smart grid communicationssite.iugaza.edu.ps/mtastal/files/sg_comm_2021-introzigbee.pdf · child...

Smart Grid Communications

By: Dr. Mohammed Taha El Astal

Email: [email protected]: 22/4/2021

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mailto:[email protected]

Acknowledgment

This presentation is prepared based on :

1. PPT of Course: Fundamentals of Smart Grid Design andAnalysis, that was prepared by eSCO: www.eAcademy.ps

2. Smart Grid Course, Topic 3, of Department of Electrical &Computer Engineering Texas Tech University

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http://www.eacademy.ps/

CONTENT

CONTENT

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2

NIST Conceptual Reference Model for Smart Grid

Smart Grid Technologies

• Overview, applications, & products

• Wireless channels & Packet structure • Device classes & addressing

• Routing (assignment)

2 ZigBee

• Collocation problem & Z-wave alternative

• Each domain involves its own actors and applications.

• Interactions across 7 Smart Grid Domains:

Texas Tech University

Composition of the Smart Grid


• Each domain involves its own actors and applications.

• Interactions across 7 Smart Grid Domains:



• Consumers:

• The end users of electricity.

• May also generate/store electricity.

• Traditionally: Residential, Commercial, and Industrial.

• Market:

• Participants in wholesale market: day‐ahead, hour‐ahead,...

• Involves prediction, bidding, auctions, …

• Service Providers:

• Organizations providing service to:

• Both utilities and consumers.

• ISPs, Cell Phone Companies, Aggregators,…

• Operations:

• Independent System Operators (ISOs)

• Regional Transmission Organization (RTOs)

• Bulk Generation:

• Major Power Plants.

• Transmission:

• Carriers of bulk electricity over long distances.

• Distribution:

• Distribution of electricity to (and from!)

consumers.

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NIST Model for Smart Grid Information Network

•There are two questions to answer:

✓ How can different smart grid entities exchange

messages?

✓ What kind of messages (and why) should they

exchange?


➢ Our focus in Topic 3 is on the first question.

•We want to learn which communication technologies may help.

Smart Grid communications?


• In particular, we cover these communications technologies:

Smart Meter

Aggregator

PLC IP WMN

ZigBee (Home Area Network)

Substations

Operation

Sensors

PLC IP/IEC


Smart Grid communications?


ZigBee


ZigBee

• ZigBee is a working group to promote IEEE 802.15.4 standard.


ZigBee

ZigBee Overview

• EEE 802.15 is for Wireless Personal Area Networking (WPAN)✓ 802.15.1: Bluetooth✓ 802.15.2: Co‐existence (e.g., with WLAN)✓ 802.15.3: High Rate WPAN via Ultra wideband (UWB)✓ 802.15.4: Low Rate

Low Power Consumption / Long Battery Life

Inexpensive!

802.16

WiMAX

802.11

WiFi

802.15

WPAN

Freq 2 – 11GHz 2.4GHz Varies

Range 31 miles 100 Meters 10 Meters

R 70 Mbps 11 - 110Mbps 20k – 55Mbps

Nodes Thousands Dozens Dozens

•WPAN vs WLAN/WiFi and WMAN/WiMax

* Data for 802.16a and 802.11a

ZigBee

ZigBee Overview

•Simpler and Less Expensive than Bluetooth

✓ Cost: One fourth of Bluetooth

✓ Complexity:▪ Complex ZigBee Nodes: 10% Code of a Bluetooth node

▪ Simple ZigBee Nodes: 2% Code of a Bluetooth node

ZigBee

ZigBee Application

• Automatic Notification: Call the owner if problem occurs.

• Door Control: When the door is locked, lights are turned off.

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ZigBee

ZigBee Building Solution

http://www.ti.com/

•Smart appliances can also communicate with smart meters.

• Example: They can obtain prices and adjust their load. (Demand Response topic)

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ZigBee

ZigBee Building Solution

http://www.ti.com/

•ZigBee solutions by Texas Instrument (TI) at different layers:

• Refer to TI’s ZigBee pages for more detail.

