Frequently Asked Questions - Explosion in spectrum demand

As the number of tablets and smart phones grows, telecom operators vie for access to new frequency bands, but the traditional methods of adjudicating the spectrum are facing limitations.

Keep in mind that the spectrum is used for radio and television broadcasts, for satellite communications, for airplane traffic control, for geolocation (Global Positioning Systems – GPS), as well as for military, police and other governmental purposes. Traditionally, the demand for additional spectrum has been met due to the advances in electronics that have permitted the use of higher frequencies at an affordable cost. Higher frequencies are well suited for high speed transmissions, but they have a limited range and are highly attenuated by walls and other obstacles as well as by rain.

This is exemplified by comparing the coverage of an AM radio broadcasting station to that of an FM station: the great range of the AM station is due to its use of lower frequencies. On the other hand, FM stations can make use of higher bandwidths and as consequence can offer greater audio quality at the expense of a more limited range.

Accordingly, TV broadcasting frequencies are coveted by cellular telephone providers: using lower frequencies means they will need fewer base stations, with corresponding savings in deployment, operation and maintenance. This is why these frequencies are commonly referred as “beach front property”.

The greatest impact of advanced modulation and coding methods for more efficient spectrum use has been the availability of more bits/s per Hz of bandwidth. This advance was made economically possible by great strides in integrated circuit manufacture.

According to calculations performed in 1948 by Claude Shannon, the father of modern telecommunications, a typical telephone line can, in theory, carry up 30 Kbit/s. But this rate was achieved only in the 1990s with the invention of integrated circuits that could implement the required techniques.

Figure 4: An example of TV channels adjudication in two cities that are close enough in proximity such that transmissions from one can reach the other. White spaces are kept fallow to minimize interferenceFigure 4: An example of TV channels adjudication in two cities that are close enough in proximity such that transmissions from one can reach the other. White spaces are kept fallow to minimize interference In traditional analogue TV broadcasting, adjacent channels cannot be used at the same time, because the signal from one channel will “spill” over the two adjacent channels and cause interference. This is similar to the median used in freeways to separate the two directions of traffic in order to prevent collisions. A “white space” must be left between two contiguous analogue TV channels to prevent interference. Digital TV broadcasting is much more efficient in spectrum use, and several digital TV channels can be accommodated in the same frequency band formerly used by a single analogue channel without “spillover” in adjacent channels. In places where analogue TV is replaced by digital TV a “digital dividend” is being harvested. The concept of white spaces can be applied to three different ranges of frequency: a) Spectrum that has been assigned to TV broadcasting but it is not currently being used. This applies particularly to developing countries, in which there has been no economic incentive for broadcasters to use every available TV channel. b) Spectrum that historically had to be left unused in between two adjacent analogue TV channels to prevent interference. c) The spectrum that has been reclaimed (“refarmed”) in the transition to digital terrestrial TV. This currently applies to developed countries, but will soon apply to developing countries as well. The last 20 years has seen tremendous growth in demand for spectrum for mobile communication services, in which data services are consuming much more bandwidth than voice and the growing use of video is presenting an additional challenge. Not surprisingly, telecom operators everywhere are vying for a portion of these “white spaces”. Broadcasters, on the other hand, are very reluctant to cede any spectrum to direct competitors.

Steve Song, CEO, Village Telco talks about what TV White Spaces are; what they enable; how different operators might use them; and why they are important for Africa. He concludes by talking about the new investor in his company Village Telco and what its future plans are.

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