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WO1999033215A1 - Techniques d'optimisation spectrale et de signalisation mixtes pour les communications soumises a des interferences - Google Patents

Techniques d'optimisation spectrale et de signalisation mixtes pour les communications soumises a des interferences Download PDF

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Publication number
WO1999033215A1
WO1999033215A1 PCT/US1998/027154 US9827154W WO9933215A1 WO 1999033215 A1 WO1999033215 A1 WO 1999033215A1 US 9827154 W US9827154 W US 9827154W WO 9933215 A1 WO9933215 A1 WO 9933215A1
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WO
WIPO (PCT)
Prior art keywords
self
channel
determining
interference
transfer function
Prior art date
Application number
PCT/US1998/027154
Other languages
English (en)
Inventor
Rohit V. Gaikwad
Richard G. Baraniuk
Original Assignee
Rice University
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from US09/144,934 external-priority patent/US6317495B1/en
Application filed by Rice University filed Critical Rice University
Priority to AU20063/99A priority Critical patent/AU2006399A/en
Priority to CA002315196A priority patent/CA2315196A1/fr
Publication of WO1999033215A1 publication Critical patent/WO1999033215A1/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B3/00—Line transmission systems
    • H04B3/02—Details
    • H04B3/32—Reducing cross-talk, e.g. by compensating
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2614—Peak power aspects
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L5/00—Arrangements affording multiple use of the transmission path
    • H04L5/003—Arrangements for allocating sub-channels of the transmission path
    • H04L5/0044—Allocation of payload; Allocation of data channels, e.g. PDSCH or PUSCH
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L5/00—Arrangements affording multiple use of the transmission path
    • H04L5/14—Two-way operation using the same type of signal, i.e. duplex

Definitions

  • the invention relates to electronic communication and, more particularly, to techniques for communicating on communications channels subject to interference such as cross talk and noise.
  • Twisted pair telephone lines Telephone service is provided to most businesses and homes via a pair of copper wires (a "twisted pair").
  • a telephone cable contains many twisted pairs: 25 twisted pairs are grouped in close proximity into 2 "binder groups,” and several binder groups are packed together to form a cable.
  • the two terminations of a telephone cable are at the user (subscriber) end and at the telephone company (central office, CO) end.
  • CO central office
  • Voice telephony uses only the first 4 kHz of bandwidth available on the lines.
  • POTS "Plain Old Telephone Service.” This is the basic telephone service carrying voice traffic in the 0 - 4 kHz bandwidth. Conventional analog modems also use the same bandwidth.
  • ISDN - Integrated Services Digital Network This service allows end-to-end digital connectivity at bit rates of up to 128 kbps (kilo-bits-per-second).
  • TI - Transmission 1 This is a physical transmission standard for twisted pairs that uses 24 multiplexed channels (each at 64 kbps) to give a total bit rate of 1.544 Mbps (Mega-bits-per-second). It uses costly repeaters.
  • HDSL - High bit-rate Digital Subscriber Line This is a full-duplex (two-way) Tl- like (1.544 Mbps) signal transmission service using only two twisted pairs and no repeaters.
  • ADSL - Asymmetric Digital Subscriber Line Over one twisted pair, this service provides a high-speed (on the order of 6 Mbps) downstream (from central office
  • CO to subscriber
  • a low-speed (on the order of 640 kbps) upstream from subscriber to the central office) channel.
  • This service preserves the POTS service over a single twisted pair.
  • VDSL Very high bit-rate DSL.
  • This yet-to-be-standardized service will provide a very high speed (on the order of 25 Mbps) downstream channel to subscribers and a lower speed upstream channel to the central office over a single twisted pair less than 3 to 6 kft long. Further, it will preserve the POTS service.
  • HDSL2 High bit-rate Digital Subscriber Line 2. This soon-to-be-standardized service will provide full-duplex 1.544 Mbps signal transmission service in both directions (full duplex) over a single twisted pair ( ⁇ 18 kft long) without repeaters.
  • GDSL General Digital Subscriber Line. This hypothetical service would (for illustration purposes) carry 25 Mbps full-duplex data rate over a single twisted pair (see Sections 2.2.2 and 4.6J0).
  • VDSL2 Very high bit-rate DSL Line 2. This hypothetical service would (for illustration purposes) carry 12.4 Mbps full-duplex data rate over a single twisted pair less than 3 to 6 kft long (see Sections 2.2.3 and 4.6J0).
  • NEDT Near-end crosstalk
  • FXT Far-end crosstalk
  • FIG. 3 shows that crosstalk interference can be modeled as additive interference.
  • Channel noise will be modeled as additive Gaussian noise (AGN). 1.3.2 Notation for self-NEXT and self-FEXT
  • T° transmitter (Tx) on twisted pair i in direction o.
  • R° receiver (Rx) on twisted pair i in direction o.
  • T° intends to transmit information only to R° .
  • R° the degree of freedom
  • Self-FEXT Crosstalk from T° into R° for all j ⁇ i, o e ⁇ u, d ⁇ .
  • each twisted pair / supports transmission and reception in both directions (using echo cancelers), so each line i has a full set of transmitters and receivers: ⁇ T" , R" , T? , R? ⁇ .
  • the Channel capacity C is defined as the maximum number of bits per second that can be transmitted over a channel with an arbitrarily small bit error probability.
  • the achievable rate R A for a channel is any transmission rate below or equal to capacity, i.e., R ⁇ C. .Another channel performance metric is performance margin (or margin). It is defined (in dB) as
  • SNR KC is the received signal-to-noise ratio (SNR) and SNR min is the minimum received SNR required to achieve a fixed bit error probability (BER) at a given transmission rate.
  • SNR received signal-to-noise ratio
  • SNR min is the minimum received SNR required to achieve a fixed bit error probability (BER) at a given transmission rate.
  • the performance margin of a channel for a fixed bit error probability measures the maximum degradation (from noise and interference) in achievable bit rate that a channel can sustain before being unable to transmit at that bit rate for a fixed BER (see [12]).
  • the communications channel is the collection of twisted pairs in the telephone cable, interference is caused by:
  • HDSL2 Interference from HDSL2 into other services, such as TI, ISDN, HDSL and .ADSL, and
  • HDSL2 service in Sections 4.4 to 4.7.
  • the HDSL2 service is intended to fill a key need for fast (1.544 Mbps) yet affordable full duplex service over a single twisted pair. Efforts to define the standard are being mounted by several companies and the TlEl standards committee. The two key issues facing HDSL2 standards committee are:
  • GDSL TI
  • ISDN ISDN
  • HDSL high-density lipoprotein
  • .ADSL high-density lipoprotein
  • HDSL2 high-density lipoprotein
  • se ces not yet imagined while maintaining spectral compatibility with them.
  • the spectral optimization issue is similar to the one discussed for HDSL2 case, and we need to find an optimal transmit spectrum for "GDSL”. Further, a good modulation scheme needs to be selected.
  • DSI ⁇ - ⁇ EXT and DSI ⁇ -FEXT from TI, ISDN, HDSL, HDSL2, VDSL and ADSL,
  • VDSL2 Interference from "VDSL2" into other services, such as TI, ISDN, HDSL, HDSL2,
  • PSD power spectral density
  • Optis [5] is currently the performance standard for HDSL2 service.
  • Self-NEXT is the dominant self-interference component in symmetric-data-rate, full-duplex, long-length line xDSL service (e.g., HDSL2).
  • One simple way of completely suppressing self-NEXT is to use orthogonal signaling (for example, time division signaling (TDS), frequency division signaling (FDS), or code division signaling (CDS)).
  • TDS time division signaling
  • FDS frequency division signaling
  • CDS code division signaling
  • TDS we assign different services to different time slots.
  • FDS we separate in frequency the services that could interfere with each other.
  • CDS a unique code or signature is used in each direction of service. Further, in CDS each service occupies the entire available bandwidth for all of the time. CDS is similar to code division multiple access (CDMA), but here instead of providing multiple access, CDS separates the upstream and downstream transmit spectra using different codes.
  • Multicarrier or discrete multitone (DMT) modulation [6] can be readily used to implement a communication system using a wide variety of PSDs.
  • Multitone modulation modulates data over multiple carriers and adjusts the bit rate carried over each carrier according to the signal to noise ratio (SNR) for that carrier so as to achieve equal bit error probability (BER) for each carrier (see in FIG. 4).
  • SNR signal to noise ratio
  • BER bit error probability
  • Orthogonal FDS signaling is easily implemented using the DMT: we simply assign transmitter/receiver pairs to distinct sets of carriers. Note, however, that multitone modulation is definitely not the only modulation scheme that can be used to implement (optimal) transmit spectra. We can just as well use other techniques, such as CAP, QAM, multi-level PAM, etc.
  • Ad-hoc schemes (sometimes referred to as "optimized") have been developed that attempt to deal with self-interference and DSIN-NEXT and DSIN-FEXT as well as spectral compatibility of the designed service with other services. However, these schemes by no means optimize the capacity ofthe services considered.
  • • .An optimal signaling scheme has been developed in [3] for the case of self-NEXT and white additive Gaussian noise only. The development of [3] does not address crosstalk from other sources, such as DSlTSf-NEXT and DSIN-FEXT, or self- FEXT, or other types of additive Gaussian noise. The development of [3] also does not address spectral compatibility of the designed service with respect to other services.
  • One embodiment of the present invention comprises a method for determining a transmit spectrum for use in communicating data on a communications channel.
  • This method may be used in communicating data when the channel is subject to interference from one or more other communications channels.
  • the first steps in this method comprise determining a channel transfer function of the communications channel and an amount of self interference into the communications channel from the other communications channels that carry the same type of service.
  • the transfer function and the amount of self interference are examined, and a transmit spectrum for the channel is determined based on the examining.
  • the transfer function and the amount of interference may be determined by measurement or they may be received from a remote or local analyzer or memory storage.
  • Determining the transmit spectrum preferably comprises determining an EQPSD/FDS/MFDS transmit spectrum.
  • the method further preferably comprises a further step of determining an amount of uncorrelated interference into the communications channel, such as additive Gaussian noise (AGN) and different-service interference from one or more of the other communications channels that may carry a different type of service than the service on the communications channel. Determining the transmit spectrum is then performed in response to the amount of uncorrelated interference.
  • the present invention comprises a method for transmitting data on a communications channel that is subject to interference from one or more other communications channels. The method comprises the steps of determining a channel transfer function of the communications channel, initiating a data transfer on the communications channel, and transferring the data on the communications channel using the transmit spectrum.
  • the step of initiating the transfer comprises determining interference characteristics of the interfering communications channels, and determining a transmit spectrum in response to the channel transfer function and the interference characteristics.
  • the transmit spectrum is preferably determined to substantially maximize the data transmission rate for the communications channel, in such a manner that the communications channel has equal upstream and downstream capacities, and that the transmit spectrum is spectrally compatible with the one or more other communications channels.
  • Another embodiment of the present invention comprises a method for determining a transmit spectrum for use in communicating data on a communications channel, preferably by determining signaling techniques in one or more frequency bins in the available frequency band of the communications channel.
  • the first steps in this method comprise determining a channel transfer function of the communications channel. .An amount of self interference into the communications channel from the other communications channels carrying the same type of service is determined, preferably along with an amount of uncorrelated interference. The transfer function and the amount of self interference are examined, preferably along with the amount of uncorrelated interference. A transmit spectrum for the channel is then determined based on the examining.
  • the transmit mask may be either a discrete transmit mask or a contiguous transmit mask over the range of the neighboring bins. If the channel transfer function and the interference characteristics are substantially monotonic over the frequency band of the communications channel, then determining which frequency bins use a particular technique may comprise a binary search for transition bins in which appropriate characteristic quantities cross particular tlireshold values.
