Understanding of basic concepts of channel capacity and channel bandwidth

        Before writing this article, I have been on “ bandwidth ” This term is confusing , For example, we usually say “ bandwidth 10M Network of ”,“ The network bandwidth is 10M” wait , It is easy to follow the channel bandwidth, such as 10MHZ、100MHZ To confuse . I consulted relevant books , Finally, these two concepts have been thoroughly clarified in communication and circuit .

1、 network bandwidth

        We usually talk about network bandwidth , In standard terms, it should be channel capacity , In bits per second (bit/s). The channel capacity calculated by Shannon formula in the communication principle , The unit of network bandwidth we verbally say is bit/s; At the same time, we should note that there is also a bandwidth in this formula , Is the channel direct bandwidth , Determined by the frequency characteristics of the circuit , Unit is HZ, That is to say, as long as the circuit design is determined , Then the direct bandwidth is determined , It is what we usually call Qualcomm 、 Lowpass 、 Bandpass filter .

2、 Channel bandwidth

        Channel bandwidth is what we often call Qualcomm 、 Lowpass 、 Bandpass , It is determined by the circuit . Because the wave velocity is related to the medium , according to c=λf, It is known that in the same medium λ（ wavelength ） The bigger it is ,f（ frequency ） The lower the ; and f It is the bandwidth that determines the capacity of the channel , Transmission rate . So in wireless communication , When the power is certain , The larger the bandwidth, the higher the data rate transmitted , The transmission distance is near ; The smaller the bandwidth, the lower the data rate transmitted , The transmission distance is far .

 

 

3、 Nyquist theorem and Shannon theorem

        From time to time, these two theorems will be confused , So here is a brief explanation , Nyquist theorem is ideal for calculating channel capacity , Shannon's theorem is to calculate the channel capacity in practical engineering .