What’s Next for DAS? Challenges Call for Solutions

by: John Spindler, originally published on OSP Magazine. Republished with the permission of TE Connectivity.

Mobile operators are deploying Distributed Antenna Systems (DAS) as a way to add capacity and coverage to the network for LTE services. Still, there are challenges to deploying traditional DAS that can limit the business case for their use. Now, some new technology developments are making DAS deployments more attractive for a wider range of venues. Let’s look at a few of these challenges and see how new technologies are helping enterprises and mobile operators to overcome them.

Challenge 1: Head-End Plumbing
Deploying a DAS head-end requires the DAS head-end unit, one or more mobile operator base stations (BTS), and a lot of “plumbing” that connects the base station with the DAS. The problem is that, traditionally, base stations have connected to DAS head-ends using an RF interface. The deployment requires a remote radio head to provide the RF signal to the DAS, and racks of attenuators (in the form of passive interface panels) in-between to reduce the power output from the BTS’s 40W to the 1/4W suitable as input to the DAS head-end.

Remote radio heads and interface panels can complicate the DAS deployment, as they require a lot of additional space, power, and cooling. In many large venues like stadiums, it is necessary for the mobile operators or neutral host provider to construct a separate enclosure to house the head-end equipment because there’s not enough available space in the stadium itself. This muddies the business case for DAS and extends deployment time considerably.

Recently, 2 new technologies have emerged that promise to simplify head-end deployments by eliminating much of this plumbing. Active integration panels (AIPs) take the place of attenuators or passive panels in 2G and 3G mobile service deployments, saving much of the space, power, and cooling that would otherwise be needed for those racks. An AIP connects directly between the remote radio head and the DAS head-end to feed the BTS’s RF output into the DAS. Many DAS manufacturers are now offering AIPs, so mobile operators and neutral hosts can deploy head-ends that take up less space and are less complex.

A second technology aimed at LTE deployments is a direct Common Public Radio Interface, or CPRI, interface between the BTS and the DAS. CPRI is a digital interface that originally evolved to connect BTS with remote radio heads from the same manufacturer. Now, however, DAS makers are beginning to use CPRI as the interface between BTS and DAS head-ends. This approach not only eliminates the racks of attenuators or passive panels, but it also eliminates the need for a remote radio head in the head-end deployment. Since the interface is digital, it’s no longer necessary to use a remote radio head to provide an RF signal.

Challenge 2: BTS Signal Monitoring
Another challenge with traditional DAS deployments in 2G and 3G environments is grooming and monitoring the BTS signal as it connects to the DAS. Mobile operators want to be sure that their BTS’ signal is being delivered properly to the DAS. But with racks of attenuators or passive panels in a deployment, DAS installers need to manually adjust power inputs, and there’s no way to monitor the power (either locally or remotely) between BTS and DAS with passive attenuation panels. AIPs provide a means to configure power inputs remotely via software, to do automatic power limit controls, and to monitor BTS power levels remotely. This saves time and money on installation and gives the network operator continuous, remote control over BTS power levels as they feed the DAS. Thus, this will also save on maintenance costs.

Challenge 3: Cost and Complexity
A final challenge for DAS is that it is viewed as costly and complicated to deploy. Most of the perceived complexity lies in the convoluted nature of head-end deployments. Thankfully, recent developments such as AIPs and CPRI interfaces reduce both costs and complexity. In fact, it is estimated that CPRI interfaces can reduce head-end deployment costs and space requirements significantly. And, through the elimination of the use of remote radio heads and passive interface panels, equipment costs can be reduced as well.

DAS equipment has been around for 20 years, but DAS manufacturers continue to evolve their equipment, moving from analog to digital systems, and adding AIP and CPRI interface options between the BTS and the DAS head-end. The future of DAS looks toward simpler, less costly equipment that extends mobile coverage and capacity into underserved areas.

John Spindler is Director, Product Management for TE Connectivity’s Wireless Business Unit. During his more than 20 years of industry experience, Spindler has held a variety of product management positions with companies such as Nortel Networks, GTE, and InteCom. In these positions, he had responsibility for the areas of networking, network management, computer telephony integration, and wireless technologies. He can be reached via email at john.spindler@te.com. For more information, please visit www.te.com/das.

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