Mehmet C. Vuran

NeXt generation/dynamic spectrum access/cognitive radio wireless networks: a survey

Todays wireless networks are characterized by a fixed spectrum assignment policy. However, a large portion of the assigned spectrum is used sporadically and geographical variations in the utilization of assigned spectrum ranges from 15% to 85% with a high variance in time. The limited available spectrum and the inefficiency in the spectrum usage necessitate a new communication paradigm to exploit the existing wireless spectrum opportunistically. This new networking paradigm is referred to as NeXt Generation (xG) Networks as well as Dynamic Spectrum Access (DSA) and cognitive radio networks. The term xG networks is used throughout the paper. The novel functionalities and current research challenges of the xG networks are explained in detail. More specifically, a brief overview of the cognitive radio technology is provided and the xG network architecture is introduced. Moreover, the xG network functions such as spectrum management, spectrum mobility and spectrum sharing are explained in detail. The influence of these functions on the performance of the upper layer protocols such as routing and transport are investigated and open research issues in these areas are also outlined. Finally, the cross-layer design challenges in xG networks are discussed.

A survey on spectrum management in cognitive radio networks

Cognitive radio networks will provide high bandwidth to mobile users via heterogeneous wireless architectures and dynamic spectrum access techniques. However, CR networks impose challenges due to the fluctuating nature of the available spectrum, as well as the diverse QoS requirements of various applications. Spectrum management functions can address these challenges for the realization of this new network paradigm. To provide a better understanding of CR networks, this article presents recent developments and open research issues in spectrum management in CR networks. More specifically, the discussion is focused on the development of CR networks that require no modification of existing networks. First, a brief overview of cognitive radio and the CR network architecture is provided. Then four main challenges of spectrum management are discussed: spectrum sensing, spectrum decision, spectrum sharing, and spectrum mobility.

Spatio-temporal correlation: theory and applications for wireless sensor networks

Wireless Sensor Networks (WSN) are characterized by the dense deployment of sensor nodes that continuously observe physical phenomenon. Due to high density in the network topology, sensor observations are highly correlated in the space domain. Furthermore, the nature of the physical phenomenon constitutes the temporal correlation between each consecutive observation of a sensor node. These spatial and temporal correlations along with the collaborative nature of the WSN bring significant potential advantages for the development of efficient communication protocols well-suited for the WSN paradigm. In this paper, several key elements are investigated to capture and exploit the correlation in the WSN for the realization of advanced efficient communication protocols. A theoretical framework is developed to model the spatial and temporal correlations in WSN. The objective of this framework is to enable the development of efficient communication protocols which exploit these advantageous intrinsic features of the WSN paradigm. Based on this framework, possible approaches are discussed to exploit spatial and temporal correlation for efficient medium access and reliable event transport in WSN, respectively.

Spatial correlation-based collaborative medium access control in wireless sensor networks

Wireless Sensor Networks (WSN) are mainly characterized by dense deployment of sensor nodes which collectively transmit information about sensed events to the sink. Due to the spatial correlation between sensor nodes subject to observed events, it may not be necessary for every sensor node to transmit its data. This paper shows how the spatial correlation can be exploited on the Medium Access Control (MAC) layer. To the best of our knowledge, this is the first effort which exploits spatial correlation in WSN on the MAC layer. A theoretical framework is developed for transmission regulation of sensor nodes under a distortion constraint. It is shown that a sensor node can act as a representative node for several other sensor nodes observing the correlated data. Based on the theoretical framework, a distributed, spatial Correlation-based Collaborative Medium Access Control (CC-MAC) protocol is then designed which has two components: Event MAC (E-MAC) and Network MAC (N-MAC). E-MAC filters out the correlation in sensor records while N-MAC prioritizes the transmission of route-thru packets. Simulation results show that CC-MAC achieves high performance in terms energy, packet drop rate, and latency.

Full length article: Signal propagation techniques for wireless underground communication networks

Wireless Underground Communication Networks (WUCNs) consist of wireless devices that operate below the ground surface. These devices are either (i) buried completely under dense soil, or (ii) placed within a bounded open underground space, such as underground mines and road/subway tunnels. The main difference between WUCNs and the terrestrial wireless communication networks is the communication medium. In this paper, signal propagation characteristics are described in these constrained areas. First, a channel model is described for electromagnetic (EM) waves in soil medium. This model characterizes not only the propagation of EM waves, but also other effects such as multipath, soil composition, water content, and burial depth. Second, the magnetic induction (MI) techniques are analyzed for communication through soil. Based on the channel model, the MI waveguide technique for communication is developed to address the high attenuation challenges of MI waves through soil. Furthermore, a channel model, i.e., the multimode model, is provided to characterize the wireless channel for WUCNs in underground mines and road/subway tunnels. The multimode model can characterize two cases for underground communication, i.e., the tunnel channel and the room-and-pillar channel. Finally, research challenges for the design communication protocols for WUCNs in both underground environments are discussed based on the analysis of the signal propagation.

