Receiver Pair Research Articles

Energy-Efficient Power Loading for OFDM-Based Cognitive Radio Systems With Channel Uncertainties

In this paper, we propose a novel algorithm to optimize the energy efficiency (EE) of orthogonal frequency-division multiplexing (OFDM)-based cognitive radio systems under channel uncertainties. We formulate an optimization problem that guarantees a minimum required rate and a specified power budget for the secondary user (SU) while restricting the interference to primary users (PUs) in a statistical manner. The optimization problem is nonconvex, and it is transformed to an equivalent problem using the concept of fractional programming. Unlike all related works in the literature, we consider the effect of imperfect channel-state information (CSI) on the links between the SU transmitter and receiver pairs, and we additionally consider the effect of limited sensing capabilities of the SU. Since the interference constraints are met statistically, the SU transmitter does not require perfect CSI feedback from the PUs' receivers. Simulation results show that the EE deteriorates as the channel estimation error increases. Comparisons with relevant works from the literature show that the interference thresholds at the PUs' receivers can be severely exceeded and that the EE is slightly deteriorated if the SU does not account for spectrum sensing errors.

The Degrees of Freedom of Two-Unicast Layered MIMO Interference Networks With Feedback

Two-unicast layered interference networks under the Shannon feedback and limited Shannon feedback settings are studied from a degrees of freedom (DoF) perspective. The main focus is on the archetypal two-hop multiple-input, multiple-output (MIMO) $(M,N)\, \times \, (M,N) \,\times \, (M,N) $ network, denoted here as the $(M,N)^{3}$ network, which is a layered two-unicast network with two transmitters, two relays, and two receivers, with the first hop network between the transmitters and the relays, and the second hop network between the relays and the receivers, both being MIMO Gaussian interference channels. In particular, the first transmitter–receiver pair and the first relay have $M$ antennas each and the second transmitter–receiver pair and the second relay having $N$ antennas each. The (full) Shannon feedback setting for the $(M,N)^{3}$ network is one in which the transmitters have delayed knowledge of the first and second hop channel coefficients and the relay and destination outputs and the relays have delayed knowledge of the second hop channel coefficients and destination outputs. The DoF region under this setting is established. A key result in this paper shows that this Shannon feedback DoF region can in fact be achieved with much less side information—under what we refer to as the limited Shannon feedback setting—wherein the transmitters have no channel state or output feedback whatsoever and only the $M$ -antenna relay (assuming $M \geq N$ ) has delayed knowledge of the coefficients of the second-hop channel and of only the received signal of the $N$ -antenna receiver. For this limited Shannon feedback setting, the DoFs region of the $(M,N)^{3}$ network is established by introducing a retro-cooperative interference alignment scheme. These DoF region results for the $(M,N)^{3}$ network with feedback are also extended to more general layered interference networks including the two-unicast $l$ -hop layered networks as well as layered networks with more general numbers of antennas at the various terminals.

Interference Modeling and Capacity Analysis for Microfluidic Molecular Communication Channels

The impact of the interference on the molecular communication (MC) between a transmitter and receiver pair which are connected through a microfluidic channel containing fluid flow is investigated. The interference modeling and the capacity analysis is performed based on the microfluidic channel geometry, the flow velocity, and the distance. During the analysis, time-scale of biological oscillators is specifically targeted, which is in the range of several minutes to a few hours. The signal-to-interference and noise ratio is shown to be constant with respect to the location of the interfering transmitter. The capacity of the MC link between the designated transmitter and the corresponding receiver is shown to be upper bounded by 1 bit/per channel use when exposed to a single interfering transmitter. For the multiple, i.e., N , transmitters, the decay of pairwise MC capacity is also studied as a factor of N . Finally, placement of the two transmitter and receiver pairs on the opposite sides of the microfluidic channel is studied. Three different microfluidic interference channel configurations, i.e., both-sided interference (microfluidic X channel), one-sided interference (microfluidic Z channel), and interference-free, are proposed based on the distance of the receiver from the interfering transmitter, microfluidic channel cross section, and the fluid flow velocity. For large-scale integration of chemical analysis systems on a microfluidic chip, the provided information-theoretic analysis and the capacity expressions for the MIC can be utilized to analyze the throughput of the chip, which can lead to improvement in efficiency and optimization of the design.

