NISTIR 7943

Guideline for the Implementation of Coexistence for 

Low Frequency Narrowband Power Line Communication 

Standards in the Smart Grid

Smart Grid Interoperability Panel, Priority Action Plan 15

Power Line Communications
NISTIR 7943

Guideline for the Implementation of Coexistence for 

Low Frequency Narrowband Power Line Communication 

Standards in the Smart Grid

Smart Grid Interoperability Panel, Priority Action Plan 15

Power Line Communications

Editor: Dr. David Su, PAP15 Chair

June 2013

U.S. Department of Commerce

Cameron F. Kerry, Acting Secretary

National Institute of Standards and Technology

Patrick D. Gallagher, Under Secretary of Commerce for Standards and Technology and Director
Acknowledgement 

The following PAP15 members made significant contributions to this document.

James Allen, STMicroelectronics, editor IEEE 1901.2

Vijay Dhingra, Echelon, Chair IEEE P1901.2 CX subgroup, PAP15 Coexistence

Subgroup

Stefano Galli, Assia Inc, Rapporteur Q15/15, Chair PAP15 Coexistence Subgroup

James LeClare, Maxim Integrated, Chair IEEE 1901.2

Thierry Lys, ERDF

Don Shaver, Texas Instrument
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Guideline for the Implementation of Coexistence for Low Frequency 

Narrowband Power Line Communication Standards in the Smart Grid

1. Overview 

Power Line Communication (PLC) systems provide a bidirectional communication platform 

capable of addressing a variety of Smart Grid applications, such as home energy management 

and intelligent meter reading and control. One benefit of using power line communication on 

the power grid is that it makes use of the intrinsic electrical infrastructure rather than using

other wired or wireless alternatives. Home appliances and home energy management systems 

can communicate with no additional wiring and minimal configuration by the homeowners.

PLC Technology could be classified into two general categories: Narrowband (NB) and

Broadband (BB). The NB-PLC considered here, operates in frequency bands below 500 kiloHertz (kHz) and supports rates of tens to hundreds of kilobits per second (Kbps). BB-PLC 

operates in frequency bands above over 1.8 Mega-Hertz (MHz) and can have a data rate

ranging from several megabits per second (Mbps) to a few hundred Mbps. For a more 

detailed discussion of the PLC technology and its use in the Smart Grid, see [1].

2. Purpose of Document

The Smart Grid Interoperability Panel (SGIP) established the Priority Action Plan 15 (PAP 

15) in 2009 to address the harmonization of new PLC standards and their coexistence 

specifications. This NISTIR presents PAP15’s recommendation on the implementation of

coexistence mechanisms for NB-PLC standards. The document also gives a short 

introduction of NB-PLC standards and their coexistence mechanisms. A similar guideline on 

BB-PLC is presented in [2]. 

3. Why Coexistence is Important

Power line electrical wiring is a shared medium. It does not provide a conductor that is 

dedicated exclusively to a particular subscriber or application. More specifically, power line 

wiring may distribute energy to a set of individual homes or set of multiple dwelling units

(aka “neighbors”). The signals that are generated by one set of users have the potential of 

interfering with signals generated by other users who share the wiring.

Low frequency NB-PLC operates in the frequency band below 500 kHz. The available 

frequencies differ in various geographical regions. For example, in the U.S, the Federal 

Communication Commission (FCC) defines frequencies between 10 and 490 kHz for NBPLC; however, it does not specify how it is to be used. In Europe, the EN 50065-1 standard 

defines a set of frequencies in the range 3 kHz to 148.5 kHz for transmission of information 

on low voltage electrical systems, either on the public supply system or within installations in 

consumer’s premises. It consists of four bands, commonly referred to as the CENELEC 

bands. CENELEC A band, from 3 kHz to 95 kHz, is restricted to electricity suppliers and 

their licensees; CENELEC band B from 95 kHz to 125 kHz, CENELEC band C from 125 
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kHz to 140 kHz, and CENELEC band D from 140kHZ to 148.5 kHz are restricted to 

consumer use. Japan’s Association of Radio Industries and Businesses (ARIB) defines a 

frequency range similar to the FCC’s.

