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1402 IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 23, NO. 3, JULY
2008
Indoor Power-Line Communications ChannelCharacterization up to
100 MHzPart II:
Time-Frequency AnalysisMohamed Tlich, Member, IEEE, Ahmed
Zeddam, Fabienne Moulin, and Frederic Gauthier
AbstractEstimations of coherence bandwidth and
time-delayparameters from wideband channel sounding measurements
madein the 30 kHz100 MHz band in several indoor environments
aredescribed in [1] and taken back in this paper. Powerline
commu-nications (PLC) modems rather see a channel which starts
almostfrom 2 MHz [2]. A comparison between coherence bandwidthand
time-delay parameters estimated in both frequency bands30 kHz100
MHz and 2 MHz100 MHz is elaborated in thispaper. Results are
intended for applications in high-capacity in-door power-line
networks. The investigation is aimed to show thatthe PLC channel
studies in a band starting from a frequency lowerthan 2 MHz
distorts the real values that an implementer shouldtake, as the PLC
modem see only the frequencies from 2 MHz.The coherence bandwidth
and the time delay parameters areestimated from measurements of the
complex transfer functionsof the PLC channels. For the 30 kHz100
MHz frequency band,the 90th percentile of the estimated coherence
bandwidth at 0.9correlation level stay above 65.5 kHz and below
691.5 kHz. It wasobserved to have a minimum value of 32.5 kHz. The
maximumexcess delay spread results show that 80% of the channels
exhibitvalues between 0.6 s and 6.45 s. And a mean rms delay
spreadof 0.413 s is obtained. The passage to the 2 MHz100
MHzfrequency band induced an increase of the coherence
bandwidth,whose min value is brought back to 43.5 kHz, and an
importantreduction of the time delay parameters: The min, max,
mean, andstandard deviation values of the maximum excess delay are
almostdivided by 2. For the twice frequency bands, this paper
studies,also, the variability of the coherence bandwidth and
time-delayspread parameters with the channel class [10], and thus
with thelocation of the receiver with respect to the transmitter,
and finallyrelates the rms delay spread to the coherence
bandwidth.
Index TermsCoherence bandwidth, first-arrival delay, max-imum
excess delay, mean-excess delay, power-line communications(PLC),
RMS delay spread.
I. INTRODUCTION
POWER-LINE COMMUNICATIONS (PLC) earmarkedfor future wideband
wireline services in the 230 MHzfrequency band envisage data
transmission rates up to 200 Mb/s[2]. Generally, effective data
rates do not exceed 70 Mb/s [3]. Inorder to much further increase
the data rates, many equipment
Manuscript received May 11, 2007. Paper no. TPWRD-00282-2007.M.
Tlich is with the INNOVAS Society, Lannion 22300, France (e-mail:
mo-
[email protected]).A. Zeddam, F. Moulin, and F. Gauthier are
with the France Tlcom Division
R&D, Lannion 22300, France (e-mail:
[email protected];[email protected];
[email protected]).
Color versions of one or more of the figures in this paper are
available onlineat http://ieeexplore.ieee.org.
Digital Object Identifier 10.1109/TPWRD.2007.916095
suppliers are studying the possibility of extending the
PLCfrequency band up to 100 MHz. The successful implementa-tion of
this solution requires a detailed knowledge of signalpropagation
modes inside this enlarged frequency band.
Extensive characterizations of power-line channels have
beenreported in [6][8], and [9]. However, these studies are
mainlyfocused on frequencies up to 30 MHz.
The coherence bandwidth is a key parameter whose valuerelative
to the bandwidth of the transmitted signal, subsequentlydetermines
the need for employing channel protection tech-niques (e.g.,
equalization or coding to overcome the dispersiveeffects of
multipath [4], [5]). The impulse response of trans-mission channels
can be characterized by various parameters.The average delay is
derived from the first moment of the delaypower spectrum and is a
measure of the mean delay of signals.The delay spread is derived
from the second moment of thedelay power spectrum and describes the
dispersion in the timedomain due to multipath transmission.
For PLC channels, and for the 130 MHz frequency band,thorough
studies were undertaken in [6], [7]. It was observedthat 99% of the
studied channels have an rms delay spread below0.5 s. In [6], the
coherence bandwidth at 0.9 correlation levelwas observed to have an
average value of 1 MHz.
Also, in [8], it was indicated that for signals in the 0.515
MHzfrequency band, the maximum excess delay was below 3 s, andthe
minimum estimated value of B was 25 kHz.
