{"ID":2828049,"CreatedAt":"2026-06-01T04:54:23.091178241Z","UpdatedAt":"2026-06-01T04:54:23.091178241Z","DeletedAt":null,"paper_url":"https://arxiv.org/abs/2512.15441","arxiv_id":"2512.15441","title":"Semi-Blind Joint Channel and Symbol Estimation for Beyond Diagonal Reconfigurable Surfaces","abstract":"The beyond-diagonal reconfigurable intelligent surface (BD-RIS) is a recent architecture in which scattering elements are interconnected to enhance the degrees of freedom for wave control, yielding performance gains over traditional single-connected RISs. For BD-RIS, channel estimation, which is well studied for conventional RIS, becomes more challenging due to complex connections and a larger number of coefficients. Previous works relied on pilot-assisted estimation followed by data decoding. This paper introduces a semi-blind tensor-based approach to joint channel and symbol estimation that eliminates the need for training sequences by directly leveraging data symbols. A practical scenario with time-varying user terminal-RIS channels under mobility is considered. By reformulating the received signal from a tensor-decomposition perspective, we develop two semi-blind receivers: a two-stage method that transforms the fourth-order PARATUCK model into a third-order PARAFAC model, and a single-stage iterative process based on the fourth-order TUCKER decomposition. Identifiability conditions for reliable joint recovery are derived, and numerical results demonstrate the performance advantages and trade-offs of the proposed schemes over existing solutions.","short_abstract":"The beyond-diagonal reconfigurable intelligent surface (BD-RIS) is a recent architecture in which scattering elements are interconnected to enhance the degrees of freedom for wave control, yielding performance gains over traditional single-connected RISs. For BD-RIS, channel estimation, which is well studied for conven...","url_abs":"https://arxiv.org/abs/2512.15441","url_pdf":"https://arxiv.org/pdf/2512.15441v3","authors":"[\"Gilderlan Tavares de Araújo\",\"André L. F. de Almeida\",\"Buno Sokal\",\"Gabor Fodor\"]","published":"2025-12-17T13:38:51Z","proceeding":"eess.SP","tasks":"[\"eess.SP\"]","methods":"[]","has_code":false}