Free Channel Research Articles

Queueing Delay Performance of Schedulers in Centralized Sensing Cognitive Radio Networks

Wireless communication has become cost-effective and it can be established very rapidly in order to bring broadband access to under-served rural as well as urban area users. The underutilized spectrum has enormous, untapped, public capacity to provide high-speed and pervasive broadband connectivity. The wireless Radio Frequency (RF) spectrum is highly congested due to the continuous increase in the demand for high data rate services. Cognitive Radio (CR) allows secondary/unlicensed users to use a part/slice of a licensed spectrum, referred to as a channel, whenever the primary/licensed user is not transmitting in that channel during a period. In order to find the primary–free channels in the RF spectrum, CR performs spectrum sensing before transmitting its signal. When there are multiple secondary users trying to sense, find and access the available free channels it becomes very challenging. Scheduling resolves the problem by the use of queues. The behaviour of queues in terms of Queuing delay performance of Schedulers in Multiuser Cognitive Radio Networks when there is a Centralized Coordinator performs sensing and scheduling, has been studied. Three different scheduling policies are considered, namely Maximum Gain, Maximum Weight and Proportionally Fair scheduling. When the network is heavily loaded, each policy presents varied Queuing Delay Performance. The cases when average Signal-to-Noise Ratio of users is considered to be unequal have been analysed with varying normalized sensing duration. Queuing delay for various arrival rates of users is plotted and the performances have been compared and discussed. From the results, it can be concluded that the Maximum Weight Scheduler performs better than others do.

Beam divergence and operating wavelength bands effects on free space optics communication channels in local access networks

Abstract The paper outlines the divergence of beam and operating wavelength bands effects on free-space optics communication channels in local access networks. The max Q factor and min bit error rate are measured based on the divergence of beam and operating wavelength bands variations. The signal is tested also at the receiver side by using an optical power meter visualizer at various operating signal wavelength bands and under the optimum values of the divergence of the beam. The study has presented the optimum operating conditions for upgrading network operation efficiency.

STUDY OF THE TACTICAL AND TECHNICAL CHARACTERISTICS OF A SPECIAL FIRE BARREL FOR EXTINGUISHING UNDERGROUND FIRES IN PEAT-FOREST ECOSYSTEMS

One of the promising methods of extinguishing fire is to extinguish with water or solutions of extinguishing agents. This method is relevant for extinguishing underground fires in peat-forest ecosystems, in particular litter and peat. For this, a special fire barrel was developed to extinguish underground fires using water extinguishing agents with the addition of surfactants. In the work, the tactical and technical characteristics of a special fire barrel for extinguishing underground fires are established and a method for extinguishing them with fire extinguishing agents using surfactants is developed.A special fire barrel equipped with auger blades has been developed, which perform a number of functions: cut solid inclusions when deepening, the trunk, hold the trunk in peat layers, open free channels to withdraw excess water to the surface without erosion of the soil.Based on the studies, it is possible to select the optimal parameters of pressure and fluid flow for specific conditions of quenching of peat and litter in the peat-forest ecosystem. In addition, it should be noted that the developed special fire barrelFire Safety, №36, 2020 109 has a more than 3 times greater consumption of extinguishing agent than existing analogues, such as TS-1, TS-2, SPT-70. This suggests that in practice such trunks will be needed less, and their extinguishing efficiency will be higher. As a fire extinguishing agent, it is recommended to use not water, but aqueous solutions of Bars S-1, Bars S-1m blowing agents containing surfactants that reduce the surface tension of water and increase the wetting ability of bedding, peat and are one of the most effective ways to combat peat fires.The fluid flow rate of a special fire barrel for extinguishing underground fires in peat-forest ecosystems was determined at pressures of 0.4 and 0.7 MPa, which are respectively 13.24 and 15.98 l/s.The fluid flow rate was calculated at 0.5 and 0.6 MPa, which is 14.26 and 15.40 l/s, respectively.Based on experimental and calculated data, it was found that the increase in fluid flow at pressures of 0.4 – 0.6 MPa occurs almost uniformly, and significantly slows down in the range of 0.6 – 0.7 MPa.

