WO2025171879A1

WO2025171879A1 - Interference cancellation for backscattering communication devices

Info

Publication number: WO2025171879A1
Application number: PCT/EP2024/053924
Authority: WO
Inventors: Henrik Sjöland; Giuseppe Moschetti; Rickard Ljung; Gang ZOU; Shousheng He
Original assignee: Telefonaktiebolaget LM Ericsson AB
Current assignee: Telefonaktiebolaget LM Ericsson AB
Priority date: 2024-02-15
Filing date: 2024-02-15
Publication date: 2025-08-21
Anticipated expiration: 2026-08-15

Abstract

A backscattering communication device (101, 400) has a first dual-polarized antenna (103, 401) and a second dual-polarized antenna (105, 407). The first dual-polarized antenna (103, 401) has a first polarization port (P1) associated with a first polarization direction (403) and a second polarization port (P2) associated with a second polarization direction (405). The second dual-polarized antenna (105, 407) has a third polarization port (P3) associated with a third polarization direction (409) and a fourth polarization port (P4) associated with a fourth polarization direction (411). The device (101, 400) also has a first connection (107, 413) coupled between the first polarization port (P1) of the first dual-polarized antenna (103, 401) and the fourth polarization port (P4) of the second dual-polarized antenna (105, 407); and a second connection (109, 415) coupled between the second polarization port (P2) of the first dual- polarized antenna (103, 401) and the third polarization port (P3) of the second dual-polarized antenna (105, 407). The first polarization direction (403) is different from the fourth polarization direction (411); the second polarization direction (405) is different from the third polarization direction (409); the first connection (107, 413) has a first length (L1) and a first switch (111, 417) for opening and closing the first connection (107, 413); the second connection (109, 415) has a second length (L2) and a second switch (113, 419) for opening and closing the second connection (109, 415), wherein the second length (L2) is different from the first length (L1); and the first and second lengths (L1, L2) are configured such that a phase shift difference between a signal propagating through the first connection (107, 413) and a signal propagating through the second connection (109, 415) is non-zero at a center frequency of a frequency band of operation of the backscattering communication device (101, 400).

Description

INTERFERENCE CANCELLATION FOR BACKSCATTERING COMMUNICATION DEVICES

BACKGROUND

The present invention relates to backscattering communication technology, and more particularly to technology for achieving improved interference cancellation properties with respect to passively transmitted backscattered communication signals.

Some or all of the following abbreviations are used in this specification:

Abbreviation Explanation loT Internet of Things

PA Power Amplifier

RF Radio Frequency

RFID Radio Frequency Identification

RX Receiver

SINR Signal to Interference and Noise Ratio

SNR Signal to Noise Ratio

TX Transmitter

UE User Equipment

According to a prediction made by IBM in 2012, the growth of Internet of Things (loT) devices has the potential of reaching a trillion-unit ecosystem. However, so far, the demand for loT devices has been lower than predicted. One reason for this slower than expected growth has been the fact that powering several hundreds of billions of devices with replaceable batteries is neither feasible nor sustainable. Having to replace batteries add costs and also creates an environmental problem when hundreds of millions of batteries every day need to be discarded. In addition, there are applications where replacing a battery is not an option. Therefore, in order to create a sustainable massive loT ecosystem there is a need for the development of self- sustainable devices that do not need any maintenance for decades.

Backscattering communication has received considerable interest recently because it enables passive devices to transmit information with substantial reduction in power consumption and costs. Backscatter communication is a well-known technique in which an incoming carrier signal transmitted from a transmitter or other RF source (e.g., microwave oven) is modulated and reflected back into the environment. See, for example, H. Stockman, "Communication by Means of Reflected Power," in Proceedings of the IRE, vol. 36, no. 10, pp. 1196-1204, Oct. 1948, doi: 10.1109/JRPROC.1948.226245. This technique, which is widely used in, for instance, radio frequency identification (RFID) communication systems, allows a strong reduction in the device power consumption since no power amplifier (PA) and other power hungry components of a typical transmitter are required.

Backscattering systems can be classified into three categories: monostatic, bi-static and ambient backscattering. In the case of a monostatic system, the RF carrier transmitter and backscatter receiver antenna are integrated in the same device. An example of a monostatic system is an RFID device. A disadvantage of the monostatic backscattering is that reception of the modulated back-scattered signal suffers from proximity of a much stronger transmitted carrier signal, due to round-trip path-loss. To avoid this, bi-static and ambient backscattering system have been developed, in which the transmitter and receiver antennas are separated in different devices. Bi-static and ambient backscattering are distinguished from one another in that, in a bi-static system, the carrier signal for backscattering is generated intentionally with a dedicated radio, whereas in an ambient backscattering system, ambient signals that are already present in the environment are captured and used as a carrier.

One of the biggest challenges with bi-static and ambient backscattering communication is overcoming the interference caused by superposition of the TX signal carrier with the modulated backscattered signal that is reflected back to the receiver by the backscattering communication device. Typically, the power from the TX carrier is several orders of magnitude larger than that of the backscattered signal at the receiver. This creates a big challenge for the receiver since a very large dynamic range is needed for it to be able to differentiate between the modulated backscattered signal and the interference. Another challenge is the need for the transmitter to have low noise levels in order not to degrade the SNR of the backscattered signal.

Different techniques with the goal of reducing the interference from the TX signal have been proposed so far, such as:

• Using long symbol duration to improve SINR of the backscattered signal

• Shifting the backscattered signal to a different frequency band

• Using polarization-based reconfigurable (PR) antennas

• Using multiple receiver antennas

• Hybrid beamforming • Machine learning assisted detection approaches

These conventional techniques have problems, however. For example, a problem with frequency shifting the backscattered signal is that there isn’t always an available spectrum to shift the backscattered signal to. Frequency shifting also has a non-negligible power consumption cost at the backscattering communication device.

Techniques based on polarization could be a low cost, low complexity option that may be suitable in more scenarios. U.S. Patent 6,970,089 (“Full-spectrum passive communication system and method”) discloses a backscattering system in which the receiving device is equipped with two antennas with different polarizations to receive the carrier and the backscattering signals. The modulated signal is extracted by coupling the two received signals to a mixer. This helps to mitigate the interference from carrier signal at the receiver, but it has a significant drawback since it is only applicable when the polarization of the signals matches that of the receiving antennas.

In view of the foregoing, there is a need for technology that addresses the abovedescribed and related problems, including but not limited to providing backscattering communication technology that can overcome the interference caused by superposition of the TX signal carrier with the modulated backscattered signal that is reflected back to a receiver by the backscattering communication device.

SUMMARY

It should be emphasized that the terms “comprises” and “comprising”, when used in this specification, are taken to specify the presence of stated features, integers, steps or components; but the use of these terms does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

Moreover, reference letters may be provided in some instances (e.g., in the claims and summary) to facilitate identification of various steps and/or elements. However, the use of reference letters is not intended to impute or suggest that the so-referenced steps and/or elements are to be performed or operated in any particular order.

In accordance with one aspect of the present invention, the foregoing and other objects are achieved in technology (e.g., methods, apparatuses, nontransitory computer readable storage media, program means) for communicating a radiofrequency signal encoded with information. In an aspect of some but not necessarily all embodiments, communicating comprises receiving a first radiofrequency signal in a first polarization direction and receiving a second radiofrequency signal in a second polarization direction that is different from the first polarization direction. The first radiofrequency signal, the second radiofrequency signal, a first phase shifted signal, and a second phase shifted signal are then selectively radiated, wherein selectively radiating is in accordance with a pattern of first and second operation modes, wherein the pattern is an encoding of the information via on-off keying modulation. Further, the first operation mode comprises radiating at least a portion of the first radiofrequency signal in the first polarization direction; and radiating at least a portion of the second radiofrequency signal in the second polarization direction. The second operation mode comprises producing the first phase shifted radiofrequency signal by shifting a phase of the first radiofrequency signal by a first phase shift amount; producing the second phase shifted radiofrequency signal by shifting a phase of the second radiofrequency signal by a second phase shift amount that is different from the first phase shift amount; radiating the first phase shifted radiofrequency signal in the second polarization direction; and radiating the second phase shifted radiofrequency signal in the first polarization direction.

In another aspect of some but not necessarily all embodiments, communicating comprises capturing and storing energy of the first radiofrequency signal when the radiating is in the first operation mode.

In yet another aspect of some but not necessarily all embodiments, a first dual-polarized antenna is used to receive the first radiofrequency signal and the second radiofrequency signal; and a second dual-polarized antenna is used to radiate the first phase shifted radiofrequency signal and the second phase shifted radiofrequency signal. Further, radiofrequency signals are allowed to flow in only (e.g., substantially only) one direction from the first dual-polarized antenna to the second dual-polarized antenna.

In another aspect of some but not necessarily all embodiments, a backscattering communication device comprises a first dual-polarized antenna having a first polarization port associated with a first polarization direction and a second polarization port associated with a second polarization direction; a second dual-polarized antenna having a third polarization port associated with a third polarization direction and a fourth polarization port associated with a fourth polarization direction; a first connection coupled between the first polarization port of the first dual-polarized antenna and the fourth polarization port of the second dual-polarized antenna; and a second connection coupled between the second polarization port of the first dual-polarized antenna and the third polarization port of the second dual-polarized antenna. In such embodiments, the first polarization direction is different from the fourth polarization direction; the second polarization direction is different from the third polarization direction; the first connection has a first length and a first switch for opening and closing the first connection; the second connection has a second length and a second switch for opening and closing the second connection, wherein the second length is different from the first length; and the first and second lengths are configured such that a phase shift difference between a signal propagating through the first connection and a signal propagating through the second connection is non-zero at a center frequency of a frequency band of operation of the backscattering communication device.

