Comments on: MSK transmitter and receiver

By: Krishna Sankar

Krishna Sankar — Mon, 21 Jun 2010 00:42:47 +0000

@Sarah: Well, if your sampling period is 1/Ts, you need to sum over 2T/Ts samples
I am unable to write the precise code as I do not follow your code well. But am sure that you will be able to figure this out. Good luck.

By: Sarah

Sarah — Tue, 15 Jun 2010 13:07:04 +0000

this was the time intv i was using. The solution you gave me previously is fine for the exp msk version but doesnt work for this one.

time_sampling = [0:1/fs:T];
time_sampling = time_sampling(1:end-1);% gets ride of the final value
%Produces the time intervals

By: Sarah

Sarah — Tue, 15 Jun 2010 13:01:35 +0000

Hi,

I used this equation to modulate MSK

xt = cos(2*pi*(fc+frequency_differance_repeat).*time_sampling_repeated + Phase_value_array_repeat );

This equation is from your website. It works fine.
The i multiplied the received (xt) signal by the following (first stage of the receiver as instructed on your website):
( i hvnt added noise yet)

%even arm
stage1_cos = xt.*(cos(2*fc*pi*time_sampling_repeated)).*(cos(pi.*time_sampling_repeated/2*T));

%odd arm
stage1_sin = xt.*(sin(2*fc*pi*time_sampling_repeated)).*(sin(pi.*time_sampling_repeated/2*T));

How do i recover the signal from here. I’m still having a problem with evaluating the intergtration from 0 to 2T for the above signal.

By: Krishna Sankar

Krishna Sankar — Sun, 18 Apr 2010 09:08:12 +0000

@Sarah: The convolution operation with taps as all ones for duration of 2T takes care of the integration of 2T
conv(real(yt).*ct,ones(1,2*T))

By: Krishna Sankar

Krishna Sankar — Sun, 18 Apr 2010 09:07:20 +0000

@Sarah: Well,
a) starting from 2T+1 ensures that the first 2T symbols are ignored (to account for the delay of the integration by 2T)
b) the step size of 2T ensures that we take one symbol from the even, then from odd, then even and so on…

By: pradeep

pradeep — Wed, 14 Apr 2010 12:03:13 +0000

thanks for ur replay krishna

By: Sarah

Sarah — Wed, 14 Apr 2010 11:54:16 +0000

Just have one more basic question.

in the above steps:

(f) Multiply the I and Q arm by and respectively and integrate over period 2T
if you already have a matrix of numbers in I and Q, how do u actually intergrate it over 2T