Analytical Markov Model Research Articles

Investigation of Multiparameter Routing Processes Based on the Markov's Analytical Model

Background: The numerical decision systems of the nonlinear equations for a preset network, traffic and conditions of functioning allows to implement determination of a probability-time characteristics of a network, carry out a rating of used algorithms of routing, methods of streams control. Analysis: This paper is devoted to the problems of investigation of routing processes in large distribution systems. Findings: The identification of parameters of model of the routing process close to best values is possible during a repetitive process of search of the solution of a system of nonlinear equations. Conclusion: Multi-parameter routing process based on Markov’s model can be successfully used while routing traffic within big networks.

APDM: An adaptive multi-priority distributed multichannel MAC protocol for vehicular ad hoc networks in unsaturated conditions

Vehicular ad hoc networks (VANETs) employ multichannel to provide a variety of safety and non-safety applications. Safety applications require reliable and timely transmission, while non-safety applications need high network throughput. IEEE 802.11p and IEEE 1609.4 protocol divide the bandwidth into seven channels. One control channel (CCH) is to serve safety applications and the other six service channels (SCHs) to serve non-safety applications. The IEEE 1609.4 protocol specifies an alternating scheme to allow vehicles to switch between two types of applications. However, the IEEE 1609.4 multichannel media access control (MAC) protocol has limitations on its capability of supporting either delay- or throughput-sensitive applications. In this paper, we propose an adaptive multi-priority distributed multichannel (APDM) MAC protocol for VANETs. Considering that in realistic VANETs, the queue of MAC layer is far from saturated. We assume that generated packets with different priorities arrive at the MAC layer in a Poisson manner. A Markov analytical model is conducted to optimize the packet transmission probabilities and adjust the ratio between CCH interval and SCH interval dynamically according to the real-time traffic in a distributed way. An M/M/1 queue model is then adopted to analyze the time performance. Extensive simulation results show that the APDM MAC protocol can ensure prioritized transmission of safety packets, reduce the transmission delay of packets and enhance the unsaturated and saturated throughput of SCHs.

Non-saturated IEEE 802.11 networks. A hierarchical 3D Markov model

One of the most widely adopted IEEE 802.11 DCF modeling paradigms is the mean-field Markov model approach. It has its foundations on the analytical two-dimensional Markov model presented by Bianchi, which characterizes the basic access mechanism of DCF under a saturated traffic assumption. This basic approach has been refined by a series of follow-up models that take into account important practical issues not considered in the original model, such as non-saturated traffic load and error-prone channels. However, two-dimensional models are either based on bufferless or infinite buffer network assumptions and thus, they are unable to properly model QoS performance metrics related to finite queues. In this paper, a hierarchical three-dimensional Markov model able to fully capture the Quality of Service (QoS) performance and queueing behavior of non-saturated IEEE 802.11 DCF-based networks is proposed. The third dimension in the hierarchical three-dimensional Markov chain is used to model the queue length and the hierarchy is used to efficiently capture, on one hand, the freezing rules of backoff counters when the broadcast channel is sensed busy and, on the other hand, the error-prone channel conditions. The issue of computational complexity is addressed by devising a computationally efficient method to solve for the steady-state transition probabilities of the 3D Markov chain. The solution for the Markov chain is then exploited to obtain analytical expressions for the whole set of QoS performance metrics of the system, allowing the evaluation/prediction of the impact of buffer size, block error probability and backoff freezing rules on all relevant QoS metrics of a DCF-based IEEE 802.11 network. A close match between analytical and simulation results confirms the validity and effectiveness of the proposed approach.

An Improved Call Admission Control Mechanism with Prioritized Handoff Queuing Scheme for BWA Networks

Nowadays, due to increased demand for using the Broadband Wireless Access (BWA) networks in a satisfactory manner a promised Quality of Service (QoS) is required to manage the seamless transmission of the heterogeneous handoff calls. To this end, this paper proposes an improved Call Admission Control (CAC) mechanism with prioritized handoff queuing scheme that aims to reduce dropping probability of handoff calls. Handoff calls are queued when no bandwidth is available even after the allowable bandwidth degradation of the ongoing calls and get admitted into the network when an ongoing call is terminated with a higher priority than the newly originated call. An analytical Markov model for the proposed CAC mechanism is developed to analyze various performance parameters. Analytical results show that our proposed CAC with handoff queuing scheme prioritizes the handoff calls effectively and reduces dropping probability of the system by 78.57% for real-time traffic without degrading the number of failed new call attempts. This results in the increased bandwidth utilization of the network.

