Abstract:
A data transmission method is disclosed, and the method comprises: encoding binary data to be transmitted with encoding principle as follows: encoding binary data x1 in the manner of no jumping at middle phase; encoding binary data x2 in the manner of jumping at middle phase; and after encoding two binary data x1 consecutively with high level of no jumping at middle phase, encoding the immediate following binary data x1 with low level of no jumping at middle phase; encoding binary data x1 with high level of no jumping at middle phase, wherein the binary data x1 follows binary data x1 encoded by using low level of no jumping at middle phase; and encoding binary data x1 immediately following binary data x2 by using high level of no jumping at middle phase; modulating the encoded data; and transmitting the modulated signal.

Description:
TECHNICAL FIELD 
       [0001]    The invention relates to a data transmission technology, and in particular, to a data transmission method. 
       BACKGROUND 
       [0002]    Passive radio frequency identification (RFID) is a non-contact automatic identification technology, which can automatically identify a target object and acquire related data through a radio frequency signal without need of human intervention and can be applied to various harsh environments. The RFID technology can identify high-speed moving objects and simultaneously identify a plurality of tags, and be operated rapidly and conveniently. 
         [0003]    The RFID technology adopts the following basic operating principle: a tag, after entering into a magnetic field, receives radio frequency signal from a reader, and sends product information (a passive tag) stored in a tag chip by means of energy acquired is through induced current, or actively sends a signal at a certain frequency (a active tag); the reader reads and decodes the signal, and sends the decoded signal to an central information system for corresponding data processing. 
         [0004]    In the passive RFID technology, the energy that a tag need for working is extracted from a signal of a reader. Therefore, certain measures are required to be taken for increasing the energy acquired at the tag end during the process that information transmits from the reader to the tag; one of the common method is to increase the time that signal operates from the reader to the tag, and another method is to use high level as much as possible and reduce the use of low level in a link from the reader to the tag during a data encoding process. For example, in the 18000-6 Type C of international organization for standardization (ISO), a pulse interval encoding (PIE) method is adopted. 
         [0005]    The Manchester encoding method is a widely applied self-clocking coding method, which has the advantages of abundant timing and synchronization information carried during an encoding process, no DC drift, and simple encoding. The Manchester encoding method replaces each old binary code respectively with two new binary codes with different phases and is suitable for information transmission from a reader to a tag during radio frequency identification. 
         [0006]    One of the encoding principles of the Manchester encoding method is as follows: 
         [0007]    From 0 to 01 (a zero-phase periodic square wave); 
         [0008]    From 1 to 10 (a π-phase periodic square wave). 
         [0009]    During a specific implementation of the Manchester encoding method, data are distinguished by the change of wave electrical level; when the level changing from low to high, it indicates binary data “0”; when the level changing from high to low, it indicates binary data “1”; and a jump happens at the medium stage of a symbol period. 
         [0010]    However, when the Manchester encoding method is used for transmitting data to a passive tag, the energy acquired by the passive tag is somewhat low. 
       SUMMARY 
       [0011]    The invention aims to solve the technical problems by providing a data transmission method for increasing the energy of passive tag during RFID to overcome the disadvantages of the prior art. 
         [0012]    To solve the above-mentioned problems, the invention provides a data transmission method, encoding binary data to be transmitted with encoding principle as follows, then modulating and transmitting the binary data. 
         [0013]    Encoding binary data x1 in the manner of no jumping at middle phase; encoding binary data x2 in the manner of jumping at middle phase; and 
         [0014]    after encoding two binary data x1 consecutively with high level of no jumping at middle phase, encoding the immediate following binary data x1 with low level of no jumping at middle phase; and 
         [0015]    encoding binary data x1 with high level of no jumping at middle phase, wherein the binary data x1 follows binary data x1 encoded by using low level of no jumping at middle phase; 
         [0016]    encoding binary data x1 immediately following binary data x2 by using high level of no jumping at middle phase; 
