Change In Carrier Frequency Research Articles

CZT Algorithm for the Doppler Scale Signal Model of Multireceiver SAS Based on Shear Theorem

In multireceiver synthetic aperture sonars (SASs), the traditional non-stop-hop-stop model normally ignores the intrapulse motion of sonar platform. However, such intrapulse motion brings the Doppler scale effect (DSE) to the echo signal, which will lead to the change in carrier frequency (CF) and frequency modulation (FM) rate of echo signal and may eventually result in image defocus. In this article, considering the intrapulse motion, the time-varying time delay and range history of multireceiver SAS were derived by introducing the range time into the range history, and then the Doppler scale signal model was established. After approximating the derived time-varying range history, the 2-D spectrum was derived by using the shear theorem. When compared with the traditional 2-D spectrum, an interesting phenomenon was found that the change in FM rate has no effect on the 2-D spectrum. Actually, only two additional terms, i.e., range cell migration (ARCM) and azimuth modulation (AAM), were introduced into the new 2-D spectrum due to the change in CF. Besides, the condition of neglecting the ARCM was given by further analyzing the 2-D spectrum, while the AAM is usually small and can be easily compensated together with the ARCM correction. Finally, a chirp-z transform (CZT) algorithm for the Doppler scale signal model was proposed to correct the ARCM, which can simultaneously correct the ARCM and compensate the AAM (although not required) in the 2-D frequency domain by phase multiplication. The effectiveness of the signal model and the proposed algorithm is verified by simulations and field data.

Low-Cost Metamaterial Antennas: Forward-Looking Imaging Experiment and Analysis.

A phase error correction method is proposed to compensate for the phase error in super-resolution correlated imaging based on metamaterial antennas. The varying carrier frequencies of a metamaterial antenna can generate the random radiation field for super-resolution correlation imaging, but the variation of the signal carrier frequency leads to large phase errors in the imaging results. In this proposed method, the sampling matrix in the super-resolution correlated imaging algorithm is used to compensate for the phase errors. Each element of the matrix is multiplied by a compensation phase corresponding to the phase error, and the error is subtly removed from the algorithm. In the experiment, the antenna pattern at each frequency of the metamaterial antenna is measured and recorded. In addition, an external field experiment is also carried out, and the collected data are imaged with the improved algorithm. Experimental results show that this technology can effectively solve the effect of phase errors on imaging results caused by signal carrier frequency changes.

Octopamine affects courtship call structure in male Acheta domesticus crickets

Secondary sexual displays vary considerably in both type and structure both within and across animal species. Although such variation is of keen interest to evolutionary biologists, the functional factors driving variation in male displays are poorly understood. In crickets, acoustic calls are produced by muscular contractions via stridulation of file and scraper wing components. We tested the effect of varying octopamine, an important biogenic amine neurohormone in invertebrates, on call production in male Acheta domesticus house crickets by blocking the octopamine receptors that influence skeletal muscle function with epinastine, a synthetic octopamine antagonist. We then measured male courtship calls and analyzed the call structure to quantify the differences in call structure based on the changes in carrier frequency, and whether chirps or ticks are a more prevalently expressed frequency in treated vs untreated males. Males treated with epinastine exhibited clear differences in call structure compared to untreated controls, such that epinastine-treated males were more likely to produce simpler calls and to exhibit their carrier frequencies as ticks rather than chirps. Thus, we were able to directly modify male courtship calling performance during mating interactions by altering the neuropharmacological milieu, demonstrating the potential role of biogenic amines in contributing to the diversity of call types in nature.

