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4 results about "Critical frequency" patented technology
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In telecommunication, the term critical frequency has the following meanings: In radio propagation by way of the ionosphere, the limiting frequency at or below which a wave component is reflected by, and above which it penetrates through, an ionospheric layer. At near vertical incidence, the limiting frequency at or below which incidence, the wave component is reflected by, and above which it penetrates through, an ionospheric layer. Critical Frequency changes with time of day, atmospheric conditions and angle of fire of the radio waves by antenna. The existence of the critical frequency is the result of electron limitation, i.e., the inadequacy of the existing number of free electrons to support reflection at higher frequencies. In signal processing the critical frequency it is also another name for the Nyquist frequency. Critical frequency is the highest magnitude of frequency above which the waves penetrates the ionosphere and below which the waves are reflected back from the ionosphere. It is denoted by "fc". Its value is not fixed and it depends upon electron density of ionosphere. It is given by: fc=9√Nmax Nmax is maximum electron density.
A residual network-based frequency-height map automatic measurement method and system
This invention discloses an automatic frequency-elevation map measurement method and system based on residual networks, enabling rapid and automatic extraction of key ionospheric parameters from frequency-elevation maps acquired by digital altimeters. The method first parses the header information and echo intensity data from the original binary file of the altimeter to generate a frequency-elevation map image. Then, a small number of samples are manually labeled to establish a training set with critical frequencies such as foF2 and h'F2 as ground truth. Based on this, an end-to-end model including a backbone residual network, pooling layers, and a feature extraction head is built. This model is trained to convergence through backpropagation and further fine-tuned using expanded sample data to obtain an engineering-deployable model. Finally, the frequency-elevation map to be processed is input into the model, and the predicted values of the target parameters are output and written to the results file. This method reduces the workload of manual interpretation and verification and improves the measurement accuracy of irregular and disturbed frequency-elevation maps.
Owner:WUHAN UNIV
Methods for operating electric motors
The present invention relates to a method for operating a motor (4) by means of pulse width modulation, wherein during the period duration (T) Periode During the period, with a pulse duration (T) on At least one pulse width modulation signal pulse (70) is generated at the pulse position (T0) of the pulse, wherein the resulting amplitude spectrum (64) is at the critical frequency ( kritisch The amplitude value (A) is located at a position where at least one time parameter (T) of the pulse width modulation is present. Periode T0, T on ) by time parameter (T) Periode T0, T on ) and correction factor (T) korr The sum of ) is replaced by the correction factor (T) korr The amplitude spectrum (64') is altered so that the calculated amplitude spectrum is at the critical frequency ( kritisch The amplitude value (I) is reduced at point ) Amp ), and among them, the time parameter (T) is used. Periode T0, T on ) and the changed correction factor (T) korr ) to perform pulse width modulation.
Owner:BROSE FAHRZEUGTEILE GMBH & CO KG
A method and system for frequency selection in large-scale MIMO skywave communication based on ionospheric maps
This invention proposes a frequency selection method and system for massive MIMO skywave communication based on ionospheric maps, addressing the problems of limited channel capacity, low signal-to-noise ratio, and the strong frequency selectivity of the ionosphere, which makes it difficult to support multi-user access in skywave communication. The method includes: acquiring historical ionospheric observation data to construct an ionospheric map; calculating the azimuth and elevation angles between the base station and each user based on the geographical location information of the base station and each user; determining the location of the ionospheric reflection point based on the elevation angle and obtaining the critical frequency by querying the ionospheric map, thereby determining the carrier frequency range corresponding to the user's elevation angle; within the carrier frequency range, establishing a joint optimization model of the carrier frequency and precoding vector, and solving for the optimal carrier frequency and the corresponding precoding scheme. This invention can effectively improve the multi-user transmission rate and spectrum utilization efficiency of massive MIMO skywave communication systems and is suitable for high-reliability long-distance communication scenarios in complex ionospheric environments.
Owner:SOUTHEAST UNIV
A method for determining the frequency stirring bandwidth of electrically large metal cavities based on small samples
This invention discloses a method for determining the frequency stirring bandwidth of electrically large metal cavities based on small samples, belonging to the field of electromagnetic compatibility testing technology. The method includes the following steps: S1, configuring the test system and determining the test parameters; S2, calibrating the vector network analyzer and saving the real and imaginary parts respectively; S3, calculating candidate stirring bandwidths based on the frequencies within the test band; S4, selecting a bandwidth value from S3, using a non-parametric bootstrapping algorithm to self-sample it into M×N dimensional samples, and organizing them into magnitude values; S5, performing an A / D test on the magnitude values to determine the critical frequency; S6, obtaining the critical frequency cluster corresponding to the candidate stirring bandwidths from S3, calculating the standard deviation, and selecting the candidate stirring bandwidth with the smallest standard deviation as the frequency stirring bandwidth. This method solves the technical problem of lacking an accurate method for determining the frequency stirring bandwidth of electrically large metal cavities under small sample conditions.
Owner:NANJING UNIV OF AERONAUTICS & ASTRONAUTICS +1