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Safety-Related Equipment and Services
Published in Graham D. Lees, William G. Williamson, Handbook for Marine Radio Communication, 2020
Graham D. Lees, William G. Williamson
Although the devices are capable of being mounted in different ways, as a general rule the transponder should be mounted vertically and as high as possible, particularly in a lifeboat. This gives the best option for achieving maximum coverage for line-of-sight propagation in this frequency range. Class-A AIS SARTs have a range of 7-10 nautical miles from a vessel and 40 miles from an airborne AIS receiver.
Time–Frequency Analysis for EEG Quality Measurement and Enhancement with Applications in Newborn EEG Abnormality Detection
Published in Ervin Sejdić, Tiago H. Falk, Signal Processing and Machine Learning for Biomedical Big Data, 2018
Boualem Boashash, Samir Ouelha, Mohammad Al-Sa’d, Ayat Salim, Paul Colditz
where δ(t) is the Dirac function that is defined as δ(t) = 0 for t ≠ 0 and ∫−∞∞δ(t)dt=1, while ϕ(r) is the time delay exerted on s(t) when received by x(t, r), and E is the number of received reflections. Assuming only line-of-Sight propagation, E = 1, Equation 5.43 is simplified into h(t,r)=λ(r)δ(t−ϕ(r)).
Outlines of Radio Waves and Troposphere
Published in Pranab Kumar Karmakar, Microwave Propagation and Remote Sensing: Atmospheric Influences with Models and Applications, 2017
When the value of dNdh is positive, that is, dNdh increases with height, the ray bends toward the normal. In Figure 1.13 it is shown that for the undeviated ray path the effective radius of the earth is less than the actual radius. In this case, line of sight propagation is decreased. Hence the value of R is less than one.
Evaluating the Performance of Wearable Devices for Contact Tracing in Care Home Environments
Published in Journal of Occupational and Environmental Hygiene, 2023
Kishwer Abdul Khaliq, Catherine Noakes, Andrew H. Kemp, Carl Thompson
Accuracy and reliability in digital contact tracing is important and needs to consider the epidemiological sense of sensitivity [probability of recording a contact when there really has been one] and specificity [probability of ruling out no contact when there really has not been one]. Many factors can influence the accuracy of BLE devices. Other devices using the same frequency (Wi-Fi, mobile phones, wireless technology such as speakers or baby monitors) can interfere with signals. Different building materials, furniture, and objects within the environment can affect signal strength, as can humans that block direct line-of-sight propagation (shadowing). Antenna patterns when BLE devices scan can be anisotropic, with large variations in gain from differing angles and polarization (Schulten et al. 2019). Propagation indoors is vulnerable to multi-path (Rayleigh) fading from nearby reflections. These factors make an evaluation of the accuracy and reliability of the CONTACT trial’s BLE wearables necessary.
An improved LSE-EKF optimisation algorithm for UAV UWB positioning in complex indoor environments
Published in Journal of Control and Decision, 2022
However, the above methods have limited solutions to the multi-path effect and non-line-of-sight propagation problems in the indoor complex environment positioning of UAVs. Therefore, this paper proposes an improved LSE-EKF UWB indoor UAV positioning method. Through BP the neural network corrects the original positioning data, introduces a redundant base station positioning system, uses the least squares estimation to optimise the pre-positioning coordinate error and then removes the Gaussian white noise in the pre-positioning signal through the extended Kalman filter algorithm. Compared with the traditional UWB positioning system, the improved LSE-EKF algorithm can effectively solve the problems of multi-path effect and non-line-of-sight (NLOS) propagation, which greatly improves the positioning accuracy of indoor multi-rotor UAVs.
A New Method of Spectrum Sensing in Cognitive Radio for Dynamic and Randomly Modelled Primary Users
Published in IETE Journal of Research, 2022
To facilitate the theoretical analysis of the newly proposed CuS-WED, the following mathematical model can be used where and refer to the absence and presence, respectively, of the PU in the channel. In Equation (1), N represents the total number of observed data samples and denotes the additive channel noise modelled as zero-mean white Gaussian noise (WGN) with variance . The real-valued PU signal, , is represented using zero-mean Gaussian distribution with variance as in order to more realistically model the PU signal which is formed by the addition of multiple non-line-of-sight propagation signals arriving at the CR receiver [16,17].