Interference (wave propagation)

About: Interference (wave propagation) is a research topic. Over the lifetime, 26086 publications have been published within this topic receiving 321110 citations.

Diffraction from the ionosphere and the fading of radio waves.

Abstract: WHEN a wireless wave is received partly or wholly by way of the ionosphere, it is observed to fade. Much of this fading is due to interference effects between waves which have travelled by different paths. Such waves may include the ground wave, singly or multiply reflected ionospheric waves, waves reflected from different ionospheric regions, or the two magneto-ionic components produced by the presence of the earth‘s magnetie field. It is, however, possible to isolate and observe only one downcoming wave from the ionosphere, for example, by the use of a pulse sender and a circularly polarized receiving aerial or by the use of a special aerial to suppress the ground wave under conditions when the absorption of the downcoming Wave is large enough to make second reflexions unimportant. When only one downcoming wave is observed in this way, it is still found to fade at a speed which varies from time to time. Although few detailed observations of this kind of fading have been reported, workers in the subject will probably accept the general statement that the speed of fading is roughly proportionai to the frequency of the wave and inversely proportional to the distance of the transmitter1.

High-order modulation on a single discrete eigenvalue for optical communications based on nonlinear Fourier transform.

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.

Interference alignment with asymmetric complex signaling

Abstract: It has been conjectured that complex Gaussian interference channels with constant channel coefficients have only one degree-of-freedom (DoF) regardless of the number of users. While several examples are known of constant channels that achieve more than 1 DoF, these special cases only span a subset of measure zero. In other words, for almost all channel coefficient values, it is not known if more than 1 DoF is achievable. In this paper, we settle this conjecture in the negative. We show that at least 1.2 DoF are achievable for all values of complex channel coefficients except for a subset of measure zero. To establish the achievability of 1.2 DoF we introduce the novel idea of asymmetric complex signaling — i.e., the inputs are chosen to be complex but not circularly symmetric. It is shown that unlike Gaussian point-to-point, multiple-access and broadcast channels where circularly symmetric complex Gaussian inputs are optimal, for interference channels optimal inputs are in general asymmetric. In addition, with this idea, we also show that 4/3 DoF can be achieved for 2 user X channel with constant, complex channel coefficients.

A unified model for interference analysis in unlicensed frequency bands

Abstract: This paper presents a unified framework for interference characterizations and analysis in the unlicensed frequency bands and the like, where many narrowband heterogeneous terminals coexist and share a common wideband channel using less-restrictive transmission etiquettes. Here, each transmitter/receiver pair makes his own decision regarding when to access the channel without any direct coordination with the other users. This is usually based on the local channel conditions at the receiver or/and the transmitter. Due to the nature of the wireless channel, communication in such environments is usually prone to arbitrary partial-band interference which can be generated anywhere in the space and frequency domains. In this paper, a new spatial-spectral interference model is introduced, where interferers can be of any power spectral density and are distributed according to a Poisson process in space and frequency domains. This basic model is extended to include the effects of channelization, where users are allowed only to transmit at a preassigned set of discrete frequencies. This is further extended to include also the effects of spectral-spatial guard zones, where the interferers can not exist in a given band nearby the victim receiver. Based on this multidimensional spatial-spectral Poisson model and the accurate conditional Gaussian analysis, explicit expressions are derived for average error rates of different communication systems.

Noise suppression method for wave filter

Abstract: A noise suppression method of a wave filter used to eliminate standing wave signal interferences in the acoustic wave filter consisted by a plurality of film bulk acoustic resonators (FBARs). The method is to provide a plurality of scatterers in the structured consisted by the FBARs, thereby creating an band-gap structure due to the material characteristics difference, which consequently generates a destructive interfering effect to the transverse higher harmonics vibration within a specific operating frequency range, and ultimately decreases or even eliminates any parasitic effects. Therefore, within the operation frequency range of this band-gap structure, abnormal signals created by any transverse wave modes cannot exist. In addition, an acoustic shield can be provided by phononic crystal structures between different FBARs, thus acoustic shielding any mutual interference within the operation frequency range.