A robust audio watermarking method based on the time-spread (TS) echo hiding scheme is proposed. Compared with existing TS watermarking methods, the approach is more robust as it exploits the characteristics of host signals in the encoding stage. Theoretical analysis and simulation examples demonstrate the effectiveness and advantages of the method.

For the interferences suppression of a large-scale antenna array after a subarray configuration (SC), a generalised sidelobe canceller (GSC) weighting approximation at irregular subarrays algorithm is presented. First, the SC is obtained by particle swarm optimisation. Then, digital weights of the second-class subarrays and also the analogue weights of the elements and first-class subarrays are optimised in two steps by convex optimisation to approximate GSC weights to the maximum extent, which are directly applied at the element level of the whole array. Simulation results are presented that prove that the proposed algorithm achieves better performance of anti-jamming than direct GSC weighting at subarrays.

A compact monopole antenna with enhanced bandwidth and triple band rejections for ultra-wideband applications is presented. The base of the proposed antenna is a semicircular patch which is fed by a modified tapered coplanar waveguide line. By using the trident-shaped feed line, much wider impedance bandwidth is obtained. To avoid potential interferences, two trapezoid stubs and a C-shaped stub are printed on the back surface of the substrate and are connected to the antenna through three vias. The proposed antenna is practically fabricated with a compact size of 20 × 24 mm². Good agreement is achieved between the simulation and measurement, which shows that the proposed antenna offers a very wide bandwidth from 3.02 to 20.8 GHz (149%) with triple band rejections covering the 3.5 GHz WiMAX and 5.2/5.8 GHz WLAN bands.

A novel method to design a compact, broadband circularly polarised square slot antenna (CPSSA) with a considerably wide axial ratio (AR) bandwidth is proposed. A coplanar waveguide fed square slot antenna with an impedance matching stub and a cross-shape radiating patch together with a strip line that connects the two opposite corners of the ground section is designed to provide the desired characteristics. The obtained results for the proposed antenna provide good agreement with the expected performance with a compact size of 20 × 20 mm. The measured impedance bandwidth is as large as 11 050 MHz (2950–14 000 MHz) or about 130.38% with respect to the centre frequency. The measured 3 dB AR is 3373 MHz (35.7%) from 3729 to 7102 MHz and the average measured gain of the CPSSA is almost 3.5 dBi in the operating band.

Microwave holographic techniques have been used widely in the radio astronomy area. A new surface diagnosis method based on the phase-retrieval holograph algorithm is proposed. This approach focuses on a novel application of the active deformation. Multiple far-field patterns are measured in focus by adjusting the deformation of the main reflector actively. Using the amplitude of far-field patterns, the phase distribution of the aperture can be retrieved by the phase-retrieval technique. Simulation results demonstrate the feasibility of this method.

Synthetic aperture sequential beamforming (SASB) is a two-stage delay-and-sum beamforming procedure, which can be applied to B-mode imaging with an implementation of low complexity compared to the traditional synthetic transmit aperture imaging. A new SASB imaging scheme in order to compensate the effects of axial motion is proposed. The velocity and direction of the motion can be evaluated by cross-correlation between specific beams according to adjacent focus of the SASB. The performance assessment, conducted by using simulated data, reveals that the proposed method can correct the positions of tissue motion without extra firings.

Sensory system performance and variability depend on the compensation degree against fabrication process, voltage, temperature and ageing (PVTA) variations. A pH ion sensitive field-effect transistor sensor with PVTA compensation is presented; stages for calibration and sensitivity adjustment were also included. To validate its performance, the proposed sensor was compared with a non-compensated sensor; the results showed that PVTA variations were reduced by 81.50% for fabrication process and ageing, 87.91% for voltage and 80.30% for temperature. The maximum resolution achieved was 833.33 mV/pH.

A commonly used phase rotation beamforming (PRBF) technique in medical ultrasound scanners requires four multipliers to realise phase rotation (PR) in addition to two lowpass filters for quadrature demodulation for each channel. A new scheme is presented to reduce the computational complexity of PRBF without sacrificing image quality that uses only 16 PRs located behind inter-channel adders, regardless of the number of channels, each of which is dedicated for one of 16 quantised PR values using a step size of 2π/16.

