Taking mobile coverage into indoor spaces with collaborative DAS solutions

Mobile telephony has revolutionised the way we communicate, both in business and in our personal lives.

January 28, 2013

Alan Chater, Divisional Manager, Projects at Jasco – Carrier RF

Mobile telephony has revolutionised the way we communicate, both in business and in our personal lives, and South Africa has a well established coverage network that delivers strong signal across the built-up areas of the country. However, while the outdoor coverage market is fairly saturated, cellular coverage was not designed for indoor use, and the signal from base stations cannot fully penetrate materials such as glass, concrete and brick. This means in large homes, office buildings, basement parking areas and shopping centres mobile coverage can be poor to nonexistent. Since customers demand always on connectivity wherever they happen to be, this lack of signal poses a problem and a challenge for network operators.

Distributed Antenna Systems (DAS) offer a solution to this challenge, effectively bringing mobile coverage indoors. However there is limited real estate within buildings for the cabling, splitting elements and antennas required, and there is also an inconvenience factor involved in installing this infrastructure every time a new operator needs to provide their service within a building. With the entrance of new players to the cellular market, as well as the imminent roll-out of Long Term Evolution (LTE) coverage this challenge is only set to increase. A new, collaborative DAS business model is needed, to both address the need for indoor coverage, as well as make the most of limited space and resources, to deliver seamless, high quality cellular coverage to subscribers, both indoors and out.

Cellular networks are Radio Frequency (RF) based, and higher frequencies such as those used for 3G and LTE coverage do not travel well through concrete, bricks, any type of metal and even tinted glass, which absorbs the signal. These kinds of materials are highly prevalent in large buildings such as malls and office parks, and even in modern decor. This means that most of the signal sent out by a base station has been absorbed before it can penetrate into a building, causing dead spots where there is no coverage. This is particularly noticeable in parking garages, which are mostly concrete and are also often underground, which further decreases signal penetration.

The evolution of social media and a growing demand for always on connectivity, coupled with increased amounts of time spent indoors in office buildings, malls and so on, have driven demand for improved coverage inside of buildings. Areas such as parking garages can also be a safety concern, as they are isolated and not having cellular reception means that victims of crimes are unable to call for assistance. People want to be able to use their phones and access the Internet wherever they are, particularly the younger generation with regard to Facebook, Twitter and other social media sites. Wherever people congregate and all try and use their phones at the same time, coverage problems tend to ensue, and these are worsened by the nature of buildings themselves. A DAS solution is therefore used to capture the signal from the base station, either with an antenna on top of the building or a base station inside the building, and then distributing this signal using a cabling system to various antennas placed strategically throughout a building. This ensures that signal is strong and usable particularly in areas where people congregate.

However, the downside to this type of solution, particularly in the South African context, is that each cellular service provider has traditionally built its own infrastructure and indoor coverage systems. This is an expensive process, and is also intrusive for building owners, whose business is disrupted every time a new provider wants to install antenna and cabling systems. Aside from this, there is also limited space for such solutions, as cabling needs to be run through existing ducting systems and antennas are need to be placed strategically to deliver the best signal. Antenna from different operators also need to be placed a certain distance apart, otherwise the signals from each will interfere and degrade both systems.

With the impending rollout of LTE, this problem is further compounded, as LTE in effect uses two RF signals to broadcast in tandem. This means that if networks want to have full LTE compatibility on indoor coverage networks, regardless of the frequency used, they need to have two antennas at each point where in the past there was one. With the number of cellular operators currently at four, this then means that if each network wants their own indoor coverage solution for LTE there needs to be eight sets of cabling and eight antennas at each point, which is simply not feasible given limited real estate.

In order to deal with the demand for indoor coverage and the growing technological challenges this poses, a new business model is needed that allows network operators to share the passive infrastructure which takes up physical real estate. They can then install their own active components using intelligent Point of Interface (PoI) hardware which enables base stations to be combined, and then the combined RF signal to be broadcast and distributed using a shared distributed antenna network. This will not only assist with bringing down the cost of building the infrastructure, but will enable LTE indoors to become viable and will deliver the highest levels of customer service, ensuring that all users regardless of network get the best signal possible wherever they happen to be.