KR20130060489A - Integer frequency offset estimation and cell index detection apparatus and method thereof - Google Patents

Abstract

PURPOSE: An apparatus and method for estimating an integer frequency offset and detecting a cell ID are provided to reduce hardware costs and the number of hardware and to reduce calculation complexity. CONSTITUTION: A fast Fourier transform unit(100) performs the fast Fourier transform of a PS(Primary Synchronization) signal received from a transmitter from a time domain axis to a frequency domain axis in a receiver. A first correlation value calculation unit(110) calculates the correlation values of left sub carriers and right sub carriers of a DC sub carrier in the fast Fourier transformed PS signal, and multiplies the symmetrical correlation values. A first signal sample adder(120) calculates the sum of the correlation values multiplied in the first correlation calculation unit. An integer frequency offset estimator(130) selects a real part of a value outputted from the first signal sample adder, and estimates an integer frequency offset by obtaining the maximum value from the real part. A second correlation calculation unit(140) calculates the correlation values of the left sub carriers and the right sub carriers of the DC sub carrier in the signal whose integer frequency offset is compensated, and multiplies the symmetrical correlation values. A second signal sample adder(150) calculates the sum of the correlation values multiplied in the second correlation calculation unit. A cell ID detector(160) selects a real part of a value outputted from the second signal sample adder, and detects a cell ID by obtaining the maximum value from the real part. [Reference numerals] (100) Fast Fourier transform unit; (112) First LS correlator; (114) First RS correlator; (115) First correlation value multiplier; (120) First signal sample adder; (130) IFO estimator; (142) Second LS correlator; (144) Second RS correlator; (146) Second correlation value multiplier; (150) Second signal sample adder; (160) CID detector; (AA) IPO compensation signal

Description

Integer Frequency Offset Estimation and Cell Index Detection Apparatus and Method Thereof}

The present invention relates to an integer frequency error estimation method and a cell ID index detection method in an orthogonal frequency division multiple access system. In particular, an integer frequency error estimation method performed by separating integer frequency error and cell ID detection in order to reduce high computational complexity and A cell ID index detection apparatus and method.

In next-generation wireless communication, Orthogonal Frequency Division Multiplexing (OFDMA), which divides an entire channel into multiple orthogonal subchannels and transmits it in parallel for ultra-high speed data transmission, is mainly used. LTE technology, currently standardized in the 3rd Generation Partnership Project (3GPP), is a Release 10 core technology that uses downlink orthogonal frequency division multiplexing access (OFDMA) and uplink SC FDMA (single carrier frequency division multiple access) transmission schemes. Realize the increase and high bandwidth efficiency.

The OFDMA-based downlink system is very sensitive to frequency error.

The frequency error is divided into integer and decimal frequency errors according to the subcarrier spacing. In particular, since the integer frequency error cyclically shifts the signal in the frequency domain after the fast fourier transform (FFT), the recovered data is completely displaced and demodulated into completely different data from the original transmission signal.

In addition, unlike other systems, the OFDMA-based downlink system does not have a preamble symbol, and thus uses a limited primary synchronization signal (PS) for initial cell search and synchronization. Very sensitive.

As a method for estimating the integer frequency error and performing a quick initial cell search, a method of simultaneously performing integer frequency error estimation and cell ID index detection has been proposed. The prior art obtains and estimates a cross-correlation value between the received PS signal and the PS signal previously promised at the receiver. In this case, since a large amount of complex multiplications and additions are calculated in the receiver, a high computational complexity is required, and thus there is a problem in that a large cost and high complexity of hardware are generated in actual implementation.

In order to solve this problem, an object of the present invention is to separate and perform integer frequency error estimation and cell ID detection in order to reduce the high computational complexity of a downlink system using an orthogonal frequency division multiple access scheme.

In order to achieve the above object, an integer frequency error estimation method according to a feature of the present invention and a cell ID index detection method include:

Processing a signal by performing a Fast Fourier Transform (Primary Synchronization) signal received from a transmitter from a time axis to a frequency axis at a receiver; Calculating a correlation value between left subcarriers and right subcarriers based on a direct current (DC) subcarrier in the fast Fourier transformed PS signal; Multiplying the correlation values of the calculated left subcarriers and the right subcarriers by correlation values placed at left and right symmetrical positions with respect to the DC subcarrier; Selecting a real part after summing the multiplied correlation values, estimating an integer multiple frequency error by obtaining a maximum value in the selected real part; Calculating a correlation value between left subcarriers and right subcarriers based on the DC subcarrier in the signal with the estimated integer frequency error compensated; Multiplying the correlation values of the calculated left subcarriers and the right subcarriers by correlation values placed at left and right symmetrical positions with respect to the DC subcarrier; And selecting a real part after adding up the multiplied correlation values, and obtaining a maximum value from the selected real part to detect a cell ID index.

Integer frequency error estimation and cell ID index detection apparatus according to a feature of the present invention,

A fast Fourier transform unit for processing a signal by performing a fast Fourier Transform (PS) signal received from a transmitter from a time axis to a frequency axis at a receiver; A first correlation value calculator configured to calculate a correlation value between left subcarriers and right subcarriers based on a DC (Direct Current) subcarrier in the fast Fourier transformed PS signal and multiply correlation values placed at left and right symmetric positions; A first signal sample adder for calculating a sum of correlation values multiplied by the first correlation value calculator; An integer frequency error estimator that selects a real part from an output value of the first signal sample adder, obtains a maximum value thereof, and estimates an integer frequency error; A second correlation value calculating unit that calculates a correlation value between left subcarriers and right subcarriers based on the DC subcarrier based on the DC subcarrier compensated signal output from the integer frequency error estimator and multiplies correlation values positioned at left and right symmetric positions; ; A second signal sample adder for calculating a sum of correlation values multiplied by the second correlation value calculator; And a cell ID detector for selecting a real part from an output value of the second signal sample adder, obtaining a maximum value thereof, and detecting a cell ID index.

According to the above-described configuration, the present invention estimates integer frequency error in an OFDMA-based downlink system, and then detects a cell ID index to reduce computational complexity while actually performing hardware implementation in the same manner as the conventional scheme. This can reduce the cost and the number of hardware.

1 is a conceptual diagram illustrating a frame structure of a PS signal and an SS signal in an OFDMA-based downlink system.
2 is a block diagram schematically illustrating an internal configuration of an integer frequency error estimation and cell ID index detection apparatus of an OFDMA based downlink system according to an embodiment of the present invention.
3 is a diagram illustrating an integer frequency error estimation method and a cell ID detection method using an OFDMA-based downlink system according to an embodiment of the present invention.
4 is a diagram illustrating a structure of an integer frequency error estimation technique in an OFDMA-based downlink system according to an embodiment of the present invention.
5 is a diagram illustrating a structure of a cell ID detection scheme in an OFDMA-based downlink system according to an embodiment of the present invention.
6 is a diagram illustrating a comparison of computational complexity of an integer frequency error estimation and cell ID detection technique and a conventional technique in an OFDMA-based downlink system according to an embodiment of the present invention.
FIG. 7 is a diagram illustrating a failure probability of the integer frequency error estimation according to the conventional and the present invention according to SNR at D = 3 in an OFDMA based downlink system according to an embodiment of the present invention.
FIG. 8 is a diagram illustrating a failure probability of cell ID index detection according to the prior art and the present invention according to SNR in an OFDMA-based downlink system according to an embodiment of the present invention.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention, and like reference numerals designate like parts throughout the specification.

Throughout the specification, when a part is said to "include" a certain component, it means that it can further include other components, except to exclude other components unless otherwise stated.

In the OFDMA-based downlink system according to an embodiment of the present invention, the initial cell search includes initial frame synchronization, frequency synchronization and cell ID detection, and CP length detection for the UE to access the cell. It is a process.

At this time, the initial cell search process can be roughly divided into a primary signal (PS) detection step and a secondary signal (SS) detection step.

