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Channel estimation is a key technology in indoor wireless visible light communications (VLCs). Using the training sequence (TS), this paper investigates the channel estimation in indoor wireless visible light communications. Based on the propagation and signal modulation characteristics of visible light, a link model for the indoor wireless visible light communications is established. Using the model, three channel estimation methods, i.e., the correlation method, the least square (LS) method and the minimum mean square error (MMSE) method, are proposed. Moreover, the performances of the proposed three methods are evaluated by computer simulation. The results show that the performance of the correlation method is the worst, the LS method is suitable for higher signal to noise ratio (SNR), and the MMSE method obtains the best performance at the expense of highest complexity.The indoor visible light communiation (VLC) systems [1][2][3] still have many critical issues. Generally speaking, the indoor VLC environment is a confined space and LED is not only used as a lighting device, but also to be used as a communication device. The optical signals of LED travel via different paths and arrive at the receiver at different instances in time [4] . Experimental results have shown that the multipath propagation may cause the inter-symbol-interference (ISI), which will degrade the VLC system performance significantly when the original data rate is high [5] . In order to eliminate the effects of ISI, the instantaneous channel impulse response must be obtained before the recovery of the transmitted information. Obviously, the channel estimation plays a critical role in VLC systems. Refs.[6,7] described an iterative method for infrared channel estimation. However, the effect of the irregular shape of the objects and the human's activity were ignored, which makes the results not suitable for real indoor communication systems. As far as we know, no similar results for channel estimation in VLC systems are available.Since the optical propagation environment is complicated and time-varying, this paper proposes a training sequence (TS)-based channel estimation for indoor VLC systems. Considering the propagation property of light and the characteristics of optical modulation, a mathematical channel model for indoor VLC systems is established. Further, based on the established link model, three channel estimation methods, i.e., the correlation method, the least square (LS) method and the minimum mean square error (MMSE) method, are proposed and evaluated.The intensity modulation and direct detection (IM/DD) modulation is considered for indoor VLC systems, in which the desired waveform is modulated onto the instantaneous power of the carrier and a photo-detector produces a current proportional to the received instantaneous power. The binary information is modulated into "0" and "1". As illustrated in Fig.1, the received signal of the indoor VLC systems is given by [1] OPTOELECTRONICS LETTERS

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Background Enhance recovery after surgery (ERAS) is a new and promising paradigm for spine surgery. The purpose of this study is to investigate the effectiveness and safety of a multimodal and evidence-based ERAS pathway to the patients undergoing anterior cervical discectomy and fusion (ACDF). Methods The patients treated with the ACDF-ERAS pathway were compared with a historical cohort of patients who underwent ACDF before ERAS pathway implementation. Primary outcome was length of stay (LOS). Secondary outcomes included cost, MacNab grading, complication rates and 90-day readmission and reoperation. And perioperative factors and postoperative complications were reviewed. Results The ERAS protocol was composed of 21 components. More patients undergoing multi-level surgery (n ≥ 3) were included in the ERAS group. The ERAS group showed a shorter LOS and a lower cost than the conventional group. The postoperative satisfaction of patients in ERAS group was better than that in conventional group. In addition, the rate of overall complications was significantly higher in the conventional group than that in the ERAS group. There were no significant differences in operative time, postoperative drainage, or 90-day readmission and reoperation. Conclusions The ACDF-tailored ERAS pathway can reduce LOS, cost and postoperative complications, and improve patient satisfaction without increasing 90-day readmission and reoperation.

Impulsive synchronization of chaotic systems is studied in this paper. By exploring the structural knowledge of the systems and using linear matrix inequalities, some less conservative conditions than existing results are derived. With the new conditions, the bound of intervals for transmitting impulses can be increased and this results in higher bandwidth efficiency. Our results are thus able to improve the efficiencies of the existing technologies on chaotic secure communications and chaotic spread communications.

The atmospheric corrosion behaviour of peak aged Mg-5Y-7Gd-1Nd-0?5Zr alloys in typical land (Beijing) and marine (Qingdao) environments were investigated by optical microscopy, SEM and X-ray diffraction. The weight loss rates and residual mechanical properties were analysed. The atmospheric corrosion rates of specimens in a typical marine environment were higher than those in land environment. The results demonstrated that temperature, relative humidity and inorganic salts at field exposed sites played an important role in atmospheric corrosion behaviours. The results of our investigation may find wider applications for Mg-rare earth alloys in atmospheric environments.

Since indoor wireless optical communication (WOC) systems can offer several potential advantages over their radio frequency counterparts, there has been a growing interest in indoor WOC systems. Influenced by the complicated optical propagation environment, there exist multipath propagation phenomena. In order to eliminate the effect of multipath propagation, much attention should be concentrated on the channel estimation in indoor WOC systems. This paper investigates optimal training sequences (TSs) for estimating a channel impulse response in indoor WOC systems. Based on the Cramer–Rao bound (CRB) theorem, an explicit form of search criterion is found. Optimum TSs are obtained and tabulated by computer search for different channel responses and TS lengths. Measured by mean square error (MSE) performance, channel estimation errors are also investigated. Simulation results show that the MSE of the channel estimator at the receiver can be reduced significantly by using the optimized TS set. Moreover, the longer the TS, the better the MSE performance that can be obtained when the channel order is fixed.

Channel estimation is a key technology for wireless optical communication (WOC) systems. Based on the training sequence (TS), this article develops three frequency domain (FD) channel estimation approaches for diffuse wireless optical channels. Considering the propagation property of light and the characteristics of optical modulation, this article establishes a link model for the indoor WOC systems. Using the established link model, three FD channel estimation methods, such as the LS method, the minimum mean square error (MMSE) method and the ORL-MMSE method are proposed. The computational complexity analysis gives time complexities of the three channel estimation methods in FD. This article also evaluates the performance of the proposed three methods by computer simulation, measuring in terms of MSE and BER, respectively. Further more, based on the Cramer-Rao Bound theorem, optimal TSs are found and tabulated for different channel responses and TS lengths. By using the optimal TSs, channel estimation errors measured by BER performance are also investigated.