gpx-ideas

Systems and Signals

Introduction

Overview

In recent years there has been a move towards common frequency bands centered around 1,575.42 MHz + 1,207.14 MHz + 1,176.45 MHz, simplifying the design and reducing the cost of multi-GNSS receivers.

This document lists the frequency bands currently used by each GNSS, along with the carrier frequencies for the various signals. In addition to frequency information it also lists the signals that are broadcast by each system and where applicable, lists the individuals channels (e.g. data + pilot).

The information in this page is up to date at the time of writing in Dec 2023, but additions will almost certainly be required in the future. For example, KPS (Korea Positioning System) is planned for 2035 and LEO-PNT is currently being planned by the European Space Agency.

GNSS Signals

The gpx_fix extension supports signal information in GPX files:

<trkpt lat="50.5710623" lon="-2.4563484">
  <ele>7.90</ele>
  <time>2022-04-11T10:16:01Z</time>
  <fix>dgps</fix>
  <sat>26</sat>
  <extensions>
    <gpx_fix:fix>
      <gpx_fix:gps sat="7">
        <gpx_fix:sig id="l1ca" sat="6" />
        <gpx_fix:sig id="l5" sat="3" />
      </gpx_fix:gps>
      <gpx_fix:glonass sat="6">
        <gpx_fix:sig id="l1of" sat="6" />
      </gpx_fix:glonass>
      <gpx_fix:galileo sat="5">
        <gpx_fix:sig id="e1bc" sat="4" />
        <gpx_fix:sig id="e5a" sat="2" />
      </gpx_fix:galileo>
      <gpx_fix:beidou sat="5">
        <gpx_fix:sig id="b1i" sat="5" />
      </gpx_fix:beidou>
      <gpx_fix:qzss sat="3">
        <gpx_fix:sig id="l1ca" sat="3" />
        <gpx_fix:sig id="l5" sat="2" />
      </gpx_fix:qzss>
    </gpx_fix:fix>
  </extensions>
</trkpt>

The <gpx_fix:sig> elements simply represent the number of active satellites for each of the GNSS signals. For simplicity, no distinction is made between individual channels (e.g. data and pilot). Neither is there any way to represent visible satellites, only active satellites used in the PVT solution. The example above shows 3 satellites providing L5 signals used in the PVT solution of the GNSS receiver.

The enumerated types in the gpx_fix extension use very simple names for the GNSS signals, entirely lower case and without spaces or punctuation (e.g. hyphens / pluses / slashes / brackets). So whilst different sources may refer to L2C (M), L2 CM, or L2C-M for the data channel of L2C, the gpx_fix extension simply uses “l2c”. Likewise for L1 C/A which can be written either with or without a space, but gpx_fix enumerates it as “l1ca”.

Signal Mappings

Determination of the systems and signals in use will depend on the application:

NMEA provides system and signal information via the GSA sentence.
- Guidance relating to the interpretation of GSA is available on another page.
Android devices provide the constellation type and carrier frequency via the GnssStatus class.
- Android also provides signal information via the GnssMeasurement class.
UBX provides the GNSS identifier (gnssId) and usage information (svUsed flag) in UBX-NAV-SAT
- Additional to satellite information, signal information (sigId) and detailed usage can be found in UBX-NAV-SIG.

There are likely to be additional ways that system and signal information can be determined on other hardware.

GPS

Frequency Bands

These are the GPS signals supported by the gpx_fix extension:

Band	Carrier Frequency	Signals	GPX
L1	1,575.42 MHz	L1 C/A, L1 P(Y), L1 M, L1C	l1ca, l1py, l1m, l1c
L2	1,227.60 MHz	L2 P(Y), L2 M, L2C	l2py, l2m, l2c
L5	1,176.45 MHz	L5	l5

Notes

The gpx_fix extension supports all civilian and military signals, hence the inclusion of P(Y) and M codes.
The most established GPS signals in the consumer market are L1 C/A, L2C and L5.
The newer L1C signal will soon gain popularity and is starting to appear in modern GNSS receivers.
The carrier frequency of L2 is unique to GPSS and QZSS, but L1 and L5 are becoming a common standard.

