Transmission system for OFDM-signals with optimized synchronization

Abstract

The present invention relates to a transmission apparatus for transmitting OFDM-signals comprising modulation means 4 for modulating said signals onto a plurality of subcarriers using a OFDM-modulation method, transformation means 5 for transforming said modulated signals into the time domain, and transmission means for transmitting said signals, whereby in said modulation means every M-th subcarrier is modulated, wherein M is an integer and M≧2. The present invention also relates to a corresponding transmission method for transmitting OFDM-signals. The present invention further relates to a receiving apparatus for receiving OFDM-signals comprising M identical or respectively mirrored wave forms within one OFDM-timeburst, wherein M is an integer and M≧2, comprising receiving means for receiving said OFDM-signals, correlation means 22 for correlating said wave forms to obtain time synchronization, transformation means 23 for transforming said signals into the frequency domain and demodulation means 24 for demodulating said signals. The present invention also relates to a corresponding receiving method for receiving OFDM-signals. The present invention provides a much better time and frequency synchronisation performance based on correlation techniques than conventional OFDM-systems.

1. Transmission method for transmitting OFDM-signals, comprising the steps of
 modulating said signals onto a plurality of subcarriers using a OFDM-modulation method, 
 transforming said modulated signals into the time domain, and 
 transmitting said signals characterized in that in said modulating step every M-th subcarrier is modulated with a signal, wherein M is an integer and M≧2. 
 
     
     
       2. Transmission method according to  claim 1 , characterized in, that the not modulated subcarriers are set to zero. 
     
     
       3. Transmission method according to  claim 1 , characterized in, that M=2 and only subcarriers with even indices are modulated. 
     
     
       4. Transmission method according to  claim 1 , characterized in, that said modulation step comprises the steps of
 generating integer values form 0 to L−1, wherein L is the number of available subcarriers, and 
 modulating every M-th signal onto said subcarriers on the basis of said integer values. 
 
     
     
       5. Transmission method according to  claim 1 , wherein:
 said modulating step includes providing a switch control signal to a switch having a first input and a second input, wherein the first input receives a signal to be modulated onto a subcarrier and the second input receives a zero value signal. 
 
     
     
       6. Transmission apparatus for transmitting OFDM-signals, comprising:
 modulation means ( 4 ) for modulating said signals onto a plurality of subcarriers using a OFDM-modulation method, 
 transformation means ( 5 ) for transforming said modulated signals into the time domain, and 
 transmission means for transmitting said signals characterized in that in said modulation means every M-th subcarrier is modulated, wherein M is an integer and M≧2. 
 
     
     
       7. Transmission apparatus according to  claim 6 , characterized in, that in said modulation means ( 4 ) the not modulated subcarriers are set to zero. 
     
     
       8. Transmission apparatus according to  claim 6 , characterized in, that in said modulation means ( 4 ) M=2 and only subcarriers with even indices are modulated. 
     
     
       9. Transmission apparatus according to  claim 6 , characterized in that said modulation means ( 4 ) comprises means ( 10 ) for generating integer values from 0 to L−1, wherein L is the number of available subcarriers, whereby said modulation means ( 4 ) modulates every M-th signal onto said subcarriers on the basis of said integer values. 
     
     
       10. Transmission-apparatus according to  claim 6 , wherein:
 said modulation means includes a switch having a first input and a second input, wherein the first input receives a signal to be modulated onto a subcarrier and the second input receives a zero value signal. 
 
     
     
       11. Receiving method for receiving OFDM-signals comprising M identical or respectively mirrored wave forms within one OFDM-timeburst, wherein M is an integer and M≧2, comprising the steps of
 receiving said OFDM-signals, 
 correlating said waveforms to obtain time synchronization using M−1 correlators, 
 transforming said signals into the frequency domain, and 
 demodulating said signals. 
 
     
     
       12. Receiving method according to  claim 11 , characterized in, that in said correlation step said wave form parts are correlated on the basis of a delay value L 1 =S/M samples and averaged over L 2 ≦S/M samples, whereby S is the total number of samples in one OFDM-timeburst. 
     
     
       13. Receiving method according to  claim 11 , characterized in, that after said correlation step a peak detection step is carried out to provide time synchronization for said transformation of said signals into the frequency domain. 
     
     
       14. Receiving method according to  claim 11 , characterized in, that after said correlation step a frequency offset detection step is carried out to provide frequency synchronization for said transformation of said signals into the frequency domain. 
     
     
       15. Receiving apparatus for receiving OFDM-signals comprising M identical or respectively mirrored wave forms within one OFDM-timeburst, wherein M is an integer and M≧2, comprising:
 receiving means for receiving said OFDM-signals, 
 correlating means ( 28 ,  29 ,  30 ,  31 ) correlating said waveforms to obtain time synchronization, wherein said correlation means includes M−1 correlators, 
 synchronization, transformation means for transforming said signals into the frequency domain, and 
 demodulating said signals. 
 
     
     
       16. Receiving apparatus according to  claim 15 , characterized in, that in said correlation means ( 28 ,  29 ,  30 ,  31 ) said identical wave forms are correlated on the basis of a delay value L 1 =S/M and averaged over L 2 ≧S/M samples, whereby S is the total number of samples in one OFDM-timeburst. 
     
     
       17. Receiving apparatus according to  claim 15 , characterized in, that after said correlation means ( 28 ,  29 ,  30 ,  31 ) a peak detection means ( 46 ) is provided for providing time synchronization for said transformation of said signals into the frequency domain. 
     
