Backscattering into multiple channels, including examples of simultaneous tranmission of multiple BLE backscatter packets using OFDM

Abstract

An example method involves receiving a plurality of data streams, including a first data stream and a second data stream, and an incident carrier signal. The first data stream is packetized into a first set of Bluetooth packets, and the second data stream into a second set of Bluetooth packets. These Bluetooth packets are then backscattered by a backscatter modulator using an incident carrier signal, with the first set of packets backscattered in a first Bluetooth channel and the second set in a second Bluetooth channel. In this manner, a backscatter device may backscatter into multiple Bluetooth channels simultaneously.

Description

BACKSCATTERING INTO MULTIPLE CHANNELS, INCLUDING EXAMPLES OF SIMULTANEOUS TRANMISSION OF MULTIPLE BLE BACKSCATTER PACKETS USING OFDMCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit under 35 U.S.C. § 119 of the earlier filing date of U.S. Provisional Application Serial No. 63 / 549,673 filed February 5. 2024, the entire contents of which are hereby incorporated by reference in their entirety for any purpose.STATEMENT REGARDING RESEARCH & DEVELOPMENT

[0002] This invention was made with government support under Grant No. DGE-1762114, awarded by the NSF Graduate Research Fellowship Program. The government has certain rights in the invention.TECHNICAL FIELD

[0003] Examples described herein relate generally to wireless backscatter communication. Examples of the simultaneous transmission of multiple Bluetooth low energy (BLE) backscatter packets using OFDM are described.BACKGROUND

[0004] Backscatter communication may provide wireless data uplinks with orders of magnitude lower energy consumption per data bit transferred when compared to wireless links using an active transmitter. Most existing backscatter communication systems have relied on single-carrier modulation, such as single-carrier amplitude shift keying (ASK), phase shift keying (PSK), frequency shift keying (FSK), or single-carrier quadrature amplitude modulation (QAM). However, two major drawbacks to single-carrier modulation are higher sensitivity to multipath interference and lower throughput since the data is constrained to a single channel.

[0005] Bluetooth transmitters and receivers typically transmit and receive in only a single channel at a time. For example, a typical Bluetooth transmitter may pair with only one receiver, and a receiver may pair with only one transmitter. This limits the functionality of Bluetooth devices.SUMMARY

[0006] Examples of methods are described herein. An example method includes receiving a plurality of data streams including a first data stream and a second data stream, receiving an incident carrier signal, packetizing the first data stream into a first set of Bluetooth packets, packetizing the second data stream into a second set of Bluetooth packets, and backscattering the incident carrier signal with a backscatter modulator such that the first set of Bluetooth packets is backscattered in a first Bluetooth channel and the second set of Bluetooth packets is backscattered in a second Bluetooth channel.

[0007] In some examples, the plurality of data streams include a third data stream, and the method further includes packetizing the third data stream into a third set of Bluetooth packets, and the backscattering further includes backscattering the incident carrier signal with the backscatter modulator such that the third set of Bluetooth packets is backscattered in a third Bluetooth channel.

[0008] In some example methods, the first Bluetooth channel, the second Bluetooth channel, and the third Bluetooth channel are each a Bluetooth advertising channel.

[0009] In some example methods, the backscattering in the first Bluetooth channel, the second Bluetooth channel, and the third Bluetooth channel occurs, at least in part, simultaneously.

[0010] Some example methods include providing the first set of Bluetooth packets, the second set of Bluetooth packets, and the third set of Bluetooth packets to a transform block to generate time domain signals.

[0011] In some examples, an output of the transform block includes a superposition of data corresponding to a first Bluetooth channel carrying the first set of Bluetooth packets, a second Bluetooth channel carrying the second set of Bluetooth packets, and a third Bluetooth channel carry ing the third set of Bluetooth packets. In some example methods, said backscattering is based on the time domain signals.

[0012] In some example methods, said backscattering includes coupling selective impedances to an antenna in accordance with the time domain signals. The time domain signals may represent an in-phase, I, and quadrature component, Q.

[0013] In some examples, frequency bins of the transform block correspond to the first Bluetooth channel, the second Bluetooth channel, and the third Bluetooth channel, respectively.

[0014] S ome examples include pairing with a receiver when the receiver hops to a first one of the first Bluetooth channel, the second Bluetooth channel, or the third Bluetooth channel.

[0015] Some examples include pairing with a first receiver on the first Bluetooth channel, pairing with a second receiver on the second Bluetooth channel, and pairing with a third receiver on the third Bluetooth channel.

[0016] In some examples, the three data streams each contain different data from one another.

[0017] Some example methods include backscattering additional packets of the first data stream into Bluetooth channels in accordance with a hopping sequence used by the first receiver, and backscattering additional packets of the second data stream into Bluetooth channels in accordance with a hopping sequence used by the second receiver.

[0018] In some examples, backscattering additional packets of the first data stream occurs at least partially simultaneously with said backscattering additional packets of the second data stream.

[0019] Examples of apparatuses are described herein. An example apparatus includes a first packetizer configured to packetize a first data stream into a first set of Bluetooth packets, a second packetizer configured to packetize a second data stream into a second set of Bluetooth packets, a transform block configured to receive the first set of Bluetooth packets and the second set of Bluetooth packets and generate time domain signals representing a superposition of data corresponding to a first Bluetooth channel carrying the first set of Bluetooth packets and a second Bluetooth channel carrying the second set of Bluetooth packets, and a backscatter modulator configured to couple selected impedances to at least one antenna based on the time domain signals to transmit the first data stream in the first Bluetooth channel and the second data stream in the second Bluetooth channel.

[0020] Example apparatuses may also include a third packetizer configured to packetize a third data stream into a third set of Bluetooth packets, and the transform block may be further configured to receive the third set of Bluetooth packets, and where the superposition of data further corresponds to a third Bluetooth channel carrying the third set of Bluetooth packets and where the backscatter modulator is configured to couple selected impedances to at least one antenna to further transmit the third data stream in the third Bluetooth channel.

[0021] Example apparatuses may also include a delta-sigma modulator coupled to an output of the transform block, the delta-signal modulator used to provide the time domain signals from the transform block to the backscatter modulator.

[0022] In some examples, the backscatter modulator is configured to transmit the first data stream, the second data stream, and the third data stream at least in part simultaneously. Insome examples, the first Bluetooth channel is channel 37, the second Bluetooth channel is channel 38, and the third Bluetooth channel is channel 39.

[0023] Some example apparatuses further include a memory, the memory configured to store a hopping sequence for a first Bluetooth device, a second Bluetooth device, and a third Bluetooth device.

[0024] In some examples, the backscatter modulator is configured to backscatter the first data stream in accordance with the hopping sequence for the first Bluetooth device and, at least partially simultaneously, to backscatter the second data stream in accordance with the hopping sequence for the second Bluetooth device.

[0025] In some examples, the apparatus is configured to pair with a receiver on a first one of the first Bluetooth channel, the second Bluetooth channel, or the third Bluetooth channel hopped to by the receiver.BRIEF DESCRIPTION OF THE DRAWINGS

[0026] FIG. 1 is a schematic illustration of an example system 100 arranged in accordance with examples described herein.

[0027] FIG. 2 is a schematic illustration of a backscatter device arranged in accordance with examples described herein.

[0028] FIG. 3A is a schematic illustration of BLE channels arranged in accordance with examples described herein.

[0029] FIG. 3B is a schematic illustration of a transmission of aL0’ in BLE channel 37 arranged in accordance with examples described herein.

[0030] FIG. 3C is a schematic illustration of a transmission of a ‘1 ’ in BLE channel 37 arranged in accordance with examples described herein.DETAILED DESCRIPTION

[0031] Certain details are set forth herein to provide an understanding of described embodiments of technology. However, other examples may be practiced without various of these particular details. In some instances, well-known circuits, control signals, timing protocols, and / or software operations have not been shown in detail in order to avoid unnecessarily obscuring the described embodiments. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter and / or claims presented here.

[0032] In contrast with single-carrier modulation, multi-carrier modulations, such as orthogonal frequency division multiplexing (OFDM), are more robust to multipath interference and allow for simultaneous transmission of different data streams (e.g., orthogonal data) simultaneously on different subcarriers. This has made OFDM backscatter an appealing modality when implemented with either mixed-signal or all-digital architectures.

