Selective Coherent Integration-Based Optimal Acquisition to Enhance Anti-Jam for Low SWaP-C MGUE

Anti-jam (AJ) research and product development for GPS User Equipment (UE) have historically focused on high-performance systems like adaptive antenna arrays for nearly three decades. While these systems have indeed improved AJ performance, they may not be operationally suitable for military applications and equipment with stringent Size, Weight, Power, and Cost (SWaP-C) constraints. For instance, handheld receivers, small unmanned aerial/ground vehicles, and diver underwater navigation systems may struggle to adopt adaptive antenna systems due to their array size, high cost, and computational complexity. It is desired to develop and evaluate signal processing approaches and algorithms to enhance AJ for Military GPS User Equipment (MGUE) with significant SWaP-C limitations. The expected improvement is at least 20 dB (30 dB objective) over the current AJ performance specified for the MGUE Increment 1 ground-based receiver in the presence of both narrowband and broadband jammers (e.g., CW, Pulsed CW, Swept CW, Matched Spectral, Gaussian noise). Given that Mcode is exclusively for military applications, we utilize the M' code to showcase our proposed selective coherent integration based optimal acquisition algorithm. M’-code signal acquisition relies primarily upon direct acquisition, where in effect the receiver correlates (over time and frequency shifts) a locally generated replica of an M’-code signal with the received waveform. Cross Ambiguity Function (CAF) is a tool to understand the signal acquisition. For the MGUE, neither coherent nor noncoherent integration methods perform adequately in detecting the peak of the Cross Ambiguity Function (CAF) for M' or M codes due to the unique modulation of data bits, which are exclusively modulated to odd chips. In this paper, we introduce a novel framework called Selective Coherent Integration (SCI). We define the sub-integration length as half of the navigation data's symbol duration, which amounts to either 5ms or 20ms. This setup ensures that there is, at most, one data value change within every two sub-integrations. The numerical results presented herein underscore the effectiveness of the proposed selective coherent integration-based optimal acquisition solution for MGUE in bolstering anti-jamming capabilities. Through rigorous analysis and simulation, we have demonstrated the algorithm's ability to mitigate the impact of jamming interference.