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Glossary

ACE (advanced communications engine) is a prototype multiband, multimode software radio capable of emulating both military combat net radios and commercial avionics radio systems.

ACN (airborne communications node) is an unmanned aerial vehicle designed and equipped to provide hierarchical communications services and crosslinking over a broad theater of operations. See RAP and UAV.

ACTS (Advanced Communications Technologies and Services program) is the European Commission's latest precompetitive research effort focusing on advanced communications systems.

A/D converter is an analog-to-digital converter.

AJ (antijam) refers to techniques for reducing the effectiveness of attempts to jam communications channels. See Jamming.

AMPS (advanced mobile phone system) is the standard for the analog cellular radio telephones now widely available throughout the United States.

ARQ (automatic repeat request) is a protocol used to retransmit data packets received in error.

ASIC is an application-specific integrated circuit.

ATM (asynchronous transfer mode) enables voice, data, and video to be handled with a uniform transmission protocol. It breaks up the information to be transmitted into short packets of data and intersperses them using time division with data from other sources and delivered over trunk networks.



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Page 182 C Glossary ACE (advanced communications engine) is a prototype multiband, multimode software radio capable of emulating both military combat net radios and commercial avionics radio systems. ACN (airborne communications node) is an unmanned aerial vehicle designed and equipped to provide hierarchical communications services and crosslinking over a broad theater of operations. See RAP and UAV. ACTS (Advanced Communications Technologies and Services program) is the European Commission's latest precompetitive research effort focusing on advanced communications systems. A/D converter is an analog-to-digital converter. AJ (antijam) refers to techniques for reducing the effectiveness of attempts to jam communications channels. See Jamming. AMPS (advanced mobile phone system) is the standard for the analog cellular radio telephones now widely available throughout the United States. ARQ (automatic repeat request) is a protocol used to retransmit data packets received in error. ASIC is an application-specific integrated circuit. ATM (asynchronous transfer mode) enables voice, data, and video to be handled with a uniform transmission protocol. It breaks up the information to be transmitted into short packets of data and intersperses them using time division with data from other sources and delivered over trunk networks.

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Page 183 ATM cell is an information packet containing 53 bytes of data traffic and additional ''overhead" defining the virtual circuits and paths over which the data are to be transmitted. Bandwidth is the part of a frequency band occupied by a communications channel. Sometimes the term is used to describe the number of bits per second transmitted in a channel. Bent pipe is a satellite communications system that transmits to an Earth station essentially the same signal it receives from another Earth station. BER (bit-error rate) is the probability that a bit is received in error. Bit is a binary unit of information. bps (bits per second) refers to the speed at which data is generated by a source or transmitted over a communications channel. Measurements are often stated in units of 103 bits per second (kilobits or kbps) or 106 bits per second (megabits or Mbps). Byte is a unit of 8 bits. C4I (command, control, communications, computing, intelligence) is a military concept encompassing all the functions and capabilities sought in an advanced communications system. CDMA (code division multiple access) is a technique that allows many users to share the same radio spectrum. A sequence of pseudo-random bits, known as a code, spreads the information signal over a much larger range of frequencies than is occupied by the original information signal. See FDMA, TDMA, spread spectrum. CDPD (cellular digital packet data) is a packet-switched network that uses one or more channels in an analog cellular telephone system. Cell refers to a geographic region within which cellular telephone subscribers can communicate with a particular base station (site). Cell radius ranges from 0.5-15 kilometers depending on the density of the subscribers and the extent of topological obstructions. CELP (code excited linear prediction) is a technique for encoding voice. CMOS (complementary metal oxide semiconductor) is an inexpensive, low-power integrated circuit technology. CONDOR is a National Security Agency program designed to develop and demonstrate secure voice and secure net broadcast services, using STU III-compatible units, over the commercial cellular infrastructure. COTS (commercial off-the-shelf) refers to readily available commercial technologies and systems. CSMA/CD (carrier-sense multiple access with collision detection) is a