         [0017]    Wherein, x1 and x2 are respectively 1 and 0; or, x1 and x2 are respectively 0 and 1. 
         [0018]    Further, the encoding principle also includes: encoding a binary data x2 in the manner of jumping at falling edge, wherein the binary data x2 follows binary data x2 encoded in the manner of jumping at falling edge; encoding a binary data x2 in the manner of jumping at rising edge, wherein the binary data x2 follows binary data x2 encoded in the manner of jumping at rising edge. 
         [0019]    Further, the encoding principle also includes: encoding binary data x1 and binary data x2 by adopting the same length. 
         [0020]    Further, the encoding principle also includes: phase jumping at the left edge of binary data x2. 
         [0021]    Further, the encoding principle also includes: encoding a binary data x2 in the manner of jumping at rising edge, wherein the binary data x2 follows binary data x1 encoded with high level of no jumping at middle phase. 
         [0022]    Further, the encoding principle also includes: encoding a binary data x2 in the manner of jumping at falling edge, wherein the binary data x2 follows binary data x1 encoded with low level of no jumping at middle phase. 
         [0023]    Further, the encoding principle also includes: no phase jumping at the left edge of binary data x2. 
         [0024]    Further, the encoding principle also includes: encoding a binary data x2 in the manner of jumping at falling edge, wherein the binary data x2 follows binary data x1 encoded with high level of no jumping at middle phase. 
         [0025]    Further, the encoding principle also includes: encoding a binary data x2 in the manner of jumping at rising edge, wherein the binary data x2 follows binary data x1 encoded with low level of no jumping at middle phase. 
         [0026]    In conclusion, compared with the Manchester encoding method, the encoding method for data transmission of the invention used in a link from a reader to a tag in RFID system can provide more energy for the tag on the premise of the bandwidth occupied by signal which is unchanged. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]      FIG. 1  is a flowchart of a data transmission method for radio frequency identification from a reader to a tag; 
           [0028]      FIG. 2  is a schematic diagram illustrating the data state relation between binary data encoded by using the encoding principle 1 of the invention; 
           [0029]      FIG. 3  is a schematic diagram illustrating data symbols when the encoding principle 1 of the invention is adopted; 
           [0030]    is  FIG. 4  is a data state transition diagram when the encoding principle 1 of the invention is adopted; 
           [0031]      FIG. 5  is a data sequence diagram of two binary data encoded by using the encoding principle 1 of the invention; 
           [0032]      FIG. 6  is a schematic diagram illustrating an encoding example using the encoding principle 1 of the invention; 
           [0033]      FIG. 7  is a schematic diagram illustrating an encoding example using the encoding principle 2 of the invention; 
           [0034]      FIG. 8  is a data state transition diagram when the encoding principle 3 of the invention is adopted; 
           [0035]      FIG. 9  is a data sequence diagram when two binary data are encoded by using the encoding principle 3 of the invention; 
           [0036]      FIG. 10  is a schematic diagram illustrating an encoding example using the encoding principle 3 of the invention; and 
           [0037]      FIG. 11  is a schematic diagram illustrating an encoding example using the encoding principle 4 of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0038]    The following drawings and embodiments aim to serve as the further description for the invention. 
         [0039]      FIG. 1  is a flowchart of a data transmission method for radio frequency identification from a reader to a tag; the method mainly comprises the following steps: 
         [0040]    Step  101 : a reader encodes binary data that to be transmitted; 
         [0041]    Step  102 : the reader modulates the encoded data; 
         [0042]    Step  103 : the reader performs wireless transmission to the modulated signal; 
         [0043]    Step  104 : a tag receives the wireless signal from the reader; 
         [0044]    Step  105 : the tag demodulates the received wireless signal; and 
         [0045]    Step  106 : the tag decodes the demodulated signal to acquire the above-mentioned binary data. 
         [0046]    The embodiments of the encoding principles for encoding original binary data to be transmitted in step 101 shall be described in details. The original binary data is hereinafter binary data for short. 
       EMBODIMENT 1 
       [0047]    The encoding principle 1 for encoding the original binary data to be transmitted includes the following contents: 
