MobileWorld's Glossary

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ADC - Analog to Digital Converter.

Adjacent channel interference - Refers to interference caused by the energy from a transmitting channel spilling over into an adjacent channel. This interference can be minimized by applying filters to the transmitting and receiving ends or by simply using non-adjacent frequency channels within a cell. Cellular systems typically transmit on non-adjacent frequencies within a cell in order to prevent adjacent channel interference.

Airtime - Actual time spent talking on the cellular telephone. Most carriers bill customers based on how many minutes of airtime they use each month.

AJ - Anti-Jam. A communication signal that is designed to resist interference or jamming.

Alert - Constant 10 KHz signaling tone sent on the reverse voice channel (by the mobile), in an analog conversation, while the mobile phone is ringing.

Alphanumeric - A message or other type of readout containing both letters ("alphas") and numbers ("numerics"). In cellular, "alphanumeric memory dial" is a special type of dial-from- memory option that displays both the name of the individual and that individual's phone number on the cellular phone handset.

AM - Amplitude Modulation. The simplest carrier modulation technique where the RF carrier's amplitude envelope is modulated.

AMPS - Advanced Mobile Phone System. The current analog cellular FM system in North America. It uses 30 KHz channels and signaling is done superaudio.

Analog - The traditional method of modulating radio signals so that they can carry information. AM (amplitude modulation) and FM (frequency modulation) are the two most common methods of analog modulation. Analog modulation techniques have been around for more than 50 years and offer a proven, known method of using analog, but the switch to digital is already underway.

ANSI - American National Standards Institute. The ultimate accolade for any standard is ANSI certification. This does not mean that ANSI has reviewed the standard, but that it has been circulated widely throughout the industry and that it conforms to their document design and publication guidelines.

ARDIS - A wireless two-way data network jointly owned and operated by Motorola and IBM.

Attenuation - Weakening of the RF signal due to being partially blocked or absorbed. Attenuation is heavily dependent on the frequency of the RF transmission and on the physical characteristics of the material that the transmission interacts with. For example, high frequency microwave transmissions are severely attenuated by rain, but lower frequency cellular transmissions are not.

Auto-correlation - A measure of the similarity between a signal and a time-shifted replica of itself; a special case of cross-correlation. The auto-correlation function is the theoretical basis of direct sequence spread spectrum.

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Bandit Mobile - A mobile subscriber that is revealed in the toll-ticketing records as having an invalid ESN, invalid telephone number, or other problem that warrants denial of service to that mobile.

Bandwidth - The amount of frequency allocated for an RF transmission. For example, a cellular channel typically has a bandwidth of 30 KHz, I.E. a cellular system requires 30 KHz of frequency per channel to transmit it's signal.

Base station - The base station is a multicircuit transceiver located at the center of a cell whose primary purpose is to handle all incoming & outgoing calls within the cell. The base station relays the mobile's signal to the MTSO via wireline.

BER - Bit Error Rate.

Broadband - A communications channel that has a bandwidth greater than 64 kilobits per second and that can provide higher speed data communications than a standard telephone circuit (also called wide band).

BT - Bandwidth data rate product, filter bandwidth times bit period, for various modulations including GMSK. Also referred as modulation depth. For example, GSM uses GMSK with BT=0.3.

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Call Forwarding - A feature allowing the subscriber to forward a call to another telephone number.

Call Processing - The complete process of routing, originating, terminating cellular telephone calls, along with the necessary billing and statistical collection processes.

Call Record - A record stored on DAS tape containing mobile number, dialed digits, time stamp information, and other data needed to bill or 'ticket' a cellular telephone call.

Call Setup - The call processing events that occur during the time a call is being established, but not yet connected.

Call Waiting - A feature allowing the subscriber to be alerted of another call during a current conversation. User can answer the call waiting, but cannot connect all parties (connecting all parties is considered a conference call).

Carrier - The operating frequency of a wireless system. A fixed frequency radio signal which is shifted up and down (modulated) in either frequency (FM) or level (AM) by the audio signal.

CDMA - Code Division Multiple Access. In a CDMA system, each voice circuit is labeled with a unique code and transmitted on a single channel simultaneously along with many other coded voice circuits. The receiver uses the same code to recover the signal from the noise. The only distinctions between the multiple voice circuits are the assigned codes. The channel is typically very wide with each voice circuit occupying the entire channel bandwidth. This system used 1.23 MHz wide channel sets. The full vocoder rate is 8.55 Kbits/sec, but voice activity detection and variable rate coding can cut the data rate to 1200 bits/sec. A very robust and secure channel can be established, even for an extremely low-power signal-theoretically, the signal can be weaker than the noise floor.
CDMA channel


1.25MHz     |   64 different voice circuits   |


64 different voice circuits can be simultaneously transmitted on the same channel. More impressively, by using different codes, a number of different channels can simultaneously share the same spectrum, without interfering with each other. The voice circuits are identified by their assigned codes.

CDPD - Cellular Digital Packet Data - sending digital data over the existing AMPS system, by transmitting dense packets on vacant analog channels

CDPD Forum - Cellular Digital Packet Data Forum. A trade association to promote the development of the cellular data industry and, in particular, to the standardization and effective use of cellular digital packet data (CDPD technology). This group maintains the CDPD protocol specification that allows the transmission of packet data over analog cellular channels.

Cell - The RF coverage area in the cellular system resulting from operation of a single multiple-channel set of base station frequencies. Cell can also refer to the base site equipment servicing this area. A city or county is divided into smaller "cells", each of which is equipped with a low-powered radio transmitter/receiver. The cells can vary in size depending upon terrain, capacity demands, etc. By controlling the transmission power, the radio frequencies assigned to one cell can be limited to the boundaries of that cell.

Cell splitting - A means of increasing the capacity of a cellular system by subdividing or splitting cells into two or more smaller cells.

