Reed–Muller capacity conjecture for binary-input memoryless symmetric channels

Let P\mathcal{P} be a binary-input memoryless symmetric (BMS) channel with output alphabet Y\mathcal{Y}, and let

C(P)=I(U,P)=12x{0,1},yYP(yx)log2P(yx)P(y0)/2+P(y1)/2C(\mathcal{P})=I(U,\mathcal{P})=\frac{1}{2}\sum_{x\in\{0,1\},\,y\in\mathcal{Y}}\mathcal{P}(y\mid x)\log_2\frac{\mathcal{P}(y\mid x)}{\mathcal{P}(y\mid 0)/2+\mathcal{P}(y\mid 1)/2}

be its capacity under the uniform input distribution. For a sequence of Reed–Muller codes RM(mi,ri)\operatorname{RM}(m_i,r_i) with rates Ri=(miri)2miR_i={m_i\choose\leq r_i}2^{-m_i} tending to a rate R<C(P)R<C(\mathcal{P}), the Reed–Muller capacity conjecture. the codewords can be decoded successfully with high probability: any of the 2nRi\lfloor 2^{nR_i}\rfloor codewords can be decoded with probability 1omi(1)1-o_{m_i}(1) despite corruption by P\mathcal{P}. For the binary symmetric channel BSC(ϵ)\operatorname{BSC}(\epsilon), the capacity is 1H(ϵ)1-H(\epsilon). This conjecture asserts that the explicit Reed–Muller construction achieves Shannon capacity under maximum-likelihood or an appropriate successful decoding procedure; the paper states that it proves the conjecture for all BMS channels, so the claim is solved.

Sources & referencesView supporting material

Primary source

Emmanuel Abbe and Colin Sandon, “A proof that Reed-Muller codes achieve Shannon capacity on symmetric channels”, arXiv:2304.02509 (2023).

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