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DOCSIS® Network vs. Fiber Backhaul for Outdoor Small Cells: How Larger Footprint of DOCSIS Networks Lowers TCO in the Outdoor Use Case

Shahed Mazumder
Principal Strategist, Wireless Technologies

Joey Padden
Distinguished Technologist, Wireless Technologies

Jennifer Andreoli-Fang
Distinguished Technologist, Wireless Technologies

Jan 31, 2019

In our recent blog post, we talked about how, from a total cost of ownership (TCO) perspective, DOCSIS networks triumph as either backhaul or fronthaul over traditional fiber backhaul for the indoor use case. In this blog, we bring that TCO analysis to a more intuitive, outdoor use case: a head-to-head comparison between TCO of DOCSIS backhaul and fiber backhaul, both of which serve the same set of outdoor small cells.

The basic idea here is: leverage the existing real estate of DOCSIS networks for additional use cases beyond residential/business services. This approach applies to the markets where DOCSIS networks already have a larger footprint than the fiber on the ground. We have seen data points suggesting that there typically is 3~5X more coax cable than fiber in major North American metro markets. This enables a large subset of small cells to be deployed on cable strands or at a short distance from the cable strands, using short drops.

Through primary research, one of our members with dual operations (cable + wireless) confirmed that from a small cell radio planning perspective, they exhaust all cable strand mounting options first, before looking into the gaps for additional sites. This is the key differentiator for DOCSIS technology vs. fiber, where most of the backhaul connections require either new build or premium lease rates.

In this TCO analysis, we showed >50% reduction in TCO for an outdoor use case of backhauling small cells when served by DOCSIS networks compared to a more traditional deployment served by fiber. 

But, Is DOCSIS Network the Right Solution for Small Cell Backhauling?

The short answer is – YES.

There are two major requirements associated with any small cell deployment –

  • Site acquisition/preparation/construction/powering
  • Backhaul with certain capacity/latency/timing synchronization

These two requirements are intertwined since we need to choose a site where backhauling option/s are available and, to the extent possible, cost-effective.

In terms of site (1st requirement) with ready access to backhaul, MSOs have 2 offers on the card:

  • Firstly, co-siting small cells with existing MSO owned/operated WiFi hotspots which are already served by DOCSIS backhaul.
  • Secondly, leveraging existing cable infrastructure, and in particular aerial plant i.e., cable strands, that takes out a lot of steps (and cost) from the small cell deployment process. Using existing infrastructure eliminates/lightens the need for permitting and site acquisition, preparation/construction and also powering. Along with site access (typically covered by existing pole-line attachment agreements) and power, cable strand deployments also come with readily accessible DOCSIS links as backhaul.

Figure 1 below shows a typical strand-mount small cell installation, consisting of a small cell gateway and a 4G/LTE-A small cell as reported in the technical paper prepared for SCTE-ISBE 2018 Fall Technical Forum by Dave Morley from Shaw Communications Inc./Freedom Mobile. The small cell gateway here contains a DOCSIS 3.1 cable modem and power supply.

Typical Strand Mount Small Cell

Figure 1: Typical Strand Mount Small Cell @ Shaw Communications Inc./Freedom Mobile

In terms of backhaul specifications (2nd requirement), Belal Hamzeh and Jennifer Andreoli-Fang from CableLabs® have articulated how DOCSIS technologies, with recent developments, fulfills all three fundamental backhaul needs around capacity, latency, and timing in the technical brief titled DOCSIS Technologies for Mobile Backhaul (CableLabs members only). In that paper, the authors have argued that, depending on the mobile operator’s defined SLA, even DOCSIS 3.0 can support backhaul capacity needs. And, significant downstream capacity improvement can be added with DOCSIS 3.1 and significant upstream capacity improvement can be added with Full Duplex DOCSIS.

Regarding latency, control and user plane latency is expected to improve significantly, achieving ~1-2ms latency with the pipelining/Bandwidth Report (BWR) technique across DOCSIS and mobile technologies. Finally, DOCSIS 3.1 already has the mechanism to natively distribute IEEE-1588 timing over the network. With recent CableLabs work on a DOCSIS synchronization specification, DOCSIS 3.1 will also be able to achieve the stringent phase precision as required in LTE TDD/5G networks.

Therefore, in summary, DOCSIS meets the requirements associated with small cell deployment, triggering the need to compare its TCO with traditional fiber based TCO when either one can provide the backhaul for a set of newly deployed small cells in a target market. 

Deployment Scenarios We Looked At

For TCO analysis, we considered a hypothetical market covering 100 sq.km. with 290K housing units (HU) and ~700K people in it. There will be 640 outdoor small cells deployed in the market with 150Mbps/50Mbps max DL/UL throughput per cell (20MHz 2*2 LTE cell). For simplicity, using 1:1 mapping between radio and backhaul throughput, we considered peak backhaul capacity of 150Mbps/50Mbps per small cell.

