WO2014027710A1

WO2014027710A1 - In-band communication for wireless power transfer

Info

Publication number: WO2014027710A1
Application number: PCT/KR2012/006584
Authority: WO
Inventors: Yun Jae Won; Seung Ok Lim
Original assignee: Korea Electronics Technology Institute
Priority date: 2012-08-17
Filing date: 2012-08-17
Publication date: 2014-02-20

Abstract

This item defines the physical layer and the media access control layer protocols of in-band communication for a wireless power transfer system with multiple devices charging; particularly on MFAN that shares the same frequency band for both wireless power transfer and magnetic field communication. Consumers prefer this simplified improvement in a system which supplies power wirelessly to multiple devices at the same time. In order to efficiently control and manage the multiple devices charging, a magnetic field communication link provided by MFAN should be supported for a wireless power transfer system. This item defines the physical layer and the media access control layer protocol by which a magnetic field communication link provided by iWPTN is created, and data, control signals, and wireless power are exchanged between a basestation and devices.

Description

IN-BAND COMMUNICATION FOR WIRELESS POWER TRANSFER

This item defines the physical layer and the media access control layer protocols of in-band communication for a wireless power transfer system with multiple devices charging; particularly on MFAN that shares the same frequency band for both wireless power transfer and magnetic field communication.

A wireless charging system using a magnetic induction phenomenon as wireless power transmission technologies wirelessly transmitting energy has been used.

For example, an electric toothbrush, a cordless razor, or the like, is charged by a principle of electromagnetic induction. In recent years, wireless charging products capable of charging portable devices such as mobile phones, PDAs, MP3 players, notebook computers, or the like, using the electromagnetic induction have been released.

However, the magnetic induction scheme inducing current through magnetic field from a single coil to another coil is very sensitive to a distance between the coils and a relative position of the coils to sharply degrade transmission efficiency even when the distance between two coils are slightly spaced or twisted from each other. Therefore, the wireless charging system according to the magnetic induction scheme may be used only in a short range of several centimeters or less.

Meanwhile, US Patent No. 7,741,734 discloses a method of wireless non-radiative energy transfer using coupling of resonant-field evanescent tails. The basis of this technique is that two same-frequency resonant objects tend to couple, while interacting weakly with other off-resonant environmental objects, which makes it possible to transfer energy farther away compared to the prior art magnetic induction scheme.

There are the complexity and inconvenience of wire cable chargers by transferring power wirelessly.

This item supports wireless power transfer and several kbps data transmission in one frequency band based on a formed network within a distance of several meters. And it can be applied to various services and industries such as the following areas of application:

* Mobile phones: provide ubiquitous charging environments for portable devices

* Home appliances: allow desirable decoration and placement of appliances by elimination of wire cables and plugs

The media access control layer protocol is designed for the following scope:

* Variable superframe structure for wireless power transfer to multiple devices

* Simple and effective network topology for efficient wireless power transfer

* Dynamic address assignment for efficient timesharing among multiple devices

The physical layer protocol is designed for the following scope:

* One frequency band for both wireless power transfer and magnetic field communication

* Simple and robust modulation for low-cost implementation and minimized margin of error

* Variable coding and bandwidth for dynamic charging environment

Figure 1 Wireless Power Transfer System

Figure 2 Mobile Devices

Figure 3 Home Appliances6

Figure 4 iWPTN superframe structure for MFC

Figure 5 iWPTN superframe structure for WPT

Figure 6 iWPTN

Figure 7 UID structure

Figure 8 iWPTN-B state diagram

Figure 9 iWPTN-D state diagram

Figure 10 PHY layer frame format

Figure 11 Preamble format

Figure 12 MAC layer frame format

Figure 13 Format of frame control field

Figure 14 Request frame format

Figure 15 Response frame format

Figure 16 Data frame format

Figure 17 Frame format of response acknowledgement

Figure 18 Frame format of data acknowledgement

Figure 19 Payload format of request frame

Figure 20 Block format of association request

Figure 21 Block format of disassociation request

Figure 22 Block format of association status request

Figure 23 Block format of data request

Figure 24 Block format of group ID set-up request

Figure 25 Block format of power transfer request

Figure 26 Block format of power transfer start request

Figure 27 Payload format of response frame

Figure 28 Block format of association response

Figure 29 Block format of disassociation response

Figure 30 Block format of association status response

Figure 31 Block format of data response

Figure 32 Block format of group ID set-up response

Figure 33 Block format of power transfer response

Figure 34 Payload format of data frame

Figure 35 Payload format of acknowledgement frame

Figure 36 Block format of association response confirmation

Figure 37 Block format of disassociation response confirmation

Figure 38 Block format of association status response confirmation

Figure 39 Block format of data response confirmation

Figure 40 Block format of group ID set-up response confirmation

Figure 41 PSFI in the response period for WPT

Figure 42 PS beacon format

Figure 43 Frame control in PS beacon

Figure 44 PSF in the response period for WPT

Figure 45 Frame control in PSF

Figure 46 BPTRq format

Figure 47 BPTRs format

Figure 48 Association procedure

Figure 49 Disassociation procedure

Figure 50 Procedure of association status confirmation

Figure 51 Procedure of data transmission in response period

Figure 52 Procedure of data transmission in spontaneous period

Figure 53 Procedure of group ID set-up

Figure 54 Procedure of wireless power transfer

Figure 55 Procedure of battery-out

Figure 56 Envelope waveform

Figure 57 BPSK-modulated signal

Figure 58 ASK-modulated signal

Figure 59 WPT signal

3 Terms and definitions

For the purposes of this document, the following terms and definitions apply.

3.1 Wireless power transfer (WPT)

A mechanism in which a unit having enough power wirelessly transfer it to other units

3.2 Wireless power transfer network (WPTN)

A network in which a system provides wireless power to considered devices based on the recognition of wireless power transfer status of them by wired or wireless communication

3.3 Magnetic field communication (MFC)

A wireless communication using magnetic field

3.4 In-band wireless power transfer network (iWPTN)

A wireless power transfer network that uses only one frequency band for both wireless power transfer and magnetic field communication

3.5 In-band wireless power transfer network - basestation (iWPTN-B)

A system that manages the wireless power transfer to devices, and connection and release of devices within the charging and communication area, and manages the sending and receiving time of wireless power transfer and data in an iWPTN

3.6 In-band wireless power transfer network - device (iWPTN-D)

A device except the basestation that forms a network in an iWPTN, and receives wireless power from the basestation

3.7 Magnetic field area network (MFAN)

A wireless network that provides wireless communication based on reliable in-band magnetic field communication using magnetic field

4 Symbols and abbreviated terms

The following acronyms are used in this document:

ABNR Abnormal

ARq Association Request

ARs Association Response

ARA Association Response Acknowledgement

ASC Association Status Check

ASK Amplitude Shift Keying

ASRq Association Status Request

ASRs Association Status Response

ASRA Association Status Response Acknowledgement

BPSK Binary Phase Shift Keying

BPTRq Battery-out Power Transfer Request

BPTRs Battery-out Power Transfer Response

MFC Magnetic Field Communication

CRC Cyclic Redundancy Check

DA Data Acknowledgement

DaRq Disassociation Request

DaRs Disassociation Response

DaRA Disassociation Response Acknowledgement

DRq Data Request

DRs Data Response

DRA Data Response Acknowledgement

FCS Frame Check Sequence

GSRq Group ID Set-up Request

GSRs Group ID Set-up Response

GSRA Group ID Set-up Response Acknowledgement

HCS Header Check Sequence

LSB Least Significant Bit

MAC Media Access Control

NRZ-L Non-Return-to-Zero Level

PHY Physical Layer protocol

PTRq Power Transfer Request

PTRs Power Transfer Response

PS Power Status

PSF Power Status Feedback

PSFI Power Status Feedback Interval

RA Response Acknowledgement

RR Response Request

SIFS Short Inter Frame Space

TDMA Time Division Multiple Access

UID Unique Identifier

5 Overview

iWPTN is a wireless network that can transmit power wirelessly, and required data and control commands are exchanged by MFC system utilizing the same frequency as wireless power transfer. Due to magnetic field characteristics and the level of power that meets regulations, the supported communication range is greater than the power transfer range. Based on the communication link supported by MFAN, required information can be exchanged, and iWPTN-B can take scheduling methods into account in providing an efficient WPT.

