Narrowband Waveform Research Articles

Communications and High-Precision Positioning (CHP2): Hardware Architecture, Implementation, and Validation.

Spectral congestion and modern consumer applications motivate radio technologies that efficiently cooperate with nearby users and provide several services simultaneously. We designed and implemented a joint positioning-communications system that simultaneously enables network communications, timing synchronization, and localization to a variety of airborne and ground-based platforms. This Communications and High-Precision Positioning (CHP2) system simultaneously performs communications and precise ranging (<10 cm) with a narrow band waveform (10 MHz) at a carrier frequency of 915 MHz (US ISM) or 783 MHz (EU Licensed). The ranging capability may be extended to estimate the relative position and orientation by leveraging the spatial diversity of the multiple-input, multiple-output (MIMO) platforms. CHP2 also digitally synchronizes distributed platforms with sub-nanosecond precision without support from external systems (GNSS, GPS, etc.). This performance is enabled by leveraging precise time-of-arrival (ToA) estimation techniques, a network synchronization algorithm, and the intrinsic cooperation in the joint processing chain that executes these tasks simultaneously. In this manuscript, we describe the CHP2 system architecture, hardware implementation, and in-lab and over-the-air experimental validation.

Empirical mode decomposition approach for delineating gas-hydrates and free gas in Mahanadi offshore, eastern Indian margin

Empirical mode decomposition (EMD) is an effective tool for signal analysis that splits the data into individual modes, called the intrinsic mode functions, which are associated with symmetric and narrow-band waveform ensuring that the instantaneous frequencies are smooth and positive. However, some negative features encumber its direct application namely the mode mixing and splitting, aliasing and endpoint artefacts. Two variants, ensemble EMD (EEMD) and complete ensemble EMD (CEEMD) have been recently introduced to overcome these problems. We intend to show the application of the EMD for demarcating the zones of gas-hydrates and free-gas bearing sediments. Gas-hydrates are ice-like crystalline substances that occur in shallow sediments along the outer continental margins and in the permafrost regions, and are considered as viable major future energy resources of the world. Gas-hydrates in marine environment are generally identified by an anomalous reflector, known as the bottom simulating reflector, on seismic section. The present study demonstrates that the EMD can be effectively utilised in demarcating the zones of gas-hydrates and free-gas bearing sediments with a field example in the Mahanadi basin of the eastern Indian margin.

Ultrahigh-factor frequency multiplication based on optical sideband injection locking for broadband linear frequency modulated microwave generation

In this paper, we propose and demonstrate a novel photonics-enabled frequency multiplication system with an ultrahigh multiplication factor (MF) for broadband linear frequency modulated (LFM) microwave generation. A pair of distributed feedback (DFB) lasers are injection-locked to two optical sidebands with different orders, which are excited by a narrow-band LFM waveform with a frequency range of 2∼3 GHz. Frequency-multiplied LFM waveforms are generated by beating the two DFB outputs. Thanks to the injection locking, the frequency-multiplied signals have excellent spurious suppression and linearity. The measured spurious suppression ratio exceeds 21.4 dB and the linearity is better than 1 × 10−5. The MF reconfigurability and the central frequency tunability are also demonstrated. A series of 20-fold frequency-multiplied LFM waveforms with different central frequencies and a 30-fold frequency-multiplied signal with a frequency range from 16 GHz to 46 GHz are generated. Moreover, a feedback setup is employed to stabilize the waveform phase against environmental interferences. The measured standard deviation of the remaining phase jitter is around 5.5 ∘ .

A novel hybrid narrowband/wideband networking waveform physical layer for multiuser multiband transmission and reception in software defined radio

Increasing demands of adaptability and reconfigurability impose many challenges on the design of Software Defined Radio (SDR) waveforms for highly heterogeneous wireless networks. Usually, narrowband waveforms provide robustness and work for longer distances but lack in providing higher throughput, whereas wideband waveforms provide much higher throughput but they are not much robust and operate for smaller distances. A heterogeneous SDR network having diverse Quality of Service (QoS) and range requirements, and channel conditions cannot fully rely on one of the narrowband or wideband waveform. In this paper, a novel hybrid narrowband/wideband networking waveform physical layer is proposed. The proposed waveform is based on simultaneous transmission and reception of signals having multiple bandwidths through minimal changes in the existing analog wideband front end. A digital front end architecture is proposed where sample rate conversion and channelization of multiple signals at the digital front end formulate a composite signal which is then transmitted by using the wideband RF front end settings of a wideband waveform. At the receiver, the composite signal is received by using the wideband RF front end configured to wideband mode. Individual downconversion and filtering of each of the respective signal is done digitally. In this way, multiple signals having bandwidths as per their QoS and range requirements can be transmitted/received through the same wideband front end. As a proof of concept, the proposed idea is validated on actual SDR platform by taking actual dumps from FPGA and DSP. The presented results show the viability of the proposed hybrid SDR waveform.

