KR20030090389A - Method for acqusition of frequency offset synchronous in wireless local area network which is using orthogonal frequency division multiplexing - Google Patents

Method for acqusition of frequency offset synchronous in wireless local area network which is using orthogonal frequency division multiplexing Download PDF

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KR20030090389A
KR20030090389A KR1020020028673A KR20020028673A KR20030090389A KR 20030090389 A KR20030090389 A KR 20030090389A KR 1020020028673 A KR1020020028673 A KR 1020020028673A KR 20020028673 A KR20020028673 A KR 20020028673A KR 20030090389 A KR20030090389 A KR 20030090389A
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South Korea
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value
division multiplexing
phase
frequency offset
cosine
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KR1020020028673A
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Korean (ko)
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김태성
천진희
유기희
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주식회사 신영텔레콤
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Publication of KR20030090389A publication Critical patent/KR20030090389A/en

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2647—Arrangements specific to the receiver only
    • H04L27/2655—Synchronisation arrangements
    • H04L27/2657—Carrier synchronisation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2647—Arrangements specific to the receiver only
    • H04L27/2655—Synchronisation arrangements
    • H04L27/2689—Link with other circuits, i.e. special connections between synchronisation arrangements and other circuits for achieving synchronisation
    • H04L27/2692—Link with other circuits, i.e. special connections between synchronisation arrangements and other circuits for achieving synchronisation with preamble design, i.e. with negotiation of the synchronisation sequence with transmitter or sequence linked to the algorithm used at the receiver
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/0014—Carrier regulation
    • H04L2027/0024—Carrier regulation at the receiver end
    • H04L2027/0026—Correction of carrier offset
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/0014—Carrier regulation
    • H04L2027/0044—Control loops for carrier regulation
    • H04L2027/0063—Elements of loops
    • H04L2027/0067—Phase error detectors
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/0014—Carrier regulation
    • H04L2027/0083—Signalling arrangements
    • H04L2027/0089—In-band signals
    • H04L2027/0093—Intermittant signals
    • H04L2027/0095—Intermittant signals in a preamble or similar structure

Abstract

PURPOSE: A method for synchronizing a frequency offset of a wireless LAN system using an OFDM(Orthogonal Frequency Division Multiplexing) method is provided to correct a phase within a short time by performing the first and the second phase error correction processes using a shot training sequence and a long training sequence. CONSTITUTION: A conjugating process is performed between short training sequences adjacent to a received preamble. A hexa value is decided by comparing a real number part and an imaginary number part to a stored value of a lookup table(30). A cosine value and a sine value are decided by comparing the hexa value to a value of the first NCO(Numerical Controlled Oscillator) table(41). A phase is corrected by applying the cosine value and the sine value to two long training sequences of the preamble. A phase offset is obtained by using the conjugate between the corrected long training sequences and the hexa value is added thereto. The cosine value and the sine vale are decided by comparing the added value to the value of the second NCO table(42). The phase is corrected by applying the cosine and the sine values to a received signal.

Description

직교주파수분할 다중방식을 사용하는 무선랜 시스템의 주파수옵셋 동기획득방법{METHOD FOR ACQUSITION OF FREQUENCY OFFSET SYNCHRONOUS IN WIRELESS LOCAL AREA NETWORK WHICH IS USING ORTHOGONAL FREQUENCY DIVISION MULTIPLEXING}Frequency Offset Synchronization Acquisition Method for Wireless LAN System Using Orthogonal Frequency Division Multiplexing Method

본 발명은 직교주파수분할 다중(OFDM : Orthogonal Frequency Division Multiplexing : 이하 '직교주파수분할 다중'이라 함)방식의 무선랜(WLAN : Wireless Local Area Network)시스템에 관한 것으로 특히, 정확하게 주파수 옵셋 동기를 획득 할 수 있는 방법에 관한 것이다.The present invention relates to a wireless local area network (WLAN) system of orthogonal frequency division multiplexing (OFDM), and more particularly, to accurately obtain frequency offset synchronization. It is about how it can be.