ОПТИМИЗАЦИЯ МНОГОЧАСТОТНОЙ КОММУНИКАЦИИ НИЗКОВЫСОТНЫХ БЕСПИЛОТНЫХ ЛЕТАТЕЛЬНЫХ СРЕДСТВ В РЕЖИМЕ «ВОЗДУХ – ЗЕМЛЯ»

The paper is devoted to questions on optimization of multi-frequency communication of air-ground type by utilization of unmanned aerial vehicles. The multi-frequency regime of communication of low altitude UAV with ground receivers located at different distances is considered. The known model for calculation of route losses, taking into account the probability of pres-ence or lack of direct vision and also losses of signal upon propagation on such distances is analyzed. The known model make it possible to calculate the total route losses but don’t provide any possibility to to realize any optimization procedure. The possi-bility for realization of regime of adaptation envisaging change of carrying frequency depending of distance, i.e. transfer to adap-tive multi-frequency communication regime is considered. Taking into account the known solutions on utilization of probability-convolutional estimates, the total probability of full communication upon presence or lack of direct vision zones is determined by help of such model. It was assumed that additional losses due to effect of environmental factors are lacked. The parameter χ, defined as losses at unit of distance is introduced. The solution is obtained in line of which χ reaches its minimum value. The multi-frequency communication regime is suggested in line which the carrier frequency changes depending on distance. The in-tegrated averaged parameter ср is suggested to research this regime. The target optimization functional is formulated taken into account the additionally introduced limitation condition. The solution of optimization task is calculated which provides for maxi-mum of target functional. In order to remove such a worst regime the quazy-optimum regime is suggested in line which the car-rier frequency is linearly increases on distance as far as receiver. The condition to reach gain in such regime is described.

Adaptive carrier-tracking algorithm for Global Navigation Satellite System signals in high dynamic scenarios

<p indent=0mm>Compared with urban application scenarios, Global Navigation Satellite System (GNSS) navigation receivers that are mounted on high-speed aircraft must handle a higher carrier frequency dynamic and output the measured result at a higher frequency. Both these factors adversely affect the accuracy of the carrier frequency measurement. Herein, we propose an adaptive carrier-tracking algorithm to measure the radial velocity by introducing a fuzzy logic controller in the carrier-tracking loop. The proposed algorithm adaptively adjusts the loop bandwidth as the carrier frequency changes, improving the velocity measurement accuracy while ensuring dynamic adaptability. Herein, the measured result of the loop is used to calculate the input variables of the fuzzy controller, and the output of the fuzzy controller is used to adjust the loop bandwidth. The fuzzy controller adopts a single input and single output Takagi-Sugeno model, which is easy to implement. The analysis and simulation are performed under fixed-, linear-, and sine-shaped Doppler frequency scenarios. The radial velocity between the aircraft and the receiver is set in the range of <sc>±10 km/s,</sc> and the radial acceleration is set in the range of <sc>±30<italic>g</italic>.</sc> To ensure the validity of the measurement results, we output the measurement results at a frequency of 1000 points per second. Simulation results demonstrate that when the input carrier-to-noise ratio is <sc>40 dB Hz,</sc> the velocity accuracy of the proposed algorithm is better than <sc>0.3 m/s</sc> (1<italic>σ</italic>).

Weakly electric fish distinguish between envelope stimuli arising from different behavioral contexts.

Understanding how sensory information is processed by the brain in order to give rise to behavior remains poorly understood in general. Here, we investigated the behavioral responses of the weakly electric fish Apteronotus albifrons to stimuli arising from different contexts, by measuring changes in the electric organ discharge (EOD) frequency. Specifically, we focused on envelopes, which can arise either because of movement (i.e. motion envelopes) or because of interactions between the electric fields of three of more fish (i.e. social envelopes). Overall, we found that the animal's EOD frequency effectively tracked the detailed time course of both motion and social envelopes. In general, behavioral sensitivity (i.e. gain) decreased while phase lag increased with increasing envelope and carrier frequency. However, changes in gain and phase lag as a function of changes in carrier frequency were more prominent for motion than for social envelopes in general. Importantly, we compared behavioral responses to motion and social envelopes with similar characteristics. Although behavioral sensitivities were similar, we observed an increased response lag for social envelopes, primarily for low carrier frequencies. Thus, our results imply that the organism can, based on behavioral responses, distinguish envelope stimuli resulting from movement from those that instead result from social interactions. We discuss the implications of our results for neural coding of envelopes and propose that behavioral responses to motion and social envelopes are mediated by different neural circuits in the brain.

