Additional Frequency Bands Research Articles

Cavitation monitoring, treatment strategy, and acoustic simulations of focused ultrasound blood-brain barrier disruption in patients with glioblastoma

PurposeWe report our experience disrupting the blood-brain barrier (BBB) to improve drug delivery in glioblastoma patients receiving temozolomide chemotherapy. The goals of this retrospective analysis were to compare MRI-based measures of BBB disruption and vascular damage to the exposure levels, acoustic emissions data, and acoustic simulations. We also simulated the cavitation detectors. MethodsMonthly BBB disruption (BBBD) was performed using a 220 kHz hemispherical phased array focused ultrasound system (Exablate Neuro, InSightec) and Definity microbubbles (Lantheus) over 38 sessions in nine patients. Exposure levels were actively controlled via the cavitation dose obtained by monitoring subharmonic acoustic emissions. The acoustic field and sensitivity profile of the cavitation detection system were simulated. Exposure levels and cavitation metrics were compared to the level of BBBD evident in contrast-enhanced MRI and to hypointense regions in T2*-weighted MRI. ResultsOur treatment strategy evolved from using a relatively high cavitation dose goal to a lower goal and longer sonication duration and ultimately resulted in BBBD across the treatment volume with minimal petechiae. Subsonication-level feedback control of the exposure using acoustic emissions also improved consistency. Simulations of the acoustic field suggest that reflections and standing waves appear when the focus is placed near the skull, but their effects can be mitigated with aberration correction. Simulating the cavitation detectors suggest variations in the sensitivity profile across the treatment volume and between patients. A correlation was observed with the cavitation dose, BBBD and petechial hemorrhage in 8/9 patients, but substantial variability was evident. Analysis of the cavitation spectra found that most bursts did not contain wideband emissions, a signature of inertial cavitation, but biggest contribution to the cavitation dose – the metric used to control the procedure – came from bursts with wideband emissions. ConclusionUsing a low subharmonic cavitation dose with a longer duration resulted in BBBD with minimal petechiae. The correlation between cavitation dose and outcomes demonstrates the benefits of feedback control based on acoustic emissions, although more work is needed to reduce variability. Acoustic simulations could improve focusing near the skull and inform our analysis of acoustic emissions. Monitoring additional frequency bands and improving the sensitivity of the cavitation detection could provide signatures of microbubble activity associated with BBB disruption that were undetected here and could improve our ability to achieve BBB disruption without vascular damage.

Design optimization for microstrip antennas based on polymethyl methacrylate (PMMA) substrate and carbon nanotube (CNT) conductive material in sub-6 Ghz band

Abstract Background The rapid expansion of modern smart applications, demanding faster data transfer and extensive bandwidth, has prompted the development of new-generation networks like 5G and 6G. These networks encompass additional frequency bands such as sub-6 GHz, millimeter waves, and terahertz bands to meet the growing bandwidth requirements. However, despite the substantial bandwidth available in these bands, several challenges must be addressed to overcome unfavorable propagation characteristics. Moreover, numerous applications necessitate wireless devices with antennas that exhibit high flexibility and exceptional radiation responses, particularly when subjected to bending effects. This requirement highlights the importance of polymers-based antennas that can adapt to changing conditions while maintaining optimal performance. The present comprehensive study delves into the performance evaluation of rectangular and circular microstrip antennas utilizing PMMA (polymethyl methacrylate) polymer substrate with varying thicknesses. Results Notably, CNTs (Carbon Nanotubes) are employed as an alternative to traditional copper for the conductive part and ground plane. Both PMMA-based antennas, integrated with CNTs, exhibit a compact footprint of 27.8 × 47.8 × 1.5 mm3 for the circular antenna and 22.8 × 39.5 × 1.5 mm3 for the rectangular antenna. Impressively, the realized gain of both antennas surpasses 5 dBi, demonstrating robust performance in both flat and bending scenarios across different substrate thicknesses. Conclusions The rectangular antenna achieves a bandwidth of approximately 200 MHz, while the circular microstrip antenna showcase annotable bandwidth of 500 MHz. These exceptional outcomes position the two microstrip antennas as highly suitable for a diverse range of emerging applications within the sub-6 GHz band (the frequency range below 6 GHz in the radio spectrum). Thus, the combination of PMMA substrate, CNTs and the compact form factor of the antennas presents a compelling solution for meeting the demands of modern applications requiring efficient wireless communication with enhanced performance and bandwidth.

