Welcome to the LinfinityGNSS glossary — a growing LinfinityGNSS glossary of the terms, acronyms, and concepts we cover in our Jargon Buster series. Every entry below is the short version, and this glossary is designed to be browsed rather than read start to finish. For a full technical breakdown of your exact situation, GASP, our AI GNSS expert, is available 24/7 and goes far deeper than any glossary entry can.
30 terms & growingHardware & Modules
The building blocks that determine how fast and how well a receiver performs — the first category readers usually browse in this glossary.
TTFF
Time-to-First-Fix — how long a GNSS module takes to output a valid position after startup. Critical for any application that can’t afford to wait.
Cold start: seconds–minutes · Warm start: faster
Ask GASP about this →A-GNSS
Assisted GNSS — the receiver pulls satellite orbit and clock data over a network connection instead of decoding it from the signal, cutting TTFF dramatically.
Source: network · Benefit: faster TTFF
Ask GASP about this →Dead Reckoning
Onboard sensors (IMU, wheel-tick, compass) estimate position when GNSS is unavailable — bridging tunnels, car parks, and urban canyons without a gap in output.
Input: IMU / wheel · Gap: bridged
Ask GASP about this →Ionospheric Error
Charged particles in the upper atmosphere delay GNSS signals. A dual-frequency receiver can mathematically cancel most of this delay, cutting error from metres to under a metre. Full breakdown in our article on multi-frequency & multi-constellation GNSS.
Single-freq: several m · Dual-freq: <1m
Ask GASP about this →Multi-Constellation
A GNSS receiver that uses signals from several independent satellite systems at once, instead of relying on GPS alone — giving it access to far more satellites at any moment. See the full comparison in our article on why multi-frequency & multi-constellation matters.
GPS only: 8–10 sats · Multi-const: 30–40+
Ask GASP about this →Multi-Frequency
A GNSS receiver tracking signals from different frequency bands instead of only one per satellite. More signals mean more independent data points for a stronger, more reliable position fix. Read the full technical case in our multi-frequency GNSS article.
Bands: 2+ per sat · Result: more data
Ask GASP about this →RTK Fix
A correction technique that compares a rover receiver against a fixed, surveyed base station — reaching centimetre-level accuracy far beyond a standalone GNSS fix. Full walkthrough in our article on Fixed-Base RTK.
Accuracy: cm-level · Init time: seconds
Ask GASP about this →Halfway through, and already have a question a definition can’t answer? That’s exactly what GASP is for. Ask it anything on this page, in your own words, and it’ll go straight to the specifics of your setup.
Timing
How receivers turn satellite signals into the precise clock other systems depend on, one of the more specialised categories in this glossary.
1PPS
A single electrical pulse fired precisely on the turn of every UTC second — a 3.3V or 5V TTL signal on a coaxial connector. It’s the heartbeat other GNSS systems lock onto, and the reference second is maintained internationally by the BIPM.
Signal: locked · Phase: aligned
Ask GASP about this →Timing Receiver
A GNSS receiver with a fixed, surveyed position that skips positioning entirely — using satellite signals only to extract the most precise time reference possible.
Position: fixed · Time: extracted
Ask GASP about this →Jamming & Spoofing
The threats that can quietly corrupt a position fix, and the defences built to catch them — a core section of this LinfinityGNSS glossary and one of the most-read parts of this glossary.
OS-NMA
Galileo’s Navigation Message Authentication — cryptographically signs the signal so a GNSS receiver can verify it’s genuine. See the official spec on the European GNSS Service Centre site.
Signal: signed · Source: Galileo
Ask GASP about this →Jamming
RF interference that raises the noise floor until a GNSS receiver can no longer track satellite signals at all.
State: no fix · Cause: RF noise
Ask GASP about this →Spoofing
Counterfeit GNSS signals that fool a receiver into reporting a confident position that’s completely wrong.