[0033] Examples described herein include using a digital OFDM backscatter architecture to generate BLE compatible data packets, such as BLE advertising packets, that are compatible with, and can be received by, BLE-enabled devices (e.g., smartphones, laptops, tablets). In many examples, the packets may be received without hardware or software modification to the receiving device. It should be appreciated that examples described herein may be used to generate any ty pe of packet, e.g., any type of Bluetooth packet. BLE advertising packets are one of the most commonly used types of BLE packets so examples described herein may utilize BLE advertising packets as examples. Note that, using a digital OFDM backscatter architecture, BLE advertising packets can be transmitted across all three BLE advertising channels independently, simultaneously if desired, and at orders of magnitude lower power consumption than with BLE radios not using the technique. For example, other BLE radios may employ complex and power-hungry frequency synthesizers and RF power amplifiers which may not be required or used in examples of backscatter devices and methods described herein.

[0034] An example method involves receiving a plurality of data streams, including a first data stream and a second data stream, and an incident carrier signal. The first data stream is packetized into a first set of Bluetooth packets, and the second data stream into a second set of Bluetooth packets. These Bluetooth packets are then backscattered by a backscatter modulator using an incident carrier signal, with the first set of packets backscattered in a first Bluetooth channel and the second set in a second Bluetooth channel. In this manner, a backscatter device may backscatter into multiple Bluetooth channels simultaneously.

[0035] FIG. 1 is a schematic illustration of an example system 100 arranged in accordance with examples described herein. The system may include a signal source 102, which may provide a carrier signal 114 using antenna 104. The system 100 may include a backscatter device 110 which may receive the carrier signal 114 using the antenna 112 and modulate a backscattered version of the carrier signal 114 to provide one or more backscatter signals, such as backscatter signal 116. backscatter signal 118. and backscatter signal 120 using the antenna 112. The system may further include a wireless communication device 106 that may receive the backscatter signals, including backscatter signal 116, backscatter signal 118, and / or backscatter signal 120 using antenna 108. The backscatter signals may be constructedin accordance with established wireless communication protocols, such that the wireless communication device 106 may receive and decode one or more of the backscatter signals without a need for custom programming (e.g., firmware, software) or hardware specific to communication with the backscatter device 110. The system 100 may include additional wireless communication devices, such as wireless communication device 126 and wireless communication device 122. The wireless communication device 126 may receive one or more of the backscatter signals, backscatter signal 116, backscatter signal 118, and / or backscatter signal 120, using antenna 128. The wireless communication device 122 may receive one or more of the backscatter signals, backscatter signal 116, backscatter signal 118, and / or backscatter signal 120, using antenna 124.

[0036] The components shown in FIG. 1 are exemplary. Additional, fewer, and / or different components may be used in other examples. For example, while a single respective antenna is shown as used by each of signal source 102, backscatter device 110, wireless communication device 106, wireless communication device 122, and wireless communication device 126, any of those devices may employ more than one antenna in various examples. Moreover, while three backscatter signals -backscatter signal 116, backscatter signal 118, and backscatter signal 120 - are shown in FIG. 1. any number may provided in accordance with various examples, including two backscatter signals in some examples, or more than three backscatter signals in some examples.

[0037] The signal source 102 may generally be any device that is capable of transmitting a carrier signal 114 for backscatter by the backscatter device 110. Generally, the carrier signal 114 may be a radio frequency signal, such as a wireless communication signal and / or may be a single tone signal. The carrier signal 114 may have a carrier frequency (e g. a frequency of a carrier wave that may be modulated with an input signal to provide data in the backscatter signals, such as backscatter signal 116, backscatter signal 118, and / or backscatter signal 120). The carrier signal 114 may generally be implemented using any signals which may be backscattered by backscatter devices described herein. The carrier signal 114 may be implemented using an RF signal including a wireless communication signal.

[0038] Examples of signals used to implement the carrier signal 114 include, but are not limited to, television transmission signals, radio transmission signals, cellular communication signals, Wi-Fi signals, and single tone signals such as continuous wave signals. Devices which may be used to implement the signal source 102 include but are not limited to television transmitters, base stations including cellular base stations, AM or FM broadcast stations, digital radio stations, radar, Wi-Fi (e.g., IEEE 802. il) access points, Bluetooth devices, mobile devices, telephones (including cellular telephones), computers, routers, appliances,transceivers, tablets, watches, and / or transmitters. It should be understood that any externally (e.g., external to the backscatter device 110) generated carrier having at least one frequency component in the frequency range of interest (sometimes referred to as FCamer) may be employed. In some examples, the signal source 102 may supply at least a portion of the operating power for the backscatter device 110.

[0039] The carrier signal 114 may be present in the environment from signal sources already present in an environment, and / or the carrier signal 114 may be provided by a signal source placed in an environment for the purpose of providing a signal to the backscatter device 110. While shown as having one antenna 104 the signal source 102 may be implemented having any number of antennas, including a phased array antenna, or a multiple-input-multiple- output (MIMO) array of antennas.

[0040] The signal source 102 may include a frequency source, such as an oscillator or frequency synthesizer, which may supply radio frequency energy to the signal source 102, in some examples via a power amplifier included in the signal source 102. The frequency source may include one or more of a fixed frequency source, a frequency hopping source, or a direct sequence spread spectrum source. It may be powered by batteries, by an AC power source, and / or by energy harvested from its environment (such as via a solar cell or a thermal or vibrational energy’ harvester). The signal source 102 (e.g. a transmitter) may be fixed in location or it may be mobile, as in a handheld or vehicle mounted application.

[0041] In some examples the signal source 102 may include and / or be co-located with a receiver connected to the same antenna 104 or antenna array. In some examples the signal source 102 may be implemented using an RFID reader.

[0042] The backscatter device 110 may be implemented, for example, using a tag. In some examples, the backscatter device 110 may be implemented using a device for which low power communication is desirable, such as a tag, sensor node, or the like. Tags implementing the backscatter device 110 may be associated with (e.g., placed on and / or proximate to and / or integrated with) any of a variety of items to provide information about the items. Such items include, but are not limited to, appliances, food storage containers, inventory items such as personal electronics, and portions of a building. While shown as having one antenna 112, the backscatter device 110 may utilize any number of antennas in some examples.

[0043] In some examples, the backscatter device 110 may be implemented as, may be integrated with, and / or may be in electrical communication with any electronic device and / or computing system having data to transmit. For example, the backscatter device 110 may be used to backscatter data provided from one or more servers, desktops, laptops, tablets.smartphones, smartspeakers, ear buds, headphones, wearable devices, watches, appliances, and / or vehicles.

[0044] The backscatter device 110 may modulate a backscattered version of the carrier signal 114 from the signal source 102 to provide multiple backscatter signals - such as backscatter signal 116, backscatter signal 118, and backscatter signal 120 - encoded with data to the wireless communication device 106. In some examples, the backscatter signals are provided to multiple wireless communication devices, such as wireless communication device 106, wireless communication device 122, and wireless communication device 126. Each of the backscatter signals, backscatter signal 116, backscatter signal 118, and backscatter signal 120 may be formatted in accordance with predetermined wireless communication standards, such as but not limited to OFDM signals. There are many different wireless communication standards, each of which may have a specified frequency plan, modulation scheme, and packet data format, among other specified parameters. Data encoded in the backscatter signals by the backscatter device 110 may, for example, be related to data received from a sensor or an input, or may be related to an identity or parameter of an item with which the backscatter device 110 is associated (e.g. temperature in a portion of a building, identity of an inventory item, temperature of a food storage container). Data encoded in the backscatter signals may be related to data from a computing system or other device received as input such as, but not limited to, audio data, video data, navigation data, or the like.

[0045] In examples described herein, the backscatter device 110 may provide multiple backscatter signals, with each backscatter signal provided in a particular channel (e g., at a particular frequency and / or frequency range). For example, the backscatter signal 116 may be provided in a first channel, the backscatter signal 118 may be provided in a second channel, and the backscatter signal 120 may be provided in a third channel. In some examples, the channels correspond to channels specified by a standard, such as a Bluetooth standard, such as the Bluetooth Low Energy (BLE) standard. Accordingly, the backscatter signal 116 may be in a first Bluetooth channel, the backscatter signal 118 may be in a second Bluetooth channel, and the backscatter signal 120 may be in a third Bluetooth channel. In some examples, two or three channels are backscattered simultaneously. In some examples, the three channels correspond to BLE advertising channels 37, 38, and 39.

