Definitions:

Analog-to-Digital converter (ADC). Converter that uniquely represents all analog input values within a specified total input range by a limited number of digital output codes, each of them exclusively representing a fractional part of the total analog input range.

Automatic Gain Control. System which holds the gain and, accordingly, the output of a receiver substantially constant in spite of input-signal amplitude fluctuations.

Distortion component created when frequencies present in a sampled signal are greater than half of the sample rate.

Amplitude Modulation. CW modulation using amplitude variation in proportion to the amplitude of the modulating signal; usually taken as DSB-LC for commercial broadcast transmissions and DSB-SC for multiplexed systems.

Advanced Mobile Phone Service. Analog cellular standard operating in the frequency range of 1800MHz with a bandwidth of 30kHz. First established cellular standard in the world. Analog cellular subscribers in North America are served by AMPS.

Signal sent by receiving data processing device in response to a request from a transmitting device, indicating that the receiver is ready to accept or has received data.

Filter (normally low pass) that band limits an input signal before sampling to prevent aliasing noise.

Amplitude-Phase Keying. Combining ASK and PSK to convey information.

Amplitude-Shift Keying. Switching between two amplitudes of a sinusoid to represent binary 1s and 0s.

Mode of data transmissions in which the time occurrence of the bits within each character or block of characters relates to a fixed time frame, but the start of each character or block of characters is not related to this fixed time frame.

Asynchronous Transfer Mode. New technology for digital transmission using fixed length 53 byte cells. These cells can carry voice, video and data at a very high speed, thus increasing the network bandwidth and allowing multiple new applications.

Decrease in magnitude of communication signal.

Filter designed to transmit a band of frequencies while rejecting all others.

Measure of the carrying capacity, or size, of a communication channel. For an analog circuit, the bandwidth is the difference between the highest and lowest frequencies that a medium can transmit and is expressed in hertz. (Hz - is equal to one cycle per second)

Frequency band occupied by information-bearing signals before combining with a carrier in the modulation process.

Unit of signal speed equal to the number of discrete signal conditions or events per second. Refers to the physical symbols/seconds used within a transmission channel.

Speed at which data bits are transmitted over a communication path, usually expressed in bits per second. A 9600Bps terminal is a 2400 baud system with 4 bit/baud.

Insertion of additonal bits in a plesiochronous data stream to compensate for differences in the nominal transmissions rate.

Condition in a switching system in which no paths or circuits are available to establish a connecton to the called party, even though it is not busy. This results in a busy tone to the calling party.

Also called wideband. Transmission facility whose bandwidth is greater than that available on voice-grade facilities.

Analog signal of fixed amplitude and frequency that combines with an information-bearing signal by modulation to produce an output signal suitable for transmission.

Wave that serves as the vehicle for the transmission of information applied to it.

Cellular Digital Packet Data. Wide area data network which takes advantage of existing AMPS (US) cellular network by transmitting data packets on unused voice channels. Data is transmitted using RS(63,47) at an effective rate of 14Kbit.

Wireless communications system that exhibits the following characteristics and components: cellular terminals, transmission call, Mobile Telecommunications Switching Office (MTSO), and Public Switched Telephone Network (PSTN).

Code Division Multiple Access. "Spread spectrum" method of allowing multiple users to share the radio frequency spectrum by assigning each active user an individual code. The base signal is mixed with a much higher rate individual code, thereby, spreading the signal across the spectrum. It was originally developed as a technique against jamming.

Carrier Sense Multiple Access with Collision Detection. Access technique used in the Ethernet protocol.

Digital European Cordless Telephone. Digital cordless telephone standard based on a micro-cellular radio communcation system that provides low-power radio (cordless) access between subscriber unit and base station at ranges up to a few hundred meters. DECT operates at a frequency range of 1880 - 1900MHz, with a bandwidth of 1728kHz.

