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, utilizing a computation unit, for generating a synchronization signal by using a plurality of subcarriers for an OFDM transmission system, comprising the steps of:
   mapping symbols of a predefined symbols sequence in accordance with a predefined mapping scheme on said plurality of subcarriers, wherein pre - selected symbols of the predefined symbol sequence have non - zero values and have the value                (     1   2     )       ⁢     (       +   1     +   j     )       ,         (     1   2     )       ⁢     (       +   1     -   j     )       ,     
     ⁢         (     1   2     )       ⁢     (       -   1     +   j     )       ,           ⁢     or   ⁢           ⁢       (     1   2     )       ⁢     (       -   1     -   j     )       ,             generating only one synchronization signal by Inverse Fourier Transforming said plurality of subcarriers mapped with the symbols of said predefined symbol sequence, and        copying said one synchronization signal to generate other synchronization signals in the time domain.     
     
     
       10. A method, utilizing a computation unit, for generating a synchronization signal by using a plurality of subcarriers for an OFDM transmission system, comprising the steps of:
   generating a predefined symbol sequence having a pre - selected number of symbols corresponding to respective pre - selected ones of said plurality of subcarriers, wherein said preselelected symbols are set to non - zero complex values and others of said symbols are set to zero, such that said pre - selected symbols are arranged periodically in said predefined symbols sequence in the frequency domain, and have the value               (     1   2     )       ⁢     (       +   1     +   j     )       ,         (     1   2     )       ⁢     (       +   1     -   j     )       ,     
     ⁢         (     1   2     )       ⁢     (       -   1     +   j     )       ,           ⁢     or   ⁢           ⁢       (     1   2     )       ⁢     (       -   1     -   j     )       ,             generating only one synchronization signal in time domain by performing Inverse Fourier Transforming on said pre - selected ones of said plurality of subcarriers, and        copying said one synchronization signal to generate other synchronization signals in the time domain.     
     
     
       11. A method, utilizing a computation unit, for generating a synchronization signal by using a plurality of subcarriers for an OFDM transmission system, comprising the steps of:
   generating a predefined symbol sequence having pre - selected symbols each set to a non - zero value and a plurality of further symbols each set to a zero value, wherein respective pre - selected symbols have the value               (     1   2     )       ⁢     (       +   1     +   j     )       ,         (     1   2     )       ⁢     (       +   1     -   j     )       ,     
     ⁢         (     1   2     )       ⁢     (       -   1     +   j     )       ,           ⁢     or   ⁢           ⁢       (     1   2     )       ⁢     (       -   1     -   j     )       ,             and wherein each of said symbols is mapped respectively on a predefined subcarrier of said plurality of subcarriers,        generating only one synchronization signal in time domain by performing Inverse Fourier Transforming on said plurality of subcarriers mapped with said predefined symbols sequence, and        copying said one synchronization signal to generate other synchronization signals in the time domain.     
     
     
       12. A method, utilizing a computation unit, for generating a synchronization signal by using a plurality of subcarriers for an OFDM transmission system, comprising the steps of:
   mapping symbols of a predefined symbol sequence in accordance with a predefined mapping scheme on said plurality of subcarriers, wherein pre - selected symbols of the predefined symbol sequence have non - zero values and have the value               (     1   2     )       ⁢     (       +   1     +   j     )       ,         (     1   2     )       ⁢     (       +   1     -   j     )       ,     
     ⁢         (     1   2     )       ⁢     (       -   1     +   j     )       ,           ⁢     or   ⁢           ⁢       (     1   2     )       ⁢     (       -   1     -   j     )       ,             generating only one synchronization signal by Inverse Fourier Transforming said plurality of subcarriers mapped with the symbols of said predefined symbol sequence, and        copying said one synchronization signal in the time domain to provide a synchronization signal with periodicity.     
     