일반적으로 직교 주파수 분할 다중방식 기술은 디지털 오디오 방송(DAB: Digital Audio Broadcasting)과 디지털 텔레비젼, 무선 근거리 통신망(WLAN: Wireless Local Area Network) 그리고 무선 비동기 전송 모드(WATM: Wireless Asynchronous Transfer Mode) 등의 디지털 전송 기술에 광범위하게 적용되어지고 있다. 상기 직교 주파수 분할 다중 방식은 전송하려는 데이터를 다수 개의 부반송파(Sub-Carrier)를 가지고 여러 개의데이터로 나누어 변조한 후 병렬로 전송하는 다중 반송파 기술이다.In general, orthogonal frequency division multiplexing technology includes digital audio broadcasting (DAB), digital television, wireless local area network (WLAN), and wireless asynchronous transfer mode (WATM). It is widely applied to transmission technology. The orthogonal frequency division multiplexing scheme is a multi-carrier technology in which data to be transmitted is divided into a plurality of data with a plurality of sub-carriers and then transmitted in parallel.

그러나, 상기 직교 주파수 분할 다중 방식은 하드웨어(hardware)적인복잡도(Complexity)로 인하여 널리 사용되지 못하다가 최근 고속 푸리에 변환(FFT: Fast Fourier Transform) 기술과 역 고속 푸리에 변환(IFFT: Inverse Fast FourierTransform) 기술을 포함한 각종 디지털 신호 처리 기술이 발전함으로써 실현 가능해 졌다. 상기 직교 주파수 분할 다중방식은 종래의 주파수 분할 다중 방식(FDM: Frequency Division Multiplexing)과 비슷하나 무엇보다도 다수개의 부반송파간의 직교성(Orthogonality)을 유지하여 전송함으로써 고속 데이터 전송시 최적의 전송 효율을 얻을 수 있는 특징을 갖는다. 최근 이러한 장점이 대두되어 무선 비동기 전송 모드와 같은 고속 데이터 전송시 상기 직교주파수 분할 다중 방식을이용한 직교 주파수 분할 다중 방식/시분할 다중 접속 방식(OFDM/TDMA) 시스템 및 직교주파수 분할 다중 방식/코드 분할다중 접속 방식(OFDM/CDMA) 시스템 등의 다양한 구현 기술이 제안되고 있다.However, the orthogonal frequency division multiplexing method has not been widely used due to hardware complexity, but recently, a Fast Fourier Transform (FFT) technique and an Inverse Fast Fourier Transform (IFFT) technique are used. Various digital signal processing techniques, including the development of the present technology, are made possible. The orthogonal frequency division multiplexing method is similar to the conventional frequency division multiplexing (FDM) method, but most of all, it is possible to obtain optimal transmission efficiency in high-speed data transmission by maintaining orthogonality between a plurality of subcarriers. Has characteristics. In recent years, such advantages have emerged, such as orthogonal frequency division multiplexing / time division multiple access (OFDM / TDMA) system and orthogonal frequency division multiplexing / code division multiplexing using the orthogonal frequency division multiplexing method for high speed data transmission such as wireless asynchronous transmission mode. Various implementation techniques, such as an access method (OFDM / CDMA) system, have been proposed.