Transcranial ultrasound stimulation selectively affects cortical neurovascular coupling across neuronal types and LFP frequency bands.

Previous studies have affirmed that transcranial ultrasound stimulation (TUS) can influence cortical neurovascular coupling across low-frequency (0-2Hz)/high-frequency (160-200Hz) neural oscillations and hemodynamics. Nevertheless, the selectivity of this coupling triggered by transcranial ultrasound stimulation for spike activity (> 300Hz) and additional frequency bands (4-150Hz) remains elusive. We applied transcranial ultrasound stimulation to mice visual cortex while simultaneously recording total hemoglobin concentration, spike activity, and local field potentials. Our findings include (1) a significant increase in coupling strength between spike firing rates of putative inhibitory neurons/putative excitatory neurons and total hemoglobin concentration post-transcranial ultrasound stimulation; (2) an ~ 2.1-fold higher Pearson correlation coefficient between putative inhibitory neurons and total hemoglobin concentration compared with putative excitatory neurons and total hemoglobin concentration (*P< 0.05); (3) a notably greater cross-correlation between putative inhibitory neurons and total hemoglobin concentration than that between putative excitatory neurons and total hemoglobin concentration (*P< 0.05); (4) an enhancement of Pearson correlation coefficient between the relative power of γ frequency band (30-80Hz), hγ frequency band (80-150Hz) and total hemoglobin concentration following transcranial ultrasound stimulation (*P< 0.05); and (5) strongest cross-correlation observed at negative delay for θ frequency band, and positive delay for α, β, γ, hγ frequency bands. Collectively, these results demonstrate that cortical neurovascular coupling evoked by transcranial ultrasound stimulation exhibits selectivity concerning neuronal types and local field potential frequency bands.

Corticostriatal beta oscillation changes associated with cognitive function in Parkinson's disease.

Cognitive impairment is the most frequent non-motor symptom in Parkinson's disease and is associated with deficits in a number of cognitive functions including working memory. However, the pathophysiology of Parkinson's disease cognitive impairment is poorly understood. Beta oscillations have previously been shown to play an important role in cognitive functions including working memory encoding. Decreased dopamine in motor cortico-striato-thalamo-cortical (CSTC) circuits increases the spectral power of beta oscillations and results in Parkinson's disease motor symptoms. Analogous changes in parallel cognitive CSTC circuits involving the caudate and dorsolateral prefrontal cortex (DLPFC) may contribute to Parkinson's disease cognitive impairment. The objective of our study is to evaluate whether changes in beta oscillations in the caudate and DLPFC contribute to cognitive impairment in Parkinson's disease patients. To investigate this, we used local field potential recordings during deep brain stimulation surgery in 15 patients with Parkinson's disease. Local field potentials were recorded from DLPFC and caudate at rest and during a working memory task. We examined changes in beta oscillatory power during the working memory task as well as the relationship of beta oscillatory activity to preoperative cognitive status, as determined from neuropsychological testing results. We additionally conducted exploratory analyses on the relationship between cognitive impairment and task-based changes in spectral power in additional frequency bands. Spectral power of beta oscillations decreased in both DLPFC and caudate during working memory encoding and increased in these structures during feedback. Subjects with cognitive impairment had smaller decreases in caudate and DLPFC beta oscillatory power during encoding. In our exploratory analysis, we found that similar differences occurred in alpha frequencies in caudate and theta and alpha in DLPFC. Our findings suggest that oscillatory power changes in cognitive CSTC circuits may contribute to cognitive symptoms in patients with Parkinson's disease. These findings may inform the future development of novel neuromodulatory treatments for cognitive impairment in Parkinson's disease.

MIMO 5G Smartphone Antenna with Tri-Band and Decoupled Elements.

