Apparatus and method for minimizing a PAPR in an OFDM communication system

• US 20060078066A1
• Filed: 10/11/2005
• Published: 04/13/2006
• Est. Priority Date: 10/11/2004
• Status: Active Grant

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Park, Dong-Seek, Kim, Jae-Yoel, Jeong, Hong-Sil, Joo, Pan-Yuh, Chae, Chan-Byoung, Ko, Kyun-Byoung, Oh, Jeong-Tae, Yun, Sung-Ryul, Roh, Won-Il
• Granted Patent: US 7,664,192 B2
• Time in Patent Office: Days
• US Class Current: 375/299
• CPC Class Codes: H04B 7/068 using space frequency diversity space-frequency coding H04L1/0606
• CPC Class Codes: H04B 7/0848 Joint weighting
• CPC Class Codes: H04B 7/0854 using error minimizing algorithms, e.g. minimum mean squared error [MMSE], "cross-correlation" or matrix inversion
• CPC Class Codes: H04L 1/0606 Space-frequency coding
• CPC Class Codes: H04L 1/0668 Orthogonal systems, e.g. using Alamouti codes
• CPC Class Codes: H04L 27/2615 Reduction thereof using coding
• CPC Class Codes: H04L 27/2634 Inverse fast Fourier transform [IFFT] or inverse discrete Fourier transform [IDFT] modulators in combination with other circuits for modulation
• CPC Class Codes: H04L 27/26524 Fast Fourier transform [FFT] or discrete Fourier transform [DFT] demodulators in combination with other circuits for demodulation

Abstract

A transmitter for minimizing a PAPR in OFDM communication system. The transmitter includes: a precoder for coding input symbols so that a signal rotation is generated, and generating a complex vector including the coded symbols; an encoder for performing a frequency-space mapping for the symbols generated as the complex vector according to a predetermined scheme; a random mapper for randomly mapping the symbols for which the frequency-space mapping has been performed on a frequency plane through at least one transmit antenna; an Inverse Fast Fourier Transform (IFFT) unit for performing an IFFT for the symbols for which the frequency-space mapping has been performed; and a gradient algorithm unit for receiving IFFTed signals from the IFFT unit and reducing the PAPR.

Claims

1. A transmitter for minimizing a Peak-to-Average Power Ratio (PAPR) in a multi carrier communication system, the transmitter comprising:

at least one transmit antenna;

a precoder for coding input symbols so that a signal rotation is generated, and generating a complex vector including the coded symbols;

an encoder for performing a frequency-space mapping for the symbols generated as the complex vector according to a predetermined scheme;

an Inverse Fast Fourier Transform (IFFT) unit for performing an IFFT for the symbols for which the frequency-space mapping has been performed; and

a gradient algorithm unit for receiving IFFTed signals from the IFFT unit and reducing the PAPR.

2. The transmitter as claimed in claim 1, wherein the gradient algorithm unit comprises:

a phase rotator for changing a phase of impulse signals generated with L number of tones having reserved positions to a phase of signals having a maximum peak value from among the output signals after the IFFT;

a scaling unit for scaling the signals generated with the L number of tones by a difference between the maximum peak value and a target power value; and

a complex adder for performing complex addition for the complex output signals after the IFFT and the scaled signals.

3. The transmitter as claimed in claim 2, wherein the gradient algorithm unit further comprises a PAPR operator for calculating the PAPR of a result output from the complex adder.

4. The transmitter as claimed in claim 3, wherein the gradient algorithm unit further comprises a controller for comparing a value output from the PAPR operator with the predetermined target power value and controls signal output based on the comparison.

5. The transmitter as claimed in claim 1, wherein the encoder encodes the symbols generated as the complex vector by an Alamouti scheme and performs the frequency-space mapping for the encoded symbols.

