Powering the Future of Mobile Backhaul
The wireless ecosystem is a rapidly moving marketplace, and the next milestone is the large-scale deployment of small cells to augment network capacities and to support 5G deployments. There are three main elements required to deploy small cells:
These requirements put cable operators, many of whom are also mobile operators, in an advantageous position for deploying mobile small cells.
According to the NCTA, 93% of US households are reachable via the hybrid fiber coaxial (HFC) network. While the HFC provides the necessary elements for deploying small cells, the cable infrastructure can further extend its capabilities by offering low latency mobile backhaul. Reducing latency in the DOCSIS® network will unlock that additional potential for cable operators.
Small cells are deployed to provide capacity or coverage augmentation for the macrocell network. This results in overlapping coverage areas between the various cells (between small cells and small cells, as well as between small cells and macrocells). There is significant interference generated in these overlapping areas, as the user can hear multiple cells’ transmissions. In order to provide a good quality experience for these users, the mobile operator needs to deploy advanced interference management techniques that are currently supported by LTE-Advanced and LTE-Advanced Pro. But, for these techniques to work well, adjacent cells need to be able to talk to each other quickly - at a latency of generally no more than 5 milliseconds. And because these cells talk to each other through the DOCSIS backhaul network, the DOCSIS round-trip latency must be 5 ms or less. This is not achievable today. See Fig. 1:
Searching for Solutions
We found that traditional cable equipment suppliers were also innovating in this space and working on enabling DOCSIS to provide better mobile backhaul. Together with my colleague John Chapman, Cisco Fellow and CTO Cable Access, we came up with a simple solution that reduces the DOCSIS upstream latency to 1-2 ms consistently. We developed a proof-of-concept (PoC), each supplying expertise and resources in the mobile and CMTS space.
Looking closely, LTE and DOCSIS are two independent systems – their operations occur in serial. The overall latency is the sum of the two system latencies. The two technologies have similar mechanisms to access the channel, and that is through a request-grant-data transfer loop.
Here comes the lightbulb moment: The LTE loop is much longer than DOCSIS, resulting in much higher latency than DOCSIS. This presents a hidden opportunity for DOCSIS. Rather than waiting for the LTE transaction to complete and then start the request process on the DOCSIS side as it is today, we proposed that LTE tell DOCSIS about the data that is on its way so that the DOCSIS request process can start earlier and in parallel with the LTE transaction. This will lead to much lower overall system latency. This is illustrated in Fig. 2:
Our joint team worked together on perfecting the pipelining operation and designing a new message called the “bandwidth report,” or the “BWR.” This simple solution reduces the DOCSIS upstream latency to a consistent 1-2 ms.
To build the proof-of-concept (PoC), we inserted a minimal amount of code into an open source LTE small cell and added an API on the Cisco cBR-8, enabling the CMTS to optimize its scheduling and to align it with the small cell transmissions in real time. We demonstrated the PoC to cable operators and received very positive feedback. See Fig. 3:
Our proof-of-concept was also demonstrated recently in the Cisco booth at SCTE Cable-Tec Expo 2017, as Cisco explains here. The next step for this is to make the solution available industry-wide by standardizing it through CableLabs and have it ready for the HFC network to be at the forefront of the mass deployment of small cells.
CableLabs Publishes Full Duplex DOCSIS® Specification
Recently, in a significant step for the cable industry, we announced the successful completion of the Full Duplex DOCSIS® 3.1 specification (now a part of DOCSIS 4.0 technology). Today, we are pleased to announce the release of the DOCSIS® v3.1 Physical Layer Specification, which incorporates the addition of Full Duplex in Annex F per PHYv3.1-N-17.1771-6. The specification is designed to enable cost-effective solutions for cable operators for faster broadband speeds and brings peak upstream of up to 6 Gbps and downstream up to 10 Gbps.
Current DOCSIS networks are well suited to meet today's customer’s demands and needs. Full Duplex DOCSIS networks (now a part of DOCSIS 4.0 technology) enable operators to significantly increase the network’s upstream capacity and be ready for future applications, such as the increasing use of IoT devices, telemedicine, video chats, and virtual reality. Watch the video below to see how Full Duplex DOCSIS technology (now a part of DOCSIS 4.0 technology) solves this problem by enabling simultaneous upstream and downstream transmissions in the same spectrum over existing hybrid fiber/coax (HFC) networks, significantly increasing upstream capacity.
