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

Abstract

Green low power networking with the least requirement of dedicated radio resources is need of the hour which has led to the upsurge of backscatter communication (BSC) technology. However, this inherent potential of BSC is challenged by hardware constraints of the underlying tags. We address this timely concern by investigating the practical efficacy of multiple-input-multiple-output (MIMO) technology in overcoming the fundamental limitations of BSC. Specifically, we first introduce a novel least-squares based channel estimation (CE) protocol for multi-tag BSC settings that takes care of both the unintended ambient reflections and the inability of tags in performing estimation by themselves. Then using it, a nontrivial low-complexity algorithm is proposed to obtain the optimal transceiver designs for the multiantenna reader to maximize the minimum value of the lower-bounded backscattered throughput among the single-antenna semi-passive tags. Additional analytical insights on both individually and jointlyoptimal precoding vector and detector matrix at the reader are provided by exploring the asymptotically-optimal transceiver designs. Lastly detailed numerical investigation is carried out to validate the theoretical results and quantify the practically realizable throughput fairness. Specifically, more than seven-fold increase in the common-backscattered-throughput among tags as achieved by the proposed designs over the relevant benchmarks corroborates their practical significance.

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

“…A novel least-squares estimator for the forward and backward links between the reader and the tag and also corresponding linear minimum-mean square-error estimate for the backscattered channel are derived in a single-tag BSC setting. The authors further consider multi-tag backscatter setting in [191], as shown in Fig. 9.…”

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

“…For a multiantenna reader, the transmit beamforming (BF) has been optimized taking into account channel estimation using backscatter pilot symbols [12]. Later, sum throughput and throughput fairness have been optimized in space division multiple access (SDMA) by optimizing the transmit BF and receive BF at the reader [18], [19].…”

“…To improve the power-efficiency of IoT devices further, backscatter modulation, sending data by reflecting a carrier signal excited from another source [8], [9], has been addressed into recent IoT applications [10], [11], where IoT devices are exempt from installing powerconsuming active RF circuits and even harvest the energy from the incident carrier. Such backscatter communication (BackCom) networks are classified according to a source emitting a carrier signal: monostatic if the source is also a reader decoding the backscatter signals [12]- [19], bistatic if the source and the reader are different entities [20], and ambient if the source is a transmitter of another network in the vicinity of the reader [21]- [23]. In the networks, backscatter IoT devices (BDs) may reflect the incident carrier signal for backscatter modulation fully or in part or harvest the energy from the carrier signal.…”

“…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.…”

Exploiting Capture Diversity for Performance Enhancement of ALOHA-Based Multi-Static Backscattering Systems in the 6G Perspective

“…Recent studies in this direction propose Multiple Input Multiple Output (MIMO) architectures considering multiple antennas at either node side or illuminator/receiver side. Specifically, traditional space-time coding (STC), beamforming-like techniques, receive and transmit diversity for the forward link, have been adapted for backscattering MIMO systems [ 38 , 39 , 40 , 41 , 42 , 43 ].…”