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Page 184 protocol that regulates the manner in which terminals gain access to a shared communications channel. DAMA (demand-assigned multiple access) is a technique that enables many users to share the same radio spectrum. A common signaling channel is assigned to handle requests from transmitters for network capacity. dB is decibels, a unit for expressing the relative intensity of acoustic and electromagnetic waves. DBS (direct broadcast satellite) is a system in which GEO satellites broadcast a signal with sufficient power to enable direct reception in a home, office, or vehicle with an inexpensive receiver. DFE (decision feedback equalizer) is a nonlinear equalization technique designed to reduce the effects of intersymbol interference. See ISI. Doppler effect is a change in the received signal frequency due to movement of the transmitter or receiver. DSP (digital signal processor/processing) is a specialized integrated circuit used to analyze or alter the characteristics of communications signals. Erlang is a unit reflecting the traffic intensity on a communication link. It is equivalent to the fraction of time that the link is occupied. ETSI is the European Telecommunications Standards Institute. Fading refers to changes in the amplitude of received signals due to characteristics of the transmission path and motion of the transmitter and receiver. FCC is the Federal Communications Commission. FDMA (frequency division multiple access) is a technique that enables many users to share the same radio spectrum. Each user is allocated a different frequency. This is the approach used in AMPS cellular radio. See CDMA, TDMA. FEC (forward error correction) codes give digital signals a highly specialized redundancy that enables a receiver to recognize and correct occasional errors in the received signal. FH (frequency hopping) is a technique for changing transmit frequency in a way that makes it difficult for an adversary to jam communications. FIR (finite impulse response) refers to a signal-processing operation performed by a DSP. FM (frequency modulation) is a modulation technique in which information is conveyed in the high frequency of a carrier signal. FPLMTS (future public land mobile telecommunication system) is the original name for the International Telecommunications Union's concept

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Page 185 for third-generation wireless telephone systems. It is now called IMT-2000. Frequency reuse refers to the use of the same signal spectrum at different geographical locations. GBS (global broadcast system) is an advanced military satellite communications system designed to have very high data rates (100 megabits per second) and global coverage. GEO (geosynchronous orbit) refers to an equatorial satellite orbit approximately 36,000 kilometers from the Earth in which the satellite remains stationary over one position on the Earth's surface. GloMo (Global Mobile Information Systems) is a research and demonstration program dealing with mobile, wireless communications. It is funded by the Defense Advanced Research Projects Agency. GSM (global system for mobile communications) is a combination TDMA/FDMA cellular radio system that is the current digital standard in Europe. It was originally known as group system mobile. Have Quick is a military UHF radio designed to provide secure air-to-air and air-to-ground communications with AJ capabilities. HF (high frequency) is the frequency band at 3–30 megahertz. HIPERLAN is a high-performance radio local-area network designed to operate at 20 megabits per second. Hz (hertz) refers to a unit of frequency equal to one cycle per second. Frequencies are often stated in units of 103 hertz (kilohertz or kHz), 106 hertz (megahertz or MHz), or 109 hertz (gigahertz or GHz). IC is an integrated circuit. IEEE is the Institute of Electrical and Electronics Engineers. IMT-2000 (International Mobile Telecommunications-2000) is the International Telecommunications Union's concept for third-generation mobile wireless telephone systems. Information warfare refers primarily to recent U.S. initiatives designed to protect computer network infrastructures against intentional disruptions. The term encompasses many forms of disruption aimed at communications networks (both wired and wireless) and the relevant countermeasures. INMARSAT (International Maritime Satellite) is an organization of 75 member countries that has launched several generations of satellite communications systems for voice and low-rate data applications. Intelsat is an international, government-chartered organization established in 1964 to coordinate worldwide satellite communications programs.

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Page 186 A series of INTELSAT communications satellites has been launched. IS-95 is the North American standard for second-generation CDMA digital wireless telephone systems. IS-136 is the North American standard for second-generation TDMA digital wireless telephone systems. ISDN (integrated services digital network) is a set of international standards that specify the manner in which different types of information (e.g., voice, data, video) can be transmitted in the same communications system. ISI (intersymbol interference) occurs when multipath reflections corresponding to a given bit transmission arrive at the receiver simultaneously with subsequent data bits. ISM (industrial, scientific, and medical) refers to the unlicensed frequency bands available for use by any wireless device that conforms to rules established by the FCC. ITU is the International Telecommunications Union. Jamming is a type of transmission designed to disrupt the radio communications of an adversary so as to interfere with military operations. JCIT (Joint C4I Terminal) is a software-defined radio under development by the Naval Research Laboratory that will implement combat net, intelligence communications, and military datalinks on a single platform. LAN is a local area network. LEO (low Earth orbit) is a satellite communications system deployed in a low orbit (500 to 2,000 kilometers from Earth). LOS (line of sight) refers to a radio communications systems with an unobstructed path between the transmitter and receiver. LPC (linear predictive coding) is a coding technique based on a mathematical model of a voice signal. LPD/I (low probability of detection and interception) refers to the capability to minimize an adversary's awareness of transmitted radio energy, ability to measure any properties of a detected signal, or ability to intercept the transmission. MEO (medium Earth orbit) is a satellite orbit of intermediate height between LEO and GEO orbits. Message store-forward is a system in which a message is uploaded to a satellite and held there until the satellite is in a position to download it to the destination. It is an alternative to bent-pipe systems. Millennium is a military research effort to design an ultra-wideband

