WO2009056410A1

WO2009056410A1 - A self-interfering signal elimination device and method and rfid reader

Info

Publication number: WO2009056410A1
Application number: PCT/EP2008/062814
Authority: WO
Inventors: Dieter Horst; Mattias Lampe; Dan Yu; Yong Yuan
Original assignee: Siemens Aktiengesellschaft
Priority date: 2007-11-01
Filing date: 2008-09-25
Publication date: 2009-05-07
Also published as: CN101425823A

Abstract

The present invention discloses a self-interfering signal elimination device, comprising: a phase-shifting and attenuation processing module and a signal elimination processing module, wherein the phase-shifting and attenuation processing module receives a first signal from outside, performs attenuation and phase-shifting processing on the signal to obtain an estimated self-interfering signal; the signal elimination processing module receives a second signal from outside and the estimated self-interfering signal from the phase-shifting and attenuation processing module, and eliminates the estimated self-interfering signal from the second signal. The present invention further discloses a method for eliminating a self-interfering signal, comprising: performing attenuation and phase-shifting processing on the transmitted signal to obtain an estimated self-interfering signal; eliminating the estimated self-interfering signal from the received signal. Additionally, the present invention further discloses an RFID reader. In the present invention, the estimated self-interfering signal is obtained by performing attenuation and phase-shift processing on the transmitted signal, and such estimated self-interfering signal is eliminated to reduce the impact of the self- interfering signal on receiving sensitivity.

Description

A Self-interfering Signal Elimination Device and Method and RFID Reader

Field of Invention

The present invention relates to radio frequency identification (RFID) technology, and more particularly to a self-interfering signal elimination device and method, and an RFID reader.

Background Technology

RFID technology is an automatic identification technology widely used in animal tracking, ocean container tracking and routine applications, such as supply chain management and vehicle verification at toll gates and gas stations, etc.

With increasingly stringent requirements on the RFID system, especially on reading long-distance wide-range signal, a technology to read aforesaid long-distance wide-range signal is the ultra-high frequency radio frequency identification technology (UHF RFID) . In the UHF RFID technology, how reliable the system reads relies on the reliability of the forward link from the receiver device to label and the reliability of the inverse link from the label to the receiver device. A large amount of work has been done to improve the reliability of the forward link, such as antenna switchover technology, which has made great progress.

However, the reliability of the inverse link is still very low so far.

For the inverse link, the receiving sensitivity of the RFID reader (receiver device) is the main factor impacting on the reliability of the inverse link. For all UHF RFID systems, including passive and semi-active electrical label systems, the label returns the signal to the reader by backscattering the carrier wave (CW) signal from the reader. This means that when the reader receives a signal from the label, it must first transmit the CW signal from the transmitter side (TX) , and the signal will be coupled to the receiver side (RX) in the RFID reader. In particular, when the circulator in the RFID reader adopts single static antenna configuration, the coupled signal from the TX side to the RX side will create severe self-interference in the signal received at the RX side, thereby severely impacting on the receiving sensitivity of the RFID reader.

Fig. 1 shows the distance d in relation to the power P of the received signal, as obtained through simulation, wherein the distance refers to the distance from the label to the receiving antenna of the RFID reader and the power of the received signal is the power of the signal which is returned from the label and received by the reader. The specific parameters involved in the aforesaid simulation process are shown in Table 1.

Table 1

As shown in Fig. 1, when the distance between the label and receiving antenna is within the range from 1.6m to 40 m, the power P of the signal which is returned from the label and received by the reader is less than -45dBm. Assuming the isolation degree of the circulator is 3OdB, the power of the CW signal transmitted from the reader is 33 dBm so that a self-interfering signal with a power of 3dBm will be coupled to the receiver port. The power of the self-interfering signal coupled from the transmitter port to the receiver port (3dBm) is much higher than the power of the signal returned from the label (-45dBm) so that the self-interfering signal will severely influence the receiving sensitivity of the reader.

In the prior art, as shown in Fig.2, the abovesaid self- interfering signal is estimated and eliminated in the way of feeding the RX signal received from the signal receiver unit 10 to the demodulation unit 20 for demodulation to convert the self-interfering signal to a DC signal, and then removing the DC signal converted from the self-interfering signal via a DC filter 30. In this case, the demodulation unit 20 comprises a low noise amplifier (LNA) 20 and a demodulator 22. In the prior art, in order to remove the DC signal as much as possible, it is necessary to drive the signal receiver unit 10 at the RF front in the low gain mode. In addition, the DC filter needs to be carefully designed to remove the DC self-interfering signal as far as possible while retaining the signal returned from the label as much as possible .

In the aforesaid prior art, since the power of the self- interfering signal is far greater than the power of the signal returned from the label and there will still be residual self-interfering signal with significant power after filtering by the DC filter 30, the receiving sensitivity of the RFID reader is still very low and is not effectively improved. In addition, since it is necessary to drive the receiver unit 10 in the low gain mode, the requirements on the design of the signal receiver unit are lifted.

Description of the Invention The present invention provides a self-interfering signal elimination device, a self-interfering signal elimination method, and an RFID reader. The present invention can effectively receive the self-interfering signal in the received signal to increase receiving sensitivity.

The self-interfering signal elimination device according to the present invention comprises: a phase-shifting and attenuation processing module and a signal elimination processing module, wherein said phase-shifting and attenuation processing module receives a first signal from outside, performs attenuation and phase-shifting processing on the signal to obtain an estimated self-interfering signal; said signal elimination processing module receives a second signal from outside and the estimated self-interfering signal from said phase-shifting and attenuation processing module, and eliminates the estimated self-interfering signal from the second signal.

Preferably said phase-shifting and attenuation processing module comprises: a phase-shifting processing module and an attenuation processing module, wherein,

said phase-shifting processing module receives said first signal from outside, performs phase-shifting processing on the signal and transmits the phase-shifted signal to said attenuation processing module;

said attenuation processing module receives the signal from said phase-shifting processing module, performs attenuation processing on the signal to obtain an estimated self- interfering signal, and transmits the estimated self- interfering signal to said signal elimination processing module. Preferably, said phase-shifting and attenuation processing module comprises: a phase-shifting processing module and an attenuation processing module, wherein,

said attenuation processing module receives said first signal from outside, performs attenuation processing on the signal, and transmits the attenuated signal to said phase-shifting processing module;

said phase-shifting processing module receives the signal from said attenuation processing module, performs phase- shifting processing on the signal to obtain an estimated self-interfering signal, and transmits the estimated self- interfering signal to said signal elimination processing module.

Preferably, said self-interfering signal elimination device further comprises: an attenuation parameter calculation modules,

said attenuation parameter calculation modules receives said second signal from outside, detects the power of the signal, compares the power of the signal with the power it sets for the transmitted signal to obtain an attenuation parameter, and transmits the attenuation parameter to said attenuation processing module;

said attenuation processing module receives the attenuation parameter from said attenuation parameter calculation module, and performs attenuation processing on the signal from said phase-shifting processing module according to the attenuation parameter .