Fix: valid · Source: unverified
Ask GASP about this →Holdover
When GNSS signal is lost — to jamming, multipath, or a blocked sky — a disciplined oscillator keeps time on its own. How long it holds accuracy is the critical spec.
GNSS: lost · Clock: holds
Ask GASP about this →FRPA
A Fixed Reception Pattern Antenna — its spatial response is set by geometry and installation, not software. Every conventional GNSS antenna is an FRPA by default, and once built it can’t move its pattern to follow a jammer. Full picture in our article on anti-jamming antennas.
Pattern: fixed · Adapts: no
Ask GASP about this →Spatial Nulling
The core CRPA technique for suppressing interference before it reaches the GNSS receiver — an N-element array offers roughly N−1 spatial degrees of freedom, though real performance depends on geometry, calibration and jammer separation. More in our article on CRPA anti-jam antennas.
N elements: N−1 nulls · Guarantee: none
Ask GASP about this →Partial Suppression
Even a working CRPA doesn’t guarantee every jammer is rejected. Depending on geometry, calibration and jammer separation, some interferers get nulled while others still reach the GNSS receiver. Full breakdown in our article on anti-jamming antennas.
Some: nulled · Others: leak through
Ask GASP about this →Integrity Gap
Most GNSS systems are built to maximise signal tracking and continuous output — not to verify the output is correct. A spoofed receiver can report a false position with full confidence and never trigger an alarm, which is exactly what makes it dangerous. It’s covered in more depth in our article on why a position fix is not enough.
Jammed: alarms · Spoofed: silent
Ask GASP about this →AI in GNSS
What “trustworthy AI” actually means when applied to GNSS diagnostics and threat detection — one of the newer categories in this glossary, and one of the fastest-growing parts of this LinfinityGNSS glossary.
Human Oversight
One of the six pillars regulators require for high-risk AI systems — a person stays in the loop between model output and real-world action. No silent autonomy.
Loop: closed · Autonomy: supervised
Ask GASP about this →Model Poisoning
Corrupting the data or process that trains a model, so an AI GNSS spoofing-detector quietly learns the wrong thing — while still looking fully operational.
Input: corrupted · Output: unreliable
Ask GASP about this →The “Too Well” Flag
When a model performs suspiciously above its expected range, that’s not a win to celebrate — it’s a signal to scrutinise how it’s actually achieving that score.
Score: above range · Action: investigate
Ask GASP about this →RTK & Corrections
How receivers close the gap from metres to centimetres — a compact but important category in this glossary, and the final one in this LinfinityGNSS glossary for now.
PPP-RTK
Combines global GNSS PPP coverage with RTK’s fast convergence — centimetre accuracy in seconds, almost anywhere, without needing a nearby physical base station.
Accuracy: 2–5cm · Convergence: seconds
Ask GASP about this →Testing & Simulation
Where lab results either hold up or fall apart, and the setup mistakes that quietly invalidate a test — the newest category in this LinfinityGNSS glossary, and one we expect to keep expanding as we publish more testing content.
RF Cable Loss
GNSS signals arrive at roughly -130 dBm — already extremely weak. Every metre of cable between simulator and receiver attenuates it further, and unmeasured loss quietly invalidates a test.
Typical loss: ~5 dB · Fix: measure & offset
Ask GASP about this →Multipath
GNSS signals that reach the antenna via a reflected path — off buildings, ship structures, or the ground — arrive later than the direct signal, causing ranging errors real-sky testing must account for.
Direct path: true range · Reflected path: error
Ask GASP about this →Cold, Warm & Hot Start
Three states a GNSS receiver can start from, each with different available data and a different time to first fix — the transitions test plans most often skip.
Cold: slowest · Hot: fastest
Ask GASP about this →Live-Sky Validation
Testing a GNSS receiver under real satellite signals and real-world conditions after lab simulation — the step that catches what a model of the world can’t capture.
