WO2018016756A1

WO2018016756A1 - Method and device for performing low-power communication in wireless lan system by using wakeup packet

Info

Publication number: WO2018016756A1
Application number: PCT/KR2017/006726
Authority: WO
Inventors: 박은성; 임동국; 조한규; 최진수
Original assignee: 엘지전자 주식회사
Priority date: 2016-07-21
Filing date: 2017-06-26
Publication date: 2018-01-25

Abstract

A method and device for performing low-power communication in a wireless LAN system by using a wakeup packet are proposed. Particularly, a receiving device receives a wakeup packet, including a wakeup preamble and a wakeup payload, from a transmitting device. Here, the wakeup packet is transmitted by being modulated according to an OOK method. The receiving device measures the average power or average norm value of a received signal which has passed through a channel via the wakeup preamble. The average power or average norm value is measured purely on the basis of a bit indicating a signal coming from the wakeup preamble. The receiving device checks the power of the wakeup payload on the basis of a critical value. The critical value is set at half the average power or average norm value.

Description

Method and apparatus for performing low power communication using wake-up packet in WLAN system

The present disclosure relates to a technique for performing low power communication in a WLAN system, and more particularly, to a method and apparatus for performing low power communication using a wake-up packet in a WLAN system.

Discussion is underway for the next generation wireless local area network (WLAN). In next-generation WLANs, 1) enhancements to the Institute of Electronics and Electronics Engineers (IEEE) 802.11 physical physical access (PHY) and medium access control (MAC) layers in the 2.4 GHz and 5 GHz bands, and 2) spectral efficiency and area throughput. aims to improve performance in real indoor and outdoor environments, such as in environments where interference sources exist, dense heterogeneous network environments, and high user loads.

The environment mainly considered in the next-generation WLAN is a dense environment having many access points (APs) and a station (STA), and improvements in spectral efficiency and area throughput are discussed in such a dense environment. In addition, in the next generation WLAN, there is an interest in improving practical performance not only in an indoor environment but also in an outdoor environment, which is not much considered in a conventional WLAN.

Specifically, in the next-generation WLAN, there is a great interest in scenarios such as wireless office, smart home, stadium, hotspot, building / apartment, and AP based on the scenario. And STA are discussing about improving system performance in a dense environment with many STAs.

In addition, in the next-generation WLAN, there will be more discussion about improving system performance in outdoor overlapping basic service set (OBSS) environment, improving outdoor environment performance, and cellular offloading, rather than improving single link performance in one basic service set (BSS). It is expected. The directionality of these next-generation WLANs means that next-generation WLANs will increasingly have a technology range similar to that of mobile communications. Considering the recent situation in which mobile communication and WLAN technology are discussed together in the small cell and direct-to-direct (D2D) communication area, the technical and business convergence of next-generation WLAN and mobile communication is expected to become more active.

The present specification proposes a method and apparatus for performing low power communication using a wake-up packet in a WLAN system.

An example of the present specification proposes a method and apparatus for performing low power communication using a wake-up packet in a WLAN system.

This embodiment can be applied to a receiver, the receiver can correspond to a low power wake-up receiver, and the transmitter can correspond to an AP.

First of all, the term “on signal” may correspond to a signal having an actual power value. The off signal may correspond to a signal that does not have an actual power value. The norm value represents a magnitude measure of a vector and may correspond to a magnitude measure of a signal.

The receiver receives a wakeup packet including a wakeup preamble and a wakeup payload from the transmitter. The wakeup payload may include a MAC header field, a frame body field, and a frame check sequence (FCS) field.

The receiver measures the average power or average norm value of the received signal passing through the channel through the wakeup preamble. The average power or average norm value is measured based only on bits indicating an on signal in the wakeup preamble.

The receiver checks the power of the wakeup payload based on a threshold value. The threshold is set to half the average power or average norm value.

If the power of the wakeup payload is greater than or equal to the threshold value, the power of the wakeup payload may be determined as alpha ^ 2. In addition, if the power of the wakeup payload is less than the threshold value, the power of the wakeup payload may be determined to be zero. The alpha is a power normalization factor.

However, the wakeup packet is modulated and transmitted in an on-off keying (OOK) scheme. The wakeup preamble may include a sequence including a bit indicating the on signal and a bit indicating an off signal. The bit indicating the on signal may indicate 1, and the bit indicating the off signal may indicate 0. For example, the sequence may consist of 1110. That is, the first, second, and third bits may represent an on signal and the fourth bit may represent an off signal. According to the example, the receiver may measure the average power or average norm value of the received signal passing through the channel based only on the first, second, and third bits.

The sequence may be defined in advance between the transmitter and the receiver.

In this case, the bit indicating the on signal may be transmitted through a symbol generated by applying a sequence to specific 13 consecutive subcarriers in a 20 MHz band and performing a 64-point Inverse Fast Fourier Transform (IFFT). That is, one bit indicating the on signal may be transmitted through one symbol generated by performing an IFFT.

