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Selected Areas in Communications, IEEE Journal on

Issue 5 • Date June 2002

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Displaying Results 1 - 23 of 23
  • Guest editorial twisted pair transmission-ever increasing performances on ancient telephone wires

    Publication Year: 2002 , Page(s): 877 - 880
    Cited by:  Papers (4)
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    Freely Available from IEEE
  • In memoriam Jean-Jacques Werner [1943-2000]

    Publication Year: 2002 , Page(s): 881 - 882
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    Freely Available from IEEE
  • Filtered multitone modulation for very high-speed digital subscriber lines

    Publication Year: 2002 , Page(s): 1016 - 1028
    Cited by:  Papers (95)  |  Patents (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (461 KB) |  | HTML iconHTML  

    A filter-bank modulation technique called filtered multitone (FMT) and its application to data transmission for very high-speed digital subscriber line technology are described. The proposed scheme leads to significantly lower spectral overlapping between adjacent subchannels than for known multicarrier techniques such as discrete multitone (DMT) or discrete wavelet multitone. FMT modulation mitigates interference due to echo and near-end crosstalk signals, and increases the system throughput and reach. Signal equalization in an FMT receiver is accomplished in the form of per-subchannel symbol-spaced or fractionally spaced linear or decision-feedback equalization. The problem of channel coding for this type of modulation is also addressed, and an approach that allows combined removal of intersymbol-interference via precoding and trellis coding is described. Furthermore, practical design aspects regarding filter-bank realization, initial transceiver training, adaptive equalization, and timing recovery are discussed. Finally, simulation results of the performance achieved by FMT modulation for very high-speed digital subscriber line systems, where upstream and downstream signals are separated by frequency-division duplexing, are presented and compared with DMT modulation View full abstract»

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  • An approach to analog mitigation of RFI

    Publication Year: 2002 , Page(s): 974 - 986
    Cited by:  Papers (7)  |  Patents (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (520 KB) |  | HTML iconHTML  

    Among all noise sources present in wireline transmission systems we focus on one special type: narrowband radio frequency interference generated by radio amateurs (RAM) and broadcast radio stations. This disturbance, characterized by high power and narrow bandwidth, has the potential of overloading the receiver's analog-to-digital converter (ADC). Once the ADC is in saturation, any countermeasure taken in digital domain will fail. A viable way to face this problem is cancellation using the common-mode signal as a reference. This paper describes in detail an adaptive, mixed-signal, narrowband interference canceller employing a modified recursive least-squares algorithm, which is split into an analog and a digital part. The mixed-signal approach enables the circuit to generate an interference-cancelling signal of several MHz while operating the adaptive algorithm at some kilohertz. Simulation as well as measurement results show a steady-state disturbance suppression of about 35 dB. The convergence speed is high enough to protect the ADC from overloading due to time-variant HAM interference View full abstract»

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  • Near-end crosstalk mitigation in ADSL systems

    Publication Year: 2002 , Page(s): 949 - 958
    Cited by:  Papers (14)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (346 KB) |  | HTML iconHTML  

    Near-end crosstalk (NEXT) is one of the major impairments to the current asymmetric digital subscriber line (ADSL) downstream transmission. This paper presents two methods for an ADSL receiver to cancel one (dominant) NEXT signal from other types of services (such as HDSL (high-bit-rate DSL), SDSL (single-pair, symmetric DSL), T1, etc.). The methods exploit the fact that the crosstalk signal has a large excess bandwidth and its spectra in the main lobe and in the excess band are strongly correlated. The principal idea is then to estimate the crosstalk in some frequency bands (e.g., excess band) and cancel it in other frequency bands (e.g., main lobe). The frequency-domain analysis in this paper provides an intuitive explanation of the crosstalk estimation and cancellation, as well as a guidance to select the right frequency bands to observe the crosstalk signal. Moreover, a fast algorithm is proposed for practical implementation. This algorithm avoids matrix inversion and large matrix multiplication in every transmission block. Simulation results show that one of the proposed methods, minimum mean-squares error estimation and cancellation, is very effective to cancel one (dominant) NEXT and the improvement is significant in terms of the data rate and the line reach for the ADSL service. For example, using a real measured NEXT transfer function, the proposed method can increase the ADSL downstream data rate by 200% for some loops. The methods are extended to estimate and cancel two or more crosstalkers. The amount of improvement depends on the crosstalkers' characteristics and it is generally less than that of a single crosstalker case View full abstract»

