This blog is the sequel to our previous post on Geo-Positioning System technologies. Here we cover GPS receiver module selection for embedded systems in depth — discussing key parameters, NMEA data, TTFF, A-GPS, PPS signals, and a comprehensive Anti-Jamming GNSS Receiver Design guide for hardware engineers. Whether you are designing IoT trackers, industrial devices, or automotive telematics units, this guide will help you make the right GPS receiver module selection for embedded systems.
GPS Receiver Module and Its Role in Embedded System Design
GPS Module – Connection Diagram
The picture above depicts the typical connection diagram of a GPS module with a host controller. GPS receiver module selection for embedded systems begins with understanding the available host interfaces — UART, SPI, and USB are the most common ways for a host controller to receive NMEA data from the module. The PPS (Pulse Per Second) signal is a precise timing output from the GPS module, discussed in detail below. Most GPS modules include an internal ceramic patch antenna and also support external active antenna connections, which is especially relevant for Anti-Jamming GNSS Receiver Design in challenging RF environments.
NMEA Data Parsing for GPS Embedded Devices
NMEA (National Marine Electronics Association) data is the standard output format from any GPS receiver, carrying location data such as latitude, longitude, altitude, and fix quality. NMEA data parsing for GPS embedded devices is the process of extracting this positional information from the raw byte stream delivered over the UART interface. The format ensures cross-manufacturer compatibility, much like the ASCII standard for digital characters.
Following is an example NMEA message from a GPS receiver:
$GPGGA,181908.00,3004.6040718,N,07040.3900269,W,4,13,1.00,408.135,M,29.200,M,0.10,0000*40
All NMEA messages start with a $ character, with fields separated by commas. NMEA data parsing for GPS embedded devices must handle all 19 standard sentence types — and a key criterion during GPS receiver module selection for embedded systems is verifying that the chosen module outputs the specific sentence types your application requires.
"GP" in GPGGA indicates a GPS position fix. For GLONASS receivers, "GL" replaces "GP".
GPGGA is the primary GPS fix sentence. The 19 standard NMEA sentence types are:
- $GPBOD – Bearing, origin to destination
- $GPBWC – Bearing and distance to waypoint, great circle
- $GPGGA – Global Positioning System Fix Data
- $GPGLL – Geographic position, latitude / longitude
- $GPGSA – GPS DOP and active satellites
- $GPGSV – GPS Satellites in view
- $GPHDT – Heading, True
- $GPR00 – List of waypoints in currently active route
- $GPRMA – Recommended minimum specific Loran-C data
- $GPRMB – Recommended minimum navigation info
- $GPRMC – Recommended minimum specific GPS/Transit data
- $GPRTE – Routes
- $GPTRF – Transit Fix Data
- $GPSTN – Multiple Data ID
- $GPVBW – Dual Ground / Water Speed
- $GPVTG – Track made good and ground speed
- $GPWPL – Waypoint location
- $GPXTE – Cross-track error, Measured
- $GPZDA – Date & Time
Decoding the GPGGA sentence — a core task in NMEA data parsing for GPS embedded devices:
181908.00 – UTC timestamp in hours, minutes, and seconds.
3004.6040718 – Latitude in DDMM.MMMMM format. Decimal places are variable.
N – North latitude
07040.3900269 – Longitude in DDMM.MMMMM format. Decimal places are variable.
W – West Longitude
4 – Quality Indicator: 0 = Fix not valid; 1 = Uncorrected coordinate; 2 = Differentially corrected (WAAS/DGPS); 4 = RTK Fix (centimeter precision); 5 = RTK Float (decimeter precision)
13 – Number of satellites used in the coordinate
1.00 – HDOP (horizontal dilution of precision)
408.135 – Altitude of the antenna
M – Unit of altitude (Meter or Feet) and unit of geoidal separation
29.200 – Geoidal separation. Subtracting this from antenna altitude provides Height Above Ellipsoid (HAE)
0.10 – Age of correction
0000 – Correction station ID
*40 – Checksum
Time-To-First-Fix (TTFF)
TTFF Optimization for GPS Embedded Design
TTFF optimization for GPS embedded design determines how quickly a GPS receiver module can deliver a valid position fix after power-up. TTFF values are specified in the module datasheet in seconds and must be carefully evaluated during GPS receiver module selection for embedded systems — a long TTFF can make a product unusable in time-sensitive applications. Any receiver boots in one of three modes:
- Hot Start
- Warm Start
- Cold Start
The following factors influence startup mode and TTFF optimization for GPS embedded design:
- Availability of valid almanac and ephemeris data
- Level of incoming satellite signals
- Whether the unit is within 100 km of the previous fix location
- Time elapsed since the previous fix
Cold Start Mode
A receiver enters cold start when it has not been used for a long time, has moved several hundred kilometers, or incoming satellite signals are too weak due to obstructions such as tall buildings or foliage. With no knowledge of which satellites are overhead, the receiver scans through an internal satellite list and acquires each one in turn. Cold start TTFF typically takes 2 to 4 minutes.