Signals + Channels

These are the mappings which need to be applied to RINEX / UBX / NMEA codes:

Band	Channel	Type	RINEX	UBX	NMEA 4.10	NMEA 4.11	GPX
L1	L1 C/A		C	0	1	1	l1ca
L1	L1 P(Y)		Y	-	2	2	l1py
L1	L1 M		M	-	3	3	l1m
L1	L1C (D)	data	S	-	-	-	l1c
L1	L1C (P)	pilot	L	-	-	-	l1c
L1	L1C (D+P)		X	-	-	9	l1c
L2	L2 P(Y)		Y	-	4	4	l2py
L2	L2 M		M	-	-	-	l2m
L2	L2C (M)	data	S	4	5	5	l2c
L2	L2C (L)	pilot	L	3	6	6	l2c
L2	L2C (M+L)		X	-	-	-	l2c
L5	L5 I	data	I	6	7	7	l5
L5	L5 Q	pilot	Q	7	8	8	l5
L5	L5 I+Q		X	-	-	-	l5

Notes

The L1C signal is relatively new at this time (Dec 2023), denoted by an NMEA value of “9” by Broadcom on the Pixel 7.
RINEX attributes for z-tracking, codeless and semi-codeless tracking of the P(Y) code have been omitted.
- n.b. Z-tracking, codeless and semi-codeless tracking of P(Y) should no longer be required, due to availability of the L2C signal.
There is no obvious need for the distinction of an RMP antenna being used for the M code in the GPX extension.

GLONASS

Frequency Bands

These are the GLONASS signals supported by the gpx_fix extension:

Band	Carrier Frequency	Signals	GPX
G1 / L1	1,602 MHz + k * 9 / 16 k = -7 … + 12	L1OF, L1SF	l1of, l1sf
G1a	1,600.995 MHz	L1OC, L1SC	l1oc, l1sc
G2 / L2	1,246 MHz + k * 7 / 16 k = -7 … + 12	L2OF, L2SF	l2of, l2sf
G2a	1,248.06 MHz	L2OC, L2SC	l2oc, l2sc
G3 / L3	1,202.25 MHz	L3OC	l3oc

Notes

The carrier frequencies of G1 / G1a / G2 / G2a / G3 are all unique to GLONASS.
Different sources refer to G1 / G2 / G3 or L1 / L2 / L3. The official names are L1 / L2 / L3 but G1 / G2 / G3 are less ambiguous.
Some sources may also refer to the L1OF and L1SF signals (official names) as L1 C/A and L1 P, likewise for L2OF and L2SF.
The legacy FDMA signals (L1OF / L1SF / L2OF / L2SF) will eventually be superseded by the newer CDMA signals.
L3OC is a relatively new civilian signal but was available from 47 satellites in 2022, according to the Novatel page.
L1OC and L2OC signals are much newer and will be broadcast by GLONASS-K2 satellites, launched in 2023.

Signals + Channels

These are the mappings which need to be applied to RINEX / UBX / NMEA codes:

Band	Channel	Type	RINEX	UBX	NMEA 4.10	NMEA 4.11	GPX
G1 / L1	L1OF C/A		C	0	1	1	l1of
G1 / L1	L1SF P		P	-	2	2	l1sf
G1a	L1OC (D)	data	A	-	-	-	l1oc
G1a	L1OC (P)	pilot	B	-	-	-	l1oc
G1a	L1OC (D+P)		X	-	-	-	l1oc
G1a	L1SC (D)	data	-	-	-	-	l1sc
G1a	L1SC (P)	pilot	-	-	-	-	l1sc
G1a	L1SC (D+P)		-	-	-	-	l1sc
G2 / L2	L2OF C/A		C	2	3	3	l2of
G2 / L2	L2SF P		P	-	4	4	l2sf
G2a	L2OC (N)	no data	A	-	-	-	l2oc
G2a	L2OC (P)	pilot	B	-	-	-	l2oc
G2a	L2OC (N+P)		X	-	-	-	l2oc
G2a	L2SC (D)	data	-	-	-	-	l2sc
G2a	L2SC (P)	pilot	-	-	-	-	l2sc
G2a	L2SC (D+P)		-	-	-	-	l2sc
G3 / L3	L3OC I	data	I	-	-	-	l3oc
G3 / L3	L3OC Q	pilot	Q	-	-	-	l3oc
G3 / L3	L3OC I+Q		X	-	-	-	l3oc

