Glossary

NI-USRP Help

Edition Date: March 2018

Part Number: 373380J-01

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Prefixes

Symbol Prefix Value
k kilo 10 3
M mega 10 6
G giga 10 9

Numbers/Symbols

° degrees
dB Decibel
Hz Hertz
Ohms
/ per
V Volts
W Watt

A

ADCanalog-to-digital converter—A hardware component that converts analog voltages to digitized values. An ADC can convert an analog signal to a digital signal representing equivalent information.
amplitude modulation (AM)A process that varies the amplitude of a radio frequency (RF) carrier signal according to the amplitude of the message signal.
amplitude-shift keying (ASK)Refers to a type of amplitude modulation which assigns bit values to discrete amplitude levels. The carrier signal is then modulated among the members of a set of discrete values to transmit information.

B

bandwidthThe measure of a circuit or transmission channel to pass a signal without significant attenuation over a range of frequencies. Bandwidth can also refer to the information rate (in bits per second) that can pass through a circuit or transmission channel.
baseband signalThe baseband is the range in the frequency spectrum occupied by the unmodulated message signal. Both the message signal and the downconverted complex I/Q signal are referred to as baseband signals.

C

carrierThe signal that carries the information encoded or modulated on it. Typically, the carrier is a fixed frequency sine wave, which can be amplitude-modulated, phase-modulated, or frequency-modulated.
carrier frequencyThe frequency of the carrier signal that is a sinusoidal signal upon which the desired signal to be transmitted is modulated. The sinusoidal signal "carries" the modulation.
Carson's RuleDefines the approximate modulation bandwidth required for a carrier signal that is frequency-modulated by a spectrum of frequencies rather than a single frequency. The Carson bandwidth rule is expressed by the relation CBR = 2(Δf + fm) where CBR is the bandwidth requirement, Δf is the carrier peak deviation frequency, and fm is the highest modulating frequency.
CCDF measurementThe complementary cumulative distribution function (CCDF) is a statistical characterization of the time-domain waveform that completely describes the power characteristics of a signal.
center frequencyThe middle frequency of the channel bandwidth. In frequency modulation, the center frequency is equal to the rest frequency—specifically, the frequency of the unmodulated carrier wave.
componentThe real and imaginary parts of a complex number are referred to as components. The Modulation Toolkit VIs can use complex components to describe signal properties. Use the NI-USRP Write Tx Data VI and NI-USRP Fetch Data VI in applications that use Modulation Toolkit VIs, because they also use complex components.

For example, you can represent a two-dimensional vector of length S by its components S = A + iB, where A and B are the vector x- and y-components. The real part of the vector corresponds to the x-component (A), while the imaginary part corresponds to the y-component (B).

CPMcontinuous phase modulation
CPTRcommon periodic time reference

D

DACdigital-to-analog converter—An electronic device, often an integrated circuit, that converts a digital number into a corresponding analog voltage or current.
dB, decibelThe unit for expressing a logarithmic measure of the ratio of two signal levels: dB = 20 log10(V1/V2), for signals in volts.
dBmdecibel milliwatt—Absolute power level referenced to 1 mW.
DC offsetA complex signal impairment that shifts the locus of ideal symbol coordinates off-center in the I/Q plane. A DC offset can be added to the baseband I component, the Q component, or both. The DC offset can be either positive or negative, with the sign indicating direction of the shift. DC offset is expressed as a percentage of full scale, where "full scale" (fs) is the amplitude of the baseband QM waveform.
DDCdigital downconverter—Mixes, filters, and decimates the signal to a user-specified rate.
demodulationDescribes the recovery, from a modulated wave, of a signal having the same characteristics as the original message signal.
downconverterA signal conditioning device that converts a specific band of high-frequency (RF) signals to lower, more manageable intermediate frequencies (IF) that can be digitized.
DSPDigital signal processing—The computation of signal or system transfer characteristics using numeric algorithms. Examples of areas where DSP techniques may be applied include: digital filters, echo detection or echo cancellation, speech synthesis, FFT for spectrum analysis, correlation computations, imagine recognition, and servo-feedback control.
DUCdigital upconverter—Mixes, filters, and interpolates the signal to 400 MS/s.

F

fetchProcess that transfers data from device onboard memory to PC memory.
FFTfast Fourier transform—An efficient mathematical algorithm used for spectrum analysis.
FIFOfirst-in-first-out memory buffer—A data buffering technique that functions like a shift register where the oldest values (first in) come out first.
FIRfinite impulse response—Used to describe a filter with no feedback elements, hence, its impulse response is finite. In contrast, IIR (infinite impulse response) circuitry does use feedback. FIR filters can be implemented by using analog or digital shift registers, or by using software algorithms.
FMfrequency modulation—A process that varies the frequency of a sinusoidal carrier wave from a center frequency by an amount proportional to the instantaneous value of the message signal. In FM, the center frequency is the carrier frequency.