6. A transmitter for minimizing a Peak-to-Average Power Ratio (PAPR) in a multi carrier communication system, the transmitter comprising:

at least one transmit antenna;

a precoder for coding input symbols so that a signal rotation is generated, and generating a complex vector including the coded symbols;

an encoder for performing a frequency-space mapping for the symbols generated as the complex vector according to a predetermined scheme;

a random mapper for randomly mapping the symbols for which the frequency-space mapping has been performed on a frequency plane through said at least one transmit antenna;

an Inverse Fast Fourier Transform (IFFT) unit for performing an IFFT for the symbols for which the frequency-space mapping has been performed; and

a gradient algorithm unit for receiving IFFTed signals from the IFFT unit and reducing the PAPR.

7. The transmitter as claimed in claim 6, wherein the encoder encodes the symbols generated as the complex vector by an Alamouti scheme and performs the frequency-space mapping for the encoded symbols.

8. The transmitter as claimed in claim 6, wherein the random mapper performs a random selection according each of adjacent sub-carriers.

9. The transmitter as claimed in claim 6, wherein the random mapper generates a predetermined number of vectors by bundling the symbols constituting a precoded symbol sequence by a predetermined number of symbols using a random sequence.

10. The transmitter as claimed in claim 6, wherein the gradient algorithm unit comprises:

a phase rotator for changing a phase of impulse signals generated with L number of tones having reserved positions to a phase of signals having a maximum peak value from among the output signals after the IFFT;

a scaling unit for scaling the signals generated with the L number of tones by a difference between the maximum peak value and a target power value; and

a complex adder for performing complex addition for the complex output signals after the IFFT and the scaled signals.

11. The transmitter as claimed in claim 10, wherein the gradient algorithm unit further comprises a PAPR operator for calculating the PAPR of a result output from the complex adder.

12. The transmitter as claimed in claim 11, wherein the gradient algorithm unit further comprises a controller for comparing a value output from the PAPR operator with the predetermined target power value and controls signal output based on the comparison.

13. A transmitter for minimizing a Peak-to-Average Power Ratio (PAPR) in a multi carrier communication system, the transmitter comprising:

at least one transmit antenna;

a precoder for coding input symbols so that a signal rotation is generated, and generating a complex vector including the coded symbols;

an encoder for separating the symbols output from the precoder so as to generate a predetermined number of vectors, encoding the generated vectors by a predetermined scheme, performing a frequency-space mapping for the encoded vectors, and randomly mapping the symbols for which the frequency-space mapping has been performed on a frequency plane through said at least one transmit antenna;

an Inverse Fast Fourier Transform (IFFT) unit for performing an IFFT for the symbols for which the frequency-space mapping has been performed; and

a gradient algorithm unit for receiving IFFTed signals from the IFFT unit and reducing the PAPR.

14. The transmitter as claimed in claim 13, wherein the encoder encodes the symbols generated as the complex vector by an Alamouti scheme and performs the frequency-space mapping for the encoded symbols.

15. The transmitter as claimed in claim 13, wherein the encoder performs a random selection according each of adjacent sub-carriers.

16. The transmitter as claimed in claim 13, wherein the encoder, generates a predetermined number of vectors by bundling the symbols constituting a precoded symbol sequence by a predetermined number of symbols using a random sequence.

17. The transmitter as claimed in claim 13, wherein the gradient algorithm unit comprises:

a phase rotator for changing a phase of impulse signals generated with L number of tones having reserved positions to a phase of signals having a maximum peak value from among the output signals after the IFFT;

a scaling unit for scaling the signals generated with the L number of tones by a difference between the maximum peak value and a target power value; and

a complex adder for performing complex addition for the complex output signals after the IFFT and the scaled signals.

18. The transmitter as claimed in claim 17, wherein the gradient algorithm unit further comprises a PAPR operator for calculating the PAPR of a result output from the complex adder.

19. The transmitter as claimed in claim 18, wherein the gradient algorithm unit further comprises a controller for comparing a value output from the PAPR operator with the predetermined target power value and controls signal output based on the comparison.