CELP - Code Excited Linear Predictive compression algorithm.

Central Office (CO) - The switching office that connects the MTSO (Mobile Telephone Switching Office) to the PSTN (Public Switched Telephone Network). The CO is also known as a Class 5, or 'end' office.

CGSA - Cellular Geographic Service Area. The actual area in which a cellular company provides cellular service.

Channel - A unique RF frequency that is used for communication between subscriber unit and cell site base station. Must be assigned by the FCC (Federal Communications Commission).

Chip - The time it takes to transmit a bit or single symbol of a PN code.

Click Tone - A particular progress tone injected onto the forward voice channel (mobile unit receive, base station transmit) to indicate to the subscriber that the call has not been abandoned by the system.

Cochannel interference - Cochannel interference refers to the interference caused between two cells transmitting on the same frequency within a network. Since cochannel interference is caused by another cell transmitting the same frequency, you can't simply filter out the interference. You can only minimize the cochannel interference through proper cellular network design. A cellular network must be designed to maximize the C/I ratio. The C/I ratio is the carrier-to-cochannel interference ratio. One of the ways to maximize the C/I ratio is to increase the frequency re-use distance, I.E. increase the distance between cells using the same set of transmission frequencies. The C/I ratio in part determines the frequency re-use distance of a cellular network.

Compandor - A combination of a compressor at the transmitter to reduce the dynamic range of the transmitted signal and an expander at the receiver to recover this signal to the original dynamic range. The transmitter encodes (compresses) the dynamics of the audio signal and the receiver decodes (expands) the dynamics of the audio signal. Used in communications systems to improve signal-to-noise as a result of reduced transmitted dynamic range. In analog cellular, 2:1 syllabic compression is used to limit the maximum peak voice deviation to +/- 2.9 KHz.

Constructive interference - Interference that occurs when waves occupying the same space combine to form a single stronger wave. The strength of the composite wave depends on the how close in phase the two component waves are. For example if you transmitted two waves of the same phase, each with an amplitude of 10, they would combine into a composite wave of amplitude 20, but two waves slightly out of phase would combine into a composite wave of amplitude less than 20.

Control Channel - A unique RF channel used by each base station dedicated for the transmission of digital control information from the base station to the mobile unit. Used to assign voice channels, control mobile power, authorize handoffs, etc.

Correlator - The receiver component that demodulates a spread spectrum signal; a device that measures the similarity of of an incoming signal and a stored reference code.

COTS - Commercial Off The Shelf.

Cross-correlation - A measure of the similarity of two different signals.

CT2 - Cordless Telephone 2.

CTIA - Cellular Telecommunications Industry Association.

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DAR - Digital Audio Radio.

DAS Tape - The magnetic tape that is used at the MTSO to record traffic statistics and call billing information. This tape is sent to a third-party 'billing-house' where the actual billing of the subscribers is done.

dB (decibel) - A unit stating the logarithmic ratio between two amounts of power. Typically used in receiver and transmitter measurements.

dBi - Decibel, Isotropic; decibel referenced to the gain of a theoretical isotropic radiator.

dBm - Decibel, Milliwatt; decibel referenced to one milliwatt into 50 ohms.

DBS - Direct Broadcast Satellite.

DCS - Digital Cellular System

DCS-1800 - Low power variant of GSM, with 1.8 GHz carrier, used in Europe (e.g., Mercury One-2-One)

DCS-1900 - Proposed use of GSM with 1.9 GHz carrier for PCS applications.

DCTU - Digital Cordless Telephone U.S. - a version of DECT proposed for the U.S. PCS market

DDS - Direct Digital Synthesis.

DECT - Digital European Cordless Telephone. A digital cordless telephone standard that incorporates some of the features of the cellular telephone systems. DECT telephones use picocells, and calls can be handed off from one cell to the next.

Detector (Demodulator) - The circuit in a receiver which is used to recover the intelligence (audio) from a signal.

De-Spreading - The process used by a correlator to recover narrowband information from a spread spectrum signal.

Destructive interference - Interference that occurs when waves occupying the same space combine to form a single weaker wave. This type of interference occurs when waves out of phase combine to form a composite wave which is weaker than any of it's component waves. For example if you transmitted two waves that were exactly 180 degrees out of phase, each with an amplitude of 10, they would completely cancel each other out.

DGPS - Differential GPS.

Digital modulation - A method of encoding information for transmission that will eventually replace analog transmission. Digital modulation reduces voice to binary code -- the zeros and ones of computer language. At the receiving end, the information is reconverted. Digital transmission offers stronger reception, less static, greater call handling capacity, fewer dropped calls, improved call privacy, and the potential for additional voice and data service such as fax and computer data transmission.

Direct Sequence - A pseudorandom (PN) code is added to the data signal which increases the modulation rate and signal bandwidth. This spreading of the energy over a wide bandwidth looks like a low level signal to other users in the band. The receiver must know the PN code transmitted and be synchronized to the code to assemble each data bit.

Diversity - Sharing a signal characteristic to allow more users in the same frequency band.

Diversity Receive - A method commonly employed by cellular manufactures to improve the signal strength of received signals. Uses two independent antennas that receive signals which differ in phase and amplitude resulting from the slight difference in antennas position. These two signals are either summed or the strongest is accepted by voting. The most popular methods include dual-antenna phase switching, dual-receiver audio switching and "ratio diversity" audio combining. The most effective method is ratio diversity combining.

Discontinuous Transmission (DTX) - A subscriber unit feature that allows the mobile to disable it's RF PA during conversation when the subscriber is not talking. Save on battery life to increase talk time. The cellular system must support this feature if the subscriber wants to use DTX.

DMR - Digital Mobile Radio.

DPSK - Differential Phase Shift Keying -- a simplified BPSK where only data transitions are transmitted.

