A quick guide to acronyms, jargon and buzzwords, just to bring your vocabulary up-to-date (and leave your colleagues behind at design group meetings!). Call or e-mail Bob at TDC if you’ve got anything new you’d like to see added in future editions on 01256 332800 or email bob@tdc.co.uk.

A
A/D or ADC - Analogue-to-Digital Converter. This device is what all digital imaging systems use to get real-world pictures from a TV camera, for example into a computer.
AAMP - Advanced Architecture Microprocessor.
Abis - Interface between Base Station Controller (BSC) and Base Transceiver Station (BTS).
ABS - Analysis-By-Synthesis, a group of voice compression algorithms. See LPG.
ACPR - Adjacent Channel Power Rejection.
A-D Converter - Converts an analogue signal to digital data.
Adapter Card - Circuit board or other hardware in Data Terminal Equipment (DTE) that provides the physical interface to the communications network.
Adaptive - A technology that enables high-speed modems to operate on poor lines by compensating for the types of lines. It changes the amplitude and phase to remove the distortion introduced by the channel.
Adaptive Equalization - A technology that enables high-speed modems to operate on poor lines by compensating for the types of lines. It changes the amplitude and phase to remove the distortion introduced by the channel.
Adaptive Frame Alignment - Means of ensuring that timeslots received at the Base Station (BS) from active Mobile Stations (MS) at different distances from the BS are in time alignment.
ADC - Analogue-to-Digital Converter. Converts an analogue signal to digital data.
ADM - Adaptive Differential Modulation, an example of waveform coding voice compression algorithm.
ADP - Answer Detection Pattern, a bit sequence under V.42 that answers the originating modem's ODP bit sequence.
ADPCM - Adaptive Differential Pulse Code Modulation. A form of voice compression that typically uses 32 Kbps.
ADSL - Asynchronous Digital Subscriber Line
AFC - Automatic Frequency Control (or Correction). A system that keeps a circuit automatically tuned to a desired signal frequency.
AFP - AppleTalk Filing Protocol. Allows distributed file sharing across AppleTalk networks.
AGC - Automatic Gain Control. A system that holds constant the gain and the output of a receiver or amplifier, in spite of input sign or fluctuation.
AGCH - Access Grant Channel. Used by Base Transceiver Station (BTS) to allocate initial signalling channel.
Algorithm - A prescribed finite set of well-defined rules, of processes for the solution of a problem in a finite number of steps.
Almanac - A set of orbital parameters that allows calculation of approximate GPS satellite positions and velocities. The almanac is used by a GPS receiver to determine satellite visibility and as an aid during acquisition of GPS satellite signals. The almanac is a subset of satellite ephemeris data and is updated weekly by GPS Control.
Altitude Accept Bit - Bit indicating by Logic 1 that the MicroTracker LP receiver will accept an Amended Altitude from a Message 204. The Logic 1 value also indicates that the receiver will enter Altitude Hold Mode if it is enabled and will use the current value of Held Altitude as a measurement input to the Kalman Filter.
Altitude Hold - A technique which allows navigation using measurements from three GPS satellites plus an independent value of altitude.
Altitude Hold Enable Command - This message allows the application processor to enable or disable the Altitude Hold feature (Message ID 203).
Altitude Hold Mode - A Navigation Mode during which a value of altitude is processed by the Kalman Filter as if it were a range measurement from a satellite at the Earth's centre (WGS-84 reference ellipsoid centre).
Altitude Used Bit - Bit indicating by Logic 1 that the last Kalman Filter measurement incorporation cycle used the current Held Altitude as an input measurement. The position, velocity and time solution of this Time Mark Message were computed during that cycle and extrapolated forward to the last Time Mark Pulse rising edge.
AM - Amplitude Modulation. A method of modulation in which the amplitude of the carrier voltage is varied in proportion to the changing frequency value of an applied voltage.
Amended Altitude - An altitude value provided by the application processor in a Message ID 204 for use by the receiver as the Held Altitude.
AMOS - Advanced Modem Operations Schedules.
AMPS - Advanced Mobile Phone Services. The analogue cellular service currently deployed in the United States and several other countries.
ANI - Automatic Number Identification. A charge number parameter used for billing purposes.
ANSI - American National Standards Institute. A U.S. standards body.
AP - Application Processor. The processor connected to the MicroTracker LP GPS receiver port which controls the receiver with command messages and uses data from output messages.
API - Application Programming Interface. Name given to any well-defined programming language interface between application programs and system communications software or hardware.
AppleTalk - A networking protocol developed by Apple Computer for communication between Apple products and other computers.
Application Layer - The top layer of the network protocol stack.
APS - Active Pixel Sensor.
ARAM - Audio-grade DRAM with "bad bits." An ARAM can be mapped to avoid using bad bits, and therefore deliver good performance.
ARFCN - Absolute Radio Frequency Channel Number.
ARO - Automatic Request for Retransmission.
Artifacts - In the video domain, artefacts are blemishes, noise, snow, or spots, indicating something is wrong with the picture.
ASIC - Application-Specific Integrated Circuit.
Aspect Ratio - The ratio of the width of the display screen to the height of the screen.
ASSP - Application-Specific Standard Products.
Asynchronous - A method of data transmission which allows characters to be sent at non-predetermined intervals by preceding each character with a start bit and ending each character with a stop bit.
AUP - Acceptable Use Policy.
Auto Hold - The receiver will use the last altitude calculated in 3-D navigation as the current value of Held Altitude when entering Altitude Hold 2-D navigation. It will continue to use this value throughout this Altitude Hold event unless an Amended Altitude is received from the application processor. The 3-D calculated altitude used in this way is called an Auto Hold altitude.
Autoscanning - When a digital spread spectrum cordless telephone call is initiated, the phone automatically scans the frequency band to find the best channel for link establishment.