Fixed-point Sensitivity Maps for Image Reconstruction in Tomography

This study proposes new fixed-point sensitivity maps for image reconstruction in optical tomography systems by using a linear back projection (LBP) algorithm. The projection selected is based on fan beam orientation with 16 pairs of transmitters and receivers. Many optical tomography systems previously published, focused on microcontroller implementations, which have limited processing speed for real time systems to be used in critical applications such as underwater gas transmission pipeline. To gain benefits from parallel processing in digital hardware implementations such as using FPGA or ASIC, slight modification must be done in the reconstructed images mechanism. The normalized sensitivity maps for image reconstruction are recreated without using floating numbers to optimize the digital design implementations. By multiplying the sensitivity maps matrix with 128, the new sensitivity maps matrices are developed and rounding processes are performed to eliminate floating numbers. The error was determined using Normalized Mean Square Error (NMSE) and the results show that the new fixed-point sensitivity maps produced comparable image reconstruction quality for optical tomography systems with NMSE values of 1.88 × 10-7 and 0.02 for phantoms (a) and (b) respectively.

A Smart-Card E-paper Display System Based on RF Power Harvesting

ABSTRACTThis study investigated technologies related to a smart-card display and its wireless charging system, where the wireless receiver in the smart card receives not only the data but also the power required for the display circuitry. The goal of this research was to achieve the required energy transfer during the extremely short reading time when a person swipes his or her smart card. This paper describes the design considerations and the analysis procedures of the transmitter and receiver pair for an electronic paper (E-paper) display. A series of magnetic simulations as well as experimental tests were conducted to investigate the various design factors. The design considerations included the shape and effect of using ferromagnetic cores, the component design for frequency tuning, the geometric arrangements, and the number of turns of the coils. A novel design for power transmission is then proposed using a ferromagnetic core to enhance its energy efficiency. In experiments the transmitter unit provided 250 mW of power to the transmitter antenna. The resultant transmission efficiency (S21) was −5.1 dB over a distance of 4.3 mm. Experimental results show that the smart card receives 220 mW, representing a high transmission efficiency of 88%.

Microseismic event location using an inverse method of joint P–S phase arrival difference and P-wave arrival difference in a borehole system

The accuracy of hypocenter location is the essential issue for microseismic monitoring, and is the basis for evaluating the effect of fracture. Although the signal obtained from a borehole monitoring system has a higher signal to noise ratio (SNR) than the surface system, a narrow monitoring aperture makes the location sensitive to noise and tends to be a misguided shape. In order to overcome this disadvantage and obtain a more accurate estimation of the source, we develop a ‘jointing method’, which combines the P–S phase arrival difference and P-wave arrival difference of each receiver pair (PSP) in the objective function. In the synthetic example, we compare the noise responses of three different location methods which are based on P-wave arrival time difference, P–S wave arrival time difference and the PSP method, respectively. This analysis shows that the P-wave arrival difference method is more sensitive to arrival time error than the others and the location results tend to be in a misleading line directed to the receivers. The P–S arrival difference method is more robust than the method using P-wave and its error distribution is perpendicular to the ray-path direction. The PSP method, as expected, is the most stable and accurate. When the P–S method and PSP method are applied to field data of a coal bed methane hydro-fracture process monitoring, the results indicate that the PSP method is preferable. The successful location with the PSP method proves that it is suitable for field data.

