Communications in the
Smart Grid
Prof. Jerry Sobelman
University of Minnesota
Minneapolis, MN USA
Outline of the Talk
• Smart Grid Activities in the U.S.
• Power Line Communications Techniques
• Wireless Communications Techniques
2
North American Electric Grid
• Approximately 3,200 electric generation companies:
–
–
–
–
–
Investor-owned utilities
Federal power agencies
Rural electric cooperatives
State, municipal and provincial utilities
Independent power producers
• Approximately 17,000 power generation plants
– About 1,400 of these are large-scale plants (100 MW or greater)
• 20% are nuclear, regulated by the NRC
• 80% are non-nuclear, regulated by FERC
• 800 GW peak demand
• Serves 334 million people
Sources: NIST, DOE, NERC
3
North American Electric Grid – cont.
•
•
•
•
•
211,000 miles of high-voltage transmission lines.
6 million miles of distribution lines.
25,000 substations, 150 million electric power meters.
Per capita annual electricity usage of 13,000 kWh
In 2009, wind, solar and geothermal generation was
about 39 GW, which was less than 4 percent of the total
US generation.
• Projections of a 26% increase in energy usage in the US
between 2007 and 2030.
– This would require 260 GW increase in generation.
– Renewable generation sources will be a larger percentage of the
generation in the future, which requires a smarter grid.
Sources: NIST, DOE, NERC4
Ageing Infrastructure in the US
• More than 70% of the transmission lines and
transformers are at least 25 years.
• Half of U.S. coal plants are more than 40 years old.
• Average substation transformer age is more than 40
years old.
• More than 65% of the circuit breakers are at least 25
years old.
• About 30% of the installed generation and transmission
(G&T) equipment is near the end of useful life.
• Almost 50% of G&T assets will have to be replaced by
2030, at an estimated cost of 1.5-2 trillion USD.
Sources: NIST, Black and Veatch
5
Current US Electric Grid Structure
Source: NERC
6
US Generation Sources
Sources: NIST, DOE EIA, Brattle Group, 2007
7
Smart Grid (SG) ‐ Definition
• According to US Dept. of Energy (DOE), a SG is:
– An electrical delivery system:
• from point of generation to point of consumption
– Integrated with:
• Communication technology
• Information technology
– Having benefits of:
• Enhanced grid operations
• Customer services
• Environmental benefits
=> SG is the electric grid together with sensing,
communications, computation and control.
8
SG Characteristic Features
• Self-healing from power disturbance events.
• Enable active participation by consumers in
demand response (DR).
• Robust against physical and cyber attack.
• Provides enhanced power quality.
• Accommodates wide range of power generation
and storage options.
• Enables new products, services and markets.
• Optimizing assets and operating efficiently.
Ref: S. Roy, D. Nordell and S. S. Venkata, "Lines of Communication,", IEEE Power &
Energy Magazine, pp. 64-73, September/October, 2011.
9
University of Minnesota Smart Grid: Morris Campus Project
• Campus microgrid with
renewable generation,
net-zero carbon, energy
self-sufficient.
• 300,000 to 750,000 kWh
per month, with a
summer peak.
Ref: M. Amin and A. M. Giacomoni , "Playing in the
Smart Grid Sandbox to Achieve Zero Net Energy,"
IEEE Smart Grid Newsletter, Dec., 2011.
10
UM Morris Smart Grid – Cont.
• Renewable generation sources:
– Biomass gasification plant fueled by crop
residues from nearby farms.
– Solar thermal panels.
– Solar photovoltaic (PV) system.
– Two 1.65 MW wind turbines:
• Capable of meeting 70 – 100% of load demand.
• Excess generation sold back to the local utility
company.
Ref: M. Amin and A. M. Giacomoni , "Playing in the Smart Grid Sandbox to Achieve Zero
Net Energy," IEEE Smart Grid Newsletter, Dec., 2011.
11
University of Minnesota Smart Grid: UMore Park Residential Community
• 5,000 acres of land near Minneapolis.
• Will provide housing for 20,000-30,000
people.
