Method and system for preserving frame check sequence during backscatter communication

Abstract

To provide a method and a system for preserving a frame check sequence (FCS) of a data frame during backscatter communication.SOLUTION: A method includes receiving a transmitted signal including a data frame containing a first data sequence and a frame check sequence (FCS), determining a cyclic redundancy check (CRC) preservation sequence based on a backscatter tag data sequence, a bit length of the backscatter tag data sequence and a given cyclic redundancy check (CRC) algorithm, and backscattering the transmitted signal to form a backscattered signal including a second data sequence and the FCS. The second data sequence includes a transmitted data sequence, an encoded tag data sequence, and a CRC preservation sequence that preserves the FCS of the transmitted data frame in the backscattered data frame. The FCS is used to detect a communication error in the backscattered data frame.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001]

[0001] This subject matter relates to backscatter communication systems and backscatter tags, and more particularly, to methods and systems for preserving a frame check sequence (FCS) of a data frame during backscatter communication.

Background Art

[0002]

[0002] Backscatter communication has attracted attention for applications such as embedded sensors, wearables, and smart home sensing due to its ability to provide low-power connections to these sensors. Such applications have severe power constraints. Embedded sensors, for example, must endure for several years, while more conventional smart home monitoring applications can benefit from sensors and actuators that can endure for several years. Backscatter communication can meet connection requirements while consuming low power, such as being powered by harvesting energy, or with a battery that can endure for several years.

[0003]

[0003] Backscatter systems generally require specialized hardware to generate an excitation RF signal that a backscatter radio can reflect and to decode the backscattered signal. Recent research from Wi-Fi backscatter to BackFi and passive Wi-Fi has reduced the need for specialized hardware. Passive Wi-Fi, for example, can be decoded using a standard Wi-Fi radio, but it still requires a dedicated continuous wave signal generator as an excitation RF signal source. BackFi requires a proprietary full-duplex communication hardware add-on for Wi-Fi radios to enable backscatter communication. As a result, there continues to be a need for backscatter systems that can be deployed using commodity devices such as access points, smartphones, watches, and tablets.

Summary of the Invention

[0004]

[0004] The following introductory section is provided to introduce the reader to the more detailed discussion below. The introductory section is not intended to limit or define any claimed or unclaimed invention. One or more inventions may reside in any combination or sub - combination of elements or process steps disclosed in any part of this document, including its claims and drawings.

[0005]

[0005] In one broad aspect, a backscatter tag is provided. The backscatter tag is configured to receive a transmitted signal including a transmitted data frame, where the transmitted data frame includes a first data sequence and a frame check sequence (FCS), the first data sequence includes a transmitted data sequence and a dummy sequence, the FCS is based on a first CRC value determined using a given cyclic redundancy check (CRC) algorithm for the first data sequence, the FCS is available to a receiver for detecting communication errors in the transmitted data frame, determine a CRC preservation sequence based on the backscatter tag data sequence, the bit length of the backscatter tag data sequence, and a given CRC algorithm, and backscatter the transmitted signal to form a backscattered signal including a backscattered data frame, where the backscattered data frame includes a second data sequence and an FCS, the second data sequence includes the transmitted data sequence, an encoded tag data sequence, and the CRC preservation sequence, the CRC preservation sequence results in the first CRC value using a given CRC algorithm for the second data sequence to preserve the FCS of the transmitted data frame in the backscattered data frame, and the FCS is available to a receiver for detecting communication errors in the backscattered data frame.

[0006]

[0006] In some embodiments, the dummy sequence is a sequence of zeros having a bit length that is at least equal to the sum of the bit lengths of the backscattered tag data sequence and the CRC save sequence.

[0007]

[0007] In some embodiments, the backscattered tag is configured to backscatter a signal transmitted to form a backscattered signal by modifying at least a portion of the dummy sequence in the data frame transmitted to include the tag data sequence and the CRC save sequence encoded in the backscattered data frame.

[0008]

[0008] In some embodiments, the backscattered tag is configured to determine a second CRC value of the backscattered tag data sequence using a given CRC algorithm, determine a third CRC value of a zero bit sequence having a bit length equal to the bit length of the backscattered tag data sequence using the given CRC algorithm, determine an intermediate sequence by performing an XOR operation of the second CRC value and the third CRC value, and invert the bit sequence of the intermediate sequence to form the CRC save sequence to determine the CRC save sequence.

