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Chapter 5

Smart Grid and Advance Metering

Infrastructure

This chapter presents technical review of smart grid as a case study of

application involving remote data access. Smart grid, a major paradigm

shift in electrical power system, is introduced and its scopes are

identified. Architecture and major functionalities of advance metering

infrastructure (AMI) from the point of view of data communication in

smart grid is discussed. This is followed by detailed review of

DLMS/COSEM standards that are adopted as open protocol standard

for communication in AMI. Last section of the chapter presents

discussion on communication technologies to be used in AMI. Various

challenges to be faced by communication networks in AMI are studied

and possible technology options are evaluated.

Traditionally an electrical power system consist of remote and centralized

large capacity power plant for generating power, long high-voltage

transmission lines for transmitting power from generating stations to load

centers and distribution networks for supplying power from load centers to

consumers. This design of power system, popularly called as grid, is

supported with additional infrastructure for monitoring and controlling various

parameters of grid with an aim to improve its reliability and efficiency. By time

technology in this grid has improved but not significantly. Today when world is

moving in a new era of energy consciousness, power system utilities are

facing unprecedented challenges with its infrastructure in current form.

Growing demands of high-quality power and improved grid reliability, pressing

need of alternative source of power generation, stringent regulations,

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environmental concerns and rising customer’s expectations have forced

utilities to rethink and move towards a better grid structure. Driven by these

leading utilities, technology vendors and government organizations worldwide

have started their efforts towards improved energy delivery system popularly

called as smart grid. Smart grid is a multi-faceted solution to the challenges

faced by conventional power system. It represents a shift towards a more

flexible grid topology that

encourages two-way power flow between the grid and small-scale

distributed power generating resources

encourages increased flow of information between all entities that are

part of grid for better observability and control

encourages increased cooperation between consumers and utilities to

reduce peak loads and optimize load flow

encourages optimized use of resources at high efficiency rendering

cost effective operation.

In simple terms, smart grid represents a dynamic network (similar to internet)

that has all small and big grid entities of generation, transmission and

distribution infrastructure, right from generators to end consumers, tied

together. With use of advanced information and communication technologies

(ICT) and automation systems these entities on the grid will be able to

communicate within and dynamically manage power flow, thereby rendering

more efficient, reliable and transparent power system.

To achieve these goals, compared to the infrastructure of existing

power system grid, smart grid will have few more additional components as

listed below.

1. New grid components related to energy generation and storage of

different capacities. For example distributed and small scale energy

generators like solar photovoltaic cells, domestic and industrial energy

storage units, etc

2. Sensing and controlling devices that will be responsible for gathering

and forwarding information from the physical layer (load end) to central

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system and also executing desired functionality on basis of control

commands received. For example, intelligent energy monitoring

devices, smart meters etc.

3. Communication infrastructure that will be responsible for transferring

massive amount of information over varying distances over the

network.

4. Automation and IT backend in terms of high-end servers, middle ware,

data storage and data management systems to process and manage

data coming from grid.

5. Advance analytic applications that allow utilities i.e. grid operators and

business executives, to analyze and extract useful information from

grid as required.

Thus, smart grid is a multi-domain project and has opened up directions of

research in all domains of engineering. One of the major domains from these

is ICT and automation system that is considered as a back bone of smart grid.

This is popularly refereed as Advance Metering Infrastructure (AMI). Details of

AMI including its functionality, architecture as well as possible technology

solutions are discussed in following part of this chapter.

5.1 AMI system architecture and components

AMI is a collective term to describe the whole infrastructure and applications

of smart grid related to communication and system automation. This includes

infrastructure like smart meters, communication links and central control

centers and also applications for gathering, transferring and analyzing energy

related information in real time. In the present section architecture of AMI and

its primary functionality are discussed.

5.1.1 AMI architecture

Typical architecture referring main components of AMI is shown in Figure 5.1

and discussed as follows [79].

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Figure 5.1: AMI architecture.

