Mobile House 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.
Example:
CDMA channel
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1.25MHz | 64 different voice circuits |
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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)
Example:
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.
Example:
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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Battery Comparison
- 'Energy density' is measured in watt-hours per kilogram (Wh/kg).
- 'Cycle life' indicates the typical number of charge-discharge cycles before the capacity decreases from the nominal 100% to 80%
- 'Fast-charge time' is the time required to fully charge an empty battery.
- 'Self-discharge' indicates the self-discharge rate when the battery is not in use. "Moderate" refers to 1-2% capacity-loss per day.
- 'Cell voltage' multiplied by the number of cells provides the battery terminal voltage
- 'Load current' is the maximum recommended current the battery can provide. "High" refers to a discharge rate of 1C*; "very high" is a
current higher than 1C*. - 'Exercise requirement' indicates the frequency the battery needs exercising to achieve maximum service life.
- 'Battery cost' is the estimated commercial price of a commonly available battery.
- 'Cost-per-cycle' indicates the operating cost derived by taking the average price of a commercial battery and dividing it by the cycle
count. - 'In commercial use since' is the approximate year when the battery became commercially available.
| Battery Type | NiCd | NiMH | SLA | Li-ion | Li-Polymer |
|---|---|---|---|---|---|
| Energy density (Wh/Kg) | 50 | 75 | 30 | 100 | 175 |
| Cycle life (typical) | 1500 | 500 | 200-300 | 300-500 | 150 |
| Fast-charge time | 1 1/2h | 2-3h | 8-15h | 3-6h | 8-15h |
| Self-discharge | medium | high | low | low | very low |
| Cell voltage (nom.) | 1.25V | 1.25V | 2V | 3.6V | 2.7V |
| Load current | very high | medium | low | high | low |
| Exercise req. (days) | /30 | /90 | /180 | N/A | N/A |
| Battery Cost | low | medium | very low | very high | high |
| (estimated, ref., $) | 50.00 | 80.00 | 25.00 | 100.00 | 90.00 |
| Cost per cycle ($) | 0.04 | 0.16 | 0.10 | 0.25 | 0.60 |
| In comm. use since | 1950 | 1970 | 1970 | 1990 | 1997 |
- ************************************************************************************************************************************
Wireless Security
Wireless Communications Security
Prepared by Alan Vanderploeg
Written from a US Perspective but applies to all markets.
Introduction Wireless communications, which is the use of cordless and cellular phones, has grown dramatically in the past ten years and has become a booming $11 billion market. The capability to communicate with others without being physically connected to a phone line has greatly increased the efficiency of corporate, government, and private sectors. Unfortunately, this capability has also led to a huge security problem, since the radio signals transmitted and received by these devices can be easily intercepted, compromised, and exploited.
These compromises include eavesdropping on conversations and spoofing (or cloning) cellular systems to gain fraudulent access. This high tech crime wave is costing the cellular industry alone over $300 million a year and has hit the above three sectors hard. Telecommunications experts believe this problem will only get worse as cordless and cellular use continues to increase. The cordless and cellular phone industry is just now beginning to design countermeasures into their devices and systems in an effort to combat this growing problem. In the meantime, it is imperative that everyone who uses these devices understand the threat they face, the scope of the problem, and present and future countermeasures they can implement to protect themselves from wireless security compromise.
The focus of this paper explains how cordless and cellular technology works and discusses the communications security threats to these systems, including how this technology is commonly compromised, who is affected, and what is lost. The effectiveness of some of the methods being explored to counter the problem is discussed, and conclusions about this problem and its countermeasures are also offered.
Explanation of Cordless/Cellular Phone Technology
To understand how "Phreakers" (a slang name for phone or cellular hackers) attack the vulnerabilities of these systems, one must understand how these systems work. Cordless phones are simply two-way radios that send an unprotected signal between the base unit (which is connected to a phone line) and the handset. Some of the more expensive versions even have a built-in encryption chip to increase conversation privacy. The ranges of these signals vary depending on the quality of the phone and surrounding interferences such as walls or powerlines, but most cordless phones are capable of transmitting and receiving signals up to 150 feet.
Cellular phones, like cordless phones, are also two-way radios. The cellular phone, however, is much more sophisticated and has a much greater, and in some cases, unlimited range. This is due to the honeycomb-like layout of cellular communications areas. Figure 1 shows a typical cellular system layout. These "cells," or communications areas, are controlled by a network control station, and each cell has a tower that can send and receive multiple radio frequencies.
Each tower periodically (usually once a minute) transmits an identifier signal. The cellular phone listens for this signal, adds a Mobile Identification Number (MIN -- programmed by the phone seller or service shop) and Electronic Serial Number (ESN -- installed by the factory and theoretically unique to each phone) to the signal, and sends it back to the tower, where it is then relayed to the network control station. This process identifies the cellular phone, billing account, and the cell location of the phone.
When a user wants to make a call, the network control station allocates an available frequency in that cell to the phone, charges the appropriate account, and allows the user to transmit a call. As the user nears the next cell, the network control station automatically hands-off the call to another available frequency in the next cell. This gives the cellular phone user a huge range from which to make or receive calls.
Current Threat
Because cordless and cellular phones transmit and receive radio signals, they face two main threats: electronic eavesdropping and cellular spoofing. One could argue that a third threat is the physical loss, damage, or theft of the actual device; however, for the scope of this paper, only the threats as they apply to electronic communications security will be discussed.
