Multicarrier spread spectrum techniques for downstream power-line communications on low voltage grid

INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMSInt. J. Commun. Syst. 2003; 16:401–416 (DOI: 10.1002/dac.599)

Multicarrier spread spectrum techniques for downstreampower-line communications on low voltage grid

Romano Fantaccin,y and Simone Morosiz

Electronics and Telecommunications Department, University of Florence, Firenze, Italy

SUMMARY

In this paper different spread spectrum systems are proposed for broadband downstream power-linecommunications (PLCs). Orthogonal frequency division multiplexing (OFDM) technique permits togreatly enhance the system throughput but can be strongly damaged by ‘hidden nodes’ situations. Theintroduction of suitable hybrid schemes, such as MT-CDMA, allows to efficiently face this inconvenienceby increasing system robustness.The performance of the systems considered is expressed in terms of bit error rate (BER), derived

by simulations under the assumptions of frequency-selective multipath fading channel and additivecoloured gaussian noise according to the in-building networks model, under the same overall workingconditions of bandwidth occupation, transmitted power and global data rate. Copyright # 2003 JohnWiley & Sons, Ltd.

KEY WORDS: code division multiple access (CDMA); orthogonal frequency division multiplexing(OFDM); power-line communication (PLC); hidden node

1. INTRODUCTION

Growing attention has been recently dedicated to wired communications because of liberali-zation process in telecommunications business. In particular, great interest has been devotedto low voltage grid as a way to bridge the ‘last-mile’ access network. Beyond the traditionalapplications such as monitoring, remote metering and load control, the use of existingpower lines for transmitting data and voice would provide customers of energy utilities analternative to traditional networks. In fact, power delivery network is ubiquitous, also in themajority of developing countries, with potential tremendous impact on telecommunicationsmarket.

PLCs would permit to enhance traditional lines of business, i.e. power delivery, with addedvalue services, so enabling power public utilities to tap new lucrative lines of business in fastInternet access, telephone service and home automation at an attractive price. Also in-building

Received 1 November 2002Published online 9 May 2003 Revised 15 January 2003

Accepted 19 February 2003Copyright # 2003 John Wiley & Sons, Ltd.

yE-mail: [email protected]

nCorrespondence to: R. Fantacci, Electronics and Telecommunications Department, University of Florence, Via diS. Marta 3, I-50139, Firenze, Italy.

zE-mail: [email protected]

services can be greatly enhanced if existing power lines grid is used as a local IP network in officeand residential home. However, these services claim for high data-rates and, as a consequence,carrier frequencies must be defined within the range from 1 up to 30 MHz: Besides, PLC channelis extremely challenging and claims for highly sophisticated communication techniques. Inparticular, it is characterized by frequency selective phenomena, presence of echoes, impulsiveand coloured noise with the superposition of narrow-band interference [1, 2]. Moreover, in thecase of in-home networks, additional problems can be created by topology of the systems and bythe presence of the so-called hidden nodes [3]. Particularly, if two or more LAN have to coexistin the same building, e.g. several office networks inside a factory, power lines features preventfrom perfect isolation between the systems.

All these negative features push to consider communication techniques that can effectivelyface such an hostile environment; as for the majority of the recent works, in this paper DS-CDMA [4, 5] and OFDM systems are considered [6, 7]: these techniques are real candidates forfuture broadband PLC since they permit to separate overall transmitted data in many parallelindependent sub-streams, to implement flexible resources management strategies in order tocope with channel impairments, to provide fine granularity in multimedia services by supportingvariable data rates and to achieve remarkable capacity. Moreover, we propose to consideranother multiple access scheme, namely Multi Tone CDMA (MT-CDMA) [8, 9], characterizedby a high spectral efficiency, multiple access interference rejection and complexities comparableto classical OFDM approach. Moreover, it seems to be particularly attractive in order tomitigate the interference due to hidden transmissions.

