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.

Analysis of adaptive multistage interference cancellation for CDMA using an improved Gaussian approximation

Abstract: We consider a simple model for adaptive multistage interference cancellation within a CDMA system, and seek to develop an accurate analytical expression for the performance of this system. Previous work on interference cancellation has relied heavily on simulation techniques or a simple Gaussian approximation (GA). The standard GA ran lead to bit-error rate (BER) results which are optimistic for the conventional receiver, and this also occurs when the approximation is applied to the interference cancellation problem. Additionally, this approximation does not allow the second order effects of the multiple access interference (MAI) to be included in the performance estimates. Several improvements on the standard GA have been suggested which result in accurate performance results for a standard CDMA receiver. This paper presents an analytical expression for the probability of bit error for an adaptive multistage interference canceller, using an improved Gaussian approximation (IGA) for MAI. The BER at any stage of interference cancellation can be recursively computed from the signal-to-noise ratio (SNR), the statistics of the random powers of users, and the processing gain of the CDMA system. The performance of the resulting EER expression is compared with simulation results. Since the second order effects of MAI can be included, the analytical framework presented here can also be used to evaluate the performance of multistage interference cancellation in arbitrary fading environments, and we present results for the performance of interference cancellation in lognormal fading environments.

Red-green-blue interferometer for the metrology of discontinuous structures.

Abstract: Discontinuous surface profiles, e.g., diffractive optical elements (DOEs), are commonly measured by white-light interferometry. White-light interferometry needs significantly more memory capacity and computer time than does phase-shifting interferometry; there are approximately ten times more frames to be taken to gather the required information about the object under test. But usually the grooves of the DOEs are too deep for single-wavelength phase-shifting interferometry. Here we show how phase-shifting techniques can be applied to DOEs. For this purpose three interference patterns are recorded simultaneously by a three-chip color CCD camera at three wavelengths (Red-green-blue). It is possible to calculate separately the optical path difference at each pixel from the three phase patterns modulo 2π. The algorithms used and experimental results are presented.

Single-Photon Interference in Sidebands of Phase-Modulated Light for Quantum Cryptography

Abstract: We report single-photon interference in the sidebands of modulated light. The relative phase of interacting quantum states is reliably controlled by the phase of a low-frequency modulating signal. We show how this type of interference can be used to build a robust system for quantum cryptography. An experiment was implemented at 1540 nm, over a 20-km-long standard single-mode fiber, using a germanium singlephoton avalanche photodiode.

New high-efficiency source of photon pairs for engineering quantum entanglement.

Abstract: We constructed an efficient source of photon pairs using a waveguide-type nonlinear device and performed a two-photon interference experiment with an unbalanced Michelson interferometer. As the interferometer has two arms of different lengths, photons from the short arm arrive at the detector earlier than those from the long arm. We find that the arrival time difference (Delta L/c) and the time window of the coincidence counter (Delta T) are important parameters which determine the boundary between the classical and quantum regimes. Fringes of high visibility ( 80% +/- 10%) were observed when Delta T < Delta L/c. This result is explained only by quantum theory and is clear evidence for quantum entanglement of the interferometer's optical paths.

Least Squares Approach to Joint Beam Design for Interference Alignment in Multiuser Multi-Input Multi-Output Interference Channels

Abstract: In this correspondence, the problem of interference alignment for K-user time-invariant multi-input multi-output interference channels is considered. The necessary and sufficient conditions for interference alignment are converted to a system of linear equations that have dummy variables. Based on this linear system, a new algorithm for beam design for interference alignment is proposed by minimizing the overall interference misalignment. The proposed algorithm consists of solving a least squares problem iteratively. The convergence of the proposed algorithm is established, and its complexity is analyzed. The performance of the proposed algorithm is also evaluated numerically. It is shown that the proposed algorithm has faster convergence and lower complexity than the previous method with a comparable sum rate performance in the most practical case of two receive antennas.