Electronic eavesdropping is listening to or recording a cordless or cellular call without the permission or knowledge of the calling and/or receiving parties. Eavesdroppers accomplish this feat by using radio frequency scanners and other receiving equipment to find and listen to the frequencies used by the devices.
This is a fairly simple process to scan cordless phone conversations since most brands operate on similar frequencies. Even baby-monitors and some brands of two-way radios share these frequency ranges. Because of these similar frequency bands, most people have picked up their cordless phone at some time and have been able to inadvertently listen to another person's conversation without that person's knowledge.
Cellular phones use frequencies that are very different from cordless phones, but since cellular phone frequencies are all in the same band range, it is very easy to intercept these frequencies with electronic scanners. Electronic eavesdropping is fairly common. According to Phil Karn, a Canadian telecommunications specialist, "...in a three-month study of Metro Toronto, Bell Canada found that 80 percent of all cellular telephone traffic is monitored by third parties."
While the author admits this number cannot be confirmed, similar studies suggest the actual percentage is anywhere between 20 and 50 percent, depending on the caller's location. Regardless of the actual percent, this is a growing problem. Not only is electronic eavesdropping easy to exploit, it is also readily available, inexpensive, and nearly impossible to detect. Communications magazines and the World Wide Web are full of advertisements and information describing how to eavesdrop on cordless and cellular traffic.
The July 1996 edition of Popular Communications alone has several ads aimed at the "eavesdropping hobbyist" that describe where to purchase scanners, what frequencies to scan, wiring diagrams, parts lists, and instructions on how to modify scanners to receive cordless and cellular frequencies. A good scanner that already receives cellular frequencies can be purchased for under $300. Due to recently enacted legislation, these types of scanners can no longer be produced, but plenty of the pre-ban scanners are still available, and just about any high quality scanner can be easily modified for under $100.
While communications privacy is a concern, it pales beside the threat of cellular spoofing. Cellular spoofing (also known as cloning) is the process where a person provides false identification [about a cellular account] to the cellular communications provider with the intent to defraud. The earliest form of spoofing appeared several years ago in the mobile telephone industry. Eavesdroppers would scan the airwaves until they identified a mobile phone channel. They would then monitor the transmissions on these frequencies and wait for an account owner to request a call.
The following is an example of how the spoofing would occur. The user would say, "Operator, this is Mobile 1111, may I please have 456-2345." The operator would connect the caller and bill Mobile Account 1111 for the call. Later, the eavesdroppers would call the operator and pretend to be Mobile Account 1111, thus charging the call to that particular account. The spoofing process became much more sophisticated with the implementation of high speed digital cellular technology.
Phreakers (or spoofers) now attempt to detect the MIN and ESN of cellular phones. They accomplish this feat by building electrical devices that scan cellular frequencies and detect the identifier signal the phone sends back to the cellular tower. The hacking equipment then strips the MIN and the ESN from the identifier signal. The phreaker takes the MIN and ESN and programs it into another cellular phone. Whenever the phreaker uses the reprogrammed phone, the network control station identifies the reprogrammed cellular phone and bills the stolen account for the call.
Cellular phones (which usually have been stolen) are commonly reprogrammed and sold for $5 or $10 dollars at flea markets and pawn shops. Many of these illegal enterprises "guarantee" the phone for one year. If the cellular service disables the account, the seller will reprogram the phone with a different MIN and ESN, re-enabling the phone.
Since the current trend of business people is to communicate via cellular phone, phreakers like to set up their equipment outside areas where business people congregate. Subways, freeways, traffic jams, downtown parks, and airports are prime spots for phreakers. Their equipment is small, lightweight, portable, and automatic, so all the phreaker is required to do is set up in an innocuous location, turn on the equipment, and wait until the memory of the device is full of numbers.
Scope of the Problem (Who Is Affected and What Is Lost)
Anyone who uses a cordless phone is susceptible to information compromise. Because electronic eavesdropping is easy to exploit and nearly impossible to detect, no one seems to be able to estimate the yearly losses it causes. However, with the rise of touch tone call routers, electronic operators, home shopping via credit cards, and 24-hour account assistance (credit card, banking, insurance, etc.), more people are giving out critical personal and financial information (such as credit card and bank account numbers) over the phone.
This development has led to a significant rise in financial fraud and will continue to do so. As an example of this, this author recently borrowed a friend's portable scanner (purchased prior to the legislation discussed previously) and listened to several wireless transmissions. After a few hours of listening, three credit-card account numbers, automobile insurance account number, and several social security numbers were obtained.
The amount of susceptible information is not limited to financial transactions. Private detectives, industrial espionage agents, drug dealers, and the press corps routinely scan wireless transmissions to increase their knowledge. Former President Jimmy Carter learned this lesson well. After completing a peaceful exchange of power in Haiti, he used a cellular phone onboard his airplane to discuss some of the aspects of the agreement. Several of the news services picked up his transmission via scanners, and made the information public before he landed in Washington DC.
Even small businesses may find themselves the target of electronic eavesdropping. A company that serviced machinery discovered they were losing business to a competitor. An investigation revealed that their competitor was intercepting their service dispatch orders (communicated to the maintenance personnel via cellular phone). The competitor would then dispatch their own personnel and beat the original maintenance crew to the scene, thus getting several of the jobs.