Theodoros Terzopoulos’un Dionizyak Oyuncusu ve Sahnedeki Mevcudiyeti

Theodoros Terzopoulos places the actor at the center of his theater and builds his own theater language on actor training and research he developed over the years. The main material of his acting technique, which is a product of this training and research process, is actor's body. In order to reveal the potential of the actor's body, the primary objective is to release the energies that are blocked. Thus, the actor pursues a state of being, an ecstasis through his body which becomes a free energy channel. In the state of ecstasis, the distinction between mind and body disappears completely; the actor experiences a presence in which he involves with his whole body. This study analyzes the relationship between the presence of the actor and the state of dionysiac ecstasis aimed at by Terzopoulos and examines the ways this relationship can contribute to the presence of the actor on the stage. 

Multi-functional ceramic-coated separator for lithium-ion batteries safety tolerance improvement

The separator is used to isolate the cathode and anode material, playing an important role in the safety of battery, which prevents internal short circuit of battery and provides lithium ions free flow channels. In this paper, based on the commercial ceramic-coated polyethylene (PE) separator (CPES), low-melting point PE microspheres were mixed in ceramic-coating to form the functionalized PE separator (FPES) for improving the safety tolerance of large scale lithium-ion batteries (LIBs). Compared to the CPES shutdown temperature of ~135 °C, the shutdown temperature of FPES significantly decreased to ~110 °C. Compared with 27 Ah pouch battery assembled by CPES, the FPES can effectively improve the tolerance of overcharge and internal short circuit without sacrificing the electrochemical performance. In addition, a novel internal short circuit of FPES protection mechanism model was proposed. Molten PE microspheres of FPES would flow along the edge of broken hole, reducing the contact probability between the cathode and anode, and ultimately increasing the resistance of internal short circuit by 41% compared to CPES. Therefore, the obtained results provide important implications for the development of safer separator and LIBs.

Endoscopic Transorbital Approaches to Anterior and Middle Cranial Fossa: A Laboratory Investigation on Surgical Anatomy and Potential Routes.

Background Transorbital neuroendoscopic (TONES) approaches promise to open up new horizons for skull base surgery, offering alternative routes to reach the anterior and middle cranial fossa (ACF and MCF, respectively). Objective The aim of this anatomical study is to acquire new surgical anatomy knowledge and exploit it for the refinement of TONES approaches, as an alternative to open surgery, to reduce the distance to the target, and the risk of neurovascular lesions in pathological conditions extending beyond the orbital cavity. Materials and Methods Six head specimens (12 orbits) were studied/dissected. The orbit was approached and divided in a four clockwise quadrants manner to simulate three transconjunctival routes: the precaruncular (PC), preseptal (PS), and lateral retrocanthal (LRC), and one transpalpebral route-the superior eyelid crease (SLC). The boundaries and the most important anatomical landmarks were identified and are herein duly detailed with particular attention to the neurovascular structures encountered in each of those routes. Results The dissections showed that the PC approach facilitates the treatment of optic nerve and frontal sinus pathologies, whereas LRC appears safer to reach ACF and MCF allowing for a free multiplanar working channel (up to 180 degrees) to the floor, roof, and lateral-to-medial walls. Conclusion The plane of tendon lateral canthal's insertion and the sphenofrontal suture (SFS) were identified as the key anatomical landmarks for TONES approaches. Further studies are warranted to establish a practical clinical algorithm based on the anatomical four clockwise quadrants herein implemented/proposed, and the key surgical landmarks identified.