CableLabs Completes Full Duplex DOCSIS Specification
“In the United States, more than 90 percent of households are connected to an HFC (hybrid fiber-coaxial) network, and consumers typically have higher download speeds than upload speeds. By enabling Full Duplex DOCSIS (now a part of DOCSIS 4.0 technology), the upstream can flow up to 6 Gbps and downstream traffic can flow at up to 10 Gigabits concurrently, enabling the efficiency of spectrum use.” -- Phil McKinney, president and chief executive officer of CableLabs
The number of connected devices and bandwidth-hungry online experiences are expected to increase exponentially in the next decade. Also, with the continuous development of new applications that enable new experiences, such as augmented reality and virtual reality, an increase in upstream capacity demand is a matter of “when” and not “if." Operators are continuously challenged to find cost-effective solutions to meet this growing demand for faster broadband speeds. With a focus on solving this challenge of the future, CableLabs recently completed the Full Duplex DOCSIS® (now a part of DOCSIS 4.0 technology) specification.
Full Duplex DOCSIS (now a part of DOCSIS 4.0 technology) technology builds on the successful completion of CableLabs’ DOCSIS 3.1 specification, which made deployments of 10 Gbps downstream and 1 Gbps upstream broadband possible. Full Duplex DOCSIS technology (now a part of DOCSIS 4.0 technology) improves upon the DOCSIS 3.1 standard by:
- Significantly increasing upstream capacity
- Enabling symmetric multi-gigabit services over existing hybrid fiber-coaxial (HFC) technology
- Ensuring that cable operators are ready to meet future usage needs for technologies, such as virtual and augmented reality - although widespread consumer demand for high speed upstream is not yet here, operators need to be prepared when the time comes
Current DOCSIS networks have to juggle available upstream and downstream traffic. Full Duplex DOCSIS technology (now a part of DOCSIS 4.0 technology) supports multi-gigabit symmetric services by enabling concurrent transmissions in the same spectrum, providing the ability to increase the upstream capacity without sacrificing downstream capacity. This has the potential to greatly improve network efficiency and, in turn, customer experience.
Starting from Full Duplex DOCSIS (now a part of DOCSIS 4.0 technology) as an internal innovation, CableLabs developed this solution in collaboration with our members and industry partners, enabling cable operators to deliver multi-gigabit symmetric services. Full Duplex DOCSIS technology (now a part of DOCSIS 4.0 technology) offers high speeds over the existing infrastructure and is less expensive to deploy than fiber, while still maintaining backwards compatibility with previous generations of DOCSIS technology.
You can read more about our Full Duplex DOCSIS (now a part of DOCSIS 4.0 technology) specification effort in my article “Full Duplex DOCSIS Technology: Raising the Ante with Symmetric Gigabit Service.” Make sure to check our website later this month for the complete Full Duplex DOCSIS (now a part of DOCSIS 4.0 technology) specification.
Remote PHY is a Reality
Just over two years ago, CableLabs announced the release of a new series of specifications known as “Remote PHY” in the blog “CableLabs® New Remote PHY Specifications expand DOCSIS® Network Deployment Options” authored by CableLabs principal architect Karthik Sundaresan. The blog describes what Remote PHY (R-PHY) is, how it forms a key piece of the various Distributed Access Architecture options we have established at CableLabs and upcoming plans for the further development of the technology.
Distributed Access Architectures and Remote PHY technology, in particular, provide several key benefits to the Hybrid Fiber Coax (HFC) networks that deliver cable TV and broadband to consumers and businesses:
- Takes full advantage of the capabilities of DOCSIS 3.1 technology, allowing more data capacity to be packed into the same amount of spectrum
- Supports the deployment of Full Duplex DOCSIS, which will enable multi-gigabit upstream services on existing cable plants
- Leverages lower cost/higher capacity optical Ethernet transport mechanisms, allowing cable operators to cost-effectively provide faster services to customers
Since this announcement, hundreds of engineers on dozens of teams from CableLabs, equipment manufacturers and cable operators worked vigorously to move the technology forward. We’re excited to announce that as a result of this hard work, interoperable Remote PHY devices (RPDs) now exist and will be available on the market soon.
What is Remote PHY Technology?: A Technical Recap
The R-PHY technology pushes the physical RF layer (PHY) to the edge of the access network. This design requires the CCAP to be “split” between the MAC layer and the PHY layer. In an R-PHY system, the integrated CCAP is separated into two distinct components. The first component is the CCAP Core and the second component is the RPD. The CCAP Core can contain both a CMTS Core for DOCSIS technology and an EQAM Core for Video.
