Transmitter-receiver Pair Research Articles

Secure Beamforming for Untrusted MISO Cognitive Radio Networks

In this paper, we study the secure beamforming design for a cognitive radio network (CRN), where a primary transmitter-receiver pair coexists with an untrusted secondary transmitter-receiver pair. Each pair constitutes a multiple-input single-output link. We consider an underlay scheme and a cooperative scheme. For the underlay scheme, the secondary user (SU) is allowed to transmit simultaneously in the presence of the primary transmission. For the cooperative scheme, the secondary transmitter acts as a relay to forward the secrecy information of the primary transmission in exchange for its own transmission. For both schemes, the SU is untrusted and considered a potential eavesdropper. Our goal is to minimize the total power consumption while satisfying the primary user's required secrecy rate and the SU's required information rate. Using suitable optimization tools, we design the jointly optimal secure beamforming for the underlay scheme and an alternative optimizing algorithm for the cooperative scheme. To further reduce the complexity, we also design suboptimal zero-forcing beamformers for both schemes. The simulation results verify the proposed schemes.

A 90-102 GHz CMOS based pulsed Fourier transform spectrometer: New approaches for in situ chemical detection and millimeter-wave cavity-based molecular spectroscopy.

We present a system level description of a cavity-enhanced millimeter-wave spectrometer that is the first in its class to combine source and detection electronics constructed from architectures commonly deployed in the mobile phone industry and traditional pulsed Fourier transform techniques to realize a compact device capable of sensitive and specific in situ gas detections. The instrument, which has an operational bandwidth of 90-102 GHz, employs several unique components, including a custom-designed pair of millimeter-wave transmitter and heterodyne receiver integrated circuit chips constructed with 65 nm complementary metal-oxide semiconductor (CMOS) techniques. These elements are directly mated to a hybrid coupling structure that enables free-space interaction of the electronics with a small gas volume while also acting as a cavity end mirror. Instrument performance for sensing of volatile compounds is highlighted with experimental trials taken in bulk gas flows and seeded molecular beam environments.

Performance Analysis of Joint Relay and Transmit–Receive Antenna Selection for Low Density Parity Check-Asynchronous Distributed Space Time Block Coded Cooperative Diversity System

In this work we propose a joint relay and transmit–receive antenna selection method for amplify and forward asynchronous distributed space time block coded (ADSTBC) system. To the LDPC coded signal received from the source at the relays, we apply linear dispersion codes which are optimized over the delay profile of the system to produce the ADSTBC. Selection of the best transmit–receive antenna pair between source and selected relays, and that of between the selected relays and destination is done on the basis of instantaneous signal to noise ratio (SNR) of the respective paths. The relays and transmit-receive antenna pairs are selected by maximizing the end-to-end instantaneous SNR. Performance analysis of the system is done on the basis of pair wise error probability and outage probability (Pout).

Post-processing of ultrasonic signals for the analysis of defects in wind turbine blade using guided waves

In this work, the most promising ultrasonic signal processing methods—discrete wavelet transform, variational mode decomposition and Hilbert transform—are applied for the analysis of disbond-type defects in the segment of wind turbine blade. Two disbond-type artificial defects having diameters of 81 and 25 mm were located on the main spar of wind turbine blade. The low-frequency ultrasonic system developed by Ultrasound Research Institute of the Kaunas University of Technology was used for the experimental investigation of wind turbine blade using guided waves and only one side of the blade segment was accessed. Two contact type ultrasonic transducers separated by 50 mm distance and fixed on a movable mechanical panel were used as a transmitter–receiver pair during the experiment for the ultrasonic signals recording up to the scanning distance of 250 mm with the scanning step of 1 mm. Both types of defects were marginally detected from the conventional experimental B-scan and therefore appropriate signal processing techniques were used to improve the accuracy of the analysis of defects. The discrete wavelet transform was combined with the amplitude detection method for estimating the size and location of defects. Finally, the variational mode decomposition is combined with the Hilbert transform to compare the instantaneous frequencies and amplitudes of the defect-free and defective signals as well as for the measurement of time-delays between the defect-free and defective signals.

