What kind of parameters do you want to set? I mean, is it bandwidth, center frequency, modulation or what?
And in what kind of level is your design represented? Is it in high level language (like C or Matlab), hardware language, or perhaps in prototyping board?
i mean to say how can we set our transmission bandwidth , symbol duration , number of subcarriers etc.and my design is simulated in xilinx system generator
I've never used xilinx system generator, but perhaps you can use some of these principles.
For OFDM, number of subcarriers is equal to IFFT/FFT size.
Transmission bandwidth and symbol duration are related to baseband sampling frequency and IFFT/FFT size.
Bandwidth: BW = Fs * N_used / N_FFT
OFDM symbol duration without guard interval: Tb = N_FFT / Fs
Fs is baseband sampling frequency.
N_FFT is IFFT/FFT size.
N_used is number of used subcarriers (excluding guard band subcarriers).