IEC 62980:2022

Parasitic communication protocol for radio-frequency wireless power transmission

IEC 62980:2022 defines procedures for transferring power to non-powered IoT devices using the existing ISM band communication infrastructure and RF WPT and a protocol for a two-way, long-distance wireless network in which IoT devices and APs communicate using backscatter modulation of ISM-band signals. Three components are required for two-way, long-distance wireless communication using backscatter modulation of ISM-band signals:
• an STA that transmits wireless power and data packets to SSNs by forming ISM-band signal channels between HIE-APs,
• a battery-free SSN that changes the sensitivity of the channel signals received from the STA using backscatter modulation, and
• an HIE-AP that practically decodes the channel signals whose sensitivity was changed by the SSN.
In this document, the procedures for CW-type RF WPT using communication among these three components are specified based on application of the CSI or RSSI detection method of ISM-band communication.
This document proposes a convergence communication protocol than can deploy sensors, which can operate at low power (dozens of microwatts or less) without batteries, collect energy, and perform communication, to transmit power to SSNs using RF WPT based on parasitic communication. This method can be applied to application service areas such as domestic IoT, the micro-sensor industry, and industries related to environmental monitoring in the future.

Protocole de communication parasite pour le transfert d'énergie sans fil par rayonnement radiofréquence

L'IEC 62980:2022 définit les procédures de transfert d'énergie vers des dispositifs d'IoT au moyen de l'infrastructure de communication existante sur les bandes ISM et du WPT RF, ainsi qu'un protocole de réseau sans fil longue distance bidirectionnel qui permet aux dispositifs d'IoT et aux points d'accès de communiquer par modulation de rétrodiffusion des signaux sur les bandes ISM. La communication sans fil longue distance bidirectionnelle fondée sur la modulation de rétrodiffusion des signaux sur les bandes ISM exige trois éléments:
• une STA qui assure le transfert sans fil de l'énergie et des paquets de données vers les SSN en créant des canaux de signaux dans les bandes ISM entre HIE-AP ;
• un SSN sans batterie qui modifie, par modulation de rétrodiffusion, la sensibilité des signaux de canal reçus depuis la STA ; et
• un HIE-AP qui décode de manière pratique les signaux du canal dont la sensibilité a été modifiée par le SSN.
Dans le présent document, les procédures de WPT RF de type CW qui utilisent la communication entre ces trois éléments sont spécifiées à partir de l'application d'une méthode de détection des CSI ou du RSSI de la communication sur les bandes ISM.
Le présent document propose un protocole de communication convergent qui peut déployer des capteurs, lesquels peuvent fonctionner à faible puissance (quelques dizaines de microwatts ou moins) sans batteries, collecter de l'énergie et assurer une communication, afin d'alimenter des SSN au moyen d'un WPT RF fondé sur une communication parasite. Cette méthode pourra être appliquée ultérieurement à des services d'application tels que l'IoT domestique, l'industrie des microcapteurs et les industries impliquées dans la surveillance de l'environnement.

General Information

• Status: Published
• Publication Date: 27-Sep-2022
• ICS: 29.240.99 - Other equipment related to power transmission and distribution networks
• Technical Committee: TA 15 - Wireless Power Transfer
• Drafting Committee: WG 2 - TC 100/TA 15/WG 2
• Current Stage: PPUB - Publication issued
• Start Date: 28-Sep-2022
• Completion Date: 14-Oct-2022

Overview

IEC 62980:2022 is an international standard developed by the International Electrotechnical Commission (IEC) that specifies a parasitic communication protocol for radio-frequency wireless power transmission (RF WPT). This standard enables the transfer of power and communication to battery-free IoT (Internet of Things) devices by leveraging existing ISM (Industrial, Scientific, and Medical) band communication infrastructure using backscatter modulation. It defines the procedures and protocols that facilitate two-way, long-distance wireless communication between wireless power transmitters and sensor nodes.

The protocol targets ultra-low power devices, typically operating at power levels in the order of microwatts or less, enabling sensors and IoT devices to operate without batteries by harvesting energy from RF signals. This breakthrough supports applications in domestic IoT, micro-sensors, and environmental monitoring industries, promoting sustainable and maintenance-free IoT ecosystems.