Drop Out - A momentary loss of the carrier and sound, or a buildup of background noise when the transmitter is in a certain location in the room. Moving the transmitter (even a few inches) usually restores the sound to normal.

DSP - Digital Signal Processing.

DSRR - Digital Short Range Radio. The Commission of the European Community has designated 880 to 890 MHz and 933 to 935 MHz for unlicensed, business citizens band radio in Europe. For point-to-point communications over distances up to 6 km maximum, depending on antenna height.

DTMF - Dual Tone Multi Frequency. Commonly known as 'touch-tones', this in-band signaling is made up of two tones (out of a group of 8) and is used to translate dialed digits.

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EIA/TIA-553 - The ANSI version of the analog cellular standard. Generally one step behind IS-91, and without support for NAMPS.

Electronic Serial Number (ESN) - A 32 bit code that is unique to each mobile unit. Used to validate mobile. Not alterable by both cellular operator and end user. Each cellular phone is assigned an ESN, which is automatically transmitted to the base station every time a cellular call is placed. The Mobile Telephone Switching Office checks the ESN to make sure it is valid, that the phone has not been reported stolen, that the user's monthly bill has been paid, etc., before permitting the call to go through.

Erlang - A dimensionless quantity used in the traffic statistical measurements in the cellular system. One erlang is equivalent to the average number of simultaneous calls. One erlang equals 3600 call-seconds per hour or 36 CCS (call century seconds) per hour.

ESMR - Enhanced Specialized Mobile Radio. Digital mobile telephone services offered to the public over channels previously used only for analog two-way dispatch.

ETACS - Extended TDMA. This system uses the same 30 KHz channels as TDMA, but has six users per channel. The vocoder rate is cut to 4 Kbits/sec, and the channels are dynamically assigned based on voice activity detection.

ETSI - European Telecommunications Standards Institute. The mission of ETSI is "to produce the technical standards which are necessary to achieve a large unified European telecommunications market". This includes the specification of the GSM cellular and PCS standard.

Execute source - An order sent to the mobile on the Forward Voice Channel telling mobile to change channels. Order contains new channel number and new power level.

Execute target - An order sent to the cell a mobile is being handed off to, informing the cell of the pending arrival of a mobile.

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Fade - A drop in the received signal strength as a result of the RF transmission's interactions with the transmission environment.

FCC - Federal Communications Commission. The government agency responsible for regulating telecommunications in the United States, located in Washington, D.C. Their responsibilities for public radio communications, such as cellular, include allocation of frequencies, the development of regulations that govern their use and monitoring to ensure that regulations are followed.

FDMA - Frequency Division Multiple Access. FDMA systems transmit one voice circuit per channel. Each conversation gets its own, unique, radio channel. The channels are relatively narrow, usually 30 KHz or less and are defined as either transmit or receive channels. A full duplex conversation requires a transmit & receive channel pair. For example, if a FDMA system had 200 channels, the system could handle 100 simultaneously full duplex conversations. (100 channels for transmitting and 100 channels for receiving)
FDMA channel


30KHz   | Single voice circuit - one way conversation only  |


FEC - Forward Error Correction (coding / decoding technique). 

FER - Frame Error Rate.

FH - Frequency Hopping.

FHMA - Frequency Hopping Multiple Access.

Flash- Hook - 400ms of signaling tone sent on the reverse voice channel (by the mobile) to request a hook flash.

FM - Frequency Moduation; modulation of the RF carrier frequency.

Follow-Me Roaming - The ability for the cellular system to automatically forward calls to a roaming mobile that has left it's primary service area. Without this feature, the calling party must know the location of the roamer and place a call to that areas MTSO first (calling a 'port'), then calling the mobile.

Forced Disconnect - A call processing function that forces termination of a call, usually not at the mobile subscriber's request.

Forward Control Channel (FOCC) - A Control Channel used from the base station-to-subscriber direction, also known as the control channel downlink.

Forward Voice Channel (FVC) - A voice channel used in the base station-to-subscriber direction, also known as the voice channel downlink.

Four-Wire Line - A two-way transmission circuit using two pairs of conductors, to allow full duplex (simultaneous) conversation without multiplexing.

Free space loss - This is simply the power loss of the signal as a result of the signal spreading out as it travels through space. As a wave travels, it spreads out its power over space, I.E. as the wave front spreads, so does its power.

Frequency hopping - The transmitter hops to one of many channels, The receiver knows the sequence of the frequency hopper and follows each hop.

Frequency Reuse - The ability to use the same frequencies repeatedly within a single system, made possible by the basic design approach for cellular. Since each cell is designed to use radio frequencies only within its boundaries, the same frequencies can be reused in other cells not far away with little potential for interference. The reuse of frequencies is what allows a cellular system to handle a huge number of calls with a limited number of channels.

Frequency Shift Keying (FSK) - The form of frequency modulation that used two separate audio frequencies to transmit binary ones and zeros.

Front-End - The first stage of filtering in a receiver. The first circuit stage following the antenna input to the receiver.

FSK - Frequency Shift Keying; a digital binary modulation of the RF carrier frequency.

Full Duplex - Refers to a communications system that uses two separate transmit and receive paths to allow simultaneous conversation in two directions.

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GaAs - Gallium Arsenide.

GEO - Geosynchronous Earth Orbit satellite. Geosynchronous systems include Inmarsat and OmniTRACS. The Inmarsat system uses allocations in the 6 GHz band from the ground station to the satellite, 1.5 GHz for the satellite-to-terminal downlink, 1.6 GHz for the terminal-to-satellite uplink, and 1 GHz from the satellite to the ground station.

Glare Hold and Glare Release - A method of glare resolution. Glare occurs when both the local and distant end of a trunk are seized at the same instant; this usually results in deadlock of the trunk. To prevent this, one end of the trunk is assigned a glare hold status and the other a glare release status. In the event of glare, the glare hold end holds the trunk and the glare release end releases the trunk and attempts to seize another. Used between MTSO and connecting cell sites.

