A backscattering method for arbitrary multi-frequency Bluetooth carriers

Abstract

The present invention relates to the technical field of backscatter communication, and discloses a backscatter method for any multi-frequency Bluetooth carrier, including: a carrier device can emit a carrier signal of multiple frequencies; a tag modulates tag data into the carrier signal to generate a backscatter signal; an edge device identifies the sequence number of a corresponding connection event through a data packet in a specific data channel, and sends the sequence number of the connection event to the tag, and the tag calculates the corresponding data channel sequence number according to the sequence number of the connection event, so that the tag can reflect the carrier signals of different data channels to a fixed channel; an identification field is provided in the data packet corresponding to the carrier signal and the backscatter signal, and the tag data is decoded based on the identification field content and the load content of the carrier signal and the backscatter signal. The tag in the present invention can accurately control the reflection channel, and support tag data transmission through the proposed encoding and decoding mechanism.

Description

Technical Field

[0001] The present invention relates to the technical field of backscatter communication, and in particular to a backscatter method for arbitrary multi-frequency Bluetooth carriers. Background Art

[0002] Backscatter communication technology aims to reduce the power consumption of data transmission. It reduces the deployment and maintenance costs of nodes and broadens the application scope of the Internet of Things. Backscatter technology has been successfully commercialized in the field of Radio Frequency Identification (RFID), but the further development of this technology faces challenges due to the high cost of its dedicated readers. Therefore, people have made great efforts to promote the compatibility of backscatter with commercial radios, such as WiFi, Bluetooth, and LTE.

[0003] WiFi backscatter technology (published in SIGCOMM in 2014) and FS-backscatter technology (published in SIGCOMM in 2016) use commercial WiFi to implement a general backscatter system; however, due to the use of packet-level modulation, their throughput is low. The prior art further proposed symbol-level (published in SenSys in 2016) and sample-level (published in NSDI in 2021) modulation schemes to achieve higher throughput. For Bluetooth communication technology, FreeRider technology (published in CONEXT in 2017) provides a redundant modulation scheme. Then, RBLE technology (published in INFOCOM in 2020) introduced a single-symbol modulation scheme with a low bit error rate (BER).

[0004] Although most existing technologies attempt to improve the throughput of ambient backscatter, they all use controlled carrier signals and cannot utilize carrier signals of arbitrary frequencies with arbitrary payload content. However, multi-frequency carrier signals are very common in real environments for at least the following two reasons:

[0005] First, single-frequency valid signals (such as WiFi signals) are usually transmitted on different frequency bands to avoid in-band interference from different access points. In this case, from the perspective of the backscatter tag, the environmental signal is composed of various single-frequency carrier signals in random frequency bands.

[0006] Secondly, due to frequency hopping design, many environmental signals have multiple frequencies in nature. For example, the Bluetooth protocol introduces adaptive frequency hopping (AFH) technology, which switches channels during transmission to overcome interference. LTE uplink uses different channels for different purposes.

[0007] Existing technologies cannot process carrier signals with arbitrary payload content and arbitrary frequencies because they face the following technical problems:

[0008] 1. Low carrier utilization. Simple processing of the carrier signal will result in uncontrolled distribution of the backscatter signal on different channels, resulting in low environmental utilization. In addition, the receiver in the current backscatter system cannot be synchronized with any channel, so the transmission of the backscatter signal on an unintended carrier is invalid.

[0009] 2. Decoding error. Bluetooth devices need to whiten data when sending and receiving data, and different channels have different whitening processing methods. When facing multi-frequency carriers, the actual content of each carrier signal will be different due to different whitening processing methods. The receiving device cannot decode the tag data when demodulating the backscattered signal corresponding to the carrier signal. Summary of the invention

[0010] In order to solve the problem of variable payload content and frequency of low-power Bluetooth carrier data packets in backscattering, the present invention provides a backscattering method for arbitrary multi-frequency Bluetooth carriers, designs a carrier channel calculation method so that the tag can accurately control the reflection channel, and proposes a coding and decoding mechanism to support the transmission of tag data.