Using of New Narrowband Waveforms to Ensure Proper Operation of Command and Communication Systems

Abstract Accomplishment of basic services implementation with specific quality is one of the main challenges of the command and communication systems for modern maritime safety and defense. The specificity of the marine environment imposes the use of narrowband HF (High Frequency) and VHF (Very High Frequency) radio communication devices which are capable to implement IP transmission. This paper presents the requirements for the HF and VHF radio systems according to the IP protocol requirements. At the beginning basic properties of narrowband HF and VHF waveforms in context of their operational scenarios has been described. Then results of experimental research (implementation of narrowband services — voice and data) has been presented. Finally further research directions with contribution of the authors, in NATO working groups related to the development of NBWF (Narrowband Waveform) for coalition communication has been presented.

Effect of vibration sense by frequency characteristics of impact vibration for residential floor

AbstractIn this research, we examined the effects that the frequency characteristics of impact vibration in a residential floor have on the vibration sense of humans. We obtained the following results: (i) a frequency of 30 Hz or more affects the vibration sense of humans; (ii) the influence of the broadband waveform on the vibration sense of humans is larger than that of the narrowband waveform; and (iii) for the broadband waveform but not for the narrowband, even a small vibration of approximately 4‐5 dB is perceptible.

Waveform Modeling and Generation Using Hierarchical Recurrent Neural Networks for Speech Bandwidth Extension

This paper presents a waveform modeling and generation method using hierarchical recurrent neural networks (HRNN) for speech bandwidth extension (BWE). Different from conventional BWE methods which predict spectral parameters for reconstructing wideband speech waveforms, this BWE method models and predicts waveform samples directly without using vocoders. Inspired by SampleRNN which is an unconditional neural audio generator, the HRNN model represents the distribution of each wideband or high-frequency waveform sample conditioned on the input narrowband waveform samples using a neural network composed of long short-term memory (LSTM) layers and feed-forward (FF) layers. The LSTM layers form a hierarchical structure and each layer operates at a specific temporal resolution to efficiently capture long-span dependencies between temporal sequences. Furthermore, additional conditions, such as the bottleneck (BN) features derived from narrowband speech using a deep neural network (DNN)-based state classifier, are employed as auxiliary input to further improve the quality of generated wideband speech. The experimental results of comparing several waveform modeling methods show that the HRNN-based method can achieve better speech quality and run-time efficiency than the dilated convolutional neural network (DCNN)-based method and the plain sample-level recurrent neural network (SRNN)-based method. Our proposed method also outperforms the conventional vocoder-based BWE method using LSTM-RNNs in terms of the subjective quality of the reconstructed wideband speech.

Cognitive Radio as the Facilitator for Advanced Communications Electronic Warfare Solutions

Throughout the 1990s, Software Defined Radio (SDR) technology was viewed almost exclusively as a solution for interoperability problems between various military standards, waveforms and devices. In the meantime, Cognitive Radio (CR) --- a novel communication paradigm which embodies SDR with intelligence and self-reconfigurability properties --- has emerged. Intelligence and on-the-fly self-reconfiguration abilities of CRs constitute an important next step in the Communications Electronic Warfare, as they may enable the jamming entities with the capabilities of devising and deploying advanced jamming tactics. Similarly, they may also aid the development of the advanced intelligent self-reconfigurable systems for jamming mitigation. This work outlines the development and implementation of the Spectrum Intelligence algorithm for Radio Frequency (RF) interference mitigation. The developed system is built upon the ideas of obtaining relevant spectrum-related data by using wideband energy detectors, performing narrowband waveform identification, extracting the waveforms' parameters and properly classifying the waveforms. All relevant spectrum activities are continuously monitored and stored. Coupled with the self-reconfigurability of various transmission-related parameters, Spectrum Intelligence is the facilitator for the advanced interference mitigation strategies. The implementation is done on the Cognitive Radio test bed architecture which consists of two military Software Defined Radio terminals, each interconnected with the computationally powerful System-on-Module.

