CDMA matlab simulation with gold codes

[fabbie]

cdma matlab

Hi there,

I have some questions regarding a CDMA matlab simulation result.

Figure1 here represents the FFT convertion of a randomly generated baseband signal up to 1000 bits.
On the other hand, the Figure2 here is the FFT conversion of the baseband signal after despreadin it using Walsh Hadamard code( 8chip /s).

My question is, after performing spreading, wouldn't the amplitude (power spectal density) decrease since it is spread across the bandwidth. In this case, Figure2 amplitude has rise up significantly. Am i doing anything wrong here or did i misterpret some theory i read? Thank you for any explanation

 

[Sal]

matlab cdma

Hi

I guess the right thing to do is the following
1. Generate the random signals, take the FFT and show its spectrum.
2. spread the signal using any code, take the FFT and show its spectrum.
3. add noise (the simplest case is AWGN), despread the signal, take the FFT and show its spectrum.

I am not sure if you did that in your figures above.

Sal

 

[fabbie]

cdma matlab code

I did that. Maybe im still confuse about some stuff regarding the FFT.

Therefore, let me go to the basics on how FFT works first before proceding. I generated a simple example here to describe my confusion.

Figure1 here is a periodic sine wave at a interval of 0.63s. Figure2 is the FFT of the sinewave in Figure1.
What i dont understand here is after performing FFT on the periodic sinewave in Figure1, the signal gets converted to 126 Hz in Figure2 (assuming to be Hertz since FFT was performed). Based on Figure1, the sinewave interval is 0.63s. Converting it to frequency domain should be F= 1/T =1/0.63= 1.58Hz. Thus, how did the signal appeared at 126Hz in Figure2 instead? Furthermore, the amplitude in Figure1 is 1. Figure2 amplitude increased to 60+ as well. Since the amplitude in the time domain is equal to 1, shouldn't the amplitude in the frequency domain be 1 as well?

Can anyone please help me out in this? Really really confuse here.


This is the matlab coding i used.
y=-2*pi:0.1:2*pi
t=0.01:0.01:1.26
x =sin (y .* t .* (1./t));
figure,plot(t,x);
title('Figure1');

figure,plot(abs(fft(x)));
title('Figure2')

 

[wanghui_jason]

cdma matlab simulation

your second code x=sin(wt+angle)=sin(2*pi*f+angle) why you w changed

 

[Nimer]

cdma simulation by matlab

hi

try the mathworks file exchange community where it has lots of the simulation basics already done , you can take them and build up on your own .

regards

 

[hookarm]

matlab cdma simulation

it is very good.

 

[Communications_Engineer]

cdma simulation matlab

huh?

 

[Mynul]

Re: cdma simulation matlab

please send me the simulation program you have used
mynul_77@yahoo.com

Added after 1 hours 42 minutes:

all guys
i need to smilute ocdma using orthogonal code and rayleigh channel
i have some problem doing the coding
i am facing problem to assign time period of data and code.
please help me by sending your program
mynul_77(at)yahoo.com

 

[vadherasiddharth]

Re: CDMA matlab simulation

all guys
i need to smilute ocdma using orthogonal code and rayleigh channel
i have some problem doing the coding
i am facing problem to assign time period of data and code.
please help me by sending your program

plz send me asap

siddharth.vadhera@gmail.com

 

[nonu]

i m doing my thesis if any body have verticall handoff code in matlab do send on chandnikapoor82@yahoo.co.in plz

 

[mohdelta]

I am trying to make a cdma system for different modulation schemes such as M-ary QAM, CPM and GMSK. I am having trouble with simulinks design and will be really appreciate if someone can help me. Email mohdeltapavonis@gmail.com. Thanks