[0046] In this manner, the backscatter device 110 may provide independent, simultaneous data streams on different BLE channels, which may be sent to a single BLE-enabled device (e.g., wireless communication device 106). While the transmission is described as simultaneous it is to be understood that the transmission on multiple channels may be at least partially simultaneously (e.g., transmissions on at least two channels may overlap in time).There may be time periods where only one channel contains transmissions. However, the backscatter device 110 may be used to backscatter signals into multiple (e.g., two, three, or more) channels simultaneously. The data contained in the simultaneous data streams may be the same data in some examples. This may be advantageous because, for example, it may reduce a time to pair the backscatter device 110 and the wireless communication device 106. During a pairing process, the receiving device (e.g., wireless communication device 106) ty pically implements a channel hopping sequence, where the wireless communication device 106 will attempt to receive from various frequencies and / or frequency ranges in sequence. Once the receiving device (e.g.. wireless communication device 106) detects a communication (e.g.. backscatter signal 116). the wireless communication device 106 may pair with the with the transmitting device sending the communication (e.g., backscatter device 110). In some examples, because the backscatter device 110 is transmitting on multiple channels, the single wireless communication device 106 may not take as long to pair, since data is being transmitted in multiple channels. Accordingly, the wireless communication device 106, which may be a BLE-enabled receiving device, does not have to wait as long for its single receiver to find the backscatter device 110 during its round-robin channel hop sequence during device enumeration and pairing.

[0047] In some examples, the backscatter device 110 may provide independent, simultaneous data streams on different BLE channels which may be sent to multiple BLE- enabled devices (e.g., wireless communication device 106, wireless communication device 122, and wireless communication device 126). While the transmission is described as simultaneous it is to be understood that the transmission on multiple channels may be at least partially simultaneously (e.g., transmissions on at least two channels may overlap in time). There may be time periods where only one channel contains transmissions. However, the backscatter device 110 may be used to backscatter signals into multiple channels simultaneously. The data contained in the simultaneous data streams may be different data on each stream in some examples. In this manner, independent, simultaneous data streams on multiple BLE channels may be provided to send messages to multiple BLE-enabled devices., Each device may receive a different stream of data on a different channel. Accordingly, each of multiple wireless communication devices (e.g.. wireless communication device 106, wireless communication device 122, and wireless communication device 126) may pair with the backscatter device 110 over a Bluetooth connection. Each device may be receiving on a different channel at any particular time.

[0048] The backscatter device 110 may include and / or may be in electrical communication with one or more computer readable media. For example, the computer readable media usedmay be random access memory (RAM), read only memory (ROM), disk drive, solid state drive, one or more SD cards, or other memory or electronic storage. The computer readable media may store one or more channel hopping sequences used by one or more wireless communication devices. For example, the backscatter device 110 may include a memory' which may store a channel hopping sequence used by wireless communication device 106, a channel hopping sequence used by wireless communication device 122, and a channel hopping sequence used by wireless communication device 126. The backscatter device 110 may use the stored channel hopping sequences to allocate data streams to particular channels during operation.

[0049] Backscatter communication generally includes modulating the reflection of an incident signal at an antenna, rather than generating the signal itself. The carrier signal 114 used by the backscatter device 110 may include a signal having a carrier frequency that is provided by the signal source 102 for a dedicated purpose and / or for another purpose, such as a television broadcast or cellular communication between a base station and a mobile device. In some examples, the backscatter signal 116 may be encoded with data using a modulation scheme. To generate the backscattered signal, the backscatter device 110 may modulate the impedance of one or more antennas, such as the antenna 112, to alternate between two or more discrete states, e.g., including in some embodiments reflecting and not-reflecting. The reflecting state of the antenna 112 may provide a reflection of the carrier signal 114, and the non-reflecting state may not reflect the carrier signal 114. Thus, the backscatter device 110 may indicate either a ‘0’ or a I ’ bit by switching the state of the antenna 112 between the reflecting and non-reflecting states and / or generally by connecting difference impedances to and from the antenna 112.

[0050] Switching the state of the antenna 112 of the backscatter device 110 may include adjusting an impedance of a load coupled to the antenna 112. The magnitude and / or phase of the scattered signal from the antenna 112 is typically determined by the difference in the impedance values of the load coupled to the antenna 112. By modulating the electrical impedance presented to the antenna 112, the magnitude and / or phase of incident energy that is scattered is modulated, thus allowing information to be transmitted. For example, in a first state, the antenna 112 may have a first impedance (e.g., a short circuit) to a reference node and may reflect the carrier signal 114 to provide a backscatter signal 116 that has a first signal magnitude and phase. In a second state, the antenna 112 may have a second impedance (e.g., an open circuit) to the reference node, and may reflect the carrier signal 114 to provide a backscatter signal 116 that has a second signal magnitude and phase. The first magnitude may be greater or less than the second magnitude. This yields an amplitude shift keying (ASK)backscattered signal. In further embodiments, the backscattered signal differs primarily in phase between the first state and the second state. This yields a phase shift keying (PSK) backscattered signal. It should be understood that more than two magnitude states may be employed, thus yielding a pulse amplitude modulated (PAM) backscattered signal. In some embodiments, the impedances of the loads attached to the terminals of the antenna can be chosen to achieve pulse shaping (e.g., to reduce spectral emissions). It should further be understood that more than two phase states, such as M states, may be employed, thus yielding an M-ary PSK backscattered signal. In still further embodiments, the impedances of the loads attached to the terminals of the antenna are chosen to affect both the magnitude and the phase of the backscattered signals in each of several states. In such embodiments, a quadrature amplitude modulation (QAM) backscattered signal may be produced. In some embodiments, the antenna may be switched between two or more loads at two or more different frequencies. This yields a frequency shift keying (FSK) backscattered signal.

[0051] In some examples the backscatter device 110 may provide backscatter signals - such as backscatter signal 116, backscatter signal 118, and / or backscatter signal 120 - compatible with the OFDM standard and / or technique. This may be achieved by modulating with more than one subcarrier frequency at the same time. Each subcarrier may in turn be modulated with ASK, PAM, PSK, or QAM to form the OFDM backscattered signal, such as backscatter signal 116, backscatter signal 118, and / or backscatter signal 120.

[0052] By opening and closing the modulating switch in a time varying pattern, the scattering or reflectivity' will be time varying, and thus information may be conveyed by the scattered or reflected signal. In some embodiments, the modulating switch is opened and closed once for each transmitted symbol. The rate of this time varying pattern may then be referred to as the symbol rate of the backscattered signal. The symbol rate is the rate at which the modulator changes its impedance state to convey different pieces of information (e.g., groups of one or more bits). It should be understood that circuits or structures other than a switch may be used to change the impedance state of the load connected to the antenna 112. Such devices as a PIN diode, a varactor diode, a field effect transistor, a bipolar transistor, or circuit combinations of these elements may also be used to change the impedance state of the load coupled to antenna 112. In examples described herein, an RF switch may be used.

[0053] The backscatter device 110 may include a modulator that may function to modulate the backscatter of the carrier signal 114. e.g.. to switch an impedance of the load coupled to antenna 112 from a non-reflecting to a reflecting state. The backscatter device 110 may also provide one or more subcarrier frequencies. In some examples, the subcarrier frequencies may be provided, for example, by one or more oscillators. The switching or modulating action ofthe backscatter device 110 may mix the subcarrier frequency or frequencies with the carrier frequency or frequencies of the carrier signal 114 to adjust one or more frequency components of the backscatter signals. In this manner, the backscatter signals, such as backscatter signal 116, backscatter signal 118, and / or backscatter signal 120, may each include a respective bandpass signal component having a predetermined frequency range, for example a frequency range specified by a wireless communication standard and / or a channel of a wireless communication standard.

[0054] Examples of backscatter devices described herein, including the backscatter device 110 of FIG. 1, may have parameters selected to produce frequency components corresponding to at least one band-pass signal in the frequency spectrum of the scattered or reflected signal. These frequency components may be select to be compatible with a band-pass signal expected by a wireless communication device (e.g., any or all of the wireless communication devices of FIG. 1) such that the wireless communication device will accept and properly decode the transmitted backscattered signal. The transmitted backscattered signal may contain other frequency components that are outside of the desired band-pass signal but these components may be out-of-band with respect to the communication signal and thus discarded by the receiving wireless communication device.

