Core Concepts
Deriving a wideband OFDM system model for beyond diagonal reconfigurable intelligent surface (BD-RIS) assisted communications and proposing an efficient algorithm to optimize the wideband capacity by configuring the BD-RIS reflection matrix.
Abstract
The paper derives the wideband OFDM system model for a single-input single-output (SISO) communication system assisted by a beyond diagonal reconfigurable intelligent surface (BD-RIS). The key highlights are:
The derivation of the wideband OFDM system model from first principles, resulting in a different expression compared to prior work.
Proposed an algorithm to optimize the wideband capacity by configuring the BD-RIS reflection matrix, subject to the constraints of symmetry and unitarity.
The algorithm first maximizes the total channel gain across all subcarriers, and then applies water-filling power allocation.
Simulation results show that the proposed BD-RIS configuration significantly enhances wideband capacity compared to conventional RIS, especially in non-line-of-sight (NLOS) channels. However, the gains diminish when there is a dominant static path or when the Rician K-factor is larger than 10.
Stats
The wideband channel capacity can be expressed as:
C = B/(T+S) * sum_over_subcarriers(log2(1 + qopt_nu * |hnu + tr(ΨHnu)|^2 / N0)) bit/s
The optimal power allocation qopt_nu is obtained using water-filling.