10 research outputs found
Reconfigurable intelligent surface (RIS): Eigenvalue Decomposition-Based Separate Channel Estimation
Reconfigurable intelligent surface (RIS) has recently drawn significant
attention in wireless communication technologies. However, identifying,
modeling, and estimating the RIS channel in multiple-input multiple-output
(MIMO) systems are considered challenging in recent studies. In this paper, a
disassembled channel estimation framework for the RIS-MIMO system is proposed
based on the eigenvalue decomposition (EVD) concept to separate the cascaded
channel links and estimate each link separately. This estimation is based on
modeling the RIS-MIMO channel as a keyhole MIMO system model. Numerical results
show that the proposed estimation method has a low estimation time overhead
while providing less estimation error.Comment: Published in: 2021 IEEE 32nd Annual International Symposium on
Personal, Indoor and Mobile Radio Communications (PIMRC
Reconfigurable Intelligent Surface-Empowered MIMO Systems
Reconfigurable intelligent surface (RIS)-assisted communications appear as a
promising candidate for future wireless systems due to its attractive
advantages in terms of implementation cost and end-to-end system performance.
In this paper, two new multiple-input multiple-output (MIMO) system designs
using RISs are presented to enhance the performance and boost the spectral
efficiency of state-of-the-art MIMO communication systems. Vertical Bell Labs
layered space-time (VBLAST) and Alamouti's schemes have been considered in this
study and RIS-based simple transceiver architectures are proposed. For the
VBLAST-based new system, an RIS is used to enhance the performance of the
nulling and canceling-based sub-optimal detection procedure as well as to
noticeably boost the spectral efficiency by conveying extra bits through the
adjustment of the phases of the RIS elements. In addition, RIS elements have
been utilized in order to redesign Alamouti's scheme with a single radio
frequency (RF) signal generator at the transmitter side and to enhance its bit
error rate (BER) performance. Monte Carlo simulations are provided to show the
effectiveness of our system designs and it has been shown that they outperform
the reference schemes in terms of BER performance and spectral efficiency.Comment: To appear in IEEE SYSTEMS JOURNAL, 9 pages, 6 figures, and 1 tabl
Channel Estimation for RIS-Empowered Multi-User MISO Wireless Communications
Reconfigurable Intelligent Surfaces (RISs) have been recently considered as
an energy-efficient solution for future wireless networks due to their fast and
low-power configuration, which has increased potential in enabling massive
connectivity and low-latency communications. Accurate and low-overhead channel
estimation in RIS-based systems is one of the most critical challenges due to
the usually large number of RIS unit elements and their distinctive hardware
constraints. In this paper, we focus on the downlink of a RIS-empowered
multi-user Multiple Input Single Output (MISO) downlink communication systems
and propose a channel estimation framework based on the PARAllel FACtor
(PARAFAC) decomposition to unfold the resulting cascaded channel model. We
present two iterative estimation algorithms for the channels between the base
station and RIS, as well as the channels between RIS and users. One is based on
alternating least squares (ALS), while the other uses vector approximate
message passing to iteratively reconstruct two unknown channels from the
estimated vectors. To theoretically assess the performance of the ALS-based
algorithm, we derived its estimation Cram\'er-Rao Bound (CRB). We also discuss
the achievable sum-rate computation with estimated channels and different
precoding schemes for the base station. Our extensive simulation results show
that our algorithms outperform benchmark schemes and that the ALS technique
achieve the CRB. It is also demonstrated that the sum rate using the estimated
channels reached that of perfect channel estimation under various settings,
thus, verifying the effectiveness and robustness of the proposed estimation
algorithms