Channel Delay Research Articles

Secret Key Generation From Route Propagation Delays for Underwater Acoustic Networks

With the growing use of underwater acoustic communications and the recent adoption of standards in this field, it is becoming increasingly important to secure messages against eavesdroppers. In this paper, we focus on a physical-layer security solution to generate sequences of random bits (keys) between two devices (Alice and Bob) belonging to an underwater acoustic network (UWAN); the key must remain secret to a passive eavesdropper (Eve) not belonging to the UWAN. Our method is based on measuring the propagation delay of the underwater acoustic channel over multiple hops of the UWAN: this harvests the randomness in the UWAN topology and turns the slow sound propagation in water into an advantage against eavesdropping. Our key generation protocol includes a route discovery handshake, whereby all UWAN devices at intermediate hops accumulate their message processing delays. This enables Alice and Bob to compute the actual propagation delays along each route and to map such information to a sequence of bits. Finally, from these bit sequences, Alice and Bob obtain a secret key. We analyze the performance of the protocol theoretically and assess it via extensive simulations and field experiments.

A Novel Muscle Innervation Zone Estimation Method Using Monopolar High Density Surface Electromyography.

This study presents a novel method to estimate a muscle's innervation zone (IZ) location from monopolar high density surface electromyography (EMG) signals. Based on the fact that 2nd principal component coefficients derived from principal component analysis (PCA) are linearly related with the time delay of different channels, the channels located near the IZ should have the shortest time delays. Accordingly, we applied a novel method to estimate a muscle's IZ based on PCA. The performance of the developed method was evaluated by both simulation and experimental approaches. The method based on 2nd principal component of monopolar high density surface EMG achieved a comparable performance to cross-correlation analysis of bipolar signals when noise was simulated to be independently distributed across all channels. However, in simulated conditions of specific channel contamination, the PCA based method achieved superior performance than the cross-correlation method. Experimental high density surface EMG was recorded from the biceps brachii of 9 healthy subjects during maximum voluntary contractions. The PCA and cross-correlation based methods achieved high agreement, with a difference in IZ location of 0.47 ± 0.4 IED (inter-electrode distance = 8 mm). The results indicate that analysis of 2nd principal component coefficients provides a useful approach for IZ estimation using monopolar high density surface EMG.

A collaborative channel gain and delay estimation algorithm based on dynamic state space model

In order to overcome the serious impact of the presence of fading and sensing delay factors in the channel on the performance of spectrum sensing, a novel joint channel gain and sensing delay algorithm is proposed in this paper. A dynamic state space model is constructed to establish the relationship between the PU state, the dynamic fading channel state and the perceived delay. The channel gain can be obtained by means of hidden Markov chain and maximum a posteriori probability. Moreover, the perceived delay value can be obtained by random walk model and sequential particle filtering method. The performance evaluation performed by simulation shows that the algorithm is able to eliminate the uncertainty information in the signal, and the spectrum sensing performance and the sensing delay are significantly improved.

A collaborative channel gain and delay estimation algorithm based on dynamic state space model

A collaborative channel gain and delay estimation algorithm based on dynamic state space model

Wireless Channel Delay Spread Performance Evaluation of a Building Layout

Wireless Channel Delay Spread Performance Evaluation of a Building Layout

Enhanced Frequency Stability of SAW Yarn Tension Sensor by Using the Dual Differential Channel Surface Acoustic Wave Oscillator.

This paper presents a 60 MHz surface acoustic wave (SAW) yarn tension sensor incorporating a novel SAW oscillator with high-frequency stability. A SAW delay line was fabricated on ST-X quartz substrate using the unbalanced-split electrode and bi-directional engraving slots. The dual differential channel delay linear acoustic surface wave oscillator is designed and implemented to test yarn tension, which can effectively remove the interference of temperature, humidity, and other peripheral factors through differential design. The yarn tension sensor using the surface acoustic wave has high-precision characteristics, and the SAW delay line oscillator is designed to ensure the test system’s stable operation. The effect of time and tension on oscillator frequency stability is studied in detail, and the single oscillator and the dual differential channel system were tested, respectively. After using the dual differential channel system, the short-term frequency stability from is reduced from 1.0163 ppm to 0.17726 ppm, the frequency accuracy of the tension sensor is improved from 134 Hz to 27 Hz, and the max frequency jump steady is reduced from 2.2395 ppm to 0.45123 ppm.

