- Blackwell channel
The Blackwell channel is a deterministic broadcast channel model used in
coding theory andinformation theory . It was first proposed by mathematicianDavid Blackwell . In this model, a transmitter transmits one of three symbols to two receivers. For two of the symbols, both receivers receive exactly what was sent; the third symbol, however, is received differently at each of the receivers. This is one of the simplest examples of a non-trivial capacity result for a non-stochastic channel.Definition
The Blackwell channel is composed of one input (transmitter) and two outputs (receivers). The channel input is
ternary (three symbols) and is selected from {0, 1, 2}. This symbol is broadcast to the receivers; that is, the transmitter sends one symbol simultaneously to both receivers. Each of the channel outputs is binary (two symbols), labeled {0, 1}.Whenever a 0 is sent, both outputs receive a 0. Whenever a 1 is sent, both outputs receive a 1. When a 2 is sent, however, the first output is 0 and the second output is 1. Therefore, the symbol 2 is confused by each of the receivers in a different way.
The operation of the channel is
memoryless and completely deterministic.Capacity of the Blackwell channel
The capacity of the channel was found by
S. I. Gel'fand . It is defined by the region:: 1. "R"1 = 1, 0 ≤ "R"2 ≤ ½: 2. "R"1 = H("a"), "R"2 = 1 − "a", for ⅓ ≤ "a" ≤ ½: 3. "R"1 + "R"2 = log2 3, log2 3 - ⅔ ≤ "R"1 ≤ ⅔: 4. "R"1 = 1 − "a", "R"2 = H("a"), for ⅓ ≤ "a" ≤ ½: 5. 0 ≤ "R"1 ≤ ½, "R"2 = 1References
* S. I. Gel'fand. "Capacity of one broadcast channel." "Problemy Peredachi Informatsii" (Problems in Information Transmission), Vol. 13(3), pp. 106-108, 1977.
* E. van der Meulen, "A survey of multi-way channels in information theory: 1961-1976." "IEEE Trans. on Information Theory", Vol.23, Iss.1, Jan 1977, pp 1-37. ( [http://ieeexplore.ieee.org/iel5/18/22694/01055652.pdf?isnumber=22694&prod=STD&arnumber=1055652&arnumber=1055652&arSt=+1&ared=+37&arAuthor=+van+der+Meulen%2C+E. IEEExplore pdf] )
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