[0011] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0012] A backscattering method for any multi-frequency Bluetooth carrier, wherein the backscattering system used includes a carrier device, an edge device, a tag, and a receiving device; the backscattering method specifically includes:

[0013] The carrier device can send out carrier signals of multiple frequencies; the carrier device sends a connection request on a broadcast channel and transmits data on multiple different data channels through carrier signals of corresponding frequencies;

[0014] The tag modulates the tag data into the carrier signal to generate a backscatter signal; the modulation process follows the codeword conversion mechanism, that is, the Bluetooth codeword in the carrier signal is reflected as another Bluetooth codeword; the edge device identifies the sequence number of the corresponding connection event through the data packet in the specific data channel, and sends the sequence number of the connection event to the tag, and the tag calculates the corresponding data channel sequence number according to the sequence number of the connection event, so that the tag can reflect the carrier signals of different data channels to a fixed channel and transmit the backscatter signal through the fixed channel;

[0015] The data packets corresponding to the carrier signal and the backscatter signal are both provided with identification fields, and the label data is decoded based on the identification field contents and the payload contents of the carrier signal and the backscatter signal.

[0016] Further, the edge device identifies the sequence number of the corresponding connection event through the data packet in the specific data channel, and sends the sequence number of the connection event to the tag, and the tag calculates the corresponding data channel sequence number according to the sequence number of the connection event, specifically including:

[0017] The edge device monitors the broadcast channel of the carrier device and obtains connection parameters in the data packet of the connection request of the broadcast channel; the connection parameters include: channel map map, frequency hopping parameter value hop, access address accessAddress and connection interval interval of the connection event;

[0018] The edge device calculates the index of the data channel corresponding to the first connection event of the carrier device according to the connection parameters, and jumps to the corresponding data channel, recorded as data channel A. The edge device infers the sequence number of the connection event conEventCounter through the timestamp of the data packet of the carrier signal in data channel A:

[0019] The timestamp of the first data packet in data channel A received by the edge device As an anchor point; when the edge device receives the nth data packet in data channel A, it calculates the sequence number of the corresponding connection event , is the timestamp of the nth data packet, ; The edge device sends a command to the tag, and the tag responds according to the sequence number of the connection event contained in the command , channel map map, frequency hopping parameter value hop and access address accessAddress to calculate the corresponding data channel number.

[0020] Furthermore, the accumulated error is eliminated by:

[0021] The timestamp of the n+1th data packet received by the edge device on data channel A is , the sequence number of the corresponding connection event is calculated in the following way :

[0022] .

[0023] Furthermore, the data packets corresponding to the carrier signal and the backscatter signal are both provided with identification fields, and the label data is decoded based on the identification field contents and the payload contents of the carrier signal and the backscatter signal, specifically including:

[0024] The payload content in the carrier signal is T1, and the identification field content is D1; ​​the carrier signal is whitened before being sent by the carrier device, and the payload content T1 and the identification field content D1 are changed to the payload content T2 and the identification field content D2 after the whitening process; the tag modulates the tag data into the carrier signal to obtain a backscattered signal, and the payload content in the backscattered signal is changed to R2;

[0025] The receiving device receives the carrier signal and the backscattered signal, and obtains the payload content T1, the identification field content D1, the payload content R2 and the identification field content D2;

[0026] According to the identification field content D2 and the identification field content D1, as well as the whitening sequence defined by the Bluetooth protocol, the data channel on which the carrier signal is propagated is inferred, which is recorded as data channel X; the receiving device whitens the payload content T1 according to the sequence number of the data channel X to obtain the payload content T2, and then performs an XOR operation on the payload content T2 and the payload content R2 to decode the tag data.

