Publication number | USRE43305 E1 |

Publication type | Grant |

Application number | US 11/416,477 |

Publication date | Apr 10, 2012 |

Filing date | May 3, 2006 |

Priority date | Sep 4, 1997 |

Also published as | USRE43703, USRE43829, USRE45293 |

Publication number | 11416477, 416477, US RE43305 E1, US RE43305E1, US-E1-RE43305, USRE43305 E1, USRE43305E1 |

Inventors | Ralf Boehnke |

Original Assignee | Sony Deutschland Gmbh |

Export Citation | BiBTeX, EndNote, RefMan |

Patent Citations (29), Non-Patent Citations (2), Classifications (3) | |

External Links: USPTO, USPTO Assignment, Espacenet | |

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 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 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 **1**, to a transmission apparatus according to the preamble of claim **5**, a receiving method according to claim **9**, a receiving apparatus according to claim **13** and a transmission system according to claim **17**.

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 **1**, a transmission apparatus according to the preamble of claim **5**, a receiving method according to claim **9**, and a receiving apparatus according to claim **13**, which provide optimized correlation possibilities.

This object is achieved by a transmission method according to claim **1**, a transmission apparatus according to claim **5**, a receiving method according to claim **9**, and a receiving apparatus according to claim **13**. Also, this object is achieved by a transmission system according to claim **17**.

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_{0 }(f_{0 }is the subcarrier spacing). With M identical wave forms within one OFDM-timeburst, the corresponding receiving apparatus can perform an optimized correlation in the time domain, e. g. to obtain time and frequency information and synchronization, respectively. Further on, information to be transmitted can be modulated onto every M-th subcarrier and the transmission of a special time-domain synchronization time burst usually not containing useful information in the frequency-subcarrier domain is not necessary.

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**1**=S/M and averaged over L**2**≦S/M samples, whereby S is the total number of samples in one OFDM-timeburst.

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

**1** are channel coded in a channel coding means **2** and interleaved in an interleaving means **3**. In a modulation unit **4**, the signals carrying the data to be transmitted are modulated with an OFDM-modulation method. An OFDM-system is a multicarrier system with a plurality of subcarriers. In the modulation unit **4**, the signals carrying the information to be transmitted are modulated on every M-th subcarrier, wherein M is an integer and M≧2. The modulated signals, for example APM-signals, amplitude-phase-modulated signals, are transformed into the time domain in an inverse discrete Fourier transformation means **5**. After the transformation into the time domain, the transformed signals are provided with a cyclic extension in a cyclic extension means **6**a and then shaped in a burst shaping means **6**b. In the cyclic extension means **6**a, the OFDM-time bursts are provided with a guard time (=cyclic extension of the signal) to mitigate multipath effects during transmission. This cyclic extension serves also to provide correlation (to achieve time and frequency synchronisation) in a corresponding receiving apparatus. The cyclic extension consists in a part of the signal being added to the end of the signal, so that the receiving apparatus can conduct calculations on the basis of the doubled signal parts to provide correlation. The burst shaping means **6**b does not have to be provided in the transmission apparatus according to the present invention, since the described correlation method (to achieve time and frequency synchronisation) is based on the cyclic extension only. The provision of the burst shaping means **6**b, however, improves the transmission spectrum (reduced out of band spurious emission).

After the burst shaping means **6**b, or, if the burst shaping means **6**b is not provided, after the cyclic extension means **6**a, the signals are digital/analog-converted in a D/A-converter **7** and then RF-upconverted in a RF-upconversion means **8** to be transmitted by an antenna **9**.

In **4** of the transmission apparatus shown in **4** comprises a subcarrier number generator **10** for generating integer values 0,1 . . . L−1 corresponding to the available subcarrier number L in one frequency slot in the OFDM-system. The integer values generated by the subcarrier number generator **10** are fed to a modulation unit **17**. Also, the integer values generated by the subcarrier number generator **10** are fed to a modulo means **11**, which generates series of integer values depending on the chosen modulation step of the modulation means **4**. If, for example, every 4-th subcarrier is modulated with a signal, so that M=4, the modulo means **11** outputs integer values 0,1,2,3,0,1,2,3,0,1,2,3, . . . .