GLONASS - The Russian Global Navigation Satellite System is similar in operation and may prove complimentary to the NAVSTAR system. Launched in 1996, is a 24 satellite constellation 19,100 Km above the earth in three orbital planes.

GMSK - Gaussian Minimum Shift Keying. A form of frequency shift keying which shapes pulses to minimize spectral leakage. Used in GSM.

GNSS - Global Navigation Satellite Systems. Extended GPS systems, providing users with sufficient accuracy and integrity information to be useable for critical navigation applications.

GPS - Global Positioning Satellite. Satellite-based radio positioning systems that provide 24 hour three-dimensional position, velocity and time information to suitably equipped users anywhere on or near the surface of the Earth (and sometimes off the earth). GPS is a 24 satellite constellation, 20,000 Km above the earth in six orbital planes. The NAVSTAR system, operated by the U.S. Department of Defense, was the first GPS system widely available to civilian users.

Grade-of-Service - A measure of what percentage of calls placed through an exchange fail to be completed due to congestion of that exchange. In cellular, a 2% GOS is considered acceptable.

GSM - Global System for Mobiles. The most mature digital wireless standard is GSM, usually referred to as the 'European' digital standard. GSM is a TDMA standard, with 8 users per channel. The speech is taken in 20 ms windows, which are sampled (13-bit resolution at 8 ksps), processed and compressed. The vocoder rate of 13 kbits/s is used. A channel is 200 KHz wide, and contains data from eight users. Each user has a time slot of 0.577 mS, during which a burst of 156 bits is transmitted at a modulation frequency of approximately 270 KHz. GSM is transmitted on a 900 MHz carrier.

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Half-rate - A variant on GSM; doubles capacity by more efficient coding using speech compression.

Handoff (inter-cell) - The process by which subscribers traveling throughout the system coverage area are switched from cell-to-cell (and different channels) with better coverage for that particular area when poor quality conversation is detected.

Handoff (intra-cell) - The process by which subscribers traveling throughout the system coverage area are switched from cell sector-to-sector (and different channels) with better coverage for that particular area when poor quality conversation is detected.

Hands-free: - A feature that's included with most of today's car phones. It permits the driver to use his cellular car phone without lifting or holding the handset to his ear. An important safety feature.

HO Tone - Handoff Tone. 50ms of signaling tone sent by the mobile on the REVC to indicate leaving the source cell site during handoff.

Hand Off Measurement Request. (HOMR) - A digital message sent from the MTSO to a possible target cell site requesting the scanning receiver at that cell scan and report the RSSI of a particular mobile.

Handshaking - A set of signals that coordinate the transfer of data from one device to another.

Hard-Handoff - A hand off that occurs when the subscriber is already using the TPC (three-party-conference) card, and the TPC card cannot be used to aid in a smooth handoff.

Harmonic Filter - Used in the base-station and subscriber transmitter circuits to remove unwanted harmonics from being transmitted and radiated by the antenna.

High Side Injection - A superhet receiver design in which the oscillator frequency is above the carrier frequency.

HIPERLAN - An ETSI approved wireless WLAN, operating at 5.2 GHz with data rates up to 20 Mbps per channel (5 channels).

Hybrid - A circuit used in telephony to convert 2-wire to 4-wire operation and vice-versa. Every telephone contains a hybrid to separate ear piece and mouthpiece audio and couple both into a 2-wire circuit that connects to the Central Office. If the hybrid is not balanced properly, echo or 'loop-back' can result in the circuit when the transmitted signal is reflected back into the receive path.

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Idle Channel - A channel that is assigned to a base station use but is not currently in service (being used). All idle channels for each base station are kept in a 'idle-link-list' which is constantly updated at the MTSO.

IEEE802.11 - A WLAN standard (or set of standard), operating at 2.4 GHz and with data rates of up to 1 Mbps

IF - Intermediate Frequency. Refers to the resulting signal in a superhet receiver after the incoming carrier is mixed with the oscillator signal.

Image Rejection - A measure of the ability of the receiver to reject RF signals present on the image frequency of the receiver. Image rejection is one of the purposes of front-end filtering in a superhet receiver.

IM Rejection - A measure of the ability of the receiver to reject signals which are capable of producing IM products.

Infrastructure - All parts of the cellular system, excluding the subscriber. Includes the MTSO, Base Stations, Cell Sites, and all links between them.

In-Band Signaling - A process in which audio tones between 300 and 3400 Hz provide supervisory and/or address signaling.

Interface - A common boundary between two or more systems, integrated circuits, or pieces of equipment that ensures a proper connection between them.

Intermodulation - Also referred to as "IM." The mixing of two or more signals, producing sums, differences and harmonic multiples. IM generally occurs in the gain amplifier ahead of the mixer stage within a receiver, but also occurs in any non-linear device.

IS-3 - The original analog cellular standard, now replaced by ANSI standard EIA/TIA-553 and TIA interim standard IS-91.

IS-41 - The protocol for 'roaming' within the USA, describing how services should 'hand over' between operators

IS-54 - The TDMA standard for U.S. digital cellular. A digital cellular system that squeezes three conversations into one cellular channel.

IS-88 - Narrowband Analog Cellular system developed by Motorola that squeezes three conversations into one cellular channel using analog frequency division multiplexing. First standardized in TIA interim standard IS-88, and now incorporated in IS-91.

IS-91 - Analog Cellular and PCS. The TIA version of the analog cellular standard, incorporating the functionality of IS-88 (narrowband analog) and IS-94 as well as PCS band operation.

IS-94 - Inbuilding Cellular. A standard for inbuilding operation of analog cellular systems using extremely low power. Now incorporated in IS-91.