The RPD contains PHY-related circuitry, such as downstream QAM modulators, upstream QAM demodulators, together with pseudowire logic to connect to the CCAP Core. The RPD platform is a physical layer converter whose functions are:
- To convert downstream DOCSIS, MPEG video and out-of-band signals received from a CCAP Core over a digital medium, such as Ethernet or PON to analog for transmission over RF.
- To convert upstream DOCSIS and out-of-band signals received from an analog medium, such as RF to digital for transmission over Ethernet or PON to a CCAP Core.
Testing Products at CableLabs’ R-PHY Interoperability Events
While CableLabs is known for developing specifications, we also work extensively to help manufacturers develop products that conform to our specifications and interoperate with one another. One important means of doing so is through interoperability events.
The start of interoperability testing is a crucial milestone in the lifecycle of a project at CableLabs. It represents the point at which products become real and can start to work with one another. CableLabs serves as the neutral ground that allows manufacturers, who might otherwise be competitors, to come together and – for the very first time – validate whether or not their implementations work with each other and, if not, figure out why. This is a major step for manufacturers to validate their products are commercially viable.
CableLabs hosted a series of one to two-week long interoperability events, starting in December of 2016. These events comprised of 15 equipment manufacturers from around the world. The initial events included prototype RPDs and CCAP Cores which delivered product interoperability from the beginning. Over the course of time, the products matured until they became ready for use in field trials - a massive progression of development.
As participants continued through their development of RPD and CCAP Core products, features and requirements were added to the events to advance product readiness. A number of key features to enable commercial deployment were tested and verified: RPD initialization, IPv6 support, timing, DOCSIS 3.1 network operation and the creation of and communications through upstream/downstream L2TPv3 tunnels.
Announcing the Remote PHY Device Qualification Program
As an additional step to ensure devices are ready for deployment, where appropriate, CableLabs develops Qualification Programs to formally test and verify that devices comply with the specifications. This indicates that they will successfully interoperate with one another when deployed in the field. Based on the success experienced in the interoperability events to date, CableLabs is excited to announce that we have now launched a Qualification Program for the testing of RPDs.
Similar to our highly successful DOCSIS certification programs, manufacturers can now submit RPDs, whether they’re in R-PHY Nodes or R-PHY Shelves, for formal qualification testing at CableLabs. Once submitted, these devices are extensively tested by our partner Kyrio to ensure that they comply with our specifications and that they will successfully interoperate with other compliant devices.
Remote PHY is Real
CableLabs’ Interoperability Events help to get devices to that point and the start of our Qualification Program ensures that devices are able to demonstrate their compliance and readiness.All of this serves to demonstrate that Remote PHY is real: products are real, they are here and they’ll see deployment in the field soon. This means that cable operators – and ultimately their customers – benefit from Remote PHY deployments.
Remote PHY Industry Events & News
R-PHY is playing a major roll in the cable industry and the timing couldn’t be better! This year’s SCTE Cable-Tec Expo® in Denver, CO is holding an R-PHY seminar on Tuesday, October 17th. This event will provide an in-depth look at all aspects of R-PHY including the technology, the implementation of R-PHY and the benefits for operators. Jon Schnoor is speaking at the seminar, providing a view of the current state of the project and how CableLabs and Kyrio are playing an essential role in the next generation of cable networks.
Interested in reading more about Remote PHY in the future? Subscribe to our blog and let us know your thoughts in the comment section below.
CableLabs Extends its Global Reach with the Addition of Four New Member Companies
In its continued commitment to the international cable community, CableLabs welcomes four new companies to its membership: GCable and Henan Cable (both situated in China), together with Nowo (Portugal) and Stofa (Denmark).
Guangdong Cable Network (aka Gcable)
Gcable serves Guangdong Province located in southeast China. Guangdong Province is one of the most highly industrialized provinces in China, with major technology centers in Guangzhou (served by Gcable) and Shenzhen (served by Topway, a CableLabs member). Gcable, which is the largest MSO in Guangdong Province, serves 13 million television subscribers and 1.7 million broadband subscribers.
Henan Cable serves Henan Province. The company is 49% owned by CITIC Limited, China’s largest conglomerate with diverse global businesses focused on financial services, resources and energy, manufacturing, engineering contracting, real estate and telecommunications. CITIC Limited also has similar ownership interests in two other CableLabs members – Chongqing Cable Networks (originally located in Sichuan Province) and JSCN (located in Jiangsu Province). Henan Cable serves 11 million television subscribers and 400 thousand broadband subscribers.
