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 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 twelve symbols of the predefined symbol sequence have non - zero values, and        generating a synchronization signal by Inverse Fourier Transforming said plurality of subcarriers mapped with the symbols of said predefined symbol sequence,        wherein the symbols of the predefined symbols sequence are expressed as        A −A A −A −A A −A −A A A A A      
       
         A being a complex value. 
       
     
     
       10. A method for generating a synchronization signal by using a plurality of subcarriers in an OFDM transmission system, comprising the steps of:
   generating a predefined symbol sequence having at least twelve symbols corresponding to respective pre - selected ones of said plurality of subcarriers, and        generating said synchronization signal in time domain by performing Inverse Fourier Transforming on said preselected ones of said plurality of subcarriers,        wherein said twelve symbols are set to nonzero 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 said symbol sequence of said twelve symbols is A −A A −A −A A −A −A A A A A, where A is a complex value.     
     
     
       11. A method for generating a synchronization signal by using a plurality of subcarriers in an OFDM transmission system, comprising the steps of:
   generating a predefined symbol sequence having twelve symbols each set to a non - zero value and a plurality of further symbols each set to a zero value, wherein each of said symbols is mapped respectively on a predefined subcarrier of said plurality of subcarriers, and        generating said synchronization signal in time domain by performing Inverse Fourier Transforming on said plurality of subcarriers mapped with said predefined symbol sequence,        wherein said twelve symbols of the predefined symbol sequence is expressed as        A −A A −A −A A −A −A A A A A      
       
         A being a complex value. 
       
     
     
       12. A method for transmitting OFDM 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 set to non - zero values and other symbols set to zero values, and wherein said twelve symbols of said predefined symbols sequence are expressed as        A −A A −A −A A −A −A A A A A        A being a complex value,        generating a synchronization signal in time domain by performing Inverse Fourier Transforming on said plurality of subcarriers, and        transmitting said synchronization signals and said OFDM data signals.     
     
     
       13. A method for transmitting OFDM 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 time domain by performing Inverse Fourier Transforming on said plurality of subcarriers, and        transmitting said synchronization signals and said OFDM data signals,        wherein said predefined symbol sequence has twelve symbols having complex value and said twelve symbols of said predefined symbols sequence can be expressed as        A −A A −A −A A −A −A A A A A        wherein twelve symbols are arranged in said predefined symbol sequence such that every fourth subcarrier among said plurality of subcarriers has non - zero amplitude.     
     
     
       14. A method for transmitting OFDM data signals in an OFDM transmission system, comprising the steps of:
   generating synchronization signals in time domain by performing Inverse Fourier Transforming on a plurality of subcarriers on which a predefined symbol sequence is mapped in accordance with a predefined mapping scheme, and        transmitting said synchronization signals and said OFDM data signals,        wherein said predefined symbol sequence contains the following symbol sequence comprising twelve complex values:        A −A A −A −A A −A −A A A A A        wherein said twelve symbols are mapped on every fourth subcarriers of said plurality of subcarriers.     
     
     
       15. Apparatus for generating a synchronization signal by using a plurality of subcarriers for an OFDM transmission system, comprising:
   a unit mapping symbols of a predefined symbol sequence in accordance with a predefined mapping scheme on said plurality of subcarriers, wherein pre - selected twelve symbols of the predefined symbol sequence have non - zero values, and        a unit for generating a synchronization signal by Inverse Fourier Transforming said plurality of subcarriers mapped with the symbols of said predefined symbol sequence,        wherein the symbols of the predefined symbols sequence are expressed as        A −A A −A −A A −A −A A A A A      
       
         A being a complex value. 
       
     
     
       16. Apparatus for generating a synchronization signal by using a plurality of subcarriers in an OFDM transmission system, comprising
   a unit for generating a predefined symbol sequence having at least twelve symbols corresponding to respective pre - selected ones of said plurality of subcarriers, and        a unit for generating said synchronization signal in time domain by performing Inverse Fourier Transforming on said preselected ones of said plurality of subcarriers,        wherein said twelve symbols are set to nonzero 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 said symbol sequence of said twelve symbols is A −A A −A −A A −A −A A A A A, where A is a complex value.     
     
     
       17. Apparatus for generating a synchronization signal by using a plurality of subcarriers in an OFDM transmission system, comprising:
   a unit for generating a predefined symbol sequence having twelve symbols each set to a non - zero value and a plurality of further symbols each set to a zero value, wherein each of said symbols is mapped respectively on a predefined subcarrier of said plurality of subcarriers, and        a unit for generating said synchronization signal in time domain by performing Inverse Fourier Transforming on said plurality of subcarriers mapped with said predefined symbol sequence,        wherein said twelve symbols of the predefined symbol sequence is expressed as        A −A A −A −A A −A −A A A A A      
       
         A being a complex value. 
       
     
     
       18. Apparatus for transmitting OFDM 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 set to non - zero values and other symbols set to zero values, and wherein said twelve symbols of said predefined symbols sequence are expressed as        A −A A −A −A A −A −A A A A A        A being a complex value,        a unit for generating a synchronization signal in time domain by performing Inverse Fourier Transforming on said plurality of subcarriers, and        a transmitter for transmitting said synchronization signals and said OFDM data signals.     
     
     
       19. Apparatus for transmitting OFDM 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 time domain by performing Inverse Fourier Transforming on said plurality of subcarriers, and        a transmitter for transmitting said synchronization signals and said OFDM data signals,        wherein said predefined symbol sequence has twelve symbols having complex value and said twelve symbols of said predefined symbols sequence can be expressed as        A −A A −A −A A −A −A A A A A        wherein twelve symbols are arranged in said predefined symbol sequence such that every fourth subcarrier among said plurality of subcarriers has non - zero amplitude.     
     
     
       20. Apparatus for transmitting OFDM data signals in an OFDM transmission system, comprising:
   a unit for generating synchronization signals in time domain by performing Inverse Fourier Transforming 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 OFDM data signals,        wherein said predefined symbol sequence contains the following symbol sequence comprising twelve complex values:        A −A A −A −A A −A −A A A A A        wherein said twelve symbols are mapped on every fourth subcarriers of said plurality of subcarriers.     
     
     
       21. A method for synchronizing a wireless communication device in an OFDM communication system, comprising the steps of:
   receiving data signals and a synchronization signal exhibiting periodicity, the data signals and synchronization signal being transmitted from a transmitter side by using a plurality of subcarriers, said synchronization signal being based on a predefined symbol sequence having twelve complex value symbols with the symbol sequence        A −A A −A −A A −A −A A A A A        wherein A is a complex value, and        wherein said twelve symbols are mapped on every fourth subcarrier of said plurality of subcarriers so that said periodic nature of synchronization signal contains four repetitions of one synchronization signal in time domain; and        performing time and frequency synchronization in accordance with said periodicity of synchronization signal.     
     
     
       22. A method for synchronizing a wireless communication device in an OFDM communication system, comprising the steps of:
   receiving data and synchronization signals transmitted from a transmitter side by using a plurality of subcarriers, and        performing time and frequency synchronization in accordance with said synchronization signal;        wherein said synchronization signal is generated based on a predefined symbol sequence comprising twelve symbols having complex values and a sequence of said twelve symbols is expressed as        A −A A −A −A A −A −A A A A A        wherein A is a complex value.     
     
     
       23. A method for synchronizing a wireless communication device in an OFDM communication system, comprising the steps of:
   receiving data and synchronization signals transmitted from a transmitter side by using a plurality of subcarriers, and        performing time and frequency synchronization in accordance with said synchronization signal;        wherein said synchronization signal is generated based on a predefined symbol sequence comprising twelve nonzero symbols having complex value and other symbols being set to zero so that said twelve symbols are arranged with periodicity in said predefined symbol sequence in the frequency domain, and        wherein a sequence of said twelve symbols in the frequency domain is        A −A A −A −A A −A −A A A A A        wherein A is a complex value.     
     
     
       24. A method for synchronizing a wireless communication device in an OFDM communication system, comprising the steps of:
   receiving data and synchronization signals transmitted from a transmitter side by using a plurality of subcarriers, and        performing time and frequency synchronization in accordance with said synchronization signal;        wherein said synchronization signal is based on a predefined symbol sequence comprised of twelve symbols having complex value, said twelve symbols being expressed as        A −A A −A −A A −A −A A A A A        wherein A is a complex value and        wherein the twelve symbols are arranged such that every fourth subcarrier among said plurality of subcarriers has non - zero amplitude.     
     
     
       25. A method for transmitting data signals in an OFDM transmission system, comprising the steps of:
   generating a predefined symbol sequence comprised of a plurality of complex value symbols mapped on a plurality of subcarriers,        generating a synchronization signal by supplying said plurality of subcarriers having non - zero amplitude to an inverse Fourier Transform unit, such that said plurality of subcarriers mapped with said predefined symbol sequence are transformed into a time domain signal to generate only one synchronization signal,        copying said one synchronization signal to generate other synchronization signals in the time domain; and        transmitting said generated synchronization signals and said data signals.     
     
     
       26. The method according to  claim 25 ,
   wherein the symbols of said predefined symbol sequence are expressed by C   i−1    or C   n−i   , wherein:        n is the number of symbols of said predefined symbol sequence,        m is a half value of n,        i is an integer running from  1  to m        wherein said symbols expressed by C   i−1    are supplied to one set of inputs of said inverse Fourier transform unit, and said symbols expressed by C   n−i    are supplied to another set of said inputs of said inverse Fourier transform unit.     
     
     
       27. 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 being formed of a plurality of symbols set to complex values,        transforming said plurality of subcarriers, of non - zero amplitude, mapped with said predefined symbol sequence into a time domain signal using inverse Fourier transformation, so as to generate only one synchronization signal,        copying said one synchronization signal in the time domain to provide a synchronization signal with periodicity, and        transmitting said provided synchronization signal and said data signals.     
     
