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Published in Jerry D. Gibson, The Communications Handbook, 2018
For most practical channels, where signal propagation takes place in the atmosphere and near the ground, the free-space propagation model is inadequate to describe the channel and predict system performance. In a wireless mobile communication system, a signal can travel from transmitter to receiver over multiple reflective paths; this phenomenon is referred to as multipath propagation. The effect can cause fluctuations in the received signal's amplitude, phase, and angle of arrival, giving rise to the terminology multipath fading. Another name, scintillation, having originated in radio astronomy, is used to describe the multipath fading caused by physical changes in the propagating medium, such as variations in the density of ions in the ionospheric layers that reflect high frequency (HF) radio signals. Both names, fading and scintillation, refer to a signal's random fluctuations or fading due to multipath propagation. The main difference is that scintillation involves mechanisms (e.g., ions) that are much smaller than a wavelength. The end-to-end modeling and design of systems that mitigate the effects of fading are usually more challenging than those whose sole source of performance degradation is AWGN.
M
Published in Philip A. Laplante, Comprehensive Dictionary of Electrical Engineering, 2018
multipath propagation the process by which a radio signal propagates from the transmitter to the receiver by way of multiple propagation paths. Depending on the frequency range employed in transmission, the physical propagation phenomena contributing to multipath propagation include reflections from terrain and man-made obstacles, diffraction and refraction. Multipath propagation leads, similar to acoustic echos, multiple replicas
Multidimensional High-Resolution Parameter Estimation with Applications to Channel Sounding
Published in Yingbo Hua, Alex B. Gershman, Qi Cheng, High-Resolution and Robust Signal Processing, 2017
Martin Haardt Reine, S. Thomä, Andreas Richter
In this section, we discuss multidimensional high-resolution parameter estimation in the context of wave propagation measurements of mobile radio channels. As it is well known, multipath propagation severely effects the quality of the received signal in any radio link. Figure 5.5 illustrates the basic propagation model. The base station receives the transmitted signal from the mobile station via a line-of-sight (LOS) path and multiple delayed copies from reflected, scattered, or diffracted paths. In general, these paths impinge at the base station antenna from different directions of arrival (DOAs) that correspond to specific directions of departure (DODs) at the mobile station. The superposition of the received signals causes frequency-selective and space-selective fading. Due to random user mobility and possible movements of parts of the propagation environment, the fading may also be time-variant. Moreover, the individual paths undergo a Doppler shift according to the moving speed. Slow fading arises from path shadowing (the LOS may even be temporary obscured) and also the path time delays of arrival (TDOAs), the DOAs, the DODs, and the number of relevant paths are slowly changing. This results in a random time-variant channel impulse response (CIR).
A Comprehensive Survey on GNSS Interferences and the Application of Neural Networks for Anti-jamming
Published in IETE Journal of Research, 2021
Kambham Jacob Silva Lorraine, Madhu Ramarakula
Multipath error: If the GNSS signal reaches the receiver via more than one path due to the reflections from the surrounding objects/surfaces of the antenna, it is called multipath propagation. Multipath propagation causes the signal to be delayed, thereby causing an error of ±1 m in the position estimation [3].
Triple Band Compact Monopole Antenna for Applications Like Bluetooth, WiMAX and WLAN
Published in IETE Journal of Research, 2021
Kailash Chandra, Mahendra Kumar, Madhur Deo Upadhayay
Modern wireless communication demands for high data transmission speed and high channel capacity. Multiple-input-multiple output (MIMO) is an effective technique to fulfill these requirements [29]. In MIMO configuration, multiple antennas are used in the transmitter and receiver end to transfer the same baseband signal independently. MIMO can also mitigate the path loss and channel fading due to multipath propagation. Figure 13 exhibits 2 × 2 triple-band MIMO configuration that consists of the monopole antenna designed previously. Relative position of adjacent antenna elements poses orthogonal orientation with a separation between the center and center is 68.5 mm. The overall lateral size of the MIMO is 81 mm × 81 mm or 0.68 λ0 × 0.68 λ0, where λ0 is the free space wavelength at the center frequency of the lowest resonance. The identical dimension of the four antennas indicates the identical reflection coefficient characteristics for each antenna, as shown in Figure 14. It is overserved that the four-element MIMO resonates at 2.54, 4.08, 5.84 GHz. The three resonances shift to lower frequencies as compared to isolated antenna alone due to mutual coupling between the elements. Isolation characteristics of the MIMO antenna are also shown in Figure 14. Since the MIMO presented here poses symmetric configuration, isolations between the antenna elements are observed only for Antenna-1 excitation. It is found for the adjacent antenna elements (1 and 2) the isolations are 23.6, 19.1, 24.9 because of orthogonal polarization. The diagonal antenna elements (1 and 3) with the same polarization exhibit isolation values of 23, 14.4, and 24.6 dB, respectively. A figure of merit to characterize the coupling between the antenna elements is called envelope correlation coefficient (ECC). ECC (ρe) is related to the reflection and transmission coefficients (S11 and S21) of the elements using (4) Figure 15 presents the ECC between Antenna-1 and 2 and between Antenna-1 and 3. Since the relative orientation between Antenna-1 and -2 is orthogonal, ECC between these elements is lower than ECC between Antenna-1 and -3. The antenna elements 1 and 3 share the identical polarization. In decibel unit, ECC between Antenna-1 and 2 is −88.6, −77.4 and −90.34 dB at the center frequencies of three bands. These values due to coupling between Antenna-1 and -3 are −81.76, −62.21 and −85.27 dB, respectively.