Aurora Network's key technologies:

Universal Digital Return

Universal Digital Return

Today's high-speed data applications are pushing the limits of the legacy analog return path. The rollout of DOCSIS® 3.0 services and growth of voice will demand a pristine return that can also accommodate ever-growing bandwidth consumption. Aurora Networks' fifth-generation Universal Digital Return Platform™ delivers the necessary performance improvements and upstream capacity increases that are beyond the grasp of analog solutions.

With more digital return links deployed than any other vendor, Aurora Networks has leveraged its experience and economies of scale to make significant improvements to its Universal Digital Return Platform. The new backward-compatible platform supports all existing return splits and beyond to 100 MHz — an industry first. It's upgradeable, another industry first, with higher performance, supporting up to 1024-QAM. And, its equivalent in price or even less expensive than the best analog return technology.

Aurora Networks understands that not all cable systems are alike; nor are they static. We've designed our Universal Digital Return Platform to be backward-compatible and support today's band-splits, as well as tomorrow's. This flexibility simplifies the transition to a higher-split return that may be necessary to accommodate more bandwidth-intensive applications beyond DOCSIS 3.0 services.

A Modular Approach

In keeping with its philosophy of designing "future-proof" solutions, Aurora has taken a modular approach to digital return. Both its node-based Universal Digital Transceivers and its headend-based Digital Receivers use a common platform for all band-splits. Aurora then "personalizes" the base units with software that supports the required band-split and other features, such as "1-fer" versus "2-fer," data transmission speed and operational modes. Personalization provides cable operators a cost-effective digital return solution tailored to their specific network requirements with the same hardware modules.

Should a cable operator's return path requirements change, they can upgrade the software in both the transceiver and receiver while reusing the base modules. This approach results in capex savings and helps cable operators evolve their networks to meet changing requirements.

Advantages of Digital Return

The advantages of Aurora's digital return when compared to analog return systems include:

  • Improved NPR/BER performance for all distances, independent of link budget.
  • Support for much higher return link budgets — Any system designed for the forward path will always work in the return path automatically (reaches up to 200 km without regeneration, and with optical amplification if required). Additionally, this very high return link budget enables an optical output splitter to be used for return path route redundancy, eliminating the need for a separate transmitter for redundancy.
  • Superior thermal stability, with very stable receiver output levels and NPR/BER performance over the full temperature range.
  • Greater ingress resistance, even for full return path loading, providing higher margins against plant performance degradation, improving network availability and reducing maintenance costs. Integrated ingress location/blocking is aided via a wide-range attenuator in the digital return receiver.
  • Support for advanced modulation techniques up to 1024-QAM. (Aurora's "2-fer" technology supports 40 dB CNR for a full 37 MHz load while maintaining a typical 12-13 dB dynamic range.) This provides future proofing to support DOCSIS 3.0 with 256-QAM modulation levels (and beyond) and channel bonding, even if full return path channel loading becomes the standard rather than the exception.
  • Easy plug-and-play installation with all node return paths set up the same, given the constant gain from the node input to the return receiver output, independent of distance. There is no need for a pilot generator setup of the return path. The result is a lower initial alignment cost and practically no operating alignment costs related to the optical link.
  • Integrated SNMP-compliant monitoring/management, without the additional expense of node transponders.
  • Convenience and flexibility of transmit plug-in SFPs, including 1310 nm, 1550 nm, and all CWDM and DWDM wavelengths.
  • Support for additional revenue streams from the embedded Ethernet service capability.

Aurora is leading the way in digital return technology. As demands placed on the upstream continue to grow, MSOs will need to provide more and more upstream bandwidth. Critical to success will be the ability to fully utilize the upstream, with QPSK, 16 QAM, 64 QAM and, eventually, 256 QAM loading. Digital return brings performance and operational savings to an operator, and the scalability of digital return, from return concatenation to full segmentation, is a compelling fiber-efficient solution.

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The Aurora VHub performs all the functions of a fully operational hub in a node housing, enabling MSOs to quickly and cost-effectively implement hubs wherever needed, and no longer limited by real estate considerations. The VHub moves the functionality of an indoor hub to a weather-proof node enclosure that can be sited closer to the optical nodes in the network. VHubs, which can be strand- or pedestal-mounted, can be configured in a great variety of ways with a wide assortment of standard plug-in modules.

Aurora's VHub technology saves money for operators in many ways:

  • No need to locate (or use existing) real-estate.
  • No need for HV air conditioning.
  • No need for generators.
  • No need for building permits.

All of these benefits lead to significant cost-savings and, ultimately, reduced time to market.