Preferably said phase-shifting and attenuation processing module comprises: a first attenuation processing module, a phase-shifting processing module, a second attenuation processing module and a signal superposition processing module, wherein, said first attenuation processing module receives said first signal from outside, performs attenuation processing on the signal according to the first attenuation parameter, and transmits the processed signal to the signal superposition processing module; said phase-shifting processing module receives said first signal from outside, performs 90 degree phase-shifting processing on the signal, and transmits the phase-shifted signal to said second attenuation processing module;

said second attenuation processing module receives said signal from the phase-shifting processing module, performs attenuation processing on the signal according to the second attenuation parameter, and transmits the processed signal to the signal superposition processing module;

said signal superposition processing module receives said signal from the first attenuation processing module and said signal from the second attenuation processing module, superposes the two signals to obtain an estimated self- interfering signal, and transmits the estimated self- interfering signal to the signal elimination processing module .

Preferably, said phase-shifting and attenuation processing module comprises: a first attenuation processing module, a phase-shifting processing module, a second attenuation processing module and a signal superposition processing module, wherein,

said first attenuation processing module receives said first signal from outside, performs attenuation processing on the signal according to the first attenuation parameter, and transmits the processed signal to the signal superposition processing module; said second attenuation processing module receives said signal from outside, performs attenuation processing on the signal according to the second attenuation parameter, and transmits the processed signal to the phase-shifting processing module;

said phase-shifting processing module receives said signal from the second attenuation processing module, performs 90 degrees phase-shift processing on the signal, and transmits the phase-shifted signal to the signal superposition processing module;

said signal superposition processing module receives said signal from the first attenuation processing module and said signal from the phase-shifting processing module, superposes the two signals to obtain an estimated self-interfering signal, and transmits the estimated self-interfering signal to the signal elimination processing module.

Preferably, said self-interfering signal elimination device further comprises: a feedback control module;

said feedback control module receives the signal which has undergone the elimination processing by said signal elimination processing module, determines the total attenuation parameter according to the power of the signal and the power it sets for the transmitted signal, then determines the phase-shifting parameter according to the phase of said received signal and the phase it sets for the transmitted signal, calculates the first attenuation parameter and the second attenuation parameter according to said determined total attenuation parameter and said phase- shifting parameter, transmits the calculated first attenuation parameter to said first attenuation processing module, and transmits the calculated second attenuation parameter to said second attenuation processing module; said first attenuation processing module and said second attenuation processing module separately perform attenuation processing according to said first attenuation parameter and said second attenuation parameter respectively from the feedback control module.

Preferably said self-interfering signal elimination device further comprises: a phase reversing processing module.

Said phase reversing processing module may intercept a first signal transmitted from outside to said first attenuation processing module, and transmits the intercepted signal, directly or after phase reversing processing depending on the control signal from the feedback control module, to said first processing module;

said feedback control module further determines if it is necessary to start the phase reversing processing in said phase reversing processing module according to the value of the phase-shifting parameter, and if so, it transmits a control signal to said phase reversing processing module, requesting to start the phase reversing processing, and if not, it transmits a control signal to said phase reversing processing module, requesting not to start the phase reversing processing.

Preferably said phase reversing processing module may also intercept the signal transmitted from said first attenuation processing module to said signal superposition processing module, and transmits said intercepted signal, directly or after phase reversing processing depending on the control signal from the feedback control module, to said signal superposition processing module;

Preferably, said self-interfering signal elimination device further comprises: a feedback trigger module;

said feedback trigger module receives and detects the signal which has undergone the elimination processing by said signal elimination processing module, and it transmits a trigger signal to said feedback control module when it detects that the power of the signal is greater than the set value;

said feedback control module stops working upon performing said working process once, and performs said working process again after receiving the trigger signal from said feedback trigger module.

The RFID reader according to the present invention comprises: a signal transmitter unit, a signal receiver unit and a demodulation unit, and the RFID reader further comprises a self-interfering signal elimination device, wherein,

said signal transmitter unit transmits a signal to a label, and sends the transmitted signal to said self-interfering signal elimination device;

said signal receiver unit receives the signal returned from the label, and transmits the received signal to said self- interfering signal elimination device;

said self-interfering signal elimination device receives said signal from the signal transmitter unit, performs attenuation and phase-shifting processing on the signal to obtain an estimated self-interfering signal, and receives said signal from the signal receiver unit, eliminates the estimated self- interfering signal from said signal, and transmits the signal which has undergone the elimination processing to said demodulation unit;

said demodulation unit demodulates the received signal.

Preferably, said RFID reader further comprises: a DC filtering unit;

said DC filtering unit receives the signal from said demodulation unit and filters the DC signal therein. The self-interfering signal elimination method of the present invention comprises: performing attenuation and phase- shifting processing on the transmitted signal to obtain an estimated self-interfering signal; eliminating the estimated self-interfering signal from the received signal.

Preferably said attenuation and phase-shifting processing of the transmitted signal comprises:

determining the attenuation parameter according to the power of the transmitted signal and the power of the received signal;

performing attenuation processing on said transmitted signal according to the determined attenuation parameter before or after said phase-shifting processing.

Preferably, after said elimination of the estimated self- interfering signal, said method further comprises: determining the phase-shifting parameter according to the phase of the signal with the estimated self-interfering signal removed and the phase of the transmitted signal;

said phase-shifting processing performs phase-shift processing according to said determined phase-shifting parameter . Preferably, said attenuation and phase-shift processing of the transmitted signal to obtain the estimated self- interfering signal comprises:

performing the first attenuation processing on the transmitted signal according to the first attenuation parameter; performing the second attenuation processing on the transmitted signal according to the second attenuation parameter, and performing 90 degree phase-shift processing before or after the second attenuation processing;

superposing the signal from the first attenuation processing and the signal from the second attenuation processing to obtain the estimated self-interfering signal.

Preferably, said first attenuation parameter and said second attenuation parameter are determined in the way of:

determining the total attenuation parameter and the phase- shifting parameter according to the phase and power of both said signal with the estimated self-interfering signal removed and said transmitted signal, and determining the first attenuation parameter and the second attenuation parameter according to said determined total attenuation parameter and said phase-shifting parameter.

Preferably, said total attenuation parameter and phase- shifting parameter are determined by way of PID control.

Preferably, after said determination of the phase-shift parameter, said method further comprises: determining if the determined phase-shifting parameter is greater than 90 degrees, and if so, performing further phase reversing processing on the signal before performing the first attenuation processing on the transmitted signal or before superposing the signal from the first attenuation processing. It can be seen from said described solution, the present invention can reduce the impact of the self-interfering signal on receiving sensitivity by performing attenuation and phase-shifting processing on the transmitted signal from the RFID reader to obtain an estimated self-interfering signal, and then removing the estimated self-interfering signal from the signal received by the reader.

Description of Figures

The following will describe exemplary embodiments of the present invention by consulting the drawings to allow those skilled in the art to have a better understanding of the abovesaid and other characteristics and benefits of the present invention. In the drawings:

Fig.l is a diagram showing how the distance between the label and receiving antenna relates to the power of the signal received by the label as obtained through simulation;

Fig.2 is a diagram showing the structure of an RFID reader of the prior art;

Fig. 3 is a schematic diagram showing the structure of a self-interfering signal elimination device according to the present invention;

Fig. 4 is a schematic diagram showing the structure of the RFID reader containing the self-interfering signal elimination device of the present invention;

Fig. 5 is a schematic diagram showing the structure of a first embodiment of the RFID reader containing the self-interfering signal elimination device of the present invention; Fig. 6 is a schematic diagram showing the structure of a second embodiment of the RFID reader containing the self-interfering signal elimination device of the present invention;

Fig. 7 is a schematic diagram showing a specific implementation of the second embodiment of the RFID reader containing the self-interfering signal elimination device of the present invention;

Fig. 8 is a schematic diagram showing the structure of a third embodiment of the RFID reader containing the self-interfering signal elimination device of the present invention;

Fig. 9 is a schematic diagram showing the structure of a fourth embodiment of the RFID reader containing the self-interfering signal elimination device of the present invention;

Fig. 10 is a schematic diagram showing a specific implementation of the fourth embodiment of the RFID reader containing the self-interfering signal elimination device of the present invention;

Fig. 11 is a schematic diagram showing a specific implementation of a fifth embodiment of the RFID reader containing the self-interfering signal elimination device of the present invention;

Fig. 12 is a flow chart showing the self-interfering signal elimination method of the present invention;

Fig. 13 is a flow chart showing a first embodiment of the self-interfering signal elimination method of the present invention; Fig. 14 is a flow chart showing a second embodiment of the self-interfering signal elimination method of the present invention;

Fig. 15 is a flow chart showing a third embodiment of the self-interfering signal elimination method of the present invention;

Fig. 16 is a flow chart showing a fourth embodiment of the self-interfering signal elimination method of the present invention;

Fig. 17 is a schematic diagram comparing signal bit error at different amplitude errors and phase errors, as obtained through simulation.

Embodiments

To make the objectives, technical solution and benefits of the present invention clearer and more apparent, the following will give a further description of the present invention by consulting drawings and embodiments.

According to several experiments and simulations conducted by the inventors, the self-interfering signal coupled at the receiver (RX) port of the RFID reader can be treated as the signal transmitted from the transmitter (TX) side with certain attenuation and phase shift. Therefore, a simple electric circuit can be designed to estimate and eliminate the self-interfering signal to significantly improve the receiving sensitivity of the reader.

Based on this original idea, the present invention provides a self-interfering signal elimination device and a self- interfering signal elimination method, as detailed below. For all descriptions of the self-interfering signal elimination device in the following, the self-interfering signal elimination device configured in a RFID reader is used as example .

Fig. 3 shows the structure of the self-interfering signal elimination device 50 according to the present invention. Consulting Fig. 3, the self-interfering signal elimination device comprises: a phase-shifting and attenuation processing module 51 and a signal elimination processing module 53, wherein the phase-shifting and attenuation processing module 51 receives a first signal from outside, performs attenuation and phase-shifting processing on the signal to obtain an estimated self-interfering signal; the signal elimination processing module 53 receives a second signal from outside and the estimated self-interfering signal from the phase- shifting and attenuation processing module 51, and eliminates the estimated self-interfering signal from the second signal.

The RFID reader containing a self-interfering signal elimination device 50 of the present invention is shown in Fig. 4, wherein said RFID reader comprises: a signal transmitter unit 40, a signal receiver unit 10, a demodulation unit 20 and the self-interfering signal elimination device 50. These units are connected via the signal flow as detailed in the following:

the signal transmitter unit 40 transmits an RF signal to the label, and sends the transmitted signal to the self- interfering signal elimination device 50.

The signal receiver unit 10 receives the signal returned from the label, and transmits the signal to the self-interfering signal elimination device 50.

The self-interfering signal elimination device 50 receives the signal from the signal transmitter unit 40, performs attenuation and phase-shifting processing on the signal to obtain an estimated self-interfering signal, and removes the estimated self-interfering signal from the signal received from the signal receiver unit 10, and transmits the signal which has undergone the elimination processing to the demodulation unit 20.

The demodulation unit 20 demodulates the received signal.

Similar to the prior art, the demodulation unit 20 may include a low noise amplifier (LNA) and a demodulator. The signal after demodulation by the demodulation unit 20 can still have the residual DC signal converted from the self- interfering signal removed by the DC filter. However, the residual self-interfering signal is very weak after the processing by the self-interfering signal elimination device 50; therefore there is no need to use a specially designed DC filter for DC signal removal and a common DC filter can be used.

For the RFID reader according to the invention, the signal receiver unit 10 can very effectively remove the self- interfering signal to improve the receiving sensitivity even without the need of starting in the low gain mode.

A comparison with the prior art shows that the present invention works mainly by adding a self-interfering signal elimination device 50 to the RFID reader to remove the self- interfering signal. The self-interfering signal elimination device 50 can be implemented in various ways, which will be described below through embodiments of the RFID reader containing the aforesaid self-interfering signal elimination device 50.

In the first embodiment of the RFID reader containing the self-interfering signal elimination device 50, the self- interfering signal elimination device 50 can perform attenuation and phase-shifting processing according to the attenuation parameter and phase-shifting parameter preset therein. The attenuation parameter and phase-shifting parameter remain unchanged during removal of the self- interfering signal. As shown in Fig. 5, the self-interfering signal elimination device 50 in the embodiment comprises a phase-shifting processing module 51, an attenuation processing module 52, and a signal elimination processing module 53. The phase-shifting processing module 51 and the attenuation processing module 52 can form the attenuation processing module and phase-shifting shown in Fig. 3. The connection between the modules 51, 52 and 53 and the connection of these modules with other units comprise:

the phase-shifting processing module 51 receiving a signal from the signal transmitter unit 40, performing phase- shifting processing on the signal, and transmitting the phase-shifted signal to the attenuation processing module 52.

The aforesaid attenuation processing module 52 receives the signal from the aforesaid phase-shifting processing module 51, performs attenuation processing on the signal to obtain an estimated self-interfering signal, and transmits the estimated self-interfering signal to the aforesaid signal elimination processing module 53.

The aforesaid signal elimination processing module 53 intercepts the signal transmitted from the aforesaid signal receiver unit 10 to the aforesaid demodulation unit 20, removes this signal the estimated self-interfering signal sent from the attenuation processing module 52, and transmits the signal which has undergone the elimination processing to the aforesaid demodulation unit 20.

In this embodiment, the positions in Fig. 5 of the phase- shifting processing module 51 and attenuation processing module 52 are interchangeable, i.e., the signal from the signal transmitter unit 40 goes first into the attenuation processing module 52 for attenuation, and then into the phase-shifting processing module 51 for phase-shifting to obtain the estimated self-interfering signal, and finally the estimated self-interfering signal is transmitted to the signal elimination processing module 53.

The phase shift amount for the phase-shifting processing by the aforesaid phase-shifting processing module 51 and the attenuation amount for the attenuation processing by the aforesaid attenuation processing module can be obtained beforehand through experiments and simulation. That is, the amount of phase shift and attenuation of the self-interfering signal relative to the signal sent from TX side can be predetermined through experiments and simulation. In a specific embodiment, aforesaid phase-shifting processing module 51 can be a fixed or variable phase shifter depending on the predetermined phase shift value and can have the predetermined phase shift value set within it for phase- shifting processing. Similarly, the aforesaid attenuation processing module can be a fixed or variable attenuator depending on the predetermined attenuation value and can have the predetermined attenuation value set within it for attenuation processing.

The present invention further provides a structure of an electric circuit, wherein it is not required to predetermine the phase-shifting and attenuation values, but they are determined during the signal transmission process, as described below through the second embodiment.

In the second embodiment of the RFID reader containing the self-interfering signal elimination device, a novelty electric circuit is employed to estimate the self-interfering signal. As shown in Fig. 6, the self-interfering signal elimination device in the embodiment comprises: a phase- shifting processing module 51, an attenuation parameter calculation module 54, an attenuation processing module 52, a feedback control module 55 and a signal elimination processing module 53. The connection between these modules and that between these modules and other units comprise: the phase-shifting processing module 51 receiving the signal from the signal transmitter unit 40, performing phase- shifting processing on the signal according to phase-shifting parameter Φ from the feedback control module 55, and transmitting the processed signal to the attenuation processing module 52.

The attenuation parameter calculation module 54 receives the signal from the signal receiver unit 10, determines the attenuation parameter ^a according to the power of the signal and the power it sets for the transmitted signal, and transmits the determined attenuation parameter ^a to the processing module 52 for attenuation.

The attenuation processing module 52 receives the signal from the phase-shifting processing module 51, performs attenuation processing on the signal according to the attenuation parameter ^a from attenuation parameter calculation module 54 to obtain an estimated self-interfering signal, and transmits the estimated self-interfering signal to the signal elimination processing module 53.

The signal elimination processing module 53 receives the signal from the signal receiver unit 10, removes from this signal the aforesaid estimated self-interfering signal from the attenuation processing module 52, and transmits the signal which has undergone the elimination processing to the demodulation unit 20.

The feedback control module 55 receives the signal transmitted from the signal elimination processing module 53 to the aforesaid demodulation unit 20, determines the phase- shifting parameter Φ according to the phase of the signal and the phase it presets for the transmitted signal, and transmits the determined phase-shifting parameter Φ to the aforesaid phase-shifting processing module 51. As shown in Fig. 7, in the embodiment, the attenuation processing module 52 can be a variable attenuator 52, the signal elimination processing module 53 can be a subtracter, the attenuation parameter calculation module 54 can be a power detector, the phase-shifting processing module 51 can be a variable phase shifter 51', the feedback control module 55 can be a PID controller 55, and the demodulation unit 20 contains a low noise amplifier (LNA) and an in-phase quadrant tributary demodulator (IQ), and the demodulated signal is transmitted to the AC coupler 60 for DC removal and other processing. The S module shown in Fig.7 is a simulated self- interfering signal generating module, the signal transmitted from the simulation module to the superimposer is the simulated self-interfering signal which is combined with the signal received at the RX side via the superimposer to form the interfered received signal.

As shown in Fig. 8, in the third embodiment of the RFID reader containing the self-interfering signal elimination device 50, the self-interfering signal elimination device 50 comprises: a first attenuation processing module 56, a phase- shifting processing module 57, a second attenuation processing module 58, a signal superposition processing module 59 and a signal elimination processing module 53.

The first attenuation processing module 56 receives the RF signal from the signal transmitter unit 40, performs attenuation processing on the signal according to the first attenuation parameter ^a^ preset in itself, and transmits the processed signal to the signal superposition processing module 59.

The phase-shifting processing module 57 receives the aforesaid signal from the signal transmitter unit 40, performs 90 degree phase-shifting processing on the signal, and transmits the phase-shifted signal to the attenuation processing module 58. The second attenuation processing module 58 receives the signal from the phase-shifting processing module 57, performs attenuation processing on the signal according to the second attenuation parameter ^a^ preset in itself, and transmits the processed signal to the signal superposition processing module 59.

In a specific implementation, the positions of aforesaid phase-shifting processing module 57 and the second attenuation processing module 58 are interchangeable, i.e., the second attenuation processing module 58 receives the signal from the signal transmitter unit 40, performs attenuation processing on the signal according to a second attenuation parameter ^², and transmits the processed signal to the phase-shifting processing module 57, and then the phase-shifting processing module 57 performs 90 degree phase- shifting processing on the signal transmitted from the second attenuation processing module 58, and transmits the phase- shifted signal to the signal superposition processing module 59.

The signal superposition processing module 59 receives the signal from the first attenuation processing module 56 and the aforesaid signal from the second attenuation processing module 58, superposes the two signals to obtain an estimated self-interfering signal, and transmits the estimated self- interfering signal to the signal elimination processing module 53.

The signal elimination processing module 53 intercepts the signal transmitted from the signal receiver unit 10 to demodulation unit 20, removes from this signal the estimated self-interfering signal from the signal superposition processing module 59, and transmits the signal which has undergone the elimination processing to the demodulation unit . In the embodiment, the total attenuation parameter ^a and phase-shifting parameter Φ of self-interfering signal in relation to the signal from the signal transmitter unit can be predetermined through experiments and simulation, and the aforesaid first attenuation parameter ^a\ and second attenuation parameter ^² can be calculated according to the aforesaid predetermined total attenuation parameter and aforesaid phase-shifting parameter Φ . To calculate the first attenuation parameter ^¹ and the second attenuation parameter ^² according to the total attenuation parameter ^a and aforesaid phase-shifting parameterΦ, the formulae below is used:

In the following embodiments of the RFID reader and embodiments of the self-interfering signal eliminating method used in the RFID reader where calculation of the first attenuation parameter ^a^ and the second attenuation parameter ^² according to total attenuation parameter ^a and aforesaid phase-shifting parameterΦ is involved, all calculations are made using these formulae, which will not be repeated below.

As shown in Fig. 9, in the fourth embodiment of the RFID reader containing the self-interfering signal elimination device, the self-interfering signal elimination device comprises: a first attenuation processing module 56, a phase- shifting processing module 57, a second attenuation processing module 58, a signal superposition processing module 59, a signal elimination processing module 53 and a feedback control module 55. The signal connection between these modules and that between these modules and other units comprise : the first attenuation processing module 56 receiving the RF signal from the signal transmitter unit 40, performing attenuation processing on the signal according to the first attenuation parameter ^a^ from the feedback control module 55, and transmitting the processed signal to the signal superposition processing module 59.

The phase-shifting processing module 57 receives the aforesaid signal from the signal transmitter unit 40, performs 90 degree phase-shifting processing on the signal, and transmits the phase-shifted signal to the second attenuation processing module 58.

The second attenuation processing module 58 receives the signal from the phase-shifting processing module 57, performs attenuation processing on the signal according to the second attenuation parameter ² from the feedback control module 55, and transmits the processed signal to the signal superposition processing module 59.

As with the third embodiment, in the fourth embodiment, the positions of the aforesaid phase-shifting processing module 57 and the second attenuation processing module 58 are interchangeable, and for specific implementation, the corresponding description of the third embodiment can be consulted.

The signal elimination processing module 53 intercepts the signal transmitted from the signal receiver unit 10 to the demodulation unit 20, removes from this signal the estimated self-interfering signal from the signal superposition processing module 59, and transmits the signal with the estimated self-interfering signal removed to the feedback control module 55 and the demodulation unit 20, respectively.

The feedback control module 55 receives the aforesaid signal from the signal elimination processing module 53, determines the total attenuation parameter ^a according to the power of the signal and the power it presets for the transmitted signal, then determines the phase-shift parameter Φ according to the phase of the received aforesaid signal and the phase it presets for the transmitted signal, calculates the first attenuation parameter cc^l and the second attenuation parameter a² according to the aforesaid determined total attenuation parameter ^a and the aforesaid phase-shifting parameter Φ , transmits the calculated first attenuation parameter ^l to the first attenuation processing module 56, and transmits the calculated second attenuation parameter ² to the second attenuation processing module 58.

In the embodiment, the aforesaid structure eliminates the need for a variable phase shifter 51' (Fig. 7) and can determine the variable phase-shifting parameter Φ according to feedback, thereby greatly reducing the cost as compared to the aforesaid second embodiment.

As shown in Fig. 10, in the embodiment, the first attenuation processing module 56 and the second attenuation processing module 58 can be respectively a variable attenuator, the phase-shifting processing module 57 can be a hybrid coupler, the signal superposition processing module 59 can be an adder, the signal elimination processing module 53 can be a subtracter and the feedback control module 55 can be a PID controller 55' . In the aforesaid structure of the fourth embodiment, the phase-shifting parameter Φ ranges from 0 to 90 degrees. When the generation time of the self-interfering signal is less than 0.25ns, the correct estimated self-interfering signal can be obtained by processing the transmitted signal using a phase-shifting parameter of less than 90 degrees. However, in case the generation time of the self-interfering signal is more than 0.25ns, the actual phase shift of the self- interfering signal in relation to the transmitted signal can be greater than 90 degrees, and estimation of the self- interfering signal with a phase-shifting parameter of less than 90 degrees will cause too small a phase shift for the estimated self-interfering signal. As a result, the correct estimated self-interfering signal cannot be obtained and the self-interfering signal cannot be removed from the received signal completely. To solve the problem, in the embodiment, a phase reverser for phase reversing processing can be added before receipt of the signal by the first attenuation processing module 56 or in the path after the signal is transmitted to obtain 90 to 180 degrees of phase shift through superposition processing by the signal superposition processing module 59.

The phase reverser intercepts the signal transmitted from the signal transmitter unit 40 to the first attenuation processing module 56, and transmits the aforesaid intercepted signal, directly or after the phase reversing processing depending on the control signal from the feedback control module 55, to the aforesaid first attenuation processing module 56;

alternatively, the aforesaid phase reverser intercepts the signal transmitted from the first attenuation processing module 56 to the aforesaid signal superposition processing module 59, and transmits the aforesaid intercepted signal, directly or after the phase reversing processing depending on the control signal from the feedback control module 55, to the aforesaid signal superposition processing module 59; the aforesaid feedback control module 55 further determines if it is necessary to start the phase reversing processing in the aforesaid phase reverser according to the aforesaid phase-shifting parameter Φ . If Φ is greater than 90 degrees, the phase reverser needs to be started and the feedback control module 55 transmits the control signal to the aforesaid phase reverser, requesting to start the phase reverser; otherwise, the feedback control module 55 transmits the control signal to the aforesaid phase reverser, requesting not to start the phase reverser.

In the embodiment, through adjustment of ' and ² , different ^a and Φ can be obtained for elimination of the self- interfering signal. This makes it possible for the electric circuit to use only cheap common components. It is easy to achieve, and can be easily integrated into the existing RFID readers .

Moreover, in this embodiment and the second embodiment, the feedback control module 55 can work every time the module is powered on, or can work when necessary by triggering the feedback control module 55 with a trigger module depending on whether the self-interfering signal is removed. The fifth embodiment below describes the solution of triggering the feedback control module to work with a trigger module (Fig. 11) .

The self-interfering signal elimination device 50 of the fifth embodiment of the RFID reader containing self- interfering signal elimination device 50 may, on the basis of the self-interfering signal elimination device 50 of the second or fourth embodiment, further comprise a feedback trigger module 61, which receives and detects the signal transmitted from the signal elimination processing module 53 to the demodulation unit 20, and transmits the trigger signal to the aforesaid feedback control module 55 (PID controller 55' ) when it detects that the power of the signal is greater than the set value; the feedback control module 55 stops working upon performing the working process once as described in the aforesaid second or fourth embodiment, and performs the working process again after receiving the trigger signal from the aforesaid feedback trigger module 61.

Specifically, the feedback trigger module 61 can comprise a power detector 62 and a trigger 63, wherein the power detector 62 receives and detects the signal transmitted from the aforesaid signal elimination processing module 53 to the aforesaid demodulation unit 20, and notifies the trigger 63 when it detects that the signal power is greater than the set value; the trigger transmits the trigger 63 signal to the feedback control module 55 according to the notification from the power detector 62. In Fig. 11, the aforesaid power detector 62 and trigger 63 added on the basis of Fig. 10 are used as an example, the structure of the RFID reader of this embodiment is shown.

The self-interfering signal elimination method according to the present invention as shown in Fig. 12 comprises the following steps:

step 121, performing attenuation and phase-shifting processing on the transmitted signal to obtain an estimated self-interfering signal;

step 122, removing the estimated self-interfering signal from the received signal.

In this method, after removal of the estimated self- interfering signal from the received signal, the signal can undergo low noise amplification and be demodulated. In addition, in this method, similar to prior art, the DC filtering processing can be performed on the demodulated signal. However, the residual self-interfering signal is very weak after the processing by this self-interfering signal elimination method; therefore there is no need to use a specially designed DC filter for DC signal removal and a common DC filter can be used. Moreover, in the self- interfering signal elimination method of the present invention used in the aforesaid RFID reader, the signal receiver unit in the RFID reader can very effectively remove the self-interfering signal to improve the receiving sensitivity of the reader even without the need of starting in the low gain mode.

The following uses the aforesaid self-interfering signal elimination method used in the RFID reader as an example in conjunction with embodiments.

As shown in Fig. 13, the first embodiment of the self- interfering signal elimination method used in the RFID reader comprises the following steps:

step 131, predetermining the attenuation parameter and phase- shifting parameter for the self-interfering signal relative to the RF signal transmitted from the TX side.

In this step, the aforesaid two parameters can be determined through experiments or simulation.

