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Complexity analysis of multicarrier and single-carrier systems for very high-speed digital subscriber line
Abstract
A complexity analysis of discrete multitone (DMT) and single-carrier modulation (SCM) in the context of a very high-speed digital subscriber line (VDSL) is presented in this paper. In addition to the traditional arithmetic complexity measures such as the number of multiply-and-accumulate (MAC) operations, we also compute the memory requirements. Furthermore, we normalize these metrics with respect to the number of information bits transmitted (rate normalized) and scale with respect to data path precision (precision scaled) in order to obtain more comprehensive metrics. The analysis shows that the number of MAC's per transmitted information bit (N<sub>MACb</sub>) for SCM is greater than that for DMT for all distances of interest in VDSL. The number of MACs per information bit and scaled with respect to precision (B<sub>MAC</sub>), i.e., NB<sub>MACb</sub> = N<sub>MACb</sub>B<sub>MAC</sub>, was found to be clearly smaller for SCM in loops shorter than approximately 2 kft. This metric was found to be clearly smaller for DMT in loops longer than approximately 3.25 kft. At all lengths, DMT was found to have smaller memory requirements per information bit, as well as smaller precision-scaled memory requirements.
... In this paper, we focus on the digital complexity of the underlying scheme. We discuss different generations of DSL technologies based on discrete multi-tone modulation (DMT), using the methodology presented in [5]. We compare the complexity of different DSL flavors by introducing a time scaling based on Moore's Law [6]. ...
... In Fig. 1, the general blocks of DMT modulation are shown [5,7]. In the transmitter, the input data bits are first mapped onto QAM constellations points for each of the n c carriers. ...
... In this section, we discuss the methodology for complexity analysis of DMT modulation schemes. We rely on the work, presented in [5], which we summarize below. In this paper, however, we rely on the number of multiply-accumulates per second (R MAC ) and the number of memory locations per second (R MEM ) for comparison of the different DSL technologies, rather than on the number of multiply-accumulates per bit as done in [5]. ...
Digital subscriber line (DSL) technology for copper twisted pair access networks has been evolving to meet the ever-growing demand for higher data rates. This evolution has gone hand in hand with the roll out of fiber deep in the access network. The most recent technology is vectored VDSL2, able to offer an aggregate data rate of 200 Mb/s on a single copper pair. The next step is to reach 500 to 1000 Mb/s over even shorter copper loops up to a few hundred meters. Such a DSL deployment is an enabler for the cost-effective continuation of the fiber roll-out closer to the end-user. In this paper, a reality check is performed on the digital complexity of a next-generation DSL (ΩDSL) transceiver. By taking into account Moore's law, it is shown that the time is right for this next-generation DSL.
... However, their sensitivity to RF circuit impairments in 60 GHz transmission scenarios is not yet fully investigated. A number of comparisons between MC and SC schemes can be found in literature [1]–[4]. The SC scheme was shown to have a lower complexity when used over short distances in asymmetric digital subscriber lines (ADSLs) [1]. ...
... A number of comparisons between MC and SC schemes can be found in literature [1]–[4]. The SC scheme was shown to have a lower complexity when used over short distances in asymmetric digital subscriber lines (ADSLs) [1]. SC has a lower peak-to-average-power ratio (PAPR), and is more resistant to frequency offset errors as compared to the MC scheme [2]. ...
... Denoting N MA as the number of multiply and accumulate (MA) operations required for one block of length N , it is shown in [1], that for an FFT/IFFT operation N MA = 0.75N log 2 N . The simple channel equalization strategy outlined in the previous section can be performed by 3 real multiplications per sample, i.e., 3N real multiplications per block. ...
Circuit technology for 60 GHz is still limited, and impairments due to radio frequency (RF) circuit imperfections must be taken into account. Therefore, the candidate transmission schemes, in addition to multi-path fading, should be fairly resistant to RF circuit imperfections. In this paper, a performance comparison of multi-carrier (MC) and single-carrier (SC) based transmission schemes in the presence of DAC/ADC imperfections and amplifier nonlinearities, is carried out. It is shown that the SC scheme has substantially lower front-end requirements than its MC counterpart, while having the same overall system complexity.
... Daneshrad and Samueli analysed the performance of QAM in DSL [25], which is based on baseband spectral shaping techniques, while Chow et al. proposed the classic DMT [26]. Shim and Shanbhag compared the complexity of the above single-carrier and multicarrier modulation schemes in the high-rate VDSL scenario [27]. ...
