Ahmed H. Zahran

Signal threshold adaptation for vertical handoff in heterogeneous wireless networks

The convergence of heterogeneous wireless access technologies has been envisioned to characterize the next generation wireless networks. In such converged systems, the seamless and efficient handoff between different access technologies (vertical handoff) is essential and remains a challenging problem. The heterogeneous co-existence of access technologies with largely different characteristics results in handoff asymmetry that differs from the traditional intra-network handoff (horizontal handoff) problem. In the case where one network is preferred, the vertical handoff decision should be carefully executed, based on the wireless channel state, network layer characteristics, as well as application requirements. In this paper, we study the performance of vertical handoff using the integration of 3G cellular and wireless local area networks as an example. In particular, we investigate the effect of an application-based signal strength threshold on an adaptive preferred-network lifetime-based handoff strategy, in terms of the signalling load, available bandwidth, and packet delay for an inter-network roaming mobile. We present an analytical framework to evaluate the converged system performance, which is validated by computer simulation. We show how the proposed analytical model can be used to provide design guidelines for the optimization of vertical handoff in the next generation integrated wireless networks.

Performance evaluation framework for vertical handoff algorithms in heterogeneous networks

The next generation (4G) wireless network is envisioned as a convergence of different wireless access technologies providing the user with the best anywhere anytime connection and improving the system resource utilization. The integration of wireless local area network (WLAN) hotspots and the third generation (3G) cellular network has recently received much attention. While the 3G-network can provide global coverage with a low data-rate service, the WLAN can provide a high data-rate service within the hotspots. Although increasing the underlay network utilization is expected to increase the user available bandwidth, it may violate the quality-of-service (QoS) requirements of active real-time applications. Hence, achieving seamless handoff between different wireless technologies, known as vertical handoff (VHO), is a major challenge for 4G-system implementation. Several factors, such as application QoS requirements and handoff delay, should be considered to realize an application transparent handoff. We present a novel framework to evaluate the impact of VHO algorithm design on system resource utilization and user perceived QoS. We used this framework to compare the performance of two different VHO algorithms. The results show a very good match between simulation and analytical results. In addition, it clarifies the tradeoff between achieving high resource utilization and satisfying user QoS expectations.

Mobility Modeling and Performance Evaluation of Heterogeneous Wireless Networks

The future-generation wireless systems will combine heterogeneous wireless access technologies to provide mobile users with seamless access to a diverse set of applications and services. The heterogeneity in this inter-technology roaming paradigm magnifies the mobility impact on system performance and user perceived service quality, necessitating novel mobility modeling and analysis approaches for performance evaluation. In this paper, we present and compare three mobility models in two-tier integrated heterogeneous wireless systems, the independence model as a naive extension of the traditional cell residence time modeling techniques for homogeneous cellular networks, the basic Coxian model which takes into consideration the correlation between the residence time within different access technologies, and the extended-Coxian model for further improved estimation accuracy. We propose a general stochastic performance analysis framework based on application session models derived from these mobility models, applying it to a 3G-WLAN integrated system as an example. Our numerical and simulation results demonstrate the general superiority of Coxian-based mobility modeling over the independence model. Furthermore, using the proposed modeling and analysis methods, we investigate the impact of different parameters on system performance metrics such as network utilization time, handoff rates, and forced termination probability, for a wide range of user applications.

A Generic Framework for Mobility Modeling and Performance Analysis in Next-Generation Heterogeneous Wireless Networks

Integration of different wireless radio cellular technologies is emerging as an effective approach to accommodate the increasing demand of next-generation multimedia-based applications. In such systems user roaming among different technologies, commonly known as vertical handoff, will significantly affect different aspects of network design and planning due to the characteristically wide-ranging diversity in access technologies and supported applications. Hence, the development of new mobility models that accurately depict vertical mobility is crucial for studying different design problems in these heterogeneous systems. This article presents a generic framework for mobility modeling and performance analysis of integrated heterogeneous networks using phase-type distributions. This framework realizes all modeling requirements in next-generation user mobility including accuracy, analytical tractability, and accommodating the correlation between different residence times within different access technologies. Additionally, we present general guidelines to evaluate application performance based on the new mobility models introduced in this article. We show the accuracy of our modeling approach through simulation and analysis given different applications.

Threshold-Based Media Streaming Optimization for Heterogeneous Wireless Networks

The integration of different wireless access technologies combined with the huge characteristic diversity of supported services in next-generation wireless systems creates a real heterogeneous network. In this paper, we propose a generic practical framework that optimizes media streaming in heterogeneous systems by taking advantage of cost and resource characteristic diversity of the integrated access technologies and the buffering capability of streaming applications. The proposed optimization framework represents a means to compromise the tradeoff between different performance metrics including streaming monetary cost, signaling load, and session quality. Additionally, it accommodates different design challenges including mobility randomness, limited processing capacity, and handoff delay requirements. The simulation results provide important insights on the design of pricing profiles in integrated systems. Additionally, the results show that significant cost savings can be realized using the newly proposed streaming management algorithms and optimization framework.

