CN117044067A

CN117044067A - Backscatter communications

Info

Publication number: CN117044067A
Application number: CN202280021851.7A
Authority: CN
Inventors: 纳吉·玛哈林加姆; 拉维库马尔·普拉加达; 坦比尔·哈克; H·埃尔科比
Original assignee: InterDigital Patent Holdings Inc
Current assignee: InterDigital Patent Holdings Inc
Priority date: 2021-02-08
Filing date: 2022-02-08
Publication date: 2023-11-10

Abstract

The present application provides systems, methods, and devices for wireless transmission based on backscatter. A backscatter indication message (BID) is received from an Access Point (AP). An interrogation signal is received. Uplink data is transmitted to the AP based on the BID and the interrogation signal. In some implementations, the interrogation signal is received from the AP. In some implementations, the BID indicates a backscatter duration, and the uplink data is transmitted to the AP for the backscatter duration. In some implementations, the uplink data is transmitted to the AP while the interrogation signal is received. In some implementations, energy is harvested from the interrogation signal. In some implementations, the uplink data is transmitted to the AP after the interrogation signal based on the energy collected from the interrogation signal. In some implementations, the interrogation signal includes a compensation signal based on channel conditions and/or based on backscatter from the WTRU.

Description

Backscatter communications

Cross Reference to Related Applications

The present application claims the benefit of U.S. provisional application No. 63/147,079 filed on 8 th month 2 of 2021 and U.S. provisional application No. 63/235,469 filed on 20 th 8 th year 2021, the contents of which are incorporated herein by reference.

Background

The power saving function is implemented in the IEEE and 3GPP standards for end user devices in order to save power on the device. The backscatter transmitter reflects or absorbs the incident waveform to simulate on-off keying.

Disclosure of Invention

Some implementations provide systems, methods, and/or devices for backscatter-based wireless transmission. A backscatter indication message (BID) is received from an Access Point (AP). An interrogation signal is received. Uplink data is transmitted to the AP based on the BID and the interrogation signal. In some implementations, an interrogation signal is received from an AP. In some implementations, the BID indicates a backscatter duration and uplink data is transmitted to the AP for the backscatter duration. In some implementations, the uplink data is transmitted to the AP while the interrogation signal is received. In some implementations, energy is harvested from the interrogation signal. In some implementations, the uplink data is transmitted to the AP after the interrogation signal based on energy harvested from the interrogation signal. In some implementations, the interrogation signal includes a compensation signal based on channel conditions and/or based on backscatter from the WTRU.

Drawings

A more detailed understanding of the description may be derived from the following description, taken in conjunction with the accompanying drawings, wherein like reference numerals refer to like elements, and in which:

FIG. 1A is a system diagram illustrating an exemplary communication system in which one or more disclosed embodiments may be implemented;

fig. 1B is a system diagram illustrating an exemplary wireless transmit/receive unit (WTRU) that may be used within the communication system shown in fig. 1A according to one embodiment;

fig. 1C is a system diagram illustrating an exemplary Radio Access Network (RAN) and an exemplary Core Network (CN) that may be used within the communication system shown in fig. 1A according to one embodiment;

fig. 1D is a system diagram illustrating another exemplary RAN and another exemplary CN that may be used in the communication system shown in fig. 1A according to one embodiment;

FIG. 2 is a graph illustrating exemplary backscatter in an 802.11ah frame;

FIG. 3 is a table depicting an exemplary BID message format;

FIG. 4 is a block diagram illustrating an exemplary message and associated formats;

FIG. 5 is a diagram illustrating exemplary backscatter in an 802.11 system;

FIG. 6A illustrates exemplary energy harvesting and backscatter;

FIG. 6B is a view taken from FIG. 6A;

FIG. 7 illustrates exemplary communications implementing backscatter communications in an 802.11ax system;

fig. 8 is a flowchart showing an operation of a BSTA in which a DL received signal is above or below a first threshold based on QoS requirements;

FIG. 9 is a system diagram illustrating exemplary interference in backscatter transmission;

fig. 10 illustrates an exemplary framework for learning DL channel conditions via reverse estimation;

fig. 11 shows transmit side compensation of channel impairments;

fig. 12 shows an exemplary control loop for channel estimation at an AP;

fig. 13 illustrates an exemplary control loop for multi-carrier, multi-STA estimation; and is also provided with

Fig. 14 shows an exemplary buffer estimation of the BSTA by the AP.

Detailed Description

Some implementations provide a method implemented in a wireless station, STA. The STA receives a Backscatter Indication (BID) message indicating a backscatter opportunity and a Downlink (DL) signal strength threshold. Based on the signal strength of the DL transmission exceeding the DL signal strength threshold, the STA back-scatters the DL transmission received on the Resource Unit (RU) indicated in the BID message to generate a back-scattered transmission.

In some implementations, the back-scattering of the DL transmission occurs based on the duration of the DL signal exceeding a payload transmission requirement associated with the back-scattering transmission. Some implementations include back-scattering an Uplink (UL) transmission from another STA received on a resource element indicated in the BID message to generate another back-scattered transmission based on the strength of the DL transmission not exceeding a DL signal strength threshold. In some implementations, back-scattering of UL transmissions occurs based on the signal strength of the UL transmissions exceeding a UL signal strength threshold and the duration of the UL transmissions exceeding payload transmission requirements associated with other back-scattered transmissions. Some implementations include measuring signal strength of DL transmissions based on BID messages, preambles in DL frames, or dedicated reference signals. In some implementations, the DL signal strength threshold and the UL signal strength threshold are the same threshold. In some implementations, the BID message includes a management message. In some implementations, the BID message includes an acknowledgement message. In some implementations, the DL signal strength threshold is associated with quality of service (QoS). In some implementations, the backscatter transmission is generated based on the signal strength of the DL transmission exceeding a DL signal strength threshold and the DL transmission exceeding a payload transmission requirement.

Some implementations provide STAs. The STA includes a receiver configured to receive a BID message indicating a backscatter opportunity and a DL signal strength threshold. The STA further includes a transmitter configured to backscatter DL transmissions received on the RU indicated in the BID message to generate backscatter transmissions based on the signal strength of the DL transmissions exceeding a DL signal strength threshold.

In some implementations, the transmitter is further configured to backscatter the DL signal based on the duration of the DL signal exceeding a payload transmission requirement associated with the backscatter transmission. In some implementations, the transmitter is further configured to backscatter UL transmissions from another STA received on the resource elements indicated in the BID message to generate another backscatter transmission based on the strength of the DL transmissions not exceeding the DL signal strength threshold. In some implementations, the transmitter is further configured to backscatter the UL transmission based on the signal strength of the UL transmission exceeding a UL signal strength threshold and the duration of the UL transmission exceeding payload transmission requirements associated with other backscatter transmissions. In some implementations, the receiver is further configured to measure the signal strength of the DL transmission based on the BID message, the preamble in the DL frame, or the dedicated reference signal. In some implementations, the DL signal strength threshold and the UL signal strength threshold are the same threshold. In some implementations, the BID message includes a management message. In some implementations, the BID message includes an acknowledgement message. In some implementations, the DL signal strength threshold is associated with QoS. In some implementations, the transmitter is further configured to generate the backscatter transmission based on the signal strength of the DL transmission exceeding a DL signal strength threshold and the DL transmission exceeding a payload transmission requirement.

Fig. 1A is a diagram illustrating an exemplary communication system 100 in which one or more disclosed embodiments may be implemented. Communication system 100 may be a multiple-access system that provides content, such as voice, data, video, messages, broadcasts, etc., to a plurality of wireless users. Communication system 100 may enable multiple wireless users to access such content through the sharing of system resources, including wireless bandwidth. For example, communication system 100 may employ one or more channel access methods, such as Code Division Multiple Access (CDMA), time Division Multiple Access (TDMA), frequency Division Multiple Access (FDMA), orthogonal FDMA (OFDMA), single carrier FDMA (SC-FDMA), zero-tail unique word discrete fourier transform spread OFDM (ZT-UW-DFT-S-OFDM), unique word OFDM (UW-OFDM), resource block filter OFDM, filter Bank Multicarrier (FBMC), and the like.

As shown in fig. 1A, the communication system 100 may include wireless transmit/receive units (WTRUs) 102a, 102b, 102c, 102d, a Radio Access Network (RAN) 104, a Core Network (CN) 106, a Public Switched Telephone Network (PSTN) 108, the internet 110, and other networks 112, although it should be understood that the disclosed embodiments contemplate any number of WTRUs, base stations, networks, and/or network elements. Each of the WTRUs 102a, 102b, 102c, 102d may be any type of device configured to operate and/or communicate in a wireless environment. For example, the WTRUs 102a, 102b, 102c, 102d, any of which may be referred to as a Station (STA), may be configured to transmit and/or receive wireless signals, and may include User Equipment (UE), mobile stations, fixed or mobile subscriber units, subscription-based units, pagers, cellular telephones, personal Digital Assistants (PDAs), smartphones, laptop computers, netbooks, personal computers, wireless sensors, hot spot or Mi-Fi devices, internet of things (IoT) devices, watches or other wearable devices, head Mounted Displays (HMDs), vehicles, drones, medical devices and applications (e.g., tele-surgery), industrial devices and applications (e.g., robots and/or other wireless devices operating in an industrial and/or automated processing chain environment), consumer electronic devices, devices operating on a commercial and/or industrial wireless network, and the like. Any of the WTRUs 102a, 102b, 102c, and 102d may be interchangeably referred to as a UE.

Communication system 100 may also include base station 114a and/or base station 114b. Each of the base stations 114a, 114b may be any type of device configured to wirelessly interface with at least one of the WTRUs 102a, 102b, 102c, 102d to facilitate access to one or more communication networks, such as the CN 106, the internet 110, and/or the other networks 112. As an example, the base stations 114a, 114B may be Base Transceiver Stations (BTSs), nodebs, eNode bs (enbs), home Node bs, home eNode bs, next generation nodebs, such as gnnode bs (gnbs), new air interface (NR) nodebs, site controllers, access Points (APs), wireless routers, and the like. Although the base stations 114a, 114b are each depicted as a single element, it should be appreciated that the base stations 114a, 114b may include any number of interconnected base stations and/or network elements.

Base station 114a may be part of RAN 104 that may also include other base stations and/or network elements (not shown), such as Base Station Controllers (BSCs), radio Network Controllers (RNCs), relay nodes, and the like. Base station 114a and/or base station 114b may be configured to transmit and/or receive wireless signals on one or more carrier frequencies, which may be referred to as a cell (not shown). These frequencies may be in a licensed spectrum, an unlicensed spectrum, or a combination of licensed and unlicensed spectrum. A cell may provide coverage of wireless services to a particular geographic area, which may be relatively fixed or may change over time. The cell may be further divided into cell sectors. For example, a cell associated with base station 114a may be divided into three sectors. Thus, in an embodiment, the base station 114a may include three transceivers, i.e., one for each sector of a cell. In an embodiment, the base station 114a may employ multiple-input multiple-output (MIMO) technology and may utilize multiple transceivers for each sector of a cell. For example, beamforming may be used to transmit and/or receive signals in a desired spatial direction.

The base stations 114a, 114b may communicate with one or more of the WTRUs 102a, 102b, 102c, 102d over an air interface 116, which may be any suitable wireless communication link (e.g., radio Frequency (RF), microwave, centimeter wave, millimeter wave, infrared (IR), ultraviolet (UV), visible light, etc.). The air interface 116 may be established using any suitable Radio Access Technology (RAT).

More specifically, as noted above, communication system 100 may be a multiple access system and may employ one or more channel access schemes, such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, or the like. For example, the base station 114a and WTRUs 102a, 102b, 102c in the RAN 104 may implement a radio technology such as Universal Mobile Telecommunications System (UMTS) terrestrial radio access (UTRA), which may use Wideband CDMA (WCDMA) to establish the air interface 116.WCDMA may include communication protocols such as High Speed Packet Access (HSPA) and/or evolved HSPA (hspa+). HSPA may include high speed Downlink (DL) packet access (HSDPA) and/or high speed Uplink (UL) packet access (HSUPA).

In an embodiment, the base station 114a and the WTRUs 102a, 102b, 102c may implement a radio technology such as evolved UMTS terrestrial radio access (E-UTRA), which may use Long Term Evolution (LTE) and/or LTE-advanced (LTE-a) and/or LTE-advanced Pro (LTE-a Pro) to establish the air interface 116.

In one embodiment, the base station 114a and the WTRUs 102a, 102b, 102c may implement a radio technology such as NR radio access, which may use NR to establish the air interface 116.

In embodiments, the base station 114a and the WTRUs 102a, 102b, 102c may implement multiple radio access technologies. For example, the base station 114a and the WTRUs 102a, 102b, 102c may implement LTE radio access and NR radio access together, e.g., using a Dual Connectivity (DC) principle. Thus, the air interface utilized by the WTRUs 102a, 102b, 102c may be characterized by multiple types of radio access technologies and/or transmissions sent to/from multiple types of base stations (e.g., enbs and gnbs).

In other embodiments, the base station 114a and the WTRUs 102a, 102b, 102c may implement radio technologies such as IEEE 802.11 (i.e., wireless fidelity (WiFi)), IEEE 802.16 (i.e., worldwide Interoperability for Microwave Access (WiMAX)), CDMA2000 1X, CDMA EV-DO, tentative standard 2000 (IS-2000), tentative standard 95 (IS-95), tentative standard 856 (IS-856), global system for mobile communications (GSM), enhanced data rates for GSM evolution (EDGE), GSM EDGE (GERAN), and the like.

The base station 114B in fig. 1A may be, for example, a wireless router, a home Node B, a home eNode B, or an access point, and may utilize any suitable RAT to facilitate wireless connections in local areas such as businesses, homes, vehicles, campuses, industrial facilities, air corridors (e.g., for use by drones), roads, and the like. In an embodiment, the base station 114b and the WTRUs 102c, 102d may implement a radio technology such as IEEE 802.11 to establish a Wireless Local Area Network (WLAN). In an embodiment, the base station 114b and the WTRUs 102c, 102d may implement a radio technology such as IEEE 802.15 to establish a Wireless Personal Area Network (WPAN). In yet another embodiment, the base station 114b and the WTRUs 102c, 102d may utilize a cellular-based RAT (e.g., WCDMA, CDMA2000, GSM, LTE, LTE-A, LTE-a Pro, NR, etc.) to establish a pico cell or femto cell. As shown in fig. 1A, the base station 114b may be directly connected to the internet 110. Thus, the base station 114b may not need to access the internet 110 via the CN 106.

The RAN 104 may communicate with a CN 106, which may be any type of network configured to provide voice, data, application, and/or voice over internet protocol (VoIP) services to one or more of the WTRUs 102a, 102b, 102c, 102 d. The data may have different quality of service (QoS) requirements, such as different throughput requirements, delay requirements, error tolerance requirements, reliability requirements, data throughput requirements, mobility requirements, and the like. The CN 106 may provide call control, billing services, mobile location based services, prepaid calls, internet connections, video distribution, etc., and/or perform advanced security functions such as user authentication. Although not shown in fig. 1A, it should be appreciated that RAN 104 and/or CN 106 may communicate directly or indirectly with other RANs that employ the same RAT as RAN 104 or a different RAT. For example, in addition to being connected to the RAN 104 that may utilize NR radio technology, the CN 106 may also communicate with another RAN (not shown) that employs GSM, UMTS, CDMA 2000, wiMAX, E-UTRA, or WiFi radio technology.

The CN 106 may also act as a gateway for the WTRUs 102a, 102b, 102c, 102d to access the PSTN 108, the internet 110, and/or other networks 112.PSTN 108 may include circuit-switched telephone networks that provide Plain Old Telephone Services (POTS). The internet 110 may include a global system for interconnecting computer networks and devices using common communication protocols, such as Transmission Control Protocol (TCP), user Datagram Protocol (UDP), and/or Internet Protocol (IP) in the TCP/IP internet protocol suite. Network 112 may include wired and/or wireless communication networks owned and/or operated by other service providers. For example, the network 112 may include another CN connected to one or more RANs, which may employ the same RAT as the RAN 104 or a different RAT.