Exact performance analytical model for spectrum allocation in flexible grid optical networks

Dynamic flexible grid optical networks have gained much attention because of the advantages of high spectrum efficiency and flexibility, while the performance analysis will be more complex compared with fixed grid optical networks. An analytical Markov model is first presented in the paper, which can exactly describe the stochastic characteristics of the spectrum allocation in flexible grid optical networks considering both random-fit and first-fit resource assignment policies. We focus on the effect of spectrum contiguous constraint which has not been systematically studied in respect of mathematical modeling, and three major properties of the model are presented and analyzed. The model can expose key performance features and act as the foundation of modeling the Routing and Spectrum Assignment (RSA) problem with diverse topologies. Two heuristic algorithms are also proposed to make it more tractable. Finally, several key parameters, such as blocking probability, resource utilization rate and fragmentation rate are presented and computed, and the corresponding Monte Carlo simulation results match closely with analytical results, which prove the correctness of this mathematical model.

A multi-priority supported medium access control in Vehicular Ad Hoc Networks

In recent years, Vehicular Ad Hoc Networks (VANETs) experience growing interest in both academia and industry. VANETs apply multiple channels, namely Control Channel (CCH) and Service Channels (SCHs), to provide road safety services and improve the comfort and efficiency of driving. Based on the time slotted p-persistent channel access mechanism, this paper proposes a multiple priority supported medium access control (MAC) protocol for VANETs, which differentiates the packets into multi-priority on the CCH. A Markov analytical model is presented to optimize the packet transmission probabilities with different priorities and the adjustable intervals of the CCH and SCH. Moreover, a contention-free ACK scheme is reported to guarantee the reliable broadcast of the safety packets and avoid collision caused by numerous ACK packets on CCH. Simulation results indicate that the proposed MAC protocol is able to ensure the prioritized transmission of the safety packets, and it can achieve optimal system performance in terms of saturated throughput.

When Is Carotid Angioplasty and Stenting the Cost-Effective Alternative for Revascularization of Symptomatic Carotid Stenosis? A Canadian Health System Perspective

Carotid revascularization procedures can be complicated by stroke. Additional disability adds to the already high costs of the procedure. To weigh the cost and benefit, we estimated the cost-utility of carotid angioplasty and stenting compared with carotid endarterectomy among patients with symptomatic carotid stenosis, with special emphasis on scenario analyses that would yield carotid angioplasty and stenting as the cost-effective alternative relative to carotid endarterectomy. A cost-utility analysis from the perspective of the health system payer was performed by using a Markov analytic model. Clinical estimates were based on a meta-analysis. The procedural costs were derived from a microcosting data base. The costs for hospitalization and rehabilitation of patients with stroke were based on a Canadian multicenter study. Utilities were based on a randomized controlled trial. In the base case analysis, carotid angioplasty and stenting were more expensive (incremental cost of $6107) and had a lower utility (-0.12 quality-adjusted life years) than carotid endarterectomy. The results are sensitive to changes in the risk of clinical events and the relative risk of death and stroke. Carotid angioplasty and stenting were more economically attractive among high-risk surgical patients. For carotid angioplasty and stenting to become the preferred option, their costs would need to fall from more than $7300 to $4350 or less and the risks of the periprocedural and annual minor strokes would have to be equivalent to that of carotid endarterectomy. In the base case analysis, carotid angioplasty and stenting were associated with higher costs and lower utility compared with carotid endarterectomy for patients with symptomatic carotid stenosis. Carotid angioplasty and stenting were cost-effective for patients with high surgical risk.

A Flexible Analytical Markov Model for the IEEE 802.15.4 Unslotted Mechanism in Single-Hop Hierarchical Wireless Networks with Hidden Nodes

In this paper, an analytical Markov model (AMM) for the IEEE 802.15.4 unslotted CSMA/CA mechanism in single-hop hierarchical wireless networks (HWN) with hidden nodes is presented. The proposed AMM is flexible enough to operate both in saturation and non-saturation regions. Its prediction accuracy was compared with that of two well known models in the literature as well as with simulation results obtained by using the network simulator (NS)-2. The comparison has indicated that when $$r$$ , which denotes the maximum frame retransmission attempts, is set to zero and one-tier single-hop HWN with no hidden nodes is considered, the proposed AMM predicts the simulation results with a very small mean absolute percentage error (MAPE). Similarly, when a single-hop HWN with two tiers and hidden nodes is considered, then only one of the two well known models is applicable and the proposed AMM predictions present the smallest MAPE over the simulation results. Lastly, in the case of four-tier single-hop HWN with hidden nodes, only the proposed AMM is applicable and it predicts the simulation results at a respectable level of accuracy. When $$r>0$$ and the unslotted mechanism continues by incrementing the number of retransmission attempt by one upon channel access failure events, only the proposed AMM can imitate the behavior of the NS-2 IEEE 802.15.4 module.

