Session A1: GNSS STATUS, CONTROL AND SPECTRUM MANAGEMENT
Paper #1

SPECTRUM ISSUES: POTENTIAL IMPACT FOR SPECTRUM-BASED SYSTEMS:
S.L. Frodge, U.S. Dept. of Transporation

Radionavigation systems such as the Global Positioning System (GPS) are spectrum-based. Of great concern for any spectrum-based system is interference and to what degree, if any, interference can be tolerated and still have operational requirements met. Regulation can and will affect spectrum systems. The multi-national International Telecommunications Union (ITU) holds the World Radio Conference (WRC) every 2-4 years. Decisions made at the WRC can potentially impact spectrum-based systems around the world. Further, each sovereign nation has its own structure in place to regulate such issues. Proposals for new technologies or new uses of spectrum can seek to use already used spectrum. GPS and radionavigation spectrum is not immune from such proposals going forward and taking spectrum away from these important uses. For example, at WRC-2000, the Mobile Satellite Service (MSS) proposed to share the GPS L1 spectrum. Currently, International Mobile Telephony (IMT)-2000 and ultra-wideband (UWB) are two examples of proposals that may impact radionavigation spectrum. The MSS proposal for sharing was ultimately defeated, though it was a hard fought and resource-draining effort. The IMT-2000, UWB and other current proposals and others point out how spectrum protection requires an ever-constant vigilance, even for spectrum supporting safety-of-life systems. This paper will provide background and insight into these processes and current issues.
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Session A1: GNSS STATUS, CONTROL AND SPECTRUM MANAGEMENT
Paper #2

TESTING AND RESEARCH ON INTERFERENCE TO GPS FROM UWB TRANSMITTERS:
M. Luo, M. Koenig, D. Akos, S. Pullen, P. Enge, Stanford University; B. Erlandson, Collins/ RTCA; S. Frodge, U.S. U.S. Dept. of Transporation

Ultra-Wideband (UWB) signal transmission is a potentially promising technology that is defined by a large fractional bandwidth. Most UWB systems are based on very short pulses of radio frequency energy. Because these systems offer excellent multipath immunity, they may find application in obstruction-rich environments. UWB technology has potential in a variety of applications, including communication and ranging, and is expected to see increased civil use in the future. Since signals from GPS satellites have very low power levels (-130 dBm or -160 dBW) near the surface of the earth, potential interference from UWB to GPS receivers (and therefore to GPS-based systems such as aeronautical safety-critical flight systems) is a serious concern. Thus research and testing of this possible interference source is necessary because GPS has a pivotal role in so many critical systems that the public depends upon for its safety and welfare.

In interference testing, pseudorange measurement accuracy is the primary metric of choice for aviation receivers. The most demanding applications, such as aircraft precision approach, operations require one-sigma pseudorange errors of 15 centimeters or less. Acquisition time is the metric of choice for land users, because emergency vehicles may need to quickly acquire the GPS signal after signal loss due to buildings, tunnels, or other obstructions. These users need to acquire the GPS signals and develop a new position estimate before the vehicle moves behind the next obstruction.

The majority of the tests described in this paper measured UWB impact on the accuracy and loss-of-lock performance of a high-grade GPS aviation receiver. A smaller test set measured UWB impact on the loss-of-lock performance for two different receivers: the original aviation receiver as well as a low-cost OEM receiver. This OEM receiver is similar to the ones that will find application in cell phones and therefore will deliver E-911 location information in accord with the FCC mandate for such service. Finally, an additional test set was designed to measure UWB impact on the signal acquisition performance of a third receiver, which was a high-grade, general-purpose GPS receiver. In all tests, the UWB interference impact relative to broadband-noise was measured. We have derived a noise equivalence factor that measures the UWB power level that causes a specified interference effect relative to the broadband-noise power level that causes the same effect. These tests are crafted to provide input to a separate process that considers the operational scenarios that might place UWB and GPS equipment in proximity to each other.

We found that UWB interference to GPS can be successfully analyzed using this noise equivalence factor. The determination of this factor is repeatable and corresponds to the results of theoretical analyses. The noise equivalence factor is a strong function of the UWB signal parameters and varies most strongly with the UWB pulse repetition frequency (PRF) and the spectral location of any discrete UWB spectral lines relative to the GPS signal. Low PRFs can yield noise equivalence factors much less damaging than broadband noise. High PRFs with discrete spectral lines falling within the GPS band can be significantly more damaging than broadband noise. In fact, if these discrete spectral lines fall on top of significant GPS C/A code lines, GPS receivers may lose lock at much lower interference levels than would otherwise be the case. This is a very damaging event to GPS users; thus UWB signals must be designed to eliminate this possibility.