The output of the modulo means **11** is fed to a compare means **12**, which compares the integer values provided by the modulo means **11** with integer values generated by a compare value generator **13**. The compare means **12** gives an “active” signal to a switch means **14**, if the inputs from the modulo means **11** and the compare value generator **13** are equal. If, for example in the above example, the compare value generator **13** generates an integer value “1”, the compare means **12** outputs an “active” signal every 4-th time an integer value “1” is fed from the modulo means **11** (M=4). Otherwise, the output of the compare means **12** is a “not active” signal. If the switch means **14** obtains an “active” signal from the compare means **12**, it connects a line **16** providing signals with data to be modulated with the modulation unit **17**. If the switch means **14** obtains an “not active” signal from the compare means **12**, it connects a zero terminal **15** with the modulation unit **17**. In the above example (M=4), the switch means **14** therefore connects the data line **16** every 4-th time an integer value is generated by the subcarrier number generator **10** with the modulation unit **17**. Therefore, every 4-th subcarrier is modulated with signals carrying data in the modulation unit **17**. The other subcarriers are not modulated in the modulation unit **17**, since the switch means **14** selects the zero terminal **15** at the time these subcarriers are fed to the modulation unit **17**. At the zero terminal **15**, a “0” value is input (complex: 0=0+j×0) so that the other subcarriers are not modulated.

In **0** . . . **31** and the vertical axis shows the magnitude of the subcarriers. Also, one frequency slot comprising L=24 (**0** . . . **23**) available subcarriers is shown wherein each subcarrier is sampled in the inverse discrete Fourier transformation means **5**. Each 4-th subcarrier **18** (subcarrier number 0, 4, 8, 12, 16 and 20) is modulated with a signal, wherein the spacing between adjacent subcarriers is f_{0}. The IDFT samples **0** . . . **3** and **28** . . . **31** are unmodulated guard subcarriers (to perform a power-of-2 DFT, here 32-point DFT), and the samples **4** . . . **27** are the used subcarrier samples (here we assumed one frequency slot consists of 24 subcarriers).

In _{1}=a+j×b, the corresponding sample in the second waveform is x_{2}=(−a−j×b)=(−1)*(a+j×b).

In **19** and RF-downconverted in a RF-downconversion means **20**. Then, the signals are analog to digital converted in an A/D-converter **21** and fed to a time/frequency synchronization means **22**. In the time/frequency synchronization means **22**, the received signals are correlated and synchronized, so that a proper transformation to the frequency domain in a succeeding discrete Fourier transformation means **23** can be executed. The transformed signals are then demodulated in a demodulation means **24**. The demodulated signals are de-interleaved in de-interleaving means **25** and then channel-decoded in a channel-decoding means **26**. The channel-decoding means **26** outputs data signals **27** to be further processed.

In **22** of the receiving apparatus shown in **22** consists generally of a correlation means with one or more correlator parts **28**, **29**, **30**, **31** and a moving average means **40**. After the moving average means **40**, an absolute value means **45** is provided. After the absolute value means **45**, a peak detection means **46** can be provided. The output of the peak detection means **46** and the output of the moving average means **40** can be fed to an also optionally provided frequency offset detection means **47**.

The time/frequency synchronization means **22** comprises (M−1) correlator parts. If, for example, every 4-th subcarrier is modulated, the time-/frequency synchronization means **22** comprises 3 correlator parts, as is shown in more detail in

In **21** is fed to a first correlator part **28** comprising a delay means **32** and a multiplier **35**. The output of the A/D-converter is fed to the delay means **32**, which delays the signal with a factor z^{−L1}. The output of the delay means and the output of the A/D-converter **21** are multiplied in the multiplier **35**. The output of the delay means **32** is further fed to a delay means **33** and a multiplier **36** of a second correlator part **29**. The delay means **33** delays the output of the delay means **32** with a factor z^{−L1}. The output of the delay means **33** is multiplied in the multiplier **36** with the output of the delay means **32**. The outputs of the multiplier **35** and the multiplier **36** are added in an adder **38**. Successive correlator parts and adders are symbolized by a block **30**. The (M−1)th correlator part **31** delays the output of the delay means of the preceding correlator part in a delay means **34** by a factor z^{−L1 }and multiplies the output of the delay means **34**. The output of the delay means **34** is multiplied in a multiplier **37** with the output of the preceding delay means. The output of the multiplier **37** is added in an adder **39** to the output of a preceding adder.

