Here's some terminology that you may have encountered. Browse through the telecommunication terms, and navigate by clicking on the first letter of the word. Don't hesitate to get ahold of us if you have a question concerning a term.
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
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
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
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
Call Processing - The complete process of routing, originating, terminating
cellular telephone calls, along with the necessary billing and statistical collection
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.
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
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
Correlator - The receiver component that demodulates a spread spectrum signal;
a device that measures the similarity of of an incoming signal and a stored
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
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.,
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
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
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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
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)
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
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
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
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
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
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
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
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
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.
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
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
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
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
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
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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
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
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
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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
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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
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
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
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
Spectrum - The electromagnetic spectrum. A continuous group of electromagnetic
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
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
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
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.
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
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
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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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