In [9] and for the frequency range up to 30 MHz, it has
beenfound that, for 95% of the channels, the mean-delay spread
isbetween 160 ns and 3.2 s. And 95% of the channels exhibit adelay
spread between 240 ns and 2.5 s.
In this paper, coherence bandwidth and time-delay parame-ters
studies are extended up to 100 MHz frequency band. Forthis purpose
wideband propagation measurements were under-taken in the 30 kHz100
MHz and 2 MHz100 MHz bands invarious indoor channel environments
(country and urban, newand old, apartments and houses) as shown in
Table I.
The measurements obtained using a swept frequency channelsounder
yielded sufficient statistical data from which frequencycorrelation
functions were derived. These results were used toobtain the
coherence bandwidth of the PLC channels investi-gated and their
impulse responses, obtained by applying the in-verse Fourier
transform to the estimated frequency response [5].
The PLC transfer functions study presented hereby relates
toseven measurement sites and a total of 144 transfer functions.For
each site, the transfer function is measured between a prin-cipal
outlet (most probable to receive a PLC module) and the
0885-8977/$25.00 2008 IEEE
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TLICH et al.: INDOOR POWER-LINE COMMUNICATIONS CHANNEL
CHARACTERIZATION UP TO 100 MHZPART II 1403
TABLE IDISTRIBUTION OF TRANSFER FUNCTIONS BY SITE
Fig. 1. Average transfer function magnitude by class.
whole other outlets (except improbable outlets such as
refriger-ator outlets ). The distribution of the transfer functions
by siteand the characteristics of each site are given in Table
I.
Because calculating distances separating transmitters
fromreceivers was impossible, the PLC channels were classified
into9 classes per ascending order of their capacities (according
tothe Shannons capacity formula and for a same reference noiseand
PSD emission mask).
In [10] and as shown Fig. 1, we have demonstrated that
thechannels of each class have a transfer functions with a
sameaverage magnitude. Thus, a class 9 channel will, for example,be
supposed to have a shorter transmitterreceiver distance thana class
28 channel, and so on.
II. CHANNEL SOUNDER HARDWARE
This section outlines the swept frequency channel sounderdesign,
its calibration, and the devices used in the measure-ments.
Transfer function measurements were carried out in the
fre-quency domain, by means of a vectorial network analyzer,
asshown in the block diagram of Fig. 2
The coupler box plugging into the ac wall outlet behaves likea
high-pass filter, with the 3 dB cutoff at 30 kHz. The probingsignal
passes through the coupler and the ac power line networkand exits
through a similar coupler plugged in a different outlet.A direct
coupler to coupler connection is used to calibrate thetest
setup.
Fig. 2. Power-line channel measurement system.
Two overvoltage limiting devices with a dB and dBlosses,
respectively, are used in front of the entry port of thevectorial
network analyzer 8753ES and its exit port, which canserve as an
entry port, to protect it from over-voltages producedby the impulse
noises of the ac power line.
A computer is connected to the network analyzer through aGPIB
bus. This allows it to record data and control the networkanalyzer
with INTUILINK software [13].
The network analyzer and the computer are isolated from
thepower-line network using a filtered extension. This extension
issystematically connected to an outlet unlikely to be connectedto
a PLC modem, such as washing machine outlet. These pre-cautions are
taken in order to minimize the influence of the mea-surement
devices on the measured transfer functions.
III. WIDEBAND PROPAGATION PARAMETERS
Characterization of wideband channel performance subject
tomultipath can be usefully described using the coherence
band-width and delay spread parameters.
A. Coherence Bandwidth
The frequency-selective behavior of the channel can be
de-scribed in terms of the auto-correlation function for a wide
sensestationary uncorrelated scattering (WSSUS) channel.
Equation(1) gives , the frequency correlation function (FCF)
(1)
where is the complex transfer function of the channel,is the
frequency shift, and denotes the complex conjugate.
is a measure of the magnitude of correlation betweenthe channel
response at two spaced frequencies. The coherencebandwidth is a
statistical measure of the range of frequenciesover which the FCF
can be considered flat (i.e., a channelpasses all spectral
components with approximately equal gainand linear phase).
