As vehicle automation technology advances, the accuracy requirements for GNSS positioning systems continue to increase. Carrier-phase positioning techniques like RTK and PPP can provide centimetre-level accuracy, but rely on the foundation of standard code-phase positioning. In this blog, FocalPoint Product Manager Jez Ellis-Gray highlights the importance of the accuracy and integrity of code-phase observables, enabling improved performance of high precision positioning solutions.

As BMW leads the charge towards autonomous driving, the challenge of seamlessly integrating advanced GNSS technology while maintaining the brand’s iconic design and engineering standards is more critical than ever. Known for delivering the “ultimate driving experience,” BMW is committed to combining precision, performance, and elegance in every aspect of its vehicles—including the positioning technology that powers its autonomous features. With S-GNSSⓇ, BMW can advance its vision of autonomy without compromise, balancing the need for highly accurate positioning with the brand’s dedication to innovative design, efficiency, and safety.

GNSS accuracy and integrity requirements are substantially more stringent for higher ADAS levels. Carrier phase positioning products like RTK or PPP (or hybrid solutions) are widely available to compatible receivers and raise the bar for accuracy from around 2 metres to centimetre-level precision. However, these high-accuracy carrier-phase techniques are heavily dependent on the underlying code-phase measurements.

Standard GNSS positioning uses just code phase observables to achieve position accuracies of 1-2m in open-sky environments.

Precise GNSS positioning leverages the precise (but ambiguous) carrier phase observable and the less precise (but not ambiguous) code phase observable together with some form of external range correction source to achieve position accuracies of a few decimeters or better. The increase in position accuracy comes at the cost of requiring the continuous corrections data and the fragility of the solution in the presence of multi-path or other interference.

The code-phase measurement serves a number of critical functions, and an accurate and reliable code solution enables both fast convergence and recovery to carrier-phase positioning:

1. Initialization: The code-phase measurement provides the initial position estimate, which is crucial for resolving the carrier phase ambiguities. Without a reasonably accurate starting point, the carrier phase solution cannot be reliably initialised.

2. Convergence: By providing a more precise initial position, the code-phase measurement helps the carrier phase solution converge faster to the final centimetre-level accuracy. This reduces the time needed for the system to be ready for use in safety-critical autonomous applications.

3. Cycle-slip detection: When the carrier phase tracking is interrupted, leading to a cycle slip, the code-phase measurement helps detect and estimate the size of the slip. This allows the system to recover the carrier phase solution without losing too much time or accuracy.

4. Quality control: The code-phase measurement serves as a check on the carrier phase solution. Large discrepancies between the two can indicate measurement problems that need to be addressed.

Initialization: The code-phase measurement provides the initial position estimate, which is crucial for resolving the carrier phase ambiguities. Without a reasonably accurate starting point, the carrier phase solution cannot be reliably initialised.

Convergence: By providing a more precise initial position, the code-phase measurement helps the carrier phase solution converge faster to the final centimetre-level accuracy. This reduces the time needed for the system to be ready for use in safety-critical autonomous applications.

Cycle-slip detection: When the carrier phase tracking is interrupted, leading to a cycle slip, the code-phase measurement helps detect and estimate the size of the slip. This allows the system to recover the carrier phase solution without losing too much time or accuracy.

Quality control: The code-phase measurement serves as a check on the carrier phase solution. Large discrepancies between the two can indicate measurement problems that need to be addressed.

S-GNSSⓇ Auto is FocalPoint’s software upgrade to GNSS receivers, that improves the code-phase measurement accuracy and integrity in challenging GNSS environments, such as urban canyons, under foliage, or with poor antenna performance. By delivering more reliable and precise code-phase measurements, S-GNSSⓇ enables:

• Faster convergence of the carrier phase solution to centimetre-level accuracy

• More robust handling of cycle slips and improved recovery of the carrier phase tracking

• Greater overall confidence and integrity in the final positioning solution

Faster convergence of the carrier phase solution to centimetre-level accuracy

More robust handling of cycle slips and improved recovery of the carrier phase tracking

Greater overall confidence and integrity in the final positioning solution

In autonomous driving applications where every centimetre counts, S-GNSSⓇ provides a critical enhancement to the core GNSS sensors, unlocking the full potential of carrier phase positioning techniques like RTK and PPP. This helps automated vehicles operate safely and precisely, even in complex urban environments or under challenging GNSS conditions.

By improving the reliability and precision of code-phase measurements, S-GNSSⓇ plays a crucial role in enabling the centimetre-level accuracy required by autonomous vehicles and other safety-critical applications. This technology helps overcome the challenges posed by complex GNSS environments, ensuring that carrier-phase positioning solutions can deliver on their promise of superior positioning performance.

For BMW, S-GNSSⓇ isn’t just a technical upgrade—it’s an enabler of the future. By resolving traditional trade-offs between antenna size, cost, and performance, S-GNSSⓇ offers BMW new design possibilities while supporting the brand’s uncompromising standards for quality and safety. As BMW continues to push the boundaries of autonomous technology, S-GNSSⓇ provides the flexibility needed to deliver on its promise of a premium, intelligent, and sustainable driving experience. This technology not only advances BMW’s journey toward higher levels of autonomy but also aligns perfectly with its commitment to lead the automotive industry in innovation and excellence.

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