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(12) United States Patent (10) Patent No.: US 6,922,397 B1 Chen (45) Date of Patent: Jul

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(12) United States Patent (10) Patent No.: US 6,922,397 B1 Chen (45) Date of Patent: Jul USOO6922397 B1 (12) United States Patent (10) Patent No.: US 6,922,397 B1 Chen (45) Date of Patent: Jul. 26, 2005 (54) SELECTABLE TRAINING SIGNALS BASED WO WO 99/48304 9/1999 ON STORED PREVIOUS CONNECTION WO WO 01/95580 12/2001 INFORMATION FOR DMT-BASED SYSTEM OTHER PUBLICATIONS (75) Inventor: Yuanjie Chen, San Jose, CA (US) John A. C. Bingham, “ADSL, VDSL, and Multicarrier (73) Assignee: Broadcom Corporation, Irvine, CA Modulation”, John Wiley & Sons Inc. 2000, 303 pages. (US) (Continued) (*) Notice: Subject to any disclaimer, the term of this Primary Examiner Duc Ho patent is extended or adjusted under 35 (74) Attorney, Agent, or Firm-Christie, Parker and Hale, U.S.C. 154(b) by 727 days. LLP (21) Appl. No.: 09/863,522 (57) ABSTRACT (22) Filed: May 23, 2001 Training Signals can be chosen based on Stored prior con 9 nection information to reduce the use of extra tones in Related U.S. Application Data transmitted training Signals and thereby improve receiver (60) Provisional application No. 60/261,742, filed on Jan. 16, performance. By choosing trainng signals based on the 2001. Stored prior connection information, it is possible to make the training Signals indirectly a function of the loop impair (51) Int. Cl. ............................ G01R 31/08; H04J 3/16 ments. One advantage of this Scheme is that we can choose (52) U.S. Cl. ........................................ 370/252; 370/465 to omit certain tones in the training Signals, based on (58) Field of Search ................................. 370/276, 286, previous connection information, on a loop-by-loop basis. 370/292, 352,465, 433, 480, 252; 379/93.01, For example, in an ADSL Transceiver Unit-Central office 416,417; 375/346, 222, 219 end (ATU-C) device, per-local-loop prior connection infor s s s s mation may be employed to select DMT tones to be included (56) References Cited in downstream training Signals. Similarly, in an ADSL Transceiver Unit-Remote terminal end (ATU-R) device, U.S. PATENT DOCUMENTS prior connection information may be employed to select 5.533.008 A 7/1996 Grube et all DMT tones to be included in upstream training Signals. In 2- - -2 rupe et al. each case, local echoes are effectively reduced and local 5. A : 3.E. Bish - - - - - - - - - - - - - - - - - - - - - 370/71 receiver training is improved without affecting eventual data 6,324.268 B1 - 11f2001 Rindran et al. .. 379/93.08 transmission performance in the other direction. As a result, 640so33 B1 6/2002 Chow etal ... 375260 higher AGC gain and higher Signal-to-quantization-noise 6516,027 B1 - 22003 Kapoor et al. .375,227 ratioS can be achieved, especially in the case of long loops. 65875.02 B is 7/2003 Hendrichseal. I. 375,222 These benefits can allow (1) improvements in the loop 6,611564 B1 8/2003 Linz et al. .................. 375/295 performance in the receiving direction and/or (2) reductions 6,628,704 B1 * 9/2003 Long et al. ................. 375/219 in the requirements on the receiving ADC. In addition, 6,718,019 B1 * 4/2004 Heidari et al. ........... 379/93.05 crosstalks into the other wire pairs, especially those in the 2002/0041643 A1 4/2002 Tzannes et al. Same bundle, are also reduced, improving the transmission environment on those pairs. FOREIGN PATENT DOCUMENTS WO WO 99/20027 4/1999 46 Claims, 2 Drawing Sheets f ATU200 2C M r f f 1 - 21 D f - - 241 A - ,----- \ A - ----- w NITAZATION - --e--- : SHOWTIME TRANSCEIVER TRANSMISSION US 6,922.397 B1 Page 2 OTHER PUBLICATIONS Charles K. Summers, “ADSL Standards, Implementation, and Architecture”, Saba Zamir, Ed.,CRC Press, Washington John M. Ciofi, John A. C. Bingham, “A Data Driven D.C., 1999, Chapters 2 and 3, pp. 47-80. Multitone Echo Canceller', IEEE Transactions on Commu nications, vol. 42, No. 10, Oct. 1994, pp. 2853–2869. “Discrete Multi-Tone Line Code (DMT)", ADSL Technical ITU-T Recommendation G.992.1, Asymmetric Digital Sub Overview, online printed on Jan. 12, 2001 Retrieved scriber Line (ADSL) Transceivers, 1999, pp. 256. from the Internet <URL: http://www.mot.com/SPS/MCTG/ ITU-T Recommendation G-992.2, Splitterless Asymmetric MDAD/adsl/dmit overview.html>, 2 pp. Digital Subscriber Line (ADSL) Transceivers, 1999, pp. “Echo Cancellation”, ADSL Technical Overview online 1-170. printed on Jan. 12, 2001 Retrieved from the Internet 3Com(E) Base Level ADSL Interoperability Specification, URL: http://www.mot.com/SPS/MCTG/MDAD/adsl/ Discrete Multi-Tone (DMT), Lucent Technologies, Bell echo-Cancel.html>, 1 p. Labs Innovations, Revision 1.0.43, updated May 22, 1998, 16 pp. * cited by examiner U.S. Patent Jul. 26, 2005 Sheet 1 of 2 US 6,922,397 B1 US 6,922,397 B1 1 2 SELECTABLE TRAINING SIGNALS BASED Signals, based on previous connection information, on a ON STORED PREVIOUS CONNECTION loop-by-loop basis. For example, in an ADSL Transceiver INFORMATION FOR DMT-BASED SYSTEM Unit-Central office end (ATU-C) device, per-local-loop prior connection information may be employed to select DMT CROSS-REFERENCE