In other words, coherence bandwidth is the range of frequen-cies
over which two frequency components have a strong po-tential for
amplitude correlation. It is a frequency-domain pa-rameter that is
useful for assessing the performances of variousmodulation
techniques [11]. No single definitive value of corre-lation has
emerged for the specification of coherence bandwidth.Hence,
coherence bandwidths for generally accepted values of
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1404 IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 23, NO. 3, JULY
2008
Fig. 3. Illustration of a typical power-delay profile and the
definition of thedelay parameters.
correlations coefficient equal to 0.5, 0.7, and 0.9 were
evaluatedfrom each FCF, and these are referred to as and
,respectively.
B. Time-Delay Parameters
Random and complicated PLC propagation channels can
becharacterized using the impulse response approach. Here,
thechannel is a linear filter with impulse response . The
power-delay profile provides an indication of the dispersion or
distri-bution of transmitted power over various paths in a
multipathmodel for propagation. The power-delay profile of the
channelis calculated by taking the spatial average of . It can
bethought of as a density function, of the form
(2)
The rms delay spread is the square root of the second
centralmoment of a power-delay profile. It is the standard
deviationabout the mean excess delay, and is expressed as
(3)
where is the first-arrival delay, a time delay corresponding
tothe arrival of the first transmitted signal at the receiver;
andis the mean excess delay, the first moment of the
power-delayprofile with respect to the first arrival delay
(4)
The rms delay spread is a good measure of the multipathspread.
It gives an indication of the nature of the
inter-symbolinterference (ISI). Strong echoes (relative to the
shortest path)with long delays contribute significantly to .
A fourth time-delay parameter is the maximum excess delay. This
is measured with respect to a specific power level,
which is characterized as the threshold of the signal. When
thesignal level is lower than the threshold, it is processed as
noise.For example, the maximum excess delay spread can be
specifiedas the excess delay for which falls below dBwith respect
to its peak value, as shown in Fig. 3.
A typical plot of the time delay parameters is presented inFig.
3.
Fig. 4. Frequency correlation functions of the measured
channels. (i) class 9;(ii) class 6; and (iii) class 3.
TABLE IICOHERENCE BANDWIDTH VALUES IN KHZ FOR 0.5, 0.7, AND
0.9
CORRELATION LEVELS FOR THE CURVES OF FIG. 4
IV. ANALYSIS OF RESULTS
In this section, an analysis of the measured results,
estimationof coherence bandwidth, its variability and
interrelationshipwith rms delay spread, and analysis of time-delay
spread pa-rameters are outlined for the both frequency bands 30
kHz100MHz and 2 MHz100 MHz referred to as and ,respectively.
A. Coherence Bandwidth Results
For the both frequency bands, Fig. 4 shows the frequency
cor-relation functions (FCFs) obtained for three transmitter
receiverscenarios: a class 9 channel (curves (i)), which can be
assumedto have the least multipath contributions. Curves (ii) and
(iii)correspond to the FCFs obtained from a class 6 and class 3
chan-nels, respectively.
The degradation of the frequency correlation functions
cor-responding to class 6 and class 3 channels with respect to
theclass 9 channel can be seen in Fig. 4. Rapid decrease of the
fre-quency correlation function with respect to the frequency
sepa-ration and also as the class number decreases can be
observed.The decrease in frequency correlation function is not
mono-tonic, and this is due to the presence of multipath echoes in
thePLC channel.
Concerning frequency bands comparison, a first result can
bealready released: the FCFs associated to each frequency bandare
juxtaposed for the class 9 and class 6 cases (dotted linesand
dashed lines curves respectively). Nevertheless, a signifi-cant
difference tags the class 3 case (bold lines curves).
From the shape of the FCFs, an estimation of the
coherencebandwidth corresponding to a correlation coefficient of
0.5 can
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TLICH et al.: INDOOR POWER-LINE COMMUNICATIONS CHANNEL
CHARACTERIZATION UP TO 100 MHZPART II 1405
TABLE IIISTATISTICS OF THE COHERENCE BANDWIDTH FUNCTION FOR 0.5,
0.7, AND 0.9 CORRELATION LEVELS IN KILOHERTZ
be obtained. In Fig. 4, this is almost 2.1 MHz for curves (ii)
and18.8 MHz for curves (iii). In general, the smallest
frequencyseparation value is normally chosen to estimate the
coherencebandwidth. This is in agreement with observations made in
[12]that coherence bandwidth characterization using spaced
tones[11] is not satisfactory unless measurements are taken over
alarge number of points.
