CPRI Fronthaul Solutions

Migrating to Cloud-Based RAN Fronthaul

Escalating bandwidth demand in the mobile network due to the proliferation of smart devices is driving upgrades to the Radio Access Network (RAN). The cost to build, operate and upgrade the RAN is increasing, while the revenue is not growing at the same rate.

Power and equipment space are expensive resources at cell sites, so Mobile Network Operators (MNOs) are looking to reduce these ongoing expenditures and maximize Return on Investment by enabling more dynamic use of network resources. To reduce infrastructure costs, MNOs are migrating from expensive, high-power base stations to the Heterogeneous Network (HetNet) that includes Femto cells, Pico cells, Metro cells, Distributed Antenna Systems (DAS) and Cloud-based Radio Access Networks (C-RAN).

The traditional cellular network architecture is illustrated in Figure 1. The Backhaul RAN connects to the Base Station Transceivers (BTS) / nodeB with RF, Baseband and Transport Layer functions located at each cell tower. The BTS/nodeB is connected to the antennae with coax cabling.

Migrating to C-RAN

Figure 1: Traditional Mobile Backhaul RAN Architecture

In the C-RAN architecture shown in Figure 2, the Base Band Unit (BBU) with Baseband and Transport Layer functionality is deployed with a Base Station Controller (BSC) at a consolidated location like a Central Office or BBU hotel.  The BBUs are connected to the Remote Radio Head (RRH) with fiber instead of coax, and this link is commonly referred to as fronthaul.  The fronthaul from the BBU to the RRH uses a Digital Radio over Fiber (D-RoF) protocol such as Common Public Radio Interface (CPRI) or Open Base Station Architecture Initiative (OBSAI). The RRH is collocated with the antenna at the top of the cell tower.

Cloud RAN

Figure 2: C-RAN Architecture with Fronthaul

The BBU functionality can also be consolidated at a nodeB macro tower, with fronthaul links distributed from the nodeB location to other macro towers in a hub and spoke or ring architecture.
Consolidating equipment at the BSC or at the central office lowers deployment costs and operations expenses by reducing the power requirements and the space constraints at the cell site. The collocated BBUs also simplify the X2 interface and improve the performance with no transmission delay among the BBUs. The C-RAN architecture also reduces the equipment costs at the DAS location.


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