Traffic growth has been the story of cable broadband since DOCSIS® debuted. While downstream growth has aggressively continued, lagging growth upstream has put its evolution on the back burner. However, as connected home services evolve, user generated content explodes, and machine-to-machine interactions swell among everything IP-ready, growth will rebound. The time to prepare is now before it becomes an emergency. Proper preparation will avoid a “Napster” moment.
Unlike the downstream where many knobs and levers are available to manage spectrum, most weapons on upstream have been fired or are being activated today—64-QAM, laser upgrades, S-CDMA. Serious new upstream capacity is inevitably about finding new spectrum. And, cable must plan for the best use of this most precious asset—downstream or upstream. Using it most efficiently guarantees the longest HFC lifespan.
Mid-split, in this case, refers to extending to an 85 MHz upstream band. The “plus” means enabling new bandwidth on demand, for example, up to 200 MHz, or greater. Mid-split plus is the best of both—available today to provide many years of lifespan for even aggressive CAGR, and long term additional bandwidth as required. This is true just considering technology available today. Also, this approach maintains the fundamental diplex architecture already in place, yielding the most efficient overall use of spectrum.
The industry has been considering both extended diplex and “top split” architectures, whereby new upstream is placed above the forward band. A pro-con comparison heavily favors extending the low-band return (and extending the forward too, if necessary). Consider these advantages: clear path to 15 years of capacity lifespan (see Figure), 100 Mbps peak rates, DOCSIS 3.0 compatibility, supports legacy STB out-of-band channel, and easily handled by existing return path optics.
What about a “Plus” band? Advantageously, this can also use HFC optics, ensure Gbps services, and be implemented as a smooth transition. Moreover, both single-carrier techniques (simple DOCSIS extensions) or multi-carrier approaches can be used. This approach carries almost no technology or implementation risk. The amount of additional spectrum MSOs may need depends on many factors, but 1 Gbps of upstream is a common objective. With modern forward error-correction, such as that used in MoCA and DVB-C2, upstream spectrum could be limited to 200 MHz or less. These same tools, applied to mid-split, could also further extend the 15-year lifespan identified above, at least in terms of aggregate capacity.
By contrast, consider top split. High frequency signals are transmitted upstream through triplexed actives that do not exist, or re-routed around today’s actives. The RF transmission is terminated in new actives, or modules in actives, that also do not exist. These burdens suggest an FTLA architecture or an FTTx overlay. Even so, attenuation at top-split frequencies challenges practical CPE transmit power. As a result, bandwidth efficiency (bps/Hz) is lower. The advances required and architecture changes present high risk—for less return. Finally, by introducing another guard band, close to 100 MHz of prime RF spectrum is lost. Think of it as 100 possible HD channels of 1080p60 quality—gone. Clearly, this is not how to most efficiently use spectrum long-term.
Mid-split “plus” delivers the best of both – many comforting years of immediate lifespan, additional years enabled by modern error correction tools, and a strategy for effectively dealing with the continuous traffic growth beyond.
Note: Rob will be participating in the following sessions at The Cable Show, May 21-23, in Boston:
- Monday, May 21: Redefining High-Definition: Implications of Ultra HD for Cable Providers
- Tuesday, May 22: The Gigabit Network: New Possibilities in HFC
We invite you to visit Motorola at Booth # 733 to see how we are driving the evolution of TV and a smart, simple connected home.
Product Information: BSR 64000 RX48 Decoupled Upstream Module