Distortion occurring on communication lines due to the different propagation speeds of signals at different frequencies, measured in microseconds of delay relative to the delay at 1700Hz. (This type of distortion does not affect voice communication, but can seriously impair data transmission.)

Process of recovering a low frequency signal from a modulated carrier. Examples of low frequency signals are voice or low speed data.

Telephone terminal that digitizes voice signals and DTMF tones for transmission over regular twisted pair of copper to the CO/PBX. The process is reversed on the way back from the Central Office/PBX.

Failure to reproduce accurately the characteristics of an original signal's amplitude, phase, delay, etc.

Usually an integrated device which provides gain and frequency translation to a lower frequency. May consist of the LNA, mixer and matching components. It may also include a VCO as well as other functions. The downconverter's input is a radio frequency and the output is an intermediate frequency.

Differential Phase Shift Keying. Modulation technique for transmission where the frequency remains constant but phase changes occur for 90 , 180 , and 290 to define the digital information.

Dual Tone Multi-Frequency - "Tone dialing" system based on outputting two nonharmonic related frequencies simultaneously to indentify the number dialed. Eight frequencies have been assigned to the four rows and four columns of a typical keypad.

Mode of operation permitting the simultaneous transmission and reception of signals.

Transmission equipment used to set up a semi-permanent connection under the control of the "network operator" via a Network Manager. The main difference from a switch is that a switch operates as a temporary connection which is set up under the control of the "end user".

Signal that has been reflected or returned as a result of impedance mismatches, hybrid unbalance, or time delay. Depending upon the impedance irregularities and the propagation characteristics of a facility, echo may interfere with the speaker or listener, or both.

Electrical network in which phase delay or gain varies with frequency to compensate for an undersized amplitude or phase characteristic in a frequency-dependent transmission line.

Frequency Division Multiple Access. Method of allowing multiple users to share the radio frequency spectrum by assigning each active user an individual frequency channel. In this practice, users are dynamically allocated to a group of frequencies so that the apparent availability is greater than the number of channels.

Forward Error Correction. Technique for minimizing transmission errors by adding overhead data to help the decoder interpret the received message correctly. Reed-Salomon is an example of FEC technique.

Frequency Modulation. CW modulation using frequency variation in proportion to the amplitude of the modulating signal.

In this type of spread spectrum approach, both units (base and subscriber or handset and base) hop from frequency to frequency in a simultaneous fashion. The theory is that noise tends to occur at different frequencies at different times. Therefore, even though a part of a transmission may be lost due to interference, enough of the message will come through by hopping the interference to create a noticeably better output when compared to fixed frequency systems.

High-Kevek Data Link Control. CCITT standard data communication line protocol.

High Speed Digital Subscriber Loop. Data protocol which allows full duplex transmission of 772Kbit data over twisted pair up to 20,000 feet.

Impairment created when two frequencies interact to create an erroneous frequency, in turn distorting the data signal representation.

Integrated Services Digital Network. Network capable of offering a narrowband interface to a user for a multitude of services; e.g., high-quality fax telephony data, telex etc.

Industrial, Science and Medical. Bands of frequencies that were allocatd by the FCC to spur rapid development of RF applications in a virtual open-market fashion. Licensing is automatic.

International Standards Organization.

Type of analog communication line distortion caused by abrupt, spurios signal variation from a reference timing position, and capable of causing data transmission errors, particularly at high speeds. (The variation can be amplitude, time, frequency, or phase.)

Data-only communication network between data terminals using a standard interface to the LAN.

Low noise amplifier. Usually the first active, gain device in a receiver. Its purpose is to provide amplification to a low level signal from a large number of available signals while minimizing the noise contribution to the receiver.

Circuit formed by the two subscriber wires (Tip and Ring), connect to the telephone at one end and the central office (or PBX) at the other. Generally a floating system, not referred to ground, or ac power.

The dc current that flows through the subscriber loop. It is typically provided by the central office or PBX, and ranges from 20-120mA.

