Data transmission method and apparatus in RFID and remote sensor systems

Abstract

A method and apparatus is provided for data transmission in RFID and remote sensor systems with at least one reader and a plurality of transponders or remote sensors being located in an electromagnetic field of the reader, in which a multipart return link header containing transmission parameters for the return link, such as timing or modulation references, is transmitted at the beginning of a return link transmission of useful data from a transponder or sensor to a reader. A relative time duration of individual subsymbols of the return link header is modified to select a data transfer mode from among a number of different data transfer modes. A combination of different return link transmission mechanisms is thereby possible, whereby these are mutually compatible and moreover are simple to realize in terms of circuitry and control engineering.

1 . A method for data transmission in RFID and remote sensor systems having at least one reader and at least one transponder or remote sensor being located in an electromagnetic field of the reader, the method comprising the steps of: 
 transmitting a return link header at a beginning of a return link transmission of useful data from a transponder or sensor to a reader, the return link header containing multipart transmission parameters that includes subsymbols, the subsymbols having a time duration; and    modifying the time duration of individual subsymbols to select a data transfer mode from a plurality of different data transfer modes.    
     
     
         2 . The method according to  claim 1 , wherein either a synchronous or asynchronous date transfer mode is selected.  
     
     
         3 . The method according to  claim 1 , wherein to select the data transfer mode the time durations of two successive subsymbols of the return link header are compared.  
     
     
         4 . The method according to  claim 3 , wherein, to select an asynchronous data transfer mode, a subsequent subsymbol is modified in regard to a standard length so that its time duration differs from that of a preceding subsymbol.  
     
     
         5 . The method according to  claim 4 , wherein, during the receipt of a modified subsequent subsymbol, a state of a memory element of the transponder or sensor is changed to release the asynchronous data transfer mode.  
     
     
         6 . The method according to  claim 4 , wherein the reader in a synchronous return link data transmission at predetermined time intervals sends notch signals for synchronization of the data transmission through the transponder or sensor, and wherein the transponder or sensor upon receipt of a notch signal during its useful data transmission to the reader returns to the synchronous mode.  
     
     
         7 . The method according to  claim 6 , wherein upon receipt of the notch signal during the useful data transmission to the reader, the memory element is reset.  
     
     
         8 . The method according to  claim 1 , wherein the multipart transmission parameters are modulation references that are contained in a return link header  
     
     
         9 . The method according to  claim 6 , wherein the transponder or sensor returns to the synchronous mode when a subsequent subsymbol is erroneously changed.  
     
     
         10 . A method for selecting a data transfer mode, the method comprising the steps of: 
 receiving an end of transmission symbol; and    transmitting a return link header from a transponder, the return link header including a plurality of subsymbols that are each transmitted for a predetermined time period subsequently to one another,    wherein the data transfer mode is selected on the basis of a comparison of the predetermined time period of two adjacent subsymbols.    
     
     
         11 . The method according to  claim 10 , wherein the data transfer mode is either a synchronous data transfer mode or an asynchronous data transfer mode.  
     
     
         12 . The method according to  claim 10 , wherein the return link header has four subsymbols.  
     
     
         13 . The method according to  claim 10 , wherein a first subsymbol is for adjusting a main timing, a second subsymbol is a timing reference for a modulation of a return link data transmission, a third subsymbol is for selecting the data transfer mode, and a fourth subsymbol is a reference time for an end of frame.  
     
     
         14 . The method according to  claim 10 , wherein the return link header has four subsymbols, and wherein time periods of the second and third subsymbol are compared to select the data transfer mode.  
     
     
         15 . The method according to  claim 14 , wherein the time period of the third subsymbol is modified by the transponder.  
     
     
         16 . The method according to  claim 10 , wherein the end of transmission symbol is transmitted from a reader to the transponder.  
     
     
         17 . The method according to  claim 10 , wherein data is transmitted from the transponder after the transmission of the return link header.  
     
     
         18 . A transponder comprising: 
 an antenna; and    circuitry for transmitting a return link header having at least two adjacent subsymbols,    wherein data is transmitted by the transponder in either a first data transfer mode or a second data transfer mode, and    wherein the first data transfer mode or the second data transfer mode is selected on the basis of a comparison of a transmission duration between two of the subsymbols.