Direct digital synthesizer (DDS) – Fine resolution digital frequency synthesis technology that uses a numerically controlled oscillator (NCO) to program the output frequency to the chosen value.

Decision feedback equalizer (DFE) – Digital communication receiver technology that uses data decisions to adjust its taps to correct for frequency response impairment.

Discrete multitone (DMT) – The selected ADSL physical layer standard, which uses a multicarrier technique to transport data via multiple parallel subchannels per symbol transmission period.

Differential nonlinearity (DNL) – An error associated with non-ideal A/D conversion.

Data Over Cable Service Interface Specification (DOCSIS) – The organization and document defining the cable modem standard.

Institute of Electrical and Electronic Engineers (IEEE)– The world famous organization.

Intermediate frequency (IF) – The carrier center frequency that often follows a frequency conversion stage operating on an RF input. Chosen for ease of subsequent processing, functionality, and standardization.

Inverse fast Fourier transform (IFFT) – Analytical or digital signal processing step that converts frequency domain information into a time domain sequence.

Infinite impulse response (IIR)– A form of filter often used in digital signal processing that performs functions similar to the analog filter, and uses a recursive difference equation expression.

Intermodulation distortion (IMD) – RF impairment where device non-idealities create new frequency components not in the original signal, including the common harmonic and two-tone distortion effects.

Integral nonlinearity (INL) – Impairment measuring the accumulation of the DNL non-ideality of the A/D transfer function.

Second-order intercept point. (IP2)– Figure of merit for second-order (squaring) distortion of a component. Derived by artificially extrapolating a second-order response until it intercepts the fundamental input-output response.

Third-order intercept point. (IP3)– Figure of merit for third-order (cubic) distortion of a component. Derived via artificially extrapolating a third-order response until it intercepts the fundamental input-output response.

Integrated services digital network. (ISDN)– The original very high-speed copper link for data transport. Still a viable high-speed solution, albeit less hype.

Intersymbol interference. (ISI)– Digital communication system impairment where adjacent symbols in a sequence are distorted by frequency response non-idealities, creating dispersion that interferes in the time domain with neighboring symbols.

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Low noise amplifier (LNA) – RF gain device designed specifically for very low imposition of additional noise power. Used to amplify very low signals without contributing significant SNR degradation.

Local oscillator (LO) – Refers to the frequency conversion CW source used in the RF mixing process.

Low probability of intercept (LPI) – Refers quantitatively to the likelihood of a transmitted signal (direct sequence [low power density] spread spectrum, usually) being detected, and possibly intercepted (Sept. 97).

Least significant bit (LSB) – The binary digit carrying the least weight in a digital word.

MCNS (Multimedia Cable Network System Specification)– Consortium for the development of cable modem standards. Also, the name of the cable modem standards development effort before it was called DOCSIS.

MDS (Maximum distance separable)– A forward error correction (FEC) parameter where any two blocks of data that have been converted to code words are as far away as possible in linear algebraic space, creating an encoding scheme less likely to result in errors.

Maximum likelihood (ML) – Method for determining a solution to a detection problem through probabilistic means.

Multichannel multipoint distribution system (MMDS) – Wireless alternative to a cabled video system.

Motion Picture Experts Group (MPEG) – Organization developing (and the specification for) the format of the digital video signal.

M-way phase shift keying (MPSK) – Digital communication system that uses one of M phases to represent log ₂ (M) bits, where each symbol point in the constellation rests along the circumference of a circle. QPSK is 4-PSK.

M-way quadrature amplitude modulation (M-QAM) – Digital communication which uses one of M symbols, each representing log ₂ (M) bits, where both amplitude and phase of the waveform carry information. Commonly, QAM implies a square or near-square constellation carrying information in I- and Q-data carriers.

Most significant bit (MSB) – The binary digit carrying the most weight in a digital word.

Mean square error (MSE) – A measure of inaccuracy that equally weights error both above and below the actual value. In the “Building Blocks” context, used to discuss the error that remains between actual and equalized data as part of the evaluation of equalizer performance.

Minimum shift keying (MSK) – A digital communication modulation type with very low adjacent sidelobe regrowth following power amplification due to its phase continuous properties. Can be shown to be a form of offset QPSK with symbol weighting applied.

Numerically controlled oscillator (NCO) – Digital counter technology used for frequency synthesis implementations in the discrete domain. Digital analogy to the voltage-controlled oscillator (VCO) in the analog domain.

National Cable Television Association (NCTA) – Organization serving the CATV industry.

Near-end crosstalk (NEXT) – Impairment typically associated with twisted-pair transmission, where a local transmitter interferes with a local receiver.

Noise figure (NF) – Parameter describing amount of excess noise added by a component that contributes to SNR degradation from device input to device output.

Not-return-to-zero (NRZ) – Data encoding format where each bit is represented for the entire duration of the bit period as a logic high or a logic low (July 97).

Orthogonal frequency division multiplexing (OFDM) – Multicarrier signaling technique designed to maximize throughput in channels with potentially poor frequency response. Essentially, it is the technology used in discrete multitone (DMT) used in the ADSL standard.

Probability density function (PDF) – Function that statistically describes the variation of a parameter of interest (called a random variable in stochastic terminology). Information content is comparable to a continuous function histogram.