Coherence bandwidth values for 0.5, 0.7, and 0.9
correlationlevels for the curves of Fig. 4 are given in Table II,
and statisticsof the coherence bandwidth function for 0.5, 0.7 and
0.9 correla-tion levels for all channel measurements are shown in
Table III.
For the 0.9 coherence level and the frequency band FB ,the
coherence bandwidth was observed to have a mean of291.97 kHZ,
minimum coherence bandwidth of 32.5 kHz, and334.36 kHz standard
deviation (Std). For 90% of the time,the value of obtained was
below 691.5 kHz and above65.5 kHz. If we focus on the frequency
band FB values, wesee that they are greater than the FB values. The
minimumcoherence bandwidth becomes 43.5 kHz, and 90% of the
PLCchannels have values greater than 89.5 kHz.
For the 0.7 coherence level and the frequency band FB , amean
coherence bandwidth of 833.9 kHz was obtained. Here,the minimum
value emerged as 98.5 kHz and the standard devi-ation as 1.063 MHz.
The FB values are very close to the FBones.
In the 0.5 coherence level, 80% of the channel measurementshave
a values below 13.376 MHz and above 423.5 kHz.Like the 0.9 and 0.7
coherence levels, the FB mean value of
(4.801 MHz) is greater than the FB1 one (4.539 MHz).But, the min
and max values are lower in the FB case.
In what follows, we will focus our study only on . Inorder to
characterize the channels most prone to the variationof when we
replace FB by the frequency band FB reallyseen by the PLC modem, we
will study in the next paragraphthe behavior of with the channel
classes.
B. Coherence Bandwidth Versus Channel Class
The minimum and mean values of coherence bandwidth func-tion for
0.9 correlation level as a function of the channel class isgiven in
Fig. 5. It can be observed that the coherence bandwidthis highly
variable with the location of the receiver with respectto the
transmitter.
To investigate the reasons for the fluctuations of the
coher-ence bandwidth values, magnitude curves of the complex
fre-quency responses are shown. Fig. 6 represents the channel
fre-quency response for the case where the coherence bandwidthwas
estimated at 1.859 MHz in FB . Fig. 6 clearly shows that the
Fig. 5. Min and Mean values of coherence bandwidth for 0.9
correlation levelas a function of channel class.
channel frequency response presents few notches, large peaks,and
is relatively flat over the 100 MHz bandwidth. Not surpris-ingly
therefore, the coherence bandwidth assumed a relativelyhigh
value.
Next, the least value of the coherence bandwidth (32.5 kHz)in FB
was investigated. Fig. 7 shows the magnitude responsein this case
which shows significant frequency selective fadingof the channel,
resulting in deep fades at several frequenciesand narrow peaks. The
presence of this significant frequencyselective fading explains the
relatively small value of coherencebandwidth observed. Both of
these cases demonstrate that thePLC indoor channel is considerably
affected by multipath, andthat the coherence bandwidth value
decreases with frequencyselective fading.
Fig. 5 demonstrates also that the mean values of areunaffected
by the frequency band choice for the channels ofthe classes 5 to 9.
Nevertheless, for the 2nd, 3rd, and 4th class,the mean values of
are greater in FB than in FB . Thisis due to the fact that, in the
frequency band 30 kHz2 MHz,the transfer function fluctuations are
more significant for thechannels of low numbered classes rather
than those of high-numbered classes.
Concerning the min values of , the most important resultis that
the smaller values pertain to the FB case.
From an implementation point of view, the highly
fluctuatingcoherence bandwidth means that the system designer can
relyonly on the lowest value of this parameter in such an
environ-ment. From Table III and Fig. 5, this is 43.5 kHz (in FB )
andnot 32.5 kHz of FB . Thus, considering the FB frequency band
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1406 IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 23, NO. 3, JULY
2008
Fig. 6. Measured transfer function envelope of the maximum B
value.
Fig. 7. Measured transfer function envelope of the minimum B
value.
values of coherence bandwidth distorts its real value that an
im-plementer should take.
The coherence bandwidth, determined from (1) is calculatedfrom
the complex frequency response of the channel, in whichthe phase
changes instantaneously and significantly over anychange on the
state of an electrical device. The coherence band-width thus
determined is more appropriately termed the instan-taneous
coherence bandwidth. To study the time dispersive na-ture of the
PLC channel, its more suitable to focus on the time-delay spread
parameters.
