Mehrdad Dianati

A node-cooperative ARQ scheme for wireless ad hoc networks

In this paper, the authors propose a node-cooperative automatic repeat request (ARQ) scheme for wireless ad hoc networks, which is suitable for mobile wireless channels with high and correlated frame-error profile. An analytical model based on a two-state Markovian process is proposed to describe the behavior of the proposed retransmission scheme and to obtain its throughput, average delay, and delay jitter. The results of Monte Carlo simulations are included to demonstrate the efficacy of the proposed scheme and to verify the accuracy of the analytical models. Results show that a cooperation among a small number of nodes can significantly improve the performance of the retransmission process in terms of throughput, average delay, and delay jitter by reducing the average duration of retransmission trials

Analytical Study of the IEEE 802.11p MAC Sublayer in Vehicular Networks

This paper proposes an analytical model for the throughput of the enhanced distributed channel access (EDCA) mechanism in the IEEE 802.11p medium-access control (MAC) sublayer. Features in EDCA such as different contention windows (CW) and arbitration interframe space (AIFS) for each access category (AC) and internal collisions are taken into account. The analytical model is suitable for both basic access and the request-to-send/clear-to-send (RTS/CTS) access mode. Different from most of existing 3-D or 4-D Markov-chain-based analytical models for IEEE 802.11e EDCA, without computation complexity, the proposed analytical model is explicitly solvable and applies to four access categories of traffic in the IEEE 802.11p. The proposed model can be used for large-scale network analysis and validation of network simulators under saturated traffic conditions. Simulation results are given to demonstrate the accuracy of the analytical model. In addition, we investigate service differentiation capabilities of the IEEE 802.11p MAC sublayer.

A new fairness index for radio resource allocation in wireless networks

In this paper, we investigate the measurement of fairness, discuss well known fairness notions, and propose a new utility-based framework to evaluate the degree of fairness of resource allocation schemes in wireless access networks. The proposed framework has certain desirable features. It offers clear definitions and relevant methodology, takes into account both effort and service unfairness, and can be customized for different application types with different QoS requirements. Numerical examples and case studies are given to demonstrate the effectiveness of the proposed framework.

Performance study of a Green Light Optimized Speed Advisory (GLOSA) application using an integrated cooperative ITS simulation platform

This paper proposes a Green Light Optimized Speed Advisory (GLOSA) application implementation in a typical reference area, and presents the results of its performance analysis using an integrated cooperative ITS simulation platform. Our interest was to monitor the impacts of GLOSA on fuel and traffic efficiency by introducing metrics for average fuel consumption and average stop time behind a traffic light, respectively. For gathering the results we implemented a traffic scenario defining a single route through an urban area including two traffic lights. The simulations are varied for different penetration rates of GLOSA-equipped vehicles and traffic density. Our results indicate that GLOSA systems could improve fuel consumption and reduce traffic congestion in junctions.

Energy efficiency in heterogeneous wireless access networks

In this article, we bring forward the important aspect of energy savings in wireless access networks. We specifically focus on the energy saving opportunities in the recently evolving heterogeneous networks (HetNets), both Single- RAT and Multi-RAT. Issues such as sleep/wakeup cycles and interference management are discussed for co-channel Single-RAT HetNets. In addition to that, a simulation based study for LTE macro-femto HetNets is presented, indicating the need for dynamic energy efficient resource management schemes. Multi-RAT HetNets also come with challenges such as network integration, combined resource management and network selection. Along with a discussion on these challenges, we also investigate the performance of the conventional WLAN-first network selection mechanism in terms of energy efficiency (EE) and suggest that EE can be improved by the application of intelligent call admission control policies.

