Sharif Digital Repository

Development of Smart Grid and deployment of smart meters in large scale has raised a lot of concerns regarding customers’ privacy. Consequently, several schemes have been proposed to overcome the above mentioned issue. These schemes mainly rely on data aggregation as a method of protecting users’ privacy from the grid operators. However, the main problem with most of these schemes is the fact that they require a large amount of processing power at the meter side. This, together with the fact that smart meters don't usually have a powerful processor, can cause the unavailability of smart meter data at the required time for operators of the grid, and at the same time prevents smart meters from... 

In this paper, we show how time-sharing method may reduce transmission delay in the dynamic index coding scenario. We propose a novel time-shared dynamic index coding transmission scheme that achieves the maximum index coding gain for a complete bi-directional side information graph and formulate a constrained optimization problem to tune the transmission scheme for the minimum transmission delay. A closed-form solution is presented for the special case of two-user. We also use analytical and simulation results to provide graphical intuition for the obtained results  

Dynamic index coding is a practical generalization of conventional index coding that deals with real dynamic traffic streams. We identify the code-constrained capacity region of a dynamic index coding problem with a complete bi-directional side information graph and introduce the performance metric of dynamic index coding gain to measure how dynamic index coding reduces the required data transmissions. A greedy dynamic index coding scheme is proposed that achieves the maximum coding gain almost everywhere in the identified capacity region. Although the greedy scheme attains the maximum coding gain, its selfish nature may unacceptably increase transmission delay. To address this issue, a... 

Device-to-Device communication (D2D) integrated in cellular networks emerges as a new trend in response to notable rise in traffic demand. Resource allocation is one of the important challenges in deployment of D2D networks. In this paper, we formulate an optimization problem for optimal resource allocation and then propose a novel algorithm namely maximum clique based resource allocation (MCRA) for improving the spectral reuse based on graph theoretic concept of maximum clique. Practical application of D2D communications requires each node to receive and transmit signals during the communication process. We have considered this issue in constructing the interference graph and mathematical... 

Cell-free massive MIMO network, as a promising solution for future wireless communication systems, is conven-tionally equipped with a single central processing unit. In this paper, we multiply the number of central processing units in a user-centric cell-free massive MIMO network and demonstrate its impact on communication efficiency. Specifically, we show that under a fair comparison scenario in terms of complexity and cost, having two central processing units increases the fronthaul data rate and the end-to-end peak data rate by up to 47% and 6%, respectively, compared to the conventional situation, where a single processing unit is assumed. © 2024 IEEE  

In this paper, we study the impact of sensing error and channel fading on the decision process of a multiple secondary user network in a primary network whose channel occupancy states are modelled as a Bernoulli process. We present a randomized access strategy to maximize total secondary network throughput. The proposed method guarantees that the probability of collision between primary and secondary users in each channel is less than the predefined value of Pc = ξ. To find the optimal access strategy, we formulate secondary network throughput as an optimization problem. Then, using the KKT method to find the solution, we break the original problem into multiple sub-problems. Then, we employ... 

—Mobile edge computing (MEC) is a promising technology that aims to reduce the total latency of user equipment (UE) by deploying computation resources at the edge of mobile networks. UE mobility is a challenging factor that causes the traditional MEC architecture to suffer from several issues, such as decreased efficiency and frequent service interruptions. One popular method to manage UE mobility is virtual machine (VM) migration, which requires high bandwidth and causes undesirable latency, rendering it impractical for real-time tasks with stringent latency requirements. This paper proposes a hierarchical architecture for MEC networks that facilitates mobility management and mitigates the... 

Graph signal processing is an emerging field in which traditional signal processing tools from regular Euclidean domain are adapted for use in irregular domains such as graphs. This paper demonstrates how graph signal processing can be used as an efficient tool to solve an optical resource allocation problem, particularly the routing and wavelength assignment problem, where a reduction of 25% in blocking probability can be achieved compared to the conventional counterpart schemes. © 2024 IEEE  

In this study, the authors study a fibre-optic local area network deploying optical code division multiple access technique with differential M-ary pulse position modulation (DPPM). The authors present the performance analysis of DPPM signalling using a double optical hardlimiter receiver structure considering the impairment caused by interference of other users. The analysis assumes a set of bit asynchronous transmitters employing generalised optical orthogonal codes for their DPPM signalling (GOOC-DPPM). Using mathematical analysis and simulations, the authors have demonstrated that GOOCDPPM improves both frame error probability and the maximum achievable network throughput compared with... 

In this paper we study slotted ALOHA random access optical code division multiple access packet-switching networks with a chip-level receiver structure. We use generalized optical orthogonal codes (GOOCs) and the overlapping pulse position modulation (OPPM) signaling technique to improve system performance. The impact of physical layer parameters such as the GOOC cross-correlation value and the OPPM overlapping index on key performance benchmarks such as network throughput and delay are analyzed. We also study the stability of the network based on the number of backlogged users, using the expected state drift. It has been shown that using GOOC instead of strict optical orthogonal codes... 