B
B - Boolean.
B Channels - 64 Kbps channels used in ISDN.
BA - BCCH Allocation. The radio frequency channels allocated in a cell for BCCH transmission.
BAIC - Barring of All Incoming Calls.
Bandwidth - An analogue measure derived from the difference between the highest and lowest frequency on a carrier wave. Also used to describe the amount of data that can be sent through a given communications circuit.
BAOC - Barring of All Outgoing Calls.
BAP - Baseband Analogue Processor.
Baseband - Characteristic of any network technology that uses a single carrier frequency and requires all stations attached to the network to participate in every transmission.
Basic Rate - A 2 x 64kbps ISDN connection.
Basic Rate Interface - The Integrated Services Digital Network (ISDN) interface used to connect terminals and other desktop equipment.
Baud - Unit of signal frequency in signals per second. Not synonymous with bits per second because signals can represent more than one bit. Baud equals bits per second only when the signal represents a single bit.
BBIC - Baseband IC.
BBS - Bulletin Board Service.
BCC - Basestation Colour Code.
BCCH - Broadcast Control Channel.
BCF - Base Station Control Function.
BCH - Broadcast Channel.
Bell 103 - 0-300 bps, 2-wire, full-duplex modem standard.
Bell 212A - 1200 bps, 2-wire, full-duplex modem standard.
Bellcore - Bell Communications Research. The research arm of the seven Bell Operating Companies which were originally part of Bell Laboratories and AT&T.
BER - Bit Error Rate. The percentage of received bits in error compared to the total number of bits received.
BFI - Bad Frame Indication. Used when a speech frame is corrupted.
B-ICI - Broadband Inter-Carrier Interface.
BiCMOS - Bi-polar Complementary Metal-Oxide Semiconductor.
Binary - Characteristic of having only two states, such as current on and current off. The binary number system uses only ones and zeros.
B-ISDN - Broadband Integrated Services Digital Network. See Broadband ISDN.
Bit - Binary digit. The basic unit of all digital communications. A bit is a "1" or "0" in a binary language.
Blacklisting - Call blocking capability for specific phone numbers.
Blanking - The method by which a video signal is temporarily blanked out to hide the scan line from view.
BLER - Block Error Rate.
Block I Satellite - Satellites designed and built to support GPS development and testing. A total of 10 Block I satellites were successfully launched between February 1978 and October 1989.
Block II Satellite - Satellites designed and built to support GPS Space Segment operation. A total of 28 Block II satellites have been built and launched.
Block lI R Satellite - Satellites being designed to eventually replace Block II satellites.
Blooming - An effect, sometimes caused when video becomes whiter-than-white, in which a line that is supposed to be crisp and clear, becomes fat and fuzzy on the screen.
Bluetooth - Short range radio data solution for personal networking in the 2.4GHz band.
Bm - Bearer-Mobile channel.
BP - Baseband Processor.
BPF - Bandpass Filter.
Bps - Bits per second. A measure of transmission speed.
BPSK - Binary Phase-Shift Keying.
BRI - Basic Rate Interface. Standards and specifications for provision of low-speed ISDN services.
Broadband - Originally described the frequency bandwidth of analogue circuits. The term has evolved to specify 56 Kbps, then 1.5 Mbps capability.
BS - Base Station.
BSC - Base Station Controller.
BSIC - Base Station Identity Code. Contains identity and Training Sequence Code (TSC).
BSS - Base Station System. The base station equipment that is viewed by the Mobile services Switching Centre (MSC) through a single interface as being the entity responsible for communicating with mobile stations in a given area.
BSSMAP - Base Station System Management Part.
BTA - Basic Trading Area. A subset of a Major Trading Area (MTA) consisting of several counties representing a license area for Personal Communication Services (PCS).
BTS - Base Transceiver Station. A network component that serves one cell and is controlled by a Base Station Controller. The BTS contains one or more transceivers.
Burst - The physical content of a timeslot.
Byte - A data unit of eight bits.

C
C/A - Coarse Acquisition
C/I - Carrier-to-Interference ratio.
C/No - Carrier-to-Noise density ratio.
C/R - Command/Response.
Caching - A form of replication in which information learned during a previous transaction is used to process later transactions.
CAI - Common Air Interface.
Call Progress - Network signals that allow for monitoring the call
CAP - Competitive Access Provider or Carrierless Amplitude and Phase modulation.
Carrier - A continuous signal at a fixed frequency that is capable of being modulated with a second signal.
Carrier Signal - A continuous waveform (usually electrical) with properties capable of being modulated or impressed with a second information-carrying signal.
CBC or CBCH - Cell Broadcast Channel. Used for point-to-multipoint Short Message Services (SMS).
CC - Call Control entity.
CCCH - Common Control Channel.
CCD - Charge-Coupled Device.
CCITT - Committee Consultatif Internationale de Telegraphique et Telephonique. The International Telegraph and Telephone Consultative Committee, once part of the ITU.
CCS - Centi-Call Seconds. A unit of measure used for calculating call traffic through a network.
CD Signal - Carrier Detect signal.
CDM - Charged Device Model.
CDMA - Code Division Multiple Access. A spread-spectrum cellular transmission method that allows multiple users to share the same radio frequency spectrum by assigning each active user a unique code.
CDPD - Cellular Digital Packet Data. A technology for wireless mobile communications.
CDR - Call Detail Record. A record generated by customer traffic that is later used to bill the customer for service.
CDVCC - Coded Digital Verification Colour Code.
Cell Cluster - In cellular and PCS systems, a grouping of physically proximate cells in which each cell uses a different subset of the total spectrum allocated for the wireless service.
Cellular - A mobile telephone system developed by Bell Laboratories that divides geographic areas into cells. In each cell, low-powered radio equipment allows the same frequencies to be re-used in nearby cells without interference.
CEP - Circular Error Probable. The radius of a circle, centred at the user's true location, that contains 50 per cent of the individual position measurements made using a particular navigation system.
CEPT - Conférence Européenne des Administrations des Postes et des Télécommunications. European Conference of Posts and Telecommunications Administrations.
CFU - Call Forwarding Unconditional.
CGI - Cell Global Identification. A block of code that uniquely identifies a cell.
CGSA - Cellular Geographic Service Area.
Channel - A means of one-way transmission.
Chroma Burst - The portion of the video waveform that encodes colours.
Chrominance - A video signal contains two pieces that make up what you see on the screen: the black-and-white part, and the colour part. Chrominance is the colour part.
CI - Cell Identity. A block of code that identifies a cell within a location area.
CIA Code - Coarse/Acquisition Code. A spread spectrum direct sequence code that is used primarily by commercial GPS receivers to determine the range to the transmitting GPS satellite.
CIF - Common Interchange (Intermediate) Format. Allows video images to be shared from one computer to another, at a resolution of 352 x 288 colour pixels, without difficulty.
CIS - Contact-Image Sensor. A type of scanning device.
CLEC - Competitive Local Exchange Carrier.
Client/Server - A rapidly emerging style of computing in which applications are distributed across both desktop devices and servers, turning the entire network into a computer.
Clock - A device which generates periodic signals used for synchronisation on a transmission facility. Provides a time base for the sampling of signal elements.
Clock Error - The uncompensated difference between synchronous GPS system time and time best known within the GPS receiver.
CMOS - Complementary Metal Oxide Semiconductor. An integrated circuits manufacturing technology known for requiring less electricity than other methods.
CO - Central Office. A physical facility where the telephone switch is located.
Codec - Coder-Decoder. Converts analogue signals to digital, and back.
CO-LAN - Central Office Local Area Network. A data switching service based on a Private Branch Exchange (PBX) in a carrier's CO.
Cold Start - A condition in which the GPS receiver can arrive at a navigation solution without initial position, time, current ephemeris and almanac data.
Colour Bars - A test pattern used to check whether a video system is calibrated correctly.
Colour Space - A technique for describing a colour.
Comb Filter - Provides better video quality because it more efficiently separates the luma from the chroma.
Composite Video - Encodes all image information in one signal.
Compression - Reducing the bandwidth or bits necessary to encode information.
Compression Algorithm - The arithmetic formula which converts a signal into smaller bandwidth or fewer bits.
Compression Ratio - A number used to tell how much smaller a chunk of data is after it has been compressed.
Contouring - An image artefact caused by not having enough bits to represent the image.
Contrast - Term referring to how far the whitest whites are from the blackest blacks in a video waveform.
Control Segment - The Master Control Station and the globally dispersed Monitor Stations used to manage the GPS satellites, determine their precise orbital parameters and synchronise their clocks.
Cordless Telephone - A generic term for wireless telephone communications systems evolved from the simple residential or in-building office telephones.
COT - Central Office Terminal.
CPE - Customer Premises Equipment. General industry term for computer and communications equipment that is owned and operated by a customer of a communications service.
CRC - Cyclic Redundancy Check.
Creepy-crawlies - Specific image artefacts that result from imperfections in the National Television Standard Committee (NTSC) video system.
CTIA - Cellular Telecommunications Industry Association. Formed in May 1984 to promote cellular technology, address common concerns, provide a forum for exchange of non-proprietary information, and provide a strong, effective voice in Washington for more than 90 percent of all cellular carriers.
CTM - Cordless Terminal Mobility.
CW - Continuous Wave.