A novel implementation is proposed to relax the specifications of the internal feedback path for a continuous-time delta–sigma modulator. A truncator is embedded into the digital excess loop delay (ELD) compensation path. Thermometer-coded truncation is achieved by re-ordering the reference voltages of the internal quantiser. This requires only a small amount of extra digital circuitry compared to the conventional digital ELD compensation. The digital encoder controlling the digital-to-analogue converter is simple, and it only introduces a small ELD.

Characterisation of the standard deviation of a time-series signal has uncommon, yet widespread applications. The usual requirement for a representation of signal standard deviation in real-time implies a high computation speed. A method based on a field programmable gate array (FPGA) implementation is presented. The technique is benchmarked against conventional computational approaches and shows a single windowed standard deviation update calculation of a 16 bit sample can be achieved in 11 ns on a modern CPU. The FPGA implementation is found to be superior to all other approaches examined with an operation time of below 10 ns, and thus provides a useful tool for the real-time measurement of the standard deviation of signals above 100 MHz.

Hidden attractors were reported to find in a normalised Chua's equation. To find the hidden attractors in a practical Chua's circuit, a modified Chua's diode is presented and its equivalent realisation circuit is designed. On the basis of proposed modified Chua's diode, a new Chua's circuit is rebuilt and hidden attractors under special initial conditions are captured by numerical simulations and circuit simulations.

Memristor crossbars are capable of implementing learning algorithms in a much more energy and area efficient manner compared with traditional systems. However, no results have been published that describe how large a neuromorphic memristor crossbar could theoretically become before it is inoperable. Furthermore, the input drivers to the crossbar are not typically studied in these neuromorphic system simulations. Presented is a model for determining the maximum memristor crossbar size relative to the input driver impedance. This is a powerful tool that can be used by a memristor system designers to quickly determine the trade-offs between maximum crossbar size, resistance, energy, and write speed. This information can then be used to determine how many independent crossbar circuits are required for a given neuromorphic application.

A novel low-energy write scheme, self-judgement flip coding (SJFC), for resistive random access memory (RRAM) is proposed. Lots of energy will be consumed in the write process of RRAM, especially in the reset process. Owing to RRAM being sensitive to heat, excessive heat accumulation will lead to thermal crosstalk. Through reading original data, SJFC analyses and computes the Joule heat produced in the write data flow and further judges whether to make flip coding on the write data flow. The result is that between the original write data flow and flip coding data flow, the one producing lesser energy will be transmitted to the write circuit to produce lesser energy in the RRAM write process. The stimulation result shows that SJFC could reduce energy consumption by 39% on average in the write process.

Optical cloaking for cylindrical structures with arbitrary cross-section by using scattering cancellation method is presented. Nano-strips of silver in a dielectric host are used as a cloaking shell around the cylindrical object with arbitrary cross-section shapes. In this approach, the homogeneity effect on cloaking efficiency in the cloaking structure with circle cross-section is studied. The number of silver strips is the criteria of shell homogeneity. By increasing the number of strips for a constant filling factor, their widths become narrower and so the cloaking shell becomes more homogenous. It is shown that the cloaking efficiency is affected by the homogeneity of the cloaking shell and there is an optimum size of embedded particles to achieve required homogeneity in a cloaking structure.

A robust face recognition method that utilises a set of combined features is proposed to effectively conduct face recognition with images taken under diverse illumination variations. This method extracts discriminant features from different methods, both of which have different characteristics. To exploit the respective advantage of each method, the respective discriminability of the features extracted by each method is measured based on the discriminant distance criterion of each method. The experimental results show that the proposed features result in improved recognition performance under illumination variation.

In the Letter ‘Unified VLSI architecture for photo core transform used in JPEG XR’, the authors proposed a hardware architecture to implement the three elementary 2 × 2 transform operations for the photo core transform used in JPEG XR. However, there are some errors in their implementation, dataflow and reported resources used. In this Letter, we point out those errors and suggest the corresponding corrections. We also provide constant additions which must be added to the results of the implementation to conform the standard.

