FACE=3D"Arial">>       that close the = optical eye completely; or
>
>    b) another = using a lower baud rate
>       and working = with minimal ISI so that
>       the optical eye = at the input of the
>       receiver is = widely open,
>
> which one has more chance to = meet the required
> BER of 10^(-12), and discard = accordingly the
> one that does not have a = chance.
>
> Jaime
>
> Jaime E. Kardontchik
> Micro Linear
> San Jose, CA 95131
> email: = kardontchik.jaime@ulinear.com

------_=_NextPart_001_01BF82C7.64FC96A2-- From owner-stds-802-3-hssg@ieee.org Tue Feb 29 19:54 GMT 2000 Received: from gatekeeper.pdd.3com.com (gatekeeper [161.71.169.3]) by isolan.pdd.3com.com (8.9.1b+Sun/8.9.3) with ESMTP id TAA21714; Tue, 29 Feb 2000 19:54:25 GMT Received: from ruebert.ieee.org ([199.172.136.3]) by gatekeeper.pdd.3com.com (Netscape Messaging Server 3.6) with ESMTP id AAA156F; Tue, 29 Feb 2000 19:52:44 +0000 Received: by ruebert.ieee.org (8.9.3/8.9.3) id OAA23964; Tue, 29 Feb 2000 14:11:57 -0500 (EST) From: "Edward Chang" To: "jmw" , , , Subject: RE: PAM-5, what are your BERs ? Date: Tue, 29 Feb 2000 14:17:06 -0500 Message-ID: MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Priority: 3 (Normal) X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook IMO, Build 9.0.2416 (9.0.2910.0) In-Reply-To: <4.2.0.58.20000229064314.00a867e0@mail.bayarea.net> Importance: Normal X-MimeOLE: Produced By Microsoft MimeOLE V5.00.2314.1300 Sender: owner-stds-802-3-hssg@ieee.org Precedence: bulk X-Resent-To: Multiple Recipients X-Listname: stds-802-3-hssg X-Info: [Un]Subscribe requests to majordomo@majordomo.ieee.org X-Moderator-Address: stds-802-3-hssg-approval@majordomo.ieee.org X-Lines: 110 Status: RO Content-Type: text/plain; charset="us-ascii" Content-Length: 4088 Mike: We are discussing the product developments, which are based on proved theorems and equations to mathematically calculate all designs. After that, setting up tests to confirm that the test data, and the analyses are correlated. Otherwise, repeat the procedures to achieve the goals. Finally, it will go through extensive system tests and BER tests to certify a product. Engineers do not just "looking at a scope", then make the comment. They theorize it, quantify it, then make comments. Unless, some one has extensive communication product development experience in the past, it is hard for a one to grasp, and appreciate the contents of the comments put forward on reflectors by those serious contributors. The term, S/N ratio, is a very abstract term to those who are not circuit designers. However, to the circuit designer, S/N ratio can hurt you as real as putting your finger on top of a fire. The cascading of the frequency response of each component to predict the over-all system frequency response is a well known basic tool implemented by all circuit designers. It is as predictable as, 1+1 = 2. Regards, Edward S. Chang NetWorth Technologies, Inc. EChang@NetWorthtech.com Tel: (610)292-2870 Fax: (610)292-2872 -----Original Message----- From: owner-stds-802-3-hssg@ieee.org [mailto:owner-stds-802-3-hssg@ieee.org]On Behalf Of jmw Sent: Tuesday, February 29, 2000 10:00 AM To: NetWorthTK@aol.com; vivek@cicada-semi.com; stds-802-3-hssg@ieee.org Subject: Re: PAM-5, what are your BERs ? Edward, my $0.02: it is not always the case that because a thing seems to be true on first examination, it must therefore always be true. SNR is certainly a critical issue for any receiver in any communication system. Claude Shannon proved that a long time ago. but aside from bandwidth and data rate issues (for the moment, of course), if "signal" and "noise" are sufficiently statistically independent, then the two can be separated and the signal recovered. for this case it is not enough to look at a 'scope display, say to yourself "gee, that looks like nothing but noise to me", and decide you're done. -- J M Wincn Cielo Communications, Inc. 325 Interlocken Pkwy, Bldg A Broomfield, CO 80021-3497 mwincn@cieloinc.com Voice: 303-464-2264 Cell: 408-394-5283 At 01:15 AM 29-02-2000 -0500, NetWorthTK@aol.com wrote: >Hi Vivel: > > >From theoretical point of view, you reasoning makes some points. However, >from the real implementation point of view, it is not quite true. Before >starting analyzing the frequency response, just ask a question: "If we can >simply keep equalizing the receiving signals to bring them back to the >looking-alike to the original, transmitting signal, why we bother all those >bandwidth issues? There must be some limitations to the equalization >technique. > >The eye closure is caused by the insufficient bandwidth of a