Legacy RAN vs. Cloud RAN: Key Differences Explained

This article compares Legacy RAN (Radio Access Network) with Cloud RAN (Cloud Radio Access Network), highlighting the key distinctions between the two architectures. We’ll explore the structure of both Legacy and Cloud RAN, along with the advantages offered by Cloud RAN.

Legacy RAN Architecture

Figure 1 illustrates the architecture of a Legacy RAN. As you can see, it relies on distributed RRH (Remote Radio Head) and BBU (Base Band Unit) deployments across a geographical area to provide network connectivity. Each RRH is paired with its own dedicated BBU.

The RRH and BBU communicate using a CPRI (Common Public Radio Interface) link. The BBUs, in turn, are connected via optical links to an IP Aggregation Layer (IPAG) and the Evolved Packet Core (EPC).

Cloud RAN Architecture

Figure 2 depicts a Cloud RAN architecture. Unlike Legacy RAN, Cloud RAN replaces individual BBUs with a centralized BBU (C-BBU). This C-BBU then interfaces with the RRHs using the CPRI interface.

The C-BBU connects to the IPAG via an optical link. This architecture is centralized and based on cloud computing principles.

Cloud RAN supports a variety of wireless standards, including 3G, 4G, and emerging technologies. Its characteristics, such as centralized processing, collaborative radio capabilities, and real-time operation, have led to it being also known as C-RAN. You might also hear it referred to as centralized RAN.

Cloud RAN was developed to address the growing demands on network capacity and enable broader coverage without significant infrastructure expansion.

A logical evolution of Cloud RAN (or C-RAN) is Virtualized RAN (or V-RAN). This features a programmable architecture that is software-definable and tunable. Cloud RAN is often implemented using standard servers and switches for the C-BBU or V-BBU functionality.

XILINX FPGAs and DSP cores are commonly used in the design of Cloud Radio Access Networks. FPGAs allow for easy configuration of the L1/L2 baseband layers to meet the requirements of different wireless standards (2G/3G/4G/5G, etc.). The use of FPGAs also allows for flexible configuration of features such as:

• Ethernet switching
• SyncE IEEE 1588 protocol
• CPRI/10GbE interface/switching/bridging
• Digital radio processing
• CPRI switch for daisy chaining
• L1 (physical layer) processing

Benefits of Cloud RAN

Cloud RAN offers several benefits over traditional Legacy RAN deployments:

• Enhanced Capacity and Coverage: Cloud RAN can improve both network capacity and coverage area.
• Self-Optimization and Adaptability: Using SDN/NFV (Software-Defined Networking/Network Functions Virtualization), Cloud RAN can be self-optimized, self-configured, and self-adaptive based on network needs.
• Reduced Operational Costs: Cloud RAN helps control and reduce operational expenses.
• Improved Network Security: Cloud RAN enhances overall network security posture.