Electricity meter and communication hub

This element of AMI is generally present at consumer premises and is also

referred as smart meters. It performs two basic functions [80]. First is to

measure and record electrical energy consumed and/or produced along with

other energy related information like load profile, power quality analysis, etc.

and to provide information to consumer like energy usage, billing details,

prepayment options, tariff tables, etc. Second function is to act as a

communication hub providing communication interface between in-house

network (called Home area network) and external AMI network. There can be

more than one form in which this element may exist. In new installations a

single smart meter performing both the functions of metering and

communication can be used. In existing installations where already an

electricity meter capable of satisfying metering needs of AMI exist, an add-on

module that acts as a communication hub can be used. Smart meter or

communication hub, used as an add-on unit, is an intelligent device that is

capable of data processing, data storage and data communication.

Smart meter or add-on communication hub may be directly connected

to the central system or may be connected through data concentrator unit

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(DCU). In either of the cases, communication hub operates primarily as a

proxy gateway. Communication hub buffers the periodic data received from

connected devices of HAN and forwards it to higher level on demand or as

scheduled. Similarly, commands received from higher level are buffered

before being delivered to connected device. This mode of working is also

necessary as most of the devices of HAN are generally battery operated and

hence their always on status may not be always possible. Communication hub

may also have a facility of local interface. This facilitates local operation and

maintenance (O&M) of smart meter.

Data Concentrator Unit

This element of AMI acts as an intermediate element between smart meter

and central system. Smart meter being the tail element of the network present

at consumer premises it is less likely to be directly connected to the central

system. Generally number of smart meters present in a neighboring area

communicates to central system through a DCU. Thus DCU is identified as an

element of NAN. It is an intelligent device with primary function of managing

two way data exchange. It will collect and manage information received from

various smart meters and forward it to central system and also transfer

commands or information received from central system to smart meters.

Some of the typical functions that a DCU may perform are as follows [81].

Automatically discover meters, other grid devices and topology

changes giving exact picture of asset location to central system.

Collect data from each meter connected and report to central system.

Data may include information like energy consumption, load profiles

and power quality measurements.

Monitor and report tampering.

Uploads tariff tables and configuration settings to smart meters and

other grid devices as received from central system.

Broadcast information like demand response and load shedding to

inform consumers.

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Central system and Legacy system

Central system acts as a central server responsible for management of all

information and data related to smart metering. It is also responsible for the

configuration and control of all system components and responding to all

events and alarms over the network. It is possible that central system may

delegate part of its operation to DCU or smart meter so that some operations

may be performed locally at lower level of network structure. This is generally

referred as distributed computing and control.

Legacy system represents the commercial or technical system of the

grid operator. It is responsible for the management of business processes

such as meter registrations, remote meter reading, tariff adjustments, remote

connect/disconnect, billing, outage managements, customer care, etc. Legacy

system is purely to support operational and business processes and operates

independent of type metering infrastructure and communication technologies

involved in the network. Central system will execute the received request from

the legacy system over the network and also conveys back the response

received from meters thus completing the business process.

Local operation and maintenance (O&M) devices and External devices

Local O & M devices are portable devices that may be used by system

operators to locally configure, operate and maintain various elements over the

network. This is particularly useful at the time of installations and later to

perform maintenance or reconfiguration if not possible remotely by central

system. This facility may also help to retrieve meter data as redundant

measure in case of sustained communication failure.

External devices refer to auxiliary equipments that may be optionally

connected to the DCU and utilizes network facilities to support objectives of

AMI. For example this may include electrical substation automation system

like SCADA. These devices measure and monitor data over the power system

and relay this information to concerned entities. For example, in case of

temporary overloading of a particular power feeder in a substation, the

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information could be sent to the central system as well as smart meters to

actively manage customer load in the short term to smooth-out the problem.

End consumer devices

End consumer devices are auxiliary equipments connected to the smart meter

that enables the consumer to interact with smart meter and/or load devices

within consumer’s premises. A simple example of this can be display unit that

gives details of consumption, current tariffs etc. On the other hand, a

sophisticated example can be an energy management system. Energy

management system handles HAN of major electrical loads and/or sources

present in the consumer premises. It allows consumer to monitor, analyze,

customize and control behavior of these devices in real time. Such systems

allows consumer to play a proactive role in energy management through

participation in various demand management programs proposed by utilities.

5.1.2 AMI system functionality

AMI is aimed to increase the level of observability and controllability of power

system. Scope of functions that AMI can support is quite large. Some of the

primary functions are listed as follows [79], [82].

Accommodate all energy generations and storage options in the grid.

