channel fading emulation on fpga

Hi,

I am working on a testbed which emulates the 802.11 wireless link.
The PHY is implemented on the FPGA and can emulate upto three
independent wireless channel.

I want to add some channel fading effects to the testbed. For example
implement a lognormal or rayleigh fading effects on the channel.

How hard will it be?? Is there any sample code available??

Thanks
Arvind

arvind