Ensuring successful 5G rollouts – distributed antenna systems

A high Power DAS remote

Telecoms.com periodically invites expert third-party contributors to submit analysis on a key topic affecting the telco industry. In this article John Spindler, Director of Product Management at TE Connectivity, discusses the role of distributed antenna systems (DAS) in the future 5G roll-outs, and the relationship of this technology with small cells.

With 5G networks on the horizon, mobile operators are looking at lessons learned from the 4G services rollout. One lesson was that distributed antenna systems (DAS) and small cells are essential to delivering the coverage and capacity required. But rather than looking at small cells and DAS as an either/or proposition, we can view them as complementary options that will deliver successful 5G services.

In the past two years, small cells have caught the attention of mobile operators as a solution to coverage and capacity challenges. DAS, on the other hand, have been a fixture in mobile operator infrastructure for 20 years. Let’s look at the differences between small cells and DAS and how they can work together to address the problems of those trying to implement effective and reliable 5G communications networks.

Small cell challenges

One challenge with small cells is that today they are at best dual-frequency, dual-service devices. To deploy more than two frequencies or mobile operator’s services, it will be necessary to deploy multiple small cells in each location where they are distributed. Since each small cell will require its own backhaul and power, this can be a complicated and expensive arrangement.

Another main issue that affects those trying to scale coverage with multiple small cells is figuring out how to reduce interference with cell towers and other small cells. When such interference occurs, network performance is inevitably reduced.

Avoiding interference with the outside macro network is the more challenging problem to address. To ensure sufficient coverage along the inside building perimeter, small cells are placed close to the outer walls. However, due to these cells’ proximity to the building exterior, a certain amount of interference between those cells and the macro network is almost unavoidable. Some mobile operators are considering deploying small cells on a different (perhaps dedicated) RF frequency from macro cellular networks, but this chews up precious spectrum at a time when spectrum is scarce and acquisition of additional spectrum assets is costly.

In a multi-small cell environment, additional issues can include multi-cell interference and handoffs. In such an environment the user’s handset has to hand off the connection from one cell to the next as the user moves through the building. This drains handset battery life and it occurs with far greater frequency than in the macro network due to the small cells’ coverage area size (typically 5,000 square feet or less). In buildings covered by a DAS, in contrast, there are no handoffs as the entire area is essentially one large cell.

Another challenge is signal dominance. An in-building system must establish signal dominance to minimize the potential for hand-off between the indoor and outdoor signal sources (this is particularly critical in high rises). Such hunting can adversely impact the surrounding macro network performance, as well as reduce device battery life and create a poor user experience.  But it is difficult to establish a dominant signal source with small cells due to their very low output power. With a DAS, it is easy to deliver enough power through the antennas to create a dominant signal source and minimize hunting.

Peak traffic engineering is yet another challenge. With small cells, high user density locations  (conference rooms and staff restaurants, for example) need to be over-provisioned in order to provide enough capacity for peak usage times. During low usage this investment in extra small cells is effectively wasted. Over-provisioning issues are more effectively managed with a DAS because all of the system’s capacity is available to every antenna within the coverage area. As such, there is no need to account for movement of people/devices throughout the day. If capacity needs increase in the future, additional radios can be easily added at the DAS head end to increase capacity throughout the coverage area.

Finally, data drop off at the small cell coverage edge is significant (during hand off).  The only way to prevent this would is to provide greater coverage overlap, which would require a larger number of small cells and increase chances of interference between cells.

Marrying DAS with small cells

The way to overcome the limitations of using small cells alone while providing strong and consistent mobile service in the enterprise is to combine these devices with a DAS: small cells provide the capacity, and the DAS distributes it throughout the building. Here’s how this combination solves the problems of using small cells alone.

Benefits of DAS outlined

  • DAS is multi-frequency. A DAS can distribute multiple cellular frequencies to serve more than one mobile operator, so just one set of remote antennas is required, rather than multiple small cells in each location.
  • There is no interference. Since the DAS simulcasts radio channels throughout the building, there is just one large cell. This eliminates multi-cell interference along with the need to hand off from one cell to the next as the user moves about.
  • There is one dominant signal. One signal source means one dominant signal. The DAS simply provides a uniformly strong signal throughout the interior of a building so user devices don’t hunt between signal sources.
  • There is no need to over-provision. All antennas in the DAS have access to all of the feeder cell’s capacity, so there’s no need to add new small cells for higher capacity requirements in certain areas.  If additional capacity is needed throughout the building, additional small cells or radios can be added in a central location at the DAS head-end.
  • Deployment is less expensive. It is much less expensive to deploy a DAS for coverage and capacity in a large building than to deploy dozens or hundreds of small cells.
  • Operating expenses are lower. A DAS is pretty much a set-it-and-forget-it solution, so once deployed it needs little maintenance. With multiple small cells, the cells will require continuous adjustment to function in an optimal manner. In addition, using a picocell as the RF source for a DAS eliminates having to use a much more expensive, full-sized base station. Full-sized base stations require a lot of space, power, and cooling to operate, and using them with a DAS is overkill because much of their output power must be attenuated for use with a DAS.
  • Backhaul costs are lower. A group of small cells centrally located feeding a DAS head end can be combined to use a single backhaul connection. This contrasts favorably with needing a separate backhaul connection for each of several dozen or several hundred distributed small cells.

There is a lot of talk about small cells in mobile operator infrastructure, but DAS was the original small cell and it still has many advantages over distributed networks of small cells.  Rather than choosing between small cells and DAS for 5G networks, it’s a far better idea to combine the benefits of these solutions to get lower costs, easier deployment, better quality of service, and multi-carrier coverage.


John Spindler high-res_TE ConnectivityJohn Spindler, Director of Product Management at TE Connectivity, is responsible for developing and managing the wireless product portfolio for the company’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. Spindler received a Bachelors of Arts Degree from the University of California, Los Angeles (UCLA) and an MBA from the University of Southern California, Los Angeles.

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