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learn_07_qam.m
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learn_07_qam.m
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% 研究16QAM调制与解调
Fs = 1000; % 采样率1000Hz
fc = 40; % 载波频率40Hz
t1 = 0; t2 = 0.5; % 仿真时间0-0.2s
data = [0 1 0 1 1 1 1 0 0 0 1 0 0 1 1 0 1 1]; % 待调制数据
baud = 40; % 波特率40bps
t = t1:1/Fs:t2-1/Fs;
baud_iq = baud/4; % 一次传输4位，实际波特率10bps
%%%%% 调制 %%%%%
% 原数据补零
data = [data, zeros(1, 4-mod(length(data),4) )];
% 生成IQ通道数据
iq_syms = [+3 +1 -3 -1]; % IQ映射表，对应00 01 10 11
i_send_data = zeros(1,length(data)/4);
q_send_data = zeros(1,length(data)/4);
for i=1:4:length(data)
i_send_data(ceil(i/4)) = iq_syms( data( i )*2+data(i+1)+1 ); % 转十进制来索引映射
q_send_data(ceil(i/4)) = iq_syms( data(i+2)*2+data(i+3)+1 );
end
% 生成IQ通道采样信号
i_send_signal = zeros(1,length(t));
q_send_signal = zeros(1,length(t));
for i=1:1:length(t)
i_send_signal(i) = i_send_data( ceil(i/(Fs/baud_iq)) );
q_send_signal(i) = q_send_data( ceil(i/(Fs/baud_iq)) );
end
% 调制，叠加
ci = cos( 2*pi*fc*t );
cq = sin( 2*pi*fc*t );
i_send_carry = ci.*i_send_signal;
q_send_carry = -cq.*q_send_signal;
carry = 1/sqrt(10)*(i_send_carry+q_send_carry);
%%%%% 解调 %%%%%
% 同步解调
i_recv_carry = ci.*carry;
q_recv_carry = -cq.*carry;
% 积分
sum_i = 0;
sum_q = 0;
i_recv_int = zeros(1,length(t));
q_recv_int = zeros(1,length(t));
for i = 1:length(t)
sum_i = sum_i + i_recv_carry(i);
sum_q = sum_q + q_recv_carry(i);
i_recv_int(i) = sum_i;
q_recv_int(i) = sum_q;
if ( mod(i,Fs/baud_iq)==0 ) % 接收每个码元后归零
sum_i = 0;
sum_q = 0;
end
end
% 抽样判决，IQ解码
% 注意这里并没有特意设计，实际中要判断好最佳抽样点和最佳门限
i_temp = 0;
q_temp = 0;
decoded = zeros(1,length(data)); % 解码数据
p_decoded = 1;
for i=1:length(t)
% 在码元末尾处判决
if ( mod(i,Fs/baud_iq)==Fs/baud_iq-2 )
% 判决
if ( i_recv_int(i)>40 )
i_temp = 3;
else
if ( i_recv_int(i)>10 )
i_temp = 1;
else
if ( i_recv_int(i)<-40 )
i_temp = -3;
else
i_temp = -1;
end
end
end
if ( q_recv_int(i)>40 )
q_temp = 3;
else
if ( q_recv_int(i)>10 )
q_temp = 1;
else
if ( q_recv_int(i)<-40 )
q_temp = -3;
else
q_temp = -1;
end
end
end
% 解码
switch(i_temp)
case 3
decoded(p_decoded:p_decoded+1)=[0 0];
case 1
decoded(p_decoded:p_decoded+1)=[0 1];
case -3
decoded(p_decoded:p_decoded+1)=[1 0];
case -1
decoded(p_decoded:p_decoded+1)=[1 1];
end
switch(q_temp)
case 3
decoded(p_decoded+2:p_decoded+3)=[0 0];
case 1
decoded(p_decoded+2:p_decoded+3)=[0 1];
case -3
decoded(p_decoded+2:p_decoded+3)=[1 0];
case -1
decoded(p_decoded+2:p_decoded+3)=[1 1];
end
p_decoded = p_decoded+4;
end
end
% 绘制
figure(1),
subplot(7,2,1),stem(data),title('原始数据');
subplot(7,2,3),stem(i_send_data),title('I通道数据');
subplot(7,2,4),stem(q_send_data),title('Q通道数据');
subplot(7,2,5),plot(i_send_carry),title('I通道载波');
subplot(7,2,6),plot(q_send_carry),title('Q通道载波');
subplot(7,2,7),plot(carry),title('载波');
subplot(7,2,9),plot(i_recv_carry),title('I检波载波');
subplot(7,2,10),plot(q_recv_carry),title('Q检波载波');
subplot(7,2,11),plot(i_recv_int),title('I检波积分');
subplot(7,2,12),plot(q_recv_int),title('Q检波积分');
subplot(7,2,13),stem(decoded),title('解码数据');