• Will use combined heat/power generation,
i.e. waste heat is converted to steam and
used to heat buildings.
Ref: M. Amin, "Building and Testing Smart Systems in an All-New Clean-Slate Microgrid,"
IEEE Smart Grid Newsletter, Feb., 2012.
12
UM UMore Park SG Plans – cont.
• Houses and commercial buildings will have:
–
–
–
–
–
Smart meters with in-home energy-management
Programmable major appliances
Inverters to change DC from PV solar arrays to AC
Electric vehicle charging stations
Backup battery storage
• Added cost will be from $10,670 to $27,190 per
home.
Ref: M. Amin, "Building and Testing Smart Systems in an All-New Clean-Slate Microgrid,"
IEEE Smart Grid Newsletter, Feb., 2012.
13
SG Communications Infrastructure
Source: NIST
14
SG Communication
Bandwidth/Latency Requirements
Application
Bandwidth
Latency
Power quality monitoring
Low
Low
Distribution voltage control
Low
Low
Advanced metering
Medium
High
Protective relays
Low
Low
Demand response
Low
High
Broadband access
High
Low
Ref: S. Roy, D. Nordell and S. S. Venkata, "Lines of Communication,", IEEE
Power & Energy Magazine, pp. 64-73, September/October, 2011.
15
Variability of Renewables
• Inherently variable at multiple time scales:
– Year, season, day, hour, second.
• Forecasting helps by predicting wind velocity and solar flux.
• Currently, generation variability is added to load variability
– This means, increased reserves are needed in order to
handle exceptional conditions.
• In the future, dynamic control of demand by heating, air
conditioning, refrigeration, electric vehicle charging
rates/times, etc. may lower the reserve requirements.
• Also, aggregation of multiple renewable generators can
reduce their overall variability.
16
Wind Turbine Technology
Source: DOE
17
Wind Availability vs.
Load Demand Centers
Major Demand Center
High Wind Availability
Source: EPRI
18
Electric Vehicles (EVs) in the US
.
Tesla Model S Signature
(Source: Tesla Motors) Nissan LEAF (Source: Nissan) Chevrolet Volt (Source: General Motors) 19
EV Charging Times
Ref: A. Ipakchi and F. Albuyeh, "Grid of the Future," IEEE Power & Energy Magazine, pp.
4-14, March, 2009.
20
Advanced Metering Infrastructure (AMI)
• Two-way flow of information
between the customer and the
utility:
– From customer to utility: Information
on the energy consumption.
– From utility to customer: Real-time
pricing information, appliance control
information
• By 2020, 65 million homes are
projected to use AMI.
GridstreamTM PLC
Source: L+G
OpenWayTM CentronTM
Source: Itron
21
Projected Deployments of Smart Meters in the US (by state) in 2020
(>50% )
(<50% )
Source: The Edison Foundation
22
Outline of the Talk
• Smart Grid Activities in the U.S.
• Power Line Communications Techniques
• Wireless Communications Techniques
23
Power Line Communications (PLC)
• Uses existing power lines to transmit information.
– Attractive since the wired infrastructure is already in place.
– Difficulties due to noise and signal attenuation must be
addressed in order to achieve sufficient bandwidth and
reliability.
– Types of disturbances encountered include:
• Colored background noise
• Periodic and aperiodic impulsive noise
• Electromagnetic interference (EMI)
• Reflections due to mismatches at the transformers
Ref: S. Bavarian and L. Lampe, "Communications and access technologies for smart
grid," in Smart Grid Communications and Networking (E. Hossain et al, Eds.),
Cambridge, 2012.
24
FPGA‐based Channel Emulation
• Objective:
– Enable real-time emulation of a complete transmitter,
channel and receiver system using programmable
digital hardware components.
• Parameters:
– Packet length, data rate, channel model, noise
sources, interference sources, etc.
• Emulator updates channel model coefficients using
continuously computed random variables having certain
distributions at a minimum required rate.
Ref: Wen-Chih Kan and Gerald E. Sobelman, “Hardware Channel Model for Ultra
Wideband Systems,” Proceedings, IEEE International Conference on Field
Programmable Technology, pp. 297-300, 2006.
