1,981 research outputs found
Generalized dual-mode index modulation aided OFDM
No full textDual-mode index modulation aided orthogonal frequency division multiplexing (DM-OFDM) is recently proposed, where subcarriers are partitioned into OFDM subblocks, divided into two groups within each subblock, and modulated by two differentiable constellation alphabets. In DM-OFDM, additional bits can be transmitted through indices of subcarriers modulated by the same constellation alphabet. In this letter, generalized DM-OFDM (GDM-OFDM) is proposed, where the number of subcarriers modulated by the same constellation mode in each subblock is alterable. By applying such enhancement, the spectral efficiency can be improved at the cost of marginal performance loss. Moreover, since the BER performance of GDM-OFDM degrades at low signal-to-noise ratios (SNRs), an interleaving technique is employed to address this issue. At the receiver, a maximum-likelihood (ML) detector and a reduced-complexity log-likelihood ratio (LLR) detector are employed for demodulation. Simulation results demonstrate that the proposed GDMOFDM is capable of enhancing the spectral efficiency compared with DM-OFDM at the cost of negligible performance loss, and the interleaved GDM-OFDM (IGDM-OFDM) can harvest on performance gain over GDM-OFDM
Receiver design for SPAD-based VLC systems under Poisson-Gaussian mixed noise model
Full text linkSingle-photon avalanche diode (SPAD) is a promising photosensor because of its high sensitivity to optical signals in weak illuminance environment. Recently, it has drawn much attention from researchers in visible light communications (VLC). However, existing literature only deals with the simplified channel model, which only considers the effects of Poisson noise introduced by SPAD, but neglects other noise sources. Specifically, when an analog SPAD detector is applied, there exists Gaussian thermal noise generated by the transimpedance amplifier (TIA) and the digital-to-analog converter (D/A). Therefore, in this paper, we propose an SPAD-based VLC system with pulse-amplitude-modulation (PAM) under Poisson-Gaussian mixed noise model, where Gaussian-distributed thermal noise at the receiver is also investigated. The closed-form conditional likelihood of received signals is derived using the Laplace transform and the saddle-point approximation method, and the corresponding quasi-maximum-likelihood (quasi-ML) detector is proposed. Furthermore, the Poisson-Gaussian-distributed signals are converted to Gaussian variables with the aid of the generalized Anscombe transform (GAT), leading to an equivalent additive white Gaussian noise (AWGN) channel, and a hard-decision-based detector is invoked. Simulation results demonstrate that, the proposed GAT-based detector can reduce the computational complexity with marginal performance loss compared with the proposed quasi-ML detector, and both detectors are capable of accurately demodulating the SPAD-based PAM signals
Zero-padded tri-mode index modulation aided OFDM
No full textOrthogonal frequency division multiplexing (OFDM) with index modulation has emerged as a promising complementary technique for next-generation networks due to its high energy efficiency. In this paper, zero-padded tri-mode index modulation aided OFDM (ZTM-OFDM) is proposed, where subcarriers are partitioned into subblocks. Explicitly, only a fraction of subcarriers are utilized for modulation with two distinguishable constellation alphabets in each OFDM subblock, whilst the others remain empty. By such strategy, additional bits can be conveyed by the subcarrier indices corresponding to the two constellation sets (denoted as index pattern). At the receiver, a maximum-likelihood (ML) detector and a two-stage log-likelihood ratio (LLR) detector with reduced complexity are proposed for demodulation. The proposed ZTM-OFDM is capable of enhancing the spectral and energy efficiency compared with other index modulated OFDM schemes. Theoretical analysis based on the minimum Euclidean distance and Monte Carlo simulation results validate that the proposed ZTM-OFDM can attain performance gain over conventional OFDM and other index modulated OFDM schemes.</p
sj-xlsx-1-qjp-10.1177_17470218231178787 – Supplemental material for Assessing lexical ambiguity of simplified Chinese characters: Plurality and relatedness of character meanings
No full textSupplemental material, sj-xlsx-1-qjp-10.1177_17470218231178787 for Assessing lexical ambiguity of simplified Chinese characters: Plurality and relatedness of character meanings by Huilin Chen, Xu Xu and Tianqi Wang in Quarterly Journal of Experimental Psychology</p
Ellipse-based DCO-OFDM for visible light communications
Full text linkEllipse-based DC-biased optical orthogonal frequency division multiplexing (E-DCO-OFDM) is proposed for visible light communications (VLC), which achieves a significant peak-to-average power ratio (PAPR) reduction, thus enhancing the overall performance when light-emitting diode (LED) nonlinearity is considered. In E-DCO-OFDM, the real-valued output of OFDM is modulated onto an ellipse, whereby only the imaginary part of the complex point on the ellipse is transmitted. Although the PAPR of E-DCO-OFDM decreases as the ratio of major radius to minor radius becomes larger, it may be more vulnerable to the effect of noise, leading to the performance loss. Therefore, the relationship between the system performance and the critical parameters in E-DCO-OFDM, such as the ratio between the major and minor radius of the ellipse, is investigated. Meanwhile, simulations demonstrate that E-DCO-OFDM adopting the optimal parameters achieves a considerable signal-to-noise ratio (SNR) gain over the conventional DCO-OFDM
