Abstract:
The idea on which the present invention is based is that transmitting and receiving data by an antenna or an antenna array may be performed more efficiently by analyzing protocol data of a transmit protocol, which control the data flow between a transmitting and a receiving device, by a controller, and by individually setting transmission times and receiving times on the basis of this analysis, or by specifically selecting a single antenna from an antenna array.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of copending International Application No. PCT/EP2006/002134, filed Mar. 8, 2006, which designated the United States and was not published in English. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method for antenna selection such as is applied in the area of radio/high frequency identification systems. 
     2. Description of the Related Art 
     In many technical applications, it is useful to control the active phase of an antenna. Particularly in the area of radio/high frequency identification systems, i.e. systems for identifying objects and living organisms by RFID, or transponder, technologies, it is often necessary, for example, to achieve a selection result by multiple transmitting and/or receiving. The number of such RFID systems has significantly increased over the last few years; they serve for a contactless identification of objects or products, for example. 
     The transmitting frequencies of those systems are mainly in the ISM frequency bands which may be used by industry, science and medical technology without a license. In this context, the special feature of transponder technology is that the transponders and/or receivers, which are usually passive, draw the energy which is necessary for their function from the field used for transmitting and receiving data. Depending on the function principle, one distinguishes between electromagnetic and inductive systems, both systems using different kinds of antennas for the efficient coupling of a transmitter and a receiver. In inductive coupling, for example, in a simple example, an antenna will comprise a conductor loop, wherein the voltage induced in the conductor loop by a magnetic field present throughout the loop may be evaluated as a signal. Since the magnitude of the induced voltage depends on the magnetic flux present throughout the entire conductor loop, it is necessary, for a maximum coupling of the transponder to the magnetic field, that the area normal of the area formed by the conductor loop be parallel to the field direction of the magnetic field. If the transmitter generates the magnetic field also by a coil, the area normals of the transmitting coil and the receiving coil of the transponder are ideally parallel with each other to achieve the best possible coupling between the transmitter and the receiver. In the worst case in which the area normal of the transmitting coil is orthogonal to the area normal of the receiving coil, no direct data transmission is possible anymore. In most cases, RFID systems work with only one antenna, which is the reason why, due to the fact described above, a selection is possible only in one space direction. There are application areas, however, in which, due to the orientation of one or more transponders, a single antenna is not sufficient. In this context, one consider, for example, a pallet full of products to be sensed, which are arranged in different orientations on the pallet. In such cases, in inductive systems, for example, the shape of the antenna may be altered by employing special spatially-shaped wire windings. Furthermore, several antennas which are spatially separated and arranged in different orientations with respect to one another may be employed, wherein switching between those is performed according to a predetermined established switching pattern. 
     By established switching patterns in switching between several antennas, only antenna frame times which are the time intervals in which an antenna is active having a fixed period or fixed time frame, may be adjusted, wherein the antenna frame time must be larger than the duration of the longest transmitting and/or receiving operation to be expected. Thereby, long read/write times develop during repeating read/write operations by means of different antennas. If the illumination of four space directions by four antennas is necessary, for example, a single read/write operation will need four times the transmission time of the read/write operation of maximum duration, irrespectively of how long the transmission time of the data to be transmitted actually is. 
     SUMMARY OF THE INVENTION 
     According to an embodiment, a method for determining an active phase of an antenna during a transmitting or receiving operation may have the steps of receiving protocol data of a transmit protocol controlling the data flow between a transmitting device and a receiving device, of evaluating the protocol data by control means to determine a time interval for the duration of the active phase of the antenna, and of controlling the active phase of the antenna based on the evaluation of the protocol data. 
     An embodiment may have a computer program having a program code for executing the above-mentioned method when the program runs on a computer. 
     According to another embodiment, a device for determining an active phase of an antenna, during a transmitting or receiving operation, may have a receiving device for receiving protocol data of a transmit protocol controlling the data flow between a transmitting device and a receiving device, control means for evaluating the protocol data which is implemented to be able to determine the time interval for the duration of the active phase of the antenna, and a device for controlling the active phase of the antenna based on the evaluation of the protocol data. 
     The basic idea of an embodiment of the present invention is that during a transmitting or receiving operation, an active phase of an antenna can be controlled by analyzing the protocol data of a transmit protocol controlling the data flow and by deriving therefrom the transmit duration to be expected, or by dynamically adjusting the current transmitting/receiving duration as reaction to events occurring during the communication. Thereby, the actual transmitting times can be used for controlling an antenna, and it is possible to increase the efficiency of data transmission in comparison to prior methods operating with a pre-set transmitting duration per antenna. 
     In a particular embodiment of the present invention, the data transmit protocol controlling the data flow between a transponder and a read/write device and/or an identification unit is evaluated by control means, or a control module, and is used to calculate the necessary duration of an active phase of an antenna and/or the frame time, and to select a suitable active antenna from a plurality of antennas. In this context, the payload data to be transmitted are transmitted by an external device, which may be a PC, for example, and are independent of the protocol data to be evaluated. For the purpose of evaluating the protocol information, the protocol information extracted in the read/write device are forwarded to the protocol-dependent control module. Examples of protocol information transmitted to the control module include a command code and a response code. The command code may be a write instruction or a read instruction, for example. In a write operation, the data to be written are additionally transmitted from the read/write device to the transponder. Thereby, the transmitting duration and/or request frame of a write command is prolonged in comparison to the request frame of a read command, so the necessitated turn-on time of an antenna can be calculated on the basis of this information. In the case of a response of the transponder, similar considerations may be made. The response code contains status fields, so-called flags, indicating whether errors have occurred during the transmission of the information. This may cause the control means to repeat the transmission and/or, after a predetermined maximum duration, to terminate the communication or to try again to transmit via another antenna. In the case of collisions of data packets, the frame time, for example, may be prolonged, and thus, dynamically adjusted, if additional time (time slots) is needed for the communication. 
     By the flexible determination of the antenna frame time and the possibility of antenna selection described above, different special modes describing the performance of the control unit can be derived for certain cases of applications. For example, apart from the usual identification, a secure identification may be necessitated, the information of several read operations of different antennas being evaluated in the secure identification, in contrast to the usual identification. Furthermore, a localization mode in which typically all antennas are used may be implemented, their turn-on duration and turn-on order being controlled by the control unit based on the information of the transmit protocol, so that a statement concerning the location at which a transponder is present may be made from the protocol evaluation. 
     In a further embodiment of the present invention, the method is implemented on a programmable FPGA chip. In this context, the control means obtains, from the read/write device, the command code and the response code from which, among other things, the start time and the end time of a data packet to be transmitted are determined. Furthermore, the FPGA structure includes means to parallelize the protocol data provided in serial form by the read/write device. Apart from this, the information indicating whether there was a collision of several packets during the last data transmission attempt, so that the current transmitting/receiving time must be prolonged, and indicating whether the possible multiple transmission of a data packet has returned the same respective response is forwarded by the read device to the control unit. Additionally, user inputs to the control unit are possible, such as the number of the antennas available, an antenna number, a frame time or the selection of an operational mode. Additionally, an external clock may be predetermined for the FPGA chip which is processed by a clock generation unit which in turn synchronizes the entire operations arising on the chip. After calculating the frame time and the antenna to be selected, the antenna number and the frame time are forwarded in an encoded form to an external decoder driving the antennas of an antenna array with the decoded information. 
     Other features, elements, processes, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the present invention with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present invention will be detailed subsequently referring to the appended drawings, in which: 
         FIG. 1  is a schematic flow diagram according to an embodiment of the present invention. 
         FIG. 2  is a block diagram for the realization of the method of  FIG. 1  on an FPGA structure. 
         FIG. 3  shows the timelines of selected signals as they occur on the FPGA structure of  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIG. 1  shows a control module or control means  10 , containing a control unit  10   a , an association unit  10   b , a setting unit  10   c , and an additional functional unit  10   d  and implementing the inventive method, a transponder  12 , an antenna field  14  containing a “1-from-N-decoder”  14   a , a read/write device  16  and a personal computer, or PC,  18 . 
     The functional units  10   a - 10   d  located within the control module  10  are connected with one another through data lines for the purpose of data exchange within the control module  10 . For the purpose of data exchange, the PC  18  is, via a first data connection  20 , connected to a read/write device  16  which in turn is connected to the control module  10  via a second data connection  22 . Apart from that the read/write device  16  is connected with the antenna field  14  via a connection  24 , both data and the feed energy of the transponder being transmitted from the read/write device to the antenna field  14  via the connection  24 . An antenna of the antenna field  14  establishes a connection  26  to the transponder  12  via the electromagnetic field emitted by it, both data and the feed energy for the transponder being transferred via this connection. The control module  10  is connected to the antenna field  14  via a data line  28  to control the antennas of the antenna field  14 . Via a user interface  30 , the user may additionally pass predetermined basic settings to the control module  10 . 
     The method illustrated allows the protocol-dependent control and selection of antennas and the calculation of the turn-on time of these antennas by information gained from the data transmit protocol controlling the data flow between the transponder  12  and the read/write device  16 . Payload data to be transmitted are transmitted from the PC  18  via the data connection  12  to the read/write device  16 , or a request for reading data from the transponder  12  is transmitted to the read/write device  16 . The content of the payload data itself does not play a role in the method, so that those are not further considered. The read/write device  16  combines the payload data in a suitable manner with the protocol data, which control the data flow, of the data transmit protocol used, such as ISO/IEC 15693. To enable controlling the antenna turn-on times, the protocol information extracted from the read/write device  16  is, together with further information generated in the read/write device  16 , passed on to the control module  10  via the connection  22 . The read/write device  16  transmits the data to the controllable antenna field  14  via the connection  24 , the data being transmitted to the transponder  12  by the currently active antenna or being read by the transponder. In this context, it is to be noted that the transponder  12  draws the energy it needs for functioning from the data-transmitting field itself, and, thus, this energy is in the end supplied by the read/write device  16 . The time frames for the currently selected antenna are, together with the user/basic settings applied upon the control module  10  via the user interface  30  and stored in the setting unit  10   c , identified by the control unit  10   a . In the association unit  10   b , the information about the antenna to be selected is combined with the calculated time frame and transmitted to the antenna field  14  via the data line  28 . This combined information is reconstructed by the “1-from-N-decoder”  14 , and the antenna determined by the control unit  10   a  is selected for the length of the necessitated time frame. The additional functional unit  10   d  of the control module  10  may implement additional functionalities, so a clock generator, for example, may be necessitated within the control module. 
     In this context, for calculating the time frames, the command code of the data transfer protocol substantially determining the structure of the request and response frames is evaluated by the control unit  10   a . Also, the response code substantially giving information on transfer errors is evaluated. A command instruction may be a write or a read command. If the command “write” is selected, for example, the data to be written will additionally be transmitted to the transponder. Thereby, the request frame, or request, of a write command is prolonged in comparison to the request frame for a read command which does not yet contain the data to be read. Similar considerations are also made concerning the response of the transponder, response. For example, status fields, so-called “flags”, are evaluated to see whether errors, or collisions, have occurred during the transmission of the information. This would imply, for example, repeating the transmission, terminating the communication after a determined maximum duration, trying again to communicate via another antenna, or, in the case of collisions, prolonging the current time frame. By the adjustment of the turn-on duration and/or the frame length of an antenna to the duration of the data actually waiting for transmission, a superfluous turn-on time of an antenna is avoided. If multiple transmitting is necessitated, the necessitated time expenditure will thereby be in part considerably reduced in comparison to conventional methods. This particularly applies if transmitting by means of several antennas is necessary for achieving a successful read or write operation, wherein it is additionally beneficial in this context that the determination of the antenna to be used is also protocol-dependent. 
     The possibility to derive special modes which may be mapped onto determined cases of applications results from this intelligent and flexible controllability of the antenna field  14  and from the possibility of antenna selection by the control module  10 . For example, a secure identification can be guaranteed by redundancy of the identification by means of different antennas. Thus, the difference between the usual and the secure identification is that with the secure identification, the information of several read operations of different antennas is evaluated and compared, and it is decided afterwards whether further antennas will be involved in the read operation, whose time frames are then in turn calculated from the transfer protocol. If several antennas, whose turn-on time frame is controlled by the control module, are deployed, a localization of the transponder may also be performed. As a rule, all antennas are used in the localization mode, and their turn-on time is in turn controlled by the information of the transmit protocol. 
       FIG. 2  shows for a control module structure how the method of the protocol-controlled antenna selection may be realized on an FPGA chip whose functional units are schematically illustrated. In this context, the FPGA chip includes the control unit  40 , a clock generation unit  42 , an adder  44 , a first counter  46 , a second counter  48 , a third counter  50 , a fourth counter  52 , a setting unit  54 , an association unit  56 , an SOF/EOF decoder  58  and a parallelization device  60 . 
     The clock generation unit  42  comprises a plurality of outputs connected to inputs of all further functional units to enable a clock-synchronous operation of all functional units. Additionally, an externally generated clock may be predetermined for the clock generation unit  42  via a clock input  62 , and a clock mode may be selected by the control unit  40 , for which purpose it is connected to 2 inputs of the clock generation unit  42  via lines  64  and  66 . The FPGA structure is connected to the read/write device  16  via a data interface  68  to exchange data and control signals with the read device. A user interface  70  is connected to inputs of the control unit  40  to enable user inputs. Via a data connection  72 , the control unit  40  is connected to the setting unit  54  in which the basis settings of the system parameters, such as the number of the antennas, are stored. The control unit  40  is connected to each of the counters  46 ,  48 ,  50  and  52  via data lines  74 , the number to be counted by the counter being present at an input “N” of each counter, an input “start” initiating the start of the counting operation, and an input “reset” resetting the number output at the outputs of the counters. An output of the counters  46 ,  48  and  50  is connected to an input of the adder  44 , respectively, an output of the counters  46 ,  48 ,  50  and  52  is connected to the control unit  40 , respectively, and a first output of counter  52  is connected to an input of the association unit  56 . The adder  44  is connected to a second input of the association unit  56 , and the control unit  40  is connected to a third input of the association unit  56  via a line  76 . An output  78  of the association unit  56  is connected to an input of a 1-from-N-decoder  80  outside the FPGA structure. 
     The clock generation unit  42  serves for clock generation, clock division and clock synchronization. The core of the control module of  FIG. 2  is formed by the control unit  40  calculating the turn-on time, or the frame time, of the antennas due to incoming protocol information. For calculation of the frame times and selection of the antennas, the protocol information, further data of the read device  16  and user settings are present at the control unit. The SOF/EOF decoder  58  determines the beginning, or the end, of the data transmit protocol, i.e. the beginning of a data packet, the “start of frame” SOF, and the end of a data packet, the “end of frame” EOF. Additionally, the serial information signals, or protocol information, may be converted by the parallelization device  60  into parallel information for further processing. 
     Examples of the information used by the read device  16  are the signals SOF and EOF and the command code, the response code, the collision status, and a comparison of the results. Via a user interface  70 , a user may continue to define an operational mode, an antenna number, a number of antennas, a start bit and a frame time, for example. 
     The control unit  40  also transmits diverse information and signals to the read device  16  to thereby initiate control operations of the read device, such as signals for a frame start bit indicating the beginning of a new antenna frame and signals indicating switching to the next antenna. 
     From the signals made available to it by the read device  16  and the information input via the user interface  70 , the control unit  40  calculates the control signals for the counters  46 ,  48 ,  50  and  52  building up different portions of the transmitting frames, respectively, and forwarding those to the adder  44 . The adder connects the single frame portions to a total frame time for the antenna. Splitting the total frame time into multiple single portions is necessary since, apart from various reaction portions, also protective intervals are needed. These accrue, for example, due to the fact that the transponder takes the energy needed for its function from the electromagnetic wave transmitting the data themselves. Therefore, the transponder must be exposed to the turned-on antenna field over a definite time of energy collection until it is fully functional, which may be ensured by means of a single frame portion from the counter  46 , for example. A protective interval after the transmission of the actual data may become necessary, for example, if another antenna is to be used after transmission of the data. 
     The association unit  56  combines the antenna number calculated by the control unit and transmitted to the association unit by means of the signal line  76  with the antenna frame time calculated by the adder  44  and directs the generated signals to the 1-from-N decoder  80 . There, these signals are there decoded and used for the excitation of the single antennas of the connected antenna field. 
       FIG. 3  shows the signals of the control module structure of  FIG. 2 , which are crucial for generating an antenna frame. In this context, time is plotted on the x-axis in random units. Signal  90  is the clock signal generated by the clock generation unit  42 , and all other signals are synchronized with the clock. It is the signals described on the basis of  FIG. 2  controlling the counters, “n, start” and “reset”, and generated by the control unit  40  for the counters  46 ,  48  and  50  that are illustrated. Additionally, the signal “count” indicates the numbers output at the outputs of the counters, respectively. A signal  92  shows the signal present at the output of the adder  44 , and a signal  94  indicates the number of the antenna calculated by the control unit  40 , as it is present at the input of the association unit  56  via the line  76 . A signal  96  describes the number output at the output of the association unit  56 . 
