Showing papers in "Electronics Letters in 2019"

Programmable metasurface-based RF chain-free 8PSK wireless transmitter

Abstract: In this Letter, a wireless transmitter using the new architecture of programmable metasurface is presented. The proposed transmitter does not require any filter, nor wideband mixer or wideband power amplifier, thereby making it a promising hardware architecture for cost-effective wireless communications systems in the future. Using experimental results, the authors demonstrate that a programmable metasurface-based 8-phase shift-keying (8PSK) transmitter with 8 × 32 phase adjustable unit cells can achieve 6.144 Mbps data rate over the air at 4.25 GHz with a comparable bit error rate performance as the conventional approach without channel coding, but with less hardware complexity.

5 GHz laterally-excited bulk-wave resonators (XBARs) based on thin platelets of lithium niobate

Abstract: In a free-standing 400-nm-thick platelet of crystalline ZY-LiNbO 3 , narrow electrodes (500 nm) placed periodically with a pitch of a few microns can eXcite standing shear-wave bulk acoustic resonances (XBARs), by utilising lateral electric fields oriented parallel to the crystalline Y -axis and parallel to the plane of the platelet. The resonance frequency of ~4800 MHz is determined mainly by the platelet thickness and only weakly depends on the electrode width and the pitch. Simulations show quality-factors ( Q ) at resonance and anti-resonance higher than 1000. Measurements of the first fabricated devices show a resonance Q -factor ~300, strong piezoelectric coupling ~25%, (indicated by the large Resonance-antiResonance frequency spacing, ~11%) and an impedance at resonance of a few ohms. The static capacitance of the devices, corresponds to the imaginary part of the impedance ~100 Ω. This device opens the possibility for the development of low-loss, wide band, RF filters in the 3-6 GHz range for 4th and 5th generation (4G/5G) mobile phones. XBARs can be produced using standard optical photolithography and MEMS processes. The 3rd, 5th, 7th, and 9th harmonics were observed, up to 38 GHz, and are also promising for high frequency filter design.

5 GHz Band n79 wideband microacoustic filter using thin lithium niobate membrane

Abstract: Microacoustic resonators made on suspended continuous membranes of LiNbO 3 were recently shown to have very strong coupling and low losses at ≥5 GHz, suitable for high-performance filter design. Employing these simple resonator structures, the authors have designed, fabricated, and measured a 4.7 GHz bandpass ladder-type filter having 1 dB mid-band loss and 600 MHz bandwidth to address the 5G Band n79 requirements. The filter is fabricated on a monolithic substrate using standard i-line optical lithography and standard semiconductor processing methods for membrane release, starting with commercially available ion-sliced wafers having 400 nm thickness crystalline LiNbO 3 layers. The filter is well-matched to a 50 Ω network and does not require external matching elements. Through accurate resonator engineering using our finite element method software filter design environment, the passband is spurious-free, and the filter provides better-than 30 dB rejection to the adjacent WiFi frequencies. This filter demonstrates the performance and scalable technology required for high-volume manufacturing of microacoustic filters >3.5 GHz.

Isolation improvement of UWB MIMO antenna utilising molecule fractal structure

Abstract: A compact four-element UWB MIMO antenna is proposed and its characteristics are investigated. The proposed antenna has a hexagon molecule-shaped fractal structure as its radiating element. The antenna elements are placed orthogonally to each other in order to yield good isolation, without any additional decoupling structure. The band rejection in WLAN band is attained by etching a C-shaped slot on each radiating element. The antenna has a compact size of 40 × 40 × 1.6 mm 3 and exhibits stable omni-directional radiation pattern. In addition, it shows an acceptable impedance bandwidth ( S 11 <; -10 dB) in the range 2.4-10.6 GHz with an isolation better than -20 dB over the UWB range. The performance of the proposed antenna is calculated in terms of antenna characteristics and MIMO parameters. The isolation level in-between the elements is found to be reasonable for MIMO application. The simulated and measured results are in good accord which makes the antenna a suitable candidate for massive MIMO and high-density packaging applications.