Nowo provides cable service in Portugal to 172 thousand television subscribers and 144 thousand broadband subscribers. Nowo is the second largest cable operator in Portugal. Nowo launched in September 2016. with a strategy focused on a disruptive “build your own bundle” which includes mobile voice and data together with fixed line video, broadband and voice services.
Stofa is a Danish cable company affiliated with SE Group, a customer-owned, energy and telecommunications group. Stofa, began in 1959 serving antenna, housing and land associations across Denmark, and now provides fixed and mobile services to 344 thousand television subscribers, 323 thousand broadband subscribers, 84 thousand digital voice subscribers and 10 thousand mobile subscribers. Stofa is the second largest cable operator in Denmark.
These four members join 55 other cable operators from 5 continents bringing CableLabs’ total membership to 59 – representing over 180 million video subscribers worldwide.
In its global reach, CableLabs is focused on achieving several objectives:
- Alignment: Assure alignment with CableLabs technologies across the global cable community.
- Adoption: Achieve global scale – and therefore low-cost solutions – through the adoption of common technologies by cable operators worldwide.
- Collaboration: Collaborate with global partners to share experiences, exchange best practices and advance innovation throughout the cable industry.
We look forward to bringing on more members in the future to foster innovation worldwide. You can find more information about CableLabs’ global strategy here. Please contact us to discover the value of membership in CableLabs.
CableLabs Announces an Open Source LoRaWAN Network Solution
The Internet of Things (IoT) is a growing industry comprised of a massive number of devices that connect to each other to benefit our lives. Examples of these include the Nest thermostat, security cameras, Amazon’s Alexa, and Apple Watch. Refrigerators can talk with the internet to order milk and Fitbits tell you when to step more to meet your daily exercise goals.
A new area of IoT involves the use of sensors designed to last for years on a single battery transmitting information periodically over long distances. The infrastructure to support all of these connected devices is commonly referred to as a Low Power Wide Area Network (LP-WAN).
LP-WAN networks are designed to cover large geographical areas and minimize the amount of power required for sensors to interact with the network. There are many solutions available to enable this network, including Ingenu, Sigfox, LoRaWAN, 3GPP and Weightless.
CableLabs is pleased to announce an open-source LoRaWAN solution. LoRa is a semi-proprietary solution as it is owned and licensed by Semtech, and a closed consortium (i.e. LoRa Alliance) develops the LoRaWAN specification around the Semtech solution architecture.
Once the consortium concludes a revision of this effort, they make it publicly available. Ingenu and Sigfox are examples of fully proprietary solutions with closed development and ecosystems. In an effort to be more open, they have software development kits available for sensor manufacturers to create sensors for their networks. Of course, these are merely examples of many more solutions emerging in this space. All of them are attempting to create their own advantage and benefits for network providers and consumers. We attempted to highlight some of the more commonly known solutions available, but these are not meant to be preferential or endorsed by CableLabs and are not an exhaustive listing.
LoRaWAN is a long range, low power wireless protocol that is intended for use in building IoT LP-WAN networks. IoT devices send small data packets to any number of “gateways” that may be in the several-kilometer range of a sensor via the LoRaWAN wireless protocol. The gateways then use more traditional communications such as wired Internet connections to forward the messages to a network-server which validates the packets and forwards the application payload to an application-server.
CableLabs chose to develop a LoRaWAN open-source solution because we believe it is a good compromise between proprietary and open solutions, and it provides many of our members an opportunity to compete in the low power wide area (LPWA) space.
In the past, CableLabs has often developed solutions specific to the cable industry, but we believe open-source provides consumers a great benefit as it will spur growth in an industry intended to enrich our lives. This enrichment comes through devices intended to inform us of many things. For example, many of us have driven by a city park during a rain storm and noticed the sprinkler system running. This is a waste of water and further impacts our climate. What if we had soil moisture sensors that could communicate with a sprinkler controller to inform it when it requires water? This could save countless gallons of water, which is extremely valuable, especially in drought-stricken regions.
Another example could be to inform a loved one when an aging relative has taken their pills for the day, gets out of bed or sits in a chair too long. All of these are examples of the benefits of sensors enabled by LP-WANs.
In order for us to realize these benefits, LP-WANs need to be deployed broadly across national and international regions. This will enable the use of many sensors across these same regions. As we make use of the sensor data, it will enrich our lives with information to make better choices, ensure higher quality results and guide us towards a better future. By making a portion of this network available for open-source, our goal is to lower the barrier for the cable industry and other industry participants to enable these solutions for consumers and governments. Together we can truly change the world, and it should not be limited by costly barriers.