In this article, a miniaturized antenna is proposed for 4G/5G multiple input, multiple output (MIMO) applications for smartphones. The proposed antenna is composed of an inverted L-shaped antenna with decoupled elements to cover 4G (2000-2600 MHz), and a planar inverted-F antenna (PIFA) with a J-slot to cover 5G (3400-3600 MHz and 4800-5000 MHz). Furthermore, to achieve the purposes of miniaturization and decoupling, the structure adopts a feeding stub, shorting stub, and outstanding floor, additionally adding the slot to the PIFA, to generate additional frequency bands. Due to the advantages such as multiband operation, MIMO configuration for 5G communications, high isolation, and a compact structure, the proposed antenna design is attractive for 4G/5G smartphones. The antenna array is printed on an FR4 dielectric board, measuring 140 × 70 × 0.8 mm3, with the 4G antenna located on a top 15 mm-long headroom.

A compact triple‐band printed dipole antenna using C‐shaped resonators with stable radiation for GSM/ISM/WLAN applications

AbstractA compact printed dipole antenna using an integrated balun is introduced in this work, which is achieved three frequency bands by using C‐shaped resonators. The total dimension of the proposed antenna is 42 × 72 mm2, and it covers the frequency bands of 1.62–1.88, 2.36–2.81, and 5.15–6.16 GHz with S11 &lt; −10 dB. Furthermore, the measured peak gains of the antenna in three frequency bands are equal to 8.52, 9.46, and 6.81 dB, respectively. Dipole antennas with integrated baluns have a main frequency band based on the length of the dipole arms. Nevertheless, in the presented design, two additional frequency bands have been created for the antenna, by producing suitable magnetic couplings between the C‐shaped resonators and the Γ‐shaped feed line innovatively, which has a better radiation behavior, unlike traditional triple‐band antennas. An equivalent circuit of the introduced antenna has been investigated and afterward, the optimized antenna has been fabricated and tested.

Motor-Imagery-Based Brain-Computer Interface Using Signal Derivation and Aggregation Functions.

Brain-computer interface (BCI) technologies are popular methods of communication between the human brain and external devices. One of the most popular approaches to BCI is motor imagery (MI). In BCI applications, the electroencephalography (EEG) is a very popular measurement for brain dynamics because of its noninvasive nature. Although there is a high interest in the BCI topic, the performance of existing systems is still far from ideal, due to the difficulty of performing pattern recognition tasks in EEG signals. This difficulty lies in the selection of the correct EEG channels, the signal-to-noise ratio of these signals, and how to discern the redundant information among them. BCI systems are composed of a wide range of components that perform signal preprocessing, feature extraction, and decision making. In this article, we define a new BCI framework, called enhanced fusion framework, where we propose three different ideas to improve the existing MI-based BCI frameworks. First, we include an additional preprocessing step of the signal: a differentiation of the EEG signal that makes it time invariant. Second, we add an additional frequency band as a feature for the system: the sensorimotor rhythm band, and we show its effect on the performance of the system. Finally, we make a profound study of how to make the final decision in the system. We propose the usage of both up to six types of different classifiers and a wide range of aggregation functions (including classical aggregations, Choquet and Sugeno integrals, and their extensions and overlap functions) to fuse the information given by the considered classifiers. We have tested this new system on a dataset of 20 volunteers performing MI-based brain-computer interface experiments. On this dataset, the new system achieved 88.80% accuracy. We also propose an optimized version of our system that is able to obtain up to 90.76%. Furthermore, we find that the pair Choquet/Sugeno integrals and overlap functions are the ones providing the best results.

Reconfigurable Intelligent Surface-Assisted Massive MIMO: Favorable propagation, channel hardening, and rank deficiency [Lecture Notes

Massive multiple-input multiple-output (MIMO) and reconfigurable intelligent surface (RIS) are two promising technologies for 5G-and-beyond wireless networks, capable of providing large array gain and multiuser spatial multiplexing. Without requiring additional frequency bands, those technologies offer significant improvements in both spectral and energy efficiency by simultaneously serving many users. The performance analysis of an RIS-assisted massive MIMO system as a function of channel statistics relies heavily on fundamental properties, including favorable propagation, channel hardening, and rank deficiency. The coexistence of both direct and indirect links results in aggregated channels, whose properties are the main concerns of this “Lecture Notes” article. For practical systems with a finite number of antennas and engineered scattering elements of the RIS, we evaluate the corresponding deterministic metrics, with Rayleigh fading channels as a typical example.

