Non-zero Delay Research Articles

Estimation of available bandwidth for an [formula omitted] queueing system

This paper is concerned with estimating the available bandwidth, the residual processing capacity, of a single-server queueing system whose service rate and the input traffic load are not known in advance. We analyze the minimal-backlogging method which has been proposed to estimate the available bandwidth by sending probing packets. We show that an M / G / 1 queueing system probed by the minimal-backlogging method is stable. A consistent estimator of the inverse of available bandwidth is proposed based on the sojourn times of the probing packets. We also estimate the available bandwidth of a local server which is connected to the probing node with non-zero delay as an application of the theory developed for a single-server queue. We evaluate the accuracy of the proposed available bandwidth estimation scheme by simulation.

Improved cardiac performance through pacing-induced diaphragmatic stimulation: a novel electrophysiological approach in heart failure management?

Pharmacological conditioning of the phrenic nerve can positively influence systolic performance, and diaphragm activation improves ventilatory function. Here we investigate whether pacing-induced diaphragmatic stimulation (PIDS) may improve left ventricular (LV) systolic function. We studied a total of 35 patients (4 females, mean age 67 +/- 9 years, ejection fraction 61 +/- 14%) within 7 days following open heart surgery. The haemodynamic impact of different PIDS and ventricular pacing configurations and coupling intervals was tested in 132 episodes. Success of PIDS was assessed using fluoroscopy and palpation. Left ventricular systolic performance was recorded using the electromechanical activation time (EMAT) obtained through acoustic cardiography. Eighteen subjects were tested in the catheter laboratory and 17 in the intensive care unit. For both groups, EMAT significantly improved when the diaphragm was stimulated 20 ms after the onset of ventricular pacing. In all instances, PIDS could be induced with or without causing patient symptoms, and LV systolic performance improvement was comparable in symptomatic and asymptomatic modes. No desensitization of the diaphragm was observed following PIDS delivery 4-6 and 24 h following open heart surgery. Pacing-induced diaphragmatic stimulation, if synchronized to the onset of ventricular contraction with a fixed, non-zero coupling delay, can improve LV systolic function reproducibly for at least 1 h without causing patient symptoms. The absence of diaphragm desensitization further underscores the potential of PIDS as a practical therapeutic approach in device-based heart failure management.

Statistical Properties of First-Order Bang-Bang PLL With Nonzero Loop Delay

A method to solve the stationary state probability is presented for the first-order bang-bang phase-locked loop (BBPLL) with nonzero loop delay. This is based on a delayed Markov chain model and a state flow diagram for tracing the state history due to the loop delay. As a result, an eigenequation is obtained, and its closed form solutions are derived for some cases. After obtaining the state probability, statistical characteristics such as mean gain of the binary phase detector and timing error variance are calculated and demonstrated.

Phase-Shift keyed wideband signal against noises detection by quadrature receiver with input band-pass filter

In this paper we consider wideband signal against noise receiving by quadrature correlation receiver with input band-pass filter. We obtain analytical expressions of detection characteristics. We analyzed dependences of correct receiving on delay time, signal-to-noise ratio and input filter bandwidth. It is shown, that maximal probability of signal detection is obtained in case of non-zero delay time of received signal, which depends on filter bandwidth.

Heteroclinic cycles between unstable attractors

We consider networks of pulse coupled linear oscillators with non-zero delay where the coupling between the oscillators is given by the Mirollo–Strogatz function. We prove the existence of heteroclinic cycles between unstable attractors for a network of four oscillators and for an open set of parameter values.

Robustness of unstable attractors in arbitrarily sized pulse-coupled networks with delay

We consider arbitrarily large networks of pulse-coupled oscillators with non-zero delay where the coupling is given by the Mirollo–Strogatz function. We prove that such systems have unstable attractors (saddle periodic orbits whose stable set has non-empty interior) in an open parameter region for three or more oscillators. The evolution operator of the system can be discontinuous and we propose an improved model with continuous evolution operator.