D
DAA - Data Access Arrangement.
DAC - Digital-to-Analogue Converter.
DAI - Digital Audio Interface.
D-AMPS/DAMPS - Digital-Advanced Mobile Phone Service.
DAPI - API.
Data Compression - In modems, a bit encoding process that removes redundancy from the scanned page, resulting in fewer bits to transmit.
dB - Decibel.
DB - Dummy Burst. Means of filling a timeslot with an RF signal when no information is to be delivered to a channel.
dBiC - Decibel-Isometric-Circular (measure of power relative to an isometric antenna with circular Polarisation).
dBmW - Decibels milliwatt (measure of power relative to 1mw).
DBPSK - Differential Binary Phase-Shift Keying.
dBW - Decibel-Watt (measure of power relative to one watt).
DC - Direct Current.
DCCH - Dedicated Control Channel.
DCE - Data Circuit-terminating Equipment.
DCS - Digital Cellular System.
DCS 1800 - Digital Communications System. A variant of GSM in the 1800 MHz (1.8 GHz) band.
DCT - Discrete Cosine Transform. Used in the JPEG and MPEG image compression algorithms. Also Digital Cordless Telephone.
Dead Reckoning - When not in Navigation Mode, the MicroTracker LP will estimate the next position by extrapolating the current position using the last known velocity value. This velocity value may have resulted from prior 2-D or 3-D navigation or it may have been supplied by the application processor in an Initialisation Command Message (Message 201).
Decimation - A method for image scaling.
Decimation Filter - A filter designed to provide decimation without the artefacts associated with throwing data away.
DECT - Digital European Cordless Telephone or Digit.
DET - Detach.
DFE - Decision Feedback Equalisation.
DGPS - Differential GPS. A technique to improve GPS accuracy that uses pseudo-range errors recorded at a known location to improve the measurements made by other GPS receivers within the same general geographic area.
DI - Double Precision Integer.
Digital - The method of representing information as numbers with discrete (non-continuous) values, usually expressed as a sequence of binary digits (ones and zeros).
Digital - The method of representing information as numbers with discrete (non-continuous) values, usually expressed as a sequence of binary digits (ones and zeros).
DIP - Dual In-line Packaging.
DIS - Digital Identification Signal or Dynamic Impedance Stabilisation.
Discrete Cosines Transform - Commonly used technique for digital image compression.
Dithering - Grey scale images through fax systems. Also known as half-toning.
DM - Data Mobile channel.
DMA - Direct Memory Access.
DMA Channel - Direct Memory Access Channel.
DMT - Discrete Multi-Tone.
DNMS - Dial-Up Network Management System.
DOCSIS - Data Over Cable Service Interface Specification.
DoD - Department of Defence.
DOP - Dilution of Precision (see GDOP, HDOP, PDOP, IDOP and VDOP).
Doppler Aiding - A signal processing strategy which uses a measured doppler shift to help a receiver smoothly track the GPS signal to allow a more precise velocity and position measurement.
Downlink - Physical link from the Base Station (BS) toward the Mobile Station (MS). The BS transmits, MS receives.
Downstream - Main transmission in the direction from the head end to the end nodes (household) in the network. Also called forward signal.
DPCM - Differential Pulse Code Modulation.
DPSK - Differential Phase-Shift Keying.
DQPSK - Differential Quadrature Phase-Shift Keying.
DRAM - Dynamic Random Access Memory.
DRX - Discontinuous Reception. Means of saving battery power by periodically and automatically switching the Mobile Station (MS) receiver on and off.
DSP - Digital Signal Processor. A processor designed for optimal handling of digital images, sound and video.
DSR Signal - Data Set Ready signal.
DSS - Digital Spread Spectrum. A modulation technique originally developed as a secure means of military communication, where the signal is spread over a wide range of frequencies for transmission. It is ideal for cordless telephone applications in today's crowded channel environment.
DSVD - Digital Simultaneous Voice and Data.
DTAM - Digital Telephone Answering Machine.
DTE - Data Terminal Equipment.
DTMF - Dual-Tone Multi-Frequency. Tone generation and detection (TouchTone™).
DTR - Data Terminal Ready.
DTR Signal - Data Terminal Ready signal.
DTX - Discontinuous Transmission. Optional transmission mode of a mobile station, which is used when no voice activity is detected. Also: Means of saving battery power and reducing interference by automatically switching the transmitter off when no speech or data are to be sent.
Duplex - Characteristic of data transmission. Either full or half duplex. Full permits simultaneous two-way communication. Half means only one side can talk at once.
DUT - Device Under Test.
DVB-S - Digital Video Broadcast Satellite.
DVB-T - Digital Video Broadcast Terrestrial.
DVD - Digital Versatile Disc

