kan Gür

Energy Efficiency and Satellite Networking: A Holistic Overview

With the increasing need for converged and ubiquitous broadband service support, next-generation mobile radio technologies are posed to be more efficient in different aspects such as energy and spectrum. There are also emerging critical environmental and cost concerns due to the steadily increasing energy consumption and related negative consequences such as greenhouse gas emissions and energy costs. In that respect, energy-wise optimization of satellite communications is crucial considering the objectives of cost improvement and energy efficiency (e.g., due to mobile and small form-factor end-user devices) or the strict energy constraints such as satellite power capacity for resource allocation. However, there are intrinsic challenges such as hardware complexity, algorithmic problems, and design tradeoffs. In this work, various aspects of energy efficiency and satellite networking, ranging from protocols for airborne satellite systems to mobile end-user terminals are reviewed and discussed. In addition, we present emerging factors including dynamic spectrum access, cross-layer design, the integration of space/terrestrial networks, interplanetary Internet, and emergency communications. Moreover, the enabling effect of satellite communications for greener infrastructural systems from the perspective of smart grids, so-called “enabled efficiency,” is outlined beside this “self-efficiency” issue.

Image Error Concealment Using Watermarking with Subbands for Wireless Channels

Transmission of block-coded images through error-prone wireless channels often results in lost blocks. In this study, we investigate a novel error concealment method for covering up these high packet losses and reconstructing a close approximation. Our scheme is a modified discrete wavelet transform (DWT) technique (namely, subbands based image error concealment (SIEC)) for embedding downsized replicas of original image into itself. We propose that this technique can be implemented for wireless channels to combat degradations in a backward-compatible scheme. We show that the proposed error concealment technique is promising, especially for the erroneous channels causing a wider range of packet losses, at the expense of computational burden

Environment-aware location estimation in cellular networks

We propose a novel mobile positioning algorithm for cellular networks based on the estimation of the radio propagation environment. Since radio propagation characteristics vary in different environments, knowing the environment of the mobile user is essential for accurate Received Signal Strength-(RSS-) based location estimation. The key feature of our method is its capability to estimate the environment of the mobile user using machine learning techniques and to utilize this information for enhancing RSS-based distance calculations. The proposed algorithm, namely, EARBALE, has been evaluated using field measurements collected from a GSM network in diverse geographic locations. Our approach turns out to be significantly beneficial, enhancing estimation accuracy, and thereby enabling high-performance mobile positioning in a practical and cost-effective manner. Additionally, it is computationally light-weight and can be integrated onto any RSS-based algorithm as an enhancement add-on.

A novel error concealment method for images using watermarking in error-prone channels

In this paper, we propose a new error concealment method for covering up the high packet losses of an original image after its transmission through an error-prone channel. Error-concealment techniques provide a simple framework to compensate these distortions without incurring additional delays and wasting bandwidth resources which are crucial for real-time applications over networks with limited resources. Unfortunately, most of the existing error-concealment techniques work only if the packet losses are smaller than a threshold and/or they are uniformly distributed. Utilizing data hiding techniques is a potential approach to overcome this restriction. We investigated an error concealment technique utilizing discrete wavelet transform (DWT) for embedding macroblock-based BNM (best-neighborhood-matching) information into the original image in order to utilize spatial redundancy. We propose that this technique can be implemented for error-prone channels to combat such degradations in a backward-compatible scheme. We show that the proposed error concealment technique is a promising one, especially for the erroneous channels causing a wider range of packet losses, at the expense of some degradation in the perceptual quality of the original image

Cross-layer routing-scheduling in IEEE 802.16 mesh networks

Broadband wireless access networks will be a vital component in IP-based fourth-generation (4G) wireless communication systems as part of convergent and pervasive networking architecture. IEEE 802.16 Mobile WiMAX is currently one of the most active standards for broadband wireless access. There are various challenges for the integration of WiMAX and next-generation broadband networks such as diverse operational environment, increasingly stringent QoS support, power/coverage limitations and capacity boundaries. The mesh operation mode of IEEE 802.16 has been standardized as a potential remedy to alleviate these issues. In this work, we propose and investigate a cross-layer routing-scheduling scheme in IEEE 802.16 mesh networks. Our scheme jointly utilizes the distributed and centralized scheduling capabilities of IEEE 802.16 link layer in mesh mode and routing in network layer for optimal operation. It abides with the rules of the IEEE 802.16 protocol. The experimental results indicate that our technique can significantly improve the network performance especially in case of a congestion in the Internet part of the traffic at the cost of a minor burden on the intranet traffic in the form of a slight increase in the end-to-end delay.