  • FIG. 1 is an example ofthe frequency-response for a twisted pair telephone channel
  • FIG. 2 shows NEXT and FEXT between neighboring lines in a telephone cable, with "Tx” and “Rx” indicating transmitters and receivers, respectively;
  • FIG. 3 shows how NEXT (DSIN-NEXT and self-NEXT) and FEXT (DSIN-FEXT and self-FEXT) are modeled as additive interference sources, with DSOUT- NEXT and DSOUT-FEXT representing the interference leaking out into other neighboring services;
  • FIG. 4 illustrates how multicarrier, or discrete multitone (DMT) modulation multiplexes the data onto multiple orthogonal carrier waves
  • FIG. 5 and FIG. 5A are representative views of a subscriber-line communications system and a well-logging system that use the present invention
  • FIG. 6 is a representative view of a home system using the present invention for DSL communications
  • FIG. 7 is a block diagram of one embodiment of the computer from FIG. 6;
  • FIG. 8 is a block diagram of one embodiment ofthe DSL card from FIG. 7;
  • FIG. 9 is a flowchart for determining transmission characteristics for a communications system in one embodiment ofthe invention.
  • FIG. 10 is a flowchart for determining a transmit spectrum with preliminary analyses of self interference and FEXT levels;
  • FIG. 11 is a flowchart for determining a transmit spectrum with preliminary analyses of self interference levels
  • FIG. 12 is a flowchart for determining a transmit spectrum
  • FIG. 13 is a flowchart for method for transmitting data on a communications channel
  • FIG. 14 is a flowchart for initiating a data transfer on the communications channel
  • FIG. 15 is a flowchart for determining transmission characteristics for a communications system in one embodiment of the invention.
  • FIG. 16 is a frequency-response graph showing the channel sub-division into K narrow bins (subchannels), each of width W( ⁇ z);
  • FIG. 17 shows the magnitude squared transfer function of the channel (CSA loop 6), with 39 self-NEXT interferers, and 39 self-FEXT interferers (see (l)-(3));
  • FIG. 18 shows transmit spectra for EQPSD, FDS and multi-line FDS signaling schemes in a single frequency bin k for the case where the number of lines is 3
  • FIG. 19 is a model for combined additive interference from other services (DSIN- NEXT and DSIN-FEXT) plus channel noise (AGN);
  • FIG. 20 is a flowchart of a method for determining an optimal transmit spectrum using only EQPSD signaling
  • FIG. 21 is a graph of an optimal transmit spectrum of HDSL2 (on CSA loop 6) with 49 HDSL DSIN-NEXT interferers and AGN of -140 dBm/Hz;
  • FIG. 22 is a graph of an optimal transmit spectrum of HDSL2 (on CSA loop 6) with 25 TI DSIN-NEXT interferers and AGN of -140 dBm/Hz;
  • FIG. 24 is a graph demonstrating that R is monotonic in the interval ⁇ e (0.5, 1];
  • FIG. 25 shows EQPSD and FDS signaling in a single frequency bin
  • FIG. 26 shows upstream and downstream transmit spectra with regions employing
  • FIG. 27 is a flowchart of the optimal and suboptimal schemes to determine the transmit spectrum using EQPSD and FDS signaling (and EQPSD/FDS transmit spectrum);
  • FIG. 28 shows joint EQPSD/FDS signaling for a channel with "discrete"
  • FIG. 29 is a graph of an optimal upstream transmit spectrum for CSA Loop 6 using HDSL2 with 39 self-NEXT and 39 self-FEXT interferers, with EQPSD signaling taking place to the left of bin 9 (indicated by solid line) and FDS signaling taking place to the right (indicated by dashed line);
  • FIG. 30 shows graphs of optimal "contiguous" upstream and downstream transmit spectra for CSA Loop 6 using HDSL2 with 39 self-NEXT and 39 self-FEXT interferers (EQPSD signaling taking place to the left of bin 9);
  • FIG. 31 shows graphs of another set of optimal "contiguous" upstream and downstream transmit spectra for CSA Loop 6 using HDSL2 with 39 self-NEXT .and 39 self-FEXT interferers, with the property that these spectra yield equal performance margins (equal capacities) and equal average powers in both directions of transmission (EQPSD signaling taking place to the left of bin 9);
  • FIG. 32 shows transmit spectra of signaling line (S), interfering line ⁇ Y and Z), and lumped channel noise (N) for two cases: the FDS scheme (Case 2) for interfering line yields higher capacity for signaling line (S) than other schemes like CDS (Case 1);
  • FIG. 34 shows FDS and multi-line FDS signaling in a single frequency bin k for the
  • [MFDS2MFDS + 1» K ⁇ employ multi-line FDS;
  • the downstream spectrum of line 1 ⁇ S? ⁇ f) ) is similar to S" ⁇ f) except for putting power in the complementaiy halves of FDS bins;
  • the upstream spectra of lines 2 and 3 are similar to S" (/) except for putting power in complementary thirds of multi-line FDS bins;
  • the downstream spectra for lines 2 and 3 are similar to S"(/) except for putting power in the complementary halves of the FDS bins and in the complementary thirds of multi-line FDS bins;
  • FIG. 36 illustrates practical observation 1, a case of an EQPSD/FDS/MFDS transmit spectrum in which there is no FDS spectral region; bins [1, employ EQPSD, and bins [M E2 MFDS + 1 > K] employ multi-line FDS;
  • FIG. 37 illustrates practical observation 2, a case of an EQPSD/FDS/MFDS transmit spectrum in which there is no multi-line FDS spectral portion within the EQPSD region; bins [1, employ EQPSD, bins [M MFDS 2FDS + 1, employ FDS, and bins [M E> s 2MFDS + 1 > K] employ multi-line FDS;
  • FIG. 38 shows upstream and downstream transmit spectra in a single frequency bin
  • FIG. 39 shows EQPSD and multi-line FDS signaling in a single frequency bin
  • FIG. 40 is a flowchart of a scheme for determining an optimal transmit spectrum using EQPSD, FDS, and multi-line FDS signaling (an EQPSD/FDS/MFDS transmit spectrum);
  • FIG. 43 is a graph of an optimal downstream transmit spectrum for HDSL2 (on CSA loop 6) under an OPTIS downstream constraining PSD mask with 49 HDSL
  • FIG. 44 is a graph of an optimal upstream transmit spectrum for HDSL2 (on CSA loop 6) under an OPTIS upstream constraining PSD mask with 25 TI DSIN- NEXT interferers and AGN of -140 dBm/Hz (the 'o-o' line shows the peak- constrained optimal transmit spectrum and the '-' line shows the constraining OPTIS PSD mask);
  • FIG. 45 shows graphs of optimal upstream and downstream transmit spectra for
  • HDSL2 (on CSA loop 6) under the OPTIS upstream and downstream constraining
  • FIG. 46 shows graphs of optimal upstream and downstream transmit spectra for HDSL2 (on CSA loop 6) under the OPTIS upstream and downstream constraining PSD masks with 24 HDSL2 self-NEXT and self-FEXT interferers, 24 TI interferers, and AGN of -140 dBm/Hz (the 'o-o' lines show the peak-constrained optimal transmit spectra and the '-- ' lines show the constraining OPTIS PSD masks);
  • FIG. 47 shows graphs of optimal "contiguous" upstream and downstream transmit spectra for HDSL2 (on CSA loop 4, with a non-monotonic channel function due to bridged taps) with 39 HDSL2 self-NEXT and self-FEXT interferers; these transmit spectra yield equal performance margins (equal capacities) and equal average powers in both directions of transmission (note that there is only one transition region from EQPSD to FDS signaling);
  • FIG. 48 shows (in the top graph) the channel transfer function, self-NEXT, and self- FEXT transfer functions for a short loop with bridged taps employing "GDSL" service (note that self-NEXT is very low for this hypothetical service), and shows (in the bottom graph) the distributed EQPSD and FDS spectral regions for the upstream and downstream transmit spectra, with a 0 indicating EQPSD signaling, a 1 indicating FDS, and a 0.5 indicating EQPSD or FDS signaling (note that in this case the non-monotonicity of the channel transfer function leads to several distributed signaling regions);
  • FIG. 49 shows an alternative signaling scheme: in the presence of high degrees of self-NEXT and self FEXT between group of lines 1 and 2 and lines 3 and 4, we employ multi-line FDS; there is EQPSD signaling within each group of lines (1 and 2 employ EQPSD as do 3 and 4) that have low self-interference;
  • FIG. 50 shows optimal transmit spectra (upstream and downstream) of ADSL (on CSA loop 6) with 49 HDSL DSIN-NEXT interferers and an AGN of -140 dBm/Hz;
  • FIG. 51 shows optimal transmit spectra (upstream and downstream) of .ADSL (on CSA loop 6) with 25 TI DSIN-NEXT interferers and an AGN of -140 dBm/Hz; and
  • the present invention comprises an improved system and method for communicating information such as voice, images, video, data, or other information on a transmission medium.
  • the present invention provides improved communications on the transmission medium in the presence of interference. More specifically, the present invention operates to model and then minimize the effects of interference on the transmission medium.
  • the interference may take the form of similar services being transmitted on neighboring transmission mediums and/or may take the form of uncorrelated interference from different services on neighboring transmission mediums and or interference from various noise sources which affect the transmission medium.
  • FIG. 5 illustrates a preferred embodiment for use of the present invention.
  • FIG. 5 illustrates a first location, e.g., a home 10 that is coupled through a subscriber line 12 to a second location, e.g. a telephone company central office (CO) 14.
  • CO telephone company central office
  • the first and second locations may be any of various types of sites, such as a home, an office, business, an office building, or a CO.
  • the communication system and method is comprised in a digital subscriber line (DSL) device that operates to perform xDSL communications on subscriber line 12.
  • DSL digital subscriber line
  • this figure shows a configuration that includes subscriber line 12, e.g., a twisted-pair copper line, that is coupled between home
  • the present invention is comprised in each of home 10 and CO 14.
  • subscriber lines are generally included in a cable that has a plurality of closely positioned transmission mediums, including other subscriber lines. Due to the close proximity of the transmission mediums comprised in a subscriber cable, a given subscriber line is subject to interference from neighboring transmission mediums, including self-NEXT and self-FEXT interference, and different service interference (DSrN).
  • DSP service interference
  • Some of the transmit spectra discussed herein are substantially optimized to maximize performance margins and avoid the effects of this interference, thereby providing improved communication.
  • an optimal transmit spectra give increased perfoimance margins (increased immunity against noise) and spectral compatibility margins as compared to one fixed transmit spectrum.
  • the optimal transmit spectra described herein are typically obtained by fixing the average input power and choosing the best signaling strategies and optimal power distribution to maximize the bit rate or performance margin.
  • the transmit spectra may also be used to minimize the required average input power where the desired performance margins or bit rates are fixed.
  • FIG. 5A Well Logging Embodiment
  • FIG. 5 A illustrates an alternate scenario for use of the communication system and method of the present invention.
  • FIG. 5A illustrates a drill hole and/or well-logging scenario which utilizes the communication system of the present invention.
  • communication equipment 16 on the surface communicates through a communication medium 12A to instrumentation 18 comprised in the borehole underground.
  • the communication system and method operates to reduce the effects of interference in the well hole and to provide improved communications.
  • FIG. 5 and FIG. 5A illustrate two embodiments for use of the system and method of the present invention
  • the present invention may be used in any of various types of systems or scenarios which involve communication of data on a transmission medium that is subject to noise or other interference.
  • the present invention is particularly useful in scenarios where the transmission medium is in close proximity to various sources of interference that can be ascertained, identified, and modeled.
  • the present invention is applicable to reduce the effects of interference on transmission media that are subject to interference from known or unknown sources where the spectral characteristics ofthe interference can be modeled.