In another aspect of some but not necessarily all embodiments, the center frequency has a wavelength, ; and the first length is equal to the second length plus X/2.

In yet another aspect of some but not necessarily all embodiments, the first polarization direction is orthogonal to the fourth polarization direction; and/or the second polarization direction is orthogonal to the third polarization direction.

In still another aspect of some but not necessarily all embodiments, the first and second lengths are configured such that the phase shift difference between the signal propagating through the first connection and the signal propagating through the second connection is 180 degrees at the center frequency of the frequency band of operation of the backscattering communication device.

In another aspect of some but not necessarily all embodiments, the backscattering communications device comprises an energy harvesting storage configuration connected to one or more of the first dual-polarized antenna and the second dual-polarized antenna, wherein the energy harvesting storage configuration is configured to capture and store energy of radiofrequency signals received by one or both of the first and second dual-polarized antennas when the first and second switches are open.

In yet another aspect of some but not necessarily all embodiments, the first connection further comprises a first isolator; and the second connection further comprises a second isolator, wherein the first and second isolators are configured so as to allow radiofrequency signals to flow in only one direction from a first one of the first and second dual-polarized antennas to a second one of the first and second dual-polarized antennas.

In still another aspect of some but not necessarily all embodiments, at least one of the first dual-polarized antenna and the second dual-polarized antenna is implemented using patch antennas. In another aspect of some but not necessarily all embodiments, the backscattering communication device comprises a baseband circuit connected to the first and second switches and configured to open and close the first and second switches in correspondence with a modulating data sequence. In some but not necessarily all instances, the baseband circuit is configured to use on-off keying modulation when opening and closing the first and second switches.

In yet another aspect of some but not necessarily all embodiments, an antenna array comprises a first backscattering communication device in accordance with any of the above- mentioned embodiments, and a second backscattering communication device in accordance with any of the above-mentioned embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and advantages of the invention will be understood by reading the following detailed description in conjunction with the drawings in which:

Figure 1 illustrates an exemplary embodiment of a backscattering communication device in accordance with invention.

Figure 2 is a high-level illustration of communication using an exemplary backscattering communication device that is in accordance with the invention.

Figure 3 illustrates an array of multiple antennas in accordance with an aspect of some inventive embodiments, wherein the array comprises multiple instances of an exemplary backscattering communication device that together form a larger antenna array of dual-polarized antennas.

Figure 4 is a block diagram of a backscattering communication device in accordance with aspects of some exemplary inventive embodiments.

Figure 5 is, in one respect, a flowchart of actions performed by a backscattering communication device in accordance with aspects of some exemplary inventive embodiments.

Figure 6 shows an exemplary controller that may be included in a backscattering communication device to cause any and/or all of the herein-described and illustrated actions associated with that device to be performed. DETAILED DESCRIPTION

The various features of the invention will now be described with reference to the figures, in which like parts are identified with the same reference characters.

The various aspects of the invention will now be described in greater detail in connection with a number of exemplary embodiments. To facilitate an understanding of the invention, many aspects of the invention are described in terms of sequences of actions to be performed by elements of a computer system or other hardware capable of executing programmed instructions. It will be recognized that in each of the embodiments, the various actions could be performed by specialized circuits (e.g., analog and/or discrete logic gates interconnected to perform a specialized function), by one or more processors programmed with a suitable set of instructions, or by a combination of both. The term “circuitry configured to” perform one or more described actions is used herein to refer to any such embodiment (i.e., one or more specialized circuits alone, one or more programmed processors, or any combination of these). Moreover, the invention can additionally be considered to be embodied entirely within any form of non- transitory computer readable carrier, such as solid-state memory, magnetic disk, or optical disk containing an appropriate set of computer instructions that would cause a processor to carry out the techniques described herein. Thus, the various aspects of the invention may be embodied in many different forms, and all such forms are contemplated to be within the scope of the invention. For each of the various aspects of the invention, any such form of embodiments as described above may be referred to herein as “logic configured to” perform a described action, or alternatively as “logic that” performs a described action.

Embodiments that include aspects of the invention variously relate to technology that transmits data by modulating backscatter signals. In an aspect of some but not necessarily all inventive embodiments, the effect of the interference from the TX carrier into the receiver is reduced by shifting the polarization of the modulated signal before radiating it. The backscattered signal from the backscattering communication device is reflected with a polarization that is different from that of the originally received TX signal carrier. In some embodiments, this means reflecting the backscattered signal with a polarization that is orthogonal to that of the originally received TX signal carrier.

By shifting polarization in this manner, the SNR of the backscattered signal is increased in the receiver since the interference from the TX carrier can then be suppressed by separating signals based on their having different polarizations. In another aspect of some embodiments, the technology is advantageously applied in a bi-static or ambient backscatter communication system.

In still another aspect of some but not necessarily all embodiments, the shift in polarization is accomplished by using two dual-polarized antennas. These can be implemented with, for example and without limitation, patch antennas.

In yet another aspect of some but not necessarily all embodiments, the signal from one polarization port of a first dual-polarized antenna is connected to the orthogonal polarization port of a second dual-polarized antenna, and vice versa. Additionally, the two connections between the antennas are made with a different length. For example, and without limitation, the length difference between the two connections is configured so the relative phase difference between the two connections becomes 180 degrees at the center frequency of the band of operation. A signal with a first polarization entering the first antenna will then be transmitted by the second antenna with a second polarization, where the second polarization is orthogonal to the first. Similarly, a signal entering the second antenna will be transmitted with an orthogonal polarization by the first antenna. The 180 degree phase shift has the effect of changing the sign of one of the signal components of the radiated signal, and this sign change has the effect of preventing the radiated signal from having the same 45 degree polarization as the incident signal. The signal will then be rotated by 90 degrees from the 45 degrees when radiated.

In still another aspect of some but not necessarily all embodiments, switches are interposed in the two connection paths between the antennas. The switches enable the backscattering of the signal with orthogonal polarization to be controlled, turning it on and off. The switches can be controlled by a baseband circuit so that the baseband data can be modulated onto the backscattered signal.

Arrangements such as those described above enable a modulated signal with a polarization that is orthogonal to that of the illuminating carrier to be backscattered regardless of device orientation with respect to the device generating the carrier signal. No polarization alignment is thus needed at deployment, and mobility can be allowed.

It is observed that using two antennas to transmit signals results in directional effects similar to dipole antennas, that is, there will be null directions in the backscattered signal, where the null directions will depend on both the device orientation and the illuminating carrier direction. If that is considered problematic in an intended application, in yet another aspect of some but not necessarily all embodiments, isolators can be used that allow signal flow from the first antenna to the second, but mitigating signal flow in the opposite direction. These and other aspects are now described in the following discussion.

A simple illustration of an exemplary embodiment in accordance with the invention is shown in Figure 1. More particularly, Figure 1 illustrates a device 100 that comprises an exemplary embodiment of a backscattering communication device 101 in accordance with aspects of the invention. The backscattering communication device 101 has a first dual-dual polarized antenna 103 and a second dual -polarized antenna 105. The two dual -polarized antennas 103, 105 are connected to each other via two connections (e.g., two lines) 107, 109 (one for each polarization), and two switches 111, 113. The first and second connections 107, 109 have different lengths. In this non-limiting exemplary embodiment, the first connection 107 has a length equal to X, which is the wavelength of the center of the frequency band of operation, while the second connection 109 has a length equal to X/2. More generally, some inventive embodiments encompass those in which one of the connections exceeds the other by a length corresponding to X/2. So, for example, it can be seen that in the exemplary embodiment of Figure 1, the first connection 107 exceeds the second connection 109 by a length corresponding to X/2. In the general case, the two lengths can be expressed as L, and L+X/2. In practical embodiments, L is chosen to be at least large enough so that the connection can be made between the two dual polarizing antennas 103, 105.

When the length difference between the two connections 107, 109 is X/2, signals received by the first dual -polarized antenna 103 will, for the first polarization, arrive at the orthogonal polarization port P4 of the second dual polarized antenna 105 with an additional 180 degrees phase shift at the center of the frequency band compared to, for the orthogonal polarization, signals arriving at the first polarization port P3 of the second dual polarized antenna 105. This will cause the radiated signal to have an orthogonal polarization with respect to the incoming signal. The same goes for signals received by the second dual -polarized antenna 105 and radiated by the first dual-polarized antenna 103, where signals received in the orthogonal polarization are phase shifted by 180 degrees when connected to the first polarization port Pl of the first dualpolarized antenna 103, compared to the signals received in the first polarization and connected to the orthogonal polarization port P2 of the first dual polarized antenna 103, which also causes a signal with a polarization orthogonal to the incoming signal to be radiated.

When the first and second switches 111, 113 are open (open circuited), energy captured by each of the first and second dual-polarized antennas 103, 105 may be absorbed by the device 101 or at least partially radiated (e.g., due to reflection) back into the environment by a same one of the first and second dual-polarized antennas 103, 105 (i.e., any energy radiated back into the environment will have a same polarization as the captured signal). However, when the first and second switches 111, 113 are closed (short-circuited), the two dual-polarized antennas 103, 105 are connected via the X and X/2 connections 107, 109. If an illuminating carrier is applied (e.g., due to either bi-static operation or ambient background signals), the signal captured at the first dual -polarized antenna 103 will be radiated from the second dual -polarized antenna 105 with an orthogonal polarization. Similarly, the signal captured by the second dual -polarized antenna 105 will also be radiated with an orthogonal polarization from the first dual -polarized antenna 103. Therefore, by opening and closing the first and second switches 111, 113 in accordance with a pattern that corresponds to an encoding of information to be communicated, on-off keying modulation is achieved, with the ON/OFF states being represented by the different polarization states of the signals radiated from the device 101. Notably, this permits information to be backscattered to a receiver with signaling whose polarization is different from (e.g., orthogonal to) that of the TX signal carrier. The orthogonal polarization allows the receiver to separate the backscattered signal from the much stronger illuminating signal carrier in the receiver.

As mentioned, when the first and second switches 111, 113 are open, no significant backscattering signal of orthogonal polarization is radiated. In some embodiments, some or all of the received RF signal is radiated (e.g., due to reflection) back into the environment. But in another aspect of some but not necessarily all embodiments, the energy from the captured RF signal may be presently used to power the device 101, or stored for future use. When such energy harvesting is performed, the strength of the radiated signaling may be reduced, since less energy remains for that purpose. This, however, does not hinder the communication aspect, since the reduced radiation energy in the non-different polarization state is still distinguishable from signals radiated with a different polarization.

In still another aspect of some but not necessarily all embodiments consistent with the invention, isolators can be added in the two connections 107, 109 between the two dualpolarized antennas 103, 105, in order to allow signal flow from the first dual -polarized antenna 103 to the second dual -polarized antenna 105, but not in the reverse direction. This makes the backscattered signal transmission more omni-directional, avoiding the nulls in some directions associated with two transmission antennas.

Some further aspects of inventive embodiments are illustrated in Figure 2, which is a high-level illustration of communication using an exemplary backscattering communication device 101. As described earlier, the lengths of the first and second connections 107, 109 are different. In the non-limiting example shown in Figure 1, it is assumed that a first one of the connections 107 has length equal to X, while the other connection 109 is configured to have a length of X/2. By configuring the lengths in this manner, and keeping in mind that when the switches 111, 113 are closed, an RF signal captured by one of the dual -polarized antennas 103, 105 is supplied for radiation by the other of the two dual-polarized antennas 103, 105, a phase shift difference of 180 degrees at the center of the frequency band of operation is achieved between signals propagating through one of the connections 107 and signals propagating through the other connection 109.

With this arrangement, suppose a wireless communication system node 205 as shown in Figure 2 transmits an illuminating carrier signal 201 having, for example and without limitation, a vertical polarization component 203 (or perhaps an entirely vertically polarized signal). When the illuminating carrier signal 201 is applied to the backscattering communication device 101 when the switches 111, 113 are closed, the vertically polarized signal (component) 203 captured at the first dual -polarized antenna 103 will be radiated with orthogonal polarization as the signal 207 from the second dual -polarized antenna 105. Similarly, if there is a horizontally polarized signal component of the original illuminating carrier signal 201 (not shown) it will be captured by the second antenna 105 and will be radiated as a signal (not shown) with orthogonal polarization (in this example, vertically polarized) from the first dual -polarized antenna 103.

In this example, assume that both the original illuminating carrier signal 201 and the horizontally polarized signal 207 (and when it exists, also the vertically polarized signal radiated from the backscattering communication device 101) reach a receiver 209. By modulating the Open/Closed settings of the two switches 111, 113 in accordance with an OFF/ON (or ON/OFF) pattern that represents an encoding of information to be communicated by the device, it is possible to backscatter information to the receiver 209 with a polarization that is orthogonal to that of the original illuminating carrier signal 201. The use of orthogonal polarization provides a basis for improving the receiver’s ability to separate the backscattered signal from the much stronger illuminating signal carrier, and hence increases the possible communication distance from the wireless backscattering communication device 101 to the receiver. The use of orthogonal polarization also enables the use of receivers 209 having reduced complexity, since a smaller dynamic range will be required to receive the signals compared to the dynamic range requirements associated with receiving a traditional backscattered signal at the same frequency and same polarization.

An aspect of the behavior of the device is that the inventive arrangement inherently generates a polarization of the back-scattered signal that is orthogonal to that of the illuminating signal, while being robust to any type of signal since the specific signal characteristics (e.g., the absolute polarization) are not essential for the functionality. Polarization alignment is thus not needed at deployment, and device mobility can be allowed. This is due to the fact that embodiments that are consistent with the invention receive orthogonal components of any illuminating signal and produce therefrom new orthogonal components that, when combined, form a signal whose polarization is orthogonal to that of the originally illuminating signal.

In a further aspect of embodiments consistent with the invention, arrangements involving two dual-polarized antennas configured such as in Figure 1 can be used as a building block for further, more advanced device constructions. As example, and without limitation, Figure 3 illustrates an array 301 of multiple antennas, wherein the array comprises multiple instances of the exemplary backscattering communication device 101 of Figure 1 that together form a larger antenna array of, for example and without limitation, 4 or 8 dual-polarized antennas. The backscattering can then be coordinated to be performed in similar fashion for the multiple antennas to form a different radiation pattern from the array compared to what is possible with just two dual-polarized antennas.

