WO2014128163A2

WO2014128163A2 - Interference elimination device and method

Info

Publication number: WO2014128163A2
Application number: PCT/EP2014/053236
Authority: WO
Inventors: Dieter Horst; Dan Yu; Yong Yuan
Original assignee: Siemens Aktiengesellschaft
Priority date: 2013-02-22
Filing date: 2014-02-19
Publication date: 2014-08-28
Also published as: CN104009776A; WO2014128163A3

Abstract

Disclosed in the present invention are an interference elimination device and method, used for eliminating interference in tag signals received by a reader in an RFID system. The device comprises: a control unit, a cancelling signal generating unit, a signal combining unit and a power detector. The cancelling signal generating unit is used for receiving a second carrier signal, a third carrier signal with a phase difference of 90 degrees with respect to the second carrier signal, and a fourth carrier signal with a phase difference of 180 degrees with respect to the second carrier signal, and for adjusting the amplitude of the second carrier signal, the third carrier signal and the fourth carrier signal according to an instruction from the control unit in order to generate multiple cancelling signals. The signal combining unit is used for receiving an interference signal and the multiple cancelling signals, adding or subtracting the interference signal and each of the multiple cancelling signals separately to obtain multiple combined signals, and eliminating the interference signal according to an instruction from the control unit. The power detector is used for detecting the amplitude of each combined signal. The control unit is used for determining an optimum cancelling signal according to the variation in amplitude of the combined signals, and controlling the signal combining unit to use the optimum cancelling signal to eliminate the interference signal. The adoption of the present invention enables elimination of interference to be achieved quickly and at a low cost.

Description

Description Interference elimination device and method Technical field

The present invention relates to the technical field of Radio Frequency Identification (RFID) , and in particular to an interference elimination device and method in an RFID system.

Background art

Radio Frequency Identification (RFID) technology is a contactless automatic identification technology, commonly referred to as electronic tagging, which automatically identifies a target object and acquires relevant data by means of RF signals. It comprises the following basic constituent parts :

1. A tag, consisting of a tag antenna and a chip, and attached to the object being controlled, detected or tracked. An RFID system generally comprises multiple tags, each having a unique electronic code for the purpose of uniquely identifying the object being controlled, detected or tracked. Here, the tag may also be called a transponder.

2. A reader, used for reading/writing information stored in the tag. It may be handheld or fixed. An RFID system generally comprises one reader, which reads information stored in each tag (and sometimes can also write tag information into the tag), in order to control, detect or track the object to which each tag is attached. Here, the reader may also be called an interrogator .

3. An antenna, connected to the reader, and used for transmitting RF signals between each tag and the reader, in order to transmit information between the reader and the tags. At present, a major obstacle to the development of ultra high frequency (UHF) RFID technology is its low reliability. In a UHF RFID system, the forward link (from the reader to the tag) and the backward link (from the tag to the reader) will both affect the reliability of the entire system, but many technologies in the art (such as antenna switching) are devoted to improving the reliability of the forward link; as far as improvement of the reliability of the backward link is concerned, technology in the art is in urgent need of improvement. Most UHF tags are passive or semi-active electronic tags; when outside the reading range of the reader, the UHF tag is in a passive state, but when inside the reading range of the reader, the UHF tag extracts the electrical energy required for its operation from a carrier signal (CW signal) emitted by the reader, and returns a signal to the reader by reflecting a signal on the carrier signal from the reader. Here, "carrier" denotes a waveform modulated to transmit a signal, and is in general a sine wave.

In a UHF RFID system, the reader must transmit a carrier signal on the forward link, and this will result in three types of interference signal, which will affect signal reception in the backward link; these three types of interference signal may be referred to as self-interference ( self-j ammers ) . Fig. 1 shows these three types of interference signal which are present during signal reception in the backward link. As Fig. 1 shows, a directional coupler 101 transmits a carrier signal from the reader, received from a transmitting port (TX port) of the reader, to an antenna 102, and transmits a signal from the UHF tag, received by the antenna 102, to the receiving port (RX port) of the reader. Three types of interference signal are present in the received signal transmitted to the receiving port of the reader.

Interference signal 1: a signal leaked from the transmitting port to the receiving port in the directional coupler 101 when the transmitting port transmits a carrier signal to the antenna 102. This leaked signal is relatively fixed, and related to the circuit characteristics of the directional coupler itself.

Interference signal 2: a signal reflected back by the antenna 102, related to the characteristics of the antenna 102 itself and the feed line thereof, and also relatively fixed.

Interference 3: an interference signal caused by a metal body 103 in the area surrounding the antenna 102. A near-field metal body may change the reflection characteristics of the antenna 102, while a far-field metal body may reflect a carrier signal to the antenna 102. These interference signals are unrelated to the intrinsic characteristics of the antenna 102 and the directional coupler 101, and have been referred to as dynamic self-interference.

These three types of interference signal will be transmitted to the receiving port of the reader together with received signals, and thus interfere with signals received by the reader from the UHF tag. To ensure the reliability of the backward link, the effect of these three types of interference signal on received signals must be eliminated.

Two schemes for eliminating self-interference have already been proposed in the prior art:

One scheme is to use a directional couplet with a high degree of isolation to avoid signal leakage from the transmitting port to the receiving port, i.e. eliminate the effect of interference signal 1 above. However, this scheme is unable to eliminate the effect on received signals of signals reflected by the antenna and interference signals caused by metal bodies in the area surrounding the antenna, i.e. is unable to eliminate the effect of interference signals 2 and 3 above. Another scheme uses a variable attenuator and a variable phase shifter to couple out signals having a certain phase and amplitude from the carrier of the transmitting port, so as to cancel out the effect of the three types of interference signal above on received signals, and thereby achieve the goal of eliminating self-interference . However, the cost of the variable phase shifter is very high, while the scheme has a complex design which is difficult to realize.

In summary, there is currently a need in UHF RFID technology for a simple, easily implemented scheme for eliminating interference caused to received signals by the three types of interference signal above, in order to improve the reliability of the backward link.

Content of the invention

To solve the above problem, the present invention proposes a device and method for interference elimination, which can eliminate interference on the backward link quickly and at a low cost.

An interference elimination device according to the embodiments of the present invention comprises: a control unit, a cancelling signal generating unit, a signal combining unit and a power detector, wherein: the cancelling signal generating unit is used for receiving a second carrier signal, a third carrier signal with a phase difference of 90 degrees with respect to the second carrier signal, and a fourth carrier signal with a phase difference of 180 degrees with respect to the second carrier signal, for adjusting the amplitude of the second carrier signal, the third carrier signal and the fourth carrier signal multiple times according to an instruction from the control unit, in order to generate multiple cancelling signals, and for outputting the multiple cancelling signals to the signal combining unit, wherein each cancelling signal generated is a signal obtained by adding the amplitude-adjusted second carrier signal and the amplitude-adjusted third carrier signal, or is a signal obtained by adding the amplitude-adjusted third carrier signal and the amplitude-adjusted fourth carrier signal; the signal combining unit is used for receiving an interference signal and the multiple cancelling signals, adding or subtracting the interference signal and each of the multiple cancelling signals separately to obtain multiple combined signals, outputting the multiple combined signals to the power detector, and eliminating the interference signal according to an instruction from the control unit; the power detector is used for receiving the multiple combined signals, detecting the amplitude of each combined signal, and outputting the amplitudes of the multiple combined signals to the control unit; the control unit is used for controlling the cancelling signal generating unit to generate the multiple cancelling signals, receiving the amplitudes of the multiple combined signals, determining an optimum cancelling signal according to the variation in amplitude of the multiple combined signals, and controlling the signal combining unit to use the optimum cancelling signal to eliminate the interference signal.

An interference elimination device according to another embodiment of the present invention comprises: a control unit, a vector modulator, a signal combining unit and a power detector, wherein: the vector modulator is used for receiving a second carrier signal, adjusting the amplitude and phase of the second carrier signal multiple times according to an instruction from the control unit, in order to generate multiple cancelling signals, and outputting the multiple cancelling signals to the signal combining unit; the signal combining unit is used for receiving an interference signal and the multiple cancelling signals, adding the interference signal and each of the multiple cancelling signals separately to obtain multiple combined signals, outputting the multiple combined signals to the power detector, and eliminating the interference signal according to an instruction from the control unit; the power detector is used for receiving the multiple combined signals, detecting the amplitude of each combined signal, and outputting the amplitudes of the multiple combined signals to the control unit; the control unit is used for controlling the vector modulator to generate the multiple cancelling signals, receiving the amplitudes of the multiple combined signals, determining an optimum cancelling signal according to the variation in amplitude of the multiple combined signals, and controlling the signal combining unit to use the optimum cancelling signal to eliminate the interference signal.

An interference elimination method according to the embodiments of the present invention, the method comprising: receiving a second carrier signal, a third carrier signal with a phase difference of 90 degrees with respect to the second carrier signal, and a fourth carrier signal with a phase difference of 180 degrees with respect to the second carrier signal ; receiving an interference signal; adjusting the amplitude of the second carrier signal, the third carrier signal and the fourth carrier signal multiple times, to generate multiple cancelling signals, wherein each cancelling signal generated is a signal obtained by adding the amplitude- adjusted second carrier signal and the amplitude-adjusted third carrier signal, or a signal obtained by adding the amplitude- adjusted third carrier signal and the amplitude-adjusted fourth carrier signal; adding or subtracting the interference signal and each of the multiple cancelling signals separately to obtain multiple combined signals; detecting the amplitude of each combined signal, and determining an optimum cancelling signal according to the variation in amplitude of the multiple combined signals; using the optimum cancelling signal to eliminate the interference signal.

The adoption of the interference elimination device and method provided in the embodiments of the present invention requires no changes to be made to existing reader hardware, so implementation is easy and costs are low. The two-stage seeking method provided in the embodiments of the present invention enables interference to be eliminated quickly, and in the case of frequency hopping, the use of a Look Up Table to store optimum phases corresponding to carrier signals of different frequencies enables a further improvement in the efficiency of interference elimination.

Description of the accompanying drawings

Demonstrative embodiments of the present invention will be described in detail below with reference to the accompanying drawings, to give those skilled in the art a clearer understanding of the above and other features and advantages of the present invention. Drawings: Fig. 1 shows self-interference present in a directional coupler and antenna in the prior art;

Fig. 2A is a schematic structural diagram of an interference elimination device according to an embodiment of the present invention ;

Fig. 2B is a schematic structural diagram of an interference elimination device according to an embodiment of the present invention ;

Fig. 3A shows constellation diagram coordinates of an optimum cancelling signal found when the interference signal is in the third quadrant;

Fig. 3B shows a curve of the variation in amplitude of a combined signal obtained by varying the value of Θ of a cancelling signal across the range [0°, 180°];

Fig. 3C shows constellation diagram coordinates of an optimum cancelling signal found when the interference signal is in the first quadrant;

Fig. 3D shows a curve of the variation in amplitude of a combined signal obtained by varying the value of Θ of a cancelling signal across the range [0°, 180°];

Fig. 4A is a schematic structural diagram of an interference elimination device according to an embodiment of the present invention ;

Fig. 4B is a schematic structural diagram of an interference elimination device according to an embodiment of the present invention ; Figs. 4C - 4E are schematic diagrams of variant solutions for an interference elimination device according to the embodiments of the present invention;

Fig. 5A is a schematic structural diagram of an interference elimination device according to an embodiment of the present invention ;

Fig. 5B is a schematic structural diagram of an interference elimination device according to an embodiment of the present invention ;

Fig. 6A is a flow chart of a method according to an embodiment of the present invention;

Fig. 6B is a flow chart of a method according to an embodiment of the present invention;

Fig. 7 shows the process of seeking the phase of an optimum cancelling signal in two stages.

Particular embodiments

The above characteristics, technical features and advantages of the present invention as well as embodiments thereof will be illustrated further below in a clear and easily understandable way, by explaining preferred embodiments with reference to the accompanying drawings .

Fig. 2A shows a schematic diagram of the assembled structure of an interference elimination device according to an embodiment of the present invention. As Fig. 2A shows, the interference elimination device may comprise: a transmission line 20, a cancelling signal generating unit 21, a control unit 22, a signal combining unit 23, a power detector 24 and a coupling unit 25. In this embodiment, a forward carrier signal outputted by a reader is expressed as Asin (x) , wherein A denotes the amplitude of the carrier signal. As Fig. 2A shows, the transmission line 20 connects a transmitting port (TX port) to an antenna, and transmits the forward carrier signal Asin (x) outputted by the reader to the antenna. This will result in the three types of interference signal mentioned above, expressed as Α33ΐη(χ+β) and ARCsin (χ+γ) , wherein S denotes the interference signal amplitude arising from the degree of isolation of the coupling unit 25, and is called the isolation coefficient; C denotes the interference signal amplitude arising from the coupling loss of the coupling unit 25, and is called the coupling coefficient; R denotes the interference signal amplitude arising from the reflection loss of the antenna (including: reflection from the antenna itself, and reflection from metal objects in the area surrounding the antenna) , and is called the reflection coefficient or reflection loss; β denotes the phase change arising from the degree of isolation of the coupling unit 25; and γ denotes the phase change arising from the coupling loss of the coupling unit 25 and the reflection loss of the antenna. Thus, the interference signal Α33ΐη(χ+β) corresponds to interference signal 1 above, while the interference signal ARCsin (χ+γ) corresponds to interference signals 2 and 3 above. Thus, the interference caused by the three types of interference signals mentioned above may be expressed as Α33ΐη(χ+β) + ARCsin (χ+γ) .

In the interference elimination device shown in Fig. 2A, the cancelling signal generating unit 21 receives three carrier signals from the coupling unit 25, ACsin (x+ ) , ACcos (x+ ) and -ACsin (χ+ ) , which are coupled from the transmission line 20, wherein a denotes the phase change arising from coupling loss. The signal combining unit 23 receives the interference signal Α33ΐη(χ+β) and the interference signal ARCsin (χ+γ) , which are coupled from the transmission line 20, from the coupling unit 25. The control unit 22 is used to control at least two variable attenuators in the cancelling signal generating unit 21, these variable attenuators processing received signals separately according to instructions from the control unit 22, wherein Hi and H₂ denote adjustment of signal amplitude by the variable attenuators, i.e. are attenuation coefficients. Thus, the cancelling signal generating unit 21 generates a cancelling signal and depending on the control

exerted by the control unit 22 on the variable attenuators in the cancelling signal generating unit 21, the variable attenuators may use different attenuation coefficients to adjust the signal, and thereby output multiple cancelling signals. The signal combining unit 23 receives the cancelling signal from the cancelling signal generating unit 21 and the interference signal coupled from the transmission line 20, and subjects the cancelling signal and interference signal to addition or subtraction, to obtain the sum of the cancelling signal and the interference signal, or the difference between the cancelling signal and the interference signal. At the same time, controlled by the control unit 22, the signal combining unit 23 may choose to subject the cancelling signal and the interference signal to addition or subtraction, and output a combined signal (i.e. the sum of the cancelling signal and the interference signal or the difference therebetween) to the receiving port (RX port) ; the combined signal thus outputted is the signal remaining after the cancelling signal and the interference signal have been offset against each other. The power detector 24 is connected to an output end of the signal combining unit 23, and detects the signal amplitude outputted thereby, before outputting the detection result to the control unit 22. The control unit 22 finds the optimum cancelling signal according to the detection result of the power detector 24 (i.e. the cancelling signal capable of cancelling out the interference signal to the greatest extent possible, to minimize the amplitude of the remaining signal obtained) , and sends an instruction to the cancelling signal generating unit 21 to output the optimum cancelling signal, at the same time sending an instruction to the signal combining unit 23 to add or subtract the optimum cancelling signal and the interference signal so that the amplitude of the remaining signal outputted thereby is minimized, thereby achieving the objective of eliminating interference.

Specifically, each time the cancelling signal generating unit 21 generates a cancelling signal, it can output this cancelling signal to the signal combining unit 23. Each time the signal combining unit 23 receives a cancelling signal, it can add or subtract this cancelling signal and the interference signal to obtain a combined signal, and output this combined signal to the power detector 24. The power detector 24 can receive combined signals, and each time it receives a combined signal, detect and output to the control unit 22 the amplitude of this combined signal. The control unit 22 can run a computer program for seeking an optimum cancelling signal in order to find the optimum cancelling signal for elimination of interference, wherein the control unit 22 can record the variation in phase of the multiple cancelling signals and the amplitudes of multiple combined signals corresponding thereto from the power detector 24, to obtain a first curve showing the variation of combined signal amplitude with cancelling signal phase, and determine the phase of the cancelling signal corresponding to the maximum or minimum value in the first curve as the optimum phase; it can then record the variation in amplitude of the multiple cancelling signals which have the optimum phase and the amplitudes of the multiple combined signals corresponding thereto, to obtain a second curve showing the variation of combined signal amplitude with amplitude of cancelling signals which have the optimum phase, determine the cancelling signal corresponding to the minimum value on the second curve as the optimum cancelling signal, and set whether the signal combining unit 23 adds or subtracts the optimum cancelling signal and the interference signal when eliminating interference, wherein if the optimum phase corresponds to the maximum value, the operation performed on the interference signal and the optimum cancelling signal is opposite to the operation used to obtain the multiple combined signals corresponding to the first curve, and if the optimum phase corresponds to the minimum value, the operation performed on the interference signal and the optimum cancelling signal is the same as the operation used to obtain the multiple combined signals corresponding to the first curve. Having determined the optimum cancelling signal, the control unit 22 instructs the cancelling signal generating unit 21 to generate the optimum cancelling signal according to the amplitude and phase thereof; the cancelling signal generating unit 21 generates the optimum cancelling signal according to the instruction from the control unit 22 and outputs the same to the signal combining unit 23; the control unit 22 instructs the signal combining unit 23 to add or subtract the optimum cancelling signal and the interference signal, according to whether the signal combining unit is set to add or subtract the optimum cancelling signal and the interference signal when eliminating interference; the signal combining unit 23 is connected to the receiving port, and further adds or subtracts the optimum cancelling signal and the interference signal according to the instruction from the control unit 22, to eliminate the effect of the interference signal on the received signal transmitted to the receiving port.

In this embodiment of the present invention, the transmission line 20 may be of various types, for instance: a microstrip line, coplanar stripline or coplanar waveguide line.

Based on the interference elimination device shown in Fig. 2A, Fig. 2B shows a schematic structural diagram of an interference elimination device according to another embodiment of the present invention. In this embodiment, the transmission line 20 is a microstrip line 201; the cancelling signal generating unit 21 comprises two variable attenuators 203a - 203b, a switch 204a and a power combiner 205a; the signal combining unit 23 comprises a power combiner 205b and a switch 204b; the control unit 22 is a micro control unit (MCU) 206; and the coupling unit comprises four couplers 202a - 202d. As Fig. 2B shows, the interference elimination device comprises: the microstrip line 201, the couplers 202a - 202d, the variable attenuators 203a - 203b, the switches 204a - 204b, the power combiners 205a - 205b, the micro control unit 206 and a power detector 207. As in Fig. 2A, in Fig. 2B the microstrip line 201 is connected to a transmitting port (TX port) and an antenna, and transmits a forward carrier signal Asin (x) to the antenna; this will lead to the three types of interference signal mentioned above, expressed as Α33ΐη(χ+β) and ARCsin (χ+γ) , respectively. Thus, the interference caused by these three types of interference signal to the signal received by the receiving port (RX port) can be expressed as Α33ΐη(χ+β) + ARCsin (χ+γ) .

In the interference elimination device in Fig. 2B, the coupler

202a, the coupler 202b and the coupler 202c obtain three carrier signals from the microstrip line 201 by coupling, namely ACsin (x+a) , ACcos (x+a) and -ACsin (x+a) . The coupler 202d is used to obtain an interference signal Α33ΐη(χ+β) and an interference signal ARCsin (χ+γ) from the microstrip line 201 by coupling, and to output the interference signal Α33ΐη(χ+β) +

ARCsin (X+Y) obtained by coupling to the power combiner 205b.

