How to choose a DAS for complete in-building wireless connectivity – Part 1
It’s a fact – cellular signals do not penetrate well into the buildings, writes Slavko Djukic, the chief technology officer of Zinwave, in the first of a two-part article. That’s why dropped calls and interrupted data connections continue to plague the owners and users of commercial buildings, from downtown office towers to medical centres, corporate campuses to airports and stadiums.
It’s a problem with far-reaching repercussions that range from lower customer satisfaction levels –resulting in higher churn rates, to decreased employee productivity and morale – resulting in higher turnover.
Today, 80% of cellular calls and usage are generated or initiated indoors – so for any building owners and managers that want to ensure consistent, reliable indoor connectivity, a distributed antenna system (DAS) has become the wireless solution of choice.
What is a DAS?
A DAS typically comprises active electronics, usually a central hub connected to remote units paired with amplifiers and antennas distributed throughout a building, with cabling to connect the elements. The central hub is connected to radiofrequency (RF) source – usually a small cell or base station – from the operator, which supplies the cellular signal. Through a DAS, operators’ wireless signal is most efficiently distributed to all parts of the building.
The system ensures a strong signal throughout the building, overcoming the interference on the network that typically exists in the buildings, and can work in concert with small cells as the RF source. Because the signal used to support a DAS is separate from outdoor cellular towers – except in rare instances where a repeater is used as the RF source, the added capacity is dedicated to the building – unlike repeaters, which siphon capacity away from the outdoor towers.
And because it’s an operator-approved and -supported cellular signal that’s being brought into the building, users receive a guaranteed level of service, as opposed to unguaranteed performance of voice-over-Wi-Fi, for example. Plus, calls can seamlessly hand off from the outside network to the inside network as users move from outside to inside the building, something Wi-Fi isn’t guaranteed to provide.
Not all DAS systems are created equal, however, and it’s critical that any investment in this type of network infrastructure pays off for years to come. Look for these six criteria to choose the optimal DAS.
Full spectrum on a single hardware layer
The ability to support new spectrum means a DAS system can support wireless operators’ future extension plans for their networks as capacity needs grow or as operators acquire new frequency spectrum. The ideal DAS solution is capable of supporting all of the most common cellular and public safety frequencies at the initial installation, with no additional hardware needed to add new frequencies or wireless operators in the future.
Some DAS solutions require multiple installations in order to be ready for more than four to six frequencies. This impacts businesses not just today – because multiple installations might be required simply to have access to all currently available frequencies – but also tomorrow, when a business’s needs change or when new spectrum becomes available.
Any system should be ready to absorb these types of changes without additional hardware; otherwise, a business will need to add new hardware layers – remote units, boxes in telco closets, more cabling and more fibre, often more antennas – to accommodate future technology needs. This is costly and disruptive, and may involve adding unsightly hardware outside telco closets if the closets are already full.
In addition, new layers stapled onto existing hardware may cause degradation in the existing system’s performance.
Determining the type of cabling used for a DAS is crucial. Measuring performance between fibre, CAT and coax, fibre is considered the premium cable because it can carry higher traffic loads. It has the most bandwidth available, a long cable length allowance, and is low cost to install, test and maintain.
Some DAS claim to use fibre cabling, but that may not mean the system is fibre based. Many systems do use fibre at some point, but most are hybrid fibre and coaxial cable; they use fibre cabling as the backbone, but the coaxial cabling goes out to the antennas – the equipment that distributes the now-amplified cellular signal to be consumed by mobile devices. A hybrid system is more difficult to install, test and maintain, and thus more intrusive to the business or building where it is being installed, as well as more expensive.
Without all-fibre, a business will not be set up for the growth in data traffic that occurs every year, because non-fibre cabling support less traffic than fibre. Other future technologies like 5G and high-frequency bands in unlicensed spectrum also are crippled without an all-fibre system; carrying any frequency band over any cable results in signal loss, and coax and CAT cabling have much higher RF losses than fibre, especially at higher frequency bands, which will be used for 5G.