Key Features

• Three key components are critical for the system:

  • STA (Station): Transmits wireless power and data packets over ISM-band channels between HIE-APs.
  • Battery-free SSN (Sensor Node): Uses backscatter modulation to change channel response signals, enabling communication without consuming power for transmission.
  • HIE-AP (High-Integration Endpoint Access Point): Decodes signals modulated by the SSN and manages network communication.

• Utilizes backscatter modulation for uplink and downlink communication, significantly reducing power consumption for IoT nodes by reflecting and modulating existing RF signals instead of generating new transmissions.

• Defines protocols based on continuous wave (CW) type RF WPT and leverages channel state information (CSI) or received signal strength indication (RSSI) detection methods for robust communication.

• Specifies detailed physical layer characteristics including modulation, coding, and frame structure, ensuring standardized, interoperable wireless power and data exchange.

• Incorporates datalink layer protocols managing message exchanges, encoding methods such as FM0 and Miller encoding for reliable data transmission.

• Includes a comprehensive RF WPT control protocol to manage power transmission, network operations, and IoT device behavior during energy harvesting and communication.

Key Topics

• Parasitic Communication Protocol: Enables bidirectional long-range communication between power transmitters and battery-free sensor nodes using ISM band backscatter signaling.
• Wireless Power Transmission (WPT): Provides a method to deliver power wirelessly over radio frequencies for energy harvesting by IoT devices.
• Backscatter Modulation: A low-energy communication technique where devices modulate and reflect ambient RF signals, eliminating the need for active transmitters.
• Low-Power IoT Devices: Facilitates the deployment of sensors operating at micro-watt power levels without batteries.
• Communication Layers: Defines physical and data link layers supporting modulation, coding schemes, and structured message exchanges.
• Energy-Harvesting Network Architecture: Details the coordination of STAs and HIE-APs to establish continuous wireless power feeds and communication channels.
• Parasitic Downlink and Uplink Communication Procedures: Describe stepwise protocols for sending commands and receiving responses between APs and sensor nodes.

Applications

IEC 62980:2022 is highly relevant in industries and scenarios where battery-free, long-range wireless power and communication are critical:

• Domestic IoT Systems: Smart home sensors and devices that require autonomous operation without frequent battery replacement.
• Micro-Sensor Networks: Environmental and industrial micro-sensors embedded in hard-to-reach areas operating sustainably.
• Environmental Monitoring: Continuous data collection from sensors measuring air quality, temperature, humidity, and pollution without maintenance overhead.
• Industrial Automation: Deploying maintenance-free wireless sensor nodes for process monitoring and control.
• Healthcare Wearables: Powering body sensors without batteries for extended periods.
• Smart Agriculture: Long-range sensors tracking soil and crop conditions powered wirelessly.

The standard supports developing scalable and energy-efficient wireless sensor networks that significantly reduce operational costs and improve longevity.

Related Standards

IEC 62980:2022 complements and aligns with several related standards and technologies, including:

• ISM Band Standards: Regulatory frameworks governing ISM frequency usage for communication and power transmission.
• IEEE 802.15.4 and Bluetooth LE: Wireless communication protocols commonly utilized in IoT ecosystems.
• RFID and Backscatter Communication Standards: Provide foundational technology and principles related to backscatter modulation used in wireless power systems.
• Wireless Power Transfer (WPT) Standards: Such as Qi and AirFuel for inductive and resonant wireless charging, which focus on different frequency bands and mechanisms.
• IEC 62368 and IEC 60601: For safety and performance evaluations of wireless power and communication devices in consumer electronics and medical fields.

Integrating IEC 62980 with existing and emerging wireless communication and power standards accelerates the advancement of battery-free IoT deployments and sustainable energy solutions.

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Keywords: IEC 62980, parasitic communication protocol, radio-frequency wireless power transmission, RF WPT, ISM band, backscatter modulation, battery-free IoT devices, wireless sensor network, low-power communication, energy harvesting, wireless charging protocol, environmental monitoring IoT, micro-sensors, wireless power control.

