Showing papers on "Interference (wave propagation) published in 2011"
TL;DR: Targeting at minimal interference power, a broad range of multiple-input multiple-output mitigation schemes are analyzed and the results confirm that self-interference can be mitigated effectively also in the presence of imperfect side information.
Abstract: Full-duplex relaying is more spectrally efficient than half-duplex relaying as only one channel use is needed per two hops. However, it is crucial to minimize relay self-interference to render full duplex feasible. For this purpose, we analyze a broad range of multiple-input multiple-output (MIMO) mitigation schemes: natural isolation, time-domain cancellation, and spatial suppression. Cancellation subtracts replicated interference signal from the relay input while suppression reserves spatial dimensions for receive and transmit filtering. Spatial suppression can be achieved by antenna subset selection, null-space projection, i.e., receiving and transmitting in orthogonal subspaces, or joint transmit and receive beam selection to support more spatial streams by choosing the minimum eigenmodes for overlapping subspaces. In addition, minimum mean square error (MMSE) filtering can be employed to maintain the desired signal quality, which is inherent for cancellation, and the combination of time- and spatial-domain processing may be better than either alone. Targeting at minimal interference power, we solve optimal filters for each scheme in the cases of joint, separate and independent design. The performance of mitigation schemes is evaluated and compared by simulations. The results confirm that self-interference can be mitigated effectively also in the presence of imperfect side information.
944 citations
TL;DR: A new interference management strategy is proposed to enhance the overall capacity of cellular networks (CNs) and device-to-device (D2D) systems and derive the lower bound of the ergodic capacity as a closed form.
Abstract: A new interference management strategy is proposed to enhance the overall capacity of cellular networks (CNs) and device-to-device (D2D) systems. We consider M out of K cellular user equipments (CUEs) and one D2D pair exploiting the same resources in the uplink (UL) period under the assumption of M multiple antennas at the base station (BS). First, we use the conventional mechanism which limits the maximum transmit power of the D2D transmitter so as not to generate harmful interference from D2D systems to CNs. Second, we propose a δD-interference limited area (ILA) control scheme to manage interference from CNs to D2D systems. The method does not allow the coexistence (i.e., use of the same resources) of CUEs and a D2D pair if the CUEs are located in the δD-ILA defined as the area in which the interference to signal ratio (ISR) at the D2D receiver is greater than the predetermined threshold, δD. Next, we analyze the coverage of the δD-ILA and derive the lower bound of the ergodic capacity as a closed form. Numerical results show that the δD-ILA based D2D gain is much greater than the conventional D2D gain, whereas the capacity loss to the CNs caused by using the δD-ILA is negligibly small.
557 citations
TL;DR: In this paper, an interference alignment (IA) technique for a downlink cellular system is proposed, which requires feedback only within a cell, which can provide substantial gain especially when interference from a dominant interferer is significantly stronger than the remaining interference.
Abstract: We develop an interference alignment (IA) technique for a downlink cellular system. In the uplink, IA schemes need channel-state-information exchange across base-stations of different cells, but our downlink IA technique requires feedback only within a cell. As a result, the proposed scheme can be implemented with a few changes to an existing cellular system where the feedback mechanism (within a cell) is already being considered for supporting multi-user MIMO. Not only is our proposed scheme implementable with little effort, it can in fact provide substantial gain especially when interference from a dominant interferer is significantly stronger than the remaining interference: it is shown that in the two-isolated cell layout, our scheme provides four-fold gain in throughput performance over a standard multi-user MIMO technique. We also show through simulations that our technique provides respectable gain under a more realistic scenario: it gives approximately 28% gain for a 19 hexagonal wrap-around-cell layout. Furthermore, we show that our scheme has the potential to provide substantial gain for macro-pico cellular networks where pico-users can be significantly interfered with by the nearby macro-BS.