Meter registration to incorporate new meters in the grid.

Automatic adaptation to grid changes.

Remote meter reading (cyclic and on demand) for the purpose like

billing.

Remote tariff programming for updating parameters related to tariff,

calendar, contract period etc.

Remote access to system elements over the grid and remote firmware

updation.

Management of alarm and event over the grid.

Anticipate and respond to system disturbances showing self-healing

characteristics.

Fraud detection.

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Remote programming and gathering of load profile for energy

management.

Demand response facility to connect and disconnect load on

predefined variable load settings for load management.

Power quality management.

Operate resiliently against physical and cyber attacks.

Give real time information to consumer about their energy

consumption, energy pricing, etc. and enable them to efficiently control

their energy consumption pattern and thus energy budget.

Local and remote device management at consumer end.

5.2 DLMS/COSEM standards

AMI is one of the essential steps towards realization of smart grid. However,

one of the major factors of paramount importance in success of AMI

implementation is the communication protocol adopted. In conventional power

system there is no precise definition about the communication protocol to be

used. International standards that exist and adopted are generally at the level

of substation automation and are not sufficient to answer the scope of AMI

[83]. The technology that exists is dominated majorly by proprietary protocols

as defined by the manufacturer or the solution provider. Generally, such

proprietary protocols are developed considering the needs of current project

and budget allotted and issues like scalability and interoperability are not

sufficiently emphasized. When AMI aims to integrate all grid elements,

interoperability of elements working on number of proprietary protocols

presents a serious concern. This created a need for open protocol standard

for communication in AMI and this is answered in terms of DLMS/COSEM

standards.

DLMS, which refers to Device Language Message Specification, is a

suite of open standards developed and maintained by the DLMS User

Association [84]. It defines the common international approach to data

formatting and messaging for metering equipments over AMI. COSEM, which

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refers to Companion Specification for Energy Metering, is a set of rules for

modeling meter data and is a part of overall DLMS standards [85]. The

DLMS/COSEM standard suite has been developed based on two strong and

proven concepts: object modeling of application data and the Open Systems

Interconnection (OSI) model. This allows covering the widest possible range

of applications and communication media. These standards are officially

endorsed and registered by the International Electrotechnical Commission

(IEC) under IEC 62056 [86]. DLMS/COSEM standard suit is published as set

of colored books details of which is shown in Table 5.1 along with

corresponding equivalent IEC standards. These standards are discussed as

follows.

Table 5.1 DLMS/COSEM standards and its equivalent IEC standards.

DLMS User

Association

IEC Standards about

Blue Book IEC 62056-61

IEC 62056-62

COSEM meter object model and

object identification system (OBIS)

Green Book IEC 62056-21

IEC 62056-42

IEC 62056-46

IEC 62056-47

IEC 62056-53

Architecture and protocol to

transport the model

Yellow Book -- Conformation testing process

White Book -- Glossary of DLMS/COSEM terms

Blue Book

This book specifies standards to describe object model and object

identification system for a physical device. Details of the standards are as

follows.

IEC 62056-61: This part of the standard suits specifies overall structure of the

identification system and mapping of all data items in metering domain to their

unique identification codes. This is defined by object identification system

(OBIS) [87]. OBIS covers identification of metering data of energy types other

than electrical also like gas, heat, etc. Further, it not only covers identification

of measurement values but also abstract values used for configuration or

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obtaining information about the behavior of metering equipment. As per OBIS

each identification code consists of a six-number sequence with each number

represented by value between 0 and 255 that refers to value in a group. Thus

a complete OBIS code consist of a number sequence of the form

A.B.C.D.E.F. Value in each group A to F signifies specific metering

information like energy type, measurement channels, quantity being

measured, algorithm used in measurement, billing period, etc. For example,

group A defines energy type e.g. 1 for electricity, 7 for gas. With A as 1, group

C defines various electricity related objects e.g. 1 for active power, 5 for

reactive power, etc.

IEC 62056-62: This part of the standard suits specifies a model of a meter as

it is seen through its communication interface(s) [88]. It defines generic

building blocks using object-oriented methods in form of interface classes.