C. Time-Delay Parameters Results
By means of an inverse Fourier transform the impulsive re-sponse
can be derived from the absolute value and thephase of a measured
transfer function. For the frequency bands30 kHz100 MHz (FB ) and 2
MHz100 MHz (FB ), the am-plitudes of the impulse responses of the
channels of Figs. 6 and7 are depicted in Figs. 8 and 9,
respectively.
As the maximum excess delay is specified as the excessdelay for
which falls below dB with respect to itspeak value, the lower
signal levels are processed as noise. Con-sequently, it is more
suitable to calculate the mean excess delay
Fig. 8. Impulse response of Fig. 6 channel.
Fig. 9. Impulse response of Fig. 7 channel.
and the rms delay spread on the basis of channeltime
coefficients lower than .
The impulse responses of Figs. 8 and 9 show some peakswhich
confirm the multipath characteristics of PLC channels.For the
frequency band FB , the impulse response of Fig. 8 ex-hibits a
maximum peak at a delay , a mean excessdelay s, an rms delay spread
s,and a maximum excess delay s for whichfalls below dB with respect
to its peak value.
The same parameters of the impulse response of Fig. 9 ares, s,
s, and
s. This is quite foreseeable as the impulse response ofFig. 8 is
associated to a shorter PLC channel and much lessaffected by
multipath.
More interesting are the reduced delays of the impulse
re-sponses of Figs. 8 and 9 when the frequency band FB is
con-sidered. Mean excess delay, rms delay spread, and maximumexcess
delay parameters become s,
s, and s for Fig. 8 impulse response. ForFig. 9 impulse
response, the effect is more undeniable. In fact,time delay
parameters fall spectacularly until s,
s, s, and s.
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TLICH et al.: INDOOR POWER-LINE COMMUNICATIONS CHANNEL
CHARACTERIZATION UP TO 100 MHZPART II 1407
TABLE IVSTATISTICS OF TIME DELAY PARAMETERS IN MICROSECONDS
TABLE VSTATISTICS OF THE TIME-DELAY SPREAD PARAMETERS IN
MICROSECONDS AS A FUNCTION OF THE CHANNEL CLASS
Statistics of time-delay spread parameters for all measuredPLC
channels are given in Table IV. In the frequency bandFB , the
first-arrival delay was observed to have a mean of0.17 s, minimum
of 0.01 s, and 0.11 s standard deviation.For 90% of the time, the
value of obtained was below 0.31 sand above 0.05 s. Compared to the
frequency band FB case,there is not a great difference to note for
this parameter.
For the mean-excess delay parameter and the FB case, amean value
of 0.25 s was obtained. Here, the minimum valueemerged as 1 ns and
the standard deviation as 0.23 s. Con-cerning the maximum-excess
delay, 80% of the channel mea-surements have values of between 0.6
s and 6.45 s. 80%of the channels exhibit an rms delay spread
between 0.06 s and0.78 s. The measured channels have a mean rms
delay spreadof 0.413 s.
The passage to FB induced an important reduction of themaximum
excess delay, whose min, max, mean, and standarddeviation values
were almost divided by 2.
D. Time-Delay Parameters Versus Channel Class
The mean values of first-arrival delay, mean-excess
delay,rms-delay spread, and maximum-excess delay as a function
ofthe channel class are given, for the twice frequency bands FBand
FB , in Table V. It can be observed that these parametersare highly
variable with the class number.
Generally speaking, the four considered time parametersdecrease
with the class number in both frequency bands. In fact,the
high-numbered classes are those whose channels are shorterand less
affected by multipath. The transmitted signal arrives to
Fig. 10. Maximum excess delay as a function of the class
number.
its destination more quickly; furthermore, the number of
echoesand their delay excess are less than those of
low-numberedclasses.
Because, in the frequency band 30 kHz2 MHz, the transferfunction
fluctuations are more significant for the channels oflow numbered
classes, the delay differences between FB andFB cases in Table V
are more important for the low-numberedclasses. This is especially
visible on the maximum excess delayparameter as a function of the
class number and the frequencyband, also reported in Fig. 10.
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1408 IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 23, NO. 3, JULY
2008
Fig. 11. Scatter plot of coherence bandwidth against rms delay
spread.
