Y. Ahmet Sekercioglu

Analysis of An Optical Wireless Receiver Using a Hemispherical Lens With Application in MIMO Visible Light Communications

White lighting LEDs offer great potential for high speed communications, especially for indoor applications. However, for their widespread adoption, two important issues need to be addressed: the lack of diversity in multiple-input multiple output (MIMO) systems, and the small field of view of receivers. In this paper, we describe a design using a hemispherical lens in the receiver that solves these problems. By using classical optics, we derive exact expressions for the channel gain and the optical power density of the projected images. Simulation results of a typical indoor scenario show that the new system has a wide field of view, and provides adequate channel gain for angles of incidence as large as 70 degrees. We present the distribution of optical power on the imaging plane for various receiving positions and tilted receivers over a number of representative indoor scenarios. They show that the images of LEDs are clearly distinguishable. The results demonstrate the presence of low channel correlations between individual transmitters and receivers. Consequently, this confirms that the new technique is capable of providing significant diversity order for MIMO optical wireless applications.

A survey of multipoint relay based broadcast schemes in wireless ad hoc networks

Almost every routing protocol in mobile ad hoc networks (MANETs) depends on a broadcast scheme to disseminate routing information. For this reason, creating an efficient broadcast scheme is important and a large variety of approaches have been proposed. Among them, multipoint relay (MPR) is one of the distributed broadcast schemes which is efficient and simple. Based on the MPR concept, many broadcast schemes have been proposed, which generally focus on different performance issues. In this article we present a comprehensive survey of MPR-based broadcast schemes, classified into three categories based on their objectives. Different heuristics are described, and the evaluation of their performances is provided in light of their costs. Advantages and limitations of different broadcast schemes are also highlighted.

Swarm robotics reviewed

SUMMARY We present a review of recent activities in swarm robotic research, and analyse existing literature in the field to determine how to get closer to a practical swarm robotic system for real world applications. We begin with a discussion of the importance of swarm robotics by illustrating the wide applicability of robot swarms in various tasks. Then a brief overview of various robotic devices that can be incorporated into swarm robotic systems is presented. We identify and describe the challenges that should be resolved when designing swarm robotic systems for real world applications. Finally, we provide a summary of a series of issues that should be addressed to overcome these challenges, and propose directions for future swarm robotic research based on our extensive analysis of the reviewed literature.

Position Accuracy of Time-of-Arrival Based Ranging Using Visible Light With Application in Indoor Localization Systems

This paper analyzes an indoor positioning system that uses white lighting LEDs. Modulated signals transmitted by the LEDs are used as the basis of time-of-arrival-based distance estimation. The theoretical limits on the accuracy of estimation are calculated by deriving the Cramer-Rao bound for intensity modulated windowed sinusoidal signals. Calculations for a typical indoor scenario, assuming perfect synchronization between transmitter and receiver, but using realistic values for other parameters show that very accurate distance estimates are achievable, with typical errors being in the order of centimeters depending on the frequency and power of the sinusoidal signals, the distance from the LED and the properties of the LED and the photoreceiver.

Recent approaches to non-intrusive load monitoring techniques in residential settings

The concept of Smart Grids is closely related to energy conservation and load shedding concepts. However, it is difficult to quantify the effectiveness of energy conservation efforts in residential settings without any sort of end-use energy information as feedback. In order to achieve that, load monitoring methods are normally used. In recent years, non-intrusive load monitoring (NILM) approaches are gaining popularity due to their minimal installation requirements and cost effectiveness. For a NILM system to work, only one sensor at the entry point to a home is required. Fluctuations in the aggregate power consumption signals are used to mathematically estimate the composition of operation of appliances. This approach eliminates the requirement of installing plug-meters for every appliance in the house. In this paper, we provide a review of recent research efforts on state-of-the-art NILM algorithms before concluding with a baseline and overall vision for our future research direction.

Fuzzy logic controlled RED: congestion control in TCP/IP differentiated services networks

The use of the Internet for time-sensitive services, such as voice and video applications, requires a predictable quality of service. The TCP/IP differentiated services (Diff-Serv) architecture was introduced to achieve such performance. Network congestion control, however, still remains a critical and high priority issue. A number of researchers are looking at alternative schemes such as random early detection (RED) and its variants to handle congestion. In this paper we present the results of a fuzzy logic control approach to the implementation of RED – Fuzzy-RED. We believe that with fuzzy logic we are able to use linguistic knowledge to implement better understood nonlinear probability discard functions, achieve better differentiation for packet discarding behaviors for aggregated flows, and so provide better quality of service to different kinds of traffic whilst maintaining high utilization.

