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Terahertz (THz) wireless communication is envisioned as a promising technology, which is capable of providing ultra-high-rate transmission up to Terabit per second. However, some hardware imperfections, which are generally neglected in the existing literature concerning lower data rates and traditional operating frequencies, cannot be overlooked in the THz systems. Hardware imperfections usually consist of phase noise, in-phase/quadrature imbalance, and nonlinearity of power amplifier. Due to the time-variant characteristic of phase noise, frequent pilot insertion is required, leading to decreased spectral efficiency. In this paper, to address this issue, a novel pilot design strategy is proposed based on index modulation (IM), where the positions of pilots are flexibly changed in the data frame, and additional information bits can be conveyed by indices of pilots. Furthermore, a turbo receiving algorithm is developed, which jointly performs the detection of pilot indices and channel estimation in an iterative manner. It is shown that the proposed turbo receiver works well even under the situation where the prior knowledge of channel state information is outdated. Analytical and simulation results validate that the proposed schemes achieve significant enhancement of bit-error rate performance and channel estimation accuracy, whilst attaining higher spectral efficiency in comparison with its classical counterpart. [ABSTRACT FROM AUTHOR]

Terahertz (THz) communication has emerged as a promising technology that efficiently alleviates the scarcity of the frequency resources, and is capable of providing Terabit-per-second (Tbps) data transmission. However, the hardware impairments, which are usually omitted in the low-rate systems, have a detrimental impact on the THz communication link. These hardware imperfections, including in-phase/quadrature (I/Q) imbalance, phase noise and nonlinearities of the power amplifier, can be approximately modelled as complex-Gaussian distortions at both the transmitter and the receiver. In this paper, the channel estimator and signal detector (CE/SD) design of the THz-band spatial modulation (THz-SM) system is investigated, where the counterparts for classical low-rate SM are no longer applicable. More specifically, a dual-stage maximum-likelihood (ML) channel estimator is proposed containing two phases of candidate acquirement and exhaustive search. Then a novel low-complexity mean-least-squares (MLS) channel estimator is developed by considering the hardware impairments in an averaging manner. Besides, the optimal detector for THz-SM is designed by taking hardware impairments into account. Simulation results validate that the proposed CE/SD design is capable of attaining reliable data transmission in THz-SM with hardware imperfections. [ABSTRACT FROM AUTHOR]

The media-based modulation (MBM) system, which varies its channel state by controlling the on/off status of the radio frequency (RF) mirrors, and embeds additional information bits into the mirror activation pattern, is capable of achieving significant throughput and desirable bit-error-rate (BER) performance. Hence, it has attracted increasing attention from researchers of wireless communication community. In this paper1, the information secrecy issue for MBM is investigated, and a secure single-input-multiple-output MBM (SIMO-MBM) system is proposed utilizing physical-layer security techniques. By considering the time-division duplexing (TDD) mode with channel reciprocity property, the legitimate channel state information (CSI) is applied to secure the data transmission of SIMO-MBM. More specifically, on one hand, adaptive phase rotation is imposed on the transmitted signals, where the rotation angle is determined by the phase of legitimate CSI; on the other hand, the mapping rule between the mirror activation pattern and binary bits is changed according to the amplitude of legitimate CSI. The BER performance of the eavesdropper is investigated via theoretical derivations, and the system secrecy mutual information is also derived, based on which the optimal design of the adaptive phase rotation strategy is provided. Theoretical and simulative results demonstrate that the proposed secure SIMO-MBM system is capable of enhancing the data confidentiality whilst keeping reliable data transmission. [ABSTRACT FROM AUTHOR]

In this letter, resource management (RM) for hybrid wireless communication systems between vehicles and infrastructures is investigated, where radio frequency and visible light communications coexist. Specifically, the RM issue is formulated as an optimization problem of the lower bound of energy efficiency over multiple consecutive data transmission slots, which considers the variations of link availability in high-mobility scenarios and requires merely incomplete channel state information. An RM algorithm is proposed to solve this problem and simulations results demonstrate the energy efficiency enhancement of our proposed algorithm. [ABSTRACT FROM AUTHOR]

