Cognitive Radio Applications Research Articles

An electronically switchable UWB to narrow band antenna for cognitive radio applications

AbstractCognitive radio (CR) is designed to achieve intelligent spectrum sensing and sharing, in order to solve spectrum underutilization problem. Conventional CR uses multiple/multiport antenna to switch between UWB and narrow band (NB) frequencies for primary and secondary users. In this article, we propose a compact frequency reconfigurable single port antenna using PIN diodes, to switch between UWB and NB frequencies. A circular disc monopole antenna with partial ground plane is designed to deliver UWB response. Three interdigital capacitors (IDC) are electrically connected to a partial ground plane and feed line using PIN diodes. OFF condition of all PIN diodes will provide the UWB response of 2.8 to 10.6 GHz and ON condition of the diodes will result in 36 different NB frequencies, completely covering the UWB spectrum. A simulation study carried out by incorporating a varactor diode into IDC, clearly shows that, the antenna resonance can be switched using PIN diodes and each resonant frequency can be fine‐tuned independently, with in the band of interest. This is the unique feature of proposed antenna, which facilitates the technology for CR based internet of things applications in 5G wireless communication networks.

Application aware networks' resource selection decision making technique using group mobility in vehicular cognitive radio networks

Nowadays detonation of holding vehicle has wrought overcrowded traffic. The US Federal Communication Commission officially allocated nearly 75 MHz spectrum in 5.8 GHz band to support vehicular communication and many studies found this band incapable to handle the demand for future data traffic. The application of Cognitive Radio (CR) technology will be utilized to make the Internet of Vehicles (IoV) environment in order to increase the spectrum resource opportunities available for vehicular communication. In the CR networks environment, each network supporting multiple attributes likes mobility, Quality of Service, data rates and bandwidth. Therefore, new challenges including link failures, network volatility, group mobility and decision making for the fair selection of optimal networks' resource in vehicular CR networks have become the focus of the global concern. Contrarily, future applications require the vehicular CR networks to support safety and non-safety applications and services. The contribution of this article is two folds. First, the group mobility feature of vehicular communication is considered in this work and two techniques (GRA based Vehicular CR node Assisted Networks' resource Selection (VANS) and Network Assisted Networks' resource Selection (NANS)) for vehicular CR networks are proposed. Second, a testbed using coded scripting programme and LabVIEW communications system design suite software to universal software radio peripheral (USRP-2954) is considered to analyze the practical realization issues in vehicular CR networks. Furthermore, the performance of the proposed techniques is analyzed and validated through experimental testbed and compared with the conventional decision-making techniques. Results show that the proposed techniques have outperformed traditional techniques.

CSRR‐loaded UWB monopole antenna with electronically tunable triple band‐notch characteristics for cognitive radio applications

AbstractThis article introduces a compact configuration of printed monopole antenna with electronically tunable band‐notched function for ultra‐wideband (UWB) applications. A partially grounded rectangular shaped monopole is designed initially to achieve UWB behavior. The notch characteristics are then introduced by employing three complementary split‐ring resonators (CSRRs) on the radiating surface. The proposed antenna exhibits an ultra‐wide operating band ranging from 1.98 to 10.54 GHz with the notched frequencies at 2.37, 3.03, and 4.18 GHz, respectively. In order to accomplish versatility in the antenna operation, the notched frequencies are controlled electronically by implementing three varactor diodes in between the split‐ring slots. By applying an appropriate reverse bias voltage, the triple notched bands are tuned over the frequency bands: 1.58‐2.12 GHz, 2.24‐2.68 GHz, and 3.08‐3.78 GHz, respectively. A prototype with an overall dimension of 34.9 × 31.3 × 1.6 mm3 has been fabricated to experimentally determine the tuning capability of the antenna structure. The experimental result establishes close correspondence with the simulated antenna properties. The suggested antenna can be implemented practically to reject interferences from complete 1.5‐2.1 GHz LTE systems, and 2.5/3.5 GHz‐WiMAX bands, simultaneously. The capability of tuning three notched‐bands together is distinctive and has not been reported in the published literature to the best of authors' knowledge.