The MFC system in iWPTN has the center carrier frequency band (30KHz to 300KHz) which is the same frequency band as wireless power transfer. It uses a simple and robust modulation method like BPSK for low cost implementation and low error probability, and a dynamic coding method like Manchester or NRZ-L coding for strongness against noise. It provides a data transmission speed of several kbps within a distance of several meters. For WPT, unmodulated sine sinusoidal signal is used to increase WPT efficiency.

The iWPTN uses a simple and efficient network topology like star topology for low power consumption. And it uses dynamic address assignment for small packet size and efficient address management. It uses an adaptive link quality control using variable transmission speeds and coding methods according to wireless charging environments. The participating nodes in iWPTN are divided according to their function into iWPTN-B and iWPTN-D. Only one iWPTN-B exists within one iWPTN network, and several iWPTN-D nodes form a network centered on iWPTN-B. iWPTN-B manages the connection and release of iWPTN-D. iWPTN uses the TDMA (Time Division Multiple Access) method for sending and receiving data. When iWPTN-D joins iWPTN network managed by iWPTN-B, iWPTN-B allocates time-slots for iWPTN-D’s transmission according to iWPTN-D’s request and iWPTN-B’s judgment.

As shown in Figure 1, iWPTN-B and iWPTN-Ds can be located indoor environment. If iWPTN-B receives data related to wireless power transfer such as ID, battery information, etc. from iWPTN-Ds, it collects the received data, and it calculate required factors such as power transfer sequences and the number of time slots for wireless power transfer. iWPTN-B sends control data to iWPTN-Ds to manage the iWPTN.

iWPTN is applied to various industries. It is applied to electric devices which need power to operate their own functions. For some industries, it can provide functional improvement by providing power wirelessly outside of devices. Those devices do not suffer from battery life and the problem of structure design from facilitating huge batteries.

For example, for mobile devices which always have battery issues by a huge amount of using time (Figure 2) iWPTN provide ubiquitous charging environments. For the home appliances (Figure 3), complex wire cables and plugs will be eliminated so as to allowing desirable decoration and placement of appliances.

6 Network elements

6.1 General

The main elements of iWPTN are divided into time and physical element. The time element refers to the superframe consisting of a request period, a response period, and a spontaneous period, and the physical element refers to the network consisting of iWPTN-B and iWPTN-Ds. The most basic one in the physical element is the node. Node is classified into two types: iWPTN-B to manage the network and iWPTN-D to communicate with iWPTN-B.

Figure 6-7 show the structures of superframe and network which are the time and physical elements, respectively. The node that needs to be decided first in iWPTN is iWPTN-B, and the superframe begins with iWPTN-B transmitting a request packet in the request period. iWPTN-B is charged of managing the association, disassociation, release, and scheduling of iWPTN-Ds. One iWPTN can use one channel where only one node is utilized as iWPTN-B and the rest of them become iWPTN-D. The rest of the nodes in iWPTN excluding iWPTN-B becomes iWPTN-D. Note that any nodes can become either iWPTN-B or iWPTN-D depending upon its role. Basically, a peer-to-peer connection between iWPTN-B and iWPTN-D is considered

6.2 Time element

The time element used in iWPTN is the time slot of the TDMA method. iWPTN-B manages the iWPTN-D group that transmits data in the response period, and the time slots are self-arranged by the selected iWPTN-Ds.

6.2.1 Time element for MFC

The superframe of iWPTN for magnetic field communication, as shown in Figure 4, consists of a request period, a response period, and a spontaneous period, and the lengths of the request and response period are variable. The superframe begins with iWPTN-B transmitting a RR packet to iWPTN-Ds in the request period.

The RR packet has information which iWPTN-Ds can send response packets during response periods, and the selected iWPTN-Ds can transmit the response packet in the response period according to the RR packet information.

6.2.1.1 Request period

In the request period, iWPTN-B transmits the RR packet with the information about the usage of iWPTN-Ds in order for iWPTN-D to send the response packet during response periods.

6.2.1.2 Response period

In the response period, iWPTN-D can transmit the response packet according to the received RR packet of iWPTN-B. The response period can be divided into several time slots according to the number of the selected iWPTN-Ds in iWPTN. Each time slot length is variable according to the length of the response frame, and the acknowledgement. If the iWPTN-B schedules a response period, the slot number is decided by the order of the divided time slot. Otherwise the slot number is zero. iWPTN-B assigns time slots to either iWPTN-D or a particular group for the use of the response period, and the nodes in the assigned group independently transmit the data frame in the response period.

6.2.1.3 Spontaneous period

The spontaneous period begins when there is no node transmitting the response packet for a certain period of time. In this period, nodes can transmit data even without iWPTN-B’s request. This period is maintained until iWPTN-B transmits a request packet.

6.2.2 Time element for WPT

The superframe of iWPTN for WPT, as shown in Figure 5, consists of a request period, a response period, and a spontaneous period, and the lengths of those periods are variable. The superframe begins with iWPTN-B transmitting a PTRq packet to iWPTN-Ds in the request period. When iWPTN-D receives the packet, it sends the PTRs packet as the response. Based on the PTRs packets, iWPTN-B sends the PTS packet including scheduling information that iWPTN-Ds can receive WPT during response periods, and the selected iWPTN-Ds can transmit the PSF packet as the response of the PS beacon from iWPTN-B in the power status feedback interval.

6.2.2.1 Request period

In the request period, iWPTN-B transmits the RR packet which contains WPT scheduling information. iWPTN-D receiving the RR packet prepares to take WPT from iWPTN-B according to the scheduling information.

6.2.2.2 Response period

In the response period for WPT, iWPTN-B provides WPT for iWPTN-Ds according to the sequence of scheduling. The response period can be divided into several time slots according to the number of the selected iWPTN-Ds in iWPTN. Each time slot length is variable according to the length of WPT duration. If the iWPTN-B schedules all time slots of a response period, the slot number is decided by the order of the divided time slot. Otherwise the slot number is zero. iWPTN-B assigns time slots to either iWPTN-D or a particular group. According to the scheduling sequence, one iWPTN-D receives WPT, or all iWPTN-Ds in the assigned group simultaneously receive wireless power. Compared to the response period for magnetic field communication, the response period for WPT has the PSFI. This PSFI, the length is variable, is for quick power status update and abnormal situation.

