Superior radio performance at the lowest cost using Centralized RAN

Service providers in the US have spent more than USD 241 billion on radio spectrum since 1995. This is a huge challenge for the industry and mobile service providers are constantly striving for superior network performance while seeking ways to reduce operational costs. It is becoming increasingly evident that radio frequencies, as Ericsson’s CTO predicted in a 2015 CES conference, are destined to become the scarcest resource on the planet, even more so than oil.

A sizable portion of a network's operational expenses (OpEx) can be attributed to several factors, such as exorbitant rental costs, daily operations, and energy consumption. To address these challenges and pave the way for a more efficient and cost-effective future, the concept of C-RAN has emerged, and it’s a game-changer.

In this blog, we’ll explore how C-RAN architecture offers enhanced spectral efficiency while effectively lowering costs for mobile service providers.

Centralized RAN

The “C” in C-RAN can mean different things to different people: centralized- or cloud-RAN. For this blog we focus on the centralized radio access network architecture, C-RAN. According to a recent survey by Heavy Reading, 84 percent of service providers expect that over 20 percent of RAN sites will be centralized by the end of 2025. Centralized RAN consolidates the baseband unit (BBU) processing or RAN compute resources of a cluster of cell sites in a central hub location. It uses a high-capacity, low-latency fronthaul network in front of the baseband to transport all the radio common public radio interface (CPRI)/enhanced common public radio interface (eCPRI) traffic from the antenna site to the C-RAN hub. 

Centralized RAN provides multiple advantages for service providers including higher spectrum efficiency, improved scalability and flexibility, hardware pooling, energy efficiency, simplified maintenance and upgrades, site simplification, lower costs with dark fiber, enhanced security, and future-proof capabilities.

Centralized RAN advantages

The advantages of C-RAN are:

• Higher spectrum efficiency and performance is achieved by tightly coordinating the centralized BBUs or Cloud RAN servers across different bands, locations, and macro/small cells using features like elastic-RAN (E-RAN) for long term evolution (LTE) and advanced radio coordination (ARC) for 5G.

  C-RAN tight coordination deployment results

  4G Today	5G Today	5G Future
  Elastic RAN Downlink Carrier aggregation 43% higher DL throughput measured in European operator small cell area Uplink Coordinated multi-point 50% UL throughput cell edge gain measured in Asian operator network 60% lower UE power measured in US operotor network	Advanced RAN Coordination Downlink Carrier aggregation Higher peak rate Coverage extension 58% Cell range increase measured in Australian operator network	Advanced RAN Coordination NR Multi-TRP features New opportunities to improve performance by using multiple transmission and reception points

• Scalability and flexibility are enhanced in centralized RAN as BBUs/servers can be easily scaled up, enabling efficient network expansion. C-RAN enables the pooling of hardware resources such as baseband and backhaul equipment among multiple low-capacity radio sites.
• Energy efficiency is a significant advantage of centralized RAN as it leverages less hardware and the more efficient power and cooling systems of central office environments, resulting in reduced energy consumption and operational costs compared to outdoor enclosures.
• Streamlined maintenance and upgrades with centralized operations, reduce the need for frequent field site visits and minimizes network downtime. Additionally, optimized installation and turn-up resources contribute to efficient network deployment and cost savings.
• Simplified site acquisition as the antenna site is simplified. C-RAN reduces the cell site footprint, cooling and battery backup leading to lower lease costs, especially in areas where site space is limited or expensive.
• Lower monthly recurring costs are achieved by replacing “lit fiber” backhaul services to connect the cell sites with fronthaul over dark fiber.
• Enhanced security is achieved in centralized RAN by protecting the centralized BBU/server pool within controlled environments, mitigating the risks of unauthorized access and physical damage.
• The future-proof design of having all radio traffic and facilities in a single hub makes it easier for a transition to architectures like cloud RAN. The centralized hub of a cloud RAN, typically located in a data center environment, aligns well with the concepts of centralized RAN, enabling a smooth migration to future cloud-based network infrastructures.

In conclusion, centralized RAN brings numerous benefits to mobile service providers, including improved spectrum efficiency, scalability, hardware pooling, energy efficiency, simplified maintenance, site simplification, cost savings with dark fiber, enhanced security, and future readiness. Implementing a centralized RAN architecture allows service providers to optimize their networks, reduce expenses, and prepare for upcoming advancements in wireless technologies.