Step 132, receiving the signal transmitted from the TX side, performing attenuation and phase-shifting processing on the signal according to the aforesaid attenuation parameter and phase-shifting parameter to obtain the estimated self- interfering signal.

In this step, the signal sent from the TX side can be first attenuated according to the attenuation parameter, and then the attenuated signal can be phase shifted with the phase- shifting parameter, or the signal sent from the TX side can be first phase shifted according to the phase-shifting parameter, and can then be attenuated with the attenuation parameter . Step 133, removing the aforesaid estimated self-interfering signal from the signal received at the RX side, and then amplifying with low noise and demodulating the received signal which has had the self-interfering signal removed.

Similar to the first embodiment, the second embodiment of the self-interfering signal elimination method used in the RFID reader also predetermines the aforesaid phase-shifting parameter and attenuation parameter by experiments or simulation. As shown in Fig. 14, the embodiment comprises the following steps:

Step 141, predetermining the phase-shifting parameter Φ and total attenuation parameter ^a of the self-interfering signal relative to the RF signal transmitted from the TX side by means of experiment or simulation, and calculating the first attenuation parameter cc^l and the second attenuation parameter a ² according to the two parameters .

Step 142, receiving the transmitted signal from the TX side, and attenuating the signal according to the aforesaid first attenuation parameter.

Step 143, receiving the transmitted signal from the TX side, performing 90 degree phase-shifting on the signal, and then attenuating the signal with the aforesaid second attenuation parameter .

Step 144, superposing the signal which has undergone the processing of the aforesaid step 142 and the signal which has undergone the processing of the aforesaid step 143 to obtain the estimated self-interfering signal.

step 145, eliminating the aforesaid estimated self- interfering signal from the signal received at the RX side, and then amplifying with low noise and demodulating the received signal. The aforesaid step 142 and step 143 can be performed simultaneously, or step 142 is performed first, and then step 143 is performed, or step 143 is performed first, and then step 142 is performed.

In the aforesaid two embodiments of the self-interfering signal elimination method used in the RFID reader, predetermined phase-shifting parameter and attenuation parameter are used to estimate the self-interfering signal and the parameters cannot be changed during the operations thereafter. In the third and fourth embodiment of the self- interfering signal elimination method used in the RFID reader, the aforesaid attenuation parameter and phase- shifting parameter can be determined and adjusted during the signal receiving process. The third and fourth embodiments of the self-interfering signal elimination method used in the RFID reader are described below.

As shown in Fig. 15, the third embodiment of the self- interfering signal elimination method used in the RFID reader comprises the following steps:

step 151, determining the attenuation parameter according to the power of the signal transmitted from the TX side and that of the signal received at the RX side.

In this step, when undergoing the receiving process at the RX side, the signal received by the RFID reader is influenced by the signal sent from the TX port, including the signal returned from the label and the coupled self-interfering signal. As the power of the self-interfering signal is much higher than the power of the signal returned from the label, the power of the signal received at the RX side can be treated as the power of the self-interfering signal.

Therefore, by comparing the power of the signal received at the RX side and that of the signal transmitted from the TX side, the attenuation parameter for the self-interfering signal in relation to the signal transmitted from the TX side can be obtained.

Step 152, performing attenuation processing on the transmitted signal received at the TX side according to the attenuation parameter determined in step 151.

Step 153, performing phase-shifting processing on the attenuated signal with the phase-shifting parameter to obtain the estimated self-interfering signal.

In this process, the aforesaid step 153 and step 152 are interchangeable, i.e., the phase-shifting processing can be first performed based on the phase-shifting parameter, and then the attenuation processing can be performed with the attenuation parameter to obtain the estimated self- interfering signal.

Step 154, eliminating the aforesaid estimated self- interfering signal from the signal received at the RX side, and then performing low noise amplification, demodulation and DC filtering processing on the signal which has undergone the elimination processing.

Step 155, determining the new phase-shifting parameter according to the phase of the aforesaid signal which has undergone the elimination processing and that of the signal transmitted from the TX side, and then returning to step 153. Specifically, in step 155, the PID control method can be used to determine the aforesaid phase-shifting parameter.

In step 153 of this embodiment, the first phase-shifting processing can be performed according to the preset initial value of the phase-shifting parameter; and then, when returning to step 153 after completing step 155, the new phase-shifting parameter determined in step 155 can be used for phase-shifting. As shown in Fig. 16, the fourth embodiment of the self- interfering signal elimination method used in the RFID reader comprises the following steps:

step 161, receiving the signal transmitted from the TX side, and attenuating this signal according to the first attenuation parameter.

Step 162, receiving the signal transmitted from the TX side, and having the received signal undergo the 90 degree phase- shifting processing, and then the attenuation processing according to the second attenuation parameter.

In this step, the phase-shifting processing can be performed first, and then the attenuation processing is performed; or the attenuation processing can be performed first, and then the phase-shifting processing is performed.

Step 163, superposing the signal which has undergone the processing of the aforesaid step 161 and the signal which has undergone the processing of the aforesaid step 162 to obtain the estimated self-interfering signal.

Step 164, eliminating the aforesaid estimated self- interfering signal from the signal received at the RX side, and then performing low noise amplification and demodulation processing on this received signal.

Step 165, determining the total attenuation parameter ^a and phase-shifting parameter Φ according to the phase and power of the signal which has undergone the aforesaid elimination processing and the phase and power of the signal transmitted from the TX side, and determining the first attenuation parameter and the second attenuation parameter according to the total attenuation parameter and phase-shifting parameter, and then returning to step 161 and step 162. The aforesaid step 161 and step 162 can be performed simultaneously, or step 161 can be performed first, and then step 162 is performed, or step 162 can be performed first, and then step 161 is performed.

Similar to the aforesaid embodiment, in step 161 and step 162, the first attenuation processing can be performed according to the preset initial value of the first attenuation parameter and the second attenuation parameter; and then, when the process returns to step 161 and step 162 after completing step 165, the new first attenuation parameter and second attenuation parameter determined in step 165 can be used respectively for another attenuation processing.

In this embodiment, the phase-shifting parameter Φ ranges from 0 to 90 degrees. In order to obtain a greater Φ, in this embodiment, if the determined phase-shifting parameter is greater than 90 degrees, when the process returns to step 161, the transmitted signal will be reversed before or after attenuated with the first attenuation parameter, and then in step 163, the signal, which is reversed and attenuated in step 161, and the signal, which is phase-shifted and attenuated in step 162, are superposed.

Additionally, in the third embodiment and fourth embodiment of the self-interfering signal elimination method used in the aforesaid RFID reader, whether to execute the aforesaid step 155 or step 165 can be determined after executing the determination step of: determining whether the power of the signal with the estimated self-interfering signal removed is greater than the preset value, and if yes, either step 155 or step 165 is executed, if not, neither step 155 nor step 165 will be executed.