         [0048]    1A: the length of encoded data that generated after binary data  1  and binary data  0  are encoded is the same; no jump happens to the middle phase of the binary data  1  in data symbols; a jump happens to the middle phase of the binary data  0  data symbols, and a phase jump happens between two consecutive binary data  0 ; 
         [0049]    1B: the binary data  1  is usually expressed with high level; after two or more binary data  1  are encoded consecutively with high level, the immediate following binary data  1  is encoded with low level, and the number of the binary data  1  that encoded consecutively with high level is rerecorded; 
         [0050]    1C: binary data  1  following the binary data  1  that encoded with low level is encoded with high level. 
         [0051]    In addition, to enhance the reliability of encoding codes and decoding codes, the following contents can be added to the encoding principle 1: 
         [0052]    1D: on the premise of meeting the IA and the IB, i.e. using the high level as much as possible, a phase jump happens to the left edge of the binary data  0 , and no phase jump happens to the right edge of the binary data  0 . 
         [0053]    The encoding principle 2 for encoding the original binary data that to be transmitted includes the following contents: 
         [0054]    2A: the length of encoded data generated after binary data  1  and binary data  0  are encoded is the same; no jump happens to the middle phase of the binary data  0  in data symbols; a jump happens to the middle phase of the binary data  1  in data symbols; and a phase jump happens between two consecutive binary data  1 ; 
         [0055]    2B: the binary data  0  is usually expressed with high level; after two or more binary data  0  are encoded consecutively with high level, the immediate following binary data  0  is encoded with low level, and the number of the binary data  0  that encoded consecutively with high level is rerecorded; 
         [0056]    2C: the binary data  0  following the binary data  0  that encoded with low level is encoded with high level. 
         [0057]    Similarly, to enhance the reliability of encoding codes and decoding codes, the following contents also can be added to the encoding principle 2: 
         [0058]    2D: on the premise of meeting the 2A and the 2B, i.e. using the high level as much as possible, a phase jump happens to the left edge of the binary data  1 , and no phase jump happens to the right edge of the binary data  1 . 
         [0059]      FIG. 2  is a diagram illustrating the data state relation between binary data encoded by using the encoding principle 1 of the invention. As shown in  FIG. 2 , a jump happens to the middle phase of binary data  0  in data symbols; no jump happens to the middle phase of binary data  1  in data symbols; the binary data  0  and the binary data  1  respectively have two states. The states of the binary data  0  are recorded as S 2  and S 3 , and the states of the binary data  1  are recorded as S 1  and S 4 . 
         [0060]    If high level and low level are respectively expressed with ‘1’ and ‘0’, then S 1  can be expressed as ‘11’; S 2  can be expressed as ‘10’, indicating a falling edge jump; S 4  is opposite in phase to S 1  and can be expressed as ‘00’; S 3  is opposite in phase to S 2  and can be expressed as ‘01’, indicating rising edge jump. 
         [0061]    When the encoding principle 2 of the invention is adopted, the binary data  1  and the binary data  0  in the state diagram that above-mentioned are only required to be is interchanged. In this case, a jump happens to the middle phase of the binary data  1  in the data symbols; no jump happens to the middle phase of the binary data  0  in the data symbols. The states of the binary data  1  are recorded as S 2  and S 3 , and the states of the binary data  0  are recorded as S 1  and S 4 . S 2  and S 3  have opposite phases, and S 1  and S 4  have opposite phases. 
         [0062]      FIG. 3  is a schematic diagram illustrating data symbols when the encoding principle 1 of the invention is adopted. As shown in  FIG. 3 , binary data  0  and binary data  1  respectively have two states. A jump happens to the middle phase of the binary data  0  in data symbols, and no jump happens to the middle phase of the binary data  1  in data symbols. 
         [0063]    When the encoding principle 2 is adopted, the binary data  0  and the binary data  1  in  FIG. 3  are only required to be interchanged. In this case, the binary data  0  and the binary data  1  respectively have two states, a jump happens to the middle phase of the binary data  1  in the data symbols, and no jump happens to the middle phase of the binary data  0  in the data symbols. 
         [0064]      FIG. 4  is a data state transition diagram when the encoding principle 1 of the invention is adopted. As shown in  FIG. 4 , the state transition method using the encoding principle 1 is as follows:
       When the binary data is now in a state of S 1 , i.e., the state is expressed as ‘11’.       
 