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ZigBee

ZigBee Products

http://www.ti.com/

ZigBee Protocol Stack

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• There are four layers in ZigBee Protocol Stack:

User Defined

ZigBee Alliance


IEEE 802.15.4

[DE: Data Entity, ME: Management Entity, SAP: Service Access Point]

http://www.zigbee.org/

• ZigBee devices may use different frequency bands:

PHYFrequency

Band

Channel

NumberingBit Rate

868 MHz 868 – 870 MHz 0 20 kb/s

915 MHz 902 – 928 MHz 1 - 10 40 kb/s

2.4 GHz 2.4 – 2.4835 GHz 11 - 26 250 kb/s

ZigBee

ZigBee Wireless Channel

• Frequency channels used by ZigBee devices:

868.3 MHz

Channel 0

Channels 1‐10

Channels 11‐26928 MHz902 MHz 5 MHz

2 MHz

2.4835 GHz

2.4 GHz

ZigBee

ZigBee Wireless Channel

868.3 MHz

Channel 0

Channels 1‐10

Channels 11‐26

928 MHz902 MHz

5 MHz

2 MHz

2.4835 GHz

2.4 GHz

• Some of the features for co‐existence at certain bands:

• Carrier Sense Multiple Access (CSMA)

• End‐to‐end ACK and Retransmission

• Built‐in Channel Scanning / Find Available Channels

ZigBee

ZigBee Packet Structure

• Packet Fields [specified by IEEE 802.15.4]:• Preamble: 32 bits for synchronization• Start of Packet Delimiter: 8 bits• PHY Header: 8 bits / indicates PSDU length, etc.• PSDU: 0 to 127 bytes of data

PreambleStart of

PacketDelimiter

PHYHeader

PHY Service Data Unit (PSDU)

6 Bytes 0‐127 Bytes

•Inside PSDU:

CRCLink Layer PDUPC ADDR DSN PC: Addressing Mode FlagsADDR: AddressDSN: Data Sequence NumberCRC: Cyclic Redundancy Check

•All Devices Have Address:

•Two‐bytes: We can have up to 65,536 nodes (Q: Why?)

•Addressing Modes:

•Star

• Peer‐to‐Peer

• Cluster Tree

Addressing Modes Depend on the Network Topology.

[We will see more on topologies…]


ZigBee

ZigBee Device Addressing

• ZigBee has two main Device Classes (in term of capabilities) :

1. Full Function Device (FFD)

✓ Available in any topology

✓ Can become a network coordinator

✓ Talks to any other device

2. Reduced Function Device (RFD)

✓ Limited to star topology

✓ Cannot become a network coordinator

✓ Talks to only a network coordinator

✓ Simpler Implementation & less power consumption

ZigBee

ZigBee Device Classes

• Each ZigBee network has one network coordinator.• It initiates network formation.• We need at least one Full Function Device. (Q: Why?)

• Other devices can be either FFD or RFD.

• FFDs that are not network coordinator act as routers.• Recall that RFDs only talk to the network coordinator.

in term of functionality

Q: Can we build a mesh topology with RFDs only?

ZigBee

ZigBee Network Topologies

ZigBee


Network Coordinator initiatesthe network formation.

ZigBee routers help expanding the network

We can form Tree Clusters.

ZigBee


• Each cluster has one FFD as its root.

• The root for the overall tree is the

network coordinator.

• They allow routing with minimum

overhead.

• The tree may span physically large

areas.

• In total, we can have 255 clusters of 254

nodes = 64,770 nodes.

ZigBee

ZigBee Addressing

• For each new node (i.e., associated device):

•A unique address is allocated by parent (router/coordinator)

•Recall that the parent can only be a FFD.

• The max number of devices that a parent can support = 32.

• Two types of addresses:

•Network Address: 16‐bit, only unique in this network

•Extended Address: 64‐bit, unique in all networks

ZigBee

ZigBee Addressing

•The following network attributes are important:

✓ nwkcMaxDepth:

•The maximum absolute depth allowed in this

network.

✓ nwkMaxDepth (Lm):

•The maximum absolute depth a particular device

can have.

✓ nwkMaxChildren (Cm):

•The maximum number of children a device is

allowed to have.

✓ nwkMaxRouters (Rm):

•The maximum number of routers a device can

have as children, and it set by the coordinator The network attributes for a

node/router with absolute depth d:

•These attributes let us compute:

✓ the function Cskip(d): Size of address block allocated by each parent at

depth d. A FFD parent withCskip(d) > 0 may accept

child devices.

• A parent assigns addresses to children based on whether the child is router

capable or not.

• Let Aparent denote the address of a parent at depth d.

