Prefix codes and Kraft–McMillan inequality
A binary prefix code has no whole codeword as another's initial segment, permitting immediate sequential decoding.
Key knowledge
A binary prefix code has no whole codeword as another's initial segment, permitting immediate sequential decoding. Uniquely decodable code lengths satisfy Σ2⁻ˡⁱ≤1; conversely positive integer lengths satisfying the inequality admit a prefix code. Expected length is at least source entropy.
Conditions and scope
- Finite alphabet and one nonempty binary codeword per symbol, so each length is a positive integer. The empty-word singleton is excluded: it cannot encode an unknown number of repetitions uniquely.
- Injectivity of individual words alone does not guarantee unambiguous concatenation.
Sources · 1
References
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Evidence and review
Lecture 5 Kraft–McMillan theorem, converse and expected-length lower bound, using positive lengths in the concatenation-counting proof.
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Entry details
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