[0027] Compared with the prior art, the beneficial technical effects of the present invention are:

[0028] The tag in the present invention adopts FreeRider modulation technology and backscatters a multi-frequency carrier signal of arbitrary content to a target channel. The carrier signal is a Bluetooth signal, each data packet has a load of 37 bytes and an interval of 10 ms, and the data throughput of the carrier signal is 29 kbps. In order to utilize the carrier signal of arbitrary content, the tag uses 16 redundant low-power Bluetooth symbols to encode one bit of data. In the process of decoding the tag data, the receiving device uses a known access address to receive the data packet of the backscattered signal on a fixed channel. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a schematic diagram of a backscattering system of the present invention;

[0030] Figure 2 Schematic diagram of the channel identification process of the carrier signal;

[0031] Figure 3 It is a schematic diagram of the structure of the edge device of the present invention;

[0032] Figure 4 A schematic diagram of dynamic decoding based on an identification field of the present invention;

[0033] Figure 5 It is a schematic diagram of the performance of the backscattering system of the present invention under any carrier signal;

[0034] Figure 6 Schematic diagram of recognition rate under different numbers of carrier signal data channels of the present invention;

[0035] Figure 7 Schematic diagram of the deployment environment of the present invention. DETAILED DESCRIPTION

[0036] A preferred embodiment of the present invention is described in detail below with reference to the accompanying drawings.

[0037] The backscatter system in the present invention is composed of a carrier device, an edge device, a tag and a receiving device. Figure 1 As shown. The carrier device adopts a commercial Bluetooth device, and the carrier signal in the present invention is a standard low-power Bluetooth signal provided by the commercial Bluetooth device. According to the Bluetooth protocol, the Bluetooth signal is frequency-hopping. The tag modulates and reflects the Bluetooth signal, and the modulation method follows the codeword conversion mechanism, that is, the Bluetooth codeword in the carrier is reflected into another Bluetooth codeword. The edge device identifies the frequency of the Bluetooth signal data packet and sends it to the tag. The tag can reflect Bluetooth signals of different frequencies to a fixed channel and transmit backscattered signals. The main innovation of the present invention lies in the following two parts. The first part is that the edge device can assist the tag in identifying the channel and performing error correction through low-frequency transmission, so that the tag can accurately control the channel after reflection; the second part is to design an identification field on the carrier signal and the backscattered signal to assist the receiving device in recovering the dynamic payload content and realizing tag data decoding.

[0038] 1. Accurate channel identification based on low-frequency downlink forwarding.

[0039] Identifying the channel of the carrier signal is a key step in backscattering. The present invention uses edge devices to perform channel identification and forward this information to low-power tags. In order to reduce the power consumption of tags when working, the key to the channel identification mechanism is to reduce the frequency of edge device transmission to reduce tag decoding operations. Therefore, it is necessary to design an accurate channel identification mechanism for low-frequency downlink forwarding.

[0040] like Figure 2 As shown, first introduce the basic channel change process of the Bluetooth carrier signal:

[0041] (1) Data broadcast on the advertising channel: In Bluetooth communication, the slave device first broadcasts data (Adv) on the advertising channel. These broadcast data contain the unique identifier of the slave device (such as MAC address), device name, and possibly other information, which are used to enable the master device to discover and identify the slave device.

[0042] (2) The master device sends a connection request: After receiving the broadcast data from the slave device, the master device sends a connection request (Con) to the slave device. This connection request contains various connection parameters required to establish a connection, such as the channel map, the frequency hopping parameter value hop, the access address accessAddress, and the connection interval interval of the connection event.

[0043] (3) Jump to the data channel and transmit data: Once the connection request is accepted, the slave and master devices will jump to the data channel, transmit data on the connection event, and dynamically switch channels. The intervals of these connection events are usually equal to ensure stable data transmission.

[0044] The intervals of the connection events are equal. In each connection event, the master device sends data first, and the slave device sends data. In each connection event, the carrier device switches the data channel according to the channel selection algorithm CSA#1 and CSA#2. The channel selection algorithm CSA#1 is as follows:

[0045] ;

[0046] The channel selection algorithm CSA#2 is as follows:

[0047] ;

[0048] in, Indicates the channel selection algorithm CSA#1, Indicates the channel selection algorithm CSA#2; map indicates the channel map, hop indicates the frequency hopping parameter value, and ccessAddress indicates the access address, all of which are included in the connection request data packet.