Some or all of the WTRUs 102a, 102b, 102c, 102d in the communication system 100 may include multi-mode capabilities (e.g., the WTRUs 102a, 102b, 102c, 102d may include multiple transceivers for communicating with different wireless networks over different wireless links). For example, the WTRU 102c shown in fig. 1A may be configured to communicate with a base station 114a, which may employ a cellular-based radio technology, and with a base station 114b, which may employ an IEEE 802 radio technology.

Fig. 1B is a system diagram illustrating an exemplary WTRU 102. As shown in fig. 1B, the WTRU 102 may include a processor 118, a transceiver 120, a transmit/receive element 122, a speaker/microphone 124, a keypad 126, a display/touchpad 128, non-removable memory 130, removable memory 132, a power source 134, a Global Positioning System (GPS) chipset 136, and/or other peripheral devices 138, etc. It should be appreciated that the WTRU 102 may include any sub-combination of the foregoing elements while remaining consistent with an embodiment.

The processor 118 may be a general purpose processor, a special purpose processor, a conventional processor, a Digital Signal Processor (DSP), a plurality of microprocessors, one or more microprocessors in association with a DSP core, a controller, a microcontroller, application Specific Integrated Circuits (ASICs), field Programmable Gate Arrays (FPGAs), any other type of Integrated Circuit (IC), a state machine, or the like. The processor 118 may perform signal coding, data processing, power control, input/output processing, and/or any other functions that enable the WTRU 102 to operate in a wireless environment. The processor 118 may be coupled to a transceiver 120, which may be coupled to a transmit/receive element 122. Although fig. 1B depicts the processor 118 and the transceiver 120 as separate components, it should be understood that the processor 118 and the transceiver 120 may be integrated together in an electronic package or chip.

The transmit/receive element 122 may be configured to transmit signals to and receive signals from a base station (e.g., base station 114 a) over the air interface 116. For example, in one embodiment, the transmit/receive element 122 may be an antenna configured to transmit and/or receive RF signals. In one embodiment, the transmit/receive element 122 may be an emitter/detector configured to emit and/or receive, for example, IR, UV, or visible light signals. In yet another embodiment, the transmit/receive element 122 may be configured to transmit and/or receive RF and optical signals. It should be appreciated that the transmit/receive element 122 may be configured to transmit and/or receive any combination of wireless signals.

Although the transmit/receive element 122 is depicted as a single element in fig. 1B, the WTRU 102 may include any number of transmit/receive elements 122. More specifically, the WTRU 102 may employ MIMO technology. Thus, in one embodiment, the WTRU 102 may include two or more transmit/receive elements 122 (e.g., multiple antennas) for transmitting and receiving wireless signals over the air interface 116.

The transceiver 120 may be configured to modulate signals to be transmitted by the transmit/receive element 122 and demodulate signals received by the transmit/receive element 122. As noted above, the WTRU 102 may have multi-mode capabilities. For example, therefore, the transceiver 120 may include multiple transceivers to enable the WTRU 102 to communicate via multiple RATs (such as NR and IEEE 802.11).

The processor 118 of the WTRU 102 may be coupled to and may receive user input data from a speaker/microphone 124, a keypad 126, and/or a display/touchpad 128, such as a Liquid Crystal Display (LCD) display unit or an Organic Light Emitting Diode (OLED) display unit. The processor 118 may also output user data to the speaker/microphone 124, the keypad 126, and/or the display/touchpad 128. Further, the processor 118 may access information from and store data in any type of suitable memory, such as the non-removable memory 130 and/or the removable memory 132. The non-removable memory 130 may include Random Access Memory (RAM), read Only Memory (ROM), a hard disk, or any other type of memory storage device. Removable memory 132 may include a Subscriber Identity Module (SIM) card, a memory stick, a Secure Digital (SD) memory card, and the like. In other embodiments, the processor 118 may never physically locate memory access information on the WTRU 102, such as on a server or home computer (not shown), and store the data in that memory.

The processor 118 may receive power from the power source 134 and may be configured to distribute and/or control power to other components in the WTRU 102. The power source 134 may be any suitable device for powering the WTRU 102. For example, the power source 134 may include one or more dry battery packs (e.g., nickel cadmium (NiCd), nickel zinc (NiZn), nickel metal hydride (NiMH), lithium ion (Li-ion), etc.), solar cells, fuel cells, and the like.

The processor 118 may also be coupled to a GPS chipset 136, which may be configured to provide location information (e.g., longitude and latitude) regarding the current location of the WTRU 102. In addition to or in lieu of information from the GPS chipset 136, the WTRU 102 may receive location information from base stations (e.g., base stations 114a, 114 b) over the air interface 116 and/or determine its location based on the timing of signals received from two or more nearby base stations. It should be appreciated that the WTRU 102 may obtain location information by any suitable location determination method while remaining consistent with an embodiment.

The processor 118 may also be coupled to other peripheral devices 138, which may include one or more software modules and/or hardware modules that provide additional features, functionality, and/or wired or wireless connections. For example, the number of the cells to be processed, peripheral devices 138 may include accelerometers, electronic compasses, satellite transceivers, digital cameras (for photographs and/or video), universal Serial Bus (USB) ports, vibrating devices, television transceivers, hands-free headsets, wireless communications devices, and the like,Modules, frequency Modulation (FM) radio units, digital music players, media players, video game player modules, internet browsers, virtual reality and/or augmented reality (VR/AR) devices, activity trackers, and the like. The peripheral device 138 may include one or more sensors. The sensor may be one or more of the following: gyroscopes, accelerometers, hall effect sensors, magnetometers, orientation sensors, proximity sensors, temperature sensors, time sensors; geographical position sensor, altimeter and optical sensor A touch sensor, a magnetometer, a barometer, a gesture sensor, a biometric sensor, a humidity sensor, etc.

WTRU 102 may include a full duplex radio for which transmission and reception of some or all signals (e.g., associated with a particular subframe for UL (e.g., for transmission) and DL (e.g., for reception)) may be concurrent and/or simultaneous. The full duplex radio station may include an interference management unit for reducing and/or substantially eliminating self-interference via hardware (e.g., choke) or via signal processing by a processor (e.g., a separate processor (not shown) or via processor 118). In one embodiment, the WTRU 102 may include a half-duplex radio for which some or all signals are transmitted and received (e.g., associated with a particular subframe for UL (e.g., for transmission) or DL (e.g., for reception).

Fig. 1C is a system diagram illustrating a RAN 104 and a CN 106 according to an embodiment. As described above, the RAN 104 may communicate with the WTRUs 102a, 102b, 102c over the air interface 116 using an E-UTRA radio technology. RAN 104 may also communicate with CN 106.

RAN 104 may include eNode-bs 160a, 160B, 160c, but it should be understood that RAN 104 may include any number of eNode-bs while remaining consistent with an embodiment. each of the eNode-bs 160a, 160B, 160c may include one or more transceivers to communicate with the WTRUs 102a, 102B, 102c over the air interface 116. In an embodiment, eNode-bs 160a, 160B, 160c may implement MIMO technology. Thus, for example, eNode-B160a may use multiple antennas to transmit wireless signals to WTRU 102a and/or to receive wireless signals from WTRU 102 a.

each of eNode-bs 160a, 160B, 160c may be associated with a particular cell (not shown) and may be configured to process radio resource management decisions, handover decisions, scheduling of users in UL and/or DL, and the like. As shown in fig. 1C, eNode-bs 160a, 160B, 160C may communicate with each other through an X2 interface.

The CN 106 shown in fig. 1C may include a Mobility Management Entity (MME) 162, a Serving Gateway (SGW) 164, and a Packet Data Network (PDN) gateway (PGW) 166. Although the foregoing elements are depicted as part of the CN 106, it should be appreciated that any of these elements may be owned and/or operated by entities other than the CN operator.

MME 162 may be connected to each of eNode-bs 162a, 162B, 162c in RAN 104 via an S1 interface and may function as a control node. For example, the MME 162 may be responsible for authenticating the user of the WTRUs 102a, 102b, 102c, bearer activation/deactivation, selecting a particular serving gateway during initial attach of the WTRUs 102a, 102b, 102c, and the like. MME 162 may provide control plane functionality for switching between RAN 104 and other RANs (not shown) employing other radio technologies such as GSM and/or WCDMA.

SGW 164 may be connected to each of eNode bs 160a, 160B, 160c in RAN 104 via an S1 interface. The SGW 164 may generally route and forward user data packets to/from the WTRUs 102a, 102b, 102 c. SGW 164 may perform other functions such as anchoring user planes during inter-eNode B handover, triggering paging when DL data is available to WTRUs 102a, 102B, 102c, managing and storing contexts of WTRUs 102a, 102B, 102c, and the like.

The SGW 164 may be connected to a PGW 166 that may provide the WTRUs 102a, 102b, 102c with access to a packet switched network, such as the internet 110, to facilitate communications between the WTRUs 102a, 102b, 102c and IP-enabled devices.

The CN 106 may facilitate communications with other networks. For example, the CN 106 may provide the WTRUs 102a, 102b, 102c with access to a circuit-switched network (such as the PSTN 108) to facilitate communications between the WTRUs 102a, 102b, 102c and legacy landline communication devices. For example, the CN 106 may include or may communicate with an IP gateway (e.g., an IP Multimedia Subsystem (IMS) server) that serves as an interface between the CN 106 and the PSTN 108. In addition, the CN 106 may provide the WTRUs 102a, 102b, 102c with access to other networks 112, which may include other wired and/or wireless networks owned and/or operated by other service providers.

Although the WTRU is depicted in fig. 1A-1D as a wireless terminal, it is contemplated that in some representative embodiments such a terminal may use a wired communication interface with a communication network (e.g., temporarily or permanently).

In representative embodiments, the other network 112 may be a WLAN.

A WLAN in an infrastructure Basic Service Set (BSS) mode may have an Access Point (AP) for the BSS and one or more Stations (STAs) associated with the AP. The AP may have access or interface to a Distribution System (DS) or another type of wired/wireless network that carries traffic to and/or from the BSS. Traffic originating outside the BSS and directed to the STA may arrive through the AP and may be delivered to the STA. Traffic originating from the STA and leading to a destination outside the BSS may be sent to the AP to be delivered to the respective destination. Traffic between STAs within the BSS may be sent through the AP, for example, where the source STA may send traffic to the AP and the AP may pass the traffic to the destination STA. Traffic between STAs within a BSS may be considered and/or referred to as point-to-point traffic. Point-to-point traffic may be sent between (e.g., directly between) the source and destination STAs using Direct Link Setup (DLS). In certain representative embodiments, the DLS may use 802.11e DLS or 802.11z Tunnel DLS (TDLS). A WLAN using an Independent BSS (IBSS) mode may not have an AP, and STAs (e.g., all STAs) within or using the IBSS may communicate directly with each other. The IBSS communication mode may sometimes be referred to herein as an "ad-hoc" communication mode.

When using the 802.11ac infrastructure mode of operation or similar modes of operation, the AP may transmit beacons on a fixed channel, such as a primary channel. The primary channel may be a fixed width (e.g., 20MHz wide bandwidth) or a dynamically set width. The primary channel may be an operating channel of the BSS and may be used by STAs to establish a connection with the AP. In certain representative embodiments, carrier sense multiple access/collision avoidance (CSMA/CA) may be implemented, for example, in an 802.11 system. For CSMA/CA, STAs (e.g., each STA), including the AP, may listen to the primary channel. If the primary channel is listened to/detected by a particular STA and/or determined to be busy, the particular STA may backoff. One STA (e.g., only one station) may transmit at any given time in a given BSS.

High Throughput (HT) STAs may communicate using 40MHz wide channels, for example, by combining a primary 20MHz channel with an adjacent or non-adjacent 20MHz channel to form a 40MHz wide channel.

Very High Throughput (VHT) STAs may support channels that are 20MHz, 40MHz, 80MHz, and/or 160MHz wide. 40MHz and/or 80MHz channels may be formed by combining consecutive 20MHz channels. The 160MHz channel may be formed by combining 8 consecutive 20MHz channels, or by combining two non-consecutive 80MHz channels (this may be referred to as an 80+80 configuration). For the 80+80 configuration, after channel coding, the data may pass through a segment parser that may split the data into two streams. An Inverse Fast Fourier Transform (IFFT) process and a time domain process may be performed on each stream separately. These streams may be mapped to two 80MHz channels and data may be transmitted by the transmitting STA. At the receiver of the receiving STA, the operations described above for the 80+80 configuration may be reversed and the combined data may be sent to a Medium Access Control (MAC).

The 802.11af and 802.11ah support modes of operation below 1 GHz. Channel operating bandwidth and carrier are reduced in 802.11af and 802.11ah relative to those used in 802.11n and 802.11 ac. The 802.11af supports 5MHz, 10MHz, and 20MHz bandwidths in the television white space (TVWS) spectrum, and the 802.11ah supports 1MHz, 2MHz, 4MHz, 8MHz, and 16MHz bandwidths using non-TVWS spectrum. According to representative embodiments, 802.11ah may support meter type control/Machine Type Communication (MTC), such as MTC devices in macro coverage areas. MTC devices may have certain capabilities, such as limited capabilities, including supporting (e.g., supporting only) certain bandwidths and/or limited bandwidths. MTC devices may include batteries with battery lives above a threshold (e.g., to maintain very long battery lives).

WLAN systems that can support multiple channels, and channel bandwidths such as 802.11n, 802.11ac, 802.11af, and 802.11ah, include channels that can be designated as primary channels. The primary channel may have a bandwidth equal to the maximum common operating bandwidth supported by all STAs in the BSS. The bandwidth of the primary channel may be set and/or limited by STAs from all STAs operating in the BSS (which support a minimum bandwidth mode of operation). In the example of 802.11ah, for STAs (e.g., MTC-type devices) that support (e.g., only) 1MHz mode, the primary channel may be 1MHz wide, even though the AP and other STAs in the BSS support 2MHz, 4MHz, 8MHz, 16MHz, and/or other channel bandwidth modes of operation. The carrier sense and/or Network Allocation Vector (NAV) settings may depend on the state of the primary channel. If the primary channel is busy, for example, because the STA is transmitting to the AP (only supporting 1MHz mode of operation), all available frequency bands may be considered busy even if most available frequency bands remain idle.

The available frequency band for 802.11ah in the united states is 902MHz to 928MHz. In korea, the available frequency band is 917.5MHz to 923.5MHz. In Japan, the available frequency band is 916.5MHz to 927.5MHz. The total bandwidth available for 802.11ah is 6MHz to 26MHz, depending on the country code.

Fig. 1D is a system diagram illustrating a RAN 104 and a CN 106 according to an embodiment. As noted above, the RAN 104 may employ NR radio technology to communicate with the WTRUs 102a, 102b, 102c over the air interface 116. RAN 104 may also communicate with CN 106.

RAN 104 may include gnbs 180a, 180b, 180c, although it will be appreciated that RAN 104 may include any number of gnbs while remaining consistent with an embodiment. Each of the gnbs 180a, 180b, 180c may include one or more transceivers to communicate with the WTRUs 102a, 102b, 102c over the air interface 116. In an embodiment, the gnbs 180a, 180b, 180c may implement MIMO technology. For example, gnbs 180a, 108b may utilize beamforming to transmit signals to gnbs 180a, 180b, 180c and/or to receive signals from gnbs 180a, 180b, 180 c. Thus, the gNB 180a may use multiple antennas to transmit wireless signals to the WTRU 102a and/or receive wireless signals from the WTRU 102a, for example. In an embodiment, the gnbs 180a, 180b, 180c may implement carrier aggregation techniques. For example, the gNB 180a may transmit multiple component carriers to the WTRU 102a (not shown). A subset of these component carriers may be on the unlicensed spectrum while the remaining component carriers may be on the licensed spectrum. In embodiments, the gnbs 180a, 180b, 180c may implement coordinated multipoint (CoMP) techniques. For example, WTRU 102a may receive coordinated transmissions from gNB 180a and gNB 180b (and/or gNB 180 c).