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  • Electromagnetic coupling of twisted pair cables

    Publication Year: 2002 , Page(s): 883 - 892
    Cited by:  Papers (13)  |  Patents (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (350 KB) |  | HTML iconHTML  

    Increasing deployment of digital subscriber line (DSL) technology operating in the long wave, medium wave and sometimes short wave frequency ranges, has raised the question of how such systems interact with rival radio frequency sources and equipment. Two of the major standards bodies in the field, ITU and ETSI, imposed by the standardization of such promising technologies like ADSL, SHDSL and VDSL, have begun to elaborate performance tests for radio frequency interference (RFI) scenarios for inclusion into their standards documents. Existing out-door loops of the copper telephone network can have large dimensions, are often unshielded and sometimes not even twisted, thus, they can act like antennas for both RFI egress and ingress. The RFI egress issue requires basic knowledge of the relationship between a given current distribution I(l) on a twisted pair communication cable and the electromagnetic fleld E, H generated by that current distribution at a given distance d. This problem is reciprocal to the RFI ingress issue, which requires knowledge of the relationship between a disturbing high-frequency electric field E in the surroundings of a twisted pair cable, and the terminal voltage of that cable across a load impedance. This contribution provides the theoretical background to the field theoretical problem and supplies simple yet accurate approximation formulae for the prediction of RFI egress and RFI ingress View full abstract»

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  • Perfect equalization for DMT systems without guard interval

    Publication Year: 2002 , Page(s): 987 - 996
    Cited by:  Papers (28)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (380 KB) |  | HTML iconHTML  

    We propose a new, low-complexity frequency-domain equalizer for discrete multitone (DMT) systems, which, in the absence of a guard interval, utilizes existing redundancy in the frequency-domain to completely eliminate intersymbol and interchannel interference. A perfect reconstruction condition is derived for the noise-free case leading to a sparse equalizer matrix structure. It is furthermore shown that under realistic scenarios minimum mean square error adaptation of the equalizer coefficients allows for nearly perfect reconstruction already for a much smaller amount of redundancy than indicated by the perfect reconstruction condition. The new equalization scheme has at least the same potential compared with traditional DMT while offering new degrees of freedom for designing short-latency DMT systems View full abstract»

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  • A new approach for evaluating clipping distortion in multicarrier systems

    Publication Year: 2002 , Page(s): 1037 - 1046
    Cited by:  Papers (45)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (391 KB) |  | HTML iconHTML  

    Multicarrier signals are known to suffer from a high peak-to-average power ratio, caused by the addition of a large number of independently modulated subcarriers in parallel at the transmitter. When subjected to a peak-limiting channel, such as a nonlinear power amplifier, these signals may undergo significant spectral distortion, leading to both in-band and out-of-band interference, and an associated degradation in system performance. This paper characterizes the distortion caused by the clipping of multicarrier signals in a peak-limiting (nonlinear) channel. Rather than modeling the effects of distortion as additive noise, as is widespread in the literature, we identify clipping as a rare event and focus on evaluating system performance based on the conditional probability of bit error given the occurrence of such an event. Our analysis is based on the asymptotic properties of the large excursions of a stationary Gaussian process, and offers important insights into both the true nature of clipping distortion, as well as the consequent design of schemes to alleviate this problem View full abstract»

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  • FEXT cancellation for twisted-pair transmission

    Publication Year: 2002 , Page(s): 959 - 973
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (502 KB) |  | HTML iconHTML  

    This paper discusses a far-end crosstalk (FEXT) canceller for twisted-pair transmission. Many twisted-pair systems such as fiber-to-the-curb, very high-speed digital subscriber line, and high-speed LAN systems, use frequency-division duplexing (FDD) for duplex transmission. It is shown that the maximum reach of FDD twisted-pair system is limited by the performance of its upstream channel, which is assumed to be located at higher frequencies than the downstream channel. In order to improve the performance of such an FDD transceiver, FEXT cancellation is introduced for the channel at higher frequencies. A system arrangement and its blind startup procedure are studied when the FEXT canceller and equalizer are jointly adapted to combat channel intersymbol interference, FEXT, and other additive noise. We investigate the initial convergence and the steady-state behavior of the proposed twisted-pair system without requiring transmission of an ideal training sequence. Measured characteristics as well as analytical model of the FEXT channel are used to estimate the time span needed for the FEXT canceller. It is also shown that the memory span for the FEXT canceller is almost independent of the channel, thus making our results useful for the twisted-pair system over all different channels View full abstract»

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  • Receiver window design for multicarrier communication systems

    Publication Year: 2002 , Page(s): 1029 - 1036
    Cited by:  Papers (41)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (295 KB) |  | HTML iconHTML  

    Multicarrier modulation formats have been chosen for some wireline and wireless communication systems. These systems use the Fourier transform to convert a convolutive channel into multiple memoryless subchannels, which allows for simple equalization at the receiver. However, because the received signal is windowed in time, noise is spread between subchannels. As a result, narrowband interference sources can degrade the performance over a large number of subchannels. Receiver windowing has been proposed as a computationally efficient technique for reducing noise spreading in multicarrier communication systems. We propose a receiver window design algorithm which minimizes the noise power of the demodulated multicarrier signal. Simulations demonstrate the effectiveness of the windows on a variety of different channels and noise sources View full abstract»

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  • NEXT and FEXT models for twisted-pair North American loop plant

    Publication Year: 2002 , Page(s): 893 - 900
    Cited by:  Papers (20)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (349 KB) |  | HTML iconHTML  

    Measurements of near-end crosstalk (NEXT) and far-end crosstalk (FEXT) in 26-AWG and 24-AWG polyethylene insulated cable (PIC) twisted pair cables are presented. This data is used to develop crosstalk models that indicate existing T1.417 Standard NEXT and FEXT models are probably conservative by about 5 dB for 25-pair binder groups. However, many cables start from wire centers as pulp cables of 100-pair binder groups. Even if most of these older pulp cables are 26-AWG, prudence dictates that a more conservative model be used for these cases. On a going forward basis for new and rehab construction, it should be recognized that PIC (air core and filled) cables with not larger than 25-pair binder groups are the predominant cable media supplied by manufacturers for feeder and distribution loops. Results for NEXT in 12-pair binders are also analyzed and show that 26-AWG cable has about 2 dB more NEXT loss than 24-AWG cable and 12-pair binders have about 2 dB more NEXT loss than 25-pair binders. In addition, the NEXT loss separation between adjacent binders of 12 and 13 pairs is found to be not more than 10 dB as compared with the more optimistic 15.5 dB assumed within the industry View full abstract»

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  • Pilotless timing recovery for baseband multicarrier modulation

    Publication Year: 2002 , Page(s): 1047 - 1054
    Cited by:  Papers (2)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (308 KB) |  | HTML iconHTML  

    This paper describes a multicarrier modulation timing recovery algorithm that does not require use of a designated pilot tone. Instead, all or some received subchannels are used to estimate phase and frequency errors. Algorithms for both acquisition and tracking are presented, and simulation results show excellent performance. The algorithm provides a useful timing recovery approach for environments in which use of a designated pilot is infeasible or undesirable, such as on digital subscriber lines corrupted by high levels of broadcast AM or amateur radio interference View full abstract»