Body wave extraction and tomography at Long Beach, California, with ambient‐noise interferometry

AbstractWe retrieve P diving waves by applying seismic interferometry to ambient‐noise records observed at Long Beach, California, and invert travel times of these waves to estimate 3‐D P wave velocity structure. The ambient noise is recorded by a 2‐D dense and large network, which has about 2500 receivers with 100 m spacing. Compared to surface wave extraction, body wave extraction is a much greater challenge because ambient noise is typically dominated by surface wave energy. For each individual receiver pair, the cross‐correlation function obtained from ambient‐noise data does not show clear body waves. Although we can reconstruct body waves when we stack correlation functions over all receiver pairs, we need to extract body waves at each receiver pair separately for imaging spatial heterogeneity of subsurface structure. Therefore, we employ two filters after correlation to seek body waves between individual receiver pairs. The first filter is a selection filter based on the similarity between each correlation function and the stacked function. After selecting traces containing stronger body waves, we retain about two million correlation functions (35% of all correlation functions) and successfully preserve most of body wave energy in the retained traces. The second filter is a noise suppression filter to enhance coherent energy (body waves here) and suppress incoherent noise in each trace. After applying these filters, we can reconstruct clear body waves from each virtual source. As an application of using extracted body waves, we estimate 3‐D P wave velocities from these waves with travel time tomography. This study is the first body wave tomography result obtained from only ambient noise recorded at the ground surface. The velocity structure estimated from body waves has higher resolution than estimated from surface waves.

Studying CO2 storage with ambient-noise seismic interferometry: A combined numerical feasibility study and field-data example for Ketzin, Germany

Seismic interferometry applied to ambient-noise measurements allows the retrieval of the seismic response between pairs of receivers. We studied ambient-noise seismic interferometry (ANSI) to retrieve time-lapse reflection responses from a reservoir during [Formula: see text] geologic sequestration, using the case of the experimental site of Ketzin, Germany. We applied ANSI to numerically modeled data to retrieve base and repeat reflection responses characterizing the impedances occurring at the reservoir both with and without the injection of [Formula: see text]. The modeled data represented global transmission responses from band-limited noise sources randomly triggered in space and time. We found that strong constraints on the spatial distribution of the passive sources were not required to retrieve the time-lapse signal as long as sufficient source-location repeatability was observed between the base and the repeat passive survey. To illustrate the potential of the technique, ANSI was applied to three days of passive field data recorded in 2012 at Ketzin. Comparison with the modeled results illustrated the potential to retrieve key reflection events using ANSI on field data from Ketzin. This study supports the idea that the geologic setting and characteristics of ambient noise at Ketzin may be opportune to monitor [Formula: see text] sequestration.

Automatic Railway Gate Controller with HighSpeed Alerting System

The aim of the paper is to avoid the railway accidents happening at unattended railway gates by using ATMEGA_16 microcontroller, if implemented in spirit. The model of railway track controller is designed by using four laser light sources as transmitters and four LDR as receivers; two pair of transmitters and receivers are fixed at upside (from where the train comes) at a level higher than a human being in exact alignment and similarly the other pair is fixed at down side of the train direction. The collision of two trains due to the same track also can be happened. This model is implemented using sensor technique. We placed the sensors at a certain distance from the gate detects the approaching train and accordingly controls the operation of the gate. Also an indicator light has been provided to alert the motorists about the approaching train.

Passive multi-channel analysis of surface waves with cross-correlations and beamforming. Application to a sea dike

We introduce the use of cross-correlations in the passive multi-channel analysis of surface waves (MASW), and report an improvement in the determination of subsurface shear velocities from ambient seismic noise. Velocities are measured from phase-shifts that are also related to the source location. Consequently, the accuracy with which velocities can be inferred depends on the ability of the array to locate noise sources. The computation of cross-correlations for each receiver pair allows increasing the effective spatial sampling of the array. For this reason, we show that beamforming is more efficient with cross-correlated signals. Consequently, MASW performed with cross-correlations produces a dispersion diagram where aliasing is reduced and signal-to-noise ratio increased. The proposed method is validated with synthetic records. It is then applied on passive recordings obtained on top of a sea dike at high tide, where sea waves were acting as continuous seismic sources. Surface wave velocities that favorably compare with hammer shot measurements are inferred.