20. A receiver for minimizing a Peak-to-Average Power Ratio (PAPR) in a multi carrier communication system, the receiver comprising:

at least one reception antenna;

a modulator for converting signals received through said at least one reception antenna into baseband signals, performing a Fast Fourier Transform (FFT) for the baseband signals, performing a demodulation for the FFTed signals, and outputting a demodulated data;

a channel estimator for receiving the demodulated data and estimating channel coefficients representing a channel gain;

a channel response matrix generator for generating a channel response matrix by means of the channel coefficients from the channel estimator;

a signal combiner for outputting a vector with a predetermined size by combining the demodulated data from the demodulator with the channel response matrix generated by the channel response matrix generator according to a predetermined rule; and

a first and a second signal determiner for estimating and outputting symbols transmitted from a transmitter by performing maximum likelihood decoding using the channel response matrix generated by the channel response matrix generator and the vector with the predetermined size output from the signal combiner.

21. The receiver as claimed in claim 20, wherein, when one reception antenna exists in the receiver, signals y received through the receive antenna satisfies:

$\begin{array}{c}y=H<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\Theta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>d+n\\ =\frac{1}{2}<br><br>\left[\begin{array}{cccc}{h}_1& h_1<br><br>{\mathrm{\alpha <br><br>}}_0^1& h_2& h_2<br><br>{\mathrm{\alpha <br><br>}}_0^1\\ h_2^{*}& h_2^{*}<br><br>{\mathrm{\alpha <br><br>}}_0^1& -h_1^{*}& -h_1^{*}<br><br>{\mathrm{\alpha <br><br>}}_0^1\\ h_3& h_3<br><br>{\mathrm{\alpha <br><br>}}_1^1& h_4& h_4<br><br>{\mathrm{\alpha <br><br>}}_1^1\\ h_4^{*}& h_4^{*}<br><br>{\mathrm{\alpha <br><br>}}_1^1& -h_3^{*}& -h_3^{*}<br><br>{\mathrm{\alpha <br><br>}}_1^1\end{array}\right]<br><br>\left[\begin{array}{c}{x}_1\\ x_2\\ x_3\\ x_4\end{array}\right]+\left[\begin{array}{c}{n}_1\\ n_2^{*}\\ n_3\\ n_4^{*}\end{array}\right],\\ \text{\hspace{1em}<br><br>}\end{array}$

wherein H represents the channel response matrix, Θ

represents a precoding matrix, and n represents a noise vector.

22. The receiver as claimed in claim 20, wherein the channel response matrix is acquired by a multiplication of a previous channel response matrix by a precoding matrix.

23. The receiver as claimed in claim 20, wherein the signal combiner calculates a Hermitian matrix of the channel response matrix and outputs the signals demodulated by the demodulator.

24. The receiver as claimed in claim 20, wherein the signal combiner outputs a first to a

${\left(\frac{N}{2}\right)}^{\mathrm{th}}$

symbol from among total N number of symbols to the first signal determiner and outputs a

${\left(\frac{N}{2}+1\right)}^{\mathrm{th}}$

to a N^th symbol from among the total N symbols to the second signal determiner.

25. A receiver for minimizing a Peak-to-Average Power Ratio (PAPR) in a multi carrier communication system, the receiver comprising:

at least one reception antenna;

a modulator for converting signals received through said at least one reception antenna into baseband signals, performing a Fast Fourier Transform (FFT) for the baseband signals, performing a demodulation for the FFTed signals, and outputting a demodulated data;

a random sequence unit for storing predetermined random sequences, and separating signals of adjacent sub-carriers into predetermined groups based on the stored random sequences;

a channel estimator for receiving signals output from the random sequence unit and estimating channel coefficients representing a channel gain;

a channel response matrix generator for generating a channel response matrix by means of the channel coefficients from the channel estimator;

a signal combiner for outputting a vector with a predetermined size by combining the signals output from the random sequence unit with the channel response matrix generated by the channel response matrix generator according to a predetermined rule; and

a first and a second signal determiner for estimating and outputting symbols transmitted from a transmitter by performing maximum likelihood decoding using the channel response matrix generated by the channel response matrix generator and the vector with the predetermined size output from the signal combiner.

26. The receiver as claimed in claim 25, wherein, when one reception antenna exists in the receiver, signals y received through the receive antenna satisfy:

$\begin{array}{c}y=H<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\Theta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>d+n\\ =\frac{1}{2}<br><br>\left[\begin{array}{cccc}{h}_1& h_1<br><br>{\mathrm{\alpha <br><br>}}_0^1& h_2& h_2<br><br>{\mathrm{\alpha <br><br>}}_0^1\\ h_2^{*}& h_2^{*}<br><br>{\mathrm{\alpha <br><br>}}_0^1& -h_1^{*}& -h_1^{*}<br><br>{\mathrm{\alpha <br><br>}}_0^1\\ h_3& h_3<br><br>{\mathrm{\alpha <br><br>}}_1^1& h_4& h_4<br><br>{\mathrm{\alpha <br><br>}}_1^1\\ h_4^{*}& h_4^{*}<br><br>{\mathrm{\alpha <br><br>}}_1^1& -h_3^{*}& -h_3^{*}<br><br>{\mathrm{\alpha <br><br>}}_1^1\end{array}\right]<br><br>\left[\begin{array}{c}{x}_1\\ x_2\\ x_3\\ x_4\end{array}\right]+\left[\begin{array}{c}{n}_1\\ n_2^{*}\\ n_3\\ n_4^{*}\end{array}\right],\\ \text{\hspace{1em}<br><br>}\end{array}$

wherein H represents the channel response matrix, Θ

represents a preceding matrix, and n represents a noise vector.

27. The receiver as claimed in claim 25, wherein the channel response matrix is acquired by a multiplication of a previous channel response matrix by a preceding matrix.

28. The receiver as claimed in claim 25, wherein the signal combiner calculates a Hermitian matrix of the channel response matrix and outputs the signals demodulated by the modulator.

29. The receiver as claimed in claim 25, wherein the signal combiner outputs a first to a

${\left(\frac{N}{2}\right)}^{\mathrm{th}}$

symbol from among total N symbols to the first signal determiner and outputs a

${\left(\frac{N}{2}+1\right)}^{\mathrm{th}}$

to a N^th symbol from among the total N symbols to the second signal determiner.

30. A transmission method in a transmitter for minimizing a Peak-to-Average Power Ratio (PAPR) in a multi carrier communication system, the transmitter including at least one transmit antenna, the method comprising the steps of:

receiving a data sequence to be transmitted;

generating a predecoded symbol sequence with the received data sequence through precoding using a preset preceding matrix;

generate a predetermined number of vectors by grouping symbols constituting the predecoded symbol sequence into groups having a predetermined number of symbols;

performing a frequency-space mapping for the generated vectors according to a predetermined scheme;

allocating signals for which the frequency-space mapping has been performed to sub-carriers;

performing an Inverse Fast Fourier Transform (IFFT) on the allocated signals;

outputting the IFFTed signals;

receiving the IFFTed signals;

reducing the PAPR of the received signals; and

transmitting signals having the reduced PAPR through said at least one transmit antenna.

31. The method as claimed in claim 30, wherein the step of reducing the PAPR comprises the steps of:

generating a waveform having impulse characteristics with a predetermined number of tones having reserved positions from among total multi-carriers;

performing the IFFT for the generated waveform to output signals on a time domain;

detecting a peak value of the output signals;

harmonizing phases by circularly moving the generated waveform to a position of the detected peak value;

determining a scaling value of the waveform such that the scaling value is smaller than a system setup PAPR;

performing a complex operation for the determined scaling value and the output signals;

ending output of a value obtained through the complex operation and repetition performance when the value is smaller than the system setup PAPR; and

continuing the repetition performance by a preset number of repetitions when the value is larger than the system setup PAPR.

32. The method as claimed in claim 31, wherein the tones having the reserved positions are selected from sub-carriers not transmitting data by a predetermined number.