Energy and spectrum aware unequal clustering with deep learning based primary user classification in cognitive radio sensor networks

The problem of energy efficiency in cognitive radio sensor networks (CRSN) is mainly caused by the limited energy of sensor nodes and other channel-related operations for data transmission. The unequal clustering method should be considered for balancing the energy consumption among the cluster heads (CHs) for prolonging the network lifetime. The CH selection should consider the number of accessible free channels for efficient channel assignment. To improve fairness, the channel assignment problem should consider energy consumption among the cluster members. Furthermore, the relay metric for the selection of the best next-hop should consider the stability of the link for improving the transmission time. The CH rotation for cluster maintenance should be energy and spectrum aware. With regard to the above objectives, this paper proposes an energy and spectrum aware unequal clustering (ESAUC) protocol that jointly overcomes the limitations of energy and spectrum for maximizing the lifetime of CRSN. Our proposed ESAUC protocol improves fairness by achieving residual energy balance among the sensor nodes and enhances the network lifetime by reducing the overall energy consumption. Deep Belief Networks algorithm is exploited to predict the spectrum holes. ESAUC improves the stability of the cluster by optimally adjusting the number of common channels. ESAUC uses a CogAODV based routing mechanism to perform inter-cluster forwarding. Simulation results show that the proposed scheme outperforms the existing CRSN clustering algorithms in terms of residual energy, Network Lifetime, secondary user–primary user Interference Ratio, Route Discovery Frequency, throughput, Packet Delivery Ratio, and end-to-end delay.

Rényi Entropy-Based Spectrum Sensing in Mobile Cognitive Radio Networks Using Software Defined Radio.

A very important task in Mobile Cognitive Radio Networks (MCRN) is to ensure that the system releases a given frequency when a Primary User (PU) is present, by maintaining the principle to not interfere with its activity within a cognitive radio system. Afterwards, a cognitive protocol must be set in order to change to another frequency channel that is available or shut down the service if there are no free channels to be found. The system must sense the frequency spectrum constantly through the energy detection method which is the most commonly used. However, this analysis takes place in the time domain and signals cannot be easily identified due to changes in modulation, power and distance from mobile users. The proposed system works with Gaussian Minimum Shift Keying (GMSK) and Orthogonal Frequency Division Multiplexing (OFDM) for systems from Global System for Mobile Communication (GSM) to 5G systems, the signals are analyzed in the frequency domain and the Rényi-Entropy method is used as a tool to distinguish the noise and the PU signal without prior knowledge of its features. The main contribution of this research is that uses a Software Defined Radio (SDR) system to implement a MCRN in order to measure the behavior of Primary and Secondary signals in both time and frequency using GNURadio and OpenBTS as software tools to allow a phone call service between two Secondary Users (SU). This allows to extract experimental results that are compared with simulations and theory using Rényi-entropy to detect signals from SU in GMSK and OFDM systems. It is concluded that the Rényi-Entropy detector has a higher performance than the conventional energy detector in the Additive White Gaussian Noise (AWGN) and Rayleigh channels. The system increases the detection probability (PD) to over 96% with a Signal to Noise Ratio (SNR) of 10dB and starting 5 dB below energy sensing levels.

Cooperative spectrum sensing optimization based adaptive neuro-fuzzy inference system (ANFIS) in cognitive radio networks

The tremendous growth of the wireless communications and their applications stimulate the urgent need to keep on the available radio spectrum. As a result, cognitive radio (CR) technologies are proposed and developed to manage the limitation of the available spectrum by methods of sensing and sharing the free channels. Wideband spectrum sensing algorithms have a great impact of detecting the vacant channels of the whole spectrum simultaneously. Cooperative sensing techniques are introduced based on sharing users’ sensing outcomes among other users. Therefore, it represents an efficient method to overcome signal shadowing and fading problems. Recently, artificial intelligence (AI) techniques are considered to improve the quality of service (QoS) parameters in cognitive radio networks. In this paper, an adaptive Neuro-Fuzzy interference system (ANFIS) algorithm is proposed in the process of decision-making to detect the optimal and accurate free channels. ANFIS model is trained with some pertinent features over a Music-like channel power level (PMU(k)), channel identity number (k), and channel repetition number. Consequently, the second stage is introduced by applying ANFIS technique on the adaptive blind cooperative wideband spectrum sensing basis to select the optimum required number of cooperative users with increasing performance based on the detected signal to noise ratio (SNR) level per secondary user. Simulation is based on Simulink of five users with different SNR due to fading and shadowing problems. Simulation results proved that, the proposed technique based on cooperative spectrum sensing algorithm with ANFIS model for detection outperformed other traditional detection techniques.

