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Mardani M.,University of Minnesota | Seifali Harsini J.,Guilan University | Lahouti F.,University of Tehran | Eliasi B.,Iran Telecommunication Research Center
IEEE Transactions on Vehicular Technology | Year: 2011

In a cooperative relay network, a relay (R) node may facilitate data transmission to the destination (D) node when the latter node cannot correctly decode the source (S) node data. This paper considers such a system model and presents a cross-layer approach to jointly design adaptive modulation and coding (AMC) at the physical layer and the truncated cooperative automatic repeat request (C-ARQ) protocol at the data-link layer for quality-of-service (QoS)-constrained applications. The average spectral efficiency and packet loss rate of the joint C-ARQ and AMC scheme are first derived in closed form. Aiming to maximize the system spectral efficiency, AMC schemes for the S-D and R-D links are optimized, whereas a prescribed packet-loss-rate constraint is satisfied. As an interesting application, joint link adaptation and blockage mitigation in land mobile satellite communications (LMSC) with temporally correlated channels is then investigated. In LMSC, the S node data can be delivered to the D node when the S-D is in the outage, therefore provisioning the QoS requirements. For applications without instantaneous feedback, an optimized rate selection scheme based on the channel statistics is also devised. Detailed and insightful numerical results are presented, which indicate the superior performance of the proposed joint AMC and C-ARQ schemes over their optimized joint AMC and traditional ARQ counterparts. © 2010 IEEE.

Sheibani K.,Iran Telecommunication Research Center
IEEM2010 - IEEE International Conference on Industrial Engineering and Engineering Management | Year: 2010

This paper describes a hybrid meta-heuristic for combinatorial optimization problems with specific reference to the travelling salesman problem (TSP). The method is a combination of genetic algorithms (GA) and greedy randomized adaptive search procedures (GRASP). A new adaptive fuzzy greedy search operator is developed for this hybrid method. Computational experiments using a wide range of standard benchmark problems indicate that the proposed hybrid meta-heuristic is very efficient. ©2010 IEEE.

Sheikhpour R.,Islamic Azad University at Tehran | Jabbehdari S.,Islamic Azad University at Tehran | Khademzadeh A.,Iran Telecommunication Research Center
International Journal of Multimedia and Ubiquitous Engineering | Year: 2012

Wireless sensor networks have recently emerged as an important computing platform. Energy conservation and maximization of network lifetime are commonly recognized as a key challenge in the design and implementation of wireless sensor networks. Clustering provides an effective method for prolonging the lifetime of a wireless sensor network. In this paper, we propose an Energy Efficient Cluster-Chain based Protocol (ECCP) for wireless sensor networks. The main goal of ECCP is to distribute the energy load among all sensor nodes to minimize the energy consumption and maximize the network lifetime of wireless sensor networks. ECCP organizes sensor nodes into clusters and constructs a chain among the sensor nodes within cluster so that each sensor node receives from a previous neighbor and transmits to a next neighbor. Furthermore, ECCP improves the data transmission mechanism from the cluster heads to the base station via constructing a chain among the cluster heads. Simulation results demonstrate that our proposed protocol significantly outperforms LEACH, CBRP and PEGASIS in terms of network lifetime, stability period, instability period, energy savings, balancing energy consumption among sensor nodes and network throughput.

Razavi M.,Islamic Azad University at Tehran | Aliee F.S.,Shahid Beheshti University | Badie K.,Iran Telecommunication Research Center
Knowledge and Information Systems | Year: 2011

Enterprise Architecture (EA) as a discipline that manages large amount of models and information about different aspects of the enterprise, can support decision making on enterprise-wide issues. In order to provide such support, EA information should be amenable to analysis of various utilities and quality attributes. In this regard, we have proposed the idea of characterizing and using enterprise architecture quality attributes. And this paper provides a quantitative AHP-based method toward expert-based EA analysis. Our method proposes a step-by-step process of assessing quality attribute achievement of different scenarios using AHP. By this method, most suitable EA scenarios are selected according to prioritized enterprise utilities and this selection has an important affect on decision making in enterprises. The proposed method also introduces a data structure that contains required information about quality attribute achievement of different EA scenarios in enterprises. The stored asset can be used for further decision making and progress assessment in future. Sensitivity analysis is also part of the process to identify sensitive points in the decision process. The applicability of the proposed method is demonstrated using a practical case study. © 2010 Springer-Verlag London Limited.

Daeinabi A.,Sahand University of Technology | Pour Rahbar A.G.,Sahand University of Technology | Khademzadeh A.,Iran Telecommunication Research Center
Journal of Network and Computer Applications | Year: 2011

Vehicular ad hoc networks (VANETs) are appropriate networks that can be used in intelligent transportation systems. Among challenges in VANET, scalability is a critical issue for a network designer. Clustering is one solution for the scalability problem and is vital for efficient resource consumption and load balancing in large scale networks. As our first algorithm, we propose a novel clustering algorithm, vehicular clustering based on the weighted clustering algorithm (VWCA) that takes into consideration the number of neighbors based on dynamic transmission range, the direction of vehicles, the entropy, and the distrust value parameters. These parameters can increase stability and connectivity and can reduce overhead in network. On the other hand, transmission range of a vehicle is important for forwarding and receiving messages. When a fixed transmission range mechanism is used in VANET, it is likely that vehicles are not located in the range of their neighbors. This is because of the high-rate topology changes and high variability in vehicles density. Thus, we propose an adaptive allocation of transmission range (AATR) technique as our second algorithm, where hello messages and density of traffic around vehicles are used to adaptively adjust the transmission range among them. Finally, we propose a monitoring of malicious vehicle (MMV) algorithm as our third algorithm to determine a distrust value for each vehicle used in the VWCA. The effectiveness of the proposed algorithms is illustrated in a highway scenario. © 2010 Elsevier Ltd. All rights reserved.

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