channel capacity
channel capacity reflects the maximum amount of information that can be transmitted by the channel.
The channel capacity can be expressed as the number of binary bits available in unit time (the data transfer rate, bit rate of the channel, the bit rate), in position / second (b / s), is expressed BPS.
channel bandwidth
channel bandwidth is limited to allowing the signal lower limit frequency and the upper limit frequency to pass the channel, it can be understood as a frequency passband. For example, the passband allowed by one channel is 1.5kHz to 15 kHz, and its bandwidth is 13.5 kHz.
Timeldoam Excluding
The spread of radio waves in the wireless channel is not a single path, but a plurality of paths of many paths.
Since the radio wave is different from the distance of each path, the reachable time of each path is different, that is, the delay of each signal is different. When the transmitting end sends a very narrow pulse signal, the signal received by the mobile station consists of many different pulses, we call the delay expansion.
Signal Fading
Different from the reachable time of each path, the phase is different. A plurality of signals of different phases are added to the receiving end, sometimes it is added, and the direction is the same, sometimes attenuated (opposite), resulting in a sharp change in the amplitude of the received signal, that is, fast fading. This decline is caused by a variety of paths, so it is called multipath fading.
The receiving signal is faster in addition to the transient value, and the field strong medium value (average value) will also change slowly, mainly due to changes in regional positions and changes in meteorological conditions, to cause refraction of the wavelet Variation changes over time, and multipath propagates to change the time delay of the signals of the fixed reception point. This signal change caused by shadow effects and weather causes is called slow fading.
Doppler effect
Doppler effect in the wireless channel due to the mobility of the mobile station in mobile communication. In mobile communication, when the mobile station moves to the base station, the frequency is high, and the wavelength is shortened. We have to consider "Doppler Effect" in mobile communications. Although, due to the limitations of our mobile speed, we cannot bring a very large frequency offset, but this is undeniable that will affect mobile communication, in order to avoid this impact, in order to avoid this impact, We have to consider various considerations. It also increases the complexity of mobile communication.