368 citations
TL;DR: Numerical results show that by applying the receive mode selection, the D2D receiver achieves a remarkable enhancement of outage probability in the middle interference regime from the usage of MODE3 compared to the conventional ways of using only MODE1 or MODE2.
Abstract: A new interference management scheme is proposed to improve the reliability of a device-to-device (D2D) communication in the uplink (UL) period without reducing the power of cellular user equipment (UE). To improve the reliability of the D2D receiver, two conventional receive techniques and one proposed method are introduced. One of the conventional methods is demodulating the desired signal first (MODE1), while the other is demodulating an interference first (MODE2), and the proposed method is exploiting a retransmission of the interference from the base station (BS) (MODE3). We derive their outage probabilities in closed forms and explain the mechanism of receive mode selection which selects the mode guaranteeing the minimum outage probability among three modes. Numerical results show that by applying the receive mode selection, the D2D receiver achieves a remarkable enhancement of outage probability in the middle interference regime from the usage of MODE3 compared to the conventional ways of using only MODE1 or MODE2.
346 citations
TL;DR: This work proposes a new statistical model for aggregate interference of a cognitive network, which accounts for the sensing procedure, secondary spatial reuse protocol, and environment-dependent conditions such as path loss, shadowing, and channel fading, and demonstrates the effectiveness of this model in evaluating the system performance of cognitive networks.
Abstract: Opportunistic spectrum access creates the opening of under-utilized portions of the licensed spectrum for reuse, provided that the transmissions of secondary radios do not cause harmful interference to primary users. Such a system would require secondary users to be cognitive-they must accurately detect and rapidly react to varying spectrum usage. Therefore, it is important to characterize the effect of cognitive network interference due to such secondary spectrum reuse. In this paper, we propose a new statistical model for aggregate interference of a cognitive network, which accounts for the sensing procedure, secondary spatial reuse protocol, and environment-dependent conditions such as path loss, shadowing, and channel fading. We first derive the characteristic function and cumulants of the cognitive network interference at a primary user. Using the theory of truncated-stable distributions, we then develop the statistical model for the cognitive network interference. We further extend this model to include the effect of power control and demonstrate the use of our model in evaluating the system performance of cognitive networks. Numerical results show the effectiveness of our model for capturing the statistical behavior of the cognitive network interference. This work provides essential understanding of interference for successful deployment of future cognitive networks.
330 citations
TL;DR: This design provides an effective and feasible way to construct broad band absorber in stealth technology, as well as the enhanced transmittance devices.
Abstract: We propose a design of an extremely broad frequency band absorber based on destructive interference mechanism. Metamaterial of multilayered SRRs structure is used to realize a desirable refractive index dispersion spectrum, which can induce a successive anti-reflection in a wide frequency range. The corresponding high absorptance originates from the destructive interference of two reflection waves from the two surfaces of the metamaterial. A strongly absorptive bandwidth of almost 60GHz is demonstrated in the range of 0 to 70GHz numerically. This design provides an effective and feasible way to construct broad band absorber in stealth technology, as well as the enhanced transmittance devices.
315 citations
TL;DR: It is shown that MK/M+K-1 degrees of freedom are achievable, without any knowledge of the channel coefficient values at the transmitters and with only mild assumptions on the channel coherence structure.
Abstract: We propose a blind interference alignment scheme for the vector broadcast channel where the transmitter is equipped with M antennas and there are K receivers, each equipped with a reconfigurable antenna capable of switching among M preset modes Without any knowledge of the channel coefficient values at the transmitters and with only mild assumptions on the channel coherence structure we show that MK/M+K-1 degrees of freedom are achievable The key to the blind interference alignment scheme is the ability of the receivers to switch between reconfigurable antenna modes to create short term channel fluctuation patterns that are exploited by the transmitter The achievable scheme does not require cooperation between transmit antennas and is therefore applicable to the M × K X network as well Only finite symbol extensions are used, and no channel knowledge at the receivers is required to null the interference
280 citations
TL;DR: Several downlink multiuser multiple input multiple output (MIMO) DAS strategies are proposed and compared in terms of per-user throughput and area spectral efficiency and approximations of the ergodic rate are proposed to facilitate rapid simulation and design space exploration.