The WTRUs 102a, 102b, 102c may communicate with the gnbs 180a, 180b, 180c using transmissions associated with the scalable parameter sets. For example, the OFDM symbol interval and/or OFDM subcarrier interval may vary from one transmission to another, from one cell to another, and/or from one portion of the wireless transmission spectrum to another. The WTRUs 102a, 102b, 102c may communicate with the gnbs 180a, 180b, 180c using various or scalable length subframes or Transmission Time Intervals (TTIs) (e.g., including different numbers of OFDM symbols and/or continuously varying absolute time lengths).

The gnbs 180a, 180b, 180c may be configured to communicate with the WTRUs 102a, 102b, 102c in an independent configuration and/or in a non-independent configuration. In a stand-alone configuration, the WTRUs 102a, 102B, 102c may communicate with the gnbs 180a, 180B, 180c while also not accessing other RANs (e.g., such as the eNode-bs 160a, 160B, 160 c). In an independent configuration, the WTRUs 102a, 102b, 102c may use one or more of the gnbs 180a, 180b, 180c as mobility anchor points. In an independent configuration, the WTRUs 102a, 102b, 102c may use signals in unlicensed frequency bands to communicate with the gnbs 180a, 180b, 180 c. In a non-standalone configuration, the WTRUs 102a, 102B, 102c may communicate or connect with the gnbs 180a, 180B, 180c while also communicating or connecting with another RAN (such as the eNode-bs 160a, 160B, 160 c). For example, the WTRUs 102a, 102B, 102c may implement DC principles to communicate with one or more gnbs 180a, 180B, 180c and one or more eNode-bs 160a, 160B, 160c substantially simultaneously. In a non-standalone configuration, the eNode-bs 160a, 160B, 160c may serve as mobility anchors for the WTRUs 102a, 102B, 102c, and the gnbs 180a, 180B, 180c may provide additional coverage and/or throughput for serving the WTRUs 102a, 102B, 102 c.

Each of the gnbs 180a, 180b, 180c may be associated with a particular cell (not shown) and may be configured to handle radio resource management decisions, handover decisions, scheduling of users in UL and/or DL, support of network slices, interworking between DC, NR, and E-UTRA, routing of user plane data towards User Plane Functions (UPFs) 184a, 184b, routing of control plane information towards access and mobility management functions (AMFs) 182a, 182b, and so on. As shown in fig. 1D, gnbs 180a, 180b, 180c may communicate with each other through an Xn interface.

The CN 106 shown in fig. 1D may include at least one AMF 182a, 182b, at least one UPF 184a, 184b, at least one Session Management Function (SMF) 183a, 183b, and possibly a Data Network (DN) 185a, 185b. Although the foregoing elements are depicted as part of the CN 106, it should be appreciated that any of these elements may be owned and/or operated by entities other than the CN operator.

The AMFs 182a, 182b may be connected to one or more of the gnbs 180a, 180b, 180c in the RAN 104 via an N2 interface and may function as control nodes. For example, the AMFs 182a, 182b may be responsible for authenticating users of the WTRUs 102a, 102b, 102c, support for network slices (e.g., handling of different Protocol Data Unit (PDU) sessions with different requirements), selection of a particular SMF 183a, 183b, management of registration areas, termination of non-access stratum (NAS) signaling, mobility management, etc. The AMFs 182a, 182b may use network slices to customize CN support for the WTRUs 102a, 102b, 102c based on the type of service used by the WTRUs 102a, 102b, 102 c. For example, different network slices may be established for different use cases, such as services relying on ultra high reliability low latency (URLLC) access, services relying on enhanced mobile broadband (eMBB) access, services for MTC access, and so on. The AMFs 182a, 182b may provide control plane functionality for switching between the RAN 104 and other RANs (not shown) employing other radio technologies, such as LTE, LTE-A, LTE-a Pro, and/or non-3 GPP access technologies, such as WiFi.

The SMFs 183a, 183b may be connected to AMFs 182a, 182b in the CN 106 via an N11 interface. The SMFs 183a, 183b may also be connected to UPFs 184a, 184b in the CN 106 via an N4 interface. SMFs 183a, 183b may select and control UPFs 184a, 184b and configure traffic routing through UPFs 184a, 184b. The SMFs 183a, 183b may perform other functions such as managing and assigning UE IP addresses, managing PDU sessions, controlling policy enforcement and QoS, providing DL data notifications, etc. The PDU session type may be IP-based, non-IP-based, ethernet-based, etc.

UPFs 184a, 184b may be connected to one or more of the gnbs 180a, 180b, 180c in the RAN 104 via an N3 interface that may provide the WTRUs 102a, 102b, 102c with access to a packet-switched network, such as the internet 110, to facilitate communications between the WTRUs 102a, 102b, 102c and IP-enabled devices. UPFs 184, 184b may perform other functions such as routing and forwarding packets, enforcing user plane policies, supporting multi-host PDU sessions, handling user plane QoS, buffering DL packets, providing mobility anchoring, and the like.

The CN 106 may facilitate communications with other networks. For example, the CN 106 may include or may communicate with an IP gateway (e.g., an IP Multimedia Subsystem (IMS) server) that serves as an interface between the CN 106 and the PSTN 108. In addition, the CN 106 may provide the WTRUs 102a, 102b, 102c with access to other networks 112, which may include other wired and/or wireless networks owned and/or operated by other service providers. In one embodiment, the WTRUs 102a, 102b, 102c may connect to the DNs 185a, 185b through the UPFs 184a, 184b via an N3 interface to the UPFs 184a, 184b and an N6 interface between the UPFs 184a, 184b and the local DNs 185a, 185b.

In view of fig. 1A-1D and the corresponding descriptions of fig. 1A-1D, one or more or all of the functions described herein with respect to one or more of the following may be performed by one or more emulation devices (not shown): WTRUs 102 a-102 d, base stations 114 a-114B, eNode-bs 160 a-160 c, MME 162, SGW 164, PGW 166, gnbs 180 a-180 c, AMFs 182 a-182B, UPFs 184 a-184B, SMFs 183 a-183B, DNs 185 a-185B, and/or any other devices described herein. The emulated device may be one or more devices configured to emulate one or more or all of the functions described herein. For example, the emulation device may be used to test other devices and/or analog network and/or WTRU functions.

The simulation device may be designed to enable one or more tests of other devices in a laboratory environment and/or an operator network environment. For example, the one or more emulation devices can perform one or more or all of the functions while being fully or partially implemented and/or deployed as part of a wired and/or wireless communication network in order to test other devices within the communication network. The one or more emulation devices can perform one or more functions or all functions while being temporarily implemented/deployed as part of a wired and/or wireless communication network. The emulation device can be directly coupled to another device for testing purposes and/or perform testing using over-the-air wireless communications.

The one or more emulation devices can perform one or more (including all) functions while not being implemented/deployed as part of a wired and/or wireless communication network. For example, the simulation device may be used in a test laboratory and/or a test scenario in a non-deployed (e.g., test) wired and/or wireless communication network in order to enable testing of one or more components. The one or more simulation devices may be test equipment. Direct RF coupling and/or wireless communication via RF circuitry (e.g., which may include one or more antennas) may be used by the emulation device to transmit and/or receive data.

Wherein the following abbreviations are used herein, access Points (APs); backscattering Indication (BID); backscatter STAs (BSTAs); clear To Send (CTS); a Downlink (DL); internet of things (IoT); an interrogation signal (INT_SIG); internet Protocol (IP); medium Access Control (MAC); multiple Input Multiple Output (MIMO); orthogonal Frequency Division Multiplexing (OFDM); physical layer (PHY); paging Opportunities (POs); power Optimized Waveform (POW); a Power Save Mode (PSM); a Restricted Access Window (RAW); request To Send (RTS); target Wake Time (TWT); wake-up receiver (WuR); a wake-up packet (WuP); radio Access Technology (RAT); a radio front end (RF); request To Send (RTS); stations (WiFi devices) (STAs); transmission/reception (TX/RX); transmitting an information map (TIM); user Equipment (UE); uplink (UL); and Zero Energy (ZE).

Both IEEE and 3GPP include power saving features for end user devices (e.g., 802.11 STAs, 3GPP UEs) that obtain services, for example, from an access device (e.g., 802.11 Access Point (AP) or 3GPP eNB). It should be noted that STAs and UEs are used herein as exemplary end-user devices, but any suitable end-user device may be used in place of these examples. It should also be noted that APs and enbs are used herein as exemplary access devices, but any suitable access device may be used in place of these examples. Devices implementing the power saving feature may be referred to as operating in a Power Save Mode (PSM). Typical PSM procedures include an end user device negotiating a sleep period with an access device, sleeping each sleep period (e.g., entering a PSM), waking up each pre-negotiated condition (e.g., periodic or event occurrence), indicating buffered data for reception or transmission after entering a "wake-up period," performing data transmission or data reception during the "wake-up period," and recovering the PSM (e.g., when there is an interval in the data transmission or reception). In some cases, the cyclic, limited, but relatively long duration may be considered a "wake-up period" and a portion of the period may be considered a "wake-up period" for the end-user device.

If the device wakes up, the duration of device activity during the wake-up period may depend on the amount of data waiting in the queue to be received or transmitted. In some cases, after the end user device wakes up, the end user device may remain active for the entire duration of the wake-up period. If there is no indication of pending data for reception and/or transmission during the "wake-up period", the end user device may resume sleep (e.g., resume PSM) at the end of the wake-up period. PSMs are typically entered for energy saving purposes. In some cases, the longer the device can sleep, the longer the standby time of the power supply of the end user device.

Newer versions of the 802.11 specification have incorporated Target Wake Times (TWTs). TWT implementations may include functionality that allows an AP to define a particular time or set of times for each station to access a medium. The STA and the AP may exchange information indicating the expected activity duration to allow the AP to control the amount of contention and overlap between competing STAs. The use of TWTs may be negotiated between an AP and a STA. In some implementations, the TWT involves a Restricted Access Window (RAW). The RAW helps to divide stations within a Basic Service Set (BSS) into groups, for example, by restricting channel access only to stations belonging to a given group during a specific period of time (referred to as a RAW). In other words, only a specific STA or group of STAs (or other devices) is allowed to access the channel during the RAW. In some cases, this has the advantage of reducing contention and/or avoiding simultaneous transmissions from many stations.

In some implementations, STAs grouped within a RAW contend for access to the slot to gain access to the medium. The access slot is limited to a specific STA and is a period of time within the RAW that may be selected by a specific STA or group of STAs for channel access. In some implementations, the contention amount of the access slot is on average proportional to the number of STAs grouped within the RAW and the call model requirements of each STA. The term "call model" refers to a process that may be applied to determine the arrival of a session (time of arrival of data), the associated duration of each session, and the STAs required for the data. In some cases, TWTs may be used to reduce network energy consumption, for example, by facilitating STA sleep states until their TWTs arrive.

The above features are generally implemented to provide power savings to STAs. Such STAs may be incorporated into any suitable device, such as an internet of things (IOT) device. Exemplary IOT devices include chemical sensors (e.g., oil leak sensors, smoke detectors, etc.), environmental monitors (e.g., temperature and/or pressure sensors, embedded seismic monitors, etc.), and event reporting meters (e.g., expiration of a parking meter, electricity usage report, etc.). Such devices may have relatively low data rate requirements (e.g., relative to typical 802.11 STAs) and may transmit bursty data traffic (e.g., on the order of 100 bits/second to thousands of bits/second, e.g., once a few hours/day or even once a few weeks).

Such devices may remain in PSM mode most of the time, may wake up to perform tasks (e.g., periodic monitoring), and may engage in wireless data communications at designated times to report information (e.g., measurements or other data) to a server. Such IOT sensors may be deployed in difficult to access places (e.g., such as in california and japan for wall-embedded seismic monitors for estimating seismic damage), where it would be impractical to replace power supplies in these devices at periodic intervals. Thus, an apparatus that can harvest energy from various power sources and use a reserve of power for transmit and receive functions may have the advantage of extended availability. Devices capable of harvesting energy to power their RX and TX chains may become more common in the future. Architectures involving lower power consumption transmit chains may also become ubiquitous in the future. In some implementations, the backscatter transmitters support such an architecture.

Backscattering is one such technique: a STA, WTRU, or other wireless communication device uses the incident RF signal/waveform to (a) harvest the energy needed to power its uplink transmissions; and/or (b) modulating the reflected/backscattered RF signal/waveform via a set of antenna loads. In some implementations, the term backscatter does not necessarily relate to energy harvesting, however some implementations may define energy harvesting as part of backscatter. Backscattering generally involves reflecting or absorbing an incident waveform to simulate on-off keying. It should be noted that different implementations involve variations of the backscattering concept. For example, an incident waveform, which may be referred to as an interrogation signal, carrier generator, etc., may be provided exclusively for backscatter purposes (i.e., exclusively for backscatter), or may be a signal that is not provided exclusively for backscatter purposes (i.e., for opportunistic backscatter). The dedicated interrogation signal may be provided by any suitable source, such as STA, UE, AP, nodeB, WTRU. Such sources may be referred to as dedicated sources. The interrogation signal of opportunity may include any suitable signal not specifically provided for backscatter by any suitable source, such as an environmental source (e.g., wi-Fi, TV signal, etc.), as well as signals from other devices not specifically provided for backscatter (e.g., STA, UE, AP, nodeB, WTRU, etc.). Such sources may be referred to as opportunity sources.

Because of the greater emphasis on sustainability, there is a growing interest in the areas of energy conservation and energy efficiency. For example, a common environmental source is Wi-Fi. In some implementations, it is preferable to use sources that can be integrated into existing frameworks to backscatter, for example, to enable widespread adoption. In other words, in some implementations, it may be advantageous for legacy devices that are not backscatter and devices that are backscatter to coexist in an environment without damaging the legacy devices and/or without requiring updates to the legacy device software or hardware.

Some implementations include existing, new or reused messages or other signals. Specific names are used herein to define some exemplary messages, however, it should be noted that specific names are merely exemplary. Some implementations include appropriate signals with different names that provide the same, similar, or overlapping functionality.

In some implementations, a Backscatter Station (BSTA) is a device that can transmit information by backscattering a signal. In some implementations, the BSTA may include ultra-low power devices or zero energy devices. In some implementations, a clear to send type a (CTSA) message may be used as a response from the receiver back to the initiator indicating successful receipt of the RTSB and acceptance of the request to initiate communication as indicated by the RTSB (ready/request to send signal). In some implementations, the CTSA defers transmission responsibility of the BSTA indefinitely. In some implementations, CTSA is addressed to a single initiator and the same message assigns a shortened identity to the initiator, which may be referred to as a mnemonic. In some implementations, if the BSTA does not receive the CTSA, the BSTA may be forced to not transmit RTSB later.

In some implementations, the request to send type B (RTSB) message is transmitted by the BSTA requesting a backscatter opportunity. In some implementations, the RTSB message includes a duration field or other indication specifying the requested backscatter duration, and/or a flag indicating that it can only backscatter, which may be referred to as a backscatter indicator flag. In some implementations, the receiver responds with a CTSA to the initiator of the message (i.e., the BSTA that transmitted the RTSB) that received the request.

In some implementations, a clear to send type B (CTSB) message may be transmitted as a response to the RTSB. In some implementations, the receiver responds with a CTSB message to force the initiation of all BSTA backoff request backscatter transmissions (i.e., to avoid transmitting/sending a transmission Request (RTSB) for a certain period of time). In some implementations, the CTSB message is sent to the broadcast address. In some implementations, CTSB may be part of a backoff mechanism based on an existing backoff mechanism (e.g., a backoff method already used in an 802.11 framework, e.g., in a Distributed Coordination Function (DCF)).

In some implementations, a back scatter indication message (BID) message is transmitted by the AP to one or more of the identified BSTAs. In some implementations, the BID is addressed to the BSTA based on its shortened identification (e.g., mnemonics). In some implementations, the BID message is sent to the BSTA that has previously sent RTSB to the AP and is deferred by the CTSA. In some implementations, the BID message is sent to the BSTA expected (e.g., a priori) to wake up during a certain time, e.g., due to TWT configuration. In some implementations, the BID message indicates a backscatter duration that may or may not be equal to the duration of the request in the RTSB.