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  • Impulse generation with appropriate amplitude, length, inter-arrival, and spectral characteristics

    Publication Year: 2002 , Page(s): 901 - 912
    Cited by:  Papers (25)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (386 KB) |  | HTML iconHTML  

    This paper proposes a suitable method for simulating impulses with appropriate amplitude, spectral, and inter-arrival characteristics. The statistics used to develop the parameters of this model are based on statistics derived from observations of impulse noise on the telephone networks of British Telecom (BT) and Deutsche Telekom (DT). This paper initially reviews the former DT approach to impulse noise generation for testing digital subscriber line systems, so called xDSL systems. Some problems are highlighted and an alternative technique is suggested that is capable of generating impulses with both appropriate amplitude an spectral characteristics View full abstract»

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  • Estimation of the transfer function of a subscriber loop by means of a one-port scattering parameter measurement at the central office

    Publication Year: 2002 , Page(s): 936 - 948
    Cited by:  Papers (26)  |  Patents (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (439 KB) |  | HTML iconHTML  

    In order to qualify a subscriber loop for xDSL transmission, the channel capacity has to be estimated, which depends on the transfer function of the network. A method is provided to estimate the transfer function of the subscriber loop only measuring the one-port scattering parameter at the central office. We consider three types of networks according to their topology: a single line, a homogeneous network with a bridged tap, and a cascade of two line sections. For each type of network a parametric model is derived of its one-port scattering parameter and transfer function based on the physical line model VUB0. The model for the scattering parameter is used to identify the network based on the corresponding measurements by means of a maximum-likelihood estimator. The estimated parameters are substituted in the transfer function model, which is needed for the capacity estimation. The proposed models and estimators are validated by measurements and simulations. For the measurements, which were performed with a network analyzer, three types of twisted-pair cables were used: British Telecom (BT), Deutsch Telekom (FT), and Belgacom View full abstract»

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  • The multimodulus blind equalization and its generalized algorithms

    Publication Year: 2002 , Page(s): 997 - 1015
    Cited by:  Papers (99)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (549 KB) |  | HTML iconHTML  

    This paper presents a new blind equalization algorithm called multimodulus algorithm (MMA). This algorithm combines the benefits of the well-known reduced constellation algorithm (RCA) and constant modulus algorithm (CMA). In addition, MMA provides more flexibility than RCA and CMA, and is better suited to take advantage of the symbol statistics of certain types of signal constellations, such as nonsquare constellations, very dense constellations, and some wrong solutions View full abstract»

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  • Vectored transmission for digital subscriber line systems

    Publication Year: 2002 , Page(s): 1085 - 1104
    Cited by:  Papers (163)  |  Patents (41)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (557 KB) |  | HTML iconHTML  

    This paper describes the "vectored" transmission technique for digital subscriber line (DSL) systems, which utilizes user coordination at the central office or optical network unit. This method exploits the colocation of the downstream transmitters and of the upstream receivers, in order to achieve far-end crosstalk (FEXT) cancellation and perform multiuser transmission optimization. The performance improvements are particularly pronounced in environments with strong FEXT such as in very high-speed DSL. Discrete multitone is employed for each user with additional constraints on the cyclic prefix length and with the assumption of block-synchronized transmission and reception for downstream and upstream transmission correspondingly. Within each tone, upstream crosstalk is removed by multiple-input-multiple-output decision feedback at the receiving side, while downstream crosstalk is eliminated by analogous preprocessing at the transmitting side. Additionally, the issue of transmission energy allocation in frequency and among users is addressed. Assuming frequency-division duplexing, the corresponding optimization problem is formulated and solved via convex programming both for a fixed upstream-downstream band plan and for a dynamically programmable band plan. The case of power backoff as a means to reduce the impact of crosstalk on alien systems is also treated. Interestingly, the performance of the proposed methods is shown to be very close to known information theory bounds View full abstract»

