OFDMA nonlinear distortion recovery using improved clipping localization and iterative projections

In OFDM-based systems the effect of nonlinear amplification at the transmitter is increasingly being tackled by receiver-oriented methods that aim to reduce distortion through estimating and recovering the clipped signal. However, in OFDMA systems, recovery of clipped signals poses new challenges because not all modulation information about other users is available to any individual user. Recently a scheme based on simple clip localization and band limited signal recovery has been proposed to address this problem but its performance is limited. In this paper, we propose to improve clip location estimation by exploiting key factors such as closeness of signal level to clipping threshold, clip time-span, and out-of-band power for local windowed subsequences, and then incorporate clip location estimates in iterative projection method to recover the clipped signal. Extensive simulations demonstrate that the performance is significantly improved with the proposed scheme compared with existing methods.

I Introduction

Orthogonal Frequency Division Multiple Access (OFDMA) is becoming the predominant technology for all future broadband wireless systems in the next decade. In recognition of Orthogonal Frequency Division Multiplexing (OFDM) based advantages of robustness against frequency selective fading, high bandwidth efficiency and simple equalizer structure, OFDM technology has widely being adopted in many standards such as Digital Audio Broadcasting (DAB), Digital Video Broadcasting-Terrestrial (DVB-T) and IEEE 802.11 Wi-Fi. OFDMA was first introduced in IEEE 802.16 WiMAX broadband wireless systems [1]. It was rapidly adopted in the mainstream existing and proposed standards of Long Term Evolution (LTE) and LTE-Advanced, respectively, the latter targeted for next generation 4G mobile communications.