The inherent redundancy of DS-CDMA systems can be exploited in order to increase overallcapacity; moreover, these systems exhibit excellent robustness against all kinds of narrow-bandinterference, coloured noise or selective attenuation while low power spectrum density reducesEMC problems. Unluckily, these systems are sensitive to impulse noise: during such strongpeaks information bits are irremediably lost so that proper coding and interleaving schemes areneeded to avoid remarkable performance loss. In this paper uncoded data flow is taken intoaccount so that this kind of noise is not considered.

On the other hand, Multi-carrier techniques are based on the idea of partitioning the overallbandwidth, so creating many sub-channels, each characterized by its personal carrier. Thissolution permits to achieve data rate near to the channel capacity if channel impulse responseand noise power density spectrum are known. OFDM technique can be considered as anevolution of multi-carrier techniques, it is characterized by very high spectral efficiency thanksto orthogonal sub-carriers utilization; sub-carriers orthogonality condition is guaranteed iffrequency spacing is equal to inverse of OFDM symbol duration. OFDM technique allows togreatly reduce channel equalizer complexity and to increase resistance to narrow-band andimpulsive noise; moreover, bit-loading techniques permit OFDM system to achieve capacityvery near the theoretical limit at the cost of an increase in system complexity. Besides, sinceinter-symbol interference (ISI) impairments are negligible, channel equalizer block can bedramatically simplified or, ideally, suppressed.

In this paper, these techniques are fairly compared, aiming to determine which one is moresuitable in the different contexts for a given computational complexity burden. The comparisonshave been performed assuming same overall bit-rate, same bandwidth occupation, equaltransmitted power; besides, coherent phase modulation has been assumed for both systems.Moreover, in this paper, different sub-streams allocation policies are considered and comparedin order to define smart strategies that can minimize channel impairments.

Copyright # 2003 John Wiley & Sons, Ltd. Int. J. Commun. Syst. 2003; 16:401–416

R. FANTACCI AND S. MOROSI402

Finally, hidden node problem is tackled by introducing a suitable combination of timedomain spreading and multicarrier modulation; particularly, a modified Multi Tone CDMA(MT-CDMA) scheme is introduced in order to achieve multiuser interference rejection whilemaintaining channel selection benefits. It is important to point out that in this paper the down-stream power line channel is considered and the transmission is performed according to point-to-multipoint situation, i.e. from master control station to terminal.

2. DIRECT SEQUENCE CDMA SYSTEM

In DS-CDMA systems, each bit is multiplied for a pseudonoise sequence whose fundamentalelement, called chip, is much shorter than the informative bit; as a result, signal bandwidthoccupation is increased by a factor equal to the ratio between bit and chip duration, theso-called spreading factor (SF).

Proposed multiple access scheme is based on joint utilization of orthogonal variable spreadingfactor (OVSF [5]) and random scrambling codes. Firstly, each global bit stream is divided into Nparallel sub-streams, orthogonally separated from each other by a channelization operationperformed by multiplying them by an individual orthogonal OVSF code; in the second step allthe sub-streams composing the data flow of each user are added together and scrambled bymeans of a pseudonoise user code to better protect them from multipath effects and from

RAKE MRC

n(t)

1OVSF

PN

PN

1OVSF

RAKE MRC

PN

NOVSF

NOVSF

SERIAL TO PARALLEL

BPSKMODULATOR CHANNEL

BPSK DEMODULATOR PARALLEL

TO SERIAL

Σ

Figure 1. DS-CDMA system block diagram.


MULTICARRIER SPREAD SPECTRUM TECHNIQUES 403

interference of other possible users. Considered signals are supposed to be transmittedaccording to a BPSK modulation scheme. As it is known, joint use of these two kinds of codeshelp obtaining good crosscorrelation properties, especially if a general synchronism betweenusers is assumed. Since proposed system is supposed to be used in the down-stream power linechannel, all the data streams can be assumed to be effectively synchronized, so completelydeploying MAI impairments mitigation properties. Finally, rake diversity reception is adopted:each receiver is composed by N parallel maximum ratio combining (MRC) rake blocks to detectall the sub-streams in which transmitted signal has been split. DS-CDMA scheme is described inFigure 1.

