Communications: directive radio wave systems and devices (e.g. – Directive – Including a satellite
Reexamination Certificate
2000-01-10
2001-10-09
Phan, Dao (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Including a satellite
C342S357490, C342S062000
Reexamination Certificate
active
06300898
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to guidance systems. More specifically, the present invention relates to guidance for weapons systems using the Global Positioning System (GPS).
2. Description of the Related Art
The utility of the Global Positioning System for guidance applications is well recognized. The Global Positioning System is a network of satellites that transmits information in signals, which when received and decoded, allow a receiver to accurately fix its position within a coverage area. For military applications, GPS allows self-guided weapons to find targets with heretofore unknown degrees of accuracy.
Unfortunately, GPS guidance, which uses 10 watt signals from satellites in an 11,000 nautical mile orbit, is notoriously easy to jam with low power, low cost jammers scattered around a target area. As a large number of units would be used to defend high value targets, one by one destruction of the jammers would have a low payoff. If only a few remain operational, they can effectively jam incoming weapon systems.
At least two measures are being considered to provide an anti-jamming countermeasure for GPS guided vehicles. One measure involves the use of a nulling antenna system. In accordance with this approach, the vehicle is equipped with a number of antennas which point a null in the antenna radiation pattern at the source of the jamming signal. Though somewhat effective, this approach can be expensive as the number of jammers that can be nullified is one less than the number of antenna elements. Hence, the effectiveness of this limited approach is questionable if a large number of inexpensive jammers are used.
Thus, there is a need in the art for an effective anti-jamming countermeasure for GPS guided weapon systems.
SUMMARY OF THE INVENTION
The need in the art is addressed by the present invention which provides an improved missile guidance system. The system is designed to operate on GPS signals in an anti-jamming environment. The inventive system includes first, second and third airborne vehicles. A GPS receiver is mounted on each of the three vehicles to receive signals transmitted from spaceborne satellites. Each vehicle acts as a pseudo-satellite or ‘pseudolite’. The received GPS signals are processed to provide a first intermediate signal indicating the position of the vehicle. This signal is retransmitted from each vehicle and received by a GPS receiver mounted on a missile. The received intermediate signals from multiple pseudolites are processed in the missile to provide an output signal indicating the position thereof.
In a particular implementation, the position of each pseudolite is predicted and transmitted to the missile to remove the effect of transmission delay. The use of three pseudolites allows for the calculation of x, y position and time (t). A fourth pseudolite could be used to provide for x, y, z, and t determination onboard the missile. However, in the preferred embodiment, the missile is equipped with an altimeter for the purpose of ascertaining the elevation of the missile.
The pseudolites would be airborne in the vicinity of a target area. Because the pseudolites are relatively close to the targets compared to a satellite in an 11,000 nautical mile orbit and because the pseudolites are able to transmit a 100 watts of power or more, the signal strength may be improved by 50 or 60 decibels or more. To succeed as a jammer, a 1 watt jammer, successful against GPS satellites, would need 100,000 watts or 1 megawatt of power to succeed against aircraft carried pseudolites, which would not be feasible economically at the time of filing of the present application.
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Thomas A. Stransell, Jr., Global Positioning System, “RTCM SC-104 Recommended Pseudolite Signal Specification”.
Allan J. Brockstein, GPS-Kalman-Augmented Inertial Navigation System Performance, pp. 864-870.
Schneider Arthur J.
Small James G.
Benman William J.
Lenzen, Jr. Glenn H.
Phan Dao
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