IS-95 - The CDMA (Qualcomm) standard for U.S. digital cellular. A digital cellular system that squeezes between 10 and 20 conversations into one cellular channel by combining 30 KHz cellular channels into a single 1.25 MHz channel and using code division multiplexing to combine and recover the individual conversations.

IS-136 - TIA standard that provides dual mode (analog and digital) cellular services using the TDMA technology. An enhancement to IS-54 TDMA, that includes a more advanced control channel (known as the digital control channel (DCCH), to distinguish it from the 'analog' control channel, which although less sophisticated, is still digital!).

IS-634 - TIA standard for 800 MHz cellular base-station to switch interface. Supports CDMA.

IS-651 - TIA standard for an open interface between the PCS switching center and the radio base-station subsystem in a PCS network. Supports both GSM and CDMA.

ISM Band - Industry, Scientific and Medical Band. Unlicensed 902 - 928 MHz, 2.4 - 2.4835 GHz and 5.725 - 5.850 GHz bands, RF power up to 1 watt. Frequency hopping or direct sequence transmission allowed.

Isotropic Radiator - A completely non-directional antenna (one which radiates equally well in all directions.) This antenna exists only as a mathematical concept and is used as a known reference to measure antenna gain.

ITS - Intelligent Transportation Systems.

IVHS - Intelligent Vehicle Highway Systems.

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JDC - Japanese Digital Cellular - now renamed PDC. Uses upper 900 MHz and 1.5 GHz bands.

J-TACS - Japan Total Access Communication System. Narrowband analog cellular FM system used in Japan. Channels are 12.5 KHz wide and signaling is subaudio.

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Late Target Channel Keyup - A condition when the target cell does not receive the execute target order in time for the arriving mobile, caused by link delays between MTSO and target cell site. After the mobile retunes to the target cell, noise will be heard on the downlink audio from the target cell, as the assigned voice channel is not on the air (yet). This results in noise during the handoff.

LEO - Low Earth Orbit satellite.

Little LEO - Relatively small and inexpensive satellites that provide low-cost, low-data rate, two-way digital communications, and location positioning to small handheld terminals. The frequency allocations are in the VHF band below 400 MHz. Systems include Leosat, Orbcomm, Starnet, and Vitasat. For example, the Orbcomm system requires 34 satellites for reliable full-world coverage.

LMR - Land Mobile Radio - wireless for specialized applications - e.g., taxi or emergency services

LMS - Local and Monitoring Service.

LNA - Low Noise Amplifier.

Low Side Injection - A superhet receiver design in which the oscillator frequency is below the carrier frequency.

LPC - Linear Predictive Coding compression algorithm.

LTP - Long Term Prediction compression algorithm.

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Microwave - A signal in the generic frequency range from above 1 GHz to an upper end of perhaps 30 or 40 GHz.

Microwave Hop - A microwave RF connection between MTSO and cell sites in remote locations.

Mixer - The circuit or component in a superhet receiver where the oscillator signal is combined with the incoming carrier signal.

MIN1 - The 24-bit number which corresponds to the 7-digit subscriber telephone number.

MIN2 - The 10-bit number that corresponds to the 3-digit subscriber area code.

MMI - Man/Machine Interface - how easy a phone is to use, how fun, how sexy. As phones conform to strict standards, the MMI becomes a key area of differentiation.

Mobile Coverage Area - Geographical area in which two-way radio service can be expected (between base station and mobile unit).

Mobile-ID - The 7 digit mobile telephone number. Does not include area code.

Mobile Attenuation - The power of the mobile can be adjusted (or attenuated) dynamically to one of seven discrete power levels (analog cellular). This is done so that when a mobile comes closer to a base receiver its power is reduced to prevent the chance of interfering with other mobiles operating on the same voice channel in another cell (co-channel interference). Additionally, this is even more important to portable units to keep the transmit power at a minimum to increase the talk usage time before the batteries expire.

Mobile Origination - The initiation of a telephone call by a mobile unit.

Mobile unit - The mobile unit is either a handheld or car mounted transceiver. The mobile unit connects the user to the base station via RF (radio frequency). The mobile unit is also known as the "Subscriber".

MSA - Metropolitan Service Area. A cellular coverage, defined by the FCC, which resides in a densely populated area. here are 306 MSAs in the United States, all of which now have cellular service.

MSPS - Megasamples per second. Sampling rate for analog to digital converters.

MSS - Mobile Satellite Service.

MTSO - Mobile Telephone Switching Office. The switching office that all base station cell sites connect to. It is a sophisticated computer that monitors all cellular calls, keeps track of the location of all cellular-equipped vehicles traveling in the system, arranges hand-offs, keeps track of billing information, etc. he MTSO in turn interfaces to the PSTN by connection to a CO.

MU-Law (U-Law) - An encoding format for the quantization and digitization of analog signals into Pulse Code Modulation (PCM) signals (A/D) and recovery of analog signals from PCM (D/A). U-Law specifies the parameters for compression and re-expansion of the signals during signal transmission and processing. U-Law PCM encoding is used in North America. A-Law is the European format.

Multipath - The presence of multiple signals arriving at the receiver antenna simultaneously. Signals that are in phase will add to one another. Signals that are out of phase will cancel one another.

Multipath fading - Multipath fading A.K.A. Rayleigh fading occurs when the direct-path transmitted wave destructively interferes with it's reflections at the receiving end. The destructive interference is a result of the reflected waves arriving at the receiving end out of phase with the direct-path transmitted wave. Multipath interference can vary in intensity depending on the amount of destructive interference that takes place.

Multiple Access - A method for accomodating more users in the same frequency band.

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NAM - Number Assignment Module. The NAM is the electronic memory in the cellular phone that stores the telephone number and electronic serial number. Phones with dual- or multi-NAM features offer the user the option of registering the phone so that it will have two or more phone numbers.

NAMPS - Narrowband Analog Mobile Phone System. This is an analog cellular FM system using 10 KHz wide channels. Signaling is subaudio.

