Publications

The major objective of the measurements and tests performed at Bath was to determine the mechanism by which interference is occurring, and to recommend technically feasible solutions to the interference problem. Technical feasibility of a solution does not necessarily mean that the solution will be considered to be practical or desirable from a standpoint of cost or other non-technical considerations; it only means that the solution will work under the limits of known laws of physics and current state-of-the art knowledge of electrical engineering principles. Our purpose in performing the tasks at Bath, performing analysis of the data from Bath, and in writing this report is to set forth all possible technical solutions that meet these criteria. The parties to the interference problem may use these recommendations to attempt to resolve the interference problem on a technical basis.

On behalf of the Secretary of Commerce, the National Telecommunications and Information Administration (NTIA) has prepared this report as required by Title III ­ Communication and Spectrum Allocation Provisions ­ of the Balanced Budget Act of 1997 (Title III of the BBA 97). This report identifies radio spectrum currently used by the Federal Government for reallocation to the private sector.

Title III of the BBA 97 requires the Secretary of Commerce to provide from the spectrum currently allocated for Federal use, an aggregate of at least 20 megahertz (MHz) below 3 gigahertz (GHz) for allocation and assignment by the Federal Communications Commission (FCC) to non-Federal users through the process of competitive bidding.

The National Table of Frequency Allocations allocate the 2025-2110 MHz band to Federal space science services and the entire 1990-2110 MHz band to the non-Federal government fixed and mobile communication services. The Federal space science services provide the tracking, telemetry, and command (TT&C) functions for near-Earth and geostationary-satellite network operated by the National Aeronautics and Space Administration (NASA) and the National Oceanic and Atmospheric Administration (NOAA). The transmissions made to these satellites both from the surface of the Earth and from NASA’s Tracking and Data Relay Satellites (TDRS) in the 2025-2110 MHz band are essential to the success of the scientific and manned space programs.

The objectives of this report were to: 1) identify operational characteristics of representative Government radars operating in the 3.1-3.7 GHz frequency band, 2) outline a procedure for assessing the potential for EMI from these radars to adjacent-band FSS earth station receivers, and 3) identify methods for mitigating any received EMI.

The performance of the radios was evaluated using the SINAD histograms and by listening to the radio during the tests. Radios that had histograms which showed a distribution of SINAD measurements to higher values for a greater percentage of time performed better than those radios that had low SINAD values for higher percentages of time. Some radios performed better in Savannah than New Orleans.

Mariners in the United States and other countries are experiencing interference on channels allocated to the above functions. The Radio Technical Commission for Maritime Services (RTCM) established Special Committee 117 to investigate the interference and determine if the International Electrotechnical (IEC) standard 1097-7 “Global Maritime Distress and Safety System (GMDSS)-Part 7: Shipborne VHF Radiotelephone Transmitter and Receiver-Operational and Performance Requirements, Methods of Testing and Required Test Results” would be sufficient to protect marine VHF radios from interference. In support of this effort, NTIA, in coordination with the Coast Guard and RTCM SC-117, undertook a task to test nine commercial and recreational grade marine VHF radios to the IEC standard and perform radiated tests in areas where severe cases of interference are occurring. Laboratory testing of the radios to the IEC standard was performed in Boulder, Colorado. The radiated tests were performed in Savannah, Georgia on the Savannah River and on the Mississippi River in New Orleans, Louisiana. Mariners in both locations have been reporting cases of severe interference in the marine VHF band on the waterways for quite some time now. Some of the channels experiencing the interference are key channels used for safety and bridge-to-bridge communications. The interference is very disruptive to normal operations on the river and is distracting to the radio operators.

The availability of the radio spectrum in the United States is critical to over 40 radio services that provide functions ranging from air traffic control to amateur radio operations. Although the radio frequency spectrum is not a consumable resource, the use of a frequency at a given location usually prevents that frequency from being used by others in the same geographic area. This need for exclusive geographic use to preclude harmful interference has led to current spectrum regulations that establish spectrum use rules, such as granting licenses for spectrum use, and partitioning the spectrum for shared use between radio services.

Dedicated short-range communication (DSRC) systems have been proposed for operation at locations across the United States in the 5850- to 5925-MHz band. To establish electromagnetic compatibility between DSRC and other 5-GHz systems, it is necessary to understand current and future occupancy of this spectrum. This report summarizes results of measurements made in 5-GHz spectrum for the Federal Highway Administration (FHWA) of emissions from high-power radars and a fixed satellite service (FSS) earth station.

The Coast Guard plans to operate an Automatic Identification System (AIS) Digital Selective Calling (DSC) based transponder system as part of the Ports and Waterways Safety System (PAWSS) in the lower Mississippi River. The AIS uses two duplex channels for ship-to-shore and shore-to-ship digital data transmissions and a simplex channel for channel management. The duplex channels are identified as AIS working channels. The PAWSS relies on a combination of voice and AIS working channels in the VHF maritime mobile band to provide signal coverage in the vessel traffic service area (VTSA). The proposed coverage area for the VTSA encompasses the Mississippi river starting at river mile 255 to the sea buoy located at Southwest Pass and also includes an area in the Gulf of Mexico for ships approaching the sea buoy. Other waterways such as the Mississippi River Gulf Outlet and the Industrial Canal are also included in the proposed VTSA. A contractor has installed government owned equipment at five tower sites along the river to provide the coverage for both the voice and AIS working channels. Each tower provides coverage for part of the VTSA. Before the system can reach operational status, the coverage of the RF portion of the system must be measured and documented. The Coast Guard funded NTIA to perform coverage tests on the system to examine and evaluate the adequacy of the RF coverage of the channels used for voice and AIS data transmissions. The tests were performed August 4-10, 1999. The results of these tests are given in the following sections of this report.