[0049] conEventCounter is a connection parameter defined in the Bluetooth Low Energy specification, representing the sequence number of the connection event. ChInd is the sequence number of the data channel. Figure 1 In the present invention, ChInd is abbreviated as "CH", and the number after CH represents the value of the data channel number. The master device and the slave device are collectively referred to as carrier devices in the present invention.

[0050] Therefore, the edge device assists the tag in calculating the data channel by transmitting connection parameters. The advantage of transmitting connection parameters instead of data channel sequence numbers is that the edge device does not need to send the data channel sequence number to the tag every time a connection event occurs. The tag can calculate it by itself based on the connection parameters. The edge device only needs to send the connection parameters periodically so that the tag can update and correct it. In the first phase, the edge device monitors the broadcast channel. It obtains the connection parameters from the data packet of the connection request and saves them. In the second phase, the edge device calculates the data channel index of the first connection event and jumps to the data channel, recorded as data channel A. Since the connection event has a fixed connection interval, the edge device infers the sequence number of the connection event conEventCounter through the timestamp of the data packet. When the first timestamp is received When a packet with a timestamp is received, the edge device marks it as an anchor point. Then the edge continues to monitor data channel A. When a data packet is received, the edge device calculates the sequence number of the corresponding connection event The edge device sends the sequence number of the connection event to the tag, and the tag calculates the data channel sequence number based on the sequence number of the connection event.

[0051] In practice, due to the slight difference between the device clock and the theoretical value, the carrier device cannot perfectly generate connection events according to the connection interval. As time accumulates, it will cause errors when the edge device calculates the sequence number of the connection event. In order to eliminate the error, the edge device continuously updates the reference timestamp during the calculation process. During the channel hopping process, the edge device always monitors on data channel A (the first data channel in the carrier signal hopping sequence), and the timestamp of the first data packet is recorded as , the sequence number of the corresponding connection event ; The timestamp of the second data packet is , the sequence number of the corresponding connection event ; If the nth data packet is received, the timestamp is , the corresponding connection event sequence number is , when the edge device receives the n+1th data packet on data channel A, the corresponding timestamp is , the sequence number of the corresponding connection event . The edge device obtains the sequence number of the connection event in this way, and then sends it to the tag for calculation of the data channel sequence number. The advantages of this method are as follows: First, the edge device only monitors the carrier signal on a single data channel, and the frequency of sending the connection event sequence number is low, which reduces the tag calculation burden. Second, the edge device continuously updates the reference timestamp used to calculate the sequence during the monitoring process, which can avoid the accumulation of errors.

[0052] To help the tag identify the channel of the carrier signal before modulation, the edge device needs to forward information within the connection interval of the connection event. According to the Bluetooth Low Energy (BLE) specification, the minimum connection interval of the connection event is 7.5 ms. Therefore, the edge device should make the delay less than 7.5 ms. The structure of the edge device is as follows Figure 3 As shown, the edge device includes a low-power Bluetooth (BLE) module, a controller and a WiFi module. During the channel identification process, the low-power Bluetooth module processes the data packet and sends it to the controller. The controller encodes the original data and calls the WiFi module to send a simulated amplitude modulation signal. The delay is divided into two parts, data processing delay and data transmission delay. The data processing delay is the time consumed by the controller and the WiFi module. The controller uses a microcontroller unit (MCU) with a delay of about 5 μs. The WiFi module starts the radio transmission in less than 5ms. For data transmission delay, the present invention uses a universal asynchronous receiver-transmitter (UART) with a rate of 1M between the low-power Bluetooth module and the controller, and a serial peripheral interface (SPI) with a rate of 4M between the controller and the WiFi module. These two high-speed interfaces shorten the interface delay to 200μs. The delay of the entire edge device can be reduced to less than 7ms.

