Sharif Digital Repository

The Per Tone equalization algorithm is a novel discrete multitone (DMT) equalization method with practical applications in subscriber digital loop systems. Unlike time domain DMT equalizers (TEQ), which equalize all DMT tones in a combined fashion, the Per Tone equalizer equalizes each tone separately. In this paper, the performance and complexity of this technique is investigated and compared with that of other TEQs. Furthermore, the behavior of this technique in different simulation conditions, such as over different standard CSA loops and in the presence of additive white Gaussian noise with variable power spectral density level and near end crosstalk (NEXT), is studied and compared with... 

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... 

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... 

Energy-Aware routing is a promising technique for reducing energy consumption in future networks. Under this scheme, traffic loads are aggregated over a subset of the network links, allowing other links to be turned off to save energy. Since the capacity of links is the main limiting constraint in this problem, to further improve energy saving, the idea of using redundancy elimination (RE) in energy-Aware routing has been proposed. As performing RE in routers consumes some energy, it should be specified, which routers should perform RE and which links should be deactivated so that the total energy consumption of the network is minimized. As a result, the problem of energy-Aware routing with... 

One of the main advantages of utilizing flexible backhaul in future HetNets is that it can provide better user experience through flexible resource allocation. For this purpose, it is important to provide the required quality of service (QoS) in such networks. In this paper, we consider the problem of cross-layer radio resource management in HetNets with flexible backhaul which guarantees minimum total transmit power of BSs as well as the average end-to-end data rate requirement of each data flow. The problem is formulated as a two-timescale stochastic optimisation, where the long-timescale control variables are flow control, routing control and interference mitigation, while the... 

In this paper, we focus on the problem of hierarchical cross- layer dynamic resource allocation for heterogeneous networks with flexible backhaul. We formulate the radio resource management problem as a two timescale non-convex stochastic optimisation problem which jointly optimizes flow control, routing control, interference mitigation and link scheduling in order to maximize a generic network utility. We propose an iterative hierarchical control structure where the long-term controls are adaptive to large scale fading and the short-term control is adaptive to the local CSI within a pico or macro BS, to find the optimal solution. The proposed solution benefits from low complexity and... 

Efficient resource allocation in OFDM-based optical networks is directly affected by definition and formulations of Routing and Spectrum Assignment (RSA) problem. In this paper, we propose new Binary Linear Programming (BLP) formulations for the RSA problem that provide more efficient resource allocation in comparison with previous formulations. Unlike the conventional formulations that mainly aim at minimizing used spectrum slots, our formulations simultaneously aim at defragmentation and minimization of the assigned spectrum slots. We show contiguity constraint of the conventional formulations may incorrectly make a feasible solution unattainable. To solve this problem, we remove the... 

Software Defined Networking (SDN) provides a logically centralized view of the state of the network, and as a result opens up new ways to manage and monitor networks. In this paper we introduce a novel approach to network intrusion detection in SDNs that takes advantage of these attributes. Our approach can detect compromised routers that produce faulty messages, copy or steal traffic or maliciously drop certain types of packets. To identify these attacks and the affected switches, we correlate the forwarding state of network - i.e. installed forwarding rules - with the forwarding status of packets - i.e. the actual route packets take in the network and detect anomaly in routes. Thus, our... 

Spectrum conversion can improve the performance of orthogonal frequency division multiplexing (OFDM)-based elastic optical networks (EONs) by relaxing the continuity constraint and consequently reducing connection request blocking probability during routing and spectrum assignment process. We propose three different architectures for including spectrum conversion capability in bandwidth-variable wavelength cross-connects (BVWXCs). To compare the capability of the introduced architectures, we develop an analytical method for computing average connection request blocking probability in a spectrum-convertible OFDM-based EON in which all, part, or none of the BVWXCs can convert the spectrum. An... 

Wireless Sensor Networks (WSNs) have developed in recent years and are used in many different applications such as fire detection, military operations, and healthcare. Sensor nodes have the ability to sense an environment, sending and receiving information and forwarding packets from source nodes to a sink. These tasks consume large amounts of energy. In many WSN applications, delay and reliability of data delivery and the energy consumption of nodes are important design metrics. Network protocols such as medium access control (MAC) and routing should be designed to improve these metrics. In this article, we propose a new cross layer algorithm that improves the performance of WSN networks... 

Providing backhaul connectivity for macro and pico base stations (BSs) constitutes a significant share of infrastructure costs in future heterogeneous networks (HetNets). To address this issue, the emerging idea of flexible backhaul is proposed. Under this architecture, not all the pico BSs are connected to the backhaul, resulting in a significant reduction in the infrastructure costs. In this regard, pico BSs without backhaul connectivity need to communicate with their nearby BSs in order to have indirect accessibility to the backhaul. This makes the radio resource management (RRM) in such networks more complex and challenging. In this paper, we address the problem of cross-layer RRM in... 

