Showing papers on "Interference (wave propagation) published in 2017"
TL;DR: A baseline analytical approach based on stochastic geometry that allows the computation of the statistical distributions of the downlink signal-to-interference-plus-noise ratio (SINR) and also the per link data rate, which depends on the SINR as well as the average load is presented.
Abstract: We provide a comprehensive overview of mathematical models and analytical techniques for millimeter wave (mmWave) cellular systems. The two fundamental physical differences from conventional sub-6-GHz cellular systems are: 1) vulnerability to blocking and 2) the need for significant directionality at the transmitter and/or receiver, which is achieved through the use of large antenna arrays of small individual elements. We overview and compare models for both of these factors, and present a baseline analytical approach based on stochastic geometry that allows the computation of the statistical distributions of the downlink signal-to-interference-plus-noise ratio (SINR) and also the per link data rate, which depends on the SINR as well as the average load. There are many implications of the models and analysis: 1) mmWave systems are significantly more noise-limited than at sub-6 GHz for most parameter configurations; 2) initial access is much more difficult in mmWave; 3) self-backhauling is more viable than in sub-6-GHz systems, which makes ultra-dense deployments more viable, but this leads to increasingly interference-limited behavior; and 4) in sharp contrast to sub-6-GHz systems cellular operators can mutually benefit by sharing their spectrum licenses despite the uncontrolled interference that results from doing so. We conclude by outlining several important extensions of the baseline model, many of which are promising avenues for future research.
767 citations
TL;DR: A coherent perfect absorber is a system in which complete absorption of electromagnetic radiation is achieved by controlling the interference of multiple incident waves as discussed by the authors, which can be made much more efficient by exploiting wave interference.
Abstract: Absorption of electromagnetic energy by a material is a phenomenon that underlies many applied problems, including molecular sensing, photocurrent generation and photodetection. Commonly, the incident energy is delivered to the system through a single channel, for example by a plane wave incident on one side of an absorber. However, absorption can be made much more efficient by exploiting wave interference. A coherent perfect absorber is a system in which complete absorption of electromagnetic radiation is achieved by controlling the interference of multiple incident waves. Here, we review recent advances in the design and applications of such devices. We present the theoretical principles underlying the phenomenon of coherent perfect absorption and give an overview of the photonic structures in which it can be realized, including planar and guided-mode structures, graphene-based systems, parity- and time-symmetric structures, 3D structures and quantum-mechanical systems. We then discuss possible applications of coherent perfect absorption in nanophotonics and, finally, we survey the perspectives for the future of this field.
240 citations
TL;DR: A coherent perfect absorber is a system in which the complete absorption of electromagnetic radiation is achieved by controlling the interference of multiple incident waves as mentioned in this paper, which is a phenomenon that underlies many applications including molecular sensing, photocurrent generation and photodetection.
Abstract: The absorption of electromagnetic energy by a material is a phenomenon that underlies many applications, including molecular sensing, photocurrent generation and photodetection. Typically, the incident energy is delivered to the system through a single channel, for example, by a plane wave incident on one side of an absorber. However, absorption can be made much more efficient by exploiting wave interference. A coherent perfect absorber is a system in which the complete absorption of electromagnetic radiation is achieved by controlling the interference of multiple incident waves. Here, we review recent advances in the design and applications of such devices. We present the theoretical principles underlying the phenomenon of coherent perfect absorption and give an overview of the photonic structures in which it can be realized, including planar and guided-mode structures, graphene-based systems, parity-symmetric and time-symmetric structures, 3D structures and quantum-mechanical systems. We then discuss possible applications of coherent perfect absorption in nanophotonics, and, finally, we survey the perspectives for the future of this field.
204 citations
TL;DR: In this paper, the authors present the experimental realization of a majority gate based on the interference of spin waves in an Yttrium-Iron-Garnet-based waveguiding structure.
Abstract: Featuring low heat dissipation, devices based on spin-wave logic gates promise to comply with increasing future requirements in information processing. In this work, we present the experimental realization of a majority gate based on the interference of spin waves in an Yttrium-Iron-Garnet-based waveguiding structure. This logic device features a three-input combiner with the logic information encoded in a phase of 0 or π of the input spin waves. We show that the phase of the output signal represents the majority of the three phase states of the spin waves in the three inputs. A switching time of about 10 ns in the prototype device provides evidence for the ability of sub-nanosecond data processing in future down-scaled devices.