receiving path; >as a result, the narrow pulse (higher frequency pulse) is much more >attenuated than the wider pulse (lower frequency pulse). We can cascade a >high-pass frequency response equalizer to suppers the amplitude of a wide >pulse, and keep the amplitude of the narrow pulse remain unchanged (but not >amplified) to open the eye. However, if the amplitude of a narrow pulse is >already too small to meet the minimum S/N requirement, the equalizer is >useless. Theoretically, a linear amplifier can be added to bring the signal >amplitude up to meet the minimum S/N requirement. The linear amplifier will >need a BW larger than the transmitting signal rise time. Furthermore, any >deficiencies in the linearity, will add both timing and amplitude distortion >to the received data. The additional distortion is not included in the >jitter specification; as a result, the link will cause higher BER. >Especially in a high data rate link, a linear amplifier may cause more errors >than the expected benefit. In practice, it is impractical to add a linear >amplifier. > >The right way is to keep eye open at the receiver input. > >Regards, > >Ed Chang > >NetWorth Technologies, Inc. From owner-stds-802-3-hssg@ieee.org Tue Feb 29 20:00 GMT 2000 Received: from gatekeeper.pdd.3com.com (gatekeeper [161.71.169.3]) by isolan.pdd.3com.com (8.9.1b+Sun/8.9.3) with ESMTP id UAA21818; Tue, 29 Feb 2000 20:00:14 GMT Received: from ruebert.ieee.org ([199.172.136.3]) by gatekeeper.pdd.3com.com (Netscape Messaging Server 3.6) with ESMTP id AAA1581; Tue, 29 Feb 2000 19:58:32 +0000 Received: by ruebert.ieee.org (8.9.3/8.9.3) id OAA25120; Tue, 29 Feb 2000 14:16:52 -0500 (EST) From: "Edward Chang" To: "David Martin" , Subject: RE: PAM-5, what are your BERs ? Date: Tue, 29 Feb 2000 14:22:58 -0500 Message-ID: MIME-Version: 1.0 X-Priority: 3 (Normal) X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook IMO, Build 9.0.2416 (9.0.2910.0) In-Reply-To: Importance: Normal X-MimeOLE: Produced By Microsoft MimeOLE V5.00.2314.1300 Sender: owner-stds-802-3-hssg@ieee.org Precedence: bulk X-Resent-To: Multiple Recipients X-Listname: stds-802-3-hssg X-Info: [Un]Subscribe requests to majordomo@majordomo.ieee.org X-Moderator-Address: stds-802-3-hssg-approval@majordomo.ieee.org Content-Type: multipart/alternative; boundary="----=_NextPart_000_003D_01BF82C0.79F36830" X-Lines: 1095 Status: RO Content-Length: 44411 ------=_NextPart_000_003D_01BF82C0.79F36830 Content-Type: text/plain; charset="iso-8859-1" X-Sun-Content-Length: 12910 RE: PAM-5, what are your BERs ?Dave: Are you suggesting, that if the BER of GbE is 10^-12, then the BER of the 10xGbE should be less? For example, 10^-13 to maintain the expected throughput gain from 10xGbE? Regards, Edward S. Chang NetWorth Technologies, Inc. EChang@NetWorthtech.com Tel: (610)292-2870 Fax: (610)292-2872 -----Original Message----- From: owner-stds-802-3-hssg@ieee.org [mailto:owner-stds-802-3-hssg@ieee.org]On Behalf Of David Martin Sent: Tuesday, February 29, 2000 10:12 AM To: stds-802-3-hssg@ieee.org Subject: RE: PAM-5, what are your BERs ? Jaime, A clarification on backbone transport BER spec's. For OC-48 systems, although BCR GR-253 spec'd 1E-10 for worst case end-of-life, the defacto customer requirement was 1E-12. Similarly, for OC-192 systems, although BCR GR-1377 spec'd 1E-12 for worst case end-of-life, the defacto customer requirement has been 1E-15. Note that the current target proposed for the ITU defined Optical Transport Network is also 1E-15. ...Dave David W. Martin Nortel Networks +1 613 765-2901 +1 613 763-2388 (fax) dwmartin@nortelnetworks.com ======================== -----Original Message----- From: Jaime Kardontchik [SMTP:kardontchik.jaime@ulinear.com] Sent: Monday, February 28, 2000 12:05 PM To: stds-802-3-hssg@ieee.org Subject: Re: PAM-5, what are your BERs ? Hello Vivek, A few months ago there was a discussion on the Reflector where some members claimed that the BERs in some optical backbones reached easily the 10^(-15). The repply to these claims was that although this might be true, the philosophy of the 802.3, that made its standards so successful, was to design based on worst case conditions. Therefore, the Ethernet optical networks were specficied to a BER of only 10^(-12). The same holds for the Ethernet Copper links. Although it might be true that some links of 100BASE-TX reach a BER of 10^(-12), the official BER adopted in the Standard was only 2.5*10^(-10). And the same for the 1000BASE-T, where the Standard adopted to support a BER of 10^(-10). The reason for this higher BERs in the Copper networks is ISI (Inter Symbol Interference). Or, in