In a wide range of applications including robotics, autonomous vehicles, industrial automation, logistics and asset tracking, drones, as well as agricultural and heavy construction equipment, increasingly used by European Galileo, US Global Positioning System (GPS), Russian Glo Nass, China’s Beidou Navigation Satellite System, and Japan’s QZSS multi-constellation Global Navigation Satellite System (GNSS) receivers to use various location-based functions.

Author: Jeff Shepard

In a wide range of applications including robotics, autonomous vehicles, industrial automation, logistics and asset tracking, drones, as well as agricultural and heavy construction equipment, increasingly used by European Galileo, US Global Positioning System (GPS), Russian Glo Nass, China’s Beidou Navigation Satellite System, and Japan’s QZSS multi-constellation Global Navigation Satellite System (GNSS) receivers to use various location-based functions. The advantages of using a multi-constellation GNSS receiver are: better positioning, navigation, timing (PNT) signal delivery, improved accuracy, integrity, and improved application robustness.

However, multi-constellation receiver development is a complex, time-consuming endeavor that includes: optimizing L-band antennas; designing radio frequency (RF) front ends; integrating baseband signal processing algorithms to acquire, track, and apply corrections for various PNT signals; The application’s processing software is coded to extract PNT data from each channel of baseband and use this information to implement system functions. The designer must also select the appropriate antenna and place it correctly.

Alternatively, designers can turn to prefabricated GNSS modules and development environments to quickly and efficiently integrate positioning capabilities into the system. This GNSS module includes an RF front-end, baseband processing, and embedded firmware to speed application processing software development. Some GNSS modules also include an antenna.

This article will describe the basic working principles of GNSS, PNT and multi-constellation GNSS receivers. Then, before introducing several GNSS modules (versions with and without integrated antenna) and associated evaluation boards from STMicroelectronics, Septentrio and Würth Elektronik, we discuss the pros and cons of integrating an antenna in a GNSS module. Designers can use these modules to cost-effectively develop accurate, robust location-based applications.

What are GNSS and PNT?

GNSS and PNT are closely related concepts. GNSS satellites are the most common source of PNT signals. GNSS satellites are essentially highly accurate synchronized clocks that continuously broadcast their PNT information. The GNSS module receives the PNT signal from a specific satellite and calculates its distance to that satellite. When the receiver knows the distance to at least four satellites, it can estimate its own position. However, the accuracy of location estimates is affected by various sources of error, including:

・ Clock drift of timing circuits in GNSS satellites
・ Errors in predicting the exact orbital position of GNSS satellites
・ The general performance drift of the entire satellite equipment relative to other satellites, also known as satellite offset
• Signals are distorted and delayed as they pass through the ionosphere and troposphere.
・Variable performance and drift in multipath reflections and receivers

Currently, designers can correct for satellite- and atmospheric-based GNSS errors using a variety of different techniques.

Improve GNSS performance

The best way to minimize the effects of errors originating from a GNSS receiver is to use the highest performance receiver that fits the cost and size constraints of the specific application. However, even high-performance receivers are not perfect; their performance can be improved to a large extent. It is important to understand these correction methods because they give different performance and some GNSS modules cannot use all correction methods.

There are several GNSS correction methods using ground reference base stations (Figure 1). Real-time kinematics (RTK) and precise point positioning (PPP) are the most mature methods for GNSS correction using ground reference base stations. More recently, the RTK-PPP hybrid approach has emerged.

How to quickly implement a multi-constellation GNSS module for positioning
Figure 1: GNSS user receivers can obtain atmospheric, clock, and orbital error information from a reference network to improve positioning accuracy. (Image credit: Septentrio)

RTK relies on a single base station or local reference network to obtain correction data, which can eliminate most GNSS errors. RTK assumes that the base station and receiver are located in close proximity—up to 40 kilometers or 25 miles apart, so the base station and receiver experience the same error. Post-Processed Kinematics (PPK) is a variant of RTK that is widely used in mapping to obtain high-precision positioning data or centimeter-level accuracy.

Only orbital and satellite clock errors are used for PPP correction. These errors are satellite-specific and independent of user location, which limits the number of reference base stations required. However, PPP does not take into account atmospheric-related errors and is therefore less accurate than RTK. Also, the initialization time for PPP correction can reach around 20 minutes. Long initialization times and low precision make PPP techniques unusable in many applications.