With a strong focus on innovation, CableLabs develops technologies and specifications for the secure delivery of high-speed data, video, voice and next generation services. Don't forget to subscribe to our blog to read more about our innovative technologies in the future.
Momentum Builds for 3.5 GHz Mobility in 2018
What is the 3.5 GHz Citizens Broadband Radio Service?
Last year, the U.S. allocated 150 MHz of spectrum for fixed and mobile broadband use under the newly-created Citizens Broadband Radio Service (CBRS) in the 3550-3700 MHz band. To put 150 MHz of bandwidth into perspective, this is roughly equivalent to the total spectrum that each of the Big 4 U.S. wireless operators have licensed to date. With 10 MHz channels, this is ideal for LTE TDD and small cells with transmitter powers of 1W/10 MHz EIRP for indoor use and as high as 50W/10 MHz EIRP in rural locations. This is great for MSOs who have the key locations, backhaul and power where people use data, either inside buildings or outside via their external cable infrastructure. For example, in metro areas, MSOs can place 10W/10MHz EIRP small cells on cable strands for great coverage. It is the first time that fixed operators will be allowed to use LTE in unlicensed spectrum.
CBRS is the world’s first three-tier spectrum sharing framework in which one or more Spectrum Access Systems (SASs) will actively manage 1) incumbents, 2) priority access licensed (PAL) users, and 3) general authorized access (GAA) users. Basically, the SAS will tell the Access Points, called CBRS Devices (CBRDs), which channels to use to avoid interference to other users in a given geographical area. CBRS contains both licensed spectrum, with seven PAL channels, and unlicensed spectrum, with eight GAA channels, in over 73K census tract areas across the US. The PAL license period is three years with an initial right to renew for a further three years. In areas where the auction for PAL is unsuccessful, all this spectrum becomes available as unlicensed (GAA).
Incumbents in the band include shipborne radars operated by the Department of Defense and receive-only fixed-satellite service earth stations. Wireless Internet Service Providers (WISPs), utilities, and other terrestrial users currently in the 3650-3700 MHz segment are required to transition from 50 MHz of spectrum to 150 MHz of CBRS. The main issue for use of 3.5 GHz in the coastal regions of the U.S. is the detection of shipborne radars used by approximately 30 U.S. naval carriers. However, these ships are normally stationed globally. To detect the arrival of one of these ships on either the East or West coasts of the U.S. requires building an Environmental Sensing Capacity (ESC) – a radar detection network. The ESC will inform the SAS which channels the radar is located on in a given area so that current users are moved to adjacent channels. Normally, the radars will only occupy one or two channels over a relativity small geographical area containing the current location of the ship. The rest of the spectrum is available to all.
Momentum for 3.5 GHz
The U.S. wide commercial timeline for 3.5 GHz use is dictated by the availability of the SASs, ESCs, commercial grade network equipment, and capable end-user devices. The recent Mobile World Congress (MWC 2017) in Barcelona, Spain showcased the status of many of these time critical components. CableLabs hosted its own workshop there, inviting several of the key players in the 3.5 GHz space. Many companies on the show floor demonstrated their readiness for 3.5 GHz.
Of course, the guarantee of success is not only the availability of technology but also the willingness of key players to adopt and bring consensus support for the opportunity - particularly for a U.S. specific band where wide adoption is key. In particular, this is key for the most important component of the technology – the smart phone. Recently, Verizon committed to 3.5 GHz in an interview with FierceWireless.
Equally, T-Mobile, Sprint and AT&T are eyeing LTE deployment in the 3.5 GHz band. All four of the US mobile network operators are members of the CBRS Alliance which is driving the LTE TDD use of this band for mobile. CableLabs was one of the first organizations to join to help set the direction of CBRS for our members. Charter and Comcast are now also members bringing key MSO support.
The collection of these mobile operators and the larger MSOs with interest in 3.5 GHz will help create the interest among the tier one handset vendors, such as Apple and Samsung, to support this band. Actually, at MWC 2017, Sony has already announced the support of band 42 in their new handset for Asia which supports the first 50 MHz of the CBRS band. One terminal research web site, The Global Mobile Suppliers Association (gsacom.com), claims that the new Samsung Galaxy 8 in April will also support band 42 at its launch. This is compelling since it means the engineering “tweaking” of the handset antennas has largely been solved. Beside these antennas, the silicon support of 3.5 GHz has already been achieved by Qualcomm in their latest Snapdragon modem released in October of last year. All of this bodes well for 2018 and handset support of the new CBRS band 48.