Standards Content (Sample)

IEC 62980 ®
Edition 1.0 2022-09
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Parasitic communication protocol for radio-frequency wireless power
transmission
Protocole de communication parasite pour le transfert d'énergie sans fil par
rayonnement radiofréquence
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IEC 62980 ®
Edition 1.0 2022-09
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Parasitic communication protocol for radio-frequency wireless power

transmission
Protocole de communication parasite pour le transfert d'énergie sans fil par

rayonnement radiofréquence
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 29.240.99 ISBN 978-2-8322-5700-5

– 2 – IEC 62980:2022 © IEC 2022
CONTENTS
FOREWORD . 5
INTRODUCTION . 7
1 Scope . 8
2 Normative references . 8
3 Terms, definitions and abbreviated terms . 8
3.1 Terms and definitions . 9
3.2 Abbreviated terms . 9
4 Overview . 10
5 Communication procedures for RF WPT . 11
5.1 General . 11
5.2 Communication procedures for parasitic downlink communication . 12
5.3 Communication procedures for parasitic uplink communication . 13
5.4 Backscatter downlink/uplink data flow . 14
5.5 WPT process . 15
6 Physical layer . 16
6.1 Modulation/coding method . 16
6.1.1 General . 16
6.1.2 Downlink modulation method . 16
6.1.3 Uplink modulation method . 17
6.1.4 Downlink coding method . 17
6.1.5 Uplink coding method . 18
6.2 Frame structure . 18
6.2.1 General . 18
6.2.2 Downlink frame structure . 18
6.2.3 Uplink frame structure . 20
7 Datalink layer . 21
7.1 Message definition . 21
7.1.1 General . 21
7.1.2 Select step . 24
7.1.3 Inventory step . 26
7.1.4 Access step . 29
7.2 Data encoding . 31
7.2.1 General . 31
7.2.2 FM0 encoding . 31
7.2.3 Miller encoding . 32
8 RF WPT control protocol. 33
8.1 Wireless charging architecture . 33
8.1.1 General . 33
8.1.2 Power control purpose of RF WPT . 34
8.1.3 HIE-AP operation control . 34
8.1.4 SSN operation control . 35
8.2 RF WPT process . 36
8.2.1 General . 36
8.2.2 General WPT management . 37
8.2.3 SSN control . 38
8.2.4 SSN static parameter . 39

8.2.5 SSN dynamic parameter . 40
Annex A (informative)  Regulation and certification . 42
Bibliography . 43

Figure 1 – Usage of RF-WPT . 10
Figure 2 – RF-WPT structure of using parasitic Wi-Fi communication technology . 11
Figure 3 – Parasitic downlink/uplink communication procedures . 12
Figure 4 – Specific parasitic downlink communication procedures . 13
Figure 5 – Specific parasitic uplink communication procedures . 14
Figure 6 – Data flow during parasitic downlink/uplink communication . 15
Figure 7 – RF WPT access procedures . 15
Figure 8 – RF WPT control protocol . 16
Figure 9 – PIE method packet configuration . 17
Figure 10 – Modulation and coding of the downlink preamble . 17
Figure 11 – Modulation and coding of the downlink preamble . 18
Figure 12 – Modulation and coding of the uplink preamble . 18
Figure 13 – Modulation and coding of the uplink payload . 18
Figure 14 – Physical layer structure of the downlink frame . 19
Figure 15 – Physical layer structure of the uplink frame . 20
Figure 16 – Model of command transmission between the STA and SSN . 22
Figure 17 – Diagram of sequential command transmission between the STA and SSN. 22
Figure 18 – SSN memory structure . 24
Figure 19 – Message exchange in the select step . 25
Figure 20 – CRC-16 circuit example. 26
Figure 21 – Message exchange method of the inventory step . 27
Figure 22 – Basic functions for FM0 encoding . 31
Figure 23 – State diagram for FM0 encoding generation . 31
Figure 24 – Basic functions for Miller encoding . 32
Figure 25 – State diagram for FM0 encoding generation . 32
Figure 26 – Encoding theory combining basic Miller functions . 33
Figure 27 – Basic configuration of the RF wireless charging network of the proposed

standard . 34
Figure 28 – HIE-AP operation in RF WPT in the proposed standard . 35
Figure 29 – SSN operation in RF WPT in the proposed standard . 35
Figure 30 – Operating range of the rectified battery voltage . 36
Figure 31 – RF WPT information acquisition and control protocol of the proposed
standard . 37

Table 1 – Downlink preamble structure . 19
Table 2 – Downlink payload structure . 19
Table 3 – Downlink frame check CRC . 20
Table 4 – Uplink preamble structure . 20
Table 5 – Uplink frame detection field structure . 21
Table 6 – Downlink payload structure . 21