[0009]

[0009] In some embodiments, the backscattered tag data sequence includes sensor data generated by a sensor coupled to the backscattered tag.

[0010]

[0010] In some embodiments, the backscattered tag is configured to backscatter a signal transmitted to form a backscattered signal by modifying the frequency of the signal transmitted to encode data.

[0011]

[0011] In some embodiments, the backscatter tag is configured to backscatter the signal transmitted to form the backscattered signal by modifying the amplitude and / or phase of the signal transmitted to encode the data.

[0012]

[0012] In some embodiments, the transmitted signal complies with the IEEE802.11 standard, and the transmitted data frame includes a MAC header, a payload including a first data sequence, and an FCS.

[0013]

[0013] In some embodiments, the backscattered signal complies with the IEEE802.11 standard, and the backscattered data frame includes a MAC header, a payload including a second data sequence, and an FCS.

[0014]

[0014] In another broad aspect, a method is provided for preserving a frame check sequence (FCS) of a data frame during backscatter communication. The method includes receiving, by a backscatter tag, a transmitted signal including a transmitted data frame, where the transmitted data frame includes a first data sequence and an FCS, the first data sequence includes a transmitted data sequence and a dummy sequence, the FCS is based on a first CRC value determined using a given cyclic redundancy check (CRC) algorithm for the first data sequence, the FCS is usable by a receiver to detect communication errors in the transmitted data frame, determining, by the backscatter tag, a CRC save sequence based on the backscatter tag data sequence, the bit length of the backscatter tag data sequence, and a given CRC algorithm, and backscattering, by the backscatter tag, the transmitted signal to form a backscattered signal including a backscattered data frame, where the backscattered data frame includes a second data sequence and an FCS, the second data sequence includes the transmitted data sequence, an encoded tag data sequence, and the CRC save sequence, the CRC save sequence causes the first CRC value to be yielded using a given CRC algorithm for the second data sequence, thereby preserving the FCS of the transmitted data frame in the backscattered data frame, and the FCS is usable by a receiver to detect communication errors in the backscattered data frame.

[0015]

[0015] In some embodiments, the dummy sequence is a sequence of zeros having a bit length at least equal to the sum of the bit lengths of the backscatter tag data sequence and the CRC save sequence.

[0016]

[0016] In some embodiments, backscattering includes modifying at least a portion of the dummy sequence in the transmitted data frame such that the backscattered data frame includes the encoded tag data sequence and the CRC save sequence.

[0017]

[0017] In some embodiments, determining the CRC save sequence includes determining a second CRC value of the backscatter tag data sequence using a given CRC algorithm, determining a third CRC value of a zero bit sequence having a bit length equal to the bit length of the backscatter tag data sequence using the given CRC algorithm, determining an intermediate sequence by performing an XOR operation between the third CRC value and the second CRC value, and inverting the bit sequence of the intermediate sequence to form the CRC save sequence.

[0018]

[0018] In some embodiments, the backscatter tag data sequence includes sensor data generated by a sensor coupled to the backscatter tag.

[0019]

[0019] In some embodiments, backscattering the signal transmitted to form the backscattered signal includes encoding data by modifying the frequency of the transmitted signal.

[0020]

[0020] In some embodiments, backscattering the signal transmitted to form the backscattered signal includes encoding data by modifying the amplitude and / or phase of the transmitted signal.

[0021]

[0021] In some embodiments, the transmitted signal complies with the IEEE802.11 standard, and the transmitted data frame includes a MAC header, a payload including a first data sequence, and an FCS.

[0022]

[0022] In some embodiments, the backscattered signal complies with the IEEE802.11 standard, and the backscattered data frame includes a MAC header, a payload including a second data sequence, and an FCS.

[0023]

[0023] Other features and advantages of the present application will become apparent from the following embodiments for carrying out the invention. However, it should be understood that the embodiments for carrying out the invention and specific examples are given only by way of illustration while showing the embodiments of the present application, and the scope of the claims should not be limited by these embodiments, but the broadest interpretation consistent with the description as a whole should be given.