[0055] The wireless communication devices of FIG. 1, such as wireless communication device 106 and optionally wireless communication device 122 and wireless communication device 126, may accordingly receive one or more backscatter signals, such as backscatter signal 116, backscatter signal 118, and / or backscatter signal 120, at the antenna 108. While one antenna is shown for each wireless communication device, multiple antennas per device may also be used. The wireless communication device 106, wireless communication device 122, and / or wireless communication device 126 may be implemented using any device capable of wireless communication, including but not limited to, a cellular telephone, computer, server, router, laptop, tablet, wearable device, watch, smartphone, smartspeaker, earbud, appliance, or vehicle (e.g., automobile, or airplane). The wireless communication device 106, wireless communication device 122, and / or wireless communication device 126 may communicate (e.g. include hardware and / or firmware and software for) using a particular protocol for a wireless communication signal (e.g., OFDM, Bluetooth Low Energy, Bluetooth Smart, Wi-Fi, CDMA, TDMA). The backscatter device 110 may provide multiple backscatter signals - e.g., backscatter signal 116, backscatter signal 118. and backscatter signal 120 - formatted in accordance with the wireless communication protocol expected by one or more of the wireless communication devices. In this manner, no further software, firmware, or hardware may be used for the wireless communication device 106, wireless communicationdevice 122, and / or wireless communication device 126 to receive and decode the backscatter signals than is used for the wireless communication device 106, wireless communication device 122, and / or wireless communication device 126 to receive and decode received signals from other sources that are formatted in accordance with the wireless communication protocol.

[0056] The wireless communication device 106, wireless communication device 122, and / or wireless communication device 126 may employ a frequency shift keying (FSK) or Gaussian frequency shift keying (GFSK) standard having at least one or more specified frequency deviations, one or more specified channel center frequencies, and one or more specified symbol rates. In some examples, the aforementioned FSK or GFSK standard is that of the Bluetooth Low Energy specification as defined by the Bluetooth Special Interest Group (SIG). Accordingly, in some examples the backscatter device 110 may provide one or more backscatter signals compatible with the FSK or GFSK standard employed by the wireless communication device 106, wireless communication device 122, and / or wireless communication device 126.

[0057] The wireless communication device 106, wireless communication device 122, and / or wireless communication device 126 may employ a phase shift keying (PSK) standard. Accordingly, in some examples the backscatter device 110 may provide one or more backscatter signals compatible with the PSK standard. It should be appreciated that the PSK signal so generated may use two distinct phases to encode a symbol or a bit, or it may alternatively have more than two distinct phases to encode a symbol or a group of bits as in M-ary PSK.

[0058] The wireless communication device 106, wireless communication device 122, and / or wireless communication device 126 may employ an amplitude shift keying (ASK) standard. Accordingly, in some examples the backscatter device 110 may provide backscatter signals compatible with the ASK standard. It should be appreciated that the ASK signal so generated may use two distinct amplitudes to encode a symbol or a bit, or it may alternatively have more than two distinct amplitudes to encode a symbol or a group of bits as in pulse amplitude modulation (PAM).

[0059] The wireless communication device 106, wireless communication device 122, and / or wireless communication device 126 may employ a quadrature amplitude modulation (QAM) standard. Accordingly, in some examples the backscatter device 110 may provide multiple backscatter signals compatible with the QAM standard. It should be appreciated that the QAMsignal may have more than two distinct amplitudes and phase combinations to encode a symbol or a group of bits, as in M-ary QAM.

[0060] The wireless communication device 106, wireless communication device 122, and / or wireless communication device 126 may employ an orthogonal frequency division multiplexing (OFDM) standard and / or technique. Accordingly, in some examples the backscatter device 110 may provide one or more backscatter signals - e.g., backscatter signal 116, backscatter signal 118. and backscatter signal 120 - compatible with the OFDM standard and / or technique. This may be achieved by modulating the backscatter signal 116 with more than one subcarrier frequency at the same time. Each subcarrier may in turn be modulated with ASK, PAM, PSK, or QAM to form the OFDM backscattered signal.

[0061] While FIG. 1 depicts one backscatter device 110, the system may include more than one backscatter device, and multiple backscatter devices may be in communication with the wireless communication device 106, wireless communication device 122, and / or wireless communication device 126 using signals backscattered from the signal source 102. Moreover, while FIG. 1 depicts one signal source 102, in some examples, the system may include more than one signal source.

[0062] Accordingly, in some examples, during operation, backscatter devices described herein may be utilized to generate simultaneous data streams on multiple channels for transmission to a single receiving device (e.g., a single wireless communication device). This may reduce a time for the receiver to find and / or pair with the backscatter device.

[0063] Bluetooth receivers generally use a round-robin or pseudo-random sequence to hop among multiple channels (consider n number of channels in some examples) using a single receiver. For example, the wireless communication device 106 may have a channel hopping sequence. In some examples, the wireless communication device 106 may include a memory or other computer readable media which may store the channel hopping sequence. The channel hopping sequence may specify different channels (e.g., frequency ranges) and an order in which the wireless communication device 106 may receive from each channel. For example, a channel hopping sequence which may be used by wireless communication device 106 sequence may be - Channel A, Channel B, Channel C. .... Channel #n, Channel A, Channel. B, Channel C. .... Channel #«, etc.

[0064] In this manner, examples of wireless communication devices described herein, such as wireless communication device 106, may receive only a single channel at a time. The wireless communication device 106 may cycle among channels until it finds the one used by a transmitting device (e.g., backscatter device 110). When the transmitting device istransmiting on only a single channel, on average the wireless communication device 106 must hop across n / 2 channels to find the transmission being sent by the backscatter device 110 and the average time to find the backscatter device 110 would be n / 2 time units. However, in examples described herein the backscatter device 110 may generate simultaneous data streams on multiple channels - e.g., backscatter signal 116, backscatter signal 118, and backscatter signal 120. In some examples, the data encoded in each channel may be the same. The transmission on multiple channels may reduce the time required for the wireless communication device (e.g., wireless communication device 106) to find the backscatter device 110. For example if the backscatter device 110 transmits on three channels simultaneously, the time to establish communication is reduced to n / 6 time units on average.

[0065] In some examples, during operation, backscatter devices described herein may be utilized to generate simultaneous data streams on multiple channels for transmission to multiple receiving devices (e.g., multiple wireless communication devices). This may allow multiple receiving devices to pair with a transmitting device (e.g., backscatter device 110 may pair with wireless communication device 106, wireless communication device 122, and wireless communication device 126).

[0066] Each wireless receiving device may have its own round-robin and / or pseudo-ransom hopping sequence. For example, the wireless communication device 106 may have a particular channel hopping sequence. The wireless communication device 122 may have a channel hopping sequence. The wireless communication device 126 may have a channel hopping sequence. The channel hopping sequences of the wireless communication device 106, wireless communication device 122 and / or wireless communication device 126 may generally be different and / or may be executed at different times. For example, the wireless communication device 106 may have a channel hopping sequence Channel A, Channel B, Channel C, .... Channel #n, Channel A, Channel B, Channel C, .... Channel #n, and so on. The wireless communication device 122 may have a same channel hopping sequence, but may be listening on Channel C during a time wireless communication device 106 is listening on Channel A. In some examples, the wireless communication device 122 may have a different channel hopping sequence, such as Channel B, Channel D. Channel C, Channel E, and so on. In an analogous manner, the wireless communication device 126 may have a different channel hopping sequence and / or a same channel hopping sequence executed at a different time.

[0067] Accordingly, the wireless communication device 106. wireless communication device 122, and wireless communication device 126, which may each be implemented as Bluetooth receivers, hop among multiple channels, each following its own round-robin or pseudo-random sequence. The backscatter device 110, which may be implemented as anOFDM backscatter tag, transmits multiple data streams simultaneously on multiple channels (e.g., backscatter signal 116, backscatter signal 118, and backscatter signal 120), allowing the backscatter device 110 to communicate with multiple receivers simultaneously (e.g., wireless communication device 106, wireless communication device 122, and wireless communication device 126). Accordingly, multiple receiving devices may pair with a single transmitting device in examples described herein. For example, the wireless communication device 106, wireless communication device 122, and wireless communication device 126 may each pair with backscatter device 110.

[0068] To continue communication after pairing, the backscatter device 110 may in some examples follow multiple receiver hopping sequences at the same time. For example, each of the backscatter signal 116, backscatter signal 118, and backscatter signal 120 may hop in accordance with the channel hopping sequence of their paired receiving device. For example, the backscatter device 110 may generate the backscatter signal 116 for the wireless communication device 106. The backscatter device 110 may generate the backscatter signal 118 for the wireless communication device 122. The backscatter device 110 may generate the backscatter signal 120 for the wireless communication device 126. The backscatter device 110 may allocate the data stream to be transmitted to each device in accordance with the channel hopping sequence of that device. For example, when wireless communication device 106 hops from Channel A to Channel B, and wireless communication device 122 hops from Channel B to Channel C, and wireless communication device 126 hops from Channel C to Channel D, the backscatter device 110 may re-allocate the data stream that is transmitted on each channel to follow the frequency hops made by the receivers. In some examples, the hopping sequence used by each receiving wireless communication device may be a predetermined round-robin or pseudo-random sequence. The hopping sequence used by each of the receiving devices may be stored in a memory’ of or accessible to the backscatter device 110.

[0069] FIG. 2 is a schematic illustration of a backscatter device arranged in accordance with examples described herein. The backscatter device 200 may include packetizer 210, packetizer 212, and packetizer 214. The packetizer 210 may receive data stream 204, the packetizer 212 may receive data stream 206, and the packetizer 214 may receive data stream 208. The backscatter device 200 may include packet manager 216. The packetizers provide their output to packet manager 216. The packet manager 216 may be coupled to transform block 220. Outputs of the packet manager 216 may be provided as inputs to transform block 220. The transform block 220 may have multiple input bins, including bin 222 and bin 224 shown in FIG. 2. The transform block 220 may be coupled to an optional delta-sigmamodulator 228. Outputs of the transform block 220 may be provided as inputs to optional delta-sigma modulator 228. The backscatter device 200 may include a backscatter modulator 230. Outputs of the transform block 220 may be provided to the backscatter modulator 230, which may be through intervening components such as the optional delta-sigma modulator 228. The backscatter modulator 230 may include switch 236 and impedances 238. The backscatter modulator 230 may generate backscatter signals described herein, transmitted through antenna 240.

[0070] The components of FIG. 2 are exemplary. Additional, fewer, or different components may be used in other examples. For example, although three data streams and three packetizers are shown in FIG. 2, any number may be present in other examples, including two or more than three.

[0071] The backscatter device 200 of FIG. 2 may be used to implement and / or may be implemented by backscatter devices described herein. For example, the backscatter device 200 may be used to implement and / or may be implemented by backscatter device 110 of FIG. 1. The backscatter device 200 may accordingly be used to generate backscatter signals described herein, such as the backscatter signal 116, backscatter signal 118, and backscatter signal 120 of FIG. 1. The antenna 240 may be used to implement and / or may be implemented by the antenna 112 of FIG. 1.

[0072] The backscatter device 200 of FIG. 2 generally utilizes a digital backscatter architecture (e.g., the transform block 220, and backscatter modulator 230 may be digital components that may receive and / or manipulate digital signals). The backscatter device 200 of FIG. 2 may utilize an OFDM architecture in that the transform block 220 may provide a digital baseband OFDM signal to the backscatter modulator 230 (e.g., directly or through one or more intervening components).

[0073] Examples of backscatter devices described herein may receive one or more data streams, such as by receiving from another device, generating, and / or otherwise obtaining data. A data stream refers to data. The data stream may be a serial arrangement of data which may be used to generate a time-based backscatter signal as described herein. Any of a variety of data may be used in data streams to encode into backscatter signals described herein. Examples of data include sensor data, audio data, video data, image data, navigation data and / or text data. The data may be digital data and / or analog data. The data streams may be provided to the backscatter device 200 using one or more wired or wireless interfaces. In some examples, data for one or more data streams may be generated by the backscatter device 200 itself.

[0074] Three data streams are shown in FIG. 2 - data stream 204, data stream 206, and data stream 208 - although any number may be used, including two or more than three. In some examples and / or at some times during operation, multiple data streams may contain the same data. In other examples and / or at other times during operation, one or more of the data streams may contain different data. The data for each stream may originate from a same source in some examples, The data for multiple data stream may originate from a different source in some examples, Multiple data streams may be for transmission to a same receiving device in some examples, Each data stream may be for transmission to a different receiving device in some examples. The data streams may be independent and / or simultaneous. For example, the data in each of data stream 204. data stream 206, and data stream 208 may be independent of the data in the other streams. In some examples, data from at least two of data stream 204, data stream 206, and data stream 208 may be received simultaneously by the backscatter device 200\. Data from any one of the streams may be received by the backscatter device 200 while data from one or more other streams is also being received. The data streams may include payload data for advertising packets, e.g., BLE advertising packets.

[0075] Examples of backscatter devices described herein may include one or more packetizers, such as packetizer 210, packetizer 212. and packetizer 214 of FIG. 2. A packetizer generally refers to software, firmware, and / or hardware (e.g., circuitry) which may segment a data stream into packets. A packetizer may format the data in accordance with one or more communication protocols, such as Bluetooth (e.g. BLE) and / or WiFi protocols. Packetizers may add data to form packets, such as one or more headers or other data to form a packet. In some examples, the packetizers may add one or more cyclical redundancy check (CRC) bits and / or may perform data whitening (e.g., channel-specific data whitening) for each packet. The packetizing operations may occur in accordance with the Bluetooth specification. Accordingly, data stream 204 may be input to packetizer 210. The packetizer 210 may output packets including data from data stream 204. Data stream 206 may be input to packetizer 212. The packetizer 212 may output packets including data from data stream 206. Data stream 208 may be input to packetizer 214. The packetizer 214 may output packets including data from data stream 208. The packets may represent digital signals. In the example of FIG. 2 the packetizers. packetizer 212, packetizer 214, and packet manager 216 may operate in accordance with the BLE protocol, and may generate BLE packets. The BLE packets may encode data from the data streams.

[0076] Backscatter devices described herein may include a packet manager, such as packet manager 216 of FIG. 2. The packet manager 216 may route packets to particular channels. The packet manager 216 may be implemented using software, firmware, and / or hardware(e.g.. circuitry). The packet manager 216 may, for example, include one or more switches to route packets to a selected input of the transform block 220. The packet manager 21 may in some examples route a packet based on one or more bits in a packet, such as a header. The packet manager 216 may in some examples route a packet based on a source of the packet - e.g., based on which packetizer - packetizers 210. packetizer 212. and / or packetizer 214 - provided the packet. In some examples, the packet manager 216 may route a packet based on content of the packet. Other routing strategies may be used in other examples.

[0077] In some examples, the packet manager 216 may simultaneously clock out packets destined for three Bluetooth channels (e.g., the three Bluetooth advertising channels) at a symbol rate corresponding to the Bluetooth specification (e.g., 1Mbps) into bins of an IFFT.

[0078] Examples of backscatter devices described herein may accordingly include a transform, such as transform block 220. The transform may convert packetized provided by a packet manager (e.g., by packet manager 216) to time domain signals. The time domain signals output from the transform block 220 represent a superposition of data corresponding to different channels carrying the input data streams. For example, in the example of FIG. 2, the transform block 220 may output time domain signals corresponding to a first channel (e.g., a first Bluetooth channel) carrying data stream 204, a second channel (e.g., a second Bluetooth channel) carrying data stream 206, and a third channel (e.g., a third Bluetooth channel) carrying data stream 208. The time domain signals output from the transform block 220 may correspond with in-phase (I) and quadrature (Q) values, such as I and Q values for an OFDM baseband signal.

[0079] Accordingly, the transform block 220 may be implemented using an IFFT which outputs time domain signals that correspond with the superposition of independent data streams carried by different Bluetooth channels. The time domain signals may have an in- phase, I, and quadrature, Q, component. Both components can be used to provide more control of the backscattered signal spectrum, for example by allowing for single-sideband backscatter. In some implementations, providing both I and Q could reduce the size of the IFFT used.

[0080] Examples of transform blocks which may be used to implement transform block 220 or other transforms described herein include one or more Fourier transforms, one or more inverse Fourier transforms (e.g., inverse fast Fourier transforms (IFFTs)), one or more pruned and / or sparse transforms, one or more look-up tables, sine-look-up tables, and / or numerically controlled oscillators (NCOs), such as one or more NCOs based on a sine look-up table. A pruned transform, may refer to an IFFT designed using pruning, which generally refers toreducing the complexity of the IFFT block by selectively eliminating some of the inputs or some of the outputs and thus reducing the number of computations to be computed in achieving the IFFT. An IFFT designed using pruning may be referred to as a sparse IFFT. In some examples, a transform may utilize one or more discrete Fourier transform approaches such as the inverse Goertzel algorithm. In some examples, the transform block 220 may include two or more numerically-controlled oscillators which may provide desired frequency components of an OFDM signal to be transmitted. In some examples, the transform block 220 may include one or more look-up tables including pre-computed time domain sequences, which may be indexed by groups of symbols. Accordingly, the transform block 220 may receive packets, and provide time domain signals in accordance with a look-up table. In some examples, the look-up tables may include a sparse group of pre-computed time domain sequences indexed by groups of symbols. The number of time domain sequences may be less than a number of possible groups of symbols. Accordingly, some approximation may be made by backscatter devices described herein, such that multiple input symbols may be associated with a same output time domain sequence. In this manner, the output may not be as accurate as possible, but may nonetheless be usable. In some examples, the use of one or more lookup tables and / or numerically controlled oscillators may generate OFDM subcarriers without a need for a complex and power hungry IFFT. Accordingly, an output of the transform, such as transform block 220 may be time domain signals corresponding to a sequence of digital values, and the digital values may correspond to symbol sequences. The symbol sequences may correspond to a digital baseband OFDM signal and may be multi-tone symbol sequences. Providing multi-tone symbol sequences for use in activating a switch described herein may allow a backscatter modulator to generate orthogonal subcarriers.