     As can be seen in  FIG. 3 , a first frame portion with a length of five clock cycles is calculated by the control unit  40  at time  100 , and with a starting signal  102 , the counter  46  begins, from zero and with each clock cycle, to increment the number output at its output until it is reset with a signal  106 . At time  110 , a second frame portion of a length of five clock cycles is calculated for the counter  48  by the control unit  40 . In the same way as described above for the counter  46 , the counter  48  begins to increment the number at its output. At time  120 , the control unit  40  calculates a third frame portion counted up by the counter  50  at its output. The adder  44  adds the number sequences present at its inputs, so that the signal is active at its output altogether over 15 complete clock cycles. The antenna number  94  determined by the control unit  40  is combined with the output signal of the adder  44  by the association unit  56 , so that the 1-from-N decoder  80  obtains, altogether over 15 complete clock cycles, the number of the selected antenna as input signal  96 . 
     Although the invention has been discussed herein on the basis of  FIG. 1  and  FIG. 2  for the application to a transponder read/write device, it is applicable to any data transmitting technology conceivable, in which transmitting and receiving antennas are employed, such as the Wireless Lan technology. In particular, each data transmit protocol instead of the ISO/IEC 15693 protocol exemplary quoted may be used by the control module  40  for analysis to control the antenna field  14 . Also, the protocol parameters used for the analysis, as described on the basis of  FIG. 1  and  FIG. 2 , are not established. Apart from this, all further information which can be extracted from the transmit protocol may be used for controlling the antenna field  14 . In addition, by controlling the antenna field  14  by setting certain operational modes for the control module  40 , an antenna may be pre-selected by user inputs, or the timeline of the turn-on point of different antennas may be determined on the basis of a predetermined process plan. The antenna frame times, too, may be set to a fixed value by a user input, or may be varied by a predetermined timeline. Also, it is not absolutely necessary that the antennas of the antenna field  14 , which are controlled by the control module  14  and which are spatially arranged mounted in a predetermined arrangement, for example, have the same frequency domain. 
     The functional blocks  10 ,  14  and  16  shown in  FIG. 1  may also be included in larger functional blocks, or may be split up in a different manner. In particular, any combinations may be formed from the functional blocks  10 ,  14  and  16  to include those within a single device, for example. In this context, the control module  10  and the read/write device  16 , for example, may be included within a single device, and the inclusion of the read/write device  16  and the antenna field  14  or the antenna field  14  and the control module  10  within a single device is also possible. 
     It is not necessary for the method to be realized on an FPGA structure, as is shown in  FIG. 2 , and any other execution forms of the method are conceivable, such as the realization in an ASIC or in a microcontroller, for which purpose the functional blocks shown in  FIG. 2  may be correspondingly adjusted. The clock generation unit  42  shown in  FIG. 2  serves for the clock generation and synchronization of all components, and optionally, it may be controlled by an external clock, it may generate the clock itself, it may use, by division, a present clock for synchronization, or the clock synchronization may be performed in a different manner. Coding of association unit  56  encoding the length of the antenna frame to be used and the antenna number together into one signal may be realized in any manner different from that shown in  FIG. 3 . Accordingly, any alternative execution form which is capable of controlling a field of antennas is conceivable for the 1-from-N decoder  80 ; for example, this functional unit may be integrated in the FPGA structure. 
     In a further embodiment of the present invention, the invention serves for the generation of protocol-dependent time frames for controlling antennas of an antenna field. In this process, the information needed for the generation of the respective time frames is derived from the protocol between the read/write device and the transponder, but it may also be predetermined by an algorithm which can be set or be set by the hand. 
     A further embodiment serves for generating the antenna number, the order of the antennas selected being also generated by the protocol in this process but being also capable of being predetermined by an algorithm or of being set by the hand, as with the calculation of the frame time. 
     A further embodiment serves for combining of the calculated frame times with a selected antenna. 
     Depending on the circumstances, the inventive method for protocol-controlled antenna selection may be implemented in hardware or software. The implementation may also be on a digital storage medium, in particular, on a disc or a CD with electronically readable control signals which may cooperate with a programmable computer system such that the inventive method for protocol-controlled antenna selection is executed. In general, the invention thus also is a computer program product with a program code stored on a machine-readable carrier for performing the method according to the invention when the computer program product runs on a computing device. In other words, the invention may thus be realized as a computer program with a program code for performing the method when the computer program runs on a computer. 
     While this invention has been described in terms of several advantageous embodiments, there are alterations, permutations, and equivalents which fall within the scope of this invention. It should also be noted that there are many alternative ways of implementing the methods and compositions of the present invention. It is therefore intended that the following appended claims be interpreted as including all such alterations, permutations, and equivalents as fall within the true spirit and scope of the present invention.