Narrowband - A signal whose bandwidth is on the order of its information bandwidth.

NMT - Nordic Mobile Telephone. Scandinavia cellular phone system. The latest system uses 30 KHz channels, and signaling is done using 1200 Hz and 1800 Hz tones in much the same way as a modem.

No Answer Transfer - A feature that allows calls to a mobile to be transferred to a predetermined number if the mobile does not acknowledge an incoming call or is not answered.

Non-wireline cellular company, or the Block "A" carrier - The FCC, in setting up the licensing and regulatory rules for cellular, decided to license two cellular systems in each market. It reserved one for the local telephone company, and opened the second system -- the Block A system -- to other interested applicants. Non-wireline or Block A systems operate on radio frequencies from 824 to 848 MHz.

NTIA - National Telecommunications and Information Administration, sponsored by the Commerce Department.

Numbering Plan Area (NPA) - The area code.

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Off-Hook - Circuit condition caused when the handset is lifted from the switch hook of the telephone set. Condition exists during call set-up or conversation.

Off-peak - The periods of time during which carriers offer discounted airtime charges. Usually, off-peak rates are available between 10:01 p.m. and 5:59 a.m. and on weekends and select holidays, but times can vary.

On-Hook - The normal circuit condition when the handset is on the switch hook of the telephone set.

Operator - In cellular, this is the local service provider operating company that owns the cellular system in that particular area.

OQPSK - Offset Quadrature Phase Shift Keying. QPSK with an initial phase offset (of usually 45 degrees); OQPSK has less envelope AM than QPSK.

Origination - A call that is placed by the mobile subscriber, calling either a land-line circuit or another mobile subscriber.

Oscillator - An electronic circuit which generates a signal at a specific frequency.

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PACS - Personal Access Communication System - a candidate for the U.S. PCS

Page - A message which is broadcast from a group of cell sites that carries a mobile ID, for the purpose of alerting the mobile that a call is waiting.

Parity - A self-checking code employing binary digits in which the total number of ones is always odd or even.

PCN - Personal Communication Network. PCNs are usually short range (100's of feet to 1 mile or so) and involve cellular radio type architecture. Services include digital voice, FAX, mobile data and national/international data communications. Also -- A network of pocket-size radio telephones served by clusters of receiver transmitter cells.

PCS - Personal Communications Service. Within the U.S., the 1.9 GHz band has been allocated for PCS systems; the allocated spectrum is 120 MHz wide and is licensed as two 30 MHz segments for the 51 major trading areas, and three 10 MHz segments for the 493 basic trading areas.

PCS-1900 - See DCS-1900

PDC - Personal Digital Cellular, Japanese cellular standard.

Peak: - That part of the business day in which cellular customers pay full service rates. Peak hours are generally 6:00 a.m. - 10:00 p.m.

PHS - Personal Handyphone system, Japanese cordless standard.

Pigtail antenna - The standard cellular antenna for a car. The term "pigtail" refers to the spring-like section in the lower third of the antenna known as the phasing coil.

PL - The mobile power level

PM - Phase Modulation; modulation of the phase of an RF carrier.

PN - Pseudo-random Noise. A digital signal with noise-like properties. Also a wideband modulation which imparts noise-like characteristics to an RF signal.

Port Change - A channel change from one sector to another, but staying within the same cell.

Private Mobile Radio (PMR) - Mobile communication network which is meant for a special group of users, e.g. for one or more enterprises or institutions.

Processing Gain - The ratio of the bandwidth of a spread spectrum signal to the data rate of the information.

PSK - Phase Shift Keying. A digital modulation of the phase of a signal's RF carrier.

Pulse Code Modulation (PCM) - Process in which the modulating signal is sampled, and the magnitude of each sample (with respect to a fixed reference) is quantized and converted by coding to a digital signal. Provides undistorted transmission, even in the presence of noise. The sample frequency must be at least twice the highest modulating frequency for full recovery of the original modulating information (Nyquist).

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QPSK - Quadrature Phase Shift Keying; 4 phase digital modulation.

Quantization - A process in which the continuous range of values of an input signal is divided into non-overlapping sub-ranges (chords) and to each sub-range a discrete value of the output is uniquely assigned a binary number.

Quantization Distortion - The inherent distortion introduced in the process of quantization.

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RBDS - Radio Broadcast Data System.

Receiver - The device that picks up the radio signal from the transmitter, converts it into an audio signal and feeds audio into your sound system or recorder.

Receiver Image A second frequency that a superhet receiver will respond to. The image frequency is two times the IF frequency either above or below the carrier frequency, depending upon whether the receiver design is "low side" or "high side" injection. An RF signal on the "image" frequency of the receiver will produce a difference signal in the mixer just as valid as the intended IF signal created by mixing the oscillator with the carrier.

Reflections - RF waves can reflect off of hills, buildings, moving cars, the atmosphere, and basically almost anything in the RF transmission environment. The reflections may vary in phase and strength from the original wave. Reflections are what allow radio waves to reach their targets around corners, behind buildings, under bridges, in parking garages, etc. RF transmissions bend around objects as a result of reflections.

Relative Signal Strength Indication (RSSI) - A value representing the received signal strength of both the mobile unit and the base station. This value is used to initiate a power change or handoff.

Repertory dialing - Sometimes known as "memory dialing" or "speed-calling". A feature that allows you to recall from nine to 99 (or more) phone numbers from a phone's memory with the touch of just one, two or three buttons.

Return Loss - A measure of VSWR, expressed in dB.

Reverse Control Channel (RECC) - The Control Channel that is used from the mobile station to the base station direction, also known as the control channel uplink.

Reverse Voice Channel (RVC) - The voice channel that is used in the mobile station to base station direction, also known as the voice channel uplink.

RF - Radio Frequency. Also used generally to refer to the radio signal generated by the system transmitter, or to energy present from other sources that may be picked up by a wireless receiver.

