China
Africa
Explore chapters and articles related to this topic
Wireless Coding and Modulation
Published in Mahbub Hassan, Wireless and Mobile Networking, 2022
Nyquist defines channel capacity under noiseless environment. In the absence of noise, receiving hardware can easily differentiate between a large number of different values of the symbol. As such, channel capacity according to Nyquist theorem is mainly constrained by the channel bandwidth, which defines the number of Hertz available in the channel. The higher the bandwidth, the more data rate can be achieved. Nyquist capacity is also dependent on the number of signal levels, i.e., the number of distinct symbols used in encoding. More precisely, Nyquist capacity is obtained as: Nyquist data rate = 2 × B × log2M bps where B is the channel bandwidth (in Hz) and M is the number of signal levels.
Communications
Published in Diego Galar, Uday Kumar, Dammika Seneviratne, Robots, Drones, UAVs and UGVs for Operation and Maintenance, 2020
Diego Galar, Uday Kumar, Dammika Seneviratne
The more bandwidth a data connection has, the more data it can send and receive at one time. Bandwidth can be compared to the amount of water that can flow through a water pipe. The bigger the pipe, the more water can flow through it at one time. Bandwidth works on the same principle. The higher the capacity of the communication link, or pipe, the more data can flow through it per second. End users pay for the capacity of their network connections, so the greater the capacity of the link, the more expensive it is.
Automatic Analysis Support
Published in Christian Tominski, Heidrun Schumann, Interactive Visual Data Analysis, 2020
Christian Tominski, Heidrun Schumann
In signal processing, sampling aims at representing a continuous signal by a discrete one. To this end, signals are gathered at certain sample points. The Nyquist Shannon sampling theorem tells us that in order to be able to reconstruct the original signal, the number of sample points must be greater than twice the bandwidth of the continuous signal [II91]. In statistics, sampling is understood differently. Here, sampling aims at defining a subset of individuals that are representative of or characterize an entire statistical population [Loh19].
Research on compressive sensing of strong earthquake signals for earthquake early warning
Published in Geomatics, Natural Hazards and Risk, 2021
Jiening Xia, Yuanxiang Li, Yuxiu Cheng, Juan Li, Shasha Tian
With a long-term focus on the transmission and storage of massive data in earthquake early warning systems, we find that the popular compressive sensing theory in recent years is just suitable for the application. Nyquist sampling theorem points out that in order to capture a signal with a specified bandwidth perfectly, analog-to-digital conversion usually needs to be carried out at a sampling rate greater than twice the frequency band. Compressive sensing theory states that if a signal is sparse in a certain orthogonal space, it can be sampled at a frequency much lower than the Nyquist sampling rate, and the signal may be reconstructed with a high probability. Based on the compressive sensing theory, we propose a kind of transmission architecture of signal acquisition for earthquake monitoring and early warning system, which solves the data compression problems, faced by the acquisition and transmission process in earthquake early warning systems and provides new application directions.
Impact resistance test system for the helmet based on a polyvinylidene fluoride piezoelectric sensor array
Published in International Journal of Occupational Safety and Ergonomics, 2023
Qiyue Li, Xiaomu Liao, Xing Huang, Xin’ao Wei, Xiang Zhang
The oscilloscope collects electrical signals generated by the impact pressure during the experiment and displays them as images. The selection of oscilloscope has a great influence on the quality of the collected signal, which mainly considers the four indicators of bandwidth, sampling rate, storage depth and vertical sensitivity [33]: Bandwidth: the oscilloscope bandwidth should be more than three to five times the signal bandwidth in order to obtain an accurate test signal. The relationship between signal bandwidth fB (MHz) and rise time tr (μs) can be calculated by the following equation [34]: The rise time of this test is generally above 10 ms, so the signal bandwidth is below 35 Hz. If calculated five times, the oscilloscope bandwidth should be more than 175 Hz. This test selects an DL580E oscilloscope (YOKOGAWA, Japan), and a 5-kHz bandwidth was chosen. From the point of frequency parameters, the measuring circuit composed of an oscilloscope and a PVDF sensor meets the requirements for channel CFC600 specified in Standard No. ISO 6487:2015 [35].Sampling rate: according to the Nyquist sampling theorem, to restore the original signal information without distortion, the sampling frequency should be more than twice the bandwidth of the measured signal. The maximum sampling rate of the oscilloscope is 100 MHz, and a 1-MHz sampling rate was chosen in this experiment, which meets the test requirements.Storage depth: this oscilloscope owns 12 channels in this study, and each channel storage depth is 250 MB. Under the sampling rate of 1 MHz, the maximum continuous sampling time is 250 s, and the total test time is usually a few milliseconds, which meets the test requirements.Vertical sensitivity: the maximum range of the oscilloscope in this study is 200 V, and it has other different gears. The peak value of the test signal under different test conditions should be predicted [21], and then the oscilloscope range should be adjusted to the suitable range.