  • VDSL2 in the face of noise and interference from neighboring services.
  • the invention is not, however, limited to these services, but can be applied to any communications channel that exhibits crosstalk interference.
  • FIG. 5 illustrates a subscriber line embodiment
  • the present invention may be used for any of various types of transmission media, e.g., copper wire, fiber optic, lines, co-axial cable, wave guides, etc.
  • the present invention is well suited for use in local and wide-area networks to minimize noise interference on networks, e.g., Ethernet, token ring, and wide area networks such as frame relay, Switched 56, ATM (asynchronous transfer mode), etc.
  • FIG. 5 illustrates use of the present invention between a home 10 and a central office 14 over a subscriber loop or subscriber line 12, it is noted that the present invention may also be used for the various trunks comprised in the PSTN.
  • the present invention is also useful in the various backbones or lines used for the Internet.
  • the present invention is also useful for wireless transmission applications, e.g., cellular telephones, cordless telephones, short wave radio, etc. as well as the various broadcast media such as the various digital satellite services providing television, Internet, data or voice services.
  • the present invention is applicable to any of various types of systems which involve the transmission of data over a wired or wireless medium.
  • the present invention is also applicable to any of the various types of signaling protocols such as frequency division multiple access (FDMA), time division multiple access (TDMA) and code division multiple access (CDMA) as well as hybrids of these, among others.
  • FDMA frequency division multiple access
  • TDMA time division multiple access
  • CDMA code division multiple access
  • the present invention is applicable to a variety of communications channels in a number of communication scenarios.
  • the present invention is described with respect to the preferred embodiment, the preferred embodiment being a digital subscriber line application between a first location, e.g., a home or business 10, and a telephone company central office 14.
  • FIG. 6 Home DSL System
  • FIG. 6 illustrates a system 100 comprised in location 10, i.e., in the home or business 10 which performs digital subscriber line (DSL) communication operations over subscriber line 12.
  • the DSL circuitry of the present invention is comprised in a computer system 102 coupled to subscriber line 12 through an xDSL port 106.
  • computer system 102 is also coupled to a telephone system 104.
  • the DSL system of the present invention may be comprised in any of various types of systems including computer systems, Internet appliances, televisions or dedicated boxes.
  • the DSL system of the present invention is comprised in a DSL device on an add-in card to the general purpose computer system 102.
  • the DSL card includes a port for coupling to a standard telephone jack, or "splitter,” which in turn couples to the subscriber line 12.
  • the computer system 102 may be utilized as a virtual telephone which operates through the DSL device for voice communications over the subscriber line 12.
  • a separate telephone system 104 is coupled to a second port of the DSL card, as shown in FIG. 6.
  • FIG. 7 Computer System Block Diagram
  • FIG. 7 a block diagram of one embodiment of computer system 102 is shown. Other embodiments are possible and contemplated.
  • the depicted system includes a microprocessor or CPU 110 coupled to a variety of system components through a bus bridge 114 .
  • a main memory 112 is also coupled to bus bridge 114.
  • a plurality of PCI devices are coupled to bus bridge 114 through a PCI bus 116.
  • the PCI devices include a video card 118 and a add-in card for the DSL device 120.
  • Bus bridge 114 provides an interface between microprocessor 110, main memory 112, and the devices attached to PCI bus 116. When an operation is received from one of the devices connected to bus bridge 114, bus bridge 114 identifies the target of the operation (e.g. a particular device or, in the case of PCI bus 116, that the target is on PCI bus 116). Bus bridge 114 routes the operation to the targeted device. Bus bridge 114 generally translates an operation from the protocol used by the source device or bus to the protocol used by the target device or bus.
  • Main memory 112 is a memory in which application programs are stored and from which microprocessor 110 primarily executes.
  • a suitable main memory 112 comprises DRAM (Dynamic Random Access Memory), and preferably a plurality of banks of SDRAM (Synchronous DRAM).
  • FIG. 8 is a block diagram illustrating DSL device 120 comprised in the computer 102 of FIG. 6.
  • DSL device 120 may take any of various types of forms including being comprised in a television system, Internet appliance, or dedicated device, among others systems.
  • the DSL device or add-in card 120 comprises a first port 160 for coupling to an expansion bus of the computer system, preferably a PCI expansion bus port as shown.
  • DSL device 120 also includes at least one subscriber line port 170 for coupling to the digital subscriber line 12.
  • DSL device 120 may include any of various hardware elements for performing the communication operations of the present invention.
  • the DSL communication device includes one or more programmable processing units which implement instructions from a memory.
  • the DSL communication device may include a programmable digital signal processor (DSP) 152, a general purpose processor, or other processors that execute instructions from a memory 156 to implement the communication operations of the present invention.
  • the DSL communication device 120 includes one or more application specific integrated circuits (ASICs) 154 and 158 or programmable logic devices such as FPGAs etc. that implement a portion or all of the present invention.
  • ASICs application specific integrated circuits
  • the communication system and method of the present invention may be implemented in any of various types of ways including programmable devices such as processing units, CPUs, DSPs, microcontrollers, etc., dedicated hardware such as ASICs, programmable logic devices such as FPGAs, or combinations of the above.
  • programmable devices such as processing units, CPUs, DSPs, microcontrollers, etc.
  • dedicated hardware such as ASICs
  • programmable logic devices such as FPGAs, or combinations of the above.
  • FIG. 9 is a flowchart for determining a transmit spectrum for use in communicating data on a communications channel according to one embodiment of the present invention.
  • This method may be used in communicating data on the communications channel when the communications channel is subject to interference from one or more other communications channels.
  • the communications channel of interest and one or more of the other communications channels carry a particular type of service, such as xDSL, ISDN, TI, or spread-spectrum, for example.
  • the first steps in this method comprise determining a channel transfer function of the communications channel 210 and an amount of self interference 220 into the communications channel from the other communications channels that carry the same type of service.
  • the transfer function and the amount of self interference are examined, and in step 240 a transmit spectrum for the channel is determined based on the examining.
  • Deteimining the channel transfer function in step 210 of FIG. 9 may be done by directly measuring it.
  • a transmitter on one end of the communications channel such as at CO 12 (in FIG. 1) or in well-logging instrumentation 18 (in FIG. 1A) may be directed to send a signal or a series of signals with predetermined intensities as a function of frequency, with which the a receiver at the other end of the channel may measure the attenuation, and perhaps also the phase shift, as a function of frequency.
  • the measurement may be extended to determine nonlinear responses of the channel by repeating the measurement with varying source strengths.
  • the channel characteristics may be determined in advance of the communication and stored, for example in a database at the CO or in a memory on a DSL card.
  • Determining the channel transfer function could then entail receiving it from the CO, the local memory storage, or other storage locations.
  • receiving the channel transfer function from the CO is particularly useful since the CO may rapidly look up pre-stored information on the particular physical line being used for the communications channel.
  • the amount of self interference may be determined in step 220 of FIG. 9 by receiving it or, if transmitter/receiver pairs are accessible on the other same-service channels, by measuring it. Determining the amount of self interference in step 220 may comprise determining a total self interference power, or a power distribution, or a coupling coefficient from the other same-service channels into the channel of interest, or a coupling coefficient with frequency dependence (such as a self-interference transfer function) from the other same-service channels into the channel of interest, or a combination of these characteristics, among others.
  • the amount of self interference may also include a characterization of the self interference in terms of self-NEXT and self- FEXT interference.
  • step 220 includes determining a self-NEXT transfer function and a self-FEXT transfer function from the other same-service channels into the channel of interest.
  • FIG. 10 - FIG. 12 show various embodiments 240a-c of step 240, in which the transmit spectrum is determined.
  • determining the transmit spectrum in step 240 comprises determining an EQPSD transmit spectrum if the amount of self interference is substantially low or negligible.
  • EQPSD transmit spectrum is a transmit spectrum in which EQPSD signaling is used on at least one portion ofthe available spectrum of communication frequencies.
  • the method may also include steps 242 and 247, in which an EQPSD/FDS transmit spectrum is found if the amount of self interference is substantially high or non- negligible.
  • an EQPSD/FDS transmit spectrum has a number of frequency regions in which EQPSD signaling is used, and a number of frequency regions in which FDS signaling is used. The locations of these regions in the available spectrum of communication frequencies and the transmission power as a function of frequency are preferably determined so that the data transmission rate on the channel is substantially maximized.
  • An EQPSD/FDS transmit spectrum preferably includes at least one portion using FDS signaling and one portion using FDS signaling, but in a degenerate case, the maximization may be achieved by using only EQPSD or only FDS signaling.
  • ⁇ EQPSD/FDS transmit spectrum is thus a transmit spectrum in which the available spectrum of communication frequencies includes at least one portion using EQPSD signaling or FDS signaling.
  • the method may also include step 249, in which an
  • EQPSD/TDS/MFDS transmit spectrum is found if the amount of self interference is substantially high or non-negligible and if the amount of self-FEXT interference is substantially high.
  • MFDS multi-line FDS
  • an EQPSD/FDS/MFDS transmit spectrum has a number of frequency regions in which EQPSD signaling is used, a number of frequency regions in which FDS signaling is used, and a number of frequency regions in which MFDS signaling is used.
  • EQPSD/TOS/MFDS transmit spectrum preferably includes at least one portion using FDS signaling, one portion using FDS signaling, and one portion using MFDS signaling, but in a degenerate case, the maximization may be achieved by using only EQPSD or only FDS or only MFDS signaling.
  • An EQPSD/FDS/MFDS transmit spectrum is thus a transmit spectrum in which the available spectrum of communication frequencies includes at least one portion using EQPSD signaling or FDS signaling or MFDS signaling.
  • determining the transmit spectrum in step 240 comprises determining an EQPSD transmit spectrum (in step 245) if the amount of self interference is substantially low or negligible (according to step 241), and determining an EQPSD/FDS/MFDS transmit spectrum (in step 249) if the amount of self interference is substantially high or non-negligible.
  • determining the transmit spectrum in step 240 comprises determining an EQPSD/FDS/MFDS transmit spectrum (in step 249).
  • the EQPSD/TDS/MFDS transmit spectrum will reduce to the appropriate signaling techniques.
  • the method further comprises a step of determining an amount of uncorrelated interference, such as additive Gaussian noise (AGN), into the communications channel.
  • AGN additive Gaussian noise
  • the uncorrelated interference may include different-service interference (DSIN) from the other communications channels carrying the different service.
  • DSIN different-service interference
  • the uncorrelated interference includes a total noise interference that preferably comprises AGN, DSIN, and other noise and interference whose spectral characteristics are not controlled by the user. Determining the transmit spectrum in step 240 is then performed in response to the amount of uncorrelated interference.
  • FIG. 13 is a flowchart of a method for transmitting data according to one embodiment of the present invention.
  • This method may be used in communicating data on a communications channel when the communications channel is subject to interference from one or more other communications channels.
  • the other communications channels may be located proximate to the communications channel, for example, in the case of multiple subscriber lines in a binder group of a telephone cable, or in the case of multiple radio transmission systems with closely located transmitters or overlapping coverage regions.
  • the communications channel of interest carries a particular type of service, such as xDSL, ISDN, TI, or spread-spectrum, for example.
  • the method comprises the steps of determining a channel transfer function of the communications channel in step 310, initiating a data transfer on the communications channel in step 320, and transferring the data on the communications channel using the transmit spectrum in step 330.
  • the step 320 of initiating the transfer comprises determining interference characteristics of the interfering communications channels in step 322, and determining a transmit spectrum in response to the channel transfer function and the interference characteristics in step 324.
  • step 310 of determining the channel transfer function may comprise measuring the channel transfer function, receiving the channel transfer function, or determining the channel transfer function through other means.