33. The method as claimed in claim 31, wherein the step of detecting the peak of the output signals comprises detecting a position of a peak value having deviated from a PAPR of a preset system setup value.

34. The method as claimed in claim 31, wherein the circularly moved phase is obtained by normalizing a maximum peak value and a phase of the waveform having the impulse characteristics is rotated by a phase of the maximum peak value.

35. The method as claimed in claim 30, further comprising the steps of:

encoding the generated vectors by an Alamouti scheme; and

performing the frequency-space mapping for the encoded vectors.

36. A transmission method in a transmitter for minimizing a Peak-to-Average Power Ratio (PAPR) in a multi carrier communication system, the transmitter including at least one transmit antenna, the method comprising the steps of:

receiving a data sequence to be transmitted;

generating a predecoded symbol sequence with the received data sequence through precoding using a preset preceding matrix;

performing a frequency-space mapping for the generated symbol sequence according to a predetermined scheme;

randomly mapping symbols for which the frequency-space mapping has been performed on a frequency plane through said at least one transmit antenna;

performing an Inverse Fast Fourier Transform (IFFF) for the symbols for which the frequency-space mapping has been performed;

outputting IFFTed signals;

receiving the IFFTed signals;

reducing the PAPR of the received signals; and

transmitting signals having the reduced PAPR through said at least one transmit antenna.

37. The method as claimed in claim 36, wherein the step of performing the frequency-space mapping comprises the steps of:

encoding predetermined vectors by an Alamouti scheme; and

performing the frequency-space mapping for the encoded vectors.

38. The method as claimed in claim 36, wherein, in the random mapping, a random selection is performed according to each of adjacent sub-carriers.

39. The method as claimed in claim 36, wherein, in the random mapping, adjacent random sequences are separated into predetermined groups, and the predecoded symbol sequence is mapped to a sub-carrier using a random sequence.

40. The method as claimed in claim 36, wherein the step of reducing the PAPR comprises the steps of:

generating a waveform having impulse characteristics with a predetermined number of tones having reserved positions from among total multi-carriers;

performing the IFFT for the generated waveform to output signals on a time domain;

detecting a peak value of the output signals;

harmonizing phases by circularly moving the generated waveform to a position of the detected peak value;

determining a scaling value of the waveform such that the scaling value is smaller than a system setup PAPR;

performing a complex operation for the determined scaling value and the output signals;

ending output of a value obtained through the complex operation and repetition performance, when the value is smaller than the system setup PAPR; and

continuing the repetition performance by a preset number of repetitions, when the value is larger than the system setup PAPR.

41. The method as claimed in claim 40, wherein the tones having the reserved positions are selected from sub-carriers not transmitting data by a predetermined number.

42. The method as claimed in claim 40, wherein the step of detecting the peak of the output signals comprises detecting a position of a peak value having deviated from a PAPR of a preset system setup value.

43. The method as claimed in claim 40, wherein the circularly moved phase is obtained by normalizing a maximum peak value and a phase of the waveform having the impulse characteristics is rotated by a phase of the maximum peak value.

44. A transmission method in a transmitter for minimizing a Peak-to-Average Power Ratio (PAPR) in a multi carrier communication system, the transmitter including at least one transmit antenna, the method comprising the steps of:

receiving a data sequence to be transmitted;

generating a predecoded symbol sequence with the received data sequence through precoding using a preset preceding matrix;

separating the generated predecoded symbol sequence to generate a predetermined number of vectors;

encoding the generated vectors according to a predetermined scheme;

randomly mapping the encoded vectors on a frequency plane;

performing an Inverse Fast Fourier Transform (IFFT) for the symbols for which the frequency-space mapping has been performed;

outputting IFFTed signals;

receiving the IFFTed signals and reducing the PAPR; and

transmitting signals having the reduced PAPR through said at least one transmit antenna.

45. The method as claimed in claim 44, further comprising the steps of:

encoding the generated vectors by an Alamouti scheme; and

performing the frequency-space mapping for the encoded vectors.

