Remote radio heads, better antennas, digital DAS and shared baseband resources help operators reduce the cost of ODAS
Outdoor distributed antenna system solutions enable operators to offer coverage and support capacity requirements in places that the macro network cannot reach. In dense urban areas, especially those with tunnels and subways, a new cell tower may not be a practical solution for a network trouble spot. In some suburban areas, cell towers may not be acceptable to the community leaders, although residents desperately want to use their mobile devices.
Outdoor DAS use remote nodes, which include antennas and amplifiers, to reach places that cannot be covered by a cell tower. Fiber is the typical conduit that transports the signal to and from the remote nodes. The fiber connects to a hub site that has the baseband equipment to propagate, convert, process and/or control the signal.
Over the past few years, the architecture has migrated from DAS nodes to remote radio heads, according to analyst Joe Madden of Mobile Experts.
“A remote radio head includes the digital processing for up/down conversion, as well as CPRI-based operational/maintenance features, which help the major OEMs and operators to manage and maintain the system,” said Madden. “RRH units generally work more seamlessly with the macro network.”
Remote radio heads for outdoor deployments are typically manufactured by the same vendors that make the macro base station equipment.
Madden estimates that roughly 30,000 outdoor radio nodes are shipped each year by the DAS ecosystem of neutral hosts, DAS vendors and system integrators, and that more than half of the outdoor radio nodes deployed today through the DAS ecosystem are remote radio head units made by base station vendors like Ericsson and Alcatel-Lucent. Madden said that even when operators use this type of remote radio head, DAS equipment vendors still have a role to play because they supply antennas.
Focus on antennas
As the name suggests, distributed antenna systems can succeed or fail based on the choice of antennas.
“From an antenna perspective, it’s all about the propagation, the KPIs, the form factors and the cost per square foot at the edge as well,” said Ray Hild, VP of North American sales for Galtronics. “So we kind of look at it from the end back to the beginning, and the impact of that edge.”
Hild said that one way operators can keep costs in line is by controlling the number of applications made to local zoning authorities. Antenna form factors that can accommodate multiple radio designs can streamline the process. Operators can secure approval for a given form factor and then adapt it to suit multiple deployments in the area.
DAS innovations
Two innovations that are enhancing outdoor DAS solutions are baseband pooling and digital DAS. Baseband pooling refers to the centralization of baseband units into a headend that can support more than one set of DAS remote units. Digital DAS eliminates the headend altogether by connecting the remote units directly to macro base station equipment.
During this summer’s Major League Baseball All-Star Game, AT&T made use of a digital DAS solution while Verizon Wireless used a pooled baseband.
Tower companies are key providers
American Tower and Crown Castle are two major providers of outdoor DAS solutions for mobile operators. These companies have extensive experience negotiating with municipalities as well as access to the fiber that is needed to connect DAS remotes to the headend or the network.
Crown Castle CEO Ben Moreland calls fiber “the horizontal tower” and his company has made several strategic acquisitions of fiber assets to support outdoor DAS with the purchase of Sunesys, Access Fiber Group and 24/7 Mid-Atlantic Network. Crown Castle refers to DAS remote units as small cells, reflecting the fact that many of these nodes are actually remote radio heads.
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Image source: American Tower
