What is white space?

01 December 2011 | Guy Matthews


Spectrum available to providers of mobile data services is widely perceived to be inadequate for their requirements. Mobile networks are already feeling the strain of trying to sustain the demands of business and consumer customers today, never mind the likely demands of the future.

In a world where users of phones, laptops, tablets and other smart devices expect access to applications such as TV streaming and internet access, as well as music and video downloads, the need for mobile bandwidth is outpacing existing capacity. A partial solution to this impasse may be presented by unused spectrum allocated to the broadcast sector – so-called white space.

What is white space, and why does it exist?

When regulators assign different frequencies for specific uses, the allocation process creates a ‘bandplan’ which incorporates gaps of unused spectrum between radio bands or channels to avoid interference. In addition to white space assigned for technical reasons, there also sometimes exists spare spectrum, left free as a result of technological shifts, such as the move from analog to digital TV.

White space, claim backers of its use, works in much the same way as Wifi, but because TV spectrum signals travel farther and are more penetrative than Wifi, they require fewer access points. For this reason, white space networks may also have the potential to help bring mobile broadband to non-urban areas not currently well served by existing connections.

How can this white space be used, and who benefits?

Plans are afoot in a number of countries to make use of this unused TV spectrum, which is generally at a range of between 50 MHz and 700 MHz, to provide an inexpensive solution to escalating mobile connectivity requirements. When added to existing mobile bandwidth allocations, it potentially opens the door for mobile operators to better support data-intensive services, while also facilitating future innovation.

White space is said to be ideally suited to the delivery of cost efficient broadband access in rural communities, and the offloading of mobile data demand in urban centres, opening the way for innovative business models.

The range offered by white space, it has been pointed out, makes it ideal for the M2M model, whereby a variety of connected devices communicate directly with one another over distance, for example cars and retail signs.

There are also proposed niche uses for white space, such as emergency services communications: “With [UK regulator] Ofcom committed to regulate TV white space spectrum as a free resource, public safety use could be prioritised to provide the backbone for emergency communications with far greater performance than existing systems,” says Richard Walker, head of wireless at UK-based white space pioneer TTP. “Secure pop-up networks could also be deployed quickly, removing the current dependency on local cellular networks - and with no licence or data charges to pay, the cost saving is another major benefit.”

Where are we in this process of utilising white space?

The use of white space is at different evolutionary stages in different countries. In the UK, for example, a trial is ongoing in the city of Cambridge, designed to validate that TV white space can be used without impacting on traditional broadcast television. Similar trials have already been successfully explored in the US and other European countries.

In the US this summer, a 45-day white space trial was run as a precursor to FCC approval, without which appropriate devices cannot be manufactured and marketed.

R&D efforts are continuing on both side of the Atlantic. In the UK, for example, the above quoted TPP is investigating low power communications systems that work inside white spaces without interfering with TV pictures, and is running trials streaming HD video at speeds of over 7.9Mbps across a 5.6km white space link.

Core to TTP’s efforts is the development of a geolocation database that dynamically allocates free white space channels at a particular time and geographic area. Similar data base development efforts are afoot in the US.