Most of the energy efficient routing algorithms proposed for sensor networks are reactive routing algorithms. By definition, reactive algorithms are those in which routes are constructed whenever there is data transmission. In such algorithms, to transmit data packets from a certain transmitter to the corresponding receiver, efficient route will be constructed using RREQ delivery. This delivery is performed via flooding and modified flooding algorithms. One of the most important criteria of such flooding algorithm is not to miss the best final route during RREQ delivery. Most of major algorithms ignored this fact and instead tried to minimize energy consumption during flooding algorithm. But... 

In a SEnsor Network with Mobile Agents (SENMA) is an architecture proposed for large scale sensor networks. In sensor networks, a fraction of the packets generated by only part of the sensors is sufficient to provide a good estimation of all network information. SENMA uses this inherent redundancy. However, the performance of such system is limited by estimation errors and packet errors due to collision. Estimation error is a major problem in applications such as habitat monitoring in which information is a function of node position. In this paper, we first derive the equations of distortion in a general scenario and use this model to compare the estimation error for regular networks. Then... 

Security techniques have been designed to obtain certain objectives. One of the most important objectives all security mechanisms try to achieve is the availability, which insures that network services are available to various entities in the network when required. But there has not been any certain parameter to measure this objective in network. In this paper we consider availability as a security parameter in ad-hoc networks. However this parameter can be used in other networks as well. We also present the connectivity coefficient of nodes in a network which shows how important is a node in a network and how much damage is caused if a certain node is compromised  

Performance of routing is severely degraded when misbehaving nodes drop packets instead of properly forwarding them. In this paper, we propose a Game-Theoretic Adaptive Multipath Routing (GTAMR) protocol to detect and punish selfish or malicious nodes which try to drop information packets in routing phase and defend against collaborative attacks in which nodes try to disrupt communication or save their power. Our proposed algorithm outranks previous schemes because it is resilient against attacks in which more than one node coordinate their misbehavior and can be used in networks which wireless nodes use directional antennas. We then propose a game theoretic strategy, ERTFT, for nodes to... 

In order to respond to drastically increased traffic demands in mobile networks such as cellulars, opportunistic communication has been introduced as a data offloading strategy. Delivering the contents using peer-to-peer data dissemination is more preferable compared to epidemic diffusion schemes. To implement peer-to-peer dissemination, one needs to define the peer selection and content dissemination policies. Efficient content dissemination relies on the selection of suitable peers. Besides that, the peers require to choose what contents to be transmitted between them. In this paper, we propose multi-level master/slave peer selection algorithm (MMSA) and variance-based multi-metric chunk... 

The common and traditional method for optical dispersion compensation is concatenating the transmitting optical fiber by a compensating optical fiber having a high-negative dispersion coefficient. In this Letter, we take the opposite direction and show how an optical fiber with a high-positive dispersion coefficient is used for dispersion compensation. Our optical dispersion compensating structure is the optical implementation of an iterative algorithm in signal processing. The proposed dispersion compensating system is constructed by cascading a number of compensating sub-systems, and its compensation capability is improved by increasing the number of embedded sub-systems. We also show that... 

In this paper we will propose a novel distributed architecture for overlay tree construction in collaborative virtual environments that is unlimitedly scalable due to its fully decentralized nature. The routing issue over this architecture will later be discussed and several forwarding schemes based on distributed hash tables (DHT) will be proposed. One of the main concerns for a routing algorithm is to keep a trade-off between the algorithm locality and the algorithm performance. In a global algorithm where nodes make the forwarding decision based on the information gathered from all other nodes in the network, the routing performance may obviously be better. However such a large group... 

Although collaborative distributed simulations and virtual environments (VE) have been an active area of research in the past few years, they have recently gained even more attention due to the emergence of online gaming, emergency simulation and planning systems, and disaster management applications. Such environments combine graphics, haptics, animations and networking to create interactive multimodal worlds that allows participants to collaborate in real-time. Massively Multiplayer Online Gaming (MMOG), perhaps the most widely deployed practical application of distributed virtual environments, allows players to act together concurrently in a virtual world over the Internet. IP... 

This article proposes a new architecture for distributed data management and update massage exchange in massively multiuser virtual environments. The key points in the design of such environments are scalability and QoS-aware message delivery. Therefore it requires robust distributed algorithms in a dynamic peer-to-peer system with frequent node arrivals and departures. Our proposed approach is mainly based on distributed hash tables (DHTs) in order to achieve a decentralized system where any participating node can efficiently retrieve the updates associated with a given object. Therefore, the responsibility of maintaining the mapping from names to values is distributed among the nodes in a... 

Massively multi user virtual environment (MMVE) applications must deal with the challenge of update message exchange among a large set of nodes distributed over the Internet. Therefore design of scalable network protocols is a major concern in such large scale distributed architectures. Several approaches have been proposed to aid update exchange in MMVEs. Message localization has always been a key point in the design of such distributed network protocols. Area of Interest Management (AoIM) mainly deals with the issues related to the update message localization with respect to the user's interest. As the number of users in the virtual environment increases, update message localization...