일반적으로 상기 직교주파수 분할 다중 방식을 이용한 전송 시스템에서는 채널 특성에 의하여 도플러 현상이 발생하거나 수신기의 동조기가 불안정할 경우 송신 주파수와 수신 주파수의 동기화가 이루어지지 않는 경우가 발생한다. 그래서, 송·수신기의 국부 발진기간, 즉 반송파간의 동조가 이루어지지 않으면 주파수 옵셋(Frequency Offset)이 발생하게 되고, 상기 주파수 옵셋은 수신신호의 위상(phase)을 변화시켜서 부반송파간의 직교성(Orthogonality)을 잃어버리게 하고, 그로 인해 시스템의 복호 성능을 저하시킨다. 이러한 경우 작은 주파수 옵셋도 수신 시스템의 성능을 떨어뜨리는 심각한 원인이 된다. 그러므로 직교주파수 분할 다중 방식을 이용한 전송시스템에서 부반송파간의 직교성을 유지시키는 정밀하며신속한 주파수 동기기술의 구현이 필요하지만, 일반적인 무선통신시스템에서의 주파수옵셋 동기장치를 위상의 정밀한 동조가 필요한 직교주파수분할 다중방식에 적용하는 것은 불가능한 문제점이 있다.In general, in the transmission system using the orthogonal frequency division multiplexing, when the Doppler phenomenon occurs due to channel characteristics or when the tuner of the receiver is unstable, the transmission frequency and the reception frequency are not synchronized. Therefore, if the local oscillation period of the transmitter / receiver, that is, the tuning between the carriers is not achieved, a frequency offset occurs, and the frequency offset changes the phase of the received signal to change the orthogonality between the subcarriers. Lost, thereby degrading the decoding performance of the system. In this case, even a small frequency offset is a serious cause of poor performance of the receiving system. Therefore, in a transmission system using orthogonal frequency division multiplexing, it is necessary to implement a precise and fast frequency synchronization technique that maintains orthogonality between subcarriers, but in a general wireless communication system, an orthogonal frequency division multiplexing that requires precise tuning of phases is required. There is a problem that is impossible to apply to the method.

상술한 문제점을 해결하기 위하여 본 발명의 목적은 직교주파수분할 다중방식을 사용하는 무선랜 시스템에서 정밀한 주파수 옵셋 동조가 가능한 주파수옵셋 동기획득 방법을 제공함에 있다.An object of the present invention to solve the above problems is to provide a frequency offset synchronization acquisition method capable of precise frequency offset tuning in a wireless LAN system using orthogonal frequency division multiplexing.

도 1은 본 발명의 실시예에 따른 주파수옵셋 동기획득을 위한 개념도이다.1 is a conceptual diagram for frequency offset synchronization acquisition according to an embodiment of the present invention.

도 2는 본 발명의 실시예에 따른 주파수옵셋 동기획득 장치의 개략적인 블록도이다.2 is a schematic block diagram of a frequency offset synchronization acquisition device according to an embodiment of the present invention.

도 3은 본 발명의 실시예에 따른 룩업테이블의 예를 나타낸 것이다.3 shows an example of a lookup table according to an embodiment of the present invention.

도 4는 본 발명의 실시예에 따른 NCO 테이블의 예를 나타낸 것이다.4 shows an example of an NCO table according to an embodiment of the present invention.

도 5a는 신호대 잡음 전력비가 20dB이고 정규화된 주파수 오프셋이 1.3이며, 변조방식이 OFDM_16QAM이고, 채널환경이 5-path 다중경로 페이딩 환경에서의 성좌도이다.5A is a constellation diagram of a signal-to-noise power ratio of 20 dB, a normalized frequency offset of 1.3, a modulation scheme of OFDM_16QAM, and a channel environment in a 5-path multipath fading environment.

도 5b는 본 발명의 실시예에 의해 1차보상된 신호의 성좌도이다.5B is a constellation diagram of a signal primarily compensated according to an embodiment of the present invention.

도 5c는 본 발명의 실시예에 의해 2차보상된 신호의 성좌도이다.5C is a constellation diagram of a signal that is secondarily compensated according to an embodiment of the present invention.

* 도면의 주요 부분에 대한 부호의 설명* Explanation of symbols for the main parts of the drawings

