Many wireless bands are heavily underused and regulators around the world are coming up with policies that will allow more efficient spectrum use. One such initiative is opening up more spectrum for unlicensed communication, with a particular example of TV white spaces (TVWS). TVWS are frequencies that have been used, until the recent digital switchover, by analogue TV broadcasters. These frequencies are now available and large parts have been released (e.g. in US) for unlicensed spectrum access. TVWS are prime frequencies because they are low in spectrum and signals propagate far (unlike in ISM bands), but many other underutilized frequency could potentially be reallocated in a similar fashion.
Unlicensed and decentralized access has proven to be very successful and WiFi connections currently carry most of the world’s wireless data traffic. Thus unlicensed and decentralized wide-area wireless networking (WWAN) presents a unique opportunity that could potentially provide ubiquitous and cheap Internet access for everyone. However, there are several design challenges to make a unlicensed WWAN work. Excellent signal propagation is both a bless and a curse. Since low carrier frequency signals propagate far, they will cause interference to a number of other nodes. The same issue in WiFi networking is much less pronounced because the signal propagation shorter. Dealing with the interference in an uncoordinated way on large scales is a major challenge. Another challenge is that the available spectrum is fragmented. For example, TVWS devices are secondary citizens and can use only chunks of spectrum that are not used by primary, registered users. These chunks are all around, a quality of each chunk is different at different times and for different users. It is not clear how to distribute available chunks to contending White-space nodes in an efficient and fair way.
The above mentioned problems are just illustrations of challenges lying ahead on the road towards ubiquitous wide-area wireless networking on unlicensed frequencies. The goal of this project is to deal with them and come up with technological solutions that would overcome the challenges.
- Microsoft Reinvents Wi-Fi for White Spaces, MIT Technology Review
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