METHOD FOR ADJUSTING THE TRANSMISSION TIME OF THE CARRIER WAVE IN AN RFID READER AND READER IMPLEMENTING THE METHOD

Technical field

The present invention relates to the technical field of radio frequency identification (RFID) and, particularly, to the method for adjusting the transmission time of a continuous wave by a reader and the reader for implementing the method.

Background art

In recent years, RFID technology has attracted more and more attention. Since hundreds of objects can be identified instantly by RFID technology, RFID technology can be applied to various application scenarios, such as logistics or manufacturing, etc. However, whatever the application scenario is, processing efficiency is always one of the important criteria for evaluating the performance of an RFID system.

According to the provisions of the protocol, EPC Radio- Frequency Identity Protocols Class-1 Generation-2 UHF RFID Protocol for Communications at 860MHz-960MHz Version 1.0.9, established by the worldwide EPC organization, EPC global, in an RFID system, when the distance between a tag and a reader is within the reading range of the reader, the reader will initiate a process to identify the identificatin (ID) of the tag. After having successfully identified the ID of the tag, the tag will enter into an open or secure state, and at this moment, the reader may send a corresponding command to the tag which is in the Open/Secure state to instruct it to perform a corresponding operation. For example, the reader can send a write command, a kill command, a lock command, a block-write command or a block-erase command to the tag which is in the Open/Secure state to instruct it to perform the corresponding write, kill, lock, block-write or block-erase operation. After having received one of the above-mentioned commands from the reader, the tag in the Open/Secure state will first perform a cyclic redundancy check (CRC) to the received command, and if the check is successful, then the tag performs the operation corresponding to the received instruction and feeds back a response to the reader; otherwise, if the check fails, then it discards the received command and waits for a new command from the reader. Correspondingly, after having sent a command, the reader will further send a continuous wave (CW) to the tag in the Open/Secure state to provide energy needed by the tag to perform the corresponding operation and at the same time wait for a response from the tag. According to the provisions of the protocol, the longest time for a reader to wait for a response from a tag is 20 millisecond (ms) , that is, if the reader receives a response from the tag within 20 ms after it has sent a command, then it stops sending the CW after having received the response from the tag; otherwise, if the reader does not receive a response from the tag within 20 ms after it has sent the command, then it stops sending the CW immediately. After having stopped sending the CW, the reader may go on to send a new command to the tag in the Open/Secure state. For the sake of ease of description, the time period from the moment when the reader sends out a command to the moment when the reader receives a response from the tag can be referred to as the tag's response time T _REPLY . It can be found by statistics that, if both the reader and the tag operate at the highest transmission rate, the T _REPLY is approximately 1.5 ms, which is far less than 20 ms; while even if the reader and the tag both have the lowest transmission rate, the T _REPLY is approximately 7 ms, which is still far less than 20 ms .

It can be seen from the above-mentioned performance process that, after having sent out a command, if the reader does not receive a response from the tag, then it needs to wait for a period of 20 ms then to send out a new instruction, that is to say, after having sent out a command, the reader needs to send a CW up to 20 ms . Furthermore, in an RFID system, situations where a reader cannot correctly receive a response from a tag are still quite common. Since the response time of a tag is far less than 20 ms in normal situations, it causes a reader to wait for too long when it cannot receive a response from the tag, which seriously affects the processing efficiency of the RFID system.

The object of the invention is to solve the above- mentioned problem. Embodiments of the present invention provide a method for adjusting the transmission time of a CW and a reader for implementing the method, so as to reduce the reader' s waiting time when it cannot receive a response from a tag and improve the processing efficiency of an RFID system.

Said method for adjusting the transmission time of a CW of the embodiments of the present invention comprises:

setting an initial value for a response waiting time;

sending a CW to a tag after having sent out a command to the tag and waiting for a response from the tag;

judging whether the response from the tag is received within the response waiting time,

if the response from the tag is received within the response waiting time, then stopping sending the CW and adjusting the response waiting time; and

if the response from the tag is still not received beyond the response waiting time, then stopping sending the CW.