Abstract: Distributed antenna systems (DAS) augment the base station's transmit capability by adding multiple remote radio units, connected to the base station via a high bandwidth and low latency link. With DAS, the base station operates as if it had multiple antennas, but the antennas happen to be in different geographic locations. DAS have been shown to enhance coverage and capacity in cellular systems, in a variety of different configurations. This paper proposes, analyzes, and compares several downlink multiuser multiple input multiple output (MIMO) DAS strategies in terms of per-user throughput and area spectral efficiency. Zero-forcing transmit beamforming is used for transmission, the remote radio units may have one or more antennas, and the subscriber has a single receive antenna. Techniques considered include beamforming across all remote radio units (full transmission), using the same beamforming vector for each remote radio unit (simplified transmission), and selecting a subset of remote radio units. To facilitate rapid simulation and design space exploration, approximations of the ergodic rate are proposed for each technique assuming path-loss, small-scale Rayleigh fading, and out-of-cell interference. Simulations accounting for multiple interfering cells are used to compare the different transmission techniques. Full transmission is found to have the best performance even accounting for out-of-cell interference, though gains diminish for higher numbers of active users. Simplified transmission improves over no DAS but performance degrades with more active remote radio units.
248 citations
TL;DR: In the proposed MF-SIC algorithm with shadow area constraints (SAC), an enhanced interference cancellation is achieved by introducingconstellation points as the candidates to combat the error propagation in decision feedback loops.
Abstract: In this paper, a low-complexity multiple feedback successive interference cancellation (MF-SIC) strategy is proposed for the uplink of multiuser multiple-input multiple-output (MU-MIMO) systems. In the proposed MF-SIC algorithm with shadow area constraints (SAC), an enhanced interference cancellation is achieved by introducing {constellation points as the candidates} to combat the error propagation in decision feedback loops. We also combine the MF-SIC with multi-branch (MB) processing, which achieves a higher detection diversity order. For coded systems, a low-complexity soft-input soft-output (SISO) iterative (turbo) detector is proposed based on the MF and the MB-MF interference suppression techniques. The computational complexity of the MF-SIC is comparable to the conventional SIC algorithm since very little additional complexity is required. Simulation results show that the algorithms significantly outperform the conventional SIC scheme and approach the optimal detector.
236 citations
TL;DR: In this article, the mean interference observed at a node of the hard core process and compare it with the average mean interference in a Poisson point process of the same density is compared.
Abstract: Matern hard core processes of types I and II are the point processes of choice to model concurrent transmitters in CSMA networks. We determine the mean interference observed at a node of the process and compare it with the mean interference in a Poisson point process of the same density. It turns out that despite the similarity of the two models, they behave rather differently. For type I, the excess interference (relative to the Poisson case) increases exponentially in the hard-core distance, while for type II, the gap never exceeds 1 dB.
227 citations
Posted Content•
TL;DR: It turns out that despite the similarity of the two models, they behave rather differently, for type I, the excess interference increases exponentially in the hard-core distance, while for type II, the gap never exceeds 1 dB.
Abstract: Matern hard core processes of types I and II are the point processes of choice to model concurrent transmitters in CSMA networks. We determine the mean interference observed at a node of the process and compare it with the mean interference in a Poisson point process of the same density. It turns out that despite the similarity of the two models, they behave rather differently. For type I, the excess interference (relative to the Poisson case) increases exponentially in the hard-core distance, while for type II, the gap never exceeds 1 dB.
Posted Content•
TL;DR: In this article, the authors considered a two-user Gaussian interference channel with energy harvesting transmitters and formulated an optimal power allocation problem to maximize the sum throughput with a given deadline.