Radar sensing for healthcare

Abstract: Although traditionally associated with defence and security domains, radar sensing has attracted significant interest in recent years in healthcare applications. These include the monitoring of vital signs such as respiration, heartbeat, and blood pressure, analysis of gait and mobility levels, classification of human activities to promptly detect critical events such as falls, as well as the evaluation of fitness and reactivity levels. The attractiveness of radar against alternative technologies such as wearable sensors or cameras lies in its contactless capabilities, whereby people do not need to wear, carry, or interact with any additional device, and plain images of people and private environments are not recorded. In this letter, we discuss some of the most recent achievements and outstanding research challenges related to radar applications in healthcare and present some results from our work at the University of Glasgow, including a dataset of radar signatures of human activities that are openly shared with the wider community.

Comparison of techniques for radiometric identification based on deep convolutional neural networks

Abstract: The authors investigate the application of deep convolutional neural networks (CNNs) to the problem of radiometric identification, i.e. the task of authenticating wireless devices on the basis of their radio frequency (RF) emissions, which contain features directly related to the physical properties of the wireless devices. They collected digitised RF from 12 wireless devices, and used various techniques to transform the time series derived from the RF to images. A deep CNN is then applied to the images. The authors' results show that the identification performance of the combination of deep CNN with an image representation significantly outperforms conventional methods based on dissimilarity on the original time series. Moreover, a specific comparison among RF-to-image techniques show that on their datasets the wavelet-based approach outperforms other approaches, also in the presence of white Gaussian noise.

Trimmed categorical cross-entropy for deep learning with label noise

Abstract: Deep learning methods are nowadays considered as state-of-the-art approach in many sophisticated problems, such as computer vision, speech understanding or natural language processing. However, their performance relies on the quality of large annotated datasets. If the data are not well-annotated and label noise occur, such data-driven models become less reliable. In this Letter, the authors present very simple way to make the training process robust to noisy labels. Without changing network architecture and learning algorithm, the authors apply modified error measure that improves network generalisation when trained with label noise. Preliminary results obtained for deep convolutional neural networks, trained with novel trimmed categorical cross-entropy loss function, revealed its improved robustness for several levels of label noise.

Secure and energy aware load balancing framework for cloud data centre networks

Abstract: In a cloud system, a malicious user initiates the side channel attacks to steal the private information of other users that share the computing resources through virtualisation. In this Letter, the authors propose a multi-objective load balancing framework to minimise the likelihood of these attacks by reducing the number of shared servers along with efficient use of computing resources and power. The proposed framework significantly improves the security by reducing the shared servers up to 55.83% and improves the resource and power usage up to 96.54 and 21.97%, respectively, over best fit, first fit and random heuristic schemes.

Convolutional neural network and multi-feature fusion for automatic modulation classification

Abstract: Automatic modulation classification (AMC) lies at the core of cognitive radio and spectrum sensing. In this Letter, the authors propose a novel convolutional neural network (CNN)-based AMC method with multi-feature fusion. First, the modulation signals are transformed into two image representations of cyclic spectra (CS) and constellation diagram (CD), respectively. Then, a two-branch CNN model is developed, a gradient decent strategy is adopted and a multi-feature fusion technique is exploited to integrate the features learned from CS and CD. The proposed method is computationally efficient, benefited from its simple neural network. Experimental results show that the proposed method can achieve identical or better results with much reduced learned parameters and training time, compared with the state-of-the-art deep learning-based methods.

Additive manufactured dielectric Gutman lens

Abstract: In this Letter, the design of a 3D printed fully dielectric Gutman lens is presented. The authors demonstrate the feasibility of using highly accessible and cheap additive manufacturing technology ...

Metamaterial-based wideband circularly polarised antenna with rotated V-shaped metasurface for small satellite applications

Abstract: This Letter explains the design and development of a wideband circularly polarised (CP) antenna based on composite metamaterial (MTM) structures which are applicable for use in small satellite applications. The presented antenna is based on a modified co-planar waveguide feeding technique. The proposed antenna unit cell offers compact size due to its MTM property with dimensions of 0.088λ 0 × 0.19λ 0 at 2.4 GHz. The CP radiation is obtained by placing two composite right/left-handed transmission line unit cells orthogonally and exciting two orthogonally-polarised modes simultaneously. A new 4 × 4 unit cell artificial magnetic conductor metasurface is designed with a compact size at the same operating frequency of MTM-based CP antenna as a ground plane for the proposed antenna, which is found to be increased bandwidth, improved gain, and wider axial ratio bandwidth without altering the antenna compactness. The final antenna obtains an overall dimension of 0.37λ 0 × 0.37λ 0 × 0.18λ 0 at 2.5 GHz. The measured result shows a wider impedance bandwidth of 860 MHz (33.07%), improved axial ratio bandwidth of 410 MHz (15.92%), and a good gain of 5.76 dBic is obtained which are adequate for the use in modern small satellite applications.