In some implementations, the AP transmits a buffer status report request (BSR REQ) to the BSTA to direct it to send a BSR to the AP. In some implementations, a particular BSTA is addressed by a nominal 6 byte MAC address. In some implementations, the BSTA is not addressed directly; instead, the BSTA is addressed to the broadcast address. In some implementations (e.g., to limit the number of responses and control access to the media, or to determine (i.e., filter) the content of the buffer status report), the AP may also include a mask and/or a K-bit value (i.e., a value that may be used by the AP to indicate to the BSTA that only certain content is included in the buffer status report) by which the BSTA filters its response.

In some implementations, a buffer status report (BSR RPT) is transmitted by the BSTA in response to (e.g., as a response to a request) the BSR REQ. In some implementations, the BSR RPT is transmitted by the BSTA upon request (e.g., after receiving the BSR REQ), regardless of whether the data buffer of the BSTA has any content. In some implementations, if the buffer is non-zero, the BSTA indicates a quantization buffer status in the BSR RPT, e.g., certain bits (e.g., MSB N bits (e.g., 4 bits)) are held at 0. In some implementations, if the buffer is zero, the BSTA instead indicates a link quality metric in the BSR RPT, e.g., keeping certain bits (e.g., MSB N bits (e.g., 4 bits)) set to 1. In some implementations, the AP interprets the MSB N bits to detect whether the BSR is valid (i.e., includes a buffer status) or whether the BSR reflects the link quality of the BSTA.

In some implementations, a clear BID (CLR BID) message is transmitted by the AP to the BSTAs to clear mnemonics assigned to one or more of the BSTAs. In some implementations, the AP includes a list of one or more BSTAs that have been assigned mnemonics, and the BSTAs on the list clear their mnemonics. In some implementations, the AP does not specify a receiver mnemonic in the CLR BID message and all BSTAs that receive the CLR BID message clear their mnemonics.

In some implementations, a BID short ACK (BIDA) is a shortened block acknowledgement to one or more BSTAs that have been assigned a mnemonic. The short block acknowledgement is a hexadecimal representation, where each bit position represents an ACK or NACK of the corresponding mnemonic that matches its exact position in the header. In other words, short block ACK 0xFA refers to the ACK for all mnemonics except for the BSTA in indexes 8 and 6.

In some implementations, the interrogation signal (int_sig), also known as Carrier Wave (CW), is any electronic signal sent to the receiver to trigger a particular response. In a back-scattering context, in some implementations, the int_sig is a signal that the receiver can use to back-scatter information to some intended recipients. In some implementations, AP, nodeB, WTRU or other suitable device transmits the int_sig for back-scattering by another device, such as STA, UE, WTRU or other suitable device.

In some implementations, the BSTA can be back-scattered, e.g., on the UL, e.g., based on an ambient or dedicated signal (such as int_sig or CW).

In some implementations, an existing field (e.g., a duration field) in an existing frame (e.g., an 802.11MAC frame) may be overloaded, for example, using a spare field in the existing frame or by signaling a value in the existing field of the existing frame that is not specified in the standard. This may have the advantage of providing backward compatibility, for example, because the definition of the frame format does not change. In some implementations, older devices will see valid frames, but have values that cannot be decrypted, while newer devices will see valid frames and decryptable values.

In some implementations, the mnemonic is a temporary alternative identification for a more permanent identification. For example, in some implementations, the Transmitter Address (TA) mnemonic is a temporary replacement identity of the transmitter and the Receiver Address (RA) mnemonic is a temporary replacement identity of the receiver. In some implementations, the RA mnemonic and the TA mnemonic may be the same for the device. In some implementations, the mnemonics are shorter than the permanent identification. In some implementations, this has the advantage of lower signaling overhead. In some implementations, the mnemonic is unique during the validity period that the AP deems the mnemonic valid. In some implementations, the device that assigns the mnemonic (in this example, the AP) is responsible for ensuring that the mnemonic is non-conflicting (i.e., not used by more than one device served by the same AP). In some implementations, the assignee is responsible for resolving ambiguity as to which device is addressed by the mnemonic in the event that the mnemonic is conflicting (i.e., being used by more than one device served by the same AP).

In some implementations, the Organization Unique Identifier (OUI) is an identifier (e.g., the first 3 bytes of a MAC address) that uniquely identifies an organization, such as a manufacturer. For example, in some implementations, aruba ^TM The device sets the first 3 bytes of any MAC address of the device manufactured (e.g., original Design and Manufacture (ODM), original Equipment Manufacture (OEM), or self-manufacture) for Arruba as Arruba OUI. For example, arruba OUI is different from, for example, cisco ^TM Or MediaTek ^TM OUI。

In some implementations, an epoch refers to a term of limited, recurring duration, e.g., maintained by an infrastructure node. In some implementations, the infrastructure node may apply similar functions (or perform similar functions) during each epoch in a well-defined network (i.e., a centralized network with a central controller, such as an AP or infrastructure node). In some implementations, an epoch is a time frame that an infrastructure node can apply to performing a conventional function without having the function run to completion. In other words, in some implementations, an epoch allows infrastructure nodes to preempt and reacquire system resources even though some tasks cannot be completed within the epoch. In some implementations, in some cases, pending activity may wait for the next epoch to occur.

In some implementations, the instants are variable sub-units within the epoch. In some implementations, the epoch includes a plurality (e.g., T) of instants. In some implementations, an infrastructure node assigns an instant to one activity and another instant to another activity. For example, a single instant may be dedicated, optimized, or otherwise designated for energy harvesting for a BSTA served by an infrastructure node. In some implementations, the determination and assignment of each instant of activity that may be performed by the served STAs is implementation-specific. In some implementations, the determination and assignment of each instant of activity that can be performed by the served STA is done by the infrastructure node (i.e., the AP in this context).

Some implementations include backscatter in an 802.11ah framework. In some implementations, the backscatter devices (which may be referred to herein as backscatter STAs or BSTAs) utilize aspects of the 802.11 specification to perform uplink transmissions.

Fig. 2 is a graph illustrating exemplary backscatter in an 802.11ah framework. Fig. 2 shows messages in an exemplary network that includes an AP, a plurality of legacy STAs (i.e., STAs that are not configured to backscatter), and a plurality of backscatter STAs grouped into groups 1 and 2 (BSTA 1 and BSTA 2). In the figures, blocks above the line associated with an entity represent transmissions by the corresponding entity, and blocks below the line represent receptions by the corresponding entity.

Although not explicitly shown, the BSTAs 1 and 2 may or may not be configured with TWTs and may be grouped by the AP such that they have a set of restricted access slots (e.g., contiguous or non-contiguous) within the RAW window. In some implementations, the BSTA learns of the time slots and their corresponding RAW and/or period of RAW (if any) when creating the association. In some implementations, a BSTA with a TWT may be configured to sleep until a start time of the TWT. In some implementations, such a BSTA may skip reading some beacons (e.g., beacons outside of the TWT window and/or wake duration). Some BSTAs may not have a configured TWT, and such BSTAs may periodically receive beacons and may also be configured with RAW slots during the association time.

The AP maintains a wake schedule for all devices configured with and associated with the TWT. In this exemplary fig. 2, the AP gains access to the medium by performing the necessary contention resolution and transmitting CTS-to-self before the RAW window starts, indicating to the device that the medium is occupied for the duration as indicated in CTS-to-self. Fig. 2 illustrates an exemplary modification that may be made over an existing network (e.g., supporting IEEE 802.11 ah) to enable backscatter communications.

In fig. 2, the AP senses the medium during a backoff period following a DCF inter-frame space (DIFS) and then transmits a CTS-to-Self message. In some implementations, legacy STAs also sense media and backoff during the DCF inter-Frame Space (DCFs).

After the AP transmits CTS-to-Self, legacy STAs set their NAV vectors based on receiving CTS-to-Self from the AP, which indicates a period of time that the medium will be busy. The BSTA seeks back-scattering opportunities that may exist in the NAV of legacy STAs.

In this example, the BSTA with the configured TWT may wake up within a time frame labeled RAW in FIG. 1. Other BSTAs without configured TWTs may seek to read the beacon and find a receiver opportunity for themselves or other BSTAs/STAs nearby.

In either case, to facilitate the BSTAs, the AP transmits a BID message indicating the identity and associated duration of one or more BSTAs. In some implementations, the AP may trade off between the amount of contention that will exist when it sends the BID. Thus, in some implementations, the AP may limit BID messages and signal only as many BSTA identifications as will achieve the desired amount of contention and/or only as long a duration as will achieve the desired amount of contention. For example, in some implementations, if only a few BSTAs can be indicated in the BID message (e.g., due to BID message size limitations), the AP will keep the backscatter opportunities to a small duration so that the AP can provide opportunities to the orthogonal set of BSTAs the next time it transmits a BID message.

In some implementations, more frequent BID messages transmitted by an AP may result in more channel overhead, but may effectively reduce contention rate, for example, because the AP is targeting a narrower set of BSTAs.

In fig. 2, the AP is effectively shown as operating in-band full duplex because it transmits and receives a backscatter signal from the BSTA as an int_sig for BSTA backscatter. It should be noted that in some implementations, this type of operation is not necessary, for example, where the AP uses another transmit-receive point (TRP), antenna, or other entity or ambient RF signal to provide the int_sig for use by the BSTA and the AP may receive a corresponding backscatter signal.

In some implementations, if the AP has configured TWTs on at least some of the BSTAs, e.g., anticipates the possibility of some BSTAs transmitting within the RAW, the AP gains access to the channel and transmits the int_sig. In some implementations, the backscatter STAs (BSTA 1, BSTA 2) use the interrogation signal to transmit uplink data to the AP. It should be noted that in some implementations, those BSTAs configured with TWTs may also contend for resources, e.g., only within their designated RAW slots.

In some implementations, a BSTA that does not configure a TWT will perform DCF, however, since the channel is already protected earlier by the AP (e.g., by CTS-to-self), the BSTA may treat the channel as busy for the duration set by the NAV vector. However, in some implementations, if the AP transmits a CTS-to-self, the BSTA may ignore the CTS duration and may seek a backscatter opportunity. To facilitate backscatter, in some implementations, the AP may alternately transmit a Backscatter Indication (BID) message and an int_sig. This is reflected in fig. 2, for example, where the carriers alternate with the BID. In some cases (e.g., as shown), after the AP receives one or more backscatter transmissions, the AP may send a BID instead of a BID message to acknowledge the one or more backscatter transmissions. The BIDA message may be followed by a short interframe space (SIFS) duration, and a guard interval may be introduced between consecutive RAWs. Each time a BID is transmitted, the identity of one or more backscatter STAs may be indicated in the BID message. In some implementations, if no identity is indicated in the BID message, the AP allows any BSTA to transmit with the opportunity. In some implementations, the AP may do so if the probability of the AP deciding on contention is zero or low (e.g., if contention is below a threshold contention). In some implementations, the BSTA is identified in the BID message indication by a shortened mnemonic (e.g., as described above) rather than a full 6-byte media addressing scheme.

FIG. 3 is a table describing an exemplary format of a BID message; in some implementations, the BID message is modeled after the 802.11 management message. For example, an 802.11MAC message has a 2-bit type and a 4-bit control subtype field. Thus, in this example, there are 16 possible control subtypes. The 16 subtypes have been maximally utilized in the 802.11 specification, and it is impossible to add a new subtype. However, in some implementations, it is possible to overload a particular subtype by interpreting other fields in the 802.11MAC header.

The table of fig. 3 reflects a portion 8.2.4.2 of the 802.11 standard that describes a duration/ID field that may be used as a format for BID messages in some implementations. In some implementations, the duration/ID field in the 802.11 management frame is replaced with the fields shown in fig. 3. According to the 802.11 standard, the duration field is 16 bits and 2 bits are reserved. Furthermore, 14 bits that can be used are not all defined. Any value that is not present in the STA may be ignored in the 802.11 specification, or the NAV vector of maximum duration will be set upon receipt of a MAC payload having an unexplained duration (e.g., a value not included in the table). Thus, in some implementations, new entries may be specified and/or added to this table such that an updating device conforming to the updated version of the standard will correctly interpret the new entries, while an older device not upgraded to the latest version of the standard will ignore the MAC frame (or due to the unexplained duration field).

Some implementations use MAC frames in 802.11 to implement backscatter. The exemplary duration field shown in fig. 3 is exemplary and does not exclude other fields. For example, alternative and/or unused fields may be overloaded or used to achieve the same or similar objectives.

Fig. 4 identifies several exemplary messages that may be used by a STA in some implementations (e.g., as described herein) that is capable of applying backscatter principles within an 802.11 framework. Each exemplary message includes an exemplary field and an indication (indicated in brackets) of an exemplary length of each field in bytes. In some implementations, such devices may implement the latest version of the 802.11 specification. If implemented 802.11 versions incorporate a backscatter technique, for example, as described below, in some implementations, a backscatter STA may interpret the message correctly (e.g., by interpreting the duration field) and may share media with legacy STAs that ignore or interpret the message in an indecipherable or undefined default manner (e.g., by setting a NAV of maximum duration as discussed herein).

The exemplary values in the exemplary duration field of the exemplary BID shown in fig. 4 include a value (0 x3E87 in this example) that is "new" specified (i.e., undefined in an earlier version of the 802.11 standard), so legacy devices will ignore this MAC message, or interpret the MAC message in a default manner, such as setting a maximum length NAV. In some implementations, if the AP determines that other STAs need UL transmission resources, or if the AP determines to transmit an int_sig to facilitate backscatter of the BSTA, the AP may transmit a BID message including an actual (i.e., defined in an earlier version of the 802.11 standard) 802.11 duration value (e.g., field number 3 "duration 802.11 data" after the new interpretable duration field).

In some implementations, when a STA is associated with an AP, if the STA indicates backscatter capability, the AP assigns a shortened address (e.g., 1 byte) to the device (e.g., during association or at association). The shortened address may be referred to as a TA mnemonic. In some implementations, the BID message includes one or more transmitter address mnemonics (e.g., TA mnemonic 1 (1) … TA mnemonics (1) in fig. 4), which may include a hash value or shortened value of a 6-byte TA MAC address.

In some implementations, the TA mnemonic is 1 byte, but not all bits are in use. In other words, in some implementations, the length of the "actual TA mnemonic" or the identification portion of the TA mnemonic may be less than one byte. For example, in some implementations, the AP may reserve some TA mnemonic bits (e.g., non-identification bits) for future use. In some implementations, the TA mnemonic is a temporary identification of the BSTA that can be uniquely identified while in the session. The term "session" refers herein to a particular duration of time for which a device is engaged in data communications. In some implementations, the AP coordinates the assignment of TA mnemonics so that the AP knows the identity of the BSTA that is being addressed or in communication with (e.g., in TX and/or RX).

For example, in some implementations, a complete set of N BSTAs in a system may be grouped into M smaller groups, each group having (k=n/M) BSTAs. K BSTAs may be assigned one or more slots within a RAW window, with an instance size of K < = 256. In this example, the AP may assign a TA mnemonic to each BSTA in the group and make that TA mnemonic unique within the group, but the same TA mnemonic may be reused in other smaller groups because, for example, the BSTA does not wake up outside its TWT. In some implementations, the size of the TA mnemonics is such that the MAC frame size is not too large for the device to decode (or, for example, conveniently decode, or decode within a threshold time, or decode using less than a threshold amount of resources) MAC frames with several mnemonics (e.g., threshold-sized MAC frames). In some implementations, several TA mnemonics may be signaled in cascade in the same MAC PDU, and the BID message will be interpreted by each receiving TA mnemonic. In some implementations, a BSTA that is not configured with a TWT may compete for and access media at any time. Therefore, they are not limited by TWT. For such BSTAs, the AP may reserve a subset of K mnemonics, or the AP may address the mnemonics using a long format.

In some implementations, for example, as shown in fig. 2, 802.11ah compliant devices participate in and obtain service from the AP. In some implementations, the AP and the BSTA device may interpret the newly specified value in the duration field and interpret the message from the non-BSTA device differently. In some implementations, DL and UL transmissions with the BSTA occur within the framework of an 802.11ah network.