Abstract: This paper considers a two-user Gaussian interference channel with energy harvesting transmitters. Different than conventional battery powered wireless nodes, energy harvesting transmitters have to adapt transmission to availability of energy at a particular instant. In this setting, the optimal power allocation problem to maximize the sum throughput with a given deadline is formulated. The convergence of the proposed iterative coordinate descent method for the problem is proved and the short-term throughput maximizing offline power allocation policy is found. Examples for interference regions with known sum capacities are given with directional water-filling interpretations. Next, stochastic data arrivals are addressed. Finally online and/or distributed near-optimal policies are proposed. Performance of the proposed algorithms are demonstrated through simulations.
TL;DR: To understand the working principle of the SSAW-based 3D focusing and investigate the position of the focal point, computed longitudinal waves, generated by the SAWs and radiated into the fluid media from opposite sides of the microchannel, and the resultant pressure and velocity fields due to the interference and reflection of the longitudinal waves.
Abstract: Three-dimensional (3D) continuous microparticle focusing has been achieved in a single-layer polydimethylsiloxane (PDMS) microfluidic channel using a standing surface acoustic wave (SSAW). The SSAW was generated by the interference of two identical surface acoustic waves (SAWs) created by two parallel interdigital transducers (IDTs) on a piezoelectric substrate with a microchannel precisely bonded between them. To understand the working principle of the SSAW-based 3D focusing and investigate the position of the focal point, we computed longitudinal waves, generated by the SAWs and radiated into the fluid media from opposite sides of the microchannel, and the resultant pressure and velocity fields due to the interference and reflection of the longitudinal waves. Simulation results predict the existence of a focusing point which is in good agreement with our experimental observations. Compared with other 3D focusing techniques, this method is non-invasive, robust, energy-efficient, easy to implement, and applicable to nearly all types of microparticles.
TL;DR: This paper considers average transmit and interference power constraints for both schemes, proposes two algorithms that acquire the optimal sensing time and power allocation under imperfect spectrum sensing for the two schemes, and discusses the effect of the average transmitand interference power constraint on the optimal Sensing time.
Abstract: Cognitive radio is an emerging technology that aims for efficient spectrum usage by allowing unlicensed (secondary) users to access licensed frequency bands under the condition of protecting the licensed (primary) users from harmful interference. The latter condition constraints the achievable throughput of a cognitive radio network, which should therefore access a wideband spectrum in order to provide reliable and efficient services to its users. In this paper, we study the problem of designing the optimal sensing time and power allocation strategy, in order to maximize the ergodic throughput of a cognitive radio that employs simultaneous multiband detection and operates under two different schemes, namely the wideband sensing-based spectrum sharing (WSSS) and the wideband opportunistic spectrum access (WOSA) scheme. We consider average transmit and interference power constraints for both schemes, in order to effectively protect the primary users from harmful interference, propose two algorithms that acquire the optimal sensing time and power allocation under imperfect spectrum sensing for the two schemes and discuss the effect of the average transmit and interference power constraint on the optimal sensing time. Finally, we provide simulation results to compare the two schemes and validate our theoretical analysis.
TL;DR: The proposed method is able to guarantee feasible solutions even if the interference information is outdated or incomplete, and allows for a number of special cases, where the backhaul information exchange is reduced at the cost of somewhat sub-optimal performance.
Abstract: A decentralized solution is proposed for the coordinated multi-cell multi-antenna minimum power beamformer design problem with single-antenna users. The optimal minimum power beamformers can be obtained locally at each base station (BS) relying on limited backhaul information exchange between BSs. The original centralized problem is reformulated such that the BSs are coupled by real-valued inter-cell interference terms. The coupling is handled by taking local copies of the interference terms at each BS and enforcing consistency between them. The consistency constraints are then decoupled by a standard dual decomposition approach leading to a distributed algorithm. The proposed method is able to guarantee feasible solutions even if the interference information is outdated or incomplete. In addition, the proposed approach allows for a number of special cases, where the backhaul information exchange is reduced at the cost of somewhat sub-optimal performance. The performance of the proposed coordinated multi-cell transmission is compared with the coherent multi-cell beamforming and with inter-cell interference nulling in different scenarios with varying interference. A near-optimal performance can be achieved even with significantly reduced backhaul information exchange and with relatively high velocities and/or low backhaul signaling rates.
