23 Mar 2012

In-building wireless coverage: the inside out approach for operators

Hakan Samuelsson, Chief Technology Officer at Axell Wireless, discusses how Fibre Distributed Antenna Systems (F-DAS) can enable mobile operators to provide flexible and durable wireless coverage inside buildings for 2G, 3G and next-generation networks.

More data traffic is emanating from inside buildings than ever before. According to Analysys Mason, over 80 per cent of global wireless data will be generated indoors by 2016.

This demand for data is being driven by the penetration of smartphones, tablets and other connected devices flooding the market; with the GSMA recently predicting that there will be 24 billion connected devices worldwide by 2020.

For the first time, this trend is forcing mobile operators to begin thinking about building their networks from the ‘inside out, rather than the outside in’; in order to address fundamental user demand.

Operators are facing up to an in-building capacity and coverage conundrum. High volumes of subscribers, armed with connected devices, in vast buildings, such as shopping centres and sports stadiums, attempting to access data services, make calls, or send SMS messages, causes a multitude of issues.

Traditionally, mobile networks were built to provide coverage and capacity for subscribers on the move; but that support is severely diminished once inside a building. The signal degradation and deflection caused by solid structures means operators must deploy robust systems that are capable of dealing reliably with multiple data-hungry users inside buildings.

From the outside in

Multi-band fibre optic systems now offer operators a cost-effective, upgradable and scalable indoor wireless coverage solution for larger, complex structures and smaller venues. The solution is a combination of two types of hardware. Firstly, a next-generation Optical Master Unit (OMU) that is equipped with next-generation network capability. The OMU is able to support frequency bands from FM, VHF and UHF frequencies right up to 2.6GHz. Signals from a base station, situated inside the building or nearby, are fed to the OMU, which converts the RF carriers into modulated light. The OMU then distributes the light via fibres to multiple remote repeater units stationed inside the building. Crucially, this in-building solution is capable of single or multi-operator use. This allows operators not only to share and co-ordinate on indoor deployments, but also the ability to re-farm spectrum according to which technology they want to run. Flexible spectrum deployment means an operator can run 2G services in some channels and support 3G or LTE in others, all in the same building.

Furthermore, fibre-fed repeaters – the final link in in-building coverage – have also undergone a technological revolution. Manufacturing advances have led to the introduction of a smaller, low power remote unit that can propagate signal into smaller rooms, corridors and areas that would be otherwise difficult to reach. Importantly, this improvement in repeaters highlights another facet of the OMU. The flexibility of the OMU enables operators to combine high and low power repeaters in a single installation. This ability to mix and match repeaters allows operators to tailor installations to meet the exact specification and requirement of a building’s interior. The new fibre fed repeaters also offer an extremely low noise figure; maximising both capacity and coverage by providing higher data throughput across a DAS coverage area.

The Olympic issue

To truly understand the benefits of the OMU and F-DAS to operators, it is important to comprehend the sheer scale of the in-building coverage and capacity issues. This is sure to be highlighted when the Olympics begins in London next year. Tens of thousands of tourists will flood into, and around, the Olympic sites for the duration of the world’s most famous sporting event. Visitors arriving by train services will funnel into the new Westfield shopping centre, the largest in Europe, in order to make their way to the Olympic park. Such a high volume of subscribers, interacting with connected devices, in a confined space will lead to a coverage and capacity issues for operators. Furthermore, after such a historic event attendees will want to interact with family and friends on their mobile devices in public spaces, such as cafes, restaurants and bars. Meanwhile, there will be thousands of supporters inside Olympic venues wanting to call friends and update social networks after a specific event, such as the men’s 100 metre final.

Large and complex structures

For superstructures, like Westfield, a sports stadium or large office building, operators can leverage a F-DAS solution to provide coverage and capacity in times of high usage. A base station ‘hotel’, in the vicinity of a building, can provide signal for large structures; with each base station providing coverage and capacity for a certain section of the building. This solution can be repeated throughout a large structure as a single OMU can support up to 8 high power or 24 low power repeaters. A structure with large open spaces, like a shopping mall with walkways and food halls, can be supported by high power repeaters. However, in the accompanying offices or smaller shops, low power repeaters can be leveraged to propagate coverage and capacity where necessary. They can also be deployed in areas previously inaccessible, such as tight corridors or ceiling architecture. Previously, in a structure as complex as a shopping mall, operators would have had to deploy two DAS solutions. One DAS would support a configuration of high power repeaters for larger areas and the other for low power repeaters for smaller, more confined spaces. The OMU’s ability to mix and match both low and high power repeaters requires just one F-DAS solution. This drastically reduces the cost of an in-building installation.