In this letter, we use stochastic optimization to schedule data transmissions in an adaptive optical code division multiple-access (OCDMA) system to maximize transmission rate. We employ Lyapunov drift theory to formulate a general optimization problem for rate-maximized scheduling in which user codes are adaptively assigned such that time-averaged transmission rate is maximized and important system parameters such as stability and BER performance are maintained. Simulation results show that the overall transmission rate in a rate-maximized scheduled OCDMA system can be up to 3 (1.2) times better than the transmission rate in its counterpart OCDMA system with fixed code assignment scheme... 

We propose an energy-efficient procedure for transponder configuration in few-mode fiber-based elastic optical networks in which bit error rate and physical constraints are guaranteed and joint optimization of temporal, spectral, and spatial resources are addressed. We use geometric convexification techniques to provide convex formulations for the signal-to-interference plus noise ratio, transponder power consumption, and transponder configuration problem. Simulation results demonstrate that the proposed convex formulation for the transponder configuration problem is considerably faster than its mixed-integer nonlinear counterpart. We consider transmit optical power as a configurable... 

We investigate the problem of energy-efficient resource allocation constrained to quality of service and physical requirements in orthogonal frequency division multiplexing (OFDM)-based elastic optical networks and propose a fast two-stage algorithm to solve it. The first stage of the proposed algorithm deals with routing, traffic grooming, and traffic ordering and mainly aims at minimization of the number of deployed optical amplifiers and transponders. We provide an integer linear program for routing and traffic grooming and propose a heuristic procedure, which yields its near-optimum solution in a shorter runtime. In the second stage, we optimize transponder parameters to minimize total... 

In this paper, we study the secrecy throughput in a massive Multiple-Input-Multiple-Output (MIMO) full-duplex wireless powered communication network (WPCN). The network consists of a massive MIMO base station (BS) and two groups of single- antenna sensor nodes which harvest energy from the BS. The first group, referred to as information transmitters (ITs), use the harvested energy to transmit information back to the BS; the second group, referred to as energy receivers (ERs), use the harvested energy for non- transmission related operations. We consider a two-slot protocol. In the first time slot, all nodes harvest energy from the BS. In the second slot, ITs transmit information to the BS,... 

In this paper, we study the secrecy throughput of a full-duplex wireless powered communication network (WPCN) for Internet of Things (IoT). The WPCN consists of a full-duplex multiantenna base station (BS) and a number of sensor nodes. The BS transmits energy all the time, and each node harvests energy prior to its transmission time slot. The nodes sequentially transmit their confidential information to the BS, and the other nodes are considered as potential eavesdroppers. We first aim to optimize the sum secrecy throughput of the nodes. The optimization variables are the duration of the time slots and the BS beamforming vectors in different time slots. The optimization problem is shown to... 

Consistent growth in the volume and dynamic behavior of traffic mandates new requirements for fast and adaptive resource allocation in metro networks. We propose a dynamic resource allocation technique for adaptive minimization of spectrum usage in metro elastic optical networks. We consider optical transmission as a service specified by its bandwidth profile parameters, which are minimum, average, and maximum required transmission rates. To consider random traffic events, we use a stochastic optimization technique to develop a novel formulation for dynamic resource allocation in which service level specifications and network stability constraints are addressed. Next, we employ the elegant... 

In a wireless powered communication network, an energy access point (EAP) supplies the energy needs of the network nodes through radio frequency wave transmission, and the nodes store the received energy in their batteries for their future data transmission. In this paper, we propose an online stochastic policy that jointly controls energy transmission from the EAP to the nodes and data transfer among the nodes. Our proposed policy is designed using a quadratic Lyapunov function to capture the limitations on the energy consumption of the nodes imposed by their battery level. The proposed policy is adaptive to different channel statistics of the network. We provide theoretical analysis for... 

In this paper, we investigate the secrecy throughput for a full-duplex wireless powered communication network. A multi-antenna base station (BS) transmits energy towards nodes all the time and each node harvests energy prior to its transmission time slot. Nodes sequentially transmit their confidential information to the BS in presence of other nodes which are considered as potential eavesdroppers. We derive the secrecy rate and formulate the sum secrecy throughput optimization of all nodes. The optimization variables are the time slot duration and the BS beamforming during different transmission phases. The problem is non-convex and non-trivial. We propose a suboptimal approach in which the... 

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