[0024]

[0024] To better understand the embodiments described herein and to more clearly show how they can be implemented, reference is now made, by way of example only, to the accompanying drawings which show at least one exemplary embodiment.

Brief Description of the Drawings

[0025]

Figure 1

[0025] It is a simplified schematic diagram of a backscatter communication system according to an exemplary embodiment.

Figure 2

[0026] It is a process flow for an exemplary embodiment of a method for storing the FCS of a data frame during backscatter communication.

Figure 3

[0027] It is a block diagram of an exemplary transmitted data frame received during the method of FIG. 2.

Figure 4A

[0028] It is a block diagram of an exemplary backscattered data frame backscattered during the method of FIG. 2.

Figure 4B

[0029] It is a block diagram of another exemplary backscattered data frame backscattered during the method of FIG. 2.

Embodiments for Carrying Out the Invention

[0026]

[0030] Further aspects and features of the exemplary embodiments described herein will become apparent from the following description in conjunction with the accompanying drawings.

[0027]

[0031] To simplify and clarify the illustrations, it should be recognized that reference numerals may be repeated among the figures, where appropriate, to indicate corresponding or similar elements or steps. In addition, numerous specific details are set forth in order to provide a thorough understanding of the exemplary embodiments described herein. However, it will be understood by those of ordinary skill in the art that the embodiments described herein may be practiced without these specific details. In other instances, well-known methods, procedures, and components have not been described in detail so as not to obscure the embodiments described herein. Further, this description should not be construed as limiting the scope of the embodiments described herein in any way, but rather as merely explaining the various implementations of the embodiments described herein.

[0028]

[0032] In the description and drawings herein, reference may be made to a Cartesian coordinate system in which the vertical direction, i.e., the z-axis, extends in the up and down direction from bottom to top. The x-axis extends in a first horizontal or width dimension perpendicular to the z-axis, and the y-axis extends horizontally intersecting the x-axis in a second horizontal or length dimension.

[0029]

[0033] The terms "an embodiment", "embodiment", "embodiments", "the embodiment", "the embodiments", "one or more embodiments", "some embodiments", and "one embodiment" mean, unless otherwise specified, "one or more (but not all) embodiments of the present invention(s)".

[0030]

[0034] The terms "comprising", "including", and variations thereof mean, unless otherwise specified, "including but not limited to". The listing of items does not imply that any or all of the items are mutually exclusive, unless otherwise specified. The terms "a", "an", and "the" mean "one or more", unless otherwise specified.

[0031]

[0035] As used in this specification and the claims, two or more parts are said to be "coupled", "connected", "attached", or "fastened", where the parts are joined together or operate either directly or indirectly (i.e., through one or more intermediate parts) as long as a link occurs. As used in this specification and the claims, two or more parts are said to be "directly coupled", "directly connected", "directly attached", or "directly fastened", where the parts are connected by physically contacting each other. As used herein, two or more parts are said to be "rigidly coupled", "rigidly connected", "rigidly attached", or "rigidly fastened", where the parts are joined so as to move as a unit while maintaining a fixed orientation relative to each other. The terms "coupled", "connected", "attached", and "fastened" do not distinguish the manner in which two or more parts are joined together.

[0032]

[0036] Embodiments of this specification provide systems and methods for backscattered communication that conform to existing communication protocols such as IEEE 802.11 WLAN, Bluetooth®, and ZigBee. For this purpose, and to simplify and facilitate the explanation, embodiments of this specification refer to communication via IEEE 802.11 1 Mbps DSSS-compliant frames, but it should be noted that the disclosed backscattered communication systems are not limited to operating with other similar communication standards.

[0033]

[0037] The disclosed system and method can enable the preservation of the FCS of a data frame during backscatter communication, i.e., the same FCS can be used for error detection in the original transmitted frame and the backscattered frame. This can enable the backscatter communication system to be not restricted to a transmitter / receiver and to be operable on different communication infrastructures. For example, FCS preservation can enable backscatter communication to operate on any WLAN network infrastructure.

