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

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 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 an Alamouti 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, and for performing a random selection of the symbols for adjacent sub-carriers;

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 for reducing the PAPR,

wherein the gradient algorithm unit comprises:

a P-waveform generator for receiving a predetermined number of tones having reserved positions among a total number of tone signals, and for generating a P-waveform having impulse characteristics;

a peak detector for detecting a maximum peak value of complex output signals x after the IFFT;

a position circulation movement unit for circularly moving a position of the P-waveform to a position of the detected maximum peak value;

a phase rotator for harmonizing the circularly moved P-waveform with the phase of the maximum peak value detected on a complex plane;

a scaling unit for scaling a value of the P-waveform such that it is smaller than a system setup PAPR; and

a complex adder for performing complex addition for the complex output signals x after the IFFT and the scaled value,

wherein the P-waveform is selected by repeating, a predetermined number of times, a process for randomly selecting the predetermined number of tones having positions reserved among the total number of tone signals, and

wherein in the selection process, a value having a smallest power value is selected from remaining values except for a peak value from among values generated through the repetition.

2. The transmitter as claimed in claim 1 , 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.

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

a PAPR operator for calculating the PAPR of a result output from the complex adder; and

a controller for comparing a value output from the PAPR operator with the system setup PAPR and controlling signal output based on the comparison.

4. 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 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 an Alamouti 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 by a random selection of the symbols for adjacent sub-carriers;

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,

wherein the gradient algorithm unit comprises:

a P-waveform generator for receiving a predetermined number of tones having positions reserved among a total number of tone signals, and generating a P-waveform having impulse characteristics;

a peak detector for detecting a maximum peak value of complex output signals x after the IFFT;

a position circulation movement unit for circularly moving a position of the P-waveform to a position of the detected maximum peak value;

a phase rotator for harmonizing the circularly moved P-waveform with the phase of the maximum peak value detected on a complex plane;

a scaling unit for scaling a value of the P-waveform so that the peak value of the complex output signals x after the IFFT is smaller than a system setup PAPR; and

a complex adder for performing complex addition for the complex output signals x after the IFFT and the scaled value,

wherein the P-waveform is selected by repeating, a predetermined number of times, a process for randomly selecting the predetermined number of tones having positions reserved among the total number of tone signals, and

wherein in the selection process, a value having a smallest power value is selected from remaining values except for a peak value from among values generated through the repetition.

5. The transmitter as claimed in claim 4 , 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.

6. The transmitter as claimed in claim 4 , wherein the gradient algorithm unit further comprises a PAPR operator for calculating the PAPR of a result output from the complex adder,

a controller for comparing a value output from the PAPR operator with the system setup PAPR and controlling signal output based on the comparison.

7. 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, by a precoder, a precoded symbol sequence with the received data sequence through precoding using a preset precoding matrix;

separating, by an encoder, the generated precoded symbol sequence to generate a predetermined number of vectors;

encoding, by the encoder, the generated vectors according to an Alamouti scheme;

randomly mapping, by a random mapper, the encoded vectors on a frequency plane by a random selection is performed to each of adjacent sub-carriers;

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

outputting IFFTed signals;

receiving, by a gradient algorithm unit, the IFFTed signals and reducing the PAPR; and

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

wherein the step of reducing the PAPR comprises the steps of:

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

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

detecting a peak value of the output signals;

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

determining a scaling value of the P-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.

8. The method as claimed in claim 7 , 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.

9. The method as claimed in claim 7 , wherein the tones having the reserved positions are selected from sub-carriers not transmitting data by a predetermined number.

10. The method as claimed in claim 7 , 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.

11. The method as claimed in claim 7 , wherein the circularly moved phase is obtained by normalizing a maximum peak value and a phase of the P-waveform having the impulse characteristics is rotated by a phase of the maximum peak value.