Session C4a: Latest Advancement from GNSS Receiver and Localization Algorithm Manufacturers (10-Minute Presentations)

Adaptive Dual-Frequency Acquisition in Low-Cost Low-Power GNSS Receiver
Po-Chun Chiu, Pavard Huang, Ian Tsai, Ian Chen, Willy Lo, Shi Xian Yang, Airoha Technology
Location: Holiday 4-5 (Second Floor)
Date/Time: Thursday, Sep. 11, 4:10 p.m.

Dual-frequency receivers represent a significant advancement in GPS technology, offering unparalleled accuracy and reliability in satellite-based navigation. By simultaneously utilizing signals from two different frequencies, typically the L1 and L5 bands, these receivers can achieve highly precise positioning. Utilizing the L5 band enhances pseudo-range performance due to its 10-times-faster pseudo-random noise (PRN) code rate, higher power, and better signal structure for multipath mitigation. This allows dual-frequency receivers to effectively correct ionospheric delays, one of the primary sources of positioning errors. The dual-frequency positioning offers numerous benefits for a wide range of applications. For instance, it provides the high accuracy positioning necessary for safe and reliable operation in the realm of autonomous vehicles. Autonomous vehicles rely heavily on precise GPS data to navigate and make real-time decisions, and the enhanced accuracy of dual-frequency receivers ensures that these vehicles can operate safely and efficiently. Additionally, dual-frequency receivers are crucial for applications in surveying, geodesy, and agriculture, where precise measurements are essential for success.
However, processing the L5 signal on chip-level products, like fitness watches, presents significant challenges. The higher complexity and increased power requirements of the L5 signal demand more advanced and sophisticated hardware, which can be difficult to integrate into compact, low-power devices. The L5 signal's longer PRN code length requires a larger correlator area, a significant factor in chip design. This complexity can lead to higher costs and longer development times for manufacturers aiming to incorporate L5 capabilities into their products. Despite these challenges, the potential benefits of dual-frequency receivers make them a highly attractive option for a variety of applications, and ongoing advancements in technology are likely to make these receivers more accessible and affordable in the future. As the demand for precise and reliable GPS data continues to grow, dual-frequency receivers will play an increasingly important role in meeting this need.
One promising approach to overcoming the challenges associated with processing the L5 signal is the use of L1-aided L5 digital signal processing (DSP). This technique leverages the strengths of the L1 signal to assist in the acquisition and tracking of the L5 signal. By using the L1 signal, which is easier to process due to its lower complexity and power requirements, the receiver can more efficiently lock onto the L5 signal. This L1-aided approach can significantly reduce the computational burden and power consumption associated with L5 signal time-domain processing, making it more feasible to integrate dual-frequency capabilities into smaller, low-power devices like fitness watches and smartphones. This hybrid approach ensures that users can rely on their GPS devices for accurate positioning in a wide range of scenarios, further expanding the potential applications of dual-frequency receivers. Still, the L1-aided method is not without its drawbacks. One significant shortcoming is the dependency on the L1 signal, which may not always be available or reliable in certain environments. For instance, in areas with heavy signal obstruction or interference, the L1 signal might be degraded, which in turn affects the performance of the L5 signal processing. Although there are ways to detect L1 interference, such as abnormal radio front-end (RF) performance or specific frequency tone cancellation, the interference still has a detrimental effect on L5 signal processing. This interference can degrade the accuracy and reliability of positioning, which is critical for applications that require precise navigation and timing.
To lower the risk of L5 effected by L1 jamming, integrating the new generation acquisition engine into the process reduces computational load and hardware requirements, making full-code range acquisition feasible for chip-level products. Unlike L1-aided L5 signal acquisition, the new engine does not rely on the L1 signal, offering a significant advantage in the presence of L1 jamming. Jammed L1 measurements can cause the L5 signal acquisition process to fail, but L5 full-code range searching mitigates this impact, allowing the system to regain a position fix. Thus, new engine serves as a crucial backup plan in the event of L1 failure. Optimizing the L5 acquisition strategy is essential to support both L1-aided fast search and L5-only full-range search. In scenarios involving signal blocking with L1 jamming, such as long tunnels, L5-only acquisition can disregard incorrect L1 information and help restore tracking status. This study introduces the designed strategy and analyzes performance using a signal generator to simulate the scenario. The improvement will be determined by position recovery timing, and the advantages of this design will be evaluated.
Overall, the adoption of new generation acquisition engine represents a significant step forward in overcoming the limitations of traditional L1-aided methods, providing a more robust and versatile solution for modern GPS applications. This study's findings will contribute to the ongoing development and optimization of GNSS receiver technology, ensuring that it remains a critical tool for navigation and positioning in an ever-changing world.