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Orthogonal frequency division multiplexing (OFDM), as a form of multicarrier modulation, has been popularly studied for underwater acoustic communication. Impulse noise and large scale single frequency noise often exist in the received signal in the ocean experiments, and the noise interference will degrade the performance of the communication system. This paper focuses on the OFDM performance in the presence of both impulse noise and large scale single frequency noise. One novel method is proposed to estimate impulse noise and large scale single frequency noise separately. Furthermore, based on the proposed approaches, joint impulse noise and large scale single frequency noise is investigated in OFDM receivers. Simulated results and experimental results are both shown that the two proposed schemes are more practical in underwater acoustic communication.

Summary Aims Deep-vein thrombosis (DVT) represents a serious complication in acute stroke patients with pulmonary embolus (PE) as a potential outcome. Prediction of DVT may help with formulating a proper prevention strategy. To assess of the risk of deep venous thrombosis (DVT) in acute stroke patients, we developed and validated a clinical score in a cohort study. Methods Incidence of Deep Venous Thrombosis after Acute Stroke in China (INVENT-China) is a multicenter prospective cohort study. The potential predictive variables for DVT at baseline were collected, and the presence of DVT was evaluated using ultrasonography on the 14 ± 3 days. Data were randomly assigned to either a training data set or a test data set. Multivariate logistic regression analysis was used to develop risk scores to predict DVT in the training data set and the area under the receiver operating characteristic curve to validate the score in the test data set. Results From 2006–2007, 862 hospital-based acute stroke patients were enrolled in China. The overall incidence of DVT after acute stroke within two weeks was 12.4% (95%CI 10.3–14.7%). A seven-point score derived in the training data set (age [≥65 years = 1], sex [female gender = 1]), obesity [BMI ≥ 25 kg/m2 = 1], active cancer [yes = 2], stroke subtype [cerebral hemorraghe = 1], muscle weakness [≥2 on Lower limb NIHSS score = 1] was highly predictive of 14-day risk of DVT(c statistic = 0.70, 95% CI, 0.64–0.76, P

Studies have shown that awareness of early stroke symptoms and the use of ambulances are two important factors in decreasing pre-hospital stroke delay. The purpose of this study is to evaluate a comprehensive educational stroke protocol in improving stroke response times.Two urban communities in Beijing (population ≍50 000), matched in economic status and geography, were enrolled in this study. A comprehensive educational protocol, which included public lectures and distribution of instructive material for the community and its medical staff, was implemented from August 2008 to December 2010. Surveillance of new onset stroke in both communities was carried out during the same period. Pre-hospital delay time and percentage of patients using emergency medical services (EMS) were compared between the two communities.After comprehensive educational protocol, we found that: (i) pre-hospital delay (time from stroke symptom onset to hospital arrival) decreased from 180 to 79 minutes, (ii) the proportion of patients arriving within three hours of stroke onset increased from 55·8% to 80·4%, (iii) pre-hospital delay of stroke patients with symptoms of paralysis, numbness, and speech impediments was decreased, and (iv) the proportion of stroke patients calling for EMS increased from 50·4% to 60·7%.The comprehensive educational stroke protocol was significantly effective in decreasing pre-hospital stroke delay.

Background and purposeEarly and accurate diagnosis of stroke by emergency medical service (EMS) paramedics is critical for reducing pre-hospital delays. The Los Angeles pre-hospital stroke screen (LAPSS) has been widely used as a validated screening tool for early identifying stroke patients by EMS paramedics. However, validation of LAPSS has never been performed in Chinese stroke population. This study is aimed to verify the LAPSS for early identifying stroke patients in a Chinese urban EMS.Methods76 paramedics of five urban first aid stations attached to Beijing 120 EMS were involved. The paramedics were trained by professionals to quickly screen patients based on LAPSS. Potential "target stroke" individuals who met the base LAPSS screen criteria were identified. Sensitivity and specificity analyses of the LAPSS were calculated.ResultsFrom June 10, 2009 to June 10, 2010, paramedics transported a total of 50,220 patients. 1550 patients who met the baseline screen criteria were identified as the potential "target stroke" population. 1130 patients had the completed LAPSS information datasheet and 997 patients were clinically diagnosed with stroke. The average time of completing the LAPSS was 4.3±3.0 minutes (median, 5 minutes). The sensitivity and specificity of the LAPSS in this study was 78.44% and 90.22%, respectively. After adjusting for age factor by excluding patients of >45 years old, the sensitivity was significantly increased to 82.95% with specificity unchanged.ConclusionThe paramedics of Beijing 120 EMS could efficiently use LAPSS as a screening tool for early identifying stroke patients. While the sensitivity of LAPSS in Chinese urban patient population was lower than those reported in previous LAPSS validation studies, the specificity was consistent with these studies. After excluded the item of "Age>45 years", the sensitivity was improved.