Since the present invention proposes an integer frequency error estimation and cell ID detection scheme, only the PS signal detection step is considered.

1 is a conceptual diagram illustrating a frame structure of a PS signal and an SS signal in an OFDMA-based downlink system.

The present invention generates a transmission signal of an OFDMA based downlink system having N subcarriers by an Inverse Fast Fourier Transform (IFFT).

The PS signal, which is an OFDM signal transmitted for integer frequency synchronization error and cell ID detection based on a cross correlation function, is a signal to which a ZC (Zadoff Chu) sequence is assigned.

In a frequency division duplex (FDD) mode of an OFDMA based downlink system, one frame of 10 ms length consists of 20 slots (0.5 ms).

In the extended cyclic prefix (CP) mode, one slot includes six OFDM symbols, and the last slots of the first and eleventh slots are positions of PS signals.

The PS signal is transmitted in units of 1/2 radio frames of 5ms, and is used by the receiver to distinguish frame synchronization and cell ID information.

The PS signal is assigned a ZC (Zadoff Chu) sequence having a different root index u to distinguish three kinds of cell ID information.

The ZC sequence is allocated to 63 subcarriers around a DC (direct current) subcarrier and a value of 0 is assigned to the DC subcarrier.

The index u for distinguishing the cell ID is determined by 25, 29, and 34, and the generation expression is expressed as in Equation 1 below.

는 주파수 영역에서의 PS 신호이고, DC 부반송파를 중심으로

의 부반송파 인덱스가 좌우 대칭을 이루고 있으며, 이는 본 발명에서의 중요한 특징이다.here,

Is the PS signal in the frequency domain, and is centered on the DC subcarrier.

The subcarrier index of is symmetrical, which is an important feature of the present invention.

의 위상 증가는 PS 신호의 부반송파 인덱스의 제곱에 비례하며 인접한 부반송파의 위상 차이는 다음의 [수학식 2]와 같이 나타낼 수 있다.As can be seen from the above Equation 1,

The phase increase of is proportional to the square of the subcarrier index of the PS signal, and the phase difference of the adjacent subcarriers can be expressed by Equation 2 below.

Assuming that the time and decimal frequency errors of the received signal in the OFDMA-based downlink system are completely compensated, the received k-th subcarrier signal in the frequency domain where the integer frequency error occurs is expressed by Equation 3 below.

는 주파수 영역의 수신된 PS 신호의 k번째 부반송파 신호,

는 전송된 PS 신호의 k번째 부반송파 신호,

는 보호 구간 길이,

는 부반송파 간격으로 정규화된 정수배 주파수 오차,

는 주파수 영역의 채널 응답,

는 평균이 0이고 분산이

인 복소 가산성 백색 가우시안 잡음(AWGN)이다.here,

Is the kth subcarrier signal of the received PS signal in the frequency domain,

Is the kth subcarrier signal of the transmitted PS signal,

Is the guard interval length,

Is an integer frequency error normalized to the subcarrier spacing,

Is the channel response in the frequency domain,

The average is 0 and the variance is

Phosphorus complex additive white Gaussian noise (AWGN).

와 수신기에서 미리 약속된

간의 상호 상관 값을 구하여 그 값이 최대가 되는 지점을 추정한다.The prior art is a received PS signal

In advance and in the receiver

Obtain the cross-correlation value between and estimate the point where the value is maximum.

Equation 3 described above represents a received PS signal in a frequency domain converted by the fast Fourier transform unit.

The prior art is a technique for detecting an integer frequency error and a cell ID index at the same time, which can be represented by Equation 4 below.

은 추정된 정수배 주파수 오차,

은 추정된 셀 ID 인덱스,

는 x의 실수 부분이며, d와 D는 각각 정수배 주파수 오차 추정의 시행값과 송수신기의 발진기에 의해 발생할 수 있는 최대 정수배 주파수 오차의 크기(

)는 다음의 [수학식 5]와 같이 나타낼 수 있다.here,

Is an estimated integer frequency error,

Is the estimated cell ID index,

Is the real part of x, and d and D are the magnitude of the integer frequency error estimate and the maximum integer frequency error that can be generated by the transceiver's oscillator.

