Ertan Onur

Wake-up receivers for wireless sensor networks: benefits and challenges

For successful data delivery, the destination nodes should be listening to the medium to receive data when the sender node starts data communication. To achieve this synchronization, there are different rendezvous schemes, among which the most energy-efficient is utilizing wakeup receivers. Current hardware technologies of wake-up receivers enable us to evaluate them as a promising solution for wireless sensor networks. In this article the benefits achieved with wake-up receivers are investigated along with the challenges observed. In addition, an overview of state-of-the-art hardware and networking protocol proposals is presented. As wake-up receivers offer new opportunities, new potential application areas are also presented and discussed.

Fairness in Wireless Networks:Issues, Measures and Challenges

The pervasiveness of wireless technology has indeed created massive opportunity to integrate almost everything into the Internet fabric. This can be seen with the advent of Internet of Things and Cyber Physical Systems, which involves cooperation of massive number of intelligent devices to provide intelligent services. Fairness amongst these devices is an important issue that can be analysed from several dimensions, e.g., energy usage, achieving required quality of services, spectrum sharing, and so on. This article focusses on these viewpoints while looking at fairness research. To generalize, mainly wireless networks are considered. First, we present a general view of fairness studies, and pose three core questions that help us delineate the nuances in defining fairness. Then, the existing fairness models are summarized and compared. We also look into the major fairness research domains in wireless networks such as fair energy consumption control, power control, topology control, link and flow scheduling, channel assignment, rate allocation, congestion control and routing protocols. We make a distinction amongst fairness, utility and resource allocation to begin with. Later, we present their inter-relation. At the end of this article, we list the common properties of fairness and give an example of fairness management. Several open research challenges that point to further work on fairness in wireless networks are also discussed. Indeed, the research on fairness is entangled with many other aspects such as performance, utility, optimization and throughput at the network and node levels. While consolidating the contributions in the literature, this article tries to explain the niceties of all these aspects in the domain of wireless networking.

Robust 60 GHz Indoor Connectivity: Is It Possible with Reflections?

In this paper, we investigate the robustness of the 60 GHz connectivity in typical indoor environments by analyzing the outage probability. We define three realistic indoor scenarios which may host the 60 GHz networks in the future and perform simulations with a verified 3D ray tracing tool on them. In the first set of simulations, we show the impact of access unit position on the connectivity. In the next step, we show that increasing the obstacle density linearly decreases the outage probability of the 60 GHz network and this decrease is found to be sharper for certain positions of the access point. In the last step, we demonstrate the direct effect of reflective surface availability on the connectivity. A 60 GHz indoor network relying solely on the reflections in the absence of line-of-sight path is very vulnerable to outages even in moderately populated indoor environments.

Lifetime extension for surveillance wireless sensor networks with intelligent redeployment

For wireless sensor networks (WSNs), uneven energy consumption is a major problem. A direct consequence of this is the energy hole problem, formation of sensing voids within the network field due to battery depleted sensors in the corresponding region. Hole formations are inherent in the network topology, yet it is possible to develop strategies to delay the hole formations to later stages of the network operation and essentially extend the network lifetime without sensing quality loss. In this work, we initially propose and analyze an approach that can be used to mitigate the hole problem. The approach is presented in detail and the effects on the sustained surveillance quality are presented. The results are based on simulations with different network configurations with realistic sensor models, MAC and routing protocols. By using the proposed approach, sustaining a sensing quality above a given threshold and more than doubling the network lifetime are possible. The results clearly indicate the suitability of the approach for especially demanding WSNs such as the ones used for border surveillance tasks.

Improving 60 GHz Indoor Connectivity with Relaying

The 60 GHz technology has a great potential to provide wireless communication at multi-gigabit rates in future home networks. To maintain the network connectivity with 60 GHz links, which are highly susceptible to propagation and penetration losses, is a major challenge. The quality and the robustness of the 60 GHz links can be improved by employing relay nodes in the network. In this paper, the contribution of relaying to the connectivity and the quality of the 60 GHz radio links is studied by modeling three indoor scenarios. It is analytically and through simulations shown that having a relay node in a 60 GHz network decreases the average freespace path loss 33% in the worst case scenario. The effects of relay device position and the obstacle density on the improvement of the average received signal level are investigated with a verified 3D ray tracing tool. A comparative simulation study on the performance of different relay configurations under various network conditions is conducted. The results yield that even a single relay device positioned at the height of other nodes can improve 50% of the links in considerable levels in a 60 GHz indoor network. It is also shown that additional relay nodes do not contribute to 60 GHz indoor connectivity significantly, if there are two properly positioned relay devices in a network which is moderately populated.