     
       28. 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 being formed of a plurality of symbols set to complex values,        transforming said plurality of subcarriers, set to non - zero amplitude, mapped with said predefined symbol sequence into a time domain signal by using Inverse Fourier Transformation, to generate only one synchronization signal,        copying said one synchronization signal to generate other synchronization signals in the time domain; and        transmitting said generated synchronization signals and said data signals.     
     
     
       29. A method for transmitting OFDM data signals in an OFDM transmission system, comprising the steps of:
   generating one synchronization signal 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, wherein all symbols of said predefined symbol sequence are set to complex values,        generating a synchronization signal of periodicity by copying said one synchronization signal in the time domain, and        transmitting said synchronization signal of periodicity and said OFDM data signals.     
     
     
       30. A method for transmitting OFDM data signals in an OFDM transmission system, comprising the steps of:
   generating a predefined symbol sequence having at least twelve non - zero complex value symbols, each of said twelve symbols being mapped in a periodic manner on a plurality of pre - selected subcarriers in the frequency domain,        generating a time domain signal by performing Inverse Fourier transformation on said plurality of pre - selected subcarriers mapped with said predefined symbol sequence,        said predefined symbol sequence conforming with the following equations for all symbols of said predefined symbol sequence:        n= 2 m,          C   i−1   =±C   n−   i        
       
         wherein:  
         
           n is the number of symbols of said predefined symbol sequence,  
         
         
           m is an integer larger than one,  
         
         
           C is the symbol value, and  
         
         
           i is an integer from  1  to m. 
         
       
     
     
       31. A method for transmitting OFDM data signals by using a plurality of subcarriers in an OFDM transmission system, comprising the steps of:
   generating a predefined symbol sequence having at least twelve symbols corresponding to respective pre - selected ones of said plurality of subcarriers,        generating a time domain signal by performing Inverse Fourier transformation on said plurality of pre - selected subcarriers corresponding to the symbols of said predefined symbol sequence,        wherein each of twelve symbols is set to a nonzero complex value and said predefined symbol sequence has a binary symbol sequence expressed by A and −A, where A is a complex value, and wherein said predefined symbol sequence satisfies the following equations for all symbols of said predefined symbol sequence:        n= 2 m,          C   i−1   =±C   n−   i        
       
         wherein:  
         
           n is the number of symbols of said predefined symbol sequence,  
         
         
           m is an integer larger than one,  
         
         
           C is the symbol value, and  
         
         
           i is an integer from  1  to m. 
         
       
     
     
       32. A method for transmitting OFDM data signals by using a plurality of subcarriers in an OFDM transmission system, comprising the steps of:
   generating a predefined symbol sequence having at least twelve symbols corresponding to respective pre - selected subcarriers of said plurality of subcarriers,        generating a time domain signal by performing Inverse Fourier transformation on said plurality of pre - selected subcarriers corresponding to the symbols of said predefined symbol sequence,        wherein each of said twelve symbols has a nonzero complex value expressed by A or −A, and wherein said predefined symbol sequence satisfies the following equations for all symbols of said predefined symbol sequence:        n= 2 m,          C   i−1   =±C   n−   i        
       
         wherein:  
         
           n is the number of symbols of said predefined symbol sequence,  
         
         
           m is an integer larger than one,  
         
         
           C is the symbol value, and  
         
         
           i is an integer from  1  to m. 
         
       
     
     
       33. A method for transmitting OFDM data signals by using a plurality of subcarriers in an OFDM transmission system, comprising the steps of:
   generating a predefined symbol sequence having predefined symbols, each of said symbols being mapped on a respective predefined subcarrier, and        generating a time domain signal by Inverse Fourier Transforming said plurality of subcarriers mapped with the symbols of said predefined symbol sequence,        wherein said predefined symbols are set to nonzero complex values and have a binary sequence of symbol values expressed by A or −A,        wherein said predefined symbol sequence satisfies the following equations for all symbols of said predefined symbol sequence:        n= 2 m,          C   i−1   =±C   n−   i        
       
         wherein:  
         
           n is the number of symbols of said predefined symbol sequence,  
         
         
           m is an integer larger than one,  
         
         
           C is the symbol value, and  
         
         
           i is an integer from  1  to m. 
         
       
     
     
       34. A method for transmitting OFDM data signals in 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        generating a time domain signal by Inverse Fourier Transforming said plurality of subcarriers mapped with the symbols of said predefined symbol sequence,        wherein said predefined symbol sequence satisfies the following equations for all symbols of said predefined symbol sequence:        n= 2 m,          C   i−1   =±C   n−   i        
       
         wherein:  
         
           n is the number of symbols of said predefined symbol sequence,  
         
         
           m is an integer larger than one,  
         
         
           C is the symbol value, and  
         
         
           i is an integer from  1  to m.