capacity of a communication link based on QPSK modulation

[sharlotte]

capacity of a communication link and QPSK modulation

does any body know the capacity of a communication link based on QPSK modulation;
how is it related to the Shannon theorem?

 

[David83]

Re: capacity of a communication link and QPSK modulation

does any body know the capacity of a communication link based on QPSK modulation;
how is it related to the Shannon theorem?

When a modulation scheme is used, we call the "capacity" the achievable rate. In the case of QPSK, the maximum achievable rate is 2 bit/channel use. On the other hand, when the channel input is unconstrained (Gaussian), as in the case of Shannon derivation, the capacity is much higher especially in the high SNR.