193 citations
TL;DR: This paper study the systems operating in the EHF/THF bands by explicitly capturing three phenomena inherent for these frequencies: high directivity of the transmit and receive antennas; 2) molecular absorption; and 3) blocking of high-frequency radiation.
Abstract: The fifth generation wireless systems are expected to rely on a large number of small cells to massively offload traffic from the cellular and even from the wireless local area networks. To enable this functionality, mm-wave (EHF) and Terahertz (THF) bands are being actively explored. These bands are characterized by unique propagation properties compared with microwave systems. As a result, the interference structure in these systems could be principally different to what we observed so far at lower frequencies. In this paper, using the tools of stochastic geometry, we study the systems operating in the EHF/THF bands by explicitly capturing three phenomena inherent for these frequencies: 1) high directivity of the transmit and receive antennas; 2) molecular absorption; and 3) blocking of high-frequency radiation. We also define and compare two different antenna radiation pattern models. The metrics of interest are the mean interference and the signal-to-interference-plus-noise (SINR) ratio at the receiver. Our results reveal that: 1) for the same total emitted energy by a Poisson field of interferers, both the interference and SINR significantly increase when simultaneously both transmit and receive antennas are directive and 2) blocking has a profound impact on the interference and SINR creating much more favorable conditions for communications compared with no blocking case.
189 citations
TL;DR: This work indicates that OAM multiplexing and conventional spatialmultiplexing can be simultaneously utilized to provide design flexibility and performance enhancement in line-of-sight wireless communications.
Abstract: Line-of-sight wireless communications can benefit from the simultaneous transmission of multiple independent data streams through the same medium in order to increase system capacity. A common approach is to use conventional spatial multiplexing with spatially separated transmitter/receiver antennae, for which inter-channel crosstalk is reduced by employing multiple-input-multiple-output (MIMO) signal processing at the receivers. Another fairly recent approach to transmitting multiple data streams is to use orbital-angular-momentum (OAM) multiplexing, which employs the orthogonality among OAM beams to minimize inter-channel crosstalk and enable efficient (de)multiplexing. In this paper, we explore the potential of utilizing both of these multiplexing techniques to provide system design flexibility and performance enhancement. We demonstrate a 16 Gbit/s millimeter-wave link using OAM multiplexing combined with conventional spatial multiplexing over a short link distance of 1.8 meters (shorter than Rayleigh distance). Specifically, we implement a spatial multiplexing system with a $2\times 2$ antenna aperture architecture, in which each transmitter aperture contains two multiplexed 4 Gbit/s data-carrying OAM beams. A MIMO-based signal processing is used at the receiver to mitigate channel interference. Our experimental results show performance improvements for all channels after MIMO processing, with bit-error rates of each channel below the forward error correction limit of $3.8\times 10^{-3}$ . We also simulate the capacity for both the $4\times 4$ MIMO system and the $2\times 2$ MIMO with OAM multiplexing. Our work indicates that OAM multiplexing and conventional spatial multiplexing can be simultaneously utilized to provide design flexibility. The combination of these two approaches can potentially enhance system capacity given a fixed aperture area of the transmitter/receiver (when the link distance is within a few Rayleigh distances).
144 citations
TL;DR: It is shown that the distinguishability between pairs of photons is not sufficient to fully describe the photons' behavior in a scattering process, but that a collective phase, the triad phase, plays a role.
Abstract: Quantum interference of two independent particles in pure quantum states is fully described by the particles’ distinguishability: the closer the particles are to being identical, the higher the degree of quantum interference. When more than two particles are involved, the situation becomes more complex and interference capability extends beyond pairwise distinguishability, taking on a surprisingly rich character. Here, we study many-particle interference using three photons. We show that the distinguishability between pairs of photons is not sufficient to fully describe the photons’ behaviour in a scattering process, but that a collective phase, the triad phase, plays a role. We are able to explore the full parameter space of three-photon interference by generating heralded single photons and interfering them in a fibre tritter. Using multiple degrees of freedom—temporal delays and polarisation—we isolate three-photon interference from two-photon interference. Our experiment disproves the view that pairwise two-photon distinguishability uniquely determines the degree of non-classical many-particle interference.
128 citations
TL;DR: A novel energy and interference aware power control policy is proposed, which is based on the Lax–Friedrichs scheme and the Lagrange relaxation, and the numerical results are presented to demonstrate the spectrum and energy efficiency performances of the proposed approach.
