Radio frequency identification reader having a signal canceller and method thereof

Abstract

A method, system and apparatus for generating a cancellation signal in a RFID reader to isolate a transmit section and a receive section of a RFID reader, where the RFID reader generates a local reference signal from a broadcast transmit signal, receives a receive signal from a remote device, determines at least one correction factor, e.g., an amplitude correction factor, to generate a cancellation signal. The method, system and apparatus can further include combining a cancellation signal and a receive signal to minimize or cancel out interference and noise on the receive signal.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present invention, and the attendant advantages and features thereof, will be more readily understood by reference to the following detailed description when considered in conjunction with the accompanying drawings, wherein like designations refer to like elements, and wherein:

FIG. 1 is a block diagram of a communication system constructed in accordance with the principles of the present invention;

FIG. 2 is a block diagram of various aspects of the communication system of FIG. 1 constructed in accordance with the principles of the present invention;

FIG. 3 is a block diagram of an RFID reader constructed in accordance with the principles of the present invention; and

FIG. 4 is a flowchart of a signal canceller process in accordance with the principles of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawing figures in which like reference designators refer to like elements, there is shown in FIG. 1 a diagram of an exemplary communication system constructed in accordance with the principles of the present invention and designated generally as “10”. Communication system 10 provides an electronic identification system in the embodiment described herein. Further, the described communication system 10 is configured for backscatter communications as described in detail below. Other communication protocols can be utilized in other embodiments.

The depicted communication system 10 includes at least one electronic wireless remote communication device 16 and a reader 12. Radio frequency communications can occur between remote communication devices 16 and reader 12 for use in identification systems and product monitoring systems as exemplary applications.

Devices 16 include radio frequency identification (“RFID”) devices in the embodiments described herein. Multiple wireless remote communication devices 16 typically communicate with reader 12 although only one such device 16 is illustrated in FIG. 1.

Although multiple communication devices 16 can be employed in communication system 10, there is typically no communication between multiple devices 16 themselves. Instead, the multiple communication devices 16 communicate with reader 12. Multiple communication devices 16 can be used in the same field of reader 12 i.e., within the communications range of reader 12. Similarly, multiple readers 12 can be in proximity to one or more of devices 16.

Remote communication device 16 is configured to interface with reader 12 using a wireless medium in one embodiment. More specifically, communication between communication device 16 and reader 12 occur via an electromagnetic link, such as an RF link e.g., at microwave frequencies in the described embodiment. Reader 12 is configured to output forward link wireless communication signals 15. Further, reader 12 is operable to receive return link wireless communication signals 17 e.g., a reply signal from devices 16 responsive to the outputting of forward link communication signals 15. In accordance with the above, forward link communication signals and return link communication signals are wireless signals, such as radio frequency signals. Other forms of electromagnetic communication signals, such as infrared, acoustic, and the like are possible.

Reader unit 12 includes at least one antenna 14 as well as transmitting and receiving circuitry, similar to that implemented in devices 16. Antenna 14 comprises a transmit/receive antenna connected to reader 12. In an alternative embodiment, reader 12 can have separate transmit and receive antennas.

In operation, reader 12 transmits a forward link communication signal 15 e.g., an interrogation command signal via antenna 14. Communication device 16 is operable to receive the incoming forward link signal 15. Upon receiving signal 15, communication device 16 is operable to respond by communicating the responsive return link communication signal 17 e.g., a responsive reply signal. Communications of system 10 are described in greater detail below.

In one embodiment, responsive return link communication signal 17 e.g., a responsive reply signal is encoded with information that uniquely identifies, or labels the particular device 16 that is transmitting, so as to identify any object, animal, or person with which communication device 16 is associated. Communication devices 16 can be RFID tags that are attached to objects or people where each tag is programmed with information relating to the object or person to which it is attached. The information may take a wide variety of forms and may be more or less detailed depending on the needs to be served by the information. For example, the information may include merchandise identification information, such as a universal product code. A tag may include identifying information and security clearance information for an authorized person to whom the tag has been issued. A tag may also have a unique serial number, in order to uniquely identify an associated object or person. Alternatively, a tag may include more detailed information relating to an object or person, such as a complete description of the object or person. As a further exemplary alternative, a tag may store a single bit, in order to provide for theft control or simple tracking of entry and departure through the detection of an object or person at a particular reader, without necessarily specifically identifying the object or person.

More specifically, remote device 16 is configured to output an identification signal within reply link communication 17 responsive to receiving forward link wireless communication 15. Reader 12 is configured to receive and recognize the identification signal within the reply link communication signal 17 e.g., return signal. The identification signal can be utilized to identify the particular transmitting communication device 16.

An exemplary embodiment of a reader 12 is explained with reference to FIG. 2. In this embodiment, a radio signal source 102 for synthesizing radio frequency (“RF”) signals, e.g., an interrogating RF signal, outputs a RF signal to transceiver 100 of a reader generally indicated as 12. The interrogating RF signal from the source 102 has a suitable frequency such as 915 MHz. When the radio signal source 102 is energized, transceiver 100 transmits the interrogating RF signal (typically after the RF signal has been modulated with an information signal) through antenna 14 to a suitable antenna 18 (such as a dipole antenna) at a communication device 16. Communication device 16 is associated with an object (not shown) and is used to identify the object.

Reader 12 can further include a signal processing module 104 configurable to process modulated signals received from communication device 16, which are received by antenna 14 and passed to transceiver 100. Signal processing module 104 can include a canceller module 200 configured to generate a cancellation signal to minimize or “zero out” the interference and/or noise of a reflected receive signal is described with greater detail with reference to FIG. 3. In one embodiment, signal processing module 104 produces signals in a sequence having a pattern identifying the pattern of the 1's and 0's in read only memory (“ROM”) 122 of communication device 16. For example, the received and processed sequence may be compared in reader 12 with a desired sequence to determine whether the object being identified is being sought by the reader or not.

Continuing to refer to FIG. 2, one embodiment of remote communication device 16 is explained. The depicted communication device 16 includes a modulator 120 having a receiver/transmitter as described below and a data source such as ROM 122, which provides a sequence of binary 1's and binary 0's in an individual pattern to identify the object. In this embodiment, a binary “1” in ROM 122 causes a modulator 120 to produce a first plurality of signal cycles and a binary “0” in the read only memory 122 causes the modulator 120 to produce a second plurality of signal cycles different from the first plurality of signals. The pluralities of signals cycles sequentially produced by the modulator 120 to represent the pattern of binary 1's and binary 0's which identify the object are introduced to the dipole antenna 18 for transmission to antenna 14 at reader 12. In another embodiment, the communication device 16 can have separate receive and transmit antennas.

Communication device 16 may further include an optional power source (not shown) connected to modulator 120 to supply operational power to modulator 120.

FIG. 3 illustrates the front end of an exemplary RFID reader 12 in accordance with the present invention, which may suitably be employed as readers 12 of FIGS. 1 and 2. It should be noted that the reader 12 illustrated in FIG. 3 is an exemplary reader 12 that is used in a typical RFID interrogation system of the present invention and the invention disclosed herein is not limited to a particular design or type of RFID reader 12. Reader 12 includes a canceller module 200, a RF source 102 that supplies a broadcast transmit signal, also referred to as an interrogating signal, e.g., a RF wireless continuous wave signal, to antenna 14 via a transmit section/path. The transmit section/path can include power amplifier 210, signal pick-up component 208, optional circulator 206 and bandpass filter 204.

When the antenna 14 of reader 12 is configured as a transceiver i.e., mono-static antenna, which is where a single antenna is used to both transmit and receive communication signals, for example radio frequency signals, the potential for interference between the transmit section signals of the reader 12 and the receive section signals of the reader 12 is very high. In this embodiment, antenna 14 emits or broadcasts electromagnetic radio frequency interrogation signals throughout an interrogation zone to create an electromagnetic field. The electromagnetic field produced by antenna 14 can be constantly present in instances where one or more remote communication devices 16 are present. If constant interrogation is not needed, the electromagnetic field can be activated intermittently. The electromagnetic field of interrogation signals established by antenna 14 stimulates a response from the interrogated remote communication devices 16. Further, a portion of RF energy emitted by antenna 14 is reflected back to the receiving module within reader 12 or the transceiver module of antenna 14 (or the receive module of optional antenna 228 when separate transmit and receive antennas are deployed). Thus, at antenna 14, a cumulative magnitude of RF energy reflected back from remote communication devices 16 is detected.

In another embodiment, separate antennas may be used in the transmit section/path and the receive section/path, such as antennas 14 and 228 respectively. Even when separate antennas are used to transmit the RF signals, the RF signal broadcast via transmit antenna 14 can saturate the front end of the receive section, such as antenna 228, to desensitize the receive section and thereby reduce the quality of wireless communications of reader 12 with remote communication device 16.