3. OFDM SYSTEM

OFDM technique is characterized by very high spectral efficiency thanks to orthogonal sub-carriers utilization; sub-carriers orthogonality condition is guaranteed if frequency spacing isequal to inverse of OFDM symbol duration: in the considered systems, no frequency guardinterval is assumed. Discrete Fourier transform (DFT) utilization permits to performmodulation and demodulation by base-band processing: particularly, modulation operation,that is symbol mapping upon single sub-carrier, is accomplished by inverse FourierTransforming (IDFT) of 2N hermitean complex symmetric values; these values are generatedfrom N complex symbols in order to transmit a real signal modulated upon N sub-carriers.During propagation, ISI arises because of delay spread while channel distortion takes to looseorthogonality between sub-carriers, so creating inter-channel interference (ICI). Bothimpairments can be faced by cyclic prefix (CP) introduction; in particular, if CP length ischosen to be at least equal to delay spread n; bandwidth efficiency loss is equal to n=ðnþ 2N Þ:CP introduction takes to obtain at the receiver cyclic convolution of Channel Impulse Responseand transmitted signal so that it is relatively easy to eliminate CP from the received signal.Moreover, after DFT, only a 1-tap equalizer is required for the received signal. Finally, it isworth stressing that the utilization of the bit-loading (BL) techniques permits to transmit morebits in the sub-channels characterized by less attenuation and interference and not to use lessfavourable sub-bands. This approach allows to achieve capacity near theoretical limit even iffinite granularity in choosing signal constellation and in the definition of the sub-channel bandstake to sub-optimum results. OFDM communication scheme is described in Figure 2. Note thatin OFDM approach BER minimization is performed, by assuming that the overall bit-rate andthe transmitted power are constant and margin adaptive algorithm [10] is used.

4. MODIFIED MT-CDMA SYSTEM

Recently, several multiple access schemes based on a combination of code division and OFDMtechniques have been proposed [8]. These systems are characterized by high spectral efficiency,multiple access interference rejection and complexities comparable to classical OFDMapproach. These features can be efficiently exploited to face hidden nodes situation; inparticular, the Multi-Tone CDMA (MT-CDMA) [9] seems to be a proper solution for thisproblem.



The MT-CDMA transmitter spreads the S=P converted data streams using a given spreadingcode in the time domain so that the spectrum of each sub-carrier prior to spreading operationcan satisfy the orthogonality condition with the minimum frequency separation. Therefore,the resulting spectrum of each sub-carrier no longer satisfies the orthogonality condition.

MAPPING

MAPPING

SERIAL TO PARALLEL

HERMITEANSIMMETRY IDFT

PARALLEL TO SERIAL

OFDMSYMBOL

CYCLICPREFIX

D/A

n(t)

CHANNEL A/D

SERIAL TO PARALLEL

OFDMSYMBOL

CYCLICPREFIX

DFT

–10H

–12N–1H

COMBINING

DEMAPPING

DEMAPPING

PARALLEL TO SERIAL

Figure 2. OFDM system block diagram.



MT-CDMA scheme is described in Figure 3. MT-CDMA provides interference mitigationcapabilities due to the spreading operation. Hence, this scheme can be used in order to suppresshidden node interference; on the contrary classical MT-CDMA is characterized by very highprocessing gain and cannot be utilized together with bit loading techniques. If each sub-band isspread over a too extended bandwidth, no favourable channel can be identified anymore. As aconsequence, we decided to adopt a modified MT-CDMA scheme with low-to-moderatespreading factor in order to retain bit loading benefits. Moreover, each node uses a differentrandom spreading code, in order to take the benefits due to the low values of crosscorrelation.The effectiveness of the proposed approach will be shown in Section 7.