  • the channel transfer function may be determined at power-up of a transmission system, or at regular intervals in time, or in response to temperature changes, or at other appropriate times.
  • the transmit spectrum is preferably determined in step 324 to substantially maximize the data transmission rate for the communications channel, so that the maximum infoimation may be communicated per unit time on the communications channel in light of the various sources of noise and interference.
  • the transmit spectrum is also preferably determined in such a manner that the communications channel has equal upstream and downstream capacities, and that the transmit spectrum is spectrally compatible (that is, determined with regard to spectral compatibility) with the one or more other communications channels.
  • the transmit spectrum is preferably determined so that it satisfies a predetermined average power constraint for the communications channel.
  • the water filling technique may be carried out as described in reference [16]. If the channel capacity depends on channel noise and/or different-service interference, then the classical water-filling technique is used, as described in [14].
  • the transmit spectrum is preferably determined dynamically so that it may be optimized in response to changing interference conditions or a changing channel transfer function.
  • the transmit spectrum is determined so that it satisfies both a predetermined average power constraint and a predetermined peak power constraint for the communications channel, and may be determined using a peak constrained water-filling technique.
  • the peak constrained water filling technique may be carried out as described in section 4.8.3 (which presents a modification of the technique discussed in [16]). If the channel capacity depends on channel noise and/or different-service interference, then the peak constrained water-filling technique is used, as described in section 4.8.2.
  • the transmit spectrum is preferably determined dynamically so that it may be optimized in response to changing interference conditions or a changing channel transfer function.
  • the transmit spectrum is determined so that it satisfies only a predetermined peak power constraint for the communications channel, and may be determined using a peak constrained water-filling technique.
  • steps 322 and 324 of determining the interference characteristics and of determining the transmit spectrum are perfoimed more than once so that the transmit spectrum is modified appropriately as the interference characteristics change in time. These steps 322 and 324 may be performed each time a data transfer is initiated. Or, if step 330 of transferring data occurs repeatedly at regular or irregular intervals in time, then steps 322 and 324 of determining the interference characteristics and of determining the transmit spectrum are preferably performed prior to each occurrence of transfe ⁇ ing data in step 330.
  • a new transfer function or a new set of interference characteristics may be determined during a data transfer and used to calculate a new transmit spectrum. The new transmit spectrum may then be used in a subsequent portion of the data transfer.
  • the transmit spectrum is determined so that it specifies a pair of complementary spectra: one for transmission in each of the two directions on the communications channel. These two spectra may be called the "upstream transmit spectrum” and the “downstream transmit spectrum.”
  • the transmit spectrum used in transmission from home 10 may be designated the upstream transmit spectrum
  • the transmit spectrum used in transmission from CO 14 may be designated the downstream transmit spectrum.
  • upstream and downstream indicate opposite directions of transmission as desired.
  • the upstream and downstream transmit spectra may include one or more regions of the spectrum that use FDS signaling. In these regions, the upstream and downstream transmit spectra are orthogonal with respect to each other. In a preferred embodiment of the present invention, this duplexing orthogonality is achieved by choosing two non- overlapping frequency subregions in the FDS region, using one of the subregions for upstream signaling, and using the other subregion for downstream signaling. More generally, the FDS region may be constructed by choosing two non-overlapping sets of frequency subregions in the FDS region, using one of the sets for upstream signaling, and using the other set for downstream signaling.
  • the duplexing orthogonality is achieved by using code division signaling (CDS) to separate the upstream and downstream signals in the "FDS" region.
  • CDS code division signaling
  • one access code is used in upstream signaling, and a second, orthogonal, access code is used in downstream signaling.
  • step 322 of determining interference characteristics preferably includes determining an amount of self interference into the communications from the other same-service communications channels.
  • step 324 of determining the transmit spectrum may then include examining the channel transfer function and the amount of self interference. The transmit spectrum is then preferably determined in step 324 in response to the channel transfer function and the amount of self interference.
  • the transmit spectrum is determined so that it specifies a number M of complementary spectra: one for transmission on each of M channels in a subset of the one or more of the other communications channels that carry the same type of service.
  • These M transmit spectra may include one or more regions of the spectrum that use MFDS signaling. In these regions, the M transmit spectra are orthogonal with respect to each other. In one embodiment of the present invention, this multi-line orthogonality is achieved by choosing M non-overlapping frequency subregions in the MFDS region, and using one of the subregions for transmission on each of the M lines.
  • the MFDS region may be constructed by choosing M non-overlapping sets of frequency subregions in the MFDS region, and using one of the sets for transmission on each of the M channels.
  • the multi-line orthogonality is achieved by using multi-line code division signaling (multi-line CDS) in the "MFDS" region.
  • multi-line CDS multi-line code division signaling
  • different orthogonal access codes are used on each of the M channels.
  • the transmit spectrum is determined so that it specifies a number M' ⁇ >M) of complementary spectra: one for transmission on each of M channels in the subset of same-service channels, and additional spectra to provide orthogonal duplex separation on one or more of the M channels.
  • M' transmit spectra may include one or more regions of the spectrum that use FDS signaling as well as one or more regions of the spectrum that use MFDS signaling.
  • determining the amount of self interference comprises determining (1) a self-NEXT transfer function and (2) a self- FEXT transfer function that describe the coupling from near-end and far-end transmitters, respectively, on the other same-service communications channels.
  • determining the interference characteristics in step 322 further comprises determining an amount of uncorrelated interference arising from factors such as additive Gaussian noise (AGN) and crosstalk from one or more different-service channels, which carry a type of service different than the service on the channel of interest, among the one or more other channels.
  • AGN additive Gaussian noise
  • the transmit spectrum is then determined in response to the channel transfer function, an average power constraint or requirement for the channel, the self-NEXT and the self-FEXT transfer functions, and the amount of uncorrelated interference.
  • the transmit spectrum is determined to be an EQPSD transmit spectrum.
  • the transmit spectrum is determined to be an EQPSD transmit spectrum.
  • the transmit spectrum is determined to be an MFDS transmit spectrum.
  • determining the interference characteristics in step 322 includes determining some but not all of the self-NEXT and the self-FEXT transfer functions, and the amount of uncorrelated interference and the average power constraint or requirement for the channel may or may not be determined.
  • the transmit spectrum is then determined in response to the channel transfer function and the determined quantities, and is preferably optimized in response to these quantities.
  • the transmit spectrum is determined in response to one or more characteristics of the communications channel and the sources of noise or crosstalk. Determining these characteristics comprises steps such as determining the channel transfer function, determining the self-NEXT transfer function, and determining the self-FEXT transfer function.
  • the transmit spectrum is determined in response to the power-transfer characteristics of the communications channel, so determining these characteristics preferably comprises determining only the squared modulus of the mathematical transfer functions.
  • determining the channel transfer function means determining the function H(/) ⁇
  • determining the self-NEXT transfer function means
  • the function means determining the function F ⁇ f) ⁇
  • the phases of the transfer functions H c (f) , H N (f), and H F (f) may or may not be determined in addition to their squared modulii.
  • G, (/) Another characteristic of the communications channel and the sources of noise or crosstalk is the signal to noise ratio G, (/) .
  • G, ( ) indicates, at a frequency /, the ratio of the signal (specifically, the signal power spectral density at f) in channel number i to the noise (specifically, the noise spectral density at ) in channel number 1.
  • channel number z—1 is the channel for which the transmit spectrum is being determined
  • channel number i (for i > 1) is another channel that carries the same type of service as channel number 1 , and which may provide interference into channel number 1.
  • Another embodiment ofthe present invention comprises a method for determining a transmit spectrum for use in communicating data on a communications channel, preferably by determining signaling techniques in one or more frequency bins in the available frequency band of the communications channel.
  • This method is outlined in the flowchart of FIG. 15. This method may be used in communicating data on a communications channel when the communications channel is subject to interference from one or more other communications channels, some of which carry the same type of service as the communications channel of interest. Additionally, some of the other communications channels may carry different types of service than the communications channel of interest.
  • the first steps in this method comprise determining a channel transfer function of the communications channel 410. .An amount of self interference 420 into the communications channel from the other communications channels carrying the same type of service is determined in step 420. .An additional amount of uncorrelated interference is preferably determined in step 425. In step 430, the transfer function and the amount of self interference are examined, preferably along with the amount of uncorrelated interference. In step 440 a transmit spectrum for the channel is determined based on the examining.
  • the transmit spectrum is determined in step 440 so that different signaling techniques may be used in different frequency ranges in the communications band.
  • These frequency ranges, or frequency bins are non- overlapping ranges of the frequency spectrum, preferably with uniform frequency widths, and preferably chosen so that they cover the communications band.
  • the frequency bins have non-uniform widths or do not cover the entire communications band.
  • the transmit spectrum operates to specify an amount of transmission power used in each frequency bin for at least one direction of communication on at least one communications channel.
  • the amount of transmission power in each bin is preferably determined by a water-filling technique or a peak constrained water-filling technique.
  • the transmit spectrum specifies EQPSD signaling if the amount of self interference is substantially low in that bin, and FDS signaling if the amount of self interference is substantially high in that bin.
  • the transmit spectrum specifies MFDS signaling if the amount of self-FEXT interference is substantially high in that bin. Otherwise, the transmit spectrum specifies EQPSD signaling if the amount of self-NEXT interference is substantially low in that bin, and FDS signaling if the amount of self-NEXT interference is substantially high in that bin.
  • the neighboring frequency bins are grouped into two sets of neighboring bins, one ofthe sets is used for transmission in the upstream direction, and the other set is used for transmission in the downstream direction.
  • the two sets of neighboring bins are chosen so that the contiguous FDS transmit spectrum provides equal upstream and downstream signaling capacities.
  • the two sets of neighboring bins may be chosen so that the contiguous FDS transmit spectrum provides equal upstream and downstream average power.
  • the two sets of neighboring bins are chosen so that the contiguous
  • FDS transmit spectrum provides equal upstream and downstream signaling capacities and equal upstream and downstream average powers.
  • this method of the present invention may determine a transmit spectrum that includes one or more regions of neighboring bins using MFDS signaling.
  • the step of determining a transmit spectrum comprises determining a discrete MFDS transmit spectrum in such regions of neighboring MFDS bins. In the discrete MFDS transmit spectrum, each bin has M subregions. Each of the M subregions is used for bi-directional transmission on one of the M same-service channels.
  • the step of determining a transmit spectrum comprises determining a contiguous MFDS transmit spectrum in such regions of neighboring MFDS bins. In the contiguous MFDS transmit spectrum, the neighboring bins are grouped into M sets of neighboring bins. Each of the M sets of frequency bins is used for bi-directional transmission on one of the M same-service channels.
  • the M sets of neighboring bins are preferably chosen so that the contiguous MFDS transmit spectrum provides equal signaling capacities on the M channels.
  • determining the transmit spectrum in step 440 includes one or more steps of identifying "transition bins" that mark the endpoints (in the frequency spectrum) of different types of signaling techniques. These transitions bins may be rapidly identified by searching for bins in which certain characteristic quantities meet particular predetermined criteria. These searches, which are preferably implemented as binary searches, may be carried out in the step 430 of examining the channel transfer function and interference. The following list is a sample of transition bins that may be identified.
  • M E for bins with center frequencies ⁇ or ⁇ the center frequency of M E , EQPSD signaling is used.
  • M E 2 F for bins with center frequencies ⁇ or ⁇ the center frequency of M E 2 , EQPSD signaling is used, and FDS signaling is used in higher-frequency bins. In other words, M E 2 F indicates a transition from EQPSD signaling to FDS signaling.
  • M E 2MFDS'- indicates a transition from EQPSD signaling to MFDS signaling.
