JASA Standards Handbook Version 2.0

30 October 1997

3. FRONT END PROCESSING

3.1  INTRODUCTION

     The Front End Processing chapter identifies standards necessary for data capture and distribution. It also identifies the standards necessary to deliver precision time and navigation data from the platform to the SIGINT sensor.

3.2  MANDATES

     3.2.1  Time, Frequency, Navigation, and Geodesy (TFNG)

     Time, Frequency, Navigation and Geodesy (TFNG) standards and specifications ensure accurate information for precise geolocation and time tagging applications. The TFNG standards and specifications were jointly selected with the Aircraft-Overhead Interoperability Task Force (AOITF) to ensure compatible cross platform geolocation capability.

     The JASA TFNG model (Figure 3-1) is a notional model for the purpose of providing a common frame of reference. All analysis associated with the model does not take into account atmospheric effect uncertainties. In addition, the following apply:

• Specifications shall be met over the operating environment of the host platform
• The accuracies and resolutions shall be made available and maintained at the input point(s) to the SIGINT sensor
• For all related SIGINT data, navigation and time data associated with that SIGINT data will be translated from the system's navigation and time reference point(s) to the navigation and time when the signal arrived at the collector antenna
• The specified resolutions and accuracies shall be independent of the rate the information is provided to the sensor
• The analysis supporting the standards and specifications covered in this section is contained in Annex 2.

     Table 3-1 provides the maximum allowable Time of Arrival (TOA) and Frequency of Arrival (FOA) uncertainty values to achieve cross-system collection requirements.

     Collection system TOA and FOA uncertainties shall comply with:

     3.2.1.1  Timing and Time Tagging

     Time tagging refers to the capability to determine the time of arrival of a signal to the specified accuracy in an analog or digital sample or pulse descriptor word format. A time tag for a continuous data stream should be generated initially and at a minimum of every one second thereafter. A time tag is a link between data and metadata. There is a hierarchy of time registration methods required in the collection system depending on the application. The timing data shall be available in real time and referenced to:

     To support analog recording activities such as wide band recording, time data shall be available in:

3.2.1.2  Navigation

     Navigation data from the platform needs to provide position, attitude, and velocity information tied to precision time. Accuracy of the navigation information assumes that position and velocity are continuously obtained using Precise Positioning Service (PPS) GPS in conjunction with inertial navigation systems.

     The navigation data performance standards in Table 3-3 have been demonstrated operationally and can be improved by using differential GPS (DGPS) techniques, Wide Area GPS Enhancement (WAGE), and other GPS accuracy improvements.

     Navigation data shall be available in real time referenced to:

     3.2.1.3  Frequency References

     The frequency references provide signals needed for inter- and intra-platform operations. The frequency reference provides a stable RF signal synchronized with the GPS system, which is monitored continuously and referenced to the USNO Master Clock frequency. The information provided in Tables 3-4 and 3-5 is based on projected performance of currently available COTS frequency standards in a typical operating environment.

     This data shall be available in real-time and referenced to USNO Master Clock to the specified accuracies and stabilities per:

1 Navigation data is referenced to the platform INS.

2 The frequency reference is corrected by either continuously steering it to the USNO Master Clock frequency or by applying correction factors (derived by precisely measuring the difference between the frequency reference and the USNO master Clock frequency) during processing.

3.2.2  Frequency Interfaces

     3.2.2.1  Radio Frequency (RF) Interfaces

     The interfaces between the antennas, preamplifiers, and RF distribution are unique for each installation. These interfaces must be designed to provide the necessary input signal to the system tuners and receivers to optimize system signal performance characteristics (e.g., input signal to noise ratio, second and third intercept points, etc.).

     ICDs should be developed and maintained for each platform detailing the specifics of the RF and antenna interfaces. Additional standards required supporting SIGINT collection may be identified later.

     3.2.2.2  Intermediate Frequency (IF) Interfaces

     To allow interoperability and interchangeability of tuners, digitizers, and processors, it is necessary to define a common set of intermediate frequencies down selected from the many widely used industry standards. This will standardize information transfer in the analog domain just as down selections in LANs help standardize information transfer in the digital domain.

     It is not intended to preclude the use of other internal IFs, but rather to facilitate modularity, scalability, and interoperability. Additionally, certain advanced specialized signals such as ultra-wideband Electronic Intelligence (ELINT) may require different center frequencies and/or bandwidths due to performance requirements. These should be handled as waivers.

     Bandwidth shall be defined as the minimum 3 dB bandwidth available at output nodes and maximum 3 dB bandwidth useable by an input node. Frequencies and bandwidths for analog IFs shall be:

     3.2.3  Geolocation

     Emitter locations shall be referenced to the following: