数字通信QAM调制及其MATLAB仿真程序.doc

数字通信QAM调制及其MATLAB仿真程序1. %数字通信QAM仿真2. clear3. %产生基带符号流4. M=16; %进制 16QAM5. N=40; %信源比特流长度,为保证对齐,选择是log2(M)的整倍数6. bitstream=zeros(1,N);7. symbolstream=zeros(1,N/log2(M);8. for n1=1:N9. bitstream(n1)=binornd(1,0.5,1,1);10. end11. %格雷码编码12. for n1=1:length(symbolstream)13. pack=bitstream(4*(n1-1)+1) bitstream(4*(n1-1)+2) bitstream(4*(n1-1)+3) bitstream(4*(n1-1)+4);14. ifpack=0 0 0 015. symbolstream(n1)=1+j;16. elseifpack=0 0 1 017. symbolstream(n1)=2+j;18. elseifpack=0 0 1 119. symbolstream(n1)=2+2j;20. elseifpack=0 0 0 121. symbolstream(n1)=1+2j;22. elseifpack=0 1 0 123. symbolstream(n1)=-1+2j;24. elseifpack=0 1 0 025. symbolstream(n1)=-1+j;26. elseifpack=0 1 1 127. symbolstream(n1)=-2+2j;28. elseifpack=0 1 1 029. symbolstream(n1)=-2+j;30. elseifpack=1 1 1 031. symbolstream(n1)=-2-j;32. elseifpack=1 1 1 133. symbolstream(n1)=-2-2j;34. elseifpack=1 1 0 135. symbolstream(n1)=-1-2j;36. elseifpack=1 1 0 037. symbolstream(n1)=-1-j;38. elseifpack=1 0 0 039. symbolstream(n1)=1-j;40. elseifpack=1 0 1 041. symbolstream(n1)=2-j;42. elseifpack=1 0 0 143. symbolstream(n1)=1-2j;44. else symbolstream(n1)=2-2j;45. end46. end47. figure(1)48. hold on49. for n1=-2:250. for n2=-2:251. if (n1=0)|(n2=0) 52. scatter(n1,n2);53. end54. end55. end56. axis(-3 3 -3 3);57. hold off58. title(16QAM星座图);59. xlabel(同相支路)60. ylabel(正交支路)61. %产生载波62. fc=10; %载波频率63. fs=100; %采样频率64. T=1; %每符号持续时间65. N_samples=T*fs;%每符号内的采样点数66. t=0:T/N_samples:(T-T/N_samples);67. carrier=exp(j*2*pi*fc*t);68. %产生信号脉冲g(t)69. %gt=ones(1,length(carrier);70. gt=1-cos(2*pi*(1/T)*t);71.72. %生成调制信号S(t)73. St_complex=zeros(1,length(carrier)*length(symbolstream);74. for n1=1:length(symbolstream)75. St_complex(N_samples*(n1-1)+1):(N_samples*(n1-1)+N_samples)=(symbolstream(n1)*carrier).*gt;76. end77. figure(2)78. St_real=real(St_complex);79. plot(St_real)80. title(QAM仿真波形图 载波10Hz g(t)为升余弦脉冲);81. xlabel(采样点)82. ylabel(幅度)83. %求出功率谱,这种功率谱不是按照公式直接计算的,而是对所产生的一段时间内的信号的采样点进行FFT所得到的84. spectrum=(real(fft(St_real,10*length(St_real).2;85. S_spectrum=spectrum(1:length(spectrum)/2);86. figure(3)87. F=0:fs/(2*length(S_spectrum):fs/2-fs/(2*length(S_spectrum);88. plot(F,10*log10(S_spectrum)89. axis(0 50 -70 60);90. title(QAM信号功率谱密度)91. xlabel(频率/Hz)92. ylabel(功率)93. figure(4)94. index=400:1600;95. plo