2012 10-04 achaichia

Contributions to the Improvement

of Multiuser PLC Home networks

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Pierre ACHAICHIAPierre ACHAICHIAPierre ACHAICHIAPierre ACHAICHIA, October 12, Orange Labs Rennes

Orange Labs Supervisors

Marie Le BOT Pierre SIOHAN

Supélec Supervisor

Jacques PALICOT

1. Motivations & Objectives

2. HomePlug Specifications Overview

3. The HPAV Modulation Scheme PHYPHYPHYPHY

Outline

INTROINTROINTROINTRO

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4. Windowed OFDM vs OFDM/OQAM: Capacity Analysis

5. PLC Networks Multicast Issue

6. OFDMA for Point-to-Multipoint Transmissions

7. Conclusion

MACMACMACMAC

2 Pierre Achaichia - Contributions to the Improvement of Mulltiuser PLC Home Networks – 10/12/12

Motivations & Objectives

unrestricted 3 Pierre Achaichia - Contributions to the Improvement of Mulltiuser PLC Home Networks – 10/12/12

Motivations & Objectives

� Increased data rates offered to customers (FTTH), more and

more networking devices within the Home area, leading to:

– Increased Number of QoS demanding Services

– Heterogeneous traffic: services need to be prioritized

– Wi-Fi technology cannot answer all use cases: network coverage,

not necessarily appropriate to deliver QoS demanding applications

like IPTV…

Thesis Motivations


like IPTV…

� Powerline Communication (PLC) benefits:

– "No new wire" and easy to access network

– Quasi-static channels allowing fine link adaptation

– Increased home network coverage and reliability

– Low interference between neighboring networks

FTTH: Fiber To The Home

QoS: Quality of Service

IPTV: IP Television

Thesis Objectives

� At the PHY layer:

� Bandwidth extension up to 100 MHz

� Show benefits of the OFDM/OQAM modulation for

next-generation PLC networks

� Anticipate evolution of broadband PLC networks


� At the MAC layer:

� Identify lacks of current PLC standards (HPAV-based)

� Propose novel allocation techniques to improve

network efficiency in a multi user context

PHY: Physical

MAC: Medium Access Control

HomePlug


Specifications Overview

A Little Background…

� The home power grid is a harsh communication medium:

� Multi-path channels due to impedance mismatch, resulting

in reflection signals

� Quasi-static nature

� Severe attenuation, typically comprised between 20 and 60

dB


� Various interference sources:

• Colored background noise

• Impulsive noise sources: home appliances, such as hair

dryer, vacuum cleaner… � Error bursts

• Windowed OFDM modulation in the [1.8; 30]

MHz frequency range: 3072-point FTT size, 917

active subcarriers, up to 200 Mbps PHY rate

• Fine channel adaption through the definition of

tone maps (bit-loading) -> BPSK to 1024-QAM,

various FEC rates, GI…

• Beacon-based synchronization, controlled by a

CCo (Central Coordinator), providing scheduled

channel accesses (TDMA)

� HomePlug Specifications

Evolution of Broadband PLC Specifications

Capacity

• OFDM modulation in the [4; 21] MHz

frequency range

• CSMA/CA : Distributed and prioritized

channel Access, error detection and

• Uses HPAV as baseline technology

• Introduction of an ISP protocol to

handle dual-PHY

• Bandwidth extension up to 50 MHz

(4096-point FFT), possibility to use

4096-QAM

• Up to 500 Mbps PHY rate

� Bandwidth extension up to 86 MHz

(8192-point FFT), combined with

MIMO PLC

� Between 750 Mbps and 1.5 Gbps

PHY rates, fully compliant with

P1901 standard

1.5 1.5 1.5 1.5 GbpsGbpsGbpsGbps

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• Coexistence with HP 1.0 devices, but not

backward compatible!