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Page 187 radio. One objective is to demonstrate extremely high-speed A/D converters for military and commercial applications. MISSI (Multilevel Information Systems Security Initiative) is a National Security Agency initiative designed to provide a framework for the development of interoperable, complementary security products. MMITS (Modular Multifunction Information Transfer System) is an industry forum focusing on technical standards and applications for software-defined radios, networking radios, and multimode radios. Mobile IP (mobile internetworking routing protocol) is designed to support mobile Internet users. MSE (mobile subscriber equipment) is a military radio that resembles a cellular telephone. MSRT (mobile subscriber radio terminal) is a military radio. Multipath propagation is a phenomenon in which copies of a transmitted signal arrive at different times at a receiver. NATO is the North Atlantic Treaty Organization. NES (network encryption system) is an encryption system certified by the National Security Agency that enables clusters of defense computer networks to interconnect through the unclassified Internet. OSI (Open Systems Interconnection) refers to a model that describes networks as a series of layers. Packet is a collection of information symbols transmitted together on a communications channel. PACS (personal access communications system) is a U.S. standard for second-generation digital wireless telephone systems serving subscribers moving at pedestrian speeds. PDA (personal digital assistant) is a portable, low-power computing device with a small display used for information storage. Peer-to-peer is a network architecture in which transmissions flow between terminals without passing through a central hub. Personal communications services are offered in frequency bands around 1900 megahertz allocated for this purpose by the FCC. PHS (personal handyphone system) is a Japanese standard for mobile digital telephone services. PSTN (public switched telephone network) is a collection of worldwide wired telephone networks. QoS (quality of service) refers to end-to-end performance guarantees offered by a network.

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Page 188 RACE (Research for Advanced Communications in Europe) was a program funded by the European Commission to perform precompetitive research on advanced communications systems. It was superseded by the ACTS program. Radio spectrum is a range of radio frequencies required to support one or more communications channels. RAM is random-access memory. RAP (radio access point) is a wheeled or tracked vehicle that carries extensive communication systems, including an "on the move" antenna system. It provides a variety of cross-networking, repeater, and information services. RF is radio frequency. RMS (root mean square) is the standard deviation of a random variable. RSVP (resource reservation protocol) supports the delivery of real-time information over the Internet. RTP (real-time protocol) is designed to support delay-intolerant data streams, such as video, transmitted over the Internet. S3 (Scalable Self-Organizing Simulations) is a research program that uses parallel computers to simulate communications networks. The program is sponsored by the Defense Advanced Research Projects Agency and the National Science Foundation. SHF (superhigh frequency) is the frequency band at 3-30 gigahertz used for satellite, radar, and microwave communications. SINCGARS (single-channel ground and airborne radio system) is a military radio that hops transmission frequencies within the very-high-frequency band, a capability that helps prevent jamming. SNR (signal-to-noise ratio) is the ratio of signal power to noise power. The higher the SNR, the clearer the transmission. Software-defined radio is a radio implemented on DSPs with functions defined by software, which can be downloaded as needed. Such radios can use many types of modulations. SpeakEASY is a software-defined radio designed and demonstrated with support from the Defense Advanced Research Projects Agency. SpeakEASY can emulate some legacy military radio systems and operate across a wide frequency range. Spectral link efficiency is the data rate (in bits per second) per unit of bandwidth of a communications channel. Spread spectrum is a technique in which a signal is spread over a much larger frequency range than the minimum required to deliver the message. It is often used by the military for antijam purposes. It is used by the commercial sector in CDMA mobile telephone systems and wireless LANs.

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Page 189 STU III (Secure Terminal Unit III) is a standardized voice and data telephone capable of encryption up to top-secret level for defense and civilian government purposes. STU III operates over standard dial-up telephone lines and has been extended to cellular applications. Symbol, as used in this report, refers to a series of encoded bits. TDMA (time division multiple access) is a technique that allows many users to share the same radio spectrum by transmitting information in different time slots. See CDMA, FDMA. Throughput, as used in this report, refers to the fraction of time during which a communications channel can be used. UAV (unmanned aerial vehicle) is an unmanned aircraft used to relay radio signals between two points on the ground. UHF (ultrahigh frequency) is the frequency band at 0.3–3 gigahertz used for UHF television and radar systems. UMTS (universal mobile telephone system) is a pending European standard for mobile communications services, scheduled to be deployed beginning in 2002. USAT an ultrasmall-aperture terminal. VHF is the frequency band at 30–300 megahertz used for FM radio and television. VSAT (very small aperture terminal) is a satellite communications system in which Earth stations do not require large antennas. The small antenna size (typically less than 1 meter) allows for simplified installation and possibly portability. WAN is a wide area network. Winforum (Wireless Information Network Forum) was formed by several companies in 1992 to obtain frequency bands and set protocol standards for personal communications data services. WLAN is a wireless local area network.