Narrowband photon pair generation and waveform reshaping

In this article, we review on narrowband photon pairs produced in nonlinear crystals, and especially in atomic ensembles. In atomic ensembles, “write-read” process in pulse mode and spontaneous four-wave mixing process (SFWM) in continuous mode are two popular photon pair generation schemes. We specifically discuss the experimental works with continuous SFWM scheme in cold atomic ensembles. Photon pairs produced in these systems are characteristic of controllable long coherence time, and therefore are accessible with direct temporal modulation. We elaborate on the recent techniques on modulation and waveform reshaping of narrow-band paired photons.

On designing bandwidth constrained mobile tactical networks for complex terrains

This article describes a design approach adopted in developing networking capabilities for NATO's next generation narrowband waveform tactical radios. Providing improved link spectral efficiencies and maintaining long communication range, these new radios enable an opportunity to utilize mult-hop networking features that have been developed for mobile ad hoc networks during the past decade. The challenge, however, is to select and devise networking solutions of predictable and robust performance. For this purpose, a network-science- based approach is taken to first capture and understand the fundamental network properties exhibited when connecting tactical radios. This application of an empirical foundation has proven effective in discovering the dynamic network topological behavior and connectivity attributes. The results illustrate critical implications on the network protocol design and provide important guidance on selecting required networking solutions.

Single-channel time reversal with Lanczos iterations.

Recent investigations of array-based time reversal techniques employing Lanczos iterations have demonstrated convergence properties superior to equivalent methods using power iterations [A. A. Oberai et al., “Efficient time reversal by Lanczos iterations,” J. Acoust. Soc. Am. 123, 3596 (2009)]. In numerical scattering simulations, time reversal techniques developed for a single-channel transducer are applied to study echoes from a thin-walled spherical shell. When power iterations are employed, a narrowband waveform corresponding to the dominant scattering mode of the target is selected. Lanczos iterations converge to this waveform in fewer transmissions and simultaneously identify additional higher-order target scattering features. The performance of both techniques is studied in the presence of varying levels of stochastic and deterministic noise. [Work supported by the Office of Naval Research.]

A numerical study of rough interface reverberation suppression, clutter elimination and target resonance excitation in heterogeneous media with single channel iterative time reversal.

The presence of echo returns from the rough interface of two layered medium, and the clutter of volume scattering hinders the detection of target buried in heterogeneous media. The situations are often raised in ultrasonic breast tumor diagnosis and underwater acoustic buried mine detection. This work investigates the application of monostatic single channel iterative time reversal in mitigating the difficulties with a numerical study. Simulations based on pseudospectral finite-difference time-domain method are performed with a sphere buried in the heterogeneous media of lower layer, a transmitter is situated at the upper homogeneous domain, and the interface position is normally distributed. A wideband signal is launched to initiate the process, and the time-reversed echo received at same position is emanated as renewed interrogation pulse for next iteration. Some field snapshots are taken and the echo is recorded in each iteration. The results illustrate as the number of iteration increases, small volume scattering is eliminated, and rough interface reverberation is suppressed relatively. The echoes will converge to a narrowband waveform corresponding to an object’s dominant resonance mode. The detection of target is achieved by exploiting this important acoustic signature. [Work supported by the CAS Innovation Fund.]

Laboratory investigations of the detection and characterization of buried targets by iterative, single‐channel time reversal

Due to the dynamic nature of the shallow water environment, targets are often buried beneath the seafloor, hindering their detection and identification by acoustic methods. Using iterative time reversal with a single channel transducer [Waters et al., J. Acoust. Soc. Am. 122, 3023 (2007)], the monostatic return from a buried resonant target is enhanced, yielding convergence to a narrowband waveform characteristic of the dominant mode in the target's scattering response. Scaled laboratory experiments are performed with a broadband (Q̃2) transducer operating in the 0.5‐2 MHz frequency range. Solid and evacuated metallic spheres used as targets are buried beneath a layer of simulated sediment. Images generated by scanning the transducer laterally in two dimensions over an area of sediment containing multiple targets show enhancement of different modes in a single target's scattering response and test the selectivity between targets of differing type. Experiments with the transducer positioned at normal and non‐normal incidence, quantify the enhancement in the signal‐to‐noise ratio of target returns as a function of window size and position. [Work supported by The Office of Naval Research and the Center for Subsurface Sensing and Imaging Systems (NSF ERC Award No. EEC‐9986821).]