Notes:

The restricted L1SC and L2SC signals are due to be broadcast by GLONASS-K2 satellites, but are not included in RINEX 4.01.
The restricted L3SC signal will also be broadcast by GLONASS-KM satellites, but is not included in RINEX 4.01.
The future L1OCM / L3OCM / L5OCM signals are not supported by RINEX 4.01 or the GPX extension, so may need to be added in the future.

Future

Summary of GLONASS-KM:

The GLONASS-KM satellites will broadcast L3SC / L1OCM / L3OCM / L5OCM but aren’t due for launch until 2030, and still in the research phase.
The GLONASS-KM satellites will add 3 frequency bands for CDMA signals, interoperable with the other GNSS frequency bands:
- L1 @ 1,575.42 MHz
- L2 @ 1,207.14 MHz
- L5 @ 1,176.45 MHz
The future L3SC / L1OCM / L3OCM / L5OCM signals are not supported by RINEX or the GPX extension, so may need to be added in the future.

Galileo

Frequency Bands

These are the Galileo signals supported by the gpx_fix extension:

Band	Carrier Frequency	Signals	GPX
E1	1,575.42 MHz	E1-A, E1-BC	e1a, e1bc
E5a	1,176.45 MHz	E5a	e5a
E5b	1,207.14 MHz	E5b	e5b
E5	1,191.795 MHz	E5	e5
E6	1,278.75 MHz	E6-A, E6-BC	e6a, e6bc

Notes

The most widely used Galileo signals are E1bc and E5a, using identical carrier frequencies to L1 and L5 of GPS.
The carrier frequencies for E1, E5a, E5b and E5 are pretty standard for GNSS, but the frequency of E6 is only shared with QZSS.
Galileo’s E1 band is sometimes referred to as L1, although E1 is the official name.
PRS = Public Regulated Service (channel A), OS = Open Service (channels B and C)
- Galileo refers to the E1 PRS and E6 PRS signals as channel A.
- Galileo refers to the data channels for E1 OS and E6 OS as channel B.
- Galileo refers to the pilot channels for E1 OS and E6 OS as channel C.

Signals + Channels

These are the mappings which need to be applied to RINEX / UBX / NMEA codes:

Band	Channel	Type	RINEX	UBX	NMEA 4.10	NMEA 4.11	GPX
E1	E1 A	PRS	A	-	6	6	e1a
E1	E1 B	OS data	B	1	-	-	e1bc
E1	E1 C	OS pilot	C	0	-	-	e1bc
E1	E1 B+C		X	-	7	7	e1bc
E5a	E5a I	data	I	3	-	-	e5a
E5a	E5a Q	pilot	Q	4	-	-	e5a
E5a	E5a I+Q		X	-	1	1	e5a
E5b	E5b I	data	I	5	-	-	e5b
E5b	E5b Q	pilot	Q	6	-	-	e5b
E5b	E5b I+Q		X	-	2	2	e5b
E5	E5 I	data	I	-	-	-	e5
E5	E5 Q	pilot	Q	-	-	-	e5
E5	E5 I+Q		X	-	3	3	e5
E6	E6 A	PRS	A	-	4	4	e6a
E6	E6 B	CS data	B	-	-	-	e6bc
E6	E6 C	CS pilot	C	-	-	-	e6bc
E6	E6 B+C		X	-	5	5	e6bc

Notes:

RINEX 4.01 includes combined A+B+C channels for the E1 and E6 signals, but they have been omitted from this document.
NMEA 4.11 does not distinguish between Galileo’s data channels and pilot channels.