Simultaneously-evoked auditory potentials (SEAP): A new method for concurrent measurement of cortical and subcortical auditory-evoked activity

Recent electrophysiological work has evinced a capacity for plasticity in subcortical auditory nuclei in human listeners. Similar plastic effects have been measured in cortically-generated auditory potentials but it is unclear how the two interact. Here we present Simultaneously-Evoked Auditory Potentials (SEAP), a method designed to concurrently elicit electrophysiological brain potentials from inferior colliculus, thalamus, and primary and secondary auditory cortices. Twenty-six normal-hearing adult subjects (mean 19.26 years, 9 male) were exposed to 2400 monaural (right-ear) presentations of a specially-designed stimulus which consisted of a pure-tone carrier (500 or 600 Hz) that had been amplitude-modulated at the sum of 37 and 81 Hz (depth 100%). Presentation followed an oddball paradigm wherein the pure-tone carrier was set to 500 Hz for 85% of presentations and pseudo-randomly changed to 600 Hz for the remaining 15% of presentations. Single-channel electroencephalographic data were recorded from each subject using a vertical montage referenced to the right earlobe. We show that SEAP elicits a 500 Hz frequency-following response (FFR; generated in inferior colliculus), 80 (subcortical) and 40 (primary auditory cortex) Hz auditory steady-state responses (ASSRs), mismatch negativity (MMN) and P3a (when there is an occasional change in carrier frequency; secondary auditory cortex) in addition to the obligatory N1-P2 complex (secondary auditory cortex). Analyses showed that subcortical and cortical processes are linked as (i) the latency of the FFR predicts the phase delay of the 40 Hz steady-state response, (ii) the phase delays of the 40 and 80 Hz steady-state responses are correlated, and (iii) the fidelity of the FFR predicts the latency of the N1 component. The SEAP method offers a new approach for measuring the dynamic encoding of acoustic features at multiple levels of the auditory pathway. As such, SEAP is a promising tool with which to study how relationships between subcortical and cortical processes change through early development and auditory learning as well as by hearing loss and aging.

Adaptive Duplexing for Transceivers Supporting Aggregated Transmissions

Wireless systems employing frequency-division duplexing (FDD) must use duplexing filters to isolate the sensitive receiver from its own strong transmission. The number of filters in the duplexer is equal to the total number of aggregated transmit and receive bands. These filters are nontunable; therefore, a separate duplexer is required for each combination of operating bands. This paper presents an adaptive duplexer architecture capable of handling more than one receiver channel and tunable over a wide frequency range. The structure uses a combination of a low-isolation device with multiple analog canceling loops controlled by a normalized least mean squares (N-LMS) algorithm to track changes in signal leakage. The control is a multiple-input–multiple-output (MIMO) problem. This paper shows that modeling the inverse plant can orthogonalize the problem and dramatically improve convergence times with reduced complexity over previous search algorithms. Low-power pseudonoise (PN) pilot signals are proposed to detect and cancel the transmitter noise. Simulations show that 50 dB of isolation is possible with 20-MHz Long-Term Evolution (LTE)-like channels. Convergence takes 80 iterations (10 ms) from cold or 15 iterations (1.5 ms) for changes in carrier frequency or antenna loading.

Fast carrier recovery in FHSS systems with DDS based Costas loop

Owing to fast change of carrier frequency, the usageof coherent demodulation methods in Frequency-Hopping SpreadSpectrum (FHSS) communication systems is limited by thecoherent state acquisition performed by the local oscillator. Toget around this difficulty, it is needed to implement the circuitwithin the FHSS system that is able to rapidly generate acoherent carrier. The work presented in this paper proposes arealization of Costas loop based on a combination of DirectDigital Synthesis (DDS), (Temperature-Compensated) Voltage-Controlled Oscillator ((TC)VCXO), and Phase-Locked Loop(PLL), which in particular enables a short period (less than 100μs) required for a local oscillator to reach the coherent state. Theimplemented model is thoroughly described with measurementsresults also provided.

