Synchronization symbol structure using OFDM based transmission method

Abstract

The present invention proposes a method for generating synchronization bursts for OFDM transmission systems. The symbols of a predefined symbol sequence are mapped according to a predefined mapping scheme on subcarriers of the OFDM systems by a mapping unit ( 2 ), wherein the symbols of the predefined symbol sequence represent sub-carriers of the OFDM system with nonzero amplitudes. A synchronization burst is generated by a inverse fast Fourier transforming unit ( 3 ) transforming the subcarriers of the OFDM system mapped to said predefined symbol sequence. The mapping ( 2 ) of the symbols of the predefined symbol sequence is set such that the resulting time domain signal of the synchronization burst represents a periodic nature. According to the invention the predefined symbol sequence is set such that the envelope fluctuation of the time domain signal of the synchronization burst is minimized. Therefore advantageous symbol sequences reducing said the envelope fluctuation of the time domain signal are proposed.

1. A method for generating synchronization bursts for OFDM transmission systems, comprising the following steps:
 mapping the symbols of a predefined symbol sequence according to a predefined mapping scheme on subcarriers S of the OFDM system, wherein the symbols of the predefined symbol sequence represent subcarriers of the OFDM system with non-zero-amplitude, and    generating a synchronization burst by Inverse Fourier Transforming the subcarriers S of the OFDM system mapped with the symbols of said predefined symbol sequence,    characterized in that 
 the predefined symbol sequence is set such that the envelope fluctuation of the time domain signal of the synchronization burst is minimized and the symbols of the predefined symbols sequence can be expressed as  
   A −A A −A −A A −A −A A A A A    
       A being a complex value. 
     
     
       2. A method for synchronizing wireless OFDM systems, characterized by the steps of
 generating a synchronization burst according to a method according to  claim 1 , and    transmitting the synchronization burst.    
     
     
       3. A method according to  claim 2 , characterized in that
 the time domain signal of the synchronization burst is precomputed and stored in a memory.    
     
     
       4. An OFDM transmitter, comprising:
 a unit for mapping the symbols of a predefined symbol sequence according to a predefined mapping scheme on subcarriers of the OFDM system, wherein the symbols of the predefined symbol sequence represent subcarriers of the OFDM system with non-zero-amplitude, and    a unit for generating a synchronization burst by Inverse Fourier Transforming the subcarriers of the OFDM system mapped with the symbols of said predefined symbol sequence,    characterized in that 
 the mapping unit is designed to modulate the subcarriers such that the envelope fluctuation of the time domain signal of the synchronization burst is minimized by using the following predefined symbol sequence:  
   A −A A −A −A A −A −A A A A A    
       A being a complex value. 
     
     
       5. An OFDM transmitter according to  claim 4 , characterized by
 a time extension unit copying the burst part to achieve a periodic nature of the time domain signal.    
     
     
       6. An OFDM transmitter according to  claim 4 , characterized by
 a processing unit for precomputing the time domain signal of the synchronization burst    and a memory for storing the precomputed time domain signal of the synchronization burst.    
     
     
       7. A mobile communications device, comprising a transmitter according to  claim 4 . 
     
     
       8. A synchronization burst signal for synchronizing OFDM systems generated by a method according to  claim 1 . 
     
     
       9. A method for generating a signal for frequency synchronization of OFDM systems, the method comprising the steps of:
   mapping symbols of a predefined symbol sequence in the frequency domain according to a defined mapping scheme on a plurality of subcarriers of the OFDM system, wherein the symbols of the symbol sequence define the subcarriers of the OFDM system with non - zero amplitude, where n is an integer, and        generating a time - domain synchronization signal in a time extension unit by Inverse Fourier Transforming the subcarriers of the OFDM system mapped with the symbols of the symbol sequence,        wherein the symbol sequence comprises  12  symbols C   0   , . . . C   11    wherein C   0   , C   1   , C   2   , . . . C   11    has the value              (     1   2     )       ⁢       (       ±   1     ±   j     )     .             
     
     
       10. The method of  claim 9 ,
   wherein the following equation is met for all symbols C   0   , . . . C   11 : 
     C   i−1   =±C   n−i          where i is an integer from  1  to  6  and n is the number of symbols of the predefined symbol sequence.     
     
     
       11. The method of  claim 9 , wherein the symbols of the sequence are evenly spaced in the frequency domain. 
     
     
       12. A method for generating a synchronization signal for frequency synchronization of OFDM systems, comprising the steps of:
   generating a predefined symbol sequence having twelve symbols C   0   , . . . C   11    corresponding to respective pre - selected ones of a plurality of subcarriers of the OFDM system, and        generating a time domain synchronization signal by a time extension unit performing Inverse Fourier Transformation on said pre - selected ones of said plurality of subcarriers,        wherein said twelve symbols are set to non - zero having complex values and others of said symbols are set to zero, such that said twelve symbols are arranged periodically in said predefined symbol sequence in the frequency domain and        wherein C   0   , C   1   , C   2   , . . . C   11    of the symbol sequence has the value,              (     1   2     )       ⁢       (       ±   1     ±   j     )     .             
       
        
       
     
     
       13. The method of  claim 12 , further comprising the steps of transmitting, receiving and auto- correlating said synchronization signal.   
     