46. The method as claimed in claim 44, wherein, in the random mapping, a random selection is performed according to each of adjacent sub-carriers.

47. The method as claimed in claim 44, wherein, in the encoding and the random mapping, adjacent random sequences are separated into predetermined groups, and the predecoded symbol sequence is mapped to a sub-carrier by means of a random sequence.

48. The method as claimed in claim 44, wherein the step of reducing the PAPR comprises the steps of:

generating a waveform having impulse characteristics with a predetermined number of tones having reserved positions from among total multi-carriers;

performing the IFFT for the generated waveform to output signals on a time domain;

detecting a peak value of the output signals;

harmonizing phases by circularly moving the generated waveform to a position of the detected peak value;

determining a scaling value of the waveform such that the scaling value is smaller than a system setup PAPR;

performing a complex operation for the determined scaling value and the output signals;

ending output of a value obtained through the complex operation and repetition performance, when the value is smaller than the system setup PAPR; and

continuing the repetition performance by a preset number of repetitions, when the value is larger than the system setup PAPR.

49. The method as claimed in claim 48, wherein the tones having the reserved positions are selected from sub-carriers not transmitting data by a predetermined number.

50. The method as claimed in claim 48, wherein the step of detecting the peak of the output signals comprises detecting a position of a peak value having deviated from a PAPR of a preset system setup value.

51. The method as claimed in claim 48, wherein the circularly moved phase is obtained by normalizing a maximum peak value and a phase of the waveform having the impulse characteristics is rotated by a phase of the maximum peak value.

52. A reception method in a receiver for minimizing a Peak-to-Average Power Ratio (PAPR) in an Orthogonal Frequency Division Multiplexing (OFDM) communication system, the receiver including at least one receive antenna, the method comprising the steps of:

converting signals received through said at least one receive antenna to baseband signals;

performing a Fast Fourier Transform (FFT) for the baseband signals, performing an OFDM demodulation for the FFTed signals;

outputting OFDM demodulated signals;

estimating channel coefficients representing a channel gain between a transmitter and the receiver by means of the OFDM demodulated signals;

generating a channel response matrix by means of the estimated channel coefficients;

generating a vector with a predetermined size by combining the OFDM demodulated signals with the channel response matrix according to a predetermined rule; and

estimating transmission symbols by performing maximum likelihood decoding using the channel response matrix and the vector with the predetermined size.

53. The method as claimed in claim 52, wherein, when one receive antenna exists in the receiver, signals y received through the receive antenna satisfy:

$\begin{array}{c}y=H<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\Theta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>d+n\\ =\frac{1}{2}<br><br>\left[\begin{array}{cccc}{h}_1& h_1<br><br>{\mathrm{\alpha <br><br>}}_0^1& h_2& h_2<br><br>{\mathrm{\alpha <br><br>}}_0^1\\ h_2^{*}& h_2^{*}<br><br>{\mathrm{\alpha <br><br>}}_0^1& -h_1^{*}& -h_1^{*}<br><br>{\mathrm{\alpha <br><br>}}_0^1\\ h_3& h_3<br><br>{\mathrm{\alpha <br><br>}}_1^1& h_4& h_4<br><br>{\mathrm{\alpha <br><br>}}_1^1\\ h_4^{*}& h_4^{*}<br><br>{\mathrm{\alpha <br><br>}}_1^1& -h_3^{*}& -h_3^{*}<br><br>{\mathrm{\alpha <br><br>}}_1^1\end{array}\right]<br><br>\left[\begin{array}{c}{x}_1\\ x_2\\ x_3\\ x_4\end{array}\right]+\left[\begin{array}{c}{n}_1\\ n_2^{*}\\ n_3\\ n_4^{*}\end{array}\right],\\ \text{\hspace{1em}<br><br>}\end{array}$

wherein H represents the channel response matrix, Θ

represents a precoding matrix, and n represents a noise vector.