BeiDou

Frequency Bands

These are the BeiDou / BDS signals supported by the gpx_fix extension:

Band	Carrier Frequency	Signals	GPX
B1	1,561.098 MHz	B1I, B1Q	b1i, b1q
B1C / B1A	1,575.42 MHz	B1C, B1A	b1c, b1a
B2a	1,176.45 MHz	B2a	b2a
B2 / B2b	1,207.14 MHz	B2I, B2Q, B2b	b2i, b2q, b2b
B2 (B2a + B2b)	1,191.795 MHz	B2	b2
B3	1,268.52 MHz	B3I, B3Q, B3A	b3i, b3q, b3a

Notes

The carrier frequencies of B1C / B1A, B2a, and B2 / B2b are pretty standard for GNSS, but B1 and B3 are unique to BeiDou.
The B1I / B2I / B3I signals are open services, whereas B1Q / B2Q / B3Q signals are restricted services.
The most widely used BeiDou civilian signals are B1I and B2I, using carrier frequencies that are not shared with GPS.
The newer B1C and B2a signals use the same carrier frequencies as the GPS signals in L1 and L5.

Signals + Channels

These are the mappings which need to be applied to RINEX / UBX / NMEA codes:

Band	Channel	Type	RINEX	UBX	NMEA 4.10	NMEA 4.11	GPX
B1	B1I		I	?	-	1	b1i
B1	B1Q		Q	?	-	2	b1q
B1C	B1C (D)	data	D	6	-	-	b1c
B1C	B1C (P)	pilot	P	5	-	-	b1c
B1C	B1C (D+P)		X	-	-	3	b1c
B1A	B1A (D)	data	S	-	-	-	b1a
B1A	B1A (P)	pilot	L	-	-	-	b1a
B1A	B1A (D+P)		Z	-	-	4	b1a
B2a	B2a (D)	data	D	8	-	-	b2a
B2a	B2a (P)	pilot	P	7	-	-	b2a
B2a	B2a (D+P)		X	-	-	5	b2a
B2	B2I		I	?	-	B	b2i
B2	B2Q		Q	?	-	C	b2q
B2b	B2b (D)	data	D	-	-	-	b2b
B2b	B2b (P)	pilot	P	-	-	-	b2b
B2b	B2b (D+P)		Z	-	-	6	b2b
B2 (B2a + B2b)	B2 (D)	data	D	-	-	-	b2
B2 (B2a + B2b)	B2 (P)	pilot	P	-	-	-	b2
B2 (B2a + B2b)	B2 (D+P)		X	-	-	7	b2
B3	B3I		I	-	-	8	b3i
B3	B3Q		Q	-	-	9	b3q
B3	B3A (D)	pilot	D	-	-	-	b3a
B3	B3A (P)	data	P	-	-	-	b3a
B3	B3A (D+P)		Z	-	-	A	b3a

Notes:

The I and Q channels of the B1 / B2 / B3 bands are different services, not a data channel and pilot channel.
- The table above does not combine I + Q channels, so elements for each signal should be output in the GPX.
RINEX 4.01 includes combined I+Q channels for the B1 / B2 / B3 signals, but they have been omitted from this document.
NMEA 4.10 does not include system IDs or signal IDs for BeiDou, QZSS or NavIC.
NMEA 4.11 does not distinguish between BeiDou’s data channels and pilot channels.

QZSS

Frequency Bands

These are the QZSS signals supported by the gpx_fix extension:

Band	Carrier Frequency	Signals	GPX
L1	1,575.42 MHz	L1 C/A, L1 C/B, L1C, L1S, L1Sb	l1ca, l1cb, l1c, l1s, l1sb
L2	1,227.60 MHz	L2C	l2c
L5	1,176.45 MHz	L5, L5S	l5, l5s
L6	1,278.75 MHz	L6D, L6E	l6d, l6e

Notes

QZSS has the highest level of interoperability with GPS, due to near-identical use of the L1, L2 and L5 bands.
L1 / L2 / L5 use the same carrier frequencies as GPS, whilst L6 uses the same carrier frequency as E6 for Galileo.
L1S is the Sub-meter Level Augmentation Service (SLAS) and L1Sb is a regular SBAS signal.
L5S is the positioning technology verification service.
L6 (LEX) is the Centimeter Level Augmentation Service (CLAS).

