Method and system for backscatter communication using predefined templates - Patents.com

Abstract

Various embodiments herein relate to methods and systems for backscatter communication using predefined templates. According to at least one embodiment, a backscatter communication system is provided, comprising a transmitting unit, a backscatter tag, and a receiving unit. The transmitting unit is configured to transmit a signal comprising a transmitted frame including a predefined data payload. The backscatter tag is configured to receive the signal comprising the transmitted frame from the transmitting unit, encode tag data on the predefined data payload to generate a modified data payload, and transmit a backscatter signal comprising a backscatter frame including the modified data payload. The receiving unit is configured to receive the backscatter signal from the backscatter tag and decode the modified data payload in the backscatter frame to recover the tag data, the decoding being based on the receiving unit's prior knowledge of the predefined data payload.

Description

[Technical field]

[0001] The present subject matter relates to backscatter communication systems and backscattering tags, and more particularly to methods and systems for backscatter communication using predefined templates. [Background technology]

[0002]

[0002] Backscatter communication has attracted attention for its ability to provide low-power connectivity to embedded sensors, wearables, and smart home sensing applications. Such applications have severe power constraints. For example, embedded sensors must last for a long time, but even more traditional smart home monitoring applications can benefit from sensors and actuators that can last for years. Backscatter communication can meet connectivity requirements while consuming low power, such as powered by harvesting energy or with a battery that can last for years.

[0003]

[0003] Current backscatter systems require dedicated hardware to generate an excitation RF signal that the backscatter radio can reflect, as well as to decode the backscatter signal. Recent developments such as Wi-Fi backscatter to BackFi and passive Wi-Fi have reduced the need for dedicated hardware. For example, passive Wi-Fi can be decoded using a standard Wi-Fi radio, but still requires a dedicated continuous wave signal generator as an excitation RF signal source. BackFi requires a proprietary full duplex hardware add-on to the Wi-Fi radio to enable backscatter communication. Thus, there continues to be a need for a backscatter system that can be deployed using general-purpose devices such as access points, smartphones, watches, and tablets. Summary of the Invention

[0004]

[0004] The following introduction is provided to introduce the reader to the more detailed description that follows. The introduction is not intended to limit or define the claimed or unclaimed inventions. One or more inventions may reside in any combination or subcombination of the elements or process steps disclosed in any part of this specification, including the claims and drawings.

[0005]

[0005] In one broad aspect, a backscatter communication system is provided, comprising a transmitting unit, a backscatter tag, and a receiving unit. The transmitting unit is configured to transmit a signal comprising a transmitted frame including a predefined data payload. The backscatter tag is configured to receive the signal comprising the transmitted frame from the transmitting unit, encode tag data on the predefined data payload to generate a modified data payload, and transmit a backscatter signal comprising a backscatter frame including the modified data payload. The receiving unit is configured to receive the backscatter signal from the backscatter tag and decode the modified data payload in the backscatter frame to recover the tag data, the decoding being based on the receiving unit's prior knowledge of the predefined data payload.

[0006]

[0006] In some embodiments, the tag data includes sensor data generated by a sensor coupled to the backscatter tag.

[0007]

[0007] In some embodiments, the system further comprises a backbone network path, and the receiving unit's prior knowledge of the predefined data payload is based on data received from the transmitting unit via the backbone network path.

[0008]

[0008] In some embodiments, the receiving unit includes a memory unit, and the receiving unit's prior knowledge of the predefined data payload is based on data stored in the memory unit.

[0009]

[0009] In some embodiments, the transmitted frame includes a frame header configured to indicate whether the transmitted frame includes a predefined data payload.

[0010]

[0010] In some embodiments, the backscatter tag is configured to encode tag data by modifying the frequency of the signal received from the transmitting unit.

[0011]

[0011] In some embodiments, the transmitting unit is configured to transmit a signal on a first frequency channel, the backscatter tag is configured to transmit the backscatter signal on a second frequency channel separate from the first frequency channel, and the receiving unit is configured to receive the backscatter signal on the second frequency channel.

[0012] In some embodiments, the backscatter tag is configured to encode tag data by modifying the amplitude or phase of the signal received from the transmitting unit.

[0013] In another broad aspect, there is provided a backscatter tag configured to receive a transmitted signal comprising transmitted frames having a predefined data payload from a transmitting unit, encode tag data on the predefined data payload to generate a modified data payload, and transmit a backscatter signal comprising the backscatter frame comprising the modified data payload to a receiving unit, the receiving unit configured to decode the modified data payload to recover the tag data, the decoding being based on the receiver's prior knowledge of the predefined data payload.

[0014]

[0014] In another broad aspect, a method for backscatter communication is provided, the method comprising: transmitting, by a transmitting unit, a signal comprising a transmitted frame including a predefined data payload; backscattering the signal using a backscatter tag device, the backscattering comprising receiving, from the transmitting unit, a signal comprising the transmitted frame, encoding tag data on the predefined data payload to generate a modified data payload, and transmitting a backscatter signal comprising a backscatter frame including the modified data payload; receiving, by a receiving unit, the backscatter signal; and decoding, by the receiving unit, the modified data payload in the backscatter frame to recover the tag data, the decoding being based on the receiving unit's prior knowledge of the predefined data payload.

[0015]

[0015] In some embodiments, the tag data includes sensor data generated by a sensor coupled to the backscatter tag.

[0016] In some embodiments, the receiving unit's prior knowledge of the predefined data payload is based on data received from the transmitting unit over a backbone network path.

[0017] In some embodiments, the receiving unit's prior knowledge of the predefined data payload is based on data stored in a memory unit of the receiving unit.

[0018] In some embodiments, the transmitted frame includes a frame header configured to indicate whether the transmitted frame includes a predefined data payload.

[0019]

[0019] In some embodiments, backscattering involves encoding the tag data by modifying the frequency of the signal received from the transmitting unit.

[0020]

[0020] In some embodiments, the transmitting unit transmits a signal on a first frequency channel, the backscatter tag transmits the backscatter signal on a second frequency channel separate from the first frequency channel, and the receiving unit receives the backscatter signal on the second frequency channel.

[0021] In some embodiments, the backscatter tag encodes tag data by modifying the amplitude or phase of the signal received from the transmitting unit.

[0022]

[0022] In another broad aspect, a method for backscatter communication is provided comprising: receiving a transmitted signal comprising a transmitted frame including a predefined data payload by a backscatter tag from a transmitting unit, encoding, by the backscatter tag, tag data on the predefined data payload to generate a modified data payload, and transmitting, by the backscatter tag, a backscatter signal comprising a backscatter frame including the modified data payload to a receiving unit, the receiving unit configured to decode the modified data payload to recover the tag data, the decoding being based on the receiver's prior knowledge of the predefined data payload.

[0023]

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

[0024]

[0024] In order to better understand the embodiments described in this specification and to more clearly show how they may be implemented, reference is now made, by way of example only, to the accompanying drawings, which show at least one exemplary embodiment. [Figure 1A]

[0025] FIG. 1A is a simplified diagram of a backscatter communication system in accordance with some exemplary embodiments. [Figure 1B]

[0026] FIG. 1B is a simplified diagram of a backscatter communication system in accordance with some other exemplary embodiments. [Figure 2A]

[0027] FIG. 2A is a simplified diagram of an example embodiment of a backscatter communication system in accordance with the teachings provided herein. [Figure 2B]

[0028] FIG. 2B is a simplified diagram of another exemplary embodiment of a backscatter communication system in accordance with the teachings provided herein. [Figure 2C]

[0029] FIG. 2C is a simplified diagram of another example embodiment of a backscatter communication system in accordance with the teachings provided herein. [Figure 2D]

[0030] FIG. 2D is a simplified diagram of another example embodiment of a backscatter communication system in accordance with the teachings provided herein. [Diagram 3]

[0031] FIG. 3 is a process flow for an exemplary embodiment of a method for backscatter communication.

[0025]

[0032] Further aspects and features of the exemplary embodiments described herein will become apparent from the following description taken in conjunction with the accompanying drawings. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026]

[0033] It will be understood that, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or similar elements or steps for simplicity and clarity of illustration. In addition, numerous specific details have been described to provide a thorough understanding of the exemplary embodiments described herein. However, it will be understood by those skilled 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. Furthermore, this description should in no way be considered as limiting the scope of the embodiments described herein, but rather as merely illustrating implementations of various embodiments described herein.

[0027]

[0034] In the description and drawings herein, reference may be made to a Cartesian coordinate system in which the vertical or z-axis extends in an up-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 in a second horizontal or length dimension horizontally across the x-axis.

[0028]

[0035] The terms "an embodiment," "embodiment," "embodiments," "the embodiment," "the embodiment," "one or more embodiments," "some embodiments," and "one embodiment" mean "one or more (but not all) embodiments of the invention(s)," unless expressly specified otherwise.

[0029]

[0036] The terms "including," "comprising," and variations thereof mean "including, but not limited to," unless expressly specified otherwise. A list of items does not imply that any or all of the items are mutually exclusive unless expressly specified otherwise. The terms "a," "an," and "the" mean "one or more" unless expressly specified otherwise.

[0030]

[0037] As used herein and in the claims, two or more parts are said to be "coupled," "connected," "attached," or "fastened" when the parts are joined or move together directly or indirectly (i.e., through one or more intermediate parts) to the extent that a link occurs. As used herein and in the claims, two or more parts are said to be "directly coupled," "directly connected," "directly attached," or "directly fastened" when the parts are connected in physical contact with one another. As used herein, two or more parts are said to be "rigidly coupled," "rigidly connected," "rigidly attached," or "rigidly fastened" when the parts are coupled to move as one while maintaining a constant orientation relative to one another. The terms "coupled," "connected," "attached," and "fastened" do not distinguish between the manner in which two or more parts are joined together.

[0031]

[0038] The embodiments herein provide systems and methods for backscatter communication that are compliant with existing communication protocols such as Wi-Fi 802.11g / n, Bluetooth, and ZigBee. As such, for simplicity and ease of explanation, the embodiments herein refer to communication via 802.11b compliant Wi-Fi frames, although it should be noted that the described embodiments are not limited as the disclosed backscatter communication system may operate with other similar communication standards.

[0032]

[0039] Reference is made to FIG. 1A, which is a simplified diagram of a backscatter communication system 100a according to some embodiments.

[0033]

[0040] As shown, system 100a generally includes a transmitting unit 102, a receiving unit 104, and a backscatter tag 120. It will be appreciated that in some embodiments, one or more of the transmitting and receiving units may actually comprise devices that combine transmitting and receiving capabilities.

[0034]

[0041] As shown, the transmitter 102 is configured to transmit an 802.11b compliant Wi-Fi frame 85 at a predefined frequency. To this end, the transmitter 102 is also referred to herein as an "excitation device" and the transmitted signal 85 is also referred to herein as an "excitation signal." The transmitter 102 may comprise, for example, a cellular phone having a standard Wi-Fi radio (as shown in FIG. 1B). In other cases, the transmitter 102 may be any other device configured to communicate via a Wi-Fi radio. The receiver 104 is then tuned to a predefined frequency (i.e., which may or may not be the same as the frequency of the transmitter 102) to receive the Wi-Fi frame 85. In some cases, the receiver 104 may comprise, for example, a Wi-Fi access point, or any other suitable receiving device.

[0035]

[0042] As further shown, the backscatter tag 120 operates to intercept Wi-Fi frames 85 being transmitted to the receiver 104. In particular, the tag 120 is configured to manipulate the intercepted frames in order to encode its own data information onto the Wi-Fi frames. The tag 120 can backscatter a signal 95 comprising a frame with the tag's own data that modifies the original data payload, i.e., the data payload transmitted by the transmitter 102.

[0036]

[0043] More specifically, the tag 120 receives one or more frames in the signal 85 that contain a payload transmitted by the transmitter 104. The tag 120 is then operable to manipulate the payload data to encode its own data. This process of encoding the tag's own data onto existing data in the signal 85 is also known as "dirty paper encoding."

[0037]

[0044] The tag 120 may apply a variety of different methods to manipulate the incident packet to generate the backscatter signal. For example, a codeword conversion scheme may be used as described in U.S. Patent No. 10,338,205, filed August 14, 2017, and issued July 2, 2019, to Zhang et al., and U.S. Patent Application Publication No. 2019 / 0274144, filed April 25, 2019, to Zhang et al., both of which are incorporated herein by reference in their entireties. The codeword conversion may include, for example, XORing data bits in the original transmitted payload (i.e., signal 85) with the tag's data to generate the backscatter signal. In practice, the codeword conversion is performed, for example, by modifying one of the amplitude, phase, or frequency of the incident excitation signal 85.

[0038]

[0045] To this end, backscatter tag 120 may include various passive circuit components that act on the received signal 85 to encode (i.e., manipulate) the signal 85 with the tag's own data. Various architectures and configurations of passive circuitry for backscatter tags are known in the art.

[0039]

[0046] The tag-specific data encoded by tag 102 may vary based on the application of system 100a. For example, in at least one exemplary application, the tag data may comprise sensor data generated by a sensor system 125 coupled to tag 120. In this manner, as discussed in the Background, backscatter tags 120 may facilitate the implementation of ultra-low power sensor networks.

[0040]

[0047] 1A, in system 100a, backscattered signal 95 is in the same frequency channel as original excitation signal 85. Receiver 104 then receives both original signal 85 as well as backscattered signal 95 on a single frequency channel. Receiver 104 is then configured to process the data in backscattered signal 95 to decode and separate (i.e., disentangle) the tag's own data from the originally transmitted data. In other cases, the decoding is performed by an external device (i.e., decoding block 150) connected to receiver 104.

[0041]

[0048] Again, various exemplary methods for decoding and recovering the data of the tag itself will occur to those skilled in the art. For example, as described in U.S. Pat. No. 10,338,205 to Zhang et al. and U.S. Patent Application Publication No. 2019 / 0274144 to Zhang et al., decoding may include reversing the XOR operation performed by the tag 102 and using an XOR decoder. The XOR decoder XORs bits in the data payload of the backscattered signal 95 with bits in the data payload of the original signal 85 to recover the data bits associated with the tag's data.

[0042]

[0049] In view of the above, it is appreciated that the system 100a has several significant shortcomings. For example, the ability of the receiver 104 to decode the backscattered signal is often degraded by interference created by receiving the signals 85, 95 on the same frequency channel. For at least this reason, the receiver 104 may not be able to distinguish between the original transmitted signal 85 and the backscattered signal 95. The receiver 104 may then be unable to effectively recover the tag's data, for example, by XORing the data bits in the original signal 85 with the backscattered signal 95.

[0043]

[0050] Reference is now made to FIG. 1B, which is a simplified diagram of a backscatter communication system 100b, according to some other embodiments.

[0044]

[0051] To at least partially mitigate the above-mentioned challenges inherent to system 100a, system 100b includes two receivers 104a and 104b, each tuned to listen (i.e., receive) frames on a separate frequency channel.

[0045]

[0052] In this embodiment, the transmitter 102 transmits a frame 85 on a first frequency channel. The receiver 104a is then tuned to the first frequency channel to receive the signal 85. In contrast to the system 100a, however, in addition to encoding the backscattered data, the tag 120 is further configured to frequency shift the backscattered signal 95 to a different frequency. In this manner, the tag 120 generates a frequency-shifted backscattered signal 95 that is compatible with the 802.11b standard. The second receiver 104b is then tuned to a second frequency channel to receive the backscattered signal 95.