Multicarrier modulation in the form of orthogonal frequency division multiplexing (OFDM) has been actively studied for underwater acoustic communications. In this paper, we investigate the OFDM performance in the presence of impulselike noises. We present one method that estimates the carrier frequency offset (CFO) and the impulse noise separately, based on existing approaches, and one method that estimates them jointly. Simulation results in both time-invariant and time-varying channels have verified the receiver performance.

In this paper, we consider an underwater data collection problem, where multiple underwater nodes need to send data to one common destination. With the conventional ARQ protocol, the destination requests retransmission from each node individually without any node cooperation. We propose two protocols, selective relay cooperation and dynamic network coded cooperation, utilizing the fact that underwater nodes can overhear the transmission of others. In the selective relay cooperation, one node can be selected as a relay to transmit the data from another undecoded node in the retransmission round. In the network coded cooperation, the selected relay nodes transmit network coded packets, combining the packets from several undecoded nodes to the destination. The relay nodes participating the cooperation are selected by the destination based on the measured pilot signal to noise ratio of the underlying OFDM modulation. Simulation results based on one specific underwater topology show that the proposed schemes can achieve significant gains compared with the conventional ARQ scheme.

Transform domain communication system (TDCS) has been proposed as a new kind of anti-jamming communication system, which has the advantages of the adaptive interference avoiding capability under adverse electromagnetic environments. To avoid the interference spectral regions, the system synthesizes the fundamental modulation waveform (FMW) in the transform domain rather than in the time domain at both the transmitter and the receiver. Based on the architecture of TDCS, this paper presents a fractional Fourier domain communication system (FRFDCS) for the broadband interference suppression, especially for the linear frequency modulation (LFM) jammer. It has been demonstrated that by choosing the order of the fractional Fourier transform (FRFT) optimally, the LFM signal has the best localization and energy concentration in the fractional Fourier domain. Therefore, the LFM jammer can be identified and suppressed accurately in the FRFDCS. The numerical results indicate that the FRFDCS achieves lower bit error rate (BER) and larger channel capacity comparing to the conventional TDCS. Moreover, by virtue of its flexibility and adaptive interference avoiding capability, the FRFDCS can be regarded as a potential candidate for the reliable communication system and the cognitive radio technology.

Intensive control of the risk factors of stroke and the pre-hospital delay after stroke onset both depend on the level of knowledge of stroke in the general population. Our primary objective was to assess the public knowledge about stroke among urban residents in four cities in China.A semi-structured interview and questionnaire was delivered in a survey. Standardized risk factor and symptom statements were used to measure knowledge. The setting of two communities from four different cities of China was used to target a mix of social class and geography. Using systematic sampling and the household as a unit, at least 300 households were chosen in one community. Each household selected one person to fill in the self-designed questionnaire. Uniform training of community physicians was conducted before the survey, and the community physicians completed the survey by face to face indoor-investigation.Total integral questionnaires numbered 2519. The investigation showed that (1) hypertension was identified as a risk factor by nearly 90% of residents. Dyslipidemia, smoking, diabetes, and non-modifiable risk factors were identified by less than 65%; (2) medical therapy of hypertension and diabetes was known by nearly 80% of residents, and the awareness of lifestyle modification was less; (3) weakness or numbness were the most common symptoms identified by community residents (80.2%), and the awareness of other symptoms of stroke ranged from 58.2 to 71.2%; (4) the stroke knowledge score and education level were positively correlated (r(s) = 0.088, P0.001), and age was negatively correlated (r(s) = -0.142, P0.001); (5) 53.0% of residents would call an emergency medical system once stroke symptoms began; (6) the main sources of information about stroke were television (74.4%), doctors (63.2%) and newspapers (61.8%).At present, the urban community residents in China are lacking in knowledge about stroke. Going forward, we should strengthen health education through television, medical staff, newspapers, magazines. Targeted educational populations should be directed at those who are elderly, lower education, male and high risk.

Transform domain communication system (TDCS) and wavelet domain communication system (WDCS) have been reported to have interference avoiding capability under adverse environmental conditions. These systems achieve low probability of intercept (LPI) and orthogonality simultaneously by using the pseudorandom (PR) sequences for generating the phase vector of the basic function. Conventionally, the PR phase vectors in TDCS and WDCS were generated by a maximal length binary PR sequence (m-sequence), which allows only a relatively small number of users in the systems. This paper reports a method to increase the user capacity of TDCS and WDCS by applying Gold sequence to generate the PR phase vector of the basic function. The increased user capacity of the systems based on Gold sequence is tabulated. Simulation results also demonstrate that by using Gold sequences for the PR phase generation, both TDCS and WDCS can provide a comparable interference avoiding capability with a larger user capacity, compared to those of the systems based on m-sequences in multiple access environments.

