Signal Design Research Articles

Star finches Neochmia ruficauda have a visual preference for white dot patterns: a possible case of trypophilia

Many animals have polka dot patterns on their body surface, some of which are known to have signalling functions; however, their evolutionary origins remain unclear. Dot patterns can trigger a fear response (trypophobia) in humans and are known to function as aposematic signals in non-human animals, suggesting that dots may deserve attention for biological reasons. Interestingly in many birds, plumage dot patterns serve for social/sexual signalling. To understand their evolution, we have focused on the sensory bias hypothesis, which predicts the role of pre-existing sensory preference driven by natural selection in shaping signal design. Our previous phylogenetic comparative study supported the hypothesis and showed that diet-driven visual preference promoted the evolution of plumage patterns, as there was an evolutionary correlation between termite-eating (white roundish gregarious prey) and the presence of plumage dot patterns in species of the family Estrildidae. This suggests that these species possess an intrinsic preference for dots. To test this, we compared the responses of an Estrildid species with dot plumage pattern (star finch Neochmia ruficauda) towards simultaneously presented monochrome-printed white dot vs white stripe patterns under both food-deprived and -supplied conditions. Overall, star finches preferred dots to stripes. They showed foraging-like behaviours almost only toward dots when hungry and gazed at dots frequently even when food was available, suggesting both hunger-related and hunger-neutral dot preferences. These results are rather surprising, given how strongly the subjects were attracted to abstract dot patterns without organic structure, but provided good support for the sensory bias hypothesis.

Simultaneous Localization and Communication Method Using Short-Time and Narrow-Band Dual-Carrier Acoustic Signals

This paper describes a novel acoustic localization and communication methods using multiple speakers. Acoustic signals for localization are modulated by differential phase shift keying to contain some information. Therefore, localization and communication can be conducted simultaneously. Regarding the design of acoustic signals, short-time and narrow-band acoustic signals are ideal to save time and frequency resources. However, if such signals are used with conventional methods, the interference of signals can occur and cause errors of localization and communication. Additionally, this error changes depending on the phase value that corresponds to the modulation for communication. To reduce this error, in our proposed method, a noninterference region in the received signal was constituted by using dual-carrier acoustic signals, and localization and demodulation were processed using this region. In the evaluation experiments, we estimate the azimuth of the microphone from two speakers and demodulate each of the symbols at 9 locations. Through simulation and real-environment experiments, it was confirmed that our proposed method can reduce the error caused by the interference. In real-environment experiments, the demodulation performance of our proposed method was similar to that of conventional methods. We discussed this similarity and revealed the cause.

A Comprehensive Evaluation of Possible RNSS Signals in the S-Band for the KPS.

Recently, the Korean government has announced a plan to develop a satellite-based navigation system called the Korean Positioning System (KPS). When designing a new Radio Navigation Satellite Service (RNSS) signal, the use of the S-band has emerged as an alternative to avoiding signal congestion in the L-bands, and South Korea is considering using the S-band with the L-bands. Therefore, this study proposed possible S-band signal candidates and evaluated their performance, such as the radio frequency (RF) compatibility, spectral efficiency, ranging performance, and receiver complexity. Several figures-of-merit (FoMs) were introduced for quantitative performance evaluation for each candidate. Each FoM was calculated using an analytical equation by considering the signal design parameters, such as the center frequency, modulation scheme, and chip rate. The results showed that the outstanding candidate signal was different depending on the signal performance of interest and the reception environments. Therefore, we discuss and summarize the signal performance analysis results considering the whole FoMs together. Under the assumptions given in this paper, the binary phase shift keying (BPSK)(1), sine-phased binary offset carrier (BOCs)(5,2), and BPSK signals were superior for the spectral efficiency, ranging performance, and receiver complexity, respectively.

Logic functions for mixed signal circuit design using analog block

ABSTRACT An approach to realising logic functions using analog building block is explored, with promising results in form of OR and NOR functions being tested with EXCCII as basic building current-mode block. The other functions like NAND and AND realisation is also presented. The proposed circuits employ current-mode operation and show low input and high output impedance, which makes these designs practically useable. The approach is expected to benefit the mixed signal design, without necessitating separate conventional digital blocks. Several possible application areas are thus suggested. PSPICE simulation results are shown in support of the proposed idea.

