transfer data by ultrasound between two androids phones

hello,
i want to implements app that look like this:

basically two mobiles that app open and one mobile send bits like 01010101
and in the second mobile i received this sequence...

i want to implements in java lang

there is a idea where to start?

there is a idea where to start?

Somewhere else.

What is the Arduino, programmed in C++, going to do?