Spectral Redundancy Compensation in Multi-Static Millimeter-Wave Imaging

This brief introduces a modified backprojection algorithm to compensate the effect of redundancy of captured data in spatial-fourier or ${k}$ -space domain for multi-static millimeter-wave imaging. The data measured by each transmitter-receiver pair is explained in ${k}$ -space domain and the redundancies are determined. Such redundancies act as an undesirable filter that distorts the appearance of the resulting image. Our goal is to modify SAR backprojection algorithm to address this problem, where extensive simulation and experimental results are also provided. Our measurements show a significant improvement in the overall quality and edge preservation in the reconstructed image of objects under the test through the proposed reconstruction algorithm.

Compressive sensing MTI processing in distributed MIMO radars

It is shown that the detection performance can be significantly improved using the recent technology of multiple-input multiple-output (MIMO) radar systems. This is a result of the spatial diversity in such systems due to the viewing of the target from different angles. On the other hand, the moving target indication (MTI) processing has long been known and applied in the traditional pulse radars to detect weak moving targets in the presence of strong clutter signals. The authors propose a procedure based on the compressive sensing idea, in order to apply the MTI processing in a MIMO radar with widely separated antennas. Although a clutter is included in the signal model and a different radar cross-section value for each transmitter-receiver pair is considered which makes the problem more complex, the complexity dimension is preserved as low as possible by converting the block sparse problem into a regular sparse problem.

DF Relayed Subcarrier FSO Links over Malaga Turbulence Channels with Phase Noise and Non-Zero Boresight Pointing Errors

Subcarrier free-space optical (FSO) systems using coherent recovery techniques at the receiver have acquired growing research interest in recent times. However, their optimal performance is diminished by the non-perfect synchronization of carrier frequency and phase, which is mainly due to phase noise problems. Moreover, turbulence and pointing error effects further deteriorate the overall performance. However, relay transmission schemes can extend the coverage distance and offer substantial improvements over fading conditions. In this respect, we consider a serially relayed network using decode-and-forward relays, and investigate its performance by means of average symbol error probability and mean outage duration. Turbulence is modeled by the recently unified M(alaga) distribution, which constitutes a very general statistical model that accurately describes the irradiance fluctuations from weak-to-strong turbulence conditions. Additionally, the presence of non-zero boresight pointing errors due to misalignment between the transmitter–receiver pair is considered, while the effect of phase noise is specified by a Tikhonov distribution. A comparison between single line-of-sight and serially relayed FSO configurations is provided as well. Novel approximated mathematical expressions are deduced, which are proved to be accurate enough over a wide range of turbulence strengths and signal-to-noise values. Finally, proper numerical results are presented and validated by Monte Carlo simulations.

Rate-Energy Tradeoff in Simultaneous Wireless Information and Power Transfer Over Fading Channels With Uncertain Distribution

This paper investigates the tradeoff between information rate and harvested energy in a simultaneous wireless information and power transfer system under power splitting (PS) scheme and time switching (TS) scheme. A single-input-multiple-output transmitter–receiver pair is considered. For the channel from the transmitter to the receiver, only the mean and covariance matrix are known, but the instantaneous channel information or the channel gain distribution is unknown. We define robust outage capacity that applies for all possible channel distributions with the given mean and covariance matrix, and study the tradeoff between the robust outage capacity and harvested power level. By solving optimization problems, we find the PS ratio setting for PS scheme and TS ratio setting for TS scheme to achieve the outer boundary of robust outage capacity-energy region (which includes all possible pairs of achievable robust outage capacity and harvested power level). The PS and TS ratio setting are fixed over fading blocks, and thus can avoid communication overhead and computation overhead over each fading block, and facilitate a simple implementation in a practical system. We also prove that the robust outage capacity-energy regions in PS scheme and TS scheme are both convex. Further, we prove that the PS scheme outperforms the TS scheme in terms of the rate-energy tradeoff. Numerical results are also presented to verify the correctness of our theoretical results.

On physical‐layer security for primary system in underlay cognitive radio networks

In this study, the authors consider the physical-layer security for transmission in underlay cognitive radio networks, where consisting of a primary source–destination pair, a secondary transmitter–receiver pair and a common eavesdropper (E). To transmit data in a secure and reliable manner, they propose a transmission protocol for an underlay cognitive radio network. In particular, the secondary user is allowed to operate on the primary spectrum bandwidth when the interference threshold is satisfied. To protect the transmission confidentiality of primary system, PS node transmits a signal, which is linearly combined with the jamming signal (as artificial noise) and expectation signal, to interfere E. Furthermore, they propose a superimposed coding to combine with the artificial noise and expectation signal at PS node. We also analyse the performance of the proposed transmission protocol. We obtain the outage probability of secondary and primary systems. Simultaneously, they derive the closed-form expression of intercept probability for primary system. In addition, they verify the performance of their proposed transmission protocol by numerical experiment. The numerical results show that their proposed transmission protocol not only has the better outage performance for secondary system but also has the better intercept performance for primary system.

