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Distributed Antenna Systems, Remote Radio Headend, and Compact Base Stations: What’s the Difference?

Posted on Jul 14, 2011 by Frank Rayal
Tagged as: base stations, das, mobile backhaul,

I often get asked the difference between Distributed Antenna Systems (DAS)/Remote Radio Headend (RRH) systems and compact base stations. Both topologies allow network operators to mount the radios close to the subscribers on small public utility infrastructure assets like light poles. Both are used as capacity solutions to address hot spots. So, what are the differences and more importantly when should they be used?

From an architecture perspective DAS and RRH are similar in that the baseband processing of the base station is centralized in one location while the radio modules are distributed to locations where coverage or capacity is required. In both, optical fiber is used to run very high data rates and high capacity backhaul needs to be available at the location of the baseband units.  DAS includes RF-Optical converters as an add-on module while the RRH is inherently based on optical technology and does not require a converter.

Compact base station architecture integrates the baseband processing with the radio module, and in that sense the baseband is distributed, along with the requirement for backhaul. Compact base stations require transport connectivity using traditional backhaul techniques that run at significantly lower data rates than the streams running on the fiber cable of DAS/RRH systems. This means that wireless backhaul as well as fiber are possible transport solutions. For example, OBSAI RP3.01 runs at rate of 3 Gbps while the compact base station backhaul needs to run at a maximum of the access technology peak throughput (e.g. 225 Mbps for 2x20 MHz LTE compact base station).

So, now that we outlined the basic system architecture and network topology, when should we use DAS/RRH and when should we opt for compact base stations? To answer this, I have developed a simple conceptual framework that I outline below.

But first, I like to stress that DAS/RRH and compact base stations are not necessarily competitive solutions, rather, they are complementary ones. Specifically, backhaul is a major factor in determining which solution to use. Second, I like to focus on the scenario of wireless backhaul of compact base stations because if fiber were available, then the business case would be close to that of DAS/RRH.

The framework is summarized in the table below where the number of nodes (i.e. radio locations) and length of fiber runs is considered. For high density of nodes, such as a deployment in outdoor stadium setting, DAS/RRH systems are more economical since wireless backhaul cannot effectively provide sufficient capacity to every remote node in such close quarters. However, when fiber runs are long and the density is relatively low, such as urban and suburban streets and areas, compact base stations provides a more cost effective solution: the cost of fiber is eliminated and wireless backhaul provides sufficient capacity as nodes allow non-overlapping wireless backhaul frequency reuse.

DAS have seen some recent popularity as they extend the coverage and capacity of legacy base stations while RRH systems are a new evolution of base station design that further reduces cost. Both systems excel in areas where ultra-high density of nodes is required. Compact base stations represent a further evolution of base station architecture where baseband is decentralized thereby reducing backhaul requirements in the process. Compact base stations with NLOS wireless backhaul are a cost effective solution in deployments where the cell density enables sufficient backhaul frequency reuse isolation. This is exactly where DAS/RRH solutions cannot compete effectively because longer fiber runs are required. Hence, DAS/RRH and compact base stations are complementary solutions in different deployment scenarios.