5. HIDDEN NODE PROBLEM

Hidden node problem is well-known in telecommunication networks theory. A hidden node canimpair the communication between other two nodes, since it is within the range of the intendeddestination but out of range of the sender [11]. For the sake of clarity, we can refer to thesituation depicted in Figure 4: node A is transmitting to node B; node C cannot hear thetransmission from A. During this transmission when C senses the channel, it falsely thinks thatthe channel is idle. If node C starts a transmission, it interferes with the data reception at B. Inthis case node C is a hidden node to node A. Hence, hidden nodes can cause collisions on datatransmission.

An hidden node situation for PLCs can be experimented when two Local Area Networks(LANs) are developed in the same building using the same power lines, as depicted in Figure 5,and mild or loose isolation is realized between the two systems. In the case of no isolationbetween the two local networks depicted in Figure 5, the power received from the hidden node isequal to 1

3of the intended communications. As it will be shown in Section 7, this problem is

particularly harmful for OFDM communications in PLN.

6. WORKING CONDITIONS AND COMPARISON CRITERIA

The propagation environment considered in this paper is the wired communication channelinside buildings as described in Reference [2]. PL channel impedance is highly varying withfrequency, ranging between a few Ohm and a few kOhm. Moreover, load conditions changesand discontinuities in branch cables can cause reflection and echoes. Peaks in the impedancecharacteristics may occur at certain frequencies. As a result, PL channel can be considered as amultipath propagation environment with deep narrow-band notches in the frequency response.Power lines noise spectrum is highly varying with frequency and time; in the consideredenvironment three kinds of noise can be identified: Additive Coloured Gaussian noise withspectral power density decaying with frequency, narrow-band interference which can bemodelled as single tone in frequency domain, and impulse noise. In particular, impulse noise iscomposed by strong peaks whose duration could be equal to some ms and mean time betweenoccurrence to several s. During such strong peaks, information bits are damaged so that propercoding and interleaving schemes are needed to avoid remarkable performance loss. In thispaper, an uncoded data flow is taken into account so that this kind of noise is not considered.Finally, channel characteristics are assumed to be slowly time-varying so that channel can be



MAPPING

MAPPING

SERIAL TO PARALLEL

HERMITEANSIMMETRY IDFT OFDM

SYMBOL

CYCLICPREFIX

D/A

n(t)

CHANNEL A/D

SERIAL TO PARALLEL

OFDM SYMBOL

CYCLICPREFIX

DFT

–10H

–112N–H

COMBINING

DEMAPPING

DEMAPPING

PARALLEL TO SERIAL

iPN

iPN

iPN

iPN

∫

∫

Figure 3. MT-CDMA system block diagram.



considered as quasi-stationary. In order to effectively model channel characteristics, the set ofparameters provided in Reference [2] has been adopted; it is worth stressing that, in thismultipath fading model, each replica delay, phase and attenuation are assumed known andconstant during whole simulation.

In performing our simulations the following conditions have been assumed:

* PLC channel ranging from 1 to 21:480 MHz; i.e. bandwidth occupation W equal to20:480 MHz;

* overall maximum bit-rate equal to 10:240 Mb=s;* coherent phase modulation and rectangular pulse shaping for all the considered signals;* perfect power matching, i.e. ideal power transfer.

For what concerns DS-CDMA systems the following conditions have been supposed:

* considered sub-streams bit-rate equal to 40, 160, 320, 640 and 2560 kb=s;* spreading by a OVSF code, followed by a random scrambling code; the spreading factor of

the OVSF code is variable according to the bit-rate, i.e. SF ¼ 4 for a bit-rate of 2560 kb=sand SF ¼ 256 for 40 kb=s:

It is worth stressing, that, in the proposed scheme, the same random code is supposed to beused for all the sub-streams: if different user traffic flows are supposed to be transmitted over the

AB C

Hidden Node

Figure 4. Hidden node situation.

LAN 1 LAN 2

A

B C

50 m

(-25 dB)

100 m (-35 dB)

Same Building (Factory, Offices, …)

Figure 5. Hidden node in power line networks.



same link simultaneously, it would be possible to differentiate informative streams by usingdifferent random codes utilization. Anyway, this solution is not considered in the present work.

