|« Evolution to C-RAN Architecture (II) Motivation||CEE CEE for the Balkan Region »|
With the advent of smart devices, cloud services, newer technologies for fixed and wireless connectivity and very impatient consumers,there is tremendous pressure to strengthen the access and mobile backhaul segment of the network. The copper and microwave connections to the towers can no longer endure the exploding capacity requirements. Fiber is fast becoming the de-facto solution to meet these demands.
While fibers are mostly being deployed in the backhaul networks, which interconnects the baseband unit (BBU) to the core network, a novel approach of building flexible mobile networks has been pushed forward since a couple of years where fiber is also used from the base station to the antenna, which is called fronthaul. Traditionally, the BBU and the remote radio head (RRH) are collocated inside a cabinet close to the antenna and a coax cable is used to connect the RRH to the antenna located at the top of the cell site.
With migration to fiber based connection, the RRH is placed close to the antenna at the top of the cell site and connected to the BBU. Fiber overcomes any limitation imposed by Coax, such as distance, weight and energy. Due to the possibility of longer reach with fiber optics, one can design the fronthaul network with centrally located base station at a central office equipped with the number of baseband units for several base stations.
The architecture with the stacked BBUs at the central office or hostel to form a centralized BBU (C-BBU) is referred to as centralized architecture. This architecture aids in easy maintenance at the single location and provides improved security (no cabinets to break into) and reduces energy utilization. Furthermore, in LTE networks, the collocation of BBUs simplifies the X2 interface and also makes the associated latency and synchronization issues insignificant. The X2 interface provisions information exchange between BBUs for smooth handover and coordination.
While the connection between each RRH and BBU can be deployed with a dedicated fiber, the most efficient way would be via the deployment of wavelength multiplexing over a single fiber. An active wavelength division multiplexing (WDM) solution in fronthaul would have stringent signal synchronization requirements. Additionally, space and power limitation would dominate the design of the active system based network.