Pilot-based channel estimation in spatial modulated OFDM systems for mobile wireless applications

Spatial modulation Orthogonal Frequency Division Multiplexing (SM OFDM) is a newly developed transmission technique that has been proposed as an alternative for multiple input multiple output (MIMO)-OFDM transmission. Channel estimation is important for coherent data detection in practical scenarios. This paper investigates estimate power, Mean Square Error (MSE) and Bit Error Rate (BER) parameter metrics with channel estimation algorithm for Additive White Gaussian Noise (AWGN) and Rayleigh fading channel on three test environments proposed by International Telecommunication Union (ITU) specified standard model. Simulation output shows that for an AWGN channel, an improvement of approximately 1 dB and 0.3 dB power is obtained with Minimum Mean Square Error (MMSE) estimate and Least Square (LS)-linear/Spline using DFT. Additionally, for various interpolations employed, MSE decreases as Signal to Noise Ratio (SNR) rises, and performance improvement in BER when compared to traditional LS/MMSE estimators also occurs. For Rayleigh fading channel also there arises an enhanced performance in the parameter metrics with MMSE-DFT compared to conventional estimators. In summary, simulation output shows that incorporating DFT algorithm can provide better estimate power, BER and MSE by eliminating the effect of noise externally the extreme channel delay length.

A secure event-based quantized networked control system

This paper focuses on network time delay, network congestion, and network security in the networked control system. A secure event-based quantized networked control system (SEQNCS) is proposed to address these problems. The predictive method in the SEQNCS actively compensates time delay both in the forward channel and feedback channel according to the previous states and control inputs. Both the event-driven strategy and quantizer are introduced into the SEQNCS to alleviate network congestion by the event trigger conditions and quantization density. The encrypted encoding quantizer is constructed in the SEQNCS to implement the protection of data security under deception attacks while quantifying the transmitted data. The proposed SEQNCS achieves desired system performance of the networked control system under time delay and deception attacks while alleviating network congestion. The stability of the SEQNCS is proved by the piecewise linear model approach. Practical experiments are implemented to demonstrate the effectiveness of the proposed SEQNCS.

Overview of networked supervisory control with imperfect communication channels

This paper presents an overview of the networked supervisory control frameworks for discrete event systems with imperfect communication networks, which are divided into the centralized setup, the decentralized setup and the distributed setup. The state-of-the-art works on networked supervisory control of discrete-event systems addressing the channel imperfections that are caused by channel delays, data losses or non-FIFO channels are discussed. By presenting the key concepts and main results of each representative work, we analyze the pros and cons of different approaches. Finally, we also provide a summary of the existing works, which roughly follow two different lines of thinking and result in two different verification or synthesis approaches. The first approach utilizes simple, non-networked plant models but relies on the development of sophisticated concepts of network controllability and observability to capture network imperfections, while the second approach embeds relatively complex yet verifiable channel models into the model of the networked plant and adopts the standard concepts of controllability and observability for the (verification and) synthesis of networked supervisors. Some future research topics are also presented.

Nonlinear Analysis of the Car-Following Model considering Delay under the V2X Environment

This paper proposes a model that analyzes the delay effect in V2X communication. V2X technology in the intelligent transportation system can realize the exchange of information between vehicles, people, and the environment. Still, more V2X links occupy many channel resources, and the occupation of channel resources leads to longer communication delays. Therefore, based on the optimal velocity of the car-following model, we model the channel delay in the V2X environment. The stability analysis results show that delay increases lead to system instability and traffic congestion. However, if more links are established, that is, the number of vehicles in the vehicle group ahead increases, traffic jams are less likely to occur. The numerical simulation results show that the longer the delay, the more serious the traffic congestion. In addition, we find an apparent phase transition region in the numerical simulation results, which is consistent with the theoretical analysis results. Therefore, in the intelligent transportation system, the delay caused by the complex electromagnetic environment is a factor that cannot be ignored, and thus the allocation of spectrum resources needs to be reasonably arranged. Otherwise, the V2X technology leads to traffic congestion.

Use of augmented reality for remote control of mobile robots in the presence of time delays in data transmission channels

The paper is devoted to the teleoperation of ground mobile robots in extreme conditions. The presence of time delays in information transmission channels has a significant impact on the efficiency of control. The total delay values can range from hundreds of milliseconds to units of seconds. Sufficiently large values are the reasons for the loss of stability of control systems. To reduce the negative impact of delays, it is proposed to use a method of supporting the operator, which consists in superimposing information about the robot's position on the image received from the video camera and displayed on the control panel at the moment when it receives the generated commands. The position calculation uses the fact that telemetry and command transmission delays are generally much less than video transmission delays. The proposed method is simple, requires a minimum amount of computing resources and can be implemented as a part of low-cost robotic systems. The presented simulation results demonstrate the effectiveness of the method.

