I had reinvented these symbols, without knowing Birkana, for one of my hobby alphabets at high school. I had given a lot of thought with my high-schooler leisure time and haven't been able find more simple system with enough data capacity. I think readability suffers from similarity though.

They also look like some symbols from Old Turkic alphabet, If I recall correctly it was my source of inspiration: https://en.wikipedia.org/wiki/Old_Turkic_alphabet