Warm Start Mode
A receiver enters warm start when valid almanac data is present, the current location is within 100 km of the last fix, the receiver was active in the last three days, and signal conditions are good with 4 or more satellites visible — but stored ephemeris data is stale. The receiver can predict overhead satellites but must download fresh ephemeris data. Warm start TTFF is typically 45 seconds.
Hot Start Mode
Hot start conditions are met when warm start requirements are satisfied and a fix was established within the last 2 hours with valid ephemeris data stored for at least 5 satellites. The receiver only needs to download minimal data to re-establish a position fix. Hot start TTFF is typically 22 seconds.
A-GPS
A-GPS Assisted GPS Integration for IoT Devices
A-GPS assisted GPS integration for IoT devices dramatically reduces TTFF — explaining why smartphone GPS units achieve a fix within seconds. Assisted GPS (A-GPS) improves TTFF or enables a fix in conditions where a standalone receiver might fail entirely.
An A-GPS device uses an available data connection (cellular, Wi-Fi) to contact an assistance server, which provides almanac and ephemeris data without waiting to receive them from satellites overhead. The server can also provide an approximate location derived from cell tower data, enabling an immediate fix. A-GPS assisted GPS integration for IoT devices is a major advantage in connected product designs — from fleet trackers to smart wearables — and should be a key consideration during GPS receiver module selection for embedded systems targeting always-connected platforms.
PPS Signal
Most GPS receiver modules include a Pulse Per Second (PPS) output — a digital signal with much lower jitter than anything a microcontroller can generate independently. PPS can be used to time events with nanosecond precision and is commonly used to wake a microcontroller from deep sleep at precise one-second intervals. In precision applications, PPS is also used to synchronize system time and compensate for RTC crystal drift caused by temperature variations.
Anti-Jamming GNSS Receiver Design and Module Selection Guide
Anti-Jamming GNSS Receiver Design is an increasingly critical requirement across IoT, industrial, and safety-critical embedded applications. A rigorous GPS receiver module selection for embedded systems must account for signal robustness, constellation coverage, form factor, power budget, and antenna design. The key selection criteria are:
- Multi-Constellation Support – For Anti-Jamming GNSS Receiver Design, prefer modules supporting GPS, GLONASS, BeiDou, and Galileo simultaneously. Multi-constellation support provides better redundancy and availability under signal-degraded conditions, at a marginally higher cost than GPS-only modules.
- Size – Critical for space-constrained designs. Smaller modules generally integrate a smaller antenna, which may affect lock time and accuracy. Consider this carefully during GPS receiver module selection for embedded systems with tight form-factor requirements.
- Number of Channels – More tracking channels allow the receiver to monitor more satellites simultaneously, directly improving TTFF and positional accuracy.
- Update Rate – The standard update rate is 1 Hz (one fix per second). Higher rates generate more NMEA sentences per second — verify that your host processor's NMEA data parsing pipeline can handle the increased throughput before selecting a high-rate module.
- Power Consumption – Typical GPS receiver modules consume 25–30 mA in active mode. Most modules offer power-saving modes for idle periods — an important consideration in GPS receiver module selection for embedded systems targeting battery-powered IoT or wearable devices.
- Antenna – Ceramic patch antennas are standard on most modules. External active antenna support is important for Anti-Jamming GNSS Receiver Design in automotive or enclosure-mounted applications where the module is shielded from direct sky view by the product housing.
- Accuracy – Standard modules achieve ±3 m accuracy. Sub-meter and centimeter-level modules are available for precision applications such as surveying or autonomous navigation, at a higher cost.
About Embien
Embien Technologies is a product engineering services company with deep expertise in GPS receiver module selection for embedded systems across IoT, automotive, industrial, and consumer electronics domains. Embien supports end-to-end hardware design, GPS driver development, NMEA data parsing for GPS embedded devices, and Anti-Jamming GNSS Receiver Design for programs requiring robust and reliable positioning. Embien's solutions for rapid embedded product development include Sparklet Embedded GUI library for instrument clusters, Flint IDE for GUI prototyping, and eStorm-B1 — an automotive-grade BLE module for connected devices.