Microstrip Patch Antenna with PIN Diode as Frequency Selector for Cognitive Radio Applications

An effective design of a Microstrip Patch Antenna (MPA) for cognitive radio applications was designed in this paper. Cognitive radio (CR) is the technology for spectrum access. The proposed antenna design consists of a rectangular patch and a partial ground plane. The proposed antenna has the dimension of 28 mm×29 mm. The patch of size 10 mm×13 mm is placed on Flame Retardant 4 material with 1.6 mm thickness and dielectric constant of 4.4. Proposed antenna has four cases of radiation, where PIN diodes are present to ON-OFF the stubs. MA4SPS402 pin diode is used as the switch. Antenna is simulated in HFSS software.

Compact tri-band T-shaped frequency reconfigurable antenna for cognitive radio applications

This paper presents, new compact tri-band and broadband frequency reconfigurable antenna for cognitive radio applications. The proposed antenna consists of an Ultrawideband sensing antenna and reconfigurable communicating antenna at the same substrate. The sensing antenna is a UWB printed elliptical monopole antenna operates at frequency band from 2.72 to 23.8 GHz which can cover the entire UWB frequency band from 3.1 to 10.6 GHz and cover the broadband up to 20 GHz. The communicating antenna is a T-shaped frequency reconfigurable antenna operates on three bands of 7.925 GHz, 13.16 GHz, and 14.48 GHz under (S11≤-10 dB) with a fractional bandwidth of 14.55%, 6.2%, and 3.3% respectively. The proposed antenna used to operate in two modes one for cognitive radio applications to cover WiMAX, land, Fixed and Mobile satellite, Radar, and broadband applications. The frequency reconfigurability is obtained by using only one RF switch (PIN diode) for changing the operating frequency. The antenna overall dimensions are 42x30x1.6 mm3 printed on an FR-4 epoxy substrate with relative dielectric constant εr=4.3, loss tangent tan (δ)=0.002 and 50Ω microstrip line feed. The maximum obtained simulated gain is 8.5 dB at 13.16 GHz. The S11 is under -20 dB and coupling between the two antennas is less than -15 dB at the resonant frequencies.

Adaptive time-frequency multiplexing for 5G applications

In this paper, we provide an optimization framework for channel-adaptive pulse and lattice scaling in a general Time-Frequency (T-F) multiplexing scheme. Closed form relations for the optimum pulse and lattice scaling are derived analytically considering the requirements of two important 5G applications, i.e. tactile internet and cognitive radio. For tactile internet, we solve the problem with a constraint on the time dispersion of the pulse shaping filter at the receiver in order to decrease the length of Cyclic Prefix (CP) and consequently improve the spectral efficiency. Then, aiming for limiting the Out-Of-Band (OOB) leakage in cognitive radio applications, we find a solution to the optimization problem with a constraint on frequency dispersion of pulse shaping filter at the transmitter. Finally, we consider both of these constraints and solve the problem analytically. The results show that using optimum pulse and lattice scaling, improves the Signal to Interference Ratio (SIR) significantly, compared to non-optimal pulses and lattices. Furthermore, it is shown that applying the constraint to either Receive (Rx-) filter time dispersion or Transmitter (Tx-) filter frequency dispersion does not degrade the SIR significantly while limiting both of them leads to a mismatch between pulse shaping filters and degrades the SIR considerably.

Diode Based Reconfigurable Microwave Filters for Cognitive Radio Applications: A Review

The cognitive radio paradigm for developing next-century wireless communication systems is rapidly entering the mainstream, and various aspects of it are currently being applied in 5G technology, aeronautical engineering, military communications, emergency, and public safety applications, satellite communication, and healthcare. Cognitive radio focuses on the existence of software defined radio architectures that allow dynamic reconfiguration. Many researchers have taken initiatives in the last decade to achieve the reconfiguration ability in cognitive radio systems to support the concept of dynamic spectrum access. As cognitive radio adapts dynamic spectrum allocation for its users, the physical implementation requires reconfigurable filters that can alter the carrier frequencies and bandwidth. Although there are many ways to reconfigure filter operation, diode based reconfiguration has received utmost attention among researchers because of its shorter response delay and easy implementation. In the last decade, researchers have reported several diode-based reconfigurable filters, including their characteristics such as filter function, filter combination, tuning range, variation in bandwidth, isolation, and resonance. However, to examine the potential of these filters in the application of cognitive radio, a comprehensive review needs to be pursued. In this review article, the descriptions of several diode based reconfigurable filters are illustrated with their exhibiting characteristics. The detailed information provided in this article has disclosed that primarily three different types diode based reconfigurable filters have been reported by researchers: Tunable, Switchable, and Hybrid (Both Tunable and Switchable). It is also found that each type of reconfiguration can further be segregated in terms of filter function, centre frequency variation, and bandwidth variation. The detailed categorization of the reconfiguration presented in this paper provides a systematic approach to select the correct reconfigurable filter for the desired frequency reconfiguration in cognitive radio.