Cellular spoofing is directly costing the telecommunications industry over $300 million a year. While cellular spoofing is not an actual compromise of information (unlike electronic eavesdropping), it does hinder the information security process by increasing the costs of communicating. Whenever illegal (spoofed) cellular calls are made, the phone company charges the cellular account owners with the call. If the owners do not catch the erroneous calls, they unknowingly pay for it. If the owners do catch the call, they have to notify the phone company and asked to have the charge removed.
This inconvenient process (along with looking through each month's phone bill) wastes a large amount of the account owners' time. Jonathan Feinsod, a New York businessman, has had his cellular phone spoofed four times, and it took him over a week to clear up fraudulent bills in excess of $20,000. Kenneth Crupup, a Boston telecommunications consultant, has had his cellular phone spoofed twice. When he refused to change his account number for the third time, his cellular provider disabled his ability to "roam", or use the phone outside of his designated local area.
Events such as these waste a significant amount of customers' time, and tax the resources of both the customer and the cellular provider. The current design of cellular phones leads to this spoofing. The combination of the MIN and ESN was supposed to prevent spoofing and render stolen cellular phones inoperative, since cellular providers could permanently deny service to stolen phones. According to Electronic Industries Association (EIA) cellular standards, the ESN must be factory-set, the ESN must not be alterable, and any attempt to alter the ESN should render the phone inoperative.
In theory, even if phreakers identified the MIN and ESN, they would not be able to reprogram another phone with those numbers. Unfortunately, this theory is weak in practice. Most cellular phones are not constructed so that an attempt to alter their ESN will render them inoperative. ESN chips can be readily obtained or swapped on the black market or from unscrupulous cellular phone service shops. A recent case in Washington, DC revealed that an ESN was "bought" from a local service shop employee in exchange for a one-half gram of cocaine.
Even if one cannot buy an ESN, most cellular manufacturers use industry standard ROM (Read Only Memory) chips to produce an ESN. These chips can be bought in any electronics store and easily reprogrammed or copied to produce bogus ESNs. The most threatening spoofing device is known as a Cellular Cache-Box. It is a combination of a scanner, computer, and cellular phone. The Cache-Box has the capability to not only steal and memorize MINs and ESNs off the air, but also automatically reprogram itself to emulate these numbers.
After using a MIN/ESN pair one time, the Cache-Box purges these numbers from its memory and selects a new pair. This capability makes it nearly impossible to detect the fraud or catch the perpetrator. Although this equipment is rare and very expensive, it does exist and will continue to be a threat to cellular users. All of these factors, coupled with the growing number of people who are susceptible to these threats, make wireless communications extremely vulnerable. Everyone who uses wireless technology must be aware of the threat and begin taking steps to protect themselves from compromise.
Countermeasures
Even though the threat is huge, a number of common sense and technological countermeasures exist to combat electronic eavesdropping and cellular spoofing. Also, the telecommunications industry is beginning to implement new technologies to help lessen the scope of the problem. The cheapest and easiest countermeasure to fight electronic eavesdropping is to use basic communications security procedures.
Everyone who uses a wireless phone should try to minimize (or avoid) revealing any sensitive information over the airwaves. Any communications that reveal sensitive information, such as credit card numbers, financial accounts, social security numbers, passwords, etc. should be transacted over standard hard wired phones. While these devices can be bugged, the likelihood of this occurring is small. One may argue that since most telephone calls are transmitted through microwave towers, the transmissions could be easily intercepted. This is not true because the high volume, high speed, and mix of signals sent through microwave towers make electronic interception at these points nearly impossible.
Good communications security can be very effective, but people tend to forget they are on an unsecure line and accidentally give out sensitive information. Also, this countermeasure may be inconvenient if the user prefers or has to use a cordless or cellular phone to conduct business. Another countermeasure is a high-speed, frequency-switching network. This system constantly changes transmission frequencies throughout the communication. The theory is that eavesdroppers will be unable to identify, track, and listen to calls because the frequencies are constantly changing.
This system, however, still does not prevent the eavesdropper from getting lucky and finding the correct frequency and intercepting sensitive information. Additionally, these systems usually do not have a large number of frequencies available, and once the range of the frequencies has been identified, eavesdroppers can set their scanners to quickly scan only those frequencies. Regardless of the amount of common sense or knowledge of the threat one possesses, there will still be times when one must reveal sensitive information over a wireless phone.
Digital encryption is a solution for this problem. Digital encryption converts analog vocal sounds into digital signals. The transmitting phone uses a mathematical randomization code to scramble the signals and sends the transmission. The receiving phone is able to recognize the encryption code and descrambles the signals. The descrambled signal is then converted back to analog vocal sounds. Because the system randomizes the encryption code and changes it with each transmission, the code is nearly impossible to crack. The two problems with this countermeasure are its expense and availability.
Digitally encrypted cordless and cellular phones are more expensive than non-encrypted phones, and the telecommunications industry has only recently begun producing these devices. Digital cellular networks are slowly replacing analog networks throughout the country, and are only available in certain areas. According to Peter Ruber, "A national digital standard might not be reached until 1997." Until then, wireless users will have to take their own security precautions. While digital encryption seems to be the answer to the eavesdropping threat, there is an additional problem with this technology. The federal government is worried that encryption might hinder national security and federal crimefighting efforts, since legal wiretaps, which provide a large amount of evidence for federal cases, will be unintelligible.