The issue of ambiguity of objective image quality assessment is addressed. The necessity of considering perceptual ambiguity of two objective quality scores is justified first. Then, an approach to obtain an ambiguity interval defining the quality score range is developed within which quality difference is not perceptually distinguishable. Experimental results demonstrate the validity of the developed approach and examine various aspects of the ambiguity of objective quality assessment in viewpoints of the type of image distortion, objective quality metric, image content etc.

A robust stereoscopic method is presented for rapid identification of hidden 3D objects by extracting edge and other features from computed depth planes using only a small number of X-ray projections acquired with a low-cost portable X-ray imager. The portable X-ray imager acquires X-ray projections with a single fixed sensor from different viewing angles by rotating an X-ray source attached to the end of a pivot arm. Knowing the geometry of the X-ray imaging system, a series of depth planes are computed to extract the significant features of the hidden objects for quick identification. The proposed hidden object identification algorithm can be easily parallelised and embedded in portable devices for real-time applications.

A novel least-squares (LSs) channel estimation method for OFDM systems is proposed. Compared with the conventional LS method, the proposed method employs several extra steps to suppress the noise effect. Thus, it can provide a better estimation performance than the conventional LS method. Moreover, the proposed method does not increase the occupation of frequency-band resources and has some application value for engineering. Simulation results demonstrate the performance of this method.

An efficient structure for spline-based fractional delay filtering for interpolation/decimation is introduced. Inspired by the Newton structures for Lagrange interpolation, it requires less than half the number of operations of a typical Farrow implementation. Moreover, it displays better frequency response characteristics than Lagrange-based filters. To obtain this structure, a matrix form of the Farrow transfer function is proposed and used to derive state-space transformations between the Lagrange-Farrow structure and its Newton counterpart. These transformations are then applied to the spline polynomial, giving rise to the efficient Newton-like spline filtering method.

An algorithm for compressive sensing reconstruction of signals in the Hermite expansion domain is proposed. The compressive sensing problem is formulated in the Hermite framework, allowing fast and efficient reconstruction of missing data by exploiting the concentration of signal's representation in the Hermite basis.

A parallel concatenated coding structure, which can improve the performance of polar codes in finite-length regime, is proposed. In the proposed structure, the encoder is built using two systematic polar codes (SPCs), and the decoder adopts iterative belief propagation decoding algorithm. Numerical results in the binary-input additive white Gaussian noise channel indicate that the proposed coding scheme can improve BER performance of polar codes significantly. Specially, BER of the proposed coding scheme with length 192 is almost equal to that of original SPCs with length 256, when the code rate is 1/3.

Recently, many works have focused on analysing the metrics of physical layer security over different wireless channels such as additive white Gaussian noise, Rayleigh, Rician and Nakagami-m fading distributions. To extend the analysis to the general case, the α–μ fading channel is considered, which can span the aforementioned cases. For this purpose, the physical layer security over the α–μ fading channel is presented. The closed-form expressions for the probability of positive secrecy capacity and upper bound of the secrecy outage probability are derived. Their accuracies are assessed through comparison of theoretical analysis and simulations results.

A reliable majority voter circuit using a nanometre spin transfer torque magnetic tunnel junction (STT-MTJ) is presented. The circuit tolerates single transient faults and manages process variations due to technology downscaling. The use of this magnetic device brings non-volatility memory to logic circuits and promises to overcome the rising standby power issue. By using the STMicroelectronics fully depleted silicon on insulator 28 nm design kit and a precise STT-MTJ compact model, electrical simulations have been carried out to show its low-power and high reliability performances.

A simplified model-free predictive current control (SMFPCC) for an interior permanent magnet synchronous motor (IPMSM) drive system is presented. The SMFPCC requires neither pulse width modulation nor a regulator. Unlike existing model-based predictive current controllers (MBPCCs), the proposed method is based on stator current detection, meaning that system parameters such as stator resistance, stator inductance, and back-EMF are not needed. In each sampling period, the stator current is detected only once, rather than twice, thus simplifying the process. Furthermore, to reduce both the switching losses of the inverter and the time consumed, one of four (rather than eight) candidate switching states is selected via the minimisation of a cost function. To compare their performance, both the SMFPCC and the MBPCC are realised on an IPMSM drive system and implemented through a digital signal processor.