As an important solution to ”the last mile” access, Digital Subscriber Loops (DSL) are still maintained in a huge plant to support low-cost but high-quality broadband network access through telephone lines. The Discrete multi-tone (DMT) transmissions constitute a baseband version of the ubiquitous orthogonal frequency division multiplexing (OFDM). While the DMT is ideally suited to deal with the frequency selective channel in DSL, the presence of bursty impulsive noise tends to severely degrade the transmission performance. In this paper, we analyse the statistics of impulsive noise and its effects on the received signals, with the aid of a hidden semi-Markov process. The closed-form BER expression is derived for the DMT system for Q-ary quadrature amplitude modulation (QAM) under practical noise conditions and for measured dispersive DSL channels. Instead of relying on the simplified stationary and impulsive noise process, our noise model considers both the temporal and spectral characteristics, based on the measurement results. The simulation results confirm the accuracy of the formulas derived and quantify the impact both of the impulsive noise and of the dispersive channel in DSL.
... In order to ensure reliable performance, Neq should be sufficiently larger than the length of the channel impulse response[25].5 For the QR-decomposition of the m × n matrix, 3n 2 (m − n/3) flops are required[26]. ...
In this paper, we consider a low-complexity multiuser detection for downlink of high speed packet access (HSPA) of universal mobile telecommunications system (UMTS). Instead of attempting to perform maximum likelihood (ML) detection of all users in multiple cells, which is impractical for battery powered mobile receiver, we utilize interference cancelled chips obtained from iterative linear minimum mean square error (LMMSE) estimation to perform a near ML detection in a reduced dimensional system. As a result, the worst case complexity of the detection process, achieved by the closest lattice point search (CLPS), is bounded to a controllable level irrespective of multipath spans. Furthermore, by exploiting the LMMSE estimate in tightening the hypersphere condition of the CLPS algorithm so called sphere decoding, we achieve significant improvement in search complexity. From simulations on realistic downlink communication scenario in HSPA systems, we show that the proposed method offers substantial performance gain over conventional receiver algorithms with reasonable complexity.
... The cost of the 256-point FFT in the fixed broadband wireless access is estimated to be 1024. Approximately, the simplified complexity vector c of the wordlength per bit is assumed to be {1024, 1, 128, 2} from [4, 29]. We also assume the complexity increases linearly as wordlength increases to simplify demonstration. ...
Many digital signal processing algorithms are first developed in floating point and later converted into fixed point for digital hardware implementation. During this conversion, more than 50% of the design time may be spent for complex designs, and optimum wordlengths are searched by trading off hardware complexity for arithmetic precision at system outputs. We propose a fast algorithm for searching for an optimum wordlength. This algorithm uses sensitivity information of hardware complexity and system output error with respect to the signal wordlengths, while other approaches use only one of the two sensitivities. This paper presents various optimization methods, and compares sensitivity search methods. Wordlength design case studies for a wireless demodulator show that the proposed method can find an optimum solution in one fourth of the time that the local search method takes. In addition, the optimum wordlength searched by the proposed method yields 30% lower hardware implementation costs than the sequential search method in wireless demodulators. Case studies demonstrate the proposed method is robust for searching for the optimum wordlength in a nonconvex space.
... For the complexity, the numbers of complex multiplication are measured assuming that units are not reused. The complexity vector c of the wordlength per bit is assumed {1024, 1, 128, 2} from [4] [10]. We also assume the complexity increases linearly as wordlength increases. ...
Many digital signal processing algorithms are first developed in floating point and later mapped into fixed point for digital hardware implementation. During this mapping, wordlengths are searched to minimize total hardware cost and maximize system performance. Complexity and distortion measures have been separately researched for optimum wordlength selection. This paper proposes a complexity-and-distortion measure (CDM) method that combines these two measures. The CDM method trades off these two measures using a weighting factor. The proposed method is applied to wordlength design of a fixed broadband wireless demodulator. For this case study, the proposed method finds the optimal solution in one-third the time that exhaustive search takes. The contributions of this paper are: (1) a generalization of search methods based on complexity or distortion measures; (2) a framework of automatic wordlength optimization; and (3) a wireless demodulator case study.
... For the complexity, the numbers of complex multiplication are measured assuming that units are not reused. The complexity vector c of the wordlength per bit is assumed {1024, 1, 128, 2} from [4] [10]. We also assume the complexity increases linearly as wordlength increases. ...
