KR101002536B1 - A method and apparatus for estimating ofdm frequency offset of low complexity using a periodogram - Google Patents

Abstract

The present invention relates to a low complexity OFDM frequency offset estimation method and apparatus using a period diagram.

The present invention provides a method of obtaining an extended period diagram from a received signal using a period diagram expansion technique,

Estimating the frequency offset using the extended periodogram;

An OFDM frequency offset estimation method comprising the steps of compensating the estimated frequency offset,

In estimating the frequency offset,

이고,

는 q배 확장된 주기율표를 이용한 정수 주파수 옵셋의 새로운 추정치,

는 q배 확장된 주기율표를 이용한 정수 주파수 옵셋 추정을 위한 시험 값,

(ㆍ)은 복소수의 허수 값, N은 전체 수신 신호 샘플의 수, q는 주기도표의 확장계수임)(here,

ego,

Is a new estimate of the integer frequency offset using the q times extended periodic table,

Is a test value for estimating integer frequency offset using q-folded periodic table,

(·) Is an imaginary complex number, N is the total number of received signal samples, q is the expansion factor of the period diagram.)

Reduces the complexity of the integer frequency offset estimation by

는 q배 확장된 주기율표를 이용한 소수 주파수 옵셋의 새로운 추정치임)(here,

Is a new estimate of the fractional frequency offset using the q times extended periodic table).

It is characterized in that to enable to extend the possible range of fractional frequency offset estimation.

Description

A METHOD AND APPARATUS FOR ESTIMATING OFDM FREQUENCY OFFSET OF LOW COMPLEXITY USING A PERIODOGRAM

The present invention relates to a low complexity orthogonal frequency division multiplexing (OFDM) frequency offset estimation method using a periodogram and a low complexity OFDM frequency offset estimation device using the method.

OFDM is very sensitive to frequency offset. Therefore, in the presence of a frequency offset, orthogonality between subcarriers is destroyed, and interference causes high data error rate.

To this end, many techniques for OFDM frequency offset estimation have been developed, but these techniques have a disadvantage in that the frequency offset estimation performance is poor or very complicated in the presence of time error.

Among these OFDM frequency offset estimation techniques, the conventional frequency offset estimation technique using a period chart provides high estimation accuracy even with a single training symbol, but has a high complexity and has a difficulty in actual implementation.

The present invention has been invented in view of the above, and by applying a frequency offset estimation technique using a periodic diagram extension for OFDM frequency offset estimation, a very low complexity and low accuracy using a weak periodic diagram An object of the present invention is to provide a method and apparatus for estimating complexity of an OFDM frequency offset.

(여기서,

이고,

는 q배 확장된 주기율표를 이용한 정수 주파수 옵셋의 새로운 추정치,

는 q배 확장된 주기율표를 이용한 정수 주파수 옵셋 추정을 위한 시험 값,

(ㆍ)은 복소수의 허수 값, N은 전체 수신 신호 샘플의 수, q는 주기도표의 확장계수임)
에 의해 정수 주파수 옵셋 추정의 복잡도를 감소시키고,

(여기서,

는 q배 확장된 주기율표를 이용한 소수 주파수 옵셋의 새로운 추정치임)
에 의해 소수 주파수 옵셋 추정 가능 범위를 확장시킬 수 있도록 하는 것을 특징으로 한다.A low complexity OFDM frequency offset estimation method and apparatus according to the present invention for achieving the above object comprises the steps of: obtaining an extended period diagram from a received signal using a period diagram extension technique;
Estimating the frequency offset using the extended periodogram;
An OFDM frequency offset estimation method comprising the steps of compensating the estimated frequency offset,
In estimating the frequency offset,

(here,

ego,

Is a new estimate of the integer frequency offset using the q times extended periodic table,

Is a test value for estimating integer frequency offset using q-folded periodic table,

(·) Is an imaginary complex number, N is the total number of received signal samples, q is the expansion factor of the period diagram.)
Reduces the complexity of the integer frequency offset estimation by

(here,

Is a new estimate of the fractional frequency offset using the q times extended periodic table).
It is characterized in that to enable to extend the possible range of fractional frequency offset estimation.

delete

Further, the present invention is characterized in that the step of compensating the estimated frequency offset is to compensate for any one of the frequency offset of the integer frequency offset, fractional frequency offset, the remaining frequency offset.

In addition, the present invention is characterized in that the step of compensating the estimated frequency offset, the integer frequency offset, the fractional frequency offset, the remaining frequency offset is added to compensate at once.

Further, the present invention is characterized in that the step of compensating the estimated frequency offset, by adding a portion of the integer frequency offset, fractional frequency offset, the remaining frequency offset to compensate.

Furthermore, the low-complexity OFDM frequency offset estimation apparatus using the periodic diagram according to the present invention is to generate a periodic diagram of the received signal for frequency estimation using the low-complexity OFDM frequency offset method using the above-described periodic diagram. It features.

The apparatus may be any one of an OFDM receiver, a radar, and a sonar.

According to the present invention, by applying a frequency offset estimation technique using a periodic table expansion, it has a wider frequency offset estimation range, and it is possible to estimate the frequency offset with an average complexity of less than half of the conventional method.

Therefore, the present invention can be applied to a terminal such as a wireless LAN or digital broadcasting using an OFDM transmission method, and can also be applied to a frequency estimation technique using a period diagram in a radar or sonar.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a view showing the entire process of the OFDM frequency offset estimation method according to the present invention.

First, an extended period diagram is obtained from a received signal using a period diagram extension technique. Subsequently, the frequency offset is estimated using the extended period diagram, and finally, the frequency offset (eg, integer frequency offset, fractional frequency offset, remaining frequency offset) is compensated.

