Olivia MFSK

Following the introduction of new amateur radio digital modes and the resulting overlapping with the Olivia calling frequencies on some amateur radio bands, US radio amateur Tomas Hood NW7US consulted the members subscribed to an Olivia MFSK users newsgroup and created a new list of calling frequencies in November 2017. The Olivia transmission system is constructed of two layers: the lower, modulation and forward error correcting (FEC) code layer is a classical multiple frequency-shift keying (MFSK) while the higher layer is a forward error correcting code based on Walsh functions. This way, if one symbol (tone) becomes corrupted by the noise, only one bit of every 64-bit vector becomes corrupt, thus the transmission errors are spread uniformly across the characters within a block.

Source: en.wikipedia.org