Exact Solution for Elliptic Localization in Distributed MIMO Radar Systems

Elliptic localization is a range-based positioning technique exploiting multiple transmitter-receiver pairs, each of which provides separate bistatic range (BR) measurements. In this paper, a novel computationally efficient solution for locating a single target from BR measurements in distributed MIMO radar systems is proposed. Due to nonconvex nature of the associated maximum likelihood (ML) estimation problem, its globally optimal solution is difficult to obtain. We first reformulate the ML estimation as a nonconvex constrained weighted least squares problem. Owing to special structure of the resulting problem, it is recast as a convex problem, whose exact solution can be obtained in closed-form or near closed-form manner. Moreover, the proposed method is extended to localization in the presence of antenna location uncertainties. The positioning performance of the proposed method is shown to achieve the CRLB up to relatively high noise levels. Furthermore, numerical simulations demonstrate a significant performance improvement of the proposed method over the state-of-the-art algorithms.

Throughput Analysis on 3-Dimensional Underwater Acoustic Network with One-Hop Mobile Relay.

Underwater acoustic communication network (UACN) has been considered as an essential infrastructure for ocean exploitation. Performance analysis of UACN is important in underwater acoustic network deployment and management. In this paper, we analyze the network throughput of three-dimensional randomly deployed transmitter–receiver pairs. Due to the long delay of acoustic channels, complicated networking protocols with heavy signaling overhead may not be appropriate. In this paper, we consider only one-hop or two-hop transmission, to save the signaling cost. That is, we assume the transmitter sends the data packet to the receiver by one-hop direct transmission, or by two-hop transmission via mobile relays. We derive the closed-form formulation of packet delivery rate with respect to the transmission delay and the number of transmitter–receiver pairs. The correctness of the derivation results are verified by computer simulations. Our analysis indicates how to obtain a precise tradeoff between the delay constraint and the network capacity.

Underwater Localization Based on Grid Computation and Its Application to Transmit Beamforming in Multiuser UWA Communications

Underwater localization is a challenging problem and established technologies for terrestrial systems cannot be used, notably the Global Positioning System (GPS). In this paper, we propose an underwater localization technique and demonstrate how it can be effectively used for transmit beamforming in multiuser underwater acoustic (UWA) communications. The localization is based on pre-computation of acoustic channel parameters between a transmitter-receiver pair on a grid of points covering the area of interest. This is similar to the localization process using matched field processing, which is often based on processing a priori unknown signals received by an array of hydrophones. However, in our case, every receiver is assumed to have a single hydrophone, while an array of transducers transmit (pilot) signals known at a receiver. The receiver processes the received pilot signal to estimate the Channel State Information (CSI) and compares it with the CSI pre-computed on the grid; the best match indicates the location estimate. The proposed localization technique also enables an efficient solution to the inherent problem of informing a transmitter about the CSI available at the receiver for the purpose of transmit beamforming. The receiver only needs to send a grid point index to enable the transmitter to obtain the pre-computed CSI corresponding to the particular grid point, thereby significantly reducing transmission overheads. We apply this approach to a multiuser communication scenario with orthogonal frequency-division multiplexing (OFDM) and show that the proposed approach results in accurate localization of receivers and multiuser communications with a high detection performance.

Cognitive Relaying Cooperation in Satellite-Terrestrial Systems With Multiuser Diversity

This paper investigates the outage performance of an overlay multiuser hybrid satellite-terrestrial spectrum sharing system. Herein, we exploit both direct and relay links from a primary satellite source to multiple terrestrial users with the coexistence of a secondary transmitter–receiver pair on the ground. Based on an overlay approach, the secondary transmitter provides an amplify-and-forward-based relay cooperation to the primary satellite network that employs opportunistic scheduling of multiple users. The underlying user scheduling strategy is based on satisfying the criterion of minimal outage probability (OP) for the primary network and, eventually, exploring more opportunities of the spectrum sharing for the secondary terrestrial network. By considering the widely adopted Shadowed-Rician fading model for the satellite links while the Nakagami- $m$ fading model for the terrestrial links, we derive the analytical expressions for the OP of the primary satellite network and the secondary terrestrial network and further highlight the corresponding achievable diversity orders. We also examine the impact of power splitting factor for spectrum sharing between primary and secondary networks.