The thirteen subcarriers may correspond to a partial band of the 20 MHz band. When 20 MHz is referred to as a reference band, even though 64 subcarriers (or bit sequences) can be used, only 13 subcarriers are sampled to perform IFFT, and thus, 13 subcarriers may correspond to about 4.06 MHz band. That is, a specific sequence is set only to 13 subcarriers selected as samples, and all other subcarriers except 13 subcarriers are set to 0. That is, it can be said that power is provided only for 4.06MHz in the 20MHz band in the frequency domain.

In addition, the thirteen subcarriers may be arranged from subcarrier index -6 to subcarrier index +6. In addition, the subcarrier spacing of each of the 13 subcarriers may be 312.5 KHz. Accordingly, the symbol generated by performing the IFFT may have a length of 4 us including a cyclic prefix (CP).

The wakeup packet may further include a legacy preamble. The legacy preamble may be transmitted through the 20 MHz band. The wakeup preamble and the wakeup payload may be transmitted through a partial band of the 20MHz band. That is, the legacy preamble may be modulated and transmitted in the OFDM scheme, and the wakeup preamble and the wakeup payload may be modulated and transmitted in the above-described OOK scheme.

According to the exemplary embodiment of the present specification, the wakeup packet is configured and transmitted by applying the OOK modulation scheme in the transmitter to reduce power consumption by using an envelope detector during wakeup decoding in the receiver. That is, the receiver may decode the wakeup packet with the minimum power.

1 is a conceptual diagram illustrating a structure of a wireless local area network (WLAN).

2 is a diagram illustrating an example of a PPDU used in the IEEE standard.

3 is a diagram illustrating an example of a HE PPDU.

4 illustrates a low power wake-up receiver in an environment in which data is not received.

5 illustrates a low power wake-up receiver in an environment in which data is received.

6 shows an example of a wakeup packet structure according to the present embodiment.

7 shows a signal waveform of a wakeup packet according to the present embodiment.

FIG. 8 is a diagram for describing a principle in which power consumption is determined according to a ratio of 1 and 0 of bit values constituting binary sequence information using the OOK method.

9 is an explanatory diagram of a Manchester coding scheme according to the present embodiment.

10 shows a method of designing a OOK pulse according to the present embodiment.

11 is a flowchart illustrating a procedure for performing low power communication using a wakeup packet according to the present embodiment.

12 is a block diagram illustrating a wireless device to which the present embodiment can be applied.

1 shows the structure of the infrastructure basic service set (BSS) of the Institute of Electrical and Electronic Engineers (IEEE) 802.11.

Referring to the top of FIG. 1, the WLAN system may include one or more infrastructure BSSs 100 and 105 (hereinafter, BSS). The BSSs 100 and 105 are a set of APs and STAs such as an access point 125 and a STA1 (station 100-1) capable of successfully synchronizing and communicating with each other, and do not indicate a specific area. The BSS 105 may include one or more STAs 103-1 and 105-2 that can be coupled to one AP 130.

The BSS may include at least one STA, APs 125 and 130 for providing a distribution service, and a distribution system (DS) 110 for connecting a plurality of APs.

The distributed system 110 may connect several BSSs 100 and 105 to implement an extended service set (ESS) 140 which is an extended service set. The ESS 140 may be used as a term indicating one network in which one or several APs 125 and 230 are connected through the distributed system 110. APs included in one ESS 140 may have the same service set identification (SSID).

The portal 120 may serve as a bridge for connecting the WLAN network (IEEE 802.11) with another network (for example, 802.X).

In the BSS as shown in the upper part of FIG. 1, a network between the APs 125 and 130 and a network between the APs 125 and 130 and the STAs 100-1, 105-1 and 105-2 may be implemented. However, it may be possible to perform communication by setting up a network even between STAs without the APs 125 and 130. A network that performs communication by establishing a network even between STAs without APs 125 and 130 is defined as an ad-hoc network or an independent basic service set (BSS).

1 is a conceptual diagram illustrating an IBSS.

Referring to the bottom of FIG. 1, the IBSS is a BSS operating in an ad-hoc mode. Since IBSS does not contain an AP, there is no centralized management entity. That is, in the IBSS, the STAs 150-1, 150-2, 150-3, 155-4, and 155-5 are managed in a distributed manner. In the IBSS, all STAs 150-1, 150-2, 150-3, 155-4, and 155-5 may be mobile STAs, and access to a distributed system is not allowed, thus making a self-contained network. network).

A STA is any functional medium that includes medium access control (MAC) conforming to the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard and a physical layer interface to a wireless medium. May be used to mean both an AP and a non-AP STA (Non-AP Station).

The STA may include a mobile terminal, a wireless device, a wireless transmit / receive unit (WTRU), a user equipment (UE), a mobile station (MS), a mobile subscriber unit ( It may also be called various names such as a mobile subscriber unit or simply a user.

On the other hand, the term "user" may be used in various meanings, for example, may also be used to mean an STA participating in uplink MU MIMO and / or uplink OFDMA transmission in wireless LAN communication. It is not limited to this.

2 is a diagram illustrating an example of a PPDU used in the IEEE standard.

As shown, various types of PHY protocol data units (PPDUs) have been used in the IEEE a / g / n / ac standard. Specifically, the LTF and STF fields included training signals, the SIG-A and SIG-B included control information for the receiving station, and the data fields included user data corresponding to the PSDU.

This embodiment proposes an improved technique for the signal (or control information field) used for the data field of the PPDU. The signal proposed in this embodiment may be applied on a high efficiency PPDU (HE PPDU) according to the IEEE 802.11ax standard. That is, the signals to be improved in the present embodiment may be HE-SIG-A and / or HE-SIG-B included in the HE PPDU. Each of HE-SIG-A and HE-SIG-B may also be represented as SIG-A or SIG-B. However, the improved signal proposed by this embodiment is not necessarily limited to the HE-SIG-A and / or HE-SIG-B standard, and controls / control of various names including control information in a wireless communication system for transmitting user data. Applicable to data fields.

3 is a diagram illustrating an example of a HE PPDU.

The control information field proposed in this embodiment may be HE-SIG-B included in the HE PPDU as shown in FIG. 3. The HE PPDU according to FIG. 3 is an example of a PPDU for multiple users. The HE-SIG-B may be included only for the multi-user, and the HE-SIG-B may be omitted in the PPDU for the single user.

As shown, a HE-PPDU for a multiple user (MU) includes a legacy-short training field (L-STF), a legacy-long training field (L-LTF), a legacy-signal (L-SIG), High efficiency-signal A (HE-SIG-A), high efficiency-signal-B (HE-SIG-B), high efficiency-short training field (HE-STF), high efficiency-long training field (HE-LTF) It may include a data field (or MAC payload) and a PE (Packet Extension) field. Each field may be transmitted during the time period shown (ie, 4 or 8 ms, etc.).

The PPDU used in the IEEE standard is mainly described as a PPDU structure transmitted over a channel bandwidth of 20 MHz. The PPDU structure transmitted on a bandwidth wider than the channel bandwidth of 20 MHz (eg, 40 MHz and 80 MHz) may be a structure in which linear scaling of the PPDU structure used in the channel bandwidth of 20 MHz is applied.

The PPDU structure used in the IEEE standard is generated based on 64 Fast Fourier Tranforms (FTFs), and a CP portion (cyclic prefix portion) may be 1/4. In this case, the length of the effective symbol interval (or FFT interval) may be 3.2us, the CP length is 0.8us, and the symbol duration may be 4us (3.2us + 0.8us) plus the effective symbol interval and the CP length.

Wireless networks are ubiquitous, usually indoors and often installed outdoors. Wireless networks use various techniques to send and receive information. For example, but not limited to, two widely used technologies for communication are those that comply with IEEE 802.11 standards such as the IEEE 802.11n standard and the IEEE 802.11ac standard.

The IEEE 802.11 standard specifies a common Medium Access Control (MAC) layer that provides a variety of features to support the operation of IEEE 802.11-based wireless LANs (WLANs). The MAC layer utilizes protocols that coordinate access to shared radios and improve communications over wireless media, such as IEEE 802.11 stations (such as a PC's wireless network card (NIC) or other wireless device or station (STA) and access point ( Manage and maintain communication between APs).

IEEE 802.11ax is the successor to 802.11ac and has been proposed to improve the efficiency of WLAN networks, especially in high density areas such as public hotspots and other high density traffic areas. IEEE 802.11 can also use Orthogonal Frequency Division Multiple Access (OFDMA). The High Efficiency WLAN Research Group (HEW SG) within the IEEE 802.11 Work Group is dedicated to improving system throughput / area in high-density scenarios of APs (access points) and / or STAs (stations) in relation to the IEEE 802.11 standard. We are considering improving efficiency.

Wearable devices and small computing devices such as sensors and mobile devices are constrained by small battery capacities, but use wireless communication technologies such as Wi-Fi, Bluetooth®, and Bluetooth® Low Energy (BLE). Support, connect to and exchange data with other computing devices such as smartphones, tablets, and computers. Since these communications consume power, it is important to minimize the energy consumption of such communications in these devices. One ideal strategy to minimize energy consumption is to power off the communication block as frequently as possible while maintaining data transmission and reception without increasing delay too much. That is, the communication block is transmitted immediately before the data reception, and only when there is data to wake up, the communication block is turned on and the communication block is turned off for the remaining time.

Hereinafter, a low-power wake-up receiver (LP-WUR) will be described.

The communication system (or communication subsystem) described herein includes a main radio (802.11) and a low power wake up receiver.

The main radio is used for transmitting and receiving user data. The main radio is turned off if there are no data or packets to transmit. The low power wake-up receiver wakes up the main radio when there is a packet to receive. At this time, the user data is transmitted and received by the main radio.

The low power wake-up receiver is not for user data. It is simply a receiver to wake up the main radio. In other words, the transmitter is not included. The low power wake-up receiver is active while the main radio is off. Low power wake-up receivers target a target power consumption of less than 1 mW in an active state. In addition, low power wake-up receivers use a narrow bandwidth of less than 5 MHz. In addition, the target transmission range of the low power wake-up receiver is the same as that of the existing 802.11.

4 illustrates a low power wake-up receiver in an environment in which data is not received. 5 illustrates a low power wake-up receiver in an environment in which data is received.

As shown in Figures 4 and 5, if there is data to be transmitted and received, one way to implement an ideal transmission and reception strategy is a main radio such as Wi-Fi, Bluetooth® radio, or Bluetooth® Radio (BLE). Adding a low power wake-up receiver (LP-WUR) that can wake up.

Referring to FIG. 4, the Wi-Fi / BT / BLE 420 is turned off and the low power wake-up receiver 430 is turned on without receiving data. Some studies show that the low power wake-up receiver (LP-WUR) can consume less than 1mW.

However, as shown in FIG. 5, when a wakeup packet is received, the low power wakeup receiver 530 may receive the entire Wi-Fi / BT / BLE radio 520 so that the data packet following the wakeup packet can be correctly received. Wake up). In some cases, however, actual data or IEEE 802.11 MAC frames may be included in the wakeup packet. In this case, it is not necessary to wake up the entire Wi-Fi / BT / BLE radio 520, but only a part of the Wi-Fi / BT / BLE radio 520 to perform the necessary process. This can result in significant power savings.

One example technique disclosed herein defines a method for a granular wakeup mode for Wi-Fi / BT / BLE using a low power wakeup receiver. For example, the actual data contained in the wakeup packet can be passed directly to the device's memory block without waking up the Wi-Fi / BT / BLE radio.

As another example, if a wakeup packet contains an IEEE 802.11 MAC frame, only the MAC processor of the Wi-Fi / BT / BLE wireless device needs to wake up to process the IEEE 802.11 MAC frame included in the wakeup. That is, the PHY module of the Wi-Fi / BT / BLE radio can be turned off or kept in a low power mode.

A number of granular wakeup modes have been defined for Wi-Fi / BT / BLE radios that use low power wake-up receivers, requiring that the Wi-Fi / BT / BLE radio be powered on when a wake-up packet is received. However, according to the above embodiment, only necessary parts (or components) of the Wi-Fi / BT / BLE radio can be selectively woken up, thereby saving energy and reducing the waiting time. Many solutions that use low-power wake-up receivers to receive wake-up packets wake up the entire Wi-Fi / BT / BLE radio. One exemplary aspect discussed herein wakes up only the necessary portions of the Wi-Fi / BT / BLE radio required to process the received data, saving significant amounts of energy and reducing unnecessary latency in waking up the main radio. Can be.

In addition, in the above embodiment, the low power wake-up receiver 530 may wake up the main radio 520 based on the wake-up packet transmitted from the transmitter 500.

In addition, the transmitter 500 may be set to transmit a wakeup packet to the receiver 510. For example, the low power wake-up receiver 530 may be instructed to wake up the main radio 520.

The wakeup packet may include one or more legacy preambles. One or more legacy devices may decode or process the legacy preamble.

In addition, the wakeup packet may include a payload after the legacy preamble. The payload may be modulated by a simple modulation scheme, for example, an On-Off Keying (OOK) modulation scheme.

Referring to FIG. 6, the transmitter may be configured to generate and / or transmit a wakeup packet 600. The receiving device may be configured to process the received wakeup packet 600.

In addition, the wakeup packet 600 may include a legacy preamble or any other preamble 610 as defined by the IEEE 802.11 specification. In addition, the wakeup packet 600 may include a payload 620.

Legacy preambles provide coexistence with legacy STAs. The legacy preamble 610 for coexistence uses the L-SIG field to protect the packet. The 802.11 STA may detect the start of a packet through the L-STF field in the legacy preamble 610. The 802.11 STA can know the end of the packet through the L-SIG field in the legacy preamble 610. In addition, by adding a BPSK modulated symbol after the L-SIG, a false alarm of an 802.11n terminal can be reduced. One symbol (4us) modulated with BPSK also has a 20MHz bandwidth like the legacy part. The legacy preamble 610 is a field for third party legacy STAs (STAs not including LP-WUR). The legacy preamble 610 is not decoded from the LP-WUR.

The payload 620 may include a wakeup preamble 622. Wake-up preamble 622 may include a sequence of bits configured to identify wake-up packet 600. The wakeup preamble 622 may include, for example, a PN sequence.

In addition, the payload 620 may include a MAC header 624 including address information of a receiver receiving the wakeup packet 600 or an identifier of the receiver.

In addition, the payload 620 may include a frame body 626 that may include other information of the wakeup packet. For example, the frame body 626 may include length or size information of the payload.

In addition, the payload 620 may include a Frame Check Sequence (FCS) field 628 that includes a Cyclic Redundancy Check (CRC) value. For example, it may include a CRC-8 value or a CRC-16 value of the MAC header 624 and the frame body 626.

Referring to FIG. 7, the wakeup packet 700 includes a legacy preamble (802.11 preamble, 710) and a payload modulated by OOK. That is, the legacy preamble and the new LP-WUR signal waveform coexist.

In addition, the legacy preamble 710 may be modulated according to the OFDM modulation scheme. That is, the legacy preamble 710 is not applied to the OOK method. In contrast, the payload may be modulated according to the OOK method. However, the wakeup preamble 722 in the payload may be modulated according to another modulation scheme.

If the legacy preamble 710 is transmitted on a channel bandwidth of 20 MHz to which 64 FFTs are applied, the payload may be transmitted on a channel bandwidth of about 4.06 MHz. This will be described later in the OOK pulse design method.

First, a modulation scheme using the OOK scheme and a Manchester coding scheme will be described.

Referring to FIG. 8, information in the form of a binary sequence having 1 or 0 as a bit value is represented. By using a bit value of 1 or 0 of the binary sequence information, OOK modulation can be performed. That is, in consideration of the bit values of the binary sequence information, it is possible to perform the communication of the OOK modulation method. For example, when the light emitting diode is used for visible light communication, the light emitting diode is turned on when the bit value constituting the binary sequence information is 1, and the light emitting diode is turned off when the bit value is 0. The light emitting diode can be made to blink. As the light-emitting diode blinks, the receiver receives and restores data transmitted in the form of visible light, thereby enabling communication using visible light. However, since the blinking of the light emitting diode cannot be perceived by the human eye, the person feels that the illumination is continuously maintained.

For convenience of description, as shown in FIG. 8, information in the form of a binary sequence having 10 bit values is used. Referring to FIG. 8, there is information in the form of a binary sequence having a value of '1001101011'. As described above, when the bit value is 1, the transmitter is turned on, and when the bit value is 0, the transmitter is turned off, the symbol is turned on at 6 bit values out of 10 bit values. ) do. Therefore, when the symbol is turned on in all 10 bit values, if the power consumption is 100%, the power consumption is 60% according to the duty cycle of FIG. 8.

That is, it can be said that the power consumption of the transmitter is determined according to the ratio of 1 and 0 constituting the binary sequence information. In other words, if there is a constraint that the power consumption of the transmitter must be kept at a certain value, the ratio of 1 and 0, which constitutes information in binary sequence form, must also be maintained. For example, in the case of lighting equipment, since the lighting must be maintained at a specific luminance value desired by people, the ratio of 1 and 0 constituting the information in the form of a binary sequence must also be maintained.

However, since the receiver is mainly a wake-up receiver (WUR), the transmission power is not important. The main reason for using OOK is that the power consumption is very low when decoding the received signal. Until the decoding is performed, there is no significant difference in power consumption in the main radio or WUR, but a large difference occurs in the decoding process. Below is the approximate power consumption.

-The existing Wi-Fi power consumption is about 100mW. Specifically, power consumption of Resonator + Oscillator + PLL (1500uW)-> LPF (300uW)-> ADC (63uW)-> decoding processing (OFDM receiver) (100mW) may occur.

-WUR power consumption is about 1mW. Specifically, power consumption of Resonator + Oscillator (600uW)-> LPF (300uW)-> ADC (20uW)-> decoding processing (Envelope detector) (1uW) may occur.

As shown in Fig. 9, the bit string to be transmitted, the Manchester coded signal, the clock reproduced at the receiving side, and the data reproduced at the clock are shown in order from top to bottom.

Manchester coding refers to a method of converting data from 1 to 01, 0 to 10, 1 to 10, and 0 to 01.

When the transmitter transmits data using the Manchester coding scheme, the receiver reads the data a little later based on the transition point of 1 → 0 or 0 → 1, and recovers the data, and then transitions to 1 → 0 or 0 → 1. The clock is recovered by recognizing the transition point as the clock transition point. Alternatively, when the symbol is divided based on the transition point, it can be simply decoded by comparing the power at the front and the back at the center of the symbol.

As shown in FIG. 9, the bit string to be transmitted is 10011101, the Manchester coded signal to be transmitted is 0110100101011001, and the clock reproduced on the receiving side is obtained by recognizing the transition point of the Manchester coded signal as the clock transition point. The recovered clock is used to recover the data.

By using the Manchester coding scheme, it is possible to communicate in a synchronous manner using only a data transmission channel without using a separate clock.

In addition, this method can use the TXD pin for data transmission and the RXD pin for reception by using only the data transmission channel. Therefore, synchronized bidirectional transmission is possible.

10 shows a method of designing a OOK pulse according to the present embodiment.

The OFDM transmitter of 802.11 can be reused to generate OOK pulses. The transmitter can generate a sequence having 64 bits by applying a 64-point IFFT as in 802.11.

The transmitter should generate the payload of the wakeup packet by modulating the OOK method. However, since the wakeup packet is for low power communication, the OOK method is applied to the on signal. The on signal is a signal having an actual power value, and the off signal corresponds to a signal having no actual power value. In addition, the OOK method is applied, but the signal is not generated using the transmitter, and since no signal is actually transmitted, it is not considered in the configuration of the wakeup packet.

In the OOK method, information (bit) 1 may be an on signal and information (bit) 0 may be an off signal. Alternatively, when the Manchester coding scheme is applied, information 1 may indicate a transition from an off signal to an on signal, and information 0 may indicate a transition from an on signal to an off signal. Alternatively, on the contrary, the information 1 may indicate the transition from the on signal to the off signal, and the information 0 may indicate the transition from the off signal to the on signal.

Referring to FIG. 10, as shown in the right frequency domain graph 1020, the transmitter selects 13 subcarriers located in the center of a 20 MHz band as a sample as a sample. That is, a subcarrier whose subcarrier index is from -6 to +6 is selected from the 64 subcarriers. In this case, the subcarrier index 0 may be nulled to 0 as the DC subcarrier. Set a specific sequence only to the 13 subcarriers selected as samples, and set all subcarriers except the subcarriers (subcarrier indexes -32 to -7 and subcarrier indexes +7 to +31) to 0. .

In addition, since subcarrier spacing is 312.5 KHz, 13 subcarriers have a channel bandwidth of about 4.06 MHz. That is, it can be said that power is provided only for 4.06MHz in the 20MHz band in the frequency domain. By moving the power to the center, the signal to noise ratio (SNR) can be increased and the power consumption of the AC / DC converter of the receiver can be reduced. In addition, the power consumption can be reduced by reducing the sampling frequency band to 4.06MHz.

In addition, as shown in the left time domain graph 1010 of FIG. 10, the transmitter may generate one on-signal in the time domain by performing a 64-point IFFT on 13 subcarriers. One on-signal has a size of 1 bit. That is, a sequence composed of 13 subcarriers may correspond to 1 bit. On the other hand, the transmitter may not transmit the off signal at all. When performing IFFT, a 3.2us symbol may be generated, and if a CP (Cyclic Prefix, 0.8us) is included, one symbol having a length of 4us may be generated. That is, one bit indicating one on-signal may be loaded in one symbol.

The reason for configuring and sending the bits as in the above-described embodiment is to reduce power consumption by using an envelope detector in the receiver. As a result, the receiving device can decode the packet with the minimum power.

However, the basic data rate for one information may be 125Mbps (8us) or 62.5Mbps (16us).

Hereinafter, a description will be given of a method of decoding (or receiving) a wake-up packet transmitted from a transmitter and confirming power.

There are two ways to decode the wakeup packet. The first is non-coherent detection and the second is coherent detection. In non-coherent detection, the phase relationship between the transmitter and receiver signals is not fixed. Thus, the receiver does not need to measure and adjust the phase of the received signal. In contrast, the coherent detection method requires that the phase of the signal between the transmitter and the receiver be aligned.

The receiver includes the low power wake-up receiver described above. The low power wake-up receiver may decode a packet (wake-up packet) transmitted using an OOK modulation scheme using an envelope detector to reduce power consumption.

The envelope detector measures and decodes the power or magnitude of the received signal. The receiver sets a threshold based on the power or magnitude measured by the envelope detector. When decoding the symbol to which the OOK is applied, it is determined as information 1 if it is greater than or equal to the threshold value, and as information 0 when it is smaller than the threshold value.

Here, setting the threshold is important for the performance of the low power wakeup receiver. Therefore, a method of setting a threshold in a low power wake-up receiver is proposed.

For example, a case of configuring a symbol to which a 1-bit OOK is applied using K subcarriers may be considered. As described above, K may be 12 except for the DC subcarrier and 13 may be included when including the DC subcarrier. If it is determined that the information is 0, the power of the OOK-applied symbol has a value of 0, and if it is determined to be information 1, the power of the OOK-applied symbol has an alpha ^ 2 value. Here, alpha is a power normalization factor.

There are option 1 and option 2 for decoding wake-up packets using non-coherent detection.

-Option 1-

The receiver knows the power information actually sent by the transmitter. Thus, the receiver can simply obtain the power or norm value for information 1 and set the threshold to half the power or norm value. That is, in the case of configuring a symbol to which a 1-bit OOK is applied using K subcarriers, the threshold may be set to K * alpha ^ 2/2 or sqrt (K) * alpha / 2.

However, since the receiver receives a signal that has passed through the channel, it is important to set a threshold considering the channel condition. Therefore, option 1 may not consider the channel situation, and the actual performance may be greatly degraded.