  • MMFDS2FDS'- indicates a transition from MFDS signaling to FDS signaling.
  • ME2MFDS'- indicates a transition from EQPSD signaling to FDS signaling.
  • transition frequencies may be defined for particular frequencies that mark transitions from one form of signaling to another.
  • f E2F represents a transition frequency where EQPSD is used in a region with frequency less t zm.
  • f 2F and, and, and FDS signaling is used in a region with frequency less
  • the proposed techniques combine a number of ideas into one signaling system that optimizes its performance given many different possible combinations of interferers. These ideas include:
  • Section 4.2 we give details about the interference models and the simulation conditions.
  • Section 4.3 looks at the various signaling schemes we will employ.
  • Sections 4.5 and 4.6 detail the new signaling strategies to obtain an optimal and/or suboptimal transmit spectrum in the presence of self-interference, different-service interference and AGN.
  • Section 4.7 derives some results applicable when neighboring lines vary in channel, noise and interference characteristics.
  • Sections 4.8, and 4.9 present optimal transmit spectra under additional peak-power constraint in frequency.
  • Section 4J0 We present optimal and near-optimal signaling schemes for non-monotonic channel, self-NEXT, and self-FEXT transfer functions in Section 4J0. We discuss optimal signaling for asymmetrical data-rate channels in Section 5. Finally, Section 4J2 presents several new ideas, extending the results presented here.
  • Channel noise can be modeled as additive Gaussian noise (AGN) [13].
  • Interference from other services can be modeled as additive colored Gaussian noise [13].
  • f k are the center frequencies (see Figures 16 and 17) of the K subchannels (bins) with index k e ⁇ 1, . . . , K ⁇ .
  • f k are the center frequencies (see Figures 16 and 17) of the K subchannels (bins) with index k e ⁇ 1, . . . , K ⁇ .
  • the concept of dividing a transfer function in frequency bins is very general and can include nonuniform bins of varying widths or all bins of arbitrary width (i.e., the bins need not be necessarily narrow).
  • All sources of DSIN-NEXT can be lumped into one PSD DS N ⁇ f) and all sources of DSIN- FEXT can be lumped into one PSD DS F ⁇ f).
  • All sources of self -.NEXT can be added to form one overall self-NEXT source.
  • the average input power constraint i.e., the average input power is limited to P max (Watts) in each direction of transmission in the symmetric data-rate case .
  • the average input power in upstream and downstream directions is limited to PTJ P (Watts)and P D N (Watts) (see Section 5).
  • the PSDs of the upstream and downstream transmission directions can be written using the notation introduced in Section 1.3.2.
  • Sf ⁇ f PSD on twisted pair i in upstream direction u.
  • Sf ⁇ f PSD on twisted pair i in downstream direction d.
  • the interference models for different services have been obtained from Annex B of TI.413-1995 ([9], the ADSL standard), with exceptions as in T1E1.4/97-237 [7].
  • the NEXT coupling model is 2-piece Unger model as in T1E1.4/95-127 [8].
  • BER was fixed at 10 ⁇ 7 .
  • MONET-PAM uses Decision Feedback Equalizers (DFE) [20] in the receivers along with multi-level pulse amplitude modulation (PAM) scheme.
  • DFE Decision Feedback Equalizers
  • PAM multi-level pulse amplitude modulation
  • the actual upstream and downstream power spectra can be obtained from [1].
  • MONET-PAM spectra is linearly interpolated from 2x 1552/3 Hz sampled data.
  • the RAM line-transformer hpf corner, that is, the start frequency is assumed to be at 1 kHz.
  • a 500 Hz rectangular-rule integration is carried out to compute margins.
  • the required DFE S.NR margin for 10 ⁇ 7 BER is 27.7 dB.
  • the joint signaling techniques used in the overall optimized signaling schemes use one of the basic signaling schemes (see Figure 18) in different frequency bins depending on the crosstalk and noise combination in those bins.
  • Figure 18 illustrates the three signaling schemes: EQPSD, FDS and multi-line FDS (in the case of three lines). 2
  • the Figure shows in frequency bin k the PSDs for each case (recall the notation introduced in Section 4J, Item 9):
  • EQPSD signaling When crosstalk and noise are not significant in a frequency bin, EQPSD signaling is preferred as it achieves higher bit rate than the other two orthogonal signaling schemes (see Section 4.5.5). In EQPSD signaling, the upstream and downstream PSDs are the same
  • FDS signaling yields the highest bit rates by eliminating self-NEXT (we prove this in Section 4.5.5).
  • each frequency bin is further divided into two halves, with all the upstream PSDs being same for all the lines and all the downstream PSDs being same for all the lines (s"(/) J s ⁇ f)). This type of orthogonal signaling completely eliminates self-.NEXT but does not combat self-.FEXT.
  • the signaling schemes EQPSD, FDS, and multi-line .FDS work in general for M lines.
  • line gets a separate frequency slot (W/M for M lines carrying the same service) in each bin and the upstream and downstream PSDs for each line are the same (s° ⁇ f) ⁇ s j (f) Vjf i, o G ⁇ u, d ⁇ ).
  • each xDSL line experiences no self -interference ( Figure 19 with neither self- NEXT nor self-FEXT).
  • the solution is well .known, but will be useful later in the development of the subsequent novel (Sections 4.5, 4.6, 4.7, and 4J2) signaling schemes.
  • the average xDSL input power in one direction of transmission must be limited to F max (Watts).
  • Line 1 carrying xDSL service.
  • Line 1 experiences interference from other neighboring services (DSIN-NEXT and DSIN-FEXT) and channel noise N 0 ⁇ f) (AGN) but no self- NEXT or self-F.
  • DSIN-NEXT and DSIN-FEXT channel noise
  • N 0 ⁇ f channel noise
  • EXT see Figure 19).
  • the DSIN-NEXT and DSIN-FEXT interference can be modeled as colored Gaussian noise for calculating capacity [13].
  • DS N ⁇ f is the PSD of the combined DSIN-NEXT
  • DS F ⁇ f is the PSD of the combined DSIN-FEXT.
  • S u ⁇ f) and S d ⁇ f) denote the PSDs of line 1 upstream (u) direction and downstream (d) direction transmitted signals respectively.
  • C u and C d denote the upstream and downstream direction capacities of line 1 respectively.
  • Hc(f) denote the channel transfer function of line 1.
  • the twisted pair channel is treated as a Gaussian channel with colored Gaussian noise. In this case the channel capacity (in bps) is given
  • Figure 20 gives a flowchart to obtain the optimal transmit spectrum using only EQPSD signaling in the presence of DSIN-NEXT, DSIN-.FEXT and AGN. It uses the classic water-filling solution to obtain the transmit spectrum. The novelty is in applying this to xDSL scenario to achieve a dynamic transmit spectrum (different for each interference type).
  • the channel capacities can be calculated separately for each direction of transmission in case of nonuniform interference between the two directions, i.e., when the additional assumption in Section 4.4.2 does not hold.
  • the transmit spectra in general will be different ⁇ S d (f) ⁇ S u (f)) for this case, but will still occupy the same bandwidth.
  • FIG. 21 shows the optimal upstream and downstream transmit spectrum for HDSL2 in the presence of DSIN-NEXT from 49 HDSL interferers and AGN (-140 dBm/Hz). Note the deep null in the transmit spectrum from approximately 80 to 255 kHz. This results from "water-filling" — the peak of the first main lobe of HDSL lies in the vicinity of 80 to 255 k . Hz.
  • Figure 22 shows the optimal upstream and downstream transmit spectrum for HDSL2 in the presence of DSIN-NEXT from 25 TI interferers and AGN (- 140 dBm/Hz).
  • the optimal transmit spectra for the two cases are significantly different, evidence ofthe fact that the optimal transmit spectra will change depending on the nature of the interference.
  • each xDSL line experiences self-interference (high self-NEXT and low self-FEXT) in addition to AGN and DSIN-NEXT and DSIN-.FEXT from other services (see Figure 3) in a generic xDSL service. This is the case of interest for HDSL2 service.
  • orthogonal signaling can completely reject self-NEXT.
  • FDS gives better spectral compatibility with other services than other orthogonal schemes like CDS or TDS (see Section 4.5J2 for a proof)- Therefore, we choose to use the FDS scheme for orthogonal signaling.
  • FDS signaling tradeoff FDS eliminates self-NEXT and therefore increases system capacity; however, FDS also reduces the bandwidth available to each transmitter/receiver pair and therefore decreases system capacity.
  • the average xDSL input power in each direction of transmission must be limited to P max (Watts), and
  • each line has the same self-NEXT transfer function Hw (/) and self-FEXT transfer function H F (/) for computing coupling of interference power with any other line.
  • Hw self-NEXT transfer function
  • H F self-FEXT transfer function
  • N N 0 ⁇ f k ) + DS N ⁇ f k ) + DS F ⁇ f k ), - (13) the noise PSD in bin k.
  • N consists of both AGN plus any interference (DSIN-NEXT and DSIN-FEXT) from other services.
  • s u (/) denote the PSD in bin k of line 1 upstream direction
  • s d ⁇ f) denote the PSD in bin k of line 2 downstream direction (recall the notation introduced in Section 4J, Item 9).
  • the corresponding capacities of the subchannel k are denoted by c u and c d .
  • P m is the average power over frequency range [0, W] in bin k and 0.5 ⁇ ⁇ 1.
  • s u ⁇ f) s d ⁇ f) V/ G [0, W] (EQPSD signaling);
  • the factor controls the power distribution in the bin, and W is the bandwidth of the bin.
  • the quantity a 0.5 corresponds to a maximum of R A (EQPSD) if and only if ⁇ - ⁇ 0 V ⁇ G (0.5, 1]. For all ⁇ G (0.5, 1], the quantity (2 ⁇ - 1) is positive and ⁇ jg- is negative if and only if (see (21))
  • FDS R A
  • FDS signaling scheme is a subset of the more general orthogonal signaling concept. However, of all orthogonal signaling schemes, FDS signaling gives the best results in terms of spectral compatibility under an average power constraint and hence is used here (see proof in Section 4.5J2). In the case of a peak power constraint in frequency, other orthogonal schemes, such as CDS, could be more appropriate (see Section 4J2.6). 4.5.6 Solution: All frequency bins
  • the signaling scheme switches from EQPSD to FDS signaling at some bin E 2 F > which lies in the range of bins (M E , M F ).
  • Figure 26 illustrates the situation of the 3 bins M E , M F and M E2F .
  • the next Section we develop an algorithm to find the optimal bin E2F and the optimal power distribution.
  • Standard minimization/maximization routines can be used to search for the optimal powers P E and Pp.
  • Figure 27 illustrates a flowchart showing the steps for the optimal and the suboptimal solution.
  • Figure 28 shows one possible way of grouping the bins.
  • the left-hand- side figures show the optimal upstream and downstream "discrete" transmit spectra S u (f) and S d (f) as obtained by the algorithm of Section 4.5.7.
  • the upstream transmit spectrum is completely “contiguous” while the downstream spectrum is “contiguous” except for one "hole” as shown in Figure 28.
  • bins can be grouped in a variety of different ways giving many different optimal transmit spectra. Particular modula- tion schemes and spectral compatibility with neighboring services may influence the way bins are grouped. Further, grouping of bins may lead to different input powers for opposite directions of transmission.
  • the resulting transmit spectra 5" Pt (/) anc * S d pt ⁇ f) are another manifestation of the grouping of bins and yield equal performance margins (equal capacities) and equal average powers in both directions of transmission.
  • the HDSL2 standards committee desires a high uncoded margin (preferably more than 6 dB). Table 1 shows mat we achieve very high uncoded margins far exceeding current schemes. Table 1: Uncoded performance margins (in dB) for CSA No. 6: MONET-PAM vs. Optimal.
