A Combined Approach of DPD and CFR in F-OFDM System
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A Combined Approach of DPD and CFR in F‑OFDM System Minjie Qing1 · Zhinian Luo1
© Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract The nonlinear distortion of the power amplifier (PA) is studied for Filtered Orthogonal Frequency Division Multiplexing (F-OFDM) systems, which will be adopted in the fifth generation (5G) mobile communication systems. The peak to average power ratio (PAPR) of F-OFDM signal may make the PAs work in the saturation region and result into extremely serious nonlinear saturation distortion, and the nonlinear saturation distortion is usually compensated by predistortion technology. A digital predistortion (DPD) structure is designed to compensate the nonlinear characteristics of the PA in the article. Firstly, repeated iterative clipping revision (RICR) algorithm is used to reduce the PAPR, which makes the working region of PA infinitely close to the saturation region, and as a result, the efficiency is improved. Furthermore, an integrated structure combining crest factor reduction (CFR) and DPD is employed. The experimental results show that the performance of the proposed CFR joint adaptive DPD lowers the PAPR of the predistorted signal by 2dB. The combined CFR & DPD reduces the ACPR of the transmitter by 3dB compared with the unlinearized PA. Keywords F-OFDM · Crest Factor Reduction · Digital Predistortion · 5G
1 Introduction With the large scale maturity and wide application of 4G technology, wireless communication is striding to the stage of 5G. It will greatly improve performance on the basis of the existing 4G to meet the requirements of wireless access in all aspects such as high speed, energy saving communication and mass connections [1]. In order to comply with the stringent requirement of 5G, the technology innovation should be realized from the aspects of wireless air interface technology, wireless networking and network architecture, among which wireless air interface technology is an important field in the investigation of 5G at present [2]. The waveform is the most basic technology in the physical (PHY) layer of wireless communication systems [3]. The 5G waveform * Zhinian Luo [email protected] Minjie Qing [email protected] 1
Institute of Information Science and Engineering, Hunan University, Changsha 410082, China
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candidate named F-OFDM is designed to provide the flexibility required for future applications, and considering to be OFDM-like modulation, so considerable system modifications are not required [4]. Furthermore, it exhibits excellent performance in terms of low power spectral density (PSD) side lobes. However, like other multicarrier modulation (MCM) signals, F-OFDM signal also has a high PAPR. This high PAPR signal when transmitted through a nonlinear power amplifier creates spectral broadening and increases the dynamic range of the digital to analog converter (DAC) and reduces the PA efficiency [5]. PA is one of the indispensable devices of the system. To maximize the PA linearit
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