Multi-Player Bandits: The Adversarial Case

We consider a setting where multiple players sequentially choose among a common set of actions (arms). Motivated by a cognitive radio networks application, we assume that players incur a loss upon colliding, and that communication between players is not possible. Existing approaches assume that the system is stationary. Yet this assumption is often violated in practice, e.g., due to signal strength fluctuations. In this work, we design the first Multi-player Bandit algorithm that provably works in arbitrarily changing environments, where the losses of the arms may even be chosen by an adversary. This resolves an open problem posed by Rosenski, Shamir, and Szlak (2016).

Compact reconfigurable triple notch ultra-wideband bandpass filter for cognitive radio system

This paper introduces a compact ultra-wideband (UWB) bandpass filter (BPF) with two switchable external notch structures which avoids the interference between the UWB communication with worldwide interoperability for microwave access (WiMAX) and wireless local area network (WLAN) systems, suitable for cognitive radio (CR) applications. The first external notch structure is modified C-shaped structure which generates a sharp rejection at 3.5 GHz to avoid interference with WiMAX system and second external notch structure is back to back T-shaped structure which creates sharp rejection notch bands at 5.2 GHz and 5.8 GHz frequencies for WLAN systems. The filter reconfiguration is achieved by varying the conductance of microstrip line. The response of the proposed structure shows sharp rejections at one WiMAX and two WLAN bands. The bandpass filter covers frequency of UWB system from 3.1 to 10.7 GHz having very low passband insertion loss. The proposed UWB BPF is designed, simulated, fabricated and tested to validate the results. A good agreement is achieved between simulation and experimental results.

Compact reconfigurable triple notch ultra-wideband bandpass filter for cognitive radio system

This paper introduces a compact ultra-wideband (UWB) bandpass filter (BPF) with two switchable external notch structures which avoids the interference between the UWB communication with worldwide interoperability for microwave access (WiMAX) and wireless local area network (WLAN) systems, suitable for cognitive radio (CR) applications. The first external notch structure is modified C-shaped structure which generates a sharp rejection at 3.5 GHz to avoid interference with WiMAX system and second external notch structure is back to back T-shaped structure which creates sharp rejection notch bands at 5.2 GHz and 5.8 GHz frequencies for WLAN systems. The filter reconfiguration is achieved by varying the conductance of microstrip line. The response of the proposed structure shows sharp rejections at one WiMAX and two WLAN bands. The bandpass filter covers frequency of UWB system from 3.1 to 10.7 GHz having very low passband insertion loss. The proposed UWB BPF is designed, simulated, fabricated and tested to validate the results. A good agreement is achieved between simulation and experimental results.

Omega Shaped Complementary Split Ring Resonator Loaded Bandwidth Reconfigurable Antenna for Cognitive Radio Applications

Abstract This paper presents a bandwidth reconfigurable, circular monopole antenna loaded with omega shaped complementary split ring resonator (omega-CSRR). The CSRR is designed to produce band stop response at desired frequency, in order to control bandwidth. Two slots are connected to the CSRR using PIN diodes to form the arms of omega-CSRR. Switching the diodes, ON/OFF will vary the length of arms of omega. This will vary the stop band, resulting in tuning of impedance bandwidth. Two additional slots loaded on the ground plane, controls the lower and upper band limits. Ultra wide band (UWB) response (2.6GHz – 12GHz) and narrow band response are obtained. The bandwidth of narrow band is varied from 1.5GHz to 4.85GHz, by maintaining the center frequency at 6GHz. The impedance bandwidth percentage ranges from 26% to 82.2%, exhibiting an increase by a factor of 3.16.

