I remember buying a 900 MHz phone in 2000. By 2002, almost everything had gone to 2.4 GHz, and by 2005, nobody was buying cordless phones anymore. Here was the 2.4 GHz ISM band, a huge 100 MHz band with worldwide regulatory support! What a superb arrangement.
Of course, if you are at all familiar with DASH7 marketing, you should know by now that we strongly recommend staying as far from the 2.4 GHz band as you can. By 2010, it is over-crowded and has informally become a WiFi-only band. 2.4 GHz phones from yesterday now struggle to operate amidst home WiFi routers, and for that matter so does anything else at 2.4 GHz (e.g. ZigBee).
The market is finally starting to understand the problems at 2.4 GHz. At CES this year, the most successful showing in the home-automation space was a 900 MHz solution, and even the guys in the ZigBee section made great effort to espouse the work items taking place in the 802.15.4 standards bodies to move back to 900 MHz. It looks like 2.4 GHz is dead (or dying) as a band for low power wireless sensor networks.
Soon they will find, however, that the 900 MHz band is just as fraught with problems as the 2.4 GHz band is, although for different reasons. Many of the standards bodies and their marketing alignments are directed squarely at the US domestic market, in initiatives like the “SmartGrid” or automated metering infrastructure (AMI). But the United States is unique in (at least) three ways: its utility operations are highly privatized, it has a military that drives great advances in IT (Barcode, Fax, DASH7, DarpaNet to name a few), and it is the only major nation trading nation on Earth with a favorable environment for 900 MHz operations. Other nations either use this spectrum for cellular communications (often with no regard to RF emissions regulations), or simply lack a suitable 900 MHz band at all (e.g. Europe, where the 868 MHz band is strictly regulated).
A 900 MHz strategy thus is not only US-centric, but US-limited. Nevermind the technical difficulties of developing cheap hardware that can be efficient in the USA (902-930 MHz) in addition to the EU (868-870). 433 MHz, on the other hand, is permitted in almost all nations worldwide. More importantly, in places like Europe and Korea, which are well-known early adopters of wireless technology, 433 MHz is the obvious choice for wireless sensor networking.
It is a great for the success of wireless sensor networks that people are starting to realize how hopeless the 2.4 GHz band has become, but it is not enough to merely embrace “Sub-1GHz.” If you are developing a 900 MHz technology, consider also 433 MHz and DASH7. 433 MHz has greater worldwide appeal, support by the single most import entity for emerging IT standards (the US DoD), and, also importantly, it appeals especially to markets that tend to embrace new technologies a lot faster than does the US private sector.
