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This paper establishes practical stability results for an important range of approximate discrete-time filtering problems involving mismatch between the true system and the approximating filter model. Using local consistency assumption, the practical stability established is in the sense of an asymptotic bound on the amount of bias introduced by the model approximation. Significantly, these practical stability results do not require the approximating model to be of the same model type as the true system. Our analysis applies to a wide range of estimation problems and justifies the common practice of approximating intractable infinite dimensional nonlinear filters by simpler computationally tractable filters.

Since August 2008, two production PerkinElmer Rubidium Frequency Standards (RFS) built for the GPS Block IIF satellites have been under test at the Naval Research Laboratory (NRL) Precision Clock Evaluation Facility (PCEF). NRL, in conjunction with the GPS Wing, GPS Block IIF prime contractor Boeing, and the RFS manufacturer PerkinElmer, is conducting a minimum 3-year life test on the GPS IIF RFS units, serial numbers 5 and 25. The primary objectives of the program will be the verification of the design's life and reliability. A secondary objective will be the long-term characterization and evaluation of the GPS IIF RFS performance parameters. The two units are being operated in independent thermal vacuum chambers with high-resolution monitoring of the clock's frequency compared to the NRL hydrogen maser references. The units' internal monitors that would normally be sent as telemetry and environmental test conditions are monitored and recorded with high resolution. A status will be presented of the GPS IIF RFS units under test., Presented at the Precise Time and Time Interval (PTTI) Systems and Applications Meeting (41st Annual) held in Santa Ana Pueblo, NM on 16-19 Nov 2009. Published in the Proceedings of the Precise Time and Time Interval (PTTI) Systems and Applications Meeting (41st Annual), p449-456, 2009. The original document contains color images.

Few software packages exist which address the particular needs of the time and frequency community in analyzing and simulating clocks or oscillators. None is open source. We offer the source code for a set of tools which aims to incorporate commonly used clock analysis and simulation algorithms. The goal of this release is to promote further development of the package by distributing the effort., Presneted at the Joint IEEE International Frequency Symposium and Precise Time and Time Interval "PTTI" Systems and Applications Meeting Held 29-31 Aug 2005 in Vancouver, BC, Canada. The original document contains color images.

The U.S. Naval Research Laboratory "NRL" has collected data and analyzed GPS space vehicle atomic clock performance since the beginning of the GPS Program. These analyses have largely been based on pseudorange observations and precise post-fit ephemerides provided by the National Geospatial-Intelligence Agency "NGA". Observational data and clock comparisons were limited to data collected within the GPS system due primarily to the lack of global tracking resources and effective means of gathering the data. With the successful conclusion of the International GPS Service "IGS" and Bureau International Poids and et Mesures "BIPM" Pilot Project, new capabilities to associate IGS geophysical data to Universal Coordinated Time "UTC", and integration of timing centers to contribute to the determination of UTC are evolving. Data collection from participating timing centers and analysis to form the IGS timescales and Clock Products has established new capabilities for analysis of orbiting precision atomic clocks. NRL leads the IGS Clock Products Working Group and generates the IGS timescales. These efforts joined together with the GPS on-orbit analyses offer new possibilities for analysis and improved performance for both GPS and IGS. This paper will discuss these new resources for analysis and possible improved analytical capabilities., Presented at the Joint IEEE International Frequency Symposium and Precise Time and Time Interval "PTTI" Systems and Applications Meeting Held 29-31 Aug 2005 in Vancouver, BC, Canada. The original document contains color images.

In this paper we consider the problem of grouping machine and human resources in mixed model assembly process so that sequencing and scheduling decisions may be performed more efficiently. Resource aggregation can potentially and significantly improve production efficiency and throughput by balancing production rates, and by minimising resource deficiencies and idle time inefficiencies. This resource aggregation problem in particular involves determining how many groups to have and what number of machines and workers should be assigned to each. Not only is the number important in the aggregation but also the type (identity). Hence which specific machines and workers should be assigned to each group must also be answered. There are numerous factors that affect the aggregation. For example worker experience level and preferences, job processing requirements, current and future jobs and workloads, travelling distances and adjacency conditions. Very little theory however exists to indicate what a good resource aggregation is. Few if any experimental results exist to indicate what level of improvement is also possible. In this paper we therefore provide a mathematical framework for answering these questions that includes an analysis of the complexity of the problem. A general mathematical model is formulated that is suitable for any machine scheduling environment and for any combination of distinct and indistinct resources. A number of alternative measures of performance may be used as the objective function for this model. These include workload and experience balancing and minimal travelling time and distance objectives, although the choice of objective is very much dependant on the particular process being addressed. However, due to the complexity of the problem, significant numerical investigations are left as a source of continuing research.

The simultaneous calibration of three geodetic-quality timing receivers is performed with a Global Positioning System (GPS) signal simulator. Internal delays for each receiver are measured as a function of the phase difference between the one pulse per second and 20 MHz clock inputs. A calibration curve for each receiver is derived and the curves are compared., See also ADM001482. Presented at the Annual Precise Time and Time Interval (PTTI) Systems and Applications Meeting (33rd) held in Long Beach, CA on 27-29 Nov 2001. Published in the Proceedings of the Annual Precise Time and Time Interval (PTTI) Systems and Applications Meeting (33rd), p349-358, 2001.