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`ADSL2: Taking the Next Step in Broadband Designs | EE Times
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`Design How-To
`ADSL2: Taking the Next Step in
`Broadband Designs
`ADSL2: Taking the Next Step in Broadband
`DeS'9"s
`.
`.
`.
`.
`.
`Eivid Benini and David Krinsky, Aware
`7/18/2002 07:09 AM EDT
`Posta comment
`o
`l:| lG+1l
`:1
`As members of the broadband design community have been
`perfecting their designs based on the first generation of ADSL
`standards (ITU G.992.1 and G.992.2), the ITU has quietly been
`putting the finishing touches on the latest revision of the ADSL
`standards, referred to at the ITU as "G.dmt.bis" and "G.lite.bis",
`will be better known as ADSL2.
`ADSL2 (ITU G.992.3 and G.992.4) adds new features and
`functionality targeted at improving performance and
`interoperability, and adds support for new applications, services,
`and deployment scenarios. Among the changes are
`improvements in data rate and reach performance, rate
`adaptation, diagnostics, and stand-by mode, to name a few. The
`article that follows takes an in—depth look at the ADSL2 spec by
`examining some of the opportunities it provides to improve upon
`existing ADSL system and silicon designs.
`
`Extending Reach
`Mention the words broadband connection in a room and you'll
`hear plenty of cheers and—depending on the neighborhood—a
`fewjeers. The cheers are from those fortunate DSL customers
`living close enough to a central office (CO) to quickly download
`flashy web pages. The jeers are likely from the few remaining
`subscriber—wannabes still waiting for the phone company to
`provide DSL connectivity in their neighborhood.
`
`Of course, the issues here are rate and reach. ADSL2 has been
`specifically engineered to enable designers to improve the rate
`and reach of ADSL largely by achieving better performance on
`long lines in the presence of narrowband interference. ADSL2
`accomplishes this by improving modulation efficiency, reducing
`framing overhead, achieving higher coding gain, improved the
`initialization state machine, and providing enhanced signal
`processing algorithms. As a result, ADSL2 mandates higher
`performance for all standard-compliant devices.
`
`ADSL2 provides better modulation efficiency by mandating a four-
`dimensional, 16-state trellis-coded and 1-bit quadrature amplitude
`modulation (QAM) constellations which provide higher data rates
`on long lines where the signal-to-noise ratio (SNR) is low. In
`
`http://www.eeti m es.com/docum ent.asp?doc_id= 1277699
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`Exhibit 1036, Page 1
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`7/13/2016
`
`ADSL2: Taking the Next Step in Broadband Designs | EE Times
`addition, receiver determined tone-reordering enables the
`why Nemorks Need Asics
`receiver to spread out the non-stationary noise due to AM radio
`interference to get better coding gain from the \fiterbi decoder.
`
`ADSL2 systems reduce framing overhead by providing a frame
`with a programmable number of overhead bits. Therefore, unlike
`the first-generation ADSL standards where the overhead bits per
`frame were fixed and consumed 32 kbps of actual payload data,
`in the ADSL2 standard the overhead bits per frame can be
`programmed from 4 to 32 kbps. In the first-generation ADSL
`systems on long lines where the data rate is low (.e.g < 128=""
`kbps),="" a="" fixed="" 32='"‘ kbps="" (or="" 25%="" of="" the=""
`total='"' data='"' rate)="" is="" allocated='"' to='"' overhead=
`information.
`data:
`rate="" can
`which=""provides-" an=""additional="“28=' kbps=""for=""
`pay|oad="" data.="">
`
`ADSL2 also achieves higher coding gain from the Reed-Solomon
`(RS) code when the data rates are low on long lines. This higher
`coding gain results from improved flexibility and programmability
`in the construction of RS codewords that results also from the
`improvements in the ADSL2 framers.
`
`Additionally, the initialization state machine has numerous
`improvements that provide increased data rates in ADSL2
`systems. Examples of these improvements include:
`
`- Power cutback capabilities at both ends of the line to reduce
`near-end echo and the overall crosstalk levels in the binder.
`Receiver determines the location of the pilot tone in order to
`avoid channel nulls from bridged taps or narrow band
`interference from AM radio.