Implementation of a various of band-reject filter designs are possible means of improving the compatibility of GPS and UWB. A GPS L1 notch filter and various highpass filters of different depths and rates are being analyzed and tested. The impact of such filters on UWB signal quality is also being evaluated. In addition to PRFs, the interference of UWB to GPS also strongly depends on dithering codes or modulation. A variety of dithering codes or modulations are being analyzed and compared. A set of validation tests will be done to verify the results of these analyses. The goal of this work is eliminating or mitigating the spectral lines in the GPS band to avoid the loss-of-lock problem that we discovered.
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Session A1: GNSS STATUS, CONTROL AND SPECTRUM MANAGEMENT
Paper #3

GPS RECEIVER SUSCEPTIBILITY TO ULTRA-WIDEBAND RFI: TEST RESULTS AND RFI LINK ANALYSES:
R. Erlandson, Rockwell Collins; A.J. Van Dierendonck, AJ Systems

Abstract currently not available.
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Session A1: GNSS STATUS, CONTROL AND SPECTRUM MANAGEMENT
Paper #4

IMPLEMENTATION OF NEW GPS PERFORMANCE STANDARDS:
R. Conley, Overlook Systems Technologies Inc.

The removal of Selective Availability (SA) is old history now, but we are still dealing with the implications of the SA decision on the management of GPS. The U.S. Department of Defense has been working internally and with U.S. civil government agencies since April 2000 to develop new performance standards in the absence of SA. The difficulties encountered in the process have occurred on many levels: technical, operational and institutional. The process has been difficult specifically because the U.S. government is committed to providing the best possible product to the international community.

The purpose of this paper is to provide a status of the performance standard development project, in the context of the complexities involved in development and implementation. The paper provides a brief history of actual performance, and discusses the evolution of GPS management philosophy as the program became more successful. The paper then deals with the specific considerations involved in defining sustainable performance standards, and how those considerations have shaped the DoD?s perspective on providing an international utility. Some of these considerations are:

- Organizational roles and responsibilities for managing all aspects of the GPS program within the U.S. government
- synchronizing national policies with operational capabilities
- The nature of 'assured' performance as it relates to precedence set by other utilities
- Relationship between current system performance, performance specifications, and new system requirements
- Constellation sustainment policies, to include launch and satellite disposal
- Satellite maintenance and downtime management policies
- Constellation User Range Error (URE) management policies
- Anticipation and mitigation of service degradation
- Service failure detection and response procedures
- Performance assessment and reporting procedures

The paper ends with a definition of the standards recommended for adoption by the U.S. government, along with a description of the implementation process.
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Session A1: GNSS STATUS, CONTROL AND SPECTRUM MANAGEMENT
Paper #5

THE INTERAGENCY FORUM FOR OPERATIONAL REQUIREMENTS:
J.W. Lavrakas, Overlook Systems Technologies, Inc.; H. Skalski, U.S. Dept. of Transportation

With the increased emphasis on civil involvement following the Presidential Decision Directive on GPS in March 1996 and the consequent formation of the Interagency GPS Executive Board, there has been a push to consolidate the process for defining GPS operational requirements that incorporate military and civil needs. In 2000 an interagency process for operational requirements was developed in response to OMB direction and the DoD/DOT MOA, Annex 4. This was documented in an Interagency Requirements Plan (IRP). The purpose of the process was (1) to identify how DoD and DOT future GPS requirements would be validated and (2) to develop process to integrate unique civil requirements into the DoD GPS Program. The IRP provides the necessary guidance and authority in describing the roles and responsibilities for the IROC, IRB, and IFOR participation in the GPS program. It is intended to supplement the provisions of the FY-01 Office of Management and Budget (OMB) Pass-back, and GPS National Policy prescribed in the Presidential Decision Directive, NSTC-6, March 1996.

Representatives of Headquarters Air Force Space Command, Requirements Directorate for Navigation, AFSPC/DRN and the DOT Office of the Secretary Liaison to AFSPC have developed an approach that would ensure execution of existing military and civil requirements validation processes, while providing a coordinated effort between agencies.

Up until now, the GPS requirements processes have been separated between a DoD-only process and a DOT-only process. Under the new interagency format, both processes will operate side-by-side in a cooperative manner to ensure that both military and civil objectives are met. This is done by the Interagency Requirements Oversight Committee, co-chaired by the Vice Chairman of the Joint Chiefs of Staff (VCJCS), and the DOT Assistant Secretary for Policy. See Figure 1.

