Broadband MIMO Couplers Characterization and Comparison

Broadband MIMO CouplersCharacterization and Comparison

D. Righini and A. M. Tonello

University of Udine, ItalyInstitute of Networked and Embedded Systems

Alpen-Adria-Universitat Klagenfurt, Austria

Paris, October 10th 2016

Introduction Broadband MIMO coupling devices Tests Conclusion

Content

• Brief introduction and issues on PLC;

• Broadband MIMO coupling devices: requirements, circuit andmodel;

• Tests;

• Conclusion.

D. Righini and A. M. Tonello Broadband MIMO Couplers

2/19


Smart grid

PLC can exploit conductors and wires in several scenarios.

Scenarios

• High voltage (HV)

• Medium voltage (MV)

• Low voltage (LV)

• Direct current (DC)


3/19


Frequency standards and regulations

The diversity of grid and application domains to which PLC can beapplied has naturally led to a large ecosystem of specifications andstandards.

Useful classification

• Ultra-Narrowband PLC (UNB)

• Narrowband PLC (NB)

• Broadband PLC (BB)


4/19


PLC Medium

The primary characteristics are the high frequency selectivity andattenuation; these are due to multipath signal propagation causedby the presence of branches, unmatched loads and high frequencyselective low impedance loads.

Channels types

• SISO

• MIMO


5/19


Our research

We focus on the following scenario:

• Low voltage (LV);

• Broadband PLC (BB);

• MIMO channel.


6/19


Coupling Networks requirements

In MIMO PLC, appropriate coupling methods are necessary inorder to enable the effective injection of the signal through thePLC channel.Basically a coupling network is a high pass filter that rejects 50/60Hz AC mains and passes the modulated power line signal.

Main requirements

• Low insertion loss

• Sufficient attenuation of the mains frequency voltages

• Safety


7/19


MIMO channels

• According to the Kirchhoff’s laws, with the three conductorsof the power line network, two independent circuits areavailable. Thus, MIMO communication can be established;

• We have developed a flexible architecture that enable toswitch three configurations: star, triangle and T;


8/19


Coupler schematic

The behaviour of the electrical circuits considered for the MIMO couplersare studied with SPICE software and analytic models. Each couplerconfiguration S,∆,T can be divided into blocks labelled from A to E.


9/19


Coupler topologies

Characterization of the main used topologies.

Input/output configurations

• Star

• Triangle

• T

(a) (b) (c)


10/19


Coupler topologies

Multiple topologies in a single coupler

Taking advantage of six digital switches, we can realize all thetopologies configurations needed.

Configuration ON (0V) OFF (5V)Star Vsw4, Vsw5 Vsw1, Vsw2,

Vsw3, Vsw6Triangle Vsw1, Vsw2, Vsw4, Vsw5,

Vsw3 Vsw6T Vsw1, Vsw6 Vsw2, Vsw3,

Vsw4, Vsw5


11/19


Coupler transfer function

Analyses

In this example we take into account only the effects of the inputand output generators/loads configuration.

Example:triangle-triangle transfer function∣∣∣∣∣∣iaibic

∣∣∣∣∣∣ =N

D

∣∣∣∣∣∣E1E2E3

∣∣∣∣∣∣ (1)

∣∣∣∣∣∣SaSbSc

∣∣∣∣∣∣ =

∣∣∣∣∣∣iaZaibZbicZc

∣∣∣∣∣∣ (2)

N =

∣∣∣∣ ZbZc (Zs2+Zs3)+Zs2Zs3(Zb+Zc ) −(ZbZs1(Zc+Zs3)) −(Zc Zs1(Zb+Zs2))

ZaZs2(Zc+Zs3) −(ZaZc (Zs1+Zs3)+Zs1Zs3(Za+Zc )) Zc Zs2(Za+Zs1)

ZaZs3(Zb+Zs2) ZbZs3(Za+Zs1) −(ZaZb (Zs1+Zs2)+Zs1Zs2(Za+Zb )

∣∣∣∣

D =ZaZbZc (Zs1 + Zs2 + Zs3) + ZaZb(Zs1Zs3 + Zs2Zs3) + ZaZc (Zs1Zs2+

+Zs2Zs3) + ZbZc (Zs1Zs2 + Zs1Zs3) + Zs1Zs2Zs3(Za + Zb + Zc )


12/19


Coupler configurations comparison

• Fig. 1d: back-to-back coupler schematic with fictitious networkmodel;

• Fig. 1e: back-to-back coupler schematic with H network model;

(d)

(e)D. Righini and A. M. Tonello Broadband MIMO Couplers

13/19


Coupler configurations comparison

• Fig. 1f: back-to-back coupler comparison with fictitious networkmodel;

• Fig. 1g: back-to-back coupler comparison with H network model;

100

101

102

−30

−28

−26

−24

−22

−20

−18

−16

−14

−12

−10

f [MHz]

H [dB

]

Star−Star

Star−T

Star−Triangle

Triangle−Star

Triangle−Triangle

Triangle−T

T−Star

T−Triangle

T−T

(f)

100

101

102

−50

−45

−40

−35

−30

−25

−20

−15

f [MHz]

H [dB

]

Star−Star

Star−T

Star−Triangle

Triangle−Star

Triangle−Triangle

Triangle−T

T−Star

T−Triangle

T−T

(g)

The figures show the comparison between the 9 different coupler configurations under analysis.


14/19


Line impedance effect on coupler transfer function

Triangle-T configuration transfer functions using different lineimpedances

• The figure shows the magnitude of the transfer functions with thetriangle-T configuration using different line impedances in therange: from 30Ω to 1000Ω;

• The highest transfer functions magnitude corresponds to the 30Ωline impedance, whereas the lowest corresponds to the 1000Ω, witha variation of approximately 30dB.


15/19


Configuration comparison

0 50 100 150 200 250 300−80

−60

−40

−20

0

20

40

60

Za [Ω]

Pe

rce

nta

ge

va

ria

tio

n f

rom

th

e n

om

ina

l va

lue

Sa(Za)

Sb(Za)

Sc(Za)

• Profile of the percentage output variation from the nominal value of theoutput signals Sa, Sb, Sc ;

• We refer to the case when all the source impedances (Zs1 ,Zs2 ,Zs3) are50Ω and the load impedances (Zb ,Zc) are matched as the impedancenominal condition with the exception of Za.

• The Figure shows that a change of Za in the range from 0 Ω to 300 Ω,causes an output voltages variation up to 60% from their nominal values.


16/19


Coupler prototype

We realized a coupler that allows to verify the models describedpreviously.

50 100 150 200 250 300

−45

−40

−35

−30

−25

−20

−15

−10

−5

0

f [MHz]

|H| [d

B]

The graph shows an example of average channel transfer function measured with the realized couplers.


17/19


Final remarks

Conclusions

• We developed a model able to quickly represent the coupler behaviour asa function of the chosen components;

• Exploiting the model, we described the problems that affects the actualcoupler technology;

• Furthermore, we developed a PLC coupler that follows the modelcharacteristics;

• We used the coupler to measure real PLC channels in an officeenvironment, exploring the multiple configurations available.

Challenges and future direction

• Better analyse the PLC channel transfer function for high frequencies (upto 300 MHz);

• Improve the actual coupler design;

• Better investigate the effect of the line impedance mismatches.


18/19


Thank you!

For any further question:[email protected]


19/19

Documents

Broadband MIMO Couplers Characterization and Comparison