Energy-aware routing algorithms for wireless ad hoc networks with heterogeneous power supplies

Although many energy-aware routing schemes have been proposed for wireless ad hoc networks, they are not optimized for networks with heterogeneous power supplies, where nodes may run on battery or be connected to the mains (grid network). In this paper, we propose several energy-aware routing algorithms for such ad hoc networks. The proposed algorithms feature directing the traffic load dynamically towards mains-powered devices keeping the hop count of selected routes minimal. We unify these algorithms into a framework in which the route selection is formulated as a bi-criteria decision making problem. Minimizing the energy cost for end-to-end packet transfer and minimizing the hop count are the two criteria in this framework. Various algorithms that we propose differ in the way they define the energy cost for end-to-end packet traversal or the way they solve the bi-criteria decision making problem. Some of them consider the energy consumed to transmit and receive packets, while others also consider the residual battery energy of battery-enabled nodes. The proposed algorithms use either the weighted sum approach or the lexicographic method to solve the bi-criteria decision making problem. We evaluate the performance of our algorithms in static and mobile ad hoc networks, and in networks with and without transmission power control. Through extensive simulations we show that our algorithms can significantly enhance the lifetime of battery-powered nodes while the hop count is kept close to its optimal value. We also discuss the scenarios and conditions in which each algorithm could be suitably deployed.

Cooperative Density Estimation in Random Wireless Ad Hoc Networks

Density estimation is crucial for wireless ad hoc networks for adequate capacity planning. Protocols have to adapt their operation to the density since the throughput in an ad hoc network approaches asymptotically to zero as the density increases. A wireless node can estimate the global density by using local information such as the received power from neighbors. In this paper, we propose a cross layer protocol to compute the density estimate. The accuracy of the estimate can be enhanced and its variance can be reduced through cooperation among the nodes. Nodes share the received power measurements with each other. Based on the collected observations, the maximum likelihood estimate is computed. It is shown that cooperative density estimation has better accuracy with less variance than the individual estimation. When nodes share received power measurements from further away neighbors, the variance of the estimate is further reduced.

A Novel Link Quality Assessment Method for Mobile Multi-Rate Multi-Hop Wireless Networks

Accurate and fast wireless link quality assessment (LQA) for wireless channels would bring huge benefits for mobile multi-hop and multi-rate wireless ad hoc and sensor networks in the form of improved end-to-end performance. In this paper, we propose a novel LQA method based on cross-layer information. The method is implemented in a real test-bed, which is based on IEEE 802.11b/g, and achieved a significant LQA improvement up to 50% in mobile scenarios without introducing overhead. The effectiveness of accurate and fast LQA is demonstrated by feeding it into the routing layer to enable the route decisions to adapt faster during changing situations, especially in mobile scenarios. The experiment results show that the proposed LQA method can lead to faster and smarter routing decisions and higher end-to-end throughput compared to traditional methods, which only use hello packets to determine the link quality in mobile scenario.

Realistic simulation of IEEE 802.11p channel in mobile Vehicle to Vehicle communication

Intelligent Transportation Systems (ITS) is becoming an important paradigm, because of its ability to enhance safety and to mitigate congestion on road traffic scenarios. Realizing the fact that data collection scheme from in-situ test beds for large number of vehicles is always expensive and time consuming, before being employed in large scale, such safety critical system should be tested narrowing down the gap between real circumstances and analytical models in a simulation platform. It is evident that underlying radio wave propagation models can comprise the validity of large scale vehicular network simulation results. Vehicle-to-Vehicle (V2V) channels have higher dynamics due to rapidly varying topologies and environments which have significant impact on performance study of upper layer protocols and applications. In spite of the fact that few measurement based empirical channel models are present in the literature, they are not tested for large scale vehicular networks. In this study, we simulate suburban scenarios with hundreds of IEEE802.11p nodes in the OPNET simulation environment with more realistic channel models. The standard OPNET propagation model was replaced by Nakagami-m fading channel. For the sake of modeling, changing relative velocity attribute and separation distance, power spectrum and fading parameter-m were defined as function of velocity and separation distance respectively. Then statistics were collected to evaluate performance of physical and higher layers. Primarily we have found all the vehicles within the standard requirement for Dedicated Short Range Communications (DSRC) range of 1 kilometer may not receive packets, which was also found in several earlier publications.

Cooperative Communications in Future Home Networks

The basic idea behind cooperative communications is that mobile terminals collaborate to send data to each other. This effectively adds diversity in the system and improves the overall performance. In this paper, we investigate the potential gains of cooperative communication in future home networks. We derive analytical expressions for the error probability of binary phase shift keying (BPSK) signals over Nakagami-m fading channels in a multi relay communication network. Following to the analytical study, we analyze the contribution of cooperative relaying to the 60GHz network connectivity through simulations using a realistic indoor environment model. We compare the performance of different relay configurations under variable obstacle densities. We show that a typical 60GHz indoor network should employ either a multi-relay configuration or a single-relay configuration with a smart relay selection mechanism to achieve acceptable outage rates. In the use of multiple-relay configuration, both analytical and simulation studies indicate that increasing the number of cooperative relays does not improve the system performance significantly after a certain threshold.