What are C-RAN small cells?
In traditional wireless architectures, each physical base station combines baseband processing and radio functions. With C-RAN (which stands for Cloud RAN or Centralized RAN), the baseband processing for many cells is centralized. Benefits of C-RAN include improved performance due to the ability to coordinate between cells, and also cost reductions as a result of pooling resources.
The C-RAN concept has generally been applied to outdoor macro-cells. However, it can also be applied to small cells that provide distributed coverage across a large indoor space, such as an office building, coliseum or other large venue. CommScope’s OneCell® solution applies the C-RAN architecture principle of baseband centralization to small cells. However, OneCell goes beyond ordinary C-RAN solutions in four important respects:
- It creates a single cell
- It coordinates the functions of multiple radio endpoints
- It uses standard IP Ethernet LANs for fronthaul
- It leverages many other small cell benefits
The OneCell solution’s design yields critical advantages, because it:
- Improves wireless user experience
- Adds capacity without interference via cell virtualization
- Simplifies capacity planning and upgrades
- Reduces macro network interference
- Reduces deployment costs
- Provides a future-ready solution
Improves wireless user experiences
Traditional small cells, when densely deployed across a large indoor space, create large areas of overlap between cells. Interference occurs at these borders. Some enterprise small cells use a central service controller to assist with handovers and backhaul aggregation, but it cannot overcome the physics that each cell interferes with its neighbor. CommScope testing and iBwave modeling have shown that SINR(signal-to-interference-plus-noise ratio) in these overlap zones can drop anywhere from 10 to 25 dB, reducing data speeds by up to 90 percent and impairing VoLTE voice quality.
Creating multiple independent cells also generates the need for frequent handovers, degrading the user experience in introducing the potential for handover failures or constant back-and-forth handovers between adjacent cells—a phenomenon known as “ping-ponging.”
OneCell creates a single cell that eliminates cell borders altogether. It accomplishes this by centralizing the scheduling of users across the Radio Points. Unlike a service controller, OneCell’s Baseband Controller performs LTE resource block scheduling centrally across all the Radio Points and all the users, so it provides a strong signal that is consistent throughout the coverage area—no handovers required.
In addition, each Radio Point has two antennas, so two Radio Points can deliver 4x2 MIMO (assuming the user equipment (UE) has only 2 antennas) or 4x4 MIMO for LTE-Advanced UEs that support four antennas; three Radio Points can deliver 6x2 MIMO, and so on. This distributed MIMO capability is only possible with a C-RAN approach that coordinates activity across multiple Radio Points.
Adds capacity without interference via cell virtualization
Network functions virtualization (NFV) has become a strategic tool for mobile network operators. C-RAN architecture provides an opportunity to go beyond NFV to virtualizing the actual radio resources. C-RAN-enabled cell virtualization lets operators provide higher capacity without introducing inter-cell interference.
CommScope’s OneCell solution creates a single physical cell across a large area to eliminate border interference and handovers. Even so, OneCell is not limited to the capacity of a single cell. Instead, multiple virtual cells can be created within a single physical cell using a breakthrough approach called cell virtualization.
Cell virtualization enables the transmissions of unique user data within the same LTE resources but directed to different radios for different users. The C-RAN baseband unit "knows" the location of each user, so it can determine when two users are sufficiently isolated from one another to serve them at the same time, reusing the same LTE physical resource blocks (PRBs) without risk of interference.
This form of virtualization puts intelligence into the reuse of spectrum rather than the uncoordinated, static reuse of spectrum in traditional small cells. As a result, it achieves the multi-sector capacity of many standalone small cells, with up to a 1,000 percent increase in user data rates at the cell edge—an order of magnitude improvement—through the elimination of border interference. It even improves battery life because the user device need only track a single cell.
It’s no surprise that cell virtualization is a consistent theme in discussions of 5G standards. But the benefits of cell virtualization are available in LTE today with CommScope’s OneCell solution.
Cell Virtualization increases capacity without creating border interference by dynamically assigning PRBs to users every millisecond.