layman's language: is the eye open or not at the input of the receiver ? Jaime Jaime E> Kardontchik Micro Linear San Jose, CA 95131 Vivek Telang wrote: > Hello Jaime and 10G'ers, > > I had to jump in to try and correct this misconception of the "eye opening requirement". While it is true that the "open eye" is always a good thing, it is definitely not a requirement for low BER reception. If it were a requirement, the tried and true 100BaseTX Ethernet would not be functioning today. Many existing implementations of 100BaseTX silicon easily achieve BERs of 1e-12 over 170+ meters of twisted pair cable, and the eye is very much closed in this case. Not to mention that near-end crosstalk (NEXT) makes matters significantly worse. Also, in 1000BaseT, if the only impairment was ISI, and Echo, NEXT and FEXT were absent, BERs of 1e-12 could be easily achieved, even with a 5-level symbol constellation. > > An open eye is a requirement for systems that use simple lock-and-slice techniques, where little or no processing of the signal is done, other than maybe amplification, and a PLL locks to the data clock and slices the data. In contrast, in a DSP-based system, the combination of linear feedforward equalizers and DFEs using simple LMS adaptation can easily deal with "closed eyes". Even with a blind start-up. > > The implementation of a DSP-based system (including a 6-bit ADC) at 5GHz in CMOS is a different matter altogether, and I am eagerly awaiting Oscar's presentation at the March meeting. > > Regards, > > Vivek > > *--------------------------------------- > * > * Vivek Telang > * Cicada Semiconductor Inc. > * 901 MoPac Expressway South > * Building One, Suite 540 > * Austin, Texas 78746 > * > * 512-327-3500 x114 voice > * 512-327-3550 fax > * vivek@cicada-semi.com > * http://www.cicada-semi.com > * > *--------------------------------------- > > -----Original Message----- > From: Jaime Kardontchik [SMTP:kardontchik.jaime@ulinear.com] > Sent: Sunday, February 27, 2000 6:37 PM > To: stds-802-3-hssg@ieee.org > Subject: PAM-5, what are your BERs ? > > Hello 10G'ers, > > Edward Chang was right on target. > He wrote on Feb 23: > > > In the past, the multiple voltage-level coding > > was adopted by two LAN standards, ATM and > > Ethernet. Both of them were twisted-pair > > applications, and the BER were 10^(-10). > > I proposed BER of 10^(-12) in both working > > groups to be consistent with the LAN optical > > links' BER; however, for some reason, they > > remain 10^(-10), officially in both standards. > > What was the reason ? > > Multilevel voltage coding was not the reason. > On the contrary, it was a remedy. The real reason > was the strong ISI at the maximum link lengths > that these Standards wanted to support. > Multi-level voltage coding was adopted to > lower the baud rate or the frequency content > of the signal in order to make the ISI smaller > and get a better BER. > > However, the remaining ISI in these Copper links > remained high enough that the eye at the > input of the receiver remained still > completely closed. It is this closed eye that > limited the achievable BER in the Copper media > to 10^(-10). Post-equalizers, no matter how > sophisticated they were, are not able to > completely reverse the effects of eye closening > on the achievable BER. > > ---> Conclusion ? In order to get a BER of > 10^(-12) you have to have a clear > open eye at the input of the receiver. > The maximum supported link length > is set accordingly to meet this basic > condition: open eye. > > Now we can go to the basic two PAM-5 proposals: > > 1) PAM-5 serial at 5 Gbaud > > Using 1300 nm lasers lasers at 5 Gbaud the > optical eye is completely closed already at > ~170 meters due to heavy ISI (installed MMF, > 500 MHz*km bandwidth). > > Oscar claimed a support of 500 meters of > installed MMF and pointed out that > DFEs (equalizers) have been successfuly used > in 100 and 1000 Mbps Copper networks. > However, the specs and experience of the 100 Mbps > and 1000 Mbps links over Copper - where the eye > at the input of the receiver is completely > closed at the target link length due to ISI - > put the achievable BERs around 10^(-10) only. > Even using sophisticated equalizers. > > What is the experimental support that a BER > of 10^(-12) could be achieved when a strong ISI > closes completely the eye at the input of the > receiver ? I think that none and that the > experience points to the contrary. Why then > could an equalizer running at 5 GHz achieve > here what sophisticated equalizers running > 40 times slower (125 MHz) were not able to achieve > in the Copper Ethernets ? Parallel processing > could enable perhaps to meet the timing > constraints of the design by running multiple > equalizers at a lower clock, but will not > eliminate the basic limitation on achievable > BERs once the eye at the input of the receiver > is already completely closed. > > Let us see now the case PAM-5 at 1.25 Gbaud: > > 2) PAM-5 4-WDM at 1.25 Gbaud > > Let us compare this approach to two other well > known on-off approaches: 1 GbE and 4-WDM at > 3.125 Gbaud using the 8b/10b coding. Let us > assume again 1300 nm lasers and installed > 500 MHz*km MMF. > > The figures below (I hope will not get distorted > during transmission) show the power levels of > the three systems. For 1 GbE I assumed no ISI. > For PAM-5 I assumed 400 meters link length > (there is no ISI up to this distance, ISI= 0 dB). > For 4-WDM at 3.125 Gbaud I assumed 300 meters link > length and about 3 dB optical loss due to ISI. > > | | > | | > | | 1 GbE, 1.25 Gbaud, no ISI > | | > | | > > | | | | | > | | | | | > | | | | | PAM-5 4-WDM at 1.25 Gbaud > | | | | | no ISI. > | | | | | > > |**** ****| > |**** ****| > |**** ****| 8b/10b 4-WDM at 3.125 Gbaud > |**** ****| 3 dB ISI loss > |**** ****| > > ( the asterisks denote closening of the eye due > to ISI) > > 2a) 1 GbE > > By definition, the optical power difference > between the '0' and '1' levels in the 1 GbE > case is 1: > > optical signal power = 10*log(1) = 0 dB > > optical SNR = 0 dB (reference) > > And we get a BER of 10^(-12). > > 2b) PAM-5 4-WDM at 1.25 Gbaud > > In the PAM-5 case, notice that using the > "open fiber control" method that I described > in a previous email, we get the same launched > power per channel as in the 1 GbE Ethernet. > However, in PAM-5 the power difference > between levels is 0.25 (this is the well > known 6 dB optical power penalty loss of > the PAM-5 modulation). Let us now add > the 6 dB electrical coding gain provided > by the Viterbi decoding: the effective distance > between levels doubles. Summarizing, in PAM-5 > 4-WDM at 1.25 Gbaud, the effective optical > signal power difference between levels is: > > effec optical signal power diff = > 10*log(2*0.25) = - 3 dB > > where the factor 2 inside the log comes > from the coding gain. > > The noise power at the input of the > receiver is the same as in 1 GbE because > we use the same baud rate. Hence, > > effec optical SNR = - 3 dB > > This is not bad compared to the 0 dB of 1 GbE. > Furthermore, notice that we could even bring > back the SNR for PAM5 to 0 dB (the 1 GbE > reference) if a new laser safety proposal > to move the maximum safe power from -4 dBm > to -1 dBm is accepted. See P. Kolesar et al > presentation in the next March meeting. > > 2c) 8b/10b 4-WDM at 3.125 Gbaud > > In this case the eye is half closed due > to ISI. Hence the optical power difference > is: > > optical signal power = 10*log(0.5) > = - 3 dB > > and the electrical noise power at the input > of the receiver is larger, since the receiver > needs more bandwidth: > > elec noise power = 10*log[(3.125/1.25)^2] > = 8 dB > > Hence, the optical SNR is > > optical SNR = - 3 - 8/2 = -7 dB > > This case is clearly worse than the 1 GbE > case in terms of optical SNR. And the > Task Force considers that this system > can achieve the needed 10^(-12) BER. > > Summarizing: > > PAM-5 4-WDM at 1.25 Gbaud has no > ISI, a clear and wide open eye at > the input of the receiver, an optical SNR > only slightly less than the SNR of present > 1 GbE transceivers and better than > the proposed 8b/10b 4-WDM at 3.125G > transceivers. > > Hence, it is a good choice if one > wants to reach the required BER of > 10^(-12). > > Note: the above analysis, based on simple > static SNRs, is not a substitute for a > much more careful analysis regarding > the viabibility of any PAM-5 approach. > However, a simple back-of-the-envelope > analysis is very useful to make a quick > comparison between different PAM-5 proposals > in order to find out which PAM-5 architecture, > > a) one working under strong ISI conditions > that close the optical eye completely; or > > b) another using a lower baud rate > and working with minimal ISI so that > the optical eye at the input of the > receiver is widely open, > > which one has more chance to meet the required > BER of 10^(-12), and discard accordingly the > one that does not have a chance. > > Jaime > > Jaime E. Kardontchik > Micro Linear > San Jose, CA 95131 > email: kardontchik.jaime@ulinear.com ------=_NextPart_000_003D_01BF82C0.79F36830 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable X-Sun-Content-Length: 31170 RE: PAM-5, what are your BERs ?
Dave:
 
Are=20 you suggesting, that if the BER of GbE is 10^-12, then the BER of the = 10xGbE=20 should be less?  For example, 10^-13 to maintain the expected = throughput=20 gain from 10xGbE?
 

Regards,

Edward S. Chang
NetWorth = Technologies,=20 Inc.
EChang@NetWorthtech.com
Tel: (610)292-2870
Fax: = (610)292-2872=20

-----Original Message-----
From:=20 owner-stds-802-3-hssg@ieee.org = [mailto:owner-stds-802-3-hssg@ieee.org]On=20 Behalf Of David Martin
Sent: Tuesday, February 29, 2000 = 10:12=20 AM
To: stds-802-3-hssg@ieee.org
Subject: RE: = PAM-5, what=20 are your BERs ?


Jaime,

A clarification on backbone transport = BER spec's.=20 For OC-48 systems, although BCR GR-253 spec'd
1E-10 for worst case end-of-life, the defacto customer = requirement was=20 1E-12. Similarly, for OC-192
systems,=20 although BCR GR-1377 spec'd 1E-12 for worst case end-of-life, the = defacto=20 customer
requirement has been = 1E-15. Note=20 that the current target proposed for the ITU defined Optical =
Transport Network is also 1E-15.

...Dave

David W. Martin
Nortel = Networks
+1 613 = 765-2901  =20
+1 613 763-2388 (fax) =
dwmartin@nortelnetworks.com

=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D

    -----Original=20 Message-----
    From:  =20 Jaime Kardontchik [SMTP:kardontchik.jaime@ulinear.com]=20
    Sent:   = Monday, February 28, 2000 12:05 PM
    To:     stds-802-3-hssg@ieee.org
    Subject:        = Re: PAM-5, what are your BERs ? =


    Hello Vivek,

    A few months ago there was a = discussion on the=20 Reflector where
    some members = claimed that=20 the BERs in some optical backbones
    reached easily the 10^(-15). The repply to these claims was = that
    although this might be = true, the=20 philosophy of the 802.3, that made
    its=20 standards so successful, was to design based on worst case =
    conditions. Therefore, the Ethernet optical = networks were=20 specficied
    to a BER of only=20 10^(-12).

    The same holds  for the Ethernet = Copper=20 links.

