Narrowband Processing Research Articles

Wideband off-grid direction-of-arrival estimation based on the improved finite rate of innovation method.

Off-grid direction-of-arrival estimation is a crucial research area in multi-sensor array signal processing to achieve accurate estimation in a finite sparse grid. However, current off-grid estimation methods primarily focus on narrowband processing, which may not be suitable for practical passive estimation scenarios where the targets of interest are wideband signals with various steering vectors and varying signal-to-noise ratios across frequency bins. First, we propose an improved weighting-based wideband joint finite rate of innovation algorithm to address this limitation. This algorithm extends the narrowband approach by approximating the wideband array data as multiple observations at the difference frequency using extended frequency difference weighting. Additionally, we propose an estimation method under non-ideal weighting conditions to mitigate bias caused by deviations in initial weight values through linear fitting of multiple estimation results obtained on a sparse grid. Simulation results demonstrate that our proposed algorithm outperforms existing methods by providing more accurate estimates and lower computational complexity for wideband off-grid multi-targets at low signal-to-noise ratio while unrestricted by grid limitations. Furthermore, experimental data collected from the South China Sea validate our proposed algorithm's effectiveness and superior performance for direction-of-arrival estimation of wideband off-grid targets.

Music Curriculum Research Using a Large Language Model, Cloud Computing and Data Mining Technologies

This paper presents a method to enhance the scientific nature of the music curriculum model by integrating a large language model, cloud computing and data mining technology for the analysis of the music teaching curriculum model. To maintain the integrity of the mixing matrix while employing the frequency hopping frequency, the paper suggests dividing the mixing matrix into a series of sub-matrices along the vertical time axis. This approach transforms wideband music signal processing into a narrowband processing problem. Additionally, two hybrid matrix estimation algorithms are proposed in this paper using underdetermined conditions. Furthermore, utilizing the estimated mixing matrix and the detected time-frequency support domain, the paper employs the subspace projection algorithm for underdetermined blind separation of music signals in the time-frequency domain. This procedure, along with the integration of the estimated direction of arrival (DoA), enables the completion of frequency-hopping network station music signal sorting. Extensive simulation teaching demonstrates that the music curriculum model proposed in this paper, based on a large language model, cloud computing and data mining technologies, significantly enhances the quality of modern music teaching.

The operating algorithm of the delay device processing time overlapped pulses in a matrix receiver

Matrix receiver from about the 1960s is used for wideband analysis of the signal environment (SE). Its use provides simultaneously a wide instantaneous analysis bandwidth, relatively high sensitivity, no signal gaps and the possibility of narrow-band processing of the output signal. However, there is a high probability of time-overlapping for pulses from pulse streams created by various radio emission sources in modern SE. When processing time-overlapped pulses in a classical matrix receiver, measurement ambiguities and abnormal errors occur. Therefore, multiple approaches are used to improve its efficiency in a complex SE. One such approach is based on installing a delay device to the wideband receiver's input. The principle of operation of the delay device consists of multiple signal transfers from the microwave range to the optical one and vice versa with the passage through fiber segments of various lengths. However, the operation algorithm of such a device has not been developed in detail. That's why our purpose is to substantiate and develop the algorithm for operating the delay device installed at the input of the matrix receiver to ensure the processing of time-overlapped pulses. In addition to the main algorithm for adapting the delay value to the pulse duration, we developed a nested algorithm for choosing a segment of the adjustable delay line. To store the pulse for the duration of processing by the receiver of previously received pulses, we developed a nested algorithm for executing the delay cycle. The use of the delay device operating following the proposed algorithm makes it possible to reduce the likelihood of measurement ambiguity and abnormal errors during the operation of the matrix receiver in the complex SE.

Underwater Localization via Wideband Direction-of-Arrival Estimation Using Acoustic Arrays of Arbitrary Shape.