The Clinton administration, backed by the FBI, has proposed the development and implementation of the Clipper chip as the national (and only) encryption standard. The Clipper chip is a microchip that can scramble electronic transmissions, rendering voices and digital data unintelligible. Although this sounds like an idea no one would dispute, it has caused a considerable amount of controversy amongst the telecommunications industry, civil libertarians, and the government. The controversy arises from the fact that the Clipper chip, developed by the National Security Agency, has a built-in cipher key that permits federal agents to descramble transmissions and eavesdrop on them.
Proponents of the chip point to the prospect of terrorists, spies, drug dealers, and other criminals using unbreakable scramblers to conduct business without fear of communication detection. Opponents believe the logic behind the necessity of the Clipper chip is flawed. Their main point is that since other types of electronic encryption are available, criminals could easily disable the Clipper chip and insert their own encryption chip, which would be unbreakable. Also, since there is a key to the Clipper chip, there is a chance that the key could either be broken or compromised, thereby eliminating the Clipper chip's usefulness.
Because of these concerns, the government has put a hold on the plan to implement this technology; however, this issue will continue to be controversial as more manufacturers develop and incorporate their own encryption methods in future hardware. Cellular spoofing is a harder problem to eliminate. Solutions exist, however, that can help reduce the problem. The easiest countermeasure is to keep the phone turned off until the user is ready to make a call. This technique eliminates the periodic transmissions between the network control station and the phone, making it harder to compromise number pairs. However, a phreaker only needs one transmission to steal the number pairs, so the user is still vulnerable.
Another low-tech method is to change the MIN routinely. Cellular providers and service shops can issue new MIN numbers, but this is an inconvenient and time-consuming process for both the user and the provider. It is also ineffective, since the user has no way of knowing whether their MIN/ESN has been compromised, and the phreaker can continue to use these numbers until the user changes the MIN. There are more high-tech (and more costly) countermeasures available. Many phones now incorporate a 4 digit PIN number that must be entered by the user before a call can be made. This feature hinders phreakers since their equipment usually identifies only the MIN and ESN. Most cellular phone designs now incorporate this feature.
Unfortunately, it is an easy step to modify the detection device to scan the transmission and intercept the PIN number, thereby negating the effectiveness of the countermeasure. Another high-tech countermeasure is to make the ESN chips harder to modify. Cellular phone manufactures should redesign the ESN chips and incorporate tamper-resistant circuitry. This step will make reprogramming much harder, eliminating all but the most technically advanced phreakers or phreakers with Cache-Boxes. Until ESN chips are made tamper-proof, phreakers will continue to modify and reprogram cellular phones.
The most effective countermeasure the telecommunications industry can implement is encryption. Encryption will not only help prevent unauthorized eavesdropping and compromise, it will also reduce, and possibly eliminate, cellular spoofing. The encryption design would randomly encrypt the MIN/ESN signal as well as voice communications, allowing cellular phones to identify themselves to the network control station without retransmitting the same digital signal each time. Since the encryption scheme changes with each transmission, it is extremely difficult, time-consuming, and nearly impossible to break, even with high speed computers.
Without the MIN or ESN, phreakers will be put out of business. Because the encrypted MIN/ESN signal changes after each transmission, Cache-Boxes, which retransmit the signals they intercept, would be defeated. The drawbacks to this countermeasure are complexity, cost, and time. The entire cellular system, including the phones, transmitting towers, and network control stations would need a large amount of new software and hardware.
The intricate process of establishing an encryption standard, implementing it, redesigning the current cellular system, and retrofitting the system with the new equipment presents a tough obstacle to overcome. This countermeasure is further complicated by the need to continue supporting both encrypted and nonencrypted systems during system transition. Whether the cellular industry, and ultimately the cellular customer base, are willing to shoulder these costs depends on their willingness to accept the costs and consequences of not implementing encryption countermeasures.
Conclusion
Wireless eavesdropping and cellular spoofing is a serious and costly problem that will continue to grow in the oncoming years as the cordless and cellular market increases. Electronic eavesdroppers and cellular phreakers are becoming more sophisticated in their activities, and the availability, inexpensiveness, and undetectability of this technology make eavesdropping and spoofing both effortless and profitable.
Anyone who uses these devices is vulnerable to compromise and must understand the scope of the threat they face. While the threat is large, several countermeasures exist to reduce the risk of compromise. Also, the telecommunications industry is taking a hard look at the problem and designing new high-tech countermeasures, such as digital encryption, to further combat the threat. Table 1 lists existing and future countermeasures and rates their merits and overall effectiveness.
As shown in Table 1, encryption is the most effective countermeasure to reduce both eavesdropping and cellular spoofing, and plans should be made to implement this system. The Clipper chip is not a good solution for two reasons: (1) There is nothing to prevent criminals from reprogramming their cordless and cellular phones with their own encryption schemes, thus negating the crime-fighting aspects of the Clipper chip; and (2) Since a decryption key exists, there is a good chance that this key will be compromised or that the code will be publicly broken, rendering the entire encryption system useless.