E
EAMPS - Expanded AMPS. A form of AMPS with more RF channels than the 666 channels in AMPS.
Eb/No - of energy per modulating bit to the noise spectral density.
ECEF - Earth-Centred Earth-Fixed. A Cartesian co-ordinate system with its origin located at the centre of the Earth. The co-ordinate system used by GPS to describe three-dimensional location. For the WGS-84 reference ellipsoid, ECEF co-ordinates have the Z-axis aligned with the Earth's spin axis, the X-axis through the intersection of the Prime Meridian and the Equator and the Y-axis is rotated 90 degrees East of the X-axis about the Z-axis.
Echo Cancellation - A full-duplex transmission technique requiring the receiver to cancel out its own transmitted signal which occupies the same frequency band as the receiver.
ECL - Emitter Coupled Logic.
ECM - Error Correction Mode. Sends the fax bit stream in page sections or blocks, with an error checking code for each block.
EEPROM - Electronically-Erasable Programmable Read-Only Memory.
EEROM - Electronically Erasable ROM.
EFP - Extended Floating Point.
EFR - Enhanced Full Rate (vocoder).
EGNOS - European Geostationary Navigation Overlay Service.
EGSM - Extended GSM.
EIA - Electronics Industries Association.
EIA/TIA-578 - Asynchronous facsimile DCE control standard, EIA/TIA.
EIR - Equipment Identity Register. A database repository used to verify the validity of equipment used in mobile telephone service.
EMC - Electromagnetic Compatibility.
EMI - Electromagnetic Interference.
EMMI - Electrical Man-Machine Interface.
Encapsulation - The technique used by layered protocols in which a layer adds header information to the Protocol Data Unit (PDU) from the layer above.
Encoder - Converts data into code or analogue voice into a digital signal.
Ephemeris - A set of satellite orbital parameters that is used by a GPS receiver to calculate precise GPS satellite positions and velocities. The ephemeris is used to determine the navigation solution and is updated frequently to maintain the accuracy of GPS receivers.
EPROM - Erasable Programmable Read-Only Memory.
EQ - Equaliser.
Error Detection and Correction - Errors sometimes occur on the switched telephone network and can show up as streaks on the output. In modem technology, the basic means of "correcting" errors is actually by retransmission. See ECM.
ESD - Electro-Static Discharge.
ESN - Electronic Serial Number.
ETACS - Extended Total Access Communications System.
ETS - European Telecommunications Standards.
ETSI - European Telecommunications Standards Institute. A counterpart to ANSI, facilitating integration of telecommunications standards into all of Europe and co-ordinating telecommunications policies.

F
Fallback - Ability of a modem that can operate at different speeds to fall back to its next lower speed if line conditions cannot support the higher speed. To work, both sending and receiving modems must shift to the lower rate.
FAPI - Facsimile API.
FAQ - Frequently Asked Questions.
FAXENGINE™ - A Conexant (formerley Rockwell) proprietary two-device chipset that contains the fax modem and fax machine functions like machine control and monitoring. It can serve as the functional core of Group 3 office and personal facsimile machines. The only additional parts needed to implement a complete, full-featured system are external memory chips and a telephone line interface.
FCC - Federal Communications Commission. The government agency responsible for regulating telecommunications in the United States.
FDD - Frequency-Division Duplex.
FDMA - Frequency Division Multiple Access.
FDSP - Full Duplex Speaker Phone.
FEC - Forward Error Correction.
FEES - FAXENGINE™ Evaluation System.
FERE - FAXENGINE ROM Emulator.
FET - Field Effect Transistor.
FEXT - Far End Cross Talk.
FFC - Flat Flexible Cable.
FIFO - First In First Out.
FIR - Finite Impulse Response.
Flash A/D - A fast method of digitising something.
Flash Memory - Can be reprogrammed if the software needs updating.
Flicker - Occurs when the video frame rate is too low.
Flow Control - Any procedure which actively controls the rate of traffic into or through a network.
FM - Frequency Modulation.
FN - Frame Number. Identifies the position of a particular timeframe within a hyperframe.
FP - Floating Point.
FPLMTS - Future Public Land Mobile Telephone System.
FR - Full Rate.
Frame - A segment of a signal, analogue or digital, that has a repetitive characteristic in that corresponding elements of successive frames represent the same things.
Frame Buffer - A large section of memory used to store an image to be displayed onscreen.
Frame Rate - The rate at which a source repaints the screen with a new frame.
Frame Rate Conversion - The act of converting one frame rate to another.
Framing - The process of establishing a reference so that time slots or elements within the frame can be identified.
FRP - Federal Radio navigation Plan. The U.S. Government document which contains the official policy on the commercial use of GPS.
FSK - Frequency Shift Keying modulation method.
FTA - Full Type Approval or Free-To-Air.
Full Duplex - Simultaneous transmission and reception of signals.
FVC - Forward Voice Channel.

G
GaA - Gallium Arsenide.
Gamma - The characteristics of the imaging sensor used in cameras are non-linear. A small change in brightness when the light level is low produces a change in the video signal, but this same small change in brightness at a high light level will not produce the same magnitude of change in the output. This effect is known as gamma and is present in TV cameras as well as displays.
Gamma Correction - The act of taking a non-linear video source and making it linear.
GDOP - Geometric Dilution of Precision. A factor used to describe the effect of the satellite geometry on the position and time accuracy of the GPS receiver solution. The lower the value of the GDOP parameter, the less the error in the position solution. Related indicators include PDOP, HDOP, TDOP and VDOP.
Genlock - The act of lining up the computer's sync signals with the camera's sync signals.
GMSC - Gateway Mobile Switching Centre. Provides an entry point into the Public Land Mobile Network (PLMN) from another network or service.
GMSK - Gaussian Minimum-Shift Keying. Modulation scheme used in the GSM cellular standard.
GMT - Greenwich Mean Time.
GPIO - General Purpose Input/Output.
GPRS - General Packet Radio Service
GPS - Global Positioning System. A series of satellites combined with specialised devices that allow you to pinpoint exact locations anywhere on the earth, typically in longitude and latitude. A space-based radio positioning system which provides suitably equipped users with accurate position, velocity and time data. GPS provides this data free of direct user charge world-wide, continuously and under all weather conditions. The GPS constellation consists of 24 orbiting satellites, four equally spaced around each of six different orbital planes.
GPS Time - The number of seconds since Saturday/ Sunday Midnight UTC, with time zero being this midnight. Used with GPS Week to determine a specific point in GPS time.
GPS Week - The number of weeks since January 6, 1980, with week zero being the week of January 6, 1980. Used with GPS Time to determine a specific point in GPS time.
GPSRE - GPS Receiver Engine.
Grey Scale - This term has several meanings. In some instances it means the luminance component of the NTSC or PAL signals. In others it means a black-and-white video signal.
Group 3 - ITU digital standard that ensures compatibility among fax machines.
Group 4 - The ITU digital recommendation, first adopted in 1984, designed for transmission over ISDN. Group 4 fax machines transmit at 64 Kbps, and are well suited to computer-controlled network communications.
GSA - GSM System Area. The group of GSM PLMN areas accessible by GSM mobile stations.
GSM - Global System for Mobile Communications, or Groupe Spéciale Mobile. A pan-European cellular phone system that allows European travellers to use a single cellular phone in many different countries and have all calls billed to one account. Adopted as the preferred cellular standard in Europe, Asia and North America.
GSM MS - GSM Mobile Station.
GSM PLMN - GSM Public Land Mobile Network.
GSTN - General Switched Telephone Network.
Guard Period - Period at the beginning and end of a timeslot during which Mobile Station (MS) transmission is long.
GUI - Graphical User Interface. A generic name for any computer interface that substitutes graphics for text characters.