     
       13. A method, utilizing a computation unit, for generating a synchronization signal by using a plurality of subcarriers for an OFDM transmission system, comprising the steps of:
   generating a predefined symbol sequence having a pre - selected number of symbols corresponding to respective pre - selected ones of said plurality of subcarriers, wherein said preselected symbols are set to non - zero complex values and others of said symbols are set to zero, such that said pre - selected symbols are arranged periodically in said predefined symbol sequence in the frequency domain, and wherein respective pre - selected symbols have the value               (     1   2     )       ⁢     (       +   1     +   j     )       ,         (     1   2     )       ⁢     (       +   1     -   j     )       ,     
     ⁢         (     1   2     )       ⁢     (       -   1     +   j     )       ,           ⁢     or   ⁢           ⁢       (     1   2     )       ⁢     (       -   1     -   j     )       ,             generating only one synchronization signal in time domain by performing Inverse Fourier Transforming on said pre - selected ones of said plurality of subcarriers, and        copying said one synchronization signal in the time domain to provide a synchronization signal with periodicity.     
     
     
       14. A method, utilizing a computation unit, for generating a synchronization signal by using a plurality of subcarriers for an OFDM transmission system, comprising the steps of:
   generating a predefined symbol sequence having pre - selected symbols each set to a non - zero value and a plurality of further symbols each set to a zero value, wherein respective ones of said pre - selected symbols have the value               (     1   2     )       ⁢     (       +   1     +   j     )       ,         (     1   2     )       ⁢     (       +   1     -   j     )       ,     
     ⁢         (     1   2     )       ⁢     (       -   1     +   j     )       ,           ⁢     or   ⁢           ⁢       (     1   2     )       ⁢     (       -   1     -   j     )       ,             and wherein each of said symbols is mapped respectively on a predefined subcarrier of said plurality of subcarriers,        generating only one synchronization signal in time domain by performing Inverse Fourier Transforming on said plurality of subcarriers mapped with said predefined symbols sequence, and        copying said one synchronization signal in the time domain to provide a synchronization signal with periodicity.     
     
     
       15. Apparatus for generating a synchronization signal by using a plurality of subcarriers for an OFDM transmission system, comprising:
   a unit for mapping symbols of a predefined symbols sequence in accordance with a predefined mapping scheme on said plurality of subcarriers, wherein pre - selected symbols of the predefined symbol sequence have non - zero values and have the value               (     1   2     )       ⁢     (       +   1     +   j     )       ,         (     1   2     )       ⁢     (       +   1     -   j     )       ,     
     ⁢         (     1   2     )       ⁢     (       -   1     +   j     )       ,           ⁢     or   ⁢           ⁢       (     1   2     )       ⁢     (       -   1     -   j     )       ,             a unit for generating only one synchronization signal by Inverse Fourier Transforming said plurality of subcarriers mapped with the symbols of said predefined symbol sequence, and        a unit for copying said one synchronization signal to generate other synchronization signals in the time domain.     
     
     
       16. Apparatus for generating a synchronization signal by using a plurality of subcarriers for an OFDM transmission system, comprising:
   a unit for generating a predefined symbol sequence having a pre - selected number of symbols corresponding to respective pre - selected ones of said plurality of subcarriers, wherein said preselected symbols are set to non - zero complex values and others of said symbols are set to zero, such that said pre - selected symbols are arranged periodically in said predefined symbol sequence in the frequency domain, and wherein respective ones of said pre - selected symbols have the value               (     1   2     )       ⁢     (       +   1     +   j     )       ,         (     1   2     )       ⁢     (       +   1     -   j     )       ,     
     ⁢         (     1   2     )       ⁢     (       -   1     +   j     )       ,           ⁢     or   ⁢           ⁢       (     1   2     )       ⁢     (       -   1     -   j     )       ,             a unit for generating only one synchronization signal in time domain by performing Inverse Fourier Transforming on said pre - selected ones of said plurality of subcarriers, and        a unit for copying said one synchronization signal to generate other synchronization signals in the time domain.     
     
