Tariq M. Ali

Performance Analysis Framework and Vertical Handover Triggering Algorithms for Voice over WLAN/Cellular Network

The development of handheld user equipments (UE) capable of operating over both cellular networks and wireless local area networks (WLAN) is an important step towards the evolution of next-generation integrated networks. For real-time applications, maintaining a seamless connectivity and an acceptable level of quality is quite important. Efficient vertical handoff algorithms are required to ensure the best exploitation of the available resources under certain quality constraints. This paper proposes a realistic performance analysis framework upon addressing relevant factors that affect the performance of a voice application within a heterogeneous network environment. While the existing works in this field relies on received signal strength (RSS) samples to estimate the WLAN usability, this paper also proposes an algorithm that takes into account the real-time packet error pattern along with RSS.

Analytical Framework for WLAN-Cellular Voice Handover Evaluation

The development of handheld mobile terminals (MT) capable of operating over both Wireless Local Area Networks (WLAN) and the cellular media is an important step toward the evolution of next-generation integrated networks. For real-time applications like voice, efficient vertical handover (VH) algorithms are required in maintaining a seamless connectivity and an acceptable level of quality for mobile users in heterogeneous environments. This paper proposes an analytical method for evaluating the performance of a VH algorithm that relies on the Received Signal Strength Indicator (RSSI) samples. The system model is portrayed upon addressing relevant factors that affect the quality and continuity of a voice call, and a set of performance metrics is proposed. A rigorous signal strength time series is utilized in characterizing the instantaneous decision metrics, and a novel intermediary system model, namely the N-model, is proposed to capture the large-scale shadowing effects. The performance of a generic algorithm that relies on the RSSI, which itself is susceptible to estimation error, is evaluated for an MT roaming in and out of the WLAN coverage area. Results obtained using the analytical expressions are validated by comparing them to that obtained through Monte Carlo simulation.

Vertical Handover Analysis for Voice over WLAN/Cellular Network

The development of handheld mobile terminals (MT) capable of operating over both cellular networks and Wireless Local Area Networks (WLAN) is an important step towards the evolution of next-generation integrated networks. For real-time applications, maintaining a seamless connectivity and an acceptable level of quality is essential, and efficient vertical handover (VH) algorithms are required. This paper proposes an analytical framework of evaluating the performance of VH algorithms for the voice application over a WLAN/cellular inter-working environment. The performance of a generic algorithm that uses the Received Signal Strength Indicator samples to estimate the WLAN usability is evaluated for an MT roaming in and out of the WLAN coverage area under the random waypoint model. The analytical procedure is utilized in deriving the required signal strength thresholds upon which an MT bases its handover decisions, and validated through Monte Carlo simulation.

Analysis of an Instantaneous Packet Loss Based Vertical Handover Algorithm for Heterogeneous Wireless Networks

For real-time applications running over hand-held mobile terminals in heterogeneous environments, efficient vertical handover (VH) algorithms are required in maintaining a seamless connectivity and an acceptable level of quality. While received signal strength-based methods have dominated this class of algorithms, we propose a thorough system analysis framework and perform rigorous analysis for packet-loss based algorithms for an interworking environment comprising the cellular network and the Wireless Local Area Network (WLAN). The basic VH algorithm analyzed here is based on the moving average of the packet loss rate and we employed both a simple packet loss and Gilbert packet loss pattern. Modifications to the analytical framework have been made by employing block-wise packet loss patterns in order to keep the computational burden within practical limits. Performance trends of call drop probabilities and WLAN usage efficiency are shown with varying system and handover thresholds, and analytical results are compared to that obtained from Monte Carlo simulations.

Numerically efficient generation of exponentially correlated two-dimensional shadowing

In wireless communication environments, shadow fading represents signal fluctuations around the average path loss of a transmitted signal due to the orientation of large obstructions in the way of the propagating electromagnetic waves. This paper aims at generating shadow fading maps that can be used in simulations of realistic mobile radio network scenarios. The focus is on achieving two-dimensional spatial correlation of the shadow fading values with low numerical burden. Instead of the standard filtering procedure that requires a numerically exhaustive two-dimensional convolution, we propose an iterative multi-stage algorithm that achieves close to ideal correlation properties among the shadow-faded random variables at a substantially higher computational speed.