H
H.261 - A CODEC used in compressing the frames of a video into digital form. H.261 includes a standard for video coding, called p*64. Read as "p times 64," the "p" represents the number of circuits used, and the "64" represents 64 Kbps.
HAB - Handson /Handoff Access Burst.
Half Duplex - Alternating transmission or reception of signals at one time.
HANDO - Handover or Handoff.
Handoff/Handover - The process by which the Mobile Telephone Switching Office passes a cellular phone conversation from one radio frequency in a cell to another radio frequency in another cell. Also, the action of switching a call in progress from one radio channel to another radio channel. Handover is used to allow established calls to continue by switching them to another radio resource whenever mobile stations move from one base station area to another.
Hands-free - Enables drivers to use their cellular phones without lifting or holding the handset to their ears.
Handshaking - The electrical exchange of predetermined signals when a connection is made between two modems or other devices carrying data.
HBM - Human Body Model.
HBT - Heterojunction Bipolar Transistor.
HDLC - High-Level Data Link Control. Layer 2 full-duplex protocol.
HDOP - Horizontal Dilution of Precision. A measure of how much the geometry of the satellites affects the position estimate (computed from the satellite range measurements) in the horizontal East/North plane.
HDSL - High bit-rate Digital Subscriber Line. A standard bit-oriented protocol developed by the International Standards Organisation that allows telephone companies to use existing copper-cable plants while meeting the demands for updated services, including faster modem transmissions.
HDTV - High Definition Television. This term describes several advanced standards proposed by U. S., Japanese and European companies to allow high resolution TV to be received in the home.
Head End - The physical connection where all the signals are broadcast into CATV networks and return signals are concentrated for service actions.
Header - The portion of a packet, preceding the actual data, containing source and destination addresses and error-checking fields.
Held Altitude - The altitude value that will be sent to the Kalman filter as a measurement when in Altitude Hold Mode. It is an Auto Hold Altitude unless an Amended Altitude is supplied by the application processor.
Help Key - A feature PC users can access for information about any menu or item.
HLR - Home Location Register. A permanent database used in GSM to identify a subscriber and to contain subscriber data related to features and services.
Horizontal Dilution of Precision - See HDOP.
Horizontal Scan Rate - This is how fast the scanning beam in a display or a camera is swept from side to side.
Host - A computer that allows users to communicate with other host computers on a network.
Hostname - The name given to a machine on a network.
HP - Host Port.
HPU - Hand Portable Unit.
HSN - Hopping Sequence Number. Digital spread spectrum cordless telephone frequency-hopping parameter.
HT - Hilly Terrain.
Hue - The wave length of a colour.
Huffman Coding - A method of data compression.
Hz - Hertz.

I
I - Integer.
I/O - Input/output.
I/Q - In-Phase and Quadrature.
I2C - Inter-Integrated Circuit.
IA - Integrated Analogue.
IAM - Initial Address Message.
IC - Integrated Circuit.
ICE - In-Circuit Emulation.
ICM - Image Cancel Mixer. Incoming Message.
IDN - Integrated Digital Network.
IE - Information Element.
IEEE - Institute of Electrical and Electronics Engineers. A world-wide engineering publishing and standards-making body for the electronics industry.
IEI - Information Element Identifier.
I-ETS - Interim European Telecommunications Standards.
IF - Intermediate Frequency.
IFC - Integrated Facsimile Controller.
IFS - Intra-Frame Sequencer.
ILEC - Incumbent Local Exchange Carrier.
IM - Inter-Modulation.
Image Compression - Used to reduce the representation of the image information, but not the information itself. Reduces the amount of memory required to store an image.
Image Processing - Dither coding is a method of improving the output quality of transmitted grey scale images through fax systems.
IMEI - International Mobile Equipment Identity. An equipment identification number, similar to a serial number, used to identify a mobile station.
IMSI - International Mobile Subscriber Identity. A specification used to uniquely identify a subscriber to a mobile telephone service.
IMTS - Improved Mobile Telephone Service.
InGaAs - Indium Gallium Arsenide.
Inside Plant - Everything inside a telephone company central office.
INTELSAT - Intelligence Satellite.
Interlaced - A raster system where two or more interleaved fields are used to scan out one video frame.
Internet - A collection of networks interconnected by a set of routers which allow them to function as a single, large virtual network. The Internet (with a capital "I") is the largest such network in the world, using a common protocol and allowing millions of users to share information all over the planet.
Interpolation - A mathematical way of regenerating missing or needed information.
IP - Internet Protocol. Part of the TCP/IP family of communications protocols that are designed to track an Internet address of nodes. Routes outgoing messages and recognises incoming messages. It was originally developed by the Department of Defence to support the interworking of dissimilar computers across a network.
IPB - Internal Peripherals Bus.
IrDA - Infra-red Data Adapter.
IS-54 - Interim Standard 54 for analogue cellular service in North America.
IS-95 - Interim Standard 95.
ISDN - Integrated Services Digital Network. An international standard that defines a digital end-to-end network operating at 1.544 Mbps or slower and supports voice, data, image and video simultaneously.
ISDN-2 - BT's name for Basic rate (2 x 64kpbs connections)
ISDN-30 - BT's name for Primary rate (32 x 64kbps connections)
ISM - Industrial, Scientific, Medical.
ISO - International Standards Organisation. Devoted to determining standards for international and national data communications.
Isochronous - Time relationship where relative timing is important but the actual time is not.
ISP - Internet Service Provider. Any of a number of companies that sell Internet access to individuals or organisations.
ITA - Interim Type Approval. Mobile equipment approval before Full Type Approval (FTA) was available.
ITU - International Telecommunications Union. An organisation established by the United Nations and having as its membership virtually every government in the world.
ITU-T - International Telecommunications Union Telecommunications. An international body of member countries whose task is to define recommendations and standards relating to the international telecommunications industry. Has replaced the CCITT as the world's leading telecommunications standards organisation.
IVR - Interactive Voice Response. Systems that provide information in the form of recorded messages over telephone lines in response to user input in the form of spoken words or Dual Tone Multi-Frequency (TouchTone™) signalling.

J
Jack - Any one of a number of pieces of equipment that are designed to provide quick connectivity.
JBIG - Joint Bi-level Imaging Group of the TSB, working on image compression enhancements for black and white, as well as for grey scale and colour.
JDC - Japanese Digital Cellular (also see PDC).
JPEG - Joint Photographic Experts Group. Industry organisation developing standards and specifications for the encoding and transmission of photographic images over various media and network technologies.
JPO - Joint Program Office. An office within the U.S. Air Force Systems Command, Space Systems Division. The JPO is responsible for managing the development and production aspects of the GPS system and is staffed by representatives from each branch of the U.S. military, the U.S. Department of Transportation, Defence Mapping Agency, NATO member nations and Australia.
JTACS - Japanese TACS.

K
Kalman Filter - Sequential estimation filter which combines measurements of satellite range and range rate to determine the position, velocity, and time at the GPS receiver antenna.
KBD - Keyboard/Backlight/Display.
Kbps - Kilobits per second. A measure of transmission speed.
KHz - Kilohertz. One thousand Hertz, or cycles, per second.

