GNSS Receiver Principles and Design Flashcards

A collection of vocabulary flashcards covering the basic design principles, components, and performance metrics for GNSS (Global Navigation Satellite System) receivers as described in Chapter 8.

PVT

An acronym representing the key services provided by a GNSS receiver: Position, Velocity, and Timing.

DSSS

Acronym for Direct Sequence Spread Spectrum technology, first used in the inception of GPS.

Flywheel effect (velocity dimension)

The use of an Inertial Measurement Unit (IMU) to provide velocity aiding, which improves dynamic stress performance and maintains navigation when the receiver loses signal track.

CSAC

Acronym for chip-scale atomic clock; when phase-locked with a crystal oscillator, it provides a 'flywheel effect' in the receiver time dimension to maintain precise time during outages.

SDR

Acronym for Software-Defined Receiver; a system where digital signal processing (DSP) techniques run in microprocessors. It usually refers to receivers that perform post-mission processing or non-real-time verification.

CGR

Acronym for Configurable GNSS Receiver; a system where the operational architecture is defined by reconfigurable modular functions running under a real-time operating system.

Active Antenna

A GNSS antenna that includes an internal Low Noise Amplifier (LNA) to compensate for signal losses in the connecting coaxial transmission cable.

Passive Antenna

A GNSS antenna that does not contain an internal Low Noise Amplifier (LNA).

Front End

The mostly analog portion of the receiver that provides signal conditioning, including bandpass filtering, amplification, and downconversion to an Intermediate Frequency (IF).

Wipe-off (Carrier and Code)

The digital receiver processes that remove the carrier frequency and the spreading code from the digitized signal to detect and track a satellite vehicle (SV).

Cold Start

A receiver state with no information about time, position, or accurate almanac data, resulting in a very large two-dimensional search space (code range and carrier Doppler uncertainty).

Isotropic Antenna

An idealized, lossless reference antenna that receives electromagnetic waves equally well in all directions ($0\,dBi$).

Antenna Beamwidth

The span of azimuth or elevation angles where the antenna gain is within $3\,dB$ of its peak gain.

Axial Ratio ($AR$)

The measure of variation in antenna gain (expressed in $dB$) as the incident electromagnetic wave E-field orientation is varied over all directions perpendicular to the source.

VSWR

Acronym for Voltage Standing Wave Ratio; a measurement of how well the antenna signal transmission line impedance is matched to its load (typically $50\,ohms$), with an ideal value of $1:1$.

Antenna Noise Temperature ($T_{ant}$)

A parameter (measured in Kelvin) used to analyze the signal-to-noise ratio; it depends on the temperature of the environment the antenna gain pattern 'sees,' typically assumed to be $100\,K$ for GNSS skyward operation.

FRPA

Acronym for Fixed Reception Pattern Antenna; a military antenna with a fixed gain pattern, often covering multiple frequency bands.

CRPA

Acronym for Controlled Reception Pattern Antenna; a phased array antenna that uses digital signal processing to steer deep gain nulls toward interference sources (jammers).

Cavity Filter

A high-Q, low-insertion-loss passive radio frequency ($RF$) bandpass filter used in the front end to protect active stages from out-of-band interference.

SAW Filter

Acronym for Surface Acoustic Wave filter; a type of bandpass filter used in front ends to select the Intermediate Frequency ($IF$) and reject unwanted sidebands.

NGC

Acronym for Numerical Gain Control; a digital signal that precisely controls the gain of the front-end amplifier to avoid analog control drift.

Nyquist Theorem

A fundamental sampling principle stating that the sampling frequency, $f_s$, must be equal to twice the highest frequency component, $f_c$, present in the analog signal ($f_s = 2f_c$).

Undersampling

A technique that uses an $ADC$ to sample an $IF$ signal in a higher Nyquist zone, effectively performing digital downconversion to a lower frequency in the first Nyquist zone ($NZ(1)$).

NCO

Acronym for Numerically Controlled Oscillator; a digital functional block that produces a carrier or code phase estimate based on a phase increment per sample ($M$).

FTF

Acronym for Fundamental Time Frame; a monotonic time count (typically a $32\text{-}bit$ accumulator) maintained by the receiver to synchronize all digital channels.

PIT

Acronym for Predetection Integration Time ($T$); the total duration over which digital signal samples are accumulated in the integrate-and-dump functions before being processed by slow rate functions.

Friis Formula

An equation used to calculate the total noise factor ($N_f$) of a cascaded front end: $N_f = N_{f1} + \frac{N_{f2}-1}{G_1} + \frac{N_{f3}-1}{G_1G_2} + \dots$

Tong Detector

A suboptimal sequential search algorithm used for signal acquisition that is efficient at dismissing cells containing only noise but may 'mush' under low $(C/N_0)_{dB}$ conditions.