(ION DATABASE ACCEPTS TEXT ONLY)

Figure 1. Interagency Requirements Process

The IRP creates a new entity called the Interagency Forum for Operational Requirements, whose purpose is to receive and process new operational requirements, and to clarify existing requirements. It consists of representatives from both the military and civil communities, and ensures that proposed new operational requirements address all necessary military and civil issues before they are submitted to their respective processes for validation.

This paper describes the IFOR, its origins and purpose, and its current status. This information will be of interest to anyone who is involved in GPS policy, modernization, acquisition, or implementation.
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Session A1: GNSS STATUS, CONTROL AND SPECTRUM MANAGEMENT
Paper #6

AUSTRALIAN ISSUES IN GNSS APPLICATION: OPERATIONS OF THE AUSTRALIAN GNSS COORDINATION COMMITTEE (AGCC):
D. Sinnott, K. McPherson, Cooperative Research Centre for Sensor Signal and Information Processing, Australia

Australia typifies many nations that are clients of GNSS services, markets for internationally-sourced GNSS ground-sector equipment, developers of niche GNSS equipment and users of wide and local area augmentation systems. Such nations have limited ability to influence policies of the owner/operator GNSS nations and must work within these limitations to maximise the national benefit GNSS technology can deliver.

In Australia the application of GNSS has proceeded in a free-market way, with little coordination between users. While this may be of little consequence to users of basic positioning services for non-critical applications it can lead to inefficiency, unnecessary cost, sub-optimal system design and lost opportunities in applying augmentation services. Further, heightened national awareness of the benefits accessible through GNSS application, and of vulnerabilities to which users could be exposed, is best promoted through a coordinated national-level approach.

Australia's Minister for Transport and Regional Services has established the Australian GNSS Coordination Committee (AGCC) to address these issues. The announcement of the formation of the AGCC, on 26 May 2000, followed an intensive consultative effort by an interim committee that developed a business case for the AGCC. The author of this paper was appointed as the AGCC's inaugural Chairman.

The impetus for the AGCC comes from recognition of the growing importance of GNSS to our national life. Many forms of navigation, position fixing and timing now have significant reliance on GNSS. The benefits as well as the dependencies are growing at a remarkable rate. The essentially free-market way GNSS is penetrating our national life in business and recreation has delivered great benefits at modest cost but there are important underpinning national issues to be addressed. These include the following.
Can Australia enhance its national benefit by capitalising on GNSS opportunities in a more coordinated way?
Are our international relationships with GNSS providers serving the nation to best effect?
Are GNSS vulnerabilities, dependencies and legal implications appreciated and understood?
Are there national regulatory and legal issues, including spectrum management, to be addressed arising from the pervasive application of GNSS?
Is the evolving national balance between government-provided and market-driven GNSS augmentation services appropriate?

This paper will address these questions from the perspective of Australia but its implications will clearly have relevance to GNSS application by many other countries.
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Session A1: GNSS STATUS, CONTROL AND SPECTRUM MANAGEMENT
Paper #7

QUANTITATIVE RISK ANALYSIS OF GPS AS A CRITICAL INFRASTRUCTURE FOR CIVILIAN TRANSPORTATION APPLICATIONS:
B. Mahoney, Y.Y. Haimes, University of Virginia

The Global Positioning System (GPS) has been hailed as one of the most important technological advances of the late 1900s. Initially developed as a military weapon guidance system for the United States and its allies, GPS has become a cornerstone for numerous civilian transportation applications around the globe and in space. Additionally, the system supports the precision timing needs of many important users, in particular the electric power and telecommunications industries. This paper provides a methodological framework for the assessment and management of the risks of GPS for civil transportation purposes. For example, the use of hierarchical holographic modeling is presented in order to identify the risks associated with GPS. Possible risk mitigation policies and procedures are also described. The tradeoffs for each of the policy options are included. Lastly, an integrative framework for U.S. Department of Transportation officials to use in assessing the tradeoffs among cost, benefit, and risk for civil transportation use of GPS is proposed.
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Session A1: GNSS STATUS, CONTROL AND SPECTRUM MANAGEMENT
Paper #8

GLONASS: STILL OUT THERE:
G.L. Cook, Sequoia Research Corporation

The Russians managed to launch three more GLONASS satellites into orbit in October 2000. Yet the plight of their space segment continues to deteriorate. Two older satellites were withdrawn from service at the end of September 2000, and one was withdrawn in February 2001. Another appeared to fail in February, and several show serious problems. As of mid-March 2001, only eight satellites of the 24-satellite constellation were healthy.

The deficiencies are not limited to the old satellites, as two of the brand new (October 2000) satellites appeared to have problems related to the eclipse season, and the third has been down more than expected. Problems with the young satellites could indicate pre-launch checkouts have been relaxed, or a new generation of less experienced personnel prepared the new vehicles.

