Wireless Glossary of Common Terms

Automatic Repeat-Request. (ARQ) If a receiver detects an  errors in a message it requests retransmission.
Automatic Frequency Control (AFC) A circuit that maintains the frequency of an oscillator
Automatic Gain Control (AGC) A means that adjusts gain so that the signal level is within the desired range.
Balun A device used to couple a balanced device or line to an unbalanced device or line.
Band A reference to a group of frequencies in the radio spectrum.  They are typically specified in groups of one decade starting with 3’s.  For example 300 MHz to 3 GHz is the UHF band.  Amateur and mobile radio bands are often specified by wavelength, such as the 2 meter band.
Bandwidth The difference between the highest and lowest frequency of operation of a device, such as a filter of amplifier.  In general use bandwidth also refers to the width of the transmitted signal, OR the available data rate for consumer Internet access speeds.
Baseband Refers to the analog or digital signal to be modulated onto a carrier.  This is the signal that a demodulator recovers.
Bit Error Ratio (BER) The number of erroneous bits divided by the total number of bits transmitted, received, or processed over some stipulated period.
Carrier Frequency The output of a transmitter when the modulating wave is made zero.
Carrier Leak The carrier remaining after carrier suppression in a suppressed carrier transmission system.
C-band The microwave frequencies from 4 GHz to 6 GHz used in satellite communications.
Channel Coding Techniques used for controlling errors in data transmission over unreliable or noisy communication channels including error control codes, interleaving and modulation formats.
Code Division Multiple Access (CDMA) CDMA is used as an access method that permits carriers from different stations to use the same radio equipment and spectrum by using a bandwidth wider than the individual carriers. On reception, each carrier is distinguished from the others by means of spreading codes.
Continuous Wave (CW) A wave of constant amplitude and constant frequency.
Cross Modulation Intermodulation caused by the modulation of the carrier of a desired signal by an undesired signal.
Cyclic Redundancy Check (CRC) An error-detection scheme that uses parity bits generated by polynomial encoding of digital signals, and appends those parity bits to the digital signal.
Data Link Layer Layer 2. The Data Link Layer transfers data between network entities and detects and possibly correct errors that may occur in the Physical Layer.
decibel (dB) One tenth of the common logarithm of the ratio of relative powers.  Used for measuring signal levels.
Demodulator Decodes the received modulated signal to extract the information at the receiver
Differential Phase-Shift Keying (DPSK). Phase-shift keying in which the phase difference of the carrier is varied in accordance with the data being transmitted.
Diffraction The deviation of an electromagnetic wave front when it interacts with a physical object such as an opening (aperture) or an edge.
Digital Signal Processing (DSP) The process of analyzing and manipulating signals using computer technology or customized digital hardware.
Diplexer A three-port frequency-dependent device that may be used as a separator or a combiner of signals.
Dipole antenna A center-fed one-half wavelength antenna.
Diversity reception A resultant signal is obtained by combining or selecting signals from two or more independent sources.
Double-sideband transmission (DSB) AM transmission in which both sidebands and the carrier are transmitted.
Effective Isotropic Radiated Power (EIRP) The arithmetic product of (a) the power supplied to an antenna and (b) its gain.
Electromagnetic Compatibility (EMC) The ability of systems and equipment  that utilize the electromagnetic spectrum to operate as intended without suffering unacceptable degradation because of electromagnetic radiation.
Electromagnetic Interference (EMI) Any electromagnetic disturbance that interrupts, obstructs, or otherwise degrades or limits the effective performance of electronics/electrical equipment.
Extremely High Frequency (EHF) Frequencies from 30 GHz to 300 GHz.
Far-field region That part of the radiated field that is further from the antenna than 2D2/?, where D is the  effective antenna diameter and ? is the wavelength of the signal of interest.  In the far field the energy decreases according to the square of the distance from the antenna.
Frequency-Division Multiple Access (FDMA) The division of the assigned radio spectrum to enable multiple radio transceivers to operate simultaneously
Frequency-Hopping Spread Spectrum (FHSS) A technique employing automatic switching of the transmitted frequency. Selection of the frequency to be transmitted is typically made in a pseudo-random manner from a set of frequencies covering a band wider than the information bandwidth.
Frequency-Shift Keying (FSK)  Frequency modulation in which the modulating signal shifts the output frequency between predetermined values.
Gain The ratio of output current, voltage, or power to input current, voltage, or power, respectively.  Usually expressed in dB.
Half-duplex Operation in which communication between two terminals occurs in either direction, but in only one direction at a time.
Impedance The total passive opposition to the flow of electric current.  Determined by the particular combination of resistance, inductive reactance, and capacitive reactance in a given circuit.
Inter-Facility Link (IFL) Cable that interconnects indoor radio or satellite equipment with the outdoor equipment.