Interface classes represent the classes or blueprints for objects that display

similar properties (attributes) and methods. The specification defines a large

number of interface classes to define different kind of information. For

example interface class 1 models instantaneous quantities e.g. billing period

counter, interface class 3 models quantities like energy that requires

information in terms of value, units and scaling factor, interface class 7

models historic values like load profiles, etc. In addition to classes

representing the metered data, there are also large number of classes for

abstract information like meter clock, communication profile, etc.

Modeling of a physical device (e.g. metering equipment) as per the

object model and OBIS as discussed above can be understood as follows. As

shown in Figure 5.2 a physical device would be modeled as if containing one

or more logical devices. Each logical device may represent specific

functionality of a meter e.g. a multi-utility meter may have electrical meter as

one logical device and gas meter as another logical device. Each physical

device has by default one logical device called Management logical device.

This logical device contains information of all other logical device present in

physical device. Each logical device consists of one or more objects. Objects

simply represents piece of structured information about a quantity (may be

physical or abstract). Each object is identified by its logical name that is

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defined as per OBIS code defined by IEC62056-61. Similar objects in a logical

device are grouped into a common interface class defined by IEC62056-62.

Each logical device contains by default one object of class Association that

has a predefined OBIS code of 0.0.40.0.0.255. This object contains list of all

objects present in the logical device along with details of their OBIS code and

interface class. Management logical device also contains one default object

with predefined OBIS code 0.0.41.0.0.255 that contains list of all logical

devices present in a physical device along with details of their name and

address.

Figure 5.2: COSEM model of a metering equipment.

Green Book

This book specifies communication profile for various communication media

and the protocol layers of these communication profiles. It explains how to

map data in interface model to protocol data units and transport it through the

communication channel. DLMS/COSEM communication profile [89] is shown

in Figure 5.3.

DLMS/COSEM communication profile is based on Open system

interconnection (OSI) model; however 7 layers of OSI are collapsed into

primarily 3 or 4 layer structure. As shown in Figure 5.3, DLMS/COSEM

standards specify more than one communication profile each with common

COSEM application layer. A single device may support more than one

communication profiles so as to allow data exchange using various

communication media. Various communication profiles are listed as follows.

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Figure 5.3: DLMS/COSEM communication profile.

Three layer connection oriented High-level Data Link Control (HDLC) based

communication profile: This comprises of COSEM application layer, HDLC

based data link layer and the physical layer for connection oriented

asynchronous data exchange. It supports data exchange via a local optical or

electrical port, leased lines and Public switched telephone network (PSTN) or

the GSM network. This communication profile has been covered under IEC

62056-21 and IEC 62056-42. IEC 62056-21specifies use of physical layer in

three layer connection oriented communication for the purpose of direct local

data exchange particularly for hand-held units used for local operation and

maintenance [90]. On the other hand, IEC 62056-42 specifies use of physical

layer for data exchange through PSTN [91].

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TCP-UDP/IP based communication profile: This profile supports data

exchange using the internet over various physical media like Ethernet, ISDN,

GPRS, UMTS, PSTN/GSM using PPP, etc. In these profiles the COSEM

application layer is supported by the COSEM transport layer(s), comprising a

wrapper and the Internet TCP (connection oriented) or UDP (connection less)

protocol. Lower layers can be selected according to the media to be used as

the TCP-UDP layers hide their particularities. This communication profile has

been covered under IEC 62056-47 that specifies the transport layers for

COSEM communication profiles for use on IPv4 networks [92].

S-FSK (Spread Frequency Shift Keying) PLC based communication profiles:

This profile supports data exchange via power lines using S-FSK modulation.

In this profile, either the COSEM application layer is supported by

connectionless Logical link control (LLC) sub-layer and the Medium access

control (MAC) sub-layer, or the COSEM application layer is supported by

connection oriented LLC sub-layer using the data link layer based on the

HDLC protocol and MAC sub-layer. The second option has been covered

under IEC 62056-46 [93].

Figure 5.4: COSEM application layer on top of various lower layer protocol

stack.

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In all the three communication profiles discussed above uses COSEM

application layer. COSEM application layer is structured on client-server

paradigm. Metering equipment plays the role of the server and the data

collection system like DCU or central system plays the role of a client. Here

communication takes place between Applications process (AP) of client and

server in form of request and response mechanism. In case of events or

alarms, server can also execute an unsolicited service to notify clients.