[0034]

[0038] Reference is now made to FIG. 1, which is a simplified schematic diagram of a backscatter communication system 100 according to an exemplary embodiment. System 100 includes a transmission unit 102, a reception unit 104, and a backscatter tag 120. It should be understood that in some embodiments, one or more of the transmission unit and the reception unit may actually comprise a device that combines a transmission function and a reception function.

[0035]

[0039] The transmission unit 102 may be configured to transmit a signal 30 that includes one or more transmitted data frames 20. The transmission unit 102 may transmit the data frame 20 at a predefined or controllable frequency. For this purpose, the transmission unit 102 may also be referred to herein as an "excitation device", and the transmitted signal 30 may also be referred to herein as an "excitation signal". In some embodiments, the transmission unit 102 may transmit the signal 30 in response to an input trigger.

[0036]

[0040] The transmitted signal 30 can be an IEEE 802.11 compliant WLAN signal, and the transmitted data frame 20 can be an IEEE 802.11 compliant WLAN data frame. The transmitting unit 102 can include, for example, a mobile phone having a standard Wi-Fi radio. In other examples, the transmitting unit 102 can be any other device configured to communicate via a Wi-Fi radio. In some embodiments, the transmitted signal 30 may not be an IEEE 802.11 compliant WLAN signal. For example, the transmitted signal 30 can conform to any other suitable wireless communication standard.

[0037]

[0041] The receiving unit 104 can be any suitable device configured to receive the transmitted signal 30. The receiving unit 104 can be operable at a plurality of frequencies including the frequency of the transmitted signal 30. The receiving unit 104 can operate at a predefined frequency or can be tuned to different frequencies. In some embodiments, the receiving unit 104 can be a device capable of receiving an IEEE 802.11 compliant WLAN signal. For example, the receiving unit 104 can include a Wi-Fi access point or any other suitable Wi-Fi receiving device.

[0038]

[0042] The backscatter tag 120 can be any suitable device that operates to intercept the transmitted data frame 20. In particular, the backscatter tag 120 can be configured to manipulate the intercepted frame to encode the backscatter tag's own data. The backscatter tag 120 can backscatter the transmitted signal 30 to form a backscattered signal 50 including one or more backscattered data frames 40. The backscattered data frame 40 can include the backscatter tag's own data.

[0039]

[0043] More specifically, the backscatter tag 120 may receive the transmitted data frame including the data transmitted by the transmission unit 102. The backscatter tag 120 may operate to manipulate the initially transmitted data in order to include the data of the backscatter tag itself in the backscattered data frame.

[0040]

[0044] In some embodiments, the transmitted signal 30 may be an IEEE802.11 compliant WLAN signal. The backscatter tag 120 may be configured such that the backscattered signal 50 is an 802.11b compliant Wi-Fi signal and the backscattered data frame 40 is an 802.11b compliant Wi-Fi data frame.

[0041]

[0045] The backscatter tag 120 may apply different methods for manipulating the transmitted signal 30 to generate the backscattered signal 50. For example, as described in U.S. Patent No. 10,338,205 to Zhang et al., filed on August 14, 2017 and issued on July 2, 2019, and U.S. Patent Application Publication No. 2019 / 0274144 to Zhang et al., filed on April 25, 2019, both of which are incorporated herein by reference in their entirety, a codeword conversion method can be used. Codeword conversion may involve, for example, XORing the data bits in the original transmitted payload of the transmitted signal 30 with the data of the backscatter tag 120 to generate the backscattered signal 50. In practice, codeword conversion may be performed, for example, by modifying the amplitude, phase, and / or frequency of the transmitted signal 30 received at the backscatter tag 120.

[0042]

[0046] For this purpose, the backscatter tag 120 may include various passive circuit components that operate (i.e., manipulate) on the received signal to encode the received signal with the data of the backscatter tag 120 itself. Various architectures and configurations for passive circuits for backscatter tags are known in the art.

[0043]

[0047] The data of the backscattered tag 120 itself encoded in the backscattered data frame 40 can vary based on the application of the backscatter communication system 100. For example, the backscattered tag 120 can be coupled to a sensor, and the data of the backscattered tag 120 itself can include sensor data generated by the sensor. In this way, the backscattered tag 120 can facilitate the implementation of an ultra-low power sensor network.

[0044]

[0048] In some embodiments, the backscattered signal 50 can be in the same frequency channel as the original transmitted signal 30. Next, the receiving unit 104 can receive both the original transmitted signal 30 and the backscattered signal 50 on a single frequency channel. The ability of the receiving unit 104 to decode the backscattered signal 50 to recover the data encoded by the backscattered tag 120 can be degraded by the interference generated by receiving signals 30 and 50 in the same frequency channel.

[0045]

[0049] In some embodiments, to at least partially mitigate the interference problem, the receiving unit 104 can include two receivers tuned to listen (i.e., receive) frames on separate frequency channels. The transmitting unit 102 can transmit the data frame 20 on a first frequency channel. The first of the two receivers of the receiving unit 104 is tuned to the first frequency channel to receive the transmitted data frame 20. In addition to encoding the data of the backscattered tag itself in the backscattered data frame, the backscattered tag 120 can be configured to frequency shift the backscattered signal 50 to a different frequency. In this way, the backscattered tag 120 can generate a frequency-shifted backscattered signal 50. The second of the two receivers of the receiving unit 104 is tuned to the second frequency channel to receive the backscattered data frame 40.

[0046]

[0050] The receiving unit 104 may be configured to process the data in the received backscattered data frame 40 to decode and separate (i.e., deinterleave) the data of the backscatter tag 120 itself from the originally transmitted data. In some embodiments, the decoding may be performed by an external device (e.g., a decoding block) connected to the receiving unit 104.

[0047]

[0051] Here too, various exemplary methods for decoding and restoring the data of the backscatter tag 120 itself will occur to those skilled in the art. For example, as described in U.S. Patent No. 10,338,205 to Zhang et al. and U.S. Patent Application Publication No. 2019 / 0274144 to Zhang et al., the decoding may involve reversing the XOR operation performed by the backscatter tag 120 and using an XOR decoder. The XOR decoder XORs the data bits in the backscattered data frame 40 with the data bits in the originally transmitted data frame 20 to restore the data bits associated with the data of the backscatter tag itself.

[0048]

[0052] In some embodiments, the transmitting unit 102 may transmit a transmitted data frame 20 having predefined transmitted data at predefined time or frequency intervals. That is, the transmitted data is known a priori to the receiving unit 104 (i.e., it is predefined from the perspective of the receiver). For example, the transmitted data may include a known bit sequence at known bit positions within the transmitted data frame 20. In this way, the receiving unit 104 (or a decoding block connected to the receiving unit 104) is not required to rely on the data in the originally transmitted data frame 20 to decode the backscattered data frame 40. A method and system for backscatter communication using a predefined template are described in U.S. Patent Application Publication No. 2023 / 0244883 to Nielsen et al., filed on January 27, 2023, which is hereby incorporated by reference in its entirety.

[0049]

[0053] Reference is now made to FIG. 2, which is a process flow diagram of an exemplary embodiment of method 200 for storing the FCS of a data frame during backscatter communication. Method 200 may be performed, for example, by backscatter communication system 100, and reference is made to FIG. 1 in the following description.

[0050]

[0054] In operation 210, a transmitted signal including the transmitted data frame may be received. For example, transmitting unit 102 may transmit signal 30, and backscatter tag 120 may receive the transmitted signal 30.

[0051]

[0055] The transmitted signal 30 may include one or more transmitted data frames 20. The transmitted data frame 20 may include a first data sequence and an FCS. Reference is now made to FIG. 3, which is a block diagram of an exemplary transmitted data frame 20 that may be received in operation 210. In the illustrated example, the transmitted data frame 20 includes a first data sequence 310 and an FCS 320.

[0052]

[0056] In some embodiments, the first data sequence 310 may include a transmitted data sequence 330 and a dummy sequence 340. The transmitted data sequence may include data transmitted from a transmitter (e.g., transmitting unit 102) to a receiver (e.g., receiving unit 104). The dummy sequence 340 may include a portion of the first data sequence that is modified by the backscatter tag to encode the backscatter tag's own data. In some embodiments, the dummy sequence 340 may be known a priori to the receiver (e.g., receiving unit 104). For example, the dummy sequence 340 may include a sequence of a plurality of "0" bits. During backscatter, the backscatter tag may modify at least a portion of the dummy sequence 340 to encode the backscatter tag's own data.

[0053]

[0057] The FCS 320 may be available for use by a receiver of a transmitted signal to detect communication errors in the transmitted data frames received at the receiver. For example, the receiving unit 104 may use the FCS 320 to detect errors in the transmitted data frame 20 received at the receiving unit 104.

[0054]

[0058] Any suitable technique may be used to implement the FCS. For example, the FCS may be a CRC value determined using any suitable cyclic redundancy check (CRC) algorithm. For any transmitted data frame 20, the CRC algorithm may generate a first CRC value for a first data sequence 310, and the FCS 320 may include the first CRC value.

[0055]

[0059] In some embodiments, the transmitted signal received in operation 210 complies with the IEEE 802.11 standard. Each transmitted data frame 20 may include a MAC header, a payload including a first data sequence 310, and an FCS 320.

[0056]

[0060] In operation 220, a CRC save sequence may be determined. The FCS may be invalidated when the backscatter tag modifies the content of the transmitted data frame in order to encode the data of the backscatter tag itself. To mitigate this problem and ensure that the same FCS may be valid for both the transmitted data frame 20 and the backscattered data frame 40, the backscatter tag 120 may determine a CRC save sequence and include the CRC save sequence in the backscattered data frame.

[0057]

[0061] The backscatter tag 120 may determine the CRC save sequence based on a backscatter tag data sequence to be encoded in the backscattered data frame. The backscatter tag data sequence may include, for example, sensor data generated by a sensor coupled to the backscatter tag.

[0058]

[0062] In some embodiments, the backscatter tag 120 may determine a CRC save sequence by determining a second CRC value for the backscatter tag data sequence. In operation 220, the backscatter tag uses the same CRC algorithm as that used in operation 210. Further, the backscatter tag 120 may determine a third CRC value for a bit sequence of zeros having a bit length equal to the bit length of the backscatter tag data sequence. The backscatter tag 120 may then determine an intermediate sequence by performing an XOR operation of the second CRC value and the third CRC value. Further, the backscatter tag 120 may invert the bit sequence of the intermediate sequence to form the CRC save sequence.

[0059]

[0063] In operation 230, the transmitted signal may be backscattered to form a backscattered signal. For example, the backscatter tag 120 may backscatter the transmitted signal 30 to form a backscattered signal 50.

[0060]

[0064] The backscattered signal 50 may include one or more backscattered data frames 40. The backscattered data frame 40 may include a second data sequence and an FCS. Reference is now made to FIGS. 4A and 4B, which are block diagrams of an exemplary backscattered data frame 40. In the illustrated example, the backscattered data frame 40 includes a second data sequence 410 (e.g., the second data sequence 410a shown in FIG. 4A and the second data sequence 410b shown in FIG. 4B) and an FCS 320. Simultaneous reference is also made to FIGS. 1-3.

[0061]

[0065] In some embodiments, the backscattered signal in operation 230 complies with the IEEE802.11 standard. Each backscattered data frame 40 may include a MAC header, a payload including a second data sequence 410, and an FCS 320.

[0062]

[0066] In some embodiments, the second data sequence 410 may include the transmitted data sequence 330, the encoded tag data sequence 420, and the CRC save sequence 430. The transmitted data sequence 330 may be the uncorrected data included in the transmitted data frame 20 received in operation 210. The CRC save sequence 430 may be the CRC save sequence determined in operation 220.

[0063]

[0067] The backscatter tag may modify at least a portion of the dummy sequence 340 of the transmitted data frame 20 such that the backscattered data frame 40 includes the encoded tag data sequence 420 and the CRC save sequence 430. The bit length of the dummy sequence 340 may be at least equal to the sum of the bit lengths of the backscatter tag data sequence and the CRC save sequence.

[0064]

[0068] For example, FIG. 4A shows an example where the bit length of the dummy sequence 340 is equal to the sum of the bit lengths of the backscatter tag data sequence and the CRC save sequence. In this case, the dummy sequence is completely replaced by the encoded tag data sequence 420 and the CRC save sequence 430 in the second data sequence 410a of the backscattered data frame 40.

