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Fronthaul/C-RAN

Time for Some New Acronyms for CRAN

Lunchtime "debating tables" -- I'm sure you've seen them at conferences. At a recent event, I was drawn to a table where the conversation was unusually animated. The subject was "CRAN" and I was intrigued to find out why this topic was generating so much disagreement. Out of the eight or nine people at the table, there were at least four or five different interpretations of exactly what the term CRAN means.

The industry is clearly deploying this technology in multiple phases, however, given all the various definitions of CRAN, where exactly are we as an industry? Also, what are some of the major challenges that need to be addressed, both technical and commercial, before service providers worldwide can reap the full benefits of this aspect of network virtualization?

From a business perspective, all the approaches to CRAN are intended to reduce capex and opex for service providers. By centralizing and then virtualizing processing functions that were traditionally performed by dedicated networking equipment located at the antenna sites (cell sites), CRAN enables the cell site to be simplified to where it's just the radio unit comprising power amplifiers, filters and the antenna. The cost of the baseband and call processing functions drops dramatically thanks to COTS hardware and virtualization. Simultaneously, the risk of network downtime is reduced and the overall experience for subscribers is improved.

If we consider the installed base of CRAN equipment, it's clear that this technology already represents a significant share of overall telecom spending. A recent Infonetics Research Inc. report estimates that revenue from CRAN architecture equipment was $4.9 billion in 2014, up from $4.1 billion the previous year, and projecting $10 billion by 2018. So far, the majority of deployments are in Asia, with rollouts to start in Europe, Latin America and North America this year.

The business benefits are compelling: SNS Research reports that China Mobile Ltd. (NYSE: CHL) has shown a 30% reduction in capex and a 53% reduction in opex in its CRAN trials.

The flavor of CRAN most widely deployed today is the traditional Centralized RAN architecture. In this approach, the basestation (BTS) is decomposed by decoupling its remote radio head (RRH) at the cell site from its baseband unit (BBU). Multiple RRHs are connected to a single, shared BBU over dark fiber, via a "fronthaul" interface that is either Common Protocol Radio Interface (CPRI) or Open Basestation Architecture Initiative (OBSAI). Separating the RRHs from the BBUs reduces the cost (both capex and opex) of the equipment at the cell site. Depending on the level of aggregation, it brings some economies of scale to the BBU, the cost of which is also reduced whenever it's located indoors.

In the next phase of consolidation, several such BBUs are grouped together and aggregated to form a Centralized BBU (C-BBU). Within the C-BBU, processing resources are pooled and allocated based on RRH traffic. Often, a C-BBU will support both residential and business areas, with resource allocation adjusted dynamically as traffic patterns change during the day. This solution is limited to small clusters of RRHs because complexity increases exponentially with larger clusters of RRHs. It yields significant some cost savings compared to the basic centralized RAN approach where BBUs in both residential and business areas must be sized for peak traffic.

The next step is a true Cloud RAN architecture in which the centralized BBUs supporting large clusters of cell sites are virtualized. These "vBBUs" can be instantiated on standard COTS server platforms rather than on dedicated custom, fixed-function equipment from traditional RAN vendors. Depending on the approach, the fronthaul transport provisioning may require very high bandwidth and ultra-low latency, or nominal bandwidth and low latency or nominal bandwidth and relaxed latency. Also, computational efficiency is a major concern in some of the approaches.

The challenge of computational efficiency was addressed in a European Telecommunications Standards Institute (ETSI) proof-of-concept involving Alcatel-Lucent (NYSE: ALU), China Mobile, Intel Corp. (Nasdaq: INTC) and Wind River Systems Inc. , which was completed last year. This showed that it's possible to meet the stringent real-time requirements of both TD-LTE and GSM systems using virtualized infrastructure. It also illustrated that it's possible for cloud RAN to maintain the level of reliability required for telecom infrastructure, which was demonstrated by performing functions such as live migration of LTE streams without service interruption.

The next major step in operational efficiency will come from the integration of virtualized Cloud RAN "vRAN" into the system-wide Network Functions Virtualization (NFV) architecture standardized by service providers through the ETSI initiative. vRAN resources can be dynamically optimized, scaled and orchestrated as part of the overall NFV cloud. This brings service providers the benefits of service agility and opex reductions, along with the resilient infrastructure that is expected from telecom networks.

So it's no surprise that the discussion at my lunch table was so animated. Essentially we were having parallel discussions about Centralized RAN, Centralized BBU, Cloud RAN and virtualized Cloud RAN, all under the umbrella topic of CRAN.

It's clear that all these variants of the CRAN concept have the potential to deliver major capex and opex savings in the network, while ensuring that end users experience the seamless coverage and high bandwidth that they expect. Each of these approaches can help to reduce customer churn and keep network costs under control, while NFV promises the agility that will enable the delivery of new, value-added services to drive revenue growth for service providers.

— Charlie Ashton, Director of Business Development, Wind River Systems Inc.

MichaelG951 6/9/2015 | 1:28:14 PM
Coordinated RAN Hi Charlie,

Another acronym you should add is "Coordinated RAN".

Fronthaul enables very tight coordination allowing LTE-A capabilities such as Uplink Coordinated Multi-Point. UL CoMP improves uplink throughput via increased received signal power and interference suppression by combining antenna signals from multiple sector carriers belonging to different cells. With a Coordinated RAN, the biggest benefits are for the users at the border between the macro sector and the small cell with increased cell edge bitrate of 50-100% at high load ((5th percentile) and an increased system capacity of 50-100%.

Best regards,

Michael Gronovius
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