Outside the key handset issue, it is expected that the SASs and ESCs will be up and running at the end of 2017, promising full spectrum availability across the U.S. in 2018. The PAL auctions are expected towards the middle to end of 2018, but in the meantime operators will have access to all the spectrum as GAA.
Again, there was no shortage at MWC 2017 of the availability of Access Points (CBRDs) both for indoor and external use from the likes of AirSpan, Accelleran, Juni, Nokia and Sercom. And, I am sure I missed others there as well.
On the SAS side, Federated Wireless and Google are probably the leading SAS providers at the moment. However, besides Federated and Google, other WinnForum members which were successful in gaining licenses from the FCC in the first phase include Amdocs, Comsearch, CTIA, Keybridge and Sony. The WinnForum is driving the standards for the SAS and SAS to SAS interconnections. Again, here CableLabs is also a member.
BGR found last year that the average speed of LTE in the U.S. was only 10 Mbps, placing us at number 55 in the World with Singapore at number one with an average speed of 37 Mbps according to OpenSignal’s data. Here the customers needs are met by external macro-cellular networks which lose speed as they pass thru walls. However, locating small cells inside buildings, where 80% of mobile data is consumed today, can offer speeds as high as 570 Mbps if all of the GAA spectrum (80 MHz) is used with 4x4 MIMO. Even with access to just two channels, 20 MHz, this will offer 7 times faster than the average LTE network here according to CableLabs testing with 2x2 MIMO. But why stop there? We can aggregate 3.5 GHz and WiFi to reach a potential 1.4 Gbps.
CableLabs’ UpRamp Fiterator® has already identified one company, Trinity Mobile Networks, which uses Multipath TCP to aggregate both WiFi and Macro cell LTE networks to combine the speed of both. While in 2015, SK Telecom in Korea launched “Giga cells” which combines their WiFi network with LTE to reach 1.17 Gbps speeds in Android phones.
And Finally, One Last Thought
3.5 GHz offers the potential for US operators to offer 5G connection speeds years before 5G! All of this bodes well for an exciting 2018 for 3.5 GHz and for our members to take advantage of this spectrum for both mobile and fixed plays. Remember everything is wireless and wireless is everything!
Future Proofing Cable’s Optical Access Network: “A Coherent Story”
The demand for data network capacity has been growing exponentially year after year with no sign of stopping. If the past is a guide to the future, the cable industry must come up with radically more efficient use of the existing cable infrastructure in order to meet demand.
Today, the most constrained part of the network, and the most costly to upgrade, is the fiber infrastructure between the headend and the fiber node, to the wireless cell radio or to large business customers. Avoiding costly fiber re-trenching requires a fundamentally new approach to this part of the network. This is where coherent technology provides an opportunity.
If you are familiar with coherent optics, then you are aware that the technology has been used in long-haul fiber optic networks for decades. CableLabs has adapted that technology for use in short-haul access networks, and simplified it to reduce the cost. And it has much higher capacity for future growth than the analog optics that are used in many of today’s HFC networks – possibly more than 1,000 times more capacity! We have already demonstrated 50 times more capacity than analog optics can achieve today by using coherent optics on 80 kilometers of fiber, and more improvements are on the way.
Using traditional analog optics, to achieve that high transport medium quality requires increasing the optical transmit power level, which unfortunately reduces the number of optical analog carriers the fiber can support due to fiber non-linearity effects. Figure 1 shows a representation of fiber’s wavelength spectrum with 4 analog optical carriers.
Figure 1 – Fiber spectrum with 4 analog carriers
This limitation on analog optical transport has prompted the cable industry to look into other architectural evolution approaches. One approach that solves the analog limitation problem, while also tackling space limitations that may exist in certain hubs, is the distributed architecture approach. In a distributed architecture no radio frequency (RF) is transported through the optical link. The optical link does not contribute to distortion of the DOCSIS® RF signal, only the coaxial portion of the network is responsible for the degradation of the RF signal.
Today, this digital optical link uses intensity modulated direct detection systems such as the ones found in 10 Gigabit Ethernet links and in passive optical networks (PON). In these non-coherent systems, the signal modulation used is On-Off Keying (OOK). OOK is achieved by simply switching the laser source off and on. Non-coherent systems operate at lower power than analog optics and can therefore make better use of the wavelength spectrum in fiber. Figure 2 depicts the wavelength spectrum of fiber with several non-coherent OOK optical carriers.