Extracting Seismic Body and Rayleigh Waves from the Ambient Seismic Noise Using the rms-Stacking Method

The cross correlation of ambient seismic noise recordings can be used to extract the empirical Green’s functions (hereafter EGFs) between pair of receivers (Shapiro and Compillo, 2004). In the past few years, extensive research has been performed on this topic around the world in various fields including travel‐time tomography (Sabra et al. , 2005; Shapiro et al. , 2005; Yao et al. , 2006; Yang et al. , 2007; Ward et al. 2013; Young et al. , 2013), anisotropy (Guo et al. , 2012; Shirzad and Shomali, 2014), fault detection (Shirzad et al. , 2013) and retrieving body wave (Poli et al. , 2012; Lin and Tsia, 2013; Boue et al. , 2014). Depending on various parameters including the quality of data and its frequency content, different processing approaches have been developed to obtain noise correlation. In the most approaches developed, the stacking was further assumed to be nonindependent on a particular phase. The main scope of these approaches is to remove the deterministic signals (e.g., earthquakes) and also extract the coherent part of ambient seismic noise (Stehly et al. , 2006; Pedersen et al. , 2007; Bensen et al. , 2008). In general, the extracted EGFs are dominated by the surface‐wave signal, even if two stations have a large interstation distance. Additionally, uneven noise source distribution may affect the extracted interstation EGFs of surface waves and consequently dispersion measurements (see Stehly et al. , 2006; Tsai, 2009; Yao and van der Hilst, 2009). Body waves may also be emerged by storm and/or swell interference (Landes et al. , 2010; Obrebski et al. , 2013). Obrebski et al. (2013) indicated that body and surface waves in random wavefields have different patterns resulted from distinctive amplification of ocean wave‐induced pressure …

Seismic interferometry by tangent‐phase correction

ABSTRACTWe present a modified interferometry method based on local tangent‐phase analysis, which corrects the cross‐correlated data before summation. The approach makes it possible to synthesize virtual signals usually vanishing in the conventional seismic interferometry summation. For a given pair of receivers and a set of different source positions, a plurality of virtual traces is obtained at new stationary projected points located along the signal wavefronts passing through the real reference receiver. The position of the projected points is estimated by minimizing travel times using wavefront constraint and correlation‐signal tangent information. The method uses mixed processing, which is partially based on velocity‐model knowledge and on data‐based blind interferometry. The approach can be used for selected events, including reflections with different stationary conditions and projected points with respect to those of the direct arrivals, to extend the interferometry representation in seismic exploration data where conventional illumination coverage is not sufficient to obtain the stationary‐phase condition. We discuss possible applications in crosswell geometry with a velocity anomaly and a time lapse.

Retrieval of super‐virtual refraction by cross‐correlation

ABSTRACTTopography and severe variations of near‐surface layers lead to travel‐time perturbations for the events in seismic exploration. Usually, these perturbations could be estimated and eliminated by refraction technology. The virtual refraction method is a relatively new technique for retrieval of refraction information from seismic records contaminated by noise. Based on the virtual refraction, this paper proposes super‐virtual refraction interferometry by cross‐correlation to retrieve refraction wavefields by summing the cross‐correlation of raw refraction wavefields and virtual refraction wavefields over all receivers located outside the retrieved source and receiver pair. This method can enhance refraction signal gradually as the source–receiver offset decreases. For further enhancement of refracted waves, a scheme of hybrid virtual refraction wavefields is applied by stacking of correlation‐type and convolution‐type super‐virtual refractions. Our new method does not need any information about the near‐surface velocity model, which can solve the problem of directly unmeasured virtual refraction energy from the virtual source at the surface, and extend the acquisition aperture to its maximum extent in raw seismic records. It can also reduce random noise influence in raw seismic records effectively and improve refracted waves’ signal‐to‐noise ratio by a factor proportional to the square root of the number of receivers positioned at stationary‐phase points, based on the improvement of virtual refraction's signal‐to‐noise ratio. Using results from synthetic and field data, we show that our new method is effective to retrieve refraction information from raw seismic records and improve the accuracy of first‐arrival picks.