Queueing Stability and CSI Probing of a TDD Wireless Network With Interference Alignment

This paper characterizes the performance in terms of queueing stability of a network composed of multiple MIMO transmitter-receiver pairs taking into account the dynamic traffic pattern and the probing/feedback cost. We adopt a centralized scheduling scheme that selects a number of active pairs in each time-slot. We consider that the transmitters apply interference alignment (IA) technique if two or more pairs are active, whereas in the special case where one pair is active point-to-point MIMO singular value decomposition (SVD) is used. We consider a time-division duplex (TDD) system where transmitters acquire their channel state information (CSI) by decoding the pilot sequences sent by the receivers. Since global CSI knowledge is required for IA, the transmitters have also to exchange their estimated CSIs over a backhaul of limited capacity (i.e. imperfect case). Under this setting, we characterize in this paper the stability region of the system under both the imperfect and perfect (i.e. unlimited backhaul) cases, then we examine the gap between these two resulting regions. Further, under each case we provide a centralized probing policy that achieves the max stability region. These stability regions and scheduling policies are given for the symmetric system, where all the path loss coefficients are equal to each other, as well as for the general system. For the symmetric system, we provide the conditions under which IA yields a queueing stability gain compared to SVD. Under the general system, the adopted scheduling policy is of a high computational complexity for moderate numbers of pairs, consequently we propose an approximate policy that has a reduced complexity but that achieves only a fraction of the system stability region. A characterization of this fraction is provided.

Wireless Information and Energy Transfer in MIMO Communication With Interference Channels

In this paper, we consider a wireless information and energy transfer (WIET) system, which consists of multiple information transmitter-receiver pairs, and multiple additional energy transmitters to improve the energy transfer. For such a new WIET system, we investigate the energy efficiency (EE) under two different setups, respectively: the information transmitters and energy transmitters use the same and different frequency bands. For each setup, we propose a novel centralized beamformer design method to solve the EE maximization problem, which can be transformed into a convex optimization problem using semidefinite relaxation (SDR) technique. Moreover, we develop a distributed optimization algorithm to solve the SDR approximation formulation for each setup. Simulation results show that the same frequency setup can achieve larger EE value and less computational complexity, however, suffering from lower sum rate. For each setup, the distributed scheme has slightly worse performance than the centralized one, while enjoys less computational complexity, especially when the number of the additional energy transmitters is large.

Full focal imaging of ultrasonic Lamb waves using diffuse field information

In this paper, a method is presented in which that the diffuse field information of Lamb waves is used to realize the full focal imaging of the defect that is near the transducer array. The near distance means that the defect is located in the near field of ultrasonic phased array and satisfies the near field calculation formula. Near field acoustic information of the defect is obscured by the nonlinear effects of early time saturation present in a directly acquired ultrasonic inspection. The approach proposed here is to recover near filed information through cross-correlation of diffuse fields. The diffuse field is generated through multiple scattering and reflection effects after sufficiently long time transmission of ultrasonic signal in a bounded medium. The near field information is implicitly contained throughout the diffuse field. By cross-correlating the diffuse fields of ultrasonic responses recorded at two monitoring points, the Green's functions between the two points is recovered and the direct response between them is obtained. This idea is applied to the full matrix capture of ultrasonic phased array in which the full matrix is formed by sequential acquisition of responses for each transmitter-receiver pair. A virtual array of emitters and receivers is therefore established. Typically, phase delays are used in post-processing to achieve advanced imaging. Here an undelayed full matrix of inter-element responses is reconstructed through cross-correlation of a later time diffuse full matrix. In order to evaluate the applicability of the method for ultrasonic non-destructive testing, the process of full matrix reconstruction is demonstrated experimentally on an aluminium plate containing the near field defect. Combining the full focal imaging, it is shown that a hybrid full matrix formed through a temporally weighted sum of coherent and reconstructed matrices reduces the background noise and allows the effective imaging of near field defect by direct contact experimental measurements. However, the near field defect is hidden by the region of artificial noise in conventional coherent capture images. The proposed imaging method presents a theoretical guidance for detecting and imaging near field defect in plate-like configurations by using the Lamb wave nondestructive testing method.

