Communications: directive radio wave systems and devices (e.g. – Radar ew – Eccm
Reexamination Certificate
2000-08-29
2003-10-28
Chin, Vivian (Department: 2682)
Communications: directive radio wave systems and devices (e.g.,
Radar ew
Eccm
C342S018000, C342S357490, C455S067150
Reexamination Certificate
active
06639541
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
The invention described herein may be manufactured and used by or for the government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.
FIELD OF THE INVENTION
The present invention pertains to a receiver system, in particular, a receiver with associated antenna positioned near a Global Navigation Satellite System (GNSS) receiver's antenna to allow autonomous detection, measurement, reporting and optional display of low-level interference.
BACKGROUND
Signals from Global Navigation Satellite Systems (GNSS), the most generally known being the NAVSTAR Global-Positioning System (GPS), are an important asset to systems in common use today, one example being aircraft navigation and control. Conventionally, GPS and inertial measurement units (IMUs) have been combined to provide more effective navigation with the GPS data used as reference for the IMU. This combination provides a synergistic result in that the effective bandwidth of the system can be optimally reduced, providing improved tracking.
In aircraft navigation, the precision available from GPS may even be exploited for instrument landings. For example, U.S. Pat. No. 5,311,194, Precision Approach and Landing System for Aircraft, issued to Brown, May 10, 1994, uses a pseudolite transmitter to provide three-dimensional position information to an aircraft using GPS in an automatic landing mode.
The aviation industry relies upon numerous navigation aids in order to take off, navigate enroute, and land aircraft safely. Such navigation aids (navaids) include, for example, the instrument landing system (ILS), very high frequency omni-directional range (VOR) system, and the like. The Navstar Global Positioning System (GPS) is accepted as an alternative to traditional navaids.
In a high-density airport environment requiring precision control of high performance aircraft in 3D, numerous single function airport systems have been developed over the years to support air traffic control needs. Precise landing navigation is provided by the Instrument Landing System (ILS), while airside navigation is provided by VOR/DMS, LORAN and NDB's. Air Traffic Control (ATC) surveillance is provided primarily through visual means, airport surface detection radar (ASDE), secondary surveillance radar, parallel runway monitoring radar, and, in some cases, primary radar.
With the advent of new multi-function technologies, less expensive, yet superior, performance is available. GNSS technologies and digital communications, coupled with low cost computers, are able to support ATC at airports of all sizes. Presently only the largest airports can justify the investment in a complement of dedicated single function systems, while a majority of smaller airports provide only part of an automated landing capability, if any.
GPS is well suited for use in global flight operations and flight operations from remote or unprepared airstrips. GPS accuracy is sufficient for all phases of flight, including non-precision approaches. Thus, GPS receivers are embraced by the military and those civilian carriers that require accurate, reliable navigation information in remote locations. GPS alone, however, is not accurate for vertical guidance in precision approach and landings.
A system that provides sufficient accuracy in the vertical dimension to allow precision approaches and landings has been proposed in U.S. Pat. No. 5,952,961, Low Observable Radar Augmented GPS Navigation System, issued to Denninger, Sep. 14, 1999. The GPS receiver determines velocity from measurements of the carrier phase and Doppler frequency. Accuracy of the GPS solution is limited by the errors on the GPS signals and the geometry established by the positions of the satellites relative to the user. Generally, neither the precision nor the coverage of the standard positioning service provided by the 21-satellite constellation meets the requirements for a precision approach and landing system.
Additionally, both Differential GPS (DGPS) and Integrity Beacon Landing System (IBLS) do not function in the event GPS signals are lost, jammed, interfered with, or otherwise unavailable. Both require received GPS signals to provide augmented positioning accuracy. Further, neither adds redundancy to the navigation systems already present onboard an aircraft. DGPS and IBLS augment an existing GPS receiver during the approach and landing phases rather than provide a separate source of navigation information. Thus, use of GPS in providing an ATC function is the only capability that may be universally available.
Because of increased. reliance on GPS, any interference is intolerable in particularly critical applications such as instrument landings. Further, the combination of low GNSS signal power levels, operating frequencies in L band, and use of wide bandwidth noise signals makes location of interference sources difficult. However, the interference source must be located to counter jamming or employ methods to attenuate unintentional interference.
GPS can provide sufficient accuracy to meet precision approach and landing system requirements using the GPS carrier phase data to solve for the aircraft's position. This method is termed “Kinematic GPS” or “Carrier-Ranging.” GPS carrier measurements from a ground-based reference receiver and the airborne receiver are processed to solve for the precise relative position of the aircraft with respect to the ground facility. Real-time positioning accuracy of <10 cm possible using kinematic GPS. This is sufficient to meet CAT I (i.e., ≧200 ft visibility), II (i.e., 50-200 ft, typically 100 ft visibility), and III (0-50 ft) precision approach accuracy requirements. However, the GPS satellite constellation does not provide sufficient coverage and redundancy to meet these operational requirements for a precision approach and landing system.
Another solution augments GPS satellite measurements with a range observation from a ground-based transmitter, i.e. a pseudolite. Pseudolites that broadcast a signal at the same frequency (1575.42 MHz) as GPS satellites are proposed so that the aircraft receiver can process this measurement as though it were another satellite. However, a pseudolite with this signal format will act as a jammer to users operating near the transmitter, thereby preventing the receiver from receiving clear signals from the GPS satellites. Thus, interference renders this technique unacceptable for use in a precision approach and landing system. A time-slotted signal structure for a pseudolite addresses the above problem although this pseudolite signal will interfere with satellite signals when used at close range to the receiver. Moreover, the time-slotted or pulsed signal format does not allow contiguous carrier phase measurements to be made of the pseudolite signal. This means that the pseudolite signal cannot be included in the carrier-ranging navigation solution, and the time slotting also affects the use of the pseudolite signal as a high-rate communications link for differential corrections.
To avoid the possibility of this pseudolite signal jamming the satellite signals, it can be broadcast at a different frequency from that of the GPS satellites. This is the approach described in U.S. Pat. No. 4,866,450, Advanced Instrument Landing System, issued to Chisholm, Sep. 12, 1989, wherein a ranging reference signal, modulated with correction data, is broadcast from a ground-based transmitter synchronized to GPS time. However this signal is time-slotted. Thus, it has the same disadvantages as the pseudolite design described in the SC-104 reference, supra. Another disadvantage of the method described in the '450 patent is that a second receiver is required in the aircraft to process the ground station signals broadcast at the second frequency. The timing and frequency offsets between the GPS and second receiver will introduce a significant offset of range measurements made by the two receivers. Although the additiona
Egan Mark P.
Quintana Alvin L.
Baugher Jr. Earl H.
Chin Vivian
Foster Laura R.
Pan Yuwen
The United States of America as represented by the Secretary of
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