On the Performance of Broadband Mobile Internet Access System

In this paper, we evaluate the performance of OFDMA/TDD-based broadband mobile internet access system with the features of adaptive modulation & coding (AMC) and hybrid ARQ. We present a framework of system-level simulation and furthermore, intend to derive the insightful results towards understanding the performance of broadband mobile internet access system. The average system throughput as well as delay performance is evaluated for the different channel characteristics and system parameters, which allows for predicting the system capacity in the varying cellular network environment.

Reducing the lightpath establishing time of FWM-aware dynamic RWA for wavelength-routed optical networks

A dynamic routing and wavelength allocation technique with an interplay between physical and network layer parameters encompassing Four-wave mixing (FWM) awareness and teletraffic performance of wavelength-routed optical networks has previously been proposed for a distributed approach. In this article, we present a fast computational algorithm for our routing and wavelength assignment (RWA) encompassing FWM-induced crosstalk. The objective is to minimize the time of establishing a dynamic lightpath. For this purpose, a precomputed matrix of FWM crosstalk products is used in an adapted version of the FWM-aware dynamic RWA algorithm. The approach is validated through simulations showing improvement up to 30–50% on the provisioning time of lightpaths for different network topologies compared to an online full computational scheme.

Virtual Identity Framework for Telecom Infrastructures

Identity Management has so far been a field mainly applications and Web focused. This paper describes a novel approach to cross layer identity management that extends digital identities to the network, the virtual identity (VID) framework. The VID framework provides strong privacy to the user, while easily supporting personalization cross-service providers. While other identity management solutions are tailored to one specific application and/or protocol domain, the proposed framework extends the use of one’s digital identity to all aspects of the network and services architecture. It is also the first to consider legal constrains, such as ownership of data and legal intercept issues, in such a broad scope. One major aspect reported here is the relevance for operators.

OSNR model to consider physical layer impairments in transparent optical networks

We propose a model that considers several physical impairments in all-optical networks based on optical signal-to-noise degradation. Our model considers the gain saturation effect and amplified spontaneous emission depletion in optical amplifiers, coherent crosstalk in optical switches, and four-wave mixing in transmission fibers. We apply our model to investigate the impact of different physical impairments on the performance of all-optical networks. The simulation results show the impact of each impairment on network performance in terms of blocking probability as a function of device parameters. We also apply the model as a metric for impairment-constraint routing in all-optical networks. We show that our proposed routing and wavelength assignment algorithm outperforms two common approaches.

A Tool for Unbiased Comparison between Logarithmic and Floating-point Arithmetic

For applications requiring a large dynamic, real numbers may be represented either in floating-point, or in the logarithm number system (LNS). Which system is best for a given application is difficult to know in advance, because the cost and performance of LNS operators depend on the target accuracy in a highly non linear way. Therefore, a comparison of the pros and cons of both number systems in terms of cost, performance and overall accuracy is only relevant on a per-application basis. To make such a comparison possible, two concurrent libraries of parameterized arithmetic operators, targeting recent field-programmable gate arrays, are presented. They are unbiased in the sense that they strive to reflect the state-of-the-art for both number systems. These libraries are freely available at .

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MGFs for Rayleigh Random Variables

Expressions are given for the moment generating functions of the Rayleigh and generalized Rayleigh distributions.

A dynamic hop count shifting RWA algorithm for wavelength routed optical networks

In this article, we find that the limiting hop count in a lightpath impacts on the performance of optical networks. Based on this observation, we propose a dynamic hop count shifting (DYHOS) algorithm that limits the hop count of lightpaths dynamically, depending on the traffic load. The proposed algorithm searches an available route, while minimizing the waste of network resources and limiting excessive traffic on the network. Hence, the proposed algorithm increases the network throughput and reduces the blocking probability. Comparing with shortest path routing and adaptive path routing algorithms, we show the performance of the proposed algorithm has the lowest blocking probability influenced by the hop count of lightpaths for a given routing algorithm.

D-STAR MAC Protocol: A Cross Layer Solution for Wireless Sensor Networks Endowed with Directive Antennas

This paper deals with a novel MAC layer protocol, namely Directive synchronous transmission asynchronous reception (D-STAR), which is able to logically synchronize a Wireless sensor network (WSN). In this case both sleep and active states together with integrating directional antennas within the communications framework can be managed, according to a cross-layer design. D-STAR protocol has been characterized in terms of functional characteristics and the overall performance is presented in terms of network lifetime gain, set-up latency and collision probability. A remarkable gain is shown with respect to the basic approach endowed with omnidirectional antennas without increasing the signaling overhead nor affecting the set up latency, but achieving energy consumption reduction.

HASP Overlay Cell Over Wireless ATM Microcellular Networks: A Proposed Architecture for Priority Subscribers

Wireless ATM (W-ATM) microcellular networks encounter severe problems during handovers. Microcellular solutions in W-ATM networks increase the network traffic control as a result of frequent handover requests. This paper presents a two-layer microcellular ATM architecture which optimizes the handoff blocking probability performance of priority subscribers (PS) in a congested urban area. The lower layer of the proposed architecture is based on a microcellular ATM solution for normal subscribers (NS) while the higher layer is based on a high altitude stratospheric platform (HASP) overlay solution for absorbing the traffic load of the existed handoff calls of PS. Analysis is performed using Markov state diagrams, in order to optimize the performance of W-ATM networks.

