From owner-stds-802-3-hssg@ieee.org Thu Mar 2 23:14 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 XAA07494; Thu, 2 Mar 2000 23:14:38 GMT Received: from ruebert.ieee.org ([199.172.136.3]) by gatekeeper.pdd.3com.com (Netscape Messaging Server 3.6) with ESMTP id AAA30C1; Thu, 2 Mar 2000 23:12:53 +0000 Received: by ruebert.ieee.org (8.9.3/8.9.3) id RAA22384; Thu, 2 Mar 2000 17:34:33 -0500 (EST) From: "Edward Chang" To: "Jaime Kardontchik" , Subject: RE: PAM-5, what are your BERs ? Date: Thu, 2 Mar 2000 17:40:56 -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) Importance: Normal X-MimeOLE: Produced By Microsoft MimeOLE V5.00.2314.1300 In-Reply-To: <38BEA1ED.122EE0B9@everest.ulinear.com> 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: 86 Status: RO Content-Type: text/plain; charset="us-ascii" Content-Length: 2664 Jamie: Thanks very much for your very elaborated explanation. 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 Jaime Kardontchik Sent: Thursday, March 02, 2000 12:16 PM To: stds-802-3-hssg@ieee.org Subject: Re: PAM-5, what are your BERs ? Edward Chang wrote: > Jaime: > > I agree that your analyses are solid. No question in my mind. > > My real question is what caused the PAM-5 link to yield BER of 10^-3 or > 10^-4? > > I believe the only answer is that the complex data recovery requirements of > the multilevel coding caused the BER to go up. Therefore, ..... > > > Edward S. Chang Edward, Your question is incorrect and this leads to the incorrect answer. If the electrical SNR at the input of the receiver is about 17 dB you will get a BER of about 10^(-12). Period. If you do not design your receiver properly and the effective SNR at the input of the receiver is only 11 dB instead of 17 dB, then you will get a BER of about 10^(-4). (see my presentation in Kauai, Nov 99, Part II). I do not think that the answer would be essentially different if the modulation scheme were on-off instead of PAM-5. There are many things that could go wrong in a 10 Gbps receiver that could cause the BER to drop to unnaceptable levels. This is true for all proposals using both on-off or PAM-5 modulation. It could be a low dynamic range design of the analog front end of the receiver, it could be the clock and data recovery, it could be a nominal 6-bit ADC that has an effective number of bits of only 4 at the frequencies of interest, and so on. And to make it even more clear: the problem of a low BER does not have to be necessarily in the analog front end or the Viterbi algorithm. At these high frequencies a simple logic state machine could cause from time to time errors and lower the BER to unnaceptable values if the synthesized gates do not have enough timing margin or you have a race condition. For more details about what could cause the BER to drop to 10^(-4), I think that the reachest source of information are the poor serial guys that are trying desperately to design a 10 Gbaud transceiver and are fighting over whether they could design a 10.3 Gbaud receiver or not (12.5 Gbaud seems to have dropped already) ... or whether there is a way to modify the eye safety requirements so that they can increase the signal power and get a better SNR ... Jaime Jaime E. Kardontchik Micro Linear San Jose, CA 95131 email: kardontchik.jaime@ulinear.com