World Englishes in multilingual Morocco

AbstractThis paper explores the history, politics and discourses around the situation of English(es) in Morocco. It examines how this global language succeeded to infiltrate into the Moroccan linguistic market with a focus on its various uses in various domains (education, academic research, diplomacy, mass media, tourism and finance). Albeit English(es) is spoken sporadically in the business, science and education sectors, its usage and learning have grown over the last decades with the boom of free English satellite channels and the development of the internet and social media. This language is now considered as the main vehicle for the transfer of technology and as an important tool of appropriating modernity. Indeed, it is gaining prestige among Moroccans and is quickly replacing French as Morocco's second language, both among youths and educators.

Comparative performance analysis of GFDM and UFMC under different window constraints for next generation cognitive radio communication

Wireless communication technology is the main reason for the advancement to mobile users. So each user demands for a separate frequency spectrum. But there is a limited frequency spectrum band. Hence there is need of an efficient communication system which first evaluates the need of frequency and then provides the frequency band to that user smartly. Cognitive Radio (CR) Technology is based on software defined radios (Mitola in Cognitive radio—an integrated agent architecture for software defined radio (Ph.D. Dissertation). KTH Royal Institute of Technology, Kista, 2000). When the frequency spectrum is used by the authorized primary user (PU), then cognitive radio provide the remaining available bandwidth to the secondary user (SU) which has very less interference with primary user. The main work of cognitive radio is to check the spectrum and find the available free channels for secondary users without affecting the primary user’s work. Universal Filtered Multicarrier (UFMC) technique gives better performance over other multicarrier techniques in term of PAPR. The work presented here is unique and novel in the sense that we have tried to incorporate the UFMC technique simultaneously in comparison with applied GFDM multicarrier modulation technique in the same wireless scenario for highlighting the contrast in the study presented here. The probable limitations of the proposed solutions after carrying out rigorous simulation testing on Matlab version 2018a have also been discussed.

Improved transmission length in the presences of ambient noise and scintillation effect using duobinary modulation in 40 Gbps free space optical channel

AbstractFree space optical (FSO) communication has gained significant popularity in recent years due to large bandwidth, license‐free spectrum, high data rates, less power consumption, and low mass requirements. However, system performance strongly depends on atmospheric conditions and ambient noise. In this letter, the duobinary modulation technique is applied and the system performance is investigated in the presence of ambient noise. The system is evaluated on the basis of Q‐factor, eye diagram, input power, transmission distance, and bit error rate. A significant improvement is observed in the presence of noise while using duobinary modulation. This study exploits extensive simulations to investigate the performance of the system. All simulations are performed for a single link of FSO communication network having a data rate of 40 Gbps in the Optisystem simulator and ambient noise is created using LEDs. After the exhaustive set of simulations, a significant improvement in transmission length is observed. It is also observed that at low input power, doubinary modulation provides better results when compared with on‐off keying (OOK) format. Scintillation effect has also be observed for doubinary modulation and compared with OOK modulation format. It is concluded that doubinary modulation provides better results in the presence of low and moderate scintillation.

Adaptive Deformation of Ionic Domains in Hydrogel Enforcing Dielectric Coupling for Sensitive Response to Mechanical Stretching

Understanding the role of ionic migration in salt‐doped hydrogels is crucial for designing and using ionic skins. This study systematically investigates a typical ionic skin in the aspects of variations in capacitance and conductance with respect to stretch ratio. The ionic skin exhibits a sensitive response to the stretch ratio and input frequency. The capacitance can increase by 145% with increasing stretch ratio, whereas the ratio of capacitance variation to stretch ratio can exceed ≈0.25. The capacitance decreases with increasing frequency, whereas conductance increases. Capacitance or conductance with respect to stretch ratio exhibits an inflection point when the input frequency is fixed. Herein, an ionic domain model is proposed in which the ionic domains deform adaptively with global strain and released active ions. A portion of movable ions strengthens dielectric coupling, thereby significantly enhancing capacitance, and some of them act as free ion channels to increase conductance. The dielectric coupling is weakened when the active ions arriving at the electrode are depleted by either a significantly high frequency or large strain. This study will be useful for signal handling in ionic skin with high flux and high sensitivity and may also assist in understanding computing and memory principles of biological bodies.