Abstract: Device-to-device (D2D) communications can enha-nce spectrum and energy efficiency due to direct proximity communication and frequency reuse. However, such performance enhancement is limited by mutual interference and energy availability, especially when the deployment of D2D links is ultra-dense. In this paper, we present a distributed power control method for ultra-dense D2D communications underlying cellular communications. In this power control method, in addition to the remaining battery energy of the D2D transmitter, we consider the effects of both the interference caused by the generic D2D transmitter to others and the interference from all others caused to the generic D2D receiver. We formulate a mean-field game (MFG) theoretic framework with the interference mean-field approximation. We design the cost function combining both the performance of the D2D communication and cost for transmit power at the D2D transmitter. Within the MFG framework, we derive the related Hamilton–Jacobi–Bellman and Fokker–Planck–Kolmogorov equations. Then, a novel energy and interference aware power control policy is proposed, which is based on the Lax–Friedrichs scheme and the Lagrange relaxation. The numerical results are presented to demonstrate the spectrum and energy efficiency performances of our proposed approach.
114 citations
TL;DR: It is demonstrated that anisotropic all-dielectric metamaterials open a new degree of freedom in total internal reflection to shorten the decay length of evanescent waves, and can reduce cross-talk and bending loss, which limit the integration density in photonic circuits.
Abstract: Ultra-compact, densely integrated optical components manufactured on a CMOS-foundry platform are highly desirable for optical information processing and electronic-photonic co-integration. However, the large spatial extent of evanescent waves arising from nanoscale confinement, ubiquitous in silicon photonic devices, causes significant cross-talk and scattering loss. Here, we demonstrate that anisotropic all-dielectric metamaterials open a new degree of freedom in total internal reflection to shorten the decay length of evanescent waves. We experimentally show the reduction of cross-talk by greater than 30 times and the bending loss by greater than 3 times in densely integrated, ultra-compact photonic circuit blocks. Our prototype all-dielectric metamaterial-waveguide achieves a low propagation loss of approximately 3.7 dB/cm, comparable to those of silicon strip waveguides. Our approach marks a departure from interference-based confinement as in photonic crystals or slot waveguides, which utilize nanoscale field enhancement. Its ability to suppress evanescent waves without substantially increasing the propagation loss shall pave the way for all-dielectric metamaterial-based dense integration.
109 citations
TL;DR: In this paper, the authors extend this to generic multi-level modulations by establishing connection to PHY layer multicasting with phase constraints, and design the signal processing algorithms for minimizing the required power under per-user signal to interference noise ratio or goodput constraints.
Abstract: Symbol-level precoding is a new paradigm for multiuser multiple-antenna downlink systems aimed at creating constructive interference among transmitted data streams. This can be enabled by designing the precoded signal of the multiantenna transmitter on a symbol level, taking into account both channel state information and data symbols. Previous literature has studied this paradigm for Mary phase shift keying modulations by addressing various performance metrics, such as power minimization and maximization of the minimum rate. In this paper, we extend this to generic multi-level modulations, i.e., Mary quadrature amplitude modulation by establishing connection to PHY layer multicasting with phase constraints. Furthermore, we address the adaptive modulation schemes which are crucial in enabling the throughput scaling of symbol-level precoded systems. In this direction, we design the signal processing algorithms for minimizing the required power under per-user signal to interference noise ratio or goodput constraints. Extensive numerical results show that the proposed algorithm provides considerable power and energy efficiency gains, while adapting the employed modulation scheme to match the requested data rate.
96 citations
TL;DR: A new approach to constant-envelope precoding (CEP) based on an interference-driven optimization region for generic phase-shift-keying modulations in the multi-user (MU) multiple-input-multiple-output downlink is introduced.
Abstract: We introduce a new approach to constant-envelope precoding (CEP) based on an interference-driven optimization region for generic phase-shift-keying modulations in the multi-user (MU) multiple-input-multiple-output downlink. While conventional precoding approaches aim to minimize the multi-user interference (MUI) with a total sum-power constraint at the transmitter, in the proposed scheme we consider MUI as a source of additional energy to increase the signal-to-interference-and-noise-ratio at the receiver. In our studies, we focus on two different CEP approaches: a first technique, where the power at each antenna is fixed to a specific value, and a two-step approach, where we first relax the power constraints to be lower than a defined parameter and then enforce CEP transmission. The algorithms are studied in terms of computational costs, with a detailed comparison between the proposed approach and the classical interference suppression schemes from the literature. Moreover, we analytically derive a robust optimization region to counteract the effects of channel-state estimation errors. The presented schemes are evaluated in terms of achievable symbol error rate in a perfect and imperfect channel-state information scenario for different modulation orders. Our results show that the proposed techniques further extend the benefits of classical CEP by judiciously relaxing the optimization region.
