KR100945530B1 - Apparatus and method for selecting correlation mode based on error of carrier wave frequency - Google Patents

Abstract

The present invention relates to an apparatus and method for selecting a correlation method based on a frequency error of a carrier, and in a communication system in which a frequency error for a carrier exists, a frequency error between each correlation method when calculating a correlation value for initial synchronization acquisition. An apparatus and method for selecting a correlation method based on a frequency error of a carrier for more efficiently obtaining initial synchronization by selecting a correlation method for each region after calculating a boundary point are provided.

To this end, the present invention provides a correlation method selection method, comprising: an undetected probability value calculating step of calculating undetected probability values according to a frequency offset normalized for each correlation method; Determining a point where a graph of the undetected probability values for each correlation scheme meet each other as a frequency error boundary point; And a correlation method selection step of selecting a correlation method based on the determined frequency error boundary point.

Frequency Error Boundary, Direct Correlation, Differential Correlation, Weighted Differential Correlation, False Information Rate, Undetected Probability

Description

Apparatus and method for selecting correlation mode based on error of carrier wave frequency}

The present invention relates to an apparatus and method for selecting a correlation method based on a frequency error of a carrier, and more particularly, in a communication system in which a frequency error with respect to a carrier exists, each correlation in calculating a correlation value for initial synchronization acquisition. The present invention relates to an apparatus for selecting a correlation method based on a frequency error of a carrier to more efficiently obtain initial synchronization by selecting a correlation method for each region after calculating a frequency error boundary between the methods.

The present invention is derived from the research conducted as part of the IT growth engine technology development project of the Ministry of Information and Communication and the Ministry of Information and Telecommunication Research and Development. [Task control number: 2007-S-008-01, Task name: 21GHz band satellite broadcasting transmission technology development] ].

Recently, as the boundary between broadcasting and communication is blurred and two-way service becomes possible, broadband service and reliable transmission service are required. Therefore, in satellite communication system that needs to secure high transmission capacity with given bandwidth and signal power, adaptive modulation and coding (ACM) is used.

In particular, DVB-S2 (Digital Video Broadcasting-ver.2), a standard for European digital video satellite broadcasting, is an adaptive that selects and transmits an optimal modulation scheme and coding rate adaptively to channel conditions in order to maximize transmission efficiency. Modulation and coding schemes are used.

Due to the use of this adaptive modulation and coding scheme, each receiver in a satellite communication system that provides Ka band (18 to 31 GHz) service can adaptively control the link according to radio wave conditions to secure transmission capacity up to 100-200%. Although possible, a process of detecting a structure of a variable transmission frame as well as frame synchronization is required for carrier recovery.

On the other hand, the DVB-S2 system performs correlation calculation to obtain initial synchronization in an environment in which carrier frequency error exists. In this case, the frequency error between the transceivers serves to reduce the performance of the correlator.

Therefore, the influence of the frequency error is minimized by utilizing the differential correlation between the SoF (Start of Frame) and the received signal obtained during the previous frame synchronization process.

However, in an environment where the frequency error does not exist or is below a certain level, the differential correlation method causes more severe performance degradation than the direct correlation method. Selecting and using a direct correlation method and a differential correlation method is more advantageous than using one method each.

Therefore, there is a demand for a method of adaptively selecting a direct correlation method and a differential correlation method according to a change in the magnitude of the frequency error, and an object of the present invention is to solve such a demand.

According to the present invention, in a communication system in which a frequency error exists for a carrier, a frequency error boundary point between correlation methods is calculated when calculating a correlation value for initial synchronization acquisition, and then a correlation method is selected for each region. An object of the present invention is to provide an apparatus and method for selecting a correlation method based on a frequency error of a carrier to obtain initial synchronization.

The objects of the present invention are not limited to the above-mentioned objects, and other objects and advantages of the present invention which are not mentioned above can be understood by the following description, and will be more clearly understood by the embodiments of the present invention. Also, it will be readily appreciated that the objects and advantages of the present invention may be realized by the means and combinations thereof indicated in the claims.

In accordance with another aspect of the present invention, there is provided a correlation method selection method comprising: calculating an undetected probability value according to a frequency offset normalized for each correlation method; Determining a point where a graph of the undetected probability values for each correlation scheme meet each other as a frequency error boundary point; And a correlation method selection step of selecting a correlation method based on the determined frequency error boundary point.