         [0066]    When the binary data  1  is received: if the binary data corresponding to the current state is the first one (i.e., the previous state is non-S 1  state) of consecutive binary data  1  (encoding with high level), the state S 1  remains when another binary data  1  is received; if the binary data corresponding to the current state is the second one of consecutive binary data  1  (encoding with high level), the state is transited to S 4  when another binary data  1  is received. That is to say, after two binary data  1  are encoded consecutively with high level, the third binary data  1  is encoded with low level, see 1B in the encoding principle 1. 
         [0067]    When the binary data  0  is received: the state is transited to S 3 , see 1D in the encoding principle 1. As stated above, S 1  can be expressed as ‘11’, and S 3  can be expressed as ‘01’; therefore, when the binary data  0  is received under the S 1  state, the state is transited to S 3  (i.e., encoding the binary data  0  using ‘01’), thus increasing phase jumps and enhancing the reliability of data transmission.
       When the binary data is now in a state of S 2 , i.e., the state is expressed as ‘10’.       
 
         [0069]    When the binary data  1  is received, the state is transited to S 1 ; when the binary data  0  is received, the S 2  state remains, see 1D in the encoding principle 1.
       When the binary data is now in a state of S 3 , i.e., the state is expressed as ‘01’:       
 
         [0071]    When the binary data  1  is received, the state is transited to S 1 , see 1D in the encoding principle 1; when the binary data  0  is received, the S 3  state remains, see 1D in the encoding principle 1. 
         [0072]    That is to say, in order to make the most of high level for encoding, when the binary data  1  is received under the S 3  state, ‘11’ but ‘00’ is used for encoding.
       When the binary data is now in a state of S 4 , i.e., the state is expressed as ‘00’.       
 