Identifying potential cues of species identity in complex animal signals

Communication signals are often key for encoding information on species identity, but determining the features important in conveying those cues is challenging. This is especially the case when attempting to compare across closely related sympatric taxa, where the need for accurate species recognition is critical. We developed an analytical framework to comprehensively quantify the complex movement displays used by male lizards to advertise territory ownership in 11 taxa of Puerto Rican Anolis , many of which were sympatric. Our analyses were able to assign the majority of individuals to the correct population of a given species based on only a handful of displays, showing ample information exists in these displays for species recognition. Instances where lizards were misassigned appeared to have occurred because of similarities in display design resulting from local adaptation to similar environments or recent shared evolutionary history. Our analyses also revealed there was no common (‘magic’) display characteristic for recognition across the 11 taxa. Instead lizards likely assess the entire display or a combination of different display cues. Taken together, we illustrate a powerful approach that offers a rigorous statistical and holistic evaluation of complex animal signals for elucidating features likely to be important in species recognition. We provide a guide for implementing this analytical framework in R, with associated code and worked examples. Information obtained from these analyses can then be used to design experiments testing the utility of identify cues or comparative studies investigating how those cues contribute to reproductive isolation among populations and ultimately speciation. • Communication signals are key for encoding information on species identity. • We applied a novel framework to reveal identity cues in complex animal signals. • Our approach reliably assigned individuals to their correct population and species. • The handful of misassignments reflected similarities in signal design. • Shared designs were often among closely related taxa adapted to similar habitats.

Closed-loop identification for aircraft flutter model parameters

PurposeThe purpose of this paper is to extend the authors’ previous contributions on aircraft flutter model parameters identification. Because closed-loop condition is more widely used in today’s practice, a closed-loop stochastic model of the aircraft flutter test is constructed to model the aircraft flutter process, whose input–output signals are all corrupted by the observed noises. Through using a rational transfer function, the equivalent property between the aircraft flutter model parameters and polynomial coefficients is established, and then the problem of aircraft flutter model parameters identification is turned to one closed-loop identification problem. An iterative identification algorithm is proposed to identify the unknown polynomial coefficients, being benefit for the latter flutter model parameter identification. Furthermore, as the closed-loop output corresponds to the flutter amplitude, so from the point of the minimization with respect to the variance of the closed-loop output, the optimal input signal and optimal feedback controller are all derived to achieve the zero flutter, respectively, for example, the optimal input spectrum and the detailed form for optimal feedback controller.Design/methodology/approachFirst, model parameter identification for aircraft flutter is reviewed as one problem of parameter identification and this aircraft flutter model corresponds to one closed-loop stochastic model, whose input signal and output are corrupted by external noises. Second, for aircraft flutter closed-loop statistical model with statistical noise, an iterative identification algorithm is proposed to identify the unknown model parameters. Third, from the point of minimizing with respect to the variance of the closed-loop output, the optimal input signal and optimal feedback controller are all derived to achieve the zero flutter, respectively, for example, the optimal input spectrum and the detailed form for optimal feedback controller.FindingsThis aircraft flutter model corresponds to one closed-loop stochastic model, whose input signal and output are corrupted by external noises. Then, identification algorithm and optimal input signal design are studied for aircraft flutter model parameter identification with statistical noise, respectively. It means the optimal input signal and optimal feedback controller are useful for the aircraft flutter model parameter identification within the constructed new closed-loop stochastic model.Originality/valueTo the best of the authors’ knowledge, this problem of the model parameter identification for aircraft flutter is proposed by their previous work, and they proposed many identification strategies to identify these model parameters. This paper proposes a new closed-loop stochastic model to construct the aircraft flutter test, and some related topics are considered about this closed-loop identification for aircraft flutter model parameter identification in the framework of closed-loop condition.

Phase Retrieval-Based Coherent Receivers: Signal Design and Degrees of Freedom

Kramers-Kronig (KK) detection exploits properties of minimum-phase, single-sideband signals to recover the phase of a signal from its intensity. It offers many of the benefits of standard coherent detection, while not requiring a local oscillator, quadrature hybrid, or balanced photodiodes. Adding a carrier to a transmitted signal to render it minimum-phase, however, causes a power penalty for KK detection relative to standard coherent detection. We study the mutual information (MI) achieved by KK detection and the impact of signal and system design parameters, including excess bandwidth, carrier-to-signal power ratio, modulation order, probabilistic shaping, and chromatic dispersion, making comparisons to standard coherent detection and standard direct detection. We study the effective degrees of freedom for KK detection, confirming that it tends towards unity at high signal-to-noise ratio (SNR), supporting the classification of KK detection as coherent detection. At low SNR, however, KK detection is outperformed by standard direct detection in terms of MI per symbol. This study focuses on the fundamental performance of the detection methods under comparison, by numerically approximating ideal continuous-time signals and signal processing operations. The results and conclusions reported here will be constrained, in practice, by limitations of practical implementation, including those addressed in the Discussion section.