6.2.2.3 Spontaneous period

The spontaneous period begins when iWPTN-B confirms all PSF packets from the considered iWPTN-Ds in the last time slot of the response period. In this period, nodes can transmit the EPTq packet even without iWPTN-B’s request. When iWPTN-B receives the EPTq packet, iWPTN-B provides WPT for a certain amount of time after transmitting the EPTs packet. This period is maintained until iWPTN-B transmits a request packet.

6.2.3 Network activation

The superframe of iWPTN is divided into the request period, the response period, and the spontaneous period. iWPTN-B and iWPTN-Ds in iWPTN operate in each period as follows:

6.2.3.1 Request packet transmission within the request period

In the request period, iWPTN-B sends the RR packet to iWPTN-Ds. Based on this, the iWPTN-D that have received the RR packet decide whether to transmit response packets in the response period. iWPTN-B can determine the iWPTN-D group to transmit in the response period.

6.2.3.2 Response packet transmission within the response period

The iWPTN-Ds selected by iWPTN-B can transmit the response packet in the response period. When iWPTN-D transmits the response packet in the response period, iWPTN-B that has received the response packet transmits the RA packet. iWPTN-D that has not received the RA packet transmits response packets every time-slot until it receives a RA packet from iWPTN-B.

6.2.3.3 Wireless power transfer within the response period

The iWPTN-Ds selected by iWPTN-B can receive WPT in the response period. After each time slot, there is a PSFI for quick power status update and abnormal situation. During WPT, when iWPTN-D receives the PS beacon in the PSFI, it transmits the PSF packet to iWPTN-B for notifying the updated power status as the response for the PS beacon in the PSFI. When abnormal situation is sensed by the iWPTN-B, it is notified to all iWPTN-Ds in the PSFI by the iWPTN-B. When the iWPTN-Ds recognize error by receiving the PS beacon, they wait until receiving a request from the iWPTN-B.

6.2.3.4 Data packet transmission in the spontaneous period

A spontaneous period begins if iWPTN-D does not transmit any response packets and not receive any power for a certain period of time, and this period is maintained until iWPTN-B transmits a RR packet. In the spontaneous period, iWPTN-D can transmit data without the request of iWPTN-B.

6.2.3.5 Wireless power transfer in the spontaneous period

A spontaneous period begins if iWPTN-B confirms all PSF packets from the considered iWPTN-Ds in the last time slot of the response period, and this period is maintained until iWPTN-B transmits a RR packet. In the spontaneous period, iWPTN-Ds can transmit the EPTq packet even without iWPTN-B’s request. When iWPTN-B receives the EPTq packet, iWPTN-B provides WPT for a certain amount of time after transmitting the EPTs packet as the response to the EPTq packet.

6.3 Physical element

The physical element configuring iWPTN is divided into iWPTN-B and iWPTN-D in which all iWPTN-Ds are connected into iWPTN-B (i.e. a central connectivity device). The basic element, node, is distinguished into iWPTN-B and iWPTN-D according to its role. iWPTN-B manages the whole iWPTN and there must exist only one iWPTN-B per one network. iWPTN-B manages iWPTN-D by sending the RR packet. iWPTN-D must transmit response packets according to iWPTN-B’s management. iWPTN can be configured as shown in Figure 6.

6.3.1 iWPTN-B

iWPTN-B is a node that manages iWPTN; only one iWPTN-B exists per one network, and it manages and controls iWPTN-D by the RR packet.

6.3.2 iWPTN-D

iWPTN-D is a node that resides within a iWPTN (excluding iWPTN-B), and a maximum of 65,519 iWPTN-Ds can exist per network. It transmits response packets according to the RR packet transmitted by iWPTN-B.

6.4 Address element

In order to identify iWPTN-Ds, iWPTN uses address systems such as iWPTN ID, UID, group ID, node ID, and charging ID.

6.4.1 iWPTN ID

iWPTN has its own ID that identifies each network from the others; the value should not be duplicated in other iWPTNs, and the value is maintained as long as iWPTN exists. Its value is defined by user to distinguish networks.

6.4.2 UID

UID is a unique identifier consisting of 64 bits; it consists of group ID, IC manufacturer's code, and IC manufacturer's serial number. iWPTN-D is identified by UID.

Figure 7 UID structure

6.4.3 Group ID

iWPTN-D can be grouped by applications. Group ID is the identifier for the grouped iWPTN-Ds within the network. iWPTN-B can request a response to a specific iWPTN-D group in order to mitigate the packet collision. Some group IDs are reserved in Table 1. Its value is defined by user to distinguish groups.

Table 1 Reserved group ID

6.4.4 Node ID

Node ID is an identifier used instead of UID to identify nodes, and it has a 16 bit address assigned by iWPTN-B. Some node IDs are reserved in Table 2.

Table 2 Reserved node ID

6.4.5 WPT ID

WPT ID is an identifier used during WPT. The ID has a 8 bit address assigned by iWPTN-B for quick communication during WPT. The ID can be allocated to iWPTN-Ds during the request period right before WPT in the response period. Some WPT IDs are reserved in Table 3.

Table 3 Reserved charging ID

7 Network status

7.1 General

In a iWPTN, iWPTN-D may enter the active states of network configuration, network association, response transmission, data transmission, network disassociation, network release, and wireless power transfer.

7.2 Network configuration

iWPTN-B configures a network by transmitting a request packet to iWPTN-D in the request period. iWPTN ID is included in the request packet so that iWPTN-D can identify the connecting network. The minimum period of network means when only iWPTN-B exists, and it consists of only the request period and the spontaneous period.

7.3 Network association

When iWPTN-B sends the ARq packet in the request period, iWPTN-D probes the received packet and then if it is the ARq packet for the desired iWPTN, iWPTN-D sends the ARs packet to the iWPTN-B in the response period. iWPTN-B, having received the ARs packet, transmits the ARA packet to iWPTN-D. The network association of iWPTN-D is completed upon receiving the ARA packet from iWPTN-B.

7.4 Network disassociation

iWPTN-D, associated with iWPTN, can be disassociated either by iWPTN-B’s request or by itself. iWPTN-B can send the DaRq packet to iWPTN-D according to the current network status for a forced disassociation. In the case of spontaneous disassociation due to shutting down and going out of the network coverage, iWPTN-B can know the association status of iWPTN-D by the response of ASRq from iWPTN-B.

7.5 Data transmission

When iWPTN-B sends the DRq packet in the request period to iWPTN-D, iWPTN-D sends DRs packet to iWPTN-B according to the requested data type. Upon receiving the DRs packet, iWPTN-B sends the DRA packet to iWPTN-D, and iWPTN-D, having received the DRA packet, completes the data transmission.

7.6 Wireless power transfer

When iWPTN-B sends the PTRq packet in the request period to iWPTN-Ds, iWPTN-Ds transmit the PTRs packet in the response period. Based on the information in the PTRs packet, iWPTN-B schedules time slots for WPT, and transmits the PTS packet which contains the scheduling information in the request period. iWPTN-Ds receive WPT from iWPTN-B according to the scheduling sequence in the response period. WPT can be provided to a iWPTN-D or a group during each time slot. After each iWPTN-D or a group receives WPT, there is a PSFI for quick power status update. When iWPTN-Ds receive the PS beacon from iWPTN-B in the PSFI, they send the PSF packet only if the iWPTN-B requests the packet. After confirming the PSF packets, the iWPTN-B provides WPT to iWPTN-D in the next slot. During WPT, iWPTN-B detects error, it stops WPT. When the PSFI begins, iWPTN-B notifies the detection of error to other iWPTN-Ds by sending PS beacon. WPT is completed when iWPTN-B receives the PSF packet from the last iWPTN-D or the last group in the last time slot of the response period.