Many digital signal processing algorithms are first developed in floating point and later mapped into fixed point for digital hardware implementation. During this mapping, wordlengths are searched to minimize total hardware cost and maximize system performance. Complexity and distortion measures have been separately researched for optimum wordlength selection. This paper proposes a complexityand -distortion measure (CDM) method that combines these two measures. The CDM method trades off these two measures using a weighting factor. The proposed method is applied to wordlength design of a fixed broadband wireless demodulator. For this case study, the proposed method finds the optimal solution in one-third the time that exhaustive search takes. The contributions of this paper are (1) a generalization of search methods based on complexity or distortion measures, (2) a framework of automatic wordlength optimization, and (3) a wireless demodulator case study.
We explore the potential of a future cable access technology that pushes the capacity of coaxial cable networks to its limit. We show that it is possible to achieve symmetric data rates of multiple tens of gigabit per second using the same coaxial drop cables in use today to connect households to the cable network, and discuss its feasibility and deployment characteristics.
In full-duplex communication systems with discrete multi-tone (DMT) modulation, echo cancellers are employed to cancel echo by means of adaptive filters. Generally, the structure present in the DMT signals is used to decrease the computational complexity of these cancellers by splitting the operations between the time and frequency domains. In this work, we introduce a general framework for designing echo cancellers for such systems in an arbitrary mixed domain. This is achieved by introducing a generic decomposition of the Toeplitz data matrix at the transmitter in terms of arbitrary unitary matrices. Then, based on this decomposition, a new mixed-domain echo cancellation structure is derived, which performs an exact instantaneous gradient-type adaptation. This mixed-domain configuration is also extended for realizing constrained adaptation whereby linear constraints are used to ensure the proper mapping of the weight vectors in different domains. The proposed structures offer a unified framework to study existing cancellers and to design new ones with better performance measures. This framework is employed to propose a new canceller based on discrete trigonometric transformations. The analytical and numerical results presented show that this canceller has a faster convergence rate than the existing ones with similar complexity and is more robust.
Not available Electrical and Computer Engineering
Very high-speed Digital Subscriber Lines (VDSL) is overviewed with an emphasis on the basic architecture, applications, and data rates, as well as the technological challenges of the design. A discussion of the telephone line environment, radio interference implications, impulse noise, symmetric and asymmetric multiplexing, and concentration is also included, with the consequent description of a popular implementation.
We present low-power and high-speed algorithms and architectures
for complex adaptive filters. These architectures have been derived via
the application of algebraic and algorithm transformations. The strength
reduction transformation is applied at the algorithmic level as opposed
to the traditional application at the architectural level. This results
in a power reduction by 21% as compared with the traditional
cross-coupled structure. A fine-grained pipelined architecture for the
strength-reduced algorithm is then developed via the relaxed lookahead
transformation. This technique, which is an approximation of the
conventional lookahead computation, maintains the functionality of the
algorithm rather than the input-output behavior. Convergence analysis of
the proposed architecture is presented and supported via simulation
results. The pipelined architecture allows high-speed operation with
negligible hardware overhead. It also enables an additional power
savings of 39 to 69% when combined with power-supply reduction. Thus, an
overall power reduction ranging from 60-90% over the traditional
cross-coupled architecture is achieved. The proposed architecture is
then employed as a receive equalizer in a communication system for a
data rate of 51.84 Mb/s over 100 m of UTP-3 wiring in an ATM-LAN
environment. Simulation results indicate that speedups of up to 156 can
be achieved with about a 0.8-dB loss in performance
A discrete multitone (DMT) transceiver design for high bit rate
digital subscriber line (HDSL) access is presented and analyzed. The DMT
transmitter and receiver structure and algorithms are detailed, and the
computational requirements of DMT for HDSL are estimated. At a sampling
rate of 640 kHz, using an appropriate combination of a short
finite-impulse-response (FIR) equalizer and a length-512 DMT system, 1.6
Mb/s data transmission is possible within the carrier serving area (CSA)
at an error rate of 10<sup>-7</sup> on a single twisted pair. A
significant performance margin can be achieved when two coordinated
twisted pairs are used to deliver a total data rate of 1.6 Mb/s. In
