Real-time kinematics (RTK) is a satellite navigation technique that offers precise positioning accuracy by using data from Global Navigation Satellite Systems (GNSS). We’ve covered satellite positioning on IoT Insider – more specifically looking at GNSS, GPS and now, RTK, to understand the role they play in enabling applications such as asset tracking to follow items around the world. To clarify, both GPS and GNSS use satellite signals, but GNSS receivers can use signals transmitted by four or more satellites, while GPS is usually confined to the one satellite system.
What is real-time kinematics?
RTK is a navigation technique used to improve the accuracy of positioning data provided by GNSS. It relies on two major components: a base station and a mobile receiver. The base station is positioned at a fixed, known location, where it receives signals from multiple GNSS satellites and compares the position with its known position, a process known as a “correction”.
The mobile receiver receives signals from the same satellites and uses the correction data from the base station to adjust its own calculations, reducing errors introduced by factors such as satellite signal delays caused by atmospheric conditions.
Advantages offered by RTK include high accuracy, typically improved from standard receivers; real-time operation which is suitable for applications like autonomous vehicles; and multiple GNSS compatibility, using signals provided by different constellations. Its drawbacks, however, include a limited range; signal interference and latency, as the time taken to transmit corrections can introduce small delays.
Designing an RTK system
Designing and indeed, optimising RTK systems can have significant challenges for engineers, particularly when it comes to overcoming signal interference, reducing latency, and managing any potential hardware limitations.
2. Signal interference
A primary challenge in designing RTK systems is the signal interference. RTK relies on satellite signals from GNSS constellations. These signals are vulnerable to different types of interference, such as atmospheric conditions (ionospheric and tropospheric delays), urban obstructions, and multipath errors.
To mitigate this interference, engineers use advanced GNSS receivers that use dual-frequency technology, allowing the receiver to measure both L1 and L2 signals from GPS satellites. By comparing these frequencies, the receiver can correct ionospheric delays and improve accuracy. Additionally, multipath rejection algorithms and the use of choke-ring antennas, which suppress multipath signals, can further improve RTK performance in urban environments.
2. Latency in RTK corrections
RTK systems rely on real-time corrections provided by base stations or reference networks. The base station computes the difference between its known position and the satellite-derived position and transmits correction data to the rover unit (the mobile receiver). Latency in the transmission of these corrections can significantly impact the system’s ability to maintain accurate positioning in real-time.
Minimising latency requires optimising the communication infrastructure between the base station and the rover. Engineers can use low-latency communication protocols, such as NTRIP (Networked Transport of RTCM via Internet Protocol), to transmit correction data over mobile networks or the Internet.
3. Hardware limitations
RTK systems, particularly in mobile applications, are constrained by hardware limitations such as processing power, battery life, and size. High-precision GNSS receivers often require significant computational resources to process correction data and maintain accurate positioning.
Recent developments in low-power GNSS chipsets and microcontrollers have significantly reduced the power requirements of RTK systems. Engineers can design power-efficient systems by selecting chipsets that support low-energy modes, which activate only when satellite signals are being processed. Additionally, solar-powered base stations and energy-harvesting technologies can extend the operational life of RTK systems in remote or off-grid applications.
Conclusions
Greater demands on higher precision in real-time positioning necessitates RTK systems that are sufficiently optimised. Designing and optimising these systems remains a challenge and addressing signal interference, reducing latency and managing hardware limitations are important to improving overall RTK performance.
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