Design Methodology of Multiband Printed Antennas for Future Generations of Mobile Handsets

The present paper introduces a design methodology to extend the operation of a microstrip patch antenna to operate efficiently at multiple higher-order resonances. This method depends on the geometrical modification of the antenna structure by adding well-designed inductively-loaded and capacitively-coupled elements to the primary patch so that it can efficiently radiate at the desired higher frequency bands. It is explained quantitatively how to use the geometrical parameters of the inductively and capacitively coupled elements for accurate tuning of the multiple resonant frequencies of the antenna. The proposed method is applied to modify a primary hexagonal patch antenna (designed to principally radiate at 28 GHz as its first-order resonance) so as to operate at additional higher frequency bands around 43, 52, and 57 GHz. Also, an alternative design is provided for a quad-band printed antenna of composite patch structure that operates in the same millimetric-wave (mm-wave) bands, 28, 43, 52, and 57 GHz with high radiation efficiency, excellent impedance matching, and satisfactory values of the antenna gain. The corresponding frequency bands are, respectively, (27.7-28.3 GHz), (42.7-43.3 GHz), (51.2-53.0 GHz), and (55.7-57.5 GHz). The dimensions of the area occupied by the primary patch and the parasitic elements are 5.2 &#x00D7; 3.3 mm².&#x2013; The two antennas are fabricated for experimental assessment of their performance including the impedance matching and radiation patterns. It is shown that the experimental measurements come in agreement with the simulation results over all the four operational mm-wave frequency bands. One of the advantages of the proposed method is that it can be applied to patch antennas of arbitrary shapes and is not restricted to hexagonal patch antennas. Furthermore, this method is not restricted by extending the operation of the antenna to radiate at four frequency bands. It is capable of adding any desired number of frequency bands so that the antenna can operate at five or, even, more bands.

Integrated Inter-Tower Wireless Communications Network for Terrestrial Broadcasting and Multicasting Systems

This paper describes systems, devices, and methods to implement a bi-directional integrated inter-tower wireless communications network (IITWCN). The described technology can be implemented in combination with the Broadcast Core Network (BCN) in next generation broadcast eco-system and, therefore, support new business cases for broadcast operators such as the delivery of flexible datacasting services or support broadcast or point-to-point Internet services. The introduced bi-directional inter-tower communications network (ITCN) extends the previous unidirectional in-band distribution links (IDL) and adopts the on-channel repeater (OCR) as a simplified backhaul solution in single frequency networks (SFN). The concept of the coordinated ITCN is also presented, aiming at future broadcast Internet services. The ITCN provides a scalable and configurable network solution embedded in a broadcast system, which becomes independent from any non-broadcasting telecommunication infrastructure. The described technology partially relies on the infrastructure of the underlying broadcast/multicast network, using the allocated service channels without requiring additional frequency bands or a separate frequency band. The bi-directional inter-transmitter communication links are therefore referred to as integrated transmission links and the corresponding network as an integrated network.

A compact triband miniaturized MIMO antenna for WLAN applications

This paper proposes a four-port, four-element multi-band Multiple-Input Multiple-Output (MIMO) antenna array that resonates at 2.4 GHz, 2.9 GHz, and/or 5.8 GHz frequency bands for WLAN applications. A Complementary Split Ring Resonator (CSRR) was designed on the ground plane of the FR4 substrate with a rectangular patch antenna on the top plane for antenna size miniaturization, bandwidth improvement, compactness, and isolation enhancement. At first, the presence of the CSRR on the conventional antenna creates additional frequency bands and reduces the frequency of the conventional patch antenna from 24.2 GHz to 5.8 GHz. Even though the CSRR as radiating elements are closer to each other at λ/4 in the MIMO design, minimum isolation is achieved by limiting the unnecessary surface current flow that exists between the elements of the antenna. Consequently, an orthogonal method of the antenna element is adopted for the four-port MIMO antenna system with high port-to-port measured isolation of less than −19 dB, −18 dB, and –22 dB for 2.4 GHz, 2.9 GHz, and 5.8 GHz frequency bands respectively. Antenna size reduction of 96.87%, 95.41%, and 81.10% and gain of 3.94 dBi, 3.80 dBi, and 4.08 dBi were achieved for the miniaturized multi-band antenna operating at 2.4 GHz, 2.9 GHz, and 5.8 GHz frequency bands, respectively. The results also provided overall good diversity performances with the ECC < 0.01, DG > 9.98, MEG < 3 dB, and TARC in all of the proposed multi-band MIMO antenna systems at respective frequencies. The reflection & transmission coefficients, surface currents, radiation patterns, total efficiency, and diversity parameters are presented and discussed. Moreover, the proposed integration of CSRR with the antenna for MIMO antenna arrays has the advantage of multi-band operation, size reduction, isolation enhancement, good diversity, and high gain performances. With this, it is possible to conclude that the proposed metamaterial multi-band MIMO antenna is the right candidate for WLAN applications.