terms of a performance-per-computation figure of merit, the DMT system
is an excellent candidate for HDSL implementation
This article gives an overview of very high-speed digital
subscriber lines, including the main issues of VDSL system design, such
as its basic architecture, applications, and data rates, as well as the
technological challenges of practical implementation due to different
loop plant realities and spectral compatibility considerations. Some
specific characteristics of the VDSL transceiver startup procedure and
high-level architecture, as well as a summary of first laboratory tests
and field trials, are also presented. The article concentrates on VDSL
implementations using single-carrier modulation, which integrates the
well-known carrierless amplitude/phase modulation and quadrature
amplitude modulation technologies. Currently, SCM technology is
considered one of the main candidates for the VDSL standard in the
United States and Europe, and internationally
VDSL services are overviewed with an emphasis on the basic
architecture, applications, and data rates, as well as the technological
challenges of design. Discussions of the telephone line environment,
radio-band interference ingress and egress, impulse noise, and symmetric
and asymmetric multiplexing are included, along with brief descriptions
of two popular implementations
A new method allowing a reduction in the probability of clipping
in discrete multitone (DMT)-based transceivers is described. The method
does not use any kind of precoding and can easily be implemented within
conventional DMT-transceivers. The main advantage of the proposed method
is an improvement of system performance in terms of overall
signal-to-noise ratios (SNRs): with the simplest implementation option
of the proposed method, up to about 8 dB improvement in the SNR as
compared with previously reported brute force clipping methods can be
achieved
In this paper, we present a finite-granularity, loading algorithm
for a discrete multitone (DMT) modulation system. The proposed algorithm
offers significant implementational advantages over the well-known
water-pouring method and the earlier Hughes-Hartogs algorithm, while
typically suffering only negligible performance degradation relative to
the optimal solution. We also present simulation results of this loading
algorithm applied to the newly proposed asymmetric digital subscriber
lines (ADSL) service
In this correspondence we derive the finite-length, minimum
mean-squared error decision feedback equalizer (MMSE-DFE). We include
decision delay as an explicit parameter. Our derivation yields an
algebraic interpretation of the effect of decision delay on DFE
performance (measured by mean-squared error). It also allows the fast
computation of the MMSE-DFE for several different values of both
decision delay and the number of feedback taps. Our approach is
especially useful for short filter lengths, when the decision delay can
significantly affect DFE performance
This contribution, which is based on [1], proposes a new family of methods to reduce Peak to Average power Ratio (PAR) in Discrete MultiTone (DMT) and Orthogonal Frequency Division Multiplexing (OFDM) systems. This new family of algorithms can be applied with different levels of complexity and performance depending on our application constraints. Using the low complexity algorithms in our family, we can achieve 3dB of PAR reduction with 2N multiply /adds per DMT symbol and a data rate loss of less than :2%, or achieve 4dB of PAR reduction with 6N multiply/adds per symbol and a data rate loss of less than 1%. At higher complexity, 6 Gamma 10dB of PAR reduction can be achieved for NlogN complexity per symbol. Tellado, J. and Cioffi, J.M.--PAR Reduction: 2 1 Introduction The high peak-to-average ratio of 15 dB in the Issue 1 and Issue 2 T1.413 ADSL standard DMT transmission technology has led to significant contributions on a variety of creative methods to reduce PAR [2, 3, 4, 5, 6, ...
Preface. 1. Introduction J.M. Rabaey, et al. Part I: Technology and circuit design levels. 2. Device and technology impact on low power electronics Chenming Hu. 3. Low power circuit technologies C. Svensson, Dake Liu. 4. Energy-recovery CMOS W.C. Athas. 5. Low power clock distribution J.G. Xi, W.W.-M. Dai. Part II: Logic and module design levels. 6. Logic synthesis and module design levels M. Pedram. 7. Low power arithmetic components T.K. Callawy, E.E. Schwartzlander. 8. Low power memory design K. Itoh. Part III: Architecture and system design levels. 9. Low-power microprocessor design S. Gary. 10. Portable video-on-demand in wireless communication T.H. Meng, et al. 11. Algorithm and architectural level methodologies R. Mehra, et al. Index.
This contribution compares the required resolution of an analog-to-digital converter (ADC) when analog or digital band-pass filters are used for band separating in FDD based VDSL. It considers different band allocation scenarios, mostly for FTTCab deployment, and analyzes the reduction of the received signal dynamic range when analog filters are used. The obtained results are line code independent and show that a significant possible relaxation in ADC requirements may be achieved if analog band-pass filters are used instead of digital ones.