Further variations can be made with different antenna characteristics in the different implementations, for example, to form different transmit patterns from the device. One can connect the lines in different ways. If connected as shown in Figure 3, the array becomes like a mirror, so that incoming illumination at an angle, a, from the antenna boresight will result in a backscattered wave radiating at an equal but opposite sign, (i.e., -a) from the antenna boresight. If instead, one were to use different line lengths for different elements, the reflected wave would be spread out over a wider angular range in a wider beam, so that receivers in a wider angular range would be able to receive it.

In still other examples of alternatives, it is not essential that all elements (i.e., pairs of connected dual-polarization antennas) have the same line lengths.

In order to further illustrate aspects of embodiments consistent with the invention, Figure 4 is a block diagram of a backscattering communication device 400. As shown, the backscattering communication device 400 comprises a first dual -polarized antenna 401 having a first polarization port Pl associated with a first polarization direction 403 and a second polarization port P2 associated with a second polarization direction 405.

The backscattering communication device 400 further comprises a second dual-polarized antenna 407 having a third polarization port P3 associated with a third polarization direction 409 and a fourth polarization port P4 associated with a fourth polarization direction 411. The backscattering communication device 400 further comprises a first connection 413 coupled between the first polarization port Pl of the first dual -polarized antenna 401 and the fourth polarization port P4 of the second dual-polarized antenna 407, and a second connection 415 coupled between the second polarization port P2 of the first dual -polarized antenna 401 and the third polarization port P3 of the second dual-polarized antenna 407.

In the backscattering communication device 400 as arranged in Figure 4: the first polarization direction 403 is different from the fourth polarization direction 411;

- the second polarization direction 405 is different from the third polarization direction 409;

- the first connection 413 has a first length LI and a first switch 417 for opening and closing the first connection 413;

- the second connection 415 has a second length L2 and a second switch 419 for opening and closing the second connection 415, wherein the second length L2 is different from the first length LI; and

- the first and second lengths LI, L2 are configured such that a phase shift difference between a signal propagating through the first connection 413 and a signal propagating through the second connection 415 is non-zero at a center frequency of a frequency band of operation of the backscattering communication device 400.

In some but not necessarily all alternative embodiments, when the center frequency has a wavelength, , the first length LI is equal to the second length L2 plus X/2.

In another class of some but not necessarily all alternative embodiments, the first polarization direction 403 is orthogonal to the fourth polarization direction 411, and/or the second polarization direction 405 is orthogonal to the third polarization direction 409.

In some but not necessarily all alternative embodiments, the backscattering communication device 400 further comprises an energy harvesting storage configuration 425 (i.e., some form of tangible hardware circuit or element(s), such as one or more batteries and/or capacitors, and/or rectifiers) connected to the first dual -polarized antenna 401 and/or the second dual-polarized antenna 407, wherein the energy harvesting storage configuration is configured to capture and store energy of radiofrequency signals received by the first and/or second dualpolarized antennas 401, 407 when the first and second switches 417, 419 are open.

In some but not necessarily all alternative embodiments, the first connection 413 further comprises a first isolator 421, and the second connection 415 further comprises a second isolator 423. The first and second isolators 421, 423 are configured so as to allow radiofrequency signals to flow in nominally only one direction, either from the first dual -polarized antenna 401 to the second dual-polarized antenna 407, or from the second dual-polarized antenna 407 to the first dual -polarized antenna 401. It is recognized that, in practical embodiments, isolators do not function with 100% perfection. For example, the designer can expect that there will be some amount of leakage in the reverse direction. For this reason, as used herein at least with respect to isolators, the term “in only one direction” means “primarily in one direction”, “mainly in one direction”, “substantially in one direction”, and the like, in order to account for imperfections in implementation, such as leakage in the reverse direction.

One or both of the dual -polarized antennas 401, 407 can be implemented using patch antennas.

In some but not necessarily all alternative embodiments, the backscattering communication device 400 further comprises a baseband circuit 427 that comprises a control circuit 429, configured to control the opening and closing of the switches 417, 419 in correspondence with a modulating pattern/data sequence that is an encoding of information to be radiated from the backscattering communication device 400. On/Off keying modulation can be implemented in this manner.

Further aspects of embodiments consistent with the invention are now described with reference to Figure 5, which, in one respect, is a flowchart of actions performed by a backscattering communication device 101, 400 that is engaged in communicating a radiofrequency signal encoded with information. In other respects, the blocks depicted in Figure 5 can also be considered to represent means 500 (e.g., hardwired or programmable circuitry or other processing means) for carrying out the described actions.