         [0074]    When the binary data  1  is received, the state is transited to S 1 , see 1C in the encoding principle 1; when the binary data  0  is received, the state is transited to S 2 , see 1D in the encoding principle 1. Similarly, S 4  can be expressed as ‘00’, S 2  can be expressed as ‘10’; when the binary data  0  is received, the current state S 4  is transited to S 2  to increase phase jump and enhance the accuracy of data transmission. 
         [0075]    It can be seen from  FIG. 4  that there is no state transition relation between S 2  and S 3  and between S 3  and S 4 , moreover, S 2  cannot be transited to S 4 , thus code words have certain error detecting capability after the binary data is encoded by using the above-mentioned encoding principle 1. 
         [0076]    When the encoding principle 2 is adopted, the states of the binary data  1  are denoted by S 2  and S 3 , and the states of the binary data  0  are denoted by S 1  and S 4 . The state transition diagram is similar to  FIG. 4 , and the transition condition is only required to change from receiving binary data  0  to receiving binary data  1  and to change from receiving binary data  1  to receiving binary data  0 , the specific data transition method is not repeated here. 
         [0077]      FIG. 5  is a data sequence diagram of two binary data encoded by using the encoding principle 1 of the invention. 
         [0078]    As shown in  FIG. 5 , binary data (0, 0), (0, 1) and (1, 0) respectively have two forms after being encoded; 
         [0079]    binary data (1, 1) has the following three forms after being encoded: the form of  FIG. 5(   g ) is the form of the consecutive first and the second encoded binary data  1  which follow binary data  0  or binary data  1  that encoded with low level; the form of  FIG. 5(   h ) is the form of the consecutive second and the third encoded binary data  1  which follow binary data  0  or binary data  1  that encoded with low level; the form of  FIG. 5(   i ) is the form of the consecutive third and the fourth encoded binary data  1  which follow binary data  0  or binary data  1  that encoded with low level; 
         [0080]    The forms above are uniquely determined by encoding principle and initial data state. 
         [0081]    When encoding principle 2 is adopted, the data sequence diagram is substantially the same, the binary data (0, 0) is only required to be changed into binary data (1, 1), the binary data (0, 1) is changed into binary data (1, 0), the binary data (1, 0) is changed into binary data (0, 1), and the binary data (1, 1) is changed into binary data (0, 0). In this way, the binary data (1, 1), (1, 0) and (0, 1) respectively have two forms after being encoded and the binary data (0, 0) has three forms after being encoded. The specific data sequence of two binary data encoded by using the encoding principle 1 of the invention is not repeated here. 
         [0082]      FIG. 6  is a diagram illustrating an encoding example using the encoding principle  1  of the invention. The diagrams above and below thereof respectively correspond to different initial states of the first binary data, wherein the first binary data  0  in the diagram above is encoded as ‘10’ while the first binary data  0  in the diagram below is encoded as ‘01’, and if encoding proceeds like this, the coding waveforms of the diagrams above and below tend to be identical along with the proceeding of the encoding. 
         [0083]      FIG. 7  is a diagram illustrating an encoding example using the encoding principle 2 of the invention. The diagrams above and below thereof respectively correspond to different initial states of the first binary data, wherein the first binary data  0  in the diagram above is encoded as ‘11’ while the first binary data  0  in the diagram below is encoded as ‘00’, and if encoding proceeds like this, the coding waveforms of the diagrams above and below tend to be identical along with the proceeding of the encoding. 
       EMBODIMENT 2 
       [0084]    The encoding principle 3 for encoding the original binary data to be transmitted includes the following contents: 
         [0085]    3A: the length of encoded data that generated after binary data  1  and binary data  0  are encoded is the same; no jump happens to the middle phase of the binary data  1  in data symbols, a jump happens to the middle phase of the binary data  0  in data symbols, and a phase jump happens between two consecutive binary data  0 ; 
         [0086]    3B: the binary data  1  is usually expressed with high level, after two or more binary data  1  are encoded consecutively with high level, the immediate following binary data  1  is encoded with low level, and the number of the binary data  1  that encoded consecutively with high level is rerecorded; 
         [0087]    3C: the binary data  1  following the binary data  1  that encoded with low level is encoded with high level. 
         [0088]    In addition, to enhance the reliability of encoding codes and decoding codes, the following contents can be added to the encoding principle 3: 
         [0089]    3D: on the premise of meeting the 3A and the 3B, i.e. making the most of high level, no phase jump happens to the left edge of the binary data  0 , and a phase jump happens to the right edge of the binary data  0 . 
         [0090]    The encoding principle 4 for encoding the original binary data to be transmitted includes the following contents: 
         [0091]    4A: the length of encoded data that generated after binary data  1  and binary data  0  are encoded is the same; no jump happens to the middle phase of the binary data  0  in is data symbols, a jump happens to the middle phase of the binary data  1  in data symbols, and a phase jump happens between two consecutive binary data  1 ; 
         [0092]    4B: the binary data  0  is usually expressed with high level, after two or more binary data  0  are encoded consecutively with high level, the immediate following binary data  0  is encoded with low level, and the number of the binary data  0  that encoded consecutively with high level is rerecorded; 
         [0093]    4C: the binary data  0  following the binary data  0  that encoded with low level is encoded with high level. 
         [0094]    In addition, to enhance the reliability of encoding codes and decoding codes, the following contents can be added to the encoding principle 4: 
         [0095]    4D: on the premise of meeting the 4A and the 4B, i.e. making the most of high level, no phase jump happens to the left edge of the binary data  1 , and a phase jump happens to the right edge of the binary data  1 . 
         [0096]    A schematic diagram illustrating the data state relation between binary data that encoded by using the encoding principles 3 and 4 of the invention and a data sequence diagram when the encoding principles 3 and 4 of the invention are adopted are respectively the same as those when the encoding principle 1 and the encoding principle 2 are adopted, and they shall be respectively described in details. 
         [0097]      FIG. 8  is a data state transition diagram when the encoding principle 3 of the invention is adopted. As shown in  FIG. 8 , when the encoding principle 3 is adopted, the state transition method is as follows.
       When the binary data is now in a state of S 1 , i.e., the state is expressed as ‘11’       
 
         [0099]    When the binary data  1  is received: if the binary data corresponding to the current state is the first one (i.e., the previous state is non-S 1  state) of consecutive binary data  1  (encoded with high level), the state S 1  remains when another binary data  1  is received; if the binary data corresponding to the current state is the second one of consecutive binary data  1  (encoded with high level), the state is transited to S 4  when another binary is data  1  is received. That is to say, after two binary data  1  are encoded consecutively with high level, the third binary data  1  is encoded with low level, see 3B in the encoding principle 3. 
         [0100]    When the binary data  0  is received: the state is transited to S 2 , i.e., from ‘11’ to ‘10’; see 3D in the encoding principle 3.
       When the binary data is now in a state of S 2 , i.e., the state is expressed as ‘10’.       
 