PM-DCO-OFDM for PAPR reduction in visible light communications
No full textPhase modulation is used in DCO-OFDM for visible light communications, whereby around 10 dB PAPR reduction is achieved. Considering the nonlinearity of LED emitters, our proposed method achieves better BER performance than that of conventional DCO-OFDM
Novel index modulation techniques: a survey
No full textIn 5G wireless networks, the escalating teletraffic and energy consumption has necessitated the development of green communication techniques in order to further enhance both the system&#x2019;s spectral efficiency and energy efficiency. In the past few years, the novel index modulation (IM) has emerged as a promising technology that is widely employed in wireless communications. In this paper, we present a survey on IM in order to provide the readers with a better understanding of its principles, advantages, and potential applications. We start with a comprehensive literature review, where the concept of IM is introduced, and various existing IM schemes are classified according to their signal domains, including the frequency domain, spatial domain, time domain and channel domain. Then the principles of different IM-aided systems are detailed, where the transceiver design is illustrated, followed by descriptions of typical systems and corresponding performance evaluation. A range of challenges and open issues on IM are discussed before we conclude this survey.</p
Dual-mode index modulation aided OFDM
No full textIndex modulation has become a promising technique in the context of orthogonal frequency division multiplexing (OFDM), whereby the specific activation of the frequency domain subcarriers is used for implicitly conveying extra information, hence improving the achievable throughput at a given bit error ratio (BER) performance. In this paper, a dual-mode OFDM technique (DM-OFDM) is proposed, which is combined with index modulation and enhances the attainable throughput of conventional index-modulation-based OFDM. Specifically, the subcarriers are divided into several subblocks, and in each subblock, all the subcarriers are partitioned into two groups, modulated by a pair of distinguishable modem-mode constellations, respectively. Hence the information bits are conveyed not only by the classic constellation symbols, but implicitly also by the specific activated subcarrier indices, representing the subcarriers’ constellation mode. At the receiver, a maximum likelihood (ML) detector and a reduced-complexity near optimal log-likelihood ratio (LLR) based detector are invoked for demodulation. The minimum distance between the different legitimate realizations of the OFDM subblocks is calculated for characterizing the performance of DM-OFDM. Then the associated theoretical analysis based on the pairwise error probability is carried out for estimating the BER of DM-OFDM. Furthermore, the simulation results confirm that at a given throughput DM-OFDM achieves a considerably better BER performance than other OFDM systems using index modulation, while imposing the same or lower computational complexity. The results also demonstrate that the performance of the proposed low-complexity detector is indistinguishable from that of the ML detector, provided that the system’s signal to noise ratio is sufficiently high
Chong ke Qin Shaoyou huai hai ji
No full text秦觀撰 ; 李之藻校 ; [王廷俊仝校].綫裝, 1函.框21.3x13.9公分, 9行21字, 小字雙行同. 白口, 左右雙邊, 單黑魚尾. 版心上鐫題名, 中鐫卷次, 下鐫葉次, 並記有刻一及字數.前有萬曆戊午[1618]姚鏞序 ; 序首頁版心下刻"南昌邹天奇刊"見《香港中文大學圖書館古籍善本書錄》(增訂版)(p.229)《長短句》分上, 中, 下卷.鈐"服記圖書", "界雄"印.Xian zhuang, 1 han.Kuang 21.3 x 13.9 gong fen, 9 hang 21 zi, xiao zi shuang hang tong. Bai kou, zuo you shuang bian, dan hei yu wei. Ban xin shang juan ti ming, zhong juan juan ci, xia juan ye ci, bing ji you ke yi ji zi shu.Qian you Wanli wu wu [1618] Yao Yong xu ; xu shou ye ban xin xia ke "Nanchang Zou Tianqi kan"Jian "Xianggang Zhong wen da xue tu shu guan gu ji shan ben shu lu" (zeng ding ban)(p.229)"Chang duan ju" fen shang, zhong, xia juan.Qin Guan zhuan ; Li Zhizao jiao ; [Wang Tingjun tong jiao].Qian "Fu ji tu shu", "Jie xiong" yin
An Efficient Algorithm for 1-Dimensional (Persistent) Path Homology
Full text linkThis paper focuses on developing an efficient algorithm for analyzing a directed network (graph) from a topological viewpoint. A prevalent technique for such topological analysis involves computation of homology groups and their persistence. These concepts are well suited for spaces that are not directed. As a result, one needs a concept of homology that accommodates orientations in input space. Path-homology developed for directed graphs by Grigoryan, Lin, Muranov and Yau has been effectively adapted for this purpose recently by Chowdhury and Mémoli. They also give an algorithm to compute this path-homology. Our main contribution in this paper is an algorithm that computes this path-homology and its persistence more efficiently for the 1-dimensional (H₁) case. In developing such an algorithm, we discover various structures and their efficient computations that aid computing the 1-dimensional path-homology. We implement our algorithm and present some preliminary experimental results
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