RFI - Radio Frequency Interference. A non-desired radio signal which creates noise or dropouts in the wireless system or noise in a sound system. RFI can be generated by a wide variety of sources including electronic organs, computers, switching power supplies, broadcast radio signals and outside radio devices. Radio signal energy can enter a sound system component or alter the audio signals in cabling, producing annoying hiss, whining or intelligible audio signals. Proper shielding and balanced audio cabling are the best defense against RFI problems in a sound system. High quality receivers are the best defense against RFI in wireless microphone systems.

RFID - RF Identification.

RF Noise - Radio signals generated by something other than the transmitter. Usually sounds like hiss, static or hash. RFI (Radio Frequency Interference) may be AM or FM, but the effect is that it either alters the audio signal, or adds background noise to the audio signal.

Roamer - A mobile station which operates in the cellular system other than the one from which the service is subscribed (the home system).

RPE - Regular Pulse Excitation compression algorithm.

RSA - Rural Service Area. A cellular coverage, defined by the FCC, which resides in a less populated area. he FCC designated 428 rural markets across the country to be licensed to cellular operators. The final RSA was activated in May 1992, giving the entire nation access to cellular service.

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Scan Receiver - A receiver that resides in the base station that is dedicated to measure mobile's signal strengths. These measurements are used in the handoff process (but not in the power-up/power-down process, which is handled by each voice transceiver).

Sector-Receive Cell Site - Six or three directional antennas that are used at a cell site to get additional gain required to serve mobiles. A mobile could move completely around a Sector-Receive cell site and never change channels, but would change antennas.

Sector-Sector Cell Site - The cell is broken up into two or more independent sectors that each have their own transmit and receive antennas. A mobile moving around a Sector-Sector cell would change channels (Intra-cell handoff)

Selectivity - The ability of a receiver to reject interfering signals close to the desired carrier frequency.

Sensitivity - The ability of a receiver to operate on very weak RF signal levels.

SHF - Super High Frequency. A signal in the frequency range of from 3 to 30 GHz.

Sidetone - An attenuated portion of the transmit audio returned to the originator. Can be intentional as all phones produce some sidetone and is caused by unbalanced 2-to-4 wire hybrids.

Signal-to-Noise - The ratio of the magnitude of the signal to that of the noise with no signal present, usually expressed in dB.

Signaling Tone (ST) - A 10 kHz tone transmitted by the mobile station on a voice channel to (1) confirm channel change orders (HO tone, 50ms ST), (2) request a flash-hook by the mobile (400ms ST), (3) mobile alert (continuous ST), (4) mobile ending call (1.8sec ST).

SIM - Subscriber Identification Module. A credit card size card which is owned by a subscriber, who slides it into any GSM handset to transform it into 'their' phone. It will ring when their unique phone number is dialed; calls made will be billed to their account; all options and services connected; voicemail can be collected and so on.

SMR - Specialized Mobile Radio. FCC has allocated the 896-901 MHz band (800 MHz band) which uses two paired 25 KHz channels and the 935-940 MHz band (900 MHz band) which uses two paired 12.5 KHz channels. Ten 20 channel blocks have been allocated in these frequency bands. 900 MHz SMR is primarily used for radio dispatch , paging and wireless data communications.

Source Cell - The cell that a mobile is leaving during the hand off process.

Source Channel Falsing - A condition that exists when co-channel SAT exists on the source channel during handoff, so that source channel does not squelch during the handoff process. This results in noise during the handoff process (after the handoff order) that can be heard by both the landline and mobile parties.

Spectrum - The electromagnetic spectrum. A continuous group of electromagnetic frequencies.

Spread Spectrum - A communication technique that spreads a signal bandwidth over a wide range of frequencies for transmission and then de-spreads it to the original data bandwidth at the receiver.

Squelch Circuit - A radio receiver circuit which disables the audio path when the incoming signal is below a predetermined threshold. When the radio signal from a transmitter is too weak to produce a quality audio signal, the receiver will shut off or "squelch."

Standby time - The amount of time you can leave your fully charged cellular portable or transportable phone turned on before the phone will completely discharge the batteries.

Station Class Mark (SCM) - Indicates mobile station type (mobile/transport), and if station has DTX.

Subaudio - Frequencies below the audio bandwidth for speech, which is 300 to 3000 Hz.

Subscriber - The mobile user of the cellular system.

Subscriber Files - Stored at the MTSO and contains all information pertaining to each subscriber. Includes mobile number, home service location, last known location, type of mobile, service denial flags, and special feature options available to that subscriber.

Super Audio - Frequencies above the audio bandwidth, which is 300 to 3000 Hz.

Superheterodyne - The mixing of two signals producing a third signal. Almost all other receivers) utilize an oscillator, producing a signal which is mixed with the incoming radio signal from the receiver antenna to produce a lower frequency signal (the IF signal).

Supersonic Noise Squelch - A fairly popular method of muting the audio output of a receiver when the supersonic noise reaches a preset level. The assumption is that noise buildup above the audio passband (20 to 30 KHz range) is an indication that the signal to noise ratio of the system is inadequate to produce a usable audio signal.

Supervisory Audio Tone (SAT) - One of three tones (5970, 6000, and 6030 Hz) that are transmitted by the base station and transponded by the mobile station. Used to evaluate the complete radio path, both Forward and Reverse Voice Channels. The SAT received by the mobile unit is actually regenerated by the mobile unit with the same amplitude and noise associated with the actual received SAT.

System Identification (SID) - A unique digital code assigned to each cellular system. The home system of each mobile is stored in it's internal memory so that the mobile knows when it is a roamer (outside it's normal service area).

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TACS - Total Access Communication System. This is the analog cellular FM system used in the United Kingdom and Japan. It uses 25 KHz channels and signaling is super audio.

