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Cloud-RAN beats distributed antenna system

Posted: 26 Jun 2015     Print Version  Bookmark and Share

Keywords:C-RAN  distributed antenna system  DAS  Wi-Fi  4G 

For the most part, a mobile network operator is evaluated by the quality of experience it delivers to its subscribers. Although this concept is nothing new, the context is evolving. Consumption has shifted from voice toward an exponential growth in data demand. In addition, the vast majority of the data usage on LTE networks occurs indoors.

As director of network operations and engineering for Nex-Tech Wireless, I must, with finite resources, respond to this ever-growing demand in hard-to-reach places. The outdoor, voice-centric strategy of providing broad but thin coverage from a small number of cell towers is no longer acceptable.

Until recently our options have been limited when it comes to indoor coverage. The traditional solution is a distributed antenna system or DAS. In DAS, a full macro base station connects to a network of antennas distributed throughout a building.

DAS can be effective, but at a cost. In addition to the base stations, DAS requires coax or fibre optic cabling to transmit high-bandwidth radio frequency signals to remote antennas, plus intermediate gear to power and condition the signal. DAS is expensive to design, install and configure. Many DAS systems require expensive upgrades every two to three years to keep up with capacity growth.

Small cells have emerged as an alternative. Originally targeted for residential use, small cells are tiny standalone base stations with similar size and transmit power as Wi-Fi access points, but for 3G and 4G wireless technologies.

Small cells cost less and can be deployed quicker than DAS. However, since each one acts as an independent cell they create cell borders when deployed densely throughout a large building. These borders cause radio interference and frequent cell-to-cell handovers that degrade the user experience. As a result, they require complex RF planning and they can interfere with the outdoor macro network.

In early 2015 we needed to upgrade the wireless service in Gross Memorial Coliseum at Fort Hays State University in our home city of Hays, Kansas. The coliseum has seating for up to 7,600 people and heavy wireless use during events. It already had a DAS, but it was 3G-only and the cost of upgrading it to 4G was too high. We ruled out using standalone small cells for reasons noted above.

A new technology is emerging to fill the void: Cloud RAN, or C-RAN, small cells. With C-RAN, the baseband processing is centralised, allowing multiple access points to act as a single continuous cell rather than as an array of competing cells. In this respect C-RAN small cells are similar to DAS with its central base station. C-RAN small cells cost less than half as much as upgrading a DAS to LTE.

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