     
       18. Receiving apparatus according to  claim 15 , characterized in, that after said correlation means ( 28 ,  29 ,  30 ,  31 ) a frequency offset detection means ( 47 ) is provided for providing frequency synchronization for said transformation of said signals into the frequency domain. 
     
     
       19. Transmission system for transmitting OFDM-signals, comprising:
 a transmission apparatus including modulation means for modulating said signals onto a plurality of subcarriers by OFDM-modulation, transformation means for transforming said modulated signals into the time domain, and transmission means for transmitting said signals characterized in that in said modulation means every M-th subcarrier is modulated, wherein M is an integer greater than or equal to 2; and 
 a receiving apparatus for receiving said OFDM-signals having M identical or respectively mirrored waveforms within one OFDM-timeburst, including receiving means for receiving said OFDM-signals, correlation means for correlating said waveforms to obtain time synchronization, transformation means for transforming said signals into the frequency domain, and demodulation means for demodulating said transformed signals. 
 
     
     
       20. A method for generating OFDM synchronization signals to be transmitted to synchronize a receiver device in an OFDM wireless communication system, comprising the steps of:
 obtaining a frequency domain sequence by modulating synchronization signals onto every 4-th subcarrier of a plurality of available subcarriers being used in the OFDM transmission system;   generating the time domain sequence by performing Inverse Discrete Fourier Transformation onto said frequency domain sequence into scheme to generate a time domain sequence, wherein said time domain sequence contains 4 identical waveforms and generating said OFDM synchronization signals to be transmitted from said a time domain sequence.    
     
     
       21. A method for generating OFDM synchronization signals to be transmitted to synchronize a receiver device in an OFDM wireless communication system, comprising the steps of:
 obtaining a frequency domain sequence by modulating synchronization signals onto every M-th subcarrier of a plurality of subcarriers being used in said OFDM transmission system, wherein M is an integer and M≧2, and wherein said frequency domain sequence comprises modulated subcarriers having nonzero values and un-modulated subcarriers having a zero value;   generating a frequency domain representation comprising said frequency domain sequence and second frequency domain sequences having zero amplitude symbols, and   transforming said frequency domain representation into a time domain representation by using Inverse Discrete Fourier Transformation to generate said OFDM synchronization signals,   wherein said second frequency domain sequences are arranged at the predefined frequency order in said frequency domain representation so that the number of samples in said time domain representation is equal to the number of symbols in said frequency domain representation.    
     
     
       22. A method for generating OFDM synchronization signals to be transmitted to synchronize a receiver device in an OFDM wireless communication system, comprising the steps of:
 obtaining a frequency domain sequence by modulating synchronization signals onto every M-th subcarrier of a plurality of subcarriers being used in said OFDM wireless communication system, wherein M is an integer and M≧2, and wherein said frequency domain sequence comprises modulated subcarriers having nonzero values and un-modulated subcarriers having a zero value;   generating a frequency domain representation comprising said frequency domain sequence and a second frequency sequence having zero amplitude symbols, and   transforming said frequency domain representation into a time domain representation by a transforming unit performing a process of Inverse Discrete Fourier Transformation to generate said OFDM synchronization signals,   wherein said modulated and unmodulated subcarriers of said frequency domain sequence and zero amplitude symbols of said second frequency domain sequence are assigned to predetermined inputs of said transforming unit so that so that the number of samples in said time domain representation is equal to the number of symbols in said frequency domain representation.    
     
     
       23. A method for generating OFDM synchronization signals to be transmitted to synchronize a receiver device in an OFDM wireless communication system, comprising the steps of:
 generating a frequency domain sequence by modulating synchronization signals onto every M-th subcarrier of a plurality of subcarriers being used in said OFDM transmission system, wherein M is an integer and M≧2;   transforming said frequency domain sequence into a time domain sequence by using a method of Inverse Discrete Fourier Transformation, wherein said time domain sequence contains M-th identical waveforms; and   cyclically extending said time domain sequence in time domain to generate an extended time domain sequence; and   transmitting said extended time domain sequence.    
     
     
       24. A method for generating OFDM synchronization signals to be transmitted to synchronize a receiver device in an OFDM wireless communication system, comprising the steps of:
 generating a frequency domain sequence by modulating synchronization signals onto every M-th subcarrier of a plurality of subcarriers being used in said OFDM transmission system, wherein M is an integer and M≧2;   transforming said frequency domain sequence into a time domain sequence by using a method of Inverse Discrete Fourier Transformation, wherein said time domain sequence contains M-th identical waveforms so that said time domain sequence comprises IN-phase M-th identical waveforms and QUAD-phase M-th identical waveforms, wherein each of said QUAD-phase waveforms is different from the corresponding each of said IN-phase waveforms in the time domain; and   transmitting said time domain sequence.    
     
     
       25. A method for generating OFDM synchronization signals to be transmitted to synchronize a receiver device in an OFDM wireless communication system, comprising the steps of:
 generating a frequency domain sequence by modulating synchronization signals onto every M-th subcarrier of a plurality of subcarriers being used in said OFDM transmission system, wherein M is an integer and M≧2;   transforming said frequency domain sequence into a time domain sequence by using a method of Inverse Discrete Fourier Transformation, wherein said time domain sequence contains M-th identical waveforms to be correlated in the receiver device to detect the synchronization timing information therefrom.