[0081] IFFTs, such as may be used to implement transform block 220, may generally be implemented in digital logic and may utilize multipliers and block memory for storing intermediate calculations as well as look-up tables for the complex exponential roots of unity, also known as twiddle factors. In some examples, a 128-point Radix-2 Buffered-Burst IFFT generated using the Intel Quartus Prime FPGA design software may be used, and may include multipliers, 2,000 bytes of RAM and over 3,000 logic elements. Other IFFTs, including other design software, multipliers, memory and logic elements may be used in other examples.

[0082] In some examples, a transform may have multiple inputs, with each input associated with a particular frequency or range of frequencies. For example, the transform block 220 of FIG. 2 may be an IFFT. and may have multiple frequency bins, including frequency bin 222 and frequency bin 224.

[0083] The packet manager 216 may arrange packetized data (e.g., symbols from packets) in parallel and input the packetized data into associated subcarrier frequency bins of the transform block 220 (e.g., which may be implemented using an N-point IFFT). Undesired subcarrier frequency bins may be set to zero. In some examples, the input to the IFFT may be symmetric, with the same inputs being applied to corresponding positive and negative frequency bins. In such examples, the frequency spectrum may be double sideband and an output of the transform block 220 may be a real-valued time domain signal. In some examples, the input to the transform block 220 may be asymmetric, with inputs only applied to the positive or negative frequency bins, the inputs being +1 or -1 for each bin. The inputs to the positive frequency bins are set to zero. In such examples, the output of the transform block 220 may be complex, including a real (I) and imaginary (Q) component. There may be multiple bits per each OFDM signal. Each sample will have its amplitude coded in one or more bits. In some examples, a length of a pulse may be indicative of an amplitude, for example.

[0084] When transmitting into Bluetooth channels, frequency bins of the transform block 220 (e.g., frequency bins of an IFFT) may correspond with the mark and space frequencies of the Bluetooth channels. IFFT Bins might correspond to the specific frequency shift keying (FSK) mark (‘ 1 ’) and space (‘0’) frequencies for BLE channels in some examples. Generally, a mark frequency refers to a frequency at which a BLE signal is transmitted corresponding to a bit set to ‘ 1’. A space frequency refers to a frequency at which a BLE signal is transmitted corresponding to a bit set to ‘0.’ Modulation may be performed in some examples by routing the digital outputs from the packet manager 216 to two IFFT bins corresponding to the mark and space frequencies of a specific BLE channel. Inverters might be placed on IFFT bin corresponding to the space frequency to achieve this. In the example of FIG. 2, two input frequency bins may be associated with each of multiple Bluetooth channels. For example, the bin 222 and bin 224 may be associated with Channel A. Two other bins may be associated with Channel B. Additional bins may be provided for other channels. The bin 222 may represent the mark frequency of Channel A. The bin 224 may represent the space frequency of Channel B. An inverter may be provided at the input to IFFT bins corresponding to the space frequency of the respective channel.

[0085] Generally, bits forming each packet may be input into two IFFT bins, one of which via an inverter, in order implement frequency shift keying (FSK) modulation per the BLE specification. If a given bit is ‘ 1 ’ it enables the channel-specific subcarrier corresponding to a logical ‘ 1’ while turning off the subcarrier for a logical ‘O’, and vice versa if the bit is ‘O’. The specific pair of IFFT bins employed to transmit data within a given channel (for example,BLE channel 37, 38, or 39) may be selected to correspond to the FSK frequency deviation required by the BLE specification for each channel (for example, a frequency deviation of 370 kHz to 500 kHz).

[0086] Note that any number of Bluetooth channels (e.g., anu number of advertising channels) up to one-half of the number of points int he IFFT (2V) could be supported using this approach. However, the present version of the Bluetooth specification specifies only three advertising channels.

[0087] An N-point IFFT may be calculated by transform block 220 to generate a timedomain IFFT output signal. The IFFT output signal may be clocked out at a rate of N * Kos * 1 Mbps, where Kos is an optional oversampling parameter. To reduce quantization noise, an optional delta sigma modulator (DSM) can be used (e.g.. delta-sigma modulator 226). in which case Kos > 1. If a DSM is not used, the IFFT output may be truncated to one-bit amplitude for both the in-phase (I) and quadrature (Q) components to form a single-sideband (SSB) backscatter signal. If a DSM is used, the IFFT output may be converted to pulse trains with one-bit amplitude resolution. The one-bit truncated I and Q signals may be used to actuate a two-bit RF switch that modulates the impedance presented to the device’s antenna among four selected impedance states. By modulating the impedance presented to the device’s antenna, a backscatter signal may be produced when the antenna is illuminated by an external carrier. It should be appreciated that if a double-sideband (DSB) backscatter signal is acceptable, only the in-phase (I) bit may be utilized, which may eliminate or reduce the need for one RF switch by presenting only two impedance states to the antenna.

[0088] In some examples, accordingly, backscatter devices described herein may include a pulse-density modulator. The pulse-density modulator may receive the time domain signals from the transform, such as from transform block 220, and may provide a modulated output. Examples of pulse-density modulators which may be used include delta-sigma modulators and / or sigma-delta modulators, such as optional delta-sigma modulator 226 of FIG. 2. The output of the pulse-density modulator may be provided to a backscatter modulator, such as backscatter modulator 230. In some examples, the output of the pulse-density modulator may be filtered, e.g., by an analog filter, such as a low pass filter, and then provided to the backscatter modulator 230. In some examples, an output spectrum from the pulse-density modulator (e.g., delta-sigma modulator 226) may include frequency components which are the desired frequency components of an OFDM signal to be transmitted.

[0089] Examples of backscatter devices described herein may utilize digital circuitry, and in some examples may utilize exclusively digital circuitry from receipt of the data stream(s)to be encoded through the digital signal provided to a backscatter modulator. For example, the transform used in a backscatter device may be implemented using digital circuitry. For example, the transform block 220 may be implemented using digital circuitry', such as implemented using one or more field programmable gate array (FPGA) circuits, one or more application specific integrated circuits (ASICs), complex programmable logic devices (CPLDs), and / or microcontroller units (MCUs).

[0090] Examples of backscatter devices described herein may include a backscatter modulator, such as backscatter modulator 230 of FIG. 2. The backscatter modulator 230 may include an impedance digital-to-analog converter (DAC). The backscatter modulator 230 may be implemented, for example, using one or more RF switches used to switch between different discrete impedance states, such as switch 236 of FIG. 2. The RF switches may be used to couple selected impedance(s) to an antenna of the backscatter device, such as impedances 238 of FIG. 2. The switches and impedances may impact the frequency spectrum of the backscattered signal. The backscatter modulator 230 may include one or more switches and one or more impedance elements (e.g., discrete impedances), such that the backscatter modulator 230 may receive control signals (e.g., time domain signals from the transform block 220 and / or delta-sigma modulator 228) and the switches (e.g., switch 236) may respond to the digital signal by selecting one or more of the impedance elements. In some examples, the backscatter modulator may have as few as one-bit resolution (e.g., utilizing two switched impedance states) yet still generate multi-tone OFDM signals in a backscatter signal. Other number of impedance states may also be used, such as 3. 4, 5, 6. 7, or 8 impedance states. In the example of FIG. 2, the impedances 238 include four impedances - Zo, Zi, Z2, and Z3. In some examples, a single pole-single throw (SPST) switch can be used to implement switch 236 and may provide 1-bit of impedance resolution. At a constant switching rate, a SPST switch can provide ON-OFF keying (OOK) or binary’ phase-shift keying (BPSK) modulations. However, in some examples, the switching rate of the SPST is modulated such that one of M different switching rates is selected for each symbol period, then M-ary frequency shift keying (FSK) modulation and / or phase modulation can be implemented. For example, a first switching rate (e.g., rate of switching between different impedances) may be used for one symbol of digital values provided from the transform block 220. A second switching rate (e.g., a different rate of switching between the impedances) may be used for another symbol of digital values provided from the transform block 220. In some examples, four or more impedance states may be employed to generate a single sideband backscatter modulation, wherein either the upper or lower sideband of the backscatter signal is preferentially- generated, and the unwanted sideband is suppressed.