Device which utilizes its non- linear characteristics to provide frequency conversions from one frequency to another. This may be from a relatively high frequency to an imtermediate frequency (IF). In this case it is known as a down-mixer. Or it may be from a lower frequency to a higher grequency, the carrier frequency, for example. In this case it is known as an upmixer.

MOdulator-DEModulator. Unit that modulates and demodulates digital information from a terminal or computer port to analog carrier signal for passage over an analog line.

Device that allows two or more signals to be transmitted simultaneously on a single carrier or channel.

Noise figure. Ratio of the signal- to-noise power ratio of a device under test to an ideal device.

Power Amplifier. Provides the high power gain to the transmitter. Typical figures of merit include gain, efficiency and linearity (in amplitude and phase modulated systems) and stability.

Private Automatic Branch Exchange. Customer-owner, switchable telephone system providing internal and/or external station-to-station dialing.

Pulse Code Modulation. Method of transmitting data in which signal are sampled and converted to digital words that are then transmitted serially, typically as 8-bit.

Personal Communication Service. Third generation cordless telephone service in the US-based upon WARC (World Association of Radio Commissions) frequency allocations in the 1800-2200MHz range.

Phase lock loop. PLL is a major component in the frequency synthesizer scheme. This device provides a wide flexible range of internal frequency dividers which allow the designer the ability to create a synthesizer to match his needs.

Phase Shift Keying. Switching of the phase of a sinusoid to represent binary 1s and 0s.

Public Switched Telephone Network. Generic term for the collection of networks providing public telephone switching service.

Time interval between specified reference points on the input and output voltage waveforms.

Quadrature Phase Shift Keying. Spectrally efficient modulation technique which breaks the information path into two parts called the "in phase" and the "quadrature phase" components. The combination of these two signals creates one of four unique symbols which are then used to modulate the phase of the carrier.

Signal- correlated noise generally associated with the quantizing error introduced by A/D and D/A conversions in digital transmission systems.

Amplifier and associated equipment used in communication systems to process a signal and re-transmit it.

Radio Frequency. Frequencies of the electromagnetic spectrum normally associated with radio wave propagation. Sometimes defined as transmission at any frequency at which coherent electromagnetic energy radiation is possible, usually above 150kHz.

Arrangement of active components such as the LNA and IF amplifier together with passive components such as the image filter and IF filter. Together they perform the task of recovering the modulation from a known RF signal while rejecting unwanted signals. The portion of the communication system that includes a detector and signal processing electronics to convert electrical signals (electric waves) to audio or data signals. It provides reception and, if necessary, demodulation of electronic signals.

Most often used in the context of frequency allocations. Refers to the frequencies allowed for a type of service out of the total available.

Technique to reduce and avoid interference by taking advantage of statistical means to send a signal between two points. A figure of merit for spread spectrum systems is "spreading gain" measured in DB. The two types of commercial spread spectrum techniques are frequency hopping and direct sequence.

Synchronous Transport Module. STM-1 is the basic building block in European synchronous networks. It corresponds to a data rate of 155.52Mbit or STS-3

Synchronous Transport Signal. STS-1 is the level 1 building block to North America synchronous networks. It corresponds to a data rate of 51.84Mbit.

Time division multiple access. Technique which assigns each subscriber desiring service in a different time slot on a given frequency. Signal compression is achieved by running at very high frequencies. Each user can then deliver the fixed packet message in a brief burst of time thereby increasing the capacity of the system.

Equipment which feeds the radio signal to an antenna, for radiation. It consists of active components such as the upmixer, driver and PA and passive components such as the TX filter. Together, these components impress a signal onto an RF carrier of the correct frequency, or amplitude and provide enough gain to the signal to project it through the ether to its intended target.

Voltage Controlled Oscillator. Oscillator whose output frequency varies with an applied dc of control voltage.