Folded Substrate Integrated Waveguide Based Multiband Filter for Wi-Fi6E Application

This paper presents the design and development of a multiband filter using folded substrate integrated waveguide (FSIW) for the Wi-Fi 6E application. The emerging network standard IEEE802.11ax also known as Wi-Fi 6E is the next generation of Wi-Fi, which includes an additional frequency band at 6 GHz and provides improvements over 802.11ac (Wi-Fi 5). The designed filter is based on modification of the impedance of the FSIW structure introducing longitudinal as well as transverse slots. The equivalent circuit of the slot loaded structure is derived and simulated results using ADS are compared with the simulated results of the structure using HFSS as well as with the measured results. The measured results and simulated results using HFSS and ADS show the good agreement. The size of the designed structure is 0.31λg × 0.15λg and shows insertion loss less than 0.8 dB over the desired frequency bands.

Frequency scheduling algorithm with the allocation of the main and additional frequency bands.

The subject of this research is the frequency planning algorithm for networks with an arbitrary topology of links over radio channels. The algorithm determines the total number of non-overlapping frequency ranges for the entire network and provides the distribution of each frequency range between communication nodes. The algorithm consists of two stages: at the first stage, there is a search and simultaneous distribution of frequency channels, the so-called main frequency range, as a result, only one frequency range is allocated to each node; at&amp;nbsp;the second stage, additional frequency channels are searched for, which can be used by a separate subset of nodes, thus , some nodes can use more than one frequency range, but several at once. The novelty of this research lies in the developed frequency planning algorithm for wireless communication systems with an arbitrary topology of communications over radio channels. The result of the operation of the algorithm for a wireless communication system is the allocation of radio frequencies for communication nodes from the common frequency band allocated for the wireless communication system, in terms of reuse, eliminating the effect of interference. The result for communication nodes is the allocation of a baseband and an additional frequency band, taking into account the topology of the radio network, which can be used by a separate subset that makes wireless communication systems resistant to narrowband random interference.

A Double-Veined Leaf-Shaped Bionic Meta-Element and Array Loading Antennas for Radiation Beam Control

Based on bionics, we design and analyze the left-handed (LH) characteristics of meta-elements with leaf-shaped structure. The double negative (DNG) frequency band of the initial leaf-shaped LH structure is 5.77-6.17 GHz with a fractional bandwidth of 6.7%. Inspired by two overlapping leaves, and based on topology, we evolve the leaf-shaped LH structure into a line-line coupled double-leaf LH structure. The DNG frequency bands of the line-line coupled LH structure are 2.96-3.86 GHz and 4.14-4.18 GHz. This structure not only retains some of the radiation and reflection properties of the initial design, but also gains new electromagnetic characteristics (an additional DNG frequency band). Finally, the line-line coupled LH structure is further evolved, through mostly homeomorphic deformation, into a ring-ring coupled double-veined leaf-shaped LH structure. The DNG frequency bands are 3.05-3.81 GHz and 5.31-5.41 GHz, and the fractional bandwidth are 22.2% and 1.9%, respectively. The arc-vein branches form parallel ring-ring coupling with the margin, affecting the structure’s impedance and capacitance. Similar to the line-line coupling, it can locally stretch the electromagnetic characteristics, expanding the corresponding DNG bandwidth. Through the establishment of electromagnetic topological set, we classify and analyze the topological transformation and the corresponding changes in electromagnetic characteristics. We then use formula to express the process of topological transformation intuitively. Finally, the ring-ring coupled LH structure is loaded on a microstrip antenna in several different ways, improving the antenna’s radiation properties, including bandwidth, directivity, and gain.

