[R] How to add a common title (or xlab, ylab) for multi-plots in the same window?

[F Duan]

Dear R people,

I am using par(mfrow=c()) to plot multi-figures in the same window. And I like 
to put a common title (and xlab, ylab) for all of plots. I have already left 
some margin by resetting omi values in par() and hided all (xlab, ylab) for 
each sub-plot. Could anyone tell me how to do that?

Thanks a lot,

Frank