CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority from Japanese Patent Application No. 2017-236559 filed on Dec. 11, 2017, the entire contents of which are hereby incorporated by reference.

BACKGROUND

1. Technical Field

Examples of the present invention relate to a deceiving signal detection system, a deceiving signal detection method, a deceiving signal detection program, a navigation system, and a navigation method.

2. Related Art

A navigation system using the Global Positioning System (i.e., GPS) operated by the United States of America has been known as a famous system for guiding a mobile body such as an aircraft to a destination. A GPS-based navigation system is a system for detecting the spatial position of a mobile body on which a GPS receiver is mounted by receiving radio waves from a plurality of GPS satellites with a GPS receiver. The official name of GPS satellites is NAVSTAR (i.e., Navigation Satellite with Time and Ranging).

Since GPS satellites fly at an altitude of about 20,000 km, the strength of GPS signals is weak compared to the strength of radio signals for other data links. Therefore, a GPS signal may be difficult to receive when a radio disturbance occurs in the ionosphere due to a solar flare or when an interfering radio wave is transmitted as well as when a failure occurs in the GPS satellite. Radio jamming due to deceiving signals disguised as GPS signals has also been reported. To address this, systems for preventing interference during navigation using GPS signals have been proposed in Japanese Unexamined Patent Application Publication (Translation of PCT Application) (JP-T) No. 2006-513084.

Global Navigation Satellite Systems (i.e., GNSS) using artificial satellites, such as GPS, includes other systems such as Russian GLONASS (i.e., Global'naya Navigatsionnnaya Sputnikovaya Sistema) and the Galileo planned by the European Union. More overly, a navigation satellite system (i.e., NSS) that covers a particular region are referred to as RNSS (i.e., Regional Navigation Satellite Systems).

Currently, many mobile navigation systems, such as aircrafts, rely on GPS. Therefore, development of a navigation system that does not rely on a navigation system using GPS has been considered.

As a specific example, the German Aerospace Center (DLR: Deutsches Zentrum fuer Luft- and Raumfahrt) has proposed a navigation system called LDACS-NAV using L-band Digital Aeronautical Communications System (LDACS).

LDACS is a high-speed data link system using radio wave signals wirelessly transmitted from a base station installed on the ground, and the LDACS-NAV is a navigational system for receiving navigation signals, being wirelessly transmitted from the base station installed on the ground, by a mobile body such as an airplane, so as to specify the spatial positions including latitude, longitude, and altitude of the mobile body based on the received navigation signals.

In LDACS, radio wave signals in a frequency band different from the frequency band of GPS signals is used. Therefore, LDACS-NAV is expected to be an alternative to GPS-based navigational systems when GPS satellites fail or when solar flares cause radio disturbances in the ionosphere, as well as when GPS deceiving signals are transmitted.

In addition to LDACS-NAV, a navigation system using distance-measuring apparatus (DME), a navigation system using Pseudolite (PL), and the like have been proposed.

DME is equipment that performs two-way communication for transmitting radio wave signals in response to requests from aircrafts and is installed on the ground. By measuring the time taken for the radio wave signal transmitted from the DME to reach the aircraft, the distance between the aircraft and the DME installed on the ground may be measured. Therefore, the spatial position of an aircraft may be specified based on radio wave signals transmitted from a plurality of DMEs.

On the other hand, PL is equipment that wirelessly transmits a PL signal similar to a GPS signal as a radio wave signal, and is installed on the ground. On the other hand, PL is equipment that wirelessly transmits a PL signal similar to a GPS signal as a radio wave signal, and is installed on the ground. Therefore, the spatial position of the aircraft may be specified based on PL signals transmitted from a plurality of PLs.

SUMMARY OF THE INVENTION

An aspect of the present invention provides a deceiving signal detection system including: a first antenna, a second antenna, and a signal processor. The first antenna is configured to receive four or more multiple navigation signals. Each of the multiple navigation signals indicates a transmitting position and a transmitting time of the each navigation signal. The second antenna is configured to receive the multiple navigation signals. The signal processor is configured to determine whether four or more multiple radio wave signals that are received by the first antenna and the second antenna and each indicate a transmitting position and a transmitting time of the each radio wave signal are the multiple navigation signals or deceiving signals.

An aspect of the present invention provides a navigation system including the above-described deceiving signal detection system. The signal processor is detects the position of the mobile body on a basis of the multiple navigation signals.

An aspect of the present invention provides a deceiving signal detection method. The method includes receiving at a first antenna multiple four or more radio wave signals. Each of the radio wave signals indicates a transmitting position and a transmitting time of the each radio wave signal. The method includes receiving the multiple radio wave signals at a second antenna. The method includes determining whether the multiple radio wave signals are navigation signals or deceiving signals on a basis of the multiple radio wave signals received by the first antenna and the multiple radio wave signals received by the second antenna.

An aspect of the present invention provides a non-transitory storage medium that includes a deceiving signal detection program embodied in the storage medium. The deceiving signal detection program causing, when executed by a computer the computer to implement a method. The method includes obtaining multiple four or more radio wave signals received with a first antenna. Each of the multiple radio wave signals indicates a transmitting position and a transmitting time of the each radio wave signal. The method includes obtaining the multiple radio wave signals received with a second antenna. The method includes determining whether the multiple radio wave signals are navigation signals or deceiving signals on a basis the multiple radio wave signals received by the first antenna and the multiple radio wave signals received by the second antenna.

An aspect of the present invention provides a navigation method includes receiving at a first antenna disposed in a mobile body multiple four or more radio wave signals. Each of the multiple radio wave signals indicates a transmitting position and a transmitting time of the each radio wave signal. The method includes receiving the multiple radio wave signals at a second antenna disposed in the mobile body. The method includes determining whether the multiple radio wave signals are navigation signals or deceiving signals on a basis of the multiple radio wave signals received by the first antenna and the multiple radio wave signals received by the second antenna. The method includes detecting a position of the mobile body on a basis of the multiple radio wave signals determined to be navigation signals.

An aspect of the present invention provides a deceiving signal detection system including: a first antenna, a second antenna, and circuitry. The first antenna is configured to receive four or more multiple navigation signals. Each of the multiple navigation signals indicates a transmitting position and a transmitting time of the each navigation signal. The second antenna is configured to receive the multiple navigation signals. The circuitry is configured to determine whether four or more multiple radio wave signals that are received by the first antenna and the second antenna and each indicate a transmitting position and a transmitting time of the each radio wave signal are the multiple navigation signals or deceiving signals.

