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Although investigating performances of existing chaotic communication systems (CCSs) and proposing new CCSs have been extensively investigated, designing antijamming (AJ) receivers for CCSs has been rarely considered. AJ receivers for CCS are of paramount importance in cases that the inherent AJ capability of CCSs does not work well, i.e., when the power of jamming signals is larger than that of chaotic signals. Motivated by this fact, in this article, we consider a differential chaos shift keying (DCSK) system under a Gaussian pulse jamming condition. We propose an AJ receiver with a hybrid blanking-clipping mechanism to enhance the AJ performance of the considered system. We also derive closed-form expressions of the signal-to-interference-plus-noise of the outputs of the blanking and clipping blocks, which are then to be used to obtain optimal blanking and clipping thresholds for additive white Gaussian noise (AWGN) channel. Moreover, an optimal weighting factor used for combining the outputs of the blanking and clipping blocks is also provided. We show that the proposed receiver considerably outperforms existing receivers.

Ultra wideband impulse (UWB) radars are getting much attention in the application of remote sensing of heart rate. UWB radar measures the heart rate by mean of the motion of thorax in the heartbeat activities. However, the signal of heartbeat is usually much smaller than the harmonics signal of respiration, then be easily perturbed. Thus, this paper proposed a multivariate correlation method (MCM) to improve the signal-to-noise ratio (SNR) of the heartbeat. The MCM is applied in the bandwidth of higher harmonics rather than the fundamental of heart rate to minimize the affection of the respiration signal. The experiments showed that the second harmonic of heart rate is good at minimizing the affection of the respiration signal, and the MCM is efficient to improve the SNR about 83.7 dB than the continuous wavelet transform method. The heart rate could be estimated with an average error of 2.54% compared with a referenced photoplethysmography sensor.

We consider the problem of designing waveforms for mitigating single tone jamming (STJ) signals with an estimated jamming frequency in time-hopping spread spectrum (TH SS) systems. The proposed design of waveforms optimizes the anti-jamming (AJ) performance of TH SS systems by minimizing the correlation between the template and STJ signals, in which the problem of waveform optimization is simplified by employing a finite number of rectangular pulses. The simplification eventually makes the design of waveforms be converted into a problem of finding eigenvalues and eigenvectors of a matrix. Simulation results show that the waveforms designed by the proposed scheme provide us with performance superior not only to the conventional waveforms but also to the clipper receiver in the mitigation of STJ. The waveforms from the proposed design also exhibit a desirable AJ capability even when the estimated frequency of the STJ is not perfect.

Time hopping spread spectrum (THSS) system and chaotic system have been studied as candidates of the anti-jamming (AJ) systems with substantial advantages. However, THSS systems suffer from the strict synchronization prerequisite. In order to overcome the shortcomings of the THSS system and utilize the profits of the non-coherent chaotic system, we first propose a novel TH-NRDCSK system to enhance the bit error rate (BER) performance of the conventional non-coherent THSS system and relieve the strict synchronization issue of coherent THSS systems. Then, we analyze the performance of the proposed system under additive white Gaussian noise (AWGN) channel and jamming environment. Finally, we implement the simulation to demonstrate the consistency of the analysis and the simulation results and to disclose the effects of the system parameters on system's AJ performance. Moreover, the performance of the proposed system is compared to that of conventional counterparts to look at the benefits of integrating chaotic and THSS systems. The simulation results show that the proposed system significantly outperforms conventional counterparts in a practical environment.

Due to the broadcast nature of wireless medium, wireless communication is highly vulnerable to eavesdropping attack. Traditionally, secure wireless data transmission has relied on cryptographic techniques at the network layer which incur high computational power and complexity. As an alternative, physical layer security (PLS) is emerging as a promising paradigm to protect wireless systems by exploiting the physical characteristics of the wireless channels. Among various PLS approaches, the one based on cooperative communication is favorable and has got a lot of interest from the research community. Although PLS schemes with half-duplex relays have been extensively discovered, the issue of PLS in cooperative systems with full-duplex (FD) relays is far from being comprehensively understood. In this paper, we first present the state of the art on PLS approaches proposed for FD cooperative systems. We then provide a case study in which a source-based jamming scheme is proposed to enhance the secrecy performance of a cooperative system with an untrusted FD relay. Finally, we outline several interesting yet challenging future research problems in this topic., Comment: 7 pages, 7 figures, 1 table

Sudden cardiac arrests are mainly caused by ventricular fibrillation and ventricular tachycardia, which are known as shockable (SH) rhythms and properly curable by electronic defibrillators. In this paper, we propose a novel algorithm to decide whether an electrocardiogram (ECG) signal is SH or nonshockable (NSH). The algorithm selects 20 features from both the preprocessed ECG and its NSH signal using a modified variational mode decomposition technique, and uses the support vector machine for the binary SH/NSH classification. The 20 features are identified as an efficient set of the most informative, among 54 candidate features, by comparing the balanced error rate of each combination, based on two layers of feature selection. This feature set is validated with the evaluation data in the public database using a fivefolds cross validation procedure. The proposed algorithm results in accuracy of 99.00%, sensitivity of 97.36%, and specificity of 99.16%.

For cooperative systems, in which an eavesdropper overhears source information through relays' transmission, an optimal relay selection (ORS) scheme has recently been proposed to improve the system secrecy performance. In this letter, we evaluate the secrecy outage probability (SOP) of the ORS scheme with an amplify-and-forward system over independent and non-identically distributed Rayleigh fading. More specifically, we derive a tight approximation on the SOP. Thereafter, by analyzing asymptotic behaviour of the derived approximation, novel insights are revealed. The derivations are confirmed through Monte Carlo simulations.

We consider the inefficiencies of conventional multimedia broadcast multicast systems (CVM) limited by the user with worst signal-to-noise-ratio (SNR) and we present a novel technique based on amortized weighted averaging (AWG) of users' SNR. We model the system using ordered statistics of exponential and uniform distribution and derive statistics for the density functions. We then apply the modelling results to study the performance of wireless multicasting over Rayleigh fading channels. More specifically, we obtain the outage probability and mean capacities for broadcast and multicast systems. Finally we compare our proposed scheme with the conventional scheme. Numerical results show that proposed AWG is reliable, avoids outage, accommodates more users and is more efficient than the conventional multicasting especially in the low SNR region.

The relay selection method is a promising technique for improving the performance of cooperative systems. Most of the existing studies assume that wireless channels are statistically independent. However, in reality, channel correlation is more likely to be non-negligible. In this study, we investigate the dependence of the performance of cooperative systems with single relay selection in equally correlated environments. A tight upper bound of the system outage probability is given as a function of the channel correlation coefficients. We show that even though the system performance is considerably degraded in the high signal-to-noise ratio (SNR) region when the channel correlations are sufficiently large, yet less than one, the system still achieves a diversity order equal to the number of available relays.