Here we describe and demonstrate, via analysis and simulation, the performance improvement of voice-grade modems which use a Fractionally-Spaced Equalizer (FSE) instead of a conventional synchronous equalizer. The reason for this superior performance is that the FSE adaptively realizes the optimum linear receiver; consequently it can effectively compensate for more severe delay distortion than the conventional adaptive equalizer, which suffers from aliasing effects. An additional advantage of the FSE is that data transmission can begin with an arbitrary sampling phase, since the equalizer synthesizes the correct delay during adaptation. We show that an FSE combined with a decision feedback section, which can mitigate the effect of severe amplitude distortion, can compensate for a wide range of linear distortion. At 9.6 kbit/s, the FSE provides a 2 to 3 dB gain in output signal-to-noise ratio, relative to the synchronous equalizer, over worst-case private-line channels. This translates to a theoretical improvement of approximately two orders of magnitude in bit error rate.
Printout. Thesis (M.S.)--University of Illinois at Urbana-Champaign, 1997. Includes bibliographical references (leaves 35-37).
This paper presents theoretical and numerical results on the
effect of bridged taps on the channel capacity of unshielded twisted
pair telephone wiring used in very-high-speed digital subscriber line
broadband access systems
Some emerging broadband access standards require a receiver that
can first blindly start up, then blindly distinguish between carrierless
amplitude modulation/phase modulation (CAP) and quadrature amplitude
modulation (QAM), and finally decode the signal. The “brute
force” solution to this problem would be to implement CAP and QAM
receivers in parallel. However, we propose a novel dual-mode receiver
based on a single equalizer which accommodates both line codes, yielding
significant computational savings. We describe the receiver
architecture, blind start-up methods, and line code identification
algorithms, as well as computer simulations and a laboratory experiment
to verify the theoretical receiver behavior
This research concerns comparing the performance of various
transmission and reception alternatives for the 5-45 MHz portion of the
upstream path of the return coaxial cable band. This evaluation is based
on ingress noise spectra files collected over an extended period of time
from various sites. This data has been used to evaluate the return band
capacity as a function of sub-channel bandwidth in FDMA and TDMA/FDMA
schemes. In addition, the time varying aspect of the channel is
considered using variable bit rate allocation to sub-bands, as in OFDM
with frequency division multiplexing. Furthermore, the same analysis is
repeated for a wideband system using a decision feedback equalizer
(WDFE) contending with ingress noise instead of channel distortion. This
research demonstrates that using a variable channel allocation (VCA)
scheme to match the time varying aspect of the channel enhances the
performance over a fixed channel allocation (FCA) scheme. It also shows
that a wideband system using an adaptive decision feedback equalizer
(DFE) performs similar to a multi-carrier modulation (MCM) method, and
that reasonable performance can be obtained by using a system of lower
complexity consisting of the combination of the FCA with the WDFE
In a hybrid fiber/twisted-pair architecture the transmission of
data rates much higher than the 1.5 or 2 Mbit/s of the high bit-rate
digital subscriber line (HDSL) service can be achieved by reducing the
loop length of twisted pair cables in the access network. In this paper
we present a channel model for twisted-pair cables for frequencies up to
40 MHz, which is derived from measurements and theoretical analyses.
Based on the new channel model the transmission capacity for a
symmetrical pulse amplitude modulation (PAM) system with adaptive echo
cancellation (EC) and for a carrierless AM/PM (CAP) system based on
frequency division multiplexing (FDM) is calculated, Up to a table
length of 200 m the PAM system achieves higher data rates, whereas for
longer distances CAP systems are advantageous, Over 200 m a data rate of
about 30 Mbit/s can be transmitted by both systems with 24 identical
self-crosstalk disturbers in the 50-pair distribution cable. Whereas the
reach of a 25 Mbit/s echo cancellation system can be increased to 360 m
by NEXT cancellation, the range of the FDM system can even be improved
from 300 m to 610 m for the same data rate. Crosstalk cancellation
results in a high hardware complexity but could be realized with gate
arrays in 0.5 or 0.35 μm technology
Work is under way to develop a very high-rate digital subscriber
line (VDSL) system capable of operating over twisted-pair media at data
rates in excess of 10 Mbps. The twisted-pair channel is characterized by
both an attenuation and crosstalk susceptibility which increase with
frequency and length. The signaling bandwidth for such a channel can be
selected to maximize the bit rate. This optimization is carried out for
loop lengths in the 1-5 kft range. It is shown that the optimal signal
bandwidth is quite sensitive to the loop length. For example, the
optimal bandwidth for a 1 kft loop is more than twice that of the 3 kft
loop
Techniques for achieving data rates up to 155 Mb/s over unshielded
twisted pair wiring in premises distribution systems are described.