Because the medium and frequency bands are shared, and because existing and emerging 

standards exist, it is necessary to devise a coexistence mechanism(s) that can be used to limit 

the harmful interference caused by non-interoperable neighboring devices. Because Smart 

Grid applications are expected to last much longer than In-Home applications which tend to 

change rapidly, it is important to enable coexistence in such a way that it is useful for current 

and emerging technologies over a long time horizon.

4. PAP15 Requirements on Narrowband Power Line Communication

To ensure the new standards being developed meet the Smart Grid requirements, PAP15 

members developed and agreed to NB-PLC requirements for smart appliances [3] and the NB 

coexistence mechanism requirements [4]. These documents were delivered to the Institute of 

Electrical and Electronics Engineers (IEEE) and International Telecommunication Union –

Telecommunication Sector (ITU-T) in 2011.

The Smart Appliance Low-Frequency Narrowband PLC Requirements document [3] lists the 

users, device vendors, application vendors and the utility industry functional and application 

requirements. 

The NB Coexistence Mechanism Requirements document [4] details the general agreements 

for the coexistence between existing and developing protocols that use the same low 

frequency bands. It provides a foundation for what needs to be accomplished, which 

standards need to be included and how different interests will coordinate.

5. Recent NB-PLC Standards

There has been a long history of using narrowband PLC technologies for control and 

management. Existing standards use single-carrier or double-carrier modulation technologies, 

which provide limited bandwidth in tens or hundreds of bits per second (bps). Examples of 

such standards include LonWorks (International Organization for 

Standardization/International Electrotechnical Commission ISO/IEC 14908-3), KNX 

(ISO/IEC 14543-3-5), CEBus (CEA-600.31), and IEC 61334-5-1/61334-5-2. 

A new generation of standards that uses multi-carrier orthogonal frequency division 

multiplexing (OFDM) technology has been developed by the P1901 group of IEEE and the 

G.hnem group of ITU-T. The OFDM technology enables a higher bit rate in hundreds of 

kbps. These standards include IEEE 1901.2, ITU-T documents G.9901, G.9902 (G.hnem), 

G.9903 (G3-PLC), and G.9904 (PRIME) [6-10]. They could be used for many smart grid 

applications including advanced metering infrastructure, home energy management, 

distributed energy resource management, and demand response management. PAP15

coordinated the work between these SDOs. Table 1 presents a summary of major features of 

these protocols. The major difference is the mechanisms by which a NB-PLC network is 
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established and managed, and how data are routed. There are differences in the choice of 

frequency bands, modulation methods, and error correction codes used, resulting differences 

in the available bandwidth. Even though each protocol has an intended use, there is no 

intrinsic limitation on whether each could be used for Home Area Network or Access Area 

Network (including utility or metering network) applications.

Table 1: Summary of Protocol Features for G.hnem, IEEE 1901.2, G3-PLC, and PRIME

Features G.9902 (G.hnem) 1901.2 G.9903(G3-PLC) G.9904(PRIME)

Packet layer 

support 

IPv6, IPv4, and other IPv6/UDP/TCP and 

other

IPv6/UDP IPv6, IPv4, IEC 61334-

4-32

Routing A network is preconfigured 

for either L2 (one hop, 

relay) or L3 routing. 

Mechanism for relay 

routing (source routing) is 

for further study.

L3 routing protocol not 

selected.

A network is 

reconfigurable for 

either L2 or L3 

routing.

Routing on hop-by-hop 

(mesh) basis, nodes 

uses route discovery 

procedure in LOADng 

protocol (RFC 6550, 

ROLL) to manage its 

routing table.

Switching nodes are 

assigned as tree 

branches are added. 

Routing table in each 

node is maintained by 

Beacons from switches.

Routing to other 

networks always 

through the root.

Security AES-128 key and CCM 

encryption

AES-128 key and 

CCM* encryption

EAP-PSK, RADIUS

AES-128 key and 

CCM* encryption

Two profiles - no 

encryption and AES128 key encryption.

PLC

Network

Formation/ 

Management

A Domain Master manages 

the formation and resources 

of a G.hnem network 

(called domain). Node 

joins a domain with the 

Domain Master. Nodes

within a domain may

communicate with each 

other directly, or indirectly

through a relay or a domain 

access point. Nodes not in 

the same domain must 

communicate through Inter 

Domain Bridges.

The network is 

formed and managed 

by a PAN coordinator. 

Channel access is 

supported by slotted 

CSMA/CA and 

unslotted CSMA/CA 

for non-beacon PANs.

