Preventing Cognitive User Emulation Attack in Cognitive Radio Network by Calculating Trust Values Using Fuzzy Logic

Cognitive radio has proved to be an efficient and promising technology for the future of wireless networks. Its major and fundamental aim is to utilize the spectrum bands which are not efficiently exercised. These bands can be accessed using Opportunistic Spectrum Access (OSA), by a secondary user only when primary user is not transmitting over the channel. Cognitive radio manages spectrum through its cognitive radio cycle, which performs a set of management functions such as, spectrum sensing, spectrum assignment, spectrum sharing and spectrum mobility/handoff. During this cycle, at several stages, cognitive radio is very much vulnerable to security attacks. This is also due to the exposed nature of cognitive radio architecture. One such security attack which has not been much explored and can cause serious security issues is Cognitive User Emulation Attack (CUEA). This attack is expected to occur at the time of spectrum handoff. In this article the reason of occurrence of CUEA is explained along with counter measures to prevent this threat in the network by implementing trust mechanism using fuzzy logic. The proposed system is simulated and analyzed using MATLAB tool.

On optimal number of cognitive radios considering co-site electromagnetic compatibility

With the development and wide applications of wireless communication technology, the limited spectrum resources and the fixed spectrum allocation policy could no longer satisfy the demand for wireless communication. Just for this reason, many spectrum resources become spectrum holes because they are allocated but not used. Cognitive radio is now becoming one of the most important techniques for high utility of these spectrum holes. If the holes available to cognitive users are abundant over a certain time, it is a worth consideration to increase network throughputs by orthogonal multiplexing as many as spectrum holes. A multi-transceiver configuration is one of the possible solutions for this purpose. With such a schema, all transceivers within a cognitive user work in a concurrent or parallel mode, by which the throughput of the network can be increased. However, co-site working cognitive radios may incur electromagnetic interference between each other. When more cognitive radios are equipped, much electromagnetic interference may be incurred. Many techniques are proposed to mitigate such so-siting interference; however, none of them have addressed the probability that the interference will happen. If the probability could be estimated in advance, the user will make a better planning on the configurations of the co-siting working radios. Based on an elaborated n-fold multiple integral model, we propose a novel method to decide how many cognitive radios can be installed for one cognitive user at most. This is our main contribution with this work, providing an enhanced ability to determine the optimal number of cognitive radios installed within each cognitive user. We make a strict deduction on electromagnetic compatibility probability with various parameters of cognitive radios. Simulations are performed and the results show that the electromagnetic compatibility of the simulated cognitive radio system meets the deducted probability by this method very well.

Throughput Analysis of Opportunistic Channel Access Techniques in Cognitive Radio Systems

In recent studies it was found out that previously allocated frequency spectrum is not fully utilized in all the wireless systems. Cognitive radio is the new concept to access this underutilized spectrum and, also a promising technology to cope with the ever increasing bandwidth demand for next generation wireless networks. Cognitive radio network can be classified into three different categories: interweave, underlay and overlay. In an interweave cognitive radio system, the unoccupied spectrum holes can be shared by cognitive users with minimal collision with primary users (spectrum owners) whereas in an underlay system, concurrent transmission is allowed with an interference threshold to the primary users. In an underlay system, cognitive users generally transmit at very low power. In an overlay system, cognitive users, similar to underlay cognitive radio systems, concurrently transmit with primary users but cognitive users may know the codewords of the primary transmitter. Hence, using that knowledge, cognitive transmitter may adopt different coding techniques to cancel/mitigate the interference at the primary receiver and/or it may assist the primary system by relaying primary user’s data. In this thesis, we improve the throughput/bit error rate performance of a cognitive radio system by effectively accessing the channels. Throughout the thesis we assume that cognitive user can sense only one channel at a time and we analyze the performance with perfect and imperfect sensing. First, we propose a novel opportunistic access scheme for cognitive radios in an interweave cognitive system, that considers the channel gain as well as the predicted idle channel probability (primary user occupancy: busy/idle). In contrast to previous work where a cognitive user vacates a channel only when that channel becomes busy, the proposed scheme requires the cognitive user to switch to the channel with the next highest idle probability if the current channel’s gain is below a certain threshold. We derive the threshold values that maximize the long term throughput for various primary user transition probabilities and cognitive user’s relative movement (Doppler spread). Then, we propose a three state Markov model to analyze the performance of a hybrid interweave-underlay system where the primary user’s occupancy states are hidden, but their activity statistics, ranges of transmission, and interference thresholds are known. The primary user is assumed to be in one of the three transmission modes as seen by the cognitive user: busy, concurrent and idle. We derive the transmission mode selection criteria (interweave/underlay) to improve the long term throughput of a cognitive user based on the primary user traffic characteristics and the achievable throughput ratio between the two modes of operation. Later, we incorporate the sensing error in our analysis where we study the optimal access strategy. Since the optimal policy requires the channel to be sensed in each time-slot, we propose and analyze a forward algorithm based cross-layer frame based sensing policy. Finally, we focus on the overlay cognitive radio system where cognitive relay nodes assist the primary transmission. As an initial study, we select a two-hop decode-and-forward orthogonal frequency and code division multiplexing based relay network. For this system, we propose adaptive channel allocation and, power allocation strategies and the bit error rate performance is numerically evaluated. This preliminary analysis can be extended to overlay cognitive systems.