7.7 Battery-out

When a iWPTN-D in battery-out comes to iWPTN, it receives power during the response period even though it was not considered in the scheduling. After receiving power enough to perfrom a basic function of MFC, it stops to receive power. In the spontaneous period, it then receives additional power by sending the BPTRq packet. When the iWPTN-D receives power more than a threshold level, then it stops to receive power, and waits a request period for joining the iWPTN.

7.8 Network release

iWPTN release can be divided into normal release through the request of iWPTN-Ds and abnormal release due to a sudden situation. Normal release refers to iWPTN-B releasing the network by its own decision and by sending the DaRq packet to all iWPTN-Ds. Abnormal network release refers to iWPTN-B shutting down or going out of the network coverage.

7.9 iWPTN node state

iWPTN node state includes the iWPTN-B state and the iWPTN-D state. In detail, iWPTN-B states are divided into the standby state, the packet analysis state, the packet generation state, and the power transfer state whereas iWPTN-D states are composed of the hibernation state, the activation state, the standby state, the packet analysis state, the packet generation state, the mute state, and the power receiving state.

7.9.1 iWPTN-B state

The state of iWPTN-B goes to the standby state when the power turns on. In the standby state, when the COMM system commands sending the RR packet or the superframe begins, the state of iWPTN-B goes to the packet generation state and iWPTN-B sends the RR packet to iWPTN-Ds. And then the state of iWPTN-B goes back to the standby state (see 4 path in figure 8). If iWPTN-B receives the packet (either response or data packet) from iWPTN-Ds while doing the carrier detection in the standby state, the state of iWPTN-B goes to the packet analysis state (see 1 path in figure 8). If the destination ID of the received packet and the node ID of iWPTN-B are the same, the state of iWPTN-B goes to the packet generation state, and then iWPTN-B generates the RA or DA packet and sends it to iWPTN-D in the packet generation state (see 1 path in figure 8). After that, the state of iWPTN-B goes back to the standby state (see 4 path in figure 8). On the other hand, if there are errors in the data packet, the state of iWPTN-B goes back directly to the standby state (see 3 path in figure 8). In the packet analysis state, when there are errors in the received response packet or destination ID of the received response packet and node ID of iWPTN-B do not correspond, iWPTN-B regenerates the RR packet in the packet generation state and retransmits it to iWPTN-Ds, and then the state goes to the standby state (see 2 path in figure 8). If these failures occur consecutively, the procedure of the packet analysis state is repeated as many times as needed (maximum N times). In (N+1)th procedure, the state of iWPTN-B goes from the packet analysis state to the standby state (see 2 path in figure 8).

For WPT, when superframe begins, the state of iWPTN-B goes to the packet generation state to send the PTRq packet, and goes to the standby state after sending the packet (see path 4 in figure 8). The state goes to the packet analysis state once iWPTN-B receives the PTRs packet (see path 1 in figure 8). After confirming the packet, the state goes to the packet generation state to create the PTS packet containing scheduling information (see path 5 in figure 8). After sending the PTS packet, the state of iWPTN-B goes to the power transfer state to provide WPT to a desired iWPTN-D or group which is scheduled in the first order (for the description below, see path 5 in figure 8). The state of iWPTN-B goes back to the packet generation from the power transfer state, when a PSFI begins. After transmitting the PS beacon to all iWPTN-Ds in the beginning of the PSFI, the state goes to the standby state for receiving the PSF packet from iWPTN-Ds. Once receiving the PSF packet, the state goes to the packet analysis state. After confirming PSF packet, the state goes to the power transfer state for providing WPT to the next iWPTN-D or the next group. This iteration from the power transfer state to the packet analysis state is repeated until all iWPTN-Ds receive WPT. After confirming the PSF packet in the packet analysis state, the state goes to the standby state if the PWR system command ends. When error detects, the state goes to the standby state. In battery-out situation, after confirming the BPTRq packet from iWPTN-D, iWPTN-B goes to the packet generation state from the packet analysis state. The state of iWPTN-B goes to the power transfer state after sending the BPTRs packet. When the MFC system commands or superframe begins, the state goes to the packet generation state to create the RR packet (see path 4 in figure 8). iWPTN-B state diagram is as Figure 8.

7.9.2 iWPTN-D state

The state of iWPTN-D goes into the hibernation state when the power turns on. In the hibernation state, when the wake-up sequence is detected, the state goes into the activation state (for description below, see path 1 in figure 9). The wake-up sequence is defined in 8.1. When iWPTN-D receives the RR packet, the state of iWPTN-D goes into the packet analysis state and iWPTN-D analyzes the received RR packet. If the destination ID of the RR packet and iWPTN-D ID (group ID and node ID) correspond, the state of iWPTN-D goes into the packet generation state and iWPTN-D sends the response packet to iWPTN-B, and then the state of iWPTN-D moves into the standby state (see path 3 in figure 9). If not, the state goes back to the hibernation state (see path 2 in figure 9).

While doing the carrier detection in the standby state, the state of iWPTN-D goes to the hibernation state when iWPTN-D receives the RA packet of its own node (see path 1 in figure 9) or to the packet generation state when MFNA-N receives the RA packet of other nodes (see path 1 in figure 9). And the state of iWPTN-D goes to the hibernation state when the slot-number is not allocated and the time-out period is over in the standby state (see path 1 in figure 9) or to the packet generation state when the slot-number is allocated and the time-out period is over (up to N times consecutively) (see path 1 in figure 9). However, the state goes to the hibernation state when the slot-number is allocated and the time-out period at N+1th is over (see path 1 in figure 9). If the slot-number is allocated and iWPTN-D does not receive RA packet during the time-out period, the state of iWPTN-D goes from the standby state to the packet generation state (see path 1 in figure 9). And then iWPTN-D regenerates and retransmits the response packet to iWPTN-B and the state of iWPTN-D goes from the packet generation state to the standby state (see path 3 in figure 9). The retransmission of the response packet is repeated as many times as needed (maximum N times). In the (N+1)th time-out period, the state goes from the standby state to the hibernation state (see path 1 in figure 9). If iWPTN-D receives the RR packet in the standby state while doing the carrier detection, the state is moved to the packet analysis state (see path 1 in figure 9).

When the system interrupt occurs in the hibernation state, the state of iWPTN-D is changed to the activation state (for description below, see path 3 in figure 9). If iWPTN-D receives data from the system, the state goes to the packet generation state. And then iWPTN-D generates and sends data packet to the iWPTN-B, and the state of iWPTN-D goes to the standby state. If iWPTN-D receives the DA packet, the state goes back to the hibernation state. If not, the state goes to the packet generation state and iWPTN-D retransmits the data and then the state goes back to the standby state up to N times.

