An improved and specification-compatible general precoding scheme (GPC) for adjustable peak-to-average power ratio (PAPR) reduction in discrete Fourier transform spread orthogonal frequency division multiplexing (DFT-s-OFDM) is proposed. Through the rearrangement of periodic padding for precoded data symbols in the GPC precoding matrix, the proposed algorithm does not increase any computational complexity compared to the original GPC. The LTE-based simulation shows the proposed algorithm has a better improvement of PAPR reduction especially in low-order modulations and the performances can be scaled to the other transmission bandwidth. These works contribute to the flexibility of DFT-s-OFDM for supporting 5G transmission over miscellaneous power amplifiers. Introduction: As a low peak-to-average power ratio (PAPR) variant of orthogonal frequency division multiplexing (OFDM), discrete Fourier transform (DFT) spread OFDM (DFT-s-OFDM) has been standardised as fourth generation (4G) long term evolution (LTE) for uplink (UL) transmission [1] due to its easy implementation and high symmetry to LTE OFDM downlink. Gradually, DFT-s-OFDM has been widely used for three 5G scenarios: enhanced mobile broadband, massive machine-type communication (mMTC), and ultra-reliable and lowlatency communication (uRLLC); and therefore has adopted for the UL waveform of 5G non-standalone new radio (NR) [2]. However, the services in 5G become more diverse which challenge the flexibility of DFT-s-OFDM [3]. In the viewpoint of signal linearity, 5G NR should be flexible for fitting the different-quality power amplifiers (PAs) of miscellaneous 5G devices. It is worth mentioning that the PA efficiency grows exponentially around the margin of linear and compression region [4, Fig. 5]. Within this region, even a slight improvement of PAPR reduction may significantly enhance the power efficiency. In addition, since the device-to-device (D2D) communications as an enabling 5G issue in LTE has been enthusiastically studied for improving the spectral efficiency, system capacity, and transmission range [5], the PA non-linearity and non-uniform UL power increase the inter-resource block (RB) interference and restrict the coverage dynamicity of the user equipment for D2D power control [6]. As known, lowering PAPR can ameliorate the flexibility of UL power for D2D power control especially in low-complexity PA devices. Fortunately, the mMTC and uRLLC devices in the D2D network are allowed to a low-speed transmission. This motivates us to exploit the merits of general precoding scheme (GPC) [7] on the trade-off between further PAPR reduction and transmission rate by an adjustable parameter. GPC was proposed for generalising all famous precoding transform, such as DFT [1], discrete Hartley transform [8], and Zadoff-Chu transform [9], into a scalable form consisted of periodic extended transform matrix and energy conservation matrix. In this Letter, we propose an improved version of GPC for better PAPR reduction without any increase of computational complexit...
An orthogonal frequency division multiplexing (OFDM) transmitter for 802.11ah uplink may consume unnecessarily high power due to the malicious effect of a large peak-to-average power ratio (PAPR). This is particularly a problem for client devices (CDs) under the low-power wide-area (LPWA) technology in an Internet of thing (IoT) system, where high PAPR signals may drive the power amplifier (PA) to operate with large input back-off (IBO). This article focuses on receiver-side signal compensation (SC) techniques and introduces a novel scheme called iterative subcarrier regularization (ISR), which is based on the generalization of Papoulis-Gerchberg algorithm (GPGA). We claim that the proposed scheme is completely compatible with 802.11ah as it only exploits the prior information available in the standard operations and popular system-build-in functions in the iterative signal reconstruction process. Extensive numerical evaluations demonstrate that the proposed scheme can improve PA efficiency by 4-9 dB for uplink signaling.INDEX TERMS Orthogonal frequency division multiplexing (OFDM), nonlinear noise, Papoulis-Gerchberg algorithm, peak-to-average power ratio (PAPR), 802.11ah.
The physical layer signaling of the 5G new radio still utilizes cyclic prefix orthogonal frequency division multiplexing (CP-OFDM) and discrete Fourier transform-spread-OFDM (DFT-s-OFDM) to support 5G services for the sake of system-backward compatibility. However, the transmission requirements among these services differ, and this poses a challenge to the adaptability of the waveforms with regard to the peak-to-average power ratio (PAPR) issue. In particular, DFT-s-OFDM serving as a low-PAPR option for uplink signaling still has room for PAPR improvement in cases such as machine-type and device-to-device communications. We propose polynomial cancellation coded (PCC)-DFT-s-OFDM to flexibly reduce the PAPR of conventional DFT-s-OFDM. The principle of the proposed method, including its transform, is analyzed in the time domain. The results show that it can also be regarded as a novel spectral shaping scheme for PAPR reduction. Through a parameter designed for adjusting the cost of spectral efficiency, the proposed method can regulate the extent of improvement compared with the conventional DFT-s-OFDM, not only in the PAPR, but also for the spectral radiation and bit error rate when considering the nonlinearity of the power amplifier. The increase in computational complexity is neglectable owing to the simplicity of generalized PCC, making it apt to be deployed in existing systems.
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