11 : 제1콘주게이터12 : 제2콘주게이터11: First Conjugator 12: Second Conjugator

20 : 평균기30 : 룩업테이블20: average period 30: lookup table

41 : 제1NCO테이블42 : 제2NCO테이블41: first NCO table 42: second NCO table

51 : 제1곱셈기52 : 제2곱셈기51: first multiplier 52: second multiplier

60 : 가산기60: adder

상기 목적을 달성하기 위한 본 발명은 직교주파수분할 다중방식 무선랜 시스템의 주파수옵셋 동기 방법에 있어서, 수신되는 프리엠블의 인접한 숏트래이닝시퀀스간의 콘주케이트를 수행하고, 상기 콘주게이트에 의하여 얻어진 실수 및 허수부의 값을 기 저장된 룩업테이블의 값과 비교하여 헥사값을 결정하며, 상기 결정된 헥사값을 기 저장된 엔시오테이블의 값과 비교하여 코사인 및 사인값을 결정하고, 상기 결정된 코사인 및 사인값을 상기 프리엠블에 포함된 두 개의 롱트래이닝시퀀스에 적용하여 1차로 위상을 보정하며, 상기 1차 보정된 롱트래이닝시퀀스간의 콘주케이트를 취하여 위상옵셋을 구하고, 상기 제2단계에서 획득한 헥사값을 가산하고, 상기 가산된 값을 상기 기 저장된 엔시오테이블의 값과 비교하여 코사인 및 사인값을 결정하고, 상기 결정된 코사인 및 사인값을 수신되는 신호에 적용하여 2차로 위상을 보정함을 특징으로 한다.In order to achieve the above object, the present invention provides a frequency offset synchronization method of an orthogonal frequency division multiplexing wireless LAN system, and performs conjugation between adjacent short training sequences of a received preamble, and real and imaginary numbers obtained by the conjugate. A negative value is compared with a value of a pre-stored lookup table to determine a hexa value, a cosine and a sine value are determined by comparing the determined hexa value with a value of a pre-stored enciotable, and the determined cosine and sine value are determined using the free value. Phase correction is performed first by applying to the two long training sequences included in the emblem, taking a conjugate between the first corrected long training sequences, obtaining a phase offset, and adding the hexa value obtained in the second step, Comparing the added value with a value of the pre-stored encio table to determine a cosine and a sine value, Applied to the signals received to a predetermined sine and cosine values, characterized in that the second calibration phase drive.

이하, 첨부된 도면을 참조하여 본 발명의 바람직한 실시예를 상세히 설명한다.Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

도 1은 본 발명의 실시예에 따른 주파수옵셋 동기획득을 위한 개념도이고, 도 2는 본 발명의 실시예에 따른 주파수옵셋 동기획득 장치의 개략적인 블록도이며, 도 3은 본 발명의 실시예에 따른 룩업테이블의 예를 나타낸 것이고, 도 4는 본 발명의 실시예에 따른 NCO 테이블의 예를 나타낸 것이며, 도 5a는 신호대 잡음 전력비가 20dB이고 정규화된 주파수 오프셋이 1.3이며, 변조방식이 OFDM_16QAM이고, 채널환경이 5-path 다중경로 페이딩 환경에서의 성좌도이고, 도 5b는 본 발명의 실시예에 의해 1차보상된 신호의 성좌도이며, 도 5c는 본 발명의 실시예에 의해 2차보상된 신호의 성좌도이다.1 is a conceptual diagram for frequency offset synchronization acquisition according to an embodiment of the present invention, Figure 2 is a schematic block diagram of a frequency offset synchronization acquisition apparatus according to an embodiment of the present invention, Figure 3 is an embodiment of the present invention 4 shows an example of an NCO table according to an embodiment of the present invention, FIG. 5A shows a signal-to-noise power ratio of 20 dB, a normalized frequency offset of 1.3, and a modulation scheme of OFDM_16QAM. The channel environment is a constellation diagram in a 5-path multipath fading environment, and FIG. 5B is a constellation diagram of a signal primarily compensated by an embodiment of the present invention, and FIG. 5C is a constellation diagram of a signal compensated second by an embodiment of the present invention. It is also a constellation.

직교주파수분할 다중방식을 사용하는 무선랜시스템의 프리엠블 신호는 도1에 도시된 바와 같이 S1에서 S10까지 16샘플이 10번 반복되어 숏트래이닝시퀀스가 수신된 다음 GI(Guard Interval)이 수신되고, 64샘플의 크기를 가지는 롱트래이닝시퀀스가 수신된다. 이후, GI(Guard Interval)과 정보를 담은 신호가 수신된다.In the preamble signal of the WLAN system using orthogonal frequency division multiplexing, 16 samples are repeated 10 times from S1 to S10 as shown in FIG. 1 to receive a short training sequence, and then a GI (Guard Interval) is received. A long training sequence with a size of 64 samples is received. Then, a signal containing a guard interval (GI) and information is received.