Therefore, a random cryptographic scheme is needed to reduce the chance, and possibly prevent the occurrence of communications compromise. The probability and threat of cordless and cellular compromise is high, and the effects of it are costly. We must, as a society, begin taking steps now to increase our communications security; otherwise, we will continue to risk and incur great losses in both personal and business affairs.
| Threat | Countermeasure | Technology Level | Countermeasure | Cost Comments | Overall Effectiveness |
|---|---|---|---|---|---|
| Electronic Eavesdropping | Limit sensitive conversations | Low | Low | People tend to accidentally release sensitive info, may not be user-friendly. | Medium |
| Electronic Eavesdropping | High Speed Frequency Switching | Medium | Medium | Eavesdroppers may still find the correct frequency and intercept sensitive information. | Medium |
| Electronic Eavesdropping | Digital Encryption | High | High | Cipher code will prevent information compromise, but may hinder crime-fighting efforts. | High |
| Spoofing | Keep phone turned off until ready to use | Low | Low | Low Cellular phone is harder to spoof, but can still be done when the user makes a call. | Low |
| Spoofing | Change MIN routinely | Low | Low | This can be effective, but user must routinely change MIN. The phone can still be spoofed at any time. | Medium |
| Spoofing | Incorporate PIN number | Medium | Medium | This makes it harder to spoof phone, but scanning equipment can be easily modified to intercept PIN. | Medium |
| Spoofing | Design tamper-proof ESN chips | Medium | Medium | This will prevent cellular phones from being reprogrammed, but will not stop technically advanced phreakers or eliminate the use of Cache-Boxes. | Medium to High |
| Spoofing | Digital Encryption | High | High | Cipher code will reduce and possibly prevent spoofing, including the use of Cache-Boxes. | High |
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MobileHouse Antenna Information
There are a number of factors involved including:-
- Frequency (wavelength).
- Gain.
- Impedance.
- Polarisation.
Each antenna has a resonant frequency, the frequency at which it is most efficient at either transmitting or receiving energy. The resonant frequency is set by the physical length of the antenna. Frequency and wavelength are related, the wavelength (in metres) is equal to the speed of light (in metres/sec) divided by the frequency (in Hertz - Hz).
Similarly the frequency is equal to the speed of light divided by the wavelength. So in the good old days when Radio 4 was the Long Wave it transmitted on a wavelength of 1500m. The speed of light is 300,000,000 metres a second so 300,000,000 / 1,500 = 200,000Hz or 200 kHz. Go find an old radio and you will find 1500m on the dial, newer ones have 200 kHz (and yes, thank to some interfering French politicians Radio 4 is now on 198 kHz which took away a lovely stable frequency reference - but that’s another story).
A frequency of 1800 MHz (GSM 1800) equates to a wavelength of:-
300,000,000 / 1,800,000,000 = 0.167m
or a wavelength of about 16.7cm. At 900 MHz everything is twice as big, so 900 MHz gives a wavelength of 33.4cm. Antennae are usually referred to by the fraction of a wavelength represented by their physical length, so a full wave antenna at 1800 MHz would be 16.7cm long (In practice it would be a slightly different length to allow for corrections for end effects). A half wave antenna at 1800 MHz would be 8.4cm and so on. Most phone antennae are about 1/4 wavelength long.
Gain
The basic pattern of energy coming from a “perfect” antenna with no gain is a bit like a ball (with the antenna in the middle), the antenna radiates equally in all directions (the “isotropic” antenna). This isn’t always what is wanted. In most mobile phone antennae you want most of the energy coming out near the ground and not too much going vertically into space.
A standard dipole radiation pattern is not isotropic - it looks bit like a doughnut with the antenna in place of the hole.
An antenna can only put out what is put in to it, so when you see adverts for antennae with “gain” (for example 3dB gain) what it means is that the energy is being directed more in one direction than others (It also means the area the energy was redirected FROM will get less.)
Going back to the doughnut, if you press down on the top of the ball it gets wider and shorter, the wider axis is showing gain, the shorter one loss.
You can also put directivity in the azimuth pattern - but for phones this is not a good idea! The most common antenna with gain in azimuth is the common TV antenna (a Yagi antenna design for the curious) which typically has a beamwidth of about 15 to 20°.
Antenna gain is usually expressed in decibels and refers to the gain of the design over the radiation in that direction given by a perfect isotropic antenna or a dipole. As the isotropic antenna and dipole differ anyway it is important to know which is being referred to when comparing antennae. Usually if antenna is described as having “3dB gain” it means compared with a dipole. If it says “3dBi gain” it means compared with an isotropic radiator.
The most common mobile antenna design to show gain is the co-linear. In most cases this will give about 3dB gain over a dipole. Treat all claims for greater gain from non directional antennas with severe suspicion!
Impedance
Impedance is to AC circuits roughly what resistance is to DC circuits (OK - I know that’s a shelf full of text books dismissed in one line!). It isn’t just the length of the antenna which matters but also how you get power into it. For maximum transfer of power the source, transmission line, and load must all have the same impedance In the case of your phone this means the phone, antenna lead, and antenna should all have the same value of impedance.
This value is 50 ohms for most phones so the transmitter and receiver in the phone have a 50 ohm characteristic impedance, the cable is 50 ohms and the antenna impedance should be 50 ohms.