) Can be expressed as Equation 5 below.

는 {-2, -1, 0, 1, 2}이고, u는 {25, 29, 34}의 루트 인덱스에서 검출된다.In the conventional technique of detecting an integer frequency error and a cell ID index simultaneously, assuming that a subcarrier spacing is 15 kHz and a frequency error occurs within a frequency error estimation range,

Is {-2, -1, 0, 1, 2} and u is detected at the root index of {25, 29, 34}.

The prior art estimates the integer frequency error and the cell ID index simultaneously. Thus, the total number of detected cases is fifteen.

In the conventional method of simultaneously estimating integer frequency error and cell ID index, a large amount of complex multiplication and addition are calculated at the receiver, and thus high computational complexity is required.

The present invention provides an integer frequency error regardless of cell ID detection through a symmetrical structure based on the DC subcarrier of the PS signal in the frequency domain after the fast Fourier transform in an OFDMA based downlink system to reduce the complexity of the prior art. A method of separating and estimating cell ID detection is proposed.

Next, an integer frequency error estimation and cell ID index detection apparatus of an OFDMA-based downlink system according to an embodiment of the present invention will be described in detail with reference to FIG. 2.

2 is a block diagram schematically illustrating an internal configuration of an integer frequency error estimation and cell ID index detection apparatus of an OFDMA based downlink system according to an embodiment of the present invention.

An integer frequency error estimation and cell ID index detection apparatus according to an embodiment of the present invention includes a fast Fourier transform unit 100, a first correlation value calculating unit 110, a first signal sample adder 120, and an integer frequency error (Integer Frequency). An offset (IFO) estimator 130, a second correlation value calculator 140, a second signal sample adder 150, and a cell ID detector 160. Here, the first correlation value calculator 110 includes a first left side correlator 112, a first right side correlator 114, and a first correlation value multiplier 116, and a second correlation. The value calculator 140 includes a second LS correlator 142, a second RS correlator 144, and a second correlation value multiplier 146.

An OFDMA based downlink system according to an embodiment of the present invention refers to a receiver for processing a received signal from a received signal of a transmitter.

The fast Fourier transform unit 100 processes a signal by performing a Fast Fourier Transform (Primary Synchronization) signal received from a transmitter from a time axis to a frequency axis at a receiver.

The first LS correlator 112 calculates a correlation value of the left subcarriers based on a direct current (DC) subcarrier in the fast Fourier transformed PS signal.

The first RS correlator 114 calculates a correlation value of the right subcarriers based on a direct current (DC) subcarrier in the fast Fourier transformed PS signal.

The first correlation value multiplier 116 places the correlation values of the left subcarriers calculated by the first LS correlator 112 and the right subcarriers calculated by the first RS correlator 114 at left and right symmetric positions with respect to the DC subcarriers. Multiply correlation values.

The first signal sample adder 120 calculates the sum of all signal sample values multiplied by the first correlation value multiplier 116.

The integer frequency offset (IFO) estimator 130 selects a real part after summing the correlation values multiplied by the first signal sample adder 120 and estimates the integer frequency error by obtaining a maximum value from the selected real part. .

The second LS correlator 142 calculates a correlation value of the left subcarriers based on the DC subcarriers in the compensated signal based on the integer frequency error estimated by the integer error estimator.

The second RS correlator 144 calculates a correlation value of the right subcarriers based on the DC subcarriers in the compensated signal based on the integer frequency error estimated by the integer error estimator.

The second correlation value multiplier 146 places the correlation values of the left subcarriers calculated by the second LS correlator 142 and the right subcarriers calculated by the second RS correlator 144 at left and right symmetric positions with respect to the DC subcarriers. Multiply correlation values.

The second signal sample adder 150 calculates the sum of all signal sample values multiplied by the second correlation value multiplier 146.

The cell ID detector 160 selects a real part after summing the correlation values multiplied by the second signal sample adder 150, and detects a cell ID index by obtaining a maximum value from the selected real part.

