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As single-carrier frequency division multiple access (SC-FDMA) is used in long-term evolution (LTE) uplink communications, high peak-to-average power ratio (PAPR) increases power consumption in mobile devices. It is severe when localized subcarrier mapping is used with higher-order modulations. Companding is an attractive technique that offers a tradeoff between PAPR and bit error rate (BER) performances. This paper proposes an exponential companding technique that uses two companding levels based on a threshold, to reduce PAPR in SC-FDMA systems. It does not increase the average power level of transmitted signal and maintains the BER level without significant degradation from the original system. The proposed scheme has three parameters that can be adjusted for a tradeoff between PAPR, BER, and power spectral density (PSD) performances. Hence it offers more flexibility than the conventional exponential companding scheme. We also present scatter plots to find the optimum threshold value and companding levels. Finally, we verify the proposed technique considering a real-time indoor channel by using a wireless open-access research platform (WARP).

In this paper, pilot-based time-domain channel estimation (CE) along with peak-to-average power ratio (PAPR) reduction is proposed for universal filtered multicarrier (UFMC) system. The pilots that are inserted in time domain not only estimate the channel behavior but also can be used in the reduction of PAPR. For PAPR reduction, a linear companding scheme, which can treat amplitudes of the UFMC signal separately with a different scale, is proposed. The proposed companding scheme offers more design flexibility and better performance gains by using two inflexion points. However, the proposed companding scheme requires side information (SI) to perform de-companding at the receiver. The transmission of SI decreases the data efficiency, so a pilot-assisted UFMC system that can perform both data recovery and PAPR reduction without the requirement of SI transmission is proposed. In pilot-assisted UFMC system, the inserted time-domain pilots can enable SI cancellation inherently. Furthermore, a hybrid transform, which improves PAPR performance by employing clipping scheme to the linear companded signal, is proposed. Simulation results confirm that the proposed joint CE with linear companding scheme achieves an improved net gain of 6.5dB. Additionally, the proposed hybrid scheme with clipping threshold of 1.4 provides an improved PAPR reduction of 8.8dB and enhanced net gain of 7.3dB. Moreover, the proposed joint time-domain CE with hybrid PAPR reduction scheme of UFMC system is validated over real time by employing wireless open-access research platform (WARP) board.