For WPT, if iWPTN-D receives the PTRq packet in the request period, the state goes to the packet generation state to create the PTRs packet as the response to the PTRq packet (see path 5 in figure 9). After sending the PTRs packet in the response period, the state goes to the hibernation state. When the iWPTN-D receives the PTS packet, the state goes to the packet analysis state. After confirming the packet, the state goes either to the power transfer state or the power isolation state. If the next time slot is not turn for WPT to the iWPTN-D, the state goes to the power isolation state from the packet analysis state to be not harmful to other iWPTN-Ds which will take WPT in the next time slot. When PSFI begins, iWPTN-D goes to the activation state. When it receives the PS beacon from the iWPTN-B, the state goes to the packet analysis state. On the other hand, if the iWPTN-D is the considered node for WPT in the next time slot, the state goes to the power transfer state from the packet analysis state. When power transfer is finished, the state goes to the standby state to receive the PS beacon from the iWPTN-B. Once it receives the PS beacon from the iWPTN-B, the state goes to the packet analysis state.

In the packet analysis state, when there is a request for the PSF packet, the state goes to the packet generation state to create the PSF packet and to send it to iWPTN-B for quick power status update. After sending the PSF packet, if the next time slot is not turn for WPT to the iWPTN-D goes to the power isolation state to be not harmful to other iWPTN-Ds which will take WPT in the next time slot. Otherwise, the state goes to the power transfer state to receive WPT. This iteration from the power isolation state to the packet analysis state is repeated until the response period for WPT ends. In this case, the state goes to the standby state from the packet analysis state.

The iteration also stops when the detection of error is recognized. For iWPTN-D which currently receive WPT, when it detects the stop of WPT during the current time slot (not the end of the slot), the state goes to the standby state. And then, if iWPTN-D receives the PS beacon, the state goes to the packet analysis state. Other iWPTN-Ds which do not currently receive WPT go to the activation state when PSFI begins, and go to the packet analysis state. In the packet analysis state, iWPTN-D goes to the hibernation state when it recognizes error begins by confirming the PS beacon.

When iWPTN-D is in battery-out, the state stays in the hibernation state, and gathers a small amount of power which is for other scheduled iWPTN-Ds in the response period (for description below, see path 4 in figure 9). If the iWPTN-D detects the wake-up 2 signal, the state goes to the hibernation packet analysis state to analyze the PS beacon. After confirming the PS beacon, the state goes back to the hibernation state. When the response period ends, the state goes to the hibernation packet generation state to create the BPTRq packet. After sending the packet, the state goes to the hibernation state to wait for the BPTRs packet. When the wake-up 2 signal is detected, the state goes to the hibernation packet analysis state to analyze the BPTRs packet. After confirming the packet, the state goes to the power transfer state to receive WPT in the spontaneous period. iWPTN-D state diagram is as Figure 9.

8 PHY layer

8.1 PHY layer frame format

8.1.1 General

This section describes the physical layer frame format. As shown in Figure 10, the PHY layer frame consists of three components: the preamble, the header, and the payload. When transmitting the packet, the preamble is sent first, followed by the header and finally by the payload. An LSB is the first bit transmitted.

8.1.2 Preamble

As shown in Figure 11, the preamble consists of two portions: a wake-up sequence and a synchronization sequence. An 8-bit wake-up sequence is categorized into two types: one is for general MFC, and the other one is for general WPT. The wake-up 1 sequence for MFC consists of [0000 0000], and the wake-up 2 sequence for WPT consists of [1111 1111]. A 16-bit synchronization sequence consists of a 12-bit sequence of [000000000000] followed by a 4-bit sequence of [1010]. The wake-up 1 sequence is only included in the preamble of RR packet in the request period, and the wake-up 2 sequence is only included in the preamble of the PS beacon in the request period and the BPTRs packet in the spontaneous period. The synchronization sequence can be used for the packet acquisition, the symbol timing and the carrier frequency estimation.

The preamble is coded using the TYPE 0 defined in 7.1.3. The wake-up sequence is modulated by ASK, but the synchronization sequence by BPSK.

8.1.3 Header

The header is added after the preamble to convey information about a payload. The header format is defined in ISO/IEC 15149.

8.1.4 Payload

Payload format is defined in ISO/IEC 15149.

8.1.5 Frame check sequence (FCS)

The payload is checked for errors using a CRC-16 FCS. The sequence is defined in ISO/IEC 15149.

8.2 Coding and modulation

8.2.1 Coding

The MFC between iWPTN-B and iWPTN-D uses either Manchester coding or NRZ-L coding. In addition, scrambling for the encoded data is used. Those coding and scrambling are defined in ISO/IEC 15149.

8.2.2 The data rate and coding type

The data rate and coding for preamble/header and payload is defined in ISO/IEC 15149.

8.2.3 Modulation

The MFC between iWPTN-B and iWPTN-D uses either ASK modulation or BPSK modulation. Details for those modulations are defined in ISO/IEC 15149.

8.2.4 The coding and modulation process

The coding and modulation process for the preamble, header, and payload is defined in ISO/IEC 15149.

9 MAC layer frame format

9.1 General

The MAC frame of iWPTN consists of the frame header and the frame body. The frame header has information for data among iWPTN-Ds, and the frame body has the data for transmissions between iWPTN devices.

9.2 Frame format

All frame of MAC consists of the frame header and the frame body as shown in Figure 12.

1) Frame header: Consists of the iWPTN ID, frame control, source node ID, destination node ID, and sequence number. The frame header can be used for the data transmission.

2) Frame body: Consists of the payload that contains the data for transmissions between iWPTN devices and the FCS used to check errors within the payload.

9.2.1 Frame header

Frame header has information for the transmission/reception of frames and flow control.

9.2.1.1 iWPTN ID

As shown in Figure 12, iWPTN ID field consists of 1 byte and is used to identify networks.

9.2.1.2 Frame control

Frame control fields consist of the frame type, the acknowledgement policy, the first fragment, the last fragment, and the protocol version; its format is shown in Figure 13.

Each field is explained as follows:

1) Frame type field consists of 3 bits; refer to 8.3 for the details on frame types.

2) Acknowledgement policy field consists of 2 bits; in the case where the received frame is an acknowledgement frame, it indicates the policy of the received acknowledgement frame, otherwise it indicates the policy of the acknowledgement frame for a destination node.

The following shows the acknowledgement policy:

a) No acknowledgement: Destination node does not acknowledge the transmitted frame, and the source node considers the transmission successful regardless of the transmission result. Such method can be used in the frame that is transmitted for 1:1 or 1:N, transmission which do not required the acknowledgement.

b) Single acknowledgement: The destination node that received the frame sends an acknowledgement frame as a response to the source node after an SIFS. This acknowledgement policy can only be used for 1:1 transmission.

c) Multiple acknowledgement: The destination node that received the frames sends an acknowledgement frame as a response to the multiple source nodes after an SIFS. This acknowledgement policy can be used for 1:N transmission.

d) Data acknowledgement: The destination node that received the data frame sends data acknowledgement frame as a response to the source node after an SIFS. This acknowledgement policy can only be used for 1:1 data transmission.

3) First fragment field is 1 bit; ‘1’ indicates that frame is the start of the request, response or data packet from a higher layer, while ‘0’ means that it is not the start.

4) End fragment field is 1 bit; ‘1’ indicates that frame is the end of the request, response or data packet from a higher layer, while ‘0’ means that it is not the end.

5) Protocol version field consists of 2 bits, and the size and location are fixed regardless of the protocol version of the system. The present value is 0, and increases by 1 each time a new version is released. When a node receives a packet with a version higher than its own, it discards it without notifying the source node.

6) Reserved: a field reserved for the future use.

