Re-allocating the 700MHz ‘digital dividend’ frequencies freed up by the demise of analogue TV looks set to widen the market for mobile broadband services in Brazil. However some problems with interference still remain to be solved.

Re-allocation of TV spectrum to mobile: balancing benefits and interference

The mobile telephony market in Brazil seems to be continuing along the path of strong growth on which it embarked several years ago. The country now boasts the fourth largest mobile voice and data market in the world, with more than 260 million registered mobile connections in 2012, 60 million of which were mobile broadband connections, a figure expected to reach 135 million by end-2014. However, a potential issue has now arisen over current moves to use a wider frequency spectrum in order to meet the growing demand from consumers. Last October the Brazilian regulator ANATEL made the decision to allocate the ‘digital dividend’ frequencies – i.e. those freed up due to the fact that digital television uses less radio spectrum than analogue TV – to mobile, and adopt the Asia Pacific (APT) 700MHz band plan which has hitherto been used for television broadcasting. However, although this move to APT 700MHz will foster the development of new LTE mobile services, which will in turn have a positive socio-economic impact on the country, there are a few issues relating to interference to be overcome.

Risk of overloading the spectrum

Forecasts show that using the 700MHz band for mobile broadband will contribute an additional $1.4 billion to the country’s GDP, generating additional tax revenues of $1.3 billion and potentially providing over 4,300 jobs by 2020. A major positive impact will be that the development of new mobile services should help to reduce the ‘digital divide’ in the country, encouraging access to broadband among a large percentage of the population, which is a high priority at the moment for governments all over Latin America. However, these benefits could still be curtailed by problems of interference between new LTE mobile signals and the existing and planned television services.  Hence the determination of the GSMA, an association representing close to 850 mobile operators and related companies in 218 countries worldwide, to come up with solutions for resolving interference issues.

Ways of optimising spectrum use

A report commissioned by the GSMA and drawn up by radio-communications consultant ATDI envisages a number of ways to avoid or mitigate the problem of interference in Brazil. The report suggests that initially the number of people affected will be very low, and this number can be further reduced by applying appropriate mitigation techniques to the areas of potential interference. Firstly, applying filters to both ISDB-T television transmitters and to LTE mobile base stations could help to significantly lower the probability of interference. Secondly, careful planning in order to avoid high power emissions in the upper television channels will help to facilitate the co-existence of mobile telephony and TV within the available bandwidth. The study focused on the cities of Brasilia, Campinas and Sao Paulo which, as the most densely populated regions of the country, could potentially be particularly susceptible to interference between television and mobile reception. Meanwhile Costa Rica, Chile and Ecuador are all following the same process of allocating ‘digital dividend’ spectrum to mobile, and this study may therefore prove extremely useful to operators in those countries as well.