– 4 – IEC 62980:2022 © IEC 2022
Table 7 – CMD list . 23
Table 8 – Responses for each CMD . 23
Table 9 – Select CMD . 25
Table 10 – Valid response . 26
Table 11 – Query CMD field . 27
Table 12 – QueryRep CMD field . 28
Table 13 – QueryAdj CMD field . 28
Table 14 – Valid_Query response field . 28
Table 15 – Ack CMD field . 29
Table 16 – Valid_Ack response field list . 29
Table 17 – Read CMD field . 30
Table 18 – Data field of the response to the read command . 30
Table 19 – Write CMD field . 30
Table 20 – Data field of the response to the write command . 30
Table 21 – WPT CMD field . 37
Table 22 – WPT sub-CMD list . 38
Table 23 – SSN control field . 38
Table 24 – Detailed WPT field description . 38
Table 25 – Response to the SSN control CMD . 39
Table 26 – SSN static parameter field . 39
Table 27 – Rectifier maximum power field . 39
Table 28 – Rectifier minimum constant voltage . 39
Table 29 – Rectifier maximum constant voltage . 39
Table 30 – Rectifier minimum constant voltage . 40
Table 31 – SSN dynamic parameter field . 40
Table 32 – Rectifier dynamic voltage field . 40
Table 33 – Rectifier dynamic current field . 40
Table 34 – Output dynamic voltage of the battery terminal . 40
Table 35 – Output dynamic current of the battery terminal . 41
Table 36 – Battery temperature of the SSN . 41
Table 37 – SSN critical state field . 41
Table 38 – Rectifier desired minimum voltage . 41

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
PARASITIC COMMUNICATION PROTOCOL FOR
RADIO-FREQUENCY WIRELESS POWER TRANSMISSION

FOREWORD
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IEC 62980 has been prepared by technical area 15: Wireless power transfer, of IEC technical
committee 100: Audio, video and multimedia systems and equipment. It is an International
Standard.
The text of this International Standard is based on the following documents:
Draft Report on voting
100/3797/FDIS 100/3818/RVD
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/publications.

– 6 – IEC 62980:2022 © IEC 2022
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
INTRODUCTION
This document provides a parasitic backscatter communication protocol for battery-free
internet-of-things (IoT) devices and sensors for radio-frequency (RF) wireless power
transmission (WPT) without additional infrastructure.

– 8 – IEC 62980:2022 © IEC 2022
PARASITIC COMMUNICATION PROTOCOL FOR
RADIO-FREQUENCY WIRELESS POWER TRANSMISSION

1 Scope
This document defines procedures for transferring power to non-powered IoT devices using the
existing ISM band communication infrastructure and RF WPT and a protocol for a two-way,
long-distance wireless network in which IoT devices and APs communicate using backscatter
modulation of ISM-band signals. Three components are required for two-way, long-distance
wireless communication using backscatter modulation of ISM-band signals:
• an STA that transmits wireless power and data packets to SSNs by forming ISM-band signal
channels between HIE-APs,
• a battery-free SSN that changes the sensitivity of the channel signals received from the STA
using backscatter modulation, and
• an HIE-AP that practically decodes the channel signals whose sensitivity was changed by
the SSN.
In this document, the procedures for CW-type RF WPT using communication among these three
components are specified based on application of the CSI or RSSI detection method of ISM-
band communication.
This document proposes a convergence communication protocol than can deploy sensors,
which can operate at low power (dozens of microwatts or less) without batteries, collect energy,
and perform communication, to transmit power to SSNs using RF WPT based on parasitic
communication. This method can be applied to application service areas such as domestic IoT,
the micro-sensor industry, and industries related to environmental monitoring in the future.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies.
For undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 63006:2019, Wireless Power Transfer (WPT) – Glossary of terms
IEC TR 63239:2020, Radio frequency beam wireless power transfer (WPT) for mobile devices
3 Terms, definitions and abbreviated terms
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp

3.1 Terms and definitions
3.1.1
BCU
backscatter communication unit
device that responds to a command from an STA with backscatter through load modulation, and
that enables communication without power
3.1.2
BU
battery unit
battery and circuit capable of receiving wireless power to support the operations of devices and
sensors
3.1.3
HIE-AP
hybrid information and energy access point
device that decodes the channel signals whose sensitivity was changed by the SSN into digital
signals (0 or 1)
Note 1 to entry: An HIE-AP forms an STA and ISM-band channels for communication, detects the CSI or RSSI level
of the response using backscatter from the SSN, and transmits the response data from the SSN to the STA. It also
transmits CW-type power to the SSN for RF WPT.
3.1.4
impedance modulation
method of changing the sensitivity of the received signal from the channel between the STA
and HIE-AP by using backscatter modulation in the SSN according to the data
3.1.5
SSN
smart sensor node
device that changes the sensitivity of the received channel signals using backscatter modulation
Note 1 to entry: SSNs include IoT devices, wearable devices, and micro-sensors.
Note 2 to entry: An SSN consists of a backscatter communication unit (BCU) that supports communication without
power, a smart sensor unit (SSU) that identifies various sensors, and a battery unit (BU) that receives WPT.
3.1.6
SSU
smart sensor unit
sensor that can be attached to an SSN.
Note 1 to entry: Each sensor requires a different amount of power.
3.1.7
STA
station
device that can perform communication by occupying an ISM-band channel
Note 1 to entry: It transmits wireless power and data packets to SSNs by forming a channel and using the pulse
interval encoding (PIE) method.
3.2 Abbreviated terms
ASK amplitude shift keying
BCU backscatter communication unit
BU battery unit
CRC cyclic redundancy check
CSI channel state information
– 10 – IEC 62980:2022 © IEC 2022
CW continuous wave
FCS frame check sequence
HIE-AP hybrid information and energy access point
ISM industrial scientific and medical equipment
NDP null data packet
PIE pulse interval encoding
RFID radio-frequency identification
RFU reserved for future use
RSSI received signal strength indicator
RWP response waiting packet
SSN smart sensor node
SSU smart sensor unit
STA station
4 Overview
RF WPT includes WPT using energy harvesting, magnetic induction, or magnetic resonant
methods, and involves the wireless transmission of power to sensors and facilities for practical
use by employing RF waves. This document proposes a method of performing RF WPT to
battery-free sensors or facilities. When developing the technology of this document, the
developer shall refer to IEC 63006:2019 and IEC TR 63239:2020. The overall structure of
parasitic communication for RF WPT proposed in this document is depicted in Figure 1.
Parasitic communication (or ambient backscatter) uses existing radio frequency signals, such
as radio, television and mobile telephony, to transmit data without a battery or power grid
connection. Each such device uses an antenna to pick up an existing signal and convert it into
tens to hundreds of microwatts of electricity. This document defines procedures for a bi-
directional, long-distance wireless communication protocol for communication using
backscatter modulation of industrial, scientific, and medical (ISM)-band frequency signals
between stations (STA) and smart sensor nodes (SSNs), such as IoT devices, sensors, tags,
and wearable devices, and for RF WPT from a hybrid information and energy access point (HIE-
AP) to nearby SSNs.
Figure 1 – Usage of RF-WPT
Three components are required for the bi-directional, long-distance wireless communication
protocol using backscatter modulation of ISM-band signals, as shown in Figure 2:
• STA: performs communication by occupying a communication channel and transmits
wireless power and data packets for communication to the SSN in the PIE method.

• HIE-AP: decodes the channel signals whose sensitivity was changed by the SSN into digital
signals of 0 or 1. It forms a channel with the STA for communication, detects the CSI level
of the response from the SSN that used backscatter, and transmits the response data from
the SSN to the STA. It also transmits CW-type power to the SSN for RF WPT.
• SSN: changes the sensitivity of the channel signals received from the STA using backscatter
modulation and consists of a BCU, an SSU, and a BU.
– BCU: responding to a command from an STA with backscatter through load modulation
and can respond with backscatter using the wireless power transmitted by the STA.
– SSU: various sensors that can be attached to the SSN, each of which requires a different
amount of power.
– BU: battery and circuit capable of receiving wireless power to support the operation of
nodes and sensors.
Figure 2 – RF-WPT structure of using parasitic Wi-Fi communication technology
To summarize the operation process, RF power is first transmitted from the STA to the SSN to
drive the BCU of the SSN. Then, the SSN sends its data for the STA to the channel formed
between the STA and HIE-AP by changing its load, and the HIE-AP can receive data from the
SSN by decoding the CSI level of the information sent from the SSN. The information sent from
the SSN includes ID information, battery information, and sensor data. The STA sends wireless
power to the HIE-AP. The HIE-AP performs and controls RF WPT in real time based on the
information received from the SSN on battery, voltage of the SSN itself, and remaining battery
level.
Multi-device wireless charging systems that use the in-band field communication to exchange
data and control signals utilize the same frequency within the field area to increase the
efficiency of frequency. Information relating to regulation and certification is presented in
Annex A.
5 Communication procedures for RF WPT
5.1 General
The parasitic communication technology involved in downlink and uplink RF WPT can be
described separately. In downlink transmission, information is sent from the STA to the SSN,
while in uplink transmission, information is sent from the SSN to the STA as shown in Figure 3.