9.2.1.3 Sequence number

The sequence number field has 8 bits of length, and indicates the frame sequence number. In data frames, a sequence number between 0 and 255 is assigned by means of an incremental counter for each packet, and once it reaches 255 it wraps back to 0.

9.2.2 Frame body

Frame body has a variable length and consists of the payload and the FCS. Each payload has a different format according to the frame type in the frame control field, and the FCS is used to check for error in the frame.

9.2.2.1 Payload

Payload has the transmission data between iWPTN-B and each iWPTN-D, and the length has a variable value between 0 and 247.

9.2.2.2 Frame check sequence

FCS is 16 bits in length, and is used to verify whether the frame body was received without error. It is generated by using the following 16th standard generator polynomial:

9.3 Frame type

The frame type is defined as 4 kinds of types, the request frame, the response frame, the data frame, and the n acknowledgement frame.

Table 4 Frame type value

9.3.1 Request frame

The request frame is used when iWPTN-B sends a RR packet in the request period to a certain iWPTN-D in iWPTN, or broadcasts information to all iWPTN-Ds. The request frame format is shown in Figure 14. Note that the acknowledgement policy, when broadcasting the RR packet, is no acknowledgement. And the RR packet includes ARq, DaRq, ARsRq, DRq, PRRq, and so on.

9.3.2 Response frame

The response frame is used when iWPTN-Ds send the response packet for the request of iWPTN-B in the response period. The iWPTN-D sends the response packet within a certain number of times in the response period until an acknowledgement packet is received.

9.3.3 Data frame

The data frame is used when iWPTN-D transmits data to iWPTN-B in the spontaneous period without iWPTN-B’s request.

9.3.4 Acknowledgement frame

The acknowledgement frame includes the RA frame and the DA frame. In the case that iWPTN-B transmits a RR packet, iWPTN-D receiving the RR packet transmits the response packet and iWPTN-B receiving the response packet transmits the RA packet. The payload of the acknowledgement frame includes the response confirmation data about the received response packet. iWPTN-B, having received the response packet, answers iWPTN-D by sending the RA packet after the SIFS in the response period. DA frame is the acknowledgement frame about the received data packet. iWPTN-B answers iWPTN-D that has transmitted the data packet by sending the DA packet after an SIFS in the spontaneous period.

As shown in Figure 18, the DA frame consists of the frame header and the frame body. When the destination node ID is 0xFFFE which is un-joined node ID, the UID field has been included.

9.4 Payload format

The payload format is composed of the request frame, response frame, data frame, and acknowledgement frame.

9.4.1 Request frame

As shown in Figure 19, the payload for the request frame consists of the group ID, the request code, the length, and more than one request block. When the group ID is 0xFF, it indicates that iWPTN-B requests a response to all iWPTN-D groups.

9.4.1.1 Group ID

The group ID field consists of 1 byte and is used to send RR packets to certain groups. For the details of the group ID, refer to 6.4.3.

9.4.1.2 Request code

The request code in the payload of a request frame is shown in Table 5.

Table 5 Payload request code of request frame

9.4.1.3 Length

The length field consists of 1 byte; it indicates the total length of the request block, and the length field value is variable according to the length and number of the request block.

9.4.1.4 Request block

The data format of the request block is composed differently according to the request code, and more than one request block can be included the payload of the request frame.

The details for the data format of each request block are as follows:

1) Association request

The block format of the ARq is shown in Figure 20 and consists of 8 bytes UID mask. This UID mask can be used to implement a binary search algorithm.

2) Disassociation request

The block format of the DaRq is shown in Figure 21. The first 2 bytes are the node ID of the iWPTN-D for the DaRq, and the next 1 byte is the slot number to be used in the response period. If the node ID is 0xFFFF, the DaRq is sent to all the iWPTN-Ds under the group ID.

3) Association status request

The block format of the ASRq is shown in Figure 22. The first 2 bytes are the node ID of the iWPTN-D for the ASRq. If the node ID is 0xFFFF, the ASRq is requested to all iWPTN-Ds under the group ID.

4) Data request

The block format of the DRq is shown in Figure 23. The first 2 bytes are the node ID, the next 1 byte is the slot number, and the last L bytes are the received data type. The data type is determined according to the application product. For WPT, one of the data type is charging information of iWPTN-D such as the remaining of battery, received power level, desired power level, battery discharge rate, etc.

5) Group ID set-up request

The block format of the GSRq is shown in Figure 24. The first 2 bytes are the node ID, the next 1 byte is the slot number, and the last byte is the group ID to be set up.

6) Power transfer request

The block format of the PTRq is shown in Figure 25. The first 2 bytes are the node ID of the iWPTN-D for the PTRq. If the node ID is 0xFFFF, the PTRq is requested to all iWPTN-Ds under the group ID. The next 1 byte is the slot number. The next 1 bit is for the request for the remaining amount of power in battery, the next 1 bit is for the request for the power consumption rate, and the next 1 bit is for the request for the received power level. 5 bits are reserved for the future use. The last L bytes are the data related to the iWPTN power receiving scheduling.

7) Power transfer start request

The block format of the PTS is shown in Figure 26. The first 1 byte is the WPT ID of the iWPTN-D for the PTS. If the node ID is 0xFF, the PTS is requested to all iWPTN-Ds. The next 1 byte is the slot number, and the last L bytes are the data related to the iWPTN power receiving scheduling.

9.4.2 Response frame

The payload format of the response frame has the response information about the request of iWPTN-B. The response frame payload is shown in Figure 27. The first byte is the group ID, the second byte is the response code, the third byte is the response date length (L), and the next L bytes are the response data.

9.4.2.1 Group ID

The group address field consists of 1 byte and is used to send RR packets to certain groups. For the details of the group ID, refer to 6.4.3.

9.4.2.2 Response code

Response code types are shown in Table 6.

Table 6 Response code of response frame payload

9.4.2.3 Length

The length field consists of 1 byte and indicates the length of the response data; it is variable according to the response data.

9.4.2.4 Response data

Response data are divided into ARs, DaRs, ASRs, DRs, GSRs, and PTRs. The response data format is as follows:

1) Association response

The block format of the ARs is shown in Figure 28. The ARs data consists of 8 bytes UID.

2) Disassociation response

The block format of the DaRs is shown in Figure 29. The DaRs data consists of 8 bytes UID.

3) Association status response

The block format of the ASRs is shown in Figure 30. The ASRs data consist of 8 bytes UID and 1 byte of the status value.

The status value is as shown in Table 7.

Table 7 Association status check value

4) Data response

The block format of the DRs is shown in Figure 31. The data of DRs consists of L bytes of requested data. For WPT according to the requested data type, the data is charging information of iWPTN-D such as the remaining of battery, received power level, desired power level, battery discharge rate, etc.

5) Group ID set-up response

The block format of the GSRs is shown in Figure 32. The GSRs data consist of 8 bytes for UID with the changed group ID and 1 byte for the changed group ID.

6) Power transfer response

The block format of the PTRs is shown in Figure 33. The PTRs data consist of 2 bytes for the remaining amount of power in battery, 2 bytes for the power consumption rate, and 2 bytes for the received power level. L bytes are reserved for the future use.

9.4.3 Data frame

The data frame payload includes the data to be transmitted. The data frame payload consists of 8 bytes of UID and L bytes of data as shown in Figure 34.