L
L1 Band - The 1575.42 MHz GPS carrier frequency which contains the C/A code, P-code and navigation messages used by commercial GPS receivers.
L2 Band - A secondary GPS carrier, containing only
LAC - Location Area Code.
LAI - Location Area Identification.
Land Mobile Service - A mobile service between base stations and land mobile stations.
Land Station - A station in the mobile service not intended to be used while in motion.
Landline - A telephone circuit that travels over terrestrial circuits by wire or microwave.
LAPD - Link Access Protocol Digital.
LAPDm - Link Access Protocol Digital mobile or Link Access Protocol on the Dm channel.
LAP-M - Link Access Procedure for Modems, an error detection and correction method.
LBS - Location Based Services.
LCC - Leaded Chip Carrier.
LCD - Liquid Crystal Display.
LCS - Loop Current Sense (Signals).
LDO - Low Drop Out.
Leaky Bucket - Informal term for the Generic Cell Rate Algorithm.
Leased Line - A telephone line rented from a telephone company for exclusive use 24-hours a day, seven days a week.
LEC - Local Exchange Carrier. The local phone company, either a Bell Operating Company (BOC) or an independent which provides local transmission services.
LED - Light Emitting Diode.
LF - Low Frequency.
Li-ion - Lithium Ion.
Line Probing - Handshaking signal that allows modems to determine the response of the PSTN channel.
Line Ringing - Provides the user with an audible indication of a call on a specific line.
Linearity - The straightness of a frequency response curve as an indication of accurate sound reproduction. Also a basic measurement of how well an analogue to digital or digital to analogue converter is performing.
Link - An entity that defines a topological relationship between two nodes.
Link Protocol - A set of rules by which a logical data link is established and data is transferred across the link.
Lithium Ion Battery - An efficient battery technology, supporting relatively long standby and talk time with no memory effect.
Lm - Low-mobile channel.
LMDS - Local Multipoint Distribution Service.
LMSI - Local Mobile Station Identity. Unique identity temporarily allocated to visiting mobile subscribers.
LMT - Local Maintenance Terminal.
LNA - Low Noise Amplifier.
LO - Local Oscillator/Local Operator. In the Personal Communications Service (PCS) sense, a local operator is a functional entity providing local wireless service to customers in a certain geographical region.
Loading - A method of improving the voice quality of a phone line.
Local Loop - The pair of wires connecting a subscriber's telephone, or the transmission path between a user's premises and a central office.
lODE - Issue of Data Ephemeris.
Loop Filter - Used in a Phase Lock Loop (PLL) design to smooth out tiny bumps in the output of the phase comparator that might drive the loop out of lock.
Lossless - When the reconstituted image is exactly the same as the original image.
Lossy - When the reconstructed image is different from the original image.
Low-tier PCS - An evolution of cordless systems originally intended for in-building applications, low-tier PCS is used for pedestrians or slow moving vehicles (no more than 30 to 40 mph). Low-tier systems use small cells; as a result, they can be designed with low-power transmitters and experience fewer handoffs than high-tier PCS systems (those for high-speed, mobile users).
LPC - Linear Predictive Coding. A technique for compressing voice.
LPD - Link Protocol Discriminator.
LPLMN - Local Public Land Mobile Network.
LPTS - Low Power Time Source.
LSB - Least Significant Bit.
LSI - Large Scale Integration. The art of putting tens of thousands of transistors into a single integrated circuit.
LTP - Long-Term Prediction. A speech coding technique.

M
m/sec - Metres per second (units of velocity).
m/sec/sec - Metres per second per second (units of acceleration).
m/sec/sec/sec - Metres per second per second per second (units of impulse or 'jerk').
MA - Mobile Allocation.
MACN - Mobile Allocation Channel Number.
MAHO - Mobile-Assisted Handoff.
MAI - Mobile Allocation Index.
MAIO - Mobile Allocation Index Offset. Indicates at which frequency within the hopping sequence the Mobile Station (MS) and Base Station (BS) will start to hop.
MAN - Metropolitan Area Network. A network which encompasses interconnectivity between devices in a metropolitan area such as a city. Typically, connecting LANs over the subscriber loop. Extends to 50-kilometres, operates at speeds from 1 Mbps to 200 Mbps and provides an integrated set of services for real-time data, voice and image transmission.
MAP - Mobile Application Part.
Mask Angle - The minimum GPS satellite elevation angle permitted by a particular GPS receiver design.
MBONE - Multicast Backbone.
Mbps - Megabits per second. Million bits per second, a measure of transmission speed.
Mbps - Megabits per second. Million bits per second, a measure of transmission speed.
MCC - Mobile Country Code. Three digit country code used in GSM networks.
MCI - Malicious Call Identification. Media Control Interface.
MClk - Master Clock.
MCM - Multiple Chip Module.
MCU - Micro Controller Unit.
MDP - Modem Data Pump.
ME - Mobile Equipment.
Measurement Error Variance - The square of the standard deviation of a measurement quantity. The standard deviation is representative of the error typically expected in a measured value of that quantity.
Media Cellular Adapter.
MESFET - Metal Semiconductor Field-Effect Transistor.
MF - Mandatory Fixed length or Multi-Frequency.
MFD - Multi-Function Display.
MFI - Multi-Function Interface.
MFP - Multi-Function Peripheral
MH - Modified Huffman data compression coding, a CCITT Recommendation T.4 for Group 3 fax machines.
MHz - Megahertz. One million hertz, or cycles, per second.
MIB - Management Information Base.
MIC - Microwave Integrated Circuit.
MIDI - Musical Instrument Digital Interface.
MII - Media Independent Interface.
MIN - Mobile Identity Number.
MIPS - Million Instructions Per Second. A measure of a computer's speed or power.
MLSE
MLSIE - Maximum Likelihood Sequence Estimation.
MM - Mobility Management. Man-Machine.
MMI - Man-Machine Interface.
MMIC - Microwave Monolithic Integrated Circuit.
MMR - Modified Read. Data compression coding that is about 50 percent faster than MR. Also a two-dimensional coding scheme but of higher efficiency than MR.
MMS - Multi-Media Messaging Services.
MN - Mobile Network.
MNC - Mobile Network Code. Two digit code that identifies a GSM network within a country.
MNP - Microcom Networking Protocol™, the de-facto standard for error correction and data compression in dial-up modems. Among its more popular classes are an error detection and correction method (MNP 2-4), data compression (MNP 5 & 7), and enhanced capability (MNP 10 for adverse channel reliability / MNP10EC).
MNP4 - Error correction
MNP5 - Data compression
Mobile Phone - The type of cellular phone that's installed in a vehicle. A mobile unit is attached to the vehicle, draws its power from the vehicle's battery, and has an external antenna.
MOC - Mobile-Originated Call.
Modem - A type of computer equipment that links computers via telephone lines and enables the transmission of data. Derived from the words "modulate" and "demodulate," because a modem converts, or modulates, transmission signals from digital to analogue for transmission over analogue telecommunications lines, and then converts them back, or demodulates the signals, from analogue back to digital.
Modulation - The impression of information on a carrier.
Modulator - A circuit that combines two different signals in such a way that they can be pulled apart later.
Moire - A type of image artefact that occurs when a pattern is created on the screen where there shouldn't be one.
Monochrome - A video source having only one component.
MONOFAX™ - A Rockwell proprietary single chip fax modem.
Motion Compensation - A compression technique that exploits similarities in neighbouring pixels, and divides the image up into rectangular blocks, using a displacement vector to describe movement of all pixels within the block.
Motion Estimation - The attempt to determine where an object has moved from one video frame to the other.
MoU - Memorandum of Understanding. In the context of GSM, this is signed by a number of potential GSM PLMN operators.
MPEG - Motion Picture Experts Group. An ISO standards group dealing with video and audio compression techniques and mechanisms for multiplexing and synchronising various media streams.
MR - Master Reset
MR - Modified Read data compression.
MS - Mobile Station. A wireless telephone allowing mobility so that calls may be placed both locally and in other regions; a terminal equipped with a Subscriber Identity Module (SIM).
MSC - Mobile (services) Switching Centre. Performs the functions of switching, routing, control of the call, and charging and accounting.
MSC Area - The part of the Public Land Mobile Network (PLMN) covered by an MSC.
MSCM - Mobile Station Class Mark.
MSIC - Mobile Subscriber Identification Code.
MSISDN - Mobile Station ISDN number. An ISDN number provisioned to a mobile station subscriber and used to place a call to the subscriber. This number defines the mobile station as an ISDN terminal and consists of three parts: the Country Code (CC), the National Destination Code (NDC), and the Subscriber Number (SN).
MSK - Minimum-Shift Keying.
Msps - Megasamples per second. Million samples per second.
MSRN - Mobile Station Registration Number. A code that is allocated to a mobile station for the purpose of routing calls.
MSS - Mobile Satellite Service.
MT - Message Type.
MTA - Metropolitan (Major) Trading Area. An area defined by the FCC for the purpose of issuing licenses for Personal Communications Service (PCS). Also Message Transfer Agent.
MTBF - Mean Time Between Failure. The average time a device runs until it fails.
MTC - Mobile-Terminated Call.
MTF - Modulation Transfer Function.
MTS - Mobile Telephone Service.
MTTF - Mean Time To Failure (see MTBF).
Multipath Errors - GPS positioning errors caused by the interaction of the GPS satellite signal and its reflections.
mV - Millivolt.
mW - Milliwatt.