Underwater sensing and remote telemetry tasks necessitate the accurate geo-location of sensor data series, which often requires underwater acoustic arrays. These are ensembles of hydrophones that can be jointly operated in order to, e.g., direct acoustic energy towards a given direction, or to estimate the direction of arrival of a desired signal. When the available equipment does not provide the required level of accuracy, it may be convenient to merge multiple transceivers into a larger acoustic array, in order to achieve better processing performance. In this paper, we name such a structure an “array of opportunity” to signify the often inevitable sub-optimality of the resulting array design, e.g., a distance between nearest array elements larger than half the shortest acoustic wavelength that the array would receive. The most immediate consequence is that arrays of opportunity may be affected by spatial ambiguity, and may require additional processing to avoid large errors in wideband direction of arrival (DoA) estimation, especially as opposed to narrowband processing. We consider the design of practical algorithms to achieve accurate detections, DoA estimates, and position estimates using wideband arrays of opportunity. For this purpose, we rely jointly on DoA and rough multilateration estimates to eliminate spatial ambiguities arising from the array layout. By means of emulations that realistically reproduce underwater noise and acoustic clutter, we show that our algorithm yields accurate DoA and location estimates, and in some cases it allows arrays of opportunity to outperform properly designed arrays. For example, at a signal-to-noise ratio of –20 dB, a 15-element array of opportunity achieves lower average and median localization error (27 m and 12 m, respectively) than a 30-element array with proper element spacing (33 m and 15 m, respectively). We confirm the good accuracy of our approach via emulation results, and through a proof-of-concept lake experiment, where our algorithm applied to a 10-element array of opportunity achieves a 90th-percentile DoA estimation error of 4 and a 90th-percentile total location error of 5 m when applied to a real 10-element array of opportunity.

이동하는 소음원 위치 추정을 위한 다양한 빔형성 기법 적용

Capabilities of several beamforming techniques are compared for estimating the position of a moving source. Beamforming has enabled to widen our perspective of aeroacoustics in wind tunnel experiments and has provided useful approach in array measurements. Meanwhile beamforming techniques have been developed in a way to improve estimation accuracy and to save ing effort at the same time. In order to achieve reasonable outcome from aeroacoustic measurement, it is important to identify the spectral characteristics of source and to select an appropriate beamformer. Though aeroacoustic sources normally generates broadband noises, many array signal processing have been focused on narrowband processing which makes calculation numerically efficient. However, calculation in frequency-domain requires selection of single frequency of interest which affects spatial resolution and sidelobe level as a consequence. To be able to localize broadband noise source, it is proposed to use broadband beamforming. The formulas implements the deletion of diagonal term from cross spectral matrix. In this study, trajectory of flying source emitting broadband noise was simulated and several beamformers are applied.

A new C-RAN architecture based on RF signal soft-switching

Coordinated multi-point (CoMP) is known to be one of the key technologies for long-term evolution (LTE)-advanced systems. CoMP technology can improve system capacity and the quality of wireless communication services for users in LTE networks. However, in practice, the actual performance of CoMP technology is limited by the switching capacity of the backhaul network among distributed base stations as well as its latencies. In this paper, we propose a new cloud radio access network architecture based on RF signal soft-switching to solve this problem. Furthermore, we introduce a narrow-band parallel processing technique on a common public radio interface in downlink and uplink to reduce the volume of data as well as the latencies in the transmission process among base band units and remote radio units. By combining theoretical analysis with computer simulations, we show that the technique is valid both for downlink and uplink, i.e., it does not degrade the performance of downlink and uplink propagation between BBU pool and user equipments. Moreover, the computational time of the narrow-band parallel processing technique is less than that of the standard technique.

A Reducing Relative Bandwidth Method Based on Digital up Converter

Apparently the comprehensive performance of array becomes impaired with the increasing of the relative bandwidth. In this paper, an algorithm based on Digital Up Converter (DUC) is proposed to reduce the relative bandwidth of the input broadband signal. The method works by changing the interelement spacing and sampling rate to carry the frequency spectrum of the input signal of array to higher frequency. When the carrier frequency is high enough, the broadband array signal processing will become a narrowband array signal processing, the narrowband array method can be used directly, and the computation could be reduced greatly. Simulation results and analysis confirm that the effect of reducing the relative bandwidth of the broadband signal is obvious and the proposed method is competent with any beamforming algorithm to form broadband patterns.