For those applications that require near RTK accuracy and fast initialization times, the latest GNSS correction service, RTK-PPP (sometimes called State Space Representation (SSR)) is usually employed. This technique uses a reference network with base stations spaced about 100 km (65 miles) apart, collects GNSS data and calculates combined satellite and atmospheric corrections. The reference network uses the Internet, satellite or mobile phone network to send correction data to the user. GNSS receivers using RTK-PPP can achieve sub-centimeter accuracy. Choosing to use RTK, PPP, and RTK-PPP calibration methods involves a number of design tradeoffs that developers need to review to select the best solution for their specific application. (figure 2).

How to quickly implement a multi-constellation GNSS module for positioning
Figure 2: Advantages and disadvantages of three common GNSS correction methods. (Image credit: Septentrio)

Satellite Augmentation Systems (SBAS) are beginning to be implemented regionally to replace the ground-based base station correction methods of RTK, PPP and RTK-PPP. SBAS still uses ground stations to measure GNSS errors, but these are spread across continents. Measurement errors are processed at a central location, where corrections are calculated and transmitted to geostationary satellites in the area covered. Correction data is broadcast from satellites as an overlay or addition to the original GNSS data.

The accuracy of GNSS depends on the availability and accuracy of satellite measurements and associated corrections. High-performance GNSS receivers track GNSS signals at multiple frequencies and use multiple GNSS constellations and various correction methods to provide the required accuracy and resilience. The resulting redundancy results in stable performance even when some satellite measurements and data experience interference. Designers can choose from a variety of GNSS accuracy and redundancy capabilities (Figure 3).

How to quickly implement a multi-constellation GNSS module for positioning
Figure 3: GNSS accuracy classes with corresponding correction methods and selected applications. (Image credit: Septentrio)

GNSS Module: Integrated Antenna vs External Antenna

Due to the complexity of multi-constellation positioning, using a variety of modules from vendors can help speed time-to-market, reduce costs and ensure performance. That said, designers need to consider whether to use an internal antenna or opt for an antenna that is external to the GNSS module. For applications where time-to-market and cost are a priority, an integrated antenna may be a better choice, as the amount of engineering involved is much less. For applications requiring FCC or CE certification, the use of modules with integrated antennas can also speed up the certification process. However, this increases the size of the solution and the flexibility of the integrated antenna solution is limited.

External antennas provide designers with more performance and layout options. Designers can choose between large, high-performance antennas or smaller, low-performance antennas. Additionally, antenna placement is more flexible relative to the location of the GNSS module, which will further increase design flexibility. External antennas ensure reliable GNSS operation due to flexible placement. However, antenna placement and connection cabling are complex and time-consuming, requiring special expertise, which can increase costs and delay time-to-market.

Tiny GNSS Module for Space Constrained Designs

For those design teams with expertise in antenna placement and routing, STMicroelectronics’ Teseo-LIV3F, a multi-constellation (GPS/Galileo/GLONASS/Beidou/QZSS) GNSS module using external antennas (Fig. 4). Housed in an LCC-18 package, the module measures 9.7 mm × 10.1 mm and has a 1.5 m circular error probability (CEP) positioning accuracy with a time-to-first-fix (TTFF) as low as 32 s and 1.5 s for cold start and warm start, respectively ( GPS, GLONASS). The device consumes 17 μW of standby power and 75 mW of tracking power.

How to quickly implement a multi-constellation GNSS module for positioning
Figure 4: The Tesco-LIV3F GNSS module includes the GNSS core and subsystems, as well as all necessary connectivity and power management functions, in a package size of 9.7 x 10.1 mm. This device requires an external antenna. (Image credit: STMicroelectronics)

The Tesco-LIV3F’s onboard 26 MHz temperature compensated crystal oscillator (TCXO) helps ensure high accuracy, while a dedicated 32 kHz real time clock (RTC) oscillator reduces time to first fix (TTFF). Features such as data logging, seven-day autonomous assisted GNSS, firmware (FW) reconfigurability, and FW upgrades are all enabled by 16 Mb of embedded flash memory.

Applications suitable for the Tesco-LIV3F include insurance, logistics, drones, toll collection, anti-theft systems, people and pet location, vehicle tracking and emergency calling.

The Teseo-LIV3F module serves as a pre-qualified solution to shorten the time-to-market for the end application. The device operates over a temperature range of -40°C to +85°C.

