Variable-Length Finite-Rate CSI Feedback With Generative Priors

This letter studies variable-length finite-rate CSI feedback from a structural perspective and proposes CsiCoGen, a novel generative feedback structure with a transferable codebook mechanism without joint training. The UE maps $H_0$ into an ordered sequence of codebook indices, while the BS recursively recovers CSI from any received partial sequence of feedback indices using a shared denoising prior. This enables flexible control of feedback sequence length and per-step quantization precision through codebook size. CsiCoGen does not require jointly training a task-specific feedback encoder or codebook with the reconstructor, and the same online structure can be paired with different pretrained denoisers. In this work, we instantiate the decoder with a generative diffusion model. Simulation results on COST2100 show favorable rate-NMSE and rate-$\rho$ tradeoffs against representative baselines, with CsiCoGen reaching about -31 dB indoor NMSE and -20 dB outdoor NMSE in the high-rate regime while demonstrating scalable decoding complexity and adjustable per-step quantization precision.