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Figure 3 – Parasitic downlink/uplink communication procedures
5.2 Communication procedures for parasitic downlink communication
The downlink communication procedures are illustrated in Figure 4. First, the STA and HIE-AP
form a communication channel. The STA transmits a data packet to the AP and SSN
simultaneously (① -> ②). The SSN decodes the received packet, then interprets the
information sent from the STA. And the STA performs its operation following command using
the energy contained in the packet.

Figure 4 – Specific parasitic downlink communication procedures
5.3 Communication procedures for parasitic uplink communication
The uplink communication procedures are depicted in Figure 5. In uplink communication, a
separate HIE-AP is required to read the information from the SSN (① -> ② -> ③). First, the
STA creates a channel with the HIE-AP and measures the sensitivity of the received signals
through the RSSI or the CSI. This procedure is employed because the SSN does not directly
perform active communication, but rather changes the sensitivity of the signals received from
the channel between the STA and HIE-AP through backscatter modulation when the STA
continuously sends power and packets. This signal change eventually affects the RSSI or the
CSI of the received signal strength of the HIE-AP. In this way, when the SSN changes the
sensitivity of the received signal through a kind of amplitude shift keying (ASK) method using
backscatter modulation, the HIE-AP measures the sensitivity of the received Wi-Fi signal and
decodes the information from the SSN according to the sensitivity (specifically, 1 is assigned
when the received sensitivity is better than the reference sensitivity, and 0 otherwise).

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Figure 5 – Specific parasitic uplink communication procedures
5.4 Backscatter downlink/uplink data flow
Figure 6 shows the data flow during downlink/uplink communication in detail. During downlink
transmission, the STA sends a preamble(P) + header(H) + data 1(D1) payload (P+H+D1) when
transmitting 1, and a preamble(P) + header(H) + data 0(D0) payload (P+H+D0) when
transmitting 0. Encoding is performed through a kind of PIE method. Figure 6 depicts the
process of sending 1000111b as an example. The SSN decodes the command from the STA by
detecting the energy level and measuring the length of the received packet. The SSN receives
the bit information in the Wi-Fi packet without interpretation. During uplink communication, the
tag sends a P+H+D0 payload. In this case, the SSN is decoded as 000.000b, and uplink
transmission is recognized. The SSN performs backscatter modulation on the information to be
sent. In the example, the SSN sends 1000.11b to the HIE-AP.

Figure 6 – Data flow during parasitic downlink/uplink communication
5.5 WPT process
Figure 7 depicts the RF WPT communication procedures in detail. The parasitic communication
status consists of three states: select, inventory, and access. In the select state, the STA
recognizes multiple SSNs. In the inventory state, an authentication procedure is performed to
select one of the recognized SSNs. In the access state, the SSN information is identified and
WPT is actively controlled. All of these communication methods involve downlink/uplink
transmission. In the access state, the battery and status information of the SSN is continuously
monitored, and the HIE-AP performs and controls the CW-type RF WPT. Figure 8 shows the
RF WPT control protocol.
Figure 7 – RF WPT access procedures

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Figure 8 – RF WPT control protocol
6 Physical layer
6.1 Modulation/coding method
6.1.1 General
Clause 6 describes the construction of frames for each preamble, header, and payload, and
defines a set of processes for modulation and coding.
6.1.2 Downlink modulation method
Downlink sequence of RF WPT communication uses the PIE method in which the length of a
packet is modulated according to the data. As shown in Figure 9, Data "0" in this downlink
method consists of a modulated preamble (P) + header (H) + data 0 (D0) that is a short null
data packet (NDP) without a payload. Data "1" in this downlink method consists of a modulated
into preamble(P) + header(H) + data 1(D1) that is a long null data packet (NDP) without a
payload. The OFDM training structure in Figure 9 is mainly used in time division multiple access.
The training sequence is used in order to maintain timings and to equalize them with the channel.