Environmentally corrected matched filter

Matched filtering is commonly used to process broadband active acoustic echoes providing higher levels of range resolution and reverberation noise suppression than can be realized through narrowband processing. Since theoretical processing gains are proportional to the signal bandwidth, it is typically desirable to utilize the widest band signals possible. However, as signal bandwidth increases, so do environmental effects that increase decorrelation between the received echo and the transmitted waveform. This loss of coherence often results in processing gains and range resolution much lower than theoretically predicted. Weiner filtering, commonly used in image processing to improve distorted and noisy photos, was investigated as an approach to correct for these environmental effects. This improved signal processing, environmentally corrected matched filter (ECMF), first uses a Wiener filter to estimate the environmental transfer function and then again to correct the received signal. This process can be viewed as a “smarter” inverse or whitening filter that optimally adjusts according to the signal to noise ratio across the spectrum. Sonar simulation toolset (SST) synthetic data and measured in-air data will be presented to illustrate the improved processing.

A Coherent PMI Estimation Scheme for Double Codebook

The double codebook structures are proposed and applied in LTE-advanced, which can track both long-term and short-term channel state information. In traditional incoherent estimation, precoding matrix indicators (PMI) estimation is performed on each individual subcarrier and some form of averaging procedure then follows to combine the results from individual narrow-band processing. As a result, if there is a large deviation in any estimates of a subcarrier, it will lead to a larger deviation in the final result. Thus incoherent PMI estimation has a poor performance in low signal to noise ratio. This paper introduces a new PMI feedback scheme for wideband sources with coherent signal subspace method. This new technique estimates PMI based on an approximately coherent combination of each subcarrier by a focusing matrix. Simulation results show that the coherent estimation scheme has a better throughput performance than the traditional incoherent estimation.

Development of an UHF RFID Chemical Sensor Array for Battery-Less Ambient Sensing

Battery-less ultrahigh frequency (UHF) radio frequency identification (RFID) tags coated by proper sensitive layers have been recently demonstrated capable to play as low-cost sensors of some volatile compounds. The issue of cross-sensitivity and the possibility to develop an array of differently coated sensors are, however, still completely open. This paper investigates, through an experimental campaign involving a general-purpose sensor-antenna transducer, the potentiality of functionalized tags in the UHF RFID band to sense a multiplicity of volatile compounds, as well as the cross-sensitivity effects of different coatings in array configuration. Four effective materials, such as Pedot:PSS, doped PSS, SWCNT, and PDAC, revealed a remarkable sensitivity to ammonia, ethanol, octane, and water. Wireless sensing may be hence performed by narrowband processing of the power response of the RFID tags as well as by the broadband extraction of features related to the resonance shift. It was finally observed how the inter-antenna coupling may affect the sensor capability of an array of UHF tags in term of increased cross-sensitivity.

Design and Characteristic Analysis of Multicarrier Chaotic Phase Coded Radar Pulse Train Signal

By introducing phase code into multicarrier orthogonal frequency division multiplex signal, the multicarrier phase coded (MCPC) radar signal possesses a good spectrum utilization rate and can achieve a good combination of narrowband and wideband processing. Radar pulse train signal not only reserves the high range resolution of monopulse signal, but also has the same velocity resolution performance as continuous wave signal does. In this study, we use the chaotic biphase code generated by Chebyshev mapping to conduct a phase modulation on MCPC pulse train so as to design two different types of multicarrier chaotic phase coded pulse train signal. The ambiguity functions of the two pulse train signals are compared with that of P4 code MCPC pulse train. In addition, we analyze the influences of subcarrier number, phase-modulated bit number, and period number on the pulse train’s autocorrelation performance. The low probability of intercept (LPI) performance of the two signals is also discussed. Simulation results show that the designed pulse train signals have a thumbtack ambiguity function, a periodic autocorrelation side lobe lower than P4 code MCPC pulse train, and excellent LPI performance, as well as the feature of waveform diversity.

