Multipath Patterns Research Articles

A study on unpredictable shallow water channel behavior by various multipath patterns and experimental data analysis

In shallow water applications, multipath signal propagation is a major concern for robust communication. Multipath signal propagation is not explicitly seen in the channel, even though it is a main contributor for signal degradation. This fact motivated us to simulate multipath patterns to understand its influence in short-range communication. In this paper, a three-path signal propagation model is presented, where, besides the line of sight (LOS) signal, other two non-line of sight (NLOS) signals contact any point of channel boundary to reach the receiver. In simulation, the combination of eight possible multipath patterns is converged to estimate the received signal. A source fixed in water-tank periodically transmits low frequency acoustic signals 1 kHz and 1.5 kHz to the channel, and the receiver records them. The experiment was repeated for various input signal strengths. It has been observed that the simulation results coincide with the measured values. The good reception is noticed for signal frequency 1 kHz at 2.5m and 1.5 kHz at 1.2m. This study identifies the optimal signal strength for better signal reception in short range, which drives to the establishment of high-quality communication in shallow water.

Investigating GNSS multipath effects induced by co-located Radar Corner Reflectors

Abstract Radar Corner Reflectors (CR) are increasingly used as reference targets for land surface deformation measurements with the Interferometric Synthetic Aperture Radar (InSAR) technique. When co-located with ground-based Global Navigation Satellite Systems (GNSS) infrastructure, InSAR observations at CR can be used to integrate relative measurements of surface deformation into absolute reference frames defined by GNSS. However, CR are also a potential source of GNSS multipath effects and may therefore have a detrimental effect on the GNSS observations. In this study, we compare daily GNSS coordinate time series and 30-second signal-to-noise ratio (SNR) observations for periods before and after CR deployment at a GNSS site. We find that neither the site coordinates nor the SNR values are significantly affected by the CR deployment, with average changes being within 0.1 mm for site coordinates and within 1 % for SNR values. Furthermore, we generate empirical site models by spatially stacking GNSS observation residuals to visualise and compare the spatial pattern in the surroundings of GNSS sites. The resulting stacking maps indicate oscillating patterns at elevation angles above 60 degrees which can be attributed to the CR deployed at the analysed sites. The effect depends on the GNSS antenna used at a site with the magnitude of multipath patterns being around three times smaller for a high-quality choke ring antenna compared to a ground plane antenna without choke rings. In general, the CR-induced multipath is small compared to multipath effects at other GNSS sites located in a different environment (e. g. mounted on a building).

Обнаружение многолучевого распространения хаотических радиоимпульсов в беспроводном канале

Experiments on multipath indoor propagation of ultrawideband (UWB) chaotic radio pulses of microwave band are described. The goal is to experimentally obtain propagation results for UWB chaotic signals of different power. Propagation of different-power chaotic radio pulses gives different multipath patterns detected by the receiver due to its finite sensitivity. A comparison of the chaotic pulse envelope waveforms at the receiver revealed the role of the reflected paths with different delays.

Electromagnetic Simulation of the Near-Field Distribution around a Wind Farm

An efficient approach to compute the near-field distribution around and within a wind farm under plane wave excitation is proposed. To make the problem computationally tractable, several simplifying assumptions are made based on the geometry problem. By comparing the approximations against full-wave simulations at 500 MHz, it is shown that the assumptions do not introduce significant errors into the resulting near-field distribution. The near fields around a3×3wind farm are computed using the developed methodology at 150 MHz, 500 MHz, and 3 GHz. Both the multipath interference patterns and the forward shadows are predicted by the proposed method.

Model-based passive acoustic tracking of sperm whale foraging behavior in the Gulf of Alaska

In 2004, the Southeast Alaska Sperm Whale Avoidance Project (SEASWAP) introduced the use of passive acoustics to help monitor the behavior of sperm whales depredating longline fishing operations. Acoustic data from autonomous recorders mounted on longlines provide the opportunity to demonstrate a tracking algorithm based on acoustic propagation modeling while providing insight into whales’ foraging behavior. With knowledge of azimuthally dependent bathymetry, a 3D track of whale motion can be obtained using data from just one hydrophone by exploiting multipath arrival information from recorded sperm whale clicks. The evolution of multipath arrival patterns is matched to range-, depth-, and azimuth-dependent modeled arrival patterns to generate an estimate of whale motion. This technique does not require acoustic ray identification (i.e., direct path, surface reflected, etc.) while still utilizing individual ray arrival information, and it can also account for all waveguide propagation physics such as interaction with range-dependent bathymetry and ray refraction.

Adaptive joint beamforming and B‐MMSE detection for CDMA signal reception under multipath interference

AbstractThe combination of antenna array beamforming with multiuser detection can effectively improve the detection efficiency of a wireless system under multipath interference, especially in a fast‐fading channel. This paper studies the performance of an adaptive beamformer incorporated with a block‐wise minimum mean square error(B‐MMSE) detector, which works on a unique signal frame characterized by training sequence preamble and data blocks segmented by zero‐bits. Both beam‐former weights updating and B‐MMSE detection are carried out by either least mean square (LMS) or recursive least square (RLS) algorithm. The comparison of the two adaptive algorithms applied to both beamformer and B‐MMSE detector will be made in terms of convergence behaviour and estimation mean square error. Various multipath patterns are considered to test the receiver's responding rapidity to changing multipath interference. The performance of the adaptive B‐MMSE detector is also compared with that of non‐adaptive version (i.e. through direct matrix inversion). The final performance in error probability simulation reveals that the RLS/B‐MMSE scheme outperforms non‐adaptive B‐MMSE by 1–5 dB, depending on the multipath channel delay profiles of concern. The obtained results also suggest that adaptive beamformer should use RLS algorithm for its fast and robust convergence property; while the B‐MMSE filter can choose either LMS or RLS algorithm depending on antenna array size, multipath severity and implementation complexity. Copyright © 2004 John Wiley & Sons, Ltd.

Adaptive joint beamforming and B-MMSE detection under multipath interference

The combination of antenna array beamforming with multiuser detection can effectively improve the detection efficiency for wireless communications under multipath interference, especially for the applications in a fast fading channel. The authors study the performance of an adaptive beamformer incorporated with a B-MMSE detector, which works on a unique signal frame characterised by training sequence preamble and data blocks segmented by zero-bits. Both the beamformer weight updating and B-MMSE detection are carried out by either LMS or RLS algorithms. The comparison of the two adaptive algorithms applied to both the beamformer and the B-MMSE detector is made in terms of convergence behaviour and estimation mean-square error. The final performance in error probability is also given. Various multipath patterns are considered to test the rapidity of the receiver's response to changing multipath interference. The performance of the adaptive B-MMSE detector is also compared with that of the non-adaptive version, i.e. through matrix inversion. The results obtained suggest that the adaptive beamformer should use an RLS algorithm for its fast and robust convergence property; whereas the B-MMSE filter can choose either LMS or RLS algorithms depending on the antenna array size, multipath severity and complexity.

Caractérisation de la réponse impulsionnelle du canal de transmission acoustique horizontale par petits fonds

This paper presents a shallow-water propagation analysis based on real signals. We study the influence of channel configurations (transmission ranges, water depths, natures of the bottom...) both on the multipath patterns and on the time spreading of the channel mean impulse responses. The signals fades are also investigated in term of envelope probability laws