Figure 9 – PIE method packet configuration
6.1.3 Uplink modulation method
In uplink sequence of RF WPT, the SSN changes the sensitivity of the received signal of the
channel between the STA and HIE-AP according to the data through backscatter modulation.
The uplink transmission involves utilizing the NDP, which represents a signal of 0 in Figure 9,
and the two-level method in which the sensitivities of the received signals of 0 and 1 are different.
6.1.4 Downlink coding method
6.1.4.1 Preamble
The preamble transmits the preamble sequence 1111_0000 (see 6.2.2.2) as shown in
Figure 10, using the PIE method.

Figure 10 – Modulation and coding of the downlink preamble
When SSNs are woken up using the downlink preamble, variations of the preamble can be
continuously transmitted so that the channel is not lost according to the power required by each
SSN. The preamble transmission for wakeup continues while the STA attempts to communicate
with the SSN. The variable wakeup process can require the transmission of additional
preambles depending on the distance to the SSN, as well as the power required by the SSN.

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6.1.4.2 Payload
Figure 11 – Modulation and coding of the downlink preamble
The payload in Figure 11 adds 5 bits of the payload check sequence to the data to be
transmitted, as described in 6.2.2.3, and it transmits the data using the PIE method.
6.1.5 Uplink coding method
6.1.5.1 Preamble
Figure 12 – Modulation and coding of the uplink preamble
The preamble in Figure 12 converts the preamble sequence defined in 6.2.3.2 using the two-
level method, and then transmits it using impedance modulation.
6.1.5.2 Payload
Figure 13 – Modulation and coding of the uplink payload
The payload data in Figure 13 can be a maximum of 256 bits. The payload adds 5 bits of the
payload check sequence to the data to be transmitted, as discussed in 6.2.3.3, converts the
data using the two-level method, and transmits the data using impedance modulation.
6.2 Frame structure
6.2.1 General
In 6.2, the frame structure of the physical layer is defined. The downlink frame is transmitted
from the STA to the SSN, and the uplink frame is transmitted from the SSN to the HIE-AP. The
transmission frame structure is defined accordingly. The packets to be transmitted in the frame
are coded using the method defined in 6.1 according to the transmission direction.
6.2.2 Downlink frame structure
6.2.2.1 General
The downlink frame structure consists of a preamble and payload, as shown in Figure 14. The
payload consists of data and frame check sequence fields. The frame is transmitted from the
most significant bit (MSB). The data unit of the frame is bit, and it is coded using the method
defined in 6.1.3.
Figure 14 – Physical layer structure of the downlink frame
6.2.2.2 Preamble
and 4 bits of 0000 , as shown in Table 1.
The preamble has a total of 8 bits: 4 bits of 1111
2 2
The first 4 bits of the preamble operate the SSN, which is the receiving end, and the next 4 bits
are used to find the data start position
Table 1 – Downlink preamble structure
Downlink
Wakeup Sync finder
preamble
Number of bits 4 4
1111 0000
Description
2 2
6.2.2.3 Payload
The payload consists of a data field to be transmitted and a frame check sequence (FCS) field
to check for errors in the data field as shown in Table 2. When the length of the data is zero,
the frame check sequence is not included.
Table 2 – Downlink payload structure
Downlink
Data FCS
preamble
Number of bits 256 5
a) Payload data field
The recommended value of the quasi-static guarantee ratio (=payload/data rate), which is
used to maintain channel stability during communication based on backscatter, is 0,012 8.
In other words, 256 payloads are available because 320 payloads are available at a data
rate of 30 kb/s, in accordance with this document.
b) FCS
The FCS field is created using a 5-bit cyclic redundancy code (CRC). It is calculated for the
payload data and is not created if the length of the payload data is zero. The FCS is
calculated according to the definition in Table 3 and is then replaced with a complement to
be sent after the data.
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Table 3 – Downlink frame check CRC
Residual
CRC type Length Polynomial Initial value
value
5 bits
5 3
01001 00000
- x + x + 1
2 2
(packets)
6.2.3 Uplink frame structure
6.2.3.1 General
The uplink frame structure consists of a preamble and payload, as shown in Figure 15. The
preamble consists of the frame detection, starting point finder, and data preamble. The payload
consists of data and the FCS. The data unit of the frame is the bit, and the frame is coded using
the method defined in 6.1.4. When the same data (0 or 1) occurs consecutively due to the
backscatter frequency during uplink transmission from the SSN to the STA, the data
...