On the Outage Probability of Interference-Limited Multi-Hop Linear Vehicular Ad-Hoc Network

The outage probability of an interference-limited linear vehicular ad hoc network (VANET) with random multiple access protocol is studied in this paper. All nodes in the VANET, including the intended transmitter-receiver pair and the interferers, are assumed to form a homogeneous Poisson point process. Communications between any two nodes in the network are carried out by using nodes between them as relays. For a given network section, more nodes between the source and the destination means more relays, thus a stronger signal component due to smaller pathloss between two neighboring nodes. Meanwhile, more nodes generate more mutual interference. A random multiple access protocol, where each node transmits with a certain probability, is adopted to reduce interference. To characterize the competing effects between pathloss and interference, we derive analytically the upper and lower bounds of the outage probability for a cluster of nodes over a fixed section of the network under the interference-limited environment. The outage probability bounds are derived as explicit functions of various system parameters, including the pathloss exponent, node mobility, transmission probability, and cluster size. Optimum designs are then performed to minimize the outage probability with respect to several system parameters, such as the node density, cluster size, and node mobilities.

On Link Scheduling in Dual-Hop 60-GHz mmWave Networks

We tackle the problem of minimizing the maximum expected delivery time of all transmission pairs in 60 GHz mmWave networks. The network is dual-hop with multiple transmitter-receiver pairs, relays, and a centralized controller (termed PicoNet coordinator). We jointly optimize relay and link selection for the transmitter–receiver pairs to minimize delivery time, while the reflected non-line-of-sight transmission links are exploited to get around obstacles. To reduce computational complexity, we develop a decomposition principle to transform the joint-optimization problem into a link selection subproblem and a relay assignment subproblem when there are a sufficient amount of relays. A tight performance bound for the proposed algorithm is proved. We also develop a heuristic scheme to handle the case when there are no enough relays. The superior performance of our proposed algorithms is validated with extensive simulations and comparisons with benchmark schemes.

Finite-Difference Modeling of Very-Low-Frequency Propagation in the Earth-Ionosphere Waveguide

Simulations of Very-low-frequency (VLF) transmitter signals are conducted using three models: the long-wave propagation capability, a finite-difference (FD) time-domain model, and an FD frequency-domain model. The FD models are corrected using Richardson extrapolation to minimize the numerical dispersion inherent in these models. Using identical ionosphere and ground parameters, the three models are shown to agree very well in their simulated VLF signal amplitude and phase, to within 1 dB of amplitude and a few degrees of phase, for a number of different simulation paths and transmitter frequencies. Furthermore, the three models are shown to produce comparable phase changes for the same ionosphere perturbations, again to within a few degrees. Finally, we show that the models reproduce the phase data of existing VLF transmitter-receiver pairs reasonably well, although the nighttime variation in the measured phase data is not captured by the simplified characterization of the ionosphere.

Attenuation estimation from sonic logging waveforms combining seismic interferometry and common-midpoint approach

Although attenuation estimation methods using sonic logging waveforms provide the highest resolution among seismic methods and enable us to characterize in great detail the attenuation properties of subsurface rocks, such attenuation estimation methods are not used routinely, indicating that there is still room for improvement. To further improve the performance of an existing modified median frequency shift (MMFS) method, we have developed a new algorithm by combining seismic interferometry (SI) and the common-midpoint (CMP) approach. Redatuming a transmitter position by applying SI can shorten the transmitter-receiver distance, leading not only to higher depth resolution but also to a lower signal-to-noise ratio (S/N) of the attenuation profiles. To compensate for the decrease in the S/N, we used the redundancy of overlapping receivers at each receiver level in a sonic logging measurement using the multireceiver tool; we improved the S/N by stacking the redatumed sonic logging waveforms. Then, based on the CMP approach, we constructed the workflow to estimate attenuation using redatumed sonic logging waveforms. We applied our method to numerical and real sonic logging waveforms to investigate its applicability in comparison with that of the existing MMFS method in terms of depth resolution and S/N. The results of numerical experiments on noisy data and velocity heterogeneity models demonstrate a trade-off relationship between the depth resolution and stability, which can be controlled by selecting transmitter-receiver pairs. Finally, the application of our method to real sonic logging data demonstrates the advantages in terms of resolution and the disadvantages in stability in comparison with the existing MMFS method. Similar to the numerical results, we found a trade-off relationship between such advantages and disadvantages, which can be controlled by selecting transmitter-receiver pairs.