Processing gain (PG) – Spread-spectrum term referring to the SNR improvement in an interference environment available because of the signal spreading use beyond the actual information bandwidth. Mathematically, it is the ratio of spread bandwidth to signal bandwidth.

Phase-locked loop (PLL) – Feedback control loop that provides frequency and phase synchronization of one oscillator to another reference. The range of PLL application is so vast as to make further generalization difficult, but within this column’s context, PLLs are integral parts of receiver systems requiring clock and carrier recovery, frequency generation and synthesis, and other types of data synchronization.

Phase modulation (PM) – Encoding information onto a carrier waveform by varying the phase of the carrier. Mathematically related and similar to the FM waveform structure because of the relationship between frequency and phase. Generally describes analog modulation.

Pseudorandom noise (PN) – Digital noise generated using a feedback shift register sequence. The data stream is typically used in direct-sequence, spread-spectrum (DS-SS) systems and diagnostic link testing. It looks like a random data pattern, but is actually a periodic one with well defined properties.

Quadrature-phase (Q) – The relative quadrature-phase (90º) component of a quadrature modulation system.

Quadrature amplitude modulation (QAM) – Digital modulation scheme that encodes data bits into modulation symbols that have information in both amplitude and phase of the RF carrier.

Quadrature phase shift keying (QPSK) – QAM using four symbols, or 2 bits-per-symbol. A popular and rugged digital modulation that encodes data in one of four possible phases of the RF carrier.

Radio frequency (RF) – Region of spectrum or discipline of electrical design associated with high analog frequencies that require design considerations qualitatively different from traditional analog circuit design.

Reed-Solomon (RS) – Powerful nonbinary block FEC approach used to achieve high coding gains, with unique properties well-suited to QAM systems and burst-error tolerance.

Receiver (Rx) – General abbreviation used in many situations, referring to items such as electrical data receivers, optical receivers, radio receivers, and digital communication demodulators.

Return-to-zero (RZ) – Data encoding format where each bit is represented for only a portion of the bit period as a logic high or a logic low, and what remains of the duration of the bit returns to logic zero.

Surface acoustic wave (SAW) – Filter or oscillator technology characterized by its reliance on acoustic energy and electrical/ acoustic transducers used to take advantage of impressive bandpass filter shape factors that are difficult to achieve with more traditional filter technologies.

Synchronous code division multiple access (S-CDMA) – PN-code-based DS-SS technology where the multiple access codes are kept in clock synchronization to maintain mutual orthogonality. In some literature, it is called orthogonal CDMA.

Society of Cable Telecommunications Engineers (SCTE)– Technical organization serving the CATV industry.

Synchronous digital hierarchy (SDH) – International high-speed baseband digital transport standard specifying incrementally increasing data stream rates for movement across digital optical links.

Symbol Error Rate (SER)– Similar to the BER concept, but instead refers to the likelihood of mistake detection on the digital modulation symbols themselves, which may encode multiple bits per symbol.

Spurious free dynamic range (SFDR) – Specification, common in A/D conversion systems, describing the number of dB between the desired signal and any undesired discrete spectral lines in the output spectrum. Can serve as an artificial limit to detection sensitivity.

Signal-to-noise-and-distortion (SINAD) – Ratio of desired signal power to composite impairment energy, which consists of thermal noise and intermodulation distortion components.

Signal-to-noise ratio (SNR) – Fractional relationship between the power of the desired signal to the power of the noise signal. Typically refers to the additive thermal noise impairment.

Synchronous Optical Network (SONET)– North American high-speed baseband digital transport standard specifying incrementally increasing data stream rates for movement across digital optical links.

Spurious phase modulation (SPM) – Impairment described by discrete spectral lines near the carrier, which is generated by undesired noise components entering a distorting device and creating an interaction (modulation) of noise signal with the desired signal.

Signal-to-quantization noise ratio (SQNR) – Fractional relationship between the power of the desired signal to the power of the noise signal, where (in this case) the noise component refers specifically to the artifacts of non-ideal encoding by an A/D converter.

Single Sideband (SSB)– Refers to analog modulation that implements a mechanism to remove redundant spectral information (one sideband) for bandwidth savings.

Time division multiple access (TDMA) – Approach for allotting single-channel usage amongst many users, by dividing the channel into slots of time during which each user has access to the medium.

Total harmonic distortion (THD) – Measure of total harmonic power at the output of a nonlinear device, typically given in dBc relative to a desired signal.

Travelling wave tube amplifier (TWTA) – Prior to advances in solid-state electronics, an amplifier technology designed for generation of very high-power microwave signals, such as those used in satellite communication applications.

Transmitter (Tx) – General abbreviation for items such as digital communication modulator ICs, microwave point-to-point transmit modules, satellite downlink equipment, and optical transmit components.

Very high-speed digital subscriber line (VDSL) – The next-generation twisted-pair technology (after ADSL) that targets higher data transmission rates than ADSL in exchange for shorter guaranteed distances.

Very large scale integration (VLSI)– Extremely high density digital circuitry technology that is implemented on a single IC.

Voltage standing wave ratio (VSWR) – Measure of the RF interface quality between adjacent RF circuits that require adequate impedance matching for proper transfer of electrical energy at high frequencies.