54. The method as claimed in claim 52, wherein the channel response matrix is acquired by a multiplication of a previous channel response matrix by a precoding matrix.

55. The method as claimed in claim 52, wherein the step of combining the OFDM demodulated signals with the channel response matrix comprises a the steps of:

calculating a Hermitian matrix of the channel response matrix; and

outputting the OFDM demodulated signals.

56. The method as claimed in claim 52, wherein the step of combining the OFDM demodulated signals with the channel response matrix further comprises outputting a first to a

${\left(\frac{N}{2}\right)}^{\mathrm{th}}$

symbol from among total N symbols as first signals and outputting a

${\left(\frac{N}{2}+1\right)}^{\mathrm{th}}$

to a N^th symbol from among the total N symbols to second signals.

57. A reception method in a receiver for minimizing a Peak-to-Average Power Ratio (PAPR) in an Orthogonal Frequency Division Multiplexing (OFDM) communication system, the receiver including at least one receive antenna, the method comprising the steps of:

converting signals received through said at least one receive antenna to baseband signals;

performing a Fast Fourier Transform (FFT) for the baseband signals;

performing an OFDM demodulation for the FFTed signals;

outputting OFDM demodulated signals;

separating signals of adjacent sub-carriers into predetermined groups through a random sequence initially stored in a system;

outputting the groups;

estimating channel coefficients representing a channel gain between a transmitter and the receiver using the OFDM demodulated signals and output signals through the random sequence;

generating a channel response matrix using the estimated channel coefficients;

generating a vector with a predetermined size by combining the OFDM demodulated signals with the channel response matrix according to a predetermined rule; and

estimating transmission symbols by performing maximum likelihood decoding using the channel response matrix and the vector with the predetermined size.

58. The method as claimed in claim 57, wherein, when one receive antenna exists in the receiver, signals y received through the receive antenna satisfy:

$\begin{array}{c}y=H<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\Theta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>d+n\\ =\frac{1}{2}<br><br>\left[\begin{array}{cccc}{h}_1& h_1<br><br>{\mathrm{\alpha <br><br>}}_0^1& h_2& h_2<br><br>{\mathrm{\alpha <br><br>}}_0^1\\ h_2^{*}& h_2^{*}<br><br>{\mathrm{\alpha <br><br>}}_0^1& -h_1^{*}& -h_1^{*}<br><br>{\mathrm{\alpha <br><br>}}_0^1\\ h_3& h_3<br><br>{\mathrm{\alpha <br><br>}}_1^1& h_4& h_4<br><br>{\mathrm{\alpha <br><br>}}_1^1\\ h_4^{*}& h_4^{*}<br><br>{\mathrm{\alpha <br><br>}}_1^1& -h_3^{*}& -h_3^{*}<br><br>{\mathrm{\alpha <br><br>}}_1^1\end{array}\right]<br><br>\left[\begin{array}{c}{x}_1\\ x_2\\ x_3\\ x_4\end{array}\right]+\left[\begin{array}{c}{n}_1\\ n_2^{*}\\ n_3\\ n_4^{*}\end{array}\right],\\ \text{\hspace{1em}<br><br>}\end{array}$

wherein H represents the channel response matrix, Θ

represents a precoding matrix, and n represents a noise vector.

59. The method as claimed in claim 57, wherein the channel response matrix is acquired by a multiplication of a previous channel response matrix by a precoding matrix.

60. The method as claimed in claim 57, wherein the step of combining the OFDM demodulated signals with the channel response matrix comprises the steps of:

calculating a Hermitian matrix of the channel response matrix; and

outputting the OFDM demodulated signals.

61. The method as claimed in claim 57, wherein the step of combining the OFDM demodulated signals with the channel response matrix further comprises outputting a first to a

${\left(\frac{N}{2}\right)}^{\mathrm{th}}$

symbol from among total N symbols as first signals and outputting a

${\left(\frac{N}{2}+1\right)}^{\mathrm{th}}$

to a N^th symbol from among the total N symbols to second signals.