System Resistance to Electromagnetic Interference

Electromagnetic Interference (EMI) is the disruption of operation of an electronic device when it is in the vicinity of an electromagnetic field in the radio frequency (RF) spectrum. Many electronic devices fail to work properly in the presence of strong RF fields. The disturbance may interrupt, obstruct, or otherwise degrade or limit the effective performance of the circuit. The source may be any object, artificial or natural, that carries rapidly changing electrical currents.

Electromagnetic Compatibility (EMC) is the ability of systems, equipment, and devices that utilize the electromagnetic spectrum to operate in their intended operational environments without suffering unacceptable degradation or causing unintentional degradation because of electromagnetic radiation or response. It involves the application of sound electromagnetic spectrum management; system, equipment, and device design configuration that ensures interference-free operation; and clear concepts and doctrines that maximize operational effectiveness (DAU 2010, Chapter 7).

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Overview

Spectrum

Each nation has the right of sovereignty over the use of its spectrum and must recognize that other nations reserve the same right. It is essential that regional and global forums exist for the discussion and resolution of spectrum development and infringement issues between bordering and proximal countries that might otherwise be difficult to resolve.

The oldest, largest, and unquestionably the most important such forum, with 193 member countries, is the International Telecommunications Union (ITU) agency of the United Nations, which manages spectrum at a global level. As stated in Chapter 3 of the NTIA Manual, “The International Telecommunication Union (ITU)...is responsible for international frequency allocations, worldwide telecommunications standards and telecommunication development activities” (NTIA 2011, 3-2). The broad functions of the ITU are the regulation, coordination and development of international telecommunications.

The spectrum allocation process is conducted by many different international telecommunication geographical committees. Figure 1 shows the various international forums represented worldwide.

Figure 1. International & Regional Spectrum Management Forums. (SEBoK Original)

Assigning frequencies is very complicated, as shown in the radio spectrum allocation chart in Figure 2. Sometimes, commercial entities try to use frequencies that are actually assigned to US government agencies, such as the Department of Defense (DoD). One such incident occurred when an automatic garage door vendor installed doors on homes situated near a government installation. Random opening and closing of the doors created a problem for the vendor that could have been avoided.

Four ITU organizations affect spectrum management (Stine and Portigal 2004):

World Radio-communication Conference (WRC)
Radio Regulations Board (RRB)
Radio-communications Bureau (RB)
Radio-communication Study Groups (RSG)

The WRC meets every four years to review and modify current frequency allocations. The RB registers frequency assignments and maintains the master international register. The RRB approves the Rules of Procedures used by the BR to register frequency assignments and adjudicates interference conflicts among member nations. The SG analyzes spectrum usage in terrestrial and space applications and makes allocation recommendations to the WRC. Most member nations generally develop national frequency allocation polices that are consistent with the Radio Regulations (RR). These regulations have treaty status.

Dual Management of Spectrum in the US

Whereas most countries have a single government agency to perform the spectrum management function, the US has a dual management scheme intended to insure that

decisions concerning commercial interests are made only after considering their impact on government systems; and
government usage supports commercial interests.

The details of this scheme, established by the Communications Act of 1934, are as follows:

the Federal Communications Commission (FCC) is responsible for all non-government usage
the FCC is directly responsible to Congress;
the president is responsible for federal government usage, and by executive order, delegates the federal government spectrum management to the National *Telecommunications and Information Administration (NTIA); and
the NTIA is under the authority of the Secretary of Commerce.

The FCC regulates all non-federal government telecommunications under Title 47 of the Code of Federal Regulations. For example, see FCC (2009, 11299-11318). The FCC is directed by five Commissioners appointed by the president and confirmed by the Senate for five-year terms. The Commission staff is organized by function. The responsibilities of the six operating Bureaus include processing applications for licenses, analyzing complaints, conducting investigations, implementing regulatory programs, and conducting hearings (http://www.fcc.gov).

The NTIA performs spectrum management function through the Office of Spectrum Management (OSM), governed by the Manual of Regulations and Procedures for Federal Radio Frequency Management. The IRAC develops and executes policies, procedures, and technical criteria pertinent to the allocation, management, and usage of spectrum. The Spectrum Planning and Policy Advisory Committee (SPAC) reviews the reviews IRAC plans, balancing considerations of manufacturing, commerce, research, and academic interests.

Within the DoD, spectrum planning and routine operation activities are cooperatively managed. Spectrum certification is a mandated process designed to ensure that

frequency band usage and type of service in a given band are in conformance with the appropriate national and international tables of frequency allocations;
equipment conforms to all applicable standards, specifications, and regulations; and
approval is provided for expenditures to develop equipment dependent upon wireless communications.