In addition, the apparatus of the present invention for achieving the above object, In the correlation method selection apparatus, Undetected probability value calculation means for calculating the undetected probability value according to the frequency offset normalized for each correlation method; Frequency error boundary point determining means for determining a point where a graph of undetected probability values for each correlation scheme, which are calculated by the non-detection probability value calculating means, meets each other as a frequency error boundary point; And correlation method selection means for selecting a correlation method based on the frequency error boundary point determined by the frequency error boundary point determining means.

In addition, the present invention adaptively adapts the coherent correlation method, the differential correlation method and the modified differential correlation method according to the degree of the frequency error in an environment in which frequency error exists for a carrier of several tens of GHz. We present the optimal frequency error boundary that can be used.

In addition, the present invention improves the synchronization performance by obtaining a frame synchronization and structure detection algorithm that can reduce the storage space by storing only the position determination index by using the hard decision of the correlation value, and the maximum value of the correlation sum using the soft decision. It is applied to the correlation value calculation process of frame synchronization and structure detection algorithm that can be achieved, and high initial synchronization performance can be obtained.

In the present invention as described above, in a communication system in which a frequency error exists for a carrier, by calculating a frequency error boundary between correlation methods when calculating a correlation value for initial synchronization acquisition, selecting a correlation method for each region. In other words, it is effective to obtain initial motivation more efficiently.

The above objects, features, and advantages will become more apparent from the detailed description given hereinafter with reference to the accompanying drawings, and accordingly, those skilled in the art to which the present invention pertains may share the technical idea of the present invention. It will be easy to implement. In addition, in describing the present invention, when it is determined that the detailed description of the known technology related to the present invention may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted. Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

In an embodiment of the present invention, a satellite communication system DVB-S2 will be described as an example of a wireless communication system to which the present invention is applied. However, the present invention is not limited thereto.

In addition, since the technology itself for the direct correlation method, the differential correlation method, and the weighted differential correlation method mentioned in the present invention are generally well known techniques, they will not be discussed in detail.

1 is an example of a transport frame structure of a DVB-S2 physical layer used in the present invention.

As shown in FIG. 1, the transmission frame of the DVB-S2 physical layer used in the present invention includes a Physical Layer (PL) header 101 having 90 symbols, and a Forward Error having 64800 bits or 16200 bits. Correction frame 102 is included.

Here, the PL header 101 includes a SoF (Start of Frame) 103 having 26 symbols, and a Physical Layer Signaling Code (PLSC) 104 having 64 symbols. At this time, the PLSC 104 is a codeword that encodes a modulation scheme, a coding rate, and information about whether the pilot symbol 105 in the FEC frame is inserted.

Table 1 below shows 16 variable frames according to modulation scheme (QPSK, 8PSK, 16APSK, 32APSK), data length (64800 or 16200 bits / frame), and whether a pilot symbol is inserted in the PLSC 104. The structure is shown.

Here, n represents an index of the transmission frame structure, and the total number of symbols (Ln, n = 0 to 15) per frame is transmitted according to each structure index.

2 is a flowchart illustrating a method of selecting a correlation method based on a frequency error of a carrier according to the present invention.

First, undetected probability values based on the normalized frequency offset for each correlation scheme are calculated (201).

That is, a false alarm rate calculation formula and an undetected probability calculation formula for each correlation method are calculated, and the threshold value is calculated by fixing the false alarm rate calculation formula for each correlation method to a predetermined value and then calculating the threshold value. The undetected probability value is calculated by applying to the undetected probability calculation formula of the correlation method.

Then, the point where the graphs of the calculated undetected probability values for each correlation scheme meet each other is determined as a frequency error boundary point (202).

Thereafter, a correlation method is selected based on the determined frequency error boundary point (203).

Hereinafter, a process of calculating the frequency error boundary point will be described in detail.

First, M SoF symbols are defined as s _k (k = 1, ..., M), and contiguous M symbols among transmission data symbols are defined as d _k (k = 1, ..., M). .

)을 가지는 가산성 백색 가우스 잡음(AWGN : Additive White Gaussian Noise)의 샘플인 n_k가 더해진 수신 심볼을 r_k로 표시할 때, 현재 수신된 M개의 심볼이 SoF에 해당하는 경우를 H₁(r_k = s_k + n_k, k = 1, .., M)로 정의할 수 있다.Where s _k Or spread over d _k (

When a received symbol with n _k added as a sample of Additive White Gaussian Noise (AWGN) with r ₎ is represented by r _k , H ₁ (r _k = s _k + n _k , k = 1, .., M) can be defined.

