[Discuss-gnuradio] guard band

[Sara Chérif]

In ofdm transmitter , I want to add 6 subcarriers as a guard band between symbols , so that each symbol is fft + cp + guard band .. How to add this guard band ? is there a block which add zeros ? 
I think I can make guard band included in CP , I can make cp longer by 6 then multiplying symbols by a window (multipling fft and actual cp by ones & multipling last 6 subcarriers by zeros ) . Is there a window or time domain filter in GNU Radio ?
Thanks.