A Novel Distributed Asynchronous Multichannel MAC Scheme for Large-Scale Vehicular Ad Hoc Networks

This paper proposes a novel distributed asynchronous multichannel medium access control (MAC) scheme for large-scale vehicular ad hoc networks (VANETs), i.e., asynchronous multichannel medium access control with a distributed time-division multiple-access mechanism (AMCMAC-D). The proposed scheme supports simultaneous transmissions on different service channels while allowing rendezvous and broadcast of emergency messages on the control channel. The scheme is distributed, because it handles access to the shared control channel for different access categories without relying on the beacon frames from roadside units. This condition eliminates the overhead that is associated with channel allocation, making the proposed scheme suitable for large-scale networks in terms of the number of active nodes. Service differentiation in the proposed scheme is enhanced by allocating different numbers of time slots for different access categories. We compare the performance of the proposed scheme with the IEEE 1609.4 standard and the asynchronous multichannel Coordination Protocol (AMCP) in terms of throughput, packet delivery rate, collision rate, utilization of service channels, service differentiation, and the penetration rate of noncollided emergency messages. The results show that AMCMAC-D outperforms the IEEE 1609.4 standard and AMCP in terms of system throughput by increasing the utilization of the control channel and service channels. The proposed scheme also demonstrates better performance in terms of packet delivery rate, collision rate on a service channel, load balancing, and service differentiation. Finally, AMCMAC-D mitigates the multichannel hidden terminal and missing receiver problems, which occur in asynchronous multichannel MAC schemes.

Cooperative Fair Scheduling for the Downlink of CDMA Cellular Networks

In this paper, we study cooperation among the adjacent base stations (BSs) for downlink scheduling in code division multiple access cellular networks. We propose a cooperative fair scheduling scheme, namely, cooperative utility fair scheduling, to increase multiuser diversity gain and reduce interference among BSs. The scheduler maintains fairness and smooth service delivery by balancing the long-term average throughput of users. Monte Carlo simulation results are given to demonstrate the effectiveness of the proposed scheme in terms of multiuser diversity gain, throughput, and fairness.

CLWPR — A novel cross-layer optimized position based routing protocol for VANETs

In this paper, we propose a novel position-based routing protocol designed to anticipate the characteristics of an urban VANET environment. The proposed algorithm utilizes the prediction of the nodes position and navigation information to improve the efficiency of routing protocol in a vehicular network. In addition, we use the information about link layer quality in terms of SNIR and MAC frame error rate to further improve the efficiency of the proposed routing protocol. This in particular helps to decrease end-to-end delay. Finally, carry-n-forward mechanism is employed as a repair strategy in sparse networks. It is shown that use of this technique increases packet delivery ratio, but increases end-to-end delay as well and is not recommended for QoS constraint services. Our results suggest that compared with GPSR, our proposal demonstrates better performance in the urban environment.

Opportunistic fair scheduling for the downlink of IEEE 802.16 wireless metropolitan area networks

In this paper, we propose a novel scheduling scheme for the downlink of IEEE 802.16 networks. A scheduler at the Base Station (BS) decides the order of downlink bursts to be transmitted. The decision is made based on the quality of the channel and the history of transmissions of each Subscriber Station (SS). The scheduler takes advantage of temporal channel fluctuations to increase the BSs throughput and maintain fairness by balancing the long term average throughput of SSs. Simulation results are given to demonstrate the performance of the proposed scheduling scheme.

Architecture and protocols of the future European quantum key distribution network

Summary A point-to-point quantum key distribution (QKD) system takes advantage of the laws of quantum physics to establish secret keys between two communicating parties. Compared to the classical methods, such as public-key infrastructures, QKD offers unconditional security, which makes it attractive for very high security applications. However, this unprecedent level of security is mitigated by the inherent constraints of quantum communications, such as the limited rates and ranges of an individual point-to-point QKD link. A QKD network, which can be built by combining multiple point-to-point QKD devices, can alleviate the constraints and enable point-to-multi-point key distribution based on QKD technology. The European project, secure communication based on quantum cryptography (SeCoQC) aims at deploying a prototype QKD network, which will be demonstrated in September 2008, by developing the architecture and the protocols, as well as the specific hardware for long-range QKD networks. This paper discusses the important aspects of the architecture and the network layer protocols of the SeCoQC QKD network. Copyright