Adjustable PAPR reduction for DFT‐s‐OFDM via improved general precoding scheme

Abstract

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...

Rotated DFT‐s‐OFDM for transmitting PAPR‐minimised BPSK symbols

“… ‐binary phase‐shift keying (BPSK), has been applied to DFT‐s‐OFDM as the second standard solution in long‐term evolution (LTE) [4 ] and 5G new‐radio (NR) specifications [5 ]. This is to achieve further PAPR reduction to create user equipment that boasts better power efficiency and wider signal coverage [6, 7 ].…”

Bit‐level implementation for polynomial cancellation coded DFT‐s‐OFDM transmitters

“…The third generation partnership project (3GPP) still recommend discrete Fourier transform‐spread orthogonal frequency division multiplexing (DFT‐s‐OFDM) as the uplink waveform for 5G New Radio (NR) [1, 2] with regard to the peak‐to‐average power ratio (PAPR) issue [3]. Although it provides the backward compatibility, various 5G communication scenarios may challenge the flexibility of DFT‐s‐OFDM on the PAPR aspect that adapts to different‐quality power amplifiers (PAs) of all 5G devices [4]. Further, since DFT‐s‐OFDM also serves as the sidelink waveform for proximity services for device‐to‐device (D2D) communication in 4G Long Term Evolution (LTE) [5], flexible solution to its PAPR issue plays a critical role in D2D power control [4, 6].…”

Polynomial Cancellation Coded DFT-s-OFDM for Low-PAPR Uplink Signaling

“…However, the PAPR performance of the current standard solution is fixed and cannot be further improved if the communication scenario values the PAPR than other performances. Therefore, it is important to establish a mechanism to adjust a signal's PAPR in a flexible manner that ensures a sufficient trade-off between spectral efficiency and energy efficiency (in PAPR aspect) in 5G [16]. The device capabilities for each 5G use case, including enhanced mobile broadband (eMBB), ultra-reliable and low latency communications (URLLC), and massive machine type communications (mMTC) are quite different [17].…”

“…For example, reducing the PAPR of a signal can directly increase the reliability for URLLC owing to the increased SNR, but can lower the signal nonlinearity and power consumption for mMTC devices, which are usually only equipped with basic PA. Nonlinear uplink signals bring severe interferences between users, particularly those with narrowband transmissions. Furthermore, since the sidelink used for proximity services (ProSe) in device-to-device (D2D) communication has been defined as a subset of the uplink resources [18], the issue of D2D power control critically challenges system performance [16,19]. This is because the D2D network dynamically connects various types of user equipment (i.e., various qualities of PA) to support different scenarios of ProSe.…”

“…DFT-s-OFDM signaling is expected to be a more robust waveform for uplink through adjustable PAPR reduction schemes. Hence, several data-independent schemes such as spectral shaping (SS) [20], which use extra subcarriers to further reduce PAPR, have been investigated to overcome the need for a flexible countermeasure to the PAPR problem [16,21]. Although the results in [16] successfully achieved 2-3 dB PAPR reduction compared with conventional DFT-s-OFDM with 10%-20% spectral efficiency loss, further spectral efficiency loss does not improve the PAPR performance more, and instead degrades it.…”