ZigBee

ZigBee Addressing

Router Capable Child: [nth such child at depth d+1] • End‐Device Child: [mth suchchild at depth d+1]

• Note that each child needs an address.

• A router child also needs an address block for its future children.

• Overall Idea: Assure having unique addresses for all nodes.

ZigBee

ZigBee Addressing

• Example: Rm = 1, Cm = 2, and Lm = 3.

• Cskip(0) = 1 + 2 x (3 – 0 – 1) = 5• Cskip(1) = 1 + 2 x (3 – 1 – 1) = 3• Cskip(2) = 1 + 2 x (3 – 2 – 1) = 1

Block with 5 Addresses


ZigBee

ZigBee Addressing

• Consider addressing at the network coordinator with ANC = 0.

• Router Child:

Addr = 0 + 5 x 1 + 1 = 6• End‐device Child:

Block: 1…5


0

1 6

ZigBee

ZigBee Addressing

• At the router node at depth 1 with Aparent = 1.

• Router Child: Addr = 1 + 3 x (1 – 1) + 1 = 2Addr Block = 2 … 1 + 3 x 1 = 2 … 4

• End‐device Child:

Block: 1…5

Block: 2…4

0

1 6

2 5

Addr = 0 + 5 x (1 – 1) + 1 = 1Addr Block = 1 … 5 x 1 = 1 … 5

Addr = 1 + 3 x 1 + 1 = 5

• Example: Rm = 2, Cm = 4, and Lm = 3.

• Cskip(0) = (1 + 4 – 2 – 4 x 23‐0‐1) / (1‐2) = 13

• Cskip(1) =

• Cskip(2) =

ZigBee

ZigBee Addressing

Your Job: Choose the addresses and address blocks!

• Q: What if the topology is not complete?

• Q: What if the topology is not star? Does it affect addresses?

ZigBee

ZigBee Addressing

• This routing mechanism is particularly good for tree topologies.

• Although it works for other topologies as well.

• However, for more complex networks, ZigBeeuses:

• AODV: Ad‐hoc On‐demand DistanceVector

• Uses Bellman‐Ford (BF) Equation as a DV algorithm…

• But first it requires route discoveryon‐demand

ZigBee

ZigBee Addressing

• Based on initial slides of given in Moodle, explain the ZigBee

routing mechanism (deliverables : 15 minutes video)

ZigBee

ZigBee Routing

• In addition to medium access control:

• They should automatically avoid common channels.

Ref

:P. Y

iet

al.

• ZigBee and WiFi collocate at 2.4 GHz Frequency Band

ZigBee

ZigBee Collocation with WiFi

• ZigBee (or WiFi or both) should search for unused channels.

Ref

:P. Y

iet

al.

• ZigBee and WiFi collocate at 2.4 GHz Frequency Band

WiFi:

ZigBee:

(3 Orthogonal Channels)

ZigBee


• An Algorithm for ZigBee Channel Switching:

• PER: Packet Error Rate

• To be checked by End‐Device

• LQI: Link Quality Indicator

• To be checked by Router / Coordinator

• Strength of Received Packets

• From 0 to 255 [Strongest]

• ED: Energy Detection

• RSSI: Received Signal Strength Indicator

Ref

:P. Y

iet

al.

ZigBee


• Experimental Results by P. Yi et al. to obtain:

• Safe Distance

• Safe Offset Frequency

• WiFI Uplink and Downlink as source of interference on ZigBee:

Ref

:P. Y

iet

al.

PER vs Distance (Meter)

ZigBee


• At 7 MHz Frequency Offset, “Safe Distance” is 5 Meter.


Ref

:P. Y

iet

al.

ZigBee


• 8 MHz is “Safe Frequency Offset” regardless of Distance.

• We can do similar experiments for other technologies.

• One can also study ZigBee interference on WiFi [the reverse!].

Ref

:P. Y

iet

al.


ZigBee


• An alternative home area networking technology for ZigBee:

• To resolve ZigBee/WiFi collocation problem.

• Z‐Wave operates at around 900 MHz band

• It does not collocate with WiFi

• It may compete with some cordless telephones

ZigBee

Z-Wave

• Similar to ZigBee, Z‐Wave aims to build a “smart home”:

• A wireless HAN “ecosystem”

Z‐Wave appliances can participate in AMI, AMR, and Demand Response

ZigBee

Z-Wave

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