Hi all,
I have some doubts in simulating the qam modulator and demodulator.
Let me first say what I have done till now. Here is my code
len000;M;k=log2(M);
fd6;fs6;alpha=0.5;delay0;Ts=1/fs;fc6;% sym rate fs=samp freq
x_mod=2*floor(k*rand(1,len))-k+1+1i*(2*floor(k*rand(1,len))-k+1);
%x_mod=x_mod*sqrt(3/2*Var/(M^2-1));
x_real=transmit_filter(real(x_mod),fd,fs,alpha,delay);%Upsamplg SRRC Filtg
x_img=transmit_filter(imag(x_mod),fd,fs,alpha,delay);% UPSAMPLE FACTOR=8
N=length(x); % discrete signal length
t=Ts*(0:N-1);
x=x_real.*cos(2*pi*fc*t)+x_imag.*sin(2*pi*fc*t);
n=randn(1,length(x)); % AWGN Generation
r1=x+n; % Adding Noise to the signal
b=fir1(50,((fd/2)/(fs/2)),'low');
y_real=r1.*cos(2*pi*fc*t);
Y_real=filter(b,1,y_real);
y_img=r1.*sin(2*pi*fc*t);
Y_img=filter(b,1,y_img);
y_real=receive_filter(Y_real,fd,fs,alpha,delay);%SRRC Filtg & Dowmsamplg
y_img=receive_filter(Y_img,fd,fs,alpha,delay);DOWNSAMPLE FACTOR=8
MY DOUBTS are:
1. Is my transmitter right?
2. I am quite confused about creating channel. Is it enough to add noise(AWGN
channel) or should I do a channel filtering. If so how should i determine the
filter cutoff freq and gain?
3.On the receiver side, after downsampling , I am literally not getting any
symbols. Is it because of non-synchronisation?.How should I fix my signal and
carrier's amplitude and filter's gain and delay?
4. How should I determine the SNR.
5. Do I need a equaliser?
It would be of really great help if you could guide me with your replies. Thanks
a lot in advance.
Regards,
Mahadevi.