These high data rates represent an improvement of about an order of
magnitude in speed when compared to presently available data rates for
local area networks operating over this communication medium. The
transmission scheme proposed for achieving these higher data rates is
carrierless AM/PM (CAP), which is a bandwidth-efficient two-dimensional
passband line code. It is shown that a 32-CAP line code can be used to
provide the fiber distributed data interface (FDDI) rate of 125 Mb/s
over 100 m of voicegrade unshielded twisted pair (UTP) wiring in a
channel bandwidth of 30 MHz, which results in a robust performance and
eliminates potential problems with electromagnetic radiation limits
above 30 MHz
In this correspondence, we compare the finite-precision
requirements of the traditional cross-coupled (CC) and a low-power
strength-reduced (SR) architectures. It is shown that the filter block
(F block) coefficients in the SR architecture require 0.3 bits more than
the corresponding block in the CC architecture. Similarly, the
weight-update (WUD) block in the SR architecture is shown to require 0.5
bits fewer than the corresponding block in the CC architecture. This
finite-precision architecture is then used as a near-end crosstalk
(NEXT) canceller for 155.52 Mb/s ATM-LAN over unshielded twisted pair
(UTP) category-3 cable. Simulation results are presented in support of
the analysis
An analysis of the properties of an adaptive notch filter (ANF)
applied to time-varying frequency tracking is presented. Starting from
the derivation of an expression for ANF output power, asymptotically
optimal values for the pole contraction and forgetting factors are
derived for recursive prediction error (RPE) type ANF algorithms. Based
on the obtained results, a new ANF algorithm that includes adaptation of
both pole contraction and forgetting factors is proposed. The given
experimental results confirm the theoretical conclusions and show that
the proposed algorithm is highly efficient in practice
Describes techniques for achieving data rates up to 155 Mb/s over
unshielded twisted-pair (UTP) wiring for local area network (LAN)
applications in premises distribution systems. Duplex operation at these
high data rates is achieved over two pairs of UTP wiring and with a
bandwidth utilization that is less than 30 MHz, thus avoiding potential
problems with radiation limits. The transmission scheme used for these
LAN applications is carrierless AM/PM (CAP), which is a
bandwidth-efficient two-dimensional passband encoding scheme. The paper
also discusses in some detail a technique called NEXT equalization,
which allows several users to share the same cable
An all digital-QAM system is studied here for high-speed data
transmission on digital subscriber loops. All elements of the system
have been fully investigated and their effects on overall system
performance documented. In particular, the following issues have been
explicitly addressed: utility of an adaptive error-prediction
(noise-prediction) filter; equalizer size and convergence; blind
equalization; choice of constellation size and center frequency;
combined timing/carrier recovery; and the oversampling requirements of a
numerically-controlled-oscillator (NCO) for potential use in the timing
and carrier recovery loop. The paper relies on simulation results to
investigate and quantify the overall interactions of the various blocks.
Throughout the paper emphasis has been placed on reducing the complexity
of the system for implementation on an integrated circuit (IC). It is
expected that the information provided here will serve as a good
starting point for an IC designer to start the implementation of a
transceiver ASIC
The author presents a tutorial on the physical environment in
which high bit rate digital subscriber line (HDSL) transceivers will
have to evolve and succeed. Special attention is given to the most
damaging impairments that are encountered in subscriber lines, such as
propagation loss, linear distortion, crosstalk, bridged taps, and
impulse noise. Somewhat less important impairments, such as change of
gauge, temperature variation, and thermal noise, are also briefly
described. The author concludes with a discussion of the capacity of a
twisted-pair channel in a crosstalk-dominated environment
After a background on digital subscriber line (DSL) technology,
this article evaluates the trade-offs between programmable and custom
implementations of communications products with an emphasis on xDSL
modems. These trade-offs include time to market, risk, flexibility,
power consumption, and cost. A key issue is the processing power
required to implement the modem. The article takes a detailed look at
the processing power required to implement an ADSL or VDSL modem on a
programmable platform. It is demonstrated that today's digital signal
processors meet the processing power requirements for an ADSL modem, and
it is estimated that the processing requirements of a VDSL modem will be
met in the near future
Single-carrier modulation such as quadrature amplitude modulation
(QAM) or carrierless amplitude modulation-phase modulation (CAP), and
DMT are alternative techniques for providing digital communication in a
variety of applications, in particular ADSL for communication over the
telephone company subscriber lines. Although theory predicts comparable
performance under ideal implementations, a definitive comparison of
performance over a wide range of conditions will require more experience
from field trials. Similarly, accurate comparison of implementation
costs must await the greater availability of commercial-grade devices.