In order to examine the RFID reader provided by the present invention and the improvement in the sensitivity of the RFID reader using the self-interfering signal elimination method, the inventors carried out simulation and compared the bit error of the received signal with and without the present invention under different simulation conditions. Assuming the power of the actual self-interfering signal and its phase shift relative to the transmitted signal is 2dBm and O.lπ, respectively. In order to check the effectiveness of the self-interfering signal elimination solution according to the present invention, a simulation was conducted and a comparison of the signal bit error was made for the possible amplitude error and phase error when the self-interfering signal was estimated using the solution of the present invention and the simulation and comparison results are shown in Fig. 17. Fig. 17 shows the results of bit error rate after the received signal had gone through the self-interfering signal elimination, modulation/demodulation, low noise amplification, channel filter and base-band processing.

As shown in Fig.17, even if there are amplitude and phase errors, the RFID reader using the present invention can still significantly increase receiving sensitivity, wherein amplitude and phase errors are mainly caused by the noise or quantification error of the variable attenuator. As shown in Fig. 17, the sensitivity of the reader can be greatly improved even at the maximum phase error of 0.08π (O.lδπ - O.lπ), i.e. 14.4 degrees.

However, the actual phase error is typically far lower than the aforesaid O.Oδπ. For example, in Fig. 10, with the recommended method, when the step size of the variable attenuator is 0.5dB, the maximum phase error is 3.3 degrees. The generation of the phase error is further described below: assuming the parameters for the self-interfering signal are a₁»a₂,Φ = 45°_r since the noise and quantification error of the variable attenuator a_γ is estimated to be «₂+0.5dB during the process of self-interfering signal estimation, the estimated Φ = 48.3° and a phase error of 3.3 degrees is generated. Therefore, the bit error rate obtained from self-interfering signal processing according to the present invention is very low, which significantly improves the sensitivity of the reader .

As seen from the aforesaid description of the embodiments and simulation results, in the present invention:

1. Elimination of the self-interfering signal can be achieved simply by adding a simple electric circuit between the TX port and RX port in the RFID reader, i.e., the self-interfering signal elimination device described in the aforesaid embodiments, and the device can be easily integrated into the existing electric label products .

2. The design of the TX side can be simplified by eliminating the self-interfering signal, without having to add an extra RF antenna, and the RX side can be driven in the high gain mode.

3. In the design of the filter after demodulation, it is no longer necessary to put much emphasis on DC filtering, which greatly simplifies the design of the filter.

4. The receiving sensitivity of the reader can also be improved considerably.

The aforesaid is only the preferred embodiments according to the present invention, and is not intended to limit the protective scope of the present invention. Any modification, equivalent substitution and improvement without departure from the spirit and principle of the present invention should fall under the coverage of the present invention.

Claims

DClaims

1. A self-interfering signal elimination device, characterized in that said device comprises: a phase-shifting and attenuation processing module and a signal elimination processing module, wherein,

said phase-shifting and attenuation processing module is provided for receiving a first signal from outside, performing attenuation and phase-shifting processing on the signal to obtain an estimated self-interfering signal;

said signal elimination processing module is provided for receiving a second signal from outside and the estimated self-interfering signal from said phase-shifting and attenuation processing module, and for eliminating the estimated self-interfering signal from the second signal.

2. The self-interfering signal elimination device as claimed in claim 1, characterized in that said phase-shifting and attenuation processing module comprises: a phase-shifting processing module and an attenuation processing module, wherein,

said phase-shifting processing module is provided for receiving said first signal from outside, performing phase- shifting processing on the signal and sending the phase- shifted signal to said attenuation processing module;

said attenuation processing module is provided for receiving the signal from said phase-shifting processing module, performing attenuation processing on the signal to obtain an estimated self-interfering signal, and sending the estimated self-interfering signal to said signal elimination processing module.

3. The self-interfering signal elimination device as claimed in claim 1, characterized in that said phase-shifting and attenuation processing module comprises: a phase-shifting processing module and an attenuation processing module, wherein,

said attenuation processing module is provided for receiving said first signal from outside, performing attenuation processing on the signal and sending the attenuated signal to said phase-shifting processing module;

said phase-shifting processing module is provided for receiving the signal from said phase-shifting processing module, performing phase-shifting processing on the signal to obtain an estimated self-interfering signal, and sending the estimated self-interfering signal to said signal elimination processing module.

4. The self-interfering signal elimination device as claimed in claim 2 or 3, characterized in that said self- interfering signal elimination device further comprises: an attenuation parameter calculation module,

said attenuation parameter calculation module is provided for receiving said second signal from outside, detecting the power of the signal, comparing the power of the signal with the power it sets for a transmitted signal to obtain an attenuation parameter, and sending the attenuation parameter to said attenuation processing module;

said attenuation processing module is provided for receiving the attenuation parameter from said attenuation parameter calculation module, and performing attenuation processing on the signal from said phase-shifting processing module according to the attenuation parameter.

5. The self-interfering signal elimination device as claimed in claim 2 or 3, characterized in that said self- interfering signal elimination device further comprises: a feedback control module; said feedback control module is provided for receiving the signal which has undergone the elimination processing by said signal elimination processing module, determining the phase- shifting parameter according to the phase of the signal and the phase it sets for a transmitted signal, and sending the determined phase-shifting parameter to said phase-shifting processing module;

said phase-shifting processing module is provided for performing phase-shifting processing on the received signal according to the phase-shifting parameter received from said feedback control module.

6. The self-interfering signal elimination device as claimed in claim 5, characterized in that said self- interfering signal elimination device further comprises: a feedback trigger module;

said feedback trigger module is provided for receiving and detecting the signal which has undergone the elimination processing by said signal elimination processing module, and sending a trigger signal to said feedback control module when it detects that the power of the signal is greater than the set value;

said feedback control module is provided for stoping working upon performing said working process once, and performing said working process again after receiving the trigger signal from said feedback trigger module.

7. The self-interfering signal elimination device as claimed in claim 6, characterized in that said feedback trigger module comprises: a power detector and a trigger;

said power detector is provides for receiving and detecting the signal which has undergone the elimination processing by said signal elimination processing module, and notifying the trigger when it detects that the power of the signal is greater than the set value;

said trigger is provided for sending a trigger signal to said feedback control module according to the notification from the power detector.

8. The self-interfering signal elimination device as claimed in claim 1, characterized in that said phase-shifting and attenuation processing module comprises: a first attenuation processing module, a phase-shifting processing module, a second attenuation processing module and a signal superposition processing module, wherein,

said first attenuation processing module is provided for receiving said first signal from outside, performing attenuation processing on the signal according to a first attenuation parameter and sending the processed signal to the signal superposition processing module;

said phase-shifting processing module is provided for receiving said first signal from outside, performing 90 degree phase-shifting processing on the signal, and sending the phase-shifted signal to said second attenuation processing module;

said second attenuation processing module is provided for receiving said signal from the phase-shifting processing module, performing attenuation processing on the signal according to a second attenuation parameter, and sending the processed signal to the signal superposition processing module;

said signal superposition processing module is provided for receiving said signal from the first attenuation processing module and said signal from the second attenuation processing module, superposing the two signals to obtain an estimated self-interfering signal, and sending the estimated self- interfering signal to the signal elimination processing module .