    Although it might be true that some = links of=20 100BASE-TX
    reach a BER of = 10^(-12), the=20 official BER adopted in the
    Standard was=20 only 2.5*10^(-10). And the same for the
    1000BASE-T, where the Standard adopted to support a =
    BER of 10^(-10).

    The reason for this higher BERs in = the Copper=20 networks is
    ISI (Inter Symbol = Interference). Or, in layman's language:
    is the eye open or not at the input of the receiver = ?

    Jaime

    Jaime E> Kardontchik =
    Micro Linear
    San Jose,=20 CA 95131


    Vivek Telang wrote:

    > Hello Jaime and 10G'ers, =
    >
    > I had to jump=20 in to try and correct this misconception of  the "eye opening=20 requirement". While it is true that the "open eye" is always a good = thing,=20 it is definitely not a requirement for low BER reception. If it were = a=20 requirement, the tried and true 100BaseTX Ethernet would not be = functioning=20 today. Many existing implementations of 100BaseTX silicon easily = achieve=20 BERs of 1e-12 over 170+ meters of twisted pair cable, and the eye is = very=20 much closed in this case. Not to mention that near-end crosstalk = (NEXT)=20 makes matters significantly worse. Also,  in 1000BaseT, if the = only=20 impairment was ISI, and Echo, NEXT and FEXT were absent, BERs of = 1e-12 could=20 be easily achieved, even with a 5-level symbol = constellation.

    >
    > An=20 open eye is a requirement for systems that use simple lock-and-slice = techniques, where little or no processing of the signal is done, = other than=20 maybe amplification, and a PLL locks to the data clock and slices = the data.=20 In contrast, in a DSP-based system, the combination of linear = feedforward=20 equalizers and DFEs using simple LMS adaptation can easily deal with = "closed=20 eyes". Even with a blind start-up.

    >
    > The=20 implementation of a DSP-based system (including a 6-bit ADC) at 5GHz = in CMOS=20 is a different matter altogether, and I am eagerly awaiting Oscar's=20 presentation at the March meeting.

