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Feb 27, 2010

TV-Band White Spaces Database

Google TV-Band Devices DatabaseIn the previous post about unlicensed access to television band in the US I commented that the call for proposals from intended database providers for TV-band cognitive devices was already closed.

Though this is not directly related to my research I have to confess that I was curious. This week I read the proposal by Google with its view about how this database should be. The points I want to stress are the following:

  • Google offers itself as one of multiple database providers. Its proposal suggest that ideally not one but several parties could offer the database services. Then a single entry point (denoted in the document as clearinghouse) could serve as access to the multiple databases. The clearinghouse would disseminate the information among multiple providers which have to define interfaces to keep their information synchronized.

  • The database will offer the functions required by the FCC: Repository, Registration and Query. Additionally Google's architecture proposes Synchronization with Other Databases, Public Access Interface and additional Database Services. In order to promote innovation Google suggests that rather than providing a closed functionality, a database could perform a variety of functions that add value and utility to querying devices:
    A TVWS Database Service provider could, for example, combine location-based information with detailed information in the database such as transmitter locations, and use propagation algorithms to produce a ranking of available channels.

  • Google recommends to avoid per-query fees, which would discourage database use. Since Google business plans are based on the spread of internet access and not on user fees, the database could be financially supported by Google for at least 5 years.

We see that following the philosophy that characterizes Google the proposal pushes the innovation. To this end they propose an open access interface that everyone could use for developments based on the public information of the database. Moreover, different database providers could offer a variety of functions that would add value their solutions. However, Google uses its dominating position to offer a database solution without requiring additional fees. This on the one hand is good for the final user but on the other hand difficulties the incorporation of new companies interested in offering database solutions.

Image thanks to: SQL Developer.

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Feb 19, 2010

CVX: Convex optimization made simple

I first discovered the CVX Matlab package when I followed Boyd's course 364a on Convex Optimization at Stanford. I recommend this class to everyone interested in the topic (the videos of the lectures are online for free, and they are quite funny).

My first experience with this convex optimization package was the computation of the rate regions of a Multiple Access Channel and I was amazed how easy was to perform such complicated optimization problems. However the applications of CVX cover all scientific fields were a given optimization must be performed, even if the problem is non-convex it may be possible to relax it into a convex one.

For example currently I've been working in a problem of maximum likelihood estimation of a sparse set of parameters that results into an expression with a norm 0 term in it. The optimization problem can be simplified and relaxed to obtain a convex problem similar to the basis pursuit algorithm presented in [T06].
I will use the algorithm in [T06] to show how simple is the learning curve of CVX. The proposed algorithm is based on a norm 1 penalty:

norm 1 penalty

Writing this optimization problem in Matlab reduces to

   variable b(N,1);
   minimize( 1/2 * square_pos(norm(s-Phi*b,2)) + gamma * norm(b,1) )



Joel A. Tropp. Just Relax: Convex Programming Methods for Identifying Sparse Signals in Noise. IEEE Transactions on Information Theory, 2006.

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Feb 10, 2010

Unlicensed access to television broadcasting spectrum in the US

static noiseNovember 2008 Federal Communications Commission (FCC) adopts rules for unlicensed access to unused television spectrum in the US. This was a brave decision since the detection technology required for unintrusive spectrum access (usually called cognitive radio) was (and is) not mature yet. In fact the technical proposal FCC 08-260 recognizes the difficulty of completely avoiding the harmful interference to primary users. To overcome the technical drawback of primary signal detection an alternative approach is proposed:

All devices, except personal/portable devices operating in client mode, must include a geolocation capability and provisions to access over the Internet a database of protected radio services and the locations and channels that may be used by the unlicensed devices at each location."

Moreover, to avoid co-channel interference to primary users the FCC proposal rules that even neighboring channels are prohibited to secondary devices. Fixed and personal/portable devices must also have a capability to sense TV broadcasting and wireless microphone signals as a further means to minimize potential interference. The devices that rely only on spectrum sensing to avoid causing harmful interference will be subject to a rigorous process of testing by FCC's Laboratory.

But, how did the proposal evolve?

Analogue television broadcasting switch off in the US was initially planned for the 17th February 2009, day in which unlicensed devices could start to use the spectrum. Though some reports described the transition to digital TV flowing smoothly, the official switch off date was delayed until June 2009.

But only last November the FCC did open the call for proposals from potential database managers.

Potential administrators have to demonstrate expertise and present a business plan for the next five years. Additionally proposals should outline the information stored, a process for incumbents to register, and the query procedure. Some members of the "White Spaces Database Group" are Comsearch, Dell, Fox, Google Inc., Microsoft Corporation, Motorola, NetLogix, Neustar, Phillips, Spectrum Bridge, SWIM and Waterford Consultants, LLC. Now the call is closed and public and industry have until 18th February 2010 to comment on the proposals.

All these delays on the initial plan are motivated because USA is the first country opening the unused spectrum. However the existing technical challenges are being addressed by both american industry and research community. While this happens american companies gain experience and establish an infrastructure that will assure their leadership when other countries start opening this new market.

One question comes to my mind at this point, and is What can Europe learn from this?

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Feb 2, 2010

Will LTE kill WiMAX?

4th generation
Today I found an article in the Spectrum Magazine about a fight that already started some years ago, WiMAX versus LTE. The article I am speaking about is 4G in the U.S.A..

When I visited the Research Qualcomm Quarters in San Diego in 2008 I asked about their opinion on the future evolution of the WiMAX market. Qualcomm's (and most of cellular operators) opinion was that Long Term Evolution (LTE) technology was going to kill WiMAX before it was born. In fact, most of the presentations I attended during my stay in San Diego covered different aspects of the development of the LTE standard.

Two years after that an article appears in the Spectrum describing the early sucesses of WiMAX in the United States, mostly in the "last mile" broadband connection. Moreover WiMAX has spreaded all over to world allowing small providers to offer cost-effective (and even free) internet access. An example of this is my hometown, Vilanova de Arousa (Spain) that provides to all inhabitants, even on a beach, free internet through a mixed Wifi/WiMAX network (conect@vilanova).

With this in mind it is surprising that this article still predicts LTE taking the lead. The main reasons for that, they say, are the huge base of existing mobile customers and the support by the cellular lobby. However WiMAX has (at least) three years advantage over LTE, and last decade showed us how market can change in just a couple of years. In my opinion the time until world’s mobile operators begin to upgrade to LTE will determine the fight, and the result may change due to small factors, as it could be the creation of a mobile device taking all the advantages of WiMAX.

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