[0091] Accordingly, examples of backscatter devices described herein may include a backscatter modulator having one or more switches, such as switch 236. The switches may be implemented using one or more RF switches, such as one or more digital CMOS RF switches, such as one or more digitally-controlled radio frequency (RF) switches. The switches may be coupled to the transform block 220 and may be controlled in accordance with a sequence of time domain signals provided by the transform block 220. The switches may, responsive to a control signal (e.g., the time domain signals provided by the transform block 220), couple selected impedance(s) to an antenna, such as antenna 240. By coupling the selected impedances to an antenna in accordance with the control signals, the backscatter device 200 may backscatter an incident signal (e.g., the carrier signal 114 of FIG. 1) and transmit the data stream 204, data stream 206, and data stream 208 encoded in backscattered signals (e.g., backscatter signal 116, backscatter signal 118, and backscatter signal 120 of FIG. 1). Other RF switch technologies may be used to implement switches described herein, including but not limited to silicon-on-insulator, PIN diode switches, MEMS switches, and GaAs or GaN switches.

[0092] The transform block 220 may provide control signal(s) to one or more switches of the backscatter modulator 230. A number of control signals may be related to a number of available switch states (e g., number of impedance values which may be coupled to an antenna). For an RF switch with S switch states, a number of control signals c may be used where c=log2(S). To obtain the appropriate number of control signals, an output of the transform block 220 may be truncated to obtain a number of bits equal to the number of desired control signals. For example, the backscatter modulator 230 may include a single pole-four throw (SP4T) switch which may have four switch states. The backscatter modulator 230 may utilize two control bits. Accordingly, the most significant bit (MSB) from each of the I and Q signals may be used as control bits to actuate a switch among its four possible states.

[0093] Examples of backscatter devices may accordingly include one or more impedances, such as impedances 238 of FIG. 2, which may be included in and / or coupled to the backscatter modulator, such as backscatter modulator 230 of FIG. 2. The impedances may be implemented using one or more digitally-controlled capacitors (DTCs) and / or one or more components having an impedance (e.g., one or more inductors, capacitors, and / or resistances). The impedances may be positioned to be selected by a switch, and the selected impedances coupled by the switch to an antenna, such as antenna 112 of FIG. 1.

[0094] Examples of backscatter devices may include one or more antennas. An antenna may be coupled to the backscatter modulator 230 of FIG. 2. A carrier signal may be incident onthe antenna of the backscatter device (e.g., on the antenna 112 of FIG. 1 and / or an antenna of the backscatter device 200 of FIG. 2). Examples of carrier signals which may be incident on the antenna include those described with reference to FIG. 1. For example, the incident signal may include a continuous wave signal and / or a modulated signal. By selecting impedances to couple to the backscatter device antenna, the backscatter device 200 may encode the data stream 204, data stream 206, and / or data stream 208 into backscattered signals.

[0095] FIG. 3A is a schematic illustration of BLE channels arranged in accordance with examples described herein. The BLE channels 304 depicts channel numbers across frequencies. In the BLE protocol, channels 1-36 may be referred to as data channels, and channels 37, 38, and 39 may be referred to as advertising channels. Backscatter devices described herein may be used to generate simultaneous backscattered signals in multiple BLE channels. In particular examples, backscatter signals are generated in each of the three advertising channels - channels 37, 38, and 39.

[0096] Generally , advertising channels may also carry data, however, these are the channels typically used for BLE devices to broadcast their presence and / or pair transmitting devices with receiving devices. The BLE channel 37 may in some examples be at 2400 MHz. The BLE channel 38 may in some examples be at 2426 MHz. The BLE channel 39 may in some examples be at 2480 MHz. Accordingly, the channel 37 frequency range 306 may be between 2400 MHz and 2402 MHz as shown in FIG. 3A. Generally, the range between 2400 MHz and 2401 MHz may be used for transmission of a ‘0’ in some examples, while the range between 2401 MHz and 2402 MHz may be used for transmission of a ‘1 ’.

[0097] FIG. 3B is a schematic illustration of a transmission of a ‘0’ in BLE channel 37 arranged in accordance with examples described herein. FIG. 3B illustrates an example of the frequency spectrum associated with BLE channel 37 (e.g., between 2400 MHz and 2402 MHz). During transmission of a ‘O’, backscatter devices described herein may backscatter energy into the frequency range between 2400 MHz and 2401 MHz. Energy peak 310 is shown in FIG. 3B. which may be an energy peak indicative of a ‘O’.

[0098] FIG. 3C is a schematic illustration of a transmission of a ‘1 ’ in BLE channel 37 arranged in accordance with examples described herein. FIG. 3C illustrates an example of the frequency spectrum associated with BLE channel 37 (e.g.. between 2400 MHz and 2402 MHz). During transmission of a ‘ 1 ’, backscatter devices described herein may backscatter energy into the frequency range between 2401 MHz and 2402 MHz. Energy peak 312 is shown in FIG. 3C, which may be an energy peak indicative of a ‘1 ’.

[0099] During operation of examples described herein, an incident carrier signal may be backscattered into multiple channels. Multiple data streams may be received by a backscatter device. For example, the backscatter device 110 of FIG. 1 and / or the backscatter device 200 of FIG. 2 may receive multiple data streams. In the example of FIG. 2, the backscatter device 200 may receive data stream 204, data stream 206, and data stream 208. While three data streams are described, two or more data streams may be used in other examples.

[0100] Each data stream received by a backscatter device may be packetized into a respective set of packets arranged in accordance with a wireless communication protocol, such as one or more Bluetooth packets. For example, the data stream 204 may be packetized by packetizer 210 into a first set of Bluetooth packets. The data stream 206 may be packetized by packetizer 212 into a second set of Bluetooth packets. The data stream 208 may be packetized by packetizer 214 into a third set of Bluetooth packets.

[0101] The backscatter device, such as backscatter device 110 and / or backscatter device 200 may also receive an incident carrier signal. For example, the carrier signal 114 may be incident on backscatter device 110 of FIG. 1.

[0102] The backscatter device may backscatter the incident carrier signal with a backscatter modulator such that the first set of Bluetooth packets is backscattered in a first Bluetooth channel, the second set of Bluetooth packets is backscattered in a second Bluetooth channel, and the third set of Bluetooth packets is backscattered in a third Bluetooth channel. For example, the backscatter device 200 may backscatter incident carrier signal 114 such that the first set of Bluetooth packets, generated by packetizer 210, is backscattered into a first Bluetooth channel (e.g., Channel 37), the second set of Bluetooth packets, generated by packetizer 212, is backscattered into a second Bluetooth channel (e.g., Channel 38). and the third set of Bluetooth packets, generated by packetizer 214, is backscattered into a third Bluetooth channel (e.g., Channel 39).

[0103] In order to backscatter the incident carrier signal, the backscatter device may provide the Bluetooth packets generated by its packetizers to a transform block to generate time domain signals. For example, the backscatter device 200 may provide the Bluetooth packets generated by packetizer 210, packetizer 212, and packetizer 214 to the transform block 220. In some examples, respective frequency bins of the transform block (e.g., frequency bins of the transform block 220, which may be frequency bins of an IFFT), may correspond to the first Bluetooth channel, the second Bluetooth channel, and the third Bluetooth channel.

[0104] The transform block 220 may generate time domain signals. The time domain signals may represent a superposition of data corresponding to a first Bluetooth channel carrying thefirst set of Bluetooth packets, a second Bluetooth channel carrying the second set of Bluetooth packets, and a third Bluetooth channel carrying the third set of Bluetooth packets.

[0105] Accordingly, the backscatter device may backscatter Bluetooth packets into multiple Bluetooth channels simultaneously. In some examples, the multiple Bluetooth channels are Bluetooth advertising channels (e.g., Channels 37, 38, and / or 39).

[0106] The backscattering may be performed by a backscatter modulator, such as the backscatter modulator 230 of FIG. 2. The backscatter modulator 230 may couple selective impedances to an antenna in accordance with the time domain signals output from a transform block, such as output from transform block 220. Those time domain signals may in some examples represent an in-phase, I, and quadrature component, Q.

[0107] In this manner, backscatter devices may backscatter an incident carrier signal into multiple Bluetooth channels at least in part simultaneously. This simultaneous transmission of backscattered packets into multiple channels may allow for a variety of advantageous use cases.

