The March to Budget-Friendly vRAN Continues!
As with most of my recent blog posts, I’m here to share some exciting updates on the work that CableLabs has been doing in the Telecom Infra Project (TIP) with virtualized RAN for non-ideal transport networks—for example, DOCSIS networks, passive optical networks (PONs) and really anything not on dedicated fiber. Over the past 6 months or so, we’ve reached some milestones that are worth a blog post blast. I’m going to keep each update brief, but please follow the links to dig in further where you’re interested.
TIP vRAN Fronthaul White Paper #2
On November 13, TIP’s vRAN Fronthaul Project Group is releasing a white paper discussing the results of Phase 1 of the project. The paper covers the combined learnings from the four Community Lab efforts led by Airtel, BT, CableLabs and TIM. We also include some key takeaways with which operators can assess the network assets that can be used in future vRAN deployments. You can find the paper here.
TIP Summit vRAN Fronthaul Demo
Also this week, the vRAN Fronthaul team has assembled a demo for TIP Summit ’19 in Amsterdam. The demo is showing the newly containerized multi-vendor vRAN solution running two remote radios (RUs) from a single CU/DU virtual baseband unit. In the LTE software stack, the Layer 2 and 3 containers come from Altran, and the Layer 1 container comes from Phluido, with RUs from Benetel. The containerized setup increases CPU efficiency by over 80 percent relative to our previous virtual machine–based architecture. If you’re in Amsterdam at TIP Summit, be sure to stop by the vRAN stand on the show floor.
TIP vRAN Fronthaul Trial with Shaw Communications
In July of this year, Shaw Communications, CableLabs and TIP collaborated to trial the vRAN Fronthaul LTE solution from Altran, Benetel, and Phluido over the Shaw commercial grade DOCSIS networks. In a fantastic result, we were able to demonstrate the ability of the Shaw DOCSIS networks to support Option 7-2 split fronthaul traffic for LTE services. In addition, we replicated all of our lab findings over the Shaw DOCSIS networks, validating the ability of our lab results to transfer to real world networks. “The trial demonstrated that Shaw’s hybrid fibre coaxial FibrePlus network is well positioned to support not only existing wireless services but the significant densification coming with the deployment of 5G,” said Damian Poltz, Vice President, Technology Strategy and Networks, Shaw Communications.
O-RAN Specification Includes Non-Ideal Fronthaul
While the team was busy hitting all these milestones in the TIP vRAN Fronthaul project, during the first half of the year CableLabs also led a collaborative effort to bring non-ideal fronthaul support to the O-RAN Alliance CUS plane specification. As of July, the 2.0 version of the CUS plane specification now includes support for non-ideal fronthaul with latencies up to 30ms over a common Option 7-2 interface. In addition, a new appendix was added to provide further detail on the implementation and operational specifics of deploying the lower-layer split over non-ideal transport such as DOCSIS networks, PON or managed Ethernet.
You can find out more by clicking the link below.
CoMP over DOCSIS: Femtocells in the Age of vRAN
As promised in the last couple blogs discussing DOCSIS based femtocells, we’ve saved the best for last. So far in the series, we’ve made the case for femtocells over DOCSIS networks and laid out the total cost of ownership (TCO) benefits of this deployment model. In this final blog post, I’ll share the results of some testing we’ve been doing at CableLabs on using Coordinated Multipoint (CoMP) to optimize femtocell performance in dense deployments.
Decluttering the Radio Signal
Let’s step back and look at a key issue that has limited the benefit of femtocells in the past: intercell interference. When femtocells (or any cells, for that matter) are placed in close proximity, the radio signals each cell site produces can bleed into its neighbor’s territory and negatively affect network performance.
With CoMP, neighboring cells can coordinate their transmissions in a variety of ways to work collaboratively and prevent interference. They can share scheduling and beamforming data to avoid creating interference. Or, they can use joint processing, which allows multiple cells to talk to a single cell phone at the same time, increasing the signal quality.
Although it’s not a perfect analogy, it’s a bit like trying to listen to a bunch of people singing their favorite song at the top of their lungs versus listening to a choir following a conductor, as you see in the following figure. The former is old femtocells, and the latter is virtualized RAN (vRAN) femtocells using CoMP.
Since its inception, CoMP has been largely believed to require fiber transport links to work. For example, in TR 36.819, there’s a whole section devoted to the impact of “higher latency communication between points,” where “higher” refers to 5ms, 10ms or 15ms of latency. In that text, gains decrease as latency increases, ultimately going negative (i.e., losses in performance).
However, with the increase in attention on vRAN, particularly lower-layer splits like the work going on in Telecom Infra Project (TIP) vRAN Fronthaul and O-RAN Alliance WG4, latency takes on new meanings with respect to CoMP.