`Receiver and transmitter control the length of certain key
`initializations states in order to allow optimum training of
`receiver and transmitter signal processing functions.
`Receiver determines the carriers used for initialization
`messages in order to avoid channel nulls from bridged taps
`or narrow band interference from AM radio.
`Improvement in channel identification for training receiver
`time domain equalizer with spectral shaping during Channel
`Discovery and Transceiver Training phases of initialization.
`Tone blackout (disabling tones) during initialization to
`enable Radio Frequency Interference (RFI) cancellation
`schemes.
`
`Figure 1 shows the rate and reach of ADSL2 as compared to the
`first-generation ADSL standard. On longer phone lines, ADSL2 will
`provide data rate increase of 50 kbps — a significant increase for
`those customers who need it most. This data rate increase results
`in an increase in reach of about 600 feet, which translates to an
`increase in coverage area of about 6%, or 2.5 square miles.
`
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`Figure 1: ADSL2 systems can deliver an improvement in reach of
`about 600 feet over existing copper networks.
`
`http:/lwww.eetimes.com/document.asp?docJd=1277699
`
`Dish
`Exhibit 1036, Page 2
`
`

`
`ADSL2: Taking the Next Step in Broadband Designs | EE Times
`_
`Tracking Down Problems
`_
`Determining the cause of problems in consumer ADSL service has
`EE 1-‘mes °" Twmer
`at times been a challenging obstacle in ADSL deployments. To
`tackle the problem, ADSL2 transceivers have been enhanced with
`EE -“mes Retweeted
`extensive diagnostic capabilities. These diagnostic capabilities
`provide tools for trouble resolution during and after installation,
`performance monitoring while in service, and upgrade
`qualification.
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`_
`_
`_
`In order to diagnose and fix problems, ADSL2 transceivers
`provide measurements for line noise, loop attenuation, and signal-
`to-noise ratio (SNR) at both ends of the line. These
`measurements can be collected using a special diagnostic testing
`mode even when line quality is too poor to actually complete the
`ADSL connection.
`
`Additionally, ADSL2 includes real-time performance monitoring
`capabilities that provide information on line quality and noise
`conditions at both ends of the line. This information is interpreted
`by software and then used by the service provider to monitor the
`quality of the ADSL connection and prevent future service failures.
`It can also be used to determine if a customer can be offered
`higher data rate Se,-Vice5_
`
`Power Enhancements
`First-generation ADSL transceivers operate in full-power mode
`day and night, even when not in use. With several millions of
`deployed ADSL modems, a significant amount of electricity can be
`saved if the modems engage in a stand-by/sleep mode just like
`computers. This would also save power for ADSL transceivers
`operating in small remote units and digital loop carrier (DLC)
`cabinets that operate under very strict heat dissipation
`requirements.
`
`To address these concerns, the ADSL2 brings in two power
`management modes that help reduce overall power consumption
`while maintaining ADSL's "a|ways-on" functionality for the user.
`These modes include:
`
`1. L2 low-power mode: This mode enables statistical powers
`savings at the ADSL transceiver unit in the central office
`(ATU-C) by rapidly entering and exiting low power mode
`based on Internet traffic running over the ADSL connection.
`. L3 low-power mode: This mode enables overall power
`savings at both the ATU-C and the remote ADSL
`transceiver unit (ATU-R) by entering into sleep/stand-by
`mode when the connection is not being for extended
`periods of time (i.e. user asleep, modem asleep).
`
`The L2 power mode is one of the most important innovations of
`the ADSL2 standard. ADSL2 transceivers can enter and exit the
`L2 low power mode based on the Internet traffic over the ADSL
`connection. When large files are being downloaded, ADSL2
`operates in full power mode (called "L0" power mode) in order to
`maximize the download speed. When Internet traffic decreases,
`such as when a user is reading a long text page, ADSL2 systems
`transition into L2 low power mode, in which the data rate is
`significantly decreased and overall power consumption is reduced.
