An analytical approach for performance analysis of handoffs in the next generation integrated cellular networks and WLANs

The main feature of the next generation wireless communication systems is the ability to establish ubiquitous and seamless access to various radio access technologies (RATs) and standards. For this reason the integration of cellular and wireless local area networks (WLANs) and performance evaluation of the interaction between these technologies is now an important research area. Modelling such systems for performance evaluation is essential to improve the architecture according to the quality ofbservice (QoS) requirements and performance characteristics. In this paper, an analytical model for performance evaluation of an integrated cellular network and a WLAN is considered. WLAN is deployed inside of the cellular network to support handoffs between cellular networks with higher bandwidth. Such an integrated system can be modelled as a two stage open network. An analytical model is proposed together with an exact solution technique in order to evaluate the performance of an integrated system consisting of a cellular network and a WLAN. A two stage queuing system is considered for this purpose. Numerical results are presented for mean queue length values of cellular system as well as the WLAN

A hybrid approach to minimize state space explosion problem for the solution of two stage tandem queues

Two stage open queuing networks are used for modelling the subsystem-behaviour in computers and communication networks, mass storage devices, memory servers, and queuing analysis of wireless mobile cellular networks. The queuing analysis of wireless systems are essential in order to quantify the impacts of different factors on quality of service (QoS) performance measures so that wireless protocols can be designed and/or tuned in an optimal manner. In that sense two stage open queuing systems are particularly important to model handoff phenomena, especially for the integration of two different systems such as cellular and wireless local area networks (WLANs). Analytical solutions for two dimensional Markov processes suffer from the state space explosion problem. The numerical difficulties caused by large state spaces, makes it difficult to handle multiple servers at the second stage of a tandem queuing system together with server failures and repairs. This study presents a new approach to analytical modelling of open networks offering improvements in alleviating this problem. The proposed solution is a hybrid version, which combines well known spectral expansion, and hierarchical Markov reward rate approaches. Using this approach, two-stage open networks with multiple servers, break-downs, and repairs at the second stage and feedback can be modelled as three dimensional Markov processes and solved for performability measures. Comparative results show that the new algorithm used for solution, provides high degree of accuracy, and it is computationally more efficient than the existing approaches. The proposed model is capable of solving other three dimensional Markov processes

Bivariate Chlodowsky-Stancu Variant of (p,q)-Bernstein-Schurer Operators

In this study, it is proposed to define bivariate Chlodowsky variant of (p,q)-Bernstein-Stancu-Schurer operators. Therefore, Korovkin-type approximation theorems and the error of approximation by using full modulus of continuity are presented. Beside this, we introduce a generalization of the bivariate Chlodowsky variant of (p,q)-Bernstein-Stancu-Schurer operators and investigate its approximation in more general weighted space. Moreover, the numerical results are discussed in order to validate the accuracy of the bivariate Chlodowsky variant of (p,q)-Bernstein-Schurer operators

Availability Evaluation of IoT Systems with Byzantine Fault-Tolerance for Mission-critical Applications

Byzantine fault-tolerant (BFT) systems are able to maintain the availability and integrity of IoT systems, in presence of failure of individual components, random data corruption or malicious attacks. Fault-tolerant systems in general are essential in assuring continuity of service for mission critical applications. However, their implementation may be challenging and expensive. In this study, IoT Systems with Byzantine Fault-Tolerance are considered. Analytical models and solutions are presented as well as a detailed analysis for the evaluation of the availability. Byzantine Fault Tolerance is particularly important for blockchain mechanisms, and in turn for IoT, since it can provide a secure, reliable and decentralized infrastructure for IoT devices to communicate and transact with each other. The proposed model is based on continuous-time Markov chains, and it analyses the availability of Byzantine Fault-Tolerant systems. While the availability model is based on a continuous-time Markov chain where the breakdown and repair times follow exponential distributions, the number of the Byzantine nodes in the network studied follows various distributions. The numerical results presented report availability as a function of the number of participants and the relative number of honest actors in the system. It can be concluded from the model that there is a non-linear relationship between the number of servers and network availability; i.e. the availability is inversely proportional to the number of nodes in the system. This relationship is further strengthened as the ratio of break-down rate over repair rate increases

Performance evaluation of hybrid disaster recovery framework with D2D communications

Public Safety Networks (PSNs) provide assistance before- and post-disaster events. With the help of technological advances, PSNs are able to cope with both natural and man-made disasters, protecting people, environment and property. Effective communications, better situational awareness, lower response times and greater emergency efficiency are essential to an effective response to emergencies and disasters. Long Term Evolution (LTE) has been chosen to be the key technology for public safety networks. In this study, a performance model is presented for the PSN frameworks which use cooperative devices with LTE device to device (D2D) communications features. Mobile stations that are out of cellular network coverage range use D2D communications, where mobile stations which are in a healthy area can act as relay nodes to provide information about the location of potential victims to a central system. Since relay nodes have the potential to become bottlenecks for relatively high scale disasters, the interaction between the relay node and the base station is critically considered in this study. The analytical model and solution are suitable for assessing the quality of service for PSNs with similar infrastructures. Results obtained from the analytical model are presented comparatively with those from discrete event simulations for validation. The maximum discrepancy between the results obtained from the analytical model and the simulation results is less than 1.4%, which is within the confidence interval of the simulation

Admission control and buffer management of wireless communication systems with mobile stations and integrated voice and data services

This study presents models for management of voice and data traffic and new algorithms, which use call admission control as well as buffer management to optimise the performance of single channel systems such as wireless local area networks in the presence of mobile stations. Unlike existing studies, the new approach queues incoming voice packets as well as data packets, and uses a new pre-emption algorithm in order to keep the response time of voice requests at certain levels while the blocking of data requests is minimised. A new performance metric is introduced to provide uncorrelated handling of integrated services. Queueing related issues such as overall queue capacity, individual capacities for voice and data requests, the probability of blocking, and effects of waiting time on overall quality of service are considered in detail. Analytical models are presented and the results obtained from the analytical models were validated using discrete event simulations