     
       17. Apparatus for generating a synchronization signal by using a plurality of subcarriers for an OFDM transmission system, comprising:
   a unit for generating a predefined symbol sequence having pre - selected symbols each set to a non - zero value and a plurality of further symbols each set to a zero value, wherein respective ones of said pre - selected symbols have the value               (     1   2     )       ⁢     (       +   1     +   j     )       ,         (     1   2     )       ⁢     (       +   1     -   j     )       ,     
     ⁢         (     1   2     )       ⁢     (       -   1     +   j     )       ,           ⁢     or   ⁢           ⁢       (     1   2     )       ⁢     (       -   1     -   j     )       ,             and wherein each of said symbols is mapped respectively on a predefined subcarrier of said plurality of subcarriers,        a unit for generating only one synchronization signal in time domain by performing Inverse Fourier Transforming on said plurality of subcarriers mapped with said predefined symbols sequence, and        a unit for copying said one synchronization signal to generate other synchronization signals in the time domain.     
     
     
       18. Apparatus for generating a synchronization signal by using a plurality of subcarriers for an OFDM transmission system, comprising:
   a unit for mapping symbols of a predefined symbols sequence in accordance with a predefined mapping scheme on said plurality of subcarriers, wherein respective ones of said pre - selected symbols of the predefined symbol sequence have non - zero values               (     1   2     )       ⁢     (       +   1     +   j     )       ,         (     1   2     )       ⁢     (       +   1     -   j     )       ,     
     ⁢         (     1   2     )       ⁢     (       -   1     +   j     )       ,           ⁢     or   ⁢           ⁢       (     1   2     )       ⁢     (       -   1     -   j     )       ,             a unit for generating only one synchronization signal by Inverse Fourier Transforming said plurality of subcarriers mapped with the symbols of said predefined symbol sequence, and        a unit for copying said one synchronization signal in the time domain to provide a synchronization signal with periodicity.     
     
     
       19. Apparatus for generating a synchronization signal by using a plurality of subcarriers for an OFDM transmission system, comprising:
   a unit for generating a predefined symbol sequence having a pre - selected number of symbols corresponding to respective pre - selected ones of said plurality of subcarriers, wherein said preselected symbols are set to non - zero complex values and others of said symbols are set to zero, such that said pre - selected symbols are arranged periodically in said predefined symbol sequence in the frequency domain, and respective ones of said pre - selected symbols have the value               (     1   2     )       ⁢     (       +   1     +   j     )       ,         (     1   2     )       ⁢     (       +   1     -   j     )       ,     
     ⁢         (     1   2     )       ⁢     (       -   1     +   j     )       ,           ⁢     or   ⁢           ⁢       (     1   2     )       ⁢     (       -   1     -   j     )       ,             a unit for generating only one synchronization signal in time domain by performing Inverse Fourier Transforming on said pre - selected ones of said plurality of subcarriers, and        a unit for copying said one synchronization signal in the time domain to provide a synchronization signal with periodicity.     
     
     
       20. Apparatus for generating a synchronization signal by using a plurality of subcarriers for an OFDM transmission system, comprising:
   a unit for generating a predefined symbol sequence having pre - selected symbols each set to a non - zero value and a plurality of further symbols each set to a zero value, wherein respective ones of said pre - selected symbols have the value               (     1   2     )       ⁢     (       +   1     +   j     )       ,         (     1   2     )       ⁢     (       +   1     -   j     )       ,     
     ⁢         (     1   2     )       ⁢     (       -   1     +   j     )       ,           ⁢     or   ⁢           ⁢       (     1   2     )       ⁢     (       -   1     -   j     )       ,             and wherein each of said symbols is mapped respectively on a predefined subcarrier of said plurality of subcarriers,        a unit for generating only one synchronization signal in time domain by performing Inverse Fourier Transforming on said plurality of subcarriers mapped with said predefined symbols sequence, and        a unit for copying said one synchronization signal in the time domain to provide a synchronization signal with periodicity.