Talk:Binary symmetric channel

$$k$$ $$\leq$$ $$\lfloor$$ $$(1 - H(p + \epsilon)n)$$ $$\rfloor$$

Is that last ')' misplaced? 68.239.116.212 (talk) 15:08, 2 January 2010 (UTC)

Unclear proof in "Capacity of BSCp" section
''Capacity of BSC

''The capacity of the channel is 1 − H(p), where H(p) is the binary entropy function.

''The converse can be shown by a sphere packing argument. Given a codeword, there are roughly 2n H(p) typical output sequences. There are 2n total possible outputs, and the input chooses from a codebook of size 2nR. Therefore, the receiver would choose to partition the space into "spheres" with 2n / 2nR = 2n(1 − R) potential outputs each. If R > 1 − H(p), then the spheres will be packed too tightly asymptotically and the receiver will not be able to identify the correct codeword with vanishing probability.''

Converse -- What is intended here? A statement that two things are equal does not have a converse.

sphere packing argument -- It is not a sphere-packing argument, since the geometry of the pieces is not used.

Given a codeword, there are roughly 2n H(p) typical output sequences. -- What is a codeword in this context? A binary sequence of length n? What does a "typical output sequence" mean? A possible damaged version of the original sequence? Then why not 2^n?

There are 2n total possible outputs -- What is the difference between an "output" and an "output sequence"? I suppose they can't be the same since there's a factor of H(p).

the input chooses from a codebook of size 2nR -- What is the definition of the variable R? How do we deduce it has size 2nR, or is this a hypothesis? What is a codebook? A list of possible encodings of one desired message? That sounds like only one entry, a tiny fraction of the whole codebook.

the receiver will not be able to identify the correct codeword with vanishing probability -- I think there's a double negative here. 178.38.132.253 (talk) 14:43, 20 November 2014 (UTC)


 * I rewrote the capacity section and used a proof which is as far as a know well known. Further improvements or feedback is welcome.
 * BBC89 (talk) 13:21, 22 September 2017 (UTC)

Statement of Theorem 1 was incoherent
I've attempted to clarify the (previously incoherent) statement of this theorem to something plausible, but it still has the following defect: δ is not quantified. 178.38.132.253 (talk) 14:40, 20 November 2014 (UTC)

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