qpsk_mod.m

介绍数字通信重要的内容：调制和解调的简单实现(BPSK,QPSK,16QAM)

function output_bit=QPSK_mod(input_bit)
%input_bit(i*2)==[0,0,1,1];input_bit(i*2-1)==[0,1,0,1];
%QPSK signal mapping
%0   0   constant    constant
%0   1   -constant   constant
%1   0   constant   -constant
%1   1   -constant  -constant
L=length(input_bit);
constant=1/sqrt(2);
for i=1:L/2
    if input_bit(i*2-1)==0
        if input_bit(i*2)==0
            output(i)=constant+constant*j;
        else
            output(i)=constant-constant*j;
        end
    else
        if input_bit(i*2)==0
            output(i)=-constant+constant*j;
        else
            output(i)=-constant-constant*j;
        end
    end
end
output_bit=output;