US RE43305 E1 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.Claims(46) 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
3. Transmission method according to
4. Transmission method according to
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
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, andtransmission 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
4) the not modulated subcarriers are set to zero.8. Transmission apparatus according to
4) M=2 and only subcarriers with even indices are modulated.9. Transmission apparatus according to
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
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
1=S/M samples and averaged over L2≦S/M samples, whereby S is the total number of samples in one OFDM-timeburst.13. Receiving method according to
14. Receiving method according to
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
28, 29, 30, 31) said identical wave forms are correlated on the basis of a delay value L1=S/M and averaged over L2≦S/M samples, whereby S is the total number of samples in one OFDM-timeburst.17. Receiving apparatus according to
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
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 of transmitting predetermined values on a subset of OFDM subcarriers, comprising steps of:
associating a first subset of a sequence of N subcarriers with the predetermined values, and associating a second subset of the sequence of N subcarriers with a 0 value; respectively modulating said first subset of N subcarriers with the predetermined values, and not modulating the second subset of the sequence of N subcarriers so as to form a modulated subcarrier sequence with modulated separated by unmodulated subcarriers; transforming said modulated subcarrier sequence into a time domain to create a time domain waveform, and transmitting said time domain waveform, wherein a repeating pattern of said modulated subcarrier sequence includes a subcarrier from the first subset followed by 3 unmodulated subcarriers from the second subset of N subcarriers, and said repeating pattern continues for at least 5 cycles, including at least 5 subcarriers from said first subset and 15 subcarriers from said second subset. 21. The method of claim 20, wherein:
said repeating pattern continues for at least 6 cycles, including at least 6 subcarriers from said first subset and 18 subcarriers from said second subset. 22. The method of claim 20, wherein:
said predetermined values are non-zero, and have a common magnitude. 23. The method of claim 20, wherein:
said time domain waveform includes 4 substantially identical or mirrored waveforms within one OFDM timeburst. 24. The method of claim 20, wherein said information includes synchronization information.
25. A method of transmitting predetermined values on a subset of OFDM subcarriers, comprising steps of:
associating a first subset of a sequence of N subcarriers with the predetermined values, and associating a second subset of the sequence of N subcarriers with a 0 value; modulating said first subset of N subcarriers with the predetermined values, and not modulating the second subset of the sequence of N subcarriers so as to create a modulated subcarrier sequence; time domain transforming said modulated subcarrier sequence to create a time domain waveform, and transmitting said time domain waveform, wherein respective of said N subcarriers are separated by 3 unmodulated subcarriers from the second subset of N subcarriers in a repeating pattern, the repeating pattern including one of the N subcarriers followed sequentially by 3 of the second subset of subcarriers, and said repeating pattern continues for at least 5 cycles such that the modulated subcarrier sequence includes at least 5 subcarriers from said first subset and 15 subcarriers from said second subset. 26. The method of claim 25, wherein:
said repeating pattern continues for at least 6 cycles, including at least 6 subcarriers from said first subset and 18 subcarriers from said second subset. 27. The method of claim 25, wherein:
said predetermined values are non-zero, and have a common magnitude. 28. The method of claim 25, wherein:
said time domain waveform includes 4 substantially identical or mirrored waveforms within one OFDM timeburst. 29. The method of claim 25, wherein said information includes synchronization information.
30. A transmission method for transmitting information from an OFDM transmitter, comprising the steps of:
modulating said information onto a plurality of OFDM subcarriers; transforming said modulated information into the time domain; and transmitting said information, wherein said modulating step includes modulating a first subcarrier with a first value of said information, but not modulating M−1 successive subcarriers, followed by modulating a second subcarrier with a second value of said information, but not modulating M−1 successive subcarriers, M being an integer that is 2 or larger. 31. Transmission method for transmitting OFDM synchronization signals, comprising the steps of
modulating synchronization values onto a subcarrier sequence using a OFDM-modulation method, transforming said modulated subcarrier sequence into the time domain in order to obtain a time domain OFDM synchronization signal, and transmitting said time domain OFDM synchronization signal, wherein in said modulating step every M-th subcarrier is modulated with said synchronization values, M being an integer and M≧2. 32. Transmission method for transmitting OFDM synchronization signals, comprising the steps of
modulating synchronization values onto subcarriers a subcarrier sequence using a OFDM-modulation method, said subcarrier sequence comprising at least a first and a second subset of subcarriers, wherein every M-th subcarrier of said first subset is modulated with said synchronization values, M being an integer and M≧2, and subcarriers in between modulated subcarriers of said first subset are unmodulated, transforming said subcarrier sequence into the time domain in order to obtain a time domain synchronization signal, and transmitting said time domain synchronization signal. 33. Transmission method according to claim 32, wherein at least 5 subcarriers of said first subset are modulated with synchronization information, and 3 consecutive subcarriers in between said modulated subcarriers remain unmodulated, and wherein said second subset comprises at least 3 consecutive subcarriers.