Optional circulator 206 is of the type commonly known in the art, and assists in directing the transmitted and received RF signals to and from antenna 14. More specifically, circulator 206 will separate the transmitted and received RF signals, which provides a degree of isolation between the transmit section/path and the receive section/path of reader 12. However, due to non-ideal circumstances, a portion of the transmit signal leaks or flows into the receive section/path of the reader 12. In one embodiment where antenna 14 operates to transmit and receive communication signals, optional circulator 206 is configured to separate signals based on the direction of the signal propagation. Although optional circulator 206 is shown as being separate from signal pick-up component 208, those skilled in the art will recognize that it can be integrated into a single component or module and made part of signal canceller module 200.

In another embodiment, an optional switch 224 can be used to connect an optional antenna 228 to the reader 12. Switch 224 provides for the routing of signals received by antenna 228 to the canceller module 200 for processing and error correction. In addition, an optional band pass filter 226 is coupled to antenna 228 to filter or eliminate out-of-base noise on the signals received by antenna 228.

As shown in FIG. 3, a signal canceller module 200 is provided to improve isolation between the transmit section/path and the receive section/path of reader 12. Canceller module 200 includes a signal pickup 208, e.g., a coupler, splitter or other similar device, which is positioned between optional circulator 206 and power amplifier 210. During communication operations, signal pickup 208 passes the broadcast transmit signal from power amplifier 210 to optional circulator 206 and transmission antenna 14. Signal pickup 208 also passes a portion of the broadcast transmit signal, e.g., a local reference signal, to attenuation/gain component 212. The local reference signal can be used in the receive portion of reader 12 as part of a cancellation signal, such as adjusted local reference signal where one or more signal characteristics, e.g., the amplitude and phase of the local reference signal, are adjusted.

Attenuation/gain component 212 is configured to adjust one signal characteristic, e.g., the amplitude of the local reference signal to generate a cancellation signal, such as an adjusted local reference signal. In other words, attenuation/gain component 212 provides a signal correction factor, e.g., amplitude correction factor, for use in generating a cancellation signal of signal canceller 200. In this embodiment, the attenuation/gain component 212 is an electronic device that reduces the amplitude or power of local reference signal without appreciably distorting its waveform.

In addition, canceller module 200 includes phase shifter 214, which provides an adjustment to another signal characteristic, e.g., the phase of the local reference signal, in order to generate a cancellation signal to cancel the leakage signal of the reflected transmit signal of the transmit section when the cancellation signal and the receive signal are combined in the summer 220. In other words, phase shifter 214 also provides a signal correction factor, e.g., a phase correction factor, for use in generating the cancellation signal of signal canceller 200. The received or responsive signal at antenna 14 e.g., a modulated backscatter signal, also known as a reflected signal, can be passed through a band pass filter (“BPF”) 204 that functions to filter or eliminate out-of-base noise on the received signal. A second BPF 222 can be provided between the circulator 206 and the signal-summer 220. The second BPF 222 provides further filtering of the reflected receive signal. The summer 220 functions to combine the receive signal and the cancellation signal to eliminate, cancel or minimize the reflected transmit signal and thereby improve the sensitivity of reader 12 by isolating the transmit section and the receive section of reader 12. The summer 220 can be implemented as a series of RF devices, a directional coupler having a low loss, a combiner having a low loss or similar RF devices. In addition, summer 220 can be an integrated circuit or a resistive arrangement.

Canceller module 200 further includes detector circuit 218, which is positioned in the receive path between summer 220 and signal processor 216, e.g., a digital signal processor (“DSP”). Detector circuit 218 operates to measure the amplitude and phase of the local reference signal and the reflected receive signal and report this information to signal processor 216 for processing. In one embodiment, detector circuit 220 is a received signal strength indication (“RSSI”) detector, which is configured to measure the strength of the received radio signal. Signal processor 216 in turn controls attenuation/gain component 212 and phase shifter 214 to adjust the gain and phase of the cancellation signal, e.g., adjusted local reference signal to minimize or “zero out” the reflected receive signal, while maintaining a backscatter receive signal from remote communication devices 16.

In one embodiment, the signal processor 216 may implement an error minimization algorithm to adjust the gain and phase of the cancellation signal used to minimize the unwanted reflected receive signal. The minimization algorithm may be similar to a least mean square (“LMS”) or signal equalizer procedure. LMS is known to minimize the expectation of the squared residual with the smallest operations (per iteration), but it requires a large number of iterations to converge. In this matter, the signal canceller may operate in a “phase locked loop” (“PLL”) mode to reduce or eliminate the reflected RF signal while maintaining the backscatter receive signal from the communication devices 16.