Analysis of a buffered cognitive wireless network with dynamic spectrum assignment

In a cognitive wireless network, the sudden arrival of a primary user (PU) can force one or more secondary users (SU) to terminate their ongoing communication. Buffers can be utilized to prevent them from dropping, but their effectiveness depends on the tolerance of the SUs to the buffer waiting time. In this paper, we propose to dynamically assign service rates to the SUs to complement the gain offered by the network buffers in reducing the dropping probability of the SUs. Our analysis is based on a two-dimensional Markov chain with four state variables. Performance metrics for the SUs such as dropping, blocking and completion probabilities, and the average time spent in buffer are derived. Our analytical results demonstrate that depending on the network condition, the proposed dynamic spectrum assignment scheme is alone capable of reducing the dropping probability substantially. Since the sum of call completion, blocking and dropping probabilities is 1, the reduction of dropping probability of the SUs is achieved by increasing the sum of call blocking and completion probabilities, which not necessarily implies higher blocking or reduced completion probabilities.

Waveform Transmission Scheme for MIMO Radar Imaging Based on Space-Time Block Codes

The purpose of the work presented have is to employ space-time block codes (STBC) to eliminate the cross-correlation effects among parallelly transmitted probing signals of a multiple-input multiple-output (MIMO) radar imaging system. By exploiting the diversity offered by the transmission scheme, the hardware requirement can be substantially reduced compared with conventional technology.

WLAN/cellular handover analysis for different mobility models

With the proliferation of a multitude of diverse yet coexistent array of networks in the recent past, the heterogeneous environment is foreseen to serve mobile terminals (MT) in a complementary fashion at large. Multimodal MTs can now switch interfaces between Wireless Local Area Networks (WLAN) and the cellular network. In order to exploit the heterogeneity of the wireless environment, MTs require smart medium selection methods. In this paper, we derive a practical yet tractable method of evaluating vertical handover (VH) algorithms for mobile voice users over heterogeneous environments. The random direction and the Gauss-Markov mobility models are analyzed as an extension to the previously studied random waypoint model. The performance of a VH algorithm is evaluated for an MT roaming in and out of the WLAN coverage area under these mobility models. The analytical procedure is utilized in deriving the required signal strength thresholds upon which an MT bases its handover decisions for a given outage probability.

Performance Analysis of Vertical Handover Algorithm Based on Expected WLAN Lifetime

The widespread deployment of Wireless Local Area Networks (WLAN) over the last decade, and advances in wireless access technologies, have endowed handheld mobile terminals (MT) with multimodal connectivity features. Multimodal MTs can now switch interfaces between the WLAN and the cellular network, and select their network of choice in real-time. In order to exploit the heterogeneity of the wireless environment, MTs require efficient vertical handover (VH) algorithms. In this paper, we present an analytical method of evaluating VH algorithm performance for mobile voice users over heterogeneous environments. An algorithm that computes the expected WLAN-lifetime of an MT, and uses it along with the Received Signal Strength Indicator (RSSI) in determining the appropriate handover instance, is analyzed. The average number of handovers per crossover of the WLAN border region, and the average bandwidth available to the MT, are analytically derived and compared to simulation results.

Modeling of User-Perceived Web-Browsing Performance over a WLAN/3G Inter-Working Environment

The wide deployment of Wireless Local Area Networks (WLAN) and the advent of Third Generation (3G) networks have provided users with the flexibility of switching between dissimilar networks while running different applications. A Mobile Terminal (MT) can be equipped with multimodal functionalities, and can select the wireless interface that best suits its needs. This paper specifically focuses on the web-browsing application, and models the user-perceived performance for an MT operating over a WLAN/3G environment. A system model is proposed that facilitates performance evaluation of web-browsing sessions in terms of different network metrics. The effect of user mobility and that of variations in network characteristics are incorporated. A simulation framework has been developed and the results generated are presented to demonstrate the utility of the data-session modeling and handover algorithms proposed in this paper.