Design Issues and Challenges in Indoor MIMO Antenna Systems

The promising solution for next generation wireless communication system is multiple input multiple output (MIMO) system. It can transmit and receive data from different channels simultaneously without any need of additional frequency band. In this paper the design issues and challenges in MIMO antenna system for different applications have been reviewed. The major applications of MIMO systems include Wi-Fi, High Speed Packet Access, LTE, WiMAX (4G), and also MIMO has been used in power line communication. Implementation of MIMO antenna system is dependent on important parameters such as: Peak gain, Average Gain, Mutual Coupling, Envelop Correlation Coefficient (ECC), Total Active Reflection Coefficie nt (TARC), Signal polarization and Miniaturization of antenna system. Hence an optimal MIMO antenna design to suit for communication applications in an indoor environment is a challenging task. This paper proposes comparative study for the different MIMO antenna parameters. The different modeling techniques for MIMO antenna system are surveyed and areas for future research work in line with tradeoffs between different design parameters are suggested.

A complementary Sierpinski gasket fractal antenna array integrated with a complementary Archimedean defected ground structure for portable 4G/5G UWB MIMO communication devices

AbstractThis article presents the design, development, and experimental validation of an aperture coupled complementary Sierpinski gasket equilateral triangular fractal antenna array for portable 4G/5G UWB communication devices. The proposed antenna array is printed on two FR‐4 substrate layers (ε r = 4.4, height = 1.57 mm, and tan δ = 0.024) with two fractal triangular patches on the top layer (separated by a distance of 3λ/2) and feed network on the bottom layer of FR‐4. The fractal patches (optimized up to second order of iteration) are fed using an aperture‐coupled feeding mechanism, where the aperture slots in the ground layer are modified to complementary Archimedean spiral slots which are interconnected by a modified “X” shaped slot to improve the impedance matching at the operational bands. The proposed array has overall volumetric dimensions of 41 × 99.4 × 3.245 mm3 and provides a size reduction of 46% for the metallic area using the fractal geometry. The proposed array shows a simulated UWB response from 4.3 to 11.6 GHz (fractional bandwidth of 91.8% at 7.95 GHz) with a simulated peak gain of 4.7 dB (at 9.2 GHz) and port‐to‐port isolation of ≤−15.8 dB for the entire band. For validation of simulated responses, the proposed array is fabricated and tested for S‐parameters (S11, S22, S12, and S21). A measured impedance bandwidth of 6.3 GHz is observed for a frequency band from 5.7 to 12 GHz. Two additional frequency bands are also exhibited by the array from 4.1 to 4.25 GHz and 4.7 to 5.3 GHz. The array diversity parameters such as envelope correlation coefficient (≤0.007 [simulated], ≤0.0057 [measured]), diversity gain (≥9.999 [simulated], ≥9.971 [measured]), mean effective gain (≥−3.9 dB [simulated], ≥−5.1 dB [measured]), and channel capacity loss, (≤0.37 bits/s/Hz [simulated], ≤0.4 bits/s/Hz [measured]) which are calculated using the simulated and measured S‐parameters of the array are also observed. These parameters allow the proposed fractal array to be implemented in a diversity combining technique to improve the overall SNR and hence support a high data rate for 4G/5G multimedia services.

The soundscape of the Trevi fountain in Covid-19 silence

Abstract This paper is devoted to the analyses of sound-scape at fontana di Trevi in Rome (Italy) with the aim to compare its characteristics during the Italian lockdown due to the (Sars-COV2) Covid-19 sanitary emergency and its characteristics before and after such time. The lockdown has represented an exceptional environment due to the silence everywhere, never occurred in centuries, offering the opportunity to recognize the “signature” of the sound emitted by the famous Fontana di Trevi and recognize how it interacts with other features. The signature is important for preservation issues and cultural heritage. The soundscape was documented in a field survey by means of hand held microphones, which acquired simultaneously the acoustic wavefield all around the fountain. We find that the spectral content depends on the microphone location, revealing a very complex wavefield, showing strong amplitudes during the lockdown well below 1kHz and a frequency band extending up to 10kHz. In a time period far from the lockdown, we evidence an additional frequency band around 700-1kHz, which not simply adds to the previous spectrum, but acts as a synchronization mechanism. The important observation is that the Covid-19 silence let emerge sounds that had been there for centuries, and afforded us the possibility to document them in order to study objectively a “soundprint”. Moreover, we studied the spatialization characteristics of the soundfield.