[0108] In some examples, the backscatter device may receive three independent data streams carrying the same data. Accordingly, the same data may be backscattered into the three channels. This may allow a single receiving device to pair more quickly with the backscatter device. For example, the wireless communication device 106 of FIG. 1 may pair with the backscatter device 110 when the wireless communication device 106 hops to a first one of the first Bluetooth channel, the second Bluetooth channel, or the third Bluetooth channel being backscattered into by the backscatter device 110.

[0109] In some examples, the simultaneous transmission of backscattered packets into multiple channels may allow a backscatter device to pair with multiple receiving devices simultaneously. Note that this overcomes a significant limitation of Bluetooth devices having the ability to only transmit and / or receive on a single channel. Such devices may only pair with one other device in some examples. However, in examples described herein, a backscatter device may provide backscatter signals on multiple channels. The backscatter device may accordingly pair with a receiving device on each channel. The backscatter device 110 of FIG. 1, for example, may pair with a first receiver on a first Bluetooth channel, a second receiver on a second Bluetooth channel, and a third receiver on a third Bluetooth channel. For example, the backscatter device 110 may pair with wireless communication device 106 on the Bluetooth channel associated with backscatter signal 116 (e.g., Channel 37). The backscatter device 110 may pair with wireless communication device 122 on the Bluetooth channel associated with backscatter signal 118 (e.g., Channel 38). The backscatterdevice 110 may pair with wireless communication device 126 on the Bluetooth channel associated with backscatter signal 120 (e.g., Channel 39).

[0110] Once a backscatter device described herein pairs with one or more receiving devices, the backscatter device may continue to backscatter into Bluetooth channels as specified by a hopping sequence for the paired receiving device. For example, the backscatter device 110 may backscatter additional packets of the backscatter signal 116 into various channels over time in accordance with a hopping sequence used by the wireless communication device 106. The backscatter device 110 may backscatter additional packets of the backscatter signal 118 into various channels over time in accordance with a hopping sequence used by the wireless communication device 122. The backscatter device 110 may backscatter additional packets of the backscatter signal 120 into various channels over time in accordance with a hopping sequence used by the wireless communication device 126. These additional packets may continue to be transmit at least partially simultaneously in the three channels being utilized by the three receiving devices.

[0111] Another example advantage of devices and methods described herein may be the ability to generate BLE advertising packets in multiple channels using only a single carrier wave (CW) frequency in a carrier signal, such as carrier signal 114. Other backscatter based BLE devices may produce a single subcarrier frequency, thus requiring a different CW frequency for each transmitted BLE channel. As described herein, a single CW frequency may be used to generate BLE transmissions on multiple BLE channels. Furthermore, a single CW frequency may be used to generate multiple simultaneous BLE transmissions carrying different data packets to multiple BLE channels. For example, using systems and methods described herein, a single CW frequency may be used to generate three simultaneous, distinct BLE advertising packets destined for three different BLE channels, for example BLE channels 37, 38, and 39.

[0112] From the foregoing it will be appreciated that, although specific embodiments have been described herein for purposes of illustration, various modifications may be made while remaining with the scope of the claimed technology.

[0113] Examples described herein may refer to various components as “coupled” or signals as being “provided to” or “received from” certain components. It is to be understood that in some examples the components are directly coupled one to another, while in other examples the components are coupled with intervening components disposed between them. Similarly, signal may be provided directly to and / or received directly from the recited componentswithout intervening components, but also may be provided to and / or received from the certain components through intervening components.

Claims

CLAIMSWhat is claimed is:

1. A method comprising: receiving a plurality of data streams including a first data stream and a second data stream; receiving an incident carrier signal; packetizing the first data stream into a first set of Bluetooth packets; packetizing the second data stream into a second set of Bluetooth packets; backscattering the incident carrier signal with a backscatter modulator such that the first set of Bluetooth packets is backscattered in a first Bluetooth channel and the second set of Bluetooth packets is backscattered in a second Bluetooth channel.

2. The method of claim 1, wherein the plurality of data streams includes a third data stream, and the method further comprises: packetizing the third data stream into a third set of Bluetooth packets; and wherein said backscattering further includes backscattering the incident carrier signal with the backscatter modulator such that the third set of Bluetooth packets is backscattered in a third Bluetooth channel.

3. The method of claim 2, wherein the first Bluetooth channel, the second Bluetooth channel, and the third Bluetooth channel are each a Bluetooth advertising channel.

4. The method of claim 2, wherein the backscattering in the first Bluetooth channel, the second Bluetooth channel, and the third Bluetooth channel occurs, at least in part, simultaneously.

5. The method of claim 2, further comprising, providing the first set of Bluetooth packets, the second set of Bluetooth packets, and the third set of Bluetooth packets to a transform block to generate time domain signals.

6. The method of claim 5, wherein an output of the transform block comprises a superposition of data corresponding to a first Bluetooth channel carrying the first set of Bluetooth packets, a second Bluetooth channel carrying the second set of Bluetooth packets, and a third Bluetooth channel carry ing the third set of Bluetooth packets.

7. The method of claim 5, wherein said backscattering is based on the time domain signals.

8. The method of claim 5, wherein said backscattering comprises coupling selective impedances to an antenna in accordance with the time domain signals.

9. The method of claim 5, wherein the time domain signals represent an in-phase, I, and quadrature component, Q.

10. The method of claim 5, wherein frequency bins of the transform block correspond to the first Bluetooth channel, the second Bluetooth channel, and the third Bluetooth channel, respectively.

11. The method of claim 2, further comprising: pairing with a receiver when the receiver hops to a first one of the first Bluetooth channel, the second Bluetooth channel, or the third Bluetooth channel.

12. The method of claim 2, further comprising: pairing with a first receiver on the first Bluetooth channel; pairing with a second receiver on the second Bluetooth channel; and pairing with a third receiver on the third Bluetooth channel.

13. The method of claim 12, wherein the three data streams each contain different data from one another.

14. The method of claim 12, further comprising: backscattering additional packets of the first data stream into Bluetooth channels in accordance with a hopping sequence used by the first receiver; and backscattering additional packets of the second data stream into Bluetooth channels in accordance with a hopping sequence used by the second receiver.

15. The method of claim 14, wherein said backscattering additional packets of the first data stream occurs at least partially simultaneously with said backscattering additional packets of the second data stream.

16. An apparatus comprising: a first packetizer configured to packetize a first data stream into a first set of Bluetooth packets; a second packetizer configured to packetize a second data stream into a second set of Bluetooth packets;a transform block configured to receive the first set of Bluetooth packets and the second set of Bluetooth packets and generate time domain signals representing a superposition of data corresponding to a first Bluetooth channel carrying the first set of Bluetooth packets and a second Bluetooth channel carrying the second set of Bluetooth packets; and a backscatter modulator configured to couple selected impedances to at least one antenna based on the time domain signals to transmit the first data stream in the first Bluetooth channel and the second data stream in the second Bluetooth channel.

17. The apparatus of claim 16, further comprising: a third packetizer configured to packetize a third data stream into a third set of Bluetooth packets; and wherein the transform block is further configured to receive the third set of Bluetooth packets, and wherein the superposition of data further corresponds to a third Bluetooth channel carrying the third set of Bluetooth packets and wherein the backscatter modulator is configured to couple selected impedances to at least one antenna to further transmit the third data stream in the third Bluetooth channel.

18. The apparatus of claim 17, wherein the backscatter modulator is configured to transmit the first data stream, the second data stream, and the third data stream at least in part simultaneously.

19. The apparatus of claim 17, wherein the first Bluetooth channel is channel 37, the second Bluetooth channel is channel 38, and the third Bluetooth channel is channel 39.

20. The apparatus of claim 16, further comprising a delta-sigma modulator coupled to an output of the transform block, the delta-signal modulator used to provide the time domain signals from the transform block to the backscatter modulator.

21. The apparatus of claim 17, further comprising a memory, the memory configured to store a hopping sequence for a first Bluetooth device, a second Bluetooth device, and a third Bluetooth device.

22. The apparatus of claim 21, the backscatter modulator configured to backscatter the first data stream in accordance with the hopping sequence for the first Bluetooth device and, at least partially simultaneously, to backscatter the second data stream in accordance with the hopping sequence for the second Bluetooth device.

23. The apparatus of claim 17, wherein the apparatus is configured to pair with a receiver on a first one of the first Bluetooth channel, the second Bluetooth channel, or the third Bluetooth channel hopped to by the receiver.

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