OFDM transmitter pulse shaping filter

[icanalyst]

In OFDM transmitter, the modulated symbols need to be pulse shaped before transmitting. I built a filter in Matlab2013a using

d = fdesign.pulseshaping(16,'Raised Cosine', 'Ast,Beta', 60, 0.3);
H = design(d);
fvtool(H);

In previous Matlab version, a function can be used both for filter design and apply to IFFTed symbol data:

rcosflt(subcarriers, 1, 20, 'fir',0.4,10)

However in 2013a version, I couldn't find information to apply this filter to IFFTed symbol data. Does anybody know how to do it?

Thank you!

 

[rcdaniels]

Just a minor point, but OFDM signals don't HAVE to be pulse-shaped. By adding null guard subcarriers on the edge of the spectrum (as in all OFDM standards), you are effectively bandlimiting the signal.

Now, you may want to add a pulse-shaping filter to improve the transition regions on the edges, but it is not always required.

As far as the MATLAB concerns, I'm assuming you've read this: https://www.mathworks.com/help/dsp/ref/fdesign.pulseshaping.html

I don't know the shortcut to do the up-sampling in a one-line MATLAB command, but the operation is pretty straightforward. Just multiply each time-domain OFDM sample (after IFFT and CP) by the impulse response of the pulse-shaping filter, delay each successive product by the pulse-shaping filter delay, and then add them together. This will give you the oversampled, pulse-shaped OFDM signal.

BTW, is there a reason you use 60 periods for the pulse-shaping filter? It seems like you can get away with much less. This will reduce your computational complexity substantially, especially since your oversample rate is so high.

 

[shadowpanther4real]

hello..I have a problem. I want to know how to design a pulse shaping FIR filter in Matlab when the input to this filter is Gaussian pulse. Could you help me please? In my case the output of this pulse shaping filter should be 5th order derivative Gaussian pulse.

Thanks. waiting for the reply.