At the base of a 1/4 wave antenna the impedance is indeed about 50 ohms, however at the base of a 1/2 wave one it is several thousand ohms. Making dual frequency antennae (for use on both 900 and 1800 MHz) is a compromise between length, thickness (which also affects impedance) and gain. Nearly all dual frequency antennae will work quite well at one of the frequencies and less well at the other. All are outperformed by single frequency antennas.
Polarisation
Polarisation is the alignment of the electrical part of the radio frequency energy in space. A vertical antenna produces a vertically polarised signal, a horizontal one a horizontally polarised one, and a spiral antenna a circularly polarised one (left or right hand depending upon the way the spiral goes). In theory a horizontal receiving antenna will receive no energy from a vertical transmitter antenna (and this works - many continuous wave tracking radar’s use a left hand circularly polarised signal to transmit and a right hand one to receive so they can transmit and receive on the same frequency at the same time.
However we all know the phone still works lying on the table - so what happens?
The signal from the transmitter strikes many objects along its way and is reflected from them, these reflections are often twisted because of the irregular nature of the reflecting object. By the time the signal reaches you it has lost much of its initial polarisation and become scattered. However it will usually still be the case that most of the signal will maintain its original polarisation and the more vertical you keep the antenna the better your chances of a good signal.
Special Antennas and Signal Amplifiers.
The Co-linear
The true co-linear design is a series of dipoles stacked end to end and fed by different cables such that the radiation patterns inter-react to give a lower angle of radiation with more power in the lower angles than the higher. The antenna called a colinear in mobile phones achieves a similar effect by being partial multiples of wavelengths long and having tuning and loading coils built in ( the single coiled twist in the 1800 MHz antenna shown above and the thicker tube about 1/3 of the way up the 900MHz antenna. The extra length of the co-linear explains why your antenna is longer than you expected based on the calculations at the top of this page.
The Yagi
The Yagi antenna design is probly the most common antenna with gain - nearly all TV antennae are Yagis. Its use in mobile phones is very limited because it gives directional gain in azimuth - you need to know where the base station is and point at it! However it does have its uses, models for 900MHz are made mainly for the Nordic market where mobile phones are the communication method of choice for the popular remote weekend houses. Fitted to a house and pointing at the nearest base station it gives excellent gain and will often turn a no hope signal into a strong one.
Signal Amplifiers
Touted by some as the secret panacea for all ills the linear amplifier (AKA “Burner”, Power Booster, Power Amplifier) came to infamy in the heyday of CB radio when they were brought over from the USA and fitted illegally to Ford Capris and Cortinas by numbers of CB enthusiasts. In general there were two main effects - the car battery ran down very quickly and every receiver for miles around was jammed by the spurious out of band emissions. Some of these amplifiers were quite impressive - 1kW (yes - 1000 Watt) linears sitting on the boot of ratty Fords were not unknown!
Somewhat more civilised amplifiers were fitted to car kits for analogue phones taking their power up to 5 Watts. However since the advent of GSM and PCN the benefits to be gained from these quite expensive boxes have become much less.
As far as PCN is concerned the only benefit is to overcome losses in installations where long cable runs must be employed, for example if you need an antenna on the roof of your house. In this situation the amplifier incorporates both a received signal pre-amplifier and a transmitted signal power amplifier. It is designed to overcome the quite significant losses which occur in co-axial cables at 1800MHz.
Putting one in your car will usually have little or no significant effect.
- If you use your cellphone in your motor-vehicle, an external cellphone antenna is a must !!
That’s because cars insulate cellphones from the external GSM signal, an unwanted artifact known as the "Faraday Cage." This Cage can sometimes result in poor voice quality and even dropped calls. A well-installed external car antenna usually fixes the problem. And if you’re in a rural area that’s on the periphery of the GSM coverage range, or even in a building that tends to block GSM signals, there are some novel antenna solutions available.
External antennas are available at around US$20, but are invariably professionally fitted as part of the complete installation of a cellphone car kit.
Your installer is likely to provide you either with a semi-permanent stick-on antennae design that simply sticks onto the front or back car windows using adhesive tape, magically transferring the GSM signal through the glass and then via a cable to and from the external antenna socket on your GSM cellphone or it’s special car kit.
Some installers also provide permanent boot (trunk) and car roof mount designs, but these tend to be more expensive as they invariably necessitate some car-body drilling and additional wiring. There are however many do-it-yourself clip-on designs available that don’t really require any detailed technical knowledge and can be installed in minutes. The most popular though are the installed stick-on types.
These external antenna housings usually consist of a base with a screw-on antenna rod. Some rods have an enclosed coil in the middle. Antenna efficacy is usually measured in decibels (dB) - the higher the rated dB specification, usually the better it’s performance. Longer rods of around 50cm usually have a dB level of around 5dB, the smaller 9cm types around 3dB or less.
Whatever their length, the antenna rods should be attached to a positionable, swivel-type joint on the base to allow the rod to be positioned backwards and forwards, left to right to optimize efficacy. The base positioning of the antenna on the car is also important: some installers prefer the front or back window, while others drill on the car boot or roof. The back window however is the most popular antenna position, although this invariably depends on the vehicle’s shape.
Your external antenna should also feature a position lock "memory" to ensure that the antenna rod stays in the position you set it - especially when used in high-wind areas. Some of the longer antennas tend to create high-pitched whistle effects in winds. Make sure that you can also unscrew the rod: this feature is especially useful if you want to prevent the antenna being mangled by a car-wash behemoth. Smaller, low profile 9 cm front-window mounted antennas are perfect for avoiding these situations.
