Relay capacity: decode-forward and cut-set bounds
Research context
postgraduate concept · established · As of 2026-10-10
For a discrete memoryless relay law p(y2,y3|x1,x2), decode-forward achieves the maximum over p(x1,x2) of min{I(X1,X2;Y3),I(X1;Y2|X2)}.
Key knowledge
For a discrete memoryless relay law p(y2,y3|x1,x2), decode-forward achieves the maximum over p(x1,x2) of min{I(X1,X2;Y3),I(X1;Y2|X2)}. The cut-set converse replaces the second term by I(X1;Y2,Y3|X2). These bounds coincide for the physically degraded factorization p(y2|x1,x2)p(y3|y2,x2); they need not coincide for an arbitrary relay channel.
Values and equations
max_p min{I(X1,X2;Y3),I(X1;Y2|X2)} ≤ C ≤ max_p min{I(X1,X2;Y3),I(X1;Y2,Y3|X2)}
- X1,X2
- Source and relay inputs
- Y2,Y3
- Relay and destination observations
- C
- Bits per channel use in the declared relay model
Conditions and scope
- The relay's input is causal in its past observations, with asymptotic vanishing block error and no unspecified extra links.
- Joint input laws and cost constraints are declared; an achievable inner bound is not automatically the full capacity.
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Author checked this English statement, displayed equation where present and stated hypotheses against these source locations: DM-MAC pp. 28–35, broadcast pp. 38–47, distortion pp. 48–52, Wyner–Ziv/Slepian–Wolf pp. 53–59, relay pp. 78–94, multicast pp. 100–116. The check is bounded to the recorded claims; no complete proof reconstruction, software proof replay or universal literature completeness is claimed.
2026-10-10 · Author source-body/statement/equation/domain check, with graph associations scoped individually. Separate independent content/source/inventory review is required before branch closure.
Entry details
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