Tunable Violet Laser Diode System for Optical Wireless Communication

We report a tunable self-injection locked violet laser diode external cavity system exhibiting a continuous wavelength tunability of 5.15 nm (400.28 - 405.43 nm) with mean side-mode-suppression-ratio (SMSR) and linewidth of ~23 dB and ~190 pm, respectively. The effects of injection current and temperature indicate a robust system besides being cost-effective and straightforward. Moreover, a successful indoor on-off keying transmission at two different locked modes on a 0.4 m free space channel showed ~10 times improvement in the bit-error-rate (BER) with value ~8 × 10 -4 at 2 Gb/s, and better performance on 0.8 m channel length at 1.75 Gb/s compared to the free-running laser case. Our work is a potential step towards the realization of future high data capacity narrow-wavelength-spaced multiplexed optical wireless communication system wherein continuously tunable laser sources are expected to play a crucial role as transmitters.

Deployment of Auction Theoretic Models for Spectrum Allocation in Cognitive Radio Networks

Cognitive Radio (CR) is a novel technology which empowers the unlicensed users to opportunistically avail the free channels left unoccupied by the licensed owners. This apparently resolves the spectrum scarcity problem arising in today’s telecommunication industry. In this technology, once the free bands (called spectrum holes) are detected using sensing techniques, next there is a need to efficiently redistribute the idle spectrum. Such an allocation process of CR has attracted several researchers across the world to contribute in this domain. With an initiative to analyze the functionality of spectrum allocation, this paper carries out a survey on the allocation mechanisms which have been applied to use the spectrum holes. We primarily focus our exploration on auction theoretic allocation models due to their efficacy in channel allocation. Auction formulation takes the unlicensed users as bidders where they bid for the spectrum holes as the auctioned item. Winner determination strategy and pricing strategy are two important aspects of an auction model which determines a fair allocation pattern and along with decides the monetary benefit of sellers and auctioneer. We go through a detailed study on single-sided auction and double-sided auction which are deployed with different CR network constraints to design the allocation model. Finally, we conclude the paper by underlining some future research directions in this area.

Analysis of Free Space Optics Link Performance Considering the Effect of Different Weather Conditions and Modulation Formats for Terrestrial Communication

AbstractFree space optics (FSO) links provide an effectual and efficient way of transmission of data throughout free channels due to its higher bandwidth and inbuilt capability of security. In this research analysis, the FSO link is evaluated on the basis of Q value for different modulation formats and weather conditions. Gamma–Gamma and log-normal scintillation models have been analyzed for different index of refraction in terms of Q factor versus a range of a proposed FSO link. Attenuation increases during the occurrence of different fog conditions, and there might be complete link failure in the case of dense fog and for some of the cloud conditions.

Experiments and CFD for the propeller wake of a generic submarine operating near the surface

An experimental and computational fluid dynamics (EFD and CFD) study of the appended notional submarine DARPA Suboff fitted with the 7-bladed E1658 propeller and operating near the free surface is presented. The flow measurements were taken using particle image velocimetry with a multi-camera configuration in the Large Free Surface Cavitation Channel at INM. Single-phase level set numerical simulations with an overset approach were performed for three advance coefficients (J=0.5,0.65,0.82) at three shaft depths (z/D=1,1.5,2). The results reveal that the presence of the hull and the interaction with the free surface strongly affect the inflow and wake of the propeller, producing higher local advance coefficient and blade loads near the surface. Strong free surface fluctuations at small shaft depth also cause instability and breakdown of the propeller tip vortices in the near field. CFD simulations show elliptic instability before vortex breakdown. Comparison between CFD with EFD shows that CFD matches overall trends well, mainly for the phase-averaged flow field, but underpredicts wake fluctuations and thus displays more coherent phase-averaged vorticity. In addition, CFD results also underpredict tip vortex strength and predicts vortex instabilities farther downstream from the propeller plane due to the unresolved upstream turbulence.

