An Unbiased Scattering Function Estimator for Fast Time-varying Channels*

E{S[m, I ] S*[m', l ' ] } = C[m, I ] 6[m m'] 6 [ l 1 ' 1 , (1) We propose an unbiased, computationally efficient estimator of the scattering function that is specifically suited to underspread WSSUS channels. The novel estimator allows for nonideal sounding signals, fast time-variation, and on-line where E denotes expectation, s[m, I1 = czzi h[n, m1 e-j21rln" is the (delay-Doppler) spreading function, and C[m, 21 is the scattering function [l]. Equivalently, operLtion during data transmission. Its good performance is assessed by a biaslvariance analysis and simulation results. E{ H [ n , IC] H* [n' , IC']} = RH [n n' , k IC'] , (2)