Dynamic Sensor Self-Organization for Distributive Moving Target Tracking

To support distributive tracking of moving targets in a wireless sensor network, sensors that receive signal from the same target must collaborate to facilitate collaborative, distributed target tracking. We present an efficient dynamic sensor self-organizing algorithm that clusters sensors into groups without requiring a centralized control. Extensive simulations are conducted to verify the performance improvement as well as the communication reduction for the proposed methods.

A feedback-based congestion control mechanism for labeled optical burst switched networks

In this article we describe a feedback-based OBS network architecture in which core nodes send messages to source nodes requesting them to reduce their transmission rate on congested links. Within this framework, we introduce a new congestion control mechanism called congestion control with explicit reduction request (CCERQ). Through feedback signals, CCERQ proactively attempts to prevent the network from entering the congestion state. Basic building blocks and performance tradeoffs of CCERQ are the main focus of this article.

A Policy-based Approach for Reconfiguration Management and Enforcement in Autonomic Communication Systems

This paper presents an overview of the policy-based reconfiguration management and enforcement for autonomic communication system platform (Pre-meacs). In contrast to existing management approaches, which require static priori policy configurations, policies are created dynamically. The proposed Pre-meacs framework creates new policies at runtime in response to the changing requirements. A hierarchical policy model is used to refine users and administrators’ high-level goals into low-level objectives. The new approach ensures the success of the reconfiguration through monitoring feedback. The main components of Pre-meacs framework for policy creation, storage, evaluation and enforcement are presented, and the procedures of Pre-meacs in networks reconfiguration management are also demonstrated. Illustrative example demonstrates the performance of the proposed framework.

Role of Convergence in GIMCV Development: A Vision

Path to Global Information Multimedia Communication Village (GIMCV) can be seen as a convergence process among telephony, data exchange and television. Convergence refers not only to various services provided by the same operator but also by the same device, the same access network, the same transport network, etc. This paper present authors’ vision on how convergence will lead the GIMCV development.

A new lightpath establishing method for dynamic traffic grooming under the overlay model

This paper proposes the use of the saturated cut (SC) method to improve the network performance through efficient dynamic traffic grooming in IP/MPLS over WDM networks using an overlay model. With the SC information from the IP/MPLS layer, the optical layer can calculate a lightpath between two node sets rather than the earlier suggested approach of calculating such paths just between two nodes for better performance. We have used two criteria, bandwidth and path length, to find SCs and have proposed two algorithms which incorporate this in the path inflation control (PIC) policy proposed earlier. Two typical networks, NSF and COST239, were used for examining the network performance. The simulation results show that though both methods can significantly improve the overall network performance the SC method is more efficient for a sparse network like the NSF network rather than for a dense network like the COST239 network. Since calculating lightpaths for all node pairs for a SC is time consuming, we propose a considerably simpler heuristic approach that can provide almost the same level of performance improvement as the SC method but with much lower complexity.

Performance analysis of an improved soft preemptive scheme for unevenly distributed traffic in optical wavelength-division multiplexing networks

In optical wavelength-division multiplexing (WDM) networks, traffic can be unevenly distributed across the network causing inefficient utilization of resources. To solve this problem, an improved soft preemptive (SP) scheme is proposed by considering dynamic resource distribution to deal with the uneven network utilization. A novel unevenly distributed traffic model in cross-time-zone networks is also presented to evaluate the efficiency of the new scheme. Compared with other schemes such as normal shortest path first (SPF) routing and wavelength conversion (WC), the new proposed scheme results demonstrate significantly better performance with respect to the network utilization and overall network blocking probability.

Supporting voice and video applications over IEEE 802.11n WLANs

In this paper, an analytical model is developed for the performance study of an IEEE 802.11n wireless local area network (WLAN) supporting voice and video services, considering the new features of the medium access control (MAC) protocol proposed in IEEE 802.11n, i.e., frame aggregation and bidirectional transmission. We show that these enhanced MAC mechanisms can effectively improve the network capacity by not only reducing the protocol overheads, but also smoothing the AP-bottleneck effect in an infrastructure-based WLAN. Voice and video capacity under various MAC mechanisms are compared as well.

Improving performance of TCP over mobile wireless networks

Mobile IP is a network layer protocol for handling mobility of hosts in the Internet. However, mobile IP handoff causes degradation of TCP performance. Hence, there is a need for improving performance of TCP over mobile IP in wireless mobile networks. We propose an approach which handles losses due to both wireless link errors and host mobility. To handle losses due to host mobility, a method for seamless handoff is proposed. Empirical results show that the scheme provides substantial improvement of performance.

A connectivity-based approach for the construction of hierarchical WDM network topology

A hierarchical network model can effectively reduce the complexity of routing and wavelength assignment (RWA) in wavelength division multiplexing (WDM) networks compared to a flat model. However, the resource utilization may greatly suffer if the hierarchical architecture is not properly arranged. By considering the degree of each WDM node and the location effect, this paper proposes a systematic approach to construct the hierarchical topology in WDM networks so that resource utilization can be maximized. Simulation results demonstrate that the performance of the proposed scheme is superior to that of another scheme.

Improved Fractional Fourier Transform Based Receiver for Spatial Multiplexed MIMO Antenna Systems

In this work the performance of a Fractional Fourier transform (FrFT) based Minimum Mean Squared Error receiver for MIMO systems with space time processing over Rayleigh faded channels is presented. The proposed receiver called Optimum FrFT based MIMO receiver (OFMR) shows improved performance outperforming the simple MMSE receiver in Rayleigh faded channel.