OFDM: Orthogonal Frequency Division Multiplexing

CSMA/CA: Carrier Sense Multiple Access/Collision Avoidance

FFT: Fast Fourier Transform

BPSK: Binary Phase Shift Keying

QAM: Quadrature Amplitude Modulation

Years

channel Access, error detection and

Automatic Repeat Request (ARQ)

mechanisms

• Up to 14 Mbps PHY rate, further enhanced

by Intellon with the proprietary HP 1.0 turbo

• Up to 500 Mbps PHY rate

FEC: Forward Error Correction

TDMA: Time Division Multiple Access

IEEE: Institute of Electrical and Electronics Engineers

ISP: Inter System Protocol

MIMO: Multiple Input Multiple Output

14 14 14 14 MbpsMbpsMbpsMbps



2001: HP 1.02001: HP 1.02001: HP 1.02001: HP 1.0 2005: HPAV 12005: HPAV 12005: HPAV 12005: HPAV 1 2010: IEEE P19012010: IEEE P19012010: IEEE P19012010: IEEE P1901 2012: HPAV 22012: HPAV 22012: HPAV 22012: HPAV 2

The HPAV


Modulation Scheme

OFDM principles

� Multicarrier modulations are the appropriate answer to cope

with the multipath nature of PLC channels

Attenuation


ffffminminminmin ffffmaxmaxmaxmax Frequency

OFDM principles



– OFDM: Orthogonal Frequency Division Multiplexing


T0 (FFT Size)

tT0 (FFT Size)

t

ISI+ICI

t

CHANNELCHANNELCHANNELCHANNEL

ISI: Inter-symbol Interference

ICI: Inter-Carrier Interference

OFDM principles



– CP-OFDM: OFDM with Cyclic prefix


t

ISI+ICI

t

CHANNELCHANNELCHANNELCHANNEL

T0GI T0GI T0GI

t

T0GI T0GI T0GI

ISI+ICI free

GI: Guard Interval

OFDM principles

� CP-OFDM allows interference-free transmissions, thanks to the

addition of a guard interval (counterpart: losslosslossloss in the spectral in the spectral in the spectral in the spectral

efficiencyefficiencyefficiencyefficiency)

� HoweverHoweverHoweverHowever, PLC equipments must comply with a restrictive

spectral mask


Because of the bad spectral containment of the subcarriers,the

classic CPCPCPCP----OFDM OFDM OFDM OFDM scheme is not not not not suitedsuitedsuitedsuited for broadband PLC

The Windowed OFDM Modulation

� To improve the spectral containment of the subcarriers, HPAV

introduces a Windowed OFDM modulation scheme

Windowed OFDM Pulse-Shaped OFDM


� SameSameSameSame spectral efficiency as CP-OFDM:

RI: Roll-off Interval

The Windowed OFDM Modulation

� HoweverHoweverHoweverHowever,,,, looking at the receiver side:


� ProblemProblemProblemProblem: : : : in strongly dispersive channels, an interference term

remains present in the demodulated symbol

The effective protectioneffective protectioneffective protectioneffective protection against interference is reducedreducedreducedreduced in

proportion of the RI effective GI = GIeffective GI = GIeffective GI = GIeffective GI = GI----RIRIRIRI

remaining interference

Link Adapation

� Broadband PLC specifications allow to adapt the signal to the

transmission path, using bit-loading techniques:

Signal to Signal to Signal to Signal to InterferenceInterferenceInterferenceInterference plus Noise Ratioplus Noise Ratioplus Noise Ratioplus Noise Ratio

Noise variance

Complex QAM symbol

variance

ISI+ICI power

Channel Coefficient


SINR gap:

CapacityCapacityCapacityCapacity formulaformulaformulaformula

ToneToneToneTone mapmapmapmap

Ex: in HPAV,

SER: Symbol Error Rate


transmission path, using bit-loading techniques:

– Ex. : HPAV OFDM bit-loading (917 subcarriers, [1.8: 30] MHz)� Each tone map:

• is defined on a specific link

• is defined for a one-way communication

Link Adapation

Channel frequency response Dedicated Tone Map (TM)


Allows to approach the theoretical capacity of the channel

Windowed OFDM vs

OFDM/OQAM:


OFDM/OQAM:

Capacity Analysis

� OQAM: Offset Quadrature Amplitude Modulation

� Multicarrier Modulation with frequency spacing F0

� As classic OFDM systems, FFT-based implementation is

possible

� Main Main Main Main principleprincipleprincipleprinciple:

� The transmissions of the real and imaginary parts of the complex

The OFDM/OQAM Modulation

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� The transmissions of the real and imaginary parts of the complex

symbols cm,n are delayed of one half symbol duration T0/2

� The constraint is to keep a phase shift of π/2 between adjacent

symbols in time and frequency


T0 (FFT Size)

t

T0 (FFT Size)

t

Re{cm,n}

Im{cm,n}

ClassicClassicClassicClassic OFDMOFDMOFDMOFDM OFDM/OQAMOFDM/OQAMOFDM/OQAMOFDM/OQAM

real or imaginary part of cm,n

prototype filter Phase term

T0/2

� Main Main Main Main benefitsbenefitsbenefitsbenefits::::

� No GI � same spectral efficiency as OFDM without CP with

lower interference

� Relaxing the orthogonality constraint by only imposing it in the

real field gives an additional degree of freedom to shape

transmitted symbols

� For a distortion-free channel, the interference only affects the


unrestricted

� For a distortion-free channel, the interference only affects the

imaginary part of the symbols, and is therefore removed by the

real-part extraction

� For a realistic channel, it can be well contained if the prototype

filter is appropriately selected, and using a 3-tap (ASCET [Alhava et

al., 2001]) Zero Forcing (ZF) equalizer


ASCET: Adaptive Sine/Cosine-modulated filter bank Equalizer for Transmultiplexer

� How can we efficiently exploit the additional degree of freedom

offered by OQAM in the particular context of PLC?

� Ex.: comparison between a prototype filter optimized upon the

FS (Freq. Selectivity) criterion and the HPAV window



� How can we efficiently exploit the additional degree of freedom

offered by OQAM in the particular context of PLC?

� The association of OFDM/OQAM with frequency selective filters

allows to activate more than 917 subcarriers (windowed OFDM)

� FCC mask:

� windowed OFDM: 917 active subcarriers

OFDM/OQAM + FS4: 968 active subcarriers


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� OFDM/OQAM + FS4: 968 active subcarriers

� CENELEC mask (draft standard)

� windowed OFDM: [503, 767] active subcarriers

� OFDM/OQAM + FS4: [632, 871] active subcarriers


FCC: Federal Communications Commission

CENELEC: Comité Européen de Normalisation

� Simulation parameters for the capacity analysis:

� 3 classes of PLC channels (Class 2, 5 and 9) [Tlich et al., 2010]

with:

Capacity (class 9)>Capacity(class 5)>Capacity(class 2)

�100 channel realizations

� Colored background noise [Omega D3.2, 2010]

� Target SER=10-2

Windowed OFDM vs OFDM/OQAM: HPAV 1 Context

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� Target SER=10-2

� FCC spectral mask:

• 917 active subcarriers for windowed OFDM

• 968 active subcarriers for OFDM/OQAM

� ZF per-channel equalizers:

•1-tap for windowed OFDM

• 3-tap (ASCET) for OFDM/OQAM


� Some results on class 9 channels (transmitted PSD is

increased from -120 to -50 dBm/Hz ):


Transmission capacity

(infinite granularity)


Achievable throughput

(finite granularity)

PSD: Power Spectral Density

� How can we efficiently increase the capacity of PLC networks?

� Bandwidth extension: in the scope of OMEGA, simulations were

conducted in the [1,8: 87.5] MHz bandwidth (~AV2) (3072 � 8192-

point FFT)

� Enable higher modulation orders: the 4096-QAM (12 bits) is

allowed by AV 2

� Number of active subcarriers:


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� Number of active subcarriers:

• Windowed OFDM : 917 (HPAV) + 2428 = 3354

• OFDM/OQAM : 968 (HPAV) + 2440 = 3408



increased from -120 to -50/-80 dBm/Hz ):







� HPAV 1 context: a significant throughput gain can be achieved

by OFDM/OQAM using a frequency selective prototype filter,

together with a 3-tap equalizer (ASCET)

� Up to 20 % increase in the data rates using the FCC mask

� More than 40 % increase is shown considering the new

CENELEC mask (cf. dissertation)

� HPAV 2 context: The OMEGA project has shown that Next-

PHY Layer Contributions Summary

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� HPAV 2 context: The OMEGA project has shown that Next-

generation PLC networks(HPAV 2) could reach the Gbps

connectivity, thanks to the bandwidth extension (+MIMO)

� Main Contributions Main Contributions Main Contributions Main Contributions (cf. dissertation):

� Computation of the analytical expression of the interference term

of the Windowed OFDM signal

� Generalized expression of the OFDM/OQAM interference power,

analytical expression of the noise power at the output of ASCET


Multicast Issue in PLC


Networks

Multicast Issue


transmission path, using bit-loading techniques

� HoweverHoweverHoweverHowever, a problem arises if we want to simultaneously reach

several stations

Tone maps allow to approach the theoretical

capacity of the channel.


