Multiuser Wirelessly Powered Backscatter Communications: Nonlinearity, Waveform Design, and SINR-Energy Tradeoff

Abstract

Wireless power transfer and backscatter communications have emerged as promising solutions for energizing and communicating with power limited devices. Despite some progress in wirelessly powered backscatter communications, the focus has been concentrated on backscatter and energy harvester. Recently, significant progress has been made on the design of transmit multisine waveform, adaptive to the Channel State Information at the transmitter (CSIT), in point-to-point backscatter system. In this paper, we leverage the work and study the design of transmit multisine waveform in a multiuser backscatter system, made of one transmitter, one reader and multiple tags active simultaneously. We derive an efficient algorithm to optimize the transmit waveform so as to identify the tradeoff between the amount of energy harvested at the tags and the reliability of the communication, measured in terms of Signal-to-Interference-plus-Noise Ratio (SINR) at the reader. Performance with the optimized waveform based on linear and nonlinear energy harvester (EH) models are studied. Numerical results demonstrate the benefits of accounting for the energy harvester nonlinearity, multiuser diversity, frequency diversity and multisine waveform adaptive to the CSIT to enlarge the SINR-energy region.tags can operate with low power as they do not require RF components to generate carrier signal. Although backscatter communications has originally been limited to simple radio frequency identification (RFID) applications, it has received a renewed interests in recent years with advances in backscatter communication theory, including coding [5], beamforming [4], performance analysis of large networks [6], [7].RF transmitter in backscatter communications typically transmit sinusoidal continuous waveform (CW). Significant progress has recently been made on the waveform design in wireless power transfer (WPT), in order to improve the efficiency and DC output power of the energy harvester. In particular, [8] studies the nonlinear behaviour of RF-to-DC converter and suggests that significant DC power gain can be obtained by using multisine waveform with zero phase between the sinewaves. In [9], a multisine waveform transmission has been introduced to extend the reading signal.[10] presented multisine waveform method to improve power sensitivity of the tags and conduct a survey of reading range improvement for several commercial RFID tags. Motivated by the promising gains, a systematic approach towards waveform design for WPT was proposed in [11]. In [11], optimized multisine waveforms, adaptive to the CSIT, have been shown to provide significant gain by exploiting the rectifier nonlinearity and the frequency selectivity of the channel.Backscatter communication can leverage this recent progress in WPT waveform design and depart from the conventional CW transmission. Recently, [12] studies the tradeoff between harvested energy and backscatter communication in point-to-point deployment. It is noted that waveform design for WPT and backscatter communicati...

Large-Scale Wireless-Powered Networks With Backscatter Communications—A Comprehensive Survey

“…In [154], with perfect CSIT and employing the non-linear energy harvester model in [138], a systematic design of multisine transmit waveform is designed to enlarge the tradeoff region, thereby leading to performance improvement of point-to-point backscatter communication system. Besides, in [155], the work in [154] is extended to a multi-user backscatter system. An optimization problem is formulated and solved to jointly optimize the phases and the magnitudes of the multisine waveform for multiple-tags system.…”

Beamforming and Reflection Coefficient Control for Multiantenna Backscatter Communication With Nonorthogonal Multiple Access

“…To date, several multiple access (MA) schemes have been applied to the monostatic BackCom and their performances have been optimized from different aspects. For a singleantenna reader, time division multiple access (TDMA) protocols have been designed to maximize the throughput via time allocation [15] and multisine waveforms for an excitation signal have been optimized to improve the signal-tointerference-plus-noise ratio (SINR)-energy trade-off of onoff backscatter modulation [16]. For a multiantenna reader, the transmit beamforming (BF) has been optimized taking into account channel estimation using backscatter pilot symbols [12].…”

“…This article focuses on monostatic BackCom with a fullduplex reader and multiple BDs as in [12], [15], [16], [18], [19] that excites the signals to the BDs in the downlink for reflection and energy harvesting and collects the data from the reflected signals in the uplink. The monostatic BackCom has a resemblance to a cellular network suitable for centralized resource allocation and optimization in collecting data from massive IoT devices.…”

Multi-Tag Backscattering to MIMO Reader: Channel Estimation and Throughput Fairness

“…Considering frequencymodulated continuous-wave based monostatic BSC system with multiantenna reader, whose one antenna was dedicated for transmission and remaining for the reception of backscattered signals, authors in [7] focused on determining the number of active tags and their positions. More recently, the transmit waveform and receive combiner design for wirelessly powered multi-tag BSC was studied in [8] under the assumption of perfect CSI availability for BSC channels to investigate the tradeoff between harvested energy among tags and signalto-interference-plus-noise ratio (SINR) at the reader during information decoding (ID). For the single antenna ambient BSC systems, a backscatter multiplicative multiple-access channel scheme was introduced in [9], whose achievable rate region was shown to be larger than that of the conventional time-division multiple-access systems.…”