Abstract 202: Cost-effectiveness Of Carotid Stenting In Canada

BACKGROUND To estimate the cost-effectiveness of carotid stenting (CAS) compared to endarterectomy (CEA) in symptomatic patients. METHODS A cost-utility analysis from the Canadian health system perspective was performed using a Markov analytic model. Clinical estimates were based on a recent meta-analysis. Procedural costs for CAS and CEA were derived from a local cohort. The costs for hospitalization and rehabilitation for minor and major strokes were based on the Burden of Ischemic Stroke (BURST) study. Utility scores were based on SAPPHIRE trial. A Monte Carlo simulation using a hypothetical cohort of 10,000 and sensitivity analyses were performed to investigate the model assumptions and uncertainties. RESULTS CAS was more expensive (incremental cost of $6106.84) and had a lower effectiveness (- 0.12 QALYs). The model was sensitive to the risk of annual death. At a threshold odds ratio (OR) of 0.85, CAS was associated with an incremental cost-effectiveness ratio (ICER) of $32,839.04. Using estimates from SAPPHIRE trial, CAS dominated CEA. When estimates from CREST or EVA-3S trials were used, CEA dominated CAS. Only after simultaneously reducing CAS costs and risks of periprocedural and annual minor strokes, CAS had a favorable ICER. This was achieved at a threshold CAS procedural cost of $4350, a threshold OR of periprocedural minor stroke of 1, and a threshold OR of annual minor stroke of 1.15or less; resulting in an ICER of $577.5. The figure shows CAS cost-effectiveness plane. CONCLUSIONS In this analysis, CAS was associated with higher costs and lower effectiveness compared to CEA in symptomatic carotid stenosis patients. The results were driven by the costs of periprocedural major and minor stroke. The costs associated with MI did not impact the results. For CAS to be more effective, it needs to be performed in patients with longer survival, in patients at a high surgical-risk, or at a lower procedural costs plus lower rates of periprocedural and annual minor strokes.

Cost-Effectiveness of Sacral Neuromodulation Compared to Botulinum Neurotoxin A or Continued Medical Management in Refractory Overactive Bladder

Objectives This study assessed the cost-effectiveness and health-care budget impact of sacral neuromodulation (SNM) in refractory idiopathic OAB-wet patients in Spain. Methods A 10-year Markov analytic model was developed to estimate quality-adjusted life-years (QALYs) gained and incontinence episode avoided associated with SNM therapy compared with botulinum neurotoxin A (BoNT-A) or continued optimized medical treatment (OMT). Results At 10 years, the cumulative costs of SNM, BoNT-A, and OMT were €29,166, €29,458, and €29,370, respectively, whereas the QALYs for SNM, BoNT-A, and OMT are 6.89, 6.38, and 5.12, respectively. Consequently, incremental cost-effectiveness ratios (ICERs) for SNM demonstrate that although the initial costs for SNM are higher than those for the other treatments, decreasing follow-up costs coupled with consistently greater effectiveness in the long term make SNM the economically dominant option at 10 years. Sensitivity analyses suggest that 99.7% and 99.9% (for SNM vs. BoNT-A and OMT, respectively) of the 1000 Monte Carlo iterations fall within the €30,000 cost-effectiveness threshold, considered to be acceptable in Spain. The 10-year incremental cost per incontinence episode avoided for SNM also makes this therapy the dominant option compared to BoNT-A or OMT. Additionally, the estimated budget impact of the gradually increased referral for SNM for the management of OAB patients in Spain is small. Conclusions As a treatment option for refractory idiopathic OAB, at 10 years, SNM provides a considerable possibility of symptom and quality-of-life improvement and is cost-effective compared to BoNT-A or continued OMT.