There are also a number of easily fitted removable/portable car antenna solutions. One design simply clips on to the top of a wind-up side window, allowing you to switch cars and still have external antenna support. Once you’ve placed the clip onto the top of the window, you then simply plug (hard wire) the attached antenna cable into the phone’s antenna socket. You can use it with the window open or closed as the cable signal is relayed to the antenna’s external rod via the window clip-on.
There is however another side window clip-on design available that does not use any hard wiring. Instead it uses a special cordless pick-up rod inside the car - also connected to it’s external rod via the window clip-on - to "passively" relay the GSM signal to and from the cellphone. With both these clip-on designs, the back right passenger window is recommended.
There is yet another flat "patch" passive antenna type that simply sticks down flat onto any window. This solution, although not the most effective, is useful in offices where GSM signals may be blocked by an abundance of concrete and steel in the wall.
If you’re in a fixed rural location on the coverage fringe, there are special 10dB corner reflector antennas that can be attached to poles or buildings.
No field assembly or tuning is required and they easily attached to your cellphone using ordinary cable connections.
If necessary, you might also want to consider special booster devices that increase the power of you cellphone from the average 2W to up to a powerful 8W.
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rbcomm
ORBCOMM offers affordable global wireless data and messaging communications services from space. Click here for more information.
Frequency Allocation
The ORBCOMM system uses 137-138 MHz and 400 MHz frequencies for transmissions down to mobile or fixed data communications devices; and 148-150 MHz frequencies for transmissions up to the satellites. These frequencies, approved for use by LEO satellite systems at the World Administrative Radio Conference in February 1992, were allocated by the FCC to Little LEO mobile satellite services in January 1993. The FCC granted ORBCOMM a U.S. commercial license in October 1994.
System Description
The ORBCOMM system uses LEO satellites instead of terrestrial fixed site relay repeaters to provide worldwide geographic coverage. The system is capable of sending and receiving two-way alphanumeric packets, similar to two-way paging or e-mail. The three main components of the ORBCOMM system are: the space segment - the constellation of satellites; the ground segment - gateways which include the Gateway Control Centers (GCCs) and Gateway Earth Stations (GESs) and the Network Control Center (NCC) located in the United States; and subscriber communicators (SCs) - hand-held devices for personal messaging, as well as fixed and mobile units for remote monitoring and tracking applications.
ORBCOMM System Architecture Diagram
Space Segment
ORBCOMM currently has 35 satellites in its constellation. An additional launch is planned for 2000, enhancing coverage in the equatorial regions of the world.
The main function of ORBCOMM's satellites is to complete the link between the SCs and the switching capability at the NCC in the U.S. or a licensee's GCC. The satellites are "orbiting packet routers" ideally suited to "grab" small data packets from sensors in vehicles, containers, vessels or remote fixed sites and relay them through a tracking Earth station and then to a GCC.
Satellite Characteristics
| - Weight: 90 lbs. - Solar Array Power BOL: 160 watts - Transmitters: | - Receivers: 1 DCAAS Receiver and 6 Subscriber Receivers - Guidance: Autonomous/GPS |
More ORBCOMM Satellite Facts
ORBCOMM Satellite Element Sets
Ground Segment
The ground segment, which has most of the intelligence of the ORBCOMM system, is comprised of GCCs, GESs and ORBCOMM's NCC, which is located at ORBCOMM's headquarters in Dulles, VA. The NCC also serves as North America's GCC. Additionally, within the US, there are four GESs located in Arizona, Georgia, New York State and Washington State.
Gateway Control Center (GCC)
Located in a territory that is licensed to use the ORBCOMM system, the GCC provides switching capabilities to link mobile SCs with terrestrial-based customer systems via standard communications modes including X.400, X.25, leased line, dial-up modem, public or private data networks, and e-mail networks including the Internet. Interfaces to the GCC enable reliable, efficient and cost effective integration of the ORBCOMM system into existing or new customer MIS systems.
Gateway Earth Station (GES)
ORBCOMM's GESs link the ground segment with the space segment and will be in multiple locations worldwide. The GESs provide the following functions:
- Acquire and track satellites based on orbital information from the GCC
- Transmit and receive transmissions from the satellites
- Transmit and receive transmissions from the GCC or NCC
- Monitor status of local GES hardware/software
- Monitor the system level performance of the satellite "connected" to the GCC or NCC
The NCC is responsible for managing the ORBCOMM network elements and the U.S. gateways through telemetry monitoring, system commanding and mission system analysis. It provides network management of ORBCOMM's satellite constellation and is staffed seven days a week, 24 hours a day by ORBCOMM-certified controllers.
The NCC provides the following functions:
- Monitor real-time and back-orbit telemetry from the ORBCOMM satellites
- Send real-time and stored commands to the satellites
- Provide the tools and information to assist engineering with resolution of satellite and ground anomalies
- Archive satellite and ground telemetry for analysis
- Monitor performance of the U.S. Gateway Earth Stations (GESs)
- Monitor status of the ORBCOMM U.S. Message Switch (OMS) and related software
- Provide daily and weekly performance totals
Subscriber Communicator (SC)
There are several types of SCs. ORBCOMM's SC for fixed data applications uses low-cost VHF electronics. The simple antenna design and small package provide installation flexibility. The low-power electronics allow for extended operations using batteries, a solar panel or available power.
