9.3 Wideband Delay-Scale Channel Characterization 383 For the wide-sense stationary uncorrelated scatterer (WSSUS) channel model, the correlation of the ~ samples H (m/B, d/T) in (9.2) can be represented in terms of a double integral involving the scattering function C H ( , ) (Ye & Papandreou-Suppappola, 2006), m d ~ E S H , B T ~ m , d S H B T = T 2 B 2 e j(d-d ) max max C H ( , ) sinc ( (d - T)) 0 - max × sinc d - T sinc ( (m - B)) sinc m - B d d . This shows that when the scattering function varies slowly with respect to (on the order of 1/B) and with respect to (on the order of 1/T), the coefficients are approximately uncorrelated across different time shifts and frequency shifts, that is, m d ~ E S H , B T ~ m , d S H B T TB C H m d , B T mm dd , where ij is the Kronecker delta (defined to be 1 when i = j and 0 when i = j).