Bandwidth allocation for virtual paths (BAVP): investigation of performance of classical constrained and genetic algorithm based optimisation techniques

We investigate the performance of a classical constrained optimisation (CCO) algorithm and a constrained optimisation genetic algorithm (GA) for solving the bandwidth allocation for virtual paths (BAVP) problem. We compare throughput, fairness and time complexity of GA-BAVP and CCO-BAVP for several node topologies. The results on maximising the throughput obtained with GA-BAVP and CCO-BAVP are in close agreement, however when considering fairness GA-BAVP outperforms CCO-BAVP, especially for more complex topologies, like the 7-node network, without abundant link capacity. Convergence of the two algorithms appears similar, with GA-BAVP outperforming CCO-BAVP in initial stages, and vice-versa for longer time scales. However as the problem complexity increases the solution time for the genetic algorithm does not increase as fast as the classical constrained optimisation algorithm. A hybrid scheme is also introduced, combining the benefits of both algorithms. It exhibited better overall convergence rate but the same solution as CCO-BAVP.

Fuzzy explicit marking for congestion control in differentiated services networks

This paper presents a new active queue management scheme, fuzzy explicit marking (FEM), implemented within the differentiated services (Diffserv) framework to provide the congestion control using a fuzzy logic control approach. Network congestion control remains a critical and high priority issue. The rapid growth of the Internet and increased demand to use the Internet for time-sensitive voice and video applications necessitate the design and utilization of effective congestion control algorithms, especially for new architectures, such as Diffserv. As a result, a number of researchers are now looking at alternatively schemes to TCP congestion control. RED (random early detection) and its variants are one of these alternatives to provide quality of service (QoS) in TCP/IP Diffserv networks. The proposed fuzzy logic approach for congestion control allows the use of linguistic knowledge to capture the dynamics of nonlinear probability marking functions and offer effective implementation, use of multiple inputs to capture the (dynamic) state of the network more accurately, enable finer tuning for packet marking behaviors (either dropping a packet or setting its ECN - explicit congestion notification - bit) for aggravated flows, and thus provide better QoS to different types of data streams, such as TCP/FTP traffic or TCP/Web-like traffic, whilst maintaining high utilization.

Toward a Power-Efficient Backbone Network: The State of Research

The year-by-year increase in electricity consumption significantly affects all nations today from environmental, social, and economic perspectives. Various studies show that, among the contributors of this increase, power consumption of the equipment forming the Internet infrastructure is significant. Consequently, considerable attention is given to finding solutions to reduce power consumption of the systems that run the Internet. Current literature suggests that the optical backbone network is responsible for the majority of the consumed power, particularly at high traffic loads. This highlights the importance of formulating solutions to reduce power consumption in backbone networks. In this paper, we provide a comprehensive survey of the most relevant research efforts on minimizing power consumption of backbone networks. We categorize our review into four broad approaches: network redesign, traffic engineering, power-aware networking, and load-adaptive operation. We highlight the findings of relevant studies and provide an analysis of their limitations. We also evaluate the technological differences of similar work and identify a number of future directions. Finally, we demonstrate that the adoption of these technologies is gathering pace among prominent research bodies, device manufacturers, and network operators.

Hemispherical lens based imaging receiver for MIMO optical wireless communications

White lighting LED based systems are emerging as an important form of high data rate communications, especially for indoor applications. Two limitations of existing systems are the small field of view of typical receivers and the poor performance of optical wireless MIMO due to lack of spatial diversity. In this paper we describe a novel design which overcomes these problems by using a hemispherical lens in the receiver. We show that the new system has a wide field of view and also provides significant spatial diversity for typical MIMO visible light scenarios. Numerical results are provided for a range of LED transmitters with different half power semi-angles. Our analysis shows that systems can be designed with adequate channel gain for angles of incidence as large as 70 degrees. The optical power density is also calculated to show the received optical power distributions for the case of four LED transmitters. The results indicate that the images of the LEDs are clearly separated. This reduces the channel correlations between individual transmitters and receivers and thus promises a significant diversity order for MIMO optical wireless systems.