     
       14. A wireless communication transmitting device for use in an OFDM system, comprising:
   a mapping unit for mapping symbols of a predefined symbol sequence, in the frequency domain, according to a defined mapping scheme on a plurality of subcarriers of the OFDM system, wherein symbols C   0   , C   1   , C   2   , . . . C   11    of the symbol sequence define subcarriers of the OFDM system with non - zero amplitude, and        an Inverse Fourier Transformer  ( IFFT )  for generating a time - domain synchronization signal by Inverse Fourier Transforming the subcarriers of the OFDM system mapped with the symbols of the symbol sequence,        wherein the symbol sequence comprises twelve symbols C   0   , . . . C   11    wherein C   0   , . . . C   11    of said twelve symbols has the value              (     1   2     )       ⁢       (       ±   1     ±   j     )     .             
       
        
       
     
     
       15. The device of  claim 14 ,
   wherein the following equation is met for all symbols C   0   , . . . C   11 : 
     C   i−1   =±C   n−i          where i is an integer from  1  to  6  and n is the number of symbols of the predefined symbol sequence.     
     
     
       16. The device of  claim 14 , wherein the symbols of the predefined symbol sequence are evenly spaced in the frequency domain. 
     
     
       17. Apparatus for generating a synchronization signal for frequency synchronization of OFDM systems, comprising:
   a unit for generating a predefined symbol sequence having twelve symbols C   0   , C   1   , C   2   , . . . C   11    corresponding to respective pre - selected ones of a plurality of subcarriers of the OFDM system, and        a unit for generating a time domain synchronization signal by performing Inverse Fourier Transformation on said pre - selected ones of said plurality of subcarriers,        wherein said twelve symbols are set to non - zero having complex values and others of said symbols are set to zero, such that said twelve symbols are arranged periodically in said predefined symbol sequence in the frequency domain and        wherein C   0   , C   1   , C   2   , . . . C   11    of said twelve symbols has the value              (     1   2     )       ⁢       (       ±   1     ±   j     )     .             
       
        
       
     
     
       18. A method for transmitting data signals in an OFDM transmission system, comprising the steps of:
   receiving a plurality of subcarriers on which a predefined symbol sequence is mapped, said predefined symbol sequence having twelve symbols C   0   , . . . C   11    set to non - zero values and other symbols set to zero values, wherein C   0   , . . . C   11    of said twelve symbols has the value                (     1   2     )       ⁢     (       ±   1     ±   j     )       ,             generating a time domain synchronization signal by a time extension unit performing Inverse Fourier Transformation on said plurality of subcarriers, and        transmitting said synchronization and data signals.     
     
     
       19. A method for transmitting data signals in an OFDM transmission system, comprising the steps of:
   receiving a plurality of subcarriers on which a predefined symbol sequence is mapped,        generating a time domain synchronization signal by a time extension unit performing Inverse Fourier Transformation on said plurality of subcarriers, and        transmitting said synchronization and data signals,        wherein the symbol sequence comprises twelve symbols C   0   , . . . C   11    and wherein C   0   , . . . C   11    of said twelve symbols has the value                (     1   2     )       ⁢     (       ±   1     ±   j     )       ,           
       and
   wherein said twelve symbols are arranged periodically in said predefined symbol sequence in the frequency domain.   
 
     
     
       20. A method for transmitting data signals in an OFDM transmission system, comprising the steps of:
   generating time domain synchronization signals by a time extension unit performing Inverse Fourier Transformation on a plurality of subcarriers in which a predefined symbol sequence is mapped in accordance with a predefined mapping scheme, and        transmitting said synchronization signals and said data signals,        wherein the symbol sequence includes twelve symbols C   0   , . . . C   11    and wherein C   0   , . . . C   11    of said twelve symbols has the value                (     1   2     )       ⁢     (       ±   1     ±   j     )       ,           
       
         and  
         
           wherein said twelve symbols are mapped on every fourth subcarrier of said plurality of subcarriers. 
         
       
     
     
       21. Apparatus for transmitting data signals in an OFDM transmission system, comprising:
   a unit for receiving a plurality of subcarriers on which a predefined symbol sequence is mapped, said predefined symbol sequence having twelve symbols C   0   , . . . C   11    set to non - zero values and other symbols set to zero values, wherein C   0   , . . . C   11    of said twelve has the value                (     1   2     )       ⁢     (       ±   1     ±   j     )       ,             a unit for generating a time domain synchronization signal by performing Inverse Fourier Transformation on said plurality of subcarriers, and        a transmitter for transmitting said synchronization and data signals.     
     
     
       22. Apparatus for transmitting data signals in an OFDM transmission system, comprising:
   a unit for receiving a plurality of subcarriers on which a predefined symbol sequence is mapped,        a unit for generating a time domain synchronization signal by performing Inverse Fourier Transformation on said plurality of subcarriers, and        a transmitter for transmitting said synchronization and data signals,        wherein the symbol sequence includes twelve symbols C   0   , . . . C   11    and wherein C   0   , . . . C   11    of said twelve symbols has the value                (     1   2     )       ⁢     (       ±   1     ±   j     )       ,           
       
         and  
         
           wherein said twelve symbols are arranged periodically in said predefined symbol sequence in the frequency domain. 
         
       
     
     
       23. Apparatus for transmitting data signals in an OFDM transmission system, comprising:
   a unit for generating time domain synchronization signals by performing Inverse Fourier Transformation on a plurality of subcarriers on which a predefined symbol sequence is mapped in accordance with a predefined mapping scheme, and        a transmitter for transmitting said synchronization and data signals,        wherein the symbols of the symbol sequence comprise twelve symbols C   0   , . . . C   11    and wherein C   0   , . . . C   11    of said twelve symbols has the value                (     1   2     )       ⁢     (       ±   1     ±   j     )       ,           
       
         and  
         
           wherein said twelve symbols are mapped on every fourth subcarrier of said plurality of subcarriers.