A Robust Autofocusing Approach for Estimating Directions-of-Arrival of Wideband Signals

In this paper, we introduce a robust method for wideband DOA estimation which does not require any preliminary DOA estimation or calibration of the array during the whole estimating process with the performance similar to the autofocusing approach. Our method is based on the autofocusing approach and uses the ESPRIT algorithm during the narrowband processing stage. Meanwhile, we suggest the method of selecting the best focusing frequency which minimizes the mean square error.

Robust matched-field processing using a coherent broadband white noise constraint processor

Adaptive matched-field processing (MFP) is not only very sensitive to mismatch, but also requires the received sound levels to exceed a threshold signal-to-noise ratio. Furthermore, acoustic sources and interferers have to move slowly enough across resolution cells so that a full rank cross-spectral density matrix can be constructed. Coherent-broadband MFP takes advantage of the temporal complexity of the signal, and therefore offers an additional gain over narrow-band processing by augmenting the dimension of the data space. However, the sensitivity to mismatch is also increased in the process, since a single constraint is usually not enough to achieve robustness and the snapshot requirement becomes even more problematic. The white noise constraint method, typically used for narrow-band processing, is applied to a previously derived broadband processor to enhance its robustness to environmental mismatch and snapshot deficiency. The broadband white noise constraint theory is presented and validated through simulation and experimental data. The dynamic range bias obtained from the snapshot-deficient processing is shown to be consistent with that previously presented in the literature for a single frequency.

Coherent-broadband, white noise constraint, matched-field processing

Coherent-broadband matched-field processing takes advantage of the temporal complexity of the signal and, therefore, offers an increased gain over narrowband processing. However, the problem of mismatch is aggravated in adaptive versions such as the MVDR. One constraint is not enough to achieve robustness in such high-dimensional spaces. Some coherent algorithms also require a large number of snapshots, leading to ill-conditioned cross-spectral density matrices in the context of the required MVDR matrix inversions. The white noise constraint algorithm developed by Cox et al. [IEEE Trans. on Acoustics, Speech, and Sig. Proc. 35, 1365–1376 (1987)], and typically used for narrowband processing, is applied to some previously derived broadband processors to enhance their robustness. The broadband white noise constraint theory is presented and validated through simulation and experimental data. [Work supported by ONR.]

Discrete time-scale characterization of wideband time-varying systems

Wideband time-varying systems can be found in many applications, including underwater acoustics and ultra-wideband technologies. The time variation due to Doppler scaling effects, coupled with dispersive scattering due to multipath propagation, can severely limit the performance of wideband systems. Just as the discrete time-frequency model can efficiently improve narrowband processing, a discrete time-scale system characterization is important in processing wideband time-varying systems. In this paper, a time-scale model is proposed as a discrete characterization of wideband time-varying systems. This representation decomposes a wideband system output into discrete time shifts and Doppler scalings on the input signal, weighted by a smoothed and sampled version of the wideband spreading function. The proposed transform-based approach uses the Mellin transform that is inherently matched to scalings to geometrically sample the scale parameter and the Fourier transform to arithmetically sample the time-delay parameter. Using this proposed model, and by properly designing the signaling and reception schemes using wavelet techniques, a joint multipath-scale diversity can be achieved over a dyadic time-scale framework in wideband wireless systems. The simulation results demonstrate that, based on the proposed model, performance can be increased by exploiting the diversity intrinsically afforded by the wideband system.

Normalized Error Estimates for One-Third Octave Band Filter Processing

This paper summarizes numerically derived theoretical estimates of normalized random and normalized bias errors for one-third octave band filters applied to autoregressive processes of order two. It demonstrates that one-third octave band estimates of such processes may have substantial bias errors depending upon (1) frequency location of a true spectra peak relative to the center frequency of the one-third octave band filter and (2) half-power bandwidth of the true spectra. One-third octave band processing error is contrasted with narrowband processing error. It concludes that one-third octave band processing should be avoided whenever external information would indicate that the underlying time history data may have a narrowband character.