In this case, setting an initial value for a response waiting time comprises: setting the initial value of the response waiting time to an arbitrary value, which should be generally less than or equal to the maximum response waiting time (20 ms) provided in the protocol.

The above-mentioned command is a command used for instructing the tag to modify data and a flag bit in the tag, including a write command, a kill command, a lock command, a block-write command and a block-erase command.

The above-mentioned adjusting the response waiting time comprises: recording the time from sending out the command to receiving the response from the tag, and adjusting said response waiting time according to the recorded time; or adjusting the response waiting time according to the inherent information in the tag and/or the statistic information of the tag's operations. In this case, the inherent information in the tag is the information determined during the tag' s manufacturing process, which comprises at least the type and the serial number of the tag, the model number and manufacturer of the tag's chip; and the statistic information of the tag's operations is the information obtained by statistics during the process when the tag is performing various operations, which comprises at least the number of times of receiving the tag' s response, the number of times for timeout, and the time recorded by the reader from sending out a command to receiving a response from the tag.

Particularly speaking, the reader can be adjusted for the response waiting time according to the following equation: T _out () = aT _0Ut (n-\) + (\-a)T _s , wherein, T _out (n-\) represents the response waiting time before the adjustment, and T _out {n) represents the response waiting time after the adjustment, T _s is the recorded time from sending out the command to receiving the response from the tag, and a is an adjustment factor with a value range of [0, 1] .

After said step of stopping sending the CW if the response from the tag is still not received beyond the response waiting time, it further comprises: adjusting the response waiting time . Particularly speaking, the response waiting time can be adjusted according to the following equation:

T _out (n) = min(T _out (n -1) x 2, 20ms) , wherein, T _out {n-X) represents the response waiting time before the adjustment, and T _out {n) represents the response waiting time after the adjustment.

Alternatively, the response waiting time can be adjusted according to the following equation: T _out (n) = min(T _out (n - 1) + 1,20ms) , wherein, T _out {n—\) represents the response waiting time before the adjustment, T _out {n) represents the response waiting time after the adjustment, and λ is a pre-set adjustment step length λ .

Said reader in the embodiments of the present invention comprises :

a response waiting time setting unit for pre-setting an initial value for a response waiting time;

a command processing unit for sending out a command to a tag and sending a CW to the tag after having sent out the command, waiting for a response from the tag, if the response from the tag is received by the command processing unit within the response waiting time, then triggering a response waiting time adjusting unit to adjust the response waiting time; and if the response from the tag is not received within the response waiting time, then stopping sending the CW; and

a response waiting time adjusting unit for adjusting the response waiting time.

The above-mentioned command processing unit is further used for triggering the response waiting time adjusting unit to adjust the response waiting time when the response from the tag is not received within the response waiting time.

The above-mentioned response waiting time adjusting unit comprises: a response waiting time recording module for recording the time from sending out the command by the command processing unit to receiving the response from the tag; and a response waiting time adjusting module for adjusting the response waiting time according to the time recorded by the response time recording module.

It can be seen from the above-mentioned method and reader for adjusting the transmission time of a CW that, in the embodiments of the present invention, the longest time for the reader to wait for a response from a tag is the response waiting time, which is far less than 20 ms, therefore, the reader can find a command failure early, so as to send a new command to the tag as soon as possible. It can be seen from this that said method of the embodiments of the present invention can significantly improve the processing efficiency of an RFID system, thus improving the performance of the RFID system.

Brief description of the accompanying drawings

Fig. 1 is a flow chart of said method for adjusting the transmission time of a CW by a reader in the embodiments of the present invention; and

Fig. 2 is a schematic diagram of the internal structure of said reader in the embodiments of the present invention.

Exemplary embodiments

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in detail hereinbelow in conjunction with the accompanying drawings and particular embodiments.

The embodiments of the present invention provide a method for adjusting the transmission time of a CW by a reader, with its processing procedure being illustrated in Fig. 1. It mainly comprises :

Step 101: set an initial value for the response waiting time . In this embodiment, the response waiting time refers to the longest time for the reader to wait for a response from a tag, and if the reader does not receive the response from the tag beyond the corresponding waiting time after it has sent out a command, then the reader will still stop sending the CW and prepare to send a new command to the tag.