Throughput Analysis of Opportunistic Channel Access Techniques in Cognitive Radio Systems

In recent studies it was found out that previously allocated frequency spectrum is not fully utilized in all the wireless systems. Cognitive radio is the new concept to access this underutilized spectrum and, also a promising technology to cope with the ever increasing bandwidth demand for next generation wireless networks. Cognitive radio network can be classified into three different categories: interweave, underlay and overlay. In an interweave cognitive radio system, the unoccupied spectrum holes can be shared by cognitive users with minimal collision with primary users (spectrum owners) whereas in an underlay system, concurrent transmission is allowed with an interference threshold to the primary users. In an underlay system, cognitive users generally transmit at very low power. In an overlay system, cognitive users, similar to underlay cognitive radio systems, concurrently transmit with primary users but cognitive users may know the codewords of the primary transmitter. Hence, using that knowledge, cognitive transmitter may adopt different coding techniques to cancel/mitigate the interference at the primary receiver and/or it may assist the primary system by relaying primary user’s data. In this thesis, we improve the throughput/bit error rate performance of a cognitive radio system by effectively accessing the channels. Throughout the thesis we assume that cognitive user can sense only one channel at a time and we analyze the performance with perfect and imperfect sensing. First, we propose a novel opportunistic access scheme for cognitive radios in an interweave cognitive system, that considers the channel gain as well as the predicted idle channel probability (primary user occupancy: busy/idle). In contrast to previous work where a cognitive user vacates a channel only when that channel becomes busy, the proposed scheme requires the cognitive user to switch to the channel with the next highest idle probability if the current channel’s gain is below a certain threshold. We derive the threshold values that maximize the long term throughput for various primary user transition probabilities and cognitive user’s relative movement (Doppler spread). Then, we propose a three state Markov model to analyze the performance of a hybrid interweave-underlay system where the primary user’s occupancy states are hidden, but their activity statistics, ranges of transmission, and interference thresholds are known. The primary user is assumed to be in one of the three transmission modes as seen by the cognitive user: busy, concurrent and idle. We derive the transmission mode selection criteria (interweave/underlay) to improve the long term throughput of a cognitive user based on the primary user traffic characteristics and the achievable throughput ratio between the two modes of operation. Later, we incorporate the sensing error in our analysis where we study the optimal access strategy. Since the optimal policy requires the channel to be sensed in each time-slot, we propose and analyze a forward algorithm based cross-layer frame based sensing policy. Finally, we focus on the overlay cognitive radio system where cognitive relay nodes assist the primary transmission. As an initial study, we select a two-hop decode-and-forward orthogonal frequency and code division multiplexing based relay network. For this system, we propose adaptive channel allocation and, power allocation strategies and the bit error rate performance is numerically evaluated. This preliminary analysis can be extended to overlay cognitive systems.

Cognitive User Interface for Portfolio Optimization

This paper describes the development of a chatbot as a cognitive user interface for portfolio optimization. The financial portfolio optimization chatbot is proposed to provide an easy-to-use interface for portfolio optimization, including a wide range of investment objectives and flexibility to include a variety of constraints representing investment preferences when compared to existing online automated portfolio advisory services. Additionally, the use of a chatbot interface allows investors lacking a background in quantitative finance and optimization to utilize optimization services. The chatbot is capable of extracting investment preferences from natural text inputs, handling these inputs with a backend financial optimization solver, analyzing the results, and communicating the characteristics of the optimized portfolio back to the user. The architecture and design of the chatbot are presented, along with an implementation using the IBM Cloud, SS&C Algorithmics Portfolio Optimizer, and Slack as an example of this approach. The design and implementation using cloud applications provides scalability, potential performance improvements, and could inspire future applications for financial optimization services.

On Optimal Number of Cognitive Radios Considering Co-site Electromagnetic Compatibility

Cognitive radio is becoming one of the most important techniques for high utility of spectrum holes. If the holes available to cognitive users are abundant over a certain time, it is a worth consideration to increase network throughputs by orthogonal multiplexing as many as spectrum holes. A multi-transceiver configuration is one of the possible solutions for this purpose. With such a schema, all transceivers within a cognitive user work in a concurrent or parallel mode, by which the throughput of the network can be increased. However, co-site working cognitive radios may incur electromagnetic interference between each other. When more cognitive radios are equipped, much electromagnetic interference may be incurred. Based on an electromagnetic compatibility probability analysis, this paper proposes a novel method to decide how many cognitive radios can be installed for one cognitive user at most. We make a strict deduction on electromagnetic compatibility probability with various parameters of cognitive radios. Simulations are performed and the results show that the electromagnetic compatibility of the simulated cognitive radio system meet the deducted probability very well.

UcEF for Semantic IR

At present, keyword-based techniques allow information retrieval (IR) but are unable to capture the conceptualizations in users' information needs and contents. The response to this has been semantic search computing with commendable success. Surprisingly, it is still difficult to evaluate Semantic IR (SIR) and understand the user contexts. The absence of a standardized cognitive user-centred evaluative paradigm (CUcEP) further exacerbates these challenges. This chapter provides the state-of-the-art on IR and SIR evaluation and a systematic review of contexts. Appropriate user-centred theories and the proposed evaluative framework with its integrated-context, web analytic conception, and related data analytic technique are presented. A descriptive approach is adopted, with the conclusion that multiple contexts are essential in SIR evaluation since “searching by meaning” is a multi-dimensional cognitive conception, hence the need to consider the impact of context dynamicity. Finally, the foregrounded semantic items will be applied to standardize the CUcEP in future.