Queueing Analysis for GBN and SR ARQ Protocols under Dynamic Radio Link Adaptation with Non-Zero Feedback Delay

We present a queueing model for performance analysis of go-back-N (GBN) and selective repeat (SR) automatic repeat request (ARQ) protocols in wireless networks using dynamic radio link adaptation with non-instantaneous feedback. Link adaptation technique allows multi-rate transmission which is assumed to be achieved through adaptive modulation and coding. The radio link level queueing models for these two ARQ protocols are formulated in discrete time where the exact queue length and the delay statistics are obtained by using matrix geometric methods under different feedback delay values, channel and system parameters. The link layer delay statistics are useful in many ways, for example, to perform packet level admission control under statistical delay constraints. We validate the analysis by simulation and discuss useful implications of the analytical model on system performance. For dynamic link adaptation, the mode switching thresholds for the received signal-to-noise ratio (SNR) can be chosen to obtain very good link level delay performance. This SNR partitioning is shown to achieve significant cross-layer design gain compared to the case where the mode switching thresholds are chosen to maximize the physical layer throughput.

Output effect of a quadrature receiver with an input band-pass filter at reception of a phase-keyed wideband signal

An output effect of a quadrature correlation receiver with an input band-pass filter at reception of a phase-keyed wideband signal is considered. Analytical expressions for output effect of a receiver proportional to the absolute value of a complex envelope of a cross-correlation function for received and reference signals are obtained. Dependences of cross-correlation function absolute value on a time delay, frequency mismatch of a received and reference signals, and passband width of input filter are analyzed. It is shown, that cross-correlation function’s maximum is reached in case of non-zero time delay of a received signal when there is no frequency mismatch between input and reference signals. The time delay value corresponding to cross-correlation function’s maximum depends on passband width of input filter.

Asymptotic Performance for Delayed Exponential Process

The damped and delayed sinusoidal (DDS) model can be defined as the sum of M sinusoids whose waveforms can be damped and delayed. This model is suitable for compactly modeling short time events. This property is closely related to its ability to reduce the time-support of each sinusoidal component. In this correspondence, we derive exact and approximate asymptotic Crameacuter-Rao bounds (CRBs) for the DDS model. This analysis shows that this model has better, or at least similar, theoretical performance than the well-known exponentially damped sinusoidal (EDS) model. In particular, the performance in the DDS case is significantly improved compared to that of the EDS for closely spaced sinusoids thanks to the nonzero time delays. Consequently, we can exploit the advantageous properties of the DDS model and, in the same time, we can keep high theoretical model parameter estimation accuracy

Training delays reduce the choose-short effect with keylight, but not with food, duration samples in pigeons

Pigeons were trained to match 2- and 8-s food samples. The delay on training trials was either 0s (group 0sF), 5s (group 5sF), or varied between 2 and 8s (M=5s, group 5sV). Testing at a delay that exceeded the training delay by 15s in each group revealed a robust choose-short effect in each group. The same pigeons then reacquired a previously trained matching task involving 2- and 8-s keylight samples. Different comparison stimuli were used on food-sample and keylight-sample trials. The delay on training trials was the same on both food- and keylight-sample trials. Extended-delay testing revealed a robust choose-short effect in all three groups when the durations were conveyed by food presentations, but only group 0sF revealed a choose-short effect when the durations were conveyed by keylight presentations. Hence, training with a nonzero delay, whether fixed or variable, reduces the choose-short effect with keylight durations but not with food durations. It was concluded that at least some of the psychological processes mediating performance differ as a function of the event that conveys the duration.

Feasibility of Velocity Selective Arterial Spin Labeling in Functional MRI

Arterial spin labeling (ASL) magnetically inverts or saturates the spins in arterial blood and uses them as endogenous tracers. Conventionally, the tagging band is upstream or nonselective to the target slices. In the brain, ASL-based functional magnetic resonance imaging (fMRI) has been shown to detect activation better localized in gray matter than blood oxygenation level dependent contrast. More recently, velocity selective-ASL (VS-ASL) was proposed to tag spins according to their flow velocity. One desirable characteristic of VS-ASL is its capability to generate tags sufficiently close to the target slices and thereby circumvent the complication of non-zero transit delay. In this study, we investigate the feasibility of VS-ASL in fMRI by comparing it with a conventional ASL method (PICORE). The results from the visual cortex of healthy volunteers show that VS-ASL and PICORE have comparable spatial specificity in detecting the flow change induced by neuronal activity. Velocity selective-arterial spin labeling can further distinguish the contribution from different flow directions but spurious elevation of fractional signal change may occur when the VS tagging is applied off the direction of blood supply. The flow reaches the vicinity of perfusion at a cutoff velocity (Vc) of 2 cm/sec whereas the activation exclusively detected by Vc=4 cm/sec implies the arteriolar response to the neuronal activity and a respondent vessel diameter up to 240 microm. Velocity selective imaging can remove intravascular signal from the vessels where the flow velocity is above Vc.