Use 6LoWPAN Boot

Strapping Protocol for 

devices to discover 

neighbors and connect. 

A PAN Coordinator

performs initialization/ 

management of a G3

network

A Prime network 

consists of a logical 

tree. The root node 

(Base Node) manages 

the network resources 

and connections. A 

new node (Service 

Node) attaches to the 

tree on a neighboring 

node visible to the new 

node. 

Specify procedure for 

firmware update. 

Network 

Topology

Star, tree, or mesh Star, tree, or mesh Mesh Tree

Convergent 

Layer (above 

MAC)

Use 6LoWPAN for IPv6 

service convergence, 

support of IPv6 required

Provides service 

convergence 

procedures for IPv6

Use 6LoWPAN for 

IPv6 service 

convergence

Provide service 

convergence procedures 

for IPv6, IPv4, and IEC 

61334-4-32.

Use 6LoWPAN for 

IPv6 header 

compression

Frequency 

Bands

(in kHz)

CENELEC-A(35.9375-

90.625), CENELEC-B

(98.4375-120.3125),

CENELEC-CD(125-

143.75),

FCC(34.375-478.125),

FCC-1 (34.375-137.5),

FCC-2(150.0-478.125)

CENELECA(35.9375-90.625), 

CENELEC-B

(98.4375-121.875), 

ARIB (154.6875-

403.125), 

FCC(154.6875-

487.5), 

CENELEC-A(35.9375-

90.625), CENELEC-B

(98.4375-121.875),

ARIB(154.6875-

403.125),FCC(154.687

5-487.5) 

CENELEC A (42-89).

Modulations (Coherent)

M-PSK, M=2,4,8,16

16-QAM

(Differential)

M-DPSK, M=2,4,8

(Coherent) BPSK

(Coherent - optional)

QPSK, 8PSK, 16-

QAM

(Differential)

M-DPSK, M=2,4,8

(Coherent - optional)

M-PSK,M=2,4,8

16-QAM

(Differential)

M-DPSK, M=2,4,8
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6. Coexistence of NB-PLC

6.1 NB-PLC Coexistence Mechanisms

In 2010 PAP15 established a Coexistence Sub-Group to coordinate standardization work on 

coexistence mechanisms. It produced a report examining alternatives for coexistence of NBPLC protocols [5], including use of frequency division, frequency notching, and pilot tones. 

Subsequently, in response to the PAP15 requirements cited above, both IEEE P1901.2 and 

ITU-T Q15/15 groups standardize mechanisms to allow coexistence of multiple PLC 

technologies. The resulting two mechanisms are described below. These two mechanisms 

are in addition to required CSMA coexistence mechanism detailed in EN50065-1 for 

CENELEC C devices.

Frequency separation and notching mechanism – The mechanism avoids frequencies used by 

other networks by adhering to specific band plans and by limiting the out-of-band signal level 

for a certain frequencies. Furthermore tone notching on one or more subcarriers within the 

frequency range overlapping other technologies may also be used. This mechanism is mainly

to be used for coexistence with systems complying with existing SDO standards and operating 

below 150 kHz.

Preamble-based CSMA mechanism – The preamble-based CSMA mechanism is used to fairly 

share the communications medium when the devices operate in the same or overlapping 

frequency band. This mechanism requires a sequence of neutral coexistence preamble 

symbols be transmitted by the device before the “native” preamble to provide coexistence 

signaling. The “native” preamble is the original preamble defined by the protocol of the 

device that is using this coexistence mechanism. The coexistence preamble symbols are 

transmitted only on sub-carrier frequencies that are common to the various protocols, and 

only for the band being used. This mechanism is to be used for coexistence with systems 

complying with standards referenced in this document and future standards.

The specification for the first mechanism appears in all standards listed in Table 1 above.

The preamble-based mechanism is being specified in the IEEE P1901.2 Group and is to be 

adopted by others when the specification is completed [11] and satisfies the PAP15 

Coexistence Requirements [4]. In particular, if the coexistence mechanism is defined as a 

part of a PHY/MAC specification, this part shall be stand-alone, i.e., implementation of only 

this part shall be allowed under the same IPR policy as for the incorporating its PHY/MAC 

specification.

