Distributed antenna systems (DAS) can deliver the in-building coverage and capacity needed to serve LTE users.
Coverage and capacity are the two fundamental challenges for enterprises seeking to deliver high-performance mobile services within their offices and plants. LTE promises multiple megabytes of downlink data per user, and it is impossible for a macro network alone to provide this level of capacity.
Effective LTE service requires that basestation antennas be moved much closer to end users in order to serve fewer users per antenna. A DAS enables this type of wireless architecture.
It will also be necessary to move base station antennas inside buildings to provide the required coverage for LTE users.
Many frequencies being used for 4G services attenuate much more quickly than 3G or 2G frequencies, making it more difficult for them to penetrate building walls.
To build networks with the necessary in-building coverage and capacity, there are three key considerations:
• Ease/cost of deployment – the network infrastructure must be simple and cost-effective to deploy, or else service providers won’t install it or the speed of network rollout will be unacceptable to users.
Existing buildings are particularly problematic since there is a lot of infrastructure to work around, and such installations can disrupt normal business operations.
• Scalability – the infrastructure should easily scale to cover new areas, support higher capacity, and adapt to future implementations of wireless standards such as LTE Advanced.
The in-building wireless solution should, like an optical fibre network, handle whatever applications will be required today and in the future.
• Flexibility – the solution should support multiple mobile operator services. While enterprises may have a corporate purchase agreement with a particular mobile operator, the in-building system must provide service for contractors, visitors and others in the building who use other services.
The solution should also accommodate network changes as spectrum is acquired or divested.
A DAS works with an available signal source, which is typically a small cell or basestation. The DAS then uniformly distributes that signal and channel capacity throughout a given area via a series of amplifiers and antennas.
This approach can deliver signals from one or multiple service providers, depending on the number of signal sources to which it is connected.
There are several advantages of using a DAS with base stations to create a small-cell architecture.
First, a DAS extends the signal from one or more base stations, so service providers or enterprises can use DAS to provide service to a large area while reducing the number of basestations required, maximising the use of existing radio resources. Secondly, DAS are quite reliable, easy to manage, and inherently scalable. Finally, DAS are relatively inexpensive and easy to deploy
Active DAS are the most effective type of equipment for 4G coverage.
An active DAS consists of a main hub that connects to a base station or small cell, a series of hubs that distribute the signal, and a series of remote antennas that deliver the signal to end users.
Active DAS use managed hubs and standard building cabling (i.e., single- or multi-mode fibre and CATV cabling), much like an Ethernet LAN. An active DAS aggregates all basestation capacity and simulcasts the signal to each antenna location.
Because the signal is amplified at each remote antenna unit in an active DAS, there is no end-to-end signal loss.
Active DAS thus deliver strong and consistent signals at every antenna, no matter how far away they are from the basestation and main hub. This makes the system easy to design and the user experience consistent.
In the largest facilities such as airports, stadiums and major hotels, some active DAS extend for miles. Since every antenna has predictable signal strength and coverage, it is far easier to plan the antenna placement in an active system.
The distributed hub architecture of an active system mirrors the design of an Ethernet LAN – it scales easily through addition of new antennas and hubs, and the hub electronics can be upgraded to support new services as they come on line.
This leaves the most expensive part of the system – the cabling and antenna plant – untouched. Active systems usually support simple network management protocol (SNMP) alarms as well, so a company’s IT staff can monitor the status of all remote antennas in the network using the same network management tools used for the LAN.
As we move into the 4G mobile service era, in-building mobile network solutions will be crucial to providing strong, clear, high-bandwidth connectivity for all users.
As 4G services continue their rapid growth curve, I expect we will see more DAS deployed to provide the needed coverage and capacity inside buildings.
John Spindler, director of product management at TE Connectivity
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