GNSS Satellite Signal Components and Navigation Systems II

A comprehensive set of vocabulary cards covering GNSS signal structure, modulation methods (BPSK, QPSK, BOC), message framing, and receiver signal processing steps.

Carrier Radio Wave

The radio waves in the UHF band, specifically ranging between $1100-1600\,MHz$, used to carry GNSS signals.

Navigation Message

Contains vital information for the receiver to determine its location, including satellite orbit (ephemeris) data and time corrections.

PRN (Pseudo Random Noise) Codes

Signals that contain no information but allow a receiver to distinguish between different satellites broadcasting on the same frequency.

Carrier L1

A specific primary carrier frequency used in GPS operating at $1575.42\,MHz$.

C/A Code Frequency

The chip rate for the Coarse/Acquisition PRN code, which is $1.023\,MHz$.

Navigation Info Rate

The data transmission rate for the navigation message, which is $50\,Hz$.

Bit Duration

The time length of a single bit in the navigation message, which is $20\,ms$, equivalent to $20$ full PRN cycles.

Ephemeris Parameters

Specific orbital data for the broadcasting satellite used to calculate its position; found in subframes $2$ and $3$.

Almanac Data

General orbital and health status information for all satellites in the GNSS constellation, found in subframe $5$.

Subframe

A component of a navigation data frame containing $300$ bits and lasting for $6$ seconds.

Frame

A complete set of $5$ subframes containing $1500$ bits, lasting for $30$ seconds.

Telemetry Word (TLM)

The first $30$-bit word in every subframe, starting with an $8$-bit preamble for synchronization.

Handover Word (HOW)

The second word in every subframe, containing a $17$-bit Time of Week (TOW) count.

Primary Code

Used by the receiver to distinguish individual satellites and calculate the range (distance) between the satellite and the alıcı.

Secondary Code

Assists the receiver in locking onto the satellite signal faster by shortening the time needed to identify the broadcast.

BPSK (Binary Phase Shift Keying)

A modulation technique where the phase of the carrier wave is intentionally shifted to represent digital information.

QPSK (Quadrature Phase Shift Keying)

A modulation technique using four phases ($45^\circ$, $135^\circ$, $225^\circ$, $315^\circ$), allowing for a data transmission rate twice as fast as BPSK.

BOC (Binary Offset Carrier)

A modulation technique using a square-wave subcarrier used to minimize signal interference and enhance multi-path reflection resistance.

BOC(m, n) Notation

A representation where $m$ and $n$ signify the subcarrier and code frequencies as multiples of the fundamental frequency $f_0 = 1.023\,MHz$.

FEC (Forward Error Correction)

A coding method used to detect and correct errors in the received navigation message without the need for retransmission.

Interleaving

A technique that rearranges data bits to transform burst errors caused by noise into single-bit errors, which are easier to correct.

Digitization

The step in receiver processing where the signal is cleared of noise, the carrier frequency is reduced to an intermediate frequency, and the signal is converted to digital.

Signal Acquisition

The process of comparing receiver-generated PRN codes with the incoming signal to identify the satellite.

Signal Tracking

The continuous estimation and correction of code delay, carrier phase, and Doppler shift parameters.

Clock Bias ($t_{bias}$)

The time difference between the satellite's atomic clock and the GNSS receiver's local clock.