-Option 2-

It is assumed that the receiver knows sequence information of the wake-up preamble transmitted by the transmitter. That is, the sequence information receiving apparatus and the transmitting apparatus of the wake-up preamble are promised in advance. The receiver measures the average power or average norm value of the signal received via the wakeup preamble to take into account the channel conditions. In this case, the receiving apparatus measures an average power or average norm value of the received signal in consideration of only the symbol portion to which the on signal is transmitted. As a result, the receiver may set a half of the average power or the average norm of the received signal as the threshold.

That is, the receiver may check the power of the payload following the wakeup preamble by using the threshold value determined through the sequence of the wakeup preamble.

That is, assuming that the average power is beta, the threshold may be set to beta / 2 or sqrt (beta) / 2.

However, when applying Manchester coding, it is not necessary to set a threshold. This is because information 0 and information 1 can be distinguished by checking whether the signal is larger or smaller than the transition signal before the transition.

In addition, the wakeup packet may be decoded using a coherent detection method.

If the OOK is to be decoded by the coherent detection method, the Euclidean distance between the received signal at the receiver and the original signal at the transmitter should be calculated.

In this case, channel information is required and channel estimation is performed in the wake-up preamble. The method of determining the Euclidean distance may be performed as in the following equation.

At this time,

, variance of each element in noise = 1,

,

to be.

In Equation 1, r is a received signal, X ₀ is an off signal, and X ₁ is an on signal. Based on the coherent detection method, the Euclidean distance can be calculated using the signals received by all receivers. h is a channel,

Is the channel estimated by the wake-up preamble. || || ^ 2 returns the norm value.

Using Equation 1, it may be determined whether the received signal r is closer to X ₀ or closer to X ₁ . That is, according to Equation 1,

this

If smaller, the receiver may determine that X ₀ has been transmitted. Also,

this

If greater, the receiving device may determine that X ₁ has been transmitted. This is because the closer to the received signal, the smaller the norm value.

Another example of a coherent detection method is a method of decoding a received signal considering only X ₁ , which is a signal actually sent.

Since there is only one X ₁ signal sent by the transmitter (X ₀ has no signal actually transmitted), it can be determined by measuring the received signal when X ₁ is sent instead of the channel. This may be performed as in the following equation.

In Equation 2

Denotes an average vector of received signals of symbols carrying information 1 in the wake-up preamble. In other words,

Is measuring the received signal passing through the channel.

According to Equation 2,

this

If smaller, the receiver may determine that X ₀ has been transmitted. Also,

this

If greater, the receiver may determine that X ₁ has been transmitted. This is because the closer to the received signal, the smaller the norm value.

Equation 1 measures the channel and Equation 2 differs in measuring the received signal.

11 may be applied to a receiver, the receiver may correspond to a low power wake-up receiver, and the transmitter may correspond to an AP.

In operation S1110, the receiver receives a wakeup packet including a wakeup preamble and a wakeup payload from the transmitter. The wakeup payload may include a MAC header field, a frame body field, and a frame check sequence (FCS) field.

In step S1120, the receiver measures the average power or average norm value of the received signal passed through the channel through the wakeup preamble. The average power or average norm value is measured based only on bits indicating an on signal in the wakeup preamble.

In step S1130, the receiver checks the power of the wake-up payload based on a threshold value. The threshold is set to half the average power or average norm value.

Referring to FIG. 12, the wireless device may be an AP or a non-AP station (STA) as an STA capable of implementing the above-described embodiment. The wireless device may correspond to the above-described user or may correspond to a transmission device for transmitting a signal to the user.

The AP 1200 includes a processor 1210, a memory 1220, and an RF unit 1230.

The RF unit 1230 may be connected to the processor 1210 to transmit / receive a radio signal.

The processor 1210 may implement the functions, processes, and / or methods proposed herein. For example, the processor 2010 may perform an operation according to the present embodiment described above. That is, the processor 1210 may perform an operation that may be performed by the AP during the operations disclosed in the embodiments of FIGS. 1 to 11.

The non-AP STA 1250 includes a processor 1260, a memory 1270, and an RF unit 1280.

The RF unit 1280 may be connected to the processor 1260 to transmit / receive a radio signal.

The processor 1260 may implement the functions, processes, and / or methods proposed in this embodiment. For example, the processor 1260 may be implemented to perform the non-AP STA operation according to the present embodiment described above. The processor may perform the operation of the non-AP STA in the embodiment of FIGS. 1 to 11.

Processors

1210 and 1260 may include application-specific integrated circuits (ASICs), other chipsets, logic circuits, data processing devices, and / or converters for interconverting baseband signals and wireless signals. The

memories

1220 and 1270 may include read-only memory (ROM), random access memory (RAM), flash memory, memory cards, storage media, and / or other storage devices. The

RF unit

1230 and 1280 may include one or more antennas for transmitting and / or receiving a radio signal.

