7

Golay Codes

7.1    Perfect Codes

Perfect codes have been introduced in §6.5 in connection with the Hamming bound (6.5.1) which for a q-ary code C = (n,k,d) with d ≤ 2t + 1 implies that

|C|i=0t(ni)(q1)iqn,

(7.1.1)

where |C| (= M) denotes the size of the code C (see §6.1) A code is said to be perfect if equality holds in (7.1.1). Since a terror correcting code can correct up to t errors, a perfect t-error correcting code must be such that every codeword lies within a distance of t to exactly one codeword. In other words, if the code has dmin = 2t + 1 that covers radius t, where the covering radius has the smallest number, then every codeword lies within a distance of the Hamming radius t to a codeword. In the case of a perfect code, the ...

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