The frequency response of real weight digital FIR filters used in traditional time domain broadband beamforming structure can't fit the design requirements well when the ratio of communication band to central frequency is large. This may result in mainbeam aberration and increasing of sidelobe level. In order to solve this problem, a time domain broadband beamforming structure with complex weight digital FIR filters is presented. Also a digital FIR filter design algorithm is proposed and this algorithm is used to design the complex weight FIR filters. Computer simulation is done when the ratio of central frequency to communication band is 0.8 and the results show: the frequency responses of the filters designed by the proposed algorithm fit the requirements well inside the communication band (the error of amplitude responses is less than 0.3dB and the error of phase responses is less than 0.1rad)

In recent years cooperative diversity has been widely used in wireless network, and Orthogonal frequency division multiplexing (OFDM) is a key technique of multi-carrier transmission to meet high data rate requirement of wireless communication. The aim of this project is to combine the technology of OFDM with cooperative diversity techniques, in this project, we have done simulation in matlab and compare the performances of the system while the cooperation node employs AF cooperative scheme contrast with DF cooperative scheme. The simulation results show that the OFDM system with Cooperative Diversity has a better performance when the cooperation node employs DF cooperative scheme.

Orthogonal Frequency Division Multiplexing (OFDM) is well known as a very attractive technology for communication. However, because of the spectral leakage in discrete Fourier transform, the spectrum of narrowband interference is spreaded to impact adjacent sub-carriers in OFDM system. Receiver window function was previously implemented to suppress narrow-band interference. In this paper, different kinds of receiver window functions were compared in the underwater acoustic OFDM system. The results of simulation and experiment show that the raised cosine window can suppress NBI and reduce the BER.

Detecting driver fatigue is an important method to improving transportation safety. This paper presents a fatigue detection system based on pupil detection and yawning analysis. The parameters used for detecting fatigue are: eye closure duration measured through eye state information and yawning analyzed through mouth state information. Because of the IR illuminator, the system works robustly at night time.

A PSK space-time receiver based on beam diversity technology is proposed. The receiver combined the adaptive beam forming technology based on training sequence with multi-channel equalizer. Channel estimation method is used to obtain the current multi-path structure. Then a set of beams pointing to different incident directions of multi-path signals are formed in order to obtain the SNR gain and decrease ISI. Then space diversity method is used to combine the outputs of these beams, and the diversity gain is finally obtained. Simulation results with a 12-element array show that: in the case of complex multi-path channel structure, JPAM receiver get 3–4dB SNR gain compared to the PSK receiver which only used the adaptive beamforming technology.

The DFT-SOFDM is a high speed underwater acoustic communication technology even for underwater military communication. In this paper, different kinds of modulation schemes were compared in the underwater acoustic DFTSOFDM communication system. The comparison results in real underwater acoustic channels showed that, when the underwater acoustic channels were static, each scheme had the same BER performance; when the channels were changing quickly, the BER performances of different modulation scheme were different.

The DFT-SOFDM is a high date rate underwater acoustic transmission scheme even for underwater military communication. It has been widely studied to overcome the complexity of underwater acoustic channels. Generally speaking, multi-carrier transmission systems have many obvious advantages. They are less sensitive to impulsive noise than single-carrier systems. The longer symbol duration provides an advantage in a presence of impulsive noise. Nevertheless, it was recently recognized that this advantage turns into a disadvantage, if the impulsive noise energy exceeds a certain threshold. In this paper, nonlinearity methods for impulsive noise suppression in DFT-SOFDM receivers are considered. The experimental results of this comparative study show that the blanking nonlinearity performs better than the clipping nonlinearity.

Recently, multicarrier modulation in the form of orthogonal frequency division multiplexing (OFDM) has been actively investigated in underwater acoustic communications for its effective algorithms to handle the channel time-variability. In order to improve the performance of the underwater acoustic OFDM communication system, the irregular repeat accumulate (IRA) code as a channel coding scheme is proposed in this paper. We analyzed the effect of parameters of the IRA code on the performance of the system. Computer simulation has been implemented and the sea trial has been carried out in shallow water acoustic channels near Xiamen port. The simulation results show that the IRA coding scheme has improved the SNR (signal noise ratio) performance of the system at range of 14dB to 16dB compared with the system without coding and the BER performance of the IRA code will get improvement with the increase of the code length and the iteration of decoding to a certain degree, and then tends to stable. Field test experiment results obtained with the IRA code are provided, demonstrating the feasibility of the proposed channel coding for underwater acoustic OFDM communication system.