Intermediate Frequency A frequency to which a carrier frequency is shifted as an intermediate step in transmission or reception.
Intermodulation (IM) In a nonlinear element of a system, the production of frequencies corresponding to the sum and difference frequencies of the fundamentals and harmonics that are transmitted through the element.
International Telecommunication Union (ITU) A civil international organization established to promote standardized telecommunications on a worldwide basis
Isotropic antenna A hypothetical antenna that radiates or receives equally in all directions.
Jitter Unwanted variations of the interval between successive pulses.  May also include variations in amplitude, frequency or phase of successive cycles.
Key A sequence of random or pseudorandom bits used to set up and periodically change the operations performed in encryption equipment.
Kilohertz (kHz) 1,000’s of cycles per second
Link Layer Short for Data Link Layer
Low Frequency (LF) Any frequency in the band from 30 kHz to 300 kHz
Low-power FM radio (LPFM) A broadcast service that permits the licensing of 50- to 100-watt FM radio stations within a service radius of up to 3.5 miles and 1- to 10-watt FM radio stations within a service radius of 1 to 2 miles.
Media Access Control (MAC) Data communication protocol sub-layer, also known as the medium access control, is a sub layer of the data link layer (layer 2).  It provides addressing and channel access control mechanisms that make it possible for several terminals to communicate within a multiple access network that incorporates a shared medium,
Megahertz millions of cycles per second
Mixer A nonlinear analog circuit or device that accepts as its input two different frequencies (signals) and presents at its output a signal equal in frequency to the sum and difference of the frequencies of the input signals.
Mobile Virtual Network Operation (MVNO) Mobile phone operator that provides services directly to their own customers but does not own infrastructure assets like radio spectrum, cell towers and equipment.
Modem Short for modulator/demodulator.  A device used for converting digital signals into, and recovering them from, signals suitable for transmission over analog communications channels.
Modulation The process, or result of the process, of varying a characteristic of a carrier, with a baseband signal.
Modulation Factor in AM.  The ratio of the peak variation used, to the maximum design variation.  In conventional AM, the maximum design variation is 100%.
Modulation Index The ratio of the frequency deviation of the modulated signal to the frequency of a sinusoidal modulating signal
Modulator Encodes information onto a carrier signal in preparation for RF transmission
Multiple Frequency-Shift Keying  (MFSK) Multiple Frequencies that are transmitted concurrently or sequentially.
Near-Field Region That part of the radiated field that is closer to the antenna than the D2/(4?) from the antenna, where D is the  effective antenna diameter and ? is the wavelength of the signal of interest.
Network Layer Layer 3. The Network Layer transfers variable length data sequences from a source to a destination via one or more networks while maintaining the quality of service requested by the Transport Layer. The Network Layer performs network routing, flow control, segmentation/desegmentation, and error control functions.
Noise Figure )NF) The contribution of an active device (like an amplifier) to thermal noise at its output. The noise figure is  expressed in dB and is with respect to thermal noise power at a standard noise temperature (usually 20C, 293 K).
Noise power density The noise power in a 1 Hz bandwidth.  The value is kT where k is Boltzmann’s constant, T is the effective noise temperature of the device in Kelvin.
Nyquist rate The minimum theoretical sampling rate that fully describes a given signal.  (2 x its maximum bandwidth).
Out-of-band emission Emission of a signal outside the necessary bandwidth which results from the modulation process, but excluding spurious emission
Over Modulation A condition where peaks in the modulating signal exceed the value necessary to produce 100% modulation of the carrier
Path Profile A graphic representation of the physical features of a radio propagation path in the vertical plane containing both endpoints of the path, showing the surface of the Earth and including trees, buildings, and other features that may obstruct the radio signal.
Peak Envelope Power The average power transmitted during one radio frequency cycle at the crest of the modulation envelope.
Peak-to-Average Ratio (PAR) The ratio of the instantaneous peak magnitude of a signal parameter to its time-averaged value.
Phase angle Of a periodic wave, the angular measurement between a point on the wave and a reference point. The reference point may be a point on another periodic wave.
Phase coherence The state in which two signals maintain a fixed phase relationship with each other.
Phase detector A circuit or instrument that detects the difference in phase between corresponding points on two signals.
Phase distortion Distortion that occurs when the phase-frequency characteristic is not linear
Phase inversion Introduction of a phase difference of 180°
Phase jitter Rapid, repeated phase perturbations that result in the intermittent shortening or lengthening of signal elements
Phase Modulation (PM) Angle modulation where the phase angle of a carrier is changed by an amount proportional to the instantaneous value of the modulating (baseband) signal.
Physical Layer Layer 1. The lowest of seven hierarchical layers. The Physical layer converts between the digital data the corresponding signals transmitted over a communications channel.