Then, the output of the last adder **39** is fed to the moving average means **40**. In the moving average means **49**, the incoming signal is delayed in a delay means **41** by a factor z^{−L2}. In an adder **42**, the output of the delay means **41** is subtracted from the incoming signal. The output of the adder **42** is fed to an adder **43**, which is backfed with its own output delayed by factor z^{−1 }in a delay means **44**. The moving average means thus performs the function

which means y(m)=x(m)+x(m−1)+. . . +x(m−L**2**) if the input signal of the MAV means **40** is defined as x(m) and its output signal is defined as y(m).

In the example of **1** is L**1**=S/M. The moving average value L**2** is L**2**≦S/M, so that a signal fed to the moving average means **40** is delayed over L**2**≦S/M samples. In both cases, S is the total number of samples in one OFDM-timeburst. In the example shown in **1**=8 and L**2**≦8. The best performance is achieved if L**2** is close to S/M, in the example of **2** should be close to 8 samples (e. g. 6, 7 or 8 samples).

In the correlation means **28**, **29**, **30**, **31** and the moving average means **40**, correlation in the time domain to obtain time synchronization information for further processing of the incoming signals is performed. The output of the moving average means **40** is then fed to an absolute value means **45**. The output of the absolute value means **45** is fed to a peak detection means **46**, which identifies the best correlation result for an optimum estimate of the window position of the discrete Fourier transformation in the discrete Fourier transformation means **23**. In an ideal transmission case, the imaginary part of the correlated signal is zero. In the case of a frequency offset in the transmitted signal, the imaginary part of the correlated signal is not zero, so that a frequency offset detection has to be performed in a frequency offset detection means **47**. Conventionally, if all subcarriers are modulated, the frequency offset detection range is limited to −f_{0}/2 . . . +f_{0}2, whereby f_{0 }is the subcarrier spacing. According to the present invention, the frequency offset detection range in the frequency offset detection means **47** is extended to M×(−f_{0}/2) . . . M×(+f_{0}/2), wherein f_{0 }is the subcarrier spacing. Therefore, the frequency offset detection range is advantageously extended according to the present invention. The output of the frequency offset detection means **47** and the peak detection means **46** are used for time-/frequency synchronization in the succeeding discrete Fourier transformation means **23**.

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 **40**. In order to achieve time synchronisation only this block is not necessary, because the absolute value means **45** in

In **22** is shown for M=2. In this case, the correlations means consists only of one correlator part **28**. The correlation delay value L**2** is S/2 and the moving average parameter L**2** is smaller or equal S/2, whereby the best performance is achieved if L**2** is close to S/2.

In **22** is shown for M=4. In this case, L**1**=S/4 and L**2**≦S/4.

In **47** shown in **7** and **8** is shown in more detail. As stated above, the frequency offset detection range is advantageously extended according to the present invention. The structure of the frequency offset detection means **47** shown in

The frequency offset is Δf=M×f_{0}×(½π)×arctan(q/i), wherein M is the number of the repeated wave forms in one OFDM time burst, f_{0 }the subcarrier spacing, “i” the in-phase part and “q” the quadrature part of the complex output of the MAV means **40**. As shown in **47** comprises a split means **48**, a calculation means **49** and a multiplier **50**. In the split means **48**, the complex output of the MAV means **40** is separated in an “in” and a “quad” component, when the split means **48** receives a peak detection signal from the peak detection means **46**. The peak detection means produces a peak detection signal every time it detects a peak. The “in” and “quad” component from the split means **48** are then fed to the calculation means **49**. The calculation means **49** calculates the mathematical expression of (½π)×arctan(q/i), which can be done in a look-up table (hardware implementation) or calculated in a processor. The calculation result from the calculation means **49** is supplied to the multiplier **50**. The multiplier **50** multiplies the calculation result from the calculating means **49** with M(number of repeated wave forms in one OFDM time burst). The result of the multiplication in the multiplier **50** is the frequency offset Δf as a fraction of the subcarrier spacing f_{0 }(result=Δf/f_{0}). The detected frequency offset is used in the synchronisation unit **22** of the receiving apparatus to obtain the frequency synchronisation.

In _{0}, guard samples per burst: **16**, RACH-scheme: **4**, number of RACH-slots: **4**, discrete Fourier transformation size (=number of subcarriers or number of OFDM-burst samples): 128 and used subcarriers per slot: 96.

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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