COSEM application layer consists of a Application service object (ASO) that

in turn consist of a normal Application control service element (ACSE) and a

COSEM specific element called Extended DLMS application service element

(xDLMS_ASE). xDLMS_ASE is responsible for providing services related to

COSEM interface objects. For example, it is responsible for exchanging meter

information modeled as object interface classes and named by OBSI codes.

Because of presence of xDLMS_ASE other protocol layers become

independent of COSEM model and COSEM application layer can be placed

on the top of a wide variety of lower protocol layer stacks as shown in Figure

5.4. Specifications of COSEM application layer has been covered under IEC

62056-53 [94].

Yellow Book

This book specifies standardized conformation tests for Implementation under

test (IUT) designed as per DLMS/COSEM specifications. The objective of the

conformance testing is to establish whether the IUT conforms relevant

specifications thereby indicating its capability of interworking with other similar

devices [95].

White Book

This book is glossary of important terms used in DLMS/COSEM specifications

and IEC 62056 series of standards [96].

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5.3 Communication technologies for AMI

AMI architecture as discussed in Section 5.1 can be divided into 3 segments

from the point of view of communication needs viz. HAN, NAN and wide area

network (WAN). WAN represents long distance communication e.g. between

central system and DCU. NAN manages information over a neighboring area

and acts as interface between WAN and HAN. HAN extends the

communication facility up to the endpoints i.e. within consumer premises.

While there is no doubt that communication technology is the key enabler for

smart grid, there are number of challenges that are required to be looked at

while selecting communication options. Some of the major challenges are

discussed as follows [97-99].

1. AMI consists of large number of interconnected components related to

generation, transmission, distribution and utilization system that are

required to communicate. Thus it can be envisaged that the

communication technologies involved in AMI will be of heterogeneous

in nature. In such a situation to meet goals of smart grid it is necessary

that components in AMI communicate seamlessly bridging different

standards, technologies and manufacturers. Thus one of the major

requirements of communication networks in AMI is interoperability and

support for coexistence of multiple technologies and standards.

2. Smart grid applications, components and participants are expected to

grow with time. Hence, it is essential that communication solutions

used in AMI should be conveniently scalable to support this.

3. Lot of investments has been made on power system in existing form

both by utility companies and consumers. Hence, technology solutions

in AMI should act as an overlay to the existing system where ever

possible.

4. Communication networks in AMI should have self-organizing

capabilities so that it can support functions such as communication

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resource discovery, negotiation and collaborations between network

nodes, connection establishment and its maintenance, etc.

5. Communication over AMI should be secured enough for utility

companies as well as consumer to trust the data. Because of the scale

and deployment complexity of AMI it can be envisaged that

communication network in AMI may rely on existing public networks

such as cellular and wired technologies. In such a scenario security of

data over AMI becomes an issue of paramount importance.

6. In AMI smart meters at consumer premises are expected to periodically

provide accurate energy related information to the utility companies.

The data thus obtained from consumer reveals a wealth of information

that can be used for purposes beyond energy efficiency and thus it

gives rise to challenges related to data privacy.

7. For different category of data communication, network should be able

to support different quality of service (QoS) profiles in terms of

transmission latency, bandwidth, reliability, etc. For example data

communication related to monthly bill caries low priority compared to

information related to some event generated due to abnormal behavior

over the grid.

8. Installation of AMI extends from residential to commercial properties in

urban, suburban and rural areas and hence communication networks

should be able to provide coverage over very wide and diverse

geographical regions.

Thus issues involved in design of communication networks in AMI are

highly demanding and intertwined. Needs from the communication network

are beyond the scope of some proprietary standards and/or single technology.

Hence, the solution has to be of heterogeneous type with inclusion of both

proprietary as well as off-the-shelf technologies. This has been exemplified in

the following discussion. For AMI architecture discussed in Section 5.1,

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possible communication technologies that can be used for interface between

various elements are shown in Table 5.2 and discussed below.

Table 5.2 Communication technologies for various AMI interfaces.