    >
    >=20 Regards,
    > =
    > Vivek
    >
    > = *---------------------------------------=20
    > *
    > *=20 Vivek Telang
    > * Cicada = Semiconductor=20 Inc.
    > * 901 MoPac = Expressway=20 South
    > * Building One, = Suite=20 540
    > * Austin, = Texas =20 78746
    > *
    > * 512-327-3500 x114 voice
    > * 512-327-3550      = fax=20
    > * vivek@cicada-semi.com =
    > * http://www.cicada-semi.com
    > *
    >=20 *---------------------------------------
    >
    > = -----Original=20 Message-----
    > = From:   Jaime=20 Kardontchik [SMTP:kardontchik.jaime@ulinear.com]
    > Sent:   Sunday, February 27, 2000 6:37 = PM=20
    > To:    =20 stds-802-3-hssg@ieee.org
    > = Subject:        PAM-5, what are = your BERs=20 ?
    >
    > Hello 10G'ers,
    >=20
    > Edward Chang was right on = target.=20
    > He wrote on Feb 23: =
    >
    > > In the=20 past, the multiple voltage-level coding
    > > was adopted by two LAN standards, ATM and =
    > > Ethernet. Both of them were = twisted-pair=20
    > > applications, and the BER = were=20 10^(-10).
    > > I = proposed BER of=20 10^(-12) in both working
    > = > groups=20 to be consistent with the LAN optical
    > > links' BER; however, for some reason, they =
    > > remain 10^(-10), officially in both=20 standards.
    > =
    > What was the reason ?
    >
    > Multilevel = voltage=20 coding was not the reason.
    > On the=20 contrary, it was a remedy. The real reason
    > was the strong ISI at the maximum link lengths =
    > that these Standards wanted to = support.=20
    > Multi-level voltage coding was = adopted=20 to
    > lower the baud rate = or the=20 frequency content
    > of the = signal in=20 order to make the ISI smaller
    > and=20 get a better BER.
    > =
    > However, the remaining ISI in these = Copper=20 links
    > remained high = enough that the=20 eye at the
    > input of the = receiver=20 remained still
    > = completely closed. It=20 is this closed eye that
    > = limited the=20 achievable BER in the Copper media
    >=20 to 10^(-10). Post-equalizers, no matter how
    > sophisticated they were, are not able to =
    > completely reverse the effects of eye=20 closening
    > on the = achievable=20 BER.
    >
    > --->    Conclusion ? In order to get = a BER=20 of
    >         = 10^(-12) you=20 have to have a clear
    >         open = eye at the=20 input of the receiver.
    >         The = maximum=20 supported link length
    >         is set = accordingly to meet this basic
    >         = condition: open=20 eye.
    >
    > Now we can go to the basic two PAM-5 proposals: =
    >
    > 1) PAM-5=20 serial at 5 Gbaud
    > =
    > Using 1300 nm lasers lasers at 5 Gbaud = the=20
    > optical eye is completely = closed already=20 at
    > ~170 meters due to = heavy=20 ISI  (installed MMF,
    > 500 MHz*km=20 bandwidth).
    > =
    > Oscar claimed a support of 500 meters = of=20
    > installed MMF and pointed out = that=20
    > DFEs (equalizers) have been = successfuly=20 used
    > in 100 and 1000 = Mbps Copper=20 networks.
    > However, the = specs and=20 experience of the 100 Mbps
    > and 1000=20 Mbps links over Copper - where the eye
    > at the input of the receiver is completely =
    > closed at the target link length due to = ISI -=20
    > put the achievable BERs around = 10^(-10)=20 only.
    > Even using = sophisticated=20 equalizers.
    > =
    > What is the experimental support that a = BER=20
    > of 10^(-12) could be achieved = when a strong=20 ISI
    > closes completely = the eye at the=20 input of the
    > receiver ? = I think that=20 none and that the
    > = experience points=20 to the contrary. Why then
    > could an=20 equalizer running at 5 GHz achieve
    >=20 here what sophisticated equalizers running
    > 40 times slower (125 MHz) were not able to = achieve=20
    > in the Copper Ethernets ? = Parallel=20 processing
    > could enable = perhaps to=20 meet the timing
    > = constraints of the=20 design by running multiple
    >=20 equalizers at a lower clock, but will not
    > eliminate the basic limitation on achievable =
    > BERs once the eye at the input of the = receiver=20
    > is already completely = closed.=20
    >
    > Let=20 us see now the case PAM-5 at 1.25 Gbaud:
    >
    > 2) PAM-5 = 4-WDM at 1.25=20 Gbaud
    >
    > Let us compare this approach to two other well =
    > known on-off approaches: 1 GbE and 4-WDM = at=20
    > 3.125 Gbaud using the 8b/10b = coding. Let=20 us
    > assume again 1300 nm = lasers and=20 installed
    > 500 MHz*km = MMF.=20
    >
    > The=20 figures below (I hope will not get distorted
    > during transmission) show the power levels of =
    > the three systems. For 1 GbE I assumed no = ISI.=20
    > For PAM-5 I assumed 400 meters = link=20 length
    > (there is no ISI = up to this=20 distance, ISI=3D 0 dB).
    > = For 4-WDM at=20 3.125 Gbaud I assumed 300 meters link
    > length and about 3 dB optical loss due to ISI. =
