And yet this problem has not only been solved but been subsequently broken by marketers. Some things that seem easy are actually hard. I'm sure defining the app

And yet this problem has not only been solved but been subsequently broken by marketers. Some things that seem easy are actually hard. I'm sure defining the appropriate function isn't all roses but a semi-competent software/radio engineer could figure out something with the right properties. With Apple's budget, they could easily do this.