  • the column Diff (in dB) notes the difference in performance margins between the optimal scheme and the suboptimal scheme. Note that there is hardly any difference between d e two when self-interference dominates the total crosstalk. This is a very significant result from an implementation view point for it shows that near-optimal signaling can be obtained with very little computational effort.
  • the optimal solution requires a somewhat complicated optimization over the bins starting from M E and moving towards the right. Our results clearly indicate that the near-optimal solution can give extremely attractive results with no search for the optimal bin. Further, this suggests that the optimal bin E2F is closer to M E than M F and so one should search for it to the immediate right of M E .
  • FIG. 29 An optimal upstream transmit spectrum in the case of self-interference is illustrated in Figure 29.
  • the Figure shows the optimal upstream transmit spectrum for HDSL2 service in the presence of self-NEXT and self-FEXT from 39 HDSL2 disturbers and AGN of -140 dBm/Hz.
  • the downstream transmit spectra for the HDSL2 service are symmetric with the upstream transmit spectra as discussed earlier.
  • Figure 30 illustrates optimal "contiguous" transmit spectra for the same case of 39 self-NEXT and self-FEXT disturbers with AGN of -140 dBm/Hz.
  • the upstream and down- Table 2 Uncoded performance margins (in dB) for CSA No. 6: Optimal vs. Suboptimal.
  • Figure 31 illustrates another set of optimal "contiguous" transmit spectra for the same case of 39 self-NEXT and self-FEXT disturbers with AGN of -140 dBm/Hz. These "contiguous" transmit spectra were obtained by grouping the bins as outlined in the .algorithm of Section 4.5J0 such that now we have both equal performance margins (equal capacities) and equal average powers in both directions of transmission.
  • Table 3 lists our simulation results for HDSL2 service and compares them with results from [1]. The simulations were done for die CSA loop number 6 (26 AWG, 9 kft, no bridged taps) and CSA loop number 4 (26 AWG, bridged taps).
  • the column "Our-PAM” refers to our implementation using TlEl.4/97- 180R1 [11] of the PAM scheme (MONET-PAM) suggested by the authors in [1] using their transmit spectra. We believe the slight differences in margins between MONET-PAM and "Our-PAM" exist due to the differences in our channel, self-NEXT and self-FEXT models.
  • the use of "Our-PAM" margins allows us a fair comparison of our optimal margins with the other proposed transmit spectra. From Table 3, we can clearly see that the optimal transmit spectrum has a high degree of spectral compatibility with the surrounding interfering lines.
  • Theorem .Let the line under consideration be the signaling line (with PSD S in a single bin) and the line that interferes with this line be the interfering line (with PSD s u (f) and s d (f) in a single bin). Then, using an FDS scheme instead of CDS scheme for d e interfering line results in higher capacity for the signaling line under an average power constraint and a Gaussian channel model.
  • the power-peaky .FDS transmit spectra should be very compatible with the ADSL standard, since ADSL can balance how many bits it places in each of its DMT subchannels using a bit loading algorithm [17].
  • multi-line FDS To reject self-.FEXT and self-NEXT, we use multi-line FDS (see Section 4.3 and Figure 18).
  • multi-line FDS we separate each line by transmitting on each in different frequency bands. This reduces die transmission bandwidth to 1/ the total channel bandwidth, with M the number of lines carrying the service under consideration.
  • multi-line FDS signaling can increase the capacity only when there are a few number of lines.
  • the average xDSL input power in each direction of transmission must be limited to P max (Watts), and
  • each line has the same self-NEXT transfer function H ⁇ f (/) and self-FEXT transfer function H F (/) for computing coupling of interference power with any other line.
  • H ⁇ f self-NEXT transfer function
  • H F self-FEXT transfer function
  • the level of self-.NEXT and self-FEXT varies over frequency (recall Figure 17).
  • EQPSD signaling is the best choice.
  • orthogonal signaling scheme like FDS is preferred (due to its self -.NEXT rejection, as we saw in Section 4.5). But, in regions of high self-FEXT, multi-line FDS signaling might be required for gaining capacity.
  • line 1 for our capacity calculations.
  • Line 1 upstream and downstream capacities for EQPSD signaling are denoted by C" EQPSD a ⁇ C I , EQ P SD respectively.
  • line 1 upstream and downstream capacities for multi-line FDS signaling are denoted by c" MFDS and c MFDS respectively. Since the upstream and downstream transmit spectra of line 1 in bin k for EQPSD and multi-line FDS are the same, we have:
  • EQPSD is better (gives higher capacity) than multi-line FDS when D ⁇ 0, i.e., iff
  • line 1 for our capacity calculations.
  • Line 1 upstream and downstream capacities for FDS signaling are denoted by c" FDS and cf FDS respectively.
  • line 1 upstream and downstream capacities for multi-line FDS signaling are denoted by C" MFDS a ⁇ C I , MFDS respectively. Since the upstream and downstream transmit spectra of line 1 in bin k for EQPSD and multi-line .FDS are die same, we have:
  • FDS is better (gives higher capacity) than multi-line FDS when D ⁇ 0, i.e., iff
  • Figure 35 illustrates the 3 bins E2 MFD S , -MMFD S 2FD S and FDS2 MFD S and the EQPSD, FDS and multi-line FDS regions.
  • E2 MFD S -MMFD S 2FD S
  • FDS2 MFD S the EQPSD, FDS and multi-line FDS regions.
  • FDS signaling is not employed in this case.
  • Bins [ FDS2 MFDs + 1 > K] employ multi-line FDS signaling. There is no switch to multi-line FDS signaling within the EQPSD signaling region (bins
  • P m is the average power over frequency range [0, W] in bin k and 0.5 ⁇ a ⁇ 1.
  • the PSDs s"(/) and s d (f) are "symmetrical" or power complementary to each otiier. This ensures the
  • the achievable rate for one frequency bin can be written as
  • the quantity a 0.5 corresponds to a maximum of RA (EQPSD) if and only if — ⁇ ⁇ 0 V ⁇ G (0.5, 1]. For all a G (0.5, 1], the quantity (2 ⁇ — 1) is positive and ⁇ - is negative iff (see (65))
  • Figure 40 gives a flowchart to obtain the optimal transmit spectrum using EQPSD, FDS, and multi-line FDS (MFDS) signaling in the presence of self-interference (self-NEXT and self-FEXT), DSIN-NEXT, DSIN-FEXT and AGN.
  • self-NEXT and self-FEXT self-interference
  • DSIN-NEXT DSIN-FEXT
  • AGN AGN
  • Optimal transmit spectra were used in all examples to compute performance margins and channel capacities.
  • HDSL2 service Table 4 lists our simulation results performance margins and channel capacities using the EQPSD, FDS and multi-line FDS signaling schemes.
  • Cf denotes the upstream capacity of line i using EQPSD and FDS signaling only and G (M.FDS) denotes the upstream capacity of line i using EQPSD, FDS and multi-line FDS signaling schemes. All the rates are in Mbps.
  • Table 4 Uncoded performance margins (in dB) and channel capacities (in Mbps) using EQPSD, FDS and multi-line FDS for HDSL2 (CSA No. 6).
  • Diff Difference between bottom half and top half of each row of Margin.
  • the column Diff denotes the gain in performance margins between using EQPSD and FDS versus EQPSD, FDS and multi-line FDS signaling, i.e., the difference in margins between the bottom half and top half of each row.
  • Each HDSL2 line contributes NEXT and FEXT calculated using 2-piece Unger model [8].
  • GDSL GDSL service: Table 5 lists our simulation results performance margins and channel capacities using the EQPSD, FDS and multi-line FDS signaling schemes in the case of "GDSL".
  • Table 5 Uncoded performance margins (in dB) and channel capacities (in Mbps) using EQPSD, FDS and multi-line FDS for "GDSL" (3 kft line).
  • Diff Difference between bottom half and top half of each row of Margin.
  • Cf denotes the upstream capacity of line i using EQPSD and FDS signaling only and G"(MFDS) denotes the upstream capacity of line i using EQPSD, FDS and multi-line FDS signaling schemes. All die rates are in Mbps.
  • the column Diff denotes the gain in performance margins between using EQPSD and FDS versus EQPSD, FDS and multi-line FDS signaling, i.e., the difference in margins between the bottom half and top half of each row.
  • Each "GDSL” line contributes self-NEXT and self-FEXT calculated using 2-piece Unger model [8].
  • the self-FEXT level is more dominant than self- NEXT. To model this we take only 1% of the self-NEXT power calculated using 2- piece Unger model in our simulations.
  • Diff Difference between bottom half and top half of each row of Margin.
  • VDSL2 "VDSL2" service: Table 6 lists our simulation results performance margins and channel capacities using d e EQPSD, FDS and multi-line FDS signaling schemes in me case of "VDSL2". Notes:
  • Cf denotes the upstream capacity of line i using EQPSD and FDS signaling only and G"(MFDS) denotes the upstream capacity of line i using EQPSD, FDS and multi-line FDS signaling schemes. All e rates are in Mbps.
  • the column Diff denotes the gain in performance margins between using EQPSD and FDS versus EQPSD, FDS and multi-line FDS signaling, i.e., the difference in margins between the bottom half and top half of each row.
  • Each NDSL2 line contributes self- ⁇ EXT and self-FEXT calculated using 2-piece Unger model [8].
  • self- EXT and self-.FE.XT both are high but self-I EXT dominates self-FEXT.
  • Ni N 0 (f k ) + DS N (f k ) + DSp(f k ), - (71) be the lumped noise PSD in line 1 bin k.
  • P ml and P m be the average powers over range [0, W] Hz in bin k of line 1 and 2 respectively.
  • s" (/) and sf (/) denote die PSDs in bin k of line 1 upstream and downstream directions
  • s 2 (/) and s d (f) denote the PSDs in bin k of line 2 upstream and downstream directions (recall the notation introduced in Section 4J, Item 9).
  • the corresponding capacities of the subchannel k are denoted by c", c , (r and d > .
  • the factor a controls the power distribution in the bin, and W is the bandwidtii of the bin.
  • the achievable rate for one frequency bin can be written as
  • the quantity a 0.5 corresponds to a maximum of R A (EQPSD) if and only if ⁇ - ⁇ 0 V ⁇ e (0.5, 1]. For all ⁇ e (0.5, 1], ⁇ is negative if and only if (see (80))
  • the factor ⁇ controls the power distribution in the bin and W is the bandwidth of the bin.
  • the achievable rate for one frequency bin can be written as
  • ⁇ 0.5 corresponds to a maximum of R A (EQPSD) if and only if ⁇ - ⁇ 0 V ⁇ G (0.5, 1]. For all ⁇ G (0.5, 1], ⁇ is negative if and only if (see (93))
  • ⁇ - is positive if and only if (see (93))
  • the xDSL transmit spectra are limited by constraining static PSD masks; Q u (/) for upstream and Q d ⁇ f) for downstream.
  • the average xDSL input power in each direction of transmission must be limited to F max (Watts).
  • Do tii is by designing die distribution of energy over frequency (the transmit spectrum) of the xDSL transmission.
  • Line 1 carrying an xDSL service.
  • Line 1 experiences interference from otiier neighboring services (DSIN-NEXT and DSIN-FEXT) and channel noise N 0 ⁇ f) (AGN) but no self-NEXT or self-FEXT (see Figure 19).
  • the twisted pair channel can be treated as a Gaussian channel with colored Gaussian noise [13].
  • DS N ⁇ f) is the PSD of the combined DSIN-NEXT
  • DS F ⁇ f) is the PSD of the combined DSIN-FEXT.
  • S u ⁇ f) and S d ⁇ f) denote the PSDs of line 1 upsfream (u) direction and downstream (d) direction transmitted signals, respectively.
