T echnical F ield

The present invention relates to a system and method for keeping PA PR (Peak-to- Average Power Ratio) value at a desired level by use of artificial noise used for physical layer security in OFDM (Orthogonal Frequency Division Multiplexing) technique.

Background of the Invention Today, OFDM technique has an important position in communication sector due to the fact that it can use band width efficiently in new generation communication systems and reach high data transmission speeds. However, one of the most important disadvantages of this technique is that PA PR values are high as compared with single-carrier systems in particular. It is known that high PA PR values reduce SQNR (Signal-to-Quantization Noise Ratio) and following that, analog- digital and digital-to-analog converters are subject to performance losses.

In usages included in the state of the art, PA PR reduction methods are developed in OFDM-based systems differently from one another. These methods are generally grouped as clipping technique, coding technique, scrambling technique, adaptive predistortion technique and DFT (Discrete Fourier Transform) distribution technique. A mong these techniques, the clipping technique is the one which can be easily applied for reducing peak values at non-linear saturation values as well as it leads to interference within the frequency band since it may distort verticality among subcarriers. This approach is used in block scaling technique, clipping and filtering technique, peak windowing technique and peak removing technique.

Whereas coding technique is applied in the way that the code sequence is selected so as to reduce PA PR. The fact that it is difficult to find the correct code array is a disadvantage of this technique. This approach is used in Reed Muller code sequence, Golay complementary array and Hadamard code sequence.

Whereas scrambling technique is carried out in the way that the symbol sequences that will bring PA PR values in the OFDM entry sequence, to the lowest level. T his technique does not guarantee that PA PR value falls below a sharp val ue.

Whereas adaptive predistortion technique balances non-linear effects of high power amplifiers.

In DFT distribution technique, input signal is divided according to DFT and the sign to be transmitted is divided into smaller parts in comparison with IFFT (Inverse Fast Fourier Transform). Thus, smaller parts are obtained. In another common usage in the state of the art, artificial noise is used in order to provide physical layer security for eliminating various security vulnerabilities resulting from the fact that the data is transmitted from an open media in wireless communication systems. Eavesdropping attacks, which are frequently mentioned in literature, are the case that an illegal user obtains information between two users who are in legal communication. Artificial noise, which is used for physical layer security, has been successful to a great extent in terms of preventing this case. The K orean patent document no. K R 20140104315, an application in the state of the art, discloses an OFDM communication system which increases efficiency of communication network by generating clipping noises for reducing PA PR value. T he C hi nese patent document no. C N 104618290, another appl i cati on i n the state of the art, discloses an OFDM system for providing the control of PA PR value by a part reserved for noise level and to reduce PA PR value by increasing noise level i n the event that PA PR val ue i ncreases. Summary of the Invention

An objective of the present invention is to realize a system and method which carries out use of artificial noise, that is used for physical layer security, in order to reduce high PA PR value occurring in OFDM technique.

Detailed Description of the Invention

^" A System and Method for PA PR Reduction by means of Artificial Noise in OFDM Technique _, realized to fulfil the objective of the present invention is shown i n the figures attached, i n which:

F igure 1 is a schematic block diagram of the inventive system.

F igure 2 is a block diagram related to the inventive method. The components illustrated in the figures are individually numbered, where the numbers refer to the f ol I owi ng:

1. System

2. Data provision unit

3. Noise generation unit 4. Symbol merge unit

5. Conversion unit

6. Control and decision unit

100. Method

The inventive system (1 ) for reducing PA PR value by artificial noise in OFDM technique comprises:

- at least one data provision unit (2) which keeps OFDM symbols comprising the data received and/or generated by thereof, in frequency domain;

- at least one noise generation unit (3) which generates artificial noise signals in frequency domain in accordance with certain definitions;

- at least one symbol merge unit (4) which gathers data symbols and artificial noises that it receives from the data provision unit (2) and the noise generation unit (3) in frequency domain;

- at least one conversion unit (5) which converts the data transmitted by the symbol merge unit (4) and the signal comprising the artificial noise, from frequency domain into time domain;

- at least one control and decision unit (6) which determines PA PR value of the signal that is included in the time domain received from the conversion unit (5), compares the determined PA PR value with the certain limit values comprised by thereof, makes notification to the noise generation unit (3) and the symbol merge unit (4) in the event that the PA PR value is higher than the limit value as a consequence of the comparison, puts the related OFDM signal in order to be sent in the event that the PA PR value is under the limit value (Figure 1).

The data provision unit (2) included in the inventive system (1) is a unit which provides OFDM symbols comprising data. The data provision unit (2) can receive and/or generate data from certain units. The data provision unit (2) comprises signals in frequency domain and transmits these signals to the symbol merge unit (4) in accordance with certain definitions.

The noise generation unit (3) included in the inventive system (1) is a unit which generates artificial noise signals. The noise generation unit (3) generates noise signals in frequency domain in accordance with certain parameters wherein authorized users input their values. The noise generation unit (3) generates an artificial noise signal different than a previous noise signal when it receives notification from the control and decision unit (6) and transmits it to the symbol merge unit (4). In one embodiment of the invention, the noise generation unit (3) determines parameter valued of noise signal generation in accordance with the feedback values included inside the notification content that it receives from the control and decision unit (6) and generates artificial noise signal in accordance with the related values.

The symbol merge unit (4) included in the inventive system (1) is a unit which merges data symbols and artificial noise signals. The symbol merge unit (4) merges the OFDM symbols comprising the data received from the data provision unit (2) by thereof and the artificial noise signals received from the noise generation unit (3) by thereof in frequency domain. In preferred embodiment of the invention, the symbol merge unit (4) gathers the OFDM symbols and the artificial noise signals in the frequency domain as a merge transaction. The symbol merge unit (4) transmits the signal generated by thereof as a consequence of the merge transaction, to the conversion unit (5).

The symbol merge unit (4) keeps the OFDM symbol, which it receives from the data provision unit (2), under record until it receives feedback from the control and decision unit (6) and does not receive new symbol. The symbol merge unit (4) waits for the noise generation unit (3) to transmit a new artificial noise signal and carries out the merge transaction when it receives the artificial noise signal, in the event that it receives a feedback notifying that the OFDM symbol should be merged with a different artificial noise signal from the control and decision unit (6). The symbol merge unit (4) repeats transactions of merging the related OFDM symbol with different artificial noise signals until it receives a feedback notifying that the PA PR value of the merged signal is compatible from the control and decision unit (6). The symbol merge unit (4) receives a new OFDM symbol from the data provision unit (2) in the event that the control and decision unit (6) transmits a feedback notifying that the merged signal is compatible for transmission.

The conversion unit (5) included in the inventive system (1) is a unit which converts the signal included in the frequency domain into time domain. The conversion unit (5) converts the signal in the frequency domain generated by merging the OFDM symbol received from the symbol merge unit (4) by thereof and the artificial noise signal, into time domain. In preferred embodiment of the invention, the conversion unit (5) uses IFFT (Inverse Fast Fourier Transform) method for the conversion transaction. Upon completing the conversion transaction, the conversion unit (5) transmits the signal obtained in the time domain by thereof, to the control and decision unit (6).

The control and decision unit (6) included in the inventive system (1) is a unit which controls PA PR value of the signal and takes action according to the control result. The control and decision unit (6) determines PA PR value of the signal that is merged with the noise received from the conversion unit (5) in the time domain by thereof. The control and decision unit (6) compares the determined PA PR value with the PA PR limit value that is defined on thereof. In one embodiment of the invention, the control and decision unit (6) comprises the PA PR limit value parameter the value of which can be determined by the users and compares the PA PR value of the signal with the related parameter value. The control and decision unit (6) makes notification to the noise generation unit (3) for generating a different artificial noise signal and to the symbol merge unit (4) for merging the same OFD M symbol with a new noise signal, in the event that the PA PR value is above a certain limit value. The control and decision unit (6) makes notification to the symbol merge unit (4) for receiving a new symbol and puts the signal having a PA PR value below the limit value in order so as to be transmitted, in the event that the P A P R val ue i s bel ow the I i mi t val ue.

With the inventive system (1), transactions of using artificial noise is carried out for reducing PA PR values of signals in order to increase efficiency in OFDM technique. In the said system (1), security and efficiency are provided through same systems by reducing PA PR value by means of artificial noise that is used for physical layer security.

An OFDM method (100) for reducing PA PR value by artificial noise in OFDM technique comprises steps of:

- the symbol merge unit (4) receiving new OFD M symbol in frequency domain from the data provision unit (2) (101);

- the symbol merge unit (4) receiving artificial noise signals in frequency domain from the noise generation unit (3) (102);

- the symbol merge unit (4) merging OFDM symbol and artificial noise signals (103);

- the symbol merge unit (4) transmitting the merged signal to the conversion unit (5) (104);

- the conversion unit (5) converting the merged signal from frequency domain into time domain and transmitting to the control and decision unit

(6) (105);

- the control and decision unit (6) determining the PA PR value of the signal i n the ti me domai n ( 106);

- the control and decision unit (6) comparing the PA PR value of the signal with the limit value (107); - in the event that the PA PR value is higher than the limit value, the control and decision unit (6) transmitting notification to the noise generation unit (3) for generating different noise signal (108);

- in the event that the PA PR value is higher than the limit value, the control and decision unit (6) transmitting notification to the symbol merge unit (4) for merging a previous OFDM symbol with the new artificial noise signal (109);

- upon receiving the notification, the symbol merge unit (4) receiving the new noise signal from the noise generation unit (3) and merging it with the OFDM symbol in the frequency domain (110); ;

- in the event that the PA PR value is less than the limit value, the control and decision unit (6) putting the signal on the list so as to be transmitted (111);

- in the event that the PA PR value is less than the limit value, the control and decision unit (6) making notification to the symbol merge unit (4) for receiving the new OFDM symbol (112).

With the inventive method (100), it is ensured that security and efficiency are provided by means of the same transaction steps in OFDM technique by use of artificial noise signals used for physical layer security in order to reduce PA PR value for increasing efficiency in OFDM technique.

It is possible to develop various embodiments of the inventive system (1) and method (100), the invention cannot be limited to examples disclosed herein and it is essentially according to claims.