The SC for mobile two-way messaging is a hand-held, stand-alone unit. Typically, the units have an alphanumeric keyboard and small display screen.
Click here for more information on ORBCOMM Subscriber Communicator manufacturers.
Source: Orbcomm Website
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MobileHouse Mobile App: Build mobile applications easily
Mobile applications creator tool to easily make mobile applications customized for each mobile phone, without programming skills, using a visual interface, web-based, sending the application via SMS Push or Bluetooth with FuturLink APs.
Key Features
- Easy creation of interactive rich mobile applications without programming skills.
- Advanced functionalities such as click to call, RSS, agenda, forms, maps, templates, etc.
- Automatic adaptation of the mobile application to the different mobile phones, through mobile device detection technology, ensuring the correct view of the applications.
- Ideal for product catalogues, tourism, events, agendas, stores lists, etc.
- Hosting of the created applications.
- Web-based solution compatible with most common browsers.
Downloads
Technical Specifications
Category
- Mobile
System
System Requirements for the computer:
Handset compatibility:
- Compatible with the following browsers: - Internet Explorer 7+
- Google Chrome
- Mozilla Firefox
- Internet connection required
Handset compatibility:
- Around 1,400 Java compatible phones (Nokia, Blackberry, Samsung, LG, Sony-Ericsson, Motorola, etc).
- For iPhones the content of the mobile application is available on a mobile website.
- Android coming soon.
Others
Access MobileHouse MobileApp here.
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MobileHouse Mobile Synchronization
UME-36Pro - Universal Memory Exchanger |
Synchronizing a world of content
MobileHouse's UME-36Pro, the newest member in the Universal Memory Exchanger family, is a professional, stand-alone phone memory transfer and backup solution that transfers all forms of content, including pictures, videos, ringtones, SMS, as well as phonebook contacts data between a wide range of mobile phones, smart phones and PDAs. The UME-36Pro was designed with the needs of the mobile phone industry in mind. Rugged and easy to use the UME-36Pro promises mobile communication service providers years of service thanks to CelleBrite's constant firmware updates that keep the UME-36Pro current with the latest cellular phone models. The UME-36Pro still operates with the ease, speed and reliability that customers have come to expect from CelleBrite. learn How It WorksUME-36Pro TutorialCheck Supported PhonesCheck the UME-36Pro kit contentsCommercial MovieClip | |
Main Features and Capabilities
- Based on Windows CE.
- Supports transfer of content across all mobile handset technologies - GSM, CDMA, UMTS, 3G, TDMA, IDEN and more.
- Transfer of phones internal memory and SIM card content
- Transfer of phonebooks, pictures, videos, ring-tones, and SMS.
- Supports multiple language encodings.
- Available connectivity: USB, Serial, IrDA and Bluetooth connections to phones.
- Transfer, backup and restore of mobile phone content
- Supports SymbianTM, Microsoft Mobile™ Palm™ , and Blackberry™ operating systems.
- Integrated SIM/Smart Card reader.
- Integrated PC connection allowing content backup and management.
- Stand-alone device or an integrated PC solution.
- User-friendly and self-explanatory.
- Easily upgraded through software file downloads.
UME-36Pro offers mobile operators and retailers:
- New sources of revenue.
- Rapid Return on Investment.
- Enhanced quality of service.
- Increased customer retention and monthly activation.
- An easy way to remove customer hesitation re: upgrading to new phones, applications and services- even from complex multimedia models.
- Elimination of barriers to switching networks.
System Highlights
- Supports most mobile phones available in the market for all carriers and technologies (see List of Supported Phones).
- Protects customer privacy by securely transferring content without exposure to store personnel.
- Easily upgradeable to support new handsets via the Internet or flash drive.
- Easy to learn and simple to use.
- Built in Ethernet card for advanced capabilities.
- Built in SIM reader.
- Supports SD Card.
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Mobile House Instructions
Water Damage
.* The FIRST thing to do when you drop your phone in water is to IMMEDIATELY pull the battery off. DON'T turn the phone off first, pull the battery off.
.* As soon as possible after this place the phone into some clean water, preferably some kind of pure water. If the phone was dropped into salt water, immediately rinse the phone thoroughly in clean water then place the phone into the water. Do not place the battery in the water, consider replacing it or at least dry it out thoroughly with a hair drier.
.* Next step is to disassemble the phone OR take it to a service centre depending on your skills.
.* Completely disassemble the phone and clean each part again in water. Dry the parts with a hair drier and leave at least 24 hours in a warm area to get rid of any water built up under IC's etc. Shake the parts a few times in this period and also attack them with the hair drier again.
.* Check the phone for corrosion etc, if there's none you may be ok. If there's corrosion you really need to remove it, there are many PCB cleaning products on the market for this sort of work. Check with your local electronics store.
.* Next step is to carefully reassemble the phone. Use a new battery if available or borrow one.
.* Using the battery that was soaked is not recommended but normally works ok.
.* All going well the phone still works, if not pull it apart and check that it was assembled properly. If still no go, dry it again with the hair drier and leave for another 24 hours to make sure that it's really dry. In most cases the phone will still work.
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