Size matters

Despite F-DAS being an ideal solution for large scale indoor deployments, it is not appropriate as an in-building solution for smaller venues. When considering how to propagate signal in smaller venues, operators must estimate how many users and how much capacity they must support in order to ensure the correct business case for the installation. Alternative methods of providing coverage indoors such as femtocells or picocells only have limited capacity and would not be able to support a large number of concurrent users in an office or coffee shop. Femtocells have been deployed for residential use and tend to only support up to six channels at any one time, they do not have the capacity to scale to meet the demands for in-building implementations. Picocells are adequate for providing coverage for wireless hotspots, but they are also capacity limited and prone to overload if too many users want access at the same time.

Within smaller venues off-air repeaters can play a vital role, particularly when there is no business case for deploying a new base station due to the limited number of subscribers it will have to service. The repeater can borrow capacity from an existing base station, within close proximity, to propagate the coverage and capacity needed for that dedicated group of subscribers. This method provides operators with a cost-effective solution to deploy in-building coverage in areas that tend to be neglected because they fall outside of the range of a base station. In fact, in some cases if the venue is very small, and there are only a small number of users, it might be more economical to deploy a repeater that feeds of a femtocell or picocell as oppose to a base station. This scenario is dependent on the size, and specification, of the venue and the number of subscribers.

Future-proof solution

Traditionally, off-air repeaters have been used as a temporary solution to provide coverage, borrowing capacity from an outdoor base station. However, the adoption of fibre linked repeaters, driven by the increase in data usage, has seen repeaters deployed as a permanent solution for in-building wireless coverage. Previously, copper cables were used to link repeaters. In comparison to fibre, copper cables are less flexible leading to signal losses at higher frequencies. The introduction of fibre and its ability to manage high frequencies constantly adds to the longevity of the repeaters. By being able to mitigate higher frequencies, F-DAS can upgrade easily as new standards and higher frequencies are developed in the future.

The switch to all-IP networks will not happen overnight, so any in-building solution must be able to support the full range of current standards and be easily upgraded to allow the delivery of LTE. To enable this, off-air repeaters are now fitted with Software Defined Radio (SDR) technology. SDR enables an operator to specify and change sub-band allocation through software updates. Digital multi-band repeaters, employing SDR, can effectively, and efficiently, manage multi-megabit connection requirements: which is highly relevant for next-generation networks.

Landlords of public buildings, such as shopping malls or office buildings, are reluctant to allow multiple operators to install their individual equipment into their building, as this can have large cost and time implications. The installation of a Fibre-DAS system means that multiple operators can install one solution they can all share at a considerable cost reduction for the landlord and the operators. Furthermore, SDR enabled repeaters mean that operators can make upgrades remotely without having to affect the running of the building. Operators can simply install new software, without replacing or manually upgrading equipment, when the move to next-generation networks materialises. The operator has at their disposal a system that can be modified using software updates according to any changes of technology (from GSM to UMTS or LTE) or a mix of technologies.

Key to delivering wireless coverage indoors

The trend of data traffic emanating from indoors shows no signs of abating as connected devices saturate the market. Operators’ must now consider the most cost-effective and efficient ways of supporting mobile coverage inside buildings. The flexibility and dexterity of Fiber DAS solutions are revolutionising in-building cellular coverage. The introduction of F- DAS has ensured repeaters can become a permanent solution for propagating signal and capacity in large structures. The new-found ability to mix and match high and low power repeaters allows operators to meet the exact output power needed in complex structures. This means operators can tailor in-building solutions to fit to the business case and to cater for the amount of cellular usage taking place in the area. Scaled down repeaters, built with SDR capability, also provide an ideal solution for in-building coverage within small to medium sized buildings. Moreover, SDR enabled repeaters are able to allowing scope for new standards. Overall, repeater technology has been modernised to provide an ideal, future-proof solution to help combat the growth in data traffic emanating from inside buildings.

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