On the other hand, OFDM systems are based on the following assumptions:

* considered sub-channels number equal to 64 and 256;* bit loading technique based on the utilization of constellations formed by 2, 4 and 8

symbols; besides the power is distributed between the sub-channels so that each bit has thesame energy

* overall bit-rate equal to 10:240 Mb=s:

There are several comparison studies about CDMA and OFDM systems [12, 13]: in ourstudy, the two systems have been compared under the same conditions of bandwidthoccupation, overall transmitted power and global data rate. The BER performance of theconsidered systems have been evaluated for different values of the signal-to-noise ratio (SNR):in particular, SNR is defined for each sub-stream, that is to say for each informative flow, as

SNRflow ¼S0N

¼EsR

N0eqWð1Þ

where S0; N ; E; R; W and N0eq are signal and noise power, symbol energy and rate, occupiedbandwidth and the equivalent mean noise power density, respectively: in particular, N0eq isdefined as

N0eq ¼1

W

ZWN ðf Þ df ð2Þ

where N ðf Þ is the noise power spectral density. In the OFDM systems, the overall SNR is equalto SNRflow; in fact, if the number of sub-streams is doubled, also symbol time is doubled, so thattransmitted power is the same. On the contrary, in CDMA systems, the number of sub-streamscan be doubled if the SF is doubled, that is to say the symbol time is halved. As a consequence,the overall transmitted power depends on the number of active sub-streams; in particular, theoverall SNR is equal to SNRflowSF: In order to have a fair comparison between the two systems,same power is assumed to be transmitted, that is to say that overall SNR is assumed equal forboth systems.

Finally, MT-CDMA scheme is characterized by the following assumptions:

* considered sub-channels number equal to 256;* considered spreading factor equal to 3, 11, 21;* bit loading technique based on the utilization of constellations formed by 2, 4 and 8

symbols; besides, the power is distributed between the sub-channels so that each bit has thesame energy

* overall bit-rate equal to 10:240 Mb=s:

Also in this case, the same power is assumed to be transmitted.

7. NUMERICAL RESULTS

In this section, performance of the proposed systems are described in different environmentalconditions and for several load configurations.



In Figures 6–8, CDMA system is evaluated for different sub-streams configurations; inparticular, in Figure 6, single sub-stream system is considered for all the possible bit-ratevalue, showing benefits caused by greater spreading factor. In Figures 7 and 8, full loadsystems are considered in the case of uniform and non-uniform rate allocation. Particularly,for the non-uniform case, transmitted signal is given by superposing 32 sub-streams, 8 with640 kb=s bit-rate, 8 with 320 kb=s bit-rate and 16 whose rate is equal to 160 kb=s: It can bededuced that, even if same power is transmitted for all the systems, the strategy of dividing thewhole data flow in as many as possible low rate sub-streams is the most profitable. It is evidentthat the choice of uniformly splitting overall rate is taken to obtain remarkably betterperformance.

In Figure 9 effective equivalent base-band noise spectrum is reported. This distribution iscaused by the combination of the contributes relative to positive and negative frequencies, dueto the hermitean symmetry, in OFDM receiver. It is important to point out that this is theequivalent noise effectively affecting each OFDM symbol. In Figure 10 the BER performance ofall the different sub-channels of the proposed OFDM system is evaluated in the case of 64 sub-streams when SNR is equal to �14 dB; for the same overall power and bit-rate, i.e. 10:240Mb=s; the performance of OFDM system with BL is shown with bold line while thin linerepresents the performance of no BL system. Note that OFDM technique with no BL leads topoor performance for the sub-streams whose band are located over the narrow-bandinterference; on the contrary, BL technique introduction allows to transmit only overfavourable channels, avoiding bands characterized by worse propagation conditions. It isworth underlining that for the most favourable channels 4 and 8 PSK constellations are used.Note that BER curves match to noise spectrum depicted in Figure 10 while local fluctuations aremainly due to channel selective attenuation. In Figures 11 and 12 CDMA and OFDM with and