TL;DR: In this article, a displacement sensor with sub-nanometer resolution based on the fiber-optic Fabry-Perot interferometer is proposed, which is able to provide sub-nodes of up to 0.084 nm over a dynamic range of 3 mm.
Abstract: A displacement sensor with subnanometer resolution based on the fiber-optic Fabry-Perot interferometer is proposed. The Fabry-Perot cavity is formed between the fiber end face and a high reflectivity mirror, which effectively improved the contrast of the interference fringe. Meanwhile, since the measuring range and the demodulate resolution for Fabry-Perot sensor are difficult to be improved simultaneously, a novel demodulation method based on the combination of the Fourier transform method and the minimum mean square error estimation-based signal processing method has been presented, which is capable of providing subnanometer resolution and absolute measurement over a wide dynamic range. The experimental results show that the resolution of the sensor is up to 0.084 nm over a dynamic range of 3 mm.
TL;DR: In this article, an all-fiber high-sensitivity temperature fiber sensor based on a Mach-Zehnder interferometer in standard single-mode fibers (SMFs) is described.
Abstract: An all-fiber high-sensitivity temperature fiber sensor based on a Mach-Zehnder interferometer in standard single-mode fibers (SMFs) is described. The interferometer consists of two concatenated waist-enlarged fusion bitapers which are fabricated simply by cleaving and fusion splicing. It is demonstrated that such an all-fiber Mach-Zehnder interferometer incorporates intermodal interference between the LP01 mode and a high-order cladding mode of LP07 mode. Its response to temperature is investigated and a high sensitivity of 0.070 nm/°C is obtained by a 7.5 mm interferometer. This simple, low-cost and easy-to-fabricate core-cladding modal interferometer with entire SMF-based structure also has great potential in diverse sensing applications.
TL;DR: Numerical results show that cooperative transmission can improve the capacity performance of multi-cell multi-antenna cooperative cellular networks, especially in a scenario with a high density of interfering base stations.
Abstract: Characterization and modeling of co-channel interference is critical for the design and performance evaluation of realistic multi-cell cellular networks. In this paper, based on alpha stable processes, an analytical co-channel interference model is proposed for multi-cell multiple-input multi-output (MIMO) cellular networks. The impact of different channel parameters on the new interference model is analyzed numerically. Furthermore, the exact normalized downlink average capacity is derived for a multi-cell MIMO cellular network with co-channel interference. Moreover, the closed-form normalized downlink average capacity is derived for cell-edge users in multi-cell multiple-input single-output (MISO) cooperative cellular networks with co-channel interference. From the new co-channel interference model and capacity formulas, the impact of cooperative antennas and base stations on cell-edge user performance in the multi-cell multi-antenna cellular network is investigated by numerical methods. Numerical results show that cooperative transmission can improve the capacity performance of multi-cell multi-antenna cooperative cellular networks, especially in a scenario with a high density of interfering base stations. The capacity performance gain is degraded with the increased number of cooperative antennas or base stations.
01 Dec 2011
TL;DR: This work uses the Monte Carlo approach to simulate the trajectories of emitted photons propagating in water towards the receiver and shows that in most practical cases, the time dispersion is negligible and does not induce any inter-symbol interference on the received symbols.