A compact waveguide 3-dB hybrid with full bandwidth is proposed in this Letter. The tight coupling and full bandwidth of Ka-band (from 26.3 to 40 GHz) are achieved by introducing multi-sections of waveguide with different width and depth, together with loaded posts on the bottom of some waveguide sections. The whole structure is symmetric both longitudinally and transversely (patent pending). The measured results show that return loss and isolation of the hybrid better than 25 dB and 26 dB, respectively, phase difference of the two output terminals within 90° ± 3° and the power-split unbalance within 3.1 dB ± 0.5 dB are achieved over the full Ka-band waveguide bandwidth.

It is demonstrated, using the example of a T-junction, that not every multiport structure can be accurately described by a discrete and separated modelling approach at millimetre and sub-millimetre wavelengths. It is shown that especially stub-networks, which are typically used in RF-matching networks, are affected. In this case, the discrete modelling approach predicts a different resonance frequency than the S-parameter measurement as well as the 3D electromagnetic field simulation (3D-EMFS) of the whole structure. However, these resonances are of particular importance for the design of a RF matching network and should be predicted by the model as precisely as possible. Therefore, the reason for the mismatch by accurate 3D-EMFS is investigated and a possible solution on how to model the so-called complex interactions in passive multiport structures at millimetre and sub-millimetre wavelengths is provided.

The prospects of the practical application of reflex triodes are connected with the constructional features of these high-power microwave oscillators. The results of experimental investigations of an original design of a reflex triode are presented. A scheme of the triode allows provision of a symmetric current supply to the device grid. A linear induction accelerator (LIA) with low source impedance has been used. The LIA is made using a composition approach, where the main parts of the accelerator are placed within one cylindrical tank.

Based on a novel composite right/left-handed unit cell, a wideband frequency-scanning network with a large scanning angle ranging towards both negative and positive elevation angles is proposed. The measured results show that the insertion loss variation of the designed frequency-scanning network is 7.2 ± 1 dB when the frequency ranges from 4.33 to 8.53 GHz and the phase differences of adjacent output ports scan from −50° to 50° when the frequency ranges from 4.76 to 8.26 GHz (53.8%). The proposed network can be used in wideband systems that require a large scanning angle range.

A wideband tunable single bandpass microwave photonic filter (MPF) based on the four-wave mixing (FWM) nonlinear dynamics of a distributed feedback (DFB) semiconductor laser under optical injection is proposed and experimentally demonstrated. Utilising the wavelength-selective optical gain of the optical-injected DFB laser, phase-modulation to intensity-modulation conversion is obtained, leading to the realisation of a single bandpass MPF. By changing the injection parameters, an MPF with a frequency tuning range of 27.72 GHz has been achieved. The minimum 3 dB bandwidth and the out-of-band suppression ratio are measured to be 61.2 MHz and 25 dB, respectively.

The use of a high k composite dielectric composed of La₂O₃ and HfO₂ layers as the gate dielectric for In_0.53Ga_0.47As MOS application is proposed. Two multi-layer structures of La₂O₃ (1 nm)/HfO₂ (1 nm) and La₂O₃ (0.5 nm)/HfO₂ (0.5 nm) were deposited and annealed at 450 and 500°C for device performance comparison. X-ray photoelectron spectroscopy, TEM and C–V measurements were used for the interface analysis between the oxide and the semiconductor. Finally, a 1 nm equivalent-oxide-thickness dielectric with small hysteresis of 88 mV and D _it of 1.9 × 10¹² cm⁻² eV⁻¹ was achieved for six layers of an La₂O₃ (0.5 nm)/HfO₂ (0.5 nm) composite oxide structure on an In_0.53Ga_0.47As MOS capacitor with a post-deposition annealing temperature of 450°C.