N
NAB - National Association of Broadcasters.
NADC - North American Digital Cellular.
NAM - Number Assignment Module. The electronic memory in a cellular phone that stores the telephone number.
NAMPS - Narrowband Advanced Mobile Phone Service.
Narrowband - Mobile or portable radio services, usually paging and data services.
NAVSTAR - Navigation Satellite Timing and Ranging.
NB - Normal Burst.
NCC - National Colour Code.
N-CDMA - Narrowband CDMA.
Negative Compression - Compression resulting in more pixels than originally present.
NF - Noise Factor.
NGR - National Grid Reference.
NiCad - Nickel Cadmium.
NiMH - Nickel Metal Hydride.
NM - Network Management.
NMC - Network Management Control/Centre.
NMEA - National Marine Electronics Association.
NMI - Non-Maskable Interrupt.
NMT - Nordic Mob
Noninterlaced - A method of scanning out a video display that is the complete opposite of interlaced. All lines in the frame are scanned out sequentially, one right after the other.
NT - Network Termination.
NTSC - National Television Standards Committee. NTSC is one of the standards used to get video signals into homes and onto video tapes (see PAL and SECAM).
NVRAM - Non-Volatile Random Access Memory.

O
O & M - Operation and Maintenance.
ODP - Originator Detection Pattern. A bit sequence under V.42 transmitted by the originating modem to the receiving modem and answered by an ADP.
OEM - Original Equipment Manufacturer.
OGM - Outgoing Message.
OQPSK - Offset Quadrature Phase-Shift Keying.
OSI - Open Systems Interconnection. Standard model of electronic communications defined by the ISO; a 7-layer architecture model for communications systems developed by ISO and used as a reference model for most network architectures; the only internationally accepted framework of standards for communication between different systems made by different vendors.
OSI RM - OSI Reference Model.

P
PAL - Phase Alternate Line. The European video standard counterpart to NTSC.
Part 68 - The section of the FCC's ruling that governs the direct electrical connection of the non-telephone company-provided equipment to the telephone network. Part 68 requirements are specifications established by the FCC as the minimum acceptable protection which communications equipment must provide the telephone network.
PBX - Private Branch eXchange. U.S. terminology for PABX.
PBX Tie Line - A line between two PBXs permitting connection of a conversation without going through the public telephone system.
PCB - Printed Circuit Board.
PCI - Peripheral Component Interconnect.
PCM - Pulse Code Modulation. The most common method that North American telephone systems use to sample voice signals and convert them into equivalent digital code.
PCMCIA - Personal Computer Memory Card International Association. Consortium which sets standards for small, credit-card sized plug-ins for portable and desktop personal computers, sometimes referred to as PC cards. The PCMCIA standards include three types, distinguished by increasing thickness: Type 1: very thin memory cards. Type 2 :most modems and interfaces.
PDA - Personal Digital Assistant.
PICA - PCMCIA Interface Control Adapter for PC card modems.
Pixel - A picture element. The smallest division that makes up the raster scan line for computers. For example, when the horizontal resolution is defined as 640, that means there are 640 individual locations or spots that make up the horizontal scan line.
Pixel Clock - Used to divide incoming horizontal video into pixels. This clock has to be stable (a very small amount of jitter) relative to the incoming video or the picture will not be stored correctly.
PLCC - Plastic Chip Carrier Component. A type of surface-mount packaging.
PLL - Phase Lock Loop. A circuit that acts as a phase detector.
Point-to-Multipoint Connection - A circuit in which a single signal goes from one origination point to many destination points. The classic example is a TV signal. A collection of associated ATM links, with associated endpoint nodes, containing the following properties: one ATM link, called the Root Link, serves as the root in a simple tree topology; when the Root Node sends information, all of the remaining nodes on the connection, called Leaf Nodes, receive copies of the information; each of the Leaf Nodes on the connection can send information directly to the Root Node; the Leaf Nodes cannot communicate directly to each other with this connection type.
Point-to-Point - Any connection between two locations that can be either dial-up (established by telephone call), or dedicated (the two points on the connection are fixed).
Polling - A data network arrangement whereby a central computer asks each remote location whether or not they want to send information.
POTS - Plain Old Telephone Service. The basic service supplying standard single-line telephones and access to the public switched network.
P-P - Peak-to-Peak.
PPM - Pulse-Position Modulation.
PPS - Passive Pixel Sensor.
PQFP - Plastic Quad Flat Package. A type of surface-mount packaging.
Premises - Denotes the space occupied by a customer or authorised joint user in a building or location.
Private Network - A series of offices connected together by leased or non-leased phone lines, with switching facilities and transmission equipment owned and operated by the user or by the carrier.
Private Voiceband Network - A network that is made up of voice band circuits, and sometimes switching arrangements, for the exclusive use of one customer.
PROM - Programmable Read Only Memory, which can be programmed once by the user and then becomes permanent storage.
Protocol - A specific set of rules, procedures or conventions relating to format and timing of data transmission between two devices.
PSK - Phase Shift Keying modulation method, a more bandwidth-efficient method than FSK.
PSPDN - Packet-Switched Public Data Network.
PSTN - Public Switched Telephone Network. Usually refers to the world-wide voice telephone network accessible to all those with telephones and access privileges. The PSTN is a gigantic maze of switching computers that can connect any two telephony points in potentially hundreds of different ways.
PTT - Post Telephone & Telegraph administration. Controlled by governments to provide telephone and telecommunications services in most foreign countries.
PUC - Public Utilities Commission. State body that regulates telephone companies.
PWB - Printed Wiring Board.
PWM - Pulse Width Modulator.