Tumour Oscillation Analysis in Angiogenesis Models

In this paper we describe Hopf point analysis for several systems of ordinary and time delay differential equations which encode the most important assumptions concerning anguigenesis processes induced by tumours It is shown that in most cases Hopf points exist only if time delays are nonzero and for most nonzero time delays there are Hopf points in these families of models.

Upper semi continuity of attractors of delay differential equations in the delay

It is shown that if a retarded delay differential equation has a global attractor in the space C ([—τ0, ], ℝd) for a given nonzero constant delay τ0, then the equation has an attractor Aτ in the space C ([—τ, 0], ℝd) for nearby constant delays τ. Moreover the attractors Aτ converge upper semi continuously to in C ([—τ0, 0], ℝd) in the sense that they are identified through corresponding segments of entire trajectories in ℝd with nonempty compact subsets of C ([—τ0, 0], ℝd) which converge upper semi continuously to in C ([—τ0, 0], ℝd).

Training delays reduce the choose-short effect with keylight duration samples in pigeons

Pigeons were trained to matching 2- and 8-s keylight samples. The delay on training trials was either 0s (group 0sF), 2s (group 2sF), or varied between 1 and 3s (M=2s, group 2sV). Testing at delays of 10 and 20s revealed a choose-short tendency in all three groups. The magnitude of this tendency was largest in group 0sF and was highly similar in magnitude in groups 2sF and 2sV. In Experiment 2, the training delay remained at 0s in group 0sF and was increased to 5s in group 2sF (now group 5sF). Group 2sV (now group 5sV) received variable training delays ranging from 2 to 8s (M=5s). Testing at a 20-s delay and at a delay that exceeded the training delay by 15s for each group revealed a robust choose-short effect only in group 0sF. Groups 5sF and 5sV both demonstrated a weak and statistically nonsignificant choose-short tendency. When different durations of keylight are employed as samples, training with a nonzero delay, whether fixed or variable, reduces the magnitude of the choose-short effect, with longer training delays producing a greater reduction in the choose-short effect.

Stability of linear systems with time-varying delays: A direct frequency domain approach

The stability of linear systems with uncertain bounded time-varying delays (without any constraints on the delay derivatives) is analyzed. It is assumed that the system is stable for some known constant values of the delays (but may be unstable for zero delay values). The existing (Lyapunov-based) stability methods are restricted to the case of a single non-zero constant delay value, and lead to complicated and restrictive results. In the present note for the first time a stability criterion is derived in the general multiple delay case without any constraints on the delay derivative. The simple sufficient stability condition is given in terms of the system matrices and the lengths of the delay segments. Different from the existing frequency domain methods which usually apply the small gain theorem, the suggested approach is based on the direct application of the Laplace transform to the transformed system and on the bounding technique in L 2 . A numerical example illustrates the efficiency of the method.

Sensitivity Analysis of Handoff Algorithms on CDMA Forward Link

We analyze the performance of different handoff algorithms on the forward link or downlink of a code-division multiple-access (CDMA) cellular system. Unlike the reverse link, soft handoff on the forward link requires additional resources such as CDMA codes and transmit power and also causes additional interference. If handoff requests can be processed and completed instantaneously, transmission from the base station with the best link to the user would achieve a significant fraction of the macrodiversity gain without utilizing additional resources. However, in practical systems, there is a nonzero handoff completion delay and soft handoff provides the required robustness to delays, although it comes at the expense of additional network resources. Thus, there is a tradeoff between the extent of soft handoff required and the handoff execution delay. We compare the performance of hard and soft handoff schemes and study their sensitivity to the delay in the execution of the handoff. Outage probability and the total average power required are used as performance metrics. We present an analytical framework to study this tradeoff and also discuss simulation results with field data. The results provide insights on the conditions under which soft handoff can be eliminated and on the effect of relevant handoff thresholds on the performance.