Interface tag

in Figure 5.1

Technology

type

Proposed technology and lower

layer protocol

I1 Wired PLC

IEC 61334

I2, I3 Wireless and

wide area

GPRS,3G,4G

UMTS,TCP-UDP/IP

I4,I5, I7 Wireless and

local area

ZigBee, Wi-fi, Bluetooth

IEEE 802.15.4

IEEE 802.11

IEEE 802.15.1

I6 Wireless and

local area

ZigBee, Wi-Fi, Substation

Automation

IEEE 802.15.4

IEEE 802.11

IEC 61850

IEEE 802.11 Standards

IEEE 802.11 is a set of IEEE standards that govern wireless networking

transmission methods [100]. They are commonly used today in their 802.11b,

802.11g, and 802.11n versions to provide indoor or in-campus wireless local

area network (WLAN) and home area network (HAN). They are popularly

referred as WiFi. They can be used in AMI for HAN and home automation.

Use of these standards supports design of low cost application devices to be

used at consumer end. Use of this however is up to 100m and security issues

arising due to multiple networks operating in the same locations has to be

resolved.

IEEE 802.11s is amendment to IEEE 802.11 for mesh networking in

WLAN, popularly known as wireless mesh network (WMN). This consists of

radio nodes organized in a mesh topology. In AMI this can be an option for

defining how wireless devices can interconnect to create a WLAN mesh

network, which may be used for static topologies and ad-hoc networks. This

can act as an AMI backhaul particularly at distribution end supporting

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automation, demand response and remote monitoring. It is easily scalable

and allows improved coverage around obstacles, node failures and path

degradation.

IEC 61334

IEC 61334 is a standard for low-speed reliable power line communications. It

is also known as S-FSK (spread frequency shift keying). A typical PLC system

in AMI may consist of a backbone-coupled DCU close to a MV/LV

transformer. All traffic on the line is initiated by the DCU, which acts on behalf

of central system. More recent narrowband PLC technology include

sophisticated techniques such as OFDM (orthogonal frequency-division

multiplexing) to provide higher data rates, and to target broadband solutions

operating in the 1-30 MHz band [101]. Further, installation of filters highly

improves SNR ratios. Despite the difficulties, PLC technologies are at a clear

advantage for utility companies as no separate communication channel is

required and it can prove to be relatively cheaper [102].

ZigBee

ZigBee is a low-cost, low-power communication standard maintained and

published by ZigBee Alliance and is suitable particularly for personal area

network. It is based on IEEE 802 standard and works in industrial, scientific

and medical (ISM) radio bands. One of the important advantages of ZigBee is

that it supports mesh-networking. This provides high reliability and more

extensive range. For AMI, ZigBee is very suitable for realizing HAN that

includes interface between smart meter and other elements like multi-utility

meter, local O&M device, end customer device etc. Currently, under ZigBee

Smart Energy profile [103], number of agencies is jointly working to develop a

standard for interoperable products that monitor, control, inform and automate

the delivery and use of energy to support goals of smart grid.

Bluetooth

Bluetooth technology is one of the very popular short-range communication

technologies in applications related to mobile phones, computers, medical

devices and home entertainment products. Like ZigBee it is also based on

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IEEE 802 standard and works in industrial, scientific and medical (ISM) radio

bands. Bluetooth low energy (BLE), that is subset of the latest Core version,

Bluetooth v4.0, is designed to support applications that require low power

wireless connectivity. BLE technology can be used in HAN for wireless

connectivity between energy sensors to smart meters [104]. One of the major

advantages of this technology is presence of many other Bluetooth devices in

home with BLE based smart grid applications can be seamlessly connected.

IEC 61850

IEC 61850 [105] is primarily designed for intra-substation communication for

substation automation. The standard defines the application layer and is thus

independent of the underlying communication medium. All services and

models are designed in an abstract form called ACSI (abstract communication

service interface) which then can be mapped to protocols such as MMS

(manufacturing message specification) and TCP/IP over Ethernet. Typical use

of this standard in AMI is for interface between DCU and External devices e.g.

a SCADA system.

Cellular Technologies

For data communication over a wide geographic area (WAN) cellular

technologies are one of the best available options. With evolution of cellular

technology from 2G to 3G and presently towards 4G it has became possible

to achieve higher data rates, better security and wide coverage [106].

Scalability is another important advantage that these technologies provide.

These technologies can be used for interface between DCU and central

system or where smart meter is directly connected to Central system.

Because of continuous rapid growth in this domain the major concern in use

of these technologies is their life span.