This document discusses issues with increasing congestion in unlicensed WiFi spectrum bands and potential solutions. It notes that WiFi has become integral to modern communications by offloading traffic from cellular networks, but the main 2.4GHz band is becoming crowded. Potential solutions discussed include preventing interference, moving some usage to the less crowded but shorter range 5GHz band, using femtocells to avoid unlicensed spectrum, and employing "cognitive" devices that identify available channels via databases instead of sensing. However, many solutions may undermine the open nature of unlicensed spectrum or have other limitations. Regulatory changes may be needed to allocate more dedicated spectrum for WiFi or clear existing uses to avoid a "meltdown" as

2. Turning junk into gold and then back againHow unlicensed usage has become a core part of modern communications Professor William Webb October 2009

3. WiFi is becoming ever more prevalent 2 Source: Perspective

4. WiFi plays an increasing role in keeping the cellular networks from congestion 3

5. But the WiFi band is showing signs of congestion Height of bars indicates number of base stations Colour indicates quality of link 4 Source: Work conducted by MASS for Ofcom

6. Solutions exist Prevent interference in 2.4GHz (for example by banning video senders or encouraging “WiFi friendly” systems May be too late Somewhat contrary to the whole idea of unlicensed bands Move to 5GHz (around 400MHz of spectrum available compared with 80MHz at 2.4GHz) Limited take-up – perhaps to do with the reduced range Make use of femtocells to avoid unlicensed spectrum See later Move to “cognitive” or “white space” systems See later 5

7. Femtocells can make a difference Strong industry support But key issues remain around “openness” In the home can only off-load traffic from home owner and perhaps not even all family members In urban areas need one per operator, not desirable for owners of malls or buildings Closed femtocells can create small coverage holes And the commercial model still not certain Will the operators need to subsidise? Will they be prepared to do this? 6

8. Considerable evidence of little-used spectrum 7 Source: Measurements by CRFS for Ofcom

9. Cognitive devices have evolved from sensing to databases Original idea was to sense whether the spectrum was used Considerable work has shown that the “hidden terminal problem” requires devices to be extremely sensitive Focus has now shifted to a “geo-location database” Device locates itself Asks a master database for local channel availability 8

10. Is regulatory change needed to prevent a meltdown in unlicensed bands? A low-value “best effort” service has become a key part of our communications infrastructure But the openness of the spectrum that helped make it successful is now contributing to the problem Is it time to change the rules? Dedicate some spectrum to WiFi? Open up enough spectrum to all to avoid congestion? Move WiFi ? Clear out the 2.4GHz band of other uses? Is “TV white space” the key hope for the future? 9