Analytical Models for Multipath and Switch Leakage for the SWOT Interferometer.

The Ka-Band Radar Interferometer (KaRIn) instrument on the Surface Water and Ocean Topography (SWOT) mission is a single-pass synthetic aperture radar (SAR) interferometer tasked with, among others, measuring ocean topography to within a few centimeters over kilometer scale resolutions. A SAR interferometer relies on very precise phase difference measurements between two spatially distant antennas to estimate topography. Multipath phase caused by unintended scattering off the spacecraft structure is a known error source for radar interferometers and takes up a significant portion of the KaRIn error budget. This paper outlines some analytical multipath models that were used for instrument design, performance analysis and mitigation of the multipath signal.

Guest Editorial Special Issue on Radar and Microwave Sensor Systems

This Special Issue is devoted to technical papers on radar and sensor systems in microwave and millimeter-wave bands. Massive technological progress has been made in recent years at the microwave device and component level, enabling new research directions on sophisticated microwave and millimeter-wave systems. Among the most significant fields of application for such systems has been sensor technology, with a major emphasis on radar systems. Interest in automotive sensing, wireless human-computer interaction, biometric measurements, industrial monitoring, and target tracking—among many other applications—has driven this interest. Advances in device and component technology are supporting system design concepts that treat the microwave hardware as a co-design element of the system, along with signal processing and antenna design. Such co-design is of particular importance in radar and sensor systems, where a rapidly increasing number of wireless devices and an increasingly crowded spectrum necessitates the design and use of specialized signals (both temporal waveform designs and spatial beamforming) to maintain and improve sensor performance. Systems designed for general broad applicability are becoming more challenging to implement, while specialized systems that co-design the aperture, microwave hardware, and signal processing are becoming increasingly relevant. Technologies such as digital array radar, distributed and networked sensors, computational imagers, high-sensitivity Doppler radars, and integrated millimeter-wave radar, to name only a few, have supported system-level developments.

Frequency design of LEO-based navigation augmentation signals for dual-band ionospheric-free ambiguity resolution

Frequency design of LEO-based navigation augmentation signals for dual-band ionospheric-free ambiguity resolution

Making Intelligent Reflecting Surfaces More Intelligent: A Roadmap Through Reservoir Computing

This article introduces a neural network-based signal processing framework for intelligent Reflecting surface-aided (IRS) wireless communications systems. By modeling radio frequency (RF) impairments inside the meta-atoms of IRS - including nonlinearity and memory effects) - we present an approach that generalizes the entire IRS-aided system as a reservoir computing (RC) system, an efficient recurrent neural network (RNN) operating in a state near the “edge of chaos.” This framework enables us to take advantage of the nonlinearity of this “fabricated” wireless environment to overcome link degradation due to model mismatch. Accordingly, the randomness of the wireless channel and RF imperfections are naturally embedded into the RC framework, enabling the internal RC dynamics lying on the edge of chaos. Furthermore, several practical issues, such as channel state information acquisition, passive beamforming design, and physical layer reference signal design, are discussed.

Reference signal design to mitigate co-channel interference in 5G OFDM systems with multiple numerologies

The 5G cellular technology is expected to support diverse services by flexible use of the allocated spectrum. It is achieved by allowing multiple subcarrier spacing and dynamically changing downlink (DL) and uplink (UL) transmissions based on the instantaneous traffic and latency requirements. The problem of mitigating co-channel interference (CCI) with different subcarrier spacings becomes more challenging, and the dynamic DL–UL configuration makes it further difficult. In this paper, a reference signal design to measure the CCI is proposed along with detailed mathematical analysis. Furthermore, novel algorithms to estimate the CCI are proposed which along with advanced receivers are used to effectively mitigate the interference. Simulations are performed to evaluate the performance of reference signal design and the proposed estimation algorithms. The results confirm the efficacy of the proposed methods.

The Impact of Different Types of Auditory Warnings on Working Memory.