Deep venous thrombosis (DVT) is a common complication in acute stroke. Evidence-based guidelines recommend the use of prophylactic heparins in patients with risk of DVT. We aimed to evaluate the clinical practices for DVT prophylaxis in acute stroke inpatients enrolled in a multicenter observational longitudinal study on deep venous thrombosis (Incidence of Deep Venous Thrombosis after Acute Stroke in China, INVENT-China).Patients' characteristics and DVT prophylaxis was extracted from the database of INVENT-China. Appropriate adherence to the guidelines was analysed.Six hundred and fifty-six patients with acute stroke were eligible for analysis in this study. Pharmacologic prophylaxis with low-molecular-weight heparins (LMWH) was applied to 18 patients with ischemic stroke (3.4%) and one patient with cerebral hemorrhage. Independent factors associated with use of prophylactic anticoagulant treatment were stroke subtype (OR=0.07, 95% CI=0.01-0.78, p=0.03), baseline NIHSS score (OR=0.25, 95% CI=0.07-0.95, p=0.04), baseline motor leg function (NIHSS score) (score=1, OR=0.16, 95% CI=0.03-0.79, p=0.025; score=2, OR=0.20, 95% CI=0.05-0.84, p=0.028; score=3, OR=0.23, 95% CI=0.06-0.91, p=0.037; score=4, reference), diabetes mellitus (OR=3.86, 95% CI=1.39-10.72, p=0.009), malignancy (OR=9.55, 95% CI=1.98-46.2, p=0.005), varicose veins (OR=12.48, 95% CI=1.64-94.9, p=0.015) and central venous catheterization (OR=6.96, 95% CI=1.36-35.79, p=0.02).Thromboprophylaxis is inadequate in acute stroke inpatients in China. Guidelines for prevention DVT in acute stroke should be established and efforts should be made to improve venous thromboembolism prophylaxis practice.

Based on our previous work, a novel design of a carrier interferometry (CI) orthogonal frequency division multiplexing (OFDM) system had been tested in a real underwater acoustic channel - the experimental pool in Xiamen University. Since the CI/OFDM system is very sensitive to phase offsets, a simplified 2D estimator is used to reconstruct the channel response at the receiver. The performance of the CI/OFDM and OFDM underwater acoustic communication systems had been compared based on Peak-to-average power ratio (PAPR) and BER characteristics. Experiment results showed that the CI/OFDM underwater acoustic communication system could achieve excellent performance.

In this paper, we present a method of transform-domain channel estimation for orthogonal frequency division multiplexing (OFDM). The estimator based on minimum mean squared error (MMSE), and a process of FFT and IFFT is added. The system has been tested in a real underwater acoustic channel - the experimental pool in Xiamen University. The experimental result shows that the transform-domain channel estimation has improved the performance of the OFDM system in underwater acoustic channels.

This paper presents a method to detect weak harmonic signal embedded in chaotic 'noise'. Since harmonic signal and chaotic signal have different correlation characteristic ,we can transform the mixed signal to a new data sequence, which has new harmonic signal. The new harmonic signal's frequency is in proportion to the harmonic signal to be detected and it's frequency is beyond the center bandwidth of other elements . Then we can detect the weak harmonic signal on the basis of extended empirical mode decomposition (EEMD). The method is also suit for the situation which background signals is mixture of chaotic signal and strong Gaussian white noise. The Simulation experiments show that the method is effective and feasible.

BackgroundStudies show tranexamic acid can reduce the risk of death and early neurological deterioration after intracranial haemorrhage. We aimed to assess whether tranexamic acid reduces haematoma expansion and improves outcome in intracerebral haemorrhage patients susceptible to haemorrhage expansion.MethodsWe did a prospective, double-blind, randomised, placebo-controlled trial at 10 stroke centres in China. Acute supratentorial intracerebral haemorrhage patients were eligible if they had indication of haemorrhage expansion on admission imaging (eg, spot sign, black hole sign or blend sign), and were treatable within 8 hours of symptom onset. Patients were randomly assigned (1:1) to receive either tranexamic acid or a matching placebo. The primary outcome was intracerebral haematoma growth (>33% relative or >6 mL absolute) at 24 hours. Clinical outcomes were assessed at 90 days.ResultsOf the 171 included patients, 124 (72.5%) were male, and the mean age was 55.9±11.6 years. 89 patients received tranexamic acid and 82 received placebo. The primary outcome did not differ significantly between the groups: 36 (40.4%) patients in the tranexamic acid group and 34 (41.5%) patients in the placebo group had intracranial haemorrhage growth (OR 0.96, 95% CI 0.52 to 1.77, p=0.89). The proportion of death was lower in the tranexamic acid treatment group than placebo group (8.1% vs 10.0%), but there were no significant differences in secondary outcomes including absolute intracranial haemorrhage growth, death and dependency.ConclusionsAmong patients susceptible to haemorrhage expansion treated within 8 hours of stroke onset, tranexamic acid did not significantly prevent intracerebral haemorrhage growth. Larger studies are needed to assess safety and efficacy of tranexamic acid in intracerebral haemorrhage patients.