In addition, if the received M symbols correspond to general data symbols (including the case where the SoF symbol is partially present), H ₀ (r _k = d _k + n _k , k = 1, .., M) Can be defined

In general, the receiver uses a correlation structure to determine H ₀ or H ₁ .

That is, the calculation method for calculating the correlation exists in various forms, but the most basic form is a direct correlation method between the received symbol string and the pre-stored SoF symbol string, which can be expressed as Equation 1 below.

Here, i represents the index of the received symbol.

Since the direct correlation method causes performance deterioration when there is a frequency error, the differential correlation method using phase difference information between adjacent symbols is more efficient. Equation 2 below shows one form of the differential correlation scheme.

In addition, the weighted differential correlation method using the differential information to which the weight is applied according to the distance between adjacent symbols in a modified manner of Equation 2 is expressed by Equation 3 below.

)에 대해 H₀인 조건하에서

일 확률을 허위 경보율(False Alarm Rate, 이하 "FAR"라 함)로 정의하고, H₁인 조건하에서

일 확률을 미검출 확률(Mis-Detection Probability, 이하 "MDP"라 함)로 정의한다.Next, the threshold (

Under conditions of H ₀

Work probability is defined as False Alarm Rate (hereinafter referred to as "FAR"), and under the condition of H ₁

One probability is defined as a misdetection probability (hereinafter referred to as "MDP").

)은 수신 심볼이 프레임의 시작 심볼인 경우 상관값이 미검출 확률에 포함되기 위한 값, 또는 수신 심볼이 일반 데이터 심볼인 경우 상관값이 허위 경보율에 포함되기 위한 값을 의미한다.Where threshold (

) Denotes a value for including a correlation value in an undetected probability when the received symbol is a start symbol of a frame, or a value for including a correlation value in a false alarm rate when the received symbol is a general data symbol.

의 확률 분포는 카이제곱(chi-square) 분포를 가진다.At this time, the correlation value of Equation 1

The probability distribution of has a chi-square distribution.

Therefore, each probability density function (PDF: Probability Density Function, hereinafter referred to as "PDF") for H ₀ (at asynchronous) and H ₁ (at synchronous) can be obtained.

로 정의할 때, Xi는 평균이 0이고, 분산이

인 자유도 2의 중앙 카이제곱(central chi- square) 분포를 따르며, 이때 PDF는 하기의 [수학식 4]와 같다.In other words, the square of the magnitude of the correlation for a symbol

Is defined as 0, the mean is 0 and the variance is

Follows the central chi-square distribution of 2 degrees of freedom, where PDF is given by Equation 4 below.

로 정의할 때, Yi는 자유도 2를 갖는 비 중앙 카이제곱(non-central chi-square) 분포를 따르며, 이때 PDF의 형태는 하기의 [수학식 5]와 같다.Also, the square of the correlation magnitude for the symbol

When defined as Yi, Yi follows a non-central chi-square distribution with 2 degrees of freedom, where the form of the PDF is shown in Equation 5 below.

)은

를 만족하고, 비 구심성(non-centrality) 파라미터(

)는

를 만족한다.Where variance (

)silver

, The non-centrality parameter (

)

Satisfies.

는 주파수 오차를 나타내고, BW는 대역폭을 나타내며, Iz(ㆍ)는 "z-th order modified Bessel function of the first kind"를 나타낸다.Also,

Denotes a frequency error, BW denotes a bandwidth, and Iz (·) denotes a "z-th order modified Bessel function of the first kind".

Next, FAR is expressed using Equation 4 and Equation 5, and EAR is represented by Equation 6 below, and MDP is represented by Equation 7 below.

와

의 확률 분포는 모의 실험을 통하여 결정하였으며, 이에 대한 FAR과 MDP를 SNR 3dB의 환경에서 문턱값(

)의 변화에 따라 도 3 및 도 4에 각각 도시하였다.On the other hand, each of the differential correlation values of [Equation 2] and [Equation 3]

Wow

The probability distribution of was determined by simulation, and the FAR and MDP were calculated using the threshold value in the environment of SNR 3dB.

As shown in FIG. 3 and FIG.

As shown in FIG. 3, the differential correlation method is represented by 'Differential correlation method 1', and as shown in FIG. 4, the weighted differential correlation method is represented by 'Differential correlation method 2'.

As a result, the present invention proposes a frequency error boundary point to adaptively use the direct correlation method, the differential correlation method, and the weighted differential correlation method according to the degree of the frequency error in the environment where the frequency error exists.