A non-recursive switched-capacitor filter implementation for narrow-band signal processing applications

This paper considers the implementation of nonrecursive switched-capacitor filters realized in transversal form for narrow-band signal processing. Nonideal effects, such as finite gain and bandwidth of the operational amplifiers and capacitance mismatches, are studied. In particular, analytical formulas are derived to predict effects of capacitance mismatches and amplifier finite gain-bandwidth product, which can be taken into account when dimensioning devices in an integrated circuit implementation, to make the filter less sensitive to process variations. Computer simulations and experimental results obtained in the laboratory are presented to verify the main theoretical results.

The degradation of higher order spectral detection using narrowband processing

In certain scenarios, higher order statistic (HOS)-based detectors exploiting the Gaussian noise rejection property of HOS have been shown to have performances superior to widely used second-order (SOS) techniques. However, a crucial limitation on these detectors that has not been addressed is a constraint on the processing bandwidth. We study the effects of commonly used narrowband processing on these detectors. As the processing bandwidth is decreased, we characterize the tradeoff between HOS and SOS detectors and demonstrate that the performance of HOS detectors degrades faster than that of SOS ones. We then consider distributed wideband detection by a bank of local narrowband detectors whose decisions are fused together. Given a fixed-bandwidth input signal, we show that as the number of local detectors increases, corresponding to a decreasing amount of bandwidth for each local detector, the performance of such a scheme using HOS local detectors degrades more quickly than a scheme using SOS ones.

Source localization with broad-band matched-field processing in shallow water

Acoustic source localization using matched-field processing is presented for multitone signals from the Shallow Water Evaluation cell Experiment 3 (SWellEX-3). The experiment was carried out in July 1994 west of Point Loma, CA, in 200 m of water of complex bathymetry. The multitone signal (ten tones between 50 and 200 Hz) was transmitted from an acoustic source towed at various depths over tracks which produced complex propagation paths to a vertical line array receiver. Broad-band and narrow-hand processing, localization, and tracking results are compared with each other and with independent estimates of source position. With narrow-band processing, mismatch between the data and the predicted signal replica of /spl sim/1 dB reduced the mainlobe to levels equal to or below the sidelobes. Incoherently averaging the processing output over the multiple tones reduced range/depth sidelobe levels, allowing accurate source localization and tracking.

Effect of reducing slow temporal modulations on speech reception

The effect of reducing low-frequency modulations in the temporal envelope on the speech-reception threshold (SRT) for sentences in noise and on phoneme identification was investigated. For this purpose, speech was split up into a series of frequency bands (1/4, 1/2, or 1 oct wide) and the amplitude envelope for each band was high-pass filtered at cutoff frequencies of 1, 2, 4, 8, 16, 32, 64, or 128 Hz, or infinity (completely flattened). Results for 42 normal-hearing listeners show: (1) A clear reduction in sentence intelligibility with narrow-band processing for cutoff frequencies above 64 Hz; and (2) no reduction of sentence intelligibility when only amplitude variations below 4 Hz are reduced. Based on the modulation transfer function of some conditions, it is concluded that fast multichannel dynamic compression leads to an insignificant change in masked SRT. Combining these results with previous data on low-pass envelope filtering (temporal smearing) [Drullman et al., J. Acoust. Soc. Am. 95, 1053-1064 (1994)] shows that at 8-10 Hz the temporal modulation spectrum is divided into two equally important parts. Vowel and consonant identification with nonsense syllables were studied for cutoff frequencies of 2, 8, 32, 128 Hz, and infinity, processed in 1/4-oct bands. Results for 12 subjects indicate that, just as for low-pass envelope filtering, consonants are more affected than vowels. Errors in vowel identification mainly consist of reduced recognition of diphthongs and of durational confusions. For the consonants there are no clear confusion patterns, but stops appear to suffer least. In most cases, the responses tend to fall into the correct category (stop, fricative, or vowel-like).