TL;DR: In this paper, the authors proposed a multi-cell minimum mean square error (M-MMSE) scheme for massive MIMO networks, which includes an uplink MMSE detector and a downlink MMSE precoder.
Abstract: A new state-of-the-art multi-cell minimum mean square error (M-MMSE) scheme is proposed for massive multiple-input-multiple-output (MIMO) networks, which includes an uplink MMSE detector and a downlink MMSE precoder. Contrary to conventional single-cell schemes that suppress interference using only channel estimates for intra-cell users, our scheme shows the optimal way to suppress both intra-cell and inter-cell interference instantaneously by fully utilizing the available pilot resources. Specifically, let K and B denote the number of users per cell and the number of orthogonal pilot sequences in the network, respectively, where β=B/K is the pilot reuse factor. Our scheme utilizes all B channel directions that can be estimated locally at each base station, to actively suppress both intra-cell and inter-cell interference. Our scheme is practical and general, since power control, imperfect channel estimation, and arbitrary pilot allocation are all accounted for. Simulations show that significant spectral efficiency (SE) gains are obtained over the conventional single-cell MMSE scheme and the multi-cell zero-forcing (ZF) scheme. Furthermore, large-scale approximations of the uplink and downlink signal-to-interference-and-noise ratios (SINRs) are derived, which are tight in the large-system limit. These approximations are easy to compute and very accurate even for small system dimensions. Using these SINR approximations, a low-complexity power control algorithm is further proposed to maximize the sum SE.
TL;DR: In this paper, a multipole decomposition of the electromagnetic field is proposed to describe the scattering intensity of an arbitrary nanoscale object, which can be characterized by a multi-particle decomposition.
Abstract: Scattering of electromagnetic waves by an arbitrary nanoscale object can be characterized by a multipole decomposition of the electromagnetic field that allows one to describe the scattering intens...
TL;DR: In this paper, the authors present a design framework for hybrid beamforming for multi-cell multiuser massive MIMO systems over mmWave channels characterized by sparse propagation paths, where different factors of the analog beamformer are designed for either nulling interference paths or coherently combining data paths.
Abstract: Millimeter-wave (mmWave) massive multiple-input multiple-output (MIMO) seamlessly integrates two wireless technologies, mmWave communications and massive MIMO , which provides spectrums with tens of GHz of total bandwidth and supports aggressive space division multiple access using large-scale arrays. Though it is a promising solution for next-generation systems, the realization of mmWave massive MIMO faces several practical challenges. In particular, implementing massive MIMO in the digital domain requires hundreds to thousands of radio frequency chains and analog-to-digital converters matching the number of antennas. Furthermore, designing these components to operate at the mmWave frequencies is challenging and costly. These motivated the recent development of the hybrid-beamforming architecture, where MIMO signal processing is divided for separate implementation in the analog and digital domains, called the analog and digital beamforming , respectively. Analog beamforming using a phase array introduces uni-modulus constraints on the beamforming coefficients. They render the conventional MIMO techniques unsuitable and call for new designs. In this paper, we present a systematic design framework for hybrid beamforming for multi-cell multiuser massive MIMO systems over mmWave channels characterized by sparse propagation paths. The framework relies on the decomposition of analog beamforming vectors and path observation vectors into Kronecker products of factors being uni-modulus vectors. Exploiting properties of Kronecker mixed products, different factors of the analog beamformer are designed for either nulling interference paths or coherently combining data paths. Furthermore, a channel estimation scheme is designed for enabling the proposed hybrid beamforming. The scheme estimates the angles-of-arrival (AoA) of data and interference paths by analog beam scanning and data-path gains by analog beam steering. The performance of the channel estimation scheme is analyzed. In particular, the AoA spectrum resulting from beam scanning, which displays the magnitude distribution of paths over the AoA range, is derived in closed form. It is shown that the inter-cell interference level diminishes inversely with the array size, the square root of pilot sequence length, and the spatial separation between paths, suggesting different ways of tackling pilot contamination.
