1. 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

2. 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

3. D Joint Transmission M Combiner PLC Link Wireless Link Frequency band
Transmitter side: send same info over PLC and wireless links
Receiver side:
combine received signals into one
Combiner D M
PLC Link
Wireless Link
Frequency band
3-500kHz
(unlicensed)
MHz
Introduction |PLC/Wireless Links| PLC/Wireless Combining| Wireless Receiver| Summary

4. Narrowband PLC Noise Dominant noise Caused by Modeled by
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
hτ(1)
hτ(2)
hτ(3)
AWGN
60%
30%
10%
Cyclo-
stationary
noise
N (0,1) 1 2 3 1 1 1
[Nassar et al., 2012]
Introduction |PLC/Wireless Links| PLC/Wireless Combining| Wireless Receiver| Summary

5. 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

6. Wireless Link Dominant noise Noise sources Noise model Channel Model
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

7. Combining Reception Combining Schemes Selection Combining Largest SNR
Saturated Metric Combining
Saturated log likelihood
Maximum Ratio Combining
Log likelihood ratio
[Lai, 2012]
Introduction |PLC/Wireless Links| PLC/Wireless Combining| Wireless Receiver| Summary

8. Combining Reception FFT (N) Cyclic Prefix Length Modulation
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

9. 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

10. Wireless Receiver Design
Parameter
Value
Channel
Multipath
Channel Model
Rayleigh
Channel Taps 6
Noise Model
AWGN, GMM
GMM Parameters
99% σw= 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

11. 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 ah & g
Interferer separation (find critical distance for victim receiver)
Link quality indicator for the IEEE g standard
Introduction |PLC/Wireless Links| PLC/Wireless Combining| Wireless Receiver| Summary

12. References
[1] M. Sayed and N. Al-Dhahir, “Narrowband-PLC/wireless diversity for smart grid communications,” Proc. IEEE Global Comm. Conf., Dec [2] H. Ferreira, Power Line Communications: Theory and Applications for Narrowband and Broadband Communications Over Power Lines, [3] K. F. Nieman, J. Lin, M. Nassar, K. Waheed, and B. L. Evans, “Cyclic spectral analysis of power line noise in the kHz band,” Proc. IEEE Int. Symp. On Power Line Comm. and Its Applications, [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 [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 [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 [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: [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 [9] S. W. Lai and G. G. Messier, “Using the wireless and PLC channel for diversity,” IEEE Trans. on Comm., Dec