9. The self-interfering signal elimination device as claimed in claim 1, characterized in that said phase-shifting and attenuation processing module comprises: a first attenuation processing module, a phase-shifting processing module, a second attenuation processing module and a signal superposition processing module, wherein,

said first attenuation processing module is provided for receiving said first signal from outside, performing attenuation processing on the signal according a the first attenuation parameter, and sending the processed signal to the signal superposition processing module;

said second attenuation processing module is provided for receiving said first signal from outside, performing attenuation processing on the signal according to a second attenuation parameter, and sending the processed signal to the phase-shifting processing module;

the phase-shifting processing module is provided for receiving said signal from the second attenuation processing module, performing 90 degree phase-shift processing on the signal, and sends the phase-shifted signal to the signal superposition processing module;

the signal superposition processing module is provided for receiving said signal from the first attenuation processing module and said signal from the phase-shifting processing module, superposing the two signals to obtain an estimated self-interfering signal, and sending the estimated self- interfering signal to the signal elimination processing module.

10. The self-interfering signal elimination device as claimed in claim 8 or 9, characterized in that said self- interfering signal elimination device further comprises: a feedback control module;

said feedback control module is provided for receiving said signal which has undergone the elimination processing by said signal elimination processing module, determining the total attenuation parameter according to the power of the signal and the power it sets for a transmitted signal, then determining the phase-shifting parameter according to said received signal and the phase it set for a transmitted signal, calculating said first attenuation parameter and said second attenuation parameter according to said determined total attenuation parameter and said phase-shifting parameter, sending the calculated first attenuation parameter to said first attenuation processing module, and sending the calculated second attenuation parameter to said second attenuation processing module;

said first attenuation processing module and said second attenuation processing module are provided for separately performing attenuation processing according to said first attenuation parameter and said second attenuation parameter respectively from the feedback control module.

11. The self-interfering signal elimination device as claimed in claim 10, characterized in that said self- interfering signal elimination device further comprises: a phase reversing processing module;

said phase reversing processing module is provided for intercepting said first signal sent from outside to said first attenuation processing module, and sending said intercepted signal, directly or after phase reversing processing depending on the control signal from the feedback control module, to said first attenuation processing module;

said feedback control module further is provided for determing if it is necessary to start the phase reversing processing in said phase reversing processing module according to the value of the phase-shifting parameter, and if so, sending a control signal to said phase reversing processing module, requesting to start the phase reversing processing; if not, sending a control signal to said phase reversing processing module, requesting not to start the phase reversing processing.

12. The self-interfering signal elimination device as claimed in claim 10, characterized in that said self- interfering signal elimination device further comprises: a phase reversing processing module;

said phase reversing processing module is provided for intercepting the signal sent from said first attenuation processing module to said signal superposition processing module, and sending said intercepted signal, directly or after phase reversing processing depending on the control signal from the feedback control module, to said signal superposition processing module;

said feedback control module further is provided for determining if it is necessary to start the phase reversing processing in said phase reversing processing module according to the value of the phase-shifting parameter, and if so, sending a control signal to said phase reversing processing module, requesting to start the phase reversing processing, and if not, sending a control signal to the phase reversing processing module, requesting not to start the phase reversing processing.

13. The self-interfering signal elimination device as claimed in claim 10, characterized in that said self- interfering signal elimination device further comprises: a feedback trigger module;

said feedback trigger module is provided for receiving and detecting the signal which has undergone the elimination processing by said signal elimination processing module, and sending a trigger signal to said feedback control module when it detects that the power of the signal is greater than the set value; said feedback control module is provided for stoping working upon performing said working process once, and performing said operation process again after receiving the trigger signal from said feedback trigger module.

14. The self-interfering signal elimination device as claimed in claim 13, characterized in that said feedback trigger module comprises: a power detector and a trigger;

said power detector is provided for receiving and detecting the signal which has undergone the elimination processing by said signal elimination processing module, and notifying the trigger when it detects that the power of the signal is greater than the set value;

15. A RFID (radio frequency identification) reader, wherein said RFID reader comprises: a signal transmitter unit, a signal receiver unit and a demodulation unit, wherein said RFID reader further comprises: a self-interfering signal elimination device, wherein,

said signal transmitter unit is provided for transmitting a signal to a label, and transfers the transmitted signal to said self-interfering signal elimination device;

said signal receiver unit is provided for receiving the signal returned from the label, and transmitting the received signal to said self-interfering signal elimination device; said self-interfering signal elimination device is provided for receiving said signal from the signal transmitter unit, performing attenuation and phase-shifting processing on the signal to obtain an estimated self-interfering signal, and receiving said signal from the signal receiver unit, eliminating the estimated self-interfering signal from said signal, and transmitting the signal which has undergone the elimination processing to said demodulation unit;

said demodulation unit is provided for performing demodulation on the received signal.

16. The RFID reader as claimed in claim 15, characterized in that said RFID reader further comprises: a DC filtering unit; said DC filtering unit is provided for receiving the signal from said demodulation unit and filtering the DC signal therein .

17. A self-interfering signal elimination method, characterized in that said method comprises:

performing attenuation and phase-shifting processing on the transmitted signal to obtain an estimated self-interfering signal;

eliminating the estimated self-interfering signal from the received signal.

18. The method as claimed in claim 17, characterized in that said attenuation and phase-shifting processing of the transmitted signal comprises:

determining the attenuation parameter according to the power of the transmitted signal and the power of the received signal; performing attenuation processing on said transmitted signal according to said determined attenuation parameter before or after performing said phase-shift processing.

19. The method as claimed in claim 17, characterized in that after said elimination of said estimated self-interfering signal, said method further comprises: determining the phase- shift parameter according to the phase of the signal with the estimated self-interfering signal removed and the phase of said transmitted signal;

said phase-shifting processing performs phase-shifting processing according to said determined phase-shift parameter .

20. The method as claimed in claim 17, characterized in that said attenuation and phase-shift processing of the transmitted signal to obtain the estimated self-interfering signal comprises:

performing first attenuation processing on the transmitted signal according to the first attenuation parameter; performing second attenuation processing on the transmitted signal according to the second attenuation parameter, and performing 90 degree phase-shift processing before or after said second attenuation processing;

21. The method as claimed in claim 20, characterized in that said first attenuation parameter and said second attenuation parameter are determined in the way of:

determining the total attenuation parameter and the phase- shifting parameter according to the phase and power of both said signal with the estimated self-interfering signal removed and said transmitted signal, and determining said first attenuation parameter and said second attenuation parameter according to the determined total attenuation parameter and phase-shifting parameter.

22. The method as claimed in claim 21, characterized in that said total attenuation parameter and phase-shifting parameter are determined in the way of PID control.

23. The method as claimed in claim 21, characterized in that after said determination of the phase-shifting parameter, said method further comprises: determining if the determined phase-shifting parameter is greater than 90 degrees, and if so, performing further phase reversing processing on the signal before performing the first attenuation processing on the transmitted signal or before superposing the signal from the first attenuation processing.