    >
    >=20 = |            =   =20 |
    >=20 = |            =   =20 |
    >=20 = |            =   =20 |       1 GbE, 1.25 Gbaud, no = ISI=20
    >=20 = |            =   =20 |
    >=20 = |            =   =20 |
    >
    > |   |   |   = |   |=20
    > |   |   = |  =20 |   |
    > = |  =20 |   |   |  =20 |       PAM-5 4-WDM at 1.25 = Gbaud=20
    > |   |   = |  =20 |   |       no ISI. =
    > |   |   |   = |   |
    > =
    > |****       = ****|
    >=20 |****       ****|
    > |****      =20 ****|       8b/10b 4-WDM at 3.125 = Gbaud=20
    > = |****      =20 ****|       3 dB ISI loss =
    > |****       = ****|
    >
    > ( the asterisks denote closening of the eye due =
    > to ISI)
    >
    > 2a) 1 = GbE=20
    >
    > By=20 definition, the optical power difference
    > between the '0' and '1' levels in the 1 GbE =
    > case is 1:
    >
    >   =20 optical signal power =3D 10*log(1) =3D 0 dB
    >
    >   =20 optical SNR =3D 0 dB (reference)
    >
    > And we get = a BER of=20 10^(-12).
    > =
    > 2b) PAM-5 4-WDM at 1.25 Gbaud =
    >
    > In the PAM-5=20 case, notice that using the
    > "open=20 fiber control" method that I described
    > in a previous email, we get the same launched =
    > power per channel as in the 1 GbE = Ethernet.=20
    > However, in PAM-5 the power=20 difference
    > between = levels is 0.25=20 (this is the well
    > known = 6 dB optical=20 power penalty loss of
    > = the PAM-5=20 modulation). Let us now add
    > the 6 dB=20 electrical coding gain provided
    > by=20 the Viterbi decoding: the effective distance
    > between levels doubles. Summarizing, in PAM-5 =
    > 4-WDM at 1.25 Gbaud, the effective = optical=20
    > signal power difference between = levels=20 is:
    >
    >    effec optical signal power diff = =3D=20
    >          =       =20 10*log(2*0.25) =3D - 3 dB
    >=20
    > where the factor 2 inside the = log=20 comes
    > from the coding = gain.=20
    >
    > The=20 noise power at the input of the
    >=20 receiver is the same as in 1 GbE because
    > we use the same baud rate. Hence,
    >
    >    effec=20 optical SNR =3D - 3 dB
    >=20
    > This is not bad compared to the = 0 dB of 1=20 GbE.
    > Furthermore, notice = that we=20 could even bring
    > back = the SNR for=20 PAM5 to 0 dB (the 1 GbE
    > = reference)=20 if a new laser safety proposal
    > to=20 move the maximum safe power from -4 dBm
    > to -1 dBm is accepted. See P. Kolesar et al =
    > presentation in the next March = meeting.=20
    >
    > 2c)=20 8b/10b 4-WDM at 3.125 Gbaud
    >=20
    > In this case the eye is half = closed=20 due
    > to ISI. Hence the = optical power=20 difference
    > is: =
    >
    >    optical signal power =3D = 10*log(0.5)=20
    >          =        =20 =3D - 3 dB
    > =
    > and the electrical noise power at the input =
    > of the receiver is larger, since the = receiver=20
    > needs more bandwidth: =
    >
    >    elec noise power =3D=20 10*log[(3.125/1.25)^2]
    >          =           =20 =3D 8 dB
    > =
    > Hence, the optical SNR is
    >
    >   =20 optical SNR =3D - 3 - 8/2 =3D -7 dB
    >
    > This case = is clearly=20 worse than the 1 GbE
    > = case in terms=20 of optical SNR. And the
    > = Task Force=20 considers that this system
    > can=20 achieve the needed 10^(-12) BER.
    >
    > = Summarizing:=20
    >
    >         PAM-5 = 4-WDM at=20 1.25 Gbaud has no
    >         ISI, a = clear and=20 wide open eye at
    >         the = input of the=20 receiver, an optical SNR
    >         only = slightly=20 less than the SNR of present
    >         1 GbE=20 transceivers and better than
    >         the = proposed=20 8b/10b 4-WDM at 3.125G
    >        =20 transceivers.
    > =
    >        =20 Hence, it is a good choice if one
    >         wants = to reach=20 the required BER of
    >         = 10^(-12).=20
    >
    >=20 Note: the above analysis, based on simple
    >      static SNRs, is not a = substitute=20 for a
    > much more careful = analysis=20 regarding
    > the = viabibility of any=20 PAM-5 approach.
    > However, = a simple=20 back-of-the-envelope
    > = analysis is=20 very useful to make a quick
    >=20 comparison between different PAM-5 proposals
    > in order to find out which PAM-5 architecture, =
    >
    >    a) one working under strong ISI=20 conditions
    >       that close the = optical eye=20 completely; or
    > =
    >    b) another using a = lower baud=20 rate
    >       and working with = minimal ISI=20 so that
    >       the optical eye at = the input=20 of the
    >       receiver is widely = open,
    >
    > which one has more chance to meet the required =
    > BER of 10^(-12), and discard accordingly = the=20
    > one that does not have a = chance.=20
    >
    >=20 Jaime
    >
    > Jaime E. Kardontchik
    >=20 Micro Linear
    > San Jose, = CA=20 95131
    > email:=20 kardontchik.jaime@ulinear.com =

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