25
Wallace Gaussian Architecture
• Initial ROM contains precomputed 1024 Gaussians.
• Both RAMs are dual-ported to increase throughput.
• A pass from RAM0 to RAM1, or vice versa, needs 512 cycles
plus the latency of the orthogonal transform of the A matrix.
• Sum-of-squares (SoS) correction is a multiply/add
Ref: Wen-Chih Kan and Gerald E. Sobelman, “Hardware Channel Model for Ultra
Wideband Systems,” Proceedings, IEEE International Conference on Field
Programmable Technology, pp. 297-300, 2006.
26
Example: UWB Channel Emulation
Max. Freq.
(MHz)
Latency
(clocks)
FPGA Slices
Wallace Gaussian
125.471
1051
1629
Radix-4 SRT division
133.156
32
2250
Dijkstra SQRT
150.263
48
1038
Base-2 powering
135.117
14
1973
Channel model
simulator
80.186
1089
7747
Faster than the
required rate.
Ref: Wen-Chih Kan and Gerald E. Sobelman, “Hardware Channel Model for Ultra
Wideband Systems,” Proceedings, IEEE International Conference on Field
Programmable Technology, pp. 297-300, 2006.
27
Narrowband High Data Rate PLC
• Data rates from 10 Kbps to 1 Mbps.
• AMI, EVs and HAN applications:
– AMI: between smart meter and utility company.
– EVs: between the EV and EVSE (Electric Vehicle
Service Equipment) over charging cordset and
between the EV and the utility company.
– HAN: between smart meter and smart appliances.
• Several standards (PRIME, G3 PLC, ITU-T G.hnem
and IEEE P1901.2) are all based on OFDM.
Ref: D. P. Shaver, "Narrowband PLC Solutions for AMI Achieve Long Distance
Communications and Flexibility with Immediate Market Impact," IEEE International
Conference on Consumer Electronics, pp. 601-602, 2011.
28
Orthogonal Frequency Division Multiplexing (OFDM)
• OFDM is a multicarrier technology used in many
communications systems.
• Several adjacent frequencies ("subcarriers") are
used in such a way that a high data rate can be
sent through the channel.
• At the transmitter:
– Inverse Fast Fourier Transform (IFFT)
• At the receiver:
– Fast Fourier Transform (FFT)
29
An OFDM Signal
N subcarriers (also called "tones")
30
OFDM Baseband Transceiver
.
.
OFDM Transmitter:
Data
In
S/P
Symbol
Mapper
To
Channel
add
cyclic
prefix
IFFT
P/S
D/A
OFDM Receiver:
Data
Out
P/S
Demapper
Equalizer
FFT
S/P
remove
cyclic
prefix
From
Channel
A/D
31
Example FFT Signal Flow Graphs
Radix‐2
Mixed‐Radix 4‐4‐2
Mixed‐Radix 8‐4
.
x(0)
X(0)
x(1)
X(16)
x(2)
w0
X(8)
x(3)
w8
X(24)
w0
x(4)
X(4)
w4
x(5)
x(6)
x(7)
X(20)
w8
w0
w12
w8
w0
x(8)
X(28)
X(2)
w2
x(9)
X(12)
X(18)
x(10)
w4
w0
X(10)
x(11)
w6
w8
X(26)
x(12)
w8
w0
w10
w4
x(14)
w12
w8
w0
x(15)
w14
w12
w8
x(13)
x(16)
x(17)
X(6)
X(22)
w0
X(14)
X(30)
X(1)
w1
X(17)
x(18)
w2
w0
X(9)
x(19)
w3
w8
X(25)
x(20)
w4
w0
w5
w4
x(22)
w6
w8
w0
x(23)
w7
w12
w8
x(24)
w8
w0
x(25)
w9
w2
x(26)
w10
w4
w0
X(11)
w11
w6
w8
X(27)
x(28)
w12
w8
w0
x(29)
w13
w10
w4
x(30)
w14
w12
w8
w0
x(31)
w15
w14
w12
w8
x(21)
x(27)
X(5)
X(21)
X(13)
X(29)
X(3)
X(19)
X(7)
X(23)
X(15)
X(31)
32
Pipeline FFT Architectures
• Radix-2 Multi-path Delay Commutator (R2MDC)
.