Features and Benefits

Aurora's VHubs offer the following features and benefits:

  • Service for up to 20,000 households from a single VHub location, providing broadcast and narrowcast services for up to 24 nodes using as few as six fibers (including redundant routes for broadcast/ narrowcast and return fibers), when used in conjunction with Aurora's DWDM return path transponders.
  • Cost-effective service for multiple small markets from a single controlled VHub.
  • Low fiber consumption, enabling 24 nodes to be served by as few as two fibers.
  • Deployment of EDFAs without costly environmentally controlled facilities or cabinets. VHubs overcome passive optical splitting and combining losses to create broadcast/narrowcast feeds for 16 to 24 downstream nodes.
  • Support for up to 12 plug-in modules (including EDFAs, Broadcast/Narrowcast Combiners, Optical Switches, Monitoring Transceivers, Digital Transceivers, and Digital Transponders).
  • Full monitoring and control via Aurora's Opti-Trace EMS software.
  • Provisioning redundancy and route diversity with switching times less than 20 milliseconds (typically <5 milliseconds).
VHub Applications

Typical applications for the VHub include:

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Many factors contribute to increasing network capacity, including availability of fiber, construction costs, network architecture and type of nodes deployed. Operators have worked hard to standardize their networks — typically using a 1310 nm transport for shorter hauls when there was sufficient fiber in place, as well as 1550 nm technologies to cover longer distances and/or to overcome fiber scarcity. Today, fiber availability is still a major challenge to network growth due to the high cost of installing new fiber.

A variety of wavelength division multiplexing (xWDM) techniques have evolved to address the problems of fiber scarcity and continuing demands for increased network capacity. Several of those techniques have been standardized on wavelength "grids" across the optical spectrum (see Figure 1).

Wave Graph
Figure 1. A simplified graphical representation of the wavelength plans.


Since the 1990s, equipment manufacturers have been pioneering Dense Wavelength Division Multiplexing (DWDM) technology for the distribution of narrowcast signals. This technique enables more and more wavelengths, and hence narrowcast services, to be carried on the same fiber. DWDM wavelengths are positioned between 1530 nm and 1565 nm (C-band) as shown in Figure 1. The technology has evolved from early 8-wavelength systems on a 200 GHz spaced grid to the current industry-standard (ITU-T G.694.1) 40-wavelength system with 100 GHz optical spacing.

Initially, each DWDM wavelength carried just 8 RF QAM narrowcast channels, containing a mix of video, high-speed data and voice. However, the technology has matured to full-spectrum channel loading, including analog and QAM channels.


Like DWDM, Coarse Wavelength Division Multiplexing (CWDM) is centered in the C-band. However, the wavelengths here are spaced 20 nm apart. Initially, the standard extended from 1470 nm to 1610 nm, with up to eight wavelengths supported. However, ITU-T Recommendation G694-2 was approved in June 2002, bringing this down to 1270 nm and supporting up to 18 wavelengths (see Figure 1), assuming no "water-peak." (At the end of 2003, it was further decided to jog the wavelength grid by 1 nm to align it with current industry practice ,while maintaining symmetrical nominal central wavelength deviations.)

For systems installed today, Aurora has taken advantage of 15 of the CWDM wavelengths, avoiding the "water-peak," to provide a very cost-effective solution for its digital return technology.


O-band (1260 to 1360 nm) dense WDM solutions for CATV optical transport have been investigated for some time. However, until recently, there were no obvious cost-effective solutions to the many non-linear effects associated with optical transmission in close proximity to the zero-dispersion wavelength of the fiber. It should be noted that basically every fiber optimized for the 1310 nm window of operation, including SMF-28® and SMF-28e® fibers, and installed since the early 1980s, shares those similar zero-dispersion characteristics.

A breakthrough has now made it possible for MSOs to deploy more densely spaced multi-wavelengths in the O-band. This O-band multi-wavelength solution, which Aurora has trademarked under the name Low Cost Wavelength Division Multiplexing (LcWDM ), enables up to 8 separate wavelengths to be carried in this band in the downstream on one fiber — and for a reach up to 30 km. Previously, the limitation was just 1 wavelength in this band — using traditional 1310 nm DFBs, which have been extensively deployed in our industry for the last 1520 years.

Multi-wavelength solutions for the O-band were first introduced in 2006. Careful research around O-band non-linearity effects demonstrated that the choice of wavelength and its relative position to other wavelengths is critical to developing a field-deployable system. The correct wavelength positioning "neutralizes" or avoids the impact of fiber phenomena such as dispersion, four-wave mixing, SRS and cross phase modulation on RF signals modulated onto the laser light. Those phenomena, interacting with laser transmitter characteristics in the multi-wavelength system, all cause distortions, mostly composite second order (CSO), in the RF spectrum. Further research has led to the tightening of specifications for optical filters while incorporating the same robust and reliable filter technology that has been proven over many years in DWDM C-band applications.

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xWDM, Vhubs, Universal Digital Return