본 발명에 따른 주파수옵셋 동기획득 방법은 도1 및 도2에 도시된 바와 같이 프리엠블에 수신되는 숏트래이닝시퀀스(Short Training Sequence)를 이용하여 주파수옵셋을 계산하고, 이를 롱트래이닝시퀀스(Long Training Sequence)에 적용한 다음, 롱트래이닝시퀀스의 옵셋을 계산하여 얻은 값으로 이후에 수신되는 신호의 주파수 옵셋을 보정하는 것이다.In the frequency offset synchronization acquisition method according to the present invention, as shown in FIGS. 1 and 2, a frequency offset is calculated using a short training sequence received in a preamble, and a long training sequence is obtained. ), And then the offset of the long training sequence is calculated to compensate for the frequency offset of the subsequent received signal.

이를 상세히 설명하면 다음과 같다.This will be described in detail as follows.

도 1의 숏트래이닝시퀀스가 수신되면 제1콘주게이트(11)를 통해 콘주게이트를 수행한다. 즉, 연속해서 수신되는 S3과 S4, S4와 S5의 콘주게이트 값을 구한다. 하기 식은 상술한 콘주게이트값을 구하기 위한 것이다. 수신된 숏트래이닝시퀀스를 하기 수학식으로 가정하면 S1과 S2는 16 sample 간격의 신호로 주파수 오프셋이 발생되지 않았다면 동일한 값이 될 것이다.When the short training sequence of FIG. 1 is received, the conjugate is performed through the first conjugate 11. In other words, the conjugate values of S3 and S4, S4 and S5 that are continuously received are obtained. The following formula is for obtaining the above-mentioned conjugate value. Assuming that the received short training sequence is represented by the following equation, S1 and S2 will be the same value if the frequency offset is not generated with a signal of 16 sample intervals.

하지만, 16 sample 간격에 일정양의 주파수가 틀어졌다고 가정한다면, 수신단에서는 일정양의 차이를 갖는 주파수 오프셋은 동일한 두 신호에 콘주게이트(conjugate)를 취한 곱의 형태로 하기 수학식과 같이 추정할 수 있다.However, if it is assumed that a certain amount of frequency is distorted at intervals of 16 samples, the receiver may estimate a frequency offset having a certain amount of difference in the form of a product of conjugates to the same two signals as shown in the following equation. .

여기서 θ1 - θ2를 θ라 하면 이것이 위상 오류가 됩니다. 즉 입력되는 신호에 θ만큼의 의상을 보정해야 하는데 이것은 입력신호에 위상 θ를 빼는 것과 동일하게 된다. 여기서 θ는 주파수 옵셋을 표현하고 있다. 즉, 수신되는 신호에서 θ를 빼주면 위상이 보정되는 것이다.If θ1-θ2 are θ, this is a phase error. That is, it is necessary to correct the clothes of the input signal by θ, which is the same as subtracting the phase θ from the input signal. Where θ represents the frequency offset. That is, the phase is corrected by subtracting θ from the received signal.

이때 엔시오테이블(41)을 통해 cos(θ)와 sin(θ)를 구하게 된다.At this time, cos (θ) and sin (θ) are obtained through the encio table 41.