         [0102]    When the binary data  1  is received, the state is transited to S 1 , see 3D in the encoding principle 3; when the binary data  0  is received, the state S 2  remains, see 3A in the encoding principle 3.
       When the binary data is now in a state of S 3 , i.e., the state is expressed as ‘01’.       
 
         [0104]    When the binary data  1  is received, the state is transited to S 1 , i.e., making the most of high level; when the binary data  0  is received, the state S 3  remains, see 3A in the encoding principle 3.
       When the binary data is now in a state of S 4 , i.e., the state is expressed as ‘00’.       
 
         [0106]    When the binary data  1  is received, the state is transited to S 1 , see 3C in the encoding principle 3; when the binary data  0  is received, the state is transited to S 3 , see 3D in the encoding principle 3. 
         [0107]    It can be seen from  FIG. 8  that there is no state transition relation between S 2  and S 3  and between S 2  and S 4 ; the state S 1  cannot be transited into state S 3 , thus the code words have certain error detecting capability after the binary data is encoded by using the encoding principle. 
         [0108]      FIG. 9  is a data sequence diagram of two binary data encoded by using the encoding principle 3 of the invention. 
         [0109]    As shown in  FIG. 9 , binary data (0, 0), (0, 1) and (1, 0) respectively have two forms after being encoded; 
         [0110]    The binary data (1, 1) has the following three forms after being encoded: the form of  FIG. 9(   g ) is the form of the consecutive first and the second encoded binary data  1  is which follow binary data  0  or binary data  1  that encoded with low level; the form of  FIG. 9(   h ) is the form of the consecutive second and the third encoded binary data  1  which follow binary data  0  or binary data  1  that encoded with low level; the form of  FIG. 9(   i ) is the form of the consecutive third and the fourth encoded binary data  1  which follow binary data  0  or binary data  1  that encoded with low level; 
         [0111]    The forms above are uniquely determined by encoding principle and the initial data state. 
         [0112]    When the encoding principle 4 is adopted, the above-mentioned data sequence diagram is substantially the same, the binary data (0, 0) is only required to be changed into binary data (1, 1), the binary data (0, 1) is changed into binary data (1, 0), the binary data (1, 0) is changed into binary data (0, 1), and the binary data (1, 1) is changed into binary data (0, 0). In this way, the binary data (1, 1), (1, 0) and (0, 1) respectively have two forms after being encoded, and the binary data (0, 0) has three forms after being encoded. The specific data sequence of two binary data encoded by using the encoding principle 4 of the invention is not repeated here. 
         [0113]      FIG. 10  is a diagram illustrating an encoding example using the encoding principle 3 of the invention. The diagrams above and below thereof respectively correspond to different initial states of the first binary data, wherein the first binary data  0  in the diagram above is encoded as ‘10’ while the first binary data  0  in the diagram below is encoded as ‘01’, and if encoding proceeds like this, the coding waveforms of the diagrams above and below tend to be identical along with the proceeding of the encoding. 
         [0114]      FIG. 11  is a diagram illustrating an encoding example using the encoding principle 4 of the invention. The diagrams above and below thereof respectively correspond to different initial states of the first binary data, wherein the first binary data  0  in the diagram above is encoded as ‘11’ while the first binary data  0  in the diagram below is encoded as ‘00’, and if encoding proceeds like this, the coding waveforms of the diagrams above and below tend to be identical along with the proceeding of the encoding. 
         [0115]    Taking the encoding principle 1 as an example, a comparative analysis shall be is performed between the encoding method of the invention and the Manchester encoding method in terms of the energy provided for a tag and the bandwidth occupied by a signal. 
         [0116]    (1) Comparison on Energy Provided for a Tag 
         [0117]    The more the number of ‘1’ after binary data is encoded, the longer the high level continues, and the more the energy provided for the tag. When the binary data is encoded by using the Manchester encoding method, the duration time of the high level and that of the low level are the same, both of which respectively account for a half. 
         [0118]    When binary data  0  is encoded, compare encoding principle 1 of the invention that is adopted with Manchester encoding method that is adopted, the duration time (length) of high level is the same; while as to binary data  1 , after being encoded according to 1B, 1C and 1D in the encoding principle 1, the duration time (length) of high level is longer than that in the Manchester encoding method. Therefore, the encoding principle 1 provided by the invention is superior to the Manchester encoding method from the aspect of the energy provided for a tag. 
         [0119]    The encoding principles 2, 3 and 4 of the invention also have the same effects. 
         [0120]    (2) Analysis on Signal Bandwidth After Encoding 
         [0121]    Refer to  FIG. 2  for symbol waveforms representing binary data  1  and binary data  0 , the symbolic expressions are assumed to be g 1 (t) and g 0 (t), the power spectrum of a random sequence formed by the encoding method of this invention is as follows: 
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         [0122]    In the expression, p denotes the transmission probability of g 1 (t), 1-p denotes the transmission probability of g 0 (t), ƒ s  denotes the speed of transmitting a symbol, and G 1 (f) and G 0 (f) respectively denote spectrum functions of g 1 (t) and g 0 (t). Wherein 
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                      
                   
                   = 
                   
                     
                       T 
                       s 
                     
                      
                     
                       [ 
                       
                         
                           sin 
                            
                           
                             ( 
                             
                               π 
                                
                               
                                   
                               
                                
                               
                                 fT 
                                 s 
                               
                             
                             ) 
                           
                         
                         
                           π 
                            
                           
                               
                           
                            
                           
                             fT 
                             s 
                           
                         
                       
                       ] 
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
             
               
                 
                   
                      
                     
                       
                         G 
                         0 
                       
                        
                       
                         ( 
                         f 
                         ) 
                       
                     
                      
                   
                   = 
                   
                     
                       
                         T 
                         s 
                       
                       2 
                     
                      
                     
                       [ 
                       
                         
                           sin 
                            
                           
                             ( 
                             
                               π 
                                
                               
                                   
                               
                                
                               f 
                                
                               
                                 
                                   T 
                                   s 
                                 
                                 2 
                               
                             
                             ) 
                           
                         
                         
                           π 
                            
                           
                               
                           
                            
                           f 
                            
                           
                             
                               T 
                               s 
                             
                             2 
                           
                         
                       
                       ] 
                     
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
         [0123]    In the expression (2) and the expression (3), T s  denotes a symbol period, and T s =1/f s . 
         [0124]    The bandwidth of a random sequence mainly depends on the spectrum function G 0 (f) or G 1 (f) of a single code element waveform, and the larger bandwidth thereof should be taken as the sequence bandwidth. The smaller the duty cycle of a time waveform is, the wider the Frequency band is. Generally, the first zero point of a spectrum is taken as the approximate bandwidth of a rectangular pulse, it is the reciprocal of the pulse width τ, i.e., Bs=1/τ. As to a non-return-to-zero pulse, if τ=Ts, then Bs=fs; as to a half-duty-cycle return-to-zero pulse, if τ=Ts/2, then Bs=1/τ=2 fs. 
         [0125]    It is clear that when the encoding principle 1 of the invention is adopted, after binary data  1  and binary data  0  are encoded, one is a non-return-to-zero pulse, and the other one is a half-duty-cycle return-to-zero pulse, thus the bandwidth occupied by a signal after encoding is 2 fs; when the Manchester encoding method is adopted, binary data  1  and binary data  0  are both half-duty-cycle return-to-zero pulses after being encoded, thus the bandwidth occupied by a signal after encoding is also 2 fs. 
         [0126]    Therefore, under the same data rate, the bandwidth occupied by a signal after encoding with encoding principle 1 of the invention is the same as that occupied by a signal after encoding with Manchester encoding method. 
         [0127]    The encoding principles 2, 3 and 4 of the invention also have the same conclusions, thus, it is unnecessary to give more details. 
         [0128]    From the analysis above, if the encoding method of the invention is applied to a link from a reader to a tag in RFID system, compare with the Manchester encoding method, more energy can be provided for a tag on the premise of the bandwidth occupied by a signal which is unchanged. 
         [0129]    The above-mentioned are only preferable embodiments rather than limitations to the protection scope of the invention. To the skilled in the art, all modifications and changes based on the invention should not depart from the protection scope of the attendant claims of the invention. 
       INDUSTRIAL APPLICABILITY 
       [0130]    Compared with the Manchester encoding method, the encoding method of the invention applied to a link from a reader to a tag in RFID system can provide more energy for a tag on the premise of the bandwidth occupied by a signal which is unchanged, thus having great industrial applicability.