– A –
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.
AMPS – Advanced Mobile Phone System
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.
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.
– B –
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. This brings up an interesting point in that one of the fundamental problems associated with RF transmissions is the limited amount of electromagnetic spectrum available. The electromagnetic spectrum is finite, and only a limited portion of the spectrum has been allocated for cellular use by the FCC.(Federal Communications Commission) The FCC has allocated only 50 Mhz of spectrum for cellular use. Added capacity can not be achieved by simply taking up more spectrum. Since there is a limited amount of spectrum available for cellular use, added capacity must be obtained by other means.
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.
– C –
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).
CDMA – CDMA stands for 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 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.
----------------------------------------------- 1.25MHz | 64 different voice circuits | -----------------------------------------------
64 different voice circuits can be simultaneously transmitted on the same channel. The voice circuits are identified by their assigned codes.
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.
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.
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).
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. 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.
– D –
dB (decibel) – A unit stating the logarithmic ratio between two amounts of power. Typically used in receiver and transmitter measurements.
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.
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.
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.
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.
– E –
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.
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.
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.
– F –
Fade – A drop in the received signal strength as a result of the RF transmission’s interactions with the transmission environment.
FDMA – FDMA stands for Frequency Division Multiple Access. FDMA systems transmit one voice circuit per 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 |
Flash- Hook – 400ms of signaling tone sent on the reverse voice channel (by the mobile) to request a hook flash.
‘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 Shift Keying (FSK) – The form of frequency modulation that used two separate audio frequencies to transmit binary ones and zeros.
Full Duplex – Refers to a communications system that uses two separate transmit and receive paths to allow simultaneous conversation in two directions.
– G –
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.
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.
– H –
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.
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.
Hard-Handoff – A handoff that occurs abruptly at the cell boundry, independent of any other variables. A drawback to this approach is that a subscriber who is near/on a cell boundary may experience rapid, continuous hand-offs.
Harmonic Filter – Used in the base-station and subscriber transmitter circuits to remove unwanted harmonics from being transmitted and radiated by the antenna.
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.
– I –
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.
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.
– M –
Microwave Hop – A microwave RF connection between MTSO and cell sites in remote locations.
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.
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.
MTSO – Mobile Telephone Switching Office. The switching office that all base station cell sites connect to. The MTSO in turn interfaces to the PSTN by connection to a CO. Control of all cell sites, all subscriber records, statistics, and billing is maintained at the MTSO.
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 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.
– N –
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.
Numbering Plan Area (NPA) – The area code.
– O –
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.
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.
Origination – A call that is placed by the mobile subscriber, calling either a land-line circuit or another mobile subscriber.
– P –
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.
PL – The mobile power level
Port Change – A channel change from one sector to another, but staying within the same cell.
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).
– Q –
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.
– R –
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.
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.
Roamer – A mobile station which operates in the cellular system other than the one from which the service is subscribed (the home system).
RSA – Rural Service Area. A cellular coverage, defined by the FCC, which resides in a less populated area.
– S –
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)
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).
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.
Squelch Circuit – A radio receiver circuit which disables the audio path when the incoming signal is below a predetermined threshold.
Station Class Mark (SCM) – Indicates mobile station type (mobile/trans/port), and if station has DTX.
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.
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).
– T –
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.
TDMA – TDMA stands for 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. 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.
------------------------------------------------------ 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.
Termination – A call that is received by a mobile subscriber, that was placed by either a line-line party or another mobile subscriber.
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.
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.
– V –
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.
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.
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.