Communications
Terminology
(Taken
from "Communications Systems Design"
Magazine)
NOTE: I am doing this
page to be used as a reference for people unfamiliar with these terms. I am
fortunate enough to be able to get many of the trade magazines free at my work.
For many of the newer EE's (or students) out there these may be of some help.
My goal is to eventually have many pages of helpful information from designing
with MCUs, to designing RF devices.
ACI: Adjacent
channel interference - The phenomenon whereby channels that are beside one
another in the frequency domain may have some spectral overlap, causing
interference.
ADSL:
Asymmetric digital subscriber line - Standard for high speed data over twisted-pair
copper as a function of loop length.
AGC: Automatic
gain control - Receiver function that generates constant power output under
varying power input.
ALC: Automatic
level control - Sometimes used for subsystems with lessdynamic variation.
ARQ: Automatic
repeat request - Rudimentary transmission error protection whereby the receiver
requests a retransmission when it detects that errors have occurred in a frame.
ATM:
Asynchronous transfer mode - A packet switched network protocol, which uses a pre-established
connection route.
AWGN: Additive
white Gaussian noise - The common wideband channel thermal noise impairment, on
which signal-to-noise ratio (SNR) is typically based.
BER: Bit error
rate or bit error ratio - A figure of merit for a digital communication link.
It is the fraction of bits received in error divided by the total number of
bits transported.
BPSK: Binary
phase shift keying - A digital modulation format where 1 and 0 are represented
by phase shifts of 0o and 180o of the carrier.
CAP:
Carrierless amplitude-phase modulation - Quadrature amplitude modulation
(QAM)-type modulation format with a unique implementation twist designed for
ADSL applications.
CDMA: Code
division multiple access - Spread spectrum technique using high-speed pseudorandom
(PN) codes to scramble data words and spread spectral occupancy for added
robustness.
CRC: Cyclic
redundancy check - A simple form of error correction characterized by a
checksum calculation.
CW:
Continuous wave - An unmodulated carrier.
DCT: Discrete
cosine transform - A Fourier-like transform applied to picture elements to aid
in data (video) compression.
DDS: Direct
digital synthesizer - Fine resolution digital frequency synthesis technology
that uses a numerically controlled oscillator (NCO) to program the output
frequency.
DFE: Decision
feedback equalizer - Digital communications receiver technology that uses data
decisions to adjust its taps to correct for frequency response impairment.
DMT: Discrete
multitone - The selected ADSL physical layer standard, which uses a
multicarrier technique to transport data via multiple parallel subchannels per
symbol transmission period.
DNL:
Differential nonlinearity - An error associated with non-ideal A/D conversion.
DQPSK:
Differential quadrature phase shift keying - A modulation format using four
phases (see QPSK), but transmitted so that the information is encoded in the
difference from symbol to symbol for synchronization simplification purposes.
DRO:
Dielectric resonator oscillator - A type of high performance microwave
oscillator technology.
Eb/No:
Energy-per-bit to noise density ratio - A common SNR-like figure of merit for
digital communication systems, particularly those obeying Nyquist criteria.
Es/No:
Energy-per-symbol to noise density ratio - A common SNR-like figure of merit
for digital communication systems. Equivelant to SNR for systems obeying
Nyquist criteria, it relates to BER for a given modulation type, and relates to
Eb/No through number of bits per symbol.
ENOB: Effective
number of bits - Figure of merit for an A/D converter describing how many bits
of effective resolution-below actual A/D word size-exist due to limitations in
noise and distortion performance.
FDMA: Frequency division multiple access - An
approach to sharing a channel by separating the simultaneous users in
frequency.
FEC: Forward
error correction - Technique by which a data stream is modified to create added
channel robustness, improving error rate performance.
FFT: Fast
Fourier transform - A hardware implementable algorithm for spectral analysis in
signal processing applications, including basic OFDM systems.
FH-SS: Frequency-hoping
spread spectrum - Technique of spectrum spreading performed to secure the data
transmission by selecting among multiple possible tones based on a pseudorandom
sequence.
FIR: Finite
impulse response - Well known linear phase digital filter type commonly used in
DSP, which performs spectral modification in the discrete domain similar to the
function of analog filters.
FSE: Fractionally
spaced equalizer - A digital receiver equalization technique based on adaptive
filtering with half-symbol spaced tabs. It provides improved timing robustness.
FSK: Frequency
shift keying - A digital communication technique which chooses the carrier
frequency from a predetermined set, based on the input data.
GMSK: Gaussian
minimum shift keying - A form of MSK used in wireless (see MSK) applications,
which uses a filter with Gaussian impulse response, resulting in narrower
spectral containment at the expense of adding dispersion.
GDV: Group
delay variation - RF distortion impairment where different frequency components
of a signal are passed through a device and receive different time delays.
HDSL: High
speed digital subscriber line - Data transport standard for 1.5Mbps copper
twisted pair.
IF:
Intermediate frequency - 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.
IFFT: Inverse
fast Fourier transform - Analytical or digital signal processing step that
converts frequency domain information into a time domain sequence.
IIR: Infinite
impulse response - 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.
IMD:
Intermodulation distortion - RF impairment where device non-idealities create
new frequency components not in the original signal, including the common
harmonic and two-tone distortion effects.
INL: Integral
nonlinearity - Impairment measuring the accumulation of the DNL non-ideality of
the A/D transfer function
IP3:
Third-order intercept point - 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.
ISDN:
Integrated services digital network - The original very high-speed copper link
for data transport.
ISI: Intersymbol
interference - 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.
LNA: Low noise
amplifier - RF gain device designed specifically for very low imposition of
additional noise power. Used to amplify very low signals without contributing
significant SNR degradation.
LO: Local
oscillator - Refers to the frequency conversion CW source used in the RF mixing
process.
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.
MMDS:
Multichannel multipoint distribution system - Wireless alternative to a cabled
video system.
MPSK: M-way
phase shift keying - Digital communication system that uses one of M phases to
represent log2 (M) bits, where each symbol point in the
constellation rests along the circumference of a circle.
M-QAM: M-way
quadrature amplitude modulation - Digital communication which uses one of M
symbols, each representing log2 (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.
MSE: Mean
square error - A measure of inaccuracy that equally weights error both above
and below the actual value.
MSK: Minimum
shift keying - A digital communication modulation type with very low adjacent
sidelobe regrowth following power amplification due to its phase continous
properties.
NCO:
Numerically controlled oscillator - Digital counter technology used for
frequency synthesis implementations in the discrete domain.
NEXT: Near-end
crosstalk - Impairment typically associated with twisted-pair transmission,
where a local transmitter interferes with a local receiver.
NF: Noise
figure - Parameter describing amount of excess noise added by a component that
contributes to SNR degradation from device
input to device output.
OFDM:
Orthogonal frequency division multiplexing - Multicarrier signaling technique
designed to maximize throughput in channels with potentially poor frequency
response.
OQPSK: Offset
quadrature phase shift keying - QPSK system in which the two bits that make up
a QPSK symbol are offset in time by a half-bit period for non-linear
amplification (power amps) of a bandpass spectrum with fewer spectral regrowth
concerns.
PG: Processing gain - Spread-spectrum term referring to the SNR improvement in an interference environment available because of the signal spreading use beyond the actual information bandwidth..
PLL: Phase-locked loop - Feedback control loop that provides frequency and phase synchronization of one oscillator to another reference.
PM:Phase modulation - Encoding information onto a carrier waveform by varying the phase of the carrier.
PN: Pseudorandom noise - Digital noise generated using a feedback shift register sequence.
MORE TO COME…
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