Dual-Frequency GNSS (L1/L5)

The Hardware Advantage

For indoor-adjacent or transition-zone flight (stadiums with open roofs, glass atriums), the physical GNSS chip in the smartphone is the primary bottleneck. Standard single-frequency receivers are prone to "Urban Canyon" multipath, but Dual-Frequency L1/L5 support changes the physics of the fix.

The Multipath Problem (L1 Only)

Legacy GNSS chips rely on the L1 Band (1575.42 MHz).

• Chip Rate: 1.023 MHz.
• Resolution: A single code bit is roughly 300 meters wide.
• The Trap: In a reflective environment like a stadium seating bowl, a signal bouncing off a concrete wall arrives just slightly after the direct signal. Because the L1 pulses are so wide, the receiver's correlator smears them together. It cannot distinguish the "echo" from the "truth," leading to position jumps of 50-100 meters.

The L5 Solution

Modern flagships track the L5 Band (1176.45 MHz) simultaneously.

• Chip Rate: 10.23 MHz (10x faster).
• Resolution: A code bit is only ~30 meters wide.
• Leading Edge Detection: Because the pulses are narrower, the receiver sees two distinct "peaks" in the correlation window: the Early (Direct Path) and the Late (Reflected Path).
• Rejection: The chip simply discards any peak arriving after the first one. This allows a drone to maintain a stable 3D fix even when satellite signals are bouncing off metallic truss structures.

Validated Chipsets

To ensure reliable transition from indoor RTT to outdoor GPS, verify your device uses one of these subsystems:

1. Broadcom BCM47755+: The pioneer chip (Mi 8, Pixel 4/5).
2. Qualcomm FastConnect 6900/7800: Found in Snapdragon 8 Gen 2/3 devices.
3. Google Tensor: Uses integrated Exynos modems with robust L5 software compensation.

Source Code Reference

• Carrier Frequency: android/location/GnssMeasurement.java - The API's getCarrierFrequencyHz() is the programmatic way to verify your app is actually receiving L5 packets.