Abstract: We consider in this paper channel modeling for underwater optical channels. In particular, we focus on the channel impulse response and quantify the channel time dispersion under different conditions of water type, link distance, and transmitter/receiver parameters. We use the Monte Carlo approach to simulate the trajectories of emitted photons propagating in water towards the receiver. We show that in most practical cases, the time dispersion is negligible and does not induce any inter-symbol interference on the received symbols. Our results can be used to appropriately set different system design parameters.
TL;DR: In this article, the number of particles produced from vacuum by a time-dependent electric field, incorporating the interference effects that arise from an arbitrary number of distinct semiclassical turning points, is derived for both scalar and spinor QED.
Abstract: We present simple new approximate formulas, for both scalar and spinor QED, for the number of particles produced from vacuum by a time-dependent electric field, incorporating the interference effects that arise from an arbitrary number of distinct semiclassical turning points. Such interference effects are important when the temporal profile of the laser pulse has subcycle structure. We show how the resulting semiclassical intuition may be used to guide the design of temporal profiles that enhance the momentum spectrum due to interference effects. The result is easy to implement and generally applicable to time-dependent tunneling problems, such as those that appear in many other contexts in particle and nuclear physics, condensed matter physics, atomic physics, chemical physics, and gravitational physics.
TL;DR: In this paper, the role of the Coulomb-dominated interference in the interference of the Fabry-P\'erot interferometer was explored, and it was shown that Coulomb interactions couple the interfering edge mode to localized quasiparticle states in the bulk, whose occupation is quantized in integer values.
Abstract: We analyze interference phenomena in the quantum-Hall analog of the Fabry-P\'erot interferometer, exploring the roles of the Aharonov-Bohm effect, Coulomb interactions, and fractional statistics on the oscillations of the resistance as one varies the magnetic field $B$ and/or the voltage ${V}_{G}$ applied to a side gate. Coulomb interactions couple the interfering edge mode to localized quasiparticle states in the bulk, whose occupation is quantized in integer values. For the integer quantum Hall effect, if the bulk-edge coupling is absent, the resistance exhibits an Aharonov-Bohm (AB) periodicity, where the phase is equal to the number of quanta of magnetic flux enclosed by a specified interferometer area. When bulk-edge coupling is present, the actual area of the interferometer oscillates as a function of $B$ and ${V}_{G}$, with a combination of smooth variation and abrupt jumps due to changes in the number of quasiparticles in the bulk of the interferometer. This modulates the AB phase and gives rise to additional periodicities in the resistance. In the limit of strong interactions, the amplitude of the AB oscillations becomes negligible, and one sees only the new ``Coulomb-dominated'' (CD) periodicity. In the limits where either the AB or the CD periodicities dominate, a color map of resistance will show a series of parallel stripes in the $B$-${V}_{G}$ plane, but the two cases show different stripe spacings and slopes of opposite signs. At intermediate coupling, one sees a superposition of the two patterns. We discuss dependences of the interference intensities on parameters including the temperature and the backscattering strengths of the individual constrictions. We also discuss how results are modified in a fractional quantized Hall system, and the extent to which the interferometer may demonstrate the fractional statistics of the quasiparticles.
01 Dec 2011
TL;DR: Simulation results are presented for an additive white Gaussian noise channel and it is shown that the new technique can achieve better optical power performance than the conventional schemes.
Abstract: In this paper, we present a new form of orthogonal frequency division multiplexing (OFDM) for intensity modulated direct detection (IM/DD) systems. This new form of OFDM uses asymmetrically clipped optical OFDM (ACO-OFDM) on the odd frequency subcarriers and DC biased optical OFDM (DCO-OFDM) on the even subcarriers. By using a form of interference cancellation both the ACO-OFDM and the DCO-OFDM signals can be recovered at the receiver. It is shown that the DCO-OFDM component causes no interference on the odd frequency subcarriers so the receiver processing for the ACO-OFDM signal is identical to a conventional ACO-OFDM system. The ACO-OFDM signal causes clipping noise which falls on the even subcarriers. However, this interference can be estimated and cancelled at the receiver. The cancellation process results in a 3 dB noise penalty in the DCO-OFDM component. Simulation results are presented for an additive white Gaussian noise channel and it is shown that the new technique can achieve better optical power performance than the conventional schemes.