On the use of a suppression filter for CDMA overlay

This paper is concerned with a direct-sequence code-division multiple-access (DS-CDMA) system operating over a Rayleigh fading channel and sharing a common spectrum with a narrow-band waveform. A suppression filter at the receiver is employed to reduce the narrow-band interference. We evaluate the average up-link bit error rate (BER) performance and investigate how the performance is influenced by various parameters, such as the number of taps of the suppression filter, the number of multiple-access users, the ratio of narrow-band interference bandwidth to the spread-spectrum bandwidth, the interference power to signal power ratio, the ratio of the offset of the interference carrier frequency from the spread-spectrum carrier frequency to the half spread-spectrum signal bandwidth, and so on.

Nonparametric narrowband wavefront estimation from wavefront gradients

The wavefield sampled by a two-dimensional (2-D) planar array can he characterized by a delayed signal. This correspondence investigates the problem of the nonparametric estimation of the delay function (or wavefront) when the waveform is narrowband. The wavefront is estimated by integrating the local estimates of the differential time of delay (TOD) of the waveform between neighboring sensors. The ambiguity of the TOD estimator for the narrowband waveform can be conveniently limited by the a priori search interval for the cross correlation method. The reconstruction of the wavefronts is formulated as a least squares problem that is solved iteratively. Errors of the solution are quantified, and the contribution caused by noise is shown to be negligible.

Cellular CDMA overlay systems

The CDMA network is considered to share a common spectrum with a strong narrowband microwave user. An interference suppression filter at each CDMA receiver is employed to reject the narrowband waveform. Gaussian approximation is assumed for the total interference, which includes fading interference, self interference, Gaussian noise, narrowband interference, multipath and multiple access interference.

Interference suppression for CDMA overlay of a narrowbandwaveform

The performance of CDMA networks which overlay a narrowband signal to increase spectral efficiency is presented. Such systems employ interference suppression filters in the CDMA receivers to minimise the interference caused by the narrowband waveform.

CDMA overlay situations for microcellular mobile communications

Direct sequence code division multiple access communications is a promising approach to cellular mobile communications, which operates in an environment characterized by multipath Rician fading. In this paper, the CDMA network is assumed to share common spectrum with a narrowband microwave user. Because of the presence of the narrowband waveform, an interference suppression filter at each CDMA receiver is employed to reject the narrowband interference. The problem of interference from adjacent cells is also considered. Average power control is assumed to combat the near/far problem, and multipath diversity, in conjunction with simple interleaved channel coding, is considered for improving the performance of the CDMA system. >

Recent progress in the application of wavelets in surveillance systems

We briefly discuss two approaches for enhancing the resolution enhancement of range-Doppler images (including synthetic aperture radar and inverse synthetic aperture radar images). The first approach can be used in conjunction with current radar systems that use a fixed narrowband waveform to acquire target data. It measures Doppler shifts more accurately than the traditional fast Fourier transform based techniques. It performs well in low signal-to-clutter regimes regardless of the statistical structure of the clutter. The second technique assumes that the radar can transmit different waveforms that are matched to the imaging task under consideration. It is based on the fact that the most accurate reconstruction of a range-Doppler target density function from <i>N</i> waveforms and their echoes is obtained by transmitting the singular functions corresponding to the <i>N</i> largest singular values of two kernels derived from the target density. We discuss two strategies for selecting the radar waveforms. The first strategy uses fixed waveforms that act as approximate singular functions for the kernels corresponding to wide classes of target densities. The second strategy adaptively selects the transmitted waveforms by solving a simultaneous target classification and image reconstruction problem.

Some Properties and Effects of Reverberation in Acoustic Surveillance

Following the work of Van Trees,[1] the effect of wide-sense stationary clutter on signal detectability with a matched filter is determined. The improvement to be gained by a high time-bandwidth product in the transmitted waveform for the detection of low-velocity targets is clearly shown. The additional noise contributed by the clutter is reduced by a factor equal to the time-bandwidth product. This reducing effect occurs provided that the transmitted waveform is adjusted properly. The optimum transmitted waveform for detection of low-velocity targets turns out to be one whose energy density spectrum is flat over the bandwidth of interest. This derivation is made by a simple application of Schwarz's inequality rather than the application of the calculus of variations that was done by Manasse.[14] Computations were made of the loss encountered by a narrow-band single-frequency waveform and by a wide-band linear FM waveform, each used in a matched-filter detector. The contrast is especially marked for very low target speeds where the narrow-band waveform is very bad. Its loss drops off sharply with target speed while the loss of the wide-band waveform drops off very slowly in comparison. Beyond a certain small target speed, the narrow-band loss is negligible. However, with enough bandwidth, the wide-band waveform can be made to have acceptable loss at all target speeds.