Next, an integer frequency error estimation and cell ID detection method using an OFDMA-based downlink system according to an embodiment of the present invention will be described in detail with reference to FIG. 3.

3 is a diagram illustrating an integer frequency error estimation method and a cell ID detection method using an OFDMA-based downlink system according to an embodiment of the present invention.

For convenience of calculation, assuming that the index k = N / 2 of the DC subcarrier of the PS signal, the integer frequency error estimation method is expressed as Equation 6 below.

As shown in FIGS. 2, 3, and 4, the integer frequency error estimation method includes a first LS correlator 112, a first RS correlator 114, a first correlation value multiplier 116, and a first signal sample adder. 120 and an integer frequency error estimator 130.

The fast Fourier transform unit 100 performs a fast Fourier transform of the PS signal received from the transmitter from the time axis to the frequency axis (S100).

,

로 나타나 있다.The method of calculating the correlation value between the left subcarriers and the right subcarriers is described in Equation 6 above.

,

Respectively.

The first LS correlator 112 and the first RS correlator 114 calculate a correlation value between the left subcarriers and the right subcarriers based on the DC subcarriers of the frequency axis in the fast Fourier transformed signal (S102, Equation 7).

는 DC 부반송파의 좌측 연산,

는 DC 부반송파의 우측 연산으로 다음의 [수학식 7]과 같이 나타낼 수 있다.In this frequency domain

Is the left operation of the DC subcarrier,

Is the right side operation of the DC subcarrier and can be expressed as Equation 7 below.

은 통계적으로

와 유사하다.here,

Is statistically

Similar to

The first correlation value multiplier 116 multiplies the correlation values obtained from the left and the right by the correlation values placed in the symmetrical positions with respect to the DC subcarrier (S104, Equation 8).

, 이와 같이 구해진 상관 값끼리 곱하게 되고 곱해진 값들은 30개의 신호 샘플을 만들게 된다.In other words,

In this way, the correlation values obtained are multiplied and the multiplied values make 30 signal samples.

이고,

라고 가정하면,

는 다음의 [수학식 8]과 같이 나타낼 수 있다.In [Equation 7] described above

ego,

Let's say

Can be expressed as Equation 8 below.

로 나타낸다.

Respectively.

로 나타나 있다.The first signal sample adder 120 calculates the sum of the signal samples multiplied by the first correlation value multiplier 116 (S106, Equation 9). Here, step S106 is the above-described Equation 6

Respectively.

Using the above Equation 8, the average of the signal components of Equation 6 can be approximated as shown in Equation 9 below.

이며, AWGN이 다른 주파수 채널 응답으로 무상관하게 된다.here,

And AWGN has nothing to do with other frequency channel responses.

이므로 셀 ID 검출과 상관없이 정수배 주파수 오차를 추정할 수 있다.Integer frequency error estimate is obtained at all cell ID root indices {25, 29, 34}

Therefore, the integer frequency error can be estimated regardless of the cell ID detection.

The integer frequency error estimator 130 selects a real part after summing the correlation values multiplied by the first signal sample adder 120 and estimates the integer frequency error by obtaining a maximum value from the selected real part (S108).

인 경우, 셀 ID 검출과 상관없이 발생 가능한 정수배 주파수 오차 범위인 5가지의 경우만을 고려한다.When the integer frequency error and the cell ID detection are performed at the same time as compared with the prior art, 15 correlation procedures are calculated. The present invention

In this case, only five cases that are integer frequency error ranges that can occur regardless of cell ID detection are considered.

In other words, the integer frequency error estimator 130 compensates for the integer frequency error when one integer frequency error is obtained from five of {-2, -1, 0, 1, 2}.

As shown in Figs. 2, 3 and 5, the method for detecting the cell ID index includes the second LS correlator 142, the second RS correlator 144, the second correlation value multiplier 146, and the second signal. Implemented through the sample adder 150 and the cell ID detector 160.

A method of detecting a cell ID index may be expressed as shown in Equation 10 below when the cell ID index is detected using the above Equation 7.

