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Quantization of Oil Spill Imagining in Synthetic Aperture Radar
Published in Maged Marghany, Automatic Detection Algorithms of Oil Spill in Radar Images, 2019
Coherence is the immobile relationship between waves in a beam of electromagnetic (EM) radiation. Two wave trains of EM radiation are coherent when they are in phase, in which they vibrate in harmony. In terms of the application to things like radar, the term coherence is also used to describe systems that preserve the phase of the received signal. In other words, in a pulse radar system, coherence describes the phase relationships between the transmitted and the received pulses (Fig. 8.10). Oscillations and electromagnetic waves are described as coherent if their phase relationships are constant. In the case of incoherence, these phase shifts are statistically distributed. Whether a radar is coherent or no longer is decided through the kind of transmitter. As transmitters, extraordinary systems can work in the radar, which is either coherent, in part coherent or incoherent.
Frequency Analysis
Published in David A. Bies, Colin H. Hansen, Carl Q. Howard, Engineering Noise Control, 2018
David A. Bies, Colin H. Hansen, Carl Q. Howard
The coherence function is a measure of the degree of linear dependence between two signals, as a function of frequency. It is calculated from the two auto power spectra and the cross-spectrum as: () γxy2(fn)=|Gxy(fn)|2Gxx(fn)Gyy(fn);n=0,1,…,(N−1)
RF System and Circuit Challenges for WiMAX
Published in Yan Zhang, Hsiao-Hwa Chen, Mobile Wimax, 2007
For optimal SDC performance, the selection process and data gathering must be completed within the coherence time. The coherence time is the period over which a propagating wave preserves a near-constant phase relationship both temporally and spatially. After the coherence time has elapsed, the antennas should be resampled to account for expected channel variations and to allow for reselection of the optimal antenna. For a TDD system, where reciprocal uplink (UL) and downlink (DL) channel characteristics are expected, the selected receive antenna can also be used as the transmit antenna. Although the SDC technique sounds rather simple, surprisingly large system gain improvements are possible if the algorithms can be designed effectively.
Shake-Table Seismic Performance Evaluation of Direct- and Indirect-Hung Suspended Ceiling Systems
Published in Journal of Earthquake Engineering, 2022
Su-Chan Jun, Cheol-Ho Lee, Chang-Jun Bae, Kyung-Joo Lee
To verify the synchronized motion of frames 1 and 2 in the large-size test frame (see Fig. 4), the coherence function was calculated using the acceleration data measured at the top center of the two square frames. A coherence function is a statistical tool for evaluating the relationship between two measured signals. It yields a value close to one if the two signals have similar phase and frequency. As shown in Fig. 9, the calculated coherence function between the two signals is close to unity up to 17 Hz, implying that the large-size test frame moved as a single unit without any noticeable differential movements between the square frames 1 and 2. The significant fluctuation of the over 17 Hz was caused by the local vibration of the frame members and did not affect the global response of the ceiling specimens.
Exploring pilot assignment methods for pilot contamination mitigation in massive MIMO systems
Published in Cogent Engineering, 2020
Angelina Misso, Mussa Kissaka, Baraka Maiseli
Pilot contamination is a condition that occurs when the precoding matrix adopted at a base station is correlated with the channel of users in other cells because of non-orthogonal pilots allocated to users (Fatema et al., 2018). For the duration of the channel estimation process, the coherence time is limited. (Coherence time defines a time interval within which a system can acquire CSI in an attempt to estimate the channel.) CSI is computed based on the pilots used during transmission and then matched with the received pilot signals.
Biomechanical response of the human foot when standing in a natural position while exposed to vertical vibration from 10–200 Hz
Published in Ergonomics, 2019
Katie A. Goggins, Marco Tarabini, W. Brent Lievers, Tammy R. Eger
Coherence is a value between 0 and 1 where a larger number indicates a greater correlation between the two signals being measured (Mansfield 2004). The coherence function can drop below unity for a number of reasons including contaminating noise on the input or output signals, leakage measurement errors not reduced by windowing, system non-linearities or because there are non-measured inputs affecting the output (Tarabini et al. 2014). Tests where the average coherence in the range 10–200 Hz dropped below 0.5 were redone.