  • G" and C d denote the upstream and downstream direction capacities of line 1 respectively.
  • Hc(/) denote die channel transfer function of line 1.
  • the optimal solution to (98), (99), (100), (101) is basically a "peak-constrained water-filling". 6
  • Figure 43 shows the optimal downstream transmit specfrum for HDSL2 with OPTIS downstream constraining mask in the presence of DSIN-NEXT from 49 HDSL interferers and AGN (—140 dBm/Hz).
  • the key features in die case of HDSL interferers are:
  • Peak-constraine water-filling can be likened to filling water in a closed vessel with uneven top and bottom surfaces. 1. Comparing the peak-constrained transmit spectrum in Figure 43 with the unconstrained in peak power one in Figure 21 indicates that the peak-constrained optimal solution tries to follow the unconstrained in peak power optimal solution.
  • the peak-constrained optimal solution has a null in d e spectrum around 150 I Hz similar to the one in me unconstrained in peak power spectrum. The null in the transmit spectra occurs in order to avoid the interfering HDSL transmit spectrum.
  • An OPTIS fransmit spectrum achieved by tracking 1 dBm/Hz below the OPTIS PSD mask diroughout, does not yield good performance margins (see Table 7).
  • the OPTIS transmit spectrum looks different from the peak-constrained optimal spectrum (see Figure 43).
  • the null in the peak-constrained optimal spectrum indicates that it is suboptimal to distribute power according to the OPTIS transmit spectrum.
  • Figure 44 shows the optimal upstream transmit spectrum for HDSL2 with OPTIS upsfream constraining mask in the presence of DSIN-NEXT from 25 TI interferers and AGN (— 140 dBm/Hz). Again, we compare the peak-constrained transmit spectrum in Figure 44 with the unconstrained in peak power one in Figure 22. Note that the peak-constrained optimal transmit spectrum puts no power in the high-frequency spectrum (to avoid TI interference) as opposed to an OPTIS transmit spectrum.
  • Diff (Dn) Difference in Downstream margins (Optimal - O.PTIS)
  • Diff (Up) Difference in Upsfream margins (Optimal - OPTIS)
  • the xDSL transmit spectra are limited by constraining static PSD masks; Q u (/) for upsfream and Q d (f) for downstream.
  • the average xDSL input power in each direction of transmission must be limited to F max (Watts).
  • Line 1 For a line (line 1) carrying xDSL service. Line 1 experiences interference from other neighboring services (DSIN-NEXT and DSIN-FEXT), channel noise N 0 ⁇ f) (AGN), and self-interference (self-NEXT and self-FEXT) (see Figure 3).
  • DSIN-NEXT and DSIN-FEXT channel noise N 0 ⁇ f
  • AGN channel noise
  • self-interference self-NEXT and self-FEXT
  • S ⁇ ⁇ f is the water-filling solution (refer to [14, 16] if the spectral region employs EQPSD or multi-line FDS signaling and to [16] if the spectral region employs FDS signaling) (see Sections 4.5 and 4.6).
  • This is the peak-constrained water-filling solution in the presence of self-interference. As argued in die previous Section, this solution satisfies the necessary KKT conditions for optimality and therefore is d e unique optimal solution.
  • Figure 45 shows the optimal upstream and downsfream transmit spectra for HDSL2 with OPTIS constraining masks in the presence of self-NEXT and self-FEXT from 39 HDSL2 interferers and AGN (—140 dBm/Hz). Note that the optimal upsfream and downsfream transmit spectra are separated in frequency (using FDS signaling) in a large spectral region in order to avoid high self -.NEXT. On the other hand, OPTIS transmit spectra have a large spectral overlap at lower frequencies (self-NEXT is high here) mat significantly reduces its performance margins (see Table 7).
  • Figure 46 shows the optimal upstream and downsfream fransmit spectra for HDSL2 with OPTIS constraining masks in die presence of self-NEXT and self-FEXT from 24 HDSL2 interferers, DSIN-NEXT from 24 TI interferers, and AGN (-140 dBm/Hz).
  • the upsfream and downsfream optimal spectra are separated in frequency (using FDS signaling) over a large spectral region.
  • the EQPSD spectral region towards die beginning of d e spectrum is larger here man in the previous example, since we have more DSIN-NEXT from TI.
  • optimal transmit specfra employ optimal separation in frequency of upstream and downstream services in the presence of interference.
  • the "1 dB below OPTIS" fransmit spectra do not do tins, and so have inferior performance.
  • Table 7 compares the performance margins of the OPTIS transmit spectra (obtained from the OPTIS PSD mask by uniformly subtracting 1 dBm/Hz over die entire frequency range as in [5]) with die optimal transmit specfra under the O.PTIS PSD mask constraints. Table 7 shows that the optimal scheme significantly outperforms OPTIS in the case of self-interference. In cases involving different service interferers (HDSL and TI) the optimal scheme consistently outperforms OPTIS by 1 dB or more. Further, comparing these results with those in Table 1 suggests that the OPTIS PSD mask is not a good constraining PSD mask, since the unconstrained in peak power margins in Table 1 are significantly higher than die ones in Table 7. Comparing Tables 1 and 7 suggests tiiat optimal signaling with no peak power constraint (static PSD mask) gives high performance margin gains.
  • Bridged taps are short segments of twisted pairs that attach to another twisted pair that carries data between the subscriber and the CO. BTs are terminated at die otiier end witii some characteristic impedance. BTs reflect die signals on the data-carrying line. These reflections destructively interfere with the transmitted signal over certain frequencies. This leads to nulls in the channel transfer function and the self-FEXT transfer function at these frequencies (see Figure 48). These nulls in the channel transfer function significantly reduce the data transmission rate. Thus, bridged taps pose an important problem in achieving high bit rates over xDSL lines. 9
  • Bridged taps presence, location, and length vary according to each loop setup.
  • mat d e channel transfer function nulls (in frequency) vary for each separate line.
  • We need the optimal power distribution tiiat maximizes the bit-rates in the presence of bridged taps and interference. This further enforces the need for optimal dynamic fransmit specfra and indicates mat static fransmit specfra are not a good idea.
  • tiiis Section we present optimal and near-optimal solutions to find die transmit specfra in the presence of BTs.
  • EQPSD EQPSD
  • FDS FDS
  • multi-line FDS bins could be randomly distributed d roughout d e transmission bandwidtii.
  • the search for d e optimal switchover bins from one signaling scheme to die otiier could be exceedingly expensive (involving a multi- dimensional search).
  • the suboptimal solution determines the signaling strategy in each bin by simple, fast comparisons involving transfer functions and SNRs. This is followed by a simple optimal power distribution scheme using die water-filling technique.
  • the optimal and suboptimal algorithms can be implemented under a peak frequency- domain power constraint (static PSD mask). This is achieved by using peak-constrained water- filling technique (instead of just water-filling) for optimal power distribution (see Sections 4.8 and 4.9) in the algoritiims given in Sections 4J0J and 4J0.2.
  • the optimal fransmit spectrum in the presence of BTs can have several switchover bins from one signaling scheme to the other (for e.g., EQPSD to FDS and FDS to EQPSD switchover bins).
  • EQPSD EQPSD to FDS
  • FDS FDS to EQPSD switchover bins
  • the quantity X 2 k - F 2 k - H itk F i>k tends to be an increasing function of frequency or bin number k, and stays positive once it becomes positive.
  • the quantity H ⁇ tk — 2 ⁇ X ijk — F ⁇ ⁇ k ) tends to decrease witii frequency or bin number k and stays negative once it becomes negative.
  • Figure 47 illustrates a case of "contiguous" optimal transmit spectra in case of a loop with bridged taps (CSA loop 4).
  • the optimal transmit spectra have only one transition region from EQPSD to FDS signaling.
  • the transmit spectra were obtained such tiiat we have equal performance margins and equal average powers in both directions of transmission.
  • UPi and DOWNi refer to line i, upsfream and downstream direction PSDs respectively.
  • tiiis scheme we use multiline FDS between group of lines (1 and 2) having high self-lSIEXT and high self-FEXT witii otiier group of lines (3 and 4).
  • tiiere is EQPSD among group of lines (1 and 2 employ EQPSD as do 3 and 4) that have low self-NEXT and low self-FEXT within the group.
  • This scheme can be extended for M self-interfering lines (with different self-NEXT and self-FEXT combinations between them) using combination of EQPSD, FDS, and multi-line FDS signaling schemes between different lines and frequency bins.
  • the above scheme can be applied in the case of groups of lines with different self- interference (self-NEXT and self-FEXT) characteristics between different set of lines.
  • Some channels undergo a significant change in channel transfer function Hc(/) as a function of temperature. Temperature variations are a part of nature and hence we need to continuously update our channel transfer functions. Changes in channel characteristics can change the channel capacity. We can develop an adaptive optimal transmit spectrum to adjust to these as well as any other variations.
  • FDS signaling is the optimal signaling strategy (see Section 4.5J2).
  • FDS signaling sf ⁇ f) and s d (/) occupy distinct separate frequency bands that are twice as higher than those using EQPSD signaling (see Figure 25).
  • CDS signaling the transmit specfra s ⁇ f) and s d ⁇ f) look similar to EQPSD signaling but the upstream and downstream spectra are separated using two orthogonal codes.
  • CDS signaling Under a peak power constraint in frequency CDS signaling is preferred.
  • SS-CDS spread spectrum CDS
  • Multi-line CDS separates die M interfering lines using M orthogonal codes and is less power- peaky in frequency than multi-line FDS.
  • multi-line FDS signaling strategy is preferred.
  • each line gets a separate frequency slot within each bin for transmission.
  • the PSD s° ⁇ f) in each bin is M times higher (or taller) than the corresponding PSD using EQPSD signaling (see Figure 18).
  • an alternative orthogonal signaling scheme like multi-line CDS is preferred.
  • We can implement SS-CDS over this spectral region .E MFDS such that
  • Section 4 developed optimal signaling techniques for symmetric data-rate channels.
  • Asymmetrical data-rate channels have different upstream and downstream transmission rates, for e.g., .ADSL and VDSL services. These channels also employ different average powers in die two fransmission directions.
  • SPSD scaled-PSD
  • each xDSL line experiences no self-interference (Figure 19 with neither self- NEXT nor self-FEXT).
  • the solution is well known (classical water-filling [14]), but the idea is to optimally distribute power in a dynamic fashion.
  • the average xDSL input power in the upstream and downsfream directions of fransmission must be limited to P UP (Watts) and P DN (Watts).
  • Do tii is by optimally designing the distribution of energy over frequency (the transmit spectrum) of the xDSL transmission.
  • Botii directions (upstream and downsfream) of transmission experience the same channel noise (AGN) and different service interference (DSIN-NEXT and DSIN-FEXT).
  • Line 1 carrying xDSL service.
  • Line 1 experiences interference in both directions from other neighboring services (DSIN-NEXT and DSIN-FEXT) and channel noise N 0 ⁇ f) (AGN) but no self-NEXT or self-FEXT (see Figure 19).
  • the DSIN-NEXT and DSIN-.FEXT interference can be modeled as colored Gaussian noise for calculating capacity [13].
  • DS N ⁇ f is the PSD of the combined DSIN-NEXT
  • DS F ⁇ f is the PSD of the combined DSIN-FEXT.
  • S u ⁇ f) and S d ⁇ f) denote the PSDs of line 1 upsfream (u) direction and downsfream (d) direction transmitted signals respectively.
  • C" and C d denote the upstream and downstream direction capacities of line 1 respectively.
  • Hc(f) denote die channel transfer function of line 1.
  • the twisted pair channel is treated as a Gaussian channel with colored Gaussian noise.