• Radix-2 Single-path Delay Feedback (R2SDF)
• Mixed-Radix 4-4-2 Multi-path Delay Commutator (MRMDC)
33
Input Buffering and Time Multiplexing: Full Pipeline Utilization
• Input buffer holds up to two frames of data:
• One frame is loaded with new input data
• Other frame feeds the pipeline with previous block of data.
Ref: Kai-Chuan Chang, Gerald E. Sobelman, Ebrahim Saberinia and Ahmed H. Tewfik,
“Implementation of a Multi-band Pulsed-OFDM Transceiver,” Journal of VLSI Signal
Processing, Vol. 43, No. 1, pp. 73-88, April, 2006.
34
Interleaving for Robustness Against Burst Errors
• Example 1: A group of 150 bits using a 3x50 memory array:
• Example 2: A group of 50 bits using a 5x10 memory array:
• De-interleaving performs row/column operations in the
opposite order.
Ref: Kai‐Chuan Chang, Gerald E. Sobelman, Ebrahim Saberinia and Ahmed H. Tewfik, “Implementation of a Multi‐band Pulsed‐OFDM Transceiver,” Journal of VLSI Signal Processing, Vol. 43, No. 1, pp. 73‐88, April, 2006.
35
Convolutional Encoder for Forward Error Correction (FEC)
• Rate ½ nonsystematic convolutional encoder.
– Generator polynomials g0=1718 and 1338
– Constraint length equal to 7
Ref: Kai-Chuan Chang, Gerald E. Sobelman, Ebrahim Saberinia and Ahmed H. Tewfik,
“Implementation of a Multi-band Pulsed-OFDM Transceiver,” Journal of VLSI Signal
Processing, Vol. 43, No. 1, pp. 73-88, April, 2006.
36
Constellation Mapping
•
•
An IFFT operation can be implemented by combining an FFT module
with complex conjugation operations at the inputs and outputs of
the FFT.
In order to remove the required conjugating operation at the inputs
of the FFT, a modified mapping called QPSK* is used instead.
Ref: Kai-Chuan Chang, Gerald E. Sobelman, Ebrahim Saberinia and Ahmed H. Tewfik,
“Implementation of a Multi-band Pulsed-OFDM Transceiver,” Journal of VLSI Signal
Processing, Vol. 43, No. 1, pp. 73-88, April, 2006.
37
PLC Frequency Bands
• European Standard CENELEC 50065-1
– 3 kHz to 148.5 kHz low-frequency powerline
spectrum divided into 4 frequency bands.
• In the US, the spectrum between 10 kHz and
490 kHz is called the FCC (Federal
Communications Commission) band.
• G3 and PRIME are two OFDM-based standards
for PLC in these frequency bands.
– Typical data rate of 125 kb/s.
Ref: K. Razazian et al, "G3-PLC Field Trials in U.S. Distribution Grid: Initial Results and
Requirements," IEEE International Symposium on Power Line Communications and
Its Applications, pp. 153-158, 2011.
38
ITU‐T G.hnem Standard
• New standard for HDR NB-PLC.
• Applications to HAN, AMI and EVs.
• Communications including:
– Through the MV/LV transformer.
– Over MV lines.
– Over LV lines (both indoor and outdoor).
• Data rates up to 1 Mbps.
Ref: V. Oksman and J. Zhang, "G.hnem: The New ITU-T Standard on Narrowband PLC
Technology," IEEE Communications Magazine, pp. 36-44, December, 2011.
39
G.hnem Characteristics
• Physical layer (PHY):
– OFDM, QAM, convolutional and block coding,
interleaving
• Data link layer (DLL):
– CSMA/CA
• Network layer:
– IPv6 is the default
– Other protocols may be used
Ref: V. Oksman and J. Zhang, "G.hnem: The New ITU-T Standard on Narrowband PLC
Technology," IEEE Communications Magazine, pp. 36-44, December, 2011.