`
`While in L2, the ADSL2 system can instantly re-enter L0 and
`increase to the maximum data rate as soon the user initiates a file
`download. The L2 entry/exit mechanisms and resulting data rate
`adaptations are accomplished without any service interruption or
`even a single bit error, and as such, are not noticed by the user
`(Figure 2).
`
`http://www.eeti m es.com/docum ent.asp?doc_id= 1277699
`
`Dish
`Exhibit 1036, Page 3
`
`

`
`7/13/2016
`
`ADSL2: Taking the Next Step in Broadband Designs | EE Times
`
`Figure 2: ADSL’s L2 power mode allows a broadband modem to
`quickly move from L2 to L0 operation and back without limited bit
`errors.
`
`The L3 power mode is a total sleep mode where no traffic can be
`communicated over the ADSL connection when the user is not on-
`line. When the user returns to go on-line the ADSL transceiver
`require approximately three seconds to re-initialize and enter into
`steady state communication mode.
`
`Rate Adaptation
`Telephone wires are bundled together in multi-pair binders
`containing 25 or more twisted wire pairs. As a result, electrical
`signals from one pair can electromagnetically couple onto other
`adjacent pairs in the binder (Figure 3). This phenomenon is
`known as "crosstalk" and can impede ADSL data rate
`performance. As a result, changes in the crosstalk levels in the
`binder can cause an ADSL system to drop the connection.
`
`Crosstalk is just one reason that ADSL lines drop connections.
`Others include changes in the narrowband, AM radio disturbers;
`temperature changes, and water in the binder.
`
`Figure 3: When adjacent pairs couple together they can cause
`crosstalk on an copper line, thus forcing the ADSL system to drop
`a connection.
`
`ADSL2 addresses this problem by including the ability to
`seamlessly adapt the data rate on-line. This new innovation,
`called seamless rate adaptation (SRA), enables the ADSL2
`system to change the data rate of the connection while in
`operation without any service interruption or bit errors. ADSL2
`simply detects changes in the channel conditions — for example,
`a local AM radio station turning off its transmitter for the evening
`— and adapts the data rate to the new channel condition
`transparently to the user.
`
`http:llwww.eetimes.comldocument.asp?docJd=1277699
`
`Dish
`Exhibit 1036, Page 4
`
`

`
`7/13/2016
`
`ADSL2: Taking the Next Step in Broadband Designs | EE Times
`SRA is based on the decoupling of the modulation layer and the
`framing layer in ADSL2 systems. This decoupling enables the
`modulation layer to change the transmission data rate parameters
`without modifying parameters in the framing layer which would
`cause the modems to loose frame synchronization resulting in
`uncorrectable bit errors or system restart. SRA uses the
`sophisticated online reconfiguration (OLR) procedures of ADSL2
`systems to seamlessly change the data rate of the connection.
`The protocol used for SRA works as follows:
`1. The receiver monitors the SNR of the channel and
`determines that a data rate change is necessary to
`compensate for changes in channel conditions.
`. The receiver sends a message to the transmitter to initiate
`a change in data rate. This message contains all necessary
`transmission parameters for transmitting at the new data
`rate. These parameters include the number of bits
`modulated and transmit power on each subchannel in ADSL
`multicarrier system.
`. The transmitter sends a "Sync F|ag" signal which is used as
`a marker to designate the exact time at which the new data
`rate and transmission parameters are to be used.
`. The Sync Flag signal is detected by the receiver and both
`transmitter and receiver seamlessly and transparently
`transition to the data rate.
`
`Bonding For higher Data Rates
`One of the big requests by today's carriers is the ability to provide
`different service level agreements (SLAs) to different customers.
`For example, carriers want to deliver a standard bandwidth
`requirement to the majority of home users while providing higher
`bandwidth offerings for corporations.
`
`The original ADSL standard did not support bonding, so designers
`did not have the ability to deliver these advanced SLA capabilities
`in equipment designs. However, through the support for bonding,
`ADSL2 is addressing these requests.