In(Ga)As/GaAs-based quantum dot infrared photodetectors (QDIPs) are among the most efficient devices for use in the mid- and long-wavelength infrared regions, making them suitable for various defence and space applications. Considering previously reported results on In(Ga)As/GaAs QDIPs, a post-growth method is investigated to improve QDIP characteristics using high-energy proton implantation. It was found that implantation suppressed the field-assisted tunnelling of dark current generation, which decreased the dark current density by three orders, whereas the peak detectivity (D*) in the implanted devices increased by up to two orders of magnitude, from 6.1 × 10⁸ to 1.0 × 10¹⁰ cm-Hz^1/2/W at 77 K.

The passively Q-switched operation of all-fibre thulium fibre lasers using UV-curing resin doped with multi-walled carbon nanotubes as a saturable absorber is demonstrated. A single-mode thulium-doped silica fibre is pumped by a laser diode emitting at 1.63 µm through a wavelength-division multiplexing coupler. Unidirectional laser output from the fibre ring resonator is attained by using the retroreflector at the counter-directional output port. The fibre laser exhibits 1.9 µm wavelength pulsed oscillation at a repetition rate of 7.2 kHz. When the pump power is increased to 161 mW, the output pulse power is measured by 150 mW with a pulse width of 3.2 µs.

A current limiter for the low-cost hybrid energy storage system (HESS) to guarantee battery lifetime is presented. It controls the maximum battery current and makes the battery backup system responsible for the remaining load. The proposed current limiter is a controllable variable resistor which can be implemented with a bidirectional semiconductor switch, a resistor, and a filter. Its feasibility has been verified with a 25 A limiter.

A novel bearingless motor is proposed – the position of rotor and stator in switched reluctance motor is exchanged to obtain the single winding bearingless flywheel motor (SWBFM), in which the outer rotor is levitated and can directly drive the flywheel with less mechanical transmission by the combination of the levitation forces and torques. The electromagnetic characteristics are analysed by finite element analysis and the results verify the SWBFM has better torque and suspension characteristics.

A new family of faded harmonics modulations, cosine faded harmonics binary offset carrier modulations (FH-BOC_cos), is designed to account for the spectral overlap among global navigation satellite system (GNSS) signals. The generalised mathematical model and power spectral density function of FH-BOC_cos modulation are established. The spectral characteristics and modulation parameters are also analysed. The proposed modulations can suppress specific sidelobes of the spectrum while retaining similar signal performance compared with traditional BOC modulation.

A new planar wideband chessboard structure is designed to reduce the radar cross-section (RCS) of an object. This proposed chessboard configuration is composed of two different artificial magnetic conductor (AMC) tiles. One of these tiles is formed by saltire arrow unit cells, whereas the other one is formed by four E-shaped ones. A 180° ± 30° phase difference between these tiles achieved by precise design of the AMC unit cells of more than 9.4–23.28 GHz (85%) reduces the RCS by more than 10 dB. The fabricated board results show very good agreement with the simulated ones, which verify the ability and capability of the proposed structure.

A 500 V silicon-on-insulator (SOI) lateral pin diode is proposed. The proposed structure features dual deep-oxide trenches (DDOTs) arranged in the i-layer. In off-state, the dual DDOTs can help to sustain the potential between the cathode and the anode. With the breakdown voltage of 500 V level, the i-layer length of the proposed structure can be dramatically shortened compared with the conventional SOI diode. The fast reverse recovery is obtained due to the reduced amount of the stored carrier in on-state. During the reverse recovery, the holes can be trapped by the gap between the adjacent deep-oxide trenches (DOTs). Therefore, dynamic punch-through is avoided and suppressed oscillation can be realised. The proposed structure achieves a reverse recovery time of 72 ns which is an improvement by 28% compared with the conventional SOI diode. Meanwhile, the waveform oscillation of the proposed structure is successfully suppressed, which is superior to the normal DOTs SOI lateral pin diode.

n-InAs/p-GaSb Esaki diodes with 3 nm GaSb i-layers are fabricated on Si and GaSb substrates. The on Si sample devices exhibit lower peak to valley ratios and peak current density than their on GaSb counterparts at 3.27 against 4.45 and 119 against 336 kA/cm², respectively. The findings are similar to other reports of integrating III–V Esaki diodes onto Si.