Quadrature When the phase difference between two same frequency signals is one-quarter of their period (i.e. 90°)
Quadrature Amplitude Modulation (QAM) Two orthogonal carriers are amplitude modulated and combined to create a complex modulation signal.  For example, 16 QAM uses 4-levels on each carrier creating 16 possible values and is suitable for sending 4 bits of information in one symbol period.
Quadrature Phase-Shift Keying (QPSK) Digital modulation in which four different phase angles are used. In QPSK the four angles are out of phase by 90°.
Quantization A process in which the continuous range of values of an analog signal is sampled and divided into non-overlapping sub ranges, and a discrete value is assigned to each sub range
Quantizing noise Noise caused by the error of approximation in quantization.
Rayleigh fading In radio propagation, the phase-interference fading caused by multipath, and which may be approximated by the Rayleigh distribution.   Applicable to narrow band mobile radio and cellular systems.
Received noise power The noise power, within the bandwidth being used, at the receive end of a circuit, channel, link, or system.
Receiver sensitivity The minimum value of average received power to achieve a specified bit error ratio.
Redundancy Use of surplus capability to improve the reliability and quality of service.   Common examples include additional receivers, transmission attempts, communication paths and overhead bits.
Reflection loss At a discontinuity or impedance mismatch, e.g., in a transmission line, the ratio of the incident power to the reflected power, usually expressed in dB.
Return Loss The ratio, at the junction of a transmission line and a terminating impedance, of the amplitude of the reflected wave to the amplitude of the incident wave, usually expressed in dB.
Selective fading Fading in which the components of the received radio signal fluctuate independently.  Usually in reference to frequency selective fading.
Session Layer Layer 5. The Session Layer provides the mechanism for managing the dialogue between end-user application processes including initiation, termination and restart procedures.
Software Defined Radio (SDR) A radio that uses software processing to control and change a radio’s fundamental characteristics such as modulation types, operating frequencies, bandwidths, multiple access schemes, channel coding and other features.
Space Diversity A method of transmission or reception, or both, in which the effects of fading are minimized by the simultaneous use of two or more physically separated antennas, ideally separated by one or more wavelengths.
Spurious emission Emission on a frequency or frequencies outside of the necessary bandwidth for information transmission. Spurious emissions include harmonic emissions, parasitic emissions, intermodulation products and frequency conversion products, but exclude out-of-band emissions.
Squelch A circuit function that acts to suppress the audio output of a receiver in order to exclude undesired lower-power input signals that may result in the operator listening to noise.
Standing wave In a transmission line, a wave in which the distribution of current, voltage, or field strength is formed by the superposition of two waves propagating in opposite directions.  The wave is characterized by a series of nodes, maxima and minima.  A standing wave may be formed when a wave is transmitted into one end of a transmission line and is reflected from the other end by an impedance discontinuity (mismatch) such as an open or a short.
Standing Wave Ratio (SWR) The ratio of the amplitude of a standing wave at a minimum to the amplitude at a maximum.
Third-Order Intercept Point A point that is an extrapolation of the intermodulation performance so that intermodulation products of two closely spaced carriers are of the same amplitude as the desired signals.
Time Division Duplex (TDD) The application of time-division multiplexing to separate outward and return signals. It emulates full duplex communication over a half duplex communication link.
Time-Division Multiple Access (TDMA) A communications technique that uses a common channel (multipoint or broadcast) for communications among multiple users by allocating unique time slots to different users.
Transmission coefficient In a transmission line, the ratio of the amplitude of the transmitted wave to that of the incident wave at a discontinuity in the line.
Transmission line A medium or structure that forms all or part of a path from one place to another for directing the transmission of energy.  Examples of transmission lines include wires, coaxial cables, and waveguides.
Transport layer Layer 4. The Transport Layer is to provides transparent transfer of data between end users, thus relieving the upper layers from any concern with providing reliable data transfer.
Ultra High Frequency (UHF) Frequencies from 300 MHz to 3000 MHz.
Ultra Wideband (UWB) Referring to any radio or wireless device where the occupied bandwidth is greater than 25% of the center frequency or greater than 1.5 GHz.
Universal Mobile Telecommunication System (UMTS) A third generation mobile cellular technology based on the GSM standard. UMTS employs Wideband Code Division Multiple Access (W-CDMA) radio access technology.
Very High Frequency (VHF) Frequencies from 30 MHz to 300 MHz.
Very Low Frequency (VLF) Frequencies from 3 kHz to 30 kHz
Voltage Standing Wave Ratio (VSWR) The ratio of maximum to minimum voltage in a standing wave pattern in a transmission line.
Wavelength (?) The distance between points of corresponding phase of two consecutive cycles of a wave. The wavelength  is related to the propagation velocity, v, and the frequency, f, by ? = v/f.