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 synchronizing an OFDM receiver, comprising the steps of generating a synchronization signal by:
   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 symbols sequence represent subcarriers of the OFDM system with non - zero amplitude,        generating a synchronization signal by Inverse Fourier Transforming the subcarriers of the OFDM system mapped with the symbols of said predefined 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     )       ,             transmitting the synchronization signal, and        receiving said synchronization signal to synchronize a receiver.     
     
     
       10. The method of  claim 9 , wherein an AGC in the receiver is locked in using the received synchronization signal. 
     
     
       11. The method of  claim 9 , wherein a reference value of an A/D converter in the receiver is adjusted using the received synchronization signal. 
     
     
       12. A method for synchronizing a receiver 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 by using a plurality of subcarriers, said synchronization signal being based on a predefined symbol sequence having a predefined number of symbols, respective symbols having 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 periodically mapped on every fourth subcarrier of said plurality of subcarriers so that the periodicity of the synchronization signal contains a predefined number of repetitions of one synchronization signal in the time domain, and        performing time and frequency synchronization in accordance with said periodicity of the synchronization signal.     
     
     
       13. A method for synchronizing a receiver 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 and respective symbols have the value               (     1   2     )       ⁢     (       +   1     +   j     )       ,         (     1   2     )       ⁢     (       +   1     -   j     )       ,     
     ⁢         (     1   2     )       ⁢     (       -   1     +   j     )       ,           ⁢     or   ⁢           ⁢       (     1   2     )       ⁢       (       -   1     -   j     )     .               14 . A method for synchronizing a receiver in an OFDM communication system, comprising the steps of:       receiving data and synchronization signals transmitted from a transmitter 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 non - zero symbols with respective symbols having the value               (     1   2     )       ⁢     (       +   1     +   j     )       ,         (     1   2     )       ⁢     (       +   1     -   j     )       ,     
     ⁢         (     1   2     )       ⁢     (       -   1     +   j     )       ,           ⁢     or   ⁢           ⁢       (     1   2     )       ⁢     (       -   1     -   j     )                 and other symbols are set to zero, so that said non - zero symbols are arranged with periodicity in said predefined symbol sequence in the frequency domain.     
     
     
       15. A method for synchronizing a receiver 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 comprised of a predefined number of symbols and respective symbols have the value               (     1   2     )       ⁢     (       +   1     +   j     )       ,         (     1   2     )       ⁢     (       +   1     -   j     )       ,     
     ⁢         (     1   2     )       ⁢     (       -   1     +   j     )       ,           ⁢     or   ⁢           ⁢       (     1   2     )       ⁢     (       -   1     -   j     )       ,             wherein the predefined symbols are arranged such that every fourth subcarrier among said plurality of subcarriers has non - zero amplitude.     
     
     
       16. An OFDM communication system comprising a transmitter and a receiver, the transmitter comprising:
   means 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 a predefined number of the symbols of the symbol sequence define subcarriers with non - zero amplitude, and        means 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 respective 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     )       ;               and        the receiver receives said synchronization signal to perform time and frequency synchronization in accordance with said synchronization signal.     
     
     
       17. An OFDM communication system comprising a transmitter and a receiver, the transmitter comprising:
   means for 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        means 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 said predefined symbols have the value               (     1   2     )       ⁢     (       +   1     +   j     )       ,         (     1   2     )       ⁢     (       +   1     -   j     )       ,     
     ⁢         (     1   2     )       ⁢     (       -   1     +   j     )       ,           ⁢       or   ⁢           ⁢       (     1   2     )       ⁢     (       -   1     -   j     )       ;               and        the receiver receives said synchronization signal to perform time and frequency synchronization in accordance with said synchronization signal.