Fig. 4 is a block diagram illustrating an exemplary message and associated formats in accordance with some implementations. In some implementations, these messages are control subtype messages. Since the subtype is 4 bits, in some implementations it is not possible to define a new control subtype message in 802.11. Thus, in some implementations, the duration field (16-bit value) is modified to specify how the message payload is to be interpreted. For example, in some implementations, if the subtype is control and the duration field is set to hexadecimal 0x1F63, the message is interpreted as a CTSA having the format as shown in fig. 4. The messages shown in fig. 4 are discussed above and also at appropriate locations throughout this document.

Fig. 4 shows an exemplary CTSA frame, CTSB frame, RTSB frame, BID frame, BSR RPT frame, BSR REQ frame, two exemplary CLRBID frames, and BIDA frame.

An exemplary CTSA frame includes a frame control field, a duration field, an RA mnemonic field, and an FCS field. The frame control field is used to identify IEEE802.11 frame types and subtypes, the duration field is used to define a backscatter specific frame format, the RA field indicates the receiving STA address, and the RA mnemonic field is a short length address assigned for the receiving STA with address RA. FCS (frame check sequence) is used for error detection. As shown, these fields are located in first, second, third, fourth, and fifth locations within the frame, respectively. These exemplary fields are 2 bytes, 6 bytes, 4 bytes, and 4 bytes long, respectively. It should be noted that in some implementations, the CTSA frame includes other fields, a subset of these fields, fields of different sizes, and/or the fields are ordered differently. In some implementations, the frames serving the function of CTSA frames are referred to by any other suitable name. In this example, the CTSA frame is identified by a duration field having a value of 0x1F63 as shown.

An exemplary CTSB frame includes a frame control field, a duration field, an RA field, and an FCS field. As shown, these fields are located at first, second, third and fourth positions within the frame, respectively. These exemplary fields are 2 bytes, 6 bytes, 4 bytes long, respectively. It should be noted that in some implementations, CTSB frames include other fields, subsets of these fields, fields of different sizes, and/or ordering these fields differently. In some implementations, the frames that serve the function of CTSB frames are referred to by any other suitable names. In this example, the CTSB frame is identified by a duration field having a value of 0x1F63 as shown, and RA is shown to have a value of ff: ff: ff: ff. In this example, the RA value ff: ff: ff: ff (i.e., all binary values) indicates a broadcast (i.e., all receivers are addressed). In other implementations, the individual receivers are addressable by this field.

An exemplary RTSB frame includes a frame control field, two duration fields, an RA field, a TA field, a binding field, and an FCS field. Here, the second duration field indicates the time required for a frame after transmission. The RA field and the TA field indicate the receiving and transmitting STA addresses, respectively. The binding field is a flag indicating whether the BSTA requires an int_sig. As shown, these fields are located in first, second, third, fourth, fifth, sixth and seventh positions within the frame, respectively. These exemplary fields are 2 bytes, 6 bytes, 1 bit, and 4 bytes long, respectively. It should be noted that in some implementations, the RTSB frame includes other fields, a subset of these fields, fields of different sizes, and/or the fields are ordered differently. In some implementations, the frames serving the function of RTSB frames are referred to by any other suitable name. In this example, the RTSB frame is identified by a duration field having a value of 0x3E83 as shown.

An exemplary BID frame includes a frame control field, a duration 802.11 data field, TA mnemonics fields 1-n, and an FCS field. Here, the duration 802.11 data field indicates the backscattering opportunity duration for each addressed BSTA identified by the TA mnemonic field 1-n. The TA mnemonic field 1-n indicates the assigned short length address for the transmitting (i.e., back-scattering) STA. As shown, these fields are located in first, second, third, fourth through sixth and seventh positions within the frame, respectively. These exemplary fields are 2 bytes, each 1 byte, and 4 bytes long, respectively. It should be noted that in some implementations, the BID frame includes other fields, a subset of these fields, fields of different sizes, and/or ordering these fields differently. In some implementations, the frames that serve the function of the BID frame are referred to by any other suitable name. In this example, the BID frame is identified by a duration field having a value of 0x3E87 as shown.

An exemplary BSR RPT frame includes a frame control field, a duration BS data field, a TA field, and an FCS field. Here, the duration BS data field indicates information about a buffer status or link quality. As shown, these fields are located in first, second, third, fourth, and fifth locations within the frame, respectively. These exemplary fields are 2 bytes, 6 bytes, and 4 bytes long, respectively. It should be noted that in some implementations, the BSR RPT frame includes other fields, subsets of these fields, fields of different sizes, and/or ordering these fields differently. In some implementations, the frames serving the function of the BSR RPT frames are referred to by any other suitable name. In this example, the BSR RPT frame is identified by a duration field having a value of 0x3E8B as shown.

The first listed exemplary BSR REQ frame includes a frame control field, a duration field, an RA field, a TA field, and an FCS field. As shown, these fields are located in first, second, third, fourth, and fifth locations within the frame, respectively. These exemplary fields are 2 bytes, 6 bytes, and 4 bytes long, respectively. It should be noted that in some implementations, the BSR REQ frame includes other fields, subsets of these fields, fields of different sizes, and/or ordering these fields differently. In some implementations, the frame serving the function of the BSR REQ frame is referred to by any other suitable name. In this example, the BSR REQ frame is identified by a duration field having a value of 0x3E8F as shown.

The second listed exemplary BSR REQ frame includes a frame control field, a duration field, an RA field, a mask field, and an FCS field. Here, the mask field indicates a specific type of BSR report (e.g., filtered report). As shown, these fields are located in first, second, third, fourth, and fifth locations within the frame, respectively. These exemplary fields are 2 bytes, 6 bytes, and 4 bytes long, respectively. It should be noted that in some implementations, the BSR REQ frame includes other fields, subsets of these fields, fields of different sizes, and/or ordering these fields differently. In some implementations, the frame serving the function of the BSR REQ frame is referred to by any other suitable name. In this example, the BSR REQ frame is identified by a duration field having a value of 0x3E8F as shown, and RA is shown to have a value of ff: ff: ff: ff. In this example, the RA value ff: ff: ff: ff (i.e., all binary values) indicates a broadcast (i.e., all receivers are addressed). In other implementations, the individual receivers are addressable by this field.

The first listed exemplary CLRBID frame includes a frame control field, a duration field, TA mnemonic fields 1-m, and an FCS field. Here, the TA mnemonic field is used to identify the addressed BSTA using its shortened temporary ID. As shown, these fields are in the first, second, third through fifth and sixth locations within the frame, respectively. These exemplary fields are 2 bytes, each 1 byte, and 4 bytes long, respectively. It should be noted that in some implementations, the CLRBID frame includes other fields, a subset of these fields, fields of different sizes, and/or the fields are ordered differently. In some implementations, the frames that serve the function of CLRBID frames are referred to by any other suitable name. In this example, the CLRBID frame is identified by a duration field having a value of 0x3EE3 as shown.

The second listed exemplary CLRBID frame includes a frame control field, a duration field, and an FCS field. As shown, these fields are located in first, second and third locations within the frame, respectively. These exemplary fields are 2 bytes, and 4 bytes long, respectively. It should be noted that in some implementations, the CLRBID frame includes other fields, a subset of these fields, fields of different sizes, and/or the fields are ordered differently. In some implementations, the frames that serve the function of CLRBID frames are referred to by any other suitable name. In this example, the CLRBID frame is identified by a duration field having a value of 0x3EE7 as shown.

An exemplary BIDA frame includes a frame control field, a duration 802.11 data field, TA mnemonics fields 1-n, a short block acknowledgment field, and an FCS field. Here, the short block acknowledgement field indicates an acknowledgement of one or more recently received backscatter transmissions from one or more backscatter bodies. As shown, these fields are in the first, second, third, fourth through sixth, seventh and eighth locations within the frame, respectively. These exemplary fields are 2 bytes, 1 byte each,? Bytes and 4 bytes long. Here, (. For example, in some implementations, the short block acknowledgement field is 1 byte long. It should be noted that in some implementations, the CLRBID frame includes other fields, a subset of these fields, fields of different sizes, and/or the fields are ordered differently. In some implementations, the frames that serve the function of CLRBID frames are referred to by any other suitable name. In this example, the CLRBID frame is identified by a duration field having a value of 0x3EE3 as shown.

In some implementations, the BSTA receiving the BID message scans for the presence of transmit address mnemonics (TA mnemonics) in the BID message to determine if they can access the media immediately after SIFS. In some implementations, the TA mnemonic is a 1 byte short address instead of a 6 byte TA MAC address. In some implementations, the TA mnemonics are assigned to the BSTA by the AP in a CTSA message. In some implementations, the BID message indicates to the receiving BSTA the duration available for back scattering, for example in a "duration 802.11 data" field. In some implementations, the number of TA mnemonics included in the BID message is between 1 and n. In some implementations, the number of TA mnemonics included in the BID message may be controlled by the AP, e.g., depending on how little contention it allows in the network. In some implementations, in a fully scheduled network or in a congested network, the AP may limit the number of TA mnemonics to, for example, only 1 in the BID message. In some implementations, the BID message is a delay identification of one of the plurality of BSTAs transmitted by the AP to an earlier request transmission, but earlier delayed by the CTSA. In some implementations, the AP is implemented with in-band full duplex capability and may receive backscatter communications. In some implementations, if the reception of the backscatter transmission is successful, the AP transmits an acknowledgement with a BID message in a BID acknowledgement (BID) message. An exemplary format of the BIDA message is shown in FIG. 4. In some implementations, the BIDA is similar to the BID message except that it also includes an ACK (e.g., a block ACK) for a previously received transmission.

Note that in a typical 802.11 system, CTS and RTS are used to solve the hidden node problem. The hidden node problem occurs where a receiving STA (e.g., a STA transmitting CTS in this example) is experiencing interference from a nearby STA that is not detected by a transmitting STA (e.g., a STA transmitting RTS in this example). On a global level, CTS and RTS may be envisaged as mechanisms to poll and reserve media, not necessarily mechanisms to avoid interference. As discussed herein, CTS and RTS may be conceptualized as polling and reservation mechanisms, thereby acknowledging a device for a corresponding request. It should be noted, however, that CTS and RTS are existing control messages that are not modifiable in the context of existing 802.11 systems. Thus, in some implementations, new CTS and RSTS (e.g., CTS type a (CTSA) and RTS type B (RTSB)) are introduced as overload messages on the control format. In some implementations, the RTSB includes a BID flag to indicate to the receiver that assistance in the form of an interrogation signal (i.e., int_sig or carrier) for backscatter is required for transmission. In some implementations, CTSBs are addressed to broadcast addresses rather than unicast addresses.

In current 802.11 networks, the transmitter and receiver addresses (TA and RA) are 6 bytes long. In the current example of CTS and RTS, TA and RA are singular (i.e., CTS and RTS are addressed to only a single TA and RA). In some implementations, CTS and RTS creation may be unnecessary overhead in some deployments. Thus, in some implementations, the BID message may be addressed to several TA addresses simultaneously. In some implementations, the BIDA is an accompanying acknowledgement message with a similar format at the top of the BID message. In some implementations, legacy addressing in 802.11 networks is via a 6 byte MAC address. In some implementations, the first three bytes are the OUI and the remaining 3 bytes are the unique addressing under the OUI. In some implementations, the mnemonic is a temporary identification provided by the AP to any STA or BSTA.

In some implementations, the mnemonic is a 1-byte value assigned to the STA for short-term (e.g., below a threshold time or below a threshold number of messages) transactions. In some implementations, the identification is unique within the service area of the AP for the duration of the transaction. In 802.11 systems prior to 802.11ah (i.e., not conforming to 802.11 ah), access to the medium is, in some cases, via DCF, enhanced Distributed Channel Access (EDCA), or Point Coordination Function (PCF). In some such systems, legacy devices transmit and receive by performing clear channel assessment and following prescribed methods. In some implementations, such legacy devices are not affected by the various changes set forth herein, and are served seamlessly by the AP (e.g., are not negatively affected by the changes set forth herein).

Fig. 5 is a diagram illustrating exemplary backscatter in an 802.11 system. Fig. 5 shows messages in an exemplary network including an AP, legacy STAs (i.e., STAs that are not configured to backscatter or do not support backscatter communications/transmissions), and a backscatter STA. In the figures, blocks above the line associated with an entity represent transmissions by the corresponding entity, and blocks below the line represent receptions by the corresponding entity.

In the example of fig. 5, the AP enables backscatter for the backscatter STAs by placing dedicated carriers. After gaining access to the medium, for example, by transmitting the CTS-to-self message shown, the AP indicates to all legacy STAs that the channel is to be occupied for the duration indicated in the duration field. In this example, the CTS-to-self message is addressed to 0xff:0xff (i.e., broadcast to all STAs). The CTS-To-Self transmission forces a legacy device (e.g., a legacy STA shown) To set a NAV vector for the duration indicated in the duration field of the CTS-To-Self. In some implementations, this address (i.e., broadcast address 0xFF:0 xFF) also indicates to the BSTA (e.g., the illustrated backscatter STA) that a backscatter opportunity is monitored (i.e., that a backscatter opportunity will occur in the near future during the identified duration). In some implementations, the BSTA monitors the backscatter opportunities by monitoring BID, e.g., after SIFS.

In some implementations, the BSTA searches for the BID message at an appropriate time slot after the CTSB. In some implementations, the request for transmission is via RTSB and CTSA, even though not explicitly highlighted in the figure (e.g., the transmission of RTSB and CTSA/B may precede that shown in the figure). In some implementations, the CTSA/B is followed by a BID message, which is monitored by the BSTA transmitting the RTSB.

In the example of fig. 5, the backscatter STAs detect CTS-to-self messages transmitted by the serving AP indicating the availability of dedicated backscatter opportunities, monitor the channel carrying the BID message of the backscatter opportunity configuration. In this example, the backscatter STAs detect their identity via a mnemonic in the BID and receive the associated duration of the backscatter window in the BID. The backscatter STAs contend for the backscatter channel within the identified window; and receives an acknowledgement from the serving AP. In some implementations, the example BTSA includes circuitry configured and/or programmed to perform these actions. In the example of fig. 5, the backscatter STAs obtain the backscatter channel for the duration of the backscatter window and backscatter data to the AP on the carrier transmitted by the AP for this purpose during the backscatter window. In this example, the SIFS after the end of the backscatter window acknowledges receipt of the backscatter data by the AP.

In some implementations, knowing the identity of the device that has transmitted the RTSB and those devices to which the CTSA has been issued, the AP transmits a BID message that is read by the BSTA, and the identified BSTA is back-scattered to the AP using the int_sig (carrier). In some implementations, the BID message includes an indication of the duration of the backscatter opportunities.

Some implementations include both energy harvesting and backscatter in 802.11 systems. For example, fig. 6A and 6B illustrate exemplary energy harvesting and backscatter. Fig. 6B is a diagram in fig. 6A. In particular, fig. 6A and 6B illustrate exemplary modes that an AP may apply to enable a power optimized device to collect energy from an incident signal and use an interrogation signal to backscatter data.

Fig. 6A and 6B illustrate messages in an exemplary network including an AP, a legacy STA, and three backscatter STAs; backscatter STA1, backscatter STA2, and backscatter STA3. In the figures, blocks above the line associated with an entity represent transmissions by the corresponding entity, and blocks below the line represent receptions by the corresponding entity. It should be noted that the messaging in the different instants of fig. 6A and 6B is merely illustrative and is not necessarily meant to be interpreted as a time series of events. In other words, fig. 6A and 6B are not meant to be interpreted as a cascading sequence of events moving from one instant to another.

In the example of fig. 6A and 6B, the AP operates in a round-robin fashion defined by one epoch. Each epoch is divided into k time instants. Each time instant t (1.ltoreq.t.ltoreq.k) may be selected by the AP for a particular purpose. Each of the 4 exemplary instants of fig. 6A and 6B is discussed below.

In some implementations, the network is deployed to support legacy STAs that also employ various 802.11 protocols, and APs and BSTAs coexist with these legacy STAs.

Fig. 6A and 6B illustrate an exemplary epoch n, wherein the AP has first performed DCF and obtained media. For example, in time instant 1, suppose that the AP first gains access to the medium by listening to the channel for a DCF inter-frame space (DIFS) interval and backoff appropriately.