TL;DR: It is found that while modulation on the real part of the eigenvalue induces pulse timing drift and leads to neighboring pulse interactions and nonlinear inter-symbol interference (ISI), it is more bandwidth efficient than modulation in practical settings.
Abstract: In this paper, we experimentally investigate high-order modulation over a single discrete eigenvalue under the nonlinear Fourier transform (NFT) framework and exploit all degrees of freedom for encoding information. For a fixed eigenvalue, we compare different 4 bit/symbol modulation formats on the spectral amplitude and show that a 2-ring 16-APSK constellation achieves optimal performance. We then study joint spectral phase, spectral magnitude and eigenvalue modulation and found that while modulation on the real part of the eigenvalue induces pulse timing drift and leads to neighboring pulse interactions and nonlinear inter-symbol interference (ISI), it is more bandwidth efficient than modulation on the imaginary part of the eigenvalue in practical settings. We propose a spectral amplitude scaling method to mitigate such nonlinear ISI and demonstrate a record 4 GBaud 16-APSK on the spectral amplitude plus 2-bit eigenvalue modulation (total 6 bit/symbol at 24 Gb/s) transmission over 1000 km.
TL;DR: It is shown that these intensity variations can be entirely suppressed by adding disorder-specific gain and loss components to the medium and the resulting constant-intensity waves in such non-Hermitian scattering landscapes are free of any backscattering and feature perfect transmission through the disorder.
Abstract: A fundamental manifestation of wave scattering in a disordered medium is the highly complex intensity pattern the waves acquire due to multi-path interference. Here we show that these intensity variations can be entirely suppressed by adding disorder-specific gain and loss components to the medium. The resulting constant-intensity waves in such non-Hermitian scattering landscapes are free of any backscattering and feature perfect transmission through the disorder. An experimental demonstration of these unique wave states is envisioned based on spatially modulated pump beams that can flexibly control the gain and loss components in an active medium. Constant-intensity waves that can travel through a disordered medium without being scattered or reflected are being theoretically predicted. The analysis of Konstantinos Makris of the University of Crete, Greece, and co-workers from Austria and the United States suggests that such constant-intensity waves can form in a general disordered medium provided a suitable distribution of the imaginary part of the medium’s refractive index is achieved by spatially varying the gain and loss of the medium appropriately. In other words, adding a judiciously selected gain-and-loss distribution to a disordered medium causes waves to lose all of their internal intensity variations so that they travel through the disorder without being back-reflected. This behaviour should be experimentally confirmable by spatially modulating the pump beams in an active medium to create the desired gain-loss profile.
19 Mar 2017
TL;DR: The study concludes that without interference, both LoRaWAN and Sig fox provides very good indoor coverage of more than 99 % and Sigfox can provide uplink and downlink failure rates of less than 1 % for the 95 percentile of the devices for all cells without external interference.
Abstract: In this paper we analyze and discuss the coverage and capacity of Sigfox and LoRaWAN in a large scale urban environments covering 150 km$^2$ in Northern Denmark. First, the study measures and analyzes interference in the European 868 MHz license free industrial, scientific, and medical band, creating a model for the interference. The measured interference in downtown Aalborg has an occurrence rate of 22 % and a generalized extreme value distributed power level. Next, the study compares the coverage of the two Internet of Things network solutions using the existing Telenor cellular site grid both with and without interference from the measured external sources. The study concludes that without interference, both LoRaWAN and Sigfox provides very good indoor coverage of more than 99 %. Furthermore, Sigfox and LoRaWAN can provide uplink and downlink failure rates of less than 1 % for the 95 percentile of the devices for all cells without external interference. Adding the external interference results in an outdoor coverage of 90- 95 % and indoor coverage of 50-80 %. Finally, the uplink and downlink 95 percentile failure rate increases significantly to 50 % for LoRaWAN and exceeds 60 % for Sigfox.
TL;DR: This letter derives closed-form bit error probability (BEP) expressions for arbitrary linear modulation methods based on one-tap equalizers, with OFDM and FBMC being special cases, covered by the general BEP expressions.
