Successive interference canceling for CDMA. ICI may result from a signal's
multi-path effects, or by filtering/suppression of some of the component
energy of the signaling waveforms. Energy component attenuation destroys
orthogonality of CDMA symbols thereby causing ICI. An ICF suppresses
frequency domain portions(attenuates ingress), but also introduces ICI.
Following the ICF, the signal is de-spread sliced, re-spread and
convolved with the ICF echoes (except first tap echoes). Convolving
re-spread hard decisions with delayed ICF taps is equivalent to partially
re-modulating the first-pass hard decisions to efficiently "add-back-in"
the signal energy which was blanked/subtracted by the ICF. Alternatively,
parameter estimation de-rotates and re-rotates soft symbols and hard
decisions, respectively, compensating for undesirable symbol rotation.
The convolved signal is subtracted from a delayed version of the ICF
output signal. If desired, this process may be repeated successively to
enhance the accuracy of the obtained data decisions in the next stage.