It is not clear if bureaucratic inertia, military necessity, or national pride drives the program, but the ground segment maintains the system daily, and a limited software upgrade was noted. These activities argue that GLONASS will be around at least a few more years. In spite of all its shortcomings, GLONASS is still out there.
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Session A1: GNSS STATUS, CONTROL AND SPECTRUM MANAGEMENT
Alternate #1

A SYSTEMS APPROACH TO A NATIONAL POSITIONING, NAVIGATION, AND TIMING SERVICE:
R. Swider, R. Robb, Office of the Assistant Secretary of Defense for Command, Control, Communications and Intelligence; J. Lavrakas, Overlook Systems Technologies, Inc.

For years many have looked to GPS as "the" worldwide provider of global positioning, navigation, and timing services. Indeed, it is used for just this purpose in nearly every country of the world. Yet this "system" is in reality but one part of a national positioning, navigation, and timing service (PNT). In applications where GPS has been unable to provide the necessary accuracy, reliability, and integrity, it has been augmented by other systems. These include ground-based and satellite-based services, including local area differential systems, the FAA’s Wide Area Augmentation System, the National Differential GPS System, as well as commercial GPS differential services, all of which have been developed more or less independently of one another.

Conceptually, the overall utility of these individual services could be enhanced through the integrated development of a national positioning, navigation, and timing service. Such a service would incorporate GPS as a core capability, but would include other space and ground-based technologies as well.

This national service would provide separate levels of service to different user groups, such as:

Civil non-safety of life service – analogous to the current GPS Standard Positioning Service
Civil safety of life service – analogous to the current SPS with the addition of the planned third civil signal
Military services – analogous to the current GPS Precise Positioning Service enhanced by the addition of new military signals

This paper explores what is needed in order to establish a national positioning, navigation, and timing service. It discusses its basic elements and services, its intended user community, and the benefits of the service. In addition this paper outlines a systems approach to implementing such a service, including creating specification documentation, performing analyses of alternatives, and defining functional and performance requirements. The overall result of this process is an optimized design of a PNT system from a national perspective.

Two of the authors of this paper, Mr. Ray Swider and Col. Roger Robb (USAF), are assigned to the Office of the Assistant Secretary of Defense and support the United States Department of Defense Co Chair of the Interagency GPS Executive Board. The third, Mr. John Lavrakas, conducts the affairs of the Secretariat for the GPS Interagency Forum for Operational Requirements.
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Session A1: GNSS STATUS, CONTROL AND SPECTRUM MANAGEMENT
Alternate #2

GPS PERFORMANCE MONITORING RESULTS FOR OPERATIONAL AVIATION APPLICATIONS INCLUDING B-RNAV:
D. Walsh, G. Brodin, M. Daly, CAA Institute of Satellite Navigation, University of Leeds, UK; M. Denney, S. Griffin, Safety Regulation Group, UK

UK Air Traffic Services are subject to approval by the UK CAA's Safety Regulation Group (SRG). Approval of existing systems is granted once the regulator is assured that the systems employed meet necessary safety requirements. GPS, as a US military system, presents difficulties in gaining safety assurances from the provider using traditional regulatory means. Hence, the regulator is seeking other means to seek information necessary to assist in the approval of GPS-based air traffic services.

One approach is to monitor the GPS signal-in-space performance in respect to the specific needs of air traffic service (i.e. B-RNAV), and also in respect of the GPS performance specification itself. With regards to safety, of particular concern are GPS anomalies which could have safety related consequences in the aviation domain. Such anomalies have been reported by institutions in the past and in CAA MORs.

This paper firstly describes the GPS performance monitoring system which has been designed and implemented by the CAA Institute of Satellite Navigation for the SRG. The requirements for the GPS signal-in-space monitoring system were established through analysis of GPS performance specifications, B-RNAV service application requirements, and reported GPS anomalies. Over 300 possible tests on the GPS Signal In Space were identified. Four different receiver types are used including certified avionics receivers (TSO C-129a). The monitoring system was particularly designed to identify and characterise insidious anomalies.

The monitoring system has been exhaustively tested and nearly 2 years of data has been logged. This paper describes the results of the GPS monitoring system for the years 2000-2001, including pre- and post- SA performance. The results show actual GPS performance compared to expected performance over this period as experienced from Leeds, UK. The results include coverage, availability, reliability and accuracy as defined in the Standard Positioning Service standards, as well as range errors and the accuracy of NANUs. The results include any detected 'anomalies' which are then characterised to better understand any possible causes.
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