E. Coherence Bandwidth Versus RMS Delay Spread
Fig. 11 shows a scatter plot of the rms delay spread against
thecoherence bandwidth of the PLC channel measures for the
twicefrequency bands FB and FB . The scatter plot shows a
highconcentration of points in the range 0.1 s-0.9 s at which
thecoherence bandwidth is almost under 500 kHz and over 50
kHz.Higher values of coherence bandwidth are observed for rmsdelay
spread values less than 0.1 s. In system design terms,higher
coherence bandwidth translates to faster symbol trans-mission rates
[11].
For both frequency bands, Fig. 11 depicts a same and
clearrelation between the values of B and estimated in theoverall
set of measured channels, and which can be approxi-mated by
(5)
In Fig. 11, the relation (5) is represented by the red-circles
curve.
V. CONCLUSION
Based on measurements in different environments, the
paperincludes analysis of both coherence bandwidth and time
delayspread parameters for inhouse power-line channels in the
fre-quency range up to 100 MHz.
A comparison between these parameters in both frequencybands 30
kHz100 MHz and 2 MHz100 MHz, which is thefrequency band really seen
by PLC modems, was elaborated.
Rapid increase of the coherence bandwidth and decrease ofthe
time delay parameters with respect to frequency band andalso as the
channel class increases was observed.
For the first frequency band, the 90th percentile of the
esti-mated coherence bandwidth at 0.9 correlation level stayedabove
65.5 kHz. Also, 90% of estimated values of B werebelow 691.5 kHz. B
was observed to have a minimum valueof 32.5 kHz.
The maximum excess delay spread results showed that 80%of the
channels exhibit values between 0.6 s and 6.45 s. A
mean rms delay spread of 0.413 s was obtained, and 80% of
thechannels had an rms delay spread between 0.06 s and 0.78 s.
Using the second frequency band (2 MHz100 MHz) inducedan
increase of the coherence bandwidth and an important reduc-tion of
the time delay parameters.
The min value of was brought back to 43.5 kHz, thereally value
that a system designer should rely on. The min, max,mean, and
standard deviation values of the maximum excessdelay were almost
divided by 2.
Finally, a relationship between the rms delay spread and
thecoherence bandwidth was determined.
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Ramakrishna,Wideband characterization of low voltage outdoor
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[10] M. Tlich, A. Zeddam, F. Moulin, F. Gauthier, and G. Avril,
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[11] L. H.-J. Lampe and J. B. Huber, Bandwidth efficient power
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Mohamed Tlich (M04) was born on May 22, 1979,in El Alia,
Tunisia. He received the Ph.D. degreein electrical engineering from
the Ecole NationaleSuprieure des Tlcommunications de Paris
(ENSTParis) and France Tlcom Division R&D (OrangeLabs),
Lannion, France, in 2006.
His research interests include information theory,communication
theory, and digital signal processing.His current research focuses
on the applicationof multiuser communication theory to xDSL
andincreasing the quality of service (QoS) and through-
puts of PLC systems.Dr. Tlichs Ph.D. dissertation was awarded as
being one of the three best
France Tlcom R&D Ph.D. dissertations in 2005.
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TLICH et al.: INDOOR POWER-LINE COMMUNICATIONS CHANNEL
CHARACTERIZATION UP TO 100 MHZPART II 1409
Ahmed Zeddam was born on April 9, 1952. He re-ceived the Ph.D.
degree in electromagnetics from theUniversity of Lille, Lille,
France.
From 1979 to 1982, he was an Assistant Professorof Electronics
at Lille I University. Since 1982, hehas been with the Research and
Development Divi-sion of France Telecom, Lannion, where he is
Headof a research-and-development unit that deals
withelectromagnetic compatibility. He is the author andco-author of
many scientific papers, published in re-viewed journals and
international conferences.
Dr. Zeddam is a member of several technical committees of
internationalstandardization bodies dealing with electromagnetic
compatibility (ITU-T, IEC,CENELEC) and is involved in Commission E
"Electromagnetic Noise and In-terference" of the International
Union of Radio Science (URSI). He is a memberof many scientific
committees of national and international symposia on EMC.
Fabienne Moulin received the Ph.D degree from the INSA Rennes,
Rennes,France, in 2001.
Currently, she is with France Telecom R&D, Lannion, France.
Her researchdeals with increasing the quality of service (QoS) of
the xDSL and PLT audioand video services.
Frederic Gauthier received the Ph.D. degree fromthe University
Pierre et Marie Curie, Paris, France,in 1989.
He joined France Telecom R&D, Lannion, France,in 1989. His
research deals with the characterizationand modelling of the PLT
and xDSL channel.