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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.

In this paper, we consider the fundamental and most studied non-coherent differential chaotic shift keying system under a pulse jamming environment. We devote our effort to propose a novel correlation receiver with nonlinearity blanking for the considered system to improve its anti-jamming performance. In addition and importantly, we also propose a mathematical framework to derive an optimal blanking threshold for the proposed receiver. The proposed nonlinearity blanking mechanism basically blocks the received signals with a larger amplitude than the blanking threshold, while the signals with a smaller amplitude are not affected at all. We then show that the proposed receiver with optimal blanking threshold significantly outperforms the conventional correlation counterpart.

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

Ventricular fibrillation and ventricular tachycardia (VF/VT), known as shockable (SH) rhythms, are the mainly cause of sudden cardiac arrests (SCA), which is cured efficiently by the automated external defibrillator (AED). The performance of the shock advice algorithm (SAA) applied in the AED has been improved by using machine learning technique and variously conventional features, recently. In this paper, we propose a novel algorithm with relatively high performance for the SCA detection on electrocardiogram (ECG) signal. The algorithm consists of a convolutional neural network as a feature extractor (CNNE) and a Boosting (BS) classifier. A grid search with nested 5-folds cross validation (CV) is used to select the CNNE trained with preprocessed ECG, SH, and NSH signals using the modified variational mode decomposition technique. The deep feature vector learned by this CNNE is extracted at the first fully connected layer and then fed into BS classifier to validate its performance using 5-folds CV procedure. The secondary learning of the BS classifier and the use of three input channels for the CNNE improve certainly the detection performance of the proposed SAA with the validated accuracy of 99.26%, sensitivity of 97.07%, and specificity of 99.44%.

Sudden cardiac arrest is mainly caused by ventricular fibrillation and ventricular tachycardia, which are known as shockable rhythms. In this paper, a detection algorithm of shockable rhythms including support vector machine (SVM) model uses the public electrocardiogram (ECG) databases for training and testing. The databases are the Creighton University Ventricular Tachyarrhythmia Database (CUDB) and the MIT-BIH Malignant Ventricular Arrhythmia Database (VFDB). At first, to compose a set of good features, we extend a well-known set of 2 good features such as Count2 and VF-filter Leakage Measure (Lk). We supplemented 5 more good features, selected based on a binary genetic algorithm-based feature selection, among 11 new input candidate features. All the combinations of 7 good features are estimated for their performance on the training and the testing data using the SVM models to identify 6 combinations of the final feature pool. 5-Folds cross validation is then implemented carefully to validate the performance of the SVM classifier using final feature pool on separated and entire 5s-segment databases. The final combination of 4 features, which includes Count2, Lk, Threshold Crossing Interval (TCI), and Centroid Frequency (CF), is addressed by the highest validation performance of the corresponding SVM model. The Count2 shows the proportion of the signal, which is above the mean absolute values of the output of an integer coefficient recursive bandpass filter computed for every 1 s time interval. The Lk represents the output of a narrow bandstop filter, which is applied to the ECG signal with the central frequency being the mean signal frequency. The TCI shows the average time between the fixed thresholds, which are computed for every 1s-segment using the pulses converted from the ECG signal. The CF is the frequency, which bisects vertically the area under the power spectrum. For the proposed algorithm, the average accuracy of 95.9%, sensitivity of 91.7%, and specificity of 96.8% are archived on the evaluation data of the entire database. Comparing to the performance of the SVM model using a combination of the Count2 and the Lk, we report a significant improvement for the accuracy of the SVM model using the final feature combination in average, i.e. 2.6%, 22.4%, and 2.7% on the evaluation data of the entire database, the CUDB, and the VFDB, respectively. Furthermore, existence of ventricular ectopic beats in the input data shows a negligible influence on the final performance of classification.

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%.

We propose a novel TH-NRDCSK system to enjoy the advantages of both TH and chaotic systems for AJ communication purpose and alleviate the strict synchronization issue of TH systems. We then simulate the performance of the proposed system to reveal the effects of the system parameters on AJ performance. In addition, the performance of the proposed system is compared to that of the TH-BPSK system to look at the advantages of non-coherent system. The simulation results show that the proposed system significantly outperforms conventional counterparts in a practical environment.

In this work, we consider an advanced noise reduction differential chaotic shift keying (NR-DCSK) system in which a single antenna source communicates with a single antenna destination under the attack of a single antenna jammer. We devote our efforts to design a novel anti-jamming (AJ) receiver for the considered system. Particularly, we propose a variational mode decomposition-independent component analysis-wavelet packet decomposition-based (VMD-ICA-WPD-based) structure, in which the VMD method is firstly exploited to generate multiple signals from the single received one. Secondly, the ICA method is applied to coarsely separate chaotic and jamming signals. After that, the WPD method is used to finely estimate and mitigate jamming signals that exist on all outputs of the ICA method. Finally, an inverse ICA procedure is carried out, followed by a summation, and the outcome is passed through the conventional correlation-based receiver for recovering the transmitted information. Simulation results show that the proposed receiver provides significant system performance enhancement compared to that given by the conventional correlation-based receiver with WPD, i.e. 8 dB gain at BER =0.03 and Eb/N0 = 20 dB., 5 pages, 5 figures

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 a cooperative non-orthogonal multiple access system with radio frequency energy harvesting, in which a user with good channel harvests energy from its received signal and serves as a decode-and-forward relay for enhancing the performance of a user with poor channel. We here aim at maximizing the weighted sum rate of the system by optimizing the power allocation coefficient used at the source and the power splitting coefficient used at the user with good channel. By exploiting the specific structure of the considered problem, we propose a low-complexity one-dimensional search algorithm which can provide optimal solution to the problem. As a benchmark comparison, we derive analytic expressions and simple high signal-to-noise ratio (SNR) approximations of the ergodic rates achieved at two users and their weighted sum with fixed values of the power allocation and the power splitting coefficients, from which the scaling of the weighted sum in the high SNR region is revealed. Finally, we provided numerical results to demonstrate the validity of the optimized scheme. Index Terms-Cooperative NOMA, RF-energy harvesting, weighted sum rate analysis and optimization., Comment: 5 pages, 3 figures

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.

