中国电信笔试真题（China Telecom written Zhenti）.docVIP

中国电信笔试真题（China Telecom written Zhenti） China Telecom written Zhenti 1. digital communication multiplexing mode? 2. the Nyquist sampling theorem? Nyquist sampling theorem: if the band width is limited, to restore the original signal without distortion from the sampling signal, the sampling frequency should be greater than 2 times the highest frequency signal. The sampling frequency is less than 2 times the highest frequency spectrum, signal spectrum aliasing. The sampling frequency is 2 times higher than the highest frequency spectrum, signal spectrum aliasing free. The optimization principle of 3.FIR filter? 4.f (T) the frequency of 1K, f (T) *f Q (2t) what is the sampling frequency? 5.Cos (0.35pai*t) +2sin (0.45pai*t) is the number of cycles? The 7. contains a 70152Hz frequency signal is frequency of 200 window smoke, ask signal after the change in the frequency of the frequency spectrum of several nearby? 8. a periodic signal for 2n. Another is 3N, multiply them after the cycle is how much? What is 9.QPSK demodulation method. Is a kind of digital modulation. 10. the maximum signal-to-noise ratio and receiver meet the maximum likelihood criterion is? The 11. principle of avalanche diode is. In the PN junction materials lower doping concentration, when the PN junction reverse voltage increases, the electric field in the space charge region with the increase of. In this way, the space charge region of electron and hole energy will be increased under the action of electric field, the movement of electrons and holes in the crystal will continue with crystal atomic collision, when the electron and hole energy is large enough, this can make the total electron collision excitation of valence bond formation the free electron hole pairs. The new generation of electrons and holes are in the opposite direction, to get energy, but also through the collision, and then generate electron hole pairs, this is the carrier multiplication effect. When the reverse voltage is increased