34. Transmission method for transmitting OFDM-signals and synchronization signals, comprising the steps of:
modulating said OFDM signals onto a plurality of available subcarriers using an OFDM-modulation method, transforming said modulated signals into the time domain, and transmitting said transformed signals; wherein in said modulating step said synchronization signals 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. 35. Transmission method for transmitting OFDM synchronization signals by using an OFDM transmission scheme, comprising the steps of:
modulating said OFDM synchronization signals onto every 4th subcarrier of a plurality of available subcarriers being assigned to the OFDM transmission scheme in the frequency domain; transforming a frequency domain sequence of said modulated synchronization signals into the time domain to generate a time domain sequence, and transmitting said time domain sequence. 36. Transmission method for transmitting OFDM data and synchronization signals, comprising the steps of:
modulating said OFDM data onto a plurality of subcarriers using an OFDM-modulation method, wherein said synchronization signals are modulated on every M-th subcarrier of said plurality of subcarriers in the frequency domain so as to generate a frequency domain sequence comprising modulated and un-modulated subcarriers, wherein M is an integer and M≧2; generating a frequency domain representation comprising said frequency domain sequence and zero amplitude sequences being arranged at the front and end of said frequency domain sequence; transforming said frequency domain representation into a time domain representation by using Inverse Discrete Fourier Transformation, wherein the number of samples of said time domain representation is equal to the sum of the number of symbols of said frequency domain sequence and the number of symbols of said zero amplitude sequences; and transmitting said time domain representation. 37. Transmission method for transmitting OFDM synchronization signals by using OFDM transmission scheme, comprising the steps of:
generating a frequency domain sequence by modulating said OFDM synchronization signals on every M-th subcarrier of a plurality of subcarriers used in said OFDM transmission scheme, 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; providing a frequency domain representation comprising said frequency domain sequence and second frequency domain sequences having zero amplitude symbols, wherein said second frequency domain sequences are arranged at the front and end of said frequency domain sequence; transforming said frequency domain representation into a time domain representation by using Inverse Discrete Fourier Transformation, wherein the number of samples of said time domain representation is equal to the total number of symbols in said frequency domain sequence and second frequency domain sequences; and transmitting said time domain representation. 38. Transmission method for transmitting OFDM data and synchronization signals, comprising the steps of:
modulating said OFDM data onto a plurality of subcarriers using an OFDM-modulation method, wherein said synchronization signals are modulated on every M-th subcarrier of said plurality of subcarriers in the frequency domain so as to generate a frequency domain sequence wherein M is an integer and M≧2; transforming said frequency domain sequence into a time domain sequence by using Inverse Discrete Fourier Transformation, cyclically extending said time domain sequence in time domain so that the length of the extended time domain sequence is longer than the one OFDM timeburst period; and transmitting said extended time domain sequence. 39. Transmission method for transmitting OFDM synchronization signals by using an OFDM transmission scheme, comprising the steps of:
generating a frequency domain sequence by modulating said OFDM synchronization signals on every M-th subcarrier of a plurality of subcarriers used in said OFDM transmission scheme, wherein M is an integer and M≧2; transforming said frequency domain sequence into a time domain sequence by using Inverse Discrete Fourier Transformation, cyclically extending said time domain sequence in time domain so that the number of samples of the extended time domain sequence is larger than the number of samples of said time domain sequence; and transmitting said extended time domain sequence. 40. Transmission method for transmitting OFDM data and synchronization signals, comprising the steps of:
modulating said OFDM data onto a plurality of subcarriers using an OFDM-modulation method, wherein said synchronization signals are modulated on every M-th subcarrier of said plurality of subcarriers in the frequency domain so as to generate a frequency domain sequence, wherein M is an integer and M≧2; transforming said frequency domain sequence into a time domain sequence by using a scheme of Inverse Discrete Fourier Transformation 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. 41. Transmission method for transmitting OFDM synchronization signals by using OFDM transmission scheme, comprising the steps of:
generating a frequency domain sequence by modulating said OFDM synchronization signals on every M-th subcarrier of a plurality of subcarriers used in said OFDM transmission scheme, wherein M is an integer and M≧2; transforming said frequency domain sequence into a time domain sequence by using a scheme of Inverse Discrete Fourier Transformation 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. 42. Transmission method for transmitting OFDM data and synchronization signals, comprising the steps of:
modulating said OFDM data onto a plurality of subcarriers using an OFDM-modulation method, wherein said synchronization signals are modulated on every M-th subcarrier of said plurality of subcarriers in the frequency domain so as to generate a frequency domain sequence, wherein M is an integer and M≧2; transforming said frequency domain sequence into a time domain sequence by using a scheme of Inverse Discrete Fourier Transformation so that said time domain sequence comprises M-th identical waveforms, wherein each of said M-th identical waveforms is correlated in the receiver device to detect the synchronization timing information; and transmitting said time domain sequence. 43. A transmission method for transmitting OFDM signals from an OFDM transmitter, the method comprising:
modulating said OFDM signals 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;transforming said first plurality of modulated subcarriers into the time domain, and transmitting said time domain transformed modulated subcarriers. 44. The transmission method according to claim 43, wherein subcarriers of said second plurality of subcarriers that do not correspond to said first plurality of subcarriers are not modulated.
45. A transmission apparatus configured to transmit OFDM signals, the transmission apparatus comprising:
a modulation unit configured to modulate said OFDM signals 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;an inverse discrete Fourier transform unit configured to transform said first plurality of modulated subcarriers into the time domain; and a transmitter configured to transmit said time domain transformed modulated subcarriers. 46. The transmission apparatus according to claim 45, wherein subcarriers of said second plurality of subcarriers that do not correspond to said first plurality of subcarriers are not modulated.
Description The present invention relates to a transmission method according to the preamble of claim In a conventional OFDM-system signals or information contained in signals are modulated onto subcarriers in the frequency domain. The spacing between the subcarriers is equal and the subcarriers are arranged orthogonally in the frequency domain. The respectively applied modulation scheme varies for example the magnitude and phase of the described subcarriers. A conventional transmission apparatus for transmitting OFDM-signals therefore comprises as basic elements modulation means for modulating said signal onto a plurality of subcarriers using a OFDM-modulation method, transformation means for transforming said modulated signals into the time domain, and transmission means for transmitting said signals. In a conventional OFDM-system, a transmission means for OFDM-signals extends a time domain signal after a transformation into the time domain (e. g. by an inverse discrete Fourier transformation) by some guard samples to overcome multipath effects during the transmission. Usually the extension of the time domain signal is done by a cyclic extension, wherein a part of the wave form is repeated. A corresponding OFDM-signal receiving apparatus can perform correlation utilizing the two identical wave form parts to obtain information on the timing of the OFDM-time bursts for further processing. Usually this timing information is used to optimally place the discrete Fourier transformation window in the receiving apparatus to be able to transform the modulated subcarriers into the frequency domain and to demodulate them thereafter. To provide an efficient transmission system, the guard time or cyclic extension has to be as short as possible, namely slightly larger than the longest expected transmission path duration, which can result in poor cyclic extension based correlation properties in a receiving apparatus if the cyclic extension is very short (e. g. only a few samples). In this case, in known OFDM-systems synchronization bursts are used, which contain only synchronization information. This reduces the transmission efficiency, since a special synchronization burst designed in the time domain does not contain information (in the frequency/subcarrier domain) to be transmitted. The object of the present invention is therefore to provide a transmission method according to the preamble of claim This object is achieved by a transmission method according to claim The transmission method for transmitting OFDM-signals according to the present invention comprises 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. The transmission apparatus for transmitting OFDM-signals according to the present invention comprises modulation means for modulating said signals onto a plurality of subcarriers using a OFDM-modulation method, transformation means for transforming said modulated signal 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. The receiving method according to the