Epoch n includes four exemplary time instants, time instant 1, time instant 2, time instant k-1, and time instant k. It should be noted that the epoch may include any suitable number of instants. In this example, time instant 1 may be used to schedule transmission of the BSTA, e.g., when the legacy STA is blocked by its NAV, and time instant 2 may be used to transmit uplink data from the legacy STA, e.g., when the BSTA collects energy. The time instant k-1 may be used, for example, for the BSTA to transmit the data scheduled in time instant 1 (or to collect energy if they have no information to transmit) to the AP when the legacy STA is blocked by its NAV. The time instant k may be used to transmit downlink data to legacy STAs while the BSTA collects energy.

In this example, time instant 1 is used to schedule transmission of the BSTA. After the AP gains access to the medium, the AP transmits a CTS-to-self forcing legacy devices to set their NAV vectors. Thus, the legacy STA receives the CTS-to-self message and sets its NAV based on the CTS-to-self message. In this case, the NAV indicates to legacy STAs that the medium is busy for the duration of time instant 1. In time instant 1 in the figure, the NAV indicates that the legacy STA sees the medium as busy for the whole time instant 1, so it does not transmit or receive during this period. The AP then sends a BSR REQ message at the appropriate TWT of the BSTA. In this example, the AP transmits a single BSR REQ, as shown. Those BSTAs with BSR transmit BSR RPT to the AP. In this example, the BSR RPT is not shown, indicating that the BSTA does not have a BSR to be transmitted or does not have a TWT. In this example, the BSTA does not have a configured TWT, and therefore contends for the channel to transmit the RTSB. In this example, each BSTA performs DCF by appropriately waiting for DIFS and backoff (shown by dashed lines) before transmitting the RTSB message.

In some implementations, the BSTA is a low power device and transmits these RTSB messages to the AP via back-scatter. In some implementations, the RTSB message is transmitted using the primary transmitter, and subsequent and/or later uplink transmissions (e.g., primary payloads) are back-scattered to the AP. In some implementations, such a hybrid approach may have the advantage of significantly reducing the overall power consumption of the device. In some implementations, an advantage of such a hybrid approach may be to increase the resilience of RTSB transmissions by requesting the AP to provide reliable access permission to the channel without back scattering, while the primary transmission of the payload is transmitted by back scattering. In such implementations, similar approaches may be applied to avoid or minimize interference from nearby STAs.

In some implementations, if there is a usable (e.g., consistent) ambient signal, the BSTA back-scatters its RTSB. In some implementations, the BTSA does not transmit its RTSB in the absence of a consistent ambient signal. In this example, the BSTA has pending data in its buffer and is able to transmit RTSB without int_sig (e.g., based on an available environment signal) to indicate the required duration and whether backscatter needs to be enabled for further transmission. The RTSB message may also include a binding flag indicating to the AP that the BSTA requires the int_sig to transmit on the UL.

In some implementations, the APs respond to the BSTA with a CTSA (e.g., such as FSIS after an appropriate delay), e.g., indicating their RA and RA mnemonics to be used for signaling and/or addressing for a temporary duration. In some implementations, the CTSA message defines an RA-to-RA mnemonic mapping. In some implementations, the AP assigns a temporary unique RA mnemonic and indicates the temporary unique RA mnemonic to the receiving BSTA, e.g., in a CTSA message. In some implementations, the BSTA is addressed by the RA mnemonic, rather than by its full RA. In some implementations, the mnemonics are used by the receiving entity for both transmit and receive functions. In some implementations, the mnemonic identifies the BSTA as either a transmitter (TA mnemonic) or a receiver (RA mnemonic). In some implementations, the CTSA message indicates to the device addressed by the RA (and RA mnemonics) that its request has been received and queued. In some implementations, the CTSA message does not indicate to the BSTA that it is cleared to immediately send its payload and/or traffic. In some implementations, the AP sends CTSB messages instead of CTSA messages. In some implementations, if a CTSB message (i.e., broadcast) with 0xff:0xff set to the RA address is received by the receiving BSTAs, all BSTAs backoff from transmission (e.g., within a specified period of time, or until they detect a BID message).

In some implementations, if the CTSB message is transmitted by an AP, the BSTA attempts to detect BID messages indicating their opportunity to transmit on the UL. If a BID message is received, the BSTA attempts to detect their RA mnemonics and backscatter using the INT_SIG transmitted by the AP. INT_SIG is shown in the figures as carrier CW and is shown in instant k-1 of FIGS. 6A and 6B.

In some implementations, the BSTA identifies a high contention environment or a hidden node-prone environment (e.g., based on a detected CTS-to-self message and/or failure to receive CTSA/CTSB in consecutive number of attempts and/or opportunities); transmitting an RTSB message using EDCA and a master transceiver; receiving CTSA/CTSB; determining an RA mnemonic corresponding to its RA; monitoring and detecting a BID that includes an indication of its assigned TA mnemonics and backscattering opportunity duration (e.g., indicated by a duration field in the BID); and back-scatter its data at the assigned back-scatter window using the dedicated carrier. In some implementations, the example BTSA includes circuitry configured and/or programmed to perform these actions. In some implementations, the backscatter opportunity duration begins when the BID is received and lasts for the time indicated by the duration field. In some implementations, this duration takes into account overhead (e.g., handoff, search, etc., e.g., in terms of inter-frame space).

Time instant 2 is used to schedule and transmit uplink data from legacy STAs while the BSTA collects energy. After expiration of the NAV set in the instant 1, the legacy STA performs DIFS and backoff to obtain media and then transmits uplink data to the AP, which transmits ACK to acknowledge the uplink data. This is repeated in this example. During scheduling and transmitting uplink data from legacy STAs, energy in the RF waves present on the channel is timely collected by the BSTA. In some implementations, CTSA/B in instant 1 may indicate to the BSTA that they should backoff from transmission for a certain period of time or until they detect BID, so the BSTA will resort to energy harvesting.

Time instant k-1 is used by the BSTA to transmit the information scheduled in time instant 1 (or acquisition energy if they have no information to transmit) to the AP when the legacy STA is blocked by its NAV. In this example, the AP transmits a BID that schedules transmissions from the BSTA and sets the NAV of legacy STAs. The backscatter STA 1 and the backscatter STA 3 backscatter data to the AP according to the schedule received in the BID based on a dedicated int_sig (referred to as CW in the figure) provided by the AP. The backscatter STAs 2 that have no data to send or are not scheduled to transmit data timely collect the energy present in the RF wave on the channel.

The time instant K includes transmitting downlink data to legacy STAs when the BSTA collects energy. In this example, the AP transmits a BID indicating that downlink transmissions are to be transmitted to legacy STAs and indicating to the BSTA that they should timely collect energy. After DIFS and backoff, the AP transmits downlink data to legacy STAs. The legacy STA transmits an ACK to acknowledge receipt of the downlink data. This is repeated in this example. During downlink transmission to legacy STAs, energy in the RF waves present on the channel is timely collected by the BSTA.

In some implementations, the AP selects a particular instant for scheduling downlink messages to legacy STAs. For example, in some implementations, certain instants are deterministically better for the BSTA to collect energy, which may be indicated in the BID message. In some implementations, the absence of a BID message at the beginning or "top" of the instant indicates to the BSTA that there may be an opportunity interval for energy harvesting at that instant in time. In some implementations, this is true whether the energy is from a DL transmission from the AP to the STA or from a UL transmission from the STA to the AP. This occurs, for example, in instants 2 and k. As previously described, the AP assigns a mnemonic to address the BSTA to keep the overhead low.

In some implementations, the buffer status of the BSTA is reported using a BSRRPT message. In some implementations, the BSR RPT is 2 bytes, but the MSB 4 bit is always set to 0. In some implementations, the BSR is quantized representation and is represented by 12 bits. For example, the value signaled in the BSR RPT may be a truncated value expressed mathematically as FLOOR (actual value in bytes/bsc_scale), where the FLOOR () function returns a rounded integer value. In some implementations, bsr_scan is signaled by the AP during association. In some implementations, if the BSTA has no buffered data to transmit, it will need to transmit a 0-valued BSR. But instead of transmitting a BSR of value 0, the BSR RPT contains a quality measurement. In some implementations, the BSTA transmits a quality report after prefixing BSR data with 0xF in MSB 4 bits, such that the AP understands that the data is not a 0 value. In some implementations, the last 12 bits include measurements such as SINR or RSSI. As previously described, the mnemonics are temporary and unique within the subgroup until cleared. In some implementations, the AP sends a message (e.g., a clear message) to all BSTAs in the subgroup to indicate that the mnemonics previously assigned via the CTSA are cleared and addressable. In some implementations, the AP may then assign those mnemonics to other BSTAs in, for example, time epoch n+1.

Some implementations include one or more of the following. Some implementations include a device that interprets existing fields of a media header to determine a backscatter control message subtype. Some implementations include addressing a device by a semi-permanent but locally unique mnemonic (identity) rather than a permanent identity (e.g., a MAC address), where the mnemonic is a shortened identity. Some implementations include a device receiving a signal from an infrastructure node, a mnemonic for the signal indicating that there is an opportunity for backscatter for a specified duration. Some implementations include a device receiving a measurement mask and the device applying the measurement mask to its mnemonics to determine whether a report must be sent to the base node, and the device determining whether it should instead send a quality measurement, e.g., based on a buffer pending status. Some implementations include a device receiving a signal to defer UL transmissions for a specific or indeterminate duration. Some implementations include a device receiving a temporal envelope and an indication of allowed and/or disallowed access subtypes within the envelope, and the envelope maintaining a particular periodicity. Some implementations include the device receiving a backscatter opportunity and a duration limit, along with indicating the presence of an ambient signal source or a dedicated interrogation signal. Some implementations include an AP determining that a non-message carrying carrier needs to be transmitted during a particular time or period to facilitate backscatter. Some implementations include an AP determining that an energy-bearing carrier needs to be transmitted for a particular duration to facilitate energy harvesting.

Fig. 7 is a diagram illustrating exemplary multi-user backscatter in an 802.11OFDMA architecture. For example, fig. 7 illustrates exemplary communications implementing backscatter communications, such as for an 802.11ax system. Fig. 7 shows messages in an exemplary network including an AP, a backscatter STA, and a legacy STA.

In fig. 7, during a first period 700, the AP first performs DIFS and backoff, then transmits MU RTSB and receives MUCTSB. Scheduling information for legacy STAs is not provided in this frame, but this frame may be used to indicate EH opportunities to the BSTA, as previously discussed. After SIFS, the AP transmits a preamble and an HE field (described later) and transmits downlink transmission to legacy STAs STA1, STA2, STA3, STA4, STA5, STA 6, STA7, STA8, STA9, and STA11 on downlink resources as scheduled. Legacy STAs receive these signals and transmit multi-user block acknowledgements (MU-BAs) to the AP. During downlink transmission to legacy STAs, the backscatter STAs BSTA1, BSTA2, BSTA3, and BSTA4 timely collect energy from RF waves on the channel. After receiving the MU-BA, during the second period 702, the AP transmits a trigger frame and, after SIFS, receives uplink transmissions from legacy STA1 and STA 3. STA1 fills its transmissions to fill the allocated time resources. During these transmissions, the BSTA2 timely collects energy. The AP transmits the MU-BA to acknowledge the uplink transmission. After transmitting the MU-BA, during a third period 704, the AP performs DCIF and backoff, then transmits MU RTSB and receives MUCTSB. After SIFS, the AP transmits a preamble and an HE field (described later) and transmits downlink transmissions to legacy STAs STA1, STA4, STA5, STA7, STA8, and STA9 on downlink resources as scheduled. The AP also transmits a dedicated int_sig (CW in the figure) and a power optimized waveform (dedicated POW in the figure). Legacy STAs receive these signals and transmit multi-user block acknowledgements (MU-BAs) to the AP. During downlink transmission from the AP, the back-scattering STAs BSTA1, BSTA2 and BSTA3 back scatter on the CW signal and BSTA5 collects energy from the RF wave of the power optimized signal (dedicated POW). A more detailed description of the various techniques involved in fig. 7 follows.

In some deployments (e.g., deployments implementing 802.11 ax), DL and UL transmissions are typically centrally controlled and scheduled by the AP. In earlier versions of 802.11 networks, STAs may access the media by performing contention resolution at any time slot or within a Restricted Access Window (RAW). In such networks, the AP may preempt the medium and preemptively send CTS to the selected STA, obviating the need for the STA to perform DCF. In 802.11ax, the AP has greater control over the medium and can achieve multi-user transmission on DL and UL.

Fig. 7 illustrates an exemplary implementation in which an AP controls DL and UL transmissions while also enabling backscatter communications. It should be noted that in the example of fig. 7, the AP still performs DCF to access the channel, and legacy devices may similarly perform the same tasks and declare media. In this example, the 802.11ax frame starts with a 'legacy' preamble for backward compatibility. In some implementations, these fields allow older devices to recognize that an 802.11 frame is broadcasting. In some implementations, this allows the CSMA/CA protocol to continue to function in the presence of an 802.11ax transmission. In some implementations, for backward compatibility, the 'legacy' preamble and the repeated legacy SIG (RL-SIG) field are transmitted in parallel in all 20MHz subchannels for subsequent transmissions. In some implementations, the subsequent field is used for 802.11ax purposes and uses a mix of symbol formats, where 'legacy' modulation is used for the low rate field and for backward compatibility, while the other fields use close subcarrier spacing and longer OFDMA symbols from 802.11 ax.

Ext> inext> someext> implementationsext>,ext> theext> HEext> -ext> SIGext> -ext> aext> fieldext> (ext> highext> efficiencyext> SIGext>)ext> (ext> theext> "ext> HEext> fieldext>"ext> inext> theext> figureext>)ext> includesext> informationext> aboutext> theext> packetext> toext> followext>,ext> includingext> whetherext> itext> isext> downlinkext> orext> uplinkext>,ext> bssext> colorext>,ext> modulationext> mcsext> rateext>,ext> bandwidthext> andext> spatialext> streamext> informationext>,ext> andext> theext> remainingext> timeext> inext> theext> transmitext> opportunityext>,ext> etcext>.ext> In some implementations, this field has different content for single user, multi-user, and trigger-based frames, and is repeated in the 'extended range mode' of 802.11 ax. In some implementations, the HE-SIG-B field (also referred to as "HE field" in the figures) includes only for multi-user packets. In some implementations, the HE-SIG-B field includes information common to all recipients as well as other fields specific to the user, and thus its length depends on the number of users receiving the transmission. In some implementations, if OFDMA is used, the HE-SIG-B client specific field is transmitted simultaneously in each subchannel for subsequent packet transmissions. In some implementations, the HE-SIG-B is another complex domain. In some implementations, it has a variable length depending on the number of clients the AP is addressing and two different types of information: public information and user specific information.

In some implementations, a common field (a portion of the "preamble" and/or "HE field" in the figures) identifies a structure of OFDMA subchannels or Resource Units (RUs) to be used, such as 18x26 RU or 2x242 RU. In some implementations, the common field includes other information common to all transmissions. In some implementations, several user-specific fields follow a common field. In some implementations, the AP uses these fields to identify how it will transmit to each client; for example, including the number of spatial streams, the MCS it will use, and/or whether it will use beamforming. In some implementations, the 802.11ax specification requires that the transmitter form the HE-SIG-B field in multiple 20MHz channels simultaneously, occupying the total bandwidth of the allocated channels. Thus, if the AP is using an 80MHz channel, it will transmit 4 HE-SIG-B fields, one for each 20MHz sub-channel.

In 802.11ax, the following terms apply and are also used in this document. Basic trigger frame: specifying how and when the client device should respond. Multiuser block acknowledgement request (MU-BAR): this trigger frame requests block acknowledgements from multiple client devices simultaneously. The user information field specifies the frame to be acknowledged. Multiuser request to send (MU-RTS): this trigger frame is used to clear the air information prior to transmission in the same manner as a single-user RTS-CTS.