A Cross-Layer Protocol for Wireless Sensor Networks

Severe energy constraints of battery-powered sensor nodes necessitate energy-efficient communication protocols in order to fulfill application objectives of wireless sensor networks (WSN). However, the vast majority of the existing solutions are based on classical layered protocols approach. It is much more resource-efficient to have a unified scheme which melts common protocol layer functionalities into a cross-layer module resource-constrained sensor nodes. To the best of our knowledge, to date, there is no unified cross-layer communication protocol for efficient and reliable event communication which considers transport, routing, medium access functionalities with physical layer (wireless channel) effects for WSNs. In this paper, a unified cross-layer protocol is developed, which replaces the entire traditional layered protocol architecture that has been used so far in WSNs. Our design principle is complete unified cross-layering such that both the information and the functionalities of traditional communication layers are melted in a single protocol. The objective of the proposed cross-layer protocol is highly reliable communication decisions and local congestion avoidance. To this end, the protocol operation is governed by the new concept of initiative determination. Based on this concept, the cross-layer protocol performs received based contention, local congestion control, and distributed duty cycle operation in order to realize efficient and reliable communication in WSN. Performance evaluation results show that the proposed cross-layer protocol significantly improves the communication efficiency and outperforms the traditional layered protocol architectures.

The state of the art in cross-layer design for wireless sensor networks

The literature on cross-layer protocols, protocol improvements, and design methodologies for wireless sensor networks (WSNs) is reviewed and a taxonomy is proposed. The communication protocols devised for WSNs that focus on cross-layer design techniques are reviewed and classified, based on the network layers they aim at replacing in the classical open system interconnection (OSI) network stack. Furthermore, systematic methodologies for the design of cross-layer solution for sensor networks as resource allocation problems in the framework of non-linear optimization are discussed. Open research issues in the development of cross-layer design methodologies for sensor networks are discussed and possible research directions are indicated. Finally, possible shortcomings of cross-layer design techniques such as lack of modularity, decreased robustness, and instability are discussed, and precautionary guidelines are presented.

Error control in wireless sensor networks: a cross layer analysis

Error control is of significant importance for wireless sensor networks (WSNs) because of their severe energy constraints and the low power communication requirements. In this paper, a cross-layer methodology for the analysis of error control schemes in WSNs is presented such that the effects of multi-hop routing and the broadcast nature of the wireless channel are investigated. More specifically, the cross-layer effects of routing, medium access, and physical layers are considered. This analysis enables a comprehensive comparison of forward error correction (FEC) codes, automatic repeat request (ARQ), and hybrid ARQ schemes in WSNs. The validation results show that the developed framework closely follows simulation results.

XLP: A Cross-Layer Protocol for Efficient Communication in Wireless Sensor Networks

Severe energy constraints of battery-powered sensor nodes necessitate energy-efficient communication in Wireless Sensor Networks (WSNs). However, the vast majority of the existing solutions are based on the classical layered protocol approach, which leads to significant overhead. It is much more efficient to have a unified scheme, which blends common protocol layer functionalities into a cross-layer module. In this paper, a cross-layer protocol (XLP) is introduced, which achieves congestion control, routing, and medium access control in a cross-layer fashion. The design principle of XLP is based on the cross-layer concept of initiative determination, which enables receiver-based contention, initiative-based forwarding, local congestion control, and distributed duty cycle operation to realize efficient and reliable communication in WSNs. The initiative determination requires simple comparisons against thresholds, and thus, is very simple to implement, even on computationally constrained devices. To the best of our knowledge, XLP is the first protocol that integrates functionalities of all layers from PHY to transport into a cross-layer protocol. A cross-layer analytical framework is developed to investigate the performance of the XLP. Moreover, in a cross-layer simulation platform, the state-of-the-art layered and cross-layer protocols have been implemented along with XLP for performance evaluations. XLP significantly improves the communication performance and outperforms the traditional layered protocol architectures in terms of both network performance and implementation complexity.

BorderSense: Border patrol through advanced wireless sensor networks

The conventional border patrol systems suffer from intensive human involvement. Recently, unmanned border patrol systems employ high-tech devices, such as unmanned aerial vehicles, unattended ground sensors, and surveillance towers equipped with camera sensors. However, any single technique encounters inextricable problems, such as high false alarm rate and line-of-sight-constraints. There lacks a coherent system that coordinates various technologies to improve the system accuracy. In this paper, the concept of BorderSense, a hybrid wireless sensor network architecture for border patrol systems, is introduced. BorderSense utilizes the most advanced sensor network technologies, including the wireless multimedia sensor networks and the wireless underground sensor networks. The framework to deploy and operate BorderSense is developed. Based on the framework, research challenges and open research issues are discussed.