Superposition of rectangular power pulses and CP-OFDM signal for SWIPT

(2022) 2022:77 Kassab et al. J Wireless Com Network https://doi.org/10.1186/s13638-022-02151-1 EURASIP Journal on Wireless Communications and Networking Open Access RESEARCH Superposition of rectangular power pulses and CP‑OFDM signal for SWIPT Hussein Kassab* , François Rottenberg, Thomas Feuillen, Charles Wiame and Jérôme Louveaux *Correspondence: Institute of Information and Communication Technologies, Electronics and Applied Mathematics, 1348 Louvain la Neuve, Belgium Abstract Simultaneous wireless information and power transfer (SWIPT) has recently attracted researchers and may help to satisfy future technology demands. SWIPT allows wireless power transfer (WPT) and wireless information transfer (WIT) to coexist based on shared resources. Recent studies have shown that, due to the nonlinearity of the rectifiers, high-PAPR (peak to average power ratio) waveforms provide better performance in terms of energy harvesting, making the design of power signals essential. In addition, these power signals should consume the smallest amount of resources for the WIT. In this paper, a new waveform design is proposed where the information and power signals are superposed using the same frequency and time resources. The power signal is composed of a high peak modulated rectangular wave sent during the cyclic prefix of the orthogonal frequency-division multiplexing (CP-OFDM) system, which is discarded at the information receiver, such that it does not interfere with the OFDM data symbol. Although the pulse is restricted to be within the cyclic prefix, there might be a small amount of interference caused by channel dispersion. Simulations and measurements show that a good choice of signal parameters can minimize interference on the information symbols and simultaneously provide good performance in terms of energy harvesting. Keywords: SWIPT, WPT, WIT, Energy harvesting, Waveform design, CP-OFDM, Nonlinear rectifier model 1 Introduction 1.1 Background and motivations Internet of things (IoT) electronic devices such as battery-free sensors, passive radio frequency identification (RFID), and machine-to-machine (M2M) systems are expected to be extensively deployed in the near future. Beside their need for wireless information transfer (WIT), it is envisioned that these devices could harvest energy from the nearby electromagnetic sources or from dedicated power heads in order to extend their battery lifetime. The harvesting of energy is done using a harvester known as “rectenna” which is composed of an antenna concatenated with a rectifier. This dual demand of information and power attracted the research community to investigate simultaneous wireless information and power transfer (SWIPT), which consists of transferring both energy and information wirelessly using the same radio frequency resources [1, 2]. One possible © The Author(s) 2022. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http:// creativecommons.org/licenses/by/4.0/. Kassab et al. J Wireless Com Network (2022) 2022:77 Fig. 1 Illustration of a SWIPT network structure showing a possible scenario of coexistence between WIT and WPT scenario of coexistence between WIT and wireless power transfer (WPT) systems is illustrated in Fig. 1. SWIPT was first introduced by [3] where the fundamental trade-off between energy and information was addressed showing that the rate-energy (R-E) region is a nonincreasing concave function. A substantial interest in SWIPT has been observed in the communication literature, focusing on different aspects: wireless powered communication [4–6], MIMO broadcasting [7–9], interference channel [10–12], relaying [13–15], broadband system [16–18]. Another aspect is the receiver architecture [19] which can be either separate receiver [7], power-splitting [19], time switching [17], antenna switching [20], or as suggested by [21] to jointly extract information and harvest power without consuming energy in the process of collecting decoded data. Recently, an end-to-end machine learning approach was studied in [22] to jointly optimize the transmitter and the receiver using neural network (NN)-based auto-encoders. Also, a closed-loop practical SWIPT prototype with adaptive waveform optimization based on channel state information (CSI) acquisition and different receiver architectures is implemented in the works of [23, 24]. The work in [25, 26] provides a comprehensive survey of state-of-theart SWIPT techniques. Besides, the works in [27, 28] provide interesting overviews of potential applications and promising future research paths for SWIPT. In the early literature, no specific waveform design for the power signal was considered since the RF energy harvester was based on a linear model that depends only on the received power [25]. Hence, the power signal was usually set as a single tone. However, when the nonlinearity of the rectifier is considered, it has been noticed that the output DC current not only depends on the circuit parameters but also on the input waveform design [2, 29]. In addition, it has been shown in [30, 31] that high-PAPR waveforms Page 2 of 26 Kassab et al. J Wireless Com Network (2022) 2022:77 provide better performance in terms of energy harvesting. Accordingly, waveform design became an important factor that should be considered while maximizing the energy harvested to make the best out of an available RF spectrum for the same transmitter power. In the case of SWIPT, the WPT waveform design has to be taken into consideration jointly with everything that is related to the information transfer. Several methods were proposed to have an optimized waveform design for both power and information signals (i.e., SWIPT waveform design). This waveform design can be based either on a combined waveform (i.e., one common signal for both WPT and WIT) or on separate waveforms (i.e., two signals that are clearly distinct but share the same resources). One approach for combining waveforms was addressed in [32], where a multisine waveform is used for energy transfer with distinct levels of PAPR acting as information transfer, enabling a low-energy combined receiver. However, this has a very limited data rate. Other methods using combined wave (...truncated)