Abstract: Filter bank multi-carrier (FBMC) is a modulation technique with enhanced spectral properties compared with orthogonal frequency division multiplexing (OFDM). In this letter, we investigate the performance degeneration of OFDM and FBMC in doubly-selective channels, that is, time-selectivity and frequency-selectivity. For that, we derive closed-form bit error probability (BEP) expressions for arbitrary linear modulation methods based on one-tap equalizers, with OFDM and FBMC being special cases, covered by our general BEP expressions. We validate our calculations by Monte Carlo simulations and investigate the BEP error if the interference is approximated as Gaussian noise.
TL;DR: In this paper, the authors investigated the application of fast-convolution (FC) filtering schemes for flexible and effective waveform generation and processing in the 5G systems and presented a generic multimode waveform processing engine, while, following the progress of 5G new radio standardization in the Third-Generation Partnership Project, the main focus is on efficient generation of subband-filtered cyclic prefix orthogonal frequency-division multiplexing (CP-OFDM) signals.
Abstract: This paper investigates the application of fast-convolution (FC) filtering schemes for flexible and effective waveform generation and processing in the fifth generation (5G) systems. FC-based filtering is presented as a generic multimode waveform processing engine while, following the progress of 5G new radio standardization in the Third-Generation Partnership Project, the main focus is on efficient generation and processing of subband-filtered cyclic prefix orthogonal frequency-division multiplexing (CP-OFDM) signals. First, a matrix model for analyzing FC filter processing responses is presented and used for designing optimized multiplexing of filtered groups of CP-OFDM physical resource blocks (PRBs) in a spectrally well-localized manner, i.e., with narrow guardbands. Subband filtering is able to suppress interference leakage between adjacent subbands, thus supporting independent waveform parametrization and different numerologies for different groups of PRBs, as well as asynchronous multiuser operation in uplink. These are central ingredients in the 5G waveform developments, particularly at sub-6-GHz bands. The FC filter optimization criterion is passband error vector magnitude minimization subject to a given subband band-limitation constraint. Optimized designs with different guardband widths, PRB group sizes, and essential design parameters are compared in terms of interference levels and implementation complexity. Finally, extensive coded 5G radio link simulation results are presented to compare the proposed approach with other subband-filtered CP-OFDM schemes and time-domain windowing methods, considering cases with different numerologies or asynchronous transmissions in adjacent subbands. Also the feasibility of using independent transmitter and receiver processing for CP-OFDM spectrum control is demonstrated
TL;DR: Three photons can display qualitatively new interference phenomena such as genuine three-photon interference, and this work shows how to isolate three- photon interference with more than 90 % visibility, completely suppressing two-photons and single-Photon interference.
Abstract: Multiparticle quantum interference is critical for our understanding and exploitation of quantum information, and for fundamental tests of quantum mechanics. A remarkable example of multi-partite correlations is exhibited by the Greenberger-Horne-Zeilinger (GHZ) state. In a GHZ state, three particles are correlated while no pairwise correlation is found. The manifestation of these strong correlations in an interferometric setting has been studied theoretically since 1990 but no three-photon GHZ interferometer has been realized experimentally. Here we demonstrate three-photon interference that does not originate from two-photon or single photon interference. We observe phase-dependent variation of three-photon coincidences with (92.7±4.6)% visibility in a generalized Franson interferometer using energy-time entangled photon triplets. The demonstration of these strong correlations in an interferometric setting provides new avenues for multiphoton interferometry, fundamental tests of quantum mechanics, and quantum information applications in higher dimensions.
TL;DR: It is shown that the proposed probabilistic interference constraint method with a radio environment map (REM) for spatial spectrum sharing has a higher spectrum sharing opportunity than the path loss-based method, even if only a small amount of measurement data is available.
Abstract: This paper proposes a probabilistic interference constraint method with a radio environment map (REM) for spatial spectrum sharing. The REM stores the spatial distribution of the average received signal power. We can optimize the accuracy of the measurement-based REM using the Kriging interpolation. Although several researchers have maintained a continuous interest in improving the accuracy of the REM, sufficient study has not been done to actually explore the interference constraint considering the estimation error. The proposed method uses ordinary Kriging interpolation for the spectrum cartography. According to the predicted distribution of the estimation error, the allowable interference power to the primary user is approximately formulated. Numerical results show that the proposed method can achieve the probabilistic interference constraint asymptotically. Additionally, we compare the performance of the proposed technique with three methods: the perfect estimation, the path loss-based method, and the Kriging-based method without the error prediction. The comparison results show that the proposed method has a higher spectrum sharing opportunity than the path loss-based method, even if only a small amount of measurement data is available. It is also shown that the proposed method dramatically improves the outage probability of the interference power compared to the conventional Kriging-based method.
