Uses the code rule violation of the Manchester code the contention detection

摘要

A collision detection method and apparatus (10) is disclosed for detecting code rule violations in Manchester encoded data packets. The signals δ0 = S2n - S2n-1, $(d)1 = S2n+1 - S2n, δ2 = S2n + 1 - S2n-1, σ0 = S2n + S2n-1 are determined at time nT where S2n-1 and S2n are the Manchester code bit pair representative of the nth bit in a data stream having a bit period T. Processing of these signals permits the detection of most collisions since the Manchester coding rules are violated more than half the time in the signal formed by the colliding packets. To ensure 100 % collision detection, a preamble using an intentional violation of the Manchester code in the pattern 10 11 01 10 is advantageously used in each data packet and a collision is signaled upon detection of two or more coding violations.