Browsing by Author "Mao, Tianqi"
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Item Detection of Stealthy Jamming for UAV-Assisted Wireless Communications: An HMM-based Method(IEEE Transactions on Cognitive Communications and Networking, 2023-02-28) Zhang, Chen; Zhang, Leyi; Mao, Tianqi; Xiao, Zhenyu; Han, Zhu; Xia, Xiang-GenDue to the high mobility, low cost and high robustness of line-of-sight (LoS) channels, unmanned aerial vehicles (UAVs) have begun to play an important role in assisting wireless communications. However, the broadcasting nature of wireless communication networks makes the electromagnetic spectrum vulnerable to jamming attacks. To ensure communication security, this paper investigates the jamming detection issue for UAV-assisted wireless communications. Different from the existing works, we consider detection of stealthy jamming with no prior knowledge of legitimate users or channel statistics, which makes the detection more challenging. To solve this problem, we design a hidden Markov model (HMM) based jamming detection (HBJD) method. First, we process the received signals with a sliding window to calculate the logarithmic received energy and use HMM to model the signal transmission under a jamming attack. Specifically, the spectrum state and logarithmic received energy are modeled as the hidden state and observable variable of HMM. Then, the Expectation-Maximization (EM) algorithm is applied to estimate the parameters of HMM. With the estimated parameters, the spectrum state of each logarithmic received energy sample can be decided according to the maximum posterior probability (MAP) criterion. Finally, we design the test statistics and derive the threshold based on the estimated HMM parameters for the final decision. Simulation results demonstrate the superiority of the proposed solution for the detection of stealthy jamming without prior knowledge of legitimate users or the channel statistics.Item Near Space Communications: A New Regime in Space-Air-Ground Integrated Networks(IEEE Wireless Communications, 2022-12-29) Xiao, Zhenyu; Mao, Tianqi; Han, Zhu; Xia, Xiang-GenPrecipitated by the technological innovations in near-space platform stations (NSPSs), the near-space communication (NS-COM) network has emerged as an indispensable part of the next-generation space-air-ground integrated network (SAGIN) that facilitates ubiquitous coverage and broadband data transfer. This article aims to provide a comprehensive overview of NS-COM. First, we investigate the differences between NS-COM and the existing terrestrial cellular networks as well as satellite-based and unmanned-aerial-vehicle (UAV)-based communication networks, which is followed by a review of NS-COM development. Then we explore the unique characteristics of NS-COM regarding the platforms and the propagation environment of near space. The main issues of NS-COM are identified, resulting from the extremely long transmission distance, limitations of the communication payloads on NSPS, and the complex atmospheric constitution of near space. Then various application scenarios of NS-COM are discussed, where the special technical requirements are also revealed, from physical-layer aspects like transceiver design to upper-layer aspects like computational offloading and NSPS placement. Furthermore, we investigate the coexistence of NS-COM and ground networks by treating each other as interferers or collaborators. Finally, we list several potential technologies for NS-COM from the perspective of spectrum usage, and highlight their technical challenges for future research.Item Twin-Layer RIS-Aided Differential Index Modulation Dispensing With Channel Estimation(IEEE Transactions on Vehicular Technology, 2023-11-06) Xiao, Zhenyu; Liu, Guangyao; Mao, Tianqi; Liu, Ruiqi; Zhang, Wei; Xia, Xiang-Gen; Hanzo, LajosIn this correspondence, we propose a twin-layer hierarchical differential index modulation scheme for a reconfigurable intelligent surface (RIS)-aided transmitter architecture, termed as HD-RIS-IM. More specifically, the RIS array is partitioned into perfectly tiling sub-arrays. Each sub-array is mapped across multiple time slots, where each RIS element is activated only once at a particular time slot. These sub-arrays represented by sub- matrices are then used for constructing a block-based permutation matrix for data transmission. With the aid of this hierarchical structure, additional information can be conveyed by the specific order of the sub-arrays that are activated. Furthermore, extra bits are also embedded in the particular order of the RIS elements that are activated within each sub-array. By exploiting all the distinct permutations of the activated matrices, a differential modulation scheme is proposed for the RIS-aided transmitter, which maintains an M -ary phase shift keying (MPSK) and facilitates CSI-free demodulation. Furthermore, at the receiver, we propose a low-complexity distributed maximum likelihood (ML) detector, which significantly reduces the detection complexity. Our simulation results demonstrate the performance benefits of the proposed HD-RIS-IM scheme.