日期：2016-07-01 | 学术活动 - 学术会议
Topic1：Proactive eavesdropping via cognitive jamming in fading channels
To enhance the national security, there is a growing need for government agencies to legitimately monitor suspicious communication links for preventing intended crimes and error attacks. In this paper, we propose a new wireless information surveillance paradigm by investigating a scenario where a legitimate monitor aims to intercept a suspicious wireless communication link over fading channels. The legitimate monitor can successfully eavesdrop (decode) the information of the suspicious link at each fading state only when its achievable data rate is no smaller than that at the suspicious receiver. In practice, such legitimate eavesdropping is particularly challenging, since the legitimate monitor may be far away from the suspicious transmitter and cannot eavesdrop efficiently. To overcome this issue, we propose a new approach, namely proactive eavesdropping via cognitive jamming, in which the legitimate monitor purposely jams the receiver so as to change the suspicious communication (e.g., to a smaller data rate) for overhearing more efficiently. In particular, we consider delay-sensitive and delay-tolerant applications for the suspicious data communications, under which the legitimate monitor maximizes the eavesdropping non-outage probability for event-based monitoring and the relative eavesdropping rate for content analysis, respectively, by optimizing its jamming power allocation over different fading states subject to an average power constraint. Numerical results show that the proposed proactive eavesdropping via cognitive jamming approach greatly outperforms the conventional passive eavesdropping without jamming and the proactive eavesdropping with constant-power jamming.
Topic2: Design of Root-Protograph LDPC Codes for Non-Ergodic Block-Fading Channels
方毅，2013年12月获厦门大学通信工程系博士学位。先后于2012~2016年在香港理工大学、英国伦敦大学学院、新加坡南洋理工大学、香港中文大学网络编码所任研究助理、访问学者及博士后研究员；2015年1月至今，加入广东工业大学信息工程学院，任“青年百人计划”特聘副教授，广东省“珠江人才计划”引进创新团队核心成员。近年来，主持国家自然科学基金、广东省自然科学基金等各类纵项项目4项，参与国家自然科学基金项目2项，广东省创新团队项目1项。至今已在IEEE Commun. Surveys & Tutorials, IEEE Trans. Wireless Commun.等国际权威期刊和会议上发表30余篇学术论文，并担任近10个IEEE期刊的审稿专家。主要研究方向为：信息与编码理论，UWB及MIMO通信技术。
Protograph Low-density parity-check (LDPC) codes have attracted much attention in the past decade since they not only inherit the advantage of conventional LDPC codes but also possess linear encoding complexity. In this talk, the performance of protograph LDPC codes has been extensively studied over non-ergodic block-fading (BF) channels. Using the modified protograph extrinsic information transfer (PEXIT) algorithm, we observe that the existing protograph LDPC codes, which have been shown to possess excellent error performance over additive white Gaussian noise (AWGN) channels, can not perform well over non-ergodic BF channels. To address this problem, a simple design scheme is proposed to construct three new root-protograph (RP) LDPC codes, which are remarkably superior to the regular RP code and regular root-LDPC code, and exhibit outage-limit-approaching error performance. Consequently, these two proposed IRP codes appear to be better alternatives as compared to other error-correction codes (ECCs) for slowly-varying wireless communication systems.
Topic3: Design and performance analysis of a new multiresolution M-ary differential chaos shift keying communication system.
Differential chaos shift keying (DCSK) system draws much attention in the past decade due to its simple circuits and excellent anti-multipath ability. Compared with differential phase shift keying (DPSK) system, DCSK system is more robust to the multipath fading channels and is more suitable for ultra-wideband (UWB) system. Recently, chaotic signal has been an optional pulse shape for wireless body area networks (WBANs), where DCSK modulation is an important candidate. However, the significant drawback of DCSK is the fact that half the bit duration is spent sending non-information-bearing reference signal. To address this problem, a phase-constellation-based M-ary DCSK system is extended to improve the spectral efficiency. To provide different quality of services (QoS) for transmitted bits within a symbol according to their different bit error rate (BER) requirements, a new multiresolution M-ary DCSK modulation scheme is proposed based on the principle of non-uniformly spaced constellations, which further increases the spectrum efficiency and energy efficiency. Consequently, the proposed scheme is a promising technique in the video transmission for in-body WBAN applications.