USRP Implementation and Verification of GNSS Multi-Carrier Broadband Waveforms

Broadband multicarrier Global Navigation Satellite System (GNSS) waveforms were developed with a focus on onboard waveform adaptation and the mitigation of signal distortion caused by high-power amplifiers (HPAs). Constant envelope (CE) navigation signals offer a distinct advantage for GNSS transmitters due to their fixed amplitude gain and phase offset, even after passing through nonlinear HPAs. This ensures minimal impact on the positioning, navigation, and timing (PNT) performance of the received signals. Additionally, multicarrier broadband modulation reduces the number of required HPAs and improves coherence across different GNSS bands. To validate real-time performance, the waveforms were implemented on Universal Software Radio Peripheral (USRP) devices. The demonstration system consists of two computers (running the transmitter and receiver GNU Radio codes), a transmitter USRP (Ettus B210), a receiver USRP (Ettus B210), a transmitter HPA (Mini-Circuits ZX60-43-S+), and USB cables. On the transmitter side, multicarrier GNSS waveforms were used to combine Global Positioning System (GPS) L2 and L5 signals. For the USRP receiver implementation, practical challenges such as carrier and time synchronization were addressed. An online delay estimation algorithm based on convolution was also developed to efficiently estimate the delay between received pseudorandom noise (PRN) codes and the local replica. The demo system was showcased at NAVFEST 2024, a two-week GPS NAVWAR test event held in May at White Sands Missile Range (WSMR), NM. NAVFEST, also known as the Navigation Festival, provides a cost-effective, realistic GPS jamming environment for evaluating GPS-based navigation systems in GPS-contested scenarios. Our GNSS testbed demonstrated promising anti-jamming performance using GNSS multicarrier broadband waveforms