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 −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 synchronization signal for frequency synchronization of OFDM systems, comprising the steps of:
   mapping symbols of a predefined symbol sequence in the frequency domain in accordance with a predefined mapping scheme on a plurality of subcarriers of the OFDM system, wherein the symbols of the symbol sequence define subcarriers with non - zero amplitude, and        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 respective symbols of the symbol sequence have the value                (     1   2     )       ⁢     (       +   1     +   j     )       ,         (     1   2     )       ⁢     (       +   1     -   j     )       ,         (     1   2     )       ⁢     (       -   1     +   j     )       ,     or   ⁢           ⁢       (     1   2     )       ⁢       (       -   1     -   j     )     .               
       
        
       
     
     
       10. A method for generating a synchronization signal for frequency synchronization of OFDM systems, comprising the steps of:
   generating a predefined symbol sequence having a predefined number of symbols corresponding to respective pre - selected ones of a plurality of subcarriers of the OFDM system, and        generating said synchronization signal in the time domain by performing Inverse Fourier Transformation on said pre - selected ones of said plurality of subcarriers,        wherein said predefined symbols are set to non - zero having complex values and others of said symbols are set to zero, such that said predefined symbols are arranged periodically in said predefined symbol sequence in the frequency domain and        wherein respective symbols of the symbol sequence have the value                (     1   2     )       ⁢     (       +   1     +   j     )       ,         (     1   2     )       ⁢     (       +   1     -   j     )       ,         (     1   2     )       ⁢     (       -   1     +   j     )       ,     or   ⁢           ⁢       (     1   2     )       ⁢       (       -   1     -   j     )     .               
       
        
       
     
     
       11. Apparatus for generating a synchronization signal for an OFDM transmission system, comprising:
   a unit for mapping, in the frequency domain, symbols of a predefined symbol sequence in accordance with a predefined mapping scheme on a plurality of subcarriers of the OFDM system, wherein the symbols of the symbol sequence define subcarriers with non - zero amplitude, and        a unit for generating the time domain synchronization signal by Inverse Fourier Transforming the subcarriers of the OFDM system mapped with the symbols of the symbol sequence,        wherein respective symbols of the symbol sequence have the value                (     1   2     )       ⁢     (       +   1     +   j     )       ,         (     1   2     )       ⁢     (       +   1     -   j     )       ,         (     1   2     )       ⁢     (       -   1     +   j     )       ,     or   ⁢             ⁢             ⁢       (     1   2     )       ⁢       (       -   1     -   j     )     .               
       
        
       
     
     
       12. Apparatus for generating a synchronization signal for frequency synchronization of OFDM systems, comprising:
   a unit for generating a predefined symbol sequence having a predefined number of symbols corresponding to respective pre - selected ones of plural subcarriers of the OFDM system, and        a unit for generating said synchronization signal in the time domain by performing Inverse Fourier Transformation on said pre - selected ones of said plurality of subcarriers,        wherein said predefined symbols are set to non - zero having complex values and others of said symbols are set to zero, such that said predefined symbols are arranged periodically in said predefined symbol sequence in the frequency domain and        wherein respective symbols of the predefined symbol sequence have the value                (     1   2     )       ⁢     (       +   1     +   j     )       ,         (     1   2     )       ⁢     (       +   1     -   j     )       ,         (     1   2     )       ⁢     (       -   1     +   j     )       ,     or   ⁢             ⁢             ⁢       (     1   2     )       ⁢       (       -   1     -   j     )     .               
       
        
       
     
     
       13. 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 a predefined number of symbols set to non - zero values and other symbols set to zero values, wherein respective symbols of the predefined symbol sequence have the value                (     1   2     )       ⁢     (       +   1     +   j     )       ,         (     1   2     )       ⁢     (       +   1     -   j     )       ,         (     1   2     )       ⁢     (       -   1     +   j     )       ,     or   ⁢           ⁢       (     1   2     )       ⁢       (       -   1     -   j     )     .                 generating a synchronization signal in the time domain by performing Inverse Fourier Transformation on said plurality of subcarriers, and        transmitting said synchronization signals and said data signals.     
     
     
       14. 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 synchronization signal in the time domain by performing Inverse Fourier Transformation on said plurality of subcarriers, and        transmitting said synchronization signals and said data signals,        wherein the symbols of the symbol sequence comprise a predefined number of symbols and respective symbols of the symbol sequence have the value                (     1   2     )       ⁢     (       +   1     +   j     )       ,         (     1   2     )       ⁢     (       +   1     -   j     )       ,         (     1   2     )       ⁢     (       -   1     +   j     )       ,     or   ⁢           ⁢       (     1   2     )       ⁢     (       -   1     -   j     )       ,             and        wherein said predefined symbols are arranged periodically in said predefined symbol sequence in the frequency domain.     
     
     
       15. A method for transmitting data signals in an OFDM transmission system, comprising the steps of:
   generating synchronization signals in the time domain by 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 symbols of the symbol sequence comprise a number of predefined symbols and respective symbols of the symbol sequence have the value                (     1   2     )       ⁢     (       +   1     +   j     )       ,         (     1   2     )       ⁢     (       +   1     -   j     )       ,         (     1   2     )       ⁢     (       -   1     +   j     )       ,     or   ⁢           ⁢       (     1   2     )       ⁢     (       -   1     -   j     )       ,   and             wherein said predefined symbols are mapped on every fourth subcarrier of said plurality of subcarriers.     
     
     
       16. 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 a predefined number of symbols set to non - zero values and other symbols set to zero values, wherein respective ones of said predefined symbols of the symbol sequence have the value                (     1   2     )       ⁢     (       +   1     +   j     )       ,         (     1   2     )       ⁢     (       +   1     -   j     )       ,         (     1   2     )       ⁢     (       -   1     +   j     )       ,     or   ⁢           ⁢       (     1   2     )       ⁢     (       -   1     -   j     )       ,             a unit for generating a synchronization signal in the time domain by performing Inverse Fourier Transformation on said plurality of subcarriers, and        a transmitter for transmitting said synchronization signals and said data signals.     
     
     
       17. 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 synchronization signal in the time domain by performing Inverse Fourier Transformation on said plurality of subcarriers, and        a transmitter for transmitting said synchronization signals and said data signals,        wherein respective ones of said predefined symbols of the symbol sequence have the value                (     1   2     )       ⁢     (       +   1     +   j     )       ,         (     1   2     )       ⁢     (       +   1     -   j     )       ,         (     1   2     )       ⁢     (       -   1     +   j     )       ,         (     1   2     )       ⁢     (       -   1     -   j     )       ,             and        wherein said predefined symbols are arranged periodically in said predefined symbol sequence in the frequency domain.     
     
     
       18. Apparatus for transmitting data signals in an OFDM transmission system, comprising:
   a unit for generating synchronization signals in the time domain 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 signals and said data signals,        wherein the symbols of the symbol sequence comprise a number of predefined symbols and respective ones of said predefined symbols have the value                (     1   2     )       ⁢     (       +   1     +   j     )       ,         (     1   2     )       ⁢     (       +   1     -   j     )       ,         (     1   2     )       ⁢     (       -   1     +   j     )       ,     or   ⁢           ⁢       (     1   2     )       ⁢     (       -   1     -   j     )       ,   and             wherein said predefined symbols are mapped on every fourth subcarrier of said plurality of subcarriers.