Study on a New Type of HVDC Flexible Digital Pulse Width Modulated Carrier Frequency Selection

For multi_level multi_module in the flexible HVDC converter (MMC) module capacitor control algorithm is commonly based on nearest voltage level modulation (NLM), this algorithm requires the decimal part of the input sine wave for analog-to-digital conversion by digital signal (digital pulse modulation, referred to as DPWM),in the choice of hysteretic DPWM control signal is better, if the input triangle carrier wave frequency selection is not good, in each digital signal level will cause the output frequency of DPWM is not stable, some DPWM frequency is too high, and some DPWM has no output. In order to solve this problem, to meet the requirements of control precision, the carrier frequency change DPWM triangular wave, the output ideal control signal, the output control signal is analyzed, put forward how to carry out DPWM frequency selection. Through the simulation certified the feasibility of this method, the control method of downloading to the field programmable gate array (FPGA) chip, the results of the actual control operation show that this method can optimize the control of flexible HVDC.

Study on Carrier Frequency Control of AC Servo System Based on SVPWM

In this paper, the synthesis principle and realization way of voltage space vector in three-phase AC servo systems base on SVPWM are analyzed firstly; After that, the constraint relation between carrier frequency and all factors of operation conditions, and the theoretical relation of system restrained under the condition of high carrier frequency and low carrier frequency are deduces; At last, a carrier frequency modulation scheme based on the theoretical relation to make carrier frequency change with operation conditions is proposed in order to take full advantage of power devices and improve system performance. Experimental results show that the proposed scheme is feasible and effective.

Simultaneously evoked auditory potentials: A novel paradigm for measuring auditory-evoked electroencephalographic activity at successive levels of the auditory neuraxis

Recent electrophysiological work has evinced a capacity for plasticity in subcortical auditory nuclei in adults [Skoe and Kraus (2010)]. Similar plastic effects have been measured in cortically generated auditory potentials [e.g., Bosnyak et al. (2007); Näätänen (2008)], but it is unclear how the two interact. Here we present simultaneously evoked auditory potentials (SEAP), a novel paradigm designed to concurrently elicit electrophysiological brain potentials (EEG) from inferior colliculus (IC), thalamus, and primary and secondary auditory cortices. We use a specially designed stimulus consisting of a carrier frequency (500 Hz), amplitude-modulated at the sum of 37 and 81 Hz (depth 100%). We have shown that it elicits a 500 Hz frequency-following response (FFR; generated in IC), 81 (subcortical), and 37 (primary auditory cortex) Hz steady state responses, and mismatch negativity (when there is an occasional change in carrier frequency; secondary auditory cortex). Furthermore, cortical and subcortical processes are linked as the amplitude of the FFR predicts the amplitudes of the 37 and 81 Hz responses. SEAP offers a new window into the dynamics of encoding along the auditory pathway as well as a new and inexpensive tool with which to measure plasticity at multiple levels of the auditory neuraxis in individuals.

Efficient Transmission of Information using Transmission Code along FHSS

Spectrum is a modulation technique in which a signal is transmitted on a considerable larger bandwidth than the frequency contents of the original information. In other words, the signal of particular bandwidth is intentionally spread in the frequency domain, resulting in a signal having wider bandwidth. Here the minimum new bandwidth is much larger than the minimum required frequency spectrum. Frequency Hoping Spread Spectrum (FHSS) is one of the common forms/techniques of the Spread Spectrum, in which frequency is not remained fixed to the specified band of the frequency. Here the carrier frequency changes from one frequency to the other at every instant of time. Normally carrier frequency changes thousands time in a second. In FHSS synchronization of transmitter and receiver is necessary. In case, if the receiver is not synchronized with transmitter due to any reason, the recovery of the original information from its spread spectrum is merely impossible. To overcome this problem we propose a technique in which a code is combined and sent with the modulated signal before using the FHSS technique. Using this transmission code we can synchronize the receiver with transmitter at any instant of time. This proposed work is implemented and analyzed using MATLAB Simulation.