However, enough is now known about these modulation schemes to compare
their inherent similarities and differences in performance and cost.
Overall, a present view of single-carrier and multitone modulation
indicates comparable performance with some differences depending on the
type of degradation. Costs should also be approximately equal, with
multitone having some advantage in digital processing, but requiring
greater cost in analog circuitry
The minimum mean-squared-error decision-feedback equalizer
(MMSE-DFE) has properties that suggest that it is a canonical
equalization structure for systems that combine equalization with coded
modulation. The structure and performance of the MMSE-DFE are succinctly
derived using linear-estimation-theoretic principles in this first part
of this two-part paper. The front-end of the MMSE-DFE, called the
“mean-square whitened matched filter” (MS-WMF), is
preferable in some ways to a matched filter or a whitened matched filter
as a canonical receiver front end. In a coded system, the feedback
filter of the MMSE-DFE may be implemented in the transmitter using
precoding. The MMSE-DFE can perform significantly better than a
zero-forcing decision-feedback equalizer, particularly at
moderate-to-low SNR's and on severe-ISI channels. The MMSE-DFE is
biased. The optimum unbiased MMSE-DFE is the MMSE-DFE with the bias
removed. Removing bias improves error probability, but reduces the SNR
to SNR<sub>MMSE-DFE,U</sub>=SNR<sub>MMSE-DFE</sub>-1. It is shown that
this SNR relationship is a particular case of a very general result and
that SNR<sub>MMSE-DFE,U</sub> gives a more realistic estimate of SNR.
The results are extended to partial response equalization and to
equalization with correlated inputs in an appendix
For pt.I, see ibid., vol.41, no.3, p.502-208 (1993). Properties of
a specific class of interpolators that are based upon polynomials are
discussed. Several implementations are described, one of which is
particularly convenient in practical hardware. Simulations demonstrate
that simple interpolators give excellent performance. In many cases,
two-point, linear interpolation is adequate. If better performance is
needed, classical four-point, third-order polynomials could be used.
Better yet, a novel four-point interpolating filter with
piecewise-parabolic impulse response can have performance superior to
that of the standard cubic interpolator and still be implemented much
more simply. The NCO-based control method presented in Part I is shown
to be equivalent to a conventional phase locked loop and its operation
is verified by simulation
The capacity and cutoff rates for channels with linear intersymbol
interference, power dependent crosstalk noise, and additive white noise
are examined, focusing on high speed digital subscriber line data
transmission. The effects of varying the level of additive white noise,
crosstalk coupling gain, sampling rate, and input power levels are
studied in detail for a set of simulated two-wire local loops. A
closed-form expression for the shell constrained Gaussian cutoff rate on
the crosstalk limited channel is developed and related to the capacity,
showing that the relationship between these two rates is the same as on
a channel without crosstalk noise. The study also projects achievable
rates on a digital subscriber line, inside and outside of a carrier
serving area, with a sophisticated but realizable receiver
Line code complexity
- J M Cioffi
J. M. Cioffi, "Line code complexity," Amer. Nat. Stand. Inst., ANSI
T1E1.4/95-022, 1995.
6Mb/sdigital-QAMsystemforDSL transmission
- B Daneshradandh
- Samueli
B.DaneshradandH.Samueli,“A1.6Mb/sdigital-QAMsystemforDSL transmission,” IEEE J. Select. Areas Commun., vol. 13, pp. 1600–1610, Dec. 1995.
ReducingADCresolutionbyusinganalogband-passfilters in FDD based VDSL
- V Oksman
V.Oksman,“ReducingADCresolutionbyusinganalogband-passfilters in FDD based VDSL,” Amer. Nat. Stand. Inst., ANSI T1E1.4/99–334, 1999.
For telecommunications-network and customer installation interfacessymmetrical digital subscriber line (ADSL) metallic interface
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