We have developed an analytical model for a non-saturated IEEE 802.15.6 wireless body area network (WBAN) operating under an error-prone channel. The most suitable vehicle for improving network performance was found to be the choice of access phase lengths based on traffic loads for different user priorities (UPs). It was also found that the deployment of exclusive access phase (EAP) is not necessary in a typical WBAN; in fact, short exclusive and random access phases (EAP and RAP, respectively) lead to inefficient use of available bandwidth. We have also found that four user priorities (out of the eight available) typically suffice to achieve even the most stringent requirements for WBAN performance.

In this work, we develop a prioritized bridging mechanism between the IEEE 802.15.6-based wireless body area networks WBANs and the IEEE 802.11e enhanced distributed channel access EDCA-based wireless local area network WLAN to convey the medical data to the medical center. We map the eight WBAN user priorities UPs into the four WLAN access categories ACs to provide the required quality of service and prioritization for the health variables generated by the WBAN nodes. By assignment of WBAN UPs with default medium access control parameters to eight different medical data streams and under the presence of ordinary nodes, we investigate the impact of WLAN AC differentiation by arbitrary inter-frame space AIFS and contention window CW on performance of medical and regular nodes' data streams. The results of this work indicate that the AC differentiation by AIFS outperforms the differentiation by CW in the sense that it does not deteriorate the end-to-end delay of relayed WBAN traffic and ordinary WLAN traffic.Copyright © 2012 John Wiley & Sons, Ltd.

In this paper, we propose an analytical performance model that addresses the complexity of cloud centers through distinct stochastic submodels, the results of which are integrated to obtain the overall solution. Our model incorporates the important aspects of cloud centers such as pool management, compound requests (i.e., a set of requests submitted by one user simultaneously), resource virtualization and realistic servicing steps. In this manner, we obtain not only a detailed assessment of cloud center performance, but also clear insights into equilibrium arrangement and capacity planning that allows servicing delays, task rejection probability, and power consumption to be kept under control.

In this work, by bridging the IEEE 802.15.6-based WBANs and the IEEE 802.11e EDCA-based WLAN we develop a wireless healthcare network. We assign 8 WBAN User Priorities (UPs) to the WBAN nodes. By mapping the UPs into 4 WLAN Access Categories (ACs) we convey the medical data to the WLAN access point. We investigate the network performance under varying priority differentiation and number of nodes in the WLAN. We study the impacts of AC differentiation by Arbitrary Inter-Frame Space (AIFS) and Contention Window (CW) on the performance of WBAN and regular WLAN nodes. The results of this work indicate that differentiation by AIFS is more appropriate to preserve relative order of frame response times established in WBAN.

Since the signal transmission in WBANs takes place around or in the human body, the channel fading significantly affects the error performance of the networks. In this paper, we investigate MAC performance of an IEEE 802.15.6-based WBAN operating over a Rician-faded channel. We deploy Bit Error Rate (BER) as a function of channel quality, diversity order, and Signal to Noise Ratio (SNR) values for all User Priorities (UPs) in analytical and simulation models to evaluate the MAC performance. We study how varying Signal to Noise Ratio (SNR) of all UPs affects the MAC performance. Our results indicate that data frame sizes and channel quality between a node and the hub are the most effective parameters on PHY/MAC performance of a WBAN.

In this paper, we investigate the impact of transmission opportunity (TXOP), arbitration interframe space (AIFS), and contention window on the performance of an IEEE 802.11e cluster with four traffic classes under Poisson frame arrivals. We derive an analytical model of the cluster using queuing model of individual nodes, discrete time Markov chain, and probabilistic modeling of the backoff process. The analytical model demonstrates the complex interaction between TXOP, on one side, and AIFS and contention window, on the other. We derive saturation and stability points for all traffic classes and discuss their dependency on TXOP allocations. Our results indicate that use of nonzero TXOP parameter under Poisson frame arrivals improves performance slightly by separating points of saturation and instability. More substantial performance improvements should be expected by deploying TXOP differentiation under bursty traffic. Since all traffic classes need to operate in stable, nonsaturated regime, this work has important implications for the design of congestion control and admission control schemes in IEEE 802.11e clusters.

A Wireless Body Area Network (WBAN) aims to provide real-time and ubiquitous body monitoring to perform autonomous early prediction, diagnostic, and tracking the response of the body to treatments. IEEE 802.15.6 is a communication standard for WBANs which pervasively and continuously monitor the human body. In this paper, we develop an analytical model for performance evaluation of the IEEE 802.15.6 standard under non-saturation regime. We validate the analytical results by a simulation model. The results of the paper indicate that adopting appropriate EAPs and RAPs lengths noticeably improves the performance of the network. Short EAPs and RAPs result in wasting the network resources due to growth of the time periods in which the medium is inaccessible. On the other side, long EAPs and RAPs increase the collision probability at the end of EAPs and may result in undesirable frame delays.

Due to lack of an appropriate wireless technology which satisfies all the requirements of Wireless Body Area Networks (WBANs) the IEEE 802.15.6 Task Group introduced the IEEE 802.15.6 communication standard optimized for low power devices and operation on, in or around the human body. In this work we develop an analytical model for performance evaluation of an IEEE 802.15.6-based WBAN under saturation condition and error prone channel. We model the backoff procedure as specified in the standard employing a probabilistic approach. We validate results of the analytical model with a simulation model. Our results indicate that under saturation condition the medium is mostly utilized by the nodes with highest priority while other user priorities are starving.

In this paper we investigate the ratio of dwelling time in control channel (CCH) and service channel (SCH) for single channel devices deploying WAVE (Wireless Access in Vehicular Environments) protocols. Based on analytical model for both channels and four traffic types we present tradeoffs in channel performance when CCH/SCH duty cycle is changing. Our results show that, when video traffic is absent, duty cycles smaller than 0.5 can offer satisfactory performance on CCH while running larger amount of revenue generating traffic on SCH.

In this paper we investigate the transition between non-saturation and saturation regimes for the EDCA function within the IEEE 802.11e standard. We develop queueing and Markov chain models for node operation, and demonstrate interaction among traffic classes in transition from non-saturation to saturation regime. We derive probability generating functions (PGFs) for the probability distributions of packet service time and buffer occupancy. We also derive Laplace-Stieltjes transform (LST) for the probability distribution of frame response time and show stability limits for each traffic class.

In this paper, we investigate effects of two important parameters on stability boundaries between saturation and non-saturation regimes of IEEE 802.11e EDCA. We study the stability regions of four access categories by taking into account node population, TXOP value under different arrival rates. In order to operate in stable regime, the frame arrival rate of all stations in the network should not exceed the non-saturation boundaries. However, because the arrival rates of the stations are dependent on the application, the stability of network employing IEEE 802.11e EDCA must be controlled by other parameters. The simulation results show that node populations of different traffic classes and TXOP values could be suitable parameters for preserving network stability.

Pervasive computing technology as the next generation of mobile computing has new and specific characteristics such as very high dynamicity, enormous heterogeneity, pervasive access to services and information, context-awareness, invisibility, respecting user intents, and ubiquity which demarcate it from other previous network technologies. The new properties of pervasive computing make traditional security systems inefficient and often unusable for the technology. In the domain of access control as the most important part of security systems, modern frameworks and methods must be designed and implemented to meet requirements of the technology and to provide suitable security for the pervasive computing environments. In this paper, we propose an access control framework for pervasive computing environments that controls accesses in the environment based on context and user intents.