40
IEEE 1901.2 Standard
•
•
•
•
Similar goals and specifications as for G.hnem.
High Data Rate (HDR) NB-PLC, 10-500 kHz.
Data rates up to 500 kbps.
Incorporates three non-interoperable existing
standards into the PHY/MAC:
– G3 for 10-500 kHz
– G3 for CENELEC A
– PRIME for CENELEC A
Ref: http://standards.ieee.org/develop/project/1901.2.html
41
Outline of the Talk
• Smart Grid Activities in the U.S.
• Power Line Communications Techniques
• Wireless Communications Techniques
42
Wireless Communications Options
• Infrastructure independent of the power lines.
• Thus, it can continue operating (using batteries)
if the power line is cut.
• Choice of using either:
– Licensed frequency spectrum.
– Unlicensed frequency specturm (e.g., the ISM band).
• For SG applications, can use a wireless service
provider or else can create an independent,
private wireless network.
43
Point‐to‐Point (P2P) Topologies
• A dedicated wireless link, usually high-bandwidth, used
in backhaul applications. Typically uses line-of-sight
(LOS) microwave or free space optical (FSO) links.
• Microwave:
– up to 30 GHz: data rates of tens to hundreds of Mbps
– 60 GHz and 80 GHz: data rates of several Gbps
– Can be disrupted by weather conditions (e.g., rain).
• FSO:
– Range of 2-3 kilometers, data rates of hundreds of Mbps,
unlicensed operation, immunity to EMI.
– Can be disrupted by weather conditions.
Ref: S. Bavarian and L. Lampe, "Communications and access technologies for smart
grid," in Smart Grid Communications and Networking (E. Hossain et al, Eds.),
Cambridge, 2012.
44
Point‐to‐Multipoint (P2MP)
• An area is divided into cells, each cell has a
base station which can communicate with many
fixed or mobile units within the cell.
• Wireless P2MP may have link distances of up to
several kilometers and data rates up to
hundreds of Mbps.
• Public and private 3G or 4G cellular networks
are available.
Ref: S. Bavarian and L. Lampe, "Communications and access technologies for smart
grid," in Smart Grid Communications and Networking (E. Hossain et al, Eds.),
Cambridge, 2012.
45
Wireless Mesh Networks (WMNs)
• Central base stations are not used. Instead,
nodes configure their own links.
• Nodes send their own traffic and also relay traffic
from other nodes toward their destination.
• Routing algorithms are used to ensure that data
reaches its intended destination.
• Inherently reliable since there are multiple paths
from a source to a destination. In the event of a
node failure, traffic can use alternate routes.
Ref: S. Bavarian and L. Lampe, "Communications and access technologies for smart
grid," in Smart Grid Communications and Networking (E. Hossain et al, Eds.),
Cambridge, 2012.
46
Satellite Communications
• Geostationary Orbit (GEO): Placed over the equator,
appear to be at a fixed location from the earth. At a high
altitude (35,768 kilometers), which leads to large uplink
or downlink delay of approx. 0.25 secs.
• Middle Earth Orbit (MEO): At a lower altitude, moderate
link delays, used for navigation. An example is GPS.
• Low Earth Orbit (LEO): At a low altitude of 160-2000
kilometers, link delay similar to that of terrestrial wireless
links. Need a network of LEOs to maintain coverage.
Examples are the Globalstar and Iridium systems.
Lower throughput of 64 kbps for each channel, but
newer systems will have higher throughput.
Ref: S. Bavarian and L. Lampe, "Communications and access technologies for smart
grid," in Smart Grid Communications and Networking (E. Hossain et al, Eds.),
Cambridge, 2012.
47
Short‐Range Option: ZigBee
• PHY/MAC layers are based on IEEE 802.15.4.
• Uses the unlicensed ISM frequency bands:
– In Europe:
– In US/Australia:
– Worldwide:
868 MHz at a 20 kbps data rate
915 MHz at a 40 kbps data rate
2.4 GHz at a 250 kbps data rate
• Short communication range of 10-100 meters.
• Supports tree and mesh network topologies.
