Life used to be pretty simple: Cell phone handsets had some kind of wireless wide-area radio in them, and that was that. Single-technology handsets were localized to a given market and then a given carrier, and little additional customization was required. Then along came Bluetooth, and we had mandatory radio No. 2. Still, just a little more space inside the handset, and a little code, and the resulting engineering task was pretty simple.

The next big step, which we're seeing now, is the integration of a wireless-LAN interface. WLANs are still somewhat of a moving target, as 802.11n and a few additional 802.11 improvements prevent any particular implementation from having too long a shelf life. We've yet to see much in terms of deployed convergence functionality, but that's clearly going to happen. And convergence requires the integration of yet another radio into the handset.

With each additional radio come new demands not just for physical space, but also for power management (often including a battery with greater capacity) and for more engineering and testing to accommodate multiple radios operating within tight proximity. Sure, silicon integration will eventually solve most of this problem, but that takes a lot more engineering too.

The latest must-have radio for handsets may be near-field communications (NFC). The idea is to have a radio with very limited range (a few centimeters) but reasonable throughput (to about 400 kbits/second) to serve as a gateway for all transactions, particularly financial, and as a form of RF identification. NFC could allow the handset to replace the credit card, with vastly improved security. But it is also another radio.

So, let me see, that makes four. And with Sprint's decision to roll out a mobile WiMAX network while still supporting EV-DO, dual-mode WiMAX/ EV-DO phones are all but a certainty. That's potentially five radios!

Wideband software-defined radio might still be the ultimate solution. In the interim, we're going to spend lots of time figuring out how to make all these radios fit into one handset.

Craig J. Mathias (craig@farpointgroup.com) is principal at Farpoint Group (Ashland, Mass.).