TL;DR: Simulation results show that the proposed OIA scheme provides significant improvement in terms of sum rates, and does not require global channel state information, time/frequency expansion, and a number of iterations, thereby resulting in easier implementation.
Abstract: We introduce an opportunistic interference alignment (OIA) for cellular networks, where a user scheduling strategy is utilized in time-division duplexing uplink communication environments with time-invariant channel coefficients and multi-antenna base stations (BSs). In the OIA scheme, each BS opportunistically selects users who generate the minimum interference to the other BSs. More specifically, each BS broadcasts its pre-designed interference directions, e.g., orthonormal random vectors, to all the users in other cells. Then, each user computes the amount of its generating interference, affecting the other BSs, and feedbacks it to its home cell BS. Note that the proposed OIA does not require global channel state information, time/frequency expansion, and a number of iterations, thereby resulting in easier implementation. Simulation results show that the proposed scheme provides significant improvement in terms of sum rates.
TL;DR: It is shown that, for such interference channels with each receiver implementing single-user detection, transmitter beamforming can achieve all boundary points of the achievable rate region.
Abstract: For a multiuser interference channel with multi-antenna transmitters and single-antenna receivers, by restricting each transmitter to a Gaussian input and each receiver to a single-user detector, computing the largest achievable rate region amounts to solving a family of nonconvex optimization problems. Recognizing the intrinsic connection between the signal power at the intended receiver and the interference power at the unintended receiver, the original family of nonconvex optimization problems is converted into a new family of convex optimization problems. It is shown that, for such interference channels with each receiver implementing single-user detection, transmitter beamforming can achieve all boundary points of the achievable rate region.
Proceedings Article•
14 Mar 2011TL;DR: Analytical formulas were derived to be able to calculate the probability for ghost targets and the interference power per frequency bin in mutual interference between automotive FMCW radar sensors.
Abstract: Radar sensors are key components of modern driver assistance systems. Mutual interference was identified as a problem of increased importance because of the appearance of safety functions and the increasing rate of vehicles equipped with radar sensors. This paper describes mutual interference between automotive FMCW radar sensors. Analytical formulas were derived to be able to calculate the probability for ghost targets and the interference power per frequency bin. The results of the analytical calculations are compared with simulation results on the basis of a simple interference scenario with interference from an oncoming vehicle.
TL;DR: This paper showed that interference in recognition memory is due in part to interference from words other than the current test word, when each test produces a memory trace, and hence a source of interference.
05 Jun 2011
TL;DR: Low-weight channel coding is proposed as a novel mechanism to reduce interference in pulse-based nanonetworks and it is shown that by appropriately choosing the weight of a code, interference can be mitigated.
Abstract: Nanotechnology is providing the engineering community with a new set of tools to design and manufacture integrated devices just a few hundred nanometers in total size. Communication among these nano-devices will boost the range of applications of nanotechnology in several fields, ranging from biomedical research to military technology or environmental science. Within the different alternatives for communication in the nanoscale, recent developments in nanomaterials point to the Terahertz band (0.1-10 THz) as the frequency range of operation of future electromagnetic nano-transceivers. This frequency band can theoretically support very large bit-rates in the short range, i.e., for distances below one meter. Due to the limited capabilities of individual nano-devices, pulse-based communications have been proposed for electromagnetic nanonetworks in the Terahertz band. However, the expectedly very large number of nano-devices and the unfeasibility to coordinate them, can make interference a major impairment for the system. In this paper, low-weight channel coding is proposed as a novel mechanism to reduce interference in pulse-based nanonetworks. Rather than utilizing channel codes to detect and correct transmission errors, it is shown that by appropriately choosing the weight of a code, interference can be mitigated. The performance of the proposed scheme is analytically and numerically investigated both in terms of overall interference reduction and achievable information rate, by utilizing a new statistical interference model. The results show that this type of network-friendly channel coding schemes can be used to alleviate the interference problem in nanonetworks without compromising the individual user information rate.