• Higher spectrum efficiency/higher performance
  • Tighter (E-RAN, ARC) coordination across co-located BBUS for superior performance
  • Co-locate Macro with Small cell BBUS
• Improved Scalability and Flexibility
  • Easier to scale up centralized BBUS
• Hardware pooling
  • Allows BBU resources to be shared across multiple low-capacity radio sites
• Energy Efficiency
  • Power/cooling is more efficient in centralized CO environment vs outdoor enclosures
• Simplified Maintenance and Upgrades
  • Maintenance and software upgrades can be performed centrally, reducing the need for site visits and minimizing network downtime
  • Installation vs turn-up resources 
• Site simplification - Lower site lease costs
  • Smaller remote footprint for lower lease costs
• Lower cost with dark fiber
  • Lower monthly recurring costs vs lit fiber 
• Enhanced security
  • Centralized BBU pool is easier to protect
• Future proof
  • Easier transition to (centralized) Cloud RAN 
  • Hub is easier for a datacenter environment

Centralized RAN challenges 

There are several challenges to the successful implementation of centralized RAN implementation, which are: 

• Finding adequate hub space and facilities within short fiber reach of a cluster of cell sites, poses a hurdle for C-RAN implementation. Sufficient space is required to accommodate the BBUs or cloud RAN servers that serve as the central processing units of the network. Similarly, it can be challenging to have fiber availability at and connectivity to suitable hub sites.
• The risk of a single point of failure is a significant concern with C-RAN. If the C-RAN hub experiences a failure, it can impact multiple radio sites connected to it, potentially leading to a substantial network outage. Implementing redundancy measures and ensuring the resilience of the hub infrastructure are crucial to mitigate this risk.
• Higher upfront costs may be required for fronthaul transport and dark fiber. The expense of transporting data through fronthaul over dark fiber needs to be evaluated against the overall cost-effectiveness of C-RAN deployment in the long run.
• The complexity of the fronthaul network design further complicates C-RAN implementation. Designing the fronthaul network necessitates meticulous consideration of factors such as latency, capacity, and synchronization to ensure optimal network performance. Achieving the right balance among these requirements can be intricate and may require specialized expertise.

Overcoming these challenges is crucial to leveraging the benefits of C-RAN and ensuring its successful integration into wireless networks. 

• Limited Deployment Scenarios
  • For high capacity densely populated areas
  • Dark fiber, <15km,
  • Capacity requirements limits microwave
• Hub space & facilities
  • Space for basebands/vDUS
• Single Point of Failure
  • Hub failure impacts many radio sites
• Higher fronthaul vs backhaul transport cost
  • Higher transport costs vs long-term savings
• Complexity in Fronthaul Design
  • Latency, Capacity, Synchronization

C-RAN typical deployment scenarios

C-RAN is most effective in high-capacity, high traffic areas where the demand for data is substantial. The coordination functions enabled by C-RAN are more effective in cell site clusters with low inter-site distance and high coverage overlap, or when neighboring sites serve different bands, such as small cells in a macro coverage area.  

Additionally, the strict latency requirements of the fronthaul interface necessitate short direct dark fiber connections with a typical maximum distance of 15-20 kilometers between the cell site and the hub. For these reasons, typical C-RAN deployment scenarios include dense urban environments, outdoor venues and stadiums, airports and transportation hubs, and college campuses. 

C-RAN fronthaul transport

C-RAN fronthaul transport is essential for efficiently transmitting high-capacity CPRI/eCPRI radio data between remote radios and centralized RAN compute processing units in a centralized architecture. There are two main approaches: optical fronthaul and packet fronthaul. 

Optical fronthaul utilizes wave division multiplexing (WDM) to multiplex different colored CPRI or eCPRI signals onto a single fiber strand. It offers a low latency connection and its cost scales with the number of radio signals to be transported. Optical fronthaul is a mature, reliable technology that requires minimal maintenance. It is relatively easy to introduce across the RAN and transport organizations. 