[0053] 2. Dynamic decoding based on reserved identifiers:

[0054] The decoding of tag data in the backscatter signal depends on the payload content, so the receiving device needs to obtain dynamic payload content. Figure 4As shown, the carrier device provides a carrier signal with a payload content of T1, but the payload content will change after the whitening operation. The whitening operation is that the Bluetooth device generates a specific sequence according to the sequence number of the data transmission channel X, and then uses the sequence to perform an XOR operation with the payload content, and sends the obtained new sequence. The sequence content after the whitening operation is affected by the sequence number of the data transmission channel X and changes dynamically. The backscattering system in the present invention sets an identification field in the carrier data packet, the identification field is 1 byte long, and the identification field content is 0x00 (8 bits 0). During the transmission process of the carrier device, the identification field content 0x00 and the payload content T1 are respectively whitened to become the identification field content 0xAD (example value) and the payload content T2, where T2 is dynamically unknown. The tag performs reflection modulation on the payload content, skips the identification field content during the modulation process, and modulates the data from the payload content part, then the identification field content in the reflected Bluetooth data packet is still 0xAD, and the payload content becomes R2 due to the modulation of the tag. The receiving device of the backscattering system in the present invention turns off the whitening operation, receives the reflected data, and obtains the identification field content 0xAD and the payload content R2. To decode the tag data, it is also necessary to obtain the dynamic payload content T2. According to the received identification field content 0xAD and the initial value 0x00, and the whitening sequence defined by the Bluetooth protocol, the original data channel is deduced to be X. According to the data channel X sequence number, the receiving device whitens T1 to obtain T2, and then performs an XOR operation on T2 and R2 to decode the tag data.

[0055] 3. Example

[0056] 3.1 Edge device construction:

[0057] This embodiment uses off-the-shelf chips to build a low-cost edge device. TI CC2640R2F chip, TI CC3200 chip and STM32F103RC chip are used in the edge device. The controller of the edge device uses STM32 microcontroller, which is connected to CC2640R2F chip and CC3200 chip through universal asynchronous receiver and transmitter (UART) and serial peripheral interface (SPI) respectively. The CC3200 chip is set to 802.11g 6 Mbps mode on channel 1 with a transmission power of 20 dBm. It encodes data using constant and random symbols. When used as a multi-function edge device, the edge device is usually integrated into existing equipment and draws power from the wired line. When providing a carrier as an independent device, the edge device maintains a low power budget by operating at a low duty cycle. At the same time, the edge device provides a reliable redundant downlink with a high transmission success rate and avoids frequent retransmissions. In addition, the WiFi module in the edge device uses a narrowband WiFi signal, which helps to further reduce power consumption. It has been verified that the total power of the edge device in this embodiment is about 137.5 mW, of which the power of the WiFi module is 64 mW, the power of the low-power Bluetooth module is 19.5 mW, and the power of the controller based on the STM32 microcontroller is 54 mW.

[0058] 3.2 Deployment:

[0059] This embodiment conducts an end-to-end experiment on an empty second-floor platform. Figure 7 As shown in the figure, place the Bluetooth low energy carrier device (TX) next to the wall and move the Bluetooth low energy receiver (RX) in a straight line. The edge device (Edge) is deployed within five meters of the tag (Tag).

[0060] like Figure 5 As shown in the figure, under multi-frequency Bluetooth signals, the tag can achieve more than 95% utilization (ratio of received packets to carrier packets) and maintain a throughput of 1.4 kbps.

[0061] The present invention also tests the accuracy of edge devices in identifying carrier signal data channels. Figure 6 It shows that the tag can achieve 99% recognition accuracy when facing different carrier signals. According to the Bluetooth protocol, there are two frequency hopping algorithms (Channel Selection Algorithm, CSA) for data carriers: Figure 6 It is shown that when the carrier spacing is 50 ms and the number of channels takes different values ​​from 2 to 36, the accuracy of channel selection algorithms CSA #1 and CSA #2 exceeds 95% and 99% respectively.