Figure 2 – Fiber spectrum with intensity modulated non-coherent carriers
A high-capacity non-coherent (but digital) optical link can carry 100 Gbps using 10 wavelengths (optical carriers) carrying 10 Gbps each. Non-coherent systems are a suitable near term approach, but there are additional fiber resource challenges that have to be considered when evaluating a long-term strategy.
HFC Networks have been typically designed with 6 to 8 fibers connecting the hub to the fiber node. Two of these fibers are used for primary downstream and upstream connection and in some cases two additional fibers are used for redundancy purposes. The rest of the fibers were left for future use. Unfortunately, a large amount of these ‘future use’ fibers, because of an ever-increasing demand for bandwidth, have since been repurposed for business services, cell backhaul, node splits and fiber deep architectures. In some cases, only the two primary fibers that are feeding the fiber node remain available for access transport.
In fact, the architecture migration toward Full Duplex DOCSIS, which strives towards a more symmetric transport, relies on a node plus zero amplifiers (N+0) architecture. A typical node in today’s HFC networks will supply services to 500 households. When converted into an N+0 architecture, the result is the creation of 12 to 18 deeper N+0 nodes. The challenge for the optical portion of the access network becomes supplying enough bit rate capacity to 12-18 N+0 nodes, each capable of supplying 10 Gbps to residential subscribers.
This fiber shortage problem will only intensify as fiber demand for business services and wireless backhaul increases. Assuming that costly fiber re-trenching from hub to original fiber node is to be avoided, a different solution must be found to provide the required capacity. This is where coherent technology provides an opportunity!
Coherent technology has been used to achieve higher speeds than any other optical technology. In coherent optics, both amplitude and phase modulation are used to put information onto an optical carrier. This enables the generation of Quadrature Phase Shift Keying (QPSK) and Quadrature Amplitude Modulation (QAM) constellations carrying information. The nature of the coherent signal also allows the separation of the optical signal in two orthogonal polarizations. Each polarization can independently carry the two-dimensional constellations mentioned above. The signal processing used in coherent systems facilitates shaping of the spectrum of the signal to avoid interference with adjacent optical carriers. Along with the much lower power requirements, coherent technology allows for efficient multiplexing of the optical carriers within the wavelength spectrum of fiber. Figure 3 shows the wavelength spectrum of fiber with coherent optical carriers over 2 polarizations.
Figure 3 – Efficiently packed coherent optical carriers over orthogonal polarizations
Coherent optics has been used in the long-haul environment for over 30 years. The long-haul environment is a harsh environment that consists of very long distances, sometimes up to 3000 km. In a long-haul environment, significant channel compensation is employed to correct the long distance related impairments, making long haul solutions expensive.
The access network environment is very different from long haul networks in one key respect, optical links in access networks are typically no longer than 30 km. That is two orders of magnitude shorter than long haul. The complex and expensive system implementation that long haul is known for no longer applies to access implementation. The shorter fiber lengths result in minimal dispersion of the optical signal. Furthermore, since no in-line amplification is needed, non-linear distortion and noise are significantly reduced. This increases the link margin and enables much lower implementation costs. It is NOT your father’s coherent implementation!
Here at CableLabs® we have re-engineered the coherent link to meet the special conditions of the access network. We have developed technology that is higher performance and much lower cost when compared to long-haul or metro environments.
In the laboratory, we have achieved 256 Gbps over 80 km on a single wavelength with minimal dispersion compensation. That is ~26 times the capacity of what can be achieved over an analog optical carrier fully loaded with 1.2 GHz worth of DOCSIS 3.1 signals. We have achieved that using a symbol rate of 32 GBaud (32 GHz), using 16QAM modulation (4 bits per symbol) over 2 polarizations (32*4*2=256 Gbps). In addition, we have multiplexed eight of these wavelengths to achieve 2048 Gbps. That is 50 times more than what can be achieved over 4 analog optical carriers each with 10 Gbps of DOCSIS 3.1 payload!
The optical access environment could lend itself to further improvement in capacity per wavelength by further increasing symbol rate and/or modulation order. A future achievement of 64 QAM modulation could represent the pinnacle in efficiency and capacity per wavelength of our optical access environment. One can only dream of such transport efficiencies in the long-haul environment.