1.000E-05

1.000E-04

1.000E-03

1.000E-02

1.000E-01

1.000E+00

-10 -8 -6 -4 -2 0 2SNR (dB)

BE

R

1 @ 2560 kb/s1 @ 640 kb/s1 @ 320 kb/s1 @ 160 kb/s1 @ 40 kb/s

Figure 6. BER comparisons.



without BL systems are compared for 64 and 256 sub-streams; in particular, DS-CDMA systemachieves better performance than OFDM with no BL but is greatly overcome by OFDM systemwith BL. OFDM capability of select channels and modulations seem to be the best solution inthe considered environment, at a cost of more complex channel estimation. Moreover, we wouldlike to stress that a remarkable part of the noise power is concentrated in the narrow-bandinterference. This kind of disturbance is effectively faced by the proposed systems so that verygood performance is achieved for very low SNR.

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

6050403020100Sub-channels

BE

R

64 BL

64 no BL


1.00E-05

1.00E-04

1.00E-03

1.00E-02

1.00E-01

1.00E+00

-10 -8 -6 -4 2 0 2

SNR (dB)

BE

R

4 @2560 kb/s

32 @320 kb/s

non uniform




Figure 9. Effective noise amplitude spectrum.

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0 10 20 30 40 50 60

Sub-channels

BE

R

64 BL

64 no BL




In Figure 13, the performance of the OFDM system in the case of hidden node interference isreported for 256 sub-streams; in particular, the power levels of the interfering user are assumedto be equal to 30, 40, 50, 60, 80, 100% of the intended user. The impairment suffered by theOFDM system is evident. In Figure 14, positive results caused by MT-CDMA scheme adoptionare described for the case of interference power equal to 30% of desired user: the benefits due tospreading are particularly remarkable for processing gain equal to 21.

1.00E-05

1.00E-04

1.00E-03

1.00E-02

1.00E-01

1.00E+00

-10 -8 -4 -2 0 2

SNR (dB)

BE

R

64 sub-channels (no BL)

64 sub-channels (BL)

64 @ 160 kb/s

-6


1.00E-05

1.00E-04

1.00E-03

1.00E-02

1.00E-01

1.00E+00

-10 -8 -6 -4 -2 0 2

SNR (dB)

BE

R

256 subchannels (no BL)

256 sub-channels (BL)

256@40 kb/s




8. CONCLUDING REMARKS

In this paper, a fair comparison between DS-CDMA and OFDM systems for broadbanddownstream PLCs has been provided under the same overall working conditions of bandwidth

1.0E-05

1.0E-04

1.0E-03

1.0E-02

1.0E-01

1.0E-00

-10 -8 -6 -4 -2 0 2

SNR (dB)

BE

R

no interf interf 30%

interf 40% interf 50%

interf 60% interf 80%

interf 100%


1.0E-05

1.0E-04

1.0E-03

1.0E-02

1.0E-01

1.0E-00

-10 -8 -6 -4 -2 0 2

SNR (dB)

BE

R

interf 30%interf 30% sf 3interf 30% sf 11interf 30% sf 21




occupation, transmitted power and global data rate. BL technique introduction allows OFDMto achieve remarkable performance and high flexibility in resource management. On thecontrary, CDMA guarantees good performance and satisfactory allocation policies with lowcomplexity receiver. Finally, hidden node problem is faced by a proper combination oftime domain spreading and multicarrier modulation, namely MT-CDMA, with remarkableresults.

REFERENCES

1. Dostert K. Telecommunications over the power distribution grid, possibilities and limitations. Proceedings of the 1stInternational Symposium on Power Lines Communications and its Applications (ISPLC97), Essen, Germany, April1997.

2. Phillips H. Modelling of powerline communication channels. Proceedings of the 3rd International Symposium onPower Lines Communications and its Applications (ISPLC99), Lancaster, UK, March 1999.