TL;DR: In this article, the performance of underwater optical wireless communication systems employing spatial diversity and multi-pulse position modulation techniques is assessed, where the effects of inter-symbol interference, oceanic turbulence and receiver noise are taken into account.
Abstract: In this study, the performance of underwater optical wireless communication systems employing spatial diversity and multi-pulse position modulation techniques is assessed. The effects of inter-symbol interference, oceanic turbulence and receiver noise are taken into account. Oceanic turbulence is modelled by the log-normal distribution which is regarded as an appropriate model for weak turbulence conditions. For the system under consideration, approximate analytical expressions for the average bit error probability are deduced. The impact of the number of transmitting and receiving apertures, the achievable data rate and the water type on system performance is also investigated. Various numerical results are presented that demonstrate the proposed analysis.
TL;DR: In this paper, an interference detection method for multiuser-multiple input multiple output (MU-MIMO) transmission, which utilizes periodical preamble signals in the frequency domain and the concept of full-duplex transmission when assuming idle antennas at the access point (AP) in MU MIMO, is proposed.
Abstract: This paper proposes an interference detection method for multiuser-multiple input multiple output (MU-MIMO) transmission, which utilizes periodical preamble signals in the frequency domain and the concept of full-duplex transmission when assuming idle antennas at the access point (AP) in MU-MIMO. In the propose method, collision detection (CD) of MU-MIMO is achieved by utilizing asynchronous MU-MIMO called random access MU-MIMO. In random access MU-MIMO, several antennas that are not used for the transmission exist, due to asynchronous MU-MIMO. Hence, idle antennas at the AP can receive preamble signals while the transmit antennas at the AP transmit the preamble signals: this procedure is regarded as full-duplex transmission, which cancels the self-interference between AP antennas. The interference can be detected by subtracting the short preamble signal, which is multiplied by the estimated channel response using the received signal after the FFT processing. Moreover, we utilize dual polarization to reduce the mutual coupling between transmit and receive antennas at the AP. Through a computer simulation, it is shown that the proposed method can successfully detect collision from other user terminals (UTs) with OFDM signals when the interfering power from the interfering user terminal (IT) is greater than the noise power. In addition, the interfering power from IT at the AP and the desired user terminal (DT) is measured in an actual indoor environment, and the possibility of using the proposed method at the AP is discussed by using the measurement results.
TL;DR: In this paper, a generalized Gaussian noise (GGN) model is proposed to predict nonlinear interference when loss parameters relevantly vary with frequency and/or distributed amplification applies selectively to portions of the exploited spectrum.
Abstract: We develop and present a generalization of the GN-model - the generalized Gaussian noise (GGN) model - to enabling a fair application of GN-model to predict generation of nonlinear interference when loss parameters relevantly vary with frequency and/or distributed amplification applies selectively to portions of the exploited spectrum and/or stimulated-Raman-scattering-induced crosstalk is relevant.
TL;DR: In this article, the authors used hollow-core microstructured optical fibers (HC-MOFs) and direct absorption/photothermal interferometry spectroscopy for gas detection.
Abstract: Recent progress in gas detection with hollow-core microstructured optical fibers (HC-MOFs) and direct absorption/photothermal interferometry spectroscopy are reported. For direct-absorption sensors, the issue of mode interference noise is addressed and techniques to minimize such a noise are experimentally demonstrated. Large-scale drilling of hundreds of low-loss micro-channels along a single HC-MOF is performed, and reduction of diffusion-limited response time from hours to ∼40 s is demonstrated with a 2.3-m-long HC-MOF. For photothermal inteferometry sensors, novel detection configurations based on respectively a Sagnac interferometer and an in-fiber modal interferometer are experimentally demonstrated. The Sagnac configuration avoids the need for complex servo-control for interferometer stabilization while the in-fiber configuration simplifies the detection, reducing the size and cost of the sensor system. Sub ppm gas detection can be achieved easily with photothermal interferometry HC-MOF sensors but is difficult to achieve for direct-absorption sensors with the current commercial HC-MOFs.
TL;DR: This work allows a broad category of optical networks to be set up progressively and automatically, including correcting for fabrication imprecision, and null interference locally in the network based on inputs calculated by considering the network operated in reverse.
