Orthogonal frequency division multiplexing (OFDM) has been adopted for several wireless network standards due to its robustness against multipath fading. Main drawback of OFDM is its high peak-to-average power ratio (PAPR) that causes a signal degradation in a peak-limiting (e.g., clipping) channel leading to a higher bit error rate (BER). At the receiver, the effect of peak-limitation can be removed to some extent to improve the system performance. In this paper, a combined decision-feedback equalization with clipping noise reduction technique is presented. An iterative equalization weight that minimizes the mean square error (MSE) with respect to residual clipping noise is derived. It is shown that the bit error rate (BER) performance of OFDM with proposed technique can be significantly improved in a peak-limited and frequency-selective fading channel.
[Show abstract][Hide abstract] ABSTRACT: This paper proposes a new method for decoding multicarrier symbols with severe nonlinear distortion. The first part evaluates mutual information expressions for practical nonlinear models and shows the performance bounds for commonly used receiver structures. Then, we derive the maximum-likelihood (ML) sequence estimator, which unfortunately has an exponential complexity due to the nonlinear distortion. This extremely large complexity can be reduced with a simple algorithm that iteratively estimates the nonlinear distortion, thereby reducing the exponential ML to the standard ML without nonlinear distortion. The proposed method can be used to reduce the peak-to-average power ratio of multicarrier signals by clipping the transmit sequence. It can also be used to correct any nonlinear distortion present in transmitter/receiver amplifiers that are operating close to saturation.
[Show abstract][Hide abstract] ABSTRACT: Clipping is often used to reduce the large peak-to-mean envelope power ratio of orthogonal frequency-division multiplexing (OFDM) signals. However, it introduces additional noise that degrades the system performance. A technique called decision-aided reconstruction (DAR) is proposed for mitigating the clipping noise. The performance of the proposed technique is evaluated for additive white Gaussian noise and static intersymbol interference channels. The effect of using a realistic channel estimate is also examined. Results show that the DAR technique can mitigate the clipping noise significantly for OFDM systems that have large block sizes.
[Show abstract][Hide abstract] ABSTRACT: The repeated clipping and frequency domain filtering of an orthogonal frequency division multiplexing (OFDM) signal was studied to reduce peak-to-average power ratio (PAPR) of the transmitted signal. An oversize inverse fast Fourier transform (IFFT) was used to transform the input vector. The clipping was followed by filtering to reduce the out-of-band power. Analysis suggested that the clip-and-filter technique did not increase the out-of-band power and limited the PAPR reduction practical systems to in-band-distortion.
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