)을 산출한다.To this end, first, the FAR of the direct correlation method as shown in [Equation 6] and the FAR of the experimentally obtained differential correlation method and the weighted differential correlation method are fixed to 10 ^−2, and then the threshold value satisfying this (

) Is calculated.

)을 이용하여 MDP의 값을 구한다. 따라서 차등 상관 방식과 직접 상관 방식의 MDP를 성능 지표로 정의하여, 각 방식의 성능을 비교할 수 있다.Then, the calculated threshold value (

) To find the value of MDP. Therefore, the MDP of the differential correlation method and the direct correlation method can be defined as a performance index, and the performance of each method can be compared.

5 is an exemplary diagram of a frequency error boundary point according to the present invention, after fixing FAR to 10 ⁻² at SNR 3dB, MDPs of the direct correlation method, the differential correlation method, and the weighted differential correlation method are normalized to a bandwidth of 25 MHz. (Normalized) Shows the result of comparison according to frequency offset.

As shown in FIG. 5, the direct correlation method is referred to as 'Coherent correlation method', the differential correlation method as 'Differential correlation method 1', and the weighted differential correlation method as 'Differential correlation method 2'.

는 0.26, 차등 상관 방식의

는 0.45, 가중치 적용 차등 상관 방식의

는 0.52이다.At this time, SNR of 3dB of direct correlation method

0.26, differential correlation

0.45, the weighted differential correlation method

Is 0.52.

를 이용하여 각각의 MDP를 각각 구할 수 있으며, 도 4에 도시된 바와 같이 SNR 3dB에서 주파수 오차 약 1.80%가 직접 상관 방식과 차등 상관 방식의 경계점(501)이고, 주파수 오차 약 1.45%가 직접 상관 방식과 가중치 적용 차등 상관 방식의 경계점(502)이다.For each case

As shown in FIG. 4, each MDP can be obtained, and as shown in FIG. 4, the frequency error of about 1.80% is the boundary point 501 of the direct correlation method and the differential correlation method at SNR 3dB, and the frequency error of about 1.45% is directly correlated. The boundary point 502 of the method and the weighted differential correlation method.

Therefore, considering the slight error, if the frequency correlation is less than 1.78% in the SNR 3dB, if the direct correlation method is used rather than the differential correlation method, the performance degradation due to the differential correlation method can be overcome, and the frequency error is more than 1.78%. By using the differential correlation method, performance degradation caused by the direct correlation method can be overcome.

Similarly, the direct correlation method and the weighted differential correlation method may be adaptively selected based on a frequency error of about 1.47%.

Meanwhile, the correlation method selection method based on the frequency error of the carrier according to the present invention may be applied to the correlation value calculation process of the frame synchronization and structure detection algorithm to improve frame detection performance.

That is, it is applied to the frame synchronization and structure detection method in the satellite broadcasting system can improve the initial synchronization acquisition performance.

For example, in a channel environment of a satellite broadcasting system in which a low signal-to-noise ratio and a high frequency error are considered, a differential correlation value for the position of a start of frame (SOF), which is a synchronization word that marks the start of a frame in consideration of a variable frame length, is considered. By calculating the sum and selecting the maximum value, the method of detecting frame synchronization and structure in a satellite broadcasting system to obtain not only the frame synchronization position but also the transmission frame structure detection estimation value and overcome the distortion of the correlation analysis value due to the frequency error In, the present invention can be applied when generating a correlation value.

As another example, a differential correlation value of a received symbol is calculated to generate an index column of a symbol that exceeds a threshold value, and the generated at the frame start point estimation position corresponding to the total number of frames using the number of symbols per frame for each frame structure. In the method of detecting frame synchronization and structure in a satellite broadcasting system for detecting frame synchronization and structure with low complexity and low memory capacity by detecting frame synchronization and structure according to the number of points where an index column is matched, a correlation value is generated. The present invention can be applied.

6 is a diagram illustrating an embodiment of a correlation method selection apparatus based on a frequency error of a carrier according to the present invention. Here, since specific embodiments of each component are as described above, only the connection relationship and operation of each component will be described briefly here.

As shown in FIG. 6, the apparatus for selecting a correlation method based on the frequency error of a carrier according to the present invention includes an undetected probability value calculator 61 for calculating undetected probability values according to frequency offsets normalized for each correlation method. ), A frequency error boundary point determining unit 62 for determining a point where a graph of the undetected probability values for each correlation scheme, which are calculated by the undetected probability value calculating unit 61, meets each other as a frequency error boundary point, and the frequency error. A correlation method selector 63 for selecting a correlation method based on the frequency error boundary point determined by the boundary point determiner 62 is included.