Multiple access schemes for Cognitive Radio networks: A survey

Spectrum bands are the backbone of wireless networks. Every user is allocated a fraction of the spectrum from available fixed spectrum band. But, the fixed available spectrum band cannot accommodate the growing demands of wireless networks. To accommodate the growing demand of wireless networks, the different multiple access schemes and Cognitive Radio (CR) networks come to fulfill these demands. Multiple access schemes are nothing but the schemes that can multiplex the numbers of users then transmit over the medium, whereas CR networks allow using unutilized frequency bands of spectrum through dynamic or opportunistic way. Till now, OFDMA is well known and most successful multiplexing scheme among other schemes for advanced wireless networks. It can accommodate large number of users with higher data rates than others. Due to the popularity of smart devices having video and other applications, the data demand for additional frequency bands are continuously increasing. These further higher demands of spectrum by futuristic networks can be overcome by introducing Non-Orthogonal Multiple Access (NOMA) scheme. It has higher spectral efficiency than the other existing access schemes. NOMA works on the principle of superposition coding of signals at the transmitter and successive interference cancellation at the receiver. Hence, the spectrum demands due to the exponential growth in mobile data traffic can be solved by the use of optimal multiple access scheme for CR networks. Presently, there exists no detailed classification and comprehensive survey is available for multiple access schemes for CR networks. This paper provides comprehensive survey and a generic classification of the recent progress of the multiple access schemes for CR networks. The multiple access schemes are classified into various categories which provide an overview of the active research initiatives in the area of multiplexing. Finally, the paper discussed various challenges, research issues and some future aspects for research community.

Spectral information of EEG signals with respect to epilepsy classification

BackgroundThe spectral information of the EEG signal with respect to epilepsy is examined in this study.MethodIn order to assess the impact of the alternative definitions of the frequency sub-bands that are analysed, a number of spectral thresholds are defined and the respective frequency sub-band combinations are generated. For each of these frequency sub-band combination, the EEG signal is analysed and a vector of spectral characteristics is defined. Based on this feature vector, a classification schema is used to measure the appropriateness of the specific frequency sub-band combination, in terms of epileptic EEG classification accuracy.ResultsThe obtained results indicate that additional frequency band analysis is beneficial towards epilepsy detection.ConclusionsThis work includes the first systematic assessment of the impact of the frequency sub-bands to the epileptic EEG classification accuracy, and the obtained results revealed several frequency sub-band combinations that achieve high classification accuracy and have never been reported in the literature before.

OFDM-OAM Modulation for Future Wireless Communications

Orbital angular momentum (OAM) has attracted considerable attention as a novel solution for wireless communications because its orthogonal modes significantly increase the channel capacity without an additional frequency band. The joint multiplexing between OAM technologies and other modulation techniques has not been thoroughly investigated. In this paper, we first proposed the orthogonal frequency-division multiplexing-orbital angular momentum (OFDM-OAM) multiple-input-multiple-output (MIMO) system. The proposed OFDM-OAM MIMO based on the discrete Fourier transformation (DFT) operations achieves a very high sum-rate and spectrum efficiency (SE). However, the expensive hardware and software overheads for transmitting and receiving OAM waves lead to an unexpected cost for the OFDM-OAM MIMO scheme. A time-switched OFDM-OAM (TOO) MIMO is then proposed to reduce the computational complexity, and the procedure of OAM generations and recoveries has also explicitly been derived. The mathematical derivation shows that the proposed TOO MIMO system based on a simple switching sequence is suitable for small-scale and low-cost wireless broadband communications, and the simulation results demonstrate that the TOO MIMO scheme achieves a considerable SE and much less computational complexity than the OFDM-OAM MIMO scheme.