However, since the peak data rates are required/achieved only under ideal conditions, the average DL/UL throughput during the busy hour is much lower, typically 20-25% of the peak rates. We considered the average throughput to be 20% of the peak, thus forming a small cell cluster comprised of 5 small cells that results in 128 total small cell clusters in our market. Each of these clusters is served by a single cable modem capable to handle 150Mbps/50Mbps.

We have 2 identical scenarios: Scenario A, with fiber backhaul and Scenario B, with DOCSIS backhaul, both serving the same market with 128 clusters i.e. 640 total small cells.

Scenario A: Outdoor small cell served by fiber backhaul

Scenario A: Outdoor small cell served by fiber backhaul

 

Scenario B

Scenario B: Outdoor small cell served by DOCSIS backhaul

TCO Analysis and Key Takeaways

In this analysis, for both scenarios, we assumed the need for 3 types of backhaul connectivity to bring the small cells online – new build (both scenarios), existing cable strand/MSO WiFi Hotspots (scenario B only), and short drop (~300ft) to site/pole from nearby network (both scenarios).

In our base case, for the 2 scenarios, we applied the following breakdown among types of backhaul connectivity required:

Table 1:  Backhaul Connectivity Type Distribution Assumed for Base Case

Table 1:  Backhaul Connectivity Type Distribution Assumed for Base Case

The distribution of backhaul connectivity type used in our base case is informed based on primary research and market observations. Obviously, there is no one size fits all and this is a key area to assess when an operator analyzes potential TCO savings in a target market. Scenario B’s attractiveness largely depends on the ratio (2/3rd in our base case) of existing cable strand/WiFi hotspots that an MSO can leverage to deploy small cells.

The cost difference between new build and short drop does not come from site acquisition/ preparation/ installation because that need will be identical for both types. However, backhaul lease amount (/month) is different for these two types in our 100% Opex based model for backhaul cost.

Though configurable in our model, our default TCO term is 7 years. Also, we calculated the TCO per user passed and focused on the relative difference among scenarios to de-emphasis the overall cost (in dollars), which will differ by markets, the scale of deployment and supplier dynamics among other things.

Figure 2: Summary of 7-Yr. TCO between 2 Deployment Scenarios of Outdoor Use Case 

Figure 2: Summary of 7-Yr. TCO between 2 Deployment Scenarios of Outdoor Use Case

According to our base case assumptions, we see the following:

  • TCO in DOCSIS BH scenario has the potential to be >50% cheaper than the TCO in fiber BH scenario
  • The major difference in TCO between the two scenarios come from Opex. This is because, all 3 key Opex contributors – site lease, site utility cost, and backhaul lease are significantly higher (3~5X) in scenario A than in scenario B.
  • There also is a major difference in Capex between the two scenarios. This is largely because, site acquisition/preparation in scenario A costs more (2~2.5X) than the same category of Capex in scenario B, due to the advantage DOCSIS holds for leveraging more existing sites.
  • We allocated 20% of DOCSIS network upgrade (from low split to mid split) cost to the DOCSIS scenario. If we take this out (since DOCSIS network upgrades will happen anyway), the Capex associated with plant upgrade cost in scenario B will be gone, making it even more attractive from TCO perspective.
  • As mentioned earlier in Table 1, the TCO analysis outcome is primarily dependent on base case assumptions for the distribution of BH connectivity types. If existing cable strand/WiFi hotspots can handle 80% of small cell sites, then, instead of ~50%, the TCO for scenario B will be reduced by ~60%. On the contrary, if that ratio drops down to 50%, then TCO reduction in scenario B will also come down to ~40%.

In an upcoming strategy brief (CableLabs member operators only), we intend to share more details on our methodology, assumptions and breakdown of observed results (both Capex and Opex) along with a full sensitivity analysis.

Conclusion

As we also mentioned in our previous blog (on indoor use case), it’s self-evident that a DOCSIS network-based deployment would have favorable economics compared to a fiber-based model just by virtue of its larger footprint/incumbency alone. When we throw in additional advantages such as lower power requirement/utility charges, that gap only widens. Our TCO model introduced here quantifies that perceived benefit and numerically shows the cost savings in serving outdoor small cells via DOCSIS. This sort of use case strengthens our view that DOCSIS technology has a huge role to play in 5G deployments.

Subscribe to our blog and stay tuned as we continue to explore how to leverage DOCSIS network for mobile deployments. In our next blog post of this series, we intend to look at the DOCSIS networks’ ability to support advanced features such as CoMP.


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