Oscillator without a combinatorial loop and its threat to FPGA in data centre

Abstract: Virtual field-programmable gate array (FPGA) is an emerging technology to put multiple users in the same FPGA fabric with logical isolation. Security researchers have studied new threats in virtual FPGA and proposed attacks on the logical isolation by exploiting analogue natures of FPGA. These attacks use an oscillator comprising a combinatorial loop to have access to the analogue domain using digital components only. Interestingly, the system in the field prohibits a combinatorial loop by a design rule check. In this Letter, the authors study if prohibiting a combinatorial loop is sufficient to thwart the conventional attacks. They negatively answer the question by showing oscillators without a combinatorial loop. They also show how to detect and reject the proposed oscillators by a design rule check.

Secrecy outage analysis of double shadowed Rician channels

Abstract: The double shadowed Rician model was recently proposed to describe some realistic physical signal propagation phenomena, where a Rician faded signal is impacted by cascaded shadowing processes. In this Letter, the authors study the outage performance of the double shadowed Rician model. More specifically, they investigate the impact of two different shadowing processes on the secrecy performance by deriving novel and exact expressions for secrecy outage performance metrics. The obtained results reveal the following physical implications: (i) when a Rician faded signal undergoes line-of-sight shadowing, which is further cascaded by another round of composite shadowing, the latter form of shadowing imposes larger impact on the secrecy performance; (ii) the widely investigated concept of ‘protected zone’ to improve the secrecy performance should not be limited to the legitimate transmitter but also extended to the legitimate receiver due to the adverse shadowing effect caused by objects in its vicinity; and (iii) the rate of outage performance degradation grows larger as the shadowings become severe.

Metamaterial-inspired dual-band frequency-reconfigurable antenna with pattern diversity

Abstract: Multi-functional antennas are very important in modern wireless communication systems A novel dual-band frequency-reconfigurable antenna with pattern diversity is designed The antenna consists of a composite right/left-handed transmission line inspired structure, which works at the zeroth-order mode (0) around 25 GHz and at the first-order mode (1) around 35 GHz The 0 mode results in an omni-directional pattern and the 1 mode results in a broadside pattern By adding varactors to continuously reconfigure the structure, the antenna is able to tune its lower resonant frequency from 236 to 260 GHz, which fully covers the 24-25 GHz ISM band, and tune its higher resonant frequency from 334 to 373 GHz, which fully covers the 34-37 GHz WiMAX band Simulations and experiments match well, proving the validity of this new concept

FER-Net: facial expression recognition using densely connected convolutional network

Abstract: Convolutional neural network (CNN) architectures have shown excellent image classification performance on large-scale visual recognition tasks. If a CNN architecture contains a shorter connection between layers close to the input and those close to the output, the training can be deeper, more accurate and efficient. In this Lette, the authors propose a densely connected CNN architecture for facial expression recognition (FER-Net), which connects the output of each convolution layer to the inputs of the next convolution layers in the architecture. Experiments conducted on a publicly available dataset show that FER-Net produces state-of-the-art results in facial expression recognition.

Tropical cyclone intensity prediction based on recurrent neural networks

Abstract: The accurate prediction for the tropical cyclone (TC) intensity is a recognised challenge. Researchers usually develop dynamical models to address this task. However, since the TC intensity is highly influenced by various factors such as ocean and atmosphere conditions, it is difficult to build the very model which can explicitly describe the mechanism of TC. A new idea is developed, utilising the massive historical observation data by a deep learning approach, to conduct a completely data-driven TC intensity prediction model. All the TC intensity and track data which have been observed in Western North Pacific since 1949 are collected, and recurrent neural network for TC intensity prediction is constructed. In general, their motivation as well as novelty is to develop a data-driven approach instead of empirical models. There are very few researches similar to their exploratory work. The proposed method has presented 5.1 m ⋅ s − 1 error in 24 h prediction, which is better than some widely used dynamical models and is close to subjective prediction.

