Topic
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.
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TL;DR: In this article, an 8-channel system employing pulse code modulation (PCM) and embodying these principles was produced, which appears to have exceptional possibilities from the standpoint of freedom from interference, but its full significance in connection with future radio and wire transmission may take some time to reveal.
Abstract: A radically new modulation technique for multichannel telephony has been developed which involves the conversion of speech waves into coded pulses. An 8-channel system employing pulse code modulation (PCM) and embodying these principles was produced. The method appears to have exceptional possibilities from the standpoint of freedom from interference, but its full significance in connection with future radio and wire transmission may take some time to reveal.
91 citations
Patent•
19 Jun 2009TL;DR: In this article, a method for multi-radio coexistence receives historical frequency usage information and historical time usage information from a first radio and uses the time and frequency mask to schedule a second radio to avoid receiving when the first radio will likely be active.
Abstract: A method for multi-radio coexistence receives historical frequency usage information and historical time usage information from a first radio. The method creates a time and frequency mask by extrapolating the historical frequency and time usage information to future times and frequencies when the first radio will be active and uses the time and frequency mask to schedule a second radio to avoid receiving when the first radio will likely be active. A related apparatus has a collocated radio input for receiving timing usage information, a non-collocated radio input for receiving frequency usage information, and a time and frequency mask generator for creating a time and frequency mask using the timing usage information and the frequency usage information. The method and apparatus predicts collocated and non-collocated radio activity in both the time and frequency dimensions to reduce interference among radios operating in overlapping or adjacent frequency bands.
91 citations
TL;DR: Experimental results are presented that demonstrate the validity of the principle that can perform absolute measurement of the discontinuous surface profile of a microscopic object without use of mechanically moving components such as a piezoelectric transducer or a grating spectrometer.
Abstract: An optical frequency-domain interference microscope with a liquid-crystal Fabry–Perot interferometer as an optical frequency-scan device was developed for microscopic three-dimensional shape measurements. The proposed system can perform absolute measurement of the discontinuous surface profile of a microscopic object without use of mechanically moving components such as a piezoelectric transducer or a grating spectrometer. Experimental results are presented that demonstrate the validity of the principle.
91 citations
TL;DR: A new fourth-order interference experiment has been carried out and analyzed theoretically in classical and in quantum terms, which exhibits a cosine variation with the optical path difference, in agreement with quantum mechanics, but in disagreement with a classical analysis.
Abstract: A new fourth-order interference experiment has been carried out and analyzed theoretically in classical and in quantum terms. Two photons produced in the process of parametric down-conversion provide the two inputs to a Mach-Zehnder type of interferometer, while two photodetectors coupled to a coincidence counter measure the output. The coincidence rate, after subtraction of accidentals, exhibits a cosine variation with the optical path difference, in agreement with quantum mechanics, but in disagreement with a classical analysis. By contrast, when two coherent light beams from a He:Ne laser are used as inputs to the interferometer, no fourth-order interference is observed.
91 citations
TL;DR: It is shown that the interference in the network could be modeled as a mixture of Gaussian and /spl alpha/-stable noise, and expressions for the probability of error for systems with M-ary frequency shift keying (FSK) which use conventional envelope detectors are derived.
Abstract: We consider the performance of frequency-hopping spread spectrum (FH SS) radio networks in a Poisson field of interfering terminals using the same modulation and power. The problem is relevant to wireless random-access communication systems where little information about transmitters requires stochastic modeling of their positions. Assuming that the signal strength is attenuated over distance r on average as 1/r/sup m/, we show that the interference in the network could be modeled as a mixture of Gaussian and /spl alpha/-stable noise. Based on this modeling, we derive expressions for the probability of error (P/sub e/) for systems with M-ary frequency shift keying (FSK) which use conventional envelope detectors. Because conventional envelope detectors are optimum only in Gaussian noise and are suboptimum in the noise considered, we also investigate noncoherent detectors which offer improved performance. We examine receivers with limiting nonlinearities and detectors which are optimal in Cauchy noise. Numerical calculations and Monte Carlo simulations are provided to confirm the accuracy of the analysis presented. The results obtained are useful in the performance evaluation of multiple-access radio networks in environments varying from urban settings to office buildings with deterministic and stochastic propagation laws such as lognormal shadowing and Rayleigh fading.
91 citations