For example, what matters more, the latency from one radio unit to another or the latency from one virtualized baseband unit (vBBU) to another? And if it’s the latter, does that mean CoMP can provide benefit even over long-latency non-ideal vRAN fronthaul like DOCSIS?
To find out the answers to these questions, we set up a test bed at CableLabs in collaboration with Phluido to explore CoMP over DOCSIS. We used the hardware from the TIP vRAN Fronthaul project, with an LTE SW stack provided by Phluido that supports CoMP. We installed two radio units in different rooms, each radio connected via a DOCSIS® 3.0 network to the vBBU. We designated two test points, one with a phone located at the cell center, the other with both phone in the cell edge/cell overlap region.
Notably in our setup, the latency from radio unit to vBBU and radio unit to radio unit were both about 10ms. However, the latency between vBBUs was essentially zero as both radios shared the same vBBU. This setup is specifically designed to test whether vBBU-to-radio latency or vBBU-to-vBBU latency is more important for CoMP gains.
What we found is that radio-to-radio latency and radio-to-vBBU latency can be quite large in absolute terms, and we can still get good CoMP performance provided that latency is low between the vBBUs and that vBBU-to-radio unit latency is similar for the radios in the CoMP cluster, as you see below.
In other words, to realize CoMP gains, the relative latency between a set of cells is more important than the absolute latency from vBBU to each radio.
We tested four configurations of phones at the cell center versus the cell edge, or some mix thereof, as the following figure shows.
In case 1, we see full cell throughput at each phone with CoMP enabled or disabled. This is great; this result shows that we haven’t lost any system capacity at the cell center by combining the cells into a single physical cell ID (PCI) and enabling CoMP.
In case 2, the phone throughput jumped from 55 Mbps to 78 Mbps when we enabled CoMP, showing a CoMP gain of almost 50 percent.
In case 3, when we enabled CoMP, the phone at the cell edge saw a throughput gain of 84 percent. In this scenario, the throughput of the cell center phone saw a decrease in throughput. This illustrates a tradeoff of CoMP when using legacy transmission modes (TM4, in this case) where the operator must choose whether it wants to favor cell edge users or cell center users. With more advanced transmission modes (e.g., TM10), this tradeoff is no longer an issue. Note that this is true of any CoMP deployment and not related to our use of DOCSIS network fronthaul.
In case 4, we expected to see significant gains from CoMP, but so far we haven’t. This is an area of further investigation for our team.
vRAN Femtocell CoMP in MDUs
Let’s look at an example use case. Cell service in multi-dwelling units (MDUs) can be challenging. A combination of factors, such as commercial construction materials, glazing and elevation, affect the indoor signal quality. As discussed in my previous blog, serving those indoor users can be very resource intensive.
As an operator, it would be great to have a low-cost way to deploy indoor cells. With vRAN over DOCSIS networks supporting CoMP, the operator can target femtocell deployments at heavy users, then build CoMP clusters (i.e., the set of radios that collaborate) as needed to optimize the deployment.
Putting It All Together
The testing described here has shown that CoMP gains can be realized even when using long-latency fronthaul over DOCSIS networks. As these solutions mature and become commercial-ready, deployments of this type will provide the following for operators:
- Low-Cost Hardware: vRAN radios, particularly for femtocells, are low-complexity devices because the majority of the signal processing has been removed and put in the cloud. These radios can be built into the gateway customer premises equipment (CPE) already deployed by operators.
- Low-OPEX Self Installs: With vRAN radios built into DOCSIS CPEs, operators can leverage the simplicity of self-installation. The ability to dynamically reconfigure CoMP clusters means that detailed RF planning and professional installation aren’t necessary.
- High-Performing System: As shown in our testing results, CoMP gains can be realized over DOCSIS network–based vRAN femtocells. This eliminates another of the previous stumbling blocks encountered by earlier femtocell deployments.
vRAN Over DOCSIS: CableLabs Making it a Reality
In November, CableLabs announced the opening of our new Telecom Infra Project (TIP) Community Lab. Today, CableLabs joins TIP in releasing a whitepaper, making public deeper insights into the vRAN fronthaul interface under development in the TIP vRAN Fronthaul project group. With this new interface, the addressable market for virtualized RAN (vRAN) deployment architectures can grow significantly. This increased market is evidenced by the diverse set of use cases being sponsored by the growing set of operator-based TIP Community Labs.
With the release of the white paper, the project group highlights key milestones which have been reached, including agreements further defining the open API and a set of interoperability metrics to be used in validating the interface in multi-vendor configurations.
As the project continues, work on the CableLabs DOCSIS network vRAN fronthaul use case will take place at the CableLabs TIP Community Lab. We look forward to sharing more as we continue to check milestones off our list, so check back soon for updates.
You can find the whitepaper "Creating an Ecosystem for vRANs Supporting Non-Ideal Fronthaul v1.0." here.