Identification of Communication Signals Using Learning Approaches for Cognitive Radio Applications

Signal detection, identification, and characterization are among the major challenges in aerial communication systems. The ability to detect and recognize signals using cognitive technologies is still under active development when addressing uncertainties regarding signal parameters, such as blank spaces available within the transmitted signal and the utilized bandwidth. This paper proposes a learning-based identification framework for heterogeneous signals with orthogonal frequency division multiplexing (OFDM) modulation as generated in a simulated environment at an a priori unknown frequency. The implemented region-based signal identification method utilizes cyclostationary features for robust signal detection. Signal characterization is performed using a purposely-built, lightweight, region-based convolutional neural network (R-CNN). It is shown that the proposed framework is robust in the presence of additive white Gaussian noise (AWGN) and, despite its simplicity, shows better performance compared with conventional popular network architectures, such as GoogLeNet, AlexNet, and VGG 16. The signal characterization performance is validated under two degraded environments that are unknown to the system: Doppler shifted and small-scale fading. High performance is demonstrated under both degraded conditions over a wide range of signal to noise ratios (SNRs) and it is shown that the detection probability for the proposed approach is improved over those for conventional energy detectors. It is found that the signal characterization performance deteriorates under extreme conditions, such as lower SNRs and higher Doppler shifts.

A frequency reconfigurable MIMO antenna with agile feedline for cognitive radio applications

A novel frequency agile multiple-input-multiple-output (MIMO) patch antenna based on a reconfigurable feedline is proposed. The proposed antenna structure has two hexagonal-shaped patch antenna elements. A defected ground structure having hexagonal shape is included in the ground plane to make the design compact and improve isolation among antenna elements. Further compactness is achieved using reactive loading. Frequency reconfigurability is realized by employing varactor diodes in the microstrip feedline. The proposed antenna achieves a frequency reconfigurable band with wide tuning range from 1.42 to 2.27 GHz with good gain and efficiency. Furthermore, an envelope correlation coefficient value of less than 0.2 and minimum isolation of 12 dB was achieved, displaying good MIMO performance. The presented antenna has a planar, low profile design with compact size of 100 × 50 mm2. Thus, frequency agility, wide range tuning, compactness, and planar structure of the proposed antenna design make it suitable for modern wireless handheld devices particularly in cognitive radio applications.

Frequency reconfigurable slot antenna using metasurface for cognitive radio applications

A dual-port antenna system designed for cognitive radio applications is presented in this study. The structure comprises of an ultra-wideband (UWB) sensing antenna and a reconfigurable communicating antenna. The former is a stepped slot structure with an offset feed, which covers the whole UWB frequency band from 3 to 10.6 GHz, whereas the latter is a dual-band slot antenna (DBSA) fed with a fork-shaped microstrip-line feed and loaded with two identical layers of meandered metasurfaces (MSs). Frequency agility is realised by rotating the MS layers for the DBSA antenna. The dual-band communicating antenna has three switchable states with tuning ranges of 28 and 45% in the lower- and upper-frequency bands, respectively. The degree of isolation and gain in all three states are appreciable. The proposed structure is fabricated and measured, which has a good agreement with the simulated results.

An 550-650 MHz Digitally-Tunable Bandpass Filter: Design and Implementation

In this paper, a digitally-tunable band-pass filter is designed and implemented for applications of Cognitive Radio in middle Ultra high frequency television band from 550 to 650 MHz. This design is based on the 3th-order Chebyshev filter model in the combination with impedance inverters and series LC resonators, where capacitors are replaced by varactor diodes. The central frequency is tuned by means of a digital control board to adjust DC bias voltages of the diodes. Theoretical analysis, numerical simulation, and hardware implementation are described and carried out. The RF board is fabricated using SMV1736 varactor diodes with FR4-0.8mm material. The results show good match between simulations and measurements in terms of return loss, insertion loss, and fractional bandwidth over the operating range.

Rectangular Loop UHF Antenna for utilization of TVWS for Cognitive Radio Application

To utilize the TV white space 470MHz to 806MHz, several wideband antennas are designed in ultra-high frequency (UHF) band. This paper presents the monopole antenna with resonant structures arranged in rectangular loop shape. The overall dimension of the antenna is 160mm x 100mm x 1.6mm. The performance of the antenna in the operating frequency band 596MHz to 733MHz is evaluated using HFSS software. The overall peak gain of the antenna is 1.653dB. In both elevation and azimuth plane, radiation pattern is omnidirectional and the radiation efficiency is 81.79%

Cross‐layer perspective for channel assignment in cognitive radio networks: A survey