[0046]

[0053] The decode block 150 receives the original frames 85 from the first receiver 104a and the backscattered frames 95 from the second receiver 104b, and then recovers the tag data in a manner similar to that described in the system 100a. For example, the decode block 150 may include an XOR block that performs an XOR operation on the payloads contained in the two frames (i.e., the frames in signals 85 and 95) to recover the tag data.

[0047]

[0054] Various embodiments for implementing the system 100b are also described in detail in U.S. Pat. No. 10,338,205 to Zhang et al. and U.S. Patent Application Publication No. 2019 / 0274144 to Zhang et al.

[0048]

[0055] In view of the above, it is believed that system 100b mitigates at least some of the drawbacks associated with system 100a, i.e., by frequency shifting backscattered signal 95 to an adjacent frequency channel, there is less interference between backscattered signal 95 and original signal 85.

[0049]

[0056] Furthermore, the inventors have recognized that system 100b still suffers from several significant shortcomings. For example, system 100b relies on a minimum of two receivers 104a, 104b to function effectively. System 100b cannot function using a single receiver tuned to a single frequency. This, in turn, adds a layer of hardware cost to implement system 110b.

[0050]

[0057] In view of the above, embodiments herein attempt to provide a backscatter communication system that mitigates the shortcomings of each of systems 100a and 100b and allows for the use of backscatter tags having only a single receiver.

[0051]

[0058] More particularly, and as provided in more detail herein, the disclosed embodiments enable the transmitting device 102 to transmit frames having predefined templates of payload data at predefined time or frequency intervals. That is, the payload data templates are predefined in that they are known a priori to the receiver 104 (i.e., predefined from the receiver's perspective). In this manner, the receiver 104 (or a decoding device) does not need to rely on data in the original transmitted signal 85 to decode the backscattered signal 95.

[0052]

[0059] Reference is now made to FIG. 2A, which illustrates an exemplary embodiment of a backscatter communication system 200a, in accordance with embodiments provided herein.

[0053]

[0060] As shown, backscatter system 200a is generally similar to backscatter system 100a in that system 200a comprises a transmitting device 102, a single receiver 104, and one or more backscatter tags 120. Additionally, similar to system 100a, but in contrast to system 100b, the backscatter signal 95 of system 200a may be transmitted on the same or a different frequency channel as the original signal 85.

[0054]

[0061] To eliminate the need for two receivers such as 100b, system 200a relies on transmitter 102 transmitting frames 85 that carry predefined payload data templates. These payloads are known a priori to receiver 104. For example, in the illustrated embodiment, transmitter 102 may transmit a packet with a payload of all "0's" (i.e., "000000").

[0055]

[0062] Similar to system 100a, backscatter tag 120 may receive frames in signal 85 and may encode its own data onto the packet payload. Tag 120 then backscatters the combined resulting packet for reception by receiver 104. In at least some embodiments, tag 120 may also frequency shift backscatter signal 95 using passive circuit components and methods such as those described in U.S. Pat. No. 10,338,205 to Zhang et al. and U.S. Patent Application Publication No. 2019 / 0274144 to Zhang et al. This may be done to avoid interference between backscatter signal 95 and original signal 85, as previously discussed.

[0056]

[0063] On the receiver side, the receiver 104 recovers the tag's data based on a priori knowledge of a predefined template payload. For example, the receiver 104 may XOR the backscattered data payload with a known predefined template data payload to recover the tag's data. If the tag 120 frequency shifts the backscattered signal 95, the receiver 104 may also tune to the frequency of the signal 95 instead of the original signal 85.

[0057]

[0064] In this manner, system 200a may be distinguished from system 100a at least in that receiver 104 relies on a priori knowledge of the payload in signal 85 to recover the tag's data. That is, the receiver's knowledge of the payload is not based on or contingent on received signal 85. Thus, received signal 85 is not necessary to enable receiver 104 to decode the tag's data. For this reason, if tag 120 frequency shifts backscattered signal 95, receiver 104 may simply tune to the frequency-shifted channel and simply tune out of the frequency channel associated with original signal 85. In this manner, system 200a may operate using only a single receiver 104 tuned to a single frequency channel at a given time.

[0058]

[0065] As mentioned above, to implement the system 200b, the receiver 104 requires advanced knowledge of the data payload transmitted by the transmitter 102. Various methods are possible for informing the receiver 104 in advance of the predefined payload template.

[0059]

[0066] For example, in at least one exemplary embodiment, the transmitter 102 may be configured to always transmit the same template payload, and the receiver 104 may then be externally configured to store this pre-defined template, i.e., in the receiver 102's memory.

[0060]

[0067] In another exemplary embodiment, an initiation sequence between the transmitter 102 and the receiver 104 may enable the transmitter 102 to communicate a predefined template to the receiver 104. For example, as illustrated in the system 200b of FIG. 2B, a backbone network path 202 is provided. The backbone path 202 may comprise, for example, one or more switches 204a and / or routers 204b connecting the transmitter 102 to the receiver 104. Thus, the backbone path 202 may be used for an initiation sequence in which the transmitter 102 communicates (directly or indirectly) the contents of the packet payload to the receiver 104 in advance. An advantage of this system configuration is that the template payload may be dynamically changed by the transmitter 102, as long as the transmitter 102 can communicate a new predefined template payload in advance to the receiver 104 via the backbone path 202.

[0061]

[0068] In yet another exemplary embodiment, the transmitter 102 can generate frames that include a code indication reference of a predefined payload in the frame header. That is, the header of the frame that carries the original data payload template can include some code that references the known template being used. The receiver 104 can then receive the frame in the backscatter signal 95 and extract the unmodified header to determine the nature of the predefined template.

[0062]

[0069] Reference is now made to Figures 2C and 2D, which illustrate other exemplary embodiments of backscatter communication systems 200c and 200d, respectively.

[0063]

[0070] Backscatter systems 200c and 200d operate using the same principles as backscatter system 200b, except that multiple receivers 104a-104e are provided. For example, the multiple receivers 104 may include a wireless LAN access point (WLAN AP) 104a, a server 104b, a smartphone 104c, a host 104d, and a mobile computer 104e. In this embodiment, the backscatter signal 95 may be received by one or more of the multiple receivers 104. Thus, each of the receivers 104 may have advanced knowledge of the predefined template transmitted by the transmitter 102.

[0064]

[0071] To this end, in system 200c, the predefined templates have a payload of all zeros (i.e., "000000"), while in system 200d, the predefined templates have a payload of all ones (i.e., "11111"). In each example, an exemplary Phase Shift Key (PSK) modulation scheme is used by the tag 102 to encode the tag's data into the original payload data.

[0065]

[0072] Reference is now made to FIG. 3, which illustrates a process flow for an exemplary embodiment of a method 300 for backscatter communication, according to some embodiments.

[0066]

[0073] As shown, at 302, the transmitter 102 can transmit a frame having a predefined template for its data payload. At 304, the backscatter tag 120 can receive the packet and generate a backscatter frame by encoding the tag's own data on the payload data in the received frame. At 306, the backscatter tag 120 can transmit the backscatter frame. At 308, the receiver 104 can receive and decode the data in the backscatter frame to recover the tag's own data. As previously described, this can be performed based on the receiver's advanced knowledge of the payload of the original packet generated by the transmitter 102.

[0067]

[0074] Although the above description provides examples of embodiments, it will be understood that some features and / or functions of the described embodiments are susceptible to modification without departing from the spirit and principles of operation of the described embodiments. Thus, the above description is intended to illustrate, but not limit, the present invention, and those skilled in the art will appreciate that other variations and modifications can be made without departing from the scope of the present 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. 1. A backscatter communication system comprising: a transmitting unit configured to transmit a signal comprising a transmitted frame containing a predefined data payload; receiving, from the transmitting unit, the signal comprising the transmitted frame; - encoding tag data onto said predefined data payload to generate a modified data payload; - transmitting a backscatter signal comprising a backscatter frame containing said modified data payload; a backscatter tag configured to: A receiving unit including a memory unit, said receiving unit comprising: receiving the backscatter signal from the backscatter tag; decoding the modified data payload in the backscattered frame to recover the tag data, wherein the decoding is based on the receiving unit's prior knowledge of the predefined data payload, the prior knowledge being based on data stored in the memory unit; a receiving unit configured to: A system comprising:

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

3. The system of claim 1 , further comprising a backbone network path, wherein the receiving unit's prior knowledge of the predefined data payload is based on data received from the transmitting unit via the backbone network path.

4. The system of claim 1 , wherein the transmitted frame includes a frame header configured to indicate whether the transmitted frame includes the predefined data payload.

5. The system of claim 1 , wherein the backscatter tag is configured to encode the tag data by modifying the frequency of the signal received from the transmitting unit.

6. 6. The system of claim 5, wherein the transmitting unit is configured to transmit the signal on a first frequency channel, the backscatter tag is configured to transmit the backscatter signal on a second frequency channel distinct from the first frequency channel, and the receiving unit is configured to receive the backscatter signal on the second frequency channel.

7. The system of claim 1 , wherein the backscatter tag is configured to encode the tag data by modifying the amplitude or phase of the signal received from the transmitting unit.

8. - receiving, from a transmitting unit, a transmitted signal comprising transmitted frames having a predefined data payload; - encoding tag data onto said predefined data payload to generate a modified data payload; transmitting a backscatter signal comprising a backscatter frame comprising the modified data payload to a receiving unit, the receiving unit being configured to decode the modified data payload to recover the tag data, wherein the decoding is based on the receiver's prior knowledge of the predefined data payload, the prior knowledge being based on data stored in a memory unit of the receiving unit; A backscatter tag configured to:

9. 1. A method for backscatter communication, comprising: - transmitting, by a transmitting unit, a signal comprising a transmitted frame containing a predefined data payload; - backscattering said signal using a backscatter tag device, wherein said backscattering comprises: receiving, from the transmitting unit, the signal comprising the transmitted frame; - encoding tag data on said predefined data payload to generate a modified data payload; - transmitting a backscatter signal comprising a backscatter frame containing said modified data payload; Including, - receiving, by a receiving unit, said backscattered signals; decoding, by the receiving unit, the modified data payload in the backscattered frame to recover the tag data, wherein the decoding is based on the receiving unit's prior knowledge of the predefined data payload, the prior knowledge being based on data stored in a memory unit of the receiving unit; A method comprising:

10. The method of claim 9 , wherein the tag data comprises sensor data generated by a sensor coupled to the backscatter tag.

11. The method of claim 9 , wherein the receiving unit's prior knowledge of the predefined data payload is based on data received from the transmitting unit over a backbone network path.

12. 10. The method of claim 9, wherein the transmitted frame includes a frame header configured to indicate whether the transmitted frame includes the predefined data payload.

13. 10. The method of claim 9, wherein said backscattering comprises encoding said tag data by modifying the frequency of said signal received from said transmitting unit.

14. 14. The method of claim 13, wherein the transmitting unit transmits the signal on a first frequency channel, the backscatter tag transmits the backscatter signal on a second frequency channel distinct from the first frequency channel, and the receiving unit receives the backscatter signal on the second frequency channel.

15. 10. The method of claim 9, wherein the backscatter tag encodes the tag data by modifying the amplitude or phase of the signal received from the transmitting unit.

16. 1. A method for backscatter communication, comprising: - receiving a transmitted signal comprising a transmitted frame containing a predefined data payload by a backscatter tag from a transmitting unit; - encoding tag data onto the predefined data payload to generate a modified data payload by the backscatter tag; transmitting, by the backscatter tag, a backscatter signal comprising a backscatter frame including the modified data payload to a receiving unit, the receiving unit configured to decode the modified data payload to recover the tag data, wherein the decoding is based on the receiver's prior knowledge of the predefined data payload, the prior knowledge being based on data stored in a memory unit of the receiving unit; A method comprising:

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