9.4.4 Acknowledgement frame

The RA frame payload has the data about the received response packet. The RA payload format is shown in Figure 35. The first byte is the group ID, the second byte is the response confirmation code, the third byte is the length (L), and the next L bytes are the response confirmation blocks.

9.4.4.1 Group ID

The group ID field consists of 1 byte and is used to send RR packets to a certain groups. The detail of the group ID, refer to 6.4.3.

9.4.4.2 Response confirmation code

Response confirmation code types are shown in Table 8.

Table 8 Response confirmation code

9.4.4.3 Length

The length field consists of 1 byte; it indicates the length of response confirmation data and is variable according to the response confirmation data.

9.4.4.4 Response confirmation block

Response confirmation block are divided into ARs confirmation, DaRs confirmation, ASRs confirmation, DRs confirmation, and GSRs confirmation. The block format of the response confirmation is as follows:

1) Association response confirmation

The block format of the ARs confirmation is shown in Figure 36. The first 8 bytes are the UID, the next 2 bytes are the assigned node ID. If the assigned node ID is 0xFFFE which is the address of un-joined node, it means the ARq has been rejected.

2) Disassociation response confirmation

The block format of the DaRs confirmation is shown in Figure 37. The first 8 bytes are the UID, and the next 2 bytes are the node ID. The assigned node ID is used if disassociation is not allowed, the unjoined node ID, 0xFFFE is recorded if disassociation is allowed.

3) Association status response confirmation

The block format of the ASRs confirmation is shown in Figure 38. The ASRs confirmation block consists of the 8 bytes UID.

4) Data response confirmation

The block format of the DRs confirmation is shown in Figure 39. The first 2 bytes are the Node ID, and the next 1 byte is the assigned reserved.

5) Group ID set-up response confirmation

The block format of GSRs confirmation is shown in Figure 40. The GSRs confirmation block consists of 8 bytes of UID and 1 byte of status check value.

The group ID set-up status value is shown in Table 9.

Table 9 Group ID set-up status value

9.5 Frame format for the PSFI

There is a PSFI in the response period when iWPTN-B provides WPT. The PSFI begins when each time slot for WPT to a certain iWPTN-D or a group ends, and it remains until iWPTN-B receives all PSF frames from the desired iWPTN-Ds. The frame format during the PSFI has short length and simple structure to provide enough time to WPT.

9.5.1 PS beacon format

When the PSFI begins, iWPTN-B transmits the PS beacon to quick power status update and abnormal situation. The request frame format is shown in Figure 42.

9.5.1.1 Slot number

It represents the current time slot number, and it has 1 byte.

9.5.1.2 Frame control

Frame control fields consist of the frame type and the PSF policy. 4 bits are reserved for the future use. The format is shown in Figure 43.

1) Frame type

Frame type field consists of 3 bits. The frame type is defined as 2 kinds of types, the request frame and the reponse frame.

Table 10 Frame type value

2) PSF policy

PSF policy field consists of 2 bits. The PSF policy is defined as 2 kinds of types, the response frame transmission policy and no transmission policy.

Table 11 PSF policy value

3) On-going policy

On-going policy consists of 1 bit. When the value is 1, WPT is provided in the next time slot. Otherwise, WPT stops.

9.5.1.3 Number of WPT IDs

It represents the number of WPT IDs which are enumerated in the frame body

9.5.1.4 WPT ID

iWPTN-B selects a certain iWPTN-D or a certain group for the response to the PS beacon. In the PS beacon, WPT ID is used to shorten the length of the beacon and to simplify the beacon structure. Details for the WPT ID is described in the section 6.4.5.

9.5.1.5 Frame Check Sequence

FCS is 8 bits in length, and is used to verify whether the frame body was received without error. It is generated by using the following 8th standard generator polynomial:

9.5.2 PSF frame format

After receiving the PSF request in the PS beacon from the iWPTN-B, the selected iWPTN-D sends the PSF frame as the response to the iWPTN-B. The PSF frame format is shown in Figure 44.

9.5.2.1 Slot number

It represents the current time slot number, and it has 1 byte.

9.5.2.2 Frame control

Frame control fields consist of the frame type. 5 bits are reserved for the future use. The format is shown in Figure 45.

1) Frame type

Table 12 Frame type value

9.5.2.3 WPT ID

Refer to the section 6.4.5.

9.5.2.4 The remaining amount of power in battery

When iWPTN-B requests the battery information, iWPTN-D sends the information of the remaining amount of the battery. 8 bits are reserved for the battery information.

9.5.2.5 Frame check sequence

9.6 Frame format for Battery-out of WPT

When iWPTN-D is in battery-out, iWPTN-D requests WPT to iWPTN-B without the request from iWPTN-B in the spontaneous period. The frame format during battery-out is the shortest and simplest structure due to battery.

9.6.1 BPTRq frame format

When the spontaneous period begins, iWPTN-D in battery-out sends the BPTRq frame for request WPT. The frame consists only of 1 byte [00000000]. The The BPTRs frame format is shown in Figure 46.

9.6.2 BPTRs frame format

After receiving the BPTRq frame from iWPTN-D, iWPTN-B transmits the BPTRs frame to notify the length of WPT interval in the spontaneous period. The BPTRs frame format is shown in Figure 47.

10

MAC layer function

10.1 General

In the MAC layer of iWPTN, in order to manage iWPTN, the association, disassociation, and ASC process for iWPTN-Ds are considered. Data can be transmitted either in the response period or in the spontaneous period. In addition, the group ID set-up function is provided for the management of iWPTN-D groups.

10.2 Network association and disassociation

In order for iWPTN-D to communicate with iWPTN-B, it first needs to be in association with iWPTN. As a given, each iWPTN-D looks for a pre-configured iWPTN; when it finds one, it associates with that iWPTN, and when it does not find, any iWPTN-D can become iWPTN-B by user of the application(i.e. configuration of a new iWPTN which means the new iWPTN-B sends the request packet periodically). However, nodes can maintain their status as iWPTN-B or iWPTN-D, whose status is set according to the role of nodes since iWPTN is configured. In this case, if there exists iWPTN that has been configured already, network configuration is cancelled because there is only one available channel.

10.2.1 Association

When iWPTN-B in the request period sends the ARq packet to the unjoined iWPTN-D. iWPTN-D transmits the ARs packet to iWPTN-B in the response period. iWPTN-B decides whether iWPTN-D associates in iWPTN or not, and notifies this results through the ARA packet. When the association has been allowed, the assigned node ID is included in the ARA packet, and when it has been rejected, the unjoined node ID 0xFFFE is recorded. When iWPTN-B does not receive the ARs packet or iWPTN-D does not receive the ARA packet due to the ARA packet error, it sends the ARq packet continuously every superframe until it receives the ARA packet of all selected iWPTN-D without error. The procedure of association for iWPTN-D is done when iWPTN-D receives the ARA packet from iWPTN-B.

Figure 48 Association procedure

10.2.2 Disassociation

When iWPTN-B in the request period sends the DaRq packet to iWPTN-D associated with iWPTN, iWPTN-D transmits the DaRs packet to iWPTN-B in the response period. iWPTN-B decides whether iWPTN-D disassociates in iWPTN or not, and notifies this results through the DaRA packet. When the disassociation has been allowed, the node ID on the DaRA packet is recorded as the unjoined node ID 0xFFFE, and when the disassociation has been rejected, the assigned node ID is recorded. When iWPTN-B does not receive the DaRs packet or iWPTN-D does not receive the DaRA packet due to the DaRA packet error, the iWPTN-D retransmits the DaRs packet continuously every superframe until the iWPTN-D receives the DaRA packet. Disassociation is complete when iWPTN-D receives the DaRA packet from iWPTN-B.