In the exemplary embodiment of Figure 5, the backscattering communication device 101, 400 receives a first radiofrequency signal in a first polarization direction (step 501), and receives a second radiofrequency signal in a second polarization direction that is different from the first polarization direction (step 503).

Additionally, the backscattering communication device 101, 400 selectively radiates the first radiofrequency signal, the second radiofrequency signal, a first phase shifted signal, and a second phase shifted signal, wherein selectively radiating is in accordance with a pattern of first and second operation modes (step 505), wherein the pattern is an encoding of the information via on-off keying modulation. In further detail in this exemplary embodiment, this involves determining a next directive specified by the pattern (decision block 507). If the next directive value indicates that the first operation mode is to be performed, then the backscattering communication device 101, 400 radiates at least a portion of the first radiofrequency signal in the first polarization direction (step 509) and also radiates at least a portion of the second radiofrequency signal in the second polarization direction (step 511).

However, if the next directive value indicates that the second operation mode is to be performed, then the backscattering communication device 101, 400 produces the first phase shifted radiofrequency signal by shifting a phase of the first radiofrequency signal by a first phase shift amount (step 513), and also produces the second phase shifted radiofrequency signal by shifting a phase of the second radiofrequency signal by a second phase shift amount that is different from the first phase shift amount (step 515).

The backscattering communication device 101, 400 then radiates the first phase shifted radiofrequency signal in the second polarization direction (step 517) and also radiates the second phase shifted radiofrequency signal in the first polarization direction (step 519).

Further aspects of embodiments consistent with the invention will now be described with reference to Figure 6, which shows an exemplary controller 601 that may be included in a backscattering communication device to cause any and/or all of the herein-described and illustrated actions associated with that device or system to be performed. In particular, the controller 601 includes circuitry configured to carry out any one or any combination of the various functions described herein. Such circuitry could, for example, be entirely hard-wired circuitry (e.g., one or more Application Specific Integrated Circuits - “ASICs”). Depicted in the exemplary embodiment of Figure 6, however, is programmable circuitry, comprising a processor 603 coupled to one or more memory devices 605 (e.g., Random Access Memory, Magnetic Disc Drives, Optical Disk Drives, Read Only Memory, etc.) and to an interface 607 that enables bidirectional communication with other elements of a device as described above. A complete list of possible other elements is beyond the scope of this description.

The memory device(s) 605 store program means 609 (e.g., a set of processor instructions) configured to cause the processor 603 to control other device elements so as to carry out any of the aspects described herein. The memory device(s) 605 may also store data (not shown) representing various constant and variable parameters as may be needed by the processor 603 and/or as may be generated when carrying out its functions such as those specified by the program means 609.

Various embodiments that are consistent with the invention provide a number of benefits and advantages over conventional technology. Some of these advantages include low complexity implementation. The antenna/circuit arrangement is less complex than many other published alternatives for improving the link budget and separating the backscattered signal from the illuminating signal. For comparison and purposes of example, conventional technology can involve adjusting the frequency of the backscattered signal, or adding large antenna systems for improving reception with more antenna gain and spatial selectivity.

Another advantage that characterizes inventive embodiments is its robustness when deployed. The various combinations of features inherently generate a polarization of the backscattered signal that is orthogonal to the illumination, while being robust to any type of illuminating signal because the specific signal characteristics (e.g., the absolute polarization) is not essential for the functionality. Polarization alignment is thus not needed at deployment, and device mobility can be allowed.

The invention has been described with reference to particular embodiments. However, it will be readily apparent to those skilled in the art that it is possible to embody the invention in specific forms other than those of the embodiment described above. Thus, the described embodiments are merely illustrative and should not be considered restrictive in any way. The scope of the invention is further illustrated by the appended claims, rather than only by the preceding description, and all variations and equivalents which fall within the range of the claims are intended to be embraced therein.

Claims

CLAIMS:

1. A backscattering communication device (101, 400) comprising: a first dual-polarized antenna (103, 401) having a first polarization port (Pl) associated with a first polarization direction (403) and a second polarization port (P2) associated with a second polarization direction (405); a second dual-polarized antenna (105, 407) having a third polarization port (P3) associated with a third polarization direction (409) and a fourth polarization port (P4) associated with a fourth polarization direction (411); a first connection (107, 413) coupled between the first polarization port (Pl) of the first dual-polarized antenna (103, 401) and the fourth polarization port (P4) of the second dualpolarized antenna (105, 407); and a second connection (109, 415) coupled between the second polarization port (P2) of the first dual-polarized antenna (103, 401) and the third polarization port (P3) of the second dualpolarized antenna (105, 407), wherein the first polarization direction (403) is different from the fourth polarization direction (411); the second polarization direction (405) is different from the third polarization direction (409); the first connection (107, 413) has a first length (LI) and a first switch (111, 417) for opening and closing the first connection (107, 413); the second connection (109, 415) has a second length (L2) and a second switch (113, 419) for opening and closing the second connection (109, 415), wherein the second length (L2) is different from the first length (LI); and the first and second lengths (LI, L2) are configured such that a phase shift difference between a signal propagating through the first connection (107, 413) and a signal propagating through the second connection (109, 415) is non-zero at a center frequency of a frequency band of operation of the backscattering communication device (101, 400).