한편 전술한 바와 같이 S3 및 S4와의 콘주게이트를 구하여 이전에 구한 값에 더하여 평균을 구함(20)으로써, 신뢰성을 증가시킬 수 있음은 물론이다. 위의 수학식 2에서 나온 x, y값은 룩업테이블(Look Up Table : 도 3참조)을 이용하여 주파수 오파를 구하는데 사용된다. 예를들어 x의 값이 2이고 y의 값이 1이면 주파수오파인 헥사값은 4c이다. 주파수 오파가 구해 졌다면 θ에 해당하는 cos 및 sin 값을 구하는 작업을 하는데 이는 엔시오(Numerical Controlled Oscillator : 도 4) 테이블을 이용하여 이루어진다(41). 엔시오 출력 값은 다음에 오는 롱트래이닝시퀀스(l1, l2)의 주파수 오프셋을 보상하기 위한 것이다. 제1엔시오테이블(41)에 의해 주파수옵셋이 구해지면 이를 제1곱셈기(51)를 통해 수신되는 롱트래이닝시퀀스(l1, l2)에 적용하여 1차로 주파수 옵셋 보상을 실시한다. 주파수옵셋 보정이 완료되면 제2콘주게이터(12)를 통해 콘주게이트를 수행한다. 롱트래이닝시퀀스(l1, l2)를 하기수학식과 정의하면 l1 및 l2의 콘주게이트는 하기수학식 4와 같이 나타낼 수 있다.Meanwhile, as described above, by obtaining a conjugate with S3 and S4 and obtaining the average in addition to the previously obtained value, the reliability can be increased. The x and y values shown in Equation 2 are used to obtain a frequency error using a look up table (see FIG. 3). For example, if the value of x is 2 and the value of y is 1, the hexa value of frequency offset is 4c. If the frequency error is obtained, the cos and sin values corresponding to θ are calculated. This is performed by using a Numerical Controlled Oscillator (FIG. 4) table (41). The Encio output value is intended to compensate for the frequency offset of the following long training sequence (l1, l2). When the frequency offset is obtained by the first NOS table 41, the frequency offset compensation is first applied by applying the frequency offset to the long training sequences l1 and l2 received through the first multiplier 51. After the frequency offset correction is completed, the conjugate is performed through the second conjugate 12. When the long training sequence (l1, l2) is defined with the following equation, the conjugates of l1 and l2 can be expressed as Equation 4 below.

위 수학식에서의 위상오차는 하기 tan-1의 수학식으로 나타낼 수 있으며 롱트래이닝시퀀스는 1차보정에 의해 이미 충분히 θ가 작아졌기에 하기와 같이 나타낼 수 있다.The phase error in the above equation can be represented by the following tan -1 equation, and the long training sequence can be represented as follows since the θ has already been sufficiently reduced by the first order correction.

이때 얻어지는 값은 도3에서와 같은 헥사값을 가지며, 가산기(60)를 통해 이전에 숏트래이닝시퀀스에 의해 얻어진 위상오차값과 합산하여 출력한다. 그러면, 이를 다시 제2엔시오테이블(42 : 도4)에서 헥사값을 대입하여 cos 및 sin값을 찾아 이후에 들어오는 신호를 2차 보상하도록 한다. 상술한 설명에서 엔시오테이블(41, 42)이 두 개로 설명되었으나 단일의 구성을 사용할 수 있음은 물론이다.The value obtained at this time has the same hexa value as in FIG. 3, and is added to the phase error value previously obtained by the short training sequence through the adder 60 and output. Then, the hexa value is substituted in the second NSI table 42 (Fig. 4) to find the cos and sin values so as to second compensate the incoming signal. In the above description, the ncio table 41 and 42 have been described as two, but a single configuration may be used.

이상에서 살펴본 바와 같이 본 발명은 숏트래이닝시퀀스 및 롱트래이닝시퀀스를 이용하여 2차에 걸쳐 위상오차를 수정하여 위상이 틀어지는 것을 최소화하였다. 더욱이 수신되는 프리엠블의 순서에 입각하여 보상이 이루어지도록 함으로써, 짧은 시간에 정밀하게 위상보상이 이루어지도록 하였다. 도5a는 신호대 잡음 전력비가 20dB이고 정규화된 주파수 오프셋이 1.3이며, 변조방식이 OFDM_16QAM이고, 채널환경이 5-path 다중경로 페이딩 환경에서의 성좌도이다. 이렇게 수신되는 신호는 전술한 본 발명에 따른 주파수옵셋동기 방법에 signal이 1차로 보상된 성좌도를 도5b에 나타내었고, 도 5c는 2차 보상된 신호의 성좌도를 나타낸 것이다.As described above, the present invention minimizes a phase shift by correcting a phase error over two orders using a short training sequence and a long training sequence. Furthermore, compensation is performed based on the order of preambles received, so that phase compensation is precisely performed in a short time. 5A is a constellation diagram of a signal-to-noise power ratio of 20 dB, a normalized frequency offset of 1.3, a modulation scheme of OFDM_16QAM, and a channel environment in a 5-path multipath fading environment. The received signal is a constellation diagram in which a signal is firstly compensated in FIG. 5B according to the frequency offset synchronization method according to the present invention, and FIG. 5C is a constellation diagram of a second compensated signal.