Figure 49 Disassociation procedure

10.2.3

Association status check

When iWPTN-B in the request period sends the ASRq packet to the associated iWPTN-D, iWPTN-D transmits the ASRs packet to iWPTN-B in the response period. iWPTN-B checks and transmits the ASRA packet for the iWPTN-Ds association status to iWPTN. When iWPTN-B does not receive the ASRs packet or iWPTN-D cannot receive the ASRA packet due to the packet error, the iWPTN-D transmits the ASRs packet continuously every time-slot until it receives the ASRA packet. The procedure of association status confirmation for iWPTN-D’s is complete when iWPTN-D receives the ASRA packet from iWPTN-B.

Figure 50 Procedure of association status confirmation

10.3

Data transmission

In iWPTN, data can be transmitted in the response period or in the spontaneous period. Data can be transmitted on the request of iWPTN-B in the response period and without the request of iWPTN-B in the spontaneous period.

10.3.1 Transmission in the response period

When iWPTN-B in the request period sends the DRq packet to iWPTN-D associated with iWPTN, iWPTN-D transmits the DRs packet in the response period. iWPTN-B sends the DRA packet after it receives the DRs packet from iWPTN-D. When iWPTN-B does not receive the DRs packet or iWPTN-D does not receive the DRA packet due to the packet error, the iWPTN-D transmits the DRs packet continuously every time-slot until it receives the DRA packet.

The procedure of data transmission in the response period is complete when iWPTN-D receives the DRA packet from iWPTN-B.

Figure 51 Procedure of data transmission in response period

10.3.2

Transmission in the spontaneous period

The spontaneous period begins when iWPTN-D does not transmit response packets for the time-out period, and this period is maintained until iWPTN-B transmits the RR packet. iWPTN-D can transmit data without the request of iWPTN-B during this spontaneous period. When a system interruption occurs, it is possible for iWPTN-D to transmit data without the request of iWPTN-B. When iWPTN-B does not receive the data packet or iWPTN-D does not receive the DA packet due to the packet error, the iWPTN-D transmits the data packet continuously until it receives the DA packet. The procedure of data transmission in the spontaneous period is complete when iWPTN-D receives the DA packet from iWPTN-B.

Figure 52 Procedure of data transmission in spontaneous period

10.4

Group ID set-up

When iWPTN-B in the request period sends the GSRq packet to iWPTN-D, iWPTN-D sends the GSRs packet in the response period. iWPTN-B probes the group ID set-up status of iWPTN-D, and then transmits the GSRA packet.

Figure 53 Procedure of group ID set-up

10.5

Wirelss Power Transfer

When iWPTN-B transmits the PTRq packet to iWPTN-Ds, iWPTN-Ds transmits the PTRs packet to iWPTN-B. iWPTN-B computes scheduling for WPT with the received data in the PTRs packet. iWPTN-B braodcasts the PTS packet to desired iWPTN-Ds with the computed scheduling information. Once iWPTN-Ds receive the PTS packet, they follow the scheduling sequence. iWPTN-B provides WPT to the iWPTN-D which is scheduled in the first order. During WPT, other iWPTN-Ds are in the power isolation state for increasing power transfer efficiency. When the first iWPTN-D finishes receiving power, iWPTN-B generates and sends the PS beacon to all iWPTN-Ds in the PSFI. At the begining of the PSFI, other iWPTN-Ds are in the activation state to receive the PS beacon. When iWPTN-Ds receive the PS beacon, then the selected iWPTN-Ds by iWPTN-B generate and send the PSF packet to iWPTN-B. After confirming the PSF packets from the selected iWPTN-Ds, iWPTN-B starts WPT to the second iWPTN-D. When iWPTN-B detects error during WPT, it stops WPT, and iWPTN-D goes to the activation state after recognizing WPT stops. At the begining of the PSFI, iWPTN-B notifies the detection of error to other iWPTN-Ds by sending PS beacon. These are iterated until all desired iWPTN-Ds receive power, so that iWPTN-B receive PSF packets from iWPTN-D in the last time slot of the response period.

Figure 54 Procedure of wireless power transfer

10.6

Battery-out

When iWPTN-D is in battery-out, it receives WPT from iWPTN-B even though it was not considered node. The iWPTN-D in battery-out shares a small amount of power with the originally targeted iWPTN-D by iWPTN-B. When the current time slot ends, iWPTN-B transmits the PS beacon. The originally targeted iWPTN-D transmits the PSF packet as the response of the PS beacon, and then goes to the hibernation state. On the other hand, the iWPTN-D in battery-out keep staying in the hibernation state after receiving the PS beacon due to a small amount of power in battery. When the spontaneous period begins, the iWPTN-D in emergency goes to the hibernation packet generation state, and transmits the BPTRq packet. When iWPTN-B receives the packet, it transmits the BPTRs packet as the response, and provides WPT to the iWPTN-D in emergency.

Figure 55 Procedure of battery-out

11

Air interface

11.1 Frequency

iWPTN’s center frequency (fc) is between 80kHz and 400kHz; it could be 88kHz, 128kHz, and 370kHz with a maximum tolerance of ±20ppm.

11.2 Signal waveform

Figure 56 shows the envelope waveform, and the envelope parameters are defined in Table 13. Amplitude in Table 13 denotes the amplitude of the envelope. The envelope amplitude is varied from negative variation Mi to positive variation Mh within 10% of Amplitude. tr and tf denote the envelop rising time from 10% to 90% of Amplitude and the envelop falling time from 90% to 10% of Amplitude, respectively. The bit interval (Tbit) varies according to the data rate, and tr and tf cannot exceed 30% of Tbit.

Figure 56 Envelope waveform

Table 13 BPSK envelope parameters

BPSK modulation is used for the transmission between iWPTN-B and iWPTN-D. The transmitted signal, as shown in Figure 57, is modulated by BPSK according to the envelope defined in this section.

Figure 57 BPSK-modulated signal

Figure 58 ASK-modulated signal

Table 14 ASK envelope parameters

11.3 Signal waveform for WPT

Figure 59 shows the waveform for WPT, and the envelope parameters are defined in Table 15. A general sine waveform is used for WPT because it provides high power transfer efficiency. Amplitude in Table 15 denotes the amplitude of the envelope. The envelope amplitude is varied from negative variation Mi to positive variation Mh within 10% of Amplitude.

Table 15 WPT envelope parameters

* Mobile phones: provide ubiquitous charging environments for portable devices

Claims

A multi-node wireless charging method using magnetic field communication for enabling a wireless power transmission apparatus to charge wireless charging devices using magnetic field communication in a multi-node wireless power transmission system including the wireless power transmission apparatus and the plurality of wireless charging devices spaced apart from the wireless power transmission apparatus, the method comprising:

transmitting an association request frame;

receiving an association response frame from the wireless charging devices;

transmitting a charging requirement request frame;

receiving a charging requirement response frame from the wireless charging devices;

transmitting a charging preparation request frame; and

transmitting power during a receiving period of the charging preparation response frame for the charging preparation request frame.