Modifying Jakes Method to simulate multipath fading channel

Clemens Buchacher wrote:
> Steve Pope <spope33@speedymail.org> wrote:
>> But I am still not "getting" why one would use Jake's model as a
>> starting point for modeling an actual channel.  I thought the only 
>> point of Jake's was to demonstrate that you could still get a 
>> Rayleigh distribution from an unrealistically simple model.
> 
> Why? It simulates exactly what happens physically -- a superposition of
> sinusoids with uniformly distributed incidence angels. This converges to a
> Rayleigh distribution by virtue of the central limit theorem. For a
> sufficient number of sinusoids (say 20), it works quite well. The
> autocorrelation function matches the 0th order Bessel function of the first
> kind exactly (for a few of zero-crossings, which is usually enough in
> practice).
> 
> But in many situations you need more than one multi-path or channel. If you
> add two uncorrelated Jakes fading processes (generated using the techniques
> described in the papers referenced previously), you would expect to get yet
> another Jakes fading process. However, the autocorrelation function of this
> new process is distorted. Ergo, the paths are correlated. Nobody seems to
> have picked up on that so far in the literature. And I have no idea how to
> fix it either.
> 
> OTOH, it's not possible to generate a continuous fading process using the
> IDFT method. FIR-based methods require ridiculously long filters, and AR
> models have ill-conditioning issues.
> 
> So if anyone finds the holy grail of fading simulators, please let me know.
> 
> Clemens

I've been using the technique in a paper by Li and Huang, "The 
simulation of independent Rayleigh faders," IEEE Trans. Comm., Sept, 
2002, and this seems to be reliable in terms of generating results that 
match theoretical performance.

Karl Molnar