6.2 Coexistence Behavior/Fairness

Coexistence mechanisms also require a sense of fairness with respect to its effect on the 

network and access to the medium (channel). The following sections address this issue.

6.2.1 CSMA procedure
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A system will search and detect coexistence preamble while not transmitting or receiving 

frames.

When a system detects a coexistence preamble and is not followed by a native preamble, the 

system must wait for a predefined back-off time interval before attempting transmission of a 

frame.

6.2.2 Fairness procedure

Once multiple systems detect the need to coexist they need to be able to fairly share the 

medium by following two procedures:

• Long coexistence preamble sequence

• Duty cycle

A long coexistence preamble sequence consists of repeated coexistence preambles. The 

transmission of the long coexistence preamble sequence is a way of “requesting” channel 

access from devices of different technologies. If a system attempts to access the channel but 

has backed off for a predefined maximum duration then it may transmit a long coexistence 

preamble sequence. After the transmission of a long coexistence preamble sequence, it shall 

immediately transmit the data frame.

Duty cycle is another means to broker fairness among coexisting networks. The Standard 

[11] defines the maximum allowed duration for nodes of the same network to occupy the 

channel. After this duration, nodes will back-off the channel for a specified amount of time 

before transmitting again.

A node may be capable of performing both the above mentioned solutions in order to get an 

optimized solution, and avoid inefficiencies.

7. PAP15 Recommendation

The following recommendation was approved by PAP15 at its meeting on December 4, 2012:

In order to ensure that NB-PLC devices deployed in proximity do not interfere with each 

other causing performance degradation or service disruption, PAP15 recommends that all 

Smart Grid devices using frequency below 500kHz NB-PLC technologies must implement and 

activate preamble-based coexistence mechanism as specified in IEEE 1901.2, in addition to 

the frequency band plans and frequency notching mechanisms defined in standards for 

specific NB-PLC technology. 
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8. References and Bibliography

[1] S. Galli, A. Scaglione, Z. Wang, “For the Grid and Through the Grid: The role of Power Line 

Communications in the Smart Grid,” Proceedings of the IEEE. vol. 99, no. 6, June 2011.

[2] NISTIR 7862, Guideline for the Implementation of Coexistence for Broadband Power Line 

Communication Standards, April 20, 2012. http://dx.doi.org/10.6028/NIST.IR.7862

[3] D. Su, B. Singletary, editor, “Smart Appliance Low-Frequency Narrowband PLC Requirements,” 

http://collaborate.nist.gov/twiki-sggrid/pub/SmartGrid/PAP15PLCForLowBitRates/PAP-15-NB-PLCrequirements-v09.docx

[4] V. Oaksman, editor, PAP15 NB PLC coexistence requirement, 

http://collaborate.nist.gov/twikisggrid/pub/SmartGrid/PAP15PLCForLowBitRates/Requirements_on_NB_PLC_coexistence_Final_O

ct_11r1.xls

[5] PAP15 Coexistence Subgroup, Narrowband coexistence report, “Coexistence of narrow band 

power line communication technologies in the unlicensed FCC band,” April 12, 2010.

http://collaborate.nist.gov/twikisggrid/pub/SmartGrid/PAP15PLCForLowBitRates/NB_PLC_coexistence_paper_rev3.doc

[6] Recommendation ITU-T G.9901, Narrowband orthogonal frequency division multiplexing power 

line communication transceivers – power spectral density specification, 2012

[7] Recommendation ITU-T G.9902, Narrowband orthogonal frequency division multiplexing 

power line communication transceivers for ITU-T G.hnem networks,2012

[8] Recommendation ITU-T G.9903, Narrowband orthogonal frequency division 

multiplexing power line communication transceivers for G3-PLC networks,2012

[9] Recommendation ITU-T G.9904, Narrowband orthogonal frequency division 

multiplexing power line communication transceivers for PRIME networks, 2012

[10] IEEE Standard 1901.2-2013, Standard for Low Frequency (less than 500 kHz) Narrow Band 

Power Line Communications for Smart Grid Applications, 2013.

http://grouper.ieee.org/groups/1901/2/

[11] 2wg-13-0058-00-WGDC_Coexistence text from IEEE P1901.2_vD0.07.01-2013, Standard for 

Coexistence of Narrow Band Power Line Communications

http://www.techstreet.com/ieee/cgi-bin/detail?vendor_id=5638