For example, during a transmission from the reader 12, the transmit RF signal may have signal strength in the range of 30 to 35 dBm at the port of the signal pick-up component 208 and a reflected RF signal may be approximately 20 dBm. The magnitude, frequency and phase of the reflected RF signal are measured and provided to the signal processor 216 which uses this data to provide a cancellation signal to nullify or cancel out the reflected RF signal while maintaining the backscatter receive signal received from communication devices 16.

In another embodiment the attenuation/gain component 212 and the phase shifter 214 may be fixed in the design by using a signal delay component and an amount of direct coupling. Alternatively, an adjustable setting that is configured at manufacturing may be implemented to provide sufficient correction or minimization of the reflected receive signal for fixed antennas and to a lesser extent, for removable antennas.

In one embodiment, the corrected and filtered backscatter receive signal can be provided at an input port of a frequency mixer 230. The frequency mixer 230 converts RF power at one frequency into power at another frequency. This allows amplification of the received signal at a frequency other than the RF frequency. In this illustrated embodiment, the backscatter receive RF signal and a local oscillator (“LO”) signal are sinusoids and the output of mixer 230 is the sum and the difference frequencies of these two input signals. The output of mixer 230 will therefore be an intermediate frequency (“IF”). Typically either the sum frequency or the difference frequency is removed with a filter. [Please provide at least a preferred embodiment/numerical example of the input sinusoidal waveforms and related amplitude and phase. In addition, one or more graphs illustrating the waveforms received in the receive section of the reader and the resulting signal after canceller module operation would be helpful].

In one embodiment, the signals transmitted and received by reader 12 and signals transmitted and received by communication device 16 are modulated spread spectrum signals, and reader 12 transmits a command that is spread around a certain center frequency (e.g., 2.44 GHz). After the reader 12 transmits the command and is expecting a response, the reader 12 switches to a continuous wave (“CW”) mode for backscatter communications. In the continuous wave mode, reader 12 does not transmit any information. Instead, reader 12 transmits a radio frequency continuous wave signal. In the described embodiment, the continuous wave signal has a radio frequency 2.44 GHz carrier signal. In other words, the continuous wave signal transmitted by reader 12 is not modulated. After communication device 16 receives the forward link communication from reader 12, communication device 16 processes the command.

If communication device 16 is operating in a backscatter mode, communication device 16 modulates the continuous wave signal providing a modulated continuous wave signal to communicate return link communication 17 responsive to reception of forward communication signal 15. Communication device 16 may modulate the continuous wave signal according to a subcarrier or modulation signal. Modulation by device 16 includes selective reflection of the continuous wave signal. In particular, device 16 alternately reflects or does not reflect the continuous wave signal from the reader 12 to send its reply. Alternatively, communication device 16 can communicate in an active mode.

The modulated continuous wave signal communicated from device 16 has a carrier component and multiple sideband components about the carrier component resulting from the modulation. More specifically, the modulated continuous wave signal output from device 16 includes a radio frequency continuous wave signal having a first frequency (e.g., 2.44 GHz), also referred to as a carrier component, and a subcarrier modulation signal having a different frequency (e.g., 600 kHz) and which provides the side band components. In this embodiment, the reader 12 receives the reflected and modulated signal with receive antenna 228.

An exemplary mode of operation of an embodiment of the canceller module 200 of reader 12 is discussed with reference to the flowchart of FIG. 4. In step S402, a signal pickup 208 generates a local reference signal by passing a portion of a broadcast transmit signal to attenuation/gain component 212. A receive antenna 228 is configurable to receive a modulated response signal from a remote communication device 16 (step S404). Based on the received signal strength or its signal amplitude, a first signal correction factor, e.g., an amplitude correction factor, for the local reference signal is determined (step S406). In addition, at step S408, a second signal correction factor, e.g., a phase correction factor is determined with respect to the phase of the received signal from remote communication device 16. At step S410, the first correction factor and the second correction factor are applied to the local reference signal to generate a cancellation signal that will share a carrier frequency with the received signal and will approximately match the amplitude of the receive signal. Moreover, the phase correction factor can be determined or calculated to cancel, minimize or “zero out” the reflected portion of the received signal that relates to the transmit section/path of reader 12, while maintaining a backscatter receive signal from the remote communication devices 16. Accordingly, once the amplitude and phase of the cancellation signal are determined, the adjusted cancellation signal and the modulated received signal are combined by a summer 220 to minimize the leakage of the broadcast transmit signal (step S412).

