Mobile Network Operators

DAS – The Original Precursor to C-RAN


I was a speaker at the NEDAS Summit in New York in early April, which lead me to reflect on how DAS systems are the original precursors to today’s C-RAN solutions.

DAS (Distributed Antenna Systems) can be considered the first iteration on the evolutionary road to C-RAN (Centralized RAN). As the name suggests, the antennas are distributed over a wide area, typically different stories of a building. A DAS solution provides improved carrier coverage, something that is becoming increasingly harder to achieve indoor due to ever-improving building and insulation standards. Additionally, as there are more antennas, they can broadcast at lower power.

The DAS is connected to the radio equipment, the Baseband Unit (BBU). As each part of a DAS is essentially the same cell, handover issues are reduced or eliminated as no handovers are required when moving between common DAS areas.

DAS can be used outdoors, but the typical use cases are in dense, high-value public buildings such as stadiums, metro systems, concert venues, campuses, enterprises, etc.

Nowadays, it is quite common to have multi-host DAS solutions that can carry multiple carriers, making the business case to invest in hosting a DAS solution more compelling.

The DAS itself is remote from the BBU. That separation could be 50-100 meters, or even up to 4 to 5 kilometers. That BBU can be located with other BBUs, so essentially DAS is the original precursor to C-RAN. The crucial difference is that for DAS, the BBUs are uncoordinated. The primary advantage of C-RAN is to allow power and transmission management of multiple BBUs simultaneously to decease the total amount of radiated power in the network, thus improving signal quality. The Far East is leading the way, with both China Mobile and KDDI of Japan showing substantial improvements in cell throughput with C-RAN, particularly at the cell edge. China Mobile has indicated increases in throughput from 80- 300%.

Going forward, enterprise owners of DAS solutions are looking to improve customer satisfaction while increasing revenue while operators deploying C-RAN are requiring real-time visibility of subscriber location, service quality, and application usage.