Packet fronthaul, on the other hand, transports radio signals over a packet network. A fronthaul gateway converts radio CPRI interfaces into a packet eCPRI stream and combines it with the native eCPRI packet traffic from massive MIMO radios. The advantage of using a fronthaul gateway is that the conversion is done only once and the eCPRI traffic connects directly to a virtual distributed unit (vDU) server or BBU. eCPRI scales with user traffic and it saves up to 80 percent in bandwidth. It typically requires only a single 100 gigabit Ethernet (GE) eCPRI connection between a high-capacity macro site and the C-RAN hub. Packet fronthaul provides greater flexibility and automation potential as radio traffic can be redirected to different BBUs or vDUs using switches or routers. However, a packet fronthaul network requires careful network design to consider the delay and synchronization time errors introduced by each node in the network. 

C-RAN fronthaul transport can use both or a mix of optical fronthaul and packet fronthaul. Each approach has its advantages and considerations, and the choice depends on factors such as cost, latency requirements, scalability, and network design complexities. 

Ericsson 5G Transport includes both options with the optical Fronthaul 6000 portfolio and the packet fronthaul using the Router 6000 portfolio. Hybrid architectures can be created by combining packet fronthaul with wavelength division multiplexing (WDM). One example is to directly connect eCPRI small cell radios with WDM-based passive fronthaul to a packet fronthaul switch/router that uses colored optics. This switch/router then aggregates the traffic before connecting to local BBUs or vDUs.

Ericsson fronthaul transport portfolios

Optical Fronthaul

Fronthaul 6000

• Active & Passive fronthaul
• Indoor & Outdoor
• Fixed & self-tuning optics

Packet Fronthaul

Router 6673 Fronthaul Gateway

• CPRI > eCPRI conversion, RoE

Router 6678 for 100GE hubs

• 4.8Tbps, 30 x 100GE and 4 x 400GE

Conclusion

The centralized radio access network (C-RAN) architecture presents significant advantages and challenges for mobile service providers. By centralizing baseband processing or RAN compute resources, C-RAN enables higher spectrum efficiency, improved scalability, hardware pooling, energy efficiency, easier maintenance, site simplification, cost savings with dark fiber, enhanced security, and future readiness. These benefits contribute to optimizing network performance, reducing operational costs, and preparing for advancements in wireless technologies.

Main centralized RAN benefits

Superior performance

• Tighter coordination between co-located BBUs
• Macro - Small Cell

Scalability flexibility

• Easier to scale
• Re-optimize BBUs

Lower TCO

• Smaller footprint
• Easier maintenance
• High power efficiency
• Centralize hi-skilled resources
• Potential pooling gains

Future proof

• Steppingstone towards Cloud RAN
• Easier to re-optimize RAN compute resources

However, the implementation of C-RAN also poses challenges. Limited deployment scenarios, hub space and facilities requirements, the risk of a single point of failure, higher fronthaul transport costs, and the complexity associated with frontrunner design are among the hurdles that must be addressed. Overcoming these challenges is crucial to ensuring the successful integration of C-RAN into wireless networks and fully leveraging its advantages.

Planning for successful centralized RAN deployments

In terms of fronthaul transport for C-RAN, both optical fronthaul and packet fronthaul are viable options. Optical fronthaul utilizes WDM to multiplex CPRI/eCPRI signals, providing low latency and minimal maintenance. Packet fronthaul, on the other hand, transports radio signals over a packet network, offering greater flexibility and automation potential. The choice between these approaches depends on factors such as cost, latency requirements, scalability, and network design complexities. 

Overall, the adoption of a centralized RAN architecture holds great promise for mobile service providers. It offers a path toward enhanced network performance, cost reduction, and future-proof capabilities. By carefully addressing the challenges associated with C-RAN implementation and selecting the appropriate fronthaul transport solution, service providers can unlock the full potential of this architecture and pave the way for a more efficient and cost-effective mobile network ecosystem. 

Explore C-RAN for your network. See how you can prepare for the future with superior performance at a lower cost.

For more information

• Exploring new centralized RAN and fronthaul opportunities
• How to pick the best Fronthaul technology for your C-RAN network
• Optical Fronthaul
• Packet Fronthaul

Reference

CA benefits (Power of 5G Carrier Aggregation Solutions - Ericsson ) 

C-RAN advantages (Exploring new 5G CRAN and fronthaul opportunities - Ericsson).