Serhan Yarkan

Binary Time Series Approach to Spectrum Prediction for Cognitive Radio

One of the major goals of cognitive radio (CR) is to alleviate the inefficient use of the spectrum. CR can sense the spectrum steadily and gather information about the evolution of the spectrum in time. Spectrum occupancy information can be used for both learning the usage of the spectrum and predicting the future occupancy status. In this study, the use of binary time series for spectrum occupancy characterization and prediction is proposed. Both deterministic and non-deterministic occupancy schemes are examined. Numerical results and discussions are presented.

Underground Mine Communications: A Survey

After a recent series of unfortunate underground mining disasters, the vital importance of communications for underground mining is underlined one more time. Establishing reliable communication is a very difficult task for underground mining due to the extreme environmental conditions. Until now, no single communication system exists which can solve all of the problems and difficulties encountered in underground mine communications. However, combining research with previous experiences might help existing systems improve, if not completely solve all of the problems. In this survey, underground mine communication is investigated. Major issues which underground mine communication systems must take into account are discussed. Communication types, methods, and their significance are presented.

Exploiting location awareness toward improved wireless system design in cognitive radio

Rapid advances in digital technology allow people to have a single wireless device that has multiple functions such as communication, computing, and entertainment. These functions are generally embedded into the devices as add-on hardware components such as sensors, digital cameras, and so on. Currently, the functions operate independent of each other, since there is no unit that controls and coordinates the add-on hardware. However, with the aid of a cognitive engine, CR can take advantage of each component to improve its communications. In this work, location awareness is exploited to improve the wireless communication system design in CR. It is shown that several crucial wireless channel parameters are environment-dependent. In order for CR to relate a corresponding empirical model with an environment, the classification of propagation environments is outlined as well. The methods of characterizing the propagation environment for CR are also discussed. In addition, it is described how CR can carry out all these steps with the aid of a KRS along with RKRL and complete its adaptation cycle. CR networks are also discussed, including disseminating the location awareness information, propagation characteristics, and their effects on the network itself.

Interference aware vertical handoff decision algorithm for quality of service support in wireless heterogeneous networks

Next generation wireless networks concept aims at collaboration of various radio access technologies in order to provide quality of service (QoS) supported and cost efficient connections at anywhere and anytime. Since the next generation wireless systems are expected to be of heterogeneous topology, traditional handoff (horizontal handoff/handover) mechanisms are not sufficient to meet the requirements of these types of networks. More intelligent vertical handoff algorithms which consider user profiles, application requirements, and network conditions must be employed in order to provide enhanced performance results for both user and network. Moreover, frequency reuse of one (FRO) seems to be the strongest candidate of deployment options for next generation wireless networks; therefore, interference conditions gains a significant attention in vertical handoff decision making process. In this study, a fuzzy logic-based handoff decision algorithm is introduced for wireless heterogeneous networks. The parameters; data rate, received signal strength indicator (RSSI), and mobile speed are considered as inputs of the proposed fuzzy-based system in order to decide handoff initialization process and select the best candidate access point around a smart mobile terminal. Also, in contrast to the traditional fuzzy-based algorithms, the method proposed takes ambient interference power, which is referred to as interference rate, as another input to the decision process. The results show that the performance is significantly enhanced for both user and network by the method proposed.

Impact of Mobility on the Behavior of Interference in Cellular Wireless Networks

In this study, the impact of mobility is investigated in low-speed environments such as femtocells and picocells for wireless networks. Given that there is interference on the uplink of a FDD system, this study solely focuses on how interference evolves with respect to mobility of terminals which move in a random fashion. Wiener-Levy process is used as a stochastic tool for characterizing the impact of mobility on the future behavior of interference. The results show that there is a trade-off between short and long interference observation (measurement) interval. On the one hand, choosing a short interval leads to a waste of processing power, since the interference level to be observed is not expected to deviate drastically from the previous observations. Choosing a long interval, on the other hand, increases the variance of the density of future interference level. In addition, results show that if there is more than one interference source in motion, the interference level observed has a tendency to increase in the future in low mobility environments. It is also shown that mean value of the interference level density to be observed in the future increases, whereas its standard deviation decreases with respect to the number of interference sources in motion.

Statistical Wireless Channel Propagation Characteristics in Underground Mines at 900MHz

Wireless communication carries a great importance for underground mines from the perspective of safety, security, and industry. However, it is observed that commercial wireless communication systems in underground mines may not work always properly because of different environmental characteristics. In order to have wireless communication systems which work properly under the harsh environments such as underground mines, it is very important to understand the characteristics of the radio propagation within those environments. This work presents experimental results of wideband radio propagation at 900 MHz in a real underground environment. Several important wireless propagation channel parameters are obtained.

Cross-Layer Adaptation and Optimization for Cognitive Radio

When we look at the evolution of wireless communication systems, as in most systems, two major developments are most prominent: 1) addition of new features and 2) improvement of already existing capabilities. The first development arises from the fact that communication through a wireless medium makes life easier. Every development brings several new features and these new features contribute positively to this fact. These developments can be seen clearly in the evolution of cell phones. In the past, cell phones were used only for transmitting voice and short text-based messages. Currently, there are cell phones in which an operating system runs and several multimedia applications are available. The second type of development solely originates from the fact that every physical concept is finite. Therefore, according to the principal of parsimony, the newer systems restrain themselves from wasting resources. Using resources adequately under dynamically changing conditions introduces the notion of adaptation and optimization. Although systems evolve in terms of 1) and 2), particularly in communication systems, it can be observed that the fundamental design architecture, which is known as “layered architecture,” still remains the same. Despite the inefficiency of contemporary communication systems, they still accomplish their tasks. Nevertheless, it can be seen that the aforementioned evolutionary developments are approaching a saturation point for contemporary communication systems. The fundamental design architecture inherently hinders

Identification of LOS and NLOS for wireless Transmission

Distinguishing the transmission status of the communication as line-of-sight (LOS) and non-LOS (NLOS) is of great importance for the wireless communication systems. It is known that for LOS and NLOS, some statistical characteristics of the transmission differ from each other. If the distinction between LOS and NLOS can be made as quick and accurate as possible, ranging based applications and adaptive radio systems like cognitive radios can make use of this information to increase their performances significantly. In this study, a numerical and computationally low complex method for coherent receivers is proposed to discriminate the LOS/NLOS status of the transmission depending on the autocorrelation properties of individual paths. The proposed method is tested for both noise-free and noisy conditions with sum-of-sinusoids (SoS) and inverse discrete Fourier transform (IDFT) based simulation models. It is observed that the proposed method gives good results even for relatively low signal-to-noise ratio (SNR) values

Identification of LOS in time-varying, frequency selective radio channels

A method is proposed to identify the existence of line-of-sight (LOS) for time-varying, frequency selective radio channels. The proposed method considers the second-order statistical characteristics of underlying process in the channel taps. Identification is established by comparing the autocorrelation coefficients of the first tap with those of any other tap when the other tap reaches its coherence time. Numerical results and related discussions are presented considering several practical scenarios.

Real-time measurements for adaptive and cognitive radio systems

Adaptive and cognitive radios (CR) have been becoming popular for optimizing mobile radio system transmission and reception. One of the most important elements of the adaptive radio and CR concepts is the ability to measure, sense, learn about, and be aware of parameters related to the radio channel characteristics, availability of spectrum and power, interference and noise temperature, operational environment of radio, user requirements and applications, available networks and infrastructures, local policies, other operating restrictions, and so on. This paper discusses some of the important measurement parameters for enabling adaptive radio and CR systems along with their relationships and impacts on the performance including relevant challenges.