The Evolution of Fronthaul Networks: Pt. 1 – An Introduction
Fronthaul? Until few years it was unknown for most involved in network deployment. Smart phones, the explosive growth in use of media reach apps and the competitive pressure for operators to offer higher data limits have changed the role of fronthaul completely. One can hardly oversee the rising number of antennas and radios mounted on towers and rooftops in rural or metro areas. They need to be fed with power and, yes, fronthaul. In this blog series, we will talk about the evolution of fronthaul networks from the recent past to a future that will make the role of fronthaul even more critical to delivery of broadband services, but also Internet of Things (IoT) applications such as driver-less cars, smart meters and many other life changing network applications in the “5G” world. I will cover technology elements, common problems in deployment and best practices for their prevention and troubleshooting.
Fronthaul network refers to the part of the network that connects base band units BBU (aka digital units DU) to remote radio heads RRH through fiber (Figure 1).
The opposite side of the BBU connects it to the enhanced packet core (EPC) network typically located in central offices and constitutes the backhaul network. The RRH is further connected to an antenna element at the top of a tower or roof top with a coaxial cable. The RRH can be placed closer to the BBU at the ground level, or near the antenna on a tower. Placement near the antenna makes the system more energy efficient as it reduces the amount of power loss on coaxial power. However, there might be limitations for placing RRH near antennas due to proximity to power lines, concerns for wind loading, or preference for easier maintenance of RRH when they are placed near the ground level. Majority of systems place the RRH near the antenna. There also remote radio units with integrated antenna systems (Figure 2). In older systems (BTS, NodeB), the “BBU” and “RRH” were in the same location and chassis (Figure 3).
The overwhelming majority of fronthaul networks reside in the same location at a cell site, and hardly noticeable. However, the rising demand for placement of RRH on roof tops, stadiums and utility poles poses a new challenge for operators. Where do we place the BBU? It needs power and environmental control. This requirement is one of the reasons for increasing use of centralized or cloud Radio Access Networks (CRAN) where the BBU are placed in central locations and connected to a network of RRU that can be placed miles away. These connections can be implemented by means of dark fiber, Wavelength Division Multiplexing (WDM), or other aggregation technologies.
There are alternative or complementary technologies to fronthaul for coverage in remote locations or capacity in indoor applications. Metro cells, femto/nano/pico cells typically use an Ethernet connection to a host macro site. There are also referred to as small cells and include a BBU and RRH in one enclosure (Figure 4). They have lower power and processing capacity and can serve smaller coverage areas with small number of simultaneous users. Another technology deployed is Distributed Antenna Systems DAS. It has been deployed for many years in dense indoor application such as stadium, larger buildings and partially outdoor applications. They connect an array of antennas to base band units through a combination of coaxial and fiber connections, and may use standard or proprietary transport protocols.
If you would like to read more, please read my white paper, The Evolution of Fronthaul Networks.