An Algorithm for Verifying Biventricular Capture Based on Evoked‐Response Morphology

Cardiac resynchronization therapy relies on consistent beat-by-beat myocardial capture in both ventricles. A pacemaker ensuring right (RV) and left ventricular (LV) capture through reliable capture verification and automatic output adjustment would contribute to patients' safety and quality of life. We studied the feasibility of an algorithm based on evoked-response (ER) morphology for capture verification in both the ventricles. RV and LV ER signals were recorded in 20 patients (mean age 72.5 years, range 64.3-80.4 years, 4 females and 16 males) during implantation of biventricular (BiV) pacing systems. Leads of several manufacturers were tested. Pacing and intracardiac electrogram (IEGM) recording were performed using an external pulse generator. IEGM and surface-lead electrocardiogram (ECG) signals were recorded under different pacing conditions for 10 seconds each: RV pacing only, LV pacing only, and BiV pacing with several interventricular delays. Based on morphology characteristics, ERs were classified manually for capture and failure to capture, and the validity of the classification was assessed by reference to the ECG. A total of 3,401 LV- and 3,345 RV-paced events were examined. In the RV and LV, the sensitivities of the algorithm were 95.6% and 96.1% in the RV and LV, respectively, and the corresponding specificities were 91.4% and 95.2%, respectively. The lower sensitivity in the RV was attributed to signal blanking in both channels during BiV pacing with a nonzero interventricular delay. The analysis revealed that the algorithm for identifying capture and failure to capture based on the ER-signal morphology was safe and effective in each ventricle with all leads tested in the study.

Dynamics of oscillations in a multi-dimensional delay differential system

We consider a system of delay differentialequations$\dot x_i(t)=F_i(x_1(t),\ldots,x_n(t),t)-$ sign $x_i(t-h_i),\quad i=1,\ldots,n,$with positive constant delays $h_1,...,h_n$ and perturbations$F_1,...,F_n$ absolutely bounded by a constant less than 1. Thisis a model of a negative feedback controller of relay typeintended to bring the system to the origin. Non-zero delays do notallow such a stabilization, but cause oscillations around zerolevel in any variable. We introduce integral-valued relativefrequencies of zeroes of the solution components, and show thatthey always decrease to some limit values. Moreover, for anyprescribed limit relative frequencies, there exists at least an$n$-parametric family of solutions realizing these oscillationfrequencies. We also find sufficient conditions for the stabilityof slow oscillations, and show that in this case there existabsolute frequencies of oscillations.

A Continuous-Time>tex<$Sigma Delta $>/tex<Modulator With 88-dB Dynamic Range and 1.1-MHz Signal Bandwidth

This paper presents the design and experimental results of a continuous-time /spl Sigma//spl Delta/ modulator for ADSL applications. Multibit nonreturn-to-zero (NRZ) DAC pulse shaping is used to reduce clock jitter sensitivity. The nonzero excess loop delay problem in conventional continuous-time /spl Sigma//spl Delta/ modulators is solved by our proposed architecture. A prototype third-order continuous-time /spl Sigma//spl Delta/ modulator with 5-bit internal quantization was realized in a 0.5-/spl mu/m double-poly triple-metal CMOS technology, with a chip area of 2.4 /spl times/ 2.4 mm/sup 2/. Experimental results show that the modulator achieves 88-dB dynamic range, 84-dB SNR, and 83-dB SNDR over a 1.1-MHz signal bandwidth with an oversampling ratio of 16, while dissipating 62 mW from a 3.3-V supply.

Sensitivity analysis of a nonlinear lumped parameter model of HIV infection dynamics

A formal sensitivity analysis is performed on a delay differential equation model for the viral dynamics of an in vivo HIV infection during protease inhibitor therapy. We present results of both a differential analysis as well as a principle component based analysis and provide evidence that suggests the exact times at which specific parameters have the most influence over the solution. We offer insight into the pairwise mathematical relationships between the productively infected T-cell death rate δ, the viral plasma clearance rate c, and the time delay τ between infection and viral production as they relate to the viral dynamics. The results support the claim that the presence of a nonzero delay has a major impact on the model dynamics. Lastly, we comment upon the inadequacies of an alternative principle component based analysis.