Sharif Digital Repository

Many applications in wireless networks impose locally distributed traffic on the network. We consider the effect of traffic localization on throughput of large wireless networks in the scaling sense. We show that by careful exploitation of traffic localization, one can enhance the throughput of various schemes in wireless networks. Also, the important case of Small World traffic distribution in wireless networks is addressed. In this type of traffic, in addition to the local traffic, a non-negligible amount of global traffic should be handled by the network. It is shown that a non-negligible amount of network-wide traffic can be tolerated by network without any performance degradation in the... 

With the increasing use of pervasive computing environments (PCEs), developing dynamic reconfigurable software in such environments becomes an important issue. The ability to change software components in running systems has advantages such as building adaptive, long-life, and self-reconfigurable software as well as increasing invisibility in PCEs. As dynamic reconfiguration is performed in error-prone wireless mobile systems frequently, it can threaten system safety. Therefore, a mechanism to support assured dynamic reconfiguration at run-time for PCEs is required. In this paper, we propose an Assured Dynamic Reconfiguration Framework (ADRF) with emphasis on assurance analysis. The... 

In this paper, the distributed recovery units for FM and PPM demodulation in wireless sensor networks is proposed and is showed that, the method introduces very little amount of distortion to recovered signal. With simulations, we have examined several different parameters. Besides, two different filtering schemes are simulated. Effect of iteration coefficient (X) on stability and convergence rate is investigated for different sampling and filtering methods. Next, we have studied the noise effect in demodulation with this method. Simulations results are included to verify convergence. © Springer-Verlag Berlin Heidelberg 2005  

We propose a new coded cooperation scheme for wireless communications to obtain transmit diversity in the scenarios that agents such as mobile handsets, sensor network nodes and etc., due to size, power or other constraints, cannot utilize multiple antennas. New scheme supports more than two cooperative users with a relatively low cooperation level. We evaluate the performance of the proposed scheme in a frequency nonselective slow fading channel. For two cooperative users, we provide the exact analytical analysis. However, for more than two users, as the analytical analysis is very complicated, our performance evaluation is based on computer simulations. Our numerical results show that each... 

In this paper a combination of routing and power management within the context of wireless Ad-hoc Sensor Networks is considered. Using lower layer information (e.g. collision that is considered in MAC layer) is another novel concern which is used in routing decisions. More specifically in this paper we introduce a cross-layer design in which each node dynamically chooses the number of its neighbors and adjusts its power just enough to reach its farthest determined neighbor. In this algorithm the power of transmission and collision are used as metrics for routing and the number of neighbors in which the total energy consumption in data transmission will be the minimum is selected. © 2005 IEEE... 

This paper proposes a new medium-access control (MAC) protocol designed for wireless sensor networks. A wireless sensor network is an array of large number of sensors interconnected by a multi-hop ad-hoc network. The fundamental objective for sensor network is low-power consumption while latency is usually less important. This characteristic of sensor network motivates different MAC laver design from the conventional wireless network to reduce power consumption. In this paper novel algorithm based on distributed mediation device (DMD) protocol has been introduced that utilized distributed node scheduling strategy to dramatically increase energy saving principally in intermediate devices... 

A source model for secret key generation between terminals is considered. Two users, namely users 1 and 2, at one side communicate with another user, namely user 3, while at the other side via a public channel where three users can observe i.i.d. outputs of correlated sources. Each of users 1 and 2 intends to share a secret key with user 3 where user 1 acts as a wiretapper for user 2 and vice versa. In this model, two situations are considered: communication from users 1 and 2 to user 3 (the forward key strategy) and from user 3 to users 1 and 2 (the backward key strategy). In both situations, the goal is sharing a secret key between user 1 and user 3 while leaking no effective information... 

With the evolution and significant growth in wireless technology and the development of mobile commerce, businesses can achieve superior performance through the implementation of platforms for mobile payment. However, there are several platforms for mobile payment to choose from which makes the selection of an appropriate platform for specific applications a challenging task. In response to this challenge, the most common mobile payment platforms recorded in the literature have been reviewed. This paper presents the result of this review describing the advantages and disadvantages of each system and offers ranking of the technologies considered. MCDM method is used for assessing and... 

Energy harvesting has been developed as an effective technology for communication systems in order to extend their lifetime. In this paper, we consider a single-user energy harvesting wireless communication system, in which arrival data and harvested energy curves are modeled as continuous functions. Our first goal is to find an offline algorithm, which maximizes the amount of data, which is transmitted to the receiver node by a given deadline. If more than one scheme exists that transmits the maximum data, we choose the one with minimum utilized energy at the transmitter node. We find this optimal algorithm, by showing its properties. Next, we propose an online algorithm for this system and... 

Matching theory is a powerful tool to study the formation of dynamic and mutually beneficial relations among different types of rational and selfish agents. It has been widely used to develop high performance, low complexity, and decentralized protocols. In this article, a comprehensive survey of matching theory, its variants, and their significant properties appropriate for the demands of wireless communications and network engineers is provided. Recent research progress in applying matching theory to wireless communications to address major technical opportunities and challenges is presented. A novel classification of matching models from the practical perspective is provided, and the... 

