Iterative Correction of Clipped and Filtered Spatially Multiplexed OFDM Signals

Iterative decision‐directed estimation and compensation of nonlinear distortion effects for OFDM systems

“…There have been several iterative techniques that were introduced to reduce the nonlinear distortions due to clipping at the receiver end 2–10. A maximum likelihood (ML) decision based nonlinear (i.e., clipping) noise reduction for multi‐carrier signals (i.e., OFDM) was proposed in Reference 2 while taking into consideration the clipping noise at the receiver over a Gaussian channel (thus, channel equalizer was not considered).…”

“…Clipping noise reduction and cancelation technique based on DAR algorithm was proposed in Reference 5. Iterative reduction of clipping noise was presented in Reference 6 as an extension of Reference 4 to multiple‐input multiple‐output (MIMO) OFDM based on perfect knowledge of CSI, where the authors use a complex computation of clipping noise estimate using sub‐optimal linear minimum mean square error (LMMSE) filtering based on the iterative algorithm given in Reference 5. The knowledge of noise and distortion variance is required a priori to compute the weight of LMMSE filter, which requires an update of noise and distortion variance during each iteration.…”

“…The knowledge of noise and distortion variance is required a priori to compute the weight of LMMSE filter, which requires an update of noise and distortion variance during each iteration. Moreover, the clipping noise removal algorithm and channel equalization are done independently in Reference 6. In References 7–9, channel equalization and iterative clipping noise reduction techniques are used independently since the authors only focused on solving the problem caused by nonlinear degradation.…”

“…Iterative channel estimation/equalization can be applied to further improve the OFDM system performance in a doubly selective (i.e., time and frequency selective) fading channel with imperfect CSI. The clipping noise may not be perfectly compensated for, even if iterative clipping noise reduction techniques presented in References 4–10 are considered—the residual clipping noise errors remain. Consequently, the OFDM system will not be able to cope with a problem of clipping error propagation when iterative channel estimation/equalization is applied to improve the system performance with imperfect CSI.…”

“…Consequently, the OFDM system will not be able to cope with a problem of clipping error propagation when iterative channel estimation/equalization is applied to improve the system performance with imperfect CSI. Unlike the previous work 2–10, where channel equalization and nonlinear noise reduction are independent, we take a different approach to take into consideration the residual clipping noise errors.…”