In the compensating step, the integer frequency offset, the fractional frequency offset, and the remaining frequency offset may be added and compensated at once, or the integer frequency offset, the fractional frequency offset, and some of the remaining frequency offset may be added to compensate.

Here, the frequency offset estimation method shown in FIG. 1 will be described in detail.

First, the periodic chart system model is as follows.

Periodic System Model

The OFDM symbol is generated through an inverse fast Fourier transform (IFFT), and is represented by Equation 1 below.

Equation 1

는 k번째 부반송파(subcarrier)를 통해 전송되는 PSK(phase shift keying) 또는 QAM(quadrature amplitude modulation) 데이터이고, N은 역 고속 푸리에 변환의 크기이며, n= 0,1,2,---,N-1이다.here,

Is the PSK (phase shift keying) or QAM (quadrature amplitude modulation) data transmitted on the kth subcarrier, N is the magnitude of the inverse fast Fourier transform, and n = 0,1,2, ---, N -1.

After time synchronization, the received signal is expressed as follows.

Equation 2

은 부반송파 간격으로 정규화된 주파수 옵셋이고,

은 평균이 0인 AWGN(additive white Gaussian noise)이다.here,

Is the frequency offset normalized to the subcarrier interval,

Is an additive white Gaussian noise (AWGN) with an average of zero.

In order to obtain a periodogram of a received signal, an EEP (envelope equalized processing) process is performed, and the EEP process is shown in Equation 3 below.

Expression 3

The signal after the EEP process is shown in Equation 4 below.

Equation 4

이다.here,

to be.

Therefore, the square root of the periodic diagram is expressed as shown in Equation 5 below.

Equation 5

Frequency offset estimation method according to the prior art

The existing technique uses a three-step estimation method for frequency offset estimation. The process is integer, decimal, and remaining frequency offset estimation, respectively.

First, the integer frequency offset estimation equation is as shown in Equation 6 below.

Equation 6

이다.here,

to be.

Next, the fractional frequency offset estimation equation is as follows.

Equation 7

The remaining frequency offset estimation equation is shown in Equation 8 below.

Equation 8

은 각각

의 추정치이다.here,

Are each

Is an estimate of.

Configuration according to the invention

As mentioned above, looking at the square root period diagram of Equation 5, it can be seen that it takes the form of the sinc function. Also, in Equations 7 and 8, it can be seen that the frequency offset is estimated based on the geometric symmetry of the sinc function.

The main purpose of the present invention is to extend the frequency root of the equations 7 and 8 by expanding the square root period diagram of Equation 5.

When using only N / q samples consecutively instead of samples of the entire received signal in Equation 5, the period diagram is changed as in Equation 9 below.

Equation 9

As can be seen from Equation 9, it is possible to obtain a period diagram extended by q times than the original period diagram of Equation 5. According to this principle, the estimation range of Equations 7 and 8 can be extended. In addition, since only N / q samples of the entire received signal are used, the remaining samples can be used repeatedly.

Therefore, the process of Equation 5, Equation 6, and Equation 7, which is an estimation process of the existing technology, can be replaced by an estimation process represented by the following pseudocode.

FIG. 2 is a diagram illustrating an expansion process of a period diagram using a part of a received signal, and illustrates an expansion process of a period diagram when q = 1, 2, and 4. In other words, it can be seen that as the value of q increases, it expands further.

In addition, FIG. 3 is a diagram comparing the complexity between the prior art and the present invention by comparing the number of multiplications and divisions for the case where the FFT size N = 64. It can be seen that the number of multiplications and divisions decreases.

As described above, the present invention extends the frequency estimation possible range based on the extension of the periodic table. Therefore, the amount of calculation for estimating the entire range is reduced, and finally, similar performance can be achieved with low complexity.

1 is a view showing the overall determination of the OFDM frequency offset estimation method according to the present invention,

2 is a diagram illustrating an extension process of a periodic table using a part of a received signal;

3 is a diagram comparing the complexity between the prior art and the present invention by comparing the number of multiplications and divisions for the case of FFT size N = 64.

Claims (7)

Obtaining an extended period diagram from a received signal using a period diagram extension technique; Estimating the frequency offset using the extended periodogram; An OFDM frequency offset estimation method comprising the steps of compensating the estimated frequency offset, In estimating the frequency offset,

(here,

ego,

Is a new estimate of the integer frequency offset using the q times extended periodic table,

Is a test value for estimating integer frequency offset using q-folded periodic table,

(·) Is an imaginary complex number, N is the total number of received signal samples, q is the expansion factor of the period diagram.) Reduces the complexity of the integer frequency offset estimation by

(here,

Is a new estimate of the fractional frequency offset using the q times extended periodic table). A low frequency OFDM frequency offset estimation method using a periodic table, characterized in that for extending the possible range of fractional frequency offset estimation by. delete The low complexity OFDM frequency offset estimation method of claim 1, wherein the step of compensating the estimated frequency offset is to compensate for any one of an integer frequency offset, a fractional frequency offset, and the remaining frequency offset. Way. 2. The method of claim 1, wherein the step of compensating the estimated frequency offset is to compensate by adding integer frequency offset, fractional frequency offset, and remaining frequency offset at once. The method of claim 1, wherein the compensating the estimated frequency offset is performed by adding a portion of an integer frequency offset, a fractional frequency offset, and a remaining frequency offset to compensate for the frequency offset. A low-complexity OFDM frequency offset estimation apparatus using a periodogram, characterized in that to generate a periodogram of a received signal for frequency estimation using a low-complexity OFDM frequency offset method using a periodogram according to claim 1. The apparatus of claim 6, wherein the apparatus is any one of an OFDM receiver, a radar, and a sonar.

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