In some implementations, on DL, the AP schedules multiple users, populates the HE header (i.e., the AP determines the content of the preamble/HE field), and transmits DL data on the RU. In some implementations, on the UL, the AP signals to the devices that they have UL grants to utilize. In some implementations, for this purpose, the AP sends a trigger frame and transmits an identification of the STA with UL grant to utilize. The downlink packet may include an ACK and a trigger, and the uplink transmission may include a trigger-based frame that also carries the ACK. In some implementations, all of these signals are controlled and coordinated by the AP.

In some implementations, to achieve backscatter in the 802.11ax framework, the AP transmits a trigger frame with an auxiliary BSR flag and the location of one or more RUs for auxiliary BSR signaling. The AP may periodically send a query to the BSTA to determine the transmission rate on the UL and whether the BSTA has pending data to transmit.

In some implementations, if the receiving BSTA has pending data in its buffer, it selects (e.g., uniformly randomly) the indicated RU for the auxiliary BSR to be marked. In some implementations, on a current frame after the trigger frame, if the auxiliary BSR flag is set to true, the BSTA transmits a BSR concatenated with its mnemonics on the selected RU. In some implementations, the mnemonics are used for contention resolution because the identity of the BSTA transmitting the BSR is unknown (similar to the RACH procedure). In some implementations, a mnemonic is appended to the quantized BSR, and the entire content is scrambled by the mnemonic, e.g., for additional protection.

In some implementations, the AP and/or coordinating TRP provides int_sig (CW in the figure) on the auxiliary BSR RU for the devices to backscatter their BSR. After having received the BSR from the BSTA (and from other STAs that need UL transmissions, e.g., using RACH slots), the AP determines the identity of the STA that has UL transmissions to transmit and matches those opportunities and resource requirements (e.g., RU requirements) with BSR requirements received from the BSTA. If sufficient capacity is available on the next frame, the AP transmits the BSTA mnemonic and corresponding RU-map on the subsequent trigger frame for back-scattering. The BID flag may or may not be set to true.

In some implementations, if the BID flag is set to true, the AP has ensured that there will be another STA that will have a transmission on the UL on the set of indicated RUs that the BSTA is available to backscatter. In some implementations, this is typical in a reasonably loaded network, as conventional STAs have greater transmit requirements and the BSTA is unlikely to have high requirements. In some implementations, receiving a subsequent trigger frame and a BSTA mnemonic to RU mapping for backscatter and a BSTA set to true BID flag will be backscattered on a particular RU.

In some cases, the AP determines that there are no regular STAs that need to transmit, and thus selects one or more TRPs (or antennas) to provide the int_sig. In this case, the AP (or associated TRP) may allocate any RU used to provide the dedicated int_sig and is not limited to a particular RU that will be allocated for UL transmissions for a particular STA. In some implementations, the AP transmits a subsequent trigger frame and a BSTA mnemonic mapped to one or more RUs for back scattering, and sets a BID flag to indicate that the BSTA can select any RU and is not limited to a particular RU. In this case, the BSTA selects (e.g., uniformly randomly) RUs that map to its mnemonics for back-scattering.

In some implementations, the AP receives energy statistics from the BSTA within the UL transmission, which may indicate that the BSTA needs to collect energy. In some implementations, the AP may operate over a larger bandwidth (e.g., greater than a single 20MHz channel). In some implementations, the AP transmits the BSTA mnemonic, an index of one or more 20MHz subchannels assigned to the BSTA, an index of the energy-bearing RU, and a schedule, for example, in a common field within the HE-SIG-B field. In some implementations, the schedule may indicate a start time offset and duration, and may suggest possible periodic services. In some implementations, the AP may indicate that the Power Optimized Waveform (POW) schedule is periodic, or the AP may determine a different schedule for POW delivery and cancel the currently active schedule. In some implementations, if the AP indicates these in a common field in the HE-SIG-B header, it applies to any BSTA that may want to consume the opportunity. In some cases, periodic POW may be too infrequent and the BSTA may require a dedicated POW opportunity. In some implementations, in these cases, the BSTA may receive, for example, an index of one subchannel, an index of an energy-bearing RU, a start time offset, and/or a duration of a dedicated POW opportunity, and a mnemonic of the BSTA from the AP in a user-specific field within the HE-SIG-B field.

In some implementations, the AP may need to determine whether the BSTA and the participating devices have the ability to filter out interference if the BSTA is to backscatter a regular downlink transmission. In some implementations, rather than opportunistic piggybacking through regular traffic, the AP may determine whether a dedicated int_sig (CW in the figure) is needed, e.g., based on device capabilities.

For example, in fig. 7, after performing DIFS and backoff, the AP transmits a multi-user RTSB (MU-RTSB) to indicate the STA to which DL is to be transmitted. The STA indicates acceptance by transmitting a MU-CTS, MU-CTSA, or MU-CTSB (not shown). The AP schedules efficient multi-user transmissions to STAs using OFDMA and/or MIMO paradigms. Transmissions occur on one or more Resource Units (RUs) of the respective STAs for covering the operating bandwidth. As shown in fig. 7, the BSTA timely uses the transmissions to harvest energy.

In some implementations, the BSTA timely utilizes UL transmissions on the channel to backscatter its own transmissions (e.g., based on measured signal strength). For example, in some implementations, the BSTA receives BID messages indicating availability of DL and UL assist backscattering opportunities and includes a corresponding configuration (e.g., the configuration optionally includes measurement filtering rules), measures DL received signal strength (e.g., based on received BID messages, preambles in DL frames, and/or dedicated reference signals), applies filtering rules to the measured DL received signal, determines that the received signal strength is below a first threshold, receives trigger frames and/or corresponding BID messages from the serving AP, and determines a RU that is eligible for opportunistic UL assist backscattering and a corresponding plurality of common or STA-specific measurement thresholds (e.g., includes a lower second threshold and/or a higher third threshold, determines one or more sub-thresholds between the second threshold and the third threshold (e.g., based on desired QoS requirements), measures sub-band and wideband received signal strength on a compliant RU during a first portion of a UL frame, or alternatively measures signal strength on a compliant RU during one or more preceding frames transmitted by the same STA, and the one or more sub-band received signal strength on a compliant RU, and one or more threshold is selected to be reasonably programmed to be transmitted by the same. In some implementations, the BSTA selects an RU (e.g., and corresponding transmitting STA) with a measured signal strength above a lower second threshold. In some implementations, to reduce collisions between BSTAs, the BSTA may limit RU selections to those that meet a received signal strength below an upper third threshold.

Since the transmission is OFDMA, some tones are transmitted at higher power than others. Thus, in some implementations, the AP may indicate to the BSTAs (e.g., in a trigger frame or schedule frame) which RUs are optimal for energy harvesting by the appropriate BSTA in the MU-RTSB. Depending on the acquisition requirements, in some implementations, the BSTA may acquire energy from the information and power bearing RU that is intended for other STAs.

In some implementations, the AP sends a trigger frame with a transmission schedule on the UL and associated STA identities. In some implementations, scheduling may also allow random access opportunities on the UL. UL transmissions from STAs are energy-bearing and the BSTA may use them to perform energy harvesting.

In some implementations, the AP enables DL and backscatter UL transmissions simultaneously by employing in-band full duplex communication.

In some implementations, the BSTA receives BID messages indicating availability of DL and UL auxiliary backscatter opportunities and corresponding configurations including DL auxiliary backscatter first thresholds, configurations including first thresholds, or configurations including a lower first threshold and one or more additional thresholds above the lower first threshold and associated QoS for each additional threshold; determining a second threshold that is greater than or equal to the first threshold (e.g., based on a desired QoS requirement); measuring DL received signal strength (e.g., based on received BID messages, preambles in DL frames, and/or dedicated reference signals); determining a received signal strength above a lower first threshold or determining an additional threshold above a lower first threshold based on a desired QoS; selecting one or more RUs for the backscattered DL frame from the determined set of eligible RUs (e.g., based on the received BID message and/or a preamble in the DL frame); transmitting and/or reflecting on the selected one or more RUs using backscatter techniques; in some implementations, the example BTSA includes circuitry configured and/or programmed to perform these actions. In some implementations, the AP performs in-band received operations on received RUs via self-interference cancellation. In some implementations, the configuration may include a first threshold used by the BSTA to determine whether it should consider DL-assisted or UL-assisted backscatter. The lower first threshold and the larger second threshold may be used to limit contention between BSTAs during selection of an RU based on a desired QoS for the RU.

In the foregoing examples, in some implementations, either of the DL and/or UL signals may be a continuous active transmission into/out of STAs served by the AP, e.g., the BSTA timely modulates their information with these STAs over existing transmissions (e.g., modulates their information bits on existing carriers and/or RUs currently assigned to other STAs). In some implementations, for example, alternatively, any of the DL and/or UL signals may be dedicated power optimized signaling (e.g., sinusoidal transmission sent directly from the AP or requested by the AP in coordination with an associated STA).

Fig. 8 is a flow chart 800 illustrating exemplary backscatter, for example by a BSTA.

In step 802, the BSTA receives a BID message indicating DL and/or UL assistance backscatter opportunities, and may indicate a corresponding configuration. In some implementations, the configuration may indicate a signal strength threshold, RU eligible for backscatter transmission, and/or UL signal measurement configuration. In some implementations, the configuration includes a first threshold for the BSTA to determine whether it should consider DL-assisted or UL-assisted backscatter. The lower first threshold (e.g., second threshold) and the higher second threshold (e.g., third threshold) may be used to limit contention between BSTAs during selection of an RU based on a desired QoS for the RU, as discussed further herein.

In step 804, the BSTA measures the received signal strength of DL signals that may potentially be used for backscatter. In some implementations, DL received signal strength is determined based on receiving a BID message, a preamble in a DL frame, or a dedicated reference signal.

On condition 806 that the DL received signal strength exceeds a threshold (e.g., a threshold associated with a quality of service (QoS) requirement of the backscatter transmission), the BSTA selects one or more Resource Units (RUs) of the DL frame for backscatter in step 808. In some implementations, an RU is selected from a set of eligible RUs. In some implementations, the BSTA determines the set of eligible RUs based on the BID message, the preamble in the DL frame, or in any other suitable manner.

In step 810, the BSTA modulates the DL signal on the selected RU to backscatter the signal.

Under the condition 806 that the DL received signal strength does not exceed the threshold, the BSTA waits to receive a trigger frame or another BID message in step 812.

In step 814, the BSTA determines one or more eligible RUs for the backscattered UL frame. In some implementations, an RU is selected from a set of eligible RUs. In some implementations, the BSTA determines the set of eligible RUs based on a trigger frame or BID message or in any other suitable manner.

In step 816, the BSTA measures the received signal strength of UL transmissions from other STAs on the eligible RU. In some implementations, the BSTA measures the received signal strength of the UL transmission during the first portion of the UL frame, or bases the measurement on an earlier measurement of a previous UL frame from the same STA.

In step 818, the BSTA selects one or more of the eligible RUs of the UL frame, e.g., based on the measured received signal strength.

The BSTA modulates the UL signal on the selected RU to backscatter the signal, subject to a condition 820 that the UL received signal strength exceeds a threshold (e.g., a threshold associated with a quality of service (QoS) requirement of the backscatter transmission). Otherwise, the flow returns to step 802. In some implementations, this condition evaluates UL signal strength that should fall between the second threshold and the third threshold (e.g., because the STA does not know the location of the source of the UL transmission).

Flowchart 800 illustrates the operation of a BSTA in which a DL received signal is above or below a first threshold based on QoS requirements. In some implementations, if no eligible RU meets the criteria during the current transmission interval, the BSTA falls back to a future opportunity during which a backscatter opportunity may occur.

MU-RTSB indicates scheduling of DL for STAs on a specific RU and indicates the specific RU as int_sig to the BSTA. DL transmissions to STAs on a particular RU are not interfered with. The interrogation signal int_sig on a particular RU (shown as CW) is used by the BSTA to backscatter to the AP. The AP performs in-band reception on those specific RUs. The AP transmits a dedicated Power Optimized Waveform (POW) towards the BSTA.

Some implementations include one or more of the following. Some implementations include a device receiving a trigger frame and a contention opportunity signal within the trigger frame, an index of one or more time-frequency resources for indicating backscatter requirements. Some implementations include a device uniformly randomly selecting a time-frequency resource (e.g., RU) to transmit a contention-based backscatter request. Some implementations include a device transmitting a transmission request concatenated with its mnemonics on a selected time-frequency resource on a current frame subsequent to a trigger frame. Some implementations include the AP providing an interrogation signal on time-frequency resources or the AP protecting environmental sources (e.g., other STAs received from the AP on the DL) on indicated contention-based time-frequency resources. Some implementations include an AP determining the identity of a non-backscatter device with a DL transmission and matching these opportunities and resource requirements with the transmission requirements received from the backscatter device. Some implementations include the device receiving a subsequent trigger frame and a mnemonic to resource mapping and setting a backscatter tag to true. Some implementations include a backscatter device backscattering on a current frame after a trigger frame mapped to a particular RU of its mnemonic. Some implementations include the backscatter device receiving an index (or indices) of one or more energy-bearing frequency resources in a common field in the header and a time table. In some implementations, the schedule indicates a start time offset and/or duration. Some implementations include a backscatter device receiving an index and schedule of energy-bearing resources in a user-specific field of an 802.11 header and its mnemonics. The schedule includes a start time offset and a duration.

Some implementations include backscatter in an OFDMA network. In the 802.11 framework using CDMA-based waveforms, backscattering may be easier because the number of different codeword types used is very small and this knowledge can be exploited when backscattering CDMA incident waveforms. However, most deployed 802.11 networks use OFDM waveforms, and since much information is unknown, it is difficult to backscatter a modulated waveform such as OFDM. However, backscattering may be implemented in the OFDM framework.

Fig. 9 is a system diagram illustrating two exemplary systems, showing different aspects of backscatter. The uppermost system includes BSTAs a, b, c, d and APs, namely AP1 and AP2. In this example, BSTA b has a bit stream 10101 for transmission to AP 1.AP1 determines (e.g., using the techniques described herein) when scheduling of BSTA b transmissions on the UL is required and transmits DL data (a-MPDU) to the participating coordinator AP (AP 2) by forming an aggregate MAC PDU (a-MPDU) with a fixed smaller payload size and associated CRC. AP2 transmits block ACK 11111 to AP 1. In some implementations, this approach is suitable for low-rate reliable backscatter. In some implementations, during transmission of DL data (a-MPDU) by AP1, BSTA b uses backscatter to constructively or destructively interfere with the transmission received by AP2 (i.e., based on the information blocks it needs to deliver to AP 1). Subsequently, the block ACK received by AP1 from AP2 should effectively carry the information block from BSTA b (e.g., unless the channel has corrupted some MPDUs).

The bottommost system includes BSTA w, x, y, z and APs, namely AP1 and AP2. In this example, the BSTA x has a bit stream 10101 for transmission to AP 3. To backscatter the bit stream, the BSTA x causes or avoids causing interference in DL data from AP3 to AP4 in proportion to the duration of each of the a-MPDUs. In this example, the channel is changed sufficiently during the time that the BSTA x needs to signal a 1, and the channel is not modified during the time that the BSTA needs to signal a 0. The zig-zag lines represent these periods (e.g., periods of one MPDU duration) when the channel is not corrupted, and the interval between the dark zig-zag lines (e.g., of one MPDU duration) indicates when the BSTA corrupted the channel. Intermittent interference to the channel carries the information payload 10101 that the BSTA intends to transmit to the AP 3. In this example, the AP4 demodulates the DL a-MPDUs and discovers that the CRCs of the first, third, and fifth MPDUs pass and that the CRCs of the second and fourth MPDUs fail. AP4 sends a block ACK (indication 10101) to AP1, which AP1 interprets as back-scattered data from BSTA b.

In this example, dual static backscatter is enabled, e.g., with a large number of legacy STAs that may be present in the network, without modification. In some implementations, the backscatter data itself may include FCS or CRC fields, for example, to ensure that the failure of detection by the STA is due to intentional interference and not degraded channel conditions. In some implementations, this applies in practice only if the BSTA is close enough to the legacy STA to cause significant destructive interference. In some implementations, there are viable deployment scenarios.

