This work proposes an iterative code-aided detection, decoding, and channel estimation scheme for metasurface-based holographic MIMO systems employing stacked intelligent metasurfaces (SIM-RIS) and their fully connected counterparts (BD-SIM-RIS). A novel channel estimation strategy is developed by exploiting low-density parity-check (LDPC) coding in the uplink, enabling both pilot and parity bits of the encoded packet to contribute to the iterative refinement of the channel. In addition, closed-form expressions for the metasurface parameter design are derived and incorporated into an alternating-optimization (AO) procedure. Numerical results demonstrate substantial gains in normalized mean square error (NMSE) and bit error rate (BER), with particularly strong improvements observed for BD-SIM-RIS architectures.

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