Male field cricket song reflects age, allowing females to prefer young males

Sexual selection often involves female preference for males of a certain age, and a body of theory predicts preference for old males. We measured a comprehensive set of traits from the acoustic sexual display of male field crickets, Gryllus bimaculatus, and found that nearly all song traits changed predictably as males aged, involving a general slowing down of the wing movements during song production. Our female preference experiments indicated a strong and repeatable preference for the songs of young males, contradicting the existing literature, which argues that female crickets prefer older males on the basis of changes in song carrier frequency. Rather, female preference for young male song was determined by its high energetic quality. We develop the ‘old flight muscle’ hypothesis, arguing that age-related degradation of stridulatory muscle performance is likely to result in the observed changes with age. Secondary sexual characters may be subject to oxidative somatic degradation suggesting that, when males provide only sperm, females should prefer the sexual displays of young males. Our results support new modelling approaches and a growing body of empirical evidence suggesting that old males are not always preferred by females.

Neuromagnetic auditory steady-state responses to amplitude modulated sounds following dichotic or monaural presentation

The goal of the present study was to further our understanding of how attention directed to carrier frequency changes in amplitude-modulated tones (AM) affects the auditory steady-state response (ASSR). ASSR in the 40-Hz range were recorded in 15 adults using the frequency tagging method while subjects detected a carrier frequency change in amplitude-modulated tones. Spectral and temporal domain analyses were performed to examine the effect on response amplitudes during attending to the tones compared to ignoring them for both monaural and dichotic stimulations. Larger responses were found in the hemisphere contralateral to the stimulated ear. Binaural suppression for ipsilateral input was found in both hemispheres. Time series of the source waveforms were calculated from equivalent current dipoles and showed a 2Hz beat for the dichotic presentation. Attention to carrier frequency change was significant only during dichotic presentation where larger right hemisphere responses were found at the onset of carrier change. Attending to carrier frequency change in stimulation enhances the right hemisphere ASSR amplitude for dichotic stimulation. The possibility of tagging frequency specific responses up to auditory cortex makes the ASSR approach interesting for studying hearing impairment mechanisms, integrity of auditory structures and attention.

Modulation of auditory evoked responses to spectral and temporal changes by behavioral discrimination training

BackgroundDue to auditory experience, musicians have better auditory expertise than non-musicians. An increased neocortical activity during auditory oddball stimulation was observed in different studies for musicians and for non-musicians after discrimination training. This suggests a modification of synaptic strength among simultaneously active neurons due to the training. We used amplitude-modulated tones (AM) presented in an oddball sequence and manipulated their carrier or modulation frequencies. We investigated non-musicians in order to see if behavioral discrimination training could modify the neocortical activity generated by change detection of AM tone attributes (carrier or modulation frequency). Cortical evoked responses like N1 and mismatch negativity (MMN) triggered by sound changes were recorded by a whole head magnetoencephalographic system (MEG). We investigated (i) how the auditory cortex reacts to pitch difference (in carrier frequency) and changes in temporal features (modulation frequency) of AM tones and (ii) how discrimination training modulates the neuronal activity reflecting the transient auditory responses generated in the auditory cortex.ResultsThe results showed that, additionally to an improvement of the behavioral discrimination performance, discrimination training of carrier frequency changes significantly modulates the MMN and N1 response amplitudes after the training. This process was accompanied by an attention switch to the deviant stimulus after the training procedure identified by the occurrence of a P3a component. In contrast, the training in discrimination of modulation frequency was not sufficient to improve the behavioral discrimination performance and to alternate the cortical response (MMN) to the modulation frequency change. The N1 amplitude, however, showed significant increase after and one week after the training. Similar to the training in carrier frequency discrimination, a long lasting involuntary attention to the deviant stimulus was observed.ConclusionWe found that discrimination training differentially modulates the cortical responses to pitch changes and to envelope fluctuation changes of AM tones. This suggests that discrimination between AM tones requires additional neuronal mechanisms compared to discrimination process between pure tones. After the training, the subjects demonstrated an involuntary attention switch to the deviant stimulus (represented by the P3a-component in the MEG) even though attention was not prerequisite.