Simplifies capacity planning and upgrades
C-RAN small cells provide capacity benefits beyond those achieved through cell virtualization. In a traditional small cell architecture, each access point provides a fixed amount of capacity for its coverage area. This works well only if usage is evenly distributed across the venue—a condition that rarely holds true. The result is that some access points will be overloaded and others relatively idle.
With the OneCell solution, capacity is pooled in the central Baseband Controller and allocated dynamically to wherever the usage is at any given moment. This makes it possible to handle the natural movement of users throughout an area, and to take full advantage of the system’s capacity.
C-RAN also simplifies capacity expansion. With standalone small cells, the only way to add capacity is to add cells—along with the new cell border overlaps that cause interference. With OneCell, capacity can be added centrally at the Baseband Controller, without creating new cells or cell borders.
Reduces macro network interference
The single-cell C-RAN approach used in CommScope’s OneCell solution helps operators manage and mitigate interference between small cells and the macro network in several important ways:
- OneCell uses a single reference signal, allowing it to avoid neighboring macro reference signals.
- Multiple OneCell Radio Points can jointly transmit to an individual UE, helping overcome an interfering macro signal without having to boost Radio Point transmit power to the extent that it would interfere with the macro network.
- Joint uplink reception means OneCell Radio Points can jointly receive uplink transmissions from a single UE, which are then combined at the controller. This enables the UE to transmit at a lower power, reducing its interference on the macro uplink.
- Inter-Radio Point interference rejection combining enables the Baseband Controller to perform interference rejection combining (IRC) to detect and cancel the signals from a nearby macro-attached UE, minimizing its interference to the OneCell system.
- Interference from a strong macro signal at one side or corner of the building can be remedied by increasing the transmit power of access points, or by adding access points, in the affected area. Because the system forms a single cell, this can be done without creating new interference.
Reduces deployment costs
The C-RAN small-cell architecture of CommScope’s OneCell solution reduces costs throughout the deployment lifecycle. Because OneCell creates a single cell without border interference, it eliminates the need for specialized and tedious radio frequency and handover planning. Likewise, changes to the system design, for example adding or moving Radio Points, are non-disruptive.
Unlike macro baseband unit-based solutions, the OneCell solution uses standard Ethernet LANs and Cat5e cabling for fronthaul. There is no need for proprietary network elements or costly coax or fiber cabling. Radio Points are powered over Ethernet (PoE+), eliminating the need for separate power distribution to antenna sites. This “Wi-Fi-like” deployment model greatly reduces cost and complexity of design, installation and subsequent system changes. Physical installation can be performed by IT people with general LAN installation skills.
As a small cell solution, OneCell has been optimized for high-volume, low-touch deployment. The system is plug and play; the Radio Points and Baseband Controller automatically discover each other and authenticate. OneCell gets its configuration automatically from the CommScope Device Management System (DMS) in the operator’s core network. A suite of self-organizing network (SON) capabilities ensure the system is optimized for its macro environment. As a result, OneCell optimizes all aspects of performance while minimizing the effort, expertise and cost required to design, deploy and maintain the system.
Provides a future-ready solution
CommScope recognizes that in-building networks must constantly evolve in response to growing service demand and changes in technology. OneCell’s C-RAN architecture was designed from the ground up to flexibly accommodate these changes.
OneCell’s single-cell C-RAN architecture makes it easy to add capacity and coverage to existing deployments. Because capacity is pooled in the Baseband Controller, new capacity can be added at the controller without affecting the radio or antenna infrastructure. If coverage needs to be extended to a new part of the building, Radio Points can easily be added where needed. Because they create no new cell borders, the existing infrastructure is not impacted.
OneCell supports multi-carrier and multi-operator deployments. Frequency bands are software-selectable across common hardware. An initial hardware installation can be provisioned for different frequency bands or even different mobile network operators, to support neutral host business models.
OneCell’s Baseband Controller uses a powerful macro-grade chipset that can be software-upgraded to support LTE-advanced features.
OneCell’s C-RAN architecture was designed with the future in mind.