Abstract: Many interesting linear optical networks, such as lattice filters and some interferometer meshes, are difficult to fabricate precisely and cannot be configured progressively even using recent algorithms. Our approach allows a broad category of optical networks to be set up progressively and automatically, including correcting for fabrication imprecision. We null interference locally in the network based on inputs calculated by considering the network operated in reverse. Calibration is only required for the network inputs, not for individual components (though this method can also calibrate those). We illustrate specific cases of lattice filters and rectangular meshes of interferometers, and we expect the approach can be applied broadly to networks in which the light only propagates forward in the network.
TL;DR: In this paper, the existence of higher order interference terms in optical interferometry was shown to be inapplicable to quantum mechanics, to an extent that is more than four orders of magnitude smaller than the expected pairwise interference.
Abstract: Within the established theoretical framework of quantum mechanics, interference always occurs between pairs of paths through an interferometer. Higher order interferences with multiple constituents are excluded by Born's rule and can only exist in generalized probabilistic theories. Thus, high-precision experiments searching for such higher order interferences are a powerful method to distinguish between quantum mechanics and more general theories. Here, we perform such a test in an optical multi-path interferometer, which avoids crucial systematic errors, has access to the entire phase space and is more stable than previous experiments. Our results are in accordance with quantum mechanics and rule out the existence of higher order interference terms in optical interferometry to an extent that is more than four orders of magnitude smaller than the expected pairwise interference, refining previous bounds by two orders of magnitude.
TL;DR: Next-to-leading order QCD corrections to the top-bottom interference contribution to H+j production at the LHC are computed and it is found that QCD Corrections to the interference are large and similar to the QCD correction to thetop-mediated Higgs production cross section.
Abstract: We compute next-to-leading order QCD corrections to the top-bottom interference contribution to H+j production at the LHC. To achieve this, we combine the recent computation of the two-loop amplitudes for gg→Hg and qg→Hq, performed in the approximation of a small b-quark mass, and the numerical calculation of the squared one-loop amplitudes for gg→Hgg and qg→Hqg, performed within OpenLoops. We find that QCD corrections to the interference are large and similar to the QCD corrections to the top-mediated Higgs production cross section. We also observe a significant reduction in the mass-renormalization scheme uncertainty once the next-to-leading order QCD prediction for the interference is employed.
TL;DR: It is envisioned that a new class of low-power, high-speed, special-purpose signal processors can be realized by spin-waves, and all performance figures of this magnetoelectric device at room temperature may be significantly better than what is achievable in a purely electrical system.
Abstract: We present the design of a spin-wave-based microwave signal processing device. The microwave signal is first converted into spin-wave excitations, which propagate in a patterned magnetic thin-film. An interference pattern is formed in the film and its intensity distribution at appropriate read-out locations gives the spectral decomposition of the signal. We use analytic calculations and micromagnetic simulations to verify and to analyze the operation of the device. The results suggest that all performance figures of this magnetoelectric device at room temperature (speed, area, power consumption) may be significantly better than what is achievable in a purely electrical system. We envision that a new class of low-power, high-speed, special-purpose signal processors can be realized by spin-waves.
TL;DR: In this article, a composite interference structure constructed with the combination of Sagnac loop mirror and balloon-like interferometer for simultaneous measurement of refractive index (RI) and temperature is proposed and experimentally demonstrated.
Abstract: A novel composite interference structure constructed with the combination of Sagnac loop mirror and balloon-like interferometer for simultaneous measurement of refractive index (RI) and temperature is proposed and experimentally demonstrated. A polarization maintaining fiber (PMF) is embedded into the Sagnac loop structure to form a Sagnac loop interferometer, which is highly sensitive to external temperature variations. The balloon-like structure is built with a bend single mode fiber (SMF) to form a modal interferometer, which is sensitive to both external RI and temperature variations. As the two sensing structures are based different interference principles, the two interference spectra do not interfere with each other. By optimizing the bending diameter of the balloon-like interferometer and the length of PMF in the Sagnac loop mirror, separate different resonance wavelengths can be well formed. Hence, the simultaneous measurement of RI and temperature can be realized by monitoring the shift of different resonance wavelengths. Experimental results show that the optimal sensitivities of the RI and temperature can reach up to 218.56 nm/RIU and 1.7 nm/°C, respectively.