In contrast to traditional receiver where sampling happens at baseband, the bandpass-sampling receiver offers more flexibility since more signal processing is implemented in the digital domain. For this type of receivers, the sampling frequency is a very important factor since it influences both receiver performance and implementation efficiency. In this paper, the allowable sampling frequencies are analyzed for the bandpass-sampling receiver in practical cases with out-ofband interference. Preferable choices of sampling frequency are then provided.
Geomagnetic storms can cause earth surface potentials (ESPs) in the ground. ESP produces geomagnetically induced current (GIC) in a loop which is made up by rails and ground. If GIC flows into intercity railway track circuit, it will threaten the normal operation of track circuit. The reason that geomagnetic storms invade the track circuit was analyzed, and then how GIC affects the characteristics of choke transformers, was found. The calculation method of GIC according to a simulation based on the GIC flow path in the track circuit was built. Electromagnetic system model of choke transformer and track relay were designed in Maxwell software to get the magnetic flux density distribution of them. The results show that GIC values of 2.4 A can bring about serious direct current bias of choke transformers and cause the terminal voltage of track relay to decrease, resulting in relay malfunction. The numerical calculation results show that geomagnetic storms will interfere with intercity railway track circuit, which is in accordance with some phenomenon happened in some rail tracks. This method proves geomagnetic storms' influence on intercity railway track circuit and attentions should be paid to this influence.
The paper describes the trend of future wireless communications, and then analyzes the impacts of this trend on the transceiver architectures used for wireless communications. The conclusions could be used as the guidelines for the research work in this domain.
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