Cloud Radio Access Networks (C-RAN)

In C-RAN, the radio access network (RAN) functionality is moved to the cloud computing infrastructure. Remote radio units (RRU) of different cells are connected to the cloud via a high speed front-haul link, such as a fiber network. Unlike classical cellular system where a baseband processing unit is deployed in each cell cite, C-RAN has a central processing system in the cloud. This architectural change has a number of advantages. RRU’s have much less energy consumption and require less CAPEX and OPEX than traditional basestations. Due to centralized processing, C-RAN provides flexibility in terms of signal processing complexity and coordination among cells and networks such that resources can be used efficiently. Network densification with low power cells provides high capacity especially in hotspots. However, in this scenario, interference is the biggest challenge. Hence, inter-cell coordination and joint processing, which are inherent to C-RAN, are vital to achieve the maximum capacity gain. C-RAN  is likely to be one of the key solutions enabling large scale 5G networked MIMO systems. In addition to capacity, C-RAN can be applied to improving the availability and resiliency of the wireless networks, paving the way toward ultra-reliable communications. In case of dense small-cell networks controlled by C-RAN, the impact of failure in one of RRU can be easily mitigated by reconfiguring the network topology. Also the augmented interference control facilities can improve the link reliability.

C-RAN is the new way of thinking about radio network architecture. The new architecture has limitations that do not have counterparts in legacy systems. Some of the bottlenecks are

• Requirement of high speed fronthaul link between RRU and base band unit
• Data flow between the network nodes operating in the same servers needs some architectural support
• Signal processing algorithms that bind together multiple base stations in the same server have to be dimensioned for balancing data copying and data processing
• For the Radio Access Networks to fully benefit from advancements in cloud technology and economies of scale, the amount of features requiring real-time computing or special purpose hardware should be minimized.

In order to solve those challenges Aalto C-RAN research group has developed a testbed that brings together software defined radio (SDR) and cloud processing. SDR implementations that can run on general purpose processors have an advantage over real-time embedded implementations.  Namely, they can immediately benefit from all the advances of cloud computing without the need of using special purpose hardware. The drawback of using general purpose platforms is timing uncertainty that can lead to occasional loss of base band processing packets.

We have developed the network solution that hides real time issues from the base band processing.   The platform mitigates the effect of missed real time deadlines by using specific hardware abstraction and enhancement layer. In our approach the radio system developers do not have to deal with the radio transmission related real time issues. The platform is easily programmable network testbed.

Implementation

We have developed a software radio network testbed that can operate over the air and radio network or as simulation platform. The testbed separates radio interface development and process scheduling and management in the host computer.

The platform is designed for research of radio resource management in mobile networks. The platform provides environment for synchronous frame based communication. Frame timing and synchronization is done mainly by Dispatcher and RRU driver functions.  Preparation of radio frames is handled by processing pipes. Inside the pipe a programmer does not have to handle timing related issues.
Cloud-RAN for Indoor Distributed Antenna Systems - on YOUTUBE:
(embed)

https://www.youtube.com/watch?v=0POKCtAzb3E&feature=em-upload_owner