A novel Markov analytical model for the TCP/AQM systems

A novel closed-loop feedback TCP/AQM (Transfer Control Protocol/Active Queue Management) model is proposed in this paper using a discrete-time Markov chain, and a way to calculate the equilibrium distribution of this model is given. In the model, system time is divided into time slots, the bottleneck router queue model and TCP window size model in each slot are analyzed. Finally, by combining adjacent slots, an integrated TCP/AQM analytical model is developed. By this model, the average values of packets dropping ratio and queue length in the router and TCP sending rate can be estimated, hence, this model could be a useful tool for the analysis of AQMs and support the development of new AQM schemes theoretically. The proposed TCP/AQM model is extended to a TCP-UDP (Control User Datagram Protocol)/AQM model, to analyze the TCP/AQM system performance when UDP flows exist. By implementing this model on Matlab, we compare its solutions to NS2 simulated solutions, then the validity of the model to analyze the closed-loop feedback TCP/RED (Random Early Detection) system is verified.

Public health impact and cost effectiveness of mass vaccination with live attenuated human rotavirus vaccine (RIX4414) in India: model based analysis

Objectives To examine the public health impact of mass vaccination with live attenuated human rotavirus vaccine (RIX4414) in a birth cohort in India, and to estimate the cost effectiveness and...

Modeling and Analysis of Random Periodic Spectrum Sensing for Cognitive Radio Networks

A random periodic spectrum sensing scheme is proposed for cognitive radio networks. The sensing period, the transmission time for primary users and cognitive radios are extended to general forms as random variables. A generalized Markov analytical model for sensing period optimization is presented, and the applications of the proposed analytical model by using examples involving primary user systems with both voice and data traffic are illustrated. The analysis and numerical results show that sensing period does affect the maximum rewards of the channel, and the analytical model is justified by its flexibility since it uses general forms of the sensing period, the transmission time for primary users and cognitive radios. Hence the model can be easily adapted for the analysis of many different applications.

The Optimal Timing of Intestinal Transplantation for Children With Intestinal Failure

Identify an optimal approach to the timing of intestinal transplantation for children dependent on total parenteral nutrition (PN). Children with short bowel syndrome are frequently dependent on PN for growth and development. Intestinal transplantation is often considered after PN-related complications occur, but optimal timing of transplantation is controversial. A Markov analytic model was used to determine life expectancy (LY) and quality-adjusted life years on a theoretical cohort of 4-year-old subjects for two treatment strategies: (1) standard care consisting of PN and referral to transplantation according to accepted guidelines and (2) early listing for isolated small intestine transplantation. Early listing for intestinal transplantation was associated with 0.27 additional life years (13.16 vs. 12.89) and 0.76 additional quality-adjusted life years (10.51 vs. 9.75) as compared with current standard care. The unadjusted analysis was sensitive to the development of PN-associated liver disease, at a threshold of approximately 11% per year, and its related probability of dying at a threshold of 80% 2-year mortality. Early listing for transplantation was the dominant strategy until the probability of late bowel rejection reached 35% per year. Children with short bowel syndrome dependent on PN should be considered for intestinal transplantation earlier than what is current practice.

Channel Allocation Scheme for Handoff Control in Wireless Ad Hoc Network with Group Mobility

Because a wireless ad hoc network does not have a fixed backbone network and the mobile base station moves randomly, the conventional channel allocation scheme cannot efficiently predict group mobility and is not feasible to support a burst handoff traffic due to group mobility. In this paper, we propose an channel allocation scheme to solve this problem. Our scheme efficiently support burst handoff using guard channel and hello message in wireless ad hoc network with group mobility. We developed an analytical Markov model for the proposed scheme and evaluate our scheme in terms of new call and handoff blocking probability and channel utilization via simulation study. Simulation results show that our scheme offers better performance than the conventional schemes.

Predictive schemes for handoff prioritization in cellular networks based on mobile positioning

We propose and evaluate new schemes for channel reservation motivated by the rapidly evolving technology of mobile positioning. The schemes, called predictive channel reservation (PCR), work by sending reservation requests to neighboring cells based on extrapolating the motion of mobile stations (MSs). A number of design enhancements are incorporated to minimize the effect of false reservations and to improve the throughput of the cellular system. These enhancements include: (1) reservation pooling; (2) queuing of reservation requests; (3) hybrid approach for integrating guard channels (GCs); and (4) using a threshold distance (TD) to control the timing of reservation requests. The design enhancements have produced a set of highly efficient schemes that achieve significant reduction in handoff blocking rates while only incurring remarkably small increases in the new call blocking rates. The PCR approach has also been used to solve the MINBLOCK optimization problem and has given significant improvement over the fractional guard channel (FGC) protocol. Detailed performance results of the different variations of the PCR scheme and comparisons with conventional channel reservation schemes are presented. An analytical Markov model for the hybrid predictive version of the scheme is developed and its applicability and numerical results are discussed.