Energy efficiency is a subtle concept: fundamental trade-offs for cognitive radio networks

This article discusses the implications of facilitating higher energy efficiency in cognitive radio networks from the perspective of fundamental trade-offs (i.e, what needs to be sacrificed to be energy-efficient). These trade-offs are identified as QoS, fairness, PU interference, network architecture, and security, which are also essential network design dimensions. We analyze these dimensions and their interactions focusing on energy efficiency. Furthermore, future research directions related to the integration of CRN with other networking paradigms and energy efficiency are introduced and discussed.

Performance Comparison of Error Compensation Techniques with Multipath Transmission in Wireless Multimedia Sensor Networks

Due to the proliferation of the multimedia applications over unreliable medium like wireless networks, robust image and video communication have become more important. In this paper, we consider the transmission distortions on the multimedia data due to both channel impairments and instant node failures for Wireless Multimedia Sensor Networks (WMSN). Two techniques are investigated to compensate the multimedia distortions at the expense of incurring additional delays and/or wasting bandwidth resources. First technique is an error concealment technique utilizing discrete wavelet transform for embedding downsized replicas of original image into itself, thereby mitigating degradations in a backward-compatible scheme. The other is Reed-Solomon coding utilizing additional information bits to correct bit/symbol errors. Two techniques are also integrated with multipath transmission to provide fault tolerance. Performance results show that error concealment with multipath transmission technique (ECMF) is more promising to compensate for losses due to unreliable channels and instant node failures than Reed-Solomon coding with multipath transmission technique (RSMF) in WMSN.

Cost-Aware Network Hardening with Limited Budget Using Compact Attack Graphs

Attack graphs are instrumental to analyze security vulnerabilities in networks. They provide decision support to security analysts via identification of critical exploitation scenarios. However, they may suffer from scalability issues due to network size and potential vulnerabilities, and become difficult to analyze. In this paper, we propose a heuristic method to find a cost-effective solution to protect a network using compact attack graphs. First, we extract all possible attack paths which reach predetermined critical resources embedded in the network. The exploit or initial condition which contributes the most to attack paths with least cost is selected to be removed. This process continues iteratively and a security analyst can stop it when the total cost exceeds the allocated budget. The experimental results show that the algorithm scales gracefully with the size of the graphs and it can be applied to large-scale graphs with a very large number of nodes. Moreover, our proposal measures the security level of the network in every step to show how vulnerable the network is against threats.

VoIP performance in multi-layered satellite IP networks with on-board processing capability

In this study, voice over IP (VoIP) performance in multi-layered satellite IP networks with on-board processing (OBP) capability is investigated. With on-board processing, a satellite can process the received data, and according to the nature of application, it can decide on the transmission properties. Specifically, considered OBP includes error-correcting coding to combat adverse channel conditions and priority queueing mechanisms for efficient use of the system resources. After a brief overview of relevant aspects of satellite networks to VoIP, the VoIP performance for non-geostationary Earth orbit (NGEO) single layer and multi-layered constellations are examined using a network simulation tool. The outcome of these simulations justifies the premise for the multi-layered architecture for delay-sensitive and real-time traffic such as voice. Subsequently, the effects of some quality-of-service (QoS) mechanisms in multi-layered architecture are tested using various simulation parameters. The system simulation verifies that multi-layered satellite networks with OBP capabilities and QoS mechanisms are essential for feasibility of packet-based high quality voice services which are vital components of next-generation communications networks

Defense Mechanisms against DDoS Attacks in SDN Environment

SDN is a pivotal technology that relies on the fundamental idea of decoupling control and data planes in the network. This property provides several advantages such as flexibility, simplification, and lower costs. However, it also brings several drawbacks that are largely induced by the centralized control paradigm. Security is one of the most significant challenges related to centralization. In that regard, DDoS attacks are particularly pertinent to the SDN environment. This article presents a concise survey on solutions against DDoS attacks in software-defined networks. Moreover, several mechanisms are analyzed, and a comparative classification is provided for rendering the current state of the art in the literature. This analysis will help researchers to address weaknesses of these solutions and thus mitigate such attacks using more effective defense mechanisms.