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In-building From the outside in


Håkan Samuelsson, of Axell Wireless, discusses the pitfalls for mobile operators in providing comprehensive LTE network coverage indoors – and some solutions


T


he transformation to LTE will require a complete overhaul of the network to provide coverage and capacity for the


delivery of high-speed mobile broadband. Ac- cording to Infonetics Research, spending on network improvements will top $250 billion over the next fi ve years (2011–2015), while LTE spend alone is expected to skyrocket 46 per cent fi ve-year in compound annual growth rate (CAGR). However, as operators strive to smooth the


path to LTE, the same issues are arising in 4G as they did in 2G and 3G network deploy- ments. Subscribers, armed with their connect- ed devices, now expect ubiquitous coverage and capacity, regardless of whether they are using their mobile inside or outside. However, the signal degradation and defl ection caused by solid objects that currently impact on 2G and 3G networks also hinder LTE. Originally, mobile networks were built


to supply consistent coverage outside. T is means that if you are in the open with ‘line of sight’ to a cell tower, there is no issue with coverage or capacity. However, as soon as you step inside, it is an entirely diff erent matter. Recent research by Analysys Mason esti-


mates that, by 2016, over 80 per cent of global wireless data will be generated indoors. T e majority of demand for coverage and capacity will be concentrated inside public buildings such as shopping centres, where data-hungry subscribers have the chance to browse the In- ternet, update social networks or stream video. For operators this means that LTE is going


to have to penetrate solid structures in order to provide top class coverage and capacity inside. Operators will need to deploy robust systems that are capable of dealing reliably


About the author


Håkan Samuelsson is chief technology offi cer of Axell Wireless


with multiple data-hungry users, within walls, behind glass and under roofs. T e sheer scale of the in-building coverage


and capacity issues is sure to be highlighted when the Olympic Games begin in London next year. T ousands of tourists will fl ood into and around the Olympic sites for the duration of the world’s most famous sporting showcase. Visitors streaming out of venues into public spaces, such as cafés and retail outlets, will expect comprehensive coverage to share the historic moment with friends and family. Such a heavy footfall of users, all armed


with connected devices in confi ned spaces, will heap immense pressure on mobile net- works. T is leaves operators facing up to the reality that their networks will overrun due to the huge demand for faultless coverage and capacity.


Repeaters to the rescue


For larger structures such as shopping centres, operators are turning to sophisticated digital repeaters connected to a Distributed Antenna System (DAS) that propagates signal through- out the building. A single repeater linked to a roof-mounted donor antenna can ‘drive’ a DAS providing coverage for 100,000 square feet. In stark contrast to base stations, repeaters off er a smaller, easy to place, inexpensive solu- tion to supplying improved coverage indoors. Repeaters can be used to propagate LTE signal to coverage black spot areas between LTE base stations – which means they can be placed on existing masts, removing the need to identify and host new mast locations. Deploying re- peaters allows operators to reduce the cost and logistical challenges associated with rolling out LTE.


Traditionally operators have


used repeaters as a temporary fi x for indoor coverage chal- lenges. T ey may be reluctant to deploy them as a permanent solution. One barrier to the wide


use of repeater technology is interference. Repeaters were able to work exceptionally well for a limited number of users and so were deployed as a temporary solution for cover- age issues, but they were not a viable option for replacing base stations. T ey were also


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The D-MBR repeater by Axell Wireless can drive a passive Distributed Antenna System (DAS) to create coverage areas of more than 10 000m² in buildings, car parks, malls, warehouses and offi ces


LAND mobile November 2011


somewhat indiscriminate with the signals they boosted: operators could be unwittingly pay- ing to boost the coverage of a rival.


New technologies T ese diffi culties have been solved by repeaters equipped with Software Defi ned Radio (SDR), which enable an operator to specify and change sub-band allocation using software updates. Digital multi-band repeaters employing SDR can cope eff ectively and effi ciently with multi- megabit connection requirements, which is highly relevant for LTE. Operators can deploy the equipment for


their own dedicated use – but equally it opens the door to innovative micro-network sharing arrangements, common in the European mar- ket, in which operators make use of the same in-building infrastructure but retain direct ac- cess to their consumers and control over the network. T e ability of the repeater to diff erentiate between signals also stops operators potential- ly boosting their rival’s coverage in an illegal practice known as ‘piggy-back- ing’. In such a potentially com-


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