Auditory warnings have been shown to interfere with verbal working memory. However, the impact of different types of auditory warnings on working memory tasks must be further researched. This study investigated how different kinds of auditory warnings interfered with verbal and spatial working memory. Experiment 1 tested the potential interference of auditory warnings with verbal working memory. Experiment 2 tested the potential interference of auditory warnings with spatial working memory. Both experiments used a 3 × 3 mixed design: auditory warning type (auditory icons, earcons, or spearcons) was between groups, and task condition (no-warning, identify-warning, or ignore-warning) was within groups. In Experiment 1, earcons and spearcons but not auditory icons worsened the performance on the verbal serial recall task in the identify-warning condition, compared with that in the no-warning or ignore-warning conditions. In Experiment 2, only identifying earcons worsened the performance on the location recall task compared with performance without auditory warnings or when auditory warnings were ignored. Results are discussed from the perspective of working memory resource interference, and their practical application in the selection and design of auditory warning signals is involved.

Detection of EGFR mutations in non-small cell lung cancer by droplet digital PCR.

Activating mutations in EGFR predict benefit from tyrosine kinase inhibitor therapy for patients with advanced non-small cell lung cancer. Directing patients to appropriate therapy depends on accurate and timely EGFR assessment in the molecular pathology laboratory. This article describes the analytical design, performance characteristics, and clinical implementation of an assay for the rapid detection of EGFR L858R and exon 19 deletion mutations. A droplet digital polymerase chain reaction (ddPCR) assay was implemented with probe hydrolysis-dependent signal detection. A mutation-specific probe was used to detect EGFR L858R. A loss of signal design was used to detect EGFR exon 19 deletion mutations. Analytical sensitivity was dependent on DNA input and was as low as 0.01% variant allele fraction for the EGFR L858R assay and 0.1% variant allele fraction for the EGFR exon 19 deletion assay. Correlation of 20 clinical specimens tested by ddPCR and next generation sequencing showed 100% concordance. ddPCR showed 53% clinical sensitivity in the detection of EGFR mutations in plasma cell-free DNA from patients with lung cancer. The median clinical turnaround time was 5 days for ddPCR compared to 13 days for next generation sequencing. The findings show that ddPCR is an accurate and rapid method for detecting EGFR mutations in patients with non-small cell lung cancer.

Multiplexing modulation design optimization and quality evaluation of BDS-3 PPP service signal

The Precise Point Positioning (PPP) service of BeiDou-3 Navigation Satellite System (BDS-3) is implemented on its Geostationary Earth Orbit (GEO) satellites. However, its signal design is limited by the actual power of satellite and other conditions. Furthermore, the design needs to fully consider the compatibility of different service phases. Starting from the actual state of the BDS-3 GEO satellite, this paper studies the multiplexing modulation of the BDS PPP service signal that is based on the Asymmetric Constant Envelope Binary Offset Carrier (ACE-BOC) technique and proposes several feasible schemes for this signal. Comparison and optimization of these techniques are made from the aspects of transmission efficiency, multiplexing efficiency, and service forward compatibility. Based on the Type-III ACE-BOC multiplexing modulation technique, phase rotation and intermodulation reconstruction techniques are proposed to suppress the intermodulation interference issue. Finally, a signal based on improved ACE-BOC multiplexing is designed. The quality of the proposed signal was continuously monitored and tested using large-diameter antennas. The evaluation results show that the power spectrum deviation of the signal is 0.228 dB, the correlation loss is 0.110 dB, the S-curve slope deviation is 1.558% on average, the average length difference between the positive/negative chip and the ideal chip is only 0.0006 ns, and the coherence between the carrier and the pseudo code is 0.082°. All quality indicators are satisfactory, indicating that the proposed signal multiplexing modulation technique is an ideal solution that meets all the requirements of the design constraints, and can achieve efficient information broadcasting and forward compatibility of the BDS PPP service.

Hybrid Chirp Signal Design for Improved Long-Range (LoRa) Communications

Long-range (LoRa) communication has attracted much attention recently due to its utility for many Internet of Things applications. However, one of the key problems of LoRa technology is that it is vulnerable to noise/interference due to the use of only up-chirp signals during modulation. In this paper, to solve this problem, unlike the conventional LoRa modulation scheme, we propose a modulation scheme for LoRa communication based on joint up- and down-chirps. A fast Fourier transform (FFT)-based demodulation scheme is devised to detect modulated symbols. To further improve the demodulation performance, a hybrid demodulation scheme, comprised of FFT- and correlation-based demodulation, is also proposed. The performance of the proposed scheme is evaluated through extensive simulation results. Compared to the conventional LoRa modulation scheme, we show that the proposed scheme exhibits over 3 dB performance gain at a bit error rate of 10−4.

