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. |