2. The backscattering communication device (101, 400) of claim 1, wherein: the center frequency has a wavelength, ; and the first length is equal to the second length plus X/2.

3. The backscattering communication device (101, 400) of any one of the previous claims, characterized by one or more of: the first polarization direction (403) is orthogonal to the fourth polarization direction (411); and the second polarization direction (405) is orthogonal to the third polarization direction (409).

4. The backscattering communication device (101, 400) of any one of the previous claims, wherein the first and second lengths (LI, L2) are configured such that the phase shift difference between the signal propagating through the first connection (107, 413) and the signal propagating through the second connection (109, 415) is 180 degrees at the center frequency of the frequency band of operation of the backscattering communication device (101, 400).

5. The backscattering communications device (101, 400) of any one of the previous claims, comprising: an energy harvesting storage configuration (425) connected to one or more of the first dual-polarized antenna (103, 401) and the second dual-polarized antenna (105, 407), wherein the energy harvesting storage configuration (425) is configured to capture and store energy of radiofrequency signals received by one or both of the first (103, 401) and second (105, 407) dual-polarized antennas when the first and second switches (417, 419) are open.

6. The backscattering communication device (101, 400) of any one of the previous claims, wherein: the first connection (107, 413) further comprises a first isolator (421); and the second connection (109, 415) further comprises a second isolator (423), wherein the first and second isolators (421, 423) are configured so as to allow radiofrequency signals to flow in only one direction from a first one of the first and second dualpolarized antennas (103, 105, 401, 407) to a second one of the first and second dual-polarized antennas (103, 105, 401, 407).

7. The backscattering communication device (101, 400) of any one of the previous claims, wherein: at least one of the first dual -polarized antenna (103, 401) and the second dual -polarized antenna (105, 407) is implemented using patch antennas.

8. The backscattering communication device (101, 400) of any one of the previous claims, comprising: a baseband circuit (427) connected to the first and second switches (417, 419) and configured to open and close the first and second switches (417, 419) in correspondence with a modulating data sequence.

9. The backscattering communications device (101, 400) of claim 8, wherein the baseband circuit (427) is configured to use on-off keying modulation when opening and closing the first and second switches (417, 419).

10. An antenna array (301) comprising: a first backscattering communication device (101, 400) as claimed in any one of claims 1 through 6; and a second backscattering communication device (101, 400) as claimed in any one of claims 1 through 6.

11. A method of communicating a radiofrequency signal encoded with information, the method comprising: receiving (501) a first radiofrequency signal in a first polarization direction (403); receiving (503) a second radiofrequency signal in a second polarization direction (405) that is different from the first polarization direction; selectively (507) radiating (505) the first radiofrequency signal, the second radiofrequency signal, a first phase shifted signal, and a second phase shifted signal, wherein selectively radiating is in accordance with a pattern of first and second operation modes, wherein the pattern is an encoding of the information via on-off keying modulation, and wherein: the first operation mode comprises: radiating (509) at least a portion of the first radiofrequency signal in the first polarization direction (403); and radiating (511) at least a portion of the second radiofrequency signal in the second polarization direction (405); and the second operation mode comprises: producing (513) the first phase shifted radiofrequency signal by shifting a phase of the first radiofrequency signal by a first phase shift amount; producing (515) the second phase shifted radiofrequency signal by shifting a phase of the second radiofrequency signal by a second phase shift amount that is different from the first phase shift amount; radiating (517) the first phase shifted radiofrequency signal in the second polarization direction (405); and radiating (519) the second phase shifted radiofrequency signal in the first polarization direction (403).

12. The method of claim 11, comprising: capturing and storing energy of the first radiofrequency signal when the radiating is in the first operation mode.

13. The method of any one of claims 11 through 12, comprising: using a first dual -polarized antenna (103, 401) to receive the first radiofrequency signal and the second radiofrequency signal; using a second dual -polarized antenna (105, 407) to radiate the first phase shifted radiofrequency signal and the second phase shifted radiofrequency signal; and allowing radiofrequency signals to flow in only one direction from the first dualpolarized antenna (103, 401) to the second dual-polarized antenna (105, 407).

14. A computer program (609) comprising instructions that, when executed by at least one processor (603), causes the at least one processor (603) to carry out the method according to any one of claims 11 through 13.

15. A carrier comprising the computer program (609) of claim 14, wherein the carrier is one of an electronic signal, an optical signal, a radio signal, and a non-transitory computer readable storage medium (605).