Designing Mobile Interfaces

Appendix A. Mobile Radiotelephony

An Introduction to Mobile Radiotelephony

Aside from simply understanding your place in history, the underpinnings of mobile communications can be crucial to ensuring that your particular application, site, or service works correctly. Decisions made long ago, whether technical or regulatory, influence how mobile telephony evolved, and are still felt today.

An example might help. My favorite is that SMS (text messaging) isn’t data. It looks like data, because it’s typed; email and IM are data, right? But SMS is in the paging channel, or the part that is used to ring the phone and send caller ID data. What does that mean for pricing, availability, and traffic management? Well, too much to go into here, but importantly different things than managing data services.

I have gone out of my way to take actual RF engineering classes. It’s pretty arduous, and I no longer remember how to calculate Walsh codes by hand, for example. But as it turns out, almost no one does. I was in class with guys who had EE degrees and had been working as radio techs for mobile operators for years, and they still didn’t know the history or how parts of the system outside their domain work.

Hence, I feel pretty good about boiling several thousand pages of lecture slides and books into this short appendix. Just understanding the basics can matter a lot to your everyday work.

The Electromagnetic Spectrum

We’ll start with junior high physics, to make sure everyone is on the same page. ...