Angiotensin I-Converting Enzyme (ACE, CD143) Gene plays a crucial role in the pathology of carcinomas in many cancers including colorectal cancer (CRC). However, the methylation of ACE was rarely reported. In this study, our purpose was to investigate the methylation status of ACE and explored its prognostic value in CRC. The expression of ACE was detected by quantitative real-time polymerase chain reaction (qRT-PCR) analysis while the methylation status of ACE was measured via methylation-specific polymerase chain reaction (MSP). The result demonstrated that ACE expression was up-regulated in tumour tissues and HT-29 cells compared with the controls. ACE was also confirmed to be hypomethylated in CRC. Next, we evaluated the influence of ACE hypomethylation on cell growth. It was proved to be a favourable factor for the cell proliferation, cell colony forming, but an inhibitor for the cell apoptosis of CRC cells according to MST assay, colony forming assay and flow cytometry assay. ACE hypomethylation was also considered to be related to the prognosis of CRC through Cox regression analysis. Taken together, the over-expression of ACE was regulated by its hypomethylation and the ACE hypomethylation might be an independent prognostic indicator in CRC. [ABSTRACT FROM AUTHOR]

The primary objective of this study is to compare pedestrian evacuation strategies in the large-scale public space (LPS) using microscopic model. Data were collected by video recording from Tian-yi square for 36 hours in city of Ningbo, China. A pedestrian evacuation simulation model was developed based on the social force model (SFM). The simulation model parameters, such as reaction time, elasticity coefficient, sliding coefficient, et al, were calibrated using the real data extracted from the video. Five evacuation strategies, strategy 1 (S1) to strategy 5 (S5) involving distance, density and capacity factors were simulated and compared by indicators of evacuation time and channel utilization rate, as well as the evacuation efficiency. The simulation model parameters calibration results showed that a) the pedestrians walking speed is 1.0 ~ 1.5m/s; b) the pedestrians walking diameter is 0.3 ~ 0.4m; c) the frequency of pedestrian arrival and departure followed multi-normal distribution. The simulation results showed that, (a) in terms of total evacuation time, the performance of S4 and S5 which considering the capacity and density factors were best in all evacuation scenarios, the performance of S3 which only considering the density factor was the worst, relatively, and S1 and S2 which considering the distance factor were in the middle. (b) the utilization rate of channels under S5 strategy was better than other strategies, which performs best in the balance of evacuation. S3 strategy was the worst, and S1, S2 and S4 were in the middle. (c) in terms of the evacuation efficiency, when the number of evacuees is within 2, 500 peds, the S1 and S2 strategy which considering the distance factor have best evacuation efficiency than other strategies. And when the number of evacuees is above 2, 500 peds, the S4 and S5 strategy which considering the capacity factor are better than others. [ABSTRACT FROM AUTHOR]

The application of VANET can be divided into two types: security and non-security. Non-secure applications are primarily used to provide entertainment information. Secure applications will provide information to the driver in advance. Therefore, the delay and reliability of communication are strictly required for secure applications. In this paper, we propose a kind of demand-aware medium access control protocol based on multichannel cooperation in vehicular ad hoc networks. First, the scheme uses RSU (the roadside unit) to broadcast the secure query packets, and the node sends the emergency information of the vehicle node through the advance reservation control slot. Then, time slot will be divided dynamically according to the demand of the secure data, and each node will be coordinated by RSU to reduce the collision probability and safe data packet delay. The simulation results show that the proposed medium access control scheme can improve the network throughout and reduce the end-to-end transmission delay compared with the traditional 802.11p protocol. [ABSTRACT FROM AUTHOR]

Dual-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 enhancements, the spectral efficiency can be improved at the cost of marginal performance loss. Moreover, since the bit error rate performance of GDM-OFDM degrades at low signal-to-noise ratios, an interleaving technique is employed to address this issue. At the receiver, a maximum-likelihood detector and a reduced-complexity log-likelihood ratio detector are employed for demodulation. Simulation results demonstrate that the proposed GDM-OFDM is capable of enhancing the spectral efficiency compared with DM-OFDM at the cost of negligible performance loss, and the interleaved GDM-OFDM can harvest on performance gain over GDM-OFDM. [ABSTRACT FROM PUBLISHER]