[0062] It is obvious to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims are included in the present invention, and any reference numerals in the claims should not be regarded as limiting the claims involved.

[0063] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A backscattering method for arbitrary multi-frequency Bluetooth carriers, characterized in that: The backscatter system used includes a carrier device, an edge device, a tag and a receiving device; the backscatter method specifically includes: The carrier device can send out carrier signals of multiple frequencies; the carrier device sends a connection request on a broadcast channel and transmits data on multiple different data channels through carrier signals of corresponding frequencies; The tag modulates the tag data into the carrier signal to generate a backscatter signal; the modulation process follows the codeword conversion mechanism, that is, the Bluetooth codeword in the carrier signal is reflected as another Bluetooth codeword; the edge device identifies the sequence number of the corresponding connection event through the data packet in the specific data channel, and sends the sequence number of the connection event to the tag, and the tag calculates the corresponding data channel sequence number according to the sequence number of the connection event, so that the tag can reflect the carrier signals of different data channels to a fixed channel and transmit the backscatter signal through the fixed channel; The data packets corresponding to the carrier signal and the backscatter signal are both provided with identification fields, and the label data is decoded based on the identification field contents and the payload contents of the carrier signal and the backscatter signal.

2. The backscattering method for arbitrary multi-frequency Bluetooth carriers according to claim 1, characterized in that: The edge device identifies the sequence number of the corresponding connection event through the data packet in the specific data channel, and sends the sequence number of the connection event to the tag, and the tag calculates the corresponding data channel sequence number according to the sequence number of the connection event, specifically including: The edge device monitors the broadcast channel of the carrier device and obtains connection parameters in the data packet of the connection request of the broadcast channel; the connection parameters include: channel map map, frequency hopping parameter value hop, access address accessAddress and connection interval interval of the connection event; The edge device calculates the index of the data channel corresponding to the first connection event of the carrier device according to the connection parameters, and jumps to the corresponding data channel, recorded as data channel A. The edge device infers the sequence number of the connection event conEventCounter through the timestamp of the data packet of the carrier signal in data channel A: The timestamp of the first data packet in data channel A received by the edge device As an anchor point; when the edge device receives the nth data packet in data channel A, it calculates the sequence number of the corresponding connection event , is the timestamp of the nth data packet, ; The edge device sends a command to the tag, and the tag responds according to the sequence number of the connection event contained in the command , channel map map, frequency hopping parameter value hop and access address accessAddress to calculate the corresponding data channel number.

3. The backscattering method for arbitrary multi-frequency Bluetooth carriers according to claim 2, characterized in that: Eliminate accumulated errors by: The timestamp of the n+1th data packet received by the edge device on data channel A is , the sequence number of the corresponding connection event is calculated in the following way : 。 4. The backscattering method for arbitrary multi-frequency Bluetooth carriers according to claim 1, characterized in that: The data packets corresponding to the carrier signal and the backscatter signal are both provided with identification fields, and the tag data is decoded based on the identification field contents and the payload contents of the carrier signal and the backscatter signal, specifically including: The payload content in the carrier signal is T1, and the identification field content is D1; ​​the carrier signal is whitened before being sent by the carrier device, and the payload content T1 and the identification field content D1 are changed to the payload content T2 and the identification field content D2 after the whitening process; the tag modulates the tag data into the carrier signal to obtain a backscattered signal, and the payload content in the backscattered signal is changed to R2; The receiving device receives the carrier signal and the backscattered signal, and obtains the payload content T1, the identification field content D1, the payload content R2 and the identification field content D2; According to the identification field content D2 and the identification field content D1, as well as the whitening sequence defined by the Bluetooth protocol, the data channel on which the carrier signal is propagated is inferred, which is recorded as data channel X; the receiving device whitens the payload content T1 according to the sequence number of the data channel X to obtain the payload content T2, and then performs an XOR operation on the payload content T2 and the payload content R2 to decode the tag data.

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