Real-world successes for RAN virtualization
In the 2nd half of 2015, virtualized radio access network (RAN virtualization) or “Cloud RAN” field trials achieved several industry ”1sts” in unique configurations and by meeting performance targets under real-world conditions.
One field trial was conducted with Korea Telecom (KT), and the other with a Tier 1 U.S. operator. Both trials involved a limited-scale LTE RAN deployment spread over radio sites and a central location and were performed under real radio conditions.
To test the ability of a Cloud RAN architecture to perform over long distances, the trial with KT involved an LTE radio site separated from the central site by more than 200 kms. The distance of 200 km between the radio site and the central location has special significance. South Korea is preparing to host the 2018 Winter Olympic Games in a mountainous region called PyeongChang which is located approximately 200 kms away from Seoul.
For its part, the U.S. operator focused on testing standard macro key performance indicators (KPIs) including performance in different parts of the cell and during drive tests.
The primary goal of both trials was to:
- Field test the overall performance of the virtualized baseband processing
- Verify that the split in baseband processing was able to accommodate multiple transport options
Although both operators want to move to 5G quickly and consider a Cloud RAN as a 5G cornerstone, each operator had their own motivations for the trial. Beyond the validation of the architecture they foresee for 5G, KT is exploring fixed-mobile convergence and new service capabilities enabled by virtualization technology.
In the case of the U.S. operator, their main concern was to make sure—by taking accurate KPI measurements—that the Cloud RAN platform delivers the same quality of service (QoS) as their existing LTE RAN when used in real-world RF conditions. That’s important because operators cannot tolerate any kind of QoS degradation when introducing a Cloud RAN in their network.
Making matters more challenging, the test environments were designed like legacy networks rather than ”gold standard” situations. This meant that the Cloud RANs operated in environments subject to typical sources of RF interference.
In South Korea, passive optical network (PON) was used for ”mid-hauling“ over various distances between 10 and 20 kms. As a final field test, the dual site configuration over a distance of 200 km was successfully performed using PON and dark fiber—a 1st for this type of RAN.
Underlining its significance, this achievement was celebrated during KT’s 130 years of telecommunications event. Additional lab tests were successfully performed to fully validate both centralized and Cloud RAN scenarios. KT also field-trialed DNS caching as an edge application running on the Cloud RAN server platform.
Marking another 1st, the U.S. trial involved virtualized baseband processing deployed outside of the lab under real conditions. That meant test cases reflecting all sorts of typical activities were performed with LTE-enabled devices during static and drive tests.
True mobility demands seamless transition between cells meaning fast, smooth handovers. That’s why, under these realistic conditions, selected KPIs were measured and compared to KPIs of radio sites in the commercial network. These KPIs included:
- Attach and service connect delays
- Latency, throughput, and handover performance
- Mid-cell and cell edge performance
In terms of transmission, the U.S. operator tested multiple fronthaul configurations, including dark fiber and variable wavelength multiplexing/terminating line unit. Topping things off, the U.S. trial also assessed performance of a virtual mobility gateway (Packet Data Network Gateway-PGW- and Serving Gateway -SGW) as virtual network function running on the same server platform.
The results? Resounding success across the board! Both trials went smoothly and the Cloud RAN system performed on par, if not better than a traditional RAN. And, in the case of the virtual mobility gateway, the results were even close to theoretical maximum values.
RAN virtualization lessons learned
Along the way, our trial experiences with virtualized RAN have taught us a lot:
- It is simple to deploy. In fact, and despite the new aspects of IT, and virtualization technology, the Cloud RAN system proved even simpler to deploy than traditional RAN. Careful planning and preparation with our ecosystem partners really paid off, confirming the simplicity in operations brought by network function virtualization.
- For the same functionality, performance was equal to, if not better than legacy RAN equipment. This demonstrates the capability of the Cloud RAN architecture to run virtualized network functions over an off-the-shelf virtual network platform in real conditions without performance degradation.
- The Cloud RAN architecture can accommodate a variety of transport networks, such as Ethernet or PON and keeps RAN deployment models flexible.
- The architecture is suitable for long distances between the front-end unit that handles real-time processing functions and the server unit, which hosts the upper and virtualized layers of baseband processing.
So what’s next?
These excellent results and the experience gained through these field trials provide even stronger motivation for the development of our Cloud RAN solution. Within the year, we will conduct more trials to test the various capabilities enabled by RAN virtualization and get ready for early deployments in pilots and commercial networks.
Press release: Industry first live field trial of a virtualized RAN
Press release: RedHat, Advantech and 6WIND virtualized RAN
Our authors look forward to your questions and comments.
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