FPGAfield-programmable gate array—Fundamentally, an FPGA is a semi-conductor device which contains a large quantity of gates (logic devices), which are not interconnected, and whose function is determined by a wiring list, which is downloaded to the FPGA. The wiring list determines how the gates are interconnected, and this interconnection is performed dynamically by turning semiconductor switches on or off to enable the different connections.
frequencyThe number of cycles per unit time. The International System of Units has set hertz (Hz) as the standard unit of measurement for frequency, where 1 Hz equals one cycle per second.
FSKfrequency-shift keying

G

gainThe factor by which a signal is amplified, often expressed in dB. Gain as a function of frequency is commonly referred to as the magnitude of the frequency response function.
GPGGAGlobal Positioning System Fix Data
GPRMCGlobal Positioning Recommended Minimum Sentence C

H

HBhigh-band
Hertz, Hz1. The SI unit for measurement of frequency. One hertz (Hz) equals one cycle per second.
2. The number of scans read or updates written per second.

I

I/Q dataThe translation of the magnitude and phase data of a signal from a polar coordinate system to a complex Cartesian (X,Y) coordinate system.
I/Q modulationin-phase/quadrature modulation—A modulation technique where a signal is modulated by two signals 90 degrees out of phase with each other.
I/Q signalA control signal for changing an RF carrier signal.
IFintermediate frequency—In radio receivers or spectrum analyzers, the original high-frequency signal is often mixed to an intermediate frequency before demodulation.
impedance1. The electrical characteristic of a circuit expressed in ohms and/or capacitance/inductance.
2. Resistance.
information signalContains the data for transmission. The information signal is used to modulate the carrier wave to create the modulated wave for transmission. The information signal data is recovered from the modulated wave by a process of demodulation.

The information signal is often referred to as the baseband signal or message signal.

ISI inter-symbol interference
ISMLow-power radio frequencies for industrial, scientific, and medical processes, and license-free wireless communication.

L

LBlow-band
LMSleast-mean-squared
LOlocal oscillator—Refers to an internal oscillator in a radio, receiver, or instrument that tunes the frequency of the device. The local oscillator is mixed with a fixed frequency oscillator, which generates a sum and difference component.
lowpass filterReduces noise and high frequency components in the signal.

M

message signalContains the data for transmission. The message signal is used to modulate the carrier wave to create the modulated wave for transmission. The message signal data is recovered from the modulated wave by a process of demodulation.

The message signal is often referred to as the baseband signal or information signal.

MIMOmultiple input, multiple output—A measurement technique, most often used in acoustics and vibration, to identify signal paths and frequency response functions from multiple inputs to multiple outputs. Associated with this measurement class are the techniques of partial and multiple coherence, which help identify which parts of an output signal are due to a specific input signal or combinations of signals.
modulationA process, or the result of a process, by which characteristics of a carrier wave are altered according to information in the baseband signal to generate a modulated wave that is transmitted.
MSKminimum-shift keying
MTUmaximum transmission unit

N

NMEANational Marine Electronics Association

O

OCXOoven-controlled crystal oscillator
onboard device timer Time-stamps data to start acquisitions and generations at the user-specified time.
OOKon-off keying

P

passbandThe range of frequencies which a device can properly propagate or measure.
phase-locked loop (PLL)An electronic circuit that controls an oscillator so that the circuit maintains a constant phase angle relative to a reference signal.
PMphase modulation
PPSpulse per second

Q

QAMquadrature-amplitude modulation—A form of quadrature modulation in which the two carriers are both amplitude-modulated.

R

radio frequency (RF)Refers to the radio frequency range of the electromagnetic spectrum. RF is often used to describe a range of sub-infrared frequencies from the tens of MHz to several GHz.
Reference ClockClock to which a device phase locks another, usually faster, clock. A common source for the Reference Clock is the 10 MHz oscillator present on the PXI backplane.
RX, RxReceive data or signals. RX refers to the hardware receiver; Rx refers to receive operations in software.

S

sample rateThe rate at which a device acquires an analog signal, expressed in samples per second (S/s). The sample rate is typically the clock speed of the analog-to-digital converter (ADC).
SDRsoftware-defined radio
SMAA small type of threaded coaxial signal connector typically used in higher frequency applications.
symbol rateExpresses the number of symbols transmitted per second (symbols/s). To convert symbol rate into bit rate, which expresses the number of bits transferred per second, multiply the symbol rate by the number of bits per symbol used in the digital modulation scheme of interest. Symbol rate is also known as baud rate.

T

TTLtransistor-transistor logic—A digital circuit composed of bipolar transistors wired in a certain manner. A typical medium-speed digital technology. Nominal TTL logic levels are 0 and 5 V.
TX, TxTransmit data or signals. TX refers to the hardware transmitter; Tx refers to transmit operations in software.

U

upconverterA signal conditioning device that converts a specific band of IF frequencies to high-frequency (RF) signals.
USRP Universal Software Radio Peripheral—Computer-hosted hardware used to create software-defined radio systems.
UUTunit under test

V

VCO voltage-controlled oscillator—An oscillator with a frequency determined by a control voltage.

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