Streaming Delay-, Expenditure- and Quality-Balanced Video Over TV White Space

This paper develops a solution for video delivery over TV white space (TVWS) that can achieve a balanced tradeoff between expenditure, delay and quality. TVWS channels can be classified into two types, i.e., free TVWS channels (FTCs) and high-priority TVWS channels (HPCs). However, the development of this system encounters many challenges because of the time-varying TVWS available status, dynamic HPC spectrum leasing price, fluctuated data size of group of pictures, and diverse user requirements. To address the above issues, we first build a video data model and a TVWS model. Then, we formulate two optimization problems i) expenditure minimization subject to video quality requirement and target delay, and ii) delay minimization subject to video quality requirement and limited total budget, both of which are linear integer programming problems. Next, we develop online and offline algorithms for these two optimization problems. Finally, we implement a T VWS-based V ideo D elivery S ystem (TVDS) based on a cognitive wireless network, which can use FTCs or lease HPCs to provide point-to-point (P2P) video data delivery service. The proposed algorithms are implemented in the TVDS, and extensive simulations are presented to verify the effectiveness of the proposed algorithms under different conditions.

Joint Resource Allocation and Transmission Mode Selection Using a POMDP-Based Hybrid Half-Duplex/Full-Duplex Scheme for Secrecy Rate Maximization in Multi-Channel Cognitive Radio Networks

Physical layer wireless communications are more and more essential, and are vulnerable to malicious users owing to the nature of broadcast channels. Herein, we consider a centralized multi-channel cognitive radio network in the presence of eavesdroppers (EVEs). In the network, the secondary base station (SBS) shares currently free primary channels to simultaneously communicate with secondary users (SUs), while passive eavesdroppers attempt to overhear data in the secondary communications. Each limited-battery SU is equipped with two antennas (one for transmitting signals, and other for receiving signals) and is powered by a solar energy harvester. Meanwhile, the SBS equipped with multiple antennas can operate in full-duplex (FD) transmission mode (simultaneously transmit and receive signals) or in half-duplex (HD) transmission mode (transmit and receive signals in turn during each half of a time slot) with the SUs. In this paper, we propose a novel scheme to maximize the secondary system security of the multi-channel cognitive system in the presence of multiple passive EVEs, in which the EVEs are able to overhear the data of the SBS-SU transmissions on all the primary channels. The problem of decision making is formulated as the framework of a partially observable Markov decision process (POMDP), and an optimal solution is achieved by adopting value iteration-based dynamic programming. Specifically, in each time slot, the SBS allocates optimal channel and optimal action (i.e. either stay silent or employ HD/FD transmission modes with optimal transmission power) for each SU in order to obtain maximum long-term secrecy rate for the secondary system.

Prioritized data based Energy Efficient MAC protocol in Wireless Body Area Network

Wireless Body Area Network (WBAN) is an exclusively designed Wireless Sensor Networks that used in today’s health-care system. The central challenge in WBAN is to transfer the medical data with limited energy and with high reliability. The IEEE 802.15.4 MAC Protocol is a standard model used to consume less energy by providing low data rate. This paper aimed to present a novel protocol PD-MAC, an enhanced version of IEEE 802.15.4 to achieve the above goal. The main objective of this protocol is to transmit the packets according to their priorities. It also improves the retransmission and packet drop process by introducing an additional slot to define Starvation Index in the super-frame of IEEE 802.15.4. A node has to start its transmission when the timer is set to zero. A node has to sense the channel status before transmission begins. The data are transmitted according to their priorities only when it senses the free channel. However if the channel is not free then retransmission of packet will be carried out and in each retransmission process the starvation index increments the priority of the packet. When the packet priority raises to high then it transmits the packet by considering it as high emergency packet. For energy efficiency a max limit is define to retransmit a data packet. This protocol has been simulated using Castalia 3.2 environment and the result validate that our proposed protocol provides better service in terms of least Packet Delay and lowest Energy Consumption to its counterparts.