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  • Autonomous synchronization of a DMT-VDSL system in unbundled networks

    Publication Year: 2002 , Page(s): 1055 - 1063
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (334 KB) |  | HTML iconHTML  

    We present an algorithm that autonomously synchronizes all DMT-Zipper based VDSL modems in an unbundled access network, solving the problem with nonorthogonal NEXT that appears in systems with unsynchronized modems. The algorithm we present runs autonomously in each VDSL modem in the central office or in the street cabinet. We determine the other modems' relative frame offsets by exploiting their NEXT signal using the inherent cyclic redundancy found in DMT signals. By estimating the relative frame offsets of the other users, we can adjust a given user's own frame-timing relative to the mean of the others. With our method all modems in the network will be synchronized to within a small fraction of the total DMT frame-length, suppressing the nonorthogonal NEXT to a level far below the background noise-floor. This means that we can achieve the same performance in an unbundled access network without any master clock reference as in a system where all modems are perfectly synchronized using a master clock View full abstract»

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  • Defining upstream power backoff for VDSL

    Publication Year: 2002 , Page(s): 1064 - 1074
    Cited by:  Papers (8)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (336 KB) |  | HTML iconHTML  

    Very high-speed digital subscriber line (VDSL) upstream data transmission in a distributed environment will suffer from relatively strong far-end crosstalk generated by the shorter lines in the binder. This effect can dramatically reduce the upstream capacity on longer lines. To secure the capacity on lines of all lengths, shorter lines will be required to systematically reduce their transmit power. This power reduction is known as (upstream) power backoff (PBO or UPBO). This paper reviews the problem and summarizes a number of PBO techniques and results that may not be readily available in the published literature. Next, a general formulation is presented in terms of a "reference PSD" and a method is proposed to determine the optimal value of the reference PSD. This paper is mainly based on work that was done in VDSL standardization. It is an extended version of work that was previously published View full abstract»

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  • Loop makeup identification via single ended testing: beyond mere loop qualification

    Publication Year: 2002 , Page(s): 923 - 935
    Cited by:  Papers (26)  |  Patents (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (453 KB) |  | HTML iconHTML  

    Digital subscriber lines (DSLs) offer carriers the possibility of exploiting the existing loop plant to deliver high-speed data and voice services. However, before deploying DSL, local loops must be tested in order to see whether they can support service, and at what level. In fact, there are many impairments that could disqualify a loop for supporting DSL services: load coils, excessive loop length, bridged taps, and wideband noise. Single-ended automatic qualification is essential for achieving low-cost deployment of DSL, since it allows loops to be qualified in bulk and does not involve any human intervention at the customer's location. An even more ambitious challenge is to fully characterize a loop, i.e., to identify its loop makeup. If it is feasible to perform loop makeup identification via single-ended measurements with sufficient accuracy, then operators will benefit substantially because, besides qualifying a loop for DSL service, this capability will allow the updating of telephone company loop-records. These records can in turn be accessed to support engineering, provisioning and maintenance operations. Despite its potential importance, the possibility of achieving loop makeup identification via single-ended measurements is not widely addressed in the current literature. In the present contribution the feasibility of loop makeup identification via single-ended measurements is presented View full abstract»

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  • Use of the reference noise method bounds the performance loss due to upstream power backoff

    Publication Year: 2002 , Page(s): 1075 - 1084
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (334 KB) |  | HTML iconHTML  

    This paper presents mathematical proofs that the performance loss due to using the reference noise method of upstream power backoff is bounded. First, it is shown that when two lines of arbitrary lengths are considered, application of the reference noise method results in an upstream signal-to-noise ratio (SNR) degradation of less than 3 dB relative to when the two loops are the same length and the remote transceivers transmit at the maximum allowed power spectral density. Next, an extension to the reference noise method is introduced, and it is shown that the 3-dB bound holds for an arbitrary number of lines. Finally, the reference noise method is shown to minimize the maximum SNR loss relative to when all lines are the same length and all remote transceivers transmit at the maximum allowed power spectral density. The result is significant for very high-speed digital subscriber line applications because it allows service providers to determine a priori the worst case impact of upstream power backoff on upstream bit rates without consideration of the loop plant topology View full abstract»