Q
QAM - Quadrature Amplitude Modulation. Of practical modulation techniques, QAM has the best bandwidth efficiency per information symbol (baud). It is used in most modems.
QCIF - Quarter Common Intermediate Format. A mandatory part of the ITU-T video standard which requires that non-interlaced video frames be sent with 144 luminance line and 176 pixels.
QFP - Quad Flat Package. A type of surface-mount packaging.
QoS - Quality of Service.
QPSK - Quadrature Phase-Shift Keying.
Quantisation Noise - Signal errors which result from the process of digitising a continuously variable signal.

R
RAB - Random Access Burst.
RACH - Random Access CHannel.
RAM - Random Access Memory. Read-write volatile memory that is lost when power is discontinued; temporary storage.
RAND - Random number. Used as a challenge in a challenge response protocol.
RAPI - Rockwell API.
Raster - A series of scan lines that make up a TV picture or a computer's display.
RIN - Royal Institute of Navigation. A UK organisation involved with all kinds of navigation technologies.
Rx - Receiver. The receiving side of a transmission.
RXLEV - Received Signal Level.
RXQUAL - Received Signal Quality.

S
SA - Selective Availability. The method used by the DoD to control access to the full accuracy achievable with the C/A code.
SABM - Set Asynchronous Balanced Mode. Layer 2 command.
SACCH - Slow Associated Control Channel.
Sample Rate - The number of times per second that an analogue signal is measured and converted to a binary number.
SAP - Service Access Point.
SAPI - Service Access Point Identifier (or Indicator).
SAT - Supervisory Audio Tones.
Satellite Elevation - The angle of the satellite above the horizon.
Saturation - The amount of colour present. For example, a lightly saturated red looks pink, while a fully saturated red is deep and rich.
SAW - Surface Acoustic Wave.
SB - Synchronisation Burst.
SC - Signalling Controller.
Scaling - The act of changing the effective resolution of the image.
Scan Line - An individual sweep across the face of the display by the electron beam that makes the picture.
SCM - Station Class Mark.
SCN - Subchannel Number. One of the parameters defining a particular physical channel in a Base Station (BS).
SDC - Synchronous Data Compression. A technique that preserves HDLC/SDLC frame integrity for transmission across an analogue link without any jitter or delay.
SDI - Silence Deletion/Insertion.
SDLC - Synchronous Data Link Control. A subset of the more generic High-Level Data Link Control (HDLC) protocol developed by the International Organisation for Standardisation (ISO).
SDMA - Space-Division Multiple Access.
SDSL - Single-line Digital Subscriber Line.
SECAM - Systeme Electronique Couleur Avec Memoire. A TV format similar to Phase Alternate Line (PAL), used in France and the Eastern Block countries. The difference between the two is that in SECAM the chrominance is Frequency Modulation (FM) modulated.
SEP - Spherical Error Probable. The radius of a sphere, centred at the user's true location, that contains 50 per cent of the individual three-dimensional position measurements made using a particular navigation system.
Sequential Receiver - A GPS receiver in which the number of satellite signals to be tracked exceeds the number of available hardware channels. Sequential receivers periodically reassign hardware channels to particular satellite signals in a predetermined sequence.
Service Plan - A rate plan selected by subscribers when they start up cellular service, usually consisting of a base rate for system access and a per-minute rate for usage.
Set-Top - A household device which demodulates the CATV broadcast signal and remodulates it to a frequency usable by the subscriber's television and VCR. Called set-top since it usually sits on top of the television set.
SFH - Slow Frequency Hopping.
Shading Compensation - compensation corrects for non-uniformity in the scanner optical system, and includes distortions due both to light sources and to non-uniformity in the scanner sensor element.
SID - Silence Descriptor. Frame sent with no voice activity.
Signalling - Information in the form of electrical signals for the purpose of directing voice traffic over a telecommunications network.
SIM - Subscriber Identity Module. A "smart" card installed or inserted into a mobile telephone containing all subscriber-related data.
SIN - System Identification Number.
SINAD - Signal + Noise and Distortion.
SIO - Serial Input/Output.
SLC - Subscriber Loop Carrier.
Smart Channel Hopping - When a digital spread spectrum cordless telephone signal jumps to an available clear channel to avoid interference.
SMB - System Management Bus.
SMDS - Switched Multimegabit Data Services. A high-speed, cell-based carrier used to connect LANs, MANs and WANs to exchange data.
SMG - Special Mobile Group.
SMS - Short Message Service. Enables a phone to send a short text message to another phone.
SMSCB - Short Message Service Call Broadcast.
SMT - Surface-Mounted Technology.
SNR - Signal-to-Noise Ratio. The magnitude of the signal divided by the amount of unwanted data (noise) that is interfering with the signal.
SOHO - Small Office/Home Office.
SOIC - Small Outline Integrated Circuit.
Spread Spectrum - Originally developed by the military for secure communications, spread-spectrum radio transmissions essentially "spread" a radio signal over a very wide frequency band in order to make it difficult to intercept and jam.
SPS - Standard Positioning Service. A positioning service available to all GPS users on a continuous, world-wide basis with no direct charge. SPS uses the C/A code to provide a minimum dynamic and static positioning capability.
SRAM - Static Random Access Memory.
SRES - Signed Response. Response to a challenge in the challenge response protocol.
SS - Supplementary Service(s).
SSOP - Shrink Outline Package, a type of surface-mount packaging.
Standby SRAM - Portion of the SRAM that is powered by a 'keep-alive' power supply when prime power is removed to preserve important data and a