Compensation of output external disturbances for a class of linear systems with control delay

The paper considers the problem of the output external unknown disturbance compensation under unmeasurable state vector for a class of linear systems with the control channel delay. It is assumed that the disturbance is the output of an autonomous linear generator. A special observer was built to estimate the disturbance. A system with an extended state vector is formed on the base of the observer’s estimates. A controller that provides disturbance compensation is proposed. An algorithm for the output external disturbances compensation for a class of linear systems with input delay is presented. This method does not require identification of disturbance parameters. The performance of the proposed algorithm was confirmed using computer simulation in the MATLAB Simulink software. The developed algorithm can be effectively applied to a class of problems related to rocking compensation in ship systems, control of robotic complexes various kinds, etc.

Optimized channel prediction and auction‐based channel allocation for personal cognitive networks

SummaryCognitive networks are stands out as intelligent technology which evolved to enhance spectrum utilization. Secondary users are allowed to utilize the primary user's frequency bands on idling times. Identifying the idle licensed spectrum is achieved through spectrum sensing. The spectrum holes should be explored such that a suitable spectrum can be selected and allocated to the secondary users. Existing spectrum sensing and selection schemes have limitations due to interferences. Thus, an optimization algorithm based on bio‐inspired improved weed optimization was presented in this research work for enhanced channel utilization. The optimization model explores the channel characteristics and reduces the primary network interferences through its optimal solution. Further, Markov greedy‐based auction scheme was presented for channel allocation. Considering the channel capacity, delay, and switching rates the allocation is performed to enhance the overall system performance. Simulation analysis demonstrates the superior performance of the proposed model over existing techniques like particle swarm optimization and genetic algorithm.

Моделирование широкополосной шумовой помехи в системах адаптивной пространственной фильтрации радиосигналов

To investigate the characteristics of adaptive spatial filtering systems of radio signals, the simulation of signals and interferences is widely used. In such a simulation, it is usually assumed that the propagation time of the interference wave along the antenna system is much less than the interference correlation time. In this case, the interference is narrowband in the space-time sense. If this condition is not met, then to correctly determine the characteristics of the system, it is necessary to simulate an interference that is broadband in the space-time sense. Such a model should take into account the differences in the complex envelopes of the interference in the antenna-receiving channels, due to the delay caused by the difference in the propagation time of the wave. The paper describes an algorithm for simulation broadband noise interference, based on the using spectrum of the complex envelope of the interference with different delays in the antenna-receiving channels. The listing of the MATLAB function implementing the proposed algorithm is given. To test the model, the autocorrelation and cross-correlation functions of the interference were obtained. The interference spectrum at the output of the adaptive spatial filter, the radiation pattern, and the amplitude-frequency response were obtained as well. The test results confirm the correctness of the developed model.

Cell-Free Massive MIMO Meets OTFS Modulation

We provide the first-ever performance evaluation of orthogonal time frequency space (OTFS) modulation in cell-free massive multiple-input multiple-output (MIMO) systems. To investigate the trade-off between performance and overhead, we apply embedded pilot-aided and superimposed pilot-based channel estimation methods. We then derive a closed-form expression for the individual user downlink and uplink spectral efficiencies (SEs) as a function of the numbers of APs, users and delay-Doppler domain channel estimate parameters. Based on these analytical results, we also present new scaling laws that the AP’s and user’s transmit power should satisfy, to sustain a desirable quality of service. It is found that when the number of APs, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$M_{a}$ </tex-math></inline-formula> , grows without bound, we can reduce the transmit power of each user and AP proportionally to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1/M_{a}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1/M_{a}^{2}$ </tex-math></inline-formula> , respectively, during the uplink and downlink phases. We compare the OTFS performance with that of orthogonal frequency division multiplexing (OFDM) at high-mobility conditions. Our findings reveal that, OTFS modulation with embedded pilot-based channel estimation provides up to 20-fold gain over the OFDM counterpart in terms of 95%-likely per-user downlink SE. Finally, with superimposed pilot-based channel estimation, the increase in the uplink sum SE is more pronounced when the channel delay spread is increased.