TO RELATED tones to be included in downstream training Signals. APPLICATION(S) Similarly, in an ADSL Transceiver Unit-Remote terminal end (ATU-R) device, prior connection information may be This application claims benefit of U.S. Provisional Appli employed to select DMT tones to be included in upstream cation No. 60/261,742, filed Jan. 16, 2001. training Signals. In each case, local echoes are effectively reduced and local receiver training is improved without BACKGROUND OF THE INVENTION affecting eventual data transmission performance in the 1. Field of the Invention other direction. As a result, higher AGC gain and higher Signal-to-quantization-noise ratioS can be achieved, espe The invention relates to data communications and, in cially in the case of long loops. These benefits can allow (1) particular, to multitone modulation Such as employed digital improvements in the loop performance in the receiving subscriber line (DSL) communications. 15 direction and/or (2) reductions in the requirements on the 2. Description of the Related Art receiving ADC. In addition, crosstalkS into the other wire A digital Subscriber line (DSL) System uses the existing pairs, especially those in the same bundle, are also reduced, twisted-pair telephone wires to carry data between central improving the transmission environment on those pairs. offices (CO) and customer premise equipment (CPE). Data In Some realizations in accordance with the present transmissions from CO to CPE (downstream direction) and invention, prior connection information (including bit allo from CPE to CO (upstream direction) usually occupy dif cation and training signals used) is stored at the transmitting ferent bands (or Sub-channels), although in Some echo Side and training Signals are Selected based on the Stored cancelled implementations, both upstream and downstream previous connection information. In this way, the Set of tones transmissions may occupy the same band. One of the employed in training Signals for a given Sub-channel is modulation techniques used in a DSL System is called 25 indirectly a function of loop impairments. Accordingly, discrete multitone modulation (DMT). DMT techniques tones unlikely to be used in data transmission for a particular partition the transmission channel in each direction into a loop will generally not be included in the training Signals. bank of orthogonal, memoryleSS Subchannels, and transmit While stored connection information may vary from imple data through each Sub-channel independently. mentation to implementation, Some realizations Store largest In general, a DMT-based DSL connection is established and Smallest tone indices employed in various Sub-channels by training receivers, probing channels, and allocating Vary during a most recent connection. Other realizations may ing number of bits to Sub-channels for data transmission. Store other information Such as amplitude and/or phase Initially, Signals are Sent in both directions to train the information for the tones employed. If desirable, a history of receivers and to probe the channels. Then, a signal-to 35 prior connection information may be maintained and interference-plus-noise ratio (SINR) is calculated on each employed in training tone Selection. Sub-channel, and bits are allocated to each Sub-channel In one embodiment in accordance with the present based on its SINR. In this context, interference may include invention, a method of enhancing performance of a receiver echoes, crosstalk, radio frequency interference (RFI), etc. To includes Selecting a training Subset of less than all signal accommodate a wide range of loops and interference, train 40 elements based on those Signal elements employed in one or ing signals usually include a range of tones (possibly all the more recent data transmissions and transmitting, during a available tones) within the respective bands. The tones that training interval, Substantially only the Signal elements of are actually used for data transmission are determined based the training Subset. The method can be employed in a on channel probing results and bit-loading algorithms. communications configuration wherein a device receives a Training Signals have typically been Selected independent 45 Signal over a communication channel while Simultaneously of loop impairments. Accordingly, there are often tones in transmitting a training Signal thereover. In Some variations, the training Signals that are not used in the final data the method further includes Storing a encoding of employed transmission. Potentially, many tones are included in the Signal elements for use in Subsequent training Subset Selec training Signals but not employed in data transmissions over tions. In Some variations, the training Subset Selection is a given Sub-channel. These extra tones in the training Signals 50 performed as a function of plural Sets of prior connection do not contribute to actual data transmission performance. information. In Some variations, the training Subset Selection However, they may degrade performance in the receiving is performed using a design function to accommodate direction by creating unnecessarily high echoes.
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