Mobile broadband, TV white spaces and Smart radios

Posted by Kalyan Medapati Monday, February 9th, 2009

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We have to admit, web on mobile phones is simply not friendly. And it’s because mobile devices and applications are not built for the web. But fortunately, all of this is changing slowly since the “iPhone” arrived, with its amazingly intuitive design and multi-touch technology. Now every other device manufacturer wants to build one of those with wider screen, touch technology and openness to allow outside developers to write better applications. These developments probably wouldn’t have made much sense in a pre-3G world, but with HSPA networks springing up everywhere in the advanced markets the timing is perfect.

But we have to be cautious about how the mobile broadband usage grows. It didn’t take that long for the “web on PCs” to become a mass phenomenon. And it shouldn’t take that long for the same to be replicated on mobile devices. Most of the operators do see this need and prepare long term to deploy more advanced networks that offer more capacities, like WiMAX and LTE.

I think in addition to better technologies, we will need more radio spectrum. And TV white space (TWS) provides a perfect opportunity to make a start.

TWS is the unused spectrum between different TV channels. Also called as “guard bands”, the spectrum is used to prevent interference between different broadcasts. When this scheme was designed the radio technology (obviously) was backward. But since then radio systems have evolved to become more intelligent. So the argument is that we can put the “guard bands” to low power unlicensed use by smart radio devices (white space devices).

These devices avoid interfering with other transmissions by using an access to a centralised database that lists all the existing licensed transmissions in that locality. Localized information provided by this database is crucial since vacant spectrum is not uniform across different regions, for e.g., airwaves are congested with more broadcasts in Los Angeles than they are in Milford, Pennsylvania.

Some of these developmental devices have already been built by major manufactures and successfully tested by FCC. Motorola, Microsoft, Dell, HP and others have formed a group, pushing their collective effort to build the database that I mentioned earlier. Once more prototypes keep rolling in for testing and approval, FCC is going to need the database to test how the system functions in real time.

The frequency range that white spaces sit on are sub 1GHz. These are lower frequencies than the ones used by other technologies operating on unlicensed spectrum - WiFi and Home RF operate on 2.4 GHz and 5.x GHz. At these lower frequencies, it’s easier to have better coverage. The signals pass through barriers like walls better and reach longer distances. So these frequencies have qualities that are good for wireless broadband. Ideally, the white space devices can be used as extensions to fixed and mobile macro networks – offloading traffic on to the ‘last mile’.

Last November, FCC approved unlicensed use of TV white spaces, albeit with limitations on power usage etc. Unlicensed because….

First, as it goes, the white space spectrum is not uniform across different geographical regions. Second, intelligence of these white space devices makes them appropriate for unlicensed use of spectrum that lacks geographic uniformity.

The point is, we need more spectrum for mobile broadband. TV white spaces provide this spectrum in bits and pieces. And smart radios piece them together for mobile broadband use.