A digital approach for better coverage
Written by: Ingo Flomer | Published:
Ingo Flomer, coverage product director at Cobham Wireless

Ingo Flomer, coverage product director at Cobham Wireless, discusses the benefits of using digital DAS to provide coverage in large venues and outdoor areas

Efficiently distributing network capacity resources to their customers is arguably the most important factor influencing the level of service that operators can deliver today. More capacity means that a network can handle more users, offer them faster data speeds and a more reliable service. Ultimately, mobile subscribers are paying for data rather than signal (dBms,) meaning that the more data that they are able to consume, the more revenue operators can gain. Paying subscribers of 'superfast' 4G services expect a high-performance experience wherever they are, and failing to meet this demand through poor network capacity can lead to customer dissatisfaction and churn. Delivering high capacity and coverage in areas where dense numbers of people reside is one of the biggest challenges that operators face today.

Large enterprises, stadiums, outdoor public areas and transport hubs, are just a few examples of places which have a high footfall of mobile phone users, and in which vast mobile data is consumed. The demand for bandwidth in these areas will often cause a strain on network capacity, reducing the quality of service. Furthermore, traditional cellular towers fail to deliver connectivity in many large, busy indoor environments, with signals unable to penetrate and provide robust coverage throughout entire buildings.

Operators and venue owners are under growing pressure to deliver dedicated, high-capacity coverage solutions in these busy indoor and outdoor areas. This is particularly critical in venues where public safety communications are a necessity, such as schools, hospitals, transport hubs and tunnels. And with the growth in IoT technologies which require reliable coverage, operators and venues need to act now to ensure that capacity resources and coverage is available in places that need it the most.

Small cells for small venues
To increase network capacity, some operators are considering small cells. They are designed to inject needed capacity into small venues (approximately 25-35,000 square feet) and outside areas. However, if you have a very large site or area, small cells aren't appropriate. The amount of energy they consume is huge and the density of small cells needed to cover an area is high, leading to significant CAPEX and OPEX for operators or venue owners.

Many venues will also have a requirement to support multiple operators, up to four in some cases, and the various frequency bands that they operate in. This is another area where small cells fail to meet the mark, as the technology does not offer true multi-carrier support through a single cell. Instead operators need to deploy individual radios to support each operator band. This has serious impact on CAPEX and OPEX for an operator or venue, and can also affect the aesthetics of a building.

A final consideration is that small cells offer poor cellular edge performance, whereby the data throughput drops significantly. This is due to a lack of coordination and management that can be achieved between small cells. This presents difficulty in both the deployment of small cells - to ensure complete coverage - and the ongoing management of them. Whilst small cells will have their use cases in small venues and some outside areas, they can't provide the necessary connectivity and ubiquitous coverage required in many larger venues.

DAS ist gut
Distributed Antenna Systems (DAS) offer a premium solution for indoor and outdoor dense urban environments. These systems support multiple operators and high levels of data traffic. The technology uses fibre optics to carry RF signals and propagate them across a wide area. Current locations where DAS is used benefit from relatively good defined coverage, fewer coverage holes than small cells and lower power consumption. However, in some venues, traditional analogue DAS does not tick all of the boxes. These systems are not economical and result in huge chunks of capacity being used for large periods of times, a problem which also arises with small cells. Analogue DAS is also viewed as an expensive solution, involving lengthy design, implementation and commissioning processes. The technology can also be prone to interference and noise and trying to reduce these issues, whilst lowering CAPEX and OPEX, is a difficult puzzle for operators to solve.

So what is the solution for improved coverage and capacity for high density environments? Digital DAS, whereby base station data is digitised and sent as RF data packets to multiple remotes in a venue. It is based on a C-RAN (cloud radio access network) model, and offers the management capabilities and cost saving to make DAS a crucial technology for delivering capacity where it is needed.

Capacity, cost, control
Digital DAS offers a unique level of control over both uplink and downlink data transfer. Capacity management of the downlink signal means that capacity resources can be precisely directed and shifted around a location with ease, and also be scaled up or down depending on the demand at a particular time. Whilst with small cells and traditional DAS, capacity is distributed across the whole network at all times - a costly waste of capacity and energy.

Having control over network capacity makes digital DAS ideal for expansive city locations, where sites can be connected and capacity can be shared, or in large venues, which only require capacity in a certain area, at a specific time. For example, in a stadium capacity can be shifted to the concourse areas as spectators arrive, then to the seating area once an event has begun. In addition, a digital DAS network can be expanded in a city to different locations, with capacity shifted between them all as required. The model offers a much more efficient use of costly capacity.

With management over uplink data transfer, digital DAS allows for better noise management. Sophisticated noise management algorithms can constantly monitor the uplink noise performance of the system and ensure that signal to noise ratio on the network is maintained. This is particularly important for public safety communications, where reliability of the network is crucial and risk of interference can be disastrous.

A digital DAS also enables you to divide up your RF resources for different applications. This is ideal for public safety communications, allowing a venue or operator to open a dedicated window of the wide bandwidth LTE spectrum for public safety communications and transmit it wherever it is needed.

The cost saving of a cloud-RAN architecture in Digital DAS, has helped to define it as the ideal solution for high capacity coverage. The C-RAN model means that all baseband processing is focussed in a central location away from a venue, hosted in the cloud and managed virtually. This removes the complexity and cost of multiple operating and control sites for each area that needs to be connected. Network resources can then be distributed on one fibre line to a location and cascaded to different sectors of a building. In a city, a Digital DAS system can connect directly into the fibre lines that already exist in order to cost-effectively transport resources to a specific area or sector of a venue.

Deploy with digital
With both humans and technology intertwined in their voracious demand for high performance services and capacity, there's little wonder operators and providers are scrambling for effective end-to-end solutions to keep pace. The demand from users will only heighten as IoT solutions are unrolled. Digital DAS has emerged to fill the gaps that analogue DAS and small cells have produced in a precise and cost effective manner.

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