New rules clear way for denser device concentration, higher data rates.

The FCC has relaxed the rules for unlicensed PCS.

If you have no idea what unlicensed PCS is, you have a lot of company. Even among spectrum experts.

Most voice calls from a cell phone don’t actually use cellular frequencies, which are a little above 800 MHz, but instead use higher frequencies allocated to the Personal Communications Service (PCS) in the vicinity of 1.9 GHz. Some PCS frequencies carry signals from the tower to your handset, while other frequencies carry signals the other way, from the handset to the tower. The two have to be kept well separated, lest the transmitter in the handset overpower its own receiver. Of the several ways to achieve this separation, the FCC chose the simplest: a “guard band” 15 MHz wide between the tower-to-handset and handset-to-tower frequencies. But the guard band need not be completely idle, and in fact is used for multiple purposes. One segment, at 1920-1930 MHz, is available on a shared basis for unlicensed applications: hence unlicensed PCS, or in Washington-speak, UPCS.

Unlike some of the other unlicensed bands that house Wi-Wi, Bluetooth, ZigBee, and thousands of consumer applications (our own favorite is a wireless diaper wetness sensor), the UPCS band is lightly populated, mostly with cordless phones. The FCC rules for the band include a complicated “spectrum etiquette” – a listen-before-talk scheme that minimizes the odds of one device stepping on another’s transmission. But the benefit comes with downsides: added equipment costs, and an upper limit on the number of devices that can successfully operate in a given environment.

The new FCC order does not eliminate these technical rules, but it simplifies them considerably. The result will allow more devices to work in close quarters, and will allow devices to transmit at higher data rates. The new rules are closer to those used in many other countries, which simplifies life for global manufacturers. The FCC also cleaned up provisions that were needed when the 1920-1930 MHz band was transitioning from fixed microwave to UPCS and the other current applications, but are no longer needed.

All the details are here.