TL;DR: It is shown that uncorrelated transmit noise from multiple transmitters can be removed through tunable filtering or through adaptive beamforming of multiple receiving elements, both providing an additional 30-40 dB of interference reduction that is tunable over the frequency range of the system.
Abstract: A near-field cancellation duplexing system is demonstrated using multiple coordinated transceivers with symmetrically arranged antenna elements and a digital backend for baseband waveform phase and amplitude weighting controls. By adapting weights of multiple transmit elements, coupled interference at receiver elements deconstructively interferes, providing up to 50 dB of additional isolation over the coupling of a single transmitter to a receiving element. Bandwidth considerations of the array are presented. It is shown that uncorrelated transmit noise from multiple transmitters can be removed through tunable filtering or through adaptive beamforming of multiple receiving elements, both providing an additional 30-40 dB of interference reduction that is tunable over the frequency range of the system.
TL;DR: The results show that the use of interference-aware detectors can significantly alleviate the effect of interference thereby improving the achievable rates and the reliability of future wireless systems.
Abstract: This paper addresses the design of optimal and near-optimal detectors in an interference channel with fading and with additive white Gaussian noise (AWGN), where the transmitters employ discrete modulation schemes as in practical communication scenarios. The conventional detectors typically either ignore the interference or successively detect and then cancel the interference, assuming that the desired signal and/or the interference are Gaussian. This paper quantifies the significant performance gain that can be obtained if the detectors explicitly take into account the modulation formats of the desired and the interference signals. This paper first describes the optimal maximum-likelihood (ML) detector that minimizes the probability of detection error for a given modulation scheme, and the joint minimum-distance (MD) detector, which is a lower-complexity approximation of the ML detector. It is then demonstrated by analysis and by simulation that in an AWGN channel, while interference-ignorant and successive interference cancellation detectors are both prone to error floors, the optimal ML and joint MD detectors are not. This paper further analyzes the performance of joint detection in a Rayleigh fading environment. It is demonstrated that the joint detector can achieve symbol error rates that have the same dependence on the received signal-to-noise ratio (SNR) as if the channel were interference free. Thus, the performance of joint detection is fundamentally limited by the SNR rather than the signal-to-interference ratio (SIR). Moreover, the joint detector enables the use of transmit diversity schemes to achieve the same diversity order as in the absence of interference. These results show that the use of interference-aware detectors can significantly alleviate the effect of interference thereby improving the achievable rates and the reliability of future wireless systems.
TL;DR: An optimal power allocation algorithm for the orthogonal frequency division multiplexing (OFDM)-based cognitive radio (CR) systems with different statistical interference constraints imposed by different primary users (PUs) is developed and the performance has been investigated.
Abstract: In this letter, we develop an optimal power allocation algorithm for the orthogonal frequency division multiplexing (OFDM)-based cognitive radio (CR) systems with different statistical interference constraints imposed by different primary users (PUs). Given the fact that the interference constraints are met in a statistical manner, the CR transmitter does not require the instantaneous channel quality feedback from the PU receivers. A suboptimal algorithm with reduced complexity has been proposed and the performance has been investigated. Presented numerical results show that with our proposed optimal power allocation algorithm CR user can achieve significantly higher transmission capacity for given statistical interference constraints and a given power budget compared to the classical power allocation algorithms namely, uniform and water-filling power allocation algorithms. The suboptimal algorithm outperforms both water-filling algorithm and uniform power loading algorithm. The proposed suboptimal algorithm give an option of using a low complexity power allocation algorithm where complexity is an issue with a certain amount of transmission rate degradation.