Synthesis-free directional modulation for retrodirective frequency diverse array
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. RESEARCH PAPER .
October 2020, Vol. 63 202304:1–202304:22 https://doi.org/10.1007/s11432-020-2853-9
Synthesis-free directional modulation for retrodirective frequency diverse array Sheng KE, Jianping AN* & Shuai WANG School of Information and Electronics, Beijing Institute of Technology, Beijing 100081, China Received 13 February 2020/Accepted 25 March 2020/Published online 16 September 2020
Abstract Combination of directional modulation (DM) and frequency diverse array (FDA) provides a novel opportunity for enabling physical layer security because of the enhanced ability of distance resolution. However, in the existing studies, the time-varying nature of the FDA pattern is usually ignored. In this paper, a modified model of FDA-DM is proposed, in which the ignored time factor in the previous studies is taken into consideration for providing a new and more accurate perspective on evaluating the security of FDA-DM. Furthermore, we reveal that FDA-DM can achieve angle-dependent and directional-time-coupleddependent security. After that, based on the retrodirective FDA (RFDA) with a new structure, a novel synthesis-free FDA-DM scheme is proposed for both overcoming the limitations of the FDA-DM scheme and allowing self-tracking the position of the pilot signal without any prior knowledge. Meanwhile, a new set of nonlinear frequency offsets, defined as rearranged linear frequency offsets (RLFOs), is also proposed for both combining the advantages of the linear/nonlinear frequency offsets and bringing conveniences to practical implementation. In addition, the closed-form expression of the average signal-to-artificial-noise-ratio (SANR) is given out for evaluating the security performance of the proposed scheme. Finally, numerical results are presented to verify both the accuracy of the proposed theoretical analysis and the superiority of the RFDADM scheme. Keywords secure transmission, frequency diverse array (FDA), frequency offsets (FOs), retrodirective array, average SANR distribution Citation Ke S, An J P, Wang S. Synthesis-free directional modulation for retrodirective frequency diverse array. Sci China Inf Sci, 2020, 63(10): 202304, https://doi.org/10.1007/s11432-020-2853-9
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Introduction
Directional modulation (DM) [1–14], as a keyless physical-layer security transmitting technique with great potentials in wireless communications [15–17], has drawn a wide attention in the past decade. Compared with the secure beamforming techniques, where both the directions of the desired user and the eavesdropper are required in advance, DM can obtain secure transmission relying only on the prior knowledge of the desired user. In the existing studies, DM was usually realized at the radio frequency (RF) front end. For example, in [7], DM was implemented by adjusting the element weights of the phasedarray (PA). It was also the first time that a phased-array was used to realize DM. Before that, DM was achieved using the parasitic array [8]. Meanwhile, antenna subset modulation [9], which is designed based on RF switches, m
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