Datasets for AVC (H.264) and HEVC (H.265) evaluation of dynamic adaptive streaming over HTTP (DASH)

In this paper we present datasets for both trace-based simulation and real-time testbed evaluation of Dynamic Adaptive Streaming over HTTP (DASH). Our trace-based simulation dataset provides a means of evaluation in frameworks such as NS-2 and NS-3, while our testbed evaluation dataset offers a means of analysing the delivery of content over a physical network and associated adaptation mechanisms at the client. Our datasets are available in both H.264 and H.265 with encoding rates comparative to the representations and resolutions of content distribution providers such as Netflix, Hulu and YouTube. The goal of our dataset is to provide researchers with a sufficiently large dataset, in both number, and duration, of clips which provides a comparison between both encoding schemes. We provide options for evaluating not only different content and genres, but also the underlying encoding metrics, such as transmission cost, segment distribution (the range of the oscillation of the segment sizes) and associated delivery issues such as jitter and re-buffering. Finally, we also offer our datasets in a header-only compressed format, which allows researchers to download the entire dataset and uncompress locally, thus ensuring that our datasets are accessible both online via remote and local servers.

Mobile network traffic: A user behaviour model

What would the same users do in a different network? The performance of the network has a significant effect on the traffic profiles of users, which cannot be easily identified from network traces. This work combines a number of studies to compile a new responsive traffic model for mobile networks that realistically mimics user behaviour. Users continuously evaluate the performance of the network, and initiate or terminate their sessions accordingly. The presented model utilises Markov chains to capture this behaviour, while the performance of a session is depicted with the binary distinction of good and bad quality. We analyse and showcase the implications of this model, and discuss its benefits on network planning and research applications.

Application signal threshold adaptation for vertical handoff in heterogeneous wireless networks

In heterogeneous wireless systems, the seamless and efficient handoff between different access technologies (vertical handoff) is essential and remains a challenging problem. The co-existence of access technologies with largely different characteristics results in handoff asymmetry that differs from the traditional intra-network handoff problem. In the case where one network is preferred, the vertical handoff decision should be carefully executed, based on the wireless channel state, network layer characteristics, as well as application requirements. In this paper, we present an adaptive preferred-network lifetime-based handoff strategy, and investigate the effect of an application-based signal strength threshold on the signalling load, available bandwidth, and packet delay.We propose an analytical framework to evaluate the performance of the converged system.We show how the proposed analytical model can be used to provide guidelines for the optimization of vertical handoff in the next generation integrated wireless networks.

Delivery of adaptive bit rate video: balancing fairness, efficiency and quality

HTTP streaming currently dominates Internet traffic. It is increasingly common that video players employ adaptive bitrate (ABR) streaming strategies to maximise the user experience by selecting the highest video representation while targeting stall-free playback. Our interest lies in the common situation where a set of video flows are competing for access to a shared bottleneck link, such as in a cellular radio access network. We observe that ISPs (e.g. cellular operators) are considering innetwork techniques for resource allocation and sharing among different users. Buoyed by the ability of software defined networks (SDN) to offer flow-specific control and traffic shaping, we focus on traffic shaping techniques, and experimentally analyse the effect on ABR video flows when sharing a bottleneck link. We conduct experiments using the GPAC video player operating over a Mininet virtual network. We conclude that traffic shaping can allow a balance of fairness, efficiency and quality. Traffic shaping ABR videos reduce the number of stalls and quality switches, while also reducing the peaks for the aggregate network traffic.

Effective Capacity of Delay-Constrained Cognitive Radio Links Exploiting Primary Feedback

In this paper, we study the effective capacity (EC) of cognitive radio (CR) networks operating under statistical quality-of-service (QoS) constraints in an attempt to support real-time applications at the secondary users (SUs). In particular, we analyze the performance gains, in terms of EC and average transmitted power, attributed to leveraging the primary user (PU) feedback overheard at the SU, at no additional complexity or hardware cost. We characterize the EC performance improvement for the SU, in the presence of a feedback-based sensing scheme, under the signal-to-interference-plus-noise ratio (SINR) interference and collision models. Toward this objective, we develop a Markov chain model for feedback-based sensing to compare the performance of a two-link network, a single secondary link, and a primary network abstracted to a single primary link, with and without primary-feedback exploitation. We prove that exploiting the primary feedback at the secondary transmitter improves the EC of the SU under the SINR interference model. On the other hand, interestingly, exploiting the PU feedback messages does not enhance the EC of the SU under the collision model. Nevertheless, exploiting the PU feedback reduces the SU average transmitted power under the two aforementioned models. Finally, we present numerical results, for plausible scenarios, that support our analytical findings.