`
`Bonding multiple phone lines together is a relatively simple way to
`significantly increase data rates to homes and businesses. To
`provide bonding, the ADSL2 spec taps into the inverse
`multiplexing for ATM (IMA) standard developed for traditional ATM
`architectures. Through IMA, equipment designs can bind copper
`pairs in an ADSL link (Figure 4) . The result is a far greater deal
`of flexibility with downstream data rates:
`
`- 20 Mbps on 2 bonded pairs
`- 30 Mbps on 3 bonded pairs
`- 40 Mbps on 4 bonded pairs
`
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`
`Figure 4: Through bonding, design engineers can increase the
`data throughput on an ADSL channel to as high as 40 Mbps.
`
`The IMA standard specifies a new sublayer that resides between
`the ADSL physical layer (PHY) and the ATM layer. At the
`transmitter side, this sublayer, called the IMA sublayer, takes in a
`
`http:/lwww.eetimes.com/document.asp?docJd=1277699
`
`Dish
`Exhibit 1036, Page 5
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`

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`7/13/2016
`
`ADSL2: Taking the Next Step in Broadband Designs | EE Times
`single ATM stream from the ATM layer and distributes this stream
`to multiple ADSL PHYs. At the receiver side, the IMA sublayer
`takes in ATM cells from multiple ADSL PHYs and reconstructs the
`original ATM stream.
`
`The IMA sublayer specifies IMA framing, protocols and
`management functions that are used to perform these operation
`when the PHYs are lossy (bit errors), asynchronous, and have
`different delays. In order to work under these conditions, the IMA
`standard also requires modifications to some of the standard
`ADSL PHY functions such as the discarding of idle cells and
`errored cells at the receiver. The ADSL2 includes an IMA
`operation mode to provide the necessary PHY modifications for
`IMA to work in combination with ADSL.
`
`Bonding using ADSL2 is expected to play a role in helping carriers
`to provide bandwidth-hungry applications such as video and
`gaming to residential customers. It will also be effective in
`delivering high-bandwidth services to businesses who prefer
`asymmetric over symmetric data rates.
`Some Added Benefits
`Clearly, the above benefits provide some nice enhancements
`during the design and development of ADSL equipment. The
`ADSL2 specification, however, does not stop there. In addition to
`the above benefits, ADSL 2 delivers:
`
`1. Improved Interoperability: Clarifications and additions to the
`initialization state machine improve interoperability and
`provide better performance when connecting ADSL
`transceivers from different chip suppliers.
`. Fast startup: ADSL2 provides a fast startup mode that
`reduces initialization time from more 10 seconds (as is
`required for ADSL) to less than 3 seconds.
`. Channelization: ADSL2 provides the ability to split the
`bandwidth into different channels with different link
`characteristics for different applications. For example,
`ADSL2 enables simultaneous support of a voice application,
`which might have low latency but a higher error rate
`requirement, and a data application, which might have high
`latency but lower error rate requirement. ADSL2 also
`provides support for channelized voice-over-DSL (VoDSL),
`a method to transport derived lines of TDM voice
`transparently over DSL bandwidths.
`. All Digital Mode: ADSL2 enables an optional mode that
`allows for transmission of ADSL data in the voice
`bandwidth, adding 256 kbps of upstream data rate. This is
`an attractive option for businesses that have their voice and
`data services on different phone lines, and value the extra
`upstream bandwidth.
`. Support of Packet-Based Services: ADSL2 includes a
`packet mode transmission trans-convergence layer (PTM-
`TC) that enables packet-based service (such as Ethernet)
`to be transported over ADSL2.
`
`By the first quarter of next year, leading silicon vendors are
`expected to have dual-mode solutions available, supporting both
`legacy ADSL equipment as well as new ADSL equipment.
`About the Authors
`David Benini is the director of product marketing at Aware. He
`holds a BS Degree in electrical engineering from Penn State
`University and an MBA Degree from Cornell University. Dave can
`e reached at dave@aware.com.
`
`David Krinsky is the senior director of software development at
`Aware, Inc. He holds a BS from Cornell University, an MSEE from
`Northeastern University, and a Ph.D. from Northwestern
`University. David can be reached at dkrinsky@aware.com.
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`Dish
`Exhibit 1036, Page 6
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`

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`7/13/2016
`
`ADSL2: Taking the Next Step in Broadband Designs | EE Times
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