Mitigation of target distortion in pulse-agile sensors via Richardson–Lucy deconvolution

Abstract: Pulse-agile radar systems are becoming more prevalent as the demand for adaptive and cognitive systems increases. This focus is motivated by the need for interference avoidance and spectrum sharing. Pulse agility within a coherent processing interval (CPI) or intra-CPI adaption has been shown to cause distortion, which will negatively impact the radar's performance. This problem can be framed in the context of image processing such that an ideal range-Doppler image is corrupted by some point spread function. Deconvolution is then applied to remove this distortion and improve radar performance while maintaining the ability to use computationally efficient fast Fourier transform-based processing.

New construction of optimal aperiodic Z-complementary sequence sets of odd-lengths

Abstract: In this Letter, a new construction of aperiodic Z-complementary sequence sets (ZCSSs) is proposed. The constituent sequences of ZCSSs have odd-length of the form (where , and are non-negative integers). The resultant ZCSSs are optimal with respect to the Welch bound.

Direct torque and flux control of switched reluctance motor with enhanced torque per ampere ratio and torque ripple reduction

Abstract: A smooth torque control of switched reluctance motor (SRM) is essential to avoid speed fluctuations causing stability problems in vehicular applications. This can be accomplished by an appropriate motor design and/or use of direct control of torque in SRM. It is reported that high RMS current is required to minimise the torque ripple in the conventional direct torque and flux control (DTFC), thereby reducing the torque per ampere ratio. To overcome this issue, a new DTFC technique with improved torque per ampere ratio while minimising torque ripple in an SRM traction drive is presented. Results demonstrated that the proposed DTFC technique reduces torque ripple with enhanced torque per ampere. Finally, the performance of the proposed scheme is compared with conventional DTFC of a four-phase (8/6) SRM to show the improvement in the traction drive.

Wideband circularly‐polarised high‐gain diversity antenna loaded with metasurface reflector for small satellite applications

Abstract: This Letter demonstrates the design of a two-element polarisation diversity antenna, applicable for modern small satellite application systems. The intended antenna mainly consists of two monopole radiators loaded with metasurface reflector as a ground plane. The dimensions of the radiator antenna are 40 × 22 × 1.6 mm 3 . The antenna measured results offers a wider S 11 bandwidth of (2.23-2.91 GHz) and wider axial ratio bandwidth (ARBW) of (2.16-2.92 GHz) with a common S 11 and ARBW of 26.45% is obtained. A maximum gain of 7.02 dBic and isolation better than 14.5 dB is observed along with the operating frequency range. The antenna provides an ARBW( 2.38 dBic) for theta = ± 45°, for all phi values along with the complete operating frequency range. Also, the antenna port-1 provides left-handed circular polarisation and port-2 provides right-handed circular polarisation radiation with directional radiation characteristics.

Fast approach for efficient vehicle counting

Abstract: Systems for counting vehicles should be fast enough to be implemented in real-time situations. Most of the related work uses two stages for vehicle counting, vehicle detection and tracking, which increase the computational complexity. In this Letter, a fast and efficient approach for vehicle counting is proposed, where there is no need for the vehicle tracking step. A background model is created only for a narrow region, a line, in the video frames. The moving vehicles are detected as foreground objects while passing this narrow region. Morphological processes are applied to the extracted objects to enhance them and decrease the effects of vehicle occlusions. Finally, an efficient counting vehicles method is introduced employing only the extracted detection information. The experimental results performed on diverse videos show that the proposed method is fast and accurate. The average execution time per frame is 7.78 ms.

Enhanced circuit for linear ring VCO-ADCs

Abstract: Recently an extremely linear voltage-controlled ring-oscillator for use in VCO-ADCs was proposed by Babaie-Fishani and Rombouts. In this current Letter, a circuit-level technique to improve the bandwidth and noise performance of such a linear VCO is proposed. The key element is the modified delay cell, where the traditional cross-coupled inverters are modified into ` feed-forward' coupling inverters that pre-charge the subsequent elements in the ring. The resulting circuit maintains the excellent linearity, but has greatly enhanced bandwidth (up to 3 times higher) and considerably reduced power for the same circuit noise level (up to 2.5 times lower).

Vertical-cavity surface-emitting laser with integrated surface grating for high birefringence splitting

Abstract: Increasing the birefringence splitting in single-mode vertical-cavity surface-emitting lasers (VCSELs) enables high-speed polarisation dynamics which can be the basis to overcome the current bandwidth limitations in short-haul data transmission. The authors observe large birefringence splittings of up to 98 GHz in an oxide-confined AlGaAs-based VCSEL with a tailored integrated surface grating. Since surface gratings are routinely used in VCSEL production, there is a great potential of this technique to realise spin-VCSELs for ultrafast optical communication.