� HPAV / IEEE P1901: HPAV / IEEE P1901: HPAV / IEEE P1901: HPAV / IEEE P1901: Multicast/broadcast services must be

handled as multiple unicast streams (unicast conversion)

Stations are Stations are Stations are Stations are isolatedisolatedisolatedisolated fromfromfromfrom one one one one anotheranotheranotheranother

� Known solution: LCG (Lowest Channel gain)

� Computation of an equivalent channel among the K

stations to reach

� In PLC networks, LCG can be directly applied at the

transmitter side by computing a multicast tone map:

LCG Solution

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� Ex: K = 4 HPAV 2 tone maps


� Is LCG always better than the Unicast Conversion?

� From the PHY layer point of view: YES

• Study conducted for the HPAV TWG (measured PLC channels in 3 countries):

LCG Solution

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� HoweverHoweverHoweverHowever,,,, from the MAC layer point of view: not necessarily


HPAV TWG: HPAV Technical Working Group

� If we want each one of the K adressed stations to acknowledge

the Multicast transmission:

LCG Solution

LCG LCG LCG LCG cancancancan degradedegradedegradedegrade the MAC the MAC the MAC the MAC efficiencyefficiencyefficiencyefficiency

Unicast transmissionUnicast transmissionUnicast transmissionUnicast transmission

The transmission window

is limited to 2.5 ms


Unicast transmissionUnicast transmissionUnicast transmissionUnicast transmission

Multicast transmissionMulticast transmissionMulticast transmissionMulticast transmission

The K�1 additional ACK frames

must be taken into account

MAC MAC MAC MAC efficiencyefficiencyefficiencyefficiency decreasesdecreasesdecreasesdecreases as as as as K K K K increasesincreasesincreasesincreases

� IdeaIdeaIdeaIdea:

� Instead of defining a unique "multicast" tone map, the KKKK stations are

classified into NNNN multicast subsets

� Each multicast subset is associated with an exclusive multicast tone

map, contructed by applying the LCG principle among the tone maps

contained in the subset

� A tradeoff must be made between the number of simultaneously

Smart Merging Approach

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� A tradeoff must be made between the number of simultaneously

addressed stations and the transmission window length

� A smart merging algorithm has been developped (cf. manuscript),

considering both PHY and MAC layers:

� Assessing the correlation between tone maps before merging them

� Taking into account the reduction of the transmission window


� Multicast tone maps allow major improvement of the transmission

efficiency (cf. manuscript and the study conducted for the HPAV

TWG)

� HoweverHoweverHoweverHowever, special care must be taken when considering the MAC

overhead:

� If we want the K adressed stations to acknowledge the frame, the

transmission window is reduced

Multicast Summary

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transmission window is reduced

� The creation multiple multicast subsets may be more appropriate in

such a case

� Complementary studies need to be made to assess:

� The multiple overhead sources: frame headers, segmentation, inter-

frame spaces…

� The impact on system complexity and reactivity


OFDMA for

Point-to-Multipoint


Point-to-Multipoint

Transmissions

The Interest of Point-to-Multipoint

STA 3:

Bridge to

STA 1:

Bridge to set-

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�If More than 2 Stations in the network:

� Point-to-multipoint transmissions = Frequent use case


Bridge to

computer 1

Bridge to set-

top box 1

STA 0 (CCo):

Bridge to

Home GW

STA 2:

Bridge to set-

top box 2

Distant

Services

Home GW: Home Gateway

STA 3:

Bridge to

computer 1

STA 1:

Bridge to set-

top box 1

Taking advantage of the Multiuser Diversity


STA 2:

Bridge to set-

top box 2

Distant

Services

STA 0 (CCo):

Bridge to

Home GW

PLC channels have a multi-path nature, and are

quasi-static:

� Bit-loading algorithms result in the creation of

tone maps, specific to each link

Home GW: Home Gateway

Taking advantage of the Multiuser Diversity

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How can we take advantage of this multiuser diversity?