상기와 같이 본 발명은 숏트래이닝시퀀스 및 롱트래이닝시퀀스를 이용하여 2차에 걸쳐 위상오차를 수정하여 위상이 틀어지는 것을 최소화하였고, 수신되는 프리엠블의 순서에 입각하여 1차 및 2차보상이 이루어지도록 함으로써, 짧은 시간에 정밀하게 위상보상이 이루어지는 장점이 있다.As described above, the present invention uses a short training sequence and a long training sequence to correct a phase error over two orders, thereby minimizing a phase shift. By doing so, there is an advantage that the phase compensation is precisely performed in a short time.

Claims (3)

직교주파수분할 다중방식 무선랜 시스템의 주파수옵셋 동기 방법에 있어서,In the frequency offset synchronization method of orthogonal frequency division multiplexing wireless LAN system, 수신되는 프리엠블의 인접한 숏트래이닝시퀀스간의 콘주케이트를 수행하는 제1 단계;Performing a conjugate between adjacent short training sequences of the received preambles; 상기 콘주게이트에 의하여 얻어진 실수 및 허수부의 값을 기 저장된 룩업테이블의 값과 비교하여 헥사값을 결정하는 제2단계;A second step of determining a hexa value by comparing the real and imaginary values obtained by the conjugate with a value of a previously stored lookup table; 상기 결정된 헥사값을 기 저장된 엔시오테이블의 값과 비교하여 코사인 및 사인값을 결정하는 제3단계;A third step of determining a cosine and a sine value by comparing the determined hexa value with a previously stored value of an encio table; 상기 결정된 코사인 및 사인값을 상기 프리엠블에 포함된 두 개의 롱트래이닝시퀀스에 적용하여 1차로 위상을 보정하는 제4단계;A fourth step of first correcting phase by applying the determined cosine and sine to two long training sequences included in the preamble; 상기 1차 보정된 롱트래이닝시퀀스간의 콘주케이트를 취하여 위상옵셋을 구하고, 상기 제2단계에서 획득한 헥사값을 가산하는 제5단계; 및,A fifth step of obtaining a phase offset by taking a conjugate between the first corrected long training sequences and adding a hexa value obtained in the second step; And, 상기 가산된 값을 상기 기 저장된 엔시오테이블의 값과 비교하여 코사인 및 사인값을 결정하고, 상기 결정된 코사인 및 사인값을 수신되는 신호에 적용하여 2차로 위상을 보정하는 제6단계를 구비하는 직교주파수분할 다중방식을 사용하는 무선랜 시스템의 주파수옵셋 동기획득방법.And a sixth step of determining a cosine and a sine value by comparing the added value with a value of the pre-stored encio table, and correcting a phase in a second order by applying the determined cosine and sine value to a received signal. Frequency offset synchronization acquisition method of wireless LAN system using frequency division multiplexing. 청구항 1에 있어서,The method according to claim 1, 상기 제1단계는, 연속되는 3이상의 숏트래이닝시퀀스간의 콘주케이트를 수행하고, 평균을 취하여 이루어짐을 특징으로 하는 직교주파수분할 다중방식을 사용하는 무선랜 시스템의 주파수옵셋 동기획득방법.The first step is a frequency offset synchronization acquisition method of a WLAN system using an orthogonal frequency division multiplexing method characterized in that by performing a conjugate between the consecutive three or more short training sequence, taking the average. 청구항 1에 있어서,The method according to claim 1, 상기 5단계에서, 상기 롱트래이닝시퀀스간의 위상옵셋은 콘주게이트에 얻어진 허수부를 실수부의 값으로 나누어 얻어짐을 특징으로 하는 직교주파수분할 다중방식을 사용하는 무선랜 시스템의 주파수옵셋 동기획득방법.In the step 5, the phase offset between the long training sequence is obtained by dividing the imaginary part obtained in the conjugate by the value of the real part frequency offset synchronization acquisition method of a WLAN system using orthogonal frequency division multiplexing.
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