An enhanced algorithm for the reconstruction of discrete-valued sparse vectors from an underdetermined system of linear equations under the presence of noise is presented. Knowledge from the field of compressed sensing and from digital communications is combined in optimising the estimation step in the orthogonal matching pursuit (OMP) algorithm according to the minimum mean-squared error (MMSE) criterion. Thereby, a gain in performance of more than 1 dB is achieved compared with the conventional OMP.

Heterogeneous network is introduced to improve the network capacity in LTE Release 9 and system beyond. The potential traffic congestion due to increased users can be alleviated by the cooperation between macro-cell and pico-cell. However, the inter-cell interference caused by RF signal from macro-cell will reduce the performance severely. Enhanced inter-cell interference coordination is proposed in Rel. 10 to solve this problem using almost blank subframe (ABS). Yet, the cell specific reference signal in ABS can still cause interference to the data resource element (RE) from the pico-cell inevitably for non-colliding scenario. In this Letter, a novel interference cancellation (IC) algorithm is proposed to mitigate the interference. First, the timing and carrier frequency offset of interference signal is estimated and compensated. Second, the interfering channel response is estimated by utilising the channel statistics. Third, the interference signal is reconstructed based on the channel estimation and cancelled in the received signal in time domain. The experiment results show that the performance of proposed IC algorithm is robust.

A geometric distance estimation algorithm based on the reference anchor is proposed. Geometric distance estimation is widely used to estimate the distance to the remote anchor. The geometric distance estimation accuracy is considerably affected by the reliability of the sides of the geometry formed by the unknown node, the reference anchor, and the remote anchor. A new reference anchor selection method to improve the reliability of the sides of the geometry is introduced, and a novel geometric distance estimation algorithm based on the reference anchor is proposed.

A simple system that approaches the capacity of the additive white Gaussian noise channel (AWGN) is proposed. It is well known that this capacity is achieved by a Gaussian input, which is hard to obtain in practice. However, if the capacity is <1/2, then the use of a binary input incurs little capacity loss. A parallel between the AWGN and the multiple access channel (MAC) is exploited, which allows for the transformation, without loss of capacity, of the AWGN channel into several parallel channels with capacity <1/2. In this proposal, each channel uses a binary input and a capacity-achieving code, resulting in a system with simple encoding that operates close to capacity. A decoding scheme based on successive interference cancellation is also proposed. As a result, the receiver consists of a series of simple binary receivers. It is shown that the proposed system works at a small gap to the capacity of the AWGN, and that this gap may be attributed to the gap to capacity of the underlying binary code. Similar method has been proposed but the results have shown that this method is better than the iterative method (bit interleaved coded modulation).

A new cooperative spectrum sensing (CSS) scheme with two-stage reporting is proposed so as to improve the throughput of secondary users (SUs) through reducing the reporting overhead. In the proposed scheme, the reporting process of the SUs is divided into two stages (a dedicated reporting stage and a contention-based reporting stage) and the fusion centre determines the presence of primary users through combining the sensing results successfully received in the two reporting stages by using the k-out-of-N rule. Simulation results demonstrate that the proposed scheme significantly outperforms conventional CSS schemes based on the OR rule and the k-out-of-N rule.

The eigenvalue-based minimum description length (MDL) method for source number estimation is widely applied in practical scenarios. However, the performance of the MDL method degrades significantly when it is applied to an asymmetrical subarray situation due to the inequality of the noise power of each channel. Therefore, an improved MDL method for subarray level is proposed by normalising noise power to reconstruct the received signal covariance matrix. Simulation results show that the proposed method outperforms the conventional source number estimation methods for a subarray situation.

A low-noise tunable filter with high dynamic range and minimum power consumption is presented and addressed with circuit details. It is based on an active solution simulating an inductive behaviour that allows improving the filter quality factor without affecting the noise performance. The low-order bandpass filter is realised with minimum number of components and it is suitable to be integrated in integrated circuit or used in hybrid transceiver and modern reconfigurable radio systems. A prototype board with discrete components has been fabricated and tested with good results.