In this paper, we consider an overlay cognitive radio network, in which a secondary transmitter (ST) is willing to relay the information of a primary transmitter toward a primary receiver. In return, ST can access the licensed band to send its own information superimposed with the primary signal to a secondary receiver. The power-limited ST uses a power splitting protocol to harvest energy from its received signal to increase its transmit power. We analyze the performance of the primary and the secondary systems under independent Nakagami- ${m}$ fading by deriving their corresponding outage probabilities in integral-based expressions. In addition, by considering the high signal-to-noise ratio, we obtain very tight closed-form approximations of the outage probabilities. Thereafter, by further analyzing the approximations, we reveal novel insights on the diversity orders and coding gains of the two systems. Our analytical results are validated through extensive Monte-Carlo simulations.

This paper investigates the anti-jamming performance of the NR-DCSK system. We consider several practical jamming environments including broad-band jamming (BBJ), partial-time jamming (PTJ), tone jamming (TJ) consisting of both single-tone and multi-tone, and sweep jamming (SWJ). We first analytically derived the bit error rates of the considered system under the BBJ and the PTJ environments in closed-form expressions. Our derived results show that the system performances under these two jamming environments are enhanced as $P$ increases, where $P$ is the parameter of the NR-DCSK modulation scheme denoting the number of times a chaotic sample is repeated. In addition, our results demonstrate that for the PTJ, the optimal value of the jamming factor is close to zero when the jamming power is small, however, it increases and approaches one as the jamming power enlarges. We then investigate the performance of the considered system under the TJ and the SWJ environments via Monte-Carlo simulations. Our simulations show that single-tone jamming causes a more significant performance degradation than that provided by multi-tone jamming counterparts. Moreover, we point out that the system performance is significantly degraded when the starting frequency of the sweep jammer is close to the carrier frequency of the transmitted chaotic signals, the sweep bandwidth is small, and the sweep time is half of the transmitted bit duration., Comment: 7 pages, 8 figures

After the first success with SigmaK3 [1], we have designed and developed the second 8-bit microprocessor chip, dubbed HN-07, with high performance and additional features. HN-07is based on the original Sigmak3 architecture with a number of improved features, namely 5-stage pipeline architecture, interrupt controller, more on-chip peripherals, higher operational stability and frequency. This improved architecture makes HN-07 microprocessor equivalent with others such as Intel 8051, Microchip PIC, etc. Our complete design, from front-end through back-end stages, has been taped out and supplied to an overseas foreign foundry for trial fabrication. Further detail on the evaluation of its performance will be reported in the future.

This paper investigates single relay selection problem for secure communication in a cooperative system with multiple full-duplex decode-and-forward relays, in which an eavesdropper may overhear the source confidential message through relays' transmission. We propose an opportunistic relay selection scheme which selects the relay that maximizes the system secrecy capacity. We then evaluate performance of the proposed scheme in terms of secrecy outage probability. As a comparison, we also derive the secrecy outage probability of the conventional Max-Min relay selection scheme proposed for full-duplex relaying systems without the existence of eavesdroppers. We show that our proposed scheme outperforms the conventional counterpart. Our analytic derivations are also extensively verified by Monte-Carlo simulations.

In this work, we consider the relay selection (RS) method for an Amplify-and-Forward (AnF) relaying system in multi-cell environments. The selection scheme aims to maximize the instantaneous received signal-to-noise and interference ratio (SINR). We propose an idea of combining RS with interference cancellation (IC) at the receiver. Furthermore, we analyze the system outage probability performance with the proposed scheme. We use approximation approach to simplify the derivation of the probability distributed function (PDF) of the received SINR. The system outage probability bound is also given. Simulation results validate our analysis, and show that our scheme greatly improves the system outage probability as well as bit-error-rate (BER) performances.

In this paper, the behavior of relay networks in interference environments is investigated. It has been shown that the effect of interference during Amplify-and-Forward process at relays bounds the diversity slope of the system at a well-defined static point. Moreover, the conventional relay selection criteria are also shown to be inefficient. To help our systems to improve its performance, the power allocation issue is taken into account with relay selection. However, solving a jointly optimization problem, optimizing transmitted power and maximizing the received SNR corresponding with the potential relay simultaneously, are difficult. In other words, it requires high complexity manipulation procedures. By proposing a power allocation and a relay selection separately, then combining these two methods, we form a new relay selection with power allocation-based mechanism that is less complex and has comparable performance with the optimal process.

Loop-interference (LI) from relay transmission to reception reduces the channel capacity and makes the relay system unstable in full-duplex (FD) multi-input multi-output (MIMO) relay systems. conventional schemes to suppress LI still have drawbacks: 1) incur a dispensable signal-to-noise ratio (SNR) loss in low SNR regions; 2) increase the system complexity due to the requirement of weighting matrices; and 3) make insufficient practical sense due to varying signal-to-interference ratios (SIRs). In this paper, we propose a new LI suppression scheme using transmit antenna selection in order to solve the above problems. Simulation results show that the proposed scheme outperforms a conventional scheme, especially in low SNR and high SIR regions, even though the proposed scheme has a lower complexity.