Waveform-Encrypted LPI Radar Framework: Joint Sequence Design, Robust Decryption, and Analysis

Abstract

In the presence of sophisticated electronic reconnaissance, low probability of intercept (LPI) property is a key enabler for improving radar survivability. Many existing LPI waveform designs improve intercept resistance by suppressing signal features in specific domains or by countering particular reconnaissance functions, while receiver-side decryption robustness and range spread target detection are not always explicitly considered. To improve the LPI performance and the detection capability of the pulse radar system, this article develops a directsequence spread-spectrumbased waveform-encrypted LPI radar framework that disperses the focused and easily intercepted radar emission energy across the timefrequency domain. However, conventional decryption methods at the radar receiver typically involve an exhaustive sliding-window search, resulting in degraded detection performance for range spread targets and a heavy computational burden. To address the challenge, the received encrypted signal model for range spread targets is derived. Then, the joint sequence design problem is formulated by minimizing the matching error between the correlation function and an ideal template, subject to energy and constantmodulus constraints. By appropriately choosing the mainlobe width of this template, the dispersed energy from multiple scattering points can be efficiently accumulated to improve the extended target detection performance. To solve the nonconvex optimization problem, a product manifold is constructed for these constraints, and the Riemannian optimization algorithm is adopted to perform optimization over this manifold. Finally, numerical simulations and semiphysical experiments are conducted to validate the proposed decryption methods effectiveness and its superiority over the classical decryption method regarding computational complexity and range spread target detection performance.