[0065]

[0069] As another example, FIG. 4B shows an example where the bit length of the dummy sequence 340 is longer than the sum of the bit lengths of the backscatter tag data sequence and the CRC preservation sequence. In this case, the second data sequence 410b of the backscattered data frame 40 includes an encoded tag data sequence 420, a CRC preservation sequence 430, and a dummy sequence 440. The dummy sequence 440 may include an unmodified portion of the dummy sequence 340. For example, in the case of an exemplary dummy sequence 340 including a sequence of "0" bits having a bit length longer than the sum of the bit lengths of the backscatter tag data sequence and the CRC preservation sequence, the dummy sequence 440 includes a sequence of "0" bits having a bit length shorter than the bit length of the dummy sequence 340.

[0066]

[0070] The backscatter tag 120 may use any suitable method for modifying the transmitted signal / data frame to form the backscattered signal / data frame. For example, the backscatter tag 120 may modify the amplitude, phase, and / or frequency of the transmitted signal to encode the data of the backscatter tag itself and form the backscattered signal. In some embodiments, the backscatter tag 120 may frequency shift the backscattered signal using passive circuit components and method systems as described, for example, in U.S. Patent No. 10,338,205 to Zhang et al. and U.S. Patent Application Publication No. 2019 / 0274144 to Zhang et al. This may be performed to avoid interference between the backscattered signal and the original transmitted signal.

[0067]

[0071] Method 200 can enable the storage of the FCS because the same FCS 320 (contained in the transmitted data frame 20) can be used by the receiver of the backscattered data frame 40 to detect communication errors. For example, the receiving unit 104 can use the FCS 320 to detect errors in any part of the second data sequence 410 (e.g., the transmitted data sequence 330, the encoded tag data sequence 420). If there are no communication errors associated with the backscattered data frame 40, the same CRC algorithm (used in operations 210 and 220) will result in the same first CRC value for the second data sequence 410 (with respect to the first data sequence 310).

[0068]

[0072] The above description provides examples of embodiments, but it should be recognized that some features and / or functions of the described embodiments may be subject to modification without departing from the spirit and principles of the operation of the described embodiments. Therefore, what has been described above is intended to illustrate the invention and is non-limiting, and it will be understood by those skilled in the art that other variations and modifications can be made without departing from the scope of the invention as defined in the appended claims. The claims should not be limited by the preferred embodiments and examples, but should be given the broadest interpretation consistent with the description as a whole.

Claims

1. A backscatter tag comprising: receiving a transmitted signal including a transmitted data frame, wherein the transmitted data frame includes a first data sequence and a frame check sequence (FCS); the first data sequence includes a transmitted data sequence and a dummy sequence; the FCS is based on a first cyclic redundancy check (CRC) value determined using a given CRC algorithm for the first data sequence; the FCS being usable by a receiver to detect communication errors in the transmitted data frame; determining a CRC storage sequence based on a backscatter tag data sequence, a bit length of the backscatter tag data sequence, and the given CRC algorithm; backscattering the transmitted signal to form a backscattered signal including a backscattered data frame, wherein the backscattered data frame includes a second data sequence and the FCS; the second data sequence includes the transmitted data sequence, the encoded tag data sequence, and the CRC storage sequence; the CRC preservation sequence preserves the FCS of the transmitted data frame in the backscattered data frame by yielding the first CRC value using the given CRC algorithm for the second data sequence; the FCS is usable by the receiver to detect communication errors in the backscattered data frames; A backscatter tag configured to:

2. 2. The backscatter tag of claim 1, wherein the dummy sequence is a sequence of zeros having a bit length at least equal to the sum of the bit lengths of the backscatter tag data sequence and the CRC storage sequence.

3. 2. The backscatter tag of claim 1, wherein the backscatter tag is configured to backscatter the transmitted signal to form a backscattered signal by modifying at least a portion of the dummy sequence in the transmitted data frame to include the encoded tag data sequence and the CRC storage sequence in the backscattered data frame.

