An Iterative Detection Technique for DS-CDMA Signals with Strong Nonlinear Distortion Effects

Abstract

To avoid significant performance degradation in these situations, we consider improved receiver where there is an iterative estimation and cancelation of nonlinear distortion effects.Our performance results show that the proposed receiver allows significant performance improvements after just a few iterations, even when we have strong nonlinear distortion effects.

Iterative Detection of Multicode DS-CDMA Signals with Strongly Nonlinear Transmitters

“…However, nonlinear distortion levels increase when we repeat the C&F procedures, leading to performance degradation. This performance degradation can be particularly high when we have different powers assigned to different spreading codes, especially for the codes with lower power [5]. A scenario where this effect might be significant is for multi-resolution broadcasting systems [6], where we transmit simultaneously several parallel data streams with different powers so as to have different error protections.…”

“…For DS-CDMA systems, this can be achieved by assigning to each resolution a subset of the available spreading codes and a different power to each subset (i.e., the spreading codes with higher power have higher error protection and, therefore, are associated to the basic (lower) resolution). We can improve significantly the performance of nonlinearly-distorted multicode DS-CDMA systems with iterative estimation and cancelation of nonlinear distortion [5]. To cope with time-dispersive channels, a linear frequency-domain equalizer (FDE) was employed before the iterative estimation and cancelation of nonlinear distortion effects.…”

Iterative Detection of Multicode DS-CDMA Signals With Strong Nonlinear Distortion Effects

“…However, nonlinear distortion levels increase when we repeat the clipping and filtering procedures, leading to performance degradation. This performance degradation can be particularly high when we have different powers assigned to different spreading codes, especially for the spreading codes with lower power [14]. A scenario where this effect might be significant is for multi-resolution broadcasting systems [15], [16], where we transmit simultaneously several parallel data streams with different powers so as to have different error protections.…”

“…This concept was extended to multicode DS-CDMA systems in [14]. To cope with time-dispersive channels, a linear frequency-domain equalizer (FDE) was employed before the iterative estimation and cancelation of nonlinear distortion effects.…”

“…The transmitted signals have very low PMEPR thanks to the adoption of clipping (with low clipping level) and filtering techniques, which are repeated several times. We modify the approach of [14] so as to cope with its major limitations, namely: the use of a linear FDE; the separate implementation of the FDE part and estimation and compensation of nonlinear distortion effects; error propagation effects in the estimation and compensation of nonlinear distortion; poor performance in the presence of severely nonlinear distortion effects and/or at low-to-moderate SNRs. We consider an iterative frequency-domain receiver where the FDE operation and the estimation and cancelation of nonlinear distortion effects are jointly performed in an iterative way.…”