Cloud RAN and Mobile Edge Computing, a dichotomy in the making: Page 3 of 3

February 24, 2016 //By Harpinder Singh Matharu, Xilinx Inc
Over the past few years, wireless infrastructure deployment has increasingly moved to distributed base station architecture. This architecture centralizes the baseband processing pool, sometimes called super Macro, which is capable of feeding a larger number of radios and therefore is more effective for coverage and load balancing. The concept of Cloud RAN takes centralized base station pool all the way into the Cloud co-located with the content or data repositories in the data center. There are merits in Cloud RAN as it allows use of lower cost compute, leveraging off-the-shelf server chassis for cost effective RAN deployment, load balancing and significant ease in network provisioning. In parallel, Mobile Edge Computing, under the auspices of the ETSI Mobile Edge Computing Industry Standard Group (MEC ISG), is emerging with a concept of placing compute at the edge, co-located with the baseband pool, to maintain a local content cache to provide improved services to users.
5G proposals for the information society of 2020 are adding further twists to the dilemma imposed by the architecture pull between Cloud RAN and MEC. In order to meet projected data demands in 2020 with increasingly scarce and limited spectrum, 5G proposals are aiming to continue to improve spectral efficiencies using techniques such as Massive MIMO for both <6 GHz and >6 GHz spectrums. Massive MIMO systems use large number of antennas to create beams per user. This allows significant improvement in energy efficiency and throughput. An additional benefit of massive MIMO is use of inexpensive lower power components for antenna signal chains. Massive MIMO techniques are well suited for millimeter and centimeter frequencies, an inexpensive and underutilized spectrum resource that is available in large contiguous chunks. Narrow pencil beams at these frequencies result in large antenna gains that compensate for high propagation. Along with these benefits come some hurdles. There is a significant increase in complexity in supporting a large number of active radio signal chains and layer 1 baseband with pre-coding for digital beamforming. Bandwidth requirements increase sharply between baseband processing signal chains and radios. In order to economically realize these systems, it is necessary to integrate layer 1 baseband signal processing with the radio. Such a functional split in the future may lead to network nodes that may go back to traditional base station architecture where all L1-L3 and radio functions are co-located.

Figure 3: Millimeter wave massive MIMO (200 MHz, 64x64 antenna array) system. Click image to enlarge.

Mobile edge computing and massive MIMO techniques may imply consolidation of distributed base stations thereby hindering the move to Cloud RAN. In reality, limited spectrum necessitates leveraging merits of multiple different network architectures co-existing together to meet an ever increasing growth in demand for bandwidth. Cell densification enables reuse of a scarce spectrum resource. In coming years, this trend will result in distributed base station sites to become more like mini data centers. On the other hand, splitting Cloud RAN into numerous mini data center may be a way to overcome tight deterministic latency and synchronization requirements with remote radio head connectivity. The two architectures may appear to converge in the middle. Cloud RAN and MEC architectures can coexist to complement each other. Cloud RAN can rely on latency and the proximity merits of edge computing nodes and edge computing can benefit from centralized network deployment, management, and service provisioning. Only time will tell how these two architectures would see adoption in the next 3-5 years as industry gears up for 5G deployment. End user applications, operator preferences based on cost of network deployment and maintenance, and system solutions from equipment vendors may likely be key factors in dictating a delicate balance between the two.

In summary, heterogeneity in wireless network is expected to continue to increase. There is unlikely to be a clear winner. A good balance of Cloud enabled RAN and mobile edge compute equipment is needed to effectively serve wireless broadband services. Instead of letting the hype pendulum swing to one extreme, the broadband wireless ecosystem needs to make balanced investments to continue to build complimentary technologies to effectively serve the information society of 2020.

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