• Widely used to communicate with smart meters.
Ref: S. Bavarian and L. Lampe, "Communications and access technologies for smart
grid," in Smart Grid Communications and Networking (E. Hossain et al, Eds.),
Cambridge, 2012.
48
Short‐Range Option: WiFi
• The SG can utilize existing and pervasive WiFi
(IEEE 802.11) networks, especially at customer
locations.
• However, WiFi is optimized for high throughput, not
low power.
• Thus it is not well-suited for distributed sensor and
actuator nodes.
• A variation known as embedded WiFi is designed to
address this by optimizing the transceivers for lowpower through the aggressive use of a very low
power stand-by mode.
49
Long‐Range Option: WiMAX
• Based on the IEEE 802.16 standards for fixed and
mobile applications.
• Data rates above 100 Mbps, latency of 10-50 ms.
• Long range of tens of kilometers is possible.
• Orthogonal frequency-division multiple access
(OFDMA) is used for both uplink and downlink.
• Used as a wireless backhaul in SG networks, and
can also be used to connect smart meters.
50
Long‐Range Option: LTE
• 3GPP Long Term Evolution (LTE) systems have high
bandwidth and potentially low latency. However, it was
designed and optimized for voice, not SG traffic.
• Experiments have shown that the latency in an LTE
system ranges from 15-25 ms, but some SG applications
may require a latency under 10 ms.
• A possible solution is to implement a new SG real-time
scheduler (i.e., resource scheduler) for LTE that can
meet the latency requirement. A study has shown that
this is achievable.
Ref: Y. Xu and C. Fischione, "Real-Time Scheduling in LTE for Smart Grids," 5th
International Symposium on Communications, Control and Signal Processing, 2012.
51
MIMO (Multiple Antenna) Systems
• MIMO: Multiple-Input Multiple-Output
⎡ y1 ⎤ ⎡ h11
⎢ y ⎥ = ⎢h
⎢ 2 ⎥ ⎢ 21
⎢⎣ y 3 ⎥⎦ ⎢⎣ h 31
h12
h 22
h 32
h13 ⎤ ⎡ x1 ⎤ ⎡ z1 ⎤
h 23 ⎥⎥ ⎢⎢ x 2 ⎥⎥ + ⎢⎢z 2 ⎥⎥
h 33 ⎥⎦ ⎢⎣ x 3 ⎥⎦ ⎢⎣ z 3 ⎥⎦
y = Hx + z
● Multiplexing gain (capacity gain)
ƒ increasing data rates
ƒ transmitting different data streams on different antennas
●
Diversity gain
ƒ improving performance
ƒ combining paths to obtain a robust channel
52
General MIMO System Model
• Consider a system with Mt transmitting antennas and Mr
z
receiving antennas:
1
h11
y1
x1
h21
z2
y2
x2
hM r 1
zM r
xM t
yM r
• Compared to the channel capacity of a SISO system:
C = log 2 (1 + SNR) bps/Hz
the capacity of the MIMO system can be increased by a
factor of:
min(M t , M r )
53
•
MIMO‐OFDM
We can achieve the benefits of both OFDM and MIMO by
combining them together in a system design:
– At the transmitter:
• Use a MIMO encoder to create multiple data streams
• Modulate each stream using OFDM and send each one to
a separate transmitting antenna.
– At the receiver:
• Send the received information at each receiving antenna
to a separate OFDM demodulator.
• Send all of the demodulated data to a MIMO detector.
– Can also use channel encoding and decoding to improve BER
performance.
OFDM
mod.
MIMO
encoder
OFDM
mod.
...
...
channel
encoder
OFDM
demod.
MIMO
detector
OFDM
demod.
channel
decoder
54
Cognitive Radio (CR)
• Consider two kinds of users:
– Licensed users (also called primary users).
– Unlicensed users (also called secondary users).
• In any given location at any given time, there may be no
active licensed users who are transmitting.
• The unused frequencies in that local area are called
"white space."
• An unlicensed user in that same local area can
temporarily use the white space without causing harm to
any primary user. This concept is called "overlay."
