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Table 2 Current and future state of C-RAN

From: Realizing 5G vision through Cloud RAN: technologies, challenges, and trends

Concept Challenge Today Future
Software-defined networking Architecture redesign Straightforward architecture using wired technologies (i.e., Ethernet) for interconnections. Complex architecture using wireless technologies. Radio environment affects link reliability and quality.
  Controller placement Controllers are strategically placed in order to minimize latency. Increasing the number of controllers also increases control overhead. Wireless communications introduce additional requirements in placement. Also, reliability becomes more critical because of the heterogeneity of the wireless environment.
  Cognitive radio integration Controllers maintain a high-level network intelligence to achieve better network control. Network control is enhanced by adding radio environment intelligence to controllers.
  Mobility management As the current SDN is used for conventional wired networks, there is no need for mobility management. Mobility management is important, as users should experience minimal disruptions in their communications.
Network and function virtualization Performance optimization Hypervisors such as Kernel-based Virtual Machine (KVM) and Xen [99] are used for virtualizing resources. Utilize hypervisors optimized for extremely low overhead and latency.
  Network isolation Each virtual network configuration and customization is independent from others. Each virtual network configuration and customization is independent from others.
  Resource allocation Virtual machines access the physical resources through the hypervisor. Computation, storage, and network resources are the most common physical resources. Spectrum availability is an additional resource feature that has to be managed. Moreover, device mobility makes resource allocation more challenging.
  Slice management Slices are scaled depending on service requirements. Slicing in 5G mobile networks is more challenging as there are many operators sharing the same infrastructure and more diverging service requirements.
Fronthaul Data reduction CPRI uses raw I/Q samples, requiring thus huge link capacity. Techniques such as data compression, aggregation, and redundancy removal should be considered.
  Latency reduction and synchronization Mobile communications require synchronization and the lowest possible latency in order to ensure high quality of service. Mobile communications require synchronization and lowest possible latency in order to ensure high quality of service.
  Overhead analysis CPRI has standard control signaling information. The trade-off between control overhead and bandwidth efficiency must be analyzed. It can also be dynamically adjusted depending on the link and network states.
  Novel standards CPRI is not the optimal fronthaul standard for the C-RAN. Novel standards such as ORI should be researched.
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