In many wireless communication protocols, small and random delay, called jitter, is imposed before packet transmission so as to reduce packet collisions. Jitter is recommended for many routing protocols such as AODV and LOADng. Jitter can be exploited to change the order of routes about which destination is informed and, as a result, make better routes, regarding their metric, more likely to choose by the destination. However, to the best of our knowledge, there is only one mechanism, called adaptive jitter mechanism, proposed for metric-based routing protocols. In this paper, we aim to show feasibility of using different random variables for jittering and define some shaping functions to... 

Energy harvesting has been developed as an effective technology for communication systems in order to extend the lifetime of these systems. In this work, we consider a single-user energy harvesting wireless communication system, in which both of the arrival data and the harvested energy curves are modeled as continuous functions. Our goal is to find an offline algorithm, which maximizes the amount of data which is transmitted to the receiver node by a given deadline. If more than one scheme exist that transmit the maximum data, we choose the one with minimum utilized energy at the transmitter node  

the failure in cluster at a high level can bring up great damages to the system in wireless sensor networks where clustering techniques are used. Certain methods have been reported in the literature in recovering the sensors from a failure cluster. One of the most important methods is to recover the sensors in run-time and without clustering. But it is so much ideal to suppose that all the sensors will be recovered. In this paper, we proposed a method that can operate on the remained sensors that are not recovered. © 2009 IEEE  

Centralized coded caching and delivery is studied for a partially-connected fog radio access network (F-RAN), whereby a set of H edge nodes (ENs) (without caches), connected to a cloud server via orthogonal fronthaul links, serve K users over the wireless edge. The cloud server is assumed to hold a library of N files, each of size F bits; and each user, equipped with a cache of size MF bits, is connected to a distinct set of r ENs; or equivalently, the wireless edge from the ENs to the users is modeled as a partial interference channel. The objective is to minimize the normalized delivery time (NDT), which refers to the worst case delivery latency, when each user requests a single file from... 

We consider a slotted Aloha-based wireless communication network comprising a source and an active relay, both transmitting to a common destination. The relay node is able to relay the unsuccessfully transmitted packets of the source node, if it can detect them. We find the analytical closed form optimal static relaying policy in order to minimize the average transmission delay (ATD) of source packets, while ATD of its own packets is constrained. A static relaying policy is determined by acceptance and relaying probabilities of the relay node. According to acceptance probability, the relay node decides whether to accept an unsuccessfully transmitted packet from source or not, while the... 

In this paper we introduce a new class of codes for over-loaded synchronous wireless CDMA systems which increases the number of users for a fixed number of chips without introducing any errors. In addition these codes support active user detection. We derive an upper bound on the number of users with a fixed spreading factor. Also we propose an ML decoder for a subclass of these codes that is computationally implementable. Although for our simulations we consider a scenario that is worse than what occurs in practice, simulation results indicate that this coding/decoding scheme is robust against additive noise. As an example, for 64 chips and 88 users we propose a coding/decoding scheme that... 

In this paper, we illustrate the design of a cross layered MAC and routing solution for supporting the fast propagation of broadcast messages at intersections in a Vehicular Ad Hoc Network (VANET). One of the fundamental services in VANET is broadcasting, that is a challenging task due to different road topologies and network conditions. One of its challenges is broadcasting at intersections, because vehicles in different roads constituting an intersections can affect on broadcast process of other roads, message may not be propagated in some directions. In this paper we propose a cross layered method that by classifying vehicles based on their location and the road they move in, solves this... 

When there are transmission service requests for a specific sink/source pair in a transmission system, the ISO must allocate the available transfer capacity (ATC) of that pair to the requests. Since the requests could have different types, tariffs and time frames, the allocation must be accomplished in a sound and fair manner that incorporates various aspects of the requests. This paper proposes a comprehensive approach to allocation of ATC to transmission service requests. The proposed method considers types, tariffs, and priority of requests in a mixed-integer nonlinear optimization which incorporates the allocation rules. The solution to the optimization problem gives the amount of... 

To the best knowledge of us, survivability for WSN has never been studied considering failure affects on network. We perceive the network survivability as a composite measure consisting of both network failure duration and failure impact on the network. In this paper we will study network survivability in unstably state: in this state, network is affected by the failures that occur temporarily and instantly also may occur several times. In other words, the main characteristics of these failures are their frequency and being temporary. In this paper we will propose a survivability model for network in unstable state that is based on network availability. This availability model, presents... 

In this paper, the problem of resource allocation at an Ad hoc network with nodes not using any infrastructure to cooperate with each other is considered. By using a simple interference model in wireless links, the convergence and stability of a fair resource allocation scheme in the absence of delay is investigated. Also, the local stability of the scheme in the presence of upper-bounded delay is verified. Simulations results illustrate the convergence and fairness of this scheme considering different initial states for different sources. The performance of the scheme in the presence of different disturbances for each flow in transient and steady state along with its local stability in the...