Controlling DC–DC converters by chaos-based pulse width modulation to reduce EMI

In this paper, periodic and chaotic behaviors of DC–DC converters under certain parametric conditions are simulated, experimentally verified, and analyzed. Motivated by the work of J.H.B. Deane and D.C. Hamill in 1996, where chaotic phenomena are useful in suppressing electromagnetic interference (EMI) by adjusting the parameters of the DC–DC converter and making it operate in chaos, a chaos-based pulse width modulation (CPWM) is proposed to distribute the harmonics of the DC–DC converters continuously and evenly over a wide frequency range, thereby reducing the EMI. The output waves and spectral properties of the EMI are simulated and analyzed as the carrier frequency or amplitude changes with regard to different chaotic maps. Simulation and experimental results are given to illustrate the effectiveness of the proposed CPWM, which provides a good example of applying chaos theory in engineering practice.

Phase dynamics in the 40-Hz auditory steady state response

The phase of the 40-Hz auditory steady-state response (SSR) evoked by amplitude-modulated tones and recorded by MEG decreases monotonically with increasing carrier frequency, shifting about 6.25 ms or 90° over the range 250–4000 Hz. This phase shift has been attributed to propagation delays along the basilar membrane. Here we report that the slope of the SSR phase/carrier frequency characteristic is not invariant but depends on contextual factors relating to stimulus presentation. When steady-state stimuli were presented continuously with a random change to one of four carriers occurring every second, the phase difference between 500 and 1000 Hz was amplified by a factor of 2.5 compared to when the same frequencies were presented without shifting (baseline). Changing carrier frequencies in a predictable fixed order once per second resulted in a phase separation 1.6 times larger than baseline. We also tested whether a carrier frequency change was required to generate this wider phase separation. We presented continuous 15 min blocks at constant carrier frequencies of 500 or 1000 Hz, interrupted regularly once per second by increasing the amplitude of one modulation cycle. Once about every three seconds the enhancement occurred in only one ear, yielding a distinctive percept (target). The phase difference between 500 and 1000 Hz increased by 1.54 compared to baseline, regardless of whether the subject was attending to the target. Taken together, these results suggest that any disturbance in an on-going steady stimulus is sufficient to change the phase of the SSR for a period of time lasting on the order of several seconds or longer. The mechanisms responsible are unknown although a contribution of cortical dynamics to SSR phase is implied.

Concurrent Encoding of Frequency and Amplitude Modulation in Human Auditory Cortex: MEG Evidence

A natural sound can be described by dynamic changes in envelope (amplitude) and carrier (frequency), corresponding to amplitude modulation (AM) and frequency modulation (FM), respectively. Although the neural responses to both AM and FM sounds are extensively studied in both animals and humans, it is uncertain how they are corepresented when changed simultaneously but independently, as is typical for ecologically natural signals. This study elucidates the neural coding of such sounds in human auditory cortex using magnetoencephalography (MEG). Using stimuli with both sinusoidal modulated envelope (f(AM), 37 Hz) and carrier frequency (f(FM), 0.3-8 Hz), it is demonstrated that AM and FM stimulus dynamics are corepresented in the neural code of human auditory cortex. The stimulus AM dynamics are represented neurally with AM encoding, by the auditory steady-state response (aSSR) at f(AM). For sounds with slowly changing carrier frequency (f(FM) <5 Hz), it is shown that the stimulus FM dynamics are tracked by the phase of the aSSR, demonstrating neural phase modulation (PM) encoding of the stimulus carrier frequency. For sounds with faster carrier frequency change (f(FM) > or = 5 Hz), it is shown that modulation encoding of stimulus FM dynamics persists, but the neural encoding is no longer purely PM. This result is consistent with the recruitment of additional neural AM encoding over and above the original neural PM encoding, indicating that both the amplitude and phase of the aSSR at f(AM) track the stimulus FM dynamics. A neural model is suggested to account for these observations.

Detection for high resolution radars

In this paper we discuss detection problems for a high resolution radar. Fluctuation in the target radar cross section usually decreases the probability of detection. However, through integration of cells within range profiles of a high resolution radar, variation of the integrated magnitude with respect to the change of carrier frequency and target aspect becomes much smaller, and this is helpful for improving the probability of detection. Two detection algorithms, the cell integration method and the correlation method, for a high resolution radar are proposed, and their detection performances are compared with that obtained by a conventional low resolution radar. Some theoretical formulations are developed. Simulation results show the effectiveness of the proposed algorithms.