  • the channel capacity (in bps) is given by [14]
  • upsfream and downstream capacities can be independently calculated by separately maximizing (112) and (113). For illustration purposes we optimize the upsfream transmit PSD S u (f).
  • Figure 20 gives a flowchart to obtain the optimal transmit spectrum in each direction using only SPSD signaling in the presence of DSIN-NEXT, DSIN-.FEXT and AGN. It uses the classic water-filling solution to obtain the transmit spectrum. The novelty is in applying this to xDSL scenario to achieve a dynamic transmit spectrum (different for each interference type) in d e two directions of transmission.
  • Figure 51 shows the optimal upstream and downstream transmit specfra for ADSL in the presence of DSIN-NEXT from 25 TI interferers and AGN (-140 dBm/Hz).
  • Table 8 lists achievable bit rates (in Mbps) for ADSL service in presence of DSIN-NEXT from HDSL and TI interferers. Note tiiat a desired ratio (r) between the upsfream and downsfream rates can be achieved by appropriately changing the input powers Pup and Pr ⁇ - Table 8: Achievable bit rates (in Mbps) using SPSD signaling
  • the optimal fransmit spectra vary significantly with the interference combination.
  • the water-filling solution yields unique transmit spectra for each interference combination [14].
  • the fransmit spectra adapt to minimize die effects of the interference combination.
  • the optimal transmit spectra for upstream and downstream direction are scaled replicas of each other in narrow bins, i.e. tiiey employ SPSD signaling.
  • each asymmetric data-rate xDSL line experiences self-interference (high self- NEXT and low self-FEXT) in addition to AGN and DSIN-NEXT and DSIN-FEXT from other services (see Figure 3) in a generic xDSL service. Tiiis is the case of interest for the ADSL service.
  • the average xDSL input power in the upstream and downstream directions of transmission must be limited to P UP (Watts) and P DN (Watts).

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Abstract

L'invention porte sur un système et un procédé de détermination des caractéristiques de transmission d'un canal de communications et de données de transmission sur ce canal de communications. Ce procédé peut être utilisé dans la communication de données lorsque le canal est soumis aux interférences provenant d'un ou plusieurs autres canaux de communications, y compris une paradiaphonie (NEXT) et une télédiaphonie (FEXT) provenant d'autres canaux acheminant le même service et/ou différents services. Cette invention peut être utilisée dans les communications de lignes d'usagers numériques (xDSL) ou dans diverses applications telles que la diagraphie des puits de pétrole et dans des systèmes mettant en oeuvre plusieurs émetteurs radio brouilleurs. Selon une réalisation préférée, l'invention porte sur un procédé de détermination de masque de transmission optimal ou d'une fonction de densité spectrale de puissance destinée à être utilisée sur le canal de communications. La fonction de transmission est de préférence déterminée en réponse à la fonction de transfert du canal et du nombre d'interférences automatiques de type paradiaphonie, télédiaphonie et des interférences sans corrélation telles que le bruit gaussien auxiliaire, ainsi que des interférences provenant de différents canaux de communications de services.
PCT/US1998/027154 1997-12-19 1998-12-18 Techniques d'optimisation spectrale et de signalisation mixtes pour les communications soumises a des interferences WO1999033215A1 (fr)

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US09/144,934 US6317495B1 (en) 1997-12-19 1998-09-01 Spectral optimization and joint signaling techniques with multi-line separation for communication in the presence of crosstalk
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WO2007095112A3 (fr) * 2006-02-14 2008-06-05 Baker Hughes Inc Égalisation à décision rétroactive en télémétrie par impulsions dans la boue
EP2088686A4 (fr) * 2006-11-01 2009-12-16 Huawei Tech Co Ltd Procédé et dispositif de gestion du spectre de fréquences
EP1405447A4 (fr) * 2001-06-19 2009-12-30 Baker Hughes Inc Modulation a multitonalite discrete en duplex integral dans des applications de diagraphie
EP1702417A4 (fr) * 2004-01-09 2012-09-05 Ikanos Technology Ltd Formation en temps reel de masques a densite spectrale de puissance optimale
US8824979B2 (en) 2007-09-21 2014-09-02 Qualcomm Incorporated Interference management employing fractional frequency reuse
US8837305B2 (en) 2007-11-27 2014-09-16 Qualcomm Incorporated Interference management in a wireless communication system using beam and null steering
US8948095B2 (en) 2007-11-27 2015-02-03 Qualcomm Incorporated Interference management in a wireless communication system using frequency selective transmission
US9066306B2 (en) 2007-09-21 2015-06-23 Qualcomm Incorporated Interference management utilizing power control
US9065584B2 (en) 2010-09-29 2015-06-23 Qualcomm Incorporated Method and apparatus for adjusting rise-over-thermal threshold
US9078269B2 (en) 2007-09-21 2015-07-07 Qualcomm Incorporated Interference management utilizing HARQ interlaces
US9137806B2 (en) 2007-09-21 2015-09-15 Qualcomm Incorporated Interference management employing fractional time reuse
US9344973B2 (en) 2007-09-21 2016-05-17 Qualcomm Incorporated Interference management utilizing power and attenuation profiles
CN108112056A (zh) * 2016-11-24 2018-06-01 联芯科技有限公司 用户终端的扫频方法与装置

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US7035400B1 (en) 1999-03-01 2006-04-25 Wm. Marsh Rice University Signaling Techniques in channels with asymmetric powers and capacities
WO2001041388A1 (fr) * 1999-12-02 2001-06-07 Infineon Technologies Ag Procede de transmission de donnees d'emission par l'intermediaire d'un modem d'abonne
EP1802067A3 (fr) * 1999-12-02 2009-03-04 Infineon Technologies AG Procede de transmission de donnees d'emission par l'intermediaire d'un modem d'abonne
WO2001049001A1 (fr) * 1999-12-24 2001-07-05 Schlumberger Limited Procede et appareil destines a la transmission de donnees concernant un puits de forage sur des frequences porteuses multiples
AU784103B2 (en) * 1999-12-24 2006-02-02 Schlumberger Technology B.V. Method and apparatus for transmission of well-bore data on multiple carrier frequencies
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US7787525B1 (en) 1999-12-24 2010-08-31 Schlumberger Technology Corporation Method and apparatus for transmission of well-bore data on multiple carrier frequencies
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US7388925B2 (en) 2000-01-28 2008-06-17 Alcatel Carrier constellation information in multi-carrier systems
EP1120943A1 (fr) * 2000-01-28 2001-08-01 Alcatel Transmission de table d'allocation de gain et de bits dans systèmes multiporteuse
US6393052B2 (en) 2000-02-17 2002-05-21 At&T Corporation Method and apparatus for minimizing near end cross talk due to discrete multi-tone transmission in cable binders
WO2001061956A1 (fr) * 2000-02-17 2001-08-23 At & T Corp. Procede et dispositif servant a minimiser un echo du a une transmission discrete a tonalite multiple dans des liaisons cablees
US7362798B1 (en) 2000-08-07 2008-04-22 Infineon Technologies Ag Method for transmitting data to be transmitted using a subscriber modem
US6657551B2 (en) 2001-02-01 2003-12-02 Halliburton Energy Services, Inc. Downhole telemetry system having discrete multi-tone modulation and dynamic bandwidth allocation
GB2392184A (en) * 2001-03-27 2004-02-25 Halliburton Energy Serv Inc Very high data rate telemetry system for use in a wellbore
GB2392184B (en) * 2001-03-27 2005-02-16 Halliburton Energy Serv Inc Very high data rate telemetry system for use in a wellbore
WO2002077413A1 (fr) * 2001-03-27 2002-10-03 Halliburton Energy Services, Inc. Systeme de telemesure a debit binaire tres eleve pour puits de forage
EP1405447A4 (fr) * 2001-06-19 2009-12-30 Baker Hughes Inc Modulation a multitonalite discrete en duplex integral dans des applications de diagraphie
EP1283655A1 (fr) * 2001-08-08 2003-02-12 Lucent Technologies Inc. Maximalisation du débit d'une ligne DSL avec niveau de diaphonie acceptable
WO2003043262A1 (fr) 2001-11-13 2003-05-22 Telcordia Technologies, Inc. Procede et systeme de compatibilite spectrale pour le deploiement d'un terminal adsl a distance
EP1444804A4 (fr) * 2001-11-13 2010-04-14 Telcordia Tech Inc Procede et systeme de compatibilite spectrale pour le deploiement d'un terminal adsl a distance
US7042367B2 (en) 2002-02-04 2006-05-09 Halliburton Energy Services Very high data rate telemetry system for use in a wellbore
US7026952B2 (en) 2003-02-21 2006-04-11 Halliburton Energy Services, Inc. Downhole telemetry system using discrete multi-tone modulation having repeated symbols
EP1702417A4 (fr) * 2004-01-09 2012-09-05 Ikanos Technology Ltd Formation en temps reel de masques a densite spectrale de puissance optimale
US6995683B2 (en) 2004-03-12 2006-02-07 Welldynamics, Inc. System and method for transmitting downhole data to the surface
WO2007095112A3 (fr) * 2006-02-14 2008-06-05 Baker Hughes Inc Égalisation à décision rétroactive en télémétrie par impulsions dans la boue
EP2088686A4 (fr) * 2006-11-01 2009-12-16 Huawei Tech Co Ltd Procédé et dispositif de gestion du spectre de fréquences
US8000219B2 (en) 2006-11-01 2011-08-16 Huawei Technologies Co., Ltd. Method and apparatus for spectrum management
CN101174855B (zh) * 2006-11-01 2012-06-20 华为技术有限公司 频谱管理方法和装置
US8824979B2 (en) 2007-09-21 2014-09-02 Qualcomm Incorporated Interference management employing fractional frequency reuse
US9078269B2 (en) 2007-09-21 2015-07-07 Qualcomm Incorporated Interference management utilizing HARQ interlaces
US9374791B2 (en) 2007-09-21 2016-06-21 Qualcomm Incorporated Interference management utilizing power and attenuation profiles
US9344973B2 (en) 2007-09-21 2016-05-17 Qualcomm Incorporated Interference management utilizing power and attenuation profiles
US9137806B2 (en) 2007-09-21 2015-09-15 Qualcomm Incorporated Interference management employing fractional time reuse
US9066306B2 (en) 2007-09-21 2015-06-23 Qualcomm Incorporated Interference management utilizing power control
US8948095B2 (en) 2007-11-27 2015-02-03 Qualcomm Incorporated Interference management in a wireless communication system using frequency selective transmission
US9072102B2 (en) 2007-11-27 2015-06-30 Qualcomm Incorporated Interference management in a wireless communication system using adaptive path loss adjustment
US9119217B2 (en) 2007-11-27 2015-08-25 Qualcomm Incorporated Interference management in a wireless communication system using frequency selective transmission
US8837305B2 (en) 2007-11-27 2014-09-16 Qualcomm Incorporated Interference management in a wireless communication system using beam and null steering
US9288814B2 (en) 2007-11-27 2016-03-15 Qualcomm Incorporated Interface management in wireless communication system using hybrid time reuse
US8867456B2 (en) 2007-11-27 2014-10-21 Qualcomm Incorporated Interface management in wireless communication system using hybrid time reuse
US8848619B2 (en) 2007-11-27 2014-09-30 Qualcomm Incorporated Interface management in a wireless communication system using subframe time reuse
US9065584B2 (en) 2010-09-29 2015-06-23 Qualcomm Incorporated Method and apparatus for adjusting rise-over-thermal threshold
CN108112056A (zh) * 2016-11-24 2018-06-01 联芯科技有限公司 用户终端的扫频方法与装置
CN108112056B (zh) * 2016-11-24 2020-09-22 联芯科技有限公司 用户终端的扫频方法与装置

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