To test this module and speed up application development, designers can use the AEK-COM-GNSST31 evaluation board. When used with the X-CUBE-GNSS1 firmware, the evaluation kit can support acquisition, tracking, navigation and data export functions without the need for external memory. This EVB is also required to be used with the SPC5 microcontroller for the development of automotive applications.

GNSS module with interference suppression

Septentrio’s 410322 mosaic-X5 multi-constellation GNSS receiver is a low power, surface mount module measuring 31 mm x 31 mm x 4 mm. The device provides designers with a range of interfaces, including four UARTs, Ethernet, USB, SDIO, and two user-programmable GPIOs.

The mosaic-X5 is designed for robotics, autonomous systems, and other mass-market applications, with a refresh rate of 100 Hz, latency below 10 ms, and vertical and horizontal RTK positioning accuracy of 0.6 cm and 1 cm, respectively. The device tracks all GNSS constellations, supports current and future signals and is compatible with PPP, SSR, RTK and SBAS corrections. The TTFF of this module is less than 45 s at cold start and less than 20 s at warm start.

mosaic-X5 uses several Septentrio patented technologies, including AIM+. This is an on-board interference suppression technology that suppresses a variety of interferences – from simple continuous narrowband signals to complex wideband and pulsed interference.

The interface, instruction and data information of these modules will be completely recorded. The included RxTools software allows receiver configuration and monitoring, as well as recording and analysis of data.

Septentrio’s 410331P3161 mosaic-X5 development kit enables designers to explore, evaluate, and develop prototypes that fully exploit the capabilities of mosaic-X5 (Figure 5).

How to quickly implement a multi-constellation GNSS module for positioning
Figure 5: Designers can use the 410331P3161 mosaic-X5 development kit to create a prototype using various connections including Ethernet, COM port or USB 2.0, or use an SD memory card to do the job. (Image credit: Septentrio)

The kit uses the mosaic-X5’s intuitive web user interface for easy operation and monitoring, allowing designers to control the receiver module from any mobile device or computer. The web interface monitors receiver operation using easy-to-read quality metrics.

Designers can build prototypes by integrating the mosaic development kit using any of the following connections: Ethernet, COM port, USB 2.0, SD memory card.

GNSS module with integrated antenna

For designers who can take full advantage of GNSS modules with integrated antennas, Würth Elektronik presents the 2614011037000 Erinome-I module with a high-performance system-on-chip (SoC) (Figure 6). The module supports GPS, GLONASS, Galileo and BeiDou GNSS constellations and features an integrated antenna on top to simplify hardware integration and reduce time to market. The module (including the integrated antenna) measures 18 mm x 18 mm.

How to quickly implement a multi-constellation GNSS module for positioning
Figure 6: The 2614011037000 Erinome-I is a complete GNSS module. The module features a high-performance GNSS SoC and integrated antenna. (Image credit: Würth Elektronik)

The module also integrates a TCXO, RF filter, low noise amplifier (LNA) and serial flash.

Würth also provides the 2614019037001 Evaluation Board (EVB) for Erinome-I (Figure 7). EVB can also be used as a reference design for integrating GNSS modules in applications. Among them, the USB port can be used to connect EVB and PC. Through the multi-pin connector, the designer can access all pins of the GNSS module.

How to quickly implement a multi-constellation GNSS module for positioning
Figure 7: The 2614019037001 evaluation board for Erinome-I (closer to the center of the board, with the integrated antenna visible in the center of the module) is also used as a reference design. (Image credit: Würth Elektronik)

Würth Elektronik Navigation and Satellite Software (WENSS) is a simple PC tool that interacts with the Erinome-I GNSS module via a UART interface. The software supports:

・ Control EVB operation
・Bidirectional communication with Erinome-I module
・Evaluate the features and abilities of Erinome-I
・ Familiarity with Erinome-I protocol, sentences and instructions
・ Configure Erinome-I without knowing the protocol
・ Parse the sentences and commands used by Erinome-I

Positioning applications can be easily evaluated using WENSS without advanced knowledge. Experienced developers can also use WENSS for more advanced configuration.

Summarize

The best way to achieve accurate, reliable positioning is to use multiple constellations and associated correction techniques. These are complex systems, but designers can turn to prefabricated GNSS modules, associated development kits and environments to quickly and efficiently compare options and implement location-based capabilities and services.

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