The software-defined handset

Mobile phones are becoming increasingly complex. Over time they have added both additional cellular frequencies and standards and also other wireless technologies. A high-specification phone might now support 2G at 900 MHz, 1800 MHz and 1900 MHz, 3G at 2.1 GHz, Bluetooth and WiFi (both at 2.4 GHz) and GPS (at 1.4 GHz). Some even support mobile TV (DVB-H) at about 700 MHz. Phones in future years will need to support additional technologies and frequency bands.

The traditional way to design a phone supporting multiple standards has been to add an additional chipset to the phone for each standard, although, as time has progressed, some chipset vendors have developed single chips combining some of the most popular combinations of standards. This has the advantage of being relatively simple but the disadvantage of proliferating chips with associated cost. The radio-frequency (RF) design of the phone also becomes ever more complicated. As more frequency bands are supported, the possibility of interference between then increases and the difficulty of designing antennas and filters that can isolate multiple bands grows. Some have suggested that the growth in complexity might be closer to exponential than linear since each new band introduced has to be designed to work with all the other bands already used by the device. To date, these problems have been soluble, with the costs absorbed in the large quantities of handsets sold and with a degree of integration of multiple standards into one chipset.