Signals + Channels

These are the mappings which need to be applied to RINEX / UBX / NMEA codes:

Band	Channel	Type	RINEX	UBX	NMEA 4.10	NMEA 4.11	GPX
L1	L1 C/A		C	0	-	1	l1ca
L1	L1 C/B		E	-	-	-	l1cb
L1	L1C (D)	data	S	-	-	2	l1c
L1	L1C (P)	pilot	L	-	-	3	l1c
L1	L1C (D+P)		X	-	-	-	l1c
L1	L1S	SLAS	Z	1	-	4	l1s
L1	L1Sb	SBAS	B	-	-	-	l1sb
L2	L2C (M)	data	S	4	-	5	l2c
L2	L2C (L)	pilot	L	5	-	6	l2c
L2	L2C (M+L)		X	-	-	-	l2c
L5	L5 I	data	I	8	-	7	l5
L5	L5 Q	pilot	Q	9	-	8	l5
L5	L5 I + Q		X	-	-	-	l5
L5	L5S I	data	D	-	-	-	l5s
L5	L5S Q	pilot	P	-	-	-	l5s
L5	L5S I + Q		Z	-	-	-	l5s
L6	L6D	code 1	S	-	-	9	l6d
L6	L6P	pilot	L	-	-	-	l6d
L6	L6 (D+P)		X	-	-	-	l6d
L6	L6E	code 2	E	-	-	A	l6e
L6	L6 (D+E)		Z	-	-	-	l6e

Notes

NMEA 4.10 does not include a system ID or signal IDs for QZSS.

NavIC

Frequency Bands

These are the NavIC / IRNSS signals supported by the gpx_fix extension:

Band	Carrier Frequency	Signals	GPX
L1	1,575.42 MHz	L1-SPS	l1sps
L5	1,176.45 MHz	L5-SPS, L5-RS	l5sps, l5rs
S	2,492.028 MHz	S-SPS, S-RS	ssps, srs

Notes

The L1 and L5 bands have the same carrier frequencies as GPS.
SPS = Standard Positioning Service for civilian use
RS = Restricted Service

Signals + Channels

These are the mappings which need to be applied to RINEX / UBX / NMEA codes:

Band	Channel	Type	RINEX	UBX	NMEA 4.10	NMEA 4.11	GPX
L1	L1 Data	data	D	-	-	-	l1sps
L1	L1 Pilot	pilot	P	-	-	-	l1sps
L1	L1		X	-	-	5	l1sps
L5	L5 A SPS		A	-	-	1	l5sps
L5	L5 B RS (D)	data	B	-	-	-	l5rs
L5	L5 C RS (P)	pilot	C	-	-	-	l5rs
L5	L5 B+C		X	-	-	3	l5rs
S	S A SPS		A	-	-	2	ssps
S	S B RS (D)	data	B	-	-	-	srs
S	S C RS (P)	pilot	C	-	-	-	srs
S	S B+C		X	-	-	4	srs

Notes

NMEA 4.10 does not include a system ID or signal IDs for NavIC.
NMEA 4.11 does not distinguish between NavIC’s data channels and pilot channels.

SBAS

Frequency Bands

These are the SBAS signals supported by the gpx_fix extension:

Band	Carrier Frequency	Signals	GPX
L1	1,575.42 MHz	L1 C/A	l1ca
L5	1,176.45 MHz	L5	l5

Notes

The L1 and L5 bands have the same carrier frequencies as GPS.

Signals + Channels

These are the mappings which need to be applied to RINEX / UBX / NMEA codes:

Band	Channel	Type	RINEX	UBX	NMEA 4.10	NMEA 4.11	GPX
L1	L1 C/A		C	0	1	1	l1ca
L5	L5 I	Data	I	-	-	-	l5
L5	L5 Q	Pilot	Q	-	-	-	l5

Notes:

These signals are very similar in nature to L1 C/A and L5 of GPS.

References

A number of sources were used to document the signal mappings in this document.

RINEX 4.01 specification
Android location API
Novatel system and signal IDs
u-blox F9P interface specification
QZSS interface specifications for CLAS and MADOCA

In addition to the above, obvious sources such as the Wikipedia pages for each GNSS were also referenced.

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