Barker code

In telecommunication technology, a Barker code or Barker sequence is a finite sequence of digital values with the ideal autocorrelation property. It is used as a synchronising pattern between the sender and receiver of a stream of bits. Apart from the trivial sequence of length 1, the known Barker sequences have lengths 2, 3, 4, 5, 7, 11 and 13. It is conjectured that no longer sequence exists; this is proved for odd lengths, while the possible existence of an even Barker sequence longer than 4 remains open.