4. The backscatter tag comprises: determining a second CRC value for the backscatter tag data sequence using the given CRC algorithm; determining a third CRC value of a bit sequence of zeros having a bit length equal to the bit length of the backscatter tag data sequence using the given CRC algorithm; determining an intermediate sequence by performing an XOR operation of the second CRC value with the third CRC value; inverting a bit sequence of the intermediate sequence to form the CRC stored sequence; The backscatter tag of claim 1 , configured to determine the CRC stored sequence by:

5. The backscatter tag of claim 1 , wherein the backscatter tag data sequence comprises sensor data generated by a sensor coupled to the backscatter tag.

6. 10. The backscatter tag of claim 1, wherein the backscatter tag is configured to backscatter the transmitted signal to form the backscattered signal by modifying a frequency of the transmitted signal to encode data.

7. 10. The backscatter tag of claim 1, wherein the backscatter tag is configured to backscatter the transmitted signal to form the backscattered signal by modifying the amplitude and / or phase of the transmitted signal to encode data.

8. The transmitted signal is in accordance with the IEEE 802.11 standard, and the transmitted data frame is A MAC header; a payload including the first data sequence; The FCS and The backscatter tag of claim 1 , comprising:

9. The backscattered signal is compliant with the IEEE 802.11 standard, and the backscattered data frame is A MAC header; a payload including the second data sequence; The FCS and The backscatter tag of claim 1 , comprising:

10. 1. A method for preserving a frame check sequence (FCS) of a data frame during backscatter communication, the method comprising: receiving a transmitted signal including a transmitted data frame by a backscatter tag, wherein the transmitted data frame includes a first data sequence and the FCS; the first data sequence includes a transmitted data sequence and a dummy sequence; the FCS is based on a first cyclic redundancy check (CRC) value determined using a given CRC algorithm for the first data sequence; the FCS being usable by a receiver to detect communication errors in the transmitted data frame; determining, by the backscatter tag, a CRC storage sequence based on a backscatter tag data sequence, a bit length of the backscatter tag data sequence, and the given CRC algorithm; backscattering, by the backscattering tag, the transmitted signal to form a backscattered signal including a backscattered data frame, wherein the backscattered data frame includes a second data sequence and the FCS; the second data sequence includes the transmitted data sequence, the encoded tag data sequence, and the CRC storage sequence; the CRC preservation sequence preserves the FCS of the transmitted data frame in the backscattered data frame by yielding the first CRC value using the given CRC algorithm for the second data sequence; the FCS is usable by the receiver to detect communication errors in the backscattered data frames; A method comprising:

11. The method of claim 10 , wherein the dummy sequence is a sequence of zeros having a bit length at least equal to the sum of bit lengths of the backscatter tag data sequence and the CRC storage sequence.

12. 11. The method of claim 10, wherein the backscattering includes modifying at least a portion of the dummy sequences in the transmitted data frames to include the encoded tag data sequence and the CRC storage sequence in the backscattered data frames.

13. Determining the CRC storage sequence comprises: determining a second CRC value for the backscatter tag data sequence using the given CRC algorithm; determining a third CRC value of a bit sequence of zeros having a bit length equal to the bit length of the backscatter tag data sequence using the given CRC algorithm; determining an intermediate sequence by performing an XOR operation of the second CRC value with the third CRC value; inverting a bit sequence of the intermediate sequence to form the CRC stored sequence; The method of claim 10, comprising:

14. The method of claim 10 , wherein the backscatter tag data sequence includes sensor data generated by a sensor coupled to the backscatter tag.

15. 11. The method of claim 10, wherein backscattering the transmitted signal to form the backscattered signal comprises encoding data by modifying a frequency of the transmitted signal.

16. 11. The method of claim 10, wherein backscattering the transmitted signal to form the backscattered signal comprises encoding data by modifying an amplitude and / or a phase of the transmitted signal.

17. The transmitted signal is in accordance with the IEEE 802.11 standard, and the transmitted data frame is A MAC header; a payload including the first data sequence; The FCS and The method of claim 10 comprising:

18. The backscattered signal is compliant with the IEEE 802.11 standard, and the backscattered data frame is A MAC header; a payload including the second data sequence; The FCS and The method of claim 10 comprising:

Images