In-Body to On-Body Channel Characterization and Modeling Based on Heterogeneous Human Models at HBC-UWB Band

In this work, the in-body to on-body (IB2OB) channel characteristics of the ultrawideband (UWB) link from 10 to 50 MHz at the human body communication (HBC) band are studied for developing high-speed and large-capacity intrabody wireless communication systems. Incorporating the time-domain finite integration technique (FIT) with three types of anatomical human models (adult male, adult female, and teenager) and a simple geometric human model with homogeneous or multilayer biological tissues, the 10–50-MHz signal propagation characteristics are investigated, and a comprehensive path loss model is proposed based on typical in-body links of the heart, brain, and intestine to the on-body sensor nodes. The statistical results show that a linear regulation term related to the surface wave propagation should be added to construct a more accurate logarithmic-distance path loss model in the sense of least-mean-square error (LMSE), indicating that the surface wave propagation mechanism can describe the 10–50-MHz signal propagation more accurately. The shadow fading in decibel is normally distributed around the mean path loss with a standard deviation in the range of 7–9 dB. And the average group delay of the IB2OB channel fluctuates around 0–7 ns, illustrating that the channel can be approximated as a linear phase response. Moreover, the experimental verification is conducted with a tissue-equivalent liquid phantom and an adult man, demonstrating the validity of our proposed statistical path loss model. The key parameters for channel characterization in simulations and measurements are summarized to provide useful insights for HBC-UWB communication system design and performance analysis.

Robust networ ccontrol of an arm manipulator to time delays

Feedback control systems with network as information channels between sensors and between controllers and actuators, are called Network Control Systems (NCS). Network in the loop makes the analysis and design of a proper controller quite different from the traditional ones. Controllers for MIMO plants with wireless communication channels have different type of problems as to compete for the network resources, losses of data packages and presence of communication delays. This work deals with the problem of delays present in the feedback system. Various methodologies have been proposed to deal with the problem of network induced delays which depends on the nature of the delay as: constant, continuous discrete and random delays, and in MIMO systems independent channel delays This paper deals with design of a robust H∞ controller for a MIMO system with time delays limited to an interval, such as obtain a close loop system satisfy robust stability and robust performance specifications in ample ranges of time delays. The method is applied to a three degree of freedom arm manipulator.

Frequency-Packed Faster-Than-Nyquist Signaling via Symbol-Level Precoding for Multiuser MISO Redundant Transmissions

This work addresses the issue of interference generated by co-channel users in downlink multi-antenna multicarrier systems with frequency-packed faster-than-Nyquist (FTN) signaling. The resulting interference stems from an aggressive strategy for enhancing the throughput via frequency reuse across different users and the squeezing of signals in the time-frequency plane beyond the Nyquist limit. The spectral efficiency is proved to be increasing with the frequency packing and FTN acceleration factors. The lower bound for the FTN sampling period that guarantees information losslesness is derived as a function of the transmitting-filter roll-off factor, the frequency-packing factor, and the number of subcarriers. Space-time-frequency symbol-level precoders (SLPs) that trade off constructive and destructive interblock interference (IBI) at the single-antenna user terminals are proposed. Redundant elements are added as guard interval to cope with vestigial destructive IBI effects. The proposals can handle channels with delay spread longer than the multicarrier-symbol duration. The receiver architecture is simple, for it does not require digital multicarrier demodulation. Simulations indicate that the proposed SLP outperforms zero-forcing precoding and achieves a target balance between spectral and energy efficiencies by controlling the amount of added redundancy from zero (full IBI) to half (destructive IBI-free) the group delay of the equivalent channel.

A method for delay estimation between channels of Analog to Information Converters

Analog to Information Converters (AIC) implements signal acquisition in Compressed Sensing. AIC performance is affected by noise and hardware imperfections. In parallel Random Modulator Pre-Integrator (RMPI) architectures, delay among channels reduces the performance; thus, delay estimation and compensation methods are necessary. In previous works, delay estimation compares a reference signal with a reconstructed signal from the AIC output; however, such methods produce different results according to the recovery method. To avoid this problem, we present a method based on a controlled delay signal to estimate channel delay without the necessity of signal recovery. The obtained results show the technique's feasibility and the possibility of its use as a built-in calibration process for AIC.

Energy-Efficient Power and Subcarrier Allocation in Downlink OFDMA Systems with Channel Estimation Errors

In this paper, we investigate the joint optimization of power and subcarrier allocation for maximizing the energy efficiency (EE) in downlink OFDMA systems. The problem of EE maximization is formulated as a stochastic optimization to determine the optimal power and subcarrier allocation, in which many practical factors including channel estimation errors, delay requirements, and time-varying channel are considered. We first propose a dynamic power and subcarrier allocation (DPSA) algorithm to solve the formulated problem. Then, we derive the two bounds of EE and delay and reveal the tradeoff between them. The theoretical analysis and simulation results demonstrate the variations of EE and delay with channel estimation errors.