In some implementations, the BSTA detects a CTS-to-self message indicating a dedicated backscatter opportunity and determines that the received signal strength is below a first threshold; monitoring UL transmissions of nearby STAs and detecting received signal strength from the first STA above a second threshold; transmitting an RTSB requesting a dual static transmission to the first STA using the master transceiver; receive acknowledgement and dual static backscatter opportunity configuration (e.g., including information about the number of MPDUs within an a-MPDU addressed to the first STA); determining a total number of information bits (e.g., including overhead bits) available for transmission based on a number of MPDUs available within the a-MPDU and a number of single or multiple backscatter opportunities; the DL signal is modulated with a dual static backscatter opportunity configuration by causing destructive interference to a particular MPDU and/or constructive interference to the remaining MPDUs within an a-MPDU transmitted to the first STA, wherein each success or failure in receiving an MPDU corresponds to either a backscatter bit-1 (if an ACK) or a backscatter bit-0 (if a NACK) from the BSTA. In some implementations, the example BTSA includes circuitry configured and/or programmed to perform these actions.

The example of fig. 9 shows that the AP transmits to the coordinator AP at a time when there is no DL data to any STA. However, in fig. 9, the coordinating AP (e.g., AP2 or AP 4) may also represent a STA. In an exemplary case where there happens to be data consistent with the STA, in some implementations, the AP3 may transmit to the STA and the BSTA performs the same procedure as described above. In this case, in some implementations, the STA sends a block ACK showing the CRC failure of both MPDUs within the a-MPDU, and in some implementations, the AP3 retransmits this information to the STA. It should be noted that in some implementations, this use case covers a BSTA with very low transmission rates and very infrequent backscatter requirements. In these cases, in some implementations, deliberately causing interference to the channel to achieve backscatter results in a very small increase in retransmission rate and is negligible as overhead. In some implementations, this approach may prove sufficient to support a system with several STAs and several coordinator APs to support IOT sensors (which are BSTAs) with minimum data rate requirements. In some implementations, the resulting aggregate system capacity is not significantly reduced and the STA count supported by the AP is also significantly increased.

Fig. 10 illustrates an example system 1000 configured to determine DL channel conditions via reverse estimation. In the example of fig. 10, the low power BSTA 1004 uses energy harvesting to operate the electronic circuitry. Here, the BSTA 1004 performs energy harvesting and the AP 1006 determines the harvesting rate of the BSTA 1004. To facilitate this, in this example, the AP 1006 measures the backscattered uplink 1008 from the BSTA 1004 in the presence of distortion 1010 (e.g., potential intentional). In some implementations, the BSTA 1004 receives the downlink interrogation signal 1012 at a significantly greater power than the backscatter uplink 1008. In some implementations, if receiver 1014 on the AP can estimate the downlink incident waveform, the AP can implement control feedback loop 1016 and indicate to transmitter 1018 of the AP to compensate at the time of transmission.

Fig. 11 is a line graph 1100 illustrating exemplary transmit side compensation of channel impairments. For example, in fig. 11, a signal 1102 transmitted from an AP is depicted as the amplitude of several tones. Signal 1104 shows the actual incident signal at the BSTA (also known as Zero Energy (ZE) device (ZE in the figure)). It should be noted that the incident int_sig is received at unequal power levels, with the intent to show frequency selective impairments. If this is the input signal for backscatter, the actual backscatter signal 1106 is even further degraded, making communication less reliable. If the AP is able to estimate the incident signal at the BSTA/ZE device, the AP may pre-compensate the transmission so that the incident waveform at BSTA arrives at a higher quality. Compensating transmit signal 1108 shows the result of the AP pre-compensating the transmit waveform, e.g., based on the ability to reverse estimate the channel. The compensated incoming signal 1110 at ZE shows the actual incoming signal after channel impairments if compensated transmission has occurred. In some implementations, the method shown in fig. 11 enables the incident waveform at each ZE by compensating for multipath distortion that may exist on non-LOS channels. In some implementations, a control loop is required at the AP to change phase and amplitude by estimating impairments in the channel. In some implementations, the AP compensates for the varying channel gain by varying the energy harvesting target and/or varying the transmitted waveform. Alternatively, if the AP can estimate channel impairments, the AP uses a predetermined and/or stored waveform suitable for the channel representing the best waveform. In some implementations, the AP uses a particular waveform that historically performs best for a particular estimated channel. In some implementations, if the channel can be satisfactorily reverse estimated, the stored and/or predetermined waveform is used by the AP representing the best waveform.

Fig. 12 illustrates an exemplary control loop 1200 implemented at an AP 1202 for channel estimation. AP 1202 includes a controller 1210 and a filter 1212. The controller 1210 selects a waveform to be transmitted on the radio channel 1204 to deliver power to the backscatter body 1206. A reference vector 1214 is input for comparing an estimate of the acquired energy with a reference Ref (y) 1232 encoded in the backscatter vector by backscatter body 1204.

The radio channel 1204 incorporates the fading effects indicated by the downlink gain matrix 1220 and uplink gain matrix 1222, noise 1224, and distortion 1226.

Backscatter body 1206 includes Inc (y) 1230, which accumulates and/or collects energy in received signal y; and Ref (y) 1232, which is a reference signal modulated in a backscatter vector above the received signal y to assist the access point in performing reverse channel estimation.

In some implementations, compensation is performed at the AP to accommodate changing propagation conditions and distortions that may occur on the radio channel 1204, for example, due to the presence of other devices in the vicinity of the AP. In some implementations, the waveform received at ZE backscatter body 1206 can be modeled as a linear combination of attenuated control vector and distortion, for example, as shown in fig. 12. In some implementations, this allows the AP to make several determinations. For example, the AP may determine to use the RF spectrum divided into constant equal-width subcarriers and/or variable-width subcarriers. In some implementations, the gain matrix shown in fig. 12 may be sparse, for example, because the radio channel 1204 is memory-free and linear. In some implementations, therefore, mathematically, the off-diagonal element (the cross product between tones) is a 0 value.

Fig. 13 illustrates an exemplary control loop 1300 for multi-carrier, multi-STA estimation of a channel 1304 involving a BSTA 1306.

The AP 1302 includes a controller 1310 and a filter 1312. The controller 1310 selects waveforms to be transmitted on the radio channel 1304 to deliver power to the backscatter body 1306. A reference vector 1314 is input for comparing an estimate of the acquired energy to a reference Ref (y) 1332 encoded in the backscatter vector by the backscatter body 1304.

The radio channel 1304 incorporates fading effects indicated by the downlink gain matrix 1320 and uplink gain matrix 1322, noise 1324, and distortion 1326.

The backscatter body 1306 includes Inc (y) 1330 that accumulates and/or collects energy in the received signals y1, y2, and yk; and Ref (y) 1332, which is a reference signal modulated in a backscatter vector above the received signal y to assist the access point in performing reverse channel estimation.

In some implementations, control loop 1300 enables AP 1302 to model the control loop as decoupled into K subcarriers, one for each BSTA. In some implementations, the waveform closed-loop tracking system is decoupled from subcarrier tracking. In some implementations, the subcarriers are coupled at the receiver level of the BSTA via power acquisition circuitry. Fig. 13 illustrates an exemplary multi-carrier extension in which reverse channel estimation may be performed for multiple BSTAs. Thus, in some implementations, a framework is established whereby AP 1302 may categorize waveforms or patterns that may be used at a future time and associated estimated channels. In some implementations, the AP 1302 determines whether energy harvesting is needed based on the harvesting rate estimate at the BSTA 1306. In some implementations, the AP 1302 estimates (e.g., autonomously without any feedback from the BSTA) the energy acquisition rate of the BSTA 1306 by back-estimating the backscatter channel and propagation conditions. In some implementations, the AP 1302 implements a control loop to change the phase and amplitude of the carrier or subcarrier by estimating impairments in the backscatter channel. In some implementations, the AP 1302 adaptively compensates for varying channel gains by varying energy harvesting targets. In some implementations, the AP 1302 classifies waveforms suitable for estimating a channel and uses a set of predetermined or classified waveforms suitable for the current estimated channel that represent the best incident waveform at the BSTA. In some implementations, the AP 1302 uses the control vector to determine the RF spectrum divided into constant equal-width subcarriers and/or variable-width subcarriers to maximize the energy harvesting rate.

Fig. 14 shows an exemplary buffer estimation of the BSTA by the AP. Fig. 14 shows an example of how a mask may be used to limit the number of individually addressed BSR requests. For example, the application mask (0011) indicates that (single) BSR requests are addressed to all BSTAs with mnemonics defined under branch (#11), which include (1111, 0111, 1011, 0011). Alternatively, if a mask (0111) is applied, the (single) BSR request is addressed only to the BSTA with the mnemonics defined under branch (# 111), which includes (1111, 0111).

In some implementations, for example, as described herein, the AP decides when to control the channel for backscatter transmission. In some implementations, the AP does so by performing DCF, transmitting CTS-to-self, and reserving the medium for the duration of the BSTA activity. In some implementations, in these cases, the AP determines whether there is a need to protect the media. In some implementations, the APs periodically poll the BSTAs and request them to transmit buffer status reports. In some implementations, sending BSR to each BSTA is overhead, and several BSTAs may have nothing to transmit and have zero bytes in their buffers.

To minimize this, in some implementations, the AP groups the BSTAs into several uniform sets, where in each set the combined requirements of UL transmissions from the BSTAs are approximately equal. In some implementations, this is estimated from historical activity or based on device capabilities. In other words, in some implementations, the APs promote uniform groups such that none of the groups overwhelms the APs with more backscatter requirements than the other groups.

To achieve this, in some implementations, the AP assigns a mnemonic as described in detail in the earlier section. In some implementations, a predetermined number of bits is used as the unique identification number. In some implementations, the second predetermined number of bits is used for a random value used by the AP for probing. In some implementations, the AP transmits a command requesting that each BSTA having a random value within a specified set of random values respond.

In some implementations, for example, as shown in fig. 14, the AP transmits an arbitration value (e.g., a mask) that may be referred to as arbit_val, and the BSTA performs a bitwise logical operation to determine the requirements of the response. For example, in some implementations, if the equation (mnemonic & arbit_val) >0 evaluates to "0" (FALSE), then the BSTA will not answer because arbitration does not involve the BSTA. It should be noted that in some implementations, the AP may decide the arbitration value and the previously assigned mnemonics such that no more than N% of the devices will need to access the medium at the same time. In some implementations, if the equation evaluates to greater than 0 and if the BSTA has data in the buffer, the BSTA will transmit a buffer status. In some implementations, if the above equation evaluates to greater than 0, but the BSTA has no data in the buffer, the BSTA will not transmit the buffer status. In some implementations, by performing this operation in a structured manner, the BSR of all the BSTAs over a determined interval is ultimately known without collision as the number of bits in the arbit_val mask increases one at a time. In some implementations, the AP may be configured to employ tree search and Aloha techniques to determine the unique identification number.

Some implementations include a device receiving a backscatter time window and accessing allowed subtypes within an envelope, where the envelope maintains a particular periodicity. Some implementations include a device performing contention-based access requests by back-scattering an incoming signal over a set of time-frequency resources. Some implementations include a device receiving an acknowledgement to defer uplink data transmission for future backscatter opportunities. Some implementations include devices that are addressed in the future by locally unique mnemonics (identifications) rather than by permanent identifications (e.g., MAC addresses), where a mnemonic is a shortened identification. Some implementations include a device receiving a signal and a duration limit from an infrastructure node, a mnemonic of which indicates that there is an opportunity for backscatter for a specified duration. Some implementations include a device performing contention-free access by back-scattering an incoming signal on a set of time-frequency resources. Some implementations include a device receiving a measurement mask and applying the measurement mask to its mnemonics to determine whether a report needs to be sent to an infrastructure node, where in some implementations the device determines whether it should instead send a quality measurement based on a buffer pending state. Some implementations include a device receiving an energy-bearing carrier for a particular duration to facilitate energy harvesting.

Although the features and elements are described above in particular combinations, one of ordinary skill in the art will appreciate that each feature or element can be used alone or in any combination with other features and elements. Additionally, the methods described herein may be implemented in a computer program, software, or firmware incorporated in a computer readable medium for execution by a computer or processor. Examples of computer readable media include electronic signals (transmitted over a wired or wireless connection) and computer readable storage media. Examples of computer readable storage media include, but are not limited to, read-only memory (ROM), random-access memory (RAM), registers, cache memory, semiconductor memory devices, magnetic media (such as internal hard disks and removable disks), magneto-optical media, and optical media (such as CD-ROM disks and Digital Versatile Disks (DVDs)). A processor associated with the software may be used to implement a radio frequency transceiver for a WTRU, UE, terminal, base station, RNC, or any host computer.

Claims

1. A method implemented in a wireless Station (STA), the method comprising:

receiving a Backscatter Indication (BID) message indicating a backscatter opportunity and a Downlink (DL) signal strength threshold; and

Based on a signal strength of a DL transmission exceeding the DL signal strength threshold, the DL transmission received on a Resource Unit (RU) indicated in the BID message is back-scattered to generate a back-scattered transmission.

2. The method of claim 1, wherein the backscatter of the DL transmission occurs based on a duration of the DL signal exceeding a payload transmission requirement associated with the backscatter transmission.

3. The method of claim 1, the method further comprising:

based on the strength of the DL transmission not exceeding the DL signal strength threshold, uplink (UL) transmissions from another STA received on resource elements indicated in the BID message are back-scattered to generate another back-scattered transmission.

4. The method of claim 3, wherein the back-scattering of UL transmissions occurs based on a signal strength of the UL transmissions exceeding a UL signal strength threshold and a duration of the UL transmissions exceeding a payload transmission requirement associated with the other back-scattering transmission.

5. The method of claim 1, the method further comprising:

the signal strength of the DL transmission is measured based on the BID message, a preamble in a DL frame, or a dedicated reference signal.

6. The method of claim 4, wherein the DL signal strength threshold and the UL signal strength threshold are the same threshold.

7. The method of claim 1, wherein the BID message comprises a management message.

8. The method of claim 1, wherein the BID message comprises an acknowledgement message.

9. The method of claim 1, wherein the DL signal strength threshold is associated with a quality of service (QoS).

10. The method of claim 1, wherein the backscatter transmission is generated based on a signal strength of the DL transmission exceeding the DL signal strength threshold and the DL transmission exceeding a payload transmission requirement.

11. A wireless Station (STA), the STA comprising:

a receiver configured to receive a Backscatter Indication (BID) message indicating a backscatter opportunity and a Downlink (DL) signal strength threshold; and

a transmitter configured to backscatter DL transmissions received on a resource element (RU) indicated in the BID message to generate a backscatter transmission based on a signal strength of the DL transmissions exceeding the DL signal strength threshold.

12. The STA of claim 11, wherein the transmitter is further configured to backscatter the DL signal based on a duration of the DL signal exceeding a payload transmission requirement associated with the backscatter transmission.

13. The STA of claim 11, wherein the transmitter is further configured to backscatter an Uplink (UL) transmission from another STA received on a resource element indicated in the BID message to generate another backscatter transmission based on the strength of the DL transmission not exceeding the DL signal strength threshold.

14. The STA of claim 13, wherein the transmitter is further configured to backscatter the UL transmission based on a signal strength of the UL transmission exceeding a UL signal strength threshold and a duration of the UL transmission exceeding a payload transmission requirement associated with the other backscatter transmission.

15. The STA of claim 11, wherein the receiver is further configured to measure a signal strength of the DL transmission based on the BID message, a preamble in a DL frame, or a dedicated reference signal.

16. The STA of claim 14, wherein the DL signal strength threshold and the UL signal strength threshold are the same threshold.

17. The STA of claim 11, wherein the BID message comprises a management message.

18. The STA of claim 11, wherein the BID message comprises an acknowledgement message.

19. The STA of claim 11, wherein the DL signal strength threshold is associated with a quality of service (QoS).

20. The STA of claim 11, wherein the transmitter is further configured to generate the backscatter transmission based on the signal strength of the DL transmission exceeding the DL signal strength threshold and the DL transmission exceeding a payload transmission requirement.