55
Overlay Example
• Unused frequencies between signals are white space
which secondary users may use.
signal strength
white space
frequency
56
Noise Floor and Underlay
• A very wideband signal, e.g. Ultra Wideband (UWB), just
slightly increases the noise floor, providing another kind of
opportunity for secondary users, which is called underlay.
signal strength
noise floor
UWB underlay
frequency
57
Cognitive Radio Cycle of Operation
• Basic CR cycle:
– Observe:
– Decide:
– Act:
Observe the environment.
Make decisions about what to do.
Implement those decisions.
• The above 3-step process is repeated
constantly so that the CR system
dynamically adapts itself according to the
current situation.
Ref: Essentials of Cognitive Radio, Linda E. Doyle, Cambridge University Press, 2009.
58
Long‐Range Option: IEEE 802.22
• Make use of unused TV bands in rural areas to create a
Wireless Regional Area Network (WRAN) for SG
backhaul data traffic.
• IEEE 802.22 is a cognitive radio based approach for
secondary users to utilize temporarily unused radio
specturm in a local geographic area.
– Must not interfere with the primary licensed users if/when they
begin transmitting again.
• Key issue to be addressed: Need to ensure that timecritical SG data can be received within the framework of
the cognitive radio sensing cycle.
Ref: R. Ma et al, "Smart Grid Communication: Its Challenges and Opportunities," to
appear in IEEE Trans. on Smart Grid, 2013.
59
CR Architectures for the Smart Grid
• Two system architectures are possible:
– Stand-alone architecture for rural areas:
• Provide broadband access for widely separated
customer locations.
– Secondary CR architecture for urban areas:
• Support high volumes of non-critical data
• Serve as a backup system in case of an
emergency.
Ref: A. Ghassemi et al, "Cognitive Radio for Smart Grid Communications," First IEEE
International Conference on Smart Grid Communications, pp. 297-302, 2010.
Spectrum Sensing
• The CR needs to determine if primary users are
active in various frequency bands at its location.
• Methods for spectrum sensing include:
– Energy Detection:
• Try to detect if energy exists at any of the
frequencies of interest.
– Feature Detection:
• Try to identify features of known types of
wireless transmissions (e.g., modulation
type, periodic behaviors, etc.)
Ref: Essentials of Cognitive Radio, Linda E. Doyle, Cambridge University Press, 2009.
61
False Positives & Missed Detections
• There are two kinds of mistakes that can be made:
– False Positive:
• We think that a primary user is present when, in fact,
there is no primary user transmitting.
• This will not cause any harm to the primary user but
it will lead to wasted spectrum that could have been
used.
– Missed Detection:
• We think that no primary user is present when, in
fact, a primary user is transmitting.
• This will cause harm to the primary user when the
secondary user starts transmitting.
Ref: Essentials of Cognitive Radio, Linda E. Doyle, Cambridge University Press, 2009.
62
SDR Structures for Cognitive Radio
• Cognitive Radio requires dynamic reconfiguration
of baseband processing functions to customize
various characteristics, such as
– Constellation types and sizes
– Throughput rates
– Scrambling, coding, etc.
• Software Defined Radio (SDR) structures can be
used to tailor the data paths in order to flexibly
meet the above requirements at any given time.
Ref: Wenqing Lu, Shuang Zhao, Xiaofang Zhou, Junyan Ren and Gerald E. Sobelman, "Reconfigurable
Baseband Processing Architecture for Communication," IET Computers & Digital Techniques, Vol. 5,
No. 1, pp. 63-72, January, 2011.
63
Reconfigurable SDR Architecture
.
64
VLIW Instruction Format
. 65
Varieties of RCEU Slice Structures
.
66
Summary and Future Outlook
• The Smart Grid presents a large set of applications for
both wired and wireless communications techniques.
• An array of sensors and smart meters collect grid data,
and an array of actuators implement control commands.
• Machine-to-machine (M2M) communications among
potentially billions of devices worldwide, perhaps even
more than the number of mobile handsets.
• The Smart Grid will form a large part of the future
"Internet of Things."
• Security safeguards will also play an important role.
Thank You!