3. Gummalla ACV, Limb JO. Wireless medium access control protocols. IEEE Communications Surveys, http://www.comsoc.org/pubs/surveys, 2nd Quarter 2000.

4. Prasad R, Ojanper.aa T. An overview of CDMA evolution towards wideband CDMA. IEEE CommunicationsSurveys, http://www.comsoc.org/pubs/surveys, 4th Quarter 1998.

5. Adachi F, Sawahashi M, Okawa K. Tree-structured generation of orthogonal spreading codes with different lengthsfor forward link of DS-CDMA mobile radio. Electronics Letters 1997; 33(1):27–28.

6. Edfors O, Sandell M, Beek J. Landstr.oom D. An introduction to orthogonal frequency division multiplexing.Technical Report, Division of Signal Processing, Lulea University of Technology, September 1996.

7. Peled A, Ruiz PM. Frequency domain data transmission using reduced computational complexity algorithms.Proceedings Of the IEEE International Conference on Acoustic, Speech, Signal Processing, Denver, 1980.

8. Hara S, Prasad R. Overview of multicarrier CDMA. IEEE Communications Magazine 1997; 35(12):126–133.9. Vanderdorpe L. Multitone direct sequence CDMA system in an indoor wireless environment. Proceedings Of the 1st

Symposium of Communications and Vehicular Technology in the Benelux, Delft, The Netherlands, October 1993:4.1 1–4.1 8.

10. Hughes Hartogs D. Ensemble modem structure for imperfect transmission media. US Patents NOS. 4,833,706.11. Bharghavan V. A new protocol for medium access in wireless packet networks. Publication of the Timely Group,

1997, http://timely.chrc.uiuc.edu/publications.html.12. Raphaeli D, Bassin E. A comparison between OFDM, single carrier and spread for high data rate PLC. Proceedings

of the 3rd International Symposium on Power Lines Communications and its Applications (ISPLC99), Lancaster, UK,March 1999.

13. Schulz W, Schwarze S. Comparison of CDMA and OFDM for data communications on the medium voltage powergrid. Proceedings of the 4th International Symposium on Power Lines Communications and its Applications(ISPLC00), Limerick, Ireland, April 2000.

AUTHORS’ BIOGRAPHIES

Romano Fantacci, born in Pistoia, Italy, graduated from the Engineering School ofthe Universit"aa di Firenze, Florence, Italy, with a degree in electronics in 1982. Hereceived his doctorate in telecommunications in 1987. After joining the Diparti-mento di Elettronica e Telecomunicazioni as a research fellow, he was appointed asassociate professor in 1991 and full professor in 1999. His current research interestsare digital communications, computer communications, queuing theory, satellitecommunication systems, and mobile communication networks. He has beeninvolved in several European Space Agency (ESA) and INTELSAT advancedresearch projects. He is the author of numerous articles published in prestigiouscommunication science journals. He received the IEE IERE Benefactor premium in1990 and IEEE COMSOC Award Distinguished contributions to satelliteCommunications in 2002. Professor Fantacci is currently serving as Editor forTelecommunication Systems and for IEEE Transactions on Communications.



Simone Morosi was born in Florence, Italy, in 1968. He received the Dr Ing. Degreein Electronics Engineering in 1996 and the PhD Degree in Information andTelecommunication Engineering in 2000 from the University of Florence, Florence.Since 2000 he has been with the Department of Electronics and Telecommunicationsof the University of Florence, as a Research Assistant. His present research interestsinvolve Code Division Multiple Access Communications. Multiuser Detection andTurbo MUD Techniques, Adaptive Antenna Array Systems, 3rd Generation MobileCommunications. He has participated to European Projects COST 252 and COST262 and he is currently participating to the EU COST Action 273. ‘Towards MobileBroadband Multimedia Networks’.



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Multicarrier spread spectrum techniques for downstream power-line communications on low voltage grid