present invention is adapted for receiving OFDM-signals comprising M identical or respectively mirrored wave forms within one OFDM-timeburst, wherein M is an integer and M≧2, and comprises the steps of receiving said OFDM-signals, correlating said wave forms to obtain time synchronization, transforming said signals into the frequency domain, and demodulating said signals. The receiving apparatus according to the present invention is adapted for receiving OFDM-signal comprising M identical or respectively mirrored wave forms within one OFDM-timeburst, wherein M is an integer and M≧2, and comprises receiving means for receiving said OFDM-signals, correlation means for correlating said wave forms to obtain time synchronization, transformation means for transforming said signals into the frequency domain, and demodulation means for demodulating said signals. Advantageous features of the present invention are defined in the respective subclaims. The modulation of every M-th subcarrier according to the present invention, after the succeeding transformation of the signals into the time domain, e. g. by an inverse discrete Fourier transformation, results in a signal containing M identical or respectively mirrored wave forms, whereby the total duration of the OFDM-timeburst is still 1/f The present invention can be applied to every transmission system based on a multicarrier OFDM-modulation method, e. g. wireless and wired transmission systems. Possible and advantageous applications of the present invention in a wireless transmission system are for example the RACH (Random Access Channel), the BCCH (Broadcast Control Channel), and the IACH (Initial Acquisition Channel). Generally, the present invention is especially effective in scenarios where conventional algorithms to improve correlation based time synchronization, e. g. averaging over multiple time bursts is not possible. The present invention can be applied to any OFDM-system, particularly, when a robust time synchronization for further signal processing, e. g. discrete Fourier transformation, is required. Advantageously, in said modulation means the not modulated subcarriers are set to zero. Further advantageously, only subcarriers with even indices are modulated. If only subcarriers with even indices are modulated (e. g. M=2), a full (complex) time domain signal consisting of two equal wave forms is obtained after the transformation into the time domain (e. g. by an inverse discrete Fourier transformation). If, on the other hand, only subcarriers with odd indices are modulated (e. g. M=2), a full (complex) time domain signal after the transformation into the time domain is obtained, which contains two respectively mirrored wave forms. In this case, the two wave forms are mirrored so that the correlation result is negative and an additional absolute value unit (or inverter) is necessary in the receiving apparatus to achieve a positive correlation result and a correct frequency offset. Advantageously, said modulation means comprises means for generating integer values from 0 to L−1, wherein L is the number of available subcarriers, whereby said modulation means modulates every M-th signal onto said subcarriers on the basis of said integer values. Advantageously, in the correlation means of the receiving apparatus according to the present invention, the identical or respectively mirrored wave forms are correlated on the basis of a delay value L It is further advantageous in the receiving apparatus according to the present invention to provide a peak detection means after said correlation means for providing time synchronization for the transformation of said signals into the frequency domain. It is further advantageous to provide a frequency offset detection means after said correlation means for providing frequency synchronization for the transformation of the signals into the frequency domain. The transmission system for transmitting OFDM-signals according to the present invention comprises a transmission apparatus according to the present invention and a receiving apparatus according to the present invention. This transmission system can be based on a wireless or wired transmission of signals. The present invention is explained in detail by means of preferred embodiments relating to the enclosed drawings, in which After the burst shaping means In The output of the modulo means In In In In The time/frequency synchronization means In Then, the output of the last adder In the example of In the correlation means In a case, in which only subcarriers with odd indices are modulated, an additional absolute block means (or sign inverter) can be used in the receiving apparatus to achieve a positive correlation result. This additional absolute block means can, for example, be provided between the last correlation part and the moving average means In In In The frequency offset is Δf=M×f In As can be seen, the present invention provides for very good peak detection compared to the conventional correlation. The four bursts in the signal stream can be clearly identified. The detected frequency offset values are: 0,3004; 0,3081, 0,3117 and 0,3151 which is very accurate (error<5%). 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