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  • Channel modeling and system performance for HomePNA 2.0

    Publication Year: 2002 , Page(s): 913 - 922
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (396 KB) |  | HTML iconHTML  

    The new Home Phoneline Networking Alliance (HomePNA) 2.0 system is an attractive proposition for home networking since it potentially allows transmission rates comparable to those of Ethernet, using the existing installed telephone wiring. However, although the transmission standard is designed to be variable rate (variable symbol rate and bits/symbol), not all combinations are mandatory and it is, therefore, instructive to determine the level of receiver complexity required to handle the optional higher rates. An accurate channel model is devised, characterizing the home phone line network around 7 MHz, which allows the performance of the HomePNA 2.0 physical layer to be evaluated. The very good agreement obtained between the measured and modeled channel responses, in both time and frequency domains, enables a high degree of confidence in the simulation results. Due to the considerable dispersion observed in some home phone line channels, a number of equalizer structures are proposed to improve performance in the receiver. These are compared for each of the two possible symbol rates. Computer simulations show that the performance of the system can be greatly improved at the lower rate with a low complexity equalizer, but at the higher rate, which is not mandatory, a much more complex equalizer is required View full abstract»

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  • Distributed multiuser power control for digital subscriber lines

    Publication Year: 2002 , Page(s): 1105 - 1115
    Cited by:  Papers (347)  |  Patents (28)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (342 KB) |  | HTML iconHTML  

    This paper considers the multiuser power control problem in a frequency-selective interference channel. The interference channel is modeled as a noncooperative game, and the existence and uniqueness of a Nash equilibrium are established for a two-player version of the game. An iterative water-filling algorithm is proposed to efficiently reach the Nash equilibrium. The iterative water-filling algorithm can be implemented distributively without the need for centralized control. It implicitly takes into account the loop transfer functions and cross couplings, and it reaches a competitively optimal power allocation by offering an opportunity for loops to negotiate the best use of power and frequency with each other. When applied to the upstream power backoff problem in very-high bit-rate digital subscriber lines and the downstream spectral compatibility problem in asymmetric digital subscriber lines, the new power control algorithm is found to give a significant performance improvement when compared with existing methods View full abstract»

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  • Profile detection in multiuser digital subscriber line systems

    Publication Year: 2002 , Page(s): 1116 - 1125
    Cited by:  Papers (1)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (411 KB) |  | HTML iconHTML  

    Multiuser transmission methods for digital subscriber line (DSL) systems have become of interest with the potential for increased data rate and loop reach. These methods often assume that the set of crosstalk interferers, called the crosstalk profile, and their associated channel responses are known. For DSL systems, the interferers are often uncoordinated, so that in a dynamic environment where DSL transmitters can energize and deenergize, the crosstalk profile cannot be transmitted to the user of interest. While the crosstalk channel estimation problem in a dynamic environment can be intractable for general transmission systems, channel and crosstalk analysis can make use of the specific DSL environment. Namely, the physical channels in a DSL system do not change rapidly, and hence estimates of the crosstalk channel can be saved for future reference. For this reason, we introduce the concept of a channel profile. We develop several algorithms to detect the crosstalk profile and investigate the asymptotic behavior of the new algorithms. Simulations show that for typical crosstalk interference scenarios, the observation time to determine the correct crosstalk profile at probability of error less than 10-3 can be less than 2 ms View full abstract»

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Aims & Scope

IEEE Journal on Selected Areas in Communications focuses on all telecommunications, including telephone, telegraphy, facsimile, and point-to-point television, by electromagnetic propagation.

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Meet Our Editors

Editor-in-Chief
Muriel Médard
MIT