Sharif Digital Repository

MANET, which stands for Mobile Ad-hoc Network, is composed of a group of self-organized and wireless nodes that do not possess any predictable and fixed infrastructure. When nodes want to communicate with each other, they have to pass on their messages directly or indirectly. In case the destination node is out of the transmission range, the source node has to rely on intermediate nodes, which, in this case, is called indirect transmission. On the other hand, if the destination node is the neighboring node, there is no need to employ intermediate nodes, which, in this case, is called direct transmission. Over the past years, security issues in MANETs have received a great deal of attention... 

In a distributed algorithm several processing nodes communicate with each other and incorporate in order to reach a common goal. Each unit has its own locally-observed environment while it can either help or mislead other units when sharing its information. This could be either intentional or simply due to the observation noise. Previous works mainly focus on locating the agents properly and assigning weights based on stationary environment in order to minimize the impact of noisy nodes. We, however, propose a method capable of assigning combination weights in accordance with momentary performance of the neighboring nodes. In order to demonstrate this capability, the proposed algorithm has... 

The Social Internet of Things (SIoT), integration of the Internet of Things, and Social Networks paradigms, has been introduced to build a network of smart nodes that are capable of establishing social links. In order to deal with misbehaving service provider nodes, service requestor nodes must evaluate their trustworthiness levels. In this article, we propose a novel trust management mechanism in the SIoT to predict the most reliable service providers for each service requestor, which leads to reduce the risk of being exposed to malicious nodes. We model the SIoT with a flexible bipartite graph (containing two sets of nodes: service providers and service requestors), then build a social... 

Topology control in mobile ad-hoc networks allows better spatial reuse of the wireless channel and control over network resources. Topology control algorithms tend to optimize network power usage by keeping the topology connected. However, few efforts have focused on the issue of topology control with mobility. One of the most efficient mobility aware topology control protocols is the "Mobility Aware Distributed Topology Control Protocol". The major problem with this protocol is the future distance predictor which uses mobility prediction to estimate the future distance of neighboring nodes. The efficiency of this estimator varies in presence of different mobility models, sampling rates and... 

As multi-hop wireless networks are attracting more attention, the need to evaluate their performance becomes essential. In order to evaluate the performance metrics of multi-hop wireless networks, including sending and receiving rates of a node as well as the collision probability, a model based on Stochastic Reward Nets (SRNs) is proposed. The proposed SRN models a typical node in such networks, considered as a general template to be applied to any wireless node. The SRN model of a single node is designed to take transmission effects of all neighboring nodes into account, while ignoring the ones whose transmission has no effect on the node under-study. Applying the proposed SRN to each node... 

Regarding the dynamic nature of cognitive radio networks and the delay of the central decision algorithms due to collecting necessary information in a multi-hop wireless network, distributed resource allocation algorithms are of crucial importance. In this paper we propose a new distributed resource allocation algorithm that properly selects link/frequency in a multi-hop cognitive radio network for delay sensitive applications. This algorithm, uses the locally collected information from neighboring nodes to make suitable routing decisions regarding the dynamic environment and the behavior of the neighbors. We consider the delay as the routing criterion, consisting the queueing delay and the... 

This paper presents a centralized fault detection algorithm for wireless sensor networks. Faulty sensor nodes are identified based on comparisons between neighboring nodes and own central node and dissemination of the decision made at each node. RNS system is used to tolerate transient faults in sensing and communication. In this system, arithmetic operations act on residues - reminder of dividing original number in several definite modules - in parallel. Consequently computations on these residues which are smaller than the original number are performed, so speed up arithmetic and decreased power consumption is achieved. ©2009 IEEE  

In this paper, an approach for topology control has been proposed which make use of distance estimation and angle of arrival (AoA) estimation techniques. Every node in the network tries to keep the number of its neighbors to 4 or 3. These neighbors have been selected from the nearest neighbors of each node and are located in different four quarters of axis. The angular difference between these neighbors is between a minimum and maximum value. This protocol guarantees connectivity on the communication graph with high probability and enforces symmetry on the resulting communication graph, thereby easing the operation of higher level protocols. The performance of the protocol when nodes are... 

Currently, some coarse measures like global network latency are used to compare routing protocols. These measures do not provide enough insight of traffic distribution among network nodes in the presence of different fault regions. This paper presents a detailed traffic analysis of fault-tolerant planar adaptive routing (FTPAR) algorithm achieved by an especially developed tool. Per-node traffic analysis illustrates the traffic hotspots caused by fault regions and provides a great assistance in developing fault tolerant routing algorithms. Based on such detailed information, a simple yet effective improvement of FTPAR is suggested. Moreover, the effect of a traffic hotspot on the traffic of... 

In ad hoc wireless networks, there are scenarios where the desired destination is located in the range of other transmitters, so that the efforts on setting up communication with this terminal will fail due to collisions that may occur between transmitted control frames and undesired received control and data frames. This phenomenon becomes a bottleneck when most of data transmissions experience packet fragmentation. In such scenarios, the desired destination becomes unreachable during the data transfer of neighboring nodes. Using the same PHY of IEEE 802.11 and making slight modifications in its MAC, a new medium access control scheme equipped by a novel transmission scheduling algorithm is...