Radar Pulse Signal Design and Imaging Method Based on Coded Modulation

Radar faces various interferences from the reconnaissance and other devices when conducting target imaging and recognition. The properties of traditional modulation methods, such as linear frequency modulation (LFM) and phase code modulation (PCM), have been investigated in detail. Therefore, it can be intercepted and recognized easily so that the target image is difficult to be obtained. To improve the complexity of radar signals, the pulse signal design and imaging method is proposed in this paper based on coded modulation. Taking LFM signal as an example, it is modulated by the code sequences firstly. As the spectrum of LFM signal is aliasing after coded modulation, the false peaks appear in target high resolution range profile (HRRP). To eliminate the false peaks in HRRP, the plus-minus coded modulation is designed according to the duty ratio of the first coded modulation signal. Then, the HRRP can be recovered for target imaging. The whole procedure of the coded modulation and imaging is provided and analyzed. Besides, based on different coded modulation signals, the entropy of signal time-frequency image is discussed to illustrate the anti-jamming performance. Simulations and experiments are conducted to verify the effectiveness of the proposed signal design and imaging method.

Effective connectivity determines the critical dynamics of biochemical networks.

Living systems comprise interacting biochemical components in very large networks. Given their high connectivity, biochemical dynamics are surprisingly not chaotic but quite robust to perturbations—a feature C.H. Waddington named canalization. Because organisms are also flexible enough to evolve, they arguably operate in a critical dynamical regime between order and chaos. The established theory of criticality is based on networks of interacting automata where Boolean truth values model presence/absence of biochemical molecules. The dynamical regime is predicted using network connectivity and node bias (to be on/off) as tuning parameters. Revising this to account for canalization leads to a significant improvement in dynamical regime prediction. The revision is based on effective connectivity, a measure of dynamical redundancy that buffers automata response to some inputs. In both random and experimentally validated systems biology networks, reducing effective connectivity makes living systems operate in stable or critical regimes even though the structure of their biochemical interaction networks predicts them to be chaotic. This suggests that dynamical redundancy may be naturally selected to maintain living systems near critical dynamics, providing both robustness and evolvability. By identifying how dynamics propagates preferably via effective pathways, our approach helps to identify precise ways to design and control network models of biochemical regulation and signalling.

Simultaneous Optimization of Mismatched Filters and Controlled Amplitude Signals for Long-Range MIMO Radars

This study presents a new signal and filter design procedure for long-range multiple-input multiple-output (MIMO) radars with a pulse length shorter than the return time of signals reflected by the most distant targets. The proposed algorithm adopts and radically improves the method of alternating the optimization of filters and signals, which was recently published by the same authors. It introduces full control of the signal envelope variation during the pulse, preserving acceptable peak-to-average power ratio (PAR) and signal-to-noise ratio (SNR) loss values. This state-of-the-art method allows calculation simplicity and is important for high-speed computations in adaptive applications. A gradient algorithm was used for the signal amplitude and phase optimization. The signal amplitude was controlled using a special signal construction consisting of two complex exponentials.

Foundations of Wireless Information and Power Transfer: Theory, Prototypes, and Experiments

As wireless has disrupted communications, wireless will also disrupt the delivery of energy. Future wireless networks will be equipped with (radiative) wireless power transfer (WPT) capability and exploit radio waves to carry both energy and information through a unified wireless information and power transfer (WIPT). Such networks will make the best use of the RF spectrum and radiation as well as the network infrastructure for the dual purpose of communicating and energizing. Consequently those networks will enable trillions of future low-power devices to sense, compute, connect, and energize anywhere, anytime, and on the move. In this paper, we review the foundations of such future system. We first give an overview of the fundamental theoretical building blocks of WPT and WIPT. Then we discuss some state-of-the-art experimental setups and prototypes of both WPT and WIPT and contrast theoretical and experimental results. We draw a special attention to how the integration of RF, signal and system designs in WPT and WIPT leads to new theoretical and experimental design challenges for both microwave and communication engineers and highlight some promising solutions. Topics and experimental testbeds discussed include closed-loop WPT and WIPT architectures with beamforming, waveform, channel acquisition, and single/multi-antenna energy harvester, centralized and distributed WPT, reconfigurable metasurfaces and intelligent surfaces for WPT, transmitter and receiver architecture for WIPT, modulation, rate-energy trade-off. Moreover, we highlight important theoretical and experimental research directions to be addressed for WPT and WIPT to become a foundational technology of future wireless networks.