Lab: models the world · Field: confirms it
Ask GASP about this →Record & Replay
Real-world GNSS RF signals captured once in the field, then replayed with full fidelity in the lab — every firmware version tested against the exact same environment.
Field: RF captured · Lab: replayed
Ask GASP about this →DUT (Device Under Test)
The specific module, firmware version, and hardware configuration being validated in a given test run — the device the report is actually judging.
Scope: module + firmware + HW
Ask GASP about this →KPI Threshold
The pass, limit, or fail boundary set for a performance metric — some common across all products, others differentiated per test scenario and product family.
Bands: pass / limit / fail
Ask GASP about this →Truth Data
The original field-collected reference position — the baseline every replayed test result is measured against.
Source: field-collected · Role: baseline
Ask GASP about this →Regression Testing
A predefined set of tests re-run against every new firmware build to catch anything that broke — scope evolves alongside the product itself, which is exactly why this corner of the glossary keeps expanding.
Trigger: every build · Goal: catch regressions
Ask GASP about this →Why We Built This Glossary
GNSS work is full of terms that get thrown around casually — TTFF, holdover, multipath, PPP-RTK — but rarely explained clearly in one place. That gap is exactly why this glossary exists.
Every entry in this glossary starts from the same question: if an engineer, a procurement lead, or a curious client landed on this page with zero context, would they walk away actually understanding the term? If not, the entry gets rewritten until it does.
This glossary is organised by category rather than alphabetically, because most people don’t arrive already knowing the word they’re looking for — they arrive with a symptom (a receiver behaving strangely, a spec sheet full of jargon, a security concern) and need the right term to search for next. Hardware & Modules, Timing, Jamming & Spoofing, AI in GNSS, RTK & Corrections, and Testing & Simulation each group the terms that tend to come up together in real conversations, so browsing one category of this glossary usually surfaces two or three related terms worth knowing at the same time.
We also treat this glossary as a living document rather than a finished one. New entries get added roughly weekly as part of our Jargon Buster series, and older entries get revisited and tightened whenever we notice a definition that’s technically correct but not actually clear. If you’ve read through this glossary and still can’t find the term you need, that’s a gap we want to know about — use the “Suggest a term” link below and it’ll likely show up here within a few weeks.
One thing this glossary deliberately avoids is padding — every entry is written to be read in under a minute, because a glossary that takes longer to read than the problem it’s meant to solve isn’t doing its job. If a definition here raises more questions than it answers, that’s exactly what GASP and our technical articles are for.
About Linfinity GNSS
The team behind this glossary, our technical articles, and GASP.
Linfinity GNSS is a Cambridge-based team of precision positioning and timing engineers, with 20+ years of combined experience integrating and testing GNSS across maritime, defence, automotive, and autonomous systems. This glossary exists for the same reason our technical articles and GASP, our AI GNSS expert, do — real engineering work on real GNSS problems, written up and made available rather than kept internal. If a term in this glossary touches on something you’re actively working through, our engineers are also just a message away.
Most of what ends up in this glossary started as an answer to a real client question — which is also why it keeps growing rather than sitting still.
This LinfinityGNSS glossary exists because GNSS jargon multiplies fast, and half the battle in solving a positioning problem is knowing exactly what the term in front of you means. But a glossary can only ever give you the short version. When you’re dealing with a real signal dropout, a spoofing concern, or a module that isn’t behaving the way the datasheet promised, GASP, our AI GNSS expert, is built to go further — walking through your specific logs, your specific hardware, and your specific failure mode, 24/7. We publish a new definition roughly every week as part of our Jargon Buster series on Instagram and X, and our technical articles go deeper still on several of the topics above.
Can’t find the term you’re after?
This LinfinityGNSS glossary grows every week as we publish new Jargon Buster entries. If your term isn’t here yet, GASP can explain it right now, no waiting for the next post — and there’s a decent chance it ends up in this glossary anyway.