On the improvement of wireless mesh sensor network performance under hidden terminal problems

Wireless Mesh Sensor Networks (WMSNs) have recently received a great deal of attention in the scientific and developers communities due to the significant advances of this technology in the wireless communication field. The main reason was that competing WMSN approaches that emerged in the last few years provide mesh capabilities (e.g., robustness, scalability, multi-hop mesh routing, or energy efficiency, among others) to conventional WSN-based applications, encouraging researchers and end users to adopt new perspectives and solutions. Unfortunately, each one of these approaches lacks some (or many) of the aforementioned mesh capabilities, not assuring, a priori, the feasibility and, especially, the long-term stability of WMSN applications. The IEEE 802.15.5 standard and, in particular, its Asynchronous Energy Saving (ASES) mode was conceived to fill this gap since it integrates, in a single solution, most of these capabilities, guaranteeing, among other benefits, a long network lifetime. However, the ASES mode has no built-in mechanisms to mitigate the negative effects of hidden terminals, which sharply degrades the network performance. This fact leads us to conclude that any current WMSN approach is non-exempt of some problem, which prevents the definitive boost of this technology in the consumer market. Under these circumstances, our contribution to the WMSN field in this paper is a twofold proposal addressed to alleviating the hidden terminal problems in a scenario running under the most relevant design premises of ASES mode. Therefore, we first formulate a multi-objective optimization and then solve it by using Goal Programming. Both mathematical techniques are applied to obtain the best solution that simultaneously minimizes the aggregate message collision time due to hidden terminals and maximizes the network lifetime. Secondly, we propose the design of a MULti-channel TIme-scheduled algorithm for the HIdden Terminal problem avoidance (MULTI-HIT) which appropriately exploits the available bandwidth and accomplishes a straightforward coordination between any sender–receiver pair. Finally, the analysis and simulation experiments are presented and their results carefully discussed, demonstrating the effectiveness of both proposals in the WMSN arena.

Localization Based on Adaptive Regulated Neighborhood Distance for Wireless Sensor Networks With a General Radio Propagation Model

Many range-free localization algorithms estimate the distance in between two nodes based on the hop-count information, which, however, is a coarse proximity measure. Recently, the regulated neighborhood distance (RND) has been proposed as a new proximity measure, and can greatly improve the localization accuracy, compared with those hop-count-based algorithms. However, the RND algorithm and most previous hop-based approaches are based on the disk communication model, and cannot be directly applied into the practical world with some general radio propagation model. In this paper, we revisit the RND-based localization with a general propagation model, where the received transmission power is modeled as a random variable and its expectation is a nonincreasing function of the distance between a transmitter and receiver pair. In particular, we define the neighborhood based on the packet reception ratio (PRR), and propose an optimal PRR threshold selection algorithm to adaptively adjust the RND-based distance estimation. We verify the effectiveness of the adaptive RND-based localization for the log-normal shadowing model and a polynomial fitting model from our field experiments. Simulation results show that the adaptive selection of the best PRR threshold helps to improve localization accuracy. Furthermore, the proposed adaptive RND-based localization can achieve higher localization accuracy, compared with the classical DV-hop localization with the same network configurations.

Accounting for Galileo–GPS inter-system biases in precise satellite positioning

Availability of two overlapping frequencies L1/E1 and L5/E5a of the signals transmitted by GPS and Galileo systems offers the possibility of tightly combining observations from both systems in a single observational model. A tightly combined observational model assumes a single reference satellite for all observations from both Galileo and GPS systems. However, when inter-system double-differenced observations are created, receiver inter-system bias is introduced. This study presents the results and the methodology for estimation and accounting for phase and code GPS-Galileo inter-system bias in precise relative positioning. The research investigates the size and temporal stability of the estimated bias for different receiver pairs as well as examines the influence of accounting for the inter-system bias on the user position solution. The obtained numerical results are based on four experiments carried out at different locations and time periods using both real and simulated GNSS data.

