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 subcarriers 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 −AA −A −AA −A −AAAAA    
       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 −AA −A −AA −A −AAAAA    
       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 synchronization bursts for OFDM transmission systems, comprising the steps of:
   mapping the symbols of a predefined symbol sequence according to a predefined mapping scheme on subcarriers of the OFDM system, and        generating a synchronization burst by Inverse Fourier Transforming by an IFFT unit the subcarriers of the OFDM system mapped with the symbols of said predefined symbol sequence, wherein  64  subcarriers are provided and the subcarriers S   −24,+24    of the total subcarriers S   −32,+31    are modulated as follows:      
       
         S 
         −24,+24 
         =A,  0 ,  0 ,  0 , −A,  0 ,  0 ,  0 , A,  0 ,  0 ,  0 , −A,  0 ,  0 ,  0 , −A,  0 ,  0 ,  0 , A,  0 ,  0 ,  0 ,  0 ,  0 ,  0 , −A,  0 ,  0 ,  0 , −A,  0 ,  0 ,  0 , A,  0 ,  0 ,  0 , A,  0 ,  0 ,  0 , A,  0 ,  0 ,  0 , A  
       
       
         where A is a complex value, and the remaining subcarriers S 
         −32  
         . . . S 
         −25  
         and S 
         +25  
         . . . S 
         +31  
         are set to zero. 
       
     
     
       10. 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 of the OFDM system, and        generating a synchronization burst by Inverse Fast Fourier Transforming by an IFFT unit the subcarriers S of the OFDM system mapped with the symbols of said predefined symbol sequence,      
       
         wherein a  64  point Inverse Fast Fourier Transform is used and the subcarriers S 
         −24,+24  
         of the total subcarriers S 
         −32,+31  
         are modulated as follows:  
       
       
         S 
         −24,+24 
         =A,  0 ,  0 ,  0 , −A,  0 ,  0 ,  0 , A,  0 ,  0 ,  0 , −A,  0 ,  0 ,  0 , −A,  0 ,  0 ,  0 , A,  0 ,  0 ,  0 ,  0 ,  0 ,  0 , −A,  0 ,  0 ,  0 , −A,  0 ,  0 ,  0 , A,  0 ,  0 ,  0 , A,  0 ,  0 ,  0 , A,  0 ,  0 ,  0 , A  
       
       
         where A is a complex value and the remaining subcarriers S 
         −32  
         . . . S 
         −25  
         and S 
         +25  
         . . . S 
         +31  
         are set to zero. 
       
     
     
       11. An OFDM transmitter, comprising:
   a unit for mapping the symbols of a predefined symbol sequence according to a predefined mapping scheme on  64  subcarriers S   −32,+31    of an OFDM system, and        a unit for generating a synchronization burst by Inverse Fourier Transforming the subcarriers S   −32,+31    of the OFDM system mapped with the symbols of said predefined symbol sequence, wherein the mapping unit modulates subcarriers S   −24,+24    of the total subcarriers S   −32,+31    as follows:      S   −24,+24   =A,  0 ,  0 ,  0 , −A,  0 ,  0 ,  0 , A,  0 ,  0 ,  0 , −A,  0 ,  0 ,  0 , −A,  0 ,  0 ,  0 , A,  0 ,  0 ,  0 ,  0 ,  0 ,  0 , −A,  0 ,  0 ,  0 , −A,  0 ,  0 ,  0 , A,  0 ,  0 ,  0 , A,  0 ,  0 ,  0 , A,  0 ,  0 ,  0 , A        
       
         where A is a complex value and the remaining subcarriers S 
         −32  
         . . . S 
         −25  
         and S 
         +25  
         . . . S 
         +31  
         are set to zero. 
       
     
     
       12. A mobile communications device, comprising a transmitter according to  claim 11 .