OFDMA:OFDMA:OFDMA:OFDMA: distribution of the M M M M subcarrierssubcarrierssubcarrierssubcarriers amongamongamongamong the K the K the K the K usersusersusersusers


OFDMA: Orthogonal Frequency Division Multiple Access

� If we apply the σ permutation s.t.:

increasesincreasesincreasesincreases on {1,..,M}

� How can we optimally orthogonalize tone maps?

� Ex.: K = 2K = 2K = 2K = 2 tone maps to orthogonalize

The Tone Maps Orthogonalization Problem

unrestricted

with:

and


� How can we optimally orthogonalize tone maps?

� K = 3 K = 3 K = 3 K = 3 ?


� Problem:

If K>2If K>2If K>2If K>2, Finding a concave capacity

region is far from being straightforward


� 2 solutions were developped:

� A low-cost, nearly-optimal algorithm: TMSA TMSA TMSA TMSA (Tone

Maps Splitting Algorithm)

�An optimal resolution based on a geometrical

approach of the problem

region is far from being straightforward

� Geometrical approach:

� Allocation Allocation Allocation Allocation vectorvectorvectorvector::::

� CapacityCapacityCapacityCapacity balance:balance:balance:balance:



The ToneToneToneTone mapsmapsmapsmaps orthogonalisationorthogonalisationorthogonalisationorthogonalisation problemproblemproblemproblem comes down to

maximizemaximizemaximizemaximize , a K-dimentionnal vector directeddirecteddirecteddirected by

FDM: Frequency Division Multiplexing

� Geometrical approach: K = 3

� Noticing that the projection of the optimal allocation vector onto

the plane P2 , defined by vectors and is colinear to

� Starting from K = 2:K = 2:K = 2:K = 2:


unrestricted

� We extend the problem to K = 3 K = 3 K = 3 K = 3 to create


Starting with the optimal allocation optimal allocation optimal allocation optimal allocation vectorvectorvectorvector between links 1links 1links 1links 1 and 2222,

MaximizingMaximizingMaximizingMaximizing comes down to reallocatereallocatereallocatereallocate subcarrierssubcarrierssubcarrierssubcarriers maximizingmaximizingmaximizingmaximizing the

componentcomponentcomponentcomponent along basis vector , while minimizingminimizingminimizingminimizing the the the the costcostcostcost on


� Intitialization:

� What is the loss on after allocating a capacity ε on link 3 ?




� Intitialization:

� What is the loss on after allocating a capacity ε on link 3 ?


unrestricted

� C2 increases with β2, while C1 decreases with β2

� By always choosing the subcarrier ensuring the

minimal loss on , we maximize


� Geometrical approach: K > 3

� For K = 4, we can establish the following

cost functions:


unrestricted

�with

� and


� Geometrical approach: K > 3

� From which we deduce a general expression of the cost

function, for any K > 3. In the plane PK�1, the cost on link n is

expressed as follows:


unrestricted

�with

� and


Point-to-Multipoint Summary

� The tone maps orthogonalization problem has been set and

solved using a geometrical approach

� HoweverHoweverHoweverHowever, this method remains too complex to be incorporated in

real PLC systems. A fast orthogonalization algorithm has been

then developed: the Tone Maps Splitting Algorithm (TMSA)

� TMSA has been integrated in a PLC network simulator, and we

have proposed an HPAV-compliant OFDMA access scheme:


have proposed an HPAV-compliant OFDMA access scheme:

� 20% to 30 % improvement of the data rates will generally be

achieved using OFDMA (P1901, saturated throughput)

� In future HPAV 2.0 systems, as the number of subcarriers will be

increased, so will be the multiuser diversity

� Better gains have to be expected in the future

Conclusion


Conclusion

� Main Contributions:Main Contributions:Main Contributions:Main Contributions:

� On the PHY layer: On the PHY layer: On the PHY layer: On the PHY layer:

• Within the OMEGA project, we have shown that PLC systems

could benefit from a substantial troughput gain, by increasing the

bandwidth (up to 87.5 MHz for OMEGA, 86 MHz for AV 2)

• HoweverHoweverHoweverHowever, another modulation scheme than windowed OFDM,

called OFDM/OQAM, can further enhanced this capacity

Conclusion


called OFDM/OQAM, can further enhanced this capacity

improvement

• Thanks to the assocation of OFDM/OQAM with prototype filters

optimized upon the FS criterion, it is possible to activate more

tones while still complying with the spectral mask

• Considering the CENELEC draft standard, the performance gap

between the two modulation schemes will be even more

important

� Main Contributions:Main Contributions:Main Contributions:Main Contributions:

� On the MAC layer: On the MAC layer: On the MAC layer: On the MAC layer:

• Since the release of the IEEE P1901 standard in 2010, the field

of broadband PLC has stabilized

• YetYetYetYet this thesis shows that current systems could still benefit

from significant improvement

�The multicast issue The multicast issue The multicast issue The multicast issue has been firstly adressed, where we

Conclusion


�The multicast issue The multicast issue The multicast issue The multicast issue has been firstly adressed, where we

have shown that the definition of multicast tone maps could

bring major improvement in the data rates

� PointPointPointPoint----totototo----multipoint multipoint multipoint multipoint transmissions have been then studied.

In this work, we emphasize on the fact that the fine link

adaptation could be better exploited by defining an OFDMA

access mode

Contributions

� Conference papers

– P. Achaichia, M. Le Bot, P. Siohan, "Windowed OFDM versus OFDM/OQAM: A

Transmission Capacity Comparison in the HomePlug AV Context," International

Symposium on Power Line Communications , ISPLC 2011, Udine, Italy, April

2011.

– P. Achaichia, M. Le Bot, P. Siohan, " An Efficient Technique for Merging

Transmissions in a Multicarrier Context ", IWCLD 2011, Rennes, France,

November 2011.


November 2011.

– P. Achaichia, M. Le Bot, P. Siohan, "Frequency Division Multiplexing Analysis for

Point-to-Multipoint Transmissions in Power Line Networks," International

Symposium on Power Line Communications , ISPLC 2011, Udine, Italy, April

2011.

– P. Achaichia, M. Le Bot, P. Siohan, " Point-to-Multipoint Communication in Power

Line Networks: A Novel FDM Access Method", ICC 2012, Ottawa, Canada, June

2012.

– P. Achaichia, M. Le Bot, P. Siohan, ``Impact of CENELEC Transmission Spectrum

Mask on Current PLC networks,'' to be submitted, 2012.

Contributions

� Journal papers

– P. Achaichia, M. Le Bot, P. Siohan, ``OFDM/OQAM: A Solution to Efficiently

Increase the Capacity of Future PLC Networks,'' Power Delivery, IEEE

Transactions on, vol. 26, no. 4, pp. 2443-2455, Oct. 2011.

– P. Achaichia, M. Le Bot, P. Siohan, ``Adrdessing the issue of FDM Resource

Allocation for Point-to-Multipoint Communication in PLC Networks'' to be submitted,

2012.


� Patents

– P. Achaichia, M. Le Bot, P. Siohan, ``Procédé de regroupement de stations pour

optimiser la diffusion d'un flux multicast/broadcast,'' 2011.

– P. Achaichia, M. Le Bot, P. Siohan, ``Procédé de distribution des sous-porteuses

d'un système multiporteuse entre différents liens de communication,'' 2011.

Contributions

� Technical Contributions

– A. Tonello, S. D'Alessandro, M. Antoniali, M. Biondi, F. Versolatto, A. Maiga, J.-Y.

Baudais, F. S. Muhammad, P. Siohan, M. L. Bot, H. Lin, P. Achaichia, G. Ndo, G.

Mijic, B. Cerato, S. Drakul, E. Viterbo et O. Isson, " Performance report of

optimized PHY algorithms ", rap. tech., projet OMEGA, June 2010.

– P. Achaichia, M. Le Bot, P. Siohan, "Multicast Tone Maps: Gains to Expect," HPAV

face-to-face meeting, Lannion, March 2012.


– P. Achaichia, M. Le Bot, P. Siohan, "FDM to Improve Point-to-Multipoint

Communications in Powerline Networks", HPAV face-to-face meeting, Lannion,

March 2012.

– P. Achaichia, M. Le Bot, P. Siohan and P.Pagani, "Multicast Tone Maps

Performance on Measured PLC Channels", HPAV TWG, April 2012.

– P. Achaichia, M. Le Bot, P. Siohan and P.Pagani, "Multicast Communications:

Practical Use Cases", HPAV TWG, May 2012.

Thank you.

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Questions?

2012 10-04 achaichia

Technology