Individual monitoring of hearing status: Development and validation of advanced techniques to measure otoacoustic emissions in suboptimal test conditions

Scientific evidence suggests that measurement of otoacoustic emissions (OAEs) is a reliable tool to detect the early onset of noise induced hearing loss. Nevertheless, the individual field measurement of otoacoustic emissions on industrial workers is very challenging in practice because the high level of ambient noise usually disturbs the OAE measurement. The use of OAE measurement probes with high passive noise isolation allows the attenuation of most of the high frequency ambient noise, but it is often insufficient for the low frequency content of the ambient noise. In the described research, a new type of OAE system, suitable for the continuous monitoring of OAE levels on an individual worker, has been designed as a pair of earpieces each featuring an external microphone, an internal microphone and a pair of miniature receivers. Adaptive Noise Reduction (ANR) processing the measured Distortion Product OAE (DPOAE) is used to further improve the signal-to-noise ratio in frequencies mostly where passive isolation remains insufficient. The ANR technique relies on a Normalized Least-Mean-Square (NLMS) algorithm that uses the ipsilateral external microphone and the contralateral internal microphone to denoise the measured DPOAE signals for each in-ear OAE probe. A side-by-side comparison with commercially available clinical OAE equipment on 8 test-subjects successfully confirmed that the developed OAE system would be suitable for the continuous monitoring of workers’ hearing capabilities in industrial noise environments with levels up to 75dB(A).

Global S-wave tomography using receiver pairs: an alternative to get rid of earthquake mislocation

Global seismic tomography suffers from uncertainties in earthquake parameters routinely published in seismic catalogues. In particular, errors in earthquake location and origin-time may lead to strong biases in measured body wave delay-times and significantly pollute tomographic models. Common ways of dealing with this issue are to incorporate source parameters as additional unknowns into the linear tomographic equations, or to seek combinations of data to minimize the influence of source mislocations. We propose an alternative, physically-based method to desensitize direct S-wave delay-times to errors in earthquake location and origin-time. Our approach takes advantage of the fact that mislocation delay-time biases depend to first order on the earthquake-receiver azimuth, and to second order on the epicentral distance. Therefore, for every earthquake, we compute S-wave differential delay-times between optimized receiver pairs, such that a large part of their mislocation delay-time biases cancels out (for example origin-time fully subtracts out), while the difference of their sensitivity kernels remains sensitive to the model parameters of interest. Considering realistic, randomly distributed source mislocation vectors, as well as various levels of data noise and different synthetic Earths, we demonstrate that mislocation-related model errors are highly reduced when inverting for such differential delay-times, compared to absolute ones. The reduction is particularly rewarding for imaging the upper-mantle and transition zone. We conclude that using optimized receiver pairs is a suitable, low cost alternative to get rid of errors on earthquake location and origin-time for teleseismic direct S-wave traveltimes. Moreover, it can partly remove unilateral rupture propagation effects in cross-correlation delay-times, since they are similar to mislocation effects.

Coupled congestion control for RTP media

Congestion occurs at a bottleneck along an Internet path; multiple flows between the same sender and receiver pairs can benefit from using only a single congestion control instance when they share the same bottleneck. These benefits include the ability to control the rate allocation between flows and reduced overall delay (multiple congestion control instances cause more queuing delay than one since each has no knowledge of the congestion episodes experienced by the others). We present a mechanism for coupling congestion control for real-time media and show its benefits by coupling multiple congestion controlled flows that share the same bottleneck.

Outage Capacity Analysis of a Cooperative Relaying Scheme in Interference Limited Cognitive Radio Networks

In this study, we investigate the outage capacity of a cooperative relaying based cognitive radio network in slow fading channel. Our network scenario consists of a primary transmitter (PT) and primary receiver (PR) as well as a group of $$M$$ M secondary transmitter (ST)---receiver (SR) pairs. We grouped STs into active and inactive. Only one active ST may transmit data at a time in parallel with the PT satisfying a predefined interference threshold $$I_{th}$$ I t h to the PR. Due to fading/shadowing or interference caused by ST to the PR, primary user (PU) may fail to achieve its target rate $$R_{{\textit{PT}}}$$ R PT over a direct link. To overcome this, we can boost up primary capacity by using inactive STs as cooperative relay (Re) nodes for the PU. In addition, one of the inactive STs that achieves $$R_{{\textit{PT}}}$$ R PT will be act as a best decode-and-forward relay to forward the primary information. In this paper, a closed-form expression of the outage capacity is derived. Results show that outage capacity improves with increasing cooperative nodes as well as when the active ST is located farther away from the PR.