When the embodiment is implemented in software, the above-described technique may be implemented as a module (process, function, etc.) for performing the above-described function. The module may be stored in the

memories

1220 and 1270 and executed by the

processors

1210 and 1260. The memories 2020 and 2070 may be inside or outside the

processors

1210 and 1260, and may be connected to the

processors

1210 and 1260 by various well-known means.

Claims

A method of performing low power communication using a wake-up packet in a wireless LAN system,

Receiving, by the receiver, a wakeup packet including a wakeup preamble and a wakeup payload from the transmitter;

Measuring, by the receiver, an average power or average norm value of a received signal that has passed through a channel through the wakeup preamble; And

The receiving apparatus further comprises the step of checking the power of the wake-up payload based on a threshold value,

The wakeup packet is modulated and transmitted in an on-off keying (OOK) scheme,

The average power or average norm value is measured based only on a bit indicating an on signal in the wakeup preamble,

The threshold is set to half of the average power or average norm value

Way.
The method of claim 1,

If the power of the wake-up payload is greater than or equal to the threshold value, the power of the payload is determined as alpha ^ 2,

If the power of the wake-up payload is less than the threshold, the power of the payload is determined to be zero,

Alpha is a power normalization factor

Way.
The method of claim 1,

The wakeup preamble includes a sequence including a bit indicating the on signal and a bit indicating an off signal,

The bit indicating the on signal indicates 1,

The bit indicating the off signal indicates 0,

The sequence is defined in advance between the transmitter and the receiver.

Way.
The method of claim 3,

The on signal corresponds to a signal having an actual power value,

The off signal corresponds to a signal that does not have an actual power value.

Way.
The method of claim 3,

The bit indicating the on signal is transmitted through a symbol generated by applying a sequence to 13 consecutive subcarriers in a 20 MHz band and performing a 64-point Inverse Fast Fourier Transform (IFFT).

Way.
The method of claim 5,

The 13 subcarriers correspond to the partial band of the 20 MHz band,

Subcarrier spacing of each of the 13 subcarriers is 312.5 KHz,

The thirteen subcarriers are arranged from subcarrier index -6 to subcarrier index +6,

The symbol has a length of 4 us including a cyclic prefix (CP).

Way.
The method of claim 6,

The wakeup packet further includes a legacy preamble,

The legacy preamble is transmitted on the 20 MHz band,

The wakeup preamble and the wakeup payload are transmitted through a partial band of the 20MHz band.

Way.
The method of claim 1,

The wakeup payload includes a MAC header field, a frame body field, and a frame check sequence (FCS) field.

Way.
In a receiver for performing low power communication using a wake-up packet in a wireless LAN system,

RF unit for transmitting or receiving a wireless signal; And

Including a processor for controlling the RF unit,

The processor is:

Receiving a wake-up packet including a wake-up preamble and a wake-up payload from a transmitter,

Measure an average power or average norm value of a received signal that has passed through a channel through the wakeup preamble, and

Check the power of the wake-up payload based on a threshold,

The wakeup packet is modulated and transmitted in an on-off keying (OOK) scheme,

The average power or average norm value is measured based only on a bit indicating an on signal in the wakeup preamble,

The threshold is set to half of the average power or average norm value

Receiver.
The method of claim 9,

If the power of the wake-up payload is greater than or equal to the threshold value, the power of the payload is determined as alpha ^ 2,

If the power of the wake-up payload is less than the threshold, the power of the payload is determined to be zero,

Alpha is a power normalization factor

Receiver.
The method of claim 9,

The wakeup preamble includes a sequence including a bit indicating the on signal and a bit indicating an off signal,

The bit indicating the on signal indicates 1,

The bit indicating the off signal indicates 0,

The sequence is defined in advance between the transmitter and the receiver.

Receiver.
The method of claim 11,

The on signal corresponds to a signal having an actual power value,

The off signal corresponds to a signal that does not have an actual power value.

Receiver.
The method of claim 11,

The bit indicating the on signal is transmitted through a symbol generated by applying a sequence to 13 consecutive subcarriers in a 20 MHz band and performing a 64-point Inverse Fast Fourier Transform (IFFT).

Receiver.
The method of claim 13,

The 13 subcarriers correspond to the partial band of the 20 MHz band,

Subcarrier spacing of each of the 13 subcarriers is 312.5 KHz,

The thirteen subcarriers are arranged from subcarrier index -6 to subcarrier index +6,

The symbol has a length of 4 us including a cyclic prefix (CP).

Receiver.
The method of claim 14,

The wakeup packet further includes a legacy preamble,

The legacy preamble is transmitted on the 20 MHz band,

The wakeup preamble and the wakeup payload are transmitted through a partial band of the 20MHz band.

Receiver.
The method of claim 9,

The wakeup payload includes a MAC header field, a frame body field, and a frame check sequence (FCS) field.

Receiver.