On the other hand, the method of the present invention as described above can be written in a computer program. And the code and code segments constituting the program can be easily inferred by a computer programmer in the art. In addition, the written program is stored in a computer-readable recording medium (information storage medium), and read and executed by a computer to implement the method of the present invention. The recording medium may include any type of computer readable recording medium.

The present invention described above is capable of various substitutions, modifications, and changes without departing from the technical spirit of the present invention for those skilled in the art to which the present invention pertains. It is not limited by the drawings.

The present invention can be used for frame synchronization and structure detection algorithms.

1 is an example of a transmission frame structure of a DVB-S2 physical layer used in the present invention;

2 is a flowchart illustrating a method of selecting a correlation method based on a frequency error of a carrier according to the present invention;

3 is a graph showing a false alarm rate and non-detection probability per threshold in the differential correlation method according to the present invention;

4 is a graph illustrating a false alarm rate and a non-detection probability per threshold in a weighted differential correlation scheme according to the present invention;

5 is an exemplary view of a frequency error boundary point according to the present invention;

6 is a diagram illustrating an embodiment of a correlation method selection apparatus based on a frequency error of a carrier according to the present invention.

* Explanation of symbols for the main parts of the drawings

61: non-detection probability value calculating unit 62: frequency error boundary point determining unit

63: correlation method selection unit

Claims (12)

In the correlation method selection method, An undetected probability value calculating step of calculating undetected probability values composed of false alarm rates and undetected probabilities according to normalized frequency offsets for each correlation scheme; Determining an intersection point of a graph of the undetected probability values for each correlation scheme as the frequency error boundary point; And A correlation method selection step of selecting a correlation method using the determined frequency error boundary point as a threshold. Correlation method selection method based on the frequency error of the carrier comprising a. The method of claim 1, The non-detection probability value calculating step, Calculating a formula of the false alarm rate and a formula of the undetected probability for each correlation scheme; Fixing the false alarm rate calculation formula for each of the calculated correlation methods to a predetermined value, and applying the undetected probability calculation formula of the correlation method to calculate undetected probability values. Correlation method selection method based on the frequency error of the carrier comprising a. The method of claim 2, The threshold is And if the received symbol is a data symbol, a correlation value is a threshold value to be included in the false alarm rate. The method of claim 2, The threshold is And if the received symbol is a start symbol of a frame, a correlation value is a threshold value to be included in the undetected probability. The method of claim 1, The correlation method selection step, A method of selecting a correlation method based on a frequency error of a carrier, characterized in that one of a direct correlation method and a differential correlation method is selected. The method of claim 1, The correlation method selection step, A method of selecting a correlation method based on a frequency error of a carrier, characterized in that one of a direct correlation method and a weighted differential correlation method is selected. In the correlation method selection device, Undetected probability value calculating means for calculating undetected probability values consisting of a false alarm rate and an undetected probability according to a frequency offset normalized for each correlation scheme; Frequency error boundary point determining means for determining an intersection point of a graph of respective undetected probability values for each correlation scheme calculated by the non-detection probability value calculating means as a frequency error boundary point; And Correlation method selection means for selecting a correlation method using the frequency error boundary point determined by the frequency error boundary point determining means as a threshold value. Correlation method selection apparatus based on the frequency error of the carrier comprising a. The method of claim 7, wherein The non-detection probability value calculating means, The calculation formula of the false alarm rate for each correlation method and the calculation formula of the undetected probability are calculated, and the false alarm rate calculation formula for each calculated correlation method is fixed to a predetermined value, and the probability of not detecting the corresponding correlation method is determined. Apparatus for selecting a correlation method based on the frequency error of the carrier, characterized in that by applying to the calculation to calculate the undetected probability values. The method of claim 8, The threshold is And if the received symbol is a data symbol, a correlation value is a threshold value for inclusion in the false alarm rate. The method of claim 8, The threshold is And a correlation value is a threshold value to be included in the undetected probability when the received symbol is a start symbol of a frame. The method of claim 7, wherein The correlation method selection means, An apparatus for selecting a correlation method based on a frequency error of a carrier, characterized in that one of a direct correlation method and a differential correlation method is selected. The method of claim 7, wherein The correlation method selection means, An apparatus for selecting a correlation method based on a frequency error of a carrier, comprising selecting one of a direct correlation method and a weighted differential correlation method.

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