OFDM Receiver Problem

I have made an OFDM transmitter and receiver in MATLAB and it works
fine as far as baseband simulations are concerned. Now, I have play
backed this signal from a vector signal generator at a carrier
frequency and then sampled it. When, I down sample it using decimate
filter to the sampling rate at which it was play backed, the receiver
is unable to demodulate it. My questions is
1. at the transmitter, should i interpolate the sample to get better
results or i can play back the data at the same sampling rate it came
out of IFFT block
2. at the receiver, should i decimate directly to the sampling rate of
FFT block of 1). The decimation ratio is 30.

Thanks,

On Jan 17, 2:51�am, aitezaz....@gmail.com wrote:
> I have made an OFDM transmitter and receiver in MATLAB and it works
> fine as far as baseband simulations are concerned. Now, I have play
> backed this signal from a vector signal generator at a carrier
> frequency and then sampled it. When, I down sample it using decimate
> filter to the sampling rate at which it was play backed, the receiver
> is unable to demodulate it. My questions is
> 1. at the transmitter, should i interpolate the sample to get better
> results or i can play back the data at the same sampling rate it came
> out of IFFT block

Maybe.  It depends on the sampling rate of your iFFT block.
In general, it's a good idea to upsample, to not have aliasing
in time due to your channel simulation.

> 2. at the receiver, should i decimate directly to the sampling rate of
> FFT block of 1). The decimation ratio is 30.

As long as you do not have either time-domain nor frequency-domain
aliasing, MATLAB lets you do whatever you want.

>
> Thanks,

On Jan 17, 9:32&#4294967295;pm, julius <juli...@gmail.com> wrote:
> On Jan 17, 2:51&#4294967295;am, aitezaz....@gmail.com wrote:
>
> > I have made an OFDM transmitter and receiver in MATLAB and it works
> > fine as far as baseband simulations are concerned. Now, I have play
> > backed this signal from a vector signal generator at a carrier
> > frequency and then sampled it. When, I down sample it using decimate
> > filter to the sampling rate at which it was play backed, the receiver
> > is unable to demodulate it. My questions is
> > 1. at the transmitter, should i interpolate the sample to get better
> > results or i can play back the data at the same sampling rate it came
> > out of IFFT block
>
> Maybe. &#4294967295;It depends on the sampling rate of your iFFT block.
> In general, it's a good idea to upsample, to not have aliasing
> in time due to your channel simulation.
>
> > 2. at the receiver, should i decimate directly to the sampling rate of
> > FFT block of 1). The decimation ratio is 30.
>
> As long as you do not have either time-domain nor frequency-domain
> aliasing, MATLAB lets you do whatever you want.
>
>
>
> > Thanks,

you are right. but my question is still there... do we need to
interpolate the output of IFFT and then feed it to the DAC or the DAC
alone will do it better?

On Jan 17, 9:32&#4294967295;pm, julius <juli...@gmail.com> wrote:
> On Jan 17, 2:51&#4294967295;am, aitezaz....@gmail.com wrote:
>
> > I have made an OFDM transmitter and receiver in MATLAB and it works
> > fine as far as baseband simulations are concerned. Now, I have play
> > backed this signal from a vector signal generator at a carrier
> > frequency and then sampled it. When, I down sample it using decimate
> > filter to the sampling rate at which it was play backed, the receiver
> > is unable to demodulate it. My questions is
> > 1. at the transmitter, should i interpolate the sample to get better
> > results or i can play back the data at the same sampling rate it came
> > out of IFFT block
>
> Maybe. &#4294967295;It depends on the sampling rate of your iFFT block.
> In general, it's a good idea to upsample, to not have aliasing
> in time due to your channel simulation.
>
> > 2. at the receiver, should i decimate directly to the sampling rate of
> > FFT block of 1). The decimation ratio is 30.
>
> As long as you do not have either time-domain nor frequency-domain
> aliasing, MATLAB lets you do whatever you want.
>
>
>
> > Thanks,

well as far as IFFT output sampling rate is concerned, it is always on
the edge i.e. a signal of bandwidth Fs/2 with a sampling rate of Fs.
So, we should rely on DAC interpolation or should we interpolate it
ourselves and then feed it to DAC?