33 research outputs found
Optimal Channel Estimation for Reciprocity-Based Backscattering with a Full-Duplex MIMO Reader
Backscatter communication (BSC) technology can enable ubiquitous deployment
of low-cost sustainable wireless devices. In this work we investigate the
efficacy of a full-duplex multiple-input-multiple-output (MIMO) reader for
enhancing the limited communication range of monostatic BSC systems. As this
performance is strongly influenced by the channel estimation (CE) quality, we
first derive a novel least-squares estimator for the forward and backward links
between the reader and the tag, assuming that reciprocity holds and K
orthogonal pilots are transmitted from the first K antennas of an N antenna
reader. We also obtain the corresponding linear minimum-mean square-error
estimate for the backscattered channel. After defining the transceiver design
at the reader using these estimates, we jointly optimize the number of
orthogonal pilots and energy allocation for the CE and information decoding
phases to maximize the average backscattered signal-to-noise ratio (SNR) for
efficiently decoding the tag's messages. The unimodality of this SNR in
optimization variables along with a tight analytical approximation for the
jointly global optimal design is also discoursed. Lastly, the selected
numerical results validate the proposed analysis, present key insights into the
optimal resource utilization at reader, and quantify the achievable gains over
the benchmark schemes.Comment: accepted for publication in IEEE Transactions on Signal Processing,
16 pages, 15 figures, 1 tabl
Sum Throughput Maximization in Multi-Tag Backscattering to Multiantenna Reader
Backscatter communication (BSC) is being realized as the core technology for
pervasive sustainable Internet-of-Things applications. However, owing to the
resource-limitations of passive tags, the efficient usage of multiple antennas
at the reader is essential for both downlink excitation and uplink detection.
This work targets at maximizing the achievable sum-backscattered-throughput by
jointly optimizing the transceiver (TRX) design at the reader and
backscattering coefficients (BC) at the tags. Since, this joint problem is
nonconvex, we first present individually-optimal designs for the TRX and BC. We
show that with precoder and {combiner} designs at the reader respectively
targeting downlink energy beamforming and uplink Wiener filtering operations,
the BC optimization at tags can be reduced to a binary power control problem.
Next, the asymptotically-optimal joint-TRX-BC designs are proposed for both low
and high signal-to-noise-ratio regimes. Based on these developments, an
iterative low-complexity algorithm is proposed to yield an efficient
jointly-suboptimal design. Thereafter, we discuss the practical utility of the
proposed designs to other application settings like wireless powered
communication networks and BSC with imperfect channel state information.
Lastly, selected numerical results, validating the analysis and shedding novel
insights, demonstrate that the proposed designs can yield significant
enhancement in the sum-backscattered throughput over existing benchmarks.Comment: 17 pages, 5 figures, accepted for publication in IEEE Transactions on
Communication
QoS Aware Transmit Beamforming for Secure Backscattering in Symbiotic Radio Systems
This paper focuses on secure backscatter transmission in the presence of a
passive multi-antenna eavesdropper through a symbiotic radio (SR) network.
Specifically, a single-antenna backscatter device (BD) aims to transmit
confidential information to a primary receiver (PR) by using a multi-antenna
primary transmitter's (PT) signal, where the received symbols are jointly
decoded at the PR. Our objective is to achieve confidential communications for
BD while ensuring that the primary system's quality of service (QoS)
requirements are met. We propose an alternating optimisation algorithm that
maximises the achievable secrecy rate of BD by jointly optimising primary
transmit beamforming and power sharing between information and artificial noise
(AN) signals. Numerical results verify our analytical claims on the optimality
of the proposed solution and the proposed methodology's underlying low
complexity. Additionally, our simulations provide nontrivial design insights
into the critical system parameters and quantify the achievable gains over the
relevant benchmark schemes
Reconfigurable Intelligent Surface Enabled Joint Backscattering and Communication
Reconfigurable intelligent surface (RIS) as an essential topic in the
sixth-generation (6G) communications aims to enhance communication performance
or mitigate undesired transmission. However, the controllability of each
reflecting element on RIS also enables it to act as a passive backscatter
device (BD) and transmit its information to reader devices. In this paper, we
propose a RIS-enabled joint backscattering and communication (JBAC) system,
where the backscatter communication coexists with the primary communication and
occupies no extra spectrum. Specifically, the RIS modifies its reflecting
pattern to act as a passive BD and reflect its own information back to the base
station (BS) in the backscatter communication, while helping the primary
communication from the BS to the users simultaneously. We further present an
iterative active beamforming and reflecting pattern design to maximize the user
average transmission rate of the primary communication and the goodput of the
backscatter communication by solving the formulated multi-objective
optimization problem (MOOP). Numerical results fully uncover the impacts of the
number of reflecting elements and the reflecting patterns on the system
performance, and demonstrate the effectiveness of the proposed scheme.
Important practical implementation remarks have also been discussed.Comment: 11 pages, 8 figures, published to IEEE TV
Establishing Multi-User MIMO Communications Automatically Using Retrodirective Arrays
Communications in the mmWave and THz bands will be a key technological pillar for next-generation wireless networks. However, the increase in frequency results in an increase in path loss, which must be compensated for by using large antenna arrays. This introduces challenging issues due to power consumption, signalling overhead for channel estimation, hardware complexity, and slow beamforming and beam alignment schemes, which are in contrast with the requirements of next-generation wireless networks. In this paper, we propose the adoption of a retro-directive antenna array (RAA) at the user equipment (UE) side, where the signal sent by the base station (BS) is reflected towards the source after being conjugated and phase-modulated according to the UE data. By making use of modified Power Methods for the computation of the eigenvectors of the resulting round-trip channel, it is shown that, in single and multi-user multiple-input multiple-output (MIMO) scenarios, ultra-low complexity UEs can establish parallel communication links automatically with the BS in a very short time. This is done in a blind way, also by tracking fast channel variations while communicating, without the need for ADC chains at the UE as well as without explicit channel estimation and time-consuming beamforming and beam alignment schemes
Towards 6G-Enabled Internet of Things with IRS-Empowered Backscatter-Assisted WPCNs
Wireless powered communication networks (WPCNs) are expected to play a key role in the forthcoming 6G systems. However, they have not yet found their way to large-scale practical implementations due to their inherent shortcomings such as the low efficiency of energy transfer and information transmission. In this thesis, we aim to study the integration of WPCNs with other novel technologies of backscatter communication and intelligent reflecting surface (IRS) to enhance the performance and improve the efficiency of these networks so as to prepare them for being seamlessly fitted into the 6G ecosystem. We first study the incorporation of backscatter communication into conventional WPCNs and investigate the performance of backscatter-assisted WPCNs (BS-WPCNs). We then study the inclusion of IRS into the WPCN environment, where an IRS is used for improving the performance of energy transfer and information transmission in WPCNs. After that, the simultaneous integration of backscatter communication and IRS technologies into WPCNs is investigated, where the analyses show the significant performance gains that can be achieved by this integration