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arXiv · 2604.20380

CSI Feedback Under Basis Mismatch: Rate-Splitting Transform Coding for FDD Massive MIMO

Youngmok Park·Bumsu Park·Namyoon Lee
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Abstract

In frequency division duplex massive multiple-input multiple-output systems, downlink channel state information must be fed back within a limited uplink budget. While transform coding with Karhunen-Loeve transform and reverse water-filling is rate-distortion optimal for Gaussian channels, its performance is limited by basis mismatch between the user and base station. We analyze this mismatch and propose a practical architecture separating long-term basis feedback from short-term coefficient quantization. Using a random vector quantization, we derive a closed-form end-to-end mean square error expression. This allows us to characterize the optimal rate split and identify a phase transition threshold for basis updates. Simulations on correlated Gaussian and COST2100 channels demonstrate near-optimal performance, robustness to update overhead, and significant complexity reduction compared to deep-learning-based autoencoders.

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Youngmok Park, Bumsu Park, Namyoon Lee. 2026-04-22. CSI Feedback Under Basis Mismatch: Rate-Splitting Transform Coding for FDD Massive MIMO. https://arxiv.org/abs/2604.20380

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