It needs to be pointed out that, in this step, the user can set the initial value of the response waiting time to an arbitrary value, which should be generally less than or equal to the maximum response waiting time 20 ms as provided for in the protocol. For example, the user can designate the initial value of the response waiting time according to the inherent information in the tag (for example, the information determined in the tag's manufacturing process, such as the type and the serial number of the tag, the model number and manufacturer of the tag's chip and so on) or the past experiences, or directly set the initial value of the response waiting time to the maximum value specified in the RFID protocol, i.e. 20 ms .

Step 102: send a CW to a tag after a command has been sent out to it and at the same time wait for a response from the tag .

In this embodiment, the above-mentioned tag should be a tag which is in an Open/Secure state; and the above-mentioned command sent by the reader to the tag is used for instructing the tag to modify data and a flag bit in it, such as a write command, a kill command, a lock command, a block-write command or a block-erase command, etc.

As mentioned above, in an RFID system, when the distance between a tag and a reader is less than the tag reading range of the reader, the reader will start a process for identifying the tag's ID. After having successfully identified the ID of the tag, the tag will enter an Open/Secure state, and at this moment, the reader may send a corresponding instruction to the tag in the Open/Secure state to instruct it to perform the corresponding operation. Among these commands, part of them are used for instructing the tag to modify the data and the flag bit in it, including a write command, a kill command, a lock command, a block-write command and a block-erase command, etc., and the reader will continue to send a CW to the tag and wait for its response after having sent out the above-mentioned write, kill, lock, block-write or block-erase command. According to the provisions of the current RFID protocol, after having sent out the above-mentioned command, the reader will send a CW to the tag for up to 20 ms, that is, the longest time for the reader to wait for a response from the tag is 20 ms .

Step 103: judge whether the response from the tag is received within the response waiting time, if the response from the tag is received within the response waiting time, then step 104 is performed; and if the response from the tag is still not received beyond the response waiting time, then step 106 is performed;

Step 104: stop sending the CW;

Step 105: adjust the response waiting time;

in this step, various methods can be employed to re ^¬ evaluate the response waiting time. For example, the reader can adjust the response waiting time according to at least one piece of the inherent information in the tag and/or the statistic information of the tag's operations. In this case, the inherent information in the tag includes the information determined in the tag's manufacturing process, such as the type and the serial number of the tag, the model number and manufacturer of the tag's chip and so on; the statistic information of the tag's operations includes: the information obtained by statistics during the process when the tag is performing various operations, such as the number of times of receiving the tag's response, the number of times of timeout (which means the number of times of not receiving the tag' s response) , and the time recorded by the reader from sending out a command to receiving a response from the tag, etc.

During the process for adjusting the response waiting time, the reader can either increase the above-mentioned response waiting time or reduce it, and can even keep it constant in an extreme situation.

Preferably, the embodiments of the present invention provide a method for adjusting the response waiting time, which method comprises: after having stopped sending the CW, the reader recording the time from sending out the command to receiving the response from the tag and adjusting the response waiting time according to the recorded time.

The method for adjusting the response waiting time by the reader according to the recorded time will be described hereinbelow by way of examples. In this example, assuming that T _out {n—\) represents the response waiting time before the adjustment, T _out {n) represents the response waiting time after the adjustment, T _s is the time recorded by the reader from sending out the command to receiving the response from the tag, then the response waiting time T _out {n) after the adjustment can be obtained by calculating according to the following equation

(1) :

T _out (n) = aT _out (n-\) + (\-a)T _s ( 1 )

wherein, a is an adjustment factor with a value range of [0, 1] .

It needs to be pointed out that, in this example, the initial value of the response waiting time should be generally set to less than or equal to the longest waiting time (20 ms) as provided for in the protocol. After having adjusted the response waiting time, the reader can return to step 102 or end this access and start a new round of read/write operations.

Step 106: stop sending the CW.