Few-shot palmprint recognition via graph neural networks

Abstract: At present, palmprint recognition based on deep learning has been more and more widely used in identity recognition due to its many advantages. However, these algorithms often require a large amount of labelled data for training. In fact, it is difficult and expensive to get enough data that meets the requirements. In this Letter, based on a small amount of labelled images, the authors proposed a method for few-shot palmprint recognition using Graph Neural Networks (GNNs). The palmprint features extracted by the convolutional neural network are processed into nodes in the GNN. The edges in the GNN are used to represent similarities between image nodes. The parameters in the network are continuously optimised, and finally, the category to which each image belongs is obtained. Further, they adopted a mobile phone to create a palmprint database in an unconstrained way. Adequate experiments were performed on the benchmark database and the authors' self-built database. The experimental results show that their proposed GNN-based few-shot palmprint recognition can obtain state-of-the-art performance, where the accuracy is over 99.90%.

Flexible metamaterial absorber with wide incident angle insensitivity for conformal applications

Abstract: This Letter demonstrates design, simulation, fabrication and performance of a metamaterial (MTM) absorber having wide incident angle insensitivity for conformal applications in X-band region. The important feature of the proposed structure is achieving more than 90% absorptivity with very low thickness. In this design, an FR4 material having thickness 0.1 mm is used as a substrate. Hence, the overall thickness of the proposed MTM absorber is only 1/81 of the wavelength at the resonance frequency of 9.2 GHz. Also, the presented absorber is offering more than 80% absorptivity up to 50° incident angle which is very much suitable for conformal applications where curved surfaces are involved. Designed MTM absorber has been fabricated and simulation results are experimentally verified.

Grid-tied single source quasi-Z-source cascaded multilevel inverter for PV applications

Abstract: A new cascaded multilevel topology is proposed in this study. It is denominated single DC source quasi-Z-source cascaded multilevel inverter (SS qZS-CMI). The SS qZS-CMI performs at maximum power point tracking of the photovoltaic (PV) array with a single inverter module and each of the inverter modules shares an equal amount of the power of the whole system. The SS qZS-CMI has the capacity to equally regulate the peak voltage on each inverter module by means of the dual control loop of the main inverter module and the shoot-trough state of the auxiliary inverter modules, ensuring the symmetry of the cascaded multilevel inverter. Experimental results verify the proposed topology.

Service-dependent task offloading for multiuser mobile edge computing system

Abstract: Mobile edge computing (MEC) has been deemed as one of the key technologies for pushing powerful computing ability to the radio access network. Different scenarios require different services, and tasks usually require computing in a specific runtime environment. However, few studies have taken this into consideration. To this end, the authors propose a novel model of service-dependent task offloading for the multiuser MEC system with resource constraints. Through determining which services should be deployed at the network edge and how many tasks should be offloaded, a revenue maximisation problem is constructed. Accordingly, they propose an iterative optimisation algorithm with high performance for the service deploying and task offloading problem. Finally, numerical simulations reveal that their proposed algorithm outperforms other schemes.

Q-RTS: a real-time swarm intelligence based on multi-agent Q-learning

Abstract: The authors introduce a novel approach for swarm reinforcement learning that extends the standard Q-learning to multi-agent systems. State-of-the-art methods implement a knowledge sharing mechanism between the agents that is triggered by the episodes succession. This causes an intrinsic limit in the convergence speed of the algorithms. They overcame this issue by developing a Q-learning real-time swarm algorithm (Q-RTS), which is iteration-based and suitable for real-time systems. Q-RTS was tested in different environments and compared to other related methods in the literature. They obtained positive results in terms of learning time and scalability, i.e. achieving a speed-up factor of at least 1.49 with respect to standard Q-learning. Moreover, Q-RTS shows enhanced learning performance as the environments complexity increases.

Improved sufficient condition of ℓ1–2-minimisation for robust signal recovery

Abstract: By means of the restricted isometry property of order k and the restricted orthogonality property of order (k,k), this Letter mainly establishes an improved sufficient condition for a recently emerged l 1 − 2 -minimisation to guarantee the robust signal recovery. The obtained condition is proved to be much better than the state-of-the-art ones for almost all parameters k.