What is carrier bandwidth in wireless communications?

fish001

What is carrier bandwidth in wireless communications? [Copy link]

1. In wireless communication, the carrier bandwidth is the difference between the highest and lowest frequencies of the carrier, B=Fh-Fl. 2. In fact, it is the bandwidth occupied by different modulation modes. GSM200Khz, WCDMA 5Mhz, TD-SCDMA 1.6Mhz, LTE 1.4-20Mhz, 802.11 20-160Mhz If you use a wired transmission channel such as a telephone line, basically there is no carrier. The spectrum on this cable is yours, and you can use it as you want. But! If you use a wireless channel, then the carrier is very necessary. Because the wireless spectrum is public, anyone can transmit on it. If there is no restriction, you transmit this signal and I transmit that signal, everyone interferes with each other and the final result is that no one can get a good reception signal. Therefore, the government will stipulate which signal segment can be used for what purpose. For example, GSM can only be transmitted in a certain segment above 900MHz, and WCDMA under 3G uses 5MHz above 1.8GHz. However, the baseband signal is basically concentrated around 0Hz. How to get to 900MHz or 1.8GHz? At this time, the carrier is used. The carrier itself does not have any signal, it is just a carrier of the signal. Just like the picture below. Generally speaking, adding a carrier means multiplying the original signal by a cosine (2 pi ft). Note that different modulation modes determine the occupied bandwidth. The so-called 5Mhz of WCDMA, 1.6Mhz of TD-SCDMA, 1.4-20Mhz of LTE, and 20-160Mhz of 802.11 refer to how wide the signal is in the picture above. The carrier determines the center point of the frequency, that is, where the center of the waveform in the figure above is located on the frequency axis. Finally, in a nutshell, when the wireless signal just comes out of the antenna of the transmitter, it will have the following mathematical expression: a_n is a truly meaningful signal, that is, something like 0101; T is the time slot occupied by each waveform, that is, how long each waveform will last, and then p(t-nT) depends on the modulation mode. Different modulation modes will result in different expressions for p(t); finally, cos(2 pi ft) is the carrier, and f determines where you want to move this signal on the spectrum axis.

alan000345

Very good, I learned something new.