In this step, the reader can also further adjust the response waiting time after having stopped sending the CW. Since the reason for the reader not to receive a response from the tag may be due to the fact that the response waiting time is too short, the adjustment performed in this step is generally for increasing the response waiting time.

For example, in this step, the reader can adjust the response waiting time according to the following equation (2), that is, taking the minimum value between twice the response waiting time before the adjustment and 20 ms . In which the operator min[] represents the operation of taking the minimum value .

r _∞ ) = min[r _∞ -l) x 2, 20ms] (2 )

Also for example, an adjusting step length λ can be pre ^¬ set, then in this step, the reader can adjust the response waiting time according to the following equation (3) , that is, taking the minimum value between the sum of the response waiting time before the adjustment and the adjustment step length and 20 ms . In which the operator min[] represents the operation of taking the minimum value.

T _out (n) = mm[T _out (n -l) + A, 20ms] (3)

After having performed step 106, the reader can return to step 102 or end this access and start a new round of read/write operations .

According to the provisions of the RFID protocol, there are two types of responses returned by a tag to a reader: one is an operation success response returned by the tag after it has performed the operation successfully, and the other is an operation failure response returned by the tag with an error code after it has failed to perform the operation. In the embodiments of the present invention, the reader can record only the response time of the responses for successful operations but not the response time of the responses for failed operations. In this way, in the above-mentioned step 103, it further needs to judge whether a response for a successful operation from the tag is received, if it is yes, then step 104 is performed; and if a response for a failed operation is received from the tag, then step 106 is performed.

Besides the above-mentioned method for adjusting the transmission time of a CW, the embodiments of the present invention further provide a reader for implementing the method. The internal structure of this reader is illustrated in Fig. 2, which mainly includes:

a response waiting time setting unit for pre-setting an initial value for a response waiting time;

a command processing unit for sending out a command to a tag in the Open/Secure state, sending a CW to the tag after having sent out the command and waiting for a response from the tag, if the response from the tag is received by the command processing unit within the response waiting time, then triggering a response waiting time adjusting unit to adjust the response waiting time; and if the response from the tag is not received within the response waiting time, then stopping sending the CW; and

a response waiting time adjusting unit for adjusting the response waiting time.

Furthermore, if the command processing unit does not receive the response from the tag within the response waiting time, then it can also trigger the response waiting time adjusting unit to adjust the response waiting time. The above-mentioned response waiting time adjusting unit comprises :

a response time recording module for recording the time from sending out the command by the command processing unit to receiving the response from the tag; and

a response waiting time adjusting module for adjusting the response waiting time according to the time recorded by the response waiting time recording module.

As mentioned above, if the command processing unit receives a response from the tag within the response waiting time, then the response waiting time adjusting module can adjust the response waiting time according to the above- mentioned equation (1); while if the command processing unit does not receive a response from the tag within the response waiting time, then the response waiting time adjusting module can adjust the response waiting time according to the above- mentioned equation (2) or (3) .

It can be seen from the above-mentioned evaluation method that the response waiting time obtained by the evaluation is less than 20 ms . It is found by statistics that the response time from sending out a command to receiving a response from the tag is generally related to the factors such as the transmitting power of the reader and the distance between the reader and the tag, which is generally less than 8 ms, therefore, in this embodiment the response waiting time obtained by evaluating the response time will be far less than 20 ms .

It can be seen from the above-mentioned method and reader for adjusting the transmission time of a CW that, in the embodiments of the present invention, the longest time for the reader to wait for a response from the tag is the response waiting time, which is far less than 20 ms, therefore, the reader can find a command failure early so as to send a new command to the tag as early as possible. It can be seen from this that said method of the embodiments of the present invention can significantly improve the processing efficiency of an RFID system, so as to improve the performance of the RFID system.

Furthermore, said method of the embodiments of the present invention only needs to perform slight modifications to a reader, while it does not need to make any change to a tag, therefore it is easily implemented in an RFID system.

What are described above are merely preferred embodiments of the present invention, and are not intended to limit the present invention, and any modification, equivalent substitution and improvement made within the spirit and principle of the present invention should be contained in the protective scope of the present invention.