Design Tradeoffs In Joint Powerline
and Wireless Transmission For
Smart Grid Communications
Ghadi Sebaali and Brian L. Evans
Department of Electrical and Computer Engineering
Wireless Networking and Communications Group
The University of Texas at Austin
Collaboration with Prof. Naofal Al-Dhahir and Mr. Mostafa Sayed at UT Dallas
Support from National Instruments, and Semiconductor Research Corporation with
liaisons Freescale Semiconductor and Texas Instruments
1
Smart Grid Communications
Impairments
Channel distortion and time-varying gain
Impulsive and thermal noise, and external interference
Goal
Increase reliability
Approach
Jointly transmit over PLC and wireless channels
Contributions
Review channel modeling
Review of noise modeling
Explore design tradeoffs
Explore noise mitigation techniques
[MaRS Market Insights, 2012]
Introduction |PLC/Wireless Links| PLC/Wireless Combining| Wireless Receiver| Summary
2
Combiner
Joint Transmission
M
Transmitter
side:
send same info over
PLC and wireless links
Frequency
band
D
Receiver side:
combine received
signals into one
PLC Link
Wireless Link
3-500kHz
(unlicensed)
902-928MHz
(unlicensed)
Introduction |PLC/Wireless Links| PLC/Wireless Combining| Wireless Receiver| Summary
3
Narrowband PLC Noise
Dominant noise
Cyclostationary impulsive noise
in time and frequency with
T = half AC power cycle
Caused by
Switching mode power supplies
Non-linear electronic devices
Broadcast stations
Modeled by
Linear periodically time-varying
system
AWGN
N (0,1)
11 12 13
60%
hτ(1)
30%
hτ(2)
Cyclostationary
noise
10%
hτ(3)
[Nassar et al., 2012]
Introduction |PLC/Wireless Links| PLC/Wireless Combining| Wireless Receiver| Summary
4
Narrowband PLC Channel
Multi-path model
Parameters: delay, attenuation, total
number of paths, etc.
Drawback: doesn’t capture topology
of channel
Transmission-line model
Parameters: ABCD parameters
Drawback: assumes topology is known
Statistical model
Extends transmission-line model
Accounts for multipath effects due
to branches, impedance mismatch
[Ferreira, 2010]
Introduction |PLC/Wireless Links| PLC/Wireless Combining| Wireless Receiver| Summary
5
Wireless Link
Dominant noise
Uncoordinated impulsive noise
Noise sources
Uncoordinated transmissions
Non interoperable devices
Neighboring devices
Noise model
Gaussian Mixture Model (GMM)
Channel Model
Rayleigh Fading
[Interference Mitigation Toolbox, UT Austin]
Introduction |PLC/Wireless Links| PLC/Wireless Combining| Wireless Receiver| Summary
6
Combining Reception
[Lai, 2012]
Combining Schemes
Selection
Combining
Largest SNR
Saturated Metric
Combining
Saturated log likelihood
Maximum Ratio
Combining
Log likelihood ratio
Introduction |PLC/Wireless Links| PLC/Wireless Combining| Wireless Receiver| Summary
7
Combining Reception
Combining Schemes for a 5-path channel model
Combining Schemes for a 20-path channel model
FFT
(N)
Cyclic Prefix Length Modulation Number of Paths Combining Scheme
128
26
BPSK
5,20
Saturated Metric
Selection
Maximal Ratio
Introduction |PLC/Wireless Links| PLC/Wireless Combining| Wireless Receiver| Summary
8
Wireless Receiver Design
Zero Forcing: detects signal by
inverting channel matrix
Minimum Mean Square Error: ranks
received signals based on their SNR
Maximum Likelihood: chooses symbol
with least Euclidean Distance for
decoding and cancellation
[Miridakis, 2013]
Introduction |PLC/Wireless Links| PLC/Wireless Combining| Wireless Receiver| Summary
9
Wireless Receiver Design
Parameter
Value
Channel
Multipath
Channel
Model
Rayleigh
Channel Taps
6
Noise Model
AWGN, GMM
GMM
Parameters
99% σw= 0.001 and
1% σw= 100
Successive
Interference
Cancellation
Techniques
Zero Forcing
Min. Mean Squared Error
Maximum Likelihood
Introduction |PLC/Wireless Links| PLC/Wireless Combining| Wireless Receiver| Summary
10
Summary
Increased reliability via joint PLC/wireless transmission
Recommendations
Maximal ratio combining for PLC/wireless links
Zero-forcing to mitigate wireless interference
Future work
Coexistence in 900 MHz band between IEEE 802.11ah & 802.15.4g
Interferer separation (find critical distance for victim receiver)
Link quality indicator for the IEEE 802.15.4g standard
Introduction |PLC/Wireless Links| PLC/Wireless Combining| Wireless Receiver| Summary
11
References
[1] M. Sayed and N. Al-Dhahir, “Narrowband-PLC/wireless diversity for smart grid communications,” Proc. IEEE
Global Comm. Conf., Dec. 2014.
[2] H. Ferreira, Power Line Communications: Theory and Applications for Narrowband and Broadband
Communications Over Power Lines, 2010.
[3] K. F. Nieman, J. Lin, M. Nassar, K. Waheed, and B. L. Evans, “Cyclic spectral analysis of power line noise in
the 3-200 kHz band,” Proc. IEEE Int. Symp. On Power Line Comm. and Its Applications, 2013.
[4] M. Nassar, K. Gulati, Y. Mortazavi, and B.L.Evans, “Statistical modeling of asynchronous impulsive noise in
powerline communication networks,” Proc. IEEE Global Comm. Conf., Dec. 2011.
[5] M. Nassar, B. L. Evans, and P. Schniter, “A factor graph approach to joint OFDM channel estimation and
decoding in impulsive noise environments,” IEEE Trans. Signal Proc., vol. 62, no. 6, Mar. 2014.
[6] M. Nassar, A. Dabak, I. H. Kim, T. Pande, and B. L. Evans, “Cyclo- stationary noise modeling in narrowband
powerline communication for smart grid applications,” Proc. IEEE Int. Conf. Acoustics, Speech, and
Signal Proc., Mar. 2012.
[7] K. Gulati, M. Nassar, A. Chopra, N. B. Okafor, M. DeYoung, and B. L. Evans. (2011, Apr.) UT Austin
Interference Modeling and Mitigation Toolbox. [Online].
Available: http://users.ece.utexas.edu/~bevans/projects/rfi/software/
[8] N. Miridakis and D. Vergados, “A survey on the successive interference cancellation performance for
single-antenna and multiple-antenna OFDM systems,” IEEE Comm. Surveys & Tutorials, vol. 15, no.
1, Feb. 2013.
[9] S. W. Lai and G. G. Messier, “Using the wireless and PLC channel for diversity,” IEEE Trans. on Comm., Dec.
2012.