Intelligent Reflecting Surface Assisted Wireless Powered Sensor Networks for Internet of Things
ABSTARCT :
This paper studies an intelligent reflecting surface (IRS) aided wireless powered sensor network (WPSN). Specifically, a power station (PS) provides wireless energy to multiple internet of thing (IoT) devices which supports them to deliver their own messages to an access point (AP). Moreover, we deploy an IRS to enhance the performance of the WPSN by intelligently adjusting the phase shift of each reflecting element. To evaluate the performance of the IRS assisted WPSN, we maximize its sum throughput to jointly optimize the phase shift matrices and the transmission time allocations. Due to the non-convexity of the formulated optimization problem, we first derive the optimal phase shifts of the wireless information transfer (WIT) in closed-form. Consequently, a semi-definite programming (SDP) relaxed approach is considered to jointly design the phase shift matrix of the wireless energy transfer (WET) and the transmission time allocations. In addition, we propose a low complexity scheme to gain insights and reduce the computational complexity incurred by the SDP relaxed scheme. Specifically, the optimal solutions of the phase shifts and the transmission time allocation are derived in closed-form by the Majorization-Minimization (MM) algorithm, the Lagrange dual method and the Karush-Kuhn-Tucker (KKT) conditions. Finally, numerical results are presented to validate the proposed schemes and confirm the beneficial role of the IRS in comparison to the benchmark schemes, where the proposed IRS assisted scheme achieves almost 100 % higher sum throughput, in comparison to the counterpart without IRS.
EXISTING SYSTEM :
? This nonlinear EH model has been characterized in, which is a complex function of the RF power.
? However, there is still lack of a general model that can accurately characterize this nonlinear relationship by capturing all practical factors.
? Hence, for simplicity, we adopt the simple linear EH model as widely used in the existing literature . By ignoring the noise power at the ERs, the total harvested power is proportional to the total received power.
? Due to the associated severe channel attenuation, the sensors should be deployed sufficiently close to the BS, which limits their practical implementation.
DISADVANTAGE :
? This non-convex problem can not be be solved optimally using standard methods which has resulted in several suboptimal solutions.
? Almost all existing works consider the optimization of the IRS’s induced phases by solving complicated, nonconvex optimization problems.
? The optimal phases and the resulting performance are therefore computed numerically and do not have any channel-dependent theoretical expressions (except for the single user, single IRS case in ) that yield insights into the impact of the channel as well as the radio parameters on the performance of the IRS-assisted communication systems.
PROPOSED SYSTEM :
• Our extensive simulation results confirm that employing IRSs in SWIPT beneficially enhances the system performance and the proposed BCD algorithm converges rapidly, which is appealing for practical applications.
• A two-stage channel estimation method based on a sparse matrix factorization and a matrix completion was proposed in.A low-complexity bisection search method is proposed for finding the optimal dual variables.
• The associated feasibility issue is also studied by formulating an alternative optimization problem and an iterative algorithm is proposed for solving this problem.
• The proposed algorithm is again observed to significantly outperform the other two algorithms, especially when the ERs are close to the BS.
ADVANTAGE :
? It is therefore important to analyze the performance under the more practical ray-tracing or correlated Rayleigh channel models.
? Moreover, under this setting, the statistics of the received signal do not change with the values of the phase shifts as N, M grow large so asymptotically there will be no significant performance improvement due to IRS.
? The communication-theoretic performance analysis of the SREs enabled by reconfigurable metasurfaces is an important research direction that should utilize accurate communication models that describe the response of the metasurface as a function of its EM properties.
? Developing tractable analytical frameworks to study the performance of wireless networks enabled by multiple IRSs is an important research direction.
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