는 전술한 [수학식 6]을 사용하여 정수배 주파수 오차가 보상된 신호를 나타낸다.

Denotes a signal whose integer frequency error is compensated for by using Equation 6 described above.

The second LS correlator 142 and the second RS correlator 144 are correlation values of the left subcarriers and the right subcarriers based on the DC subcarriers of the frequency axis in the signal compensated for the integer frequency error received from the integer frequency error estimator 130. To calculate (S110).

The second correlation value multiplier 146 multiplies the correlation values obtained from the left subcarriers and the right subcarriers by correlation values placed at left and right symmetric positions with respect to the DC subcarrier (S112).

Step S110 and step S112 can be represented by Equation 11 below.

일 경우,

이며,

는 다음의 [수학식 11]과 같이 표현된다.In [Equation 10] described above

If it is,

Is,

Is expressed as Equation 11 below.

The second signal sample adder 150 calculates the sum of the signal samples multiplied by the second correlation value multiplier 146 (S114, Equation 12).

As can be seen from Equation 11, when the integer frequency error and the cell ID are detected at the same time as compared with the prior art, 15 correlation procedures are calculated.

The cell ID detection method of the present invention considers only three cases of possible cell ID root index ranges (one of cell ID indexes {25, 29, 34} is obtained).

일 때,

의 평균을 유도하면 다음의 [수학식 12]와 같이 표현된다.Using Equation 5 described above

when,

Deriving the average of is expressed by the following equation (12).

이고, S_pss는 PS 신호에 할당된 부반송파 인덱스들의 집합이다. 라고 가정하면, 전술한 [수학식 10]의

은

으로 근사화할 수 있다.

S _pss is a set of subcarrier indices assigned to the PS signal. Assuming that the above Equation 10

silver

Can be approximated by

The cell ID detector 160 detects the cell ID index by adding the correlation values multiplied by the second signal sample adder 150 and selecting a real part and obtaining a maximum value from the selected real part (S116).

As a result, the cell ID detection method of the prior art and the present invention have the same error detection performance.

However, it was confirmed from the above Equations 9 and 11 that the integer frequency error estimation and the cell ID detection of the present invention perform a lower correlation procedure than the prior art.

In addition, it was confirmed that the integer frequency error estimation and the cell ID detection of the present invention are only affected by the channel correlation values in the frequency domain by the above-described Equations 9 and 11 above.

The present invention proposes a method of separately estimating integer frequency error estimation and cell ID detection in order to reduce high computational complexity.

Using the cross-correlation of the frequency domain presented in [Equation 6], it was confirmed that the integer frequency error can be estimated in [Equation 9] irrespective of the cell ID detection.

Through Equations 10 and 11, a cross-correlation for detecting a cell ID index was presented and a cell ID index detection method was confirmed.

6 is a diagram illustrating a comparison of computational complexity of an integer frequency error estimation and cell ID detection technique and a conventional technique in an OFDMA-based downlink system according to an embodiment of the present invention.

인 OFDMA 시스템을 고려하였으며, ITU-R에 정의된 COST 231 채널모델(CM)을 고려하였다.The present invention conforms to the standard specification of 3GPP LTE downlink FDD mode for practical implementation and simulation

The OFDMA system is considered and the COST 231 channel model (CM) defined in ITU-R is considered.

When the computational complexity of the integer frequency error estimation and the cell ID detection method according to the embodiment of the present invention is expressed by the number of operations of complex multiplication, it is 90 · (2D + 1) and 90 · 3, respectively.

On the other hand, in the conventional art, when the complexity multiplication calculation complexity is expressed, since the integer frequency error estimation and the cell ID detection method are simultaneously estimated, the complexity is 120 · (2D + 1) · 3.

On the other hand, when the computational complexity of the integer frequency error estimation and the cell ID detection method according to the embodiment of the present invention is expressed by the number of operations of complex addition, it is 29 · (2D + 1) and 59 · 3, respectively.

In the prior art, when expressing the complex addition calculation