The MCU 206 is used to control the variable attenuator 203a, the variable attenuator 203b, the switch 204a and the switch

204b. The coupler 202b outputs a signal ACcos (x+a) to the variable attenuator 203a, which processes the signal received according to an instruction from the MCU 206 and then outputs a

A Ccost + Oi )

signal to the power combiner 205a, wherein H₂ denotes the attenuation coefficient of the variable attenuator 203a on signal amplitude. The coupler 202a and coupler 202c output signals ACsin (x+a) and -ACsin (χ+α) , respectively, to the switch 204a. The switch 204a is used to select one of the two signals from the coupler 202a and the coupler 202c (ACsin (x+a) and -ACsin (x+a) ) according to an instruction from the MCU 206, and to output the selected signal (ACsin (x+a) or -ACsin (x+a) ) to the variable attenuator 203b. The variable attenuator 203b processes the signal received according to an instruction from

. ^Csin(x + a) ^Csin(x + a) the MCU 206 and outputs a signal or to the power combiner 205a, wherein Hi denotes the attenuation coefficient of the variable attenuator 203b on signal amplitude. The power combiner 205a combines the two signals from the two variable attenuators 203a and 203b to obtain a cancelling signal for cancelling out interference, and outputs the same to the power combiner 205b. The power combiner 205b receives the cancelling signal from the power combiner 205a and the interference signal from the coupler 202d, and adds and subtracts the cancelling signal and the interference signal separately to obtain two combined signals which it then outputs, one signal being the sum of the cancelling signal and the interference signal, the other signal being the difference between the cancelling signal and the interference signal. The switch 204b selects one of the two combined signals outputted by the power combiner 205b according to an instruction from the MCU 206, and outputs the selected combined signal to the receiving port (RX port) ; the combined signal thus outputted is the signal remaining after the cancelling signal and the interference signal have been offset against each other. The power detector 207 is connected to an output end of the switch 204b, and detects the amplitude of the signal outputted by the switch 204b, then outputting the detection result to the MCU 206. The MCU 206 finds the optimum cancelling signal according to the detection result of the power detector 207 (i.e. the cancelling signal capable of cancelling out the interference signal to the greatest extent possible, to minimize the amplitude of the remaining signal obtained) , and sends instructions to the variable attenuators 203a - 203b and the switch 204a such that the power combiner 205a outputs the optimum cancelling signal, at the same time sending an instruction to the switch 204b to indicate which signal should be selected by the switch 204b to minimize the amplitude of the remaining signal outputted by the switch 204b, so as to achieve the aim of eliminating interference.

Here, since the separation of the coupler 202a, the coupler 202b and the coupler 202c from one another is λ/4, the signals they obtain by coupling differ from one another in phase by 90°, so they can obtain signals ACsin (x+ ) , ACcos (x+ ) and -ACsin (x+a) by coupling, respectively, wherein λ is the wavelength of the forward carrier signal Asin (x) outputted by the reader. The couplers 202a - 202d and the microstrip line 201 shown in Fig. 2B are conductive metal layers printed on a printed circuit board, the couplers 202a - 202d all being microstrip lines laid parallel to the microstrip line 201. The coupler 202a and coupler 202b are separated by one quarter of the wavelength of the forward carrier signal Asin (x) , while the coupler 202b and coupler 202c are also separated by one quarter of the wavelength of the forward carrier signal Asin (x) . The embodiments of the present invention do not restrict the specific shape and size of the microstrip lines 202a - 202d and the microstrip line 201; a variety of existing microstrip lines from the prior art may be used.

The principles by which the above interference elimination device eliminates interference are explained further below.

The sum of any two sinusoid signals of the same frequency but different phase and amplitude is another sinusoid wave of the same frequency. This theorem can be proved by the following formula derivation.

A sin(x)+ B sin(x + a) = A sin(x)+ B sin(x)cos a + B cos(x)sin a

= sin(x)^4 + B cos a)+ COS(X)B sin a

'+cos(x)B'

A'

wherein A = A + B cos a , 5'= B sin a , β = arccos , Asin (x) and

Bsin (x+a) are two sinusoid signals of the same frequency but different phase and amplitude, and the above formula derivation shows that the sum of these two signals may be expressed as another sinusoid signal of the same frequency,

The above theorem shows that the interference Α33ΐη(χ+β) + ARCsin (X+Y) caused by the three types of interference signal mentioned above may be expressed as a sinusoid signal of the same frequency. Moreover, the cancelling signal obtained by the interference elimination device proposed in the present invention and the interference signal are sinusoid signals of the same frequency but different phase and amplitude, and the interference signal can be eliminated to the greatest extent possible by seeking and setting the optimum cancelling signal. To facilitate understanding of the method by which the MCU 206 seeks the optimum cancelling signal, this method is explained in detail below by means of constellation diagram (IQ plot) coordinates of the cancelling signal and interference signal as well as an example of a simulated result of a combined signal obtained by combining the two. Those skilled in the art will know that the interference signal obtained by the interference elimination device is a sinusoid signal of a certain amplitude and phase, and when shown in the coordinate system of a constellation diagram, this interference signal may lie in the first and second quadrants, or in the third and fourth quadrants .

Fig. 3A shows an example of an optimum cancelling signal found when the interference signal lies in the third quadrant. As Fig. 3A shows, the interference signals Α33ΐη(χ+β) and ARCsin (x+y) can be combined to obtain one interference signal in the third quadrant; the power combiner 205a in the interference elimination device can obtain a cancelling signal

, . . , . ^Csin(x + a) _n ^Ccos(x + a) , . by combining the two signals - and -, this cancelling signal having a certain angle Θ in the constellation diagram. The MCU 206 can change the value of Θ of the cancelling signal by adjusting the attenuation coefficients Hi and ¾ of the variable attenuators 203a and 203b. As Fig. 3A shows, the range of values of Θ of the cancelling signal is [0, 180°] . Fig. 3B shows the amplitude of the combined signal obtained by the power combiner 205b by adding the interference

ARCsin (χ+γ) and the cancelling signal as the value of Θ of the cancelling

signal varies across the range [0, 180°] . Cancelling signals with different values of Θ can be obtained by adjusting the attenuation coefficients Hi and ¾ of the variable attenuators 203a and 203b; adding different cancelling signals to the interference signal gives combined signals with different amplitudes. As Fig. 3B shows, the amplitude of the combined signal is smallest when the value of Θ of the cancelling signal is close to 50°. When the cancelling signal lies in the first or second quadrant while the interference signal lies in the third or fourth quadrant, a combined signal with as small an amplitude as possible can be produced by adding these two signals, so that they cancel each other out, which is equivalent to carrying out processing to eliminate interference. Thus, if the combined signal with the smallest amplitude is found from amongst the various combined signals, the cancelling signal corresponding to this combined signal with the smallest amplitude is then the optimum cancelling signal for eliminating interference. According to the simulation results shown in Fig. 3B, the value of Θ of the cancelling signal corresponding to the smallest combined signal amplitude can be found, this value of Θ corresponding to a pair of values of Hi and ¾, i.e. the pair of values of Hi and ¾ corresponding to the optimum cancelling signal. The curve shown in Fig. 3B corresponds to a data set comprising each value of Θ in the range [0, 180°] and the amplitudes of corresponding combined signals; each value of Θ can be characterized by a pair of values of Hi and ¾ . Each pair of values of Hi and ¾ corresponding to each value of Θ can be pre-configured in the MCU 206, the variable attenuators 203a and 203b setting each pair of values of Hi and ¾ in succession according to instructions from the MCU 206. Each time the variable attenuators 203a and 203b set a pair of values of Hi and H₂ , the power combiner 205b outputs a combined signal obtained by adding the cancelling signal and the interference signal. In an initial state, the MCU 206 instructs the switch 204b to select the signal outputted by the power combiner 205b that is the sum of the cancelling signal and the interference signal; the power detector 207 detects the amplitude of the combined signal outputted from the switch 204b and outputs the same to the MCU 206. In this way, the amplitudes of combined signals corresponding to each pair of values of Hi and H₂ are recorded in the MCU 206, and the values of Hi and H₂ corresponding to the optimum cancelling signal are then found according to a preset seeking method (for example, if the interference signal lies in the third or fourth quadrant, a pair of values of Hi and H₂ corresponding to the smallest combined signal amplitude is found as the pair of values of Hi and H₂ corresponding to the optimum cancelling signal) . Next, the MCU 206 can make the variable attenuators 203a and 203b set the attenuation coefficients Hi and H₂ to the pair of values of Hi and H₂ corresponding to the optimum cancelling signal, and in turn make the power combiner 205a output the optimum cancelling signal; at the same time, the MCU 206 instructs the switch 204b to select the signal (i.e. the remaining signal) outputted by the power combiner 205b that is the sum of the optimum cancelling signal and the interference signal. At this point, the switch 204b outputs to the receiving port (RX port) the signal remaining after the optimum cancelling signal and the interference signal have been offset against one another (this remaining signal is the sum of these two signals) ; as can be seen from Figs. 3A and 3B, the amplitude of the remaining signal is nearly zero. Thus the backward link signal from the tag that is received by the reader from the receiving port suffers very little interference, so the aims of eliminating interference and improving the performance of the backward link can be achieved. Fig. 3C shows an example of an optimum cancelling signal found when the interference signal lies in the first quadrant. As Fig. 3C shows, the interference signals Α33ΐη(χ+β) and ARCsin (X+Y) can be combined to obtain one interference signal in the first quadrant; the power combiner 205a in the interference elimination device can obtain a cancelling signal

, . . , . , . by combining the two signals ± , this

cancelling signal having a certain angle Θ in the constellation diagram. The MCU 206 can change the value of Θ of the cancelling signal by adjusting the attenuation coefficients Hi and ¾ of the variable attenuators 203a and 203b. As Fig. 3C shows, the range of values of Θ of the cancelling signal is [0, 180°] . Fig. 3D shows the amplitude of the combined signal obtained by the power combiner 205b by combining the interference signal Α33ΐη(χ+β) + ARCsin (χ+γ) with the

, , . . , ^Csin(x + a) ^Ccos(x + a) , _ _^ cancelling signal ± -+ as the value of Θ of the cancelling signal varies in the range [0, 180°] . As Fig. 3D shows, the amplitude of the combined signal is greatest when the value of Θ of the cancelling signal is close to 50°. When the cancelling signal and the interference signal both lie in the first or second quadrant, a combined signal with as small an amplitude as possible can be produced by subtracting these two signals, so that they cancel each other out, which is equivalent to carrying out processing to eliminate interference. According to the simulation results shown in Fig. 3D, the value of Θ of the cancelling signal corresponding to the largest combined signal amplitude can be found, this value of Θ corresponding to a pair of values of Hi and ¾, i.e. the pair of values of Hi and ¾ corresponding to the optimum cancelling signal. The curve shown in Fig. 3D corresponds to a data set comprising each value of Θ in the range [0, 180°] and the amplitudes of corresponding combined signals; each value of Θ can be characterized by a pair of values of Hi and ¾ . Each pair of values of Hi and ¾ corresponding to each value of Θ can be pre-configured in the MCU 206, the variable attenuators 203a and 203b setting each pair of values of Hi and H₂ in succession according to instructions from the MCU 206. Each time the variable attenuators 203a and 203b set a pair of values of Hi and H₂ , the power combiner 205b outputs a combined signal obtained by adding the cancelling signal and the interference signal. In an initial state, the MCU 206 instructs the switch 204b to select the signal outputted by the power combiner 205b that is the sum of the cancelling signal and the interference signal; the power detector 207 detects the amplitude of the combined signal outputted from the switch 204b and outputs the same to the MCU 206. In this way, the amplitudes of combined signals corresponding to each pair of values of Hi and H₂ are recorded in the MCU 206, and the values of Hi and H₂ corresponding to the optimum cancelling signal are then found by a preset seeking method (for example, if the interference signal lies in the first or second quadrant, a pair of values of Hi and H₂ corresponding to the largest combined signal amplitude is found as the pair of values of Hi and H₂ corresponding to the optimum cancelling signal) . Next, the MCU 206 can make the variable attenuators 203a and 203b set the attenuation coefficients Hi and H₂ to the pair of values of Hi and H₂ corresponding to the optimum cancelling signal, and in turn make the power combiner 205a output the optimum cancelling signal; at the same time, the MCU 206 instructs the switch 204b to select the signal (i.e. the remaining signal) outputted by the power combiner 205b that is the difference between the optimum cancelling signal and the interference signal. At this point, the switch 204b outputs to the receiving port (RX port) the signal remaining after the optimum cancelling signal and the interference signal have been offset against one another (this remaining signal is the difference between these two signals); as can be seen from Figs. 3C and 3D, the optimum cancelling signal is capable of almost completely cancelling out the interference signal, so that the backward link signal from the tag that is received by the reader from the receiving port suffers very little interference, allowing the aims of eliminating interference and improving the performance of the backward link to be achieved.

Here, after recording each pair of values of Hi and H₂ and the corresponding combined signal amplitudes, the MCU 206 can judge whether the interference signal lies in the first or second quadrant or in the third or fourth quadrant according to the trend followed by the combined signal amplitude as the values of Hi and H₂ vary. For instance: the MCU 206 can make a curve similar to Fig. 3B or to Fig. 3D according to the recorded values of Θ characterized by each pair of values of Hi and H₂ and each combined signal amplitude corresponding thereto; if the curve thus made resembles Fig. 3B (i.e. as the value of Θ increases, the combined signal amplitude first falls to a minimum value, and then rises again) , then it is determined that the interference signal lies in the third or fourth quadrant; if the curve thus made resembles Fig. 3D (i.e. as the value of Θ increases, the combined signal amplitude first rises to a maximum value, and then falls again) , then it is determined that the interference signal lies in the first or second quadrant.

The interference elimination device according to the embodiments of the present invention preferably has a transmission line 20 and coupled transmission lines 202a - 202d integrated therein, with the coupled transmission lines 202a to 202d all being arranged parallel to the transmission line 20, and each forming a separate coupler with the transmission line 20, so as to obtain carrier signals and interference signals from the transmission line 20 by coupling and provide these to the cancelling signal generating unit 21 and the signal combining unit 23 for processing. In this way, the interference elimination device according to the embodiments of the present invention can be used to replace the original circulator or directional coupler of the reader directly, so as to optimize the cost of implementing the present invention. Optionally, it is also possible for the interference elimination device according to the embodiments of the present invention not to have the transmission line 20 and the coupled transmission lines 202a - 202d integrated therein, in which case a separate coupler device may be used when implementing the present invention, to provide carrier signals and interference signals to the cancelling signal generating unit 21 and the signal combining unit 23. Alternatively, it is also possible for the interference elimination device according to the embodiments of the present invention to have the transmission line 20 and the coupled transmission lines 202a - 202c integrated therein, but not to have the coupled transmission line 202d integrated therein, in which case the coupled transmission lines 202a - 202c can be used to obtain carrier signals from the transmission line 20 by coupling and provide these to the cancelling signal generating unit 21, while a separate coupler device can be used to provide interference signals to the signal combining unit 23. Various types of coupler device may be used as the separate coupler, for instance a coupling line or a circulator. Moreover, various types of variable attenuator may be used in the present invention. For example, a digital attenuator may be used, which advances in steps of, for example, 0.5 dB . An analog attenuator may also be used, for example a diode variable attenuator capable of continuous attenuation (PIN Diode variable attenuator) .

It is clear from the above description that the interference elimination device proposed in the present invention can seek an optimum cancelling signal dynamically by adjusting the carrier signal attenuation parameters, thereby bringing costs down; the interference elimination device is also integrated in an existing UHF RFID reader very easily. Furthermore, since the range over which the optimum cancelling signal is sought is reduced to [0°, 180°], with no need to search over the range [0°, 360°], the optimum cancelling signal can be found in a very short time, so the stringent requirements of certain protocols such as EPC C1G2 regarding time delays are satisfied. For instance, according to the requirements of certain protocols, the reader will only wait 1.5 ms (i.e. Ts = 1.5 ms) after each power-on before emitting the first command, in other words, the optimum cancelling signal must be found and the settings completed within 1.5 ms . Simulated experiments can demonstrate that when the interference elimination device provided by the embodiments of the present invention is used, the optimum cancelling signal can be found and the setting thereof completed within 1.5 ms; this will be illustrated in detail in the following text.

Based on the interference elimination devices shown in Figs. 2A and 2B above, the embodiments of the present invention also propose two typical variant solutions, as shown in Figs. 4A and 4B. Compared with the interference elimination device shown in Fig. 2A, in the interference elimination device shown in Fig. 4A, the transmission line is a microstrip line 201; the cancelling signal generating unit comprises two variable attenuators 203b and one variable attenuator 203a, a switch 204a and a power combiner 205a; the signal combining unit comprises a power combiner 205b and a switch 204b; the control unit is an MCU 206; and the coupling unit comprises four couplers 202a - 202d. A difference between the interference elimination device shown in Fig. 4A and that shown in Fig. 2B is that the variable attenuator 203b in Fig. 4A is connected not after the switch 204a but in front of the switch 204a, but

■ ■ -, -, ■ -, , -4Csin(x + a) _{η η} . can similarly output a signal ± - to the power combiner

205a. As Fig. 4A shows, the interference elimination device comprises two variable attenuators 203b, the attenuation coefficients of which may be kept equal; these two variable attenuators are connected to couplers 202a and 202c,

^Csin(x + a) _n ACsin(x + a) respectively, and output signals + - and ¹ to the switch 204a, respectively. The switch 204a selects one of these two signals according to an instruction from the MCU 206,

AC sin(x + a) AC sin(x + a)

and outputs + or to the power combiner

H_l Hi 205a. Compared with the interference elimination device shown in Fig. 2A, in the interference elimination device shown in

Fig. 4B, the transmission line is a microstrip line 201; the cancelling signal generating unit comprises two variable attenuators 203a - 203b, a switch 204a and a power combiner

205a; the signal combining unit comprises a power combiner 205b and a switch 204b; the control unit is an MCU 206; the coupling unit comprises two couplers 402a - 402b; in addition, also included are a power splitter 403, a 90° phase shifter 404a and a 180° phase shifter 404b. The interference elimination device shown in Fig. 4B differs from that shown in Fig. 2B by having only two couplers. As Fig. 4B shows, the interference elimination device comprises two couplers 402a and 402b, and further comprises a power splitter 403, a 90° phase shifter

404a and a 180° phase shifter 404b. The coupler 402b is the same as the coupler 202d in Fig. 2B, being used to couple an interference signal and output the same to the power combiner

205b. The coupler 402a, power splitter 403, 90° phase shifter

404a and 180° phase shifter 404b are used to obtain a carrier signal ACsin (x+ ) by coupling and to obtain therefrom carrier signals 0.5774ACcos (x+a) and -0.5774ACsin (x+a) for generating cancelling signals. Specifically, the coupler 402a outputs a signal ACsin (x+a) to the power splitter 403, which outputs signals 0.5774ACsin (x+a) to the switch 204a, 90° phase shifter

404a and 180° phase shifter 404b, respectively. The 90° phase shifter 404a and 180° phase shifter 404b then subject the signals respectively received to phase-shift processing, such that the 90° phase shifter 404a outputs a signal

0.5774ACcos (x+a) to the variable attenuator 203a, and the 180° phase shifter 404b outputs a signal -0.5774ACsin (x+a) to the switch 204a. The switch 204a in Fig. 4B is the same as the switch 204a in Fig. 2, being capable of selecting one of the two signals 0.5774ACsin (x+a) and -0.5774ACsin (x+a) so as to output a signal 0.5774ACsin (x+a) or -0.5774ACsin (x+a) to the variable attenuator 203b, which can then output a signal

A C sin ( x + (x )

+0.5774 to the power combiner 205a. The principles of operation of the other components in Figs. 4A and 4B are the same as in Figs. 2A and 2B, and are not repeated here.

Furthermore, based on the interference elimination device shown in Fig. 4B, a variant solution similar to Fig. 4A can be obtained for the variable attenuator 203b, specifically that shown in Fig. 4C. The variable attenuator 203b in Fig. 4B is connected in front of the switch 204a rather than after the switch 204a. The interference elimination device comprises two variable attenuators 203b, the attenuation coefficients of which may be kept equal; these two variable attenuators are connected to a power splitter 403 and a 180° phase shifter

„„„_n ■ , ■ ,-_^„ ACsin(x + a)

404b, respectively, and output signals +0.5774 - and

- tch

204a selects one of these two signals according to an

ACsin(x + (x ) instruction from the MCU 206, and outputs +0.5774 or

^Hi

ACsin(x + )

-0.5774 -^ to the power combiner 205a. Optionally, based on the interference elimination device shown in Fig. 4B, a variant solution may be obtained for the power splitter 403, 90° phase shifter 404a and 180° phase shifter 404b, specifically that shown in Fig. 4D. The 180° phase shifter 404b can be replaced with another 90° phase shifter 404a'; the power splitter 403 outputs a signal 0.707ACsin (x+ ) to the switch 204a and to the 90° phase shifter 404a; an output end of the phase shifter 404a is connected to another power splitter 403' , and outputs a signal 0.707ACcos (x+a) to the power splitter 403' ; the power splitter 403' outputs a signal 0.707*0.707ACcos (x+a) to the variable attenuator 203a, and also outputs a signal 0.707*0.707ACcos (x+a) to the 90° phase shifter 404a'; and the 90° phase shifter 404a' outputs a signal -0.707*0.707ACsin (x+a) to the switch 204a. Optionally, based on the interference elimination device shown in Fig. 4B, the variant solution for the variable attenuator 203b and the variant solution for the power splitter 403, 90° phase shifter 404a and 180° phase shifter 404b may also be combined to obtain another variant solution, specifically that shown in Fig. 4E. Taking the variant solution shown in Fig. 4D for the power splitter 403, 90° phase shifter 404a and 180° phase shifter 404b as a starting point, the way in which the variable attenuator 203b is connected to other components is adjusted, with the variable attenuator 203b being connected in front of the switch 204a. Specifically, the interference elimination device comprises one variable attenuator 203a and two variable attenuators 203b. The way in which the variable attenuator 203a is connected to other components does not change; the two variable attenuators 203b are connected to the power splitter

403 and the 90° phase shifter 404a', respectively, and output signals + to the switch

204a, respectively. The switch 204a selects one of these two signals according to an instruction from the MCU 206, and

0.707 * 0.707.4Csin(x + a) 0.707 * 0.707^Csin(x +a) outputs + or to the

H H

power combiner 205a.

The principal design concept of each of the above types of interference elimination device is to use a coupler to obtain a carrier signal by coupling, and to use a power splitter and fixed phase shifters to obtain signals formed by shifting the phase of this signal by 90° and 180°, respectively, and then to use these three carrier signals to generate various cancelling signals by adjusting the attenuation coefficients of the variable attenuators, in order to seek the optimum cancelling signal within the range [0°, 180°], and thereby achieve the objective of eliminating interference. This design concept can be expanded to obtain a variety of embodiments, which are not listed here one by one, but which are all within the scope of protection of the present invention. Each of the above embodiments concerns elimination of interference in the case of a forward carrier signal with a specific frequency. The above embodiments may be expanded further when the case of frequency hopping is considered, i.e. the frequency of the forward carrier signal varies within a certain range; for example, in a forward control channel band (FCC band) , the forward carrier signal may vary within the range of 902 MHz to 928 MHz. A control unit (e.g. an MCU) may further store a Look Up Table (LUT) , in which are recorded the optimum phases of cancelling signals corresponding to carrier signals of each frequency transmitted by the reader. Each time the control unit determines the optimum phase for a carrier signal of a certain frequency, the control unit then stores this optimum phase. Each time the reader is powered on, the control unit looks up the optimum phase corresponding to the carrier signal currently transmitted by the reader in the LUT. If the optimum phase is found, the control unit directly instructs the cancelling signal generating unit to generate multiple cancelling signals having this optimum phase but different amplitudes, so as to further determine the optimum cancelling signal which has this optimum phase and the optimum amplitude, and finally instructs the cancelling signal generating unit to generate this optimum cancelling signal. If the optimum phase is not found, the control unit determines the optimum phase corresponding to the carrier signal currently transmitted by the reader, then instructs the cancelling signal generating unit to generate multiple cancelling signals having this optimum phase but different amplitudes, so as to further determine the optimum cancelling signal which has this optimum phase and the optimum amplitude, and finally instructs the cancelling signal generating unit to generate this optimum cancelling signal. For instance, in the interference elimination device shown in Fig. 2B, for each frequency of forward carrier signal, the MCU 206 can find the optimum cancelling signal in the range [0°, 180°] by adjusting the attenuation coefficients of the variable attenuators 203a and 203b, and record in the LUT associated setting parameters (including the attenuation coefficients of variable attenuators 203a - 203b, the signal selection settings of switches 204a - 204b, etc.) of the various optimum phases corresponding to forward carrier signals of different frequencies; subsequently, when the frequency of the forward carrier signal changes, the MCU can find the associated setting parameters of the optimum phase corresponding to the current frequency, then instruct the variable attenuators 203a - 203b and switches 204a - 204b to implement the appropriate settings so that the power combiner 205a outputs multiple cancelling signals having the optimum phase, and determine the optimum cancelling signal, at the same time instructing the switch 204b to perform signal selection to obtain the signal remaining after the optimum cancelling signal and the interference signal have been offset against one another. Thus, once the interference elimination device has been powered on, the MCU 206 can quickly find the associated setting parameters of the optimum phase corresponding to the current frequency via the LUT, so as to set the optimum cancelling signal quickly, and achieve the goal of eliminating interference .

The embodiments of the present invention propose another interference elimination device, which uses a vector modulator to obtain cancelling signals of various phases and amplitudes, in order to find the optimum cancelling signal from amongst these, and thus achieve the goal of eliminating interference. Fig. 5A shows a schematic structural diagram of an interference elimination device using a vector modulator according to an embodiment of the present invention. This interference elimination device may comprise: a transmission line 50, a coupling unit 55, a control unit 52, a vector modulator 51, a signal combining unit 53 and a power detector 54, wherein the functions of the transmission line 50 and coupling unit 55 are the same as those of the transmission line 20 and the coupling unit 25 in Fig. 2A, and are not repeated here. The vector modulator 51 receives from the coupling unit 55 a carrier signal ACsin (x+ ) that is obtained from the transmission line 50 by coupling, adjusts the amplitude and phase of the carrier signal ACsin (x+ ) multiple times according to an instruction from the control unit 52 in order to generate multiple cancelling signals AACsin (χ+ +φ) , and outputs these cancelling signals AACsin (χ+ +φ) to the signal combining unit 53. Here, Δ represents adjustment of signal amplitude by the vector modulator 51, and may be called the amplitude change coefficient; φ represents adjustment of signal phase by the vector modulator 51, and may be called the phase difference. The vector modulator 51 can adjust the phase of the cancelling signal in the range [0, 360°] . Each time a cancelling signal is generated, the vector modulator 51 can output this cancelling signal to the signal combining unit 53. The signal combining unit 53 receives an interference signal Α33ΐη(χ+β) + ARCsin (χ+γ) from the coupling unit 55, adds the interference signal received to the multiple cancelling signals separately to obtain multiple combined signals, and then outputs these combined signals to the power detector 54. Here, each time a cancelling signal is received, the signal combining unit can add this cancelling signal to the interference signal to obtain a combined signal, and then output this combined signal to the power detector 54. The power detector 54 receives the combined signals, detects the amplitude of each combined signal separately, and outputs the amplitude of this combined signal to the control unit 52. The control unit 52 can run a computer program for seeking the optimum cancelling signal in order to find the optimum cancelling signal for elimination of interference, wherein the vector modulator 51 is controlled to generate multiple cancelling signals separately, the amplitudes of multiple combined signals from the power detector 54 as well as the amplitude and phase of multiple cancelling signals corresponding thereto are recorded, and the cancelling signal corresponding to the combined signal with the smallest amplitude from amongst these combined signals is determined as being the optimum cancelling signal. Once the optimum cancelling signal has been determined, the control unit 52 instructs the vector modulator 51 to generate the optimum cancelling signal according to the amplitude and phase of the optimum cancelling signal. The vector modulator 51 generates the optimum cancelling signal according to the instruction from the control unit 52 and outputs the same to the signal combining unit 53. The signal combining unit 53 is connected to the receiving port, and adds the optimum cancelling signal and the interference signal according to an instruction from the control unit 52, to eliminate interference caused by the interference signal to the tag signal received via the receiving port.

Similarly, the interference elimination device according to the above embodiment of the present invention can preferably have the transmission line 50 and coupling unit 55 integrated therein, so as to obtain carrier signals and interference signals from the transmission line 50 by coupling and provide these to the vector modulator 51 and signal combining unit 53 for processing. In this way, the interference elimination device according to the above embodiment of the present invention can be used to replace the original circulator or directional coupler of the reader directly, so as to optimize the cost of implementing the present invention. Optionally, it is also possible for the interference elimination device according to the above embodiment of the present invention not to have the transmission line 50 and the coupling unit 55 integrated therein, in which case a separate coupler device may be used when implementing the present invention, to provide carrier signals and interference signals to the vector modulator 51 and the signal combining unit 53.

Based on the interference elimination device shown in Fig. 5A, Fig. 5B shows an interference elimination device using a vector modulator according to another embodiment of the present invention. In this embodiment, the transmission line 50 is a microstrip line 501; the vector modulator 51 comprises a vector modulator 504 without a balun, and a balun 503; the control unit 52 is an MCU 506; and the coupling unit 55 comprises two couplers 502a - 502b. As Fig. 5B shows, the interference elimination device comprises: the microstrip line 501, two couplers 502a - 502b, balun 503, vector modulator 504, power combiner 505, MCU 506 and power detector 507. The microstrip line 501 connects the transmitting port (TX port) to the antenna, and transmits a forward carrier signal Asin (x) outputted by the reader to the antenna. The coupler 502a obtains a signal ACsin (x+ ) from the transmission line 501 by coupling and outputs the same to the balun 503. The coupler 502b is used to obtain an interference signal Α33ΐη(χ+β) and an interference signal ARCsin (χ+γ) from the transmission line 501 by coupling, and to output the interference signal Α33ΐη(χ+β) + ARCsin (X+Y) thus obtained by coupling to the power combiner 505. The MCU 506 is used to control the vector modulator 504. The balun 503 is also called a balanced-unbalanced transformer, and processes the signal ACsin (x+a) before outputting the same to the vector modulator 504. Here, the balun is used to convert single-ended signals to the differential signals demanded by the vector modulator. Since the fixed phase shifters and variable attenuators in the previous embodiments could process single-ended signals, with no requirement to process differential signals, there was no need for a balun in those previous embodiments. The vector modulator 504 adjusts the phase and amplitude of the signal ACsin (x+a) received according to an instruction from the MCU 506, and outputs a cancelling signal AACsin (χ+α+φ) to the power combiner 505, wherein Δ represents adjustment of signal amplitude by the vector modulator 504, and may be called the amplitude change coefficient, while φ represents adjustment of signal phase by the vector modulator 504, and may be called the phase difference. The vector modulator 504 can adjust the phase of the cancelling signal in the range [0, 360°] . The power combiner 505 receives the cancelling signal from the vector modulator 504 and the interference signal from the coupler 502b, combines the cancelling signal with the interference signal, and outputs the combined signal to the receiving port (RX port) . The power detector 507 is connected to an output end of the power combiner 505, and detects the amplitude of the signal outputted by the power combiner 505, outputting the detection result to the MCU 506. The MCU 506 finds the cancelling signal corresponding to the combined signal capable of obtaining the smallest amplitude according to the detection result of the power detector 507, i.e. the optimum cancelling signal which is capable of cancelling out the interference signal to the greatest extent possible such that the amplitude of the remaining signal obtained is minimized, and sends an instruction to the vector modulator 504 to output the optimum cancelling signal, so as to achieve the goal of eliminating interference .

In the interference elimination device shown in Fig. 5B the vector modulator 504 used lacks a balun, so must be connected to a separate balun. A variety of vector modulators (e.g. MAX 2047) may be used in the embodiments of the present invention; some vector modulators have their own baluns, in which case the coupler 502a can be directly connected to the vector modulator 504 with no need to connect a separate balun 503.

As stated above, the cancelling signal and interference signal are sinusoid signals with the same frequency but different phase and amplitude, and the interference signal can be eliminated as far as possible by seeking and setting an optimum cancelling signal. Both the cancelling signal and the interference signal have a certain angle in the coordinate system of a constellation diagram (IQ plot) . In the above embodiment, the vector modulator 504 may output various cancelling signals which vary across the range [0°, 360°] according to an instruction from the MCU 506, i.e. the cancelling signals outputted by the vector modulator 504 may lie in any quadrant of the constellation diagram coordinate system. Therefore there is no need for the power combiner 505 to simultaneously output two combined signals, as was the case with the power combiner 205b in a previous embodiment, with the switch 204b performing signal selection according to an instruction from the MCU. Each time the MCU 506 instructs the vector modulator 504 to output a cancelling signal with a designated phase and a designated amplitude, the MCU can then record the amplitude of a combined signal obtained by the power detector 507, and then determine associated setting parameters (including amplitude change coefficient and phase difference, etc.) of the cancelling signal corresponding to the combined signal with the smallest amplitude, i.e. determine the associated setting parameters of the optimum cancelling signal, and finally instruct the vector modulator 504 to output the optimum cancelling signal. The vector modulator 504 will set the associated setting parameters of the optimum cancelling signal according to an instruction from the MCU 506 in order to output the optimum cancelling signal, thereby minimizing the amplitude of the combined signal outputted by the power combiner 505, and achieving the goal of eliminating interference .

The embodiment above which uses a vector modulator concerns elimination of interference in the case of a forward carrier signal with a specific frequency. However, as stated above, if the case of frequency hopping is considered, the above embodiments can be expanded further. A control unit (e.g. an MCU) may further store a Look Up Table (LUT) , in which are recorded the optimum phases corresponding to carrier signals of each frequency transmitted by the reader. Each time the control unit determines the optimum phase for a carrier signal of a certain frequency, the control unit then stores this optimum phase. Each time the reader is powered on, the control unit looks up the optimum phase corresponding to the carrier signal currently transmitted by the reader in the LUT. If the optimum phase is found, the control unit directly instructs the vector modulator to generate multiple cancelling signals having this optimum phase but different amplitudes, so as to further determine the optimum cancelling signal which has this optimum phase and the optimum amplitude, and finally instructs the vector modifier to generate this optimum cancelling signal. If the optimum phase is not found, the control unit determines the optimum phase corresponding to the carrier signal currently transmitted by the reader, then instructs the vector modulator to generate multiple cancelling signals having this optimum phase but different amplitudes, so as to further determine the optimum cancelling signal which has this optimum phase and the optimum amplitude, and finally instructs the vector modulator to generate this optimum cancelling signal. For instance, in the interference elimination device shown in Fig. 5B, for each frequency of forward carrier signal, the MCU 506 can find the optimum cancelling signal in the range [0°, 360°] by adjusting the vector modulator 504, and record associated setting parameters of the various optimum phases corresponding to forward carrier signals of different frequencies; subsequently, when the frequency of the forward carrier signal changes, the MCU can find the associated setting parameters of the optimum phase corresponding to the current frequency, then instruct the vector modulator 504 to implement the appropriate settings so as to output multiple cancelling signals having the optimum phase, determine the optimum cancelling signal, and make the vector modulator 504 implement the appropriate settings so as to output the optimum cancelling signal. Here, the MCU 506 can use the Look Up Table (LUT) to record associated setting parameters of the various optimum phases corresponding to the forward carrier signals of different frequencies, so that once the interference elimination device is powered on, the MCU 506 can quickly find the associated setting parameters of the optimum phase corresponding to the current frequency via the LUT, so as to set the optimum cancelling signal quickly, and achieve the goal of eliminating interference.

Since many protocols have relatively stringent limitations in terms of time delay, in the embodiments of the various interference elimination devices using variable attenuators and vector modulators above, the control unit (such as an MCU 206 or MCU 506) must find the optimum cancelling signal quickly. During this seeking process, multiple cancelling signal samples can be set in advance, each cancelling signal sample being defined by the associated setting parameters of the cancelling signal. As stated above, these associated setting parameters can be parameters which characterize a cancelling signal of a certain phase and amplitude, for instance the values of the attenuation coefficients Hi and H₂, the phase difference and the amplitude change coefficient. The MCU can then make the variable attenuator or vector modulator implement appropriate settings according to the associated setting parameters, so that the power combiner 205a or vector modulator 504 outputs each cancelling signal in turn; at the same time, the MCU records the amplitude of the combined signal obtained by combining each cancelling signal with the interference signal, to determine the optimum cancelling signal.

The present invention also proposes an interference elimination method based on the above interference elimination device.

Fig. 6A shows a flow chart of an interference elimination method in one embodiment of the method according to the present invention. In this embodiment, a forward carrier signal outputted by the reader is expressed as Asin (x) . As Fig. 6A shows, the method comprises the following steps:

Step 601: receiving a second carrier signal ACsin (χ+ ) , a third carrier signal ACcos (x+ ) with a phase difference of 90 degrees with respect to the second carrier signal ACsin (χ+ ) , and a fourth carrier signal -ACsin (x+a) with a phase difference of 180 degrees with respect to the second carrier signal ACsin (x+a) ; and receiving an interference signal Α33ΐη(χ+β) + ARCsin (χ+γ) . Here, the mathematical representation of each signal is the same as in the various embodiments above, so the meaning of the various symbols therein will not be repeated here .

Step 602: adjusting the amplitude of the second carrier signal ACsin (χ+α) , the third carrier signal ACcos (x+a) and the fourth carrier signal -ACsin (x+ ) multiple times, to generate multiple cancelling signals, wherein each cancelling signal generated is a signal obtained by adding the amplitude-adjusted second carrier signal ACsin (x+a) and the amplitude-adjusted third carrier signal ACcos ( χ+α ) , or a signal obtained by adding the amplitude-adjusted third carrier signal ACcos (x+a) and the amplitude-adjusted fourth carrier signal -ACsin (x+a) .

Step 603: adding or subtracting the interference signal and each of the multiple cancelling signals separately to obtain multiple combined signals.

Step 604: detecting the amplitude of each combined signal, and determining an optimum cancelling signal according to the variation in amplitude of the multiple combined signals.

Step 605: using the optimum cancelling signal to eliminate the interference signal.

Fig. 6B shows a flow chart of an interference elimination method in a preferred embodiment of the method according to the present invention. In this embodiment, the operations performed in steps 611 - 613 are the same as those performed in steps 601 - 603 above. The operations performed in step 614 and step 615 are as follows:

Step 614: detecting the amplitude of each combined signal, obtaining a first curve showing the variation of combined signal amplitude with cancelling signal phase on the basis of the variation in phase of the multiple cancelling signals and the amplitudes of the multiple combined signals corresponding thereto, and determining the phase of the cancelling signal corresponding to a maximum value or a minimum value on the first curve as being an optimum phase; obtaining a second curve showing the variation of combined signal amplitude with amplitude of cancelling signals which have the optimum phase on the basis of the variation in amplitude of the multiple cancelling signals which have the optimum phase and the amplitudes of the multiple combined signals corresponding thereto, and determining the cancelling signal corresponding to a minimum value on the second curve as being an optimum cancelling signal.

Step 615: adding or subtracting the interference signal and the optimum cancelling signal, wherein if the optimum phase corresponds to the maximum value on the first curve, the operation performed on the interference signal and the optimum cancelling signal is opposite to the operation used to obtain the multiple combined signals corresponding to the first curve, and if the optimum phase corresponds to the minimum value on the first curve, the operation performed on the interference signal and the optimum cancelling signal is the same as the operation used to obtain the multiple combined signals corresponding to the first curve.

Details of the specific method of implementing the various steps above are included in each of the embodiments of the device above, and are not repeated here.

The interference elimination method in the preferred embodiment above is principally concerned with the following two problems:

One, the optimum amplitude (i.e. the amplitude of the optimum cancelling signal) and the optimum phase (i.e. the phase of the optimum cancelling signal) can be sought independently of each other, with the optimum phase being sought before the optimum amplitude is sought.

First of all, for a group of cancelling signals with different phases but the same amplitude, a maximum or minimum amplitude of a signal remaining after a cancelling signal and interference signal have been offset against one another is sought, and the phase of the cancelling signal corresponding to the remaining signal with this maximum or minimum amplitude is then the optimum phase. Once the optimum phase has been determined, a minimum amplitude of a signal remaining after a cancelling signal and interference signal have been offset against one another is sought from a group of cancelling signals having the optimum phase but different amplitudes, and the amplitude of the cancelling signal corresponding to the remaining signal with this minimum amplitude is then the optimum amplitude. Finally, the signal having the optimum amplitude and the optimum phase is then the optimum cancelling signal. Such a seeking method can significantly reduce the number of seeking steps as well as the number of cancelling signals, so is very efficient.

Specifically, when multiple cancelling signals are generated, first of all multiple first cancelling signals having the same amplitude but different phases are generated, and the amplitudes of multiple first combined signals corresponding thereto are detected; next, the optimum phase is determined on the basis of the amplitudes of the multiple first combined signals and the different phases of the multiple cancelling signals. Once the optimum phase has been determined, multiple second cancelling signals having the optimum phase but different amplitudes are generated, and the amplitudes of multiple second combined signals corresponding thereto are detected; the cancelling signal corresponding to the second combined signal with the smallest amplitude amongst these second combined signals is determined as being the optimum cancelling signal.

Two, a two-stage seeking step can be used when seeking the optimum phase.

In the course of generating multiple first cancelling signals and then determining the optimum phase, multiple first cancelling signals having a first phase difference can be generated first, with the amplitudes of multiple first combined signals corresponding thereto being detected, in order to determine the phase range in which the optimum phase lies. Multiple first cancelling signals, lying in this phase range and having a second phase difference, are then generated, with the amplitudes of multiple first combined signals corresponding thereto being detected, in order to determine the optimum phase. Here, the first phase difference is greater than the second phase difference.

Since the power detector will take multiple samples when detecting the amplitude of a given signal, the mean value of the signal amplitudes obtained as the multiple samples is taken as the amplitude of the signal. Therefore, when detecting the amplitude of a first combined signal corresponding to a first cancelling signal having the first phase difference (i.e. when performing the first stage of seeking) , a relatively small number of samples can be taken, and when detecting the amplitude of a first combined signal corresponding to a first cancelling signal having the second phase difference (i.e. when performing the second stage of seeking) , a larger number of samples can be taken.

In a preferred embodiment of the present invention, first of all, a first rough seeking stage is performed with a relatively large phase difference and a relatively small number of cancelling signals, so as to determine a rough range in which the optimum phase lies; next, a second fine seeking stage is performed in the rough range determined in the first stage of rough seeking, using a smaller phase difference and a larger number of cancelling signals, so as to precisely determine the optimum phase therefrom. For example: during rough seeking, the amplitude of each signal is sampled three times, and rough seeking is performed with a phase difference of 10°; during fine seeking, the amplitude of each signal is sampled ten times, and fine seeking is performed with a phase difference of 5°. Various fast seeking methods can be used in both the rough seeking and fine seeking steps, for instance a method based on the golden ratio. In the rough seeking and fine seeking above, the setting of each cancelling signal can be split into three steps: an MCU instructs a variable attenuator or vector modulator to set the phase of one cancelling signal, the MCU determines the phase of the next cancelling signal, and the variable attenuator or vector modulator sets the phase of the cancelling signal currently determined according to an instruction from the MCU.

Fig. 7 shows an example of a curve showing the variation of amplitude of multiple combined signals with phase of various cancelling signals, obtained by simulation. It can be seen from Fig. 7 that the phase difference between adjacent cancelling signals 701 is relatively large in the first rough seeking stage, and a rough phase range 702 can be determined. A second fine seeking stage can be performed in this rough phase range 702, wherein the phase difference between adjacent cancelling signals 703 is smaller, and finally an optimum cancelling signal 703' can be determined precisely. When detecting the amplitude of a given combined signal outputted by a power combiner, the power detector must take multiple samples to obtain a mean value of amplitude, and use this mean value as the amplitude of the combined signal. As Fig. 7 shows, the amplitude interval 704 is the amplitude error range obtained by multiple sampling when detecting the amplitude of the combined signal corresponding to a cancelling signal 701 in the first rough seeking stage, while the amplitude interval 705 is the amplitude error range obtained by multiple sampling when detecting the amplitude of the combined signal corresponding to a cancelling signal 703 in the second fine seeking stage. Obviously, the amplitude interval 704 must be greater than the amplitude interval 705. To achieve precise seeking, in the embodiments of the present invention, a relatively small number of samples are taken when sampling the amplitude of a combined signal corresponding to a cancelling signal 701 in the first rough seeking stage, and a larger number of samples are taken when sampling the amplitude of a combined signal corresponding to a cancelling signal 703 in the second fine seeking stage. In the rough seeking stage, the smaller number of samples corresponds to a larger amplitude interval 704, and there is a larger error in the combined signal amplitude obtained; however, such an error has very little effect when determining a rough phase range, and consumes less system resources. In the fine seeking stage, the larger number of samples corresponds to a smaller amplitude interval 705, and there is a smaller error in the combined signal amplitude obtained; thus system resources can be utilized effectively to achieve precise seeking .

The use of the two-stage seeking step above has the following advantages. In the rough seeking step, the use of a smaller number of samples enables time to be saved; at the same time, the use of a larger phase difference enables a reduction in the interference from noise suffered by the power detector. In the fine seeking step, the use of a larger number of samples enables a reduction in the interference from noise suffered by the power detector; at the same time, a smaller phase difference is used to accurately locate the optimum phase.

The resources consumed in seeking the optimum cancelling signal in the device and method provided in the embodiments of the present invention are analyzed and presented as statistics below with reference to Tables 1 and 2.

Table 1 sets out the resource consumption of each component of the interference elimination device shown in Fig. 5B, while Table 2 sets out the times taken when a two-stage seeking method is used with the interference elimination device. Component Parameter Parameter value

MCU System Clock Cycle 40 ns

(C8051F020) Clock cycles for 2

each instruction

A/D Sampling Rate 100 ksps

DA Enabling Time 10 us

Vector modulator Switching time 3 ns

(MAX2047)

Algorithm-related No. of samples in 3

rough seeking

Phase difference in 10 degrees rough seeking

No. of samples in 10

fine seeking

Phase difference in 5 degrees fine seeking

No. of instructions 100

used to set each

cancelling signal

samp1e

Stable time of 10 carrier signal combined signal cycles = 11 ns

Table 1

Step Parameter Parameter value

Rough seeking Time needed to set 48 us

each cancelling

signal sample

No. of cancelling 18

signal samples

needed in worst case

scenario

Fine seeking Time needed to set 118 us

each cancelling

signal sample

No. of cancelling 3

signal samples

needed

Total Total time needed in 1218 us worst case scenario

Table 2

According to the statistics in Tables 1 and 2 pertaining to the number of instructions needed by the CPU in rough seeking and fine seeking and associated time parameters, it can be seen that even a low-speed MCU can find the optimum cancelling signal and complete the setting thereof within 1.5 ms in the worst case scenario, i.e. complete rough and fine seeking of the optimum phase, seeking of the optimum amplitude, and generation of the optimum cancelling signal within 1.5 ms . If an MCU with a higher speed is used, a higher sampling rate can be achieved, enabling a further improvement in performance. Tables 1 and 2 present as statistics the number of instructions needed by the CPU and associated time parameters, taking as an example a solution in which a vector modulator is used. The inventors have gathered statistics pertaining to the number of instructions needed by the CPU and associated time parameters in a solution in which variable attenuators are used. Such a solution in which variable attenuators are used has a similar efficiency to that of a solution in which a vector modulator is used (see Tables 3 and 4 below for details) , and can similarly find the optimum cancelling signal and complete the setting thereof within 1.5 ms .

Table 3 Step Parameter Parameter value

Rough seeking Time needed to set 43.2 us

each cancelling

signal sample

No. of cancelling 18

signal samples

needed in worst case

scenario

Fine seeking Time needed to set 113.2 us

each cancelling

signal sample

No. of cancelling 3

signal samples

needed

Total Total time needed in 43.2*18+113.2*3 = worst case scenario 1117 us

Table 4

In summary, the device and method provided in the embodiments of the present invention have the following technical effects:

1) The interference elimination device for eliminating interference provided in the embodiments of the present invention can be integrated directly between a reader and an antenna, with no need to make any changes to existing reader hardware .

2) The circuitry of the interference elimination device provided in the embodiments of the present invention is simple to implement; variable attenuators or a vector modulator may be used to generate various cancelling signal samples, so implementation is easy and costs are relatively low.

3) The two-stage seeking method provided in the embodiments of the present invention can significantly improve the efficiency of interference elimination; moreover, in the case of frequency hopping, the use of a Look Up Table to store optimum phases corresponding to signals of different frequencies can also significantly improve the efficiency of interference elimination .

4) The design of certain readers capable of eliminating interference (for example high isolation circulators and high echo loss antennas) can be simplified by adopting the embodiments of the present invention, leading to a significant reduction in reader cost.

The present invention has been presented and illustrated in detail above by means of the accompanying drawings and preferred embodiments, but is not limited to these disclosed embodiments. Other solutions derived therefrom by those skilled in the art are also included in the scope of protection of the present invention.

Claims

1. An interference elimination device, comprising: a control unit (22, 206), a cancelling signal generating unit (21), a signal combining unit (23) and a power detector (24, 207), wherein :

the cancelling signal generating unit (21) is used for receiving a second carrier signal, a third carrier signal with a phase difference of 90 degrees with respect to the second carrier signal, and a fourth carrier signal with a phase difference of 180 degrees with respect to the second carrier signal, for adjusting the amplitude of the second carrier signal, the third carrier signal and the fourth carrier signal multiple times according to an instruction from the control unit (22, 206), in order to generate multiple cancelling signals, and for outputting the multiple cancelling signals to the signal combining unit (23) , wherein each cancelling signal generated is a signal obtained by adding the amplitude-adjusted second carrier signal and the amplitude-adjusted third carrier signal, or is a signal obtained by adding the amplitude- adjusted third carrier signal and the amplitude-adjusted fourth carrier signal;

the signal combining unit (23) is used for receiving an interference signal and the multiple cancelling signals, adding or subtracting the interference signal and each of the multiple cancelling signals separately to obtain multiple combined signals, outputting the multiple combined signals to the power detector (24, 207), and eliminating the interference signal according to an instruction from the control unit (22, 206); the power detector (24, 207) is used for receiving the multiple combined signals, detecting the amplitude of each combined signal, and outputting the amplitudes of the multiple combined signals to the control unit (22, 206);

the control unit (22, 206) is used for controlling the cancelling signal generating unit (21) to generate the multiple cancelling signals, receiving the amplitudes of the multiple combined signals, determining an optimum cancelling signal according to the variation in amplitude of the multiple combined signals, and controlling the signal combining unit (23) to use the optimum cancelling signal to eliminate the interference signal.

2. The device as claimed in claim 1, wherein the cancelling signal generating unit (21) comprises: a first variable attenuator (203a) , a second variable attenuator (203b) , a switch (204a) and a power combiner (205a), wherein:

the switch (204a) is used for receiving the second carrier signal and the fourth carrier signal, and selecting the second carrier signal or the fourth carrier signal according to an instruction from the control unit (22, 206), in order to output the second carrier signal or the fourth carrier signal to the second variable attenuator (203b) ;

the first variable attenuator (203a) is used for receiving the third carrier signal, adjusting the amplitude of the third carrier signal multiple times according to an instruction from the control unit (22, 206), and outputting multiple fifth carrier signals to the power combiner (205a) ;

the second variable attenuator (203b) is used for adjusting the amplitude of the second carrier signal or the fourth carrier signal outputted by the switch (204a) multiple times according to an instruction from the control unit (22, 206), and outputting multiple sixth carrier signals to the power combiner (205a) ;

the power combiner (205a) is used for adding the multiple fifth carrier signals and the multiple sixth carrier signals separately to obtain the multiple cancelling signals, and outputting the multiple cancelling signals to the signal combining unit (23) .

3. The device as claimed in claim 1, the cancelling signal generating unit (21) comprising: a first variable attenuator (203a) , a second variable attenuator (203b) , a third variable attenuator (203b) , a switch (204a) and a power combiner (205a) , wherein :

the second variable attenuator (203b) is used for receiving the second carrier signal, adjusting the amplitude of the second carrier signal multiple times according to an instruction from the control unit (22, 206), and outputting multiple sixth carrier signals to the switch (204a) ;

the third variable attenuator (203b) is used for receiving the fourth carrier signal, adjusting the amplitude of the fourth carrier signal multiple times according to an instruction from the control unit (22, 206), and outputting multiple seventh carrier signals to the switch (204a) ;

the switch (204a) is used for selecting the multiple sixth carrier signals or the multiple seventh carrier signals according to an instruction from the control unit (22, 206), in order to output the multiple sixth carrier signals or the multiple seventh carrier signals to the power combiner (205a) ; the power combiner (205a) is used for adding the multiple fifth carrier signals and the multiple sixth carrier signals separately, or adding the multiple fifth carrier signals and the multiple seventh carrier signals separately, in order to obtain the multiple cancelling signals, and outputting the multiple cancelling signals to the signal combining unit (23) .