Talk time - The length of time you can talk on your portable or transportable cellular phone without recharging the battery. The battery capacity of a cellular portable or transportable is usually expressed in terms of so many minutes of talk time OR so many hours of standby time. When you're talking, the phone draws more power from the battery.

Target Cell - The cell that a mobile is going to during the hand off process..

Target Channel Falsing - A condition that exists when co-channel SAT exists on the target channel during handoff, so that target channel does not squelch before arrival of the mobile during the handoff process. This results in noise during the handoff process (before the handoff order) that can be heard by both the landline and mobile parties.

TCM - Trellis Coded Modulation.

TDMA - Time Division Multiple Access. TDMA systems are able to transmit multiple voice circuits per channel. A TDMA channel is a single FDMA channel divided up in time into multiple time slots. Three users can take it in turn to share one radio channel. The channels can vary in bandwidth and depending on the type of system, the time slots can transmit all or part of a voice circuit. Each user's speech is stored, compressed and transmitted as a quick packet, using controlled time slots to distinguish them-hence the phrase 'time division'. Its uses 30 KHz channels and a vocoder rate of 8 Kbits/sec. At the receiver, the packet is de-compressed.
TDMA channel


30 KHz | Voice circuit #1|Voice circuit #2|Voice circuit #3|Voice circuit #4|


Depending on the type of system, slots 1, 2, 3, & 4 could each transmit a voice circuit. In this example, 4 telephone circuits are transmitted on a single 30 KHz channel, a 4X increase in capacity over the FDMA example.

TETRA - Trans European Trunked Radio Access - European digital cellular land mobile radio system

Termination - A call that is received by a mobile subscriber, that was placed by either a line-line party or another mobile subscriber.

Third Order Intercept - A measure of how well the receiver resists interference caused by multiple interfering signals. This specification gives a single, excellent measure of how well the receiver resists many kinds of overload. It is directly related to the RF compression level.

TIA - Telecommunications Industry Association - U.S. Standards making body

Toll Ticketing - DAS records that are kept at the MTSO for billing purposes. Contains subscriber number, time of call, called number, location of call origination, location of call termination, and other important statistics for proper billing of subscriber.

Toll Ticketing House - A third party company that takes the DAS toll ticketing records and actually bills the subscribers. Non-payment by subscribers is reported to the operating company so denial of service can be performed.

TPC - Three Party Conference Circuit. Used in three party conference, but more importantly, used during every handoff so that the channel-change transition can be made with less noise by connecting the audio of the source and target cells together before the hand off order is sent. (When a handoff is made during a three-party conference call, and the TPC is being used, 'hard-handoffs' exists and the potential for noise during channel changes increases significantly)

Transmitter - The device worn (or held) by the user which sends or "transmits" the sound from the microphone to the receiver. The transmitter actually converts the electrical signal coming from the microphone into a radio signal and then "transmits" it out through some sort of antenna.

Trunk - In cellular systems, this is the connection between the MTSO and CO and the connections between the MTSO and cell sites.

Tumbling ESN - Fraudulent hardware that changes the mobiles ESN every time a call is originated. Since a roamers FIRST call is often screened only for a bad ESN, an infinite number of fraudulent calls can be placed using a tumbling ESN.

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UAV - Unmanned Aerial Vehicle.

UHF - Ultra High Frequency (generally 300 MHz to 3000 MHz).

UMPS - Universal Mobile Phone Service

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Validation - The method of determining if a mobile should be given service to the cellular system. Validation often requires matching the ESN of the mobile with it's Mobile ID, and then checking the mobile against files that contain subscribers who should be denied service.

VBAP - Voice Band Audio Processor. A CODEC that handles signal conversion at the microphone and speaker.

VHF - Very High Frequency (30 to 300 MHz).
High Band wireless systems are usually 150 MHz to 216 MHz
Low band wireless systems are usually 30 MHz to 50 MHz

Voice-activated dialing - A feature that permits you to dial a number by calling them out to your cellular phone, instead of punching them in yourself.

Voice circuit - half of a full duplex conversation, I.E.one half of a two way conversation. For example, if two people are talking by phone, each of their voices is considered a separate voice circuit.

Vocoder - Voice coder, speech is encoded before transmission to reduce the number of bits required to represent speech.

Voice mail or voice messaging - A computerized answering system that automatically answers your call, plays a greeting in your own voice and records a message.

Voice Mobile Attenuation Code (VMAC) - One of eight discrete mobile power levels that are dynamically adjusted during a cellular telephone conversation. These power steps are in 4 dB increments.

VSAT -Very Small Aperture Terminal; a small (under 2 meter diameter dish) antenna and satellite receiver.

VSELP - Vector Sum Excited Linear Predictive speech compression coding.

VSWR - Voltage Standing Wave Ratio.

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Wireless - Describing radio-based systems allowing transmission or telephone and/or data signals through the air without a physical connection, such as a metal wire or fiber optical cable.

Wireline cellular carrier, or the Block "B" carrier - Under the FCC's initial licensing procedures, the Block B carrier is the local telephone company. The FCC reserved one of the two systems in every market for the local telephone, or wire-line company. Wireline or Block B systems operate on the frequencies 869 to 894 Megahertz.

WLAN - Wireless Local Area Networks. Operating in the 2.4 GHz and 5.8 GHz unlicensed ISM bands and using spread spectrum technology are presently under development. It is expected that data rates of 1 Mbps and 10 Mbps can be achieved at 2.4 GHz and 5.8 GHz, respectively. A WLAN standard operating at 2.4 GHz (IEEE 802.11) is being 'painfully' defined (with four different versions), while European countries are developing an alternative standard (HIPERLAN) for 10 Mbps transmission, using the 5.8 GHz band.

WLL - Wireless Local Loops. Any method of using wireless communication in place of a wired connection to provide subscribers with standard telephone service.

WPBX - Wireless Public Branch Exchanges.

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