein said TRACON control center adds selection of FDMA codes per beam and PN code generation functionality to generate PN code sets, and to demodulate, decode and decrypt all FDMA codes per beam and all beams that are received simultaneously, each said ground terminal being adapted to select PN code states, encryption and decryption scramble and unscramble sequences, and frequency channel assignments.

12. An ADS-S system according to claim 4, wherein an aircraft radio adds to the radio digital signal processor the ability to dynamically update the PN code state and generate PN codes on the transmitted message.

13. An ADS-S system according to claim 4, wherein (a) an aircraft radio that is adapted to support ADS-S, Enroute ADS-B and Mode S/ATCRBS radio has only one analog receive channel for a three-surveillance system, and (b) the RF output has a switch for controlling ADS-S transmissions that require a tuned radio pass band filter and a power controlled amplifier, and ADS-S transmission that require an ADS-B and Mode S/ATCRBS amplifier that includes a digital signal processor to digitally generate PN codes and decrypt and encrypt messages.

14. An ADS-S system according to claim 1, wherein the rate capability is achieved by utilizing an entire allocated bandwidth to generate a near continuous data rate.

15. An ADS-S system according to claim 1, further comprising:

a network of aircraft within the TRACON, each utilizing a multifunctional ADS-S, ADS-B, and Mode S/air traffic control radar beacon system (Mode S/ATCRBS) aircraft terminal and all operating within the same air traffic control L band (ATC L Band) frequency band allocation,

wherein said antenna is a multi beam phased array antenna;

wherein said TRACON control center includes a central TRACON control center which controls and manages said network of aircraft; and

wherein the ADS-S system further comprises a global positioning system (GPS) clock system to ensure a time synchronization between Enroute ADS-B and ADS-S transmissions and spatial diversity between Mode S/ATCRBS and ADS-S transmissions such that mutual interference is minimized.

16. An ADS-S system according to claim 15 that implements an L beam state from a possible M beam multi beam ADS-S ground antenna, that iterates over all states to cover all M beams an equal number of times and then repeats the cycle so that each aircraft in each beam receives at least one ADS-S encrypted message per cycle, wherein each aircraft receives up to two messages per beam state and wherein an aircraft replies to one or two messages per beam state.

17. The ADS-S system according to claim 15, wherein each aircraft requires individual decryption and encryption codes so that no unauthorized person listening to either the air to ground link or the ground to air link will decode and read the message, thereby preventing terrorists from using the transmitted position information to accurately target aircraft within the TRACON.

18. An ADS-S system as defined in claim 17, wherein the encryption/decryption code scrambles the order of the data bit sequence equal to 2^N, where N is equal to the message data length or is some integer fraction of the message data length.

19. An ADS-S system according to claim 18, wherein a transmitted ADS-S message of length N utilizing an encrypted code of length M is then decrypted by the receiver in the ground terminal or a receiver on the aircraft by iterating over each set of M decrypted bits until the entire N bit message is unscrambled.

20. An ADS-S system according to claim 19, wherein said TRACON control center transmits, via the ADS-S ground terminal, an air-to-ground individualized encrypted message to each aircraft as frequently as every message, which encrypted message includes information bits providing the aircraft with:

a) its next individual decryption M code bit delay sequence allowing the unscrambling of a message,

b) its next individual encryption M bit delay sequence which scrambles the reply message.

21. An ADS-S system according to claim 15, wherein ADS-S secure messages are generated and received, via the ADS-S multi beam ground terminal, by the TRACON control center for improved centralized air traffic control functionality, said ADS-S secure messages including aircraft transmitted GPS positional messages which provide a most accurate GPS aircraft position for separation assurance, metering and spacing and collision avoidance.

22. An ADS-S system according to claim 15, wherein said system is implemented, via the multi beam ADS ground antenna, on a 1030 MHz ground to air link within an 8 MHz bandwidth and on a 1090 MHz air to ground link within a 6 MHz bandwidth, wherein the system minimizes interference between ADS-B Enroute transmissions, Mode S/ATCRBS transmissions and ADS-S transmissions by (a) synchronizing ground terminal and aircraft clocks to spatially separate ADS-S and Mode S transmissions and (b) time interleaving to separate ADS-B transmissions from ADS-S transmissions.

23. An ADS-S system according to claim 15, wherein said TRACON control center utilizes digital implementation functionality to demodulate, decode and decrypt (a) all aircraft messages received per beam, and (b) all beams that are received from aircraft simultaneously, and to transmit (a) all messages that are modulated, coded and encrypted for transmission to aircraft per beam, and (b) all beams that are transmitted simultaneously.

24. An ADS-S system according to claim 15, wherein an aircraft terminal utilizes a digital radio with a common processor to support ADS-S, ADS-B and Modes/ATTCRBS functionality including encryption/decryption.

25. An ADS-S system according to claim 15, which partitions a pilot'"'"'s ADS computer between a ground element and an airborne element, the ground element receiving all ADS-S messages within the TRACON via the ground multi beam antenna and determining if an aircraft is required to perform a navigation separation assurance, collision avoidance or metering and spacing maneuver, wherein when such a maneuver is determined to be required, a ground computer transmits a secure message via the ADS-S ground terminal that allows the pilot to perform area navigation separation assurance, metering and spacing and collision avoidance.

26. A method of saboteur-proofing an automatic dependent surveillance system, said system utilizing an air traffic control (ATC) augmented global positioning system (GPS), Galileo system, or both a GPS system and a Galileo system, to transmit positional information, said method comprising the steps of imposing an encryption system on ground to air and air to ground messages within TRACON airspace controlled by a TRACON control center;

implementing PN codes in an FDMA communication structure with one aircraft link per FDMA channel; and

imposing on each aircraft;

a) its next decryption N code bit state, wherein the bit state when utilized unscrambles decrypted message and its correlated encryption state, and scrambles the order of the ADS-S reply messages,

b) its next frequency reply channel,

c) its next PN code generator restart k bit register state,

d) a randomized delay of the reply to within a data bit interval, wherein randomized bits are provided for the four elements of encryption codes, PN codes, reply start time and FDMA channel selection in a dynamic and secure manner, and

wherein said TRACON control center controls a power level and each aircraft in an airspace of the TRACON control center transmits its ADS-S signal so that the power level of all ADS-S reply transmissions arrive at the TRACON control center at about the same power level.