AI summaryⓘ
The authors studied how to protect GPS signals from interference using a special antenna technique with very simple parts that only switch between four phase states. They found that traditional methods don't work well with such limited settings, so they developed smarter ways to balance blocking interference and keeping the GPS signal strong. Their new method uses machine learning combined with a search process to quickly find good antenna settings and performs almost as well as the best possible solution. Tests showed that this approach helps GPS receivers work much better when there is strong interference. Overall, the authors demonstrate that even very simple hardware can significantly improve GPS resistance to jamming with the right algorithms.
GNSSbeamformingphase shiftersQPSKanti-jammingcombinatorial optimizationmachine learningsignal-to-noise ratiointerference suppression
Authors
Burak Soner, Ekin Uzun, Can Aksoy
Abstract
We investigate low-cost GNSS anti-jamming using beamforming with inexpensive 2-bit phase shifters, constraining each complex array weight to one of four QPSK phase states (real/imaginary = -1 or +1). This severe quantization sharply limits the beampattern solution space, making conventional real-valued beamforming and naive weight quantization highly suboptimal. We formulate a discrete optimization that trades interference suppression against satellite-direction gain, and benchmark known combinatorial optimization methods across array sizes and interference conditions. Simulations show that performance improves with array size, with oracle and greedy search achieving up to 34 dB nulling, but oracle incurs exponential latency and greedy sampling is stochastic. To obtain deterministic low-latency performance, we propose an ML-aided method based on gradient-boosted decision trees followed by local search, which performs similar to the oracle for larger arrays at fixed latency. We further validate the approach experimentally using a fully digital emulation of the QPSK oracle beamformer and compare against a GNSS receiver without beamforming capability. Under mild jamming (J/S approximately 44 dB) both receivers maintain adequate tracking, with QPSK yielding a 4.2 dB higher average C/N0 (37.3 vs. 33.1 dB-Hz). Under moderate and strong jamming (J/S approximately 62-70 dB) the benefit is substantial. At J/S = 70 dB the unprotected receiver degrades to near tracking limits (avg C/N0 = 9.3 dB-Hz) while the QPSK oracle sustains an average C/N0 of 20.8 dB-Hz. These results confirm that 2-bit phase-shift beamforming provides considerable anti-jamming benefit over a standard GNSS receiver, motivating further research on oracle-level practical methods.