Host Nation Coordination and Host Nation Approval

In peacetime, international spectrum governance requires military forces to obtain host nation permission — Host Nation Coordination (HNC)/Host Nation Approval (HNA) — to operate spectrum-dependent systems and equipment within a sovereign nation. For example, international governance is honored and enforced within the United States by the US departments of State, Defense, and the user service.

In wartime, international spectrum governance is not honored between warring countries; however, the sovereign spectrum rights of bordering countries must be respected by military forces executing their assigned missions. For example, HNA is solicited by US naval forces to use spectrum-dependent systems and equipment in bordering countries’ airspace and/or on bordering countries’ soil. HNA must be obtained before the operation of spectrum-dependent systems and equipment within a sovereign nation. The combatant commander is responsible for coordinating requests with sovereign nations within his or her area of responsibility. Because the combatant commander has no authority over a sovereign nation, the HNC/HNA process can be lengthy and needs to be started early in the development of a system. Figure 2 illustrates a spectrum example.

Figure 2. The Radio Spectrum (Department of Commerce 2003). Released by the U.S. Department of Commerce. Source is available at http://www.ntia.doc.gov/files/ntia/publications/2003-allochrt.pdf (Retrieved September 15, 2011)

Practical Considerations

EMI/EMC is difficult to achieve for systems that operate world-wide because of the different frequencies in which products are designed to operate in each of the telecommunication areas. Billions of US dollars have been spent in retrofitting US DoD equipment to operate successfully in other countries.

It is important to note that the nuclear radiation environment is drastically more stressing than, and very different from, the space radiation environment.

System Description

Narrowband and Broadband Emissions

To help in analyzing conducted and radiated interference effects, EMI is categorized into two types—narrowband and broadband—which are defined as follows:

Narrowband Emissions
A narrowband signal occupies a very small portion of the radio spectrum… Such signals are usually continuous sine waves (CW) and may be continuous or intermittent in occurrence… Spurious emissions, such as harmonic outputs of narrowband communication transmitters, power-line hum, local oscillators, signal generators, test equipment, and many other man made sources are narrowband emitters. (Bagad 2009, G-1)
Broadband Emissions
A broadband signal may spread its energy across hundreds of megahertz or more… This type of signal is composed of narrow pulses having relatively short rise and fall times. Broadband signals are further divided into random and impulse sources. These may be transient, continuous or intermittent in occurrence. Examples include unintentional emissions from communication and radar transmitters, electric switch contacts, computers, thermostats, ignition systems, voltage regulators, pulse generators, and intermittent ground connections. (Bagad 2009, G-1)

TEMPEST

TEMPEST is a codename used to refer to the field of emission security. The National Security Agency (NSA) investigations conducted to study compromising emission (CE) were codenamed TEMPEST. National Security Telecommunications Information Systems Security Issuance (NSTISSI)-7000 states:

Electronic and electromechanical information-processing equipment can produce unintentional intelligence-bearing emanations, commonly known as TEMPEST. If intercepted and analyzed, these emanations may disclose information transmitted, received, handled, or otherwise processed by the equipment. (NSTISS 1993, 3)

These compromising emanations consist of electrical, mechanical, or acoustical energy intentionally or unintentionally emitted by sources within equipment or systems which process national security information. Electronic communications equipment needs to be secured from potential eavesdroppers while allowing security agencies to intercept and interpret similar signals from other sources. The ranges at which these signals can be intercepted depends upon the functional design of the information processing equipment, its installation, and prevailing environmental conditions.

Electronic devices and systems can be designed, by means of Radiation Hardening techniques, to resist damage or malfunction caused by ionizing and other forms of radiation (Van Lint and Holmes Siedle 2000). Electronics in systems can be exposed to ionizing radiation in the Van Allen radiation belts around the Earth’s atmosphere, cosmic radiation in outer space, gamma or neutron radiation near nuclear reactors, and electromagnetic pulses (EMP) during nuclear events.

A single charged particle can affect thousands of electrons, causing electronic noise that subsequently produces inaccurate signals. These errors could affect safe and effective operation of satellites, spacecraft, and nuclear devices. Lattice displacement is permanent damage to the arrangement of atoms in element crystals within electronic devices. Lattice displacement is caused by neutrons, protons, alpha particles, and heavy ions. Ionization effects are temporary damages that create latch-up glitches in high power transistors and soft errors like bit flips in digital devices. Ionization effects are caused by charged particles.

Most radiation-hardened components are based on the functionality of their commercial equivalents. Design features and manufacturing variations are incorporated to reduce the components’ susceptibility to interference from radiation. Physical design techniques include insulating substrates, package shielding, chip shielding with depleted boron, and magneto-resistive RAM. Logical design techniques include error-correcting memory, error detection in processing paths, and redundant elements at both circuit and subsystem levels (Dawes 1991). Nuclear hardness is expressed as susceptibility or vulnerability for given environmental conditions. These environmental conditions include peak radiation levels, overpressure, dose rates, and total dosage.