SummaryWith the advent of various emerging wireless products, the usage of limited spectrum has grown exponentially in the recent years. In the next few years, that mobile data traffic globally is expected to grow up to 50 EB/month, which is nearly a five times increase over year 2018. Therefore, it will become extremely difficult to satisfy the ever increasing demand through the current fixed spectrum assignment policy in which spectrum band is exclusively used for the particular applications, and it has also led to underutilization of a significant portion of the spectrum (like TV bands). Cognitive radio networks has emerged as a possible solution for the problem which makes dynamic spectrum access possible for unlicensed user when licensed user is not active. Among various operations of cognitive radio, channel assignment to the unlicensed user is very important. Further, wireless regional area network is one of the most important application of cognitive radio, which provides wireless broadband to the rural area using vacant TV channels. This paper discusses channel assignment techniques considering various functionalities for cognitive radio networks in respect of wireless regional area network in the existing literature. Initially, a comprehensive introduction to both cognitive radio networks and wireless regional area networks is provided, and in the end, the paper summarizes the various issues and research challenges in the channel assignment for wireless regional area networks.

Theoretical Analysis of Noise Figure for Modulated Wideband Converter

The Modulated Wideband Converter (MWC) is one of the promising sub-Nyquist sampling architectures for sparse wideband signal sensing, cognitive radio applications and so on. In order to design an MWC-based RF receiver that meets a target RF specification, noise figure (NF) of the MWC has to be well-defined by its design properties. In this paper, we investigate a comprehensive explanation for NF of MWC by an analytic approach based on a proposed notation of an average noise figure (ANF) of the MWC. Consequently, the analysis is proven with simulation results in order to demonstrate its feasibility.

Compressive Joint Angular and Frequency Spectrum Sensing Based on MUSIC Spectrum Reconstruction

This paper aims to introduce a new tool for wideband spectrum sensing in cognitive radio applications based on the multiple signal classification (MUSIC) two-dimensional (2D)-pseudospectrum, which is able to locate the active sources [licenced users (LUs)] or other secondary users in both the angular and frequency domains. The proposed tool consists of two-stages compression and reconstruction procedures. The spatial-domain compression is introduced by activating only some of the antennas in the underlying uniform linear array (ULA) leading to a non-ULA of active antennas. The time-domain compression is introduced by allowing the receivers connected to every active antenna to sample the analog signals below the Nyquist rate. This compression aims to alleviate the burden on the analog-to-digital converter especially when a broad frequency band has to be sensed. The simulation study shows that the constructed MUSIC 2D-pseudospectrum can be used to locate the direction-of-arrival (DoA) and the frequency band of the LUs with a much better resolution than the one that can be afforded by the already proposed 2D power spectrum. Note that the number of sources is beyond that of active antennas and the sampling rate in each receiver is only 17 / 42 times the Nyquist rate. Moreover, the evaluation on the root mean square error in terms of DoA estimation indicates that the proposed MUSIC 2D-pseudospectrum construction approach outperforms the already proposed 2D power spectrum reconstruction method. In fact, the performance of the proposed approach based on the sub-Nyquist-rate samples is only slightly below the approach that is based on the pseudospectrum constructed from Nyquist-rate samples. Furthermore, the evaluation on the detection performance of the spectrum sensing tool based on the MUSIC 2D-pseudospectrum underlines the promising benefits of the proposed approach.

A Planar Integrated UWB/Reconfigurable Antenna with Continuous and Wide Frequency Tuning Range for Interweave Cognitive Radio Applications

This paper presents a planar ultra-wide band (UWB) sensing antenna accompanied with a monopole narrow band communicating antenna for interweave cognitive radio (CR) applications. The UWB antenna bandwidth covers the entire band specified for UWB applications (3.1–10.6 GHz). In addition to the varactor diode, a PIN diode is attached to the communicating antenna to expand the continuous frequency tuning of the varactor diode up to 3 GHz along the frequency range (3.3–6.3 GHz) including WiMAX, personal area network, and the 5 GHz wireless local area network. The UWB sensing antenna shape and the ground plane size of the communicating antenna are modified to reduce the mutual coupling between the two antennas to values less than − 15 dB. The measurements are well agreed with the simulation, and they verify the antenna suitability for CR systems. Moreover, the results show an omnidirectional power pattern for both sensing and communicating antennas which is compatible to the portable CR devices.