Cloud RAN, sometimes abbreviated C-RAN, has been a topic in macro mobile networks for several years now. Wikipedia describes C-RAN as “a centralized, cloud computing-based new radio access network architecture.” Vendors began actively promoting macro C-RAN products this year, and a new company, Altiostar, was launched around this premise alone.
But C-RAN is also relevant to small cells, and in particular enterprise small cells. In 2014, the Small Cell Forum announced an ecosystem-wide effort to understand how small cells fit into C-RAN. These moves signal an important shift in the way indoor wireless coverage is delivered, and this architecture presents an opportunity for dramatic cost reduction for operators, neutral hosts, property owners and enterprises.
That’s why we believe 2015 will be the year in which CRAN becomes the default architecture for enterprise and public venue small cells.
What is a C-RAN small cell?
C-RAN small cells can be most broadly defined as having a centralized baseband that is pooled across a large number of distributed access points. This provides significant management and self-organizing network benefits compared to a cluster of standalone small cells. However, some C-RAN small cells go far beyond this, and support these other key attributes:
1. Coordination between radios – while the baseband processing is centralized, some intelligence also must reside in the radios for coordination between multiple radios that serve the same user. This is in contrast to remote radio head or distributed antenna systems that have no such coordination.
2. Baseband pooling – baseband radio processing is centralized and pooled across a large number of distributed access points. This enables the system to create a single cell from a network perspective, as opposed to many individual standalone cells.
3. Ethernet fronthaul – IP over Ethernet is long established as the in-building infrastructure of choice, so C-RAN for small cells needs to leverage standard Ethernet switches and cabling. This is in contrast to macro cloud RAN approaches that typically use CPRI over fiber connections between the centralized base station and radios.
4. Single cell operation – the radio points act as one large cell, which thereby eliminates handovers and simplifies interactions with the macro network, rather than all the complexity of 10s or 100s of individual small cells in a given enterprise.
Solving key problems for LTE in the enterprise
C-RAN small cells have considerable advantages for enterprise small cell deployments, which is more important than ever as enterprises increasingly look to deliver reliable indoor wireless coverage to users. The creation of a single cell ensures a superior user experience by eliminating border interference. In side-by-side tests, eliminating small cell borders has been shown to increase data throughput by up to 10-times, while reducing latency by a factor of five, which is critical for voice over LTE quality. Coordination between the radios allows for techniques like downlink and uplink combining, and distributed multiple-input, multiple-output, which increase data speeds and reduce the number of small cells required.
Implemented properly, C-RAN small cells are simple and economical to deploy. The elimination of cell borders greatly simplifies radio frequency planning since there is no concern about interference between access points. C-RAN also simplifies frequency coordination and SON with the macro network since the macro “sees” a C-RAN small cell installation as a single physical cell rather than as tens or hundreds of individual cells. This also enables handsets to leverage interference cancellation (which can only cancel one or two interferers) and improves battery life.
The use of standard Ethernet cables and switching reduces both material and installation costs compared with DAS that require coaxial cabling, coupler and splitters and remote amplifiers. Even recently launched RRH architectures still require CPRI over fiber interfaces and typically only support eight antennas per RRH. C-RAN small cells also present an opportunity for an operator to share the cost of in-building deployments with an enterprise, but at a much lower cost than other solutions, for much broader enterprise penetration. We’re already seeing that many enterprises are willing to make such an investment.
C-RAN is also a multi-operator friendly architecture. Since the functionality is concentrated in the central baseband controller, the remote radio points are relatively compact and therefore can affordably support multiple bands. And a single Ethernet infrastructure can be shared among multiple operators or with other services like wireless local area networks.
Finally, C-RAN small cells can provide a high degree of investment protection. Standalone small cells are typically optimized for low cost and upgradeability is limited by their chipsets. With a C-RAN approach, the functionality is concentrated in the more powerful baseband controller. The central controller can be software-upgraded without affecting the radio points, thereby avoiding the cost of having to swap out the radio point equipment throughout the building.
Why C-RAN small cells now?
If C-RAN small cell is such a great idea, why is the industry only getting around to it now? Several factors have recently converged to make them both viable and necessary. Silicon keeps getting faster, making it now possible to pack the power of a macro base station into a 1U-sized cloud RAN small cell central controller.
The rapid deployment of LTE and the shift in focus towards high-speed data performance and capacity are also factors. While a C-RAN architecture is theoretically beneficial to any radio technology, maximizing LTE air link performance and capacity, as well as supporting LTE-Advanced features like distributed MIMO and coordinated multipoint require C-RAN’s coordination between radios. On the heels of LTE, VoLTE is also being rapidly deployed and this too would be difficult to support in large indoor spaces using traditional small cell architectures, due to the inherent interference and latency issues mentioned previously.
All of these things are happening against the backdrop of continuing growth in mobile data consumption. According to the Cisco Visual Networking Index, mobile data usage will grow 67% from 2014 to 2015, and continue at this clip for the foreseeable future. In 2015, C-RAN small cells will emerge as an important tool to help operators to respond to this insatiable demand.
Editor’s Note: With 2015 now upon us, RCR Wireless News has gathered predictions from leading industry analysts and executives on what they expect to see in the new year.