4. The device as claimed in any one of claims 1 to 3, further comprising: a transmission line (20, 201), a first coupled transmission line (202a, 402a) , a second coupled transmission line (202b) and a third coupled transmission line (202c) , wherein :

the transmission line (20, 201) is used for transmitting a first carrier signal;

the first coupled transmission line (202a, 402a) is arranged parallel to the transmission line (20, 201), and is used for obtaining the second carrier signal from the transmission line (20, 201) by coupling and outputting the same to the cancelling signal generating unit (21);

the second coupled transmission line (202b) is arranged parallel to the transmission line (20, 201), is separated from the first coupled transmission line (202a) by one quarter of the wavelength of the first carrier signal, and is used for obtaining the third carrier signal from the transmission line (20, 201) by coupling and outputting the same to the cancelling signal generating unit (21);

the third coupled transmission line (202c) is arranged parallel to the transmission line (20, 201), is separated from the second coupled transmission line (202b) by one quarter of the wavelength of the first carrier signal, and is used for obtaining the fourth carrier signal from the transmission line (20, 201) by coupling and outputting the same to the cancelling signal generating unit (21) .

5. The device as claimed in any one of claims 1 to 3, further comprising: a transmission line (20, 201), a first coupled transmission line (202a, 402a) , a first power splitter (403) , a first fixed phase shifter (404a) and a second fixed phase shifter (404b), wherein:

the first coupled transmission line (202a, 402a) is arranged parallel to the transmission line (20, 201), and is used for obtaining the second carrier signal from the transmission line (20, 201) by coupling and outputting the same to the first power splitter (403) ;

the first power splitter (403) is used for receiving the second carrier signal, splitting the second carrier signal into three channels, and outputting the second carrier signal to the cancelling signal generating unit (21), the first fixed phase shifter (404a) and the second fixed phase shifter (404b) , respectively;

the first fixed phase shifter (404a) is used for shifting the phase of the received second carrier signal by 90 degrees in order to obtain the third carrier signal, and outputting the third carrier signal to the cancelling signal generating unit (21) ;

the second fixed phase shifter (404b) is used for shifting the phase of the received second carrier signal by 180 degrees in order to obtain a fourth carrier signal, and outputting the fourth carrier signal to the cancelling signal generating unit (21) .

6. The device as claimed in any one of claims 1 to 3, further comprising: a transmission line (20, 201), a first coupled transmission line (202a, 402a) , a first power splitter (403) , a second power splitter (403' ) , a first fixed phase shifter (404a) and a third fixed phase shifter (404a')_/ wherein:

the first coupled transmission line (202a, 402a) is arranged parallel to the transmission line (20, 201), and used for obtaining the second carrier signal from the transmission line (20, 201) by coupling and outputting the same to the first power splitter (403) ;

the first power splitter (403) is used for receiving the second carrier signal, splitting the second carrier signal into two channels, and outputting the second carrier signal to the cancelling signal generating unit (21) and the first fixed phase shifter (404a) , respectively;

the first fixed phase shifter (404a) is used for shifting the phase of the received second carrier signal by 90 degrees in order to obtain the third carrier signal, and outputting the third carrier signal to the second power splitter (403' ) ;

the second power splitter (403' ) is used for receiving the third carrier signal, splitting the third carrier signal into two channels, and outputting the third carrier signal to the cancelling signal generating unit (21) and the third fixed phase shifter (404a' ) , respectively;

the third fixed phase shifter (404a' ) is used for shifting the phase of the received third carrier signal by 90 degrees in order to obtain a fourth carrier signal, and outputting the fourth carrier signal to the cancelling signal generating unit (21) .

7. The device as claimed in any one of claims 4 to 6, further comprising: a fourth coupled transmission line (202d) ;

the fourth coupled transmission line (202d) being arranged parallel to the transmission line (20, 201), and used for obtaining the interference signal from the transmission line (20, 201) by coupling and outputting the same to the signal combining unit (23) .

8. The device as claimed in any one of claims 4 to 6, wherein: the frequency of the first carrier signal is variable.

9. The device as claimed in claim 1, wherein the step of determining an optimum cancelling signal according to the variation in amplitude of the multiple combined signals further comprises :

obtaining a first curve showing the variation of combined signal amplitude with cancelling signal phase on the basis of the variation in phase of the multiple cancelling signals and the amplitudes of the multiple combined signals corresponding thereto, and determining the phase of the cancelling signal corresponding to a maximum value or a minimum value on the first curve as being an optimum phase; obtaining a second curve showing the variation of combined signal amplitude with amplitude of cancelling signals which have the optimum phase on the basis of the variation in amplitude of the multiple cancelling signals which have the optimum phase and the amplitudes of the multiple combined signals corresponding thereto, and determining the cancelling signal corresponding to a minimum value on the second curve as being an optimum cancelling signal;

the step of controlling the signal combining unit (23) to use the optimum cancelling signal to eliminate the interference signal further comprises: controlling the signal combining unit (23) to add or subtract the interference signal and the optimum cancelling signal, wherein if the optimum phase corresponds to the maximum value on the first curve, the operation performed on the interference signal and the optimum cancelling signal is opposite to the operation used to obtain the multiple combined signals corresponding to the first curve, and if the optimum phase corresponds to the minimum value on the first curve, the operation performed on the interference signal and the optimum cancelling signal is the same as the operation used to obtain the multiple combined signals corresponding to the first curve.

10. The device as claimed in claim 9, wherein the control unit (22, 206) is further used for storing the optimum phase, and seeking the stored optimum phase before determining the optimum cancelling signal; if the optimum phase is found, the control unit (22, 206) controls the cancelling signal generating unit (21) to generate the multiple cancelling signals having the optimum phase but varying amplitudes.

11. An interference elimination device, comprising: a control unit (52, 506), a vector modulator (51, 504), a signal combining unit (53, 505) and a power detector (54, 507), wherein :

the vector modulator (51, 504) is used for receiving a second carrier signal, adjusting the amplitude and phase of the second carrier signal multiple times according to an instruction from the control unit (52, 506), in order to generate multiple cancelling signals, and outputting the multiple cancelling signals to the signal combining unit (53, 505) ;

the signal combining unit (53, 505) is used for receiving an interference signal and the multiple cancelling signals, adding the interference signal and each of the multiple cancelling signals separately to obtain multiple combined signals, outputting the multiple combined signals to the power detector (54, 507), and eliminating the interference signal according to an instruction from the control unit (52, 506); the power detector (54, 507) is used for receiving the multiple combined signals, detecting the amplitude of each combined signal, and outputting the amplitudes of the multiple combined signals to the control unit (52, 506);

the control unit (52, 506) is used for controlling the vector modulator (51, 504) to generate the multiple cancelling signals, receiving the amplitudes of the multiple combined signals, determining an optimum cancelling signal according to the variation in amplitude of the multiple combined signals, and controlling the signal combining unit (53, 505) to use the optimum cancelling signal to eliminate the interference signal.

12. The device as claimed in claim 11, further comprising: a transmission line (50, 501) and a first coupled transmission line (502a), wherein:

the transmission line (50, 501) is used for transmitting a first carrier signal;

the first coupled transmission line (502a) is arranged parallel to the transmission line (50, 501), and used for obtaining the second carrier signal from the transmission line (50, 501) by coupling and outputting the same to the vector modulator (51, 504).

13. The device as claimed in claim 12, further comprising: a fourth coupled transmission line (502b) ;

the fourth coupled transmission line (502b) is arranged parallel to the transmission line (50, 501), and used for obtaining the interference signal from the transmission line (50, 501) by coupling and outputting the same to the signal combining unit (53, 505) .

14. An interference elimination method, comprising:

receiving a second carrier signal, a third carrier signal with a phase difference of 90 degrees with respect to the second carrier signal, and a fourth carrier signal with a phase difference of 180 degrees with respect to the second carrier signal ;

receiving an interference signal;

adjusting the amplitude of the second carrier signal, the third carrier signal and the fourth carrier signal multiple times, to generate multiple cancelling signals, wherein each cancelling signal generated is a signal obtained by adding the amplitude-adjusted second carrier signal and the amplitude- adjusted third carrier signal, or a signal obtained by adding the amplitude-adjusted third carrier signal and the amplitude- adjusted fourth carrier signal;

adding or subtracting the interference signal and each of the multiple cancelling signals separately to obtain multiple combined signals;

detecting the amplitude of each combined signal, and determining an optimum cancelling signal according to the variation in amplitude of the multiple combined signals;

using the optimum cancelling signal to eliminate the interference signal.

15. The method as claimed in claim 14, wherein the step of determining an optimum cancelling signal according to the variation in amplitude of the multiple combined signals further comprises :

the step of using the optimum cancelling signal to eliminate the interference signal further comprises: adding or subtracting the interference signal and the optimum cancelling signal, wherein if the optimum phase corresponds to the maximum value on the first curve, the operation performed on the interference signal and the optimum cancelling signal is opposite to the operation used to obtain the multiple combined signals corresponding to the first curve, and if the optimum phase corresponds to the minimum value on the first curve, the operation performed on the interference signal and the optimum cancelling signal is the same as the operation used to obtain the multiple combined signals corresponding to the first curve.

16. The method as claimed in claim 15, wherein the step of obtaining a first curve showing the variation of combined signal amplitude with cancelling signal phase on the basis of the variation in phase of the multiple cancelling signals and the amplitudes of the multiple combined signals corresponding thereto, and determining the phase of the cancelling signal corresponding to a maximum value or a minimum value on the first curve as being an optimum phase further comprises:

when the step length of the variation in phase of the multiple cancelling signals is a first phase difference, determining a phase range in which the optimum phase lies on the basis of the first curve;

when the step length of the variation in phase of the multiple cancelling signals is a second phase difference, determining the optimum phase in the phase range on the basis of the first curve;

wherein the first phase difference is greater than the second phase difference.

17. The method as claimed in claim 16, wherein the step of detecting the amplitude of each combined signal further comprises :

when the step length of the variation in phase of the multiple cancelling signals is a first phase difference, using a first number of samples to detect the amplitude of each combined signal;

when the step length of the variation in phase of the multiple cancelling signals is a second phase difference, using a second number of samples to detect the amplitude of each combined signal;

wherein the first number is smaller than the second number .