Coherent optics is extremely flexible. Capacities per wavelength greater than 256 Gbps may not be needed at each target end-point in the near future. Maybe 100 or 200 Gbps will do. The fact that modulation order, polarization and symbol rate can be varied enables significant flexibility in the type of supported services. Lower symbol rates allow for multiplexing 100 or 200 Gbps wavelengths to end points. In the access network, it makes sense to dedicate a single wavelength to a target end point (subscriber). In the access, since wavelength spectrum is a precious commodity, higher speed should not be wasted on multiple wavelengths but used to reach a greater diversity of target end-points. This avoids retrenching from the hub to original fiber node in order to lay additional fiber strands. Ideally, operators would only have to deploy more fiber from the original fiber node to deeper end-points in their networks.
As the industry evolves toward Node+0 architectures, the volume of optical connections to intelligent nodes will increase substantially compared to traditional architectures. Interoperability and a robust vendor ecosystem are therefore key to providing a low-cost solution using coherent optics.
With key goals being interoperability and vendor diversity, CableLabs intends to develop specifications which leverage the aforementioned benefits of coherent optics in the access network. Similar to previous specification development efforts, the coherent optics specifications will focus on interface requirements, signal integrity requirements, configuration, and management. As usual, CableLabs welcomes involvement from the vendor community to develop these specifications. In the near future, look for announcements related to the establishment of a coherent optics working group to develop the specifications.
At CableLabs, we are developing and specifying technology that allows the cable industry to support the growing requirements of broadband access. Come and join us in developing tomorrow’s high capacity network solutions!
Dr. Curtis Knittle, VP of Wired Technologies, also contributed to this article.
2017 Innovation Predictions
It’s that time of year for me to give my innovation predictions.
My top three predictions for 2017 are:
- Mixed Reality
- IoT Security
- Flexible Displays
Please take a look at the video where I elaborate on these three predictions.
Best wishes for a great year.
It's that time of year for me to give the predictions of the top three innovations coming in 2017. Now, I've been doing these predictions for many many years and actually have a pretty good track record. I've made most, I've missed a few. But also, I like to go out on a limb and give some predictions that kind of, maybe, push the envelope a little bit.
What's the number one prediction for 2017? It's around augmented reality, virtual reality, but more importantly, mixed reality. Mixed reality is really this combination of AR and VR where you actually see data and information that you can act upon. This kind of an experience is going to be really mind-blowing for people. It's really a great opportunity for content creators to think differently about the content they produce but also about the storytelling, the way of telling stories, and the way of making information interesting and actionable. So stay tuned, this is going to be a very exciting area. The first part of the year we're going to see more work in the hardware technologies. As we get into the latter half of the year, it's really going to be exciting to see some of this new content that is going to become available.
What's the second prediction? Second prediction is IoT: the Internet of Things is going to continue to be the hot area for 2017. Now, we've seen this introduction of IoT devices really explode in 2016. But one of the concerns that's really come out is security. The ability for hackers or people who are not friendly to be able to access IoT devices in consumers' homes has really become front-page news. So the question I have is, the technology is there, it's going to continue to expand, it's continued to be interesting. But as an industry, the security area has to be addressed before I predict broad consumer adoption of IoT devices. We're going to see IoT in everything from home security, home monitoring, heating, air conditioning, home appliances. We're also going to see some IoT devices and interesting areas like home health: healthcare devices that allow your doctors to monitor your healthcare, maybe after procedures or whatever, in your home and that just reinforces this one critical area which is around security to make this technology broadly available.
The third area is around display devices. Now, if you go back and you look at my predictions in previous years, I've talked about 3D the year it became a hot issue at some of the trade shows. We've talked about 4K. 4K high dynamic range (HDR) which is broadly going to be just a boon area for this year. In fact in 2016, in going into the holiday season, it became really very prevalent for people to buy these new kinds of TVs. What is left to be done in display technologies? What's left to be done is around flexible displays. Flexible displays being built on new kinds of materials such as this mylar, which is the backing material that's being used in some of the flexible displays that you'll see come available in the first part of 2017. This allows for displays to be manufactured that are one millimeter thick that literally you can attach to your wall as if it were wallpaper. What does this mean for the broad marketplace? When you have that kind of technology -- very low-cost but very flexible -- from the standpoint of how it gets used, we will see flexible displays on TVs as obvious, but also transforming things like whiteboards, collaboration technologies, technologies used in the classroom, advertising displays in retail and billboards. You'll be able to get these kinds of displays at such a low cost that you can literally transform every flat surface you see and turn that into a new kind of display for use of all kinds of ways.
So those are the three predictions for 2017. We have everything from the AR/VR/mixed reality, the Internet of Things, and these new kinds of displays.