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-time-burst, 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 receiving OFDM-signals and synchronization signals transmitted from transmitter device in an OFDM communication system, comprising the steps of:
 receiving said OFDM signals modulated onto a plurality of available subcarriers using an OFDM-modulation method and synchronization signals being modulated on every 4th subcarrier of said plurality of available subcarriers and the other subcarriers of said plurality of available subcarriers are not modulated;   detecting synchronization information by using said synchronization signals; and   decoding said received OFDM signals in accordance with said synchronization information.   
     
     
       21. A method for receiving OFDM-signals and synchronization signals transmitted from a transmitter device in an OFDM communication system, comprising the steps of:
 receiving said synchronization signals which are modulated on every 4th subcarrier of said plurality of available subcarriers and the other subcarriers of said plurality of available subcarriers are not modulated, wherein a time domain sequence of said synchronization signals contains 4 identical waveforms;   detecting synchronization information by correlating said 4 identical waveforms of said synchronization signals; and   decoding said received OFDM signals in accordance with said synchronization information.   
     
     
       22. A method for synchronizing a receiver device to receive OFDM-signals which are transmitted from a transmitter device in an OFDM communication system, comprising the steps of:
 receiving a time domain sequence of synchronization signals which are modulated onto every 4-th subcarrier of a plurality of available subcarriers being used in the OFDM transmission system, wherein said time domain sequence of said synchronization signals contains 4 identical waveforms;   detecting synchronization information by using said 4 identical waveforms of said synchronization signals; and   synchronizing a unit for decoding said received OFDM signals in accordance with said synchronization information.   
     
     
       23. A receiver for receiving OFDM-signals and synchronization signals transmitted from a transmitter in an OFDM communication system, comprising:
 an antenna configured to receive said OFDM signals modulated onto a plurality of available subcarriers using an OFDM-modulation method and synchronization signals being modulated on every 4th subcarrier of said plurality of available subcarriers and the other subcarriers of said plurality of available subcarriers are not modulated;   a detector configured to detect synchronization information by using said synchronization signals; and   a decoder configured to decode said received OFDM signals in accordance with said synchronization information.   
     
     
       24. A receiver for receiving OFDM-signals and synchronization signals transmitted from a transmitter in an OFDM communication system, comprising:
 an antenna configured to receive said synchronization signals which are modulated on every 4th subcarrier of said plurality of available subcarriers and the other subcarriers of said plurality of available subcarriers are not modulated, wherein a time domain sequence of said synchronization signals contains 4 identical waveforms;   a detector configured to detect synchronization information by correlating said 4 identical waveforms of said synchronization signals; and   a decoder configured to decode said received OFDM signals in accordance with said synchronization information.   
     
     
       25. A receiver for receiving OFDM-signals which are transmitted from a transmitter in an OFDM communication system, comprising:
 an antenna configured to receive a time domain sequence of synchronization signals which are modulated onto every 4-th subcarrier of a plurality of available subcarriers being used in the OFDM transmission system, wherein said time domain sequence of said synchronization signals contains 4 identical waveforms;   a detector configured to detect synchronization information by using said 4 identical waveforms of said synchronization signals; and   a decoder configured to decode said received OFDM signals in accordance with said synchronization information.   
     
     
       26. A method for receiving OFDM signals transmitted from an OFDM transmitter, the method comprising:
 receiving OFDM signals modulated onto a first plurality of subcarriers using an OFDM modulation method, wherein every 4 th  subcarrier of a second plurality of subcarriers corresponds to the first plurality of subcarriers, and said first plurality of modulated subcarriers are transformed into the time domain.   
     
     
       27. The method of receiving OFDM signals according to claim 26, wherein subcarriers of said second plurality of subcarriers that do not correspond to said first plurality of subcarriers are not modulated. 
     
     
       28. A receiver for receiving OFDM signals transmitted from an OFDM transmitter, comprising:
 an antenna configured to receive OFDM signals modulated onto a first plurality of subcarriers using an OFDM modulation method, wherein every 4 th  subcarrier of a second plurality of subcarriers corresponds to the first plurality of subcarriers, and said first plurality of modulated subcarriers are transformed into the time domain.   
     
     
       29. The receiving apparatus according to claim 28, wherein subcarriers of said second plurality of subcarriers that do not correspond to said first plurality of subcarriers are not modulated.