The present invention provides a system, device and method for a RFID reader having an accurate sensing circuit and a signal canceller.

The present invention can be realized in hardware, software, or a combination of hardware and software. An implementation of the method and system of the present invention can be realized in a centralized fashion in one computer system or in a distributed fashion where different elements are spread across several interconnected computer systems. Any kind of computer system, or other apparatus adapted for carrying out the methods described herein, is suited to perform the functions described herein.

It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described herein above. In addition, unless mention was made above to the contrary, it should be noted that all of the accompanying drawings are not to scale. A variety of modifications and variations are possible in light of the above teachings without departing from the scope and spirit of the invention, which is limited only by the following claims.

Claims

1. A method for generating a cancellation signal in a RFID reader, the method comprising: generating a local reference signal from a broadcast transmit signal;receiving a receive signal from a remote device;determining at least one signal correction factor; andgenerating the cancellation signal by applying the at least one signal correction factor to the local reference signal.

2. The method of claim 1, further comprising combining the correction signal and the receive signal to minimize interference on the receive signal.

3. The method of claim 1, wherein the broadcast transmit signal is one of a radio frequency (RF) signal and a RF continuous wave signal.

4. The method of claim 1, wherein the receive signal is one of a modulated RF signal and a modulated RF continuous wave signal.

5. The method of claim 1, wherein the at least one signal correction factor is one of an amplitude correction factor and a phase correction factor.

6. The method of claim 1, wherein the at least one signal correction factor includes an amplitude correction factor and a phase correction factor.

7. The method of claim 1, wherein determining at least one signal correction factor includes measuring one of an amplitude of the receive signal and a phase of the receive signal.

8. The method of claim 1, wherein determining at least one signal correction factor includes determining one of an amplitude correction factor and a phase correction factor by using a digital signal processor to execute an error minimization process.

9. The method of claim 1, wherein determining at least one signal correction factor includes determining an amplitude correction factor using a direct coupling component.

10. The method of claim 1, wherein determining at least one signal correction factor includes determining a phase correction factor using a signal delay line component.

11. A radio frequency identification (RFID) signal canceller, the signal canceller comprising: a signal pickup, the signal pickup configured to provide a local reference signal;at least one signal corrector, the at least one signal corrector configured to provide a signal correction factor;a signal processor, the signal processor configured to control the generation of a cancellation signal by applying the at least one signal correction factor to the local reference signal; anda detector, the detector configured to detect a receive signal and to provide signal parameters of the receive signal to the signal processor.

12. The signal canceller of claim 11 further comprising a signal summer in communication with the detector and the at least one signal corrector, the signal summer configured to combine the cancellation signal with the reflected receive signal to minimize the interference on the receive signal.

13. The signal canceller of claim 11, wherein the signal pickup is one of a directional coupler and a signal splitter.

14. The signal canceller of claim 11, wherein the detector is a received signal strength indication (RSSI) detector.

15. The signal canceller of claim 11, wherein the signal summer is one of a coupler device, a combiner device and a resistive arrangement circuit.

16. A RFID reader, the RFID reader comprising: a transmit section configured to output a broadcast transmit signal;a receive section configured to receive a receive signal; anda signal canceller, the signal canceller including: a signal pickup, the signal pickup configured to provide a local reference signal from the broadcast transmit signal;at least one signal corrector, the at least one signal corrector configured to provide a signal correction factor for adjusting the local reference signal;a signal processor, the signal processor configured to control the generation of a cancellation signal by applying the at least one signal correction factor to the local reference signal; anda detector configured to detect a receive signal and to provide signal parameters of the receive signal to the signal processor.

17. The RFID reader of claim 16, wherein the at least one signal corrector is an attenuator configured to provide an amplitude correction factor for adjusting the local reference signal.

18. The RFID reader of claim 16, wherein the at least one signal corrector is a phase shifter configured to provide a phase shift correction factor for adjusting the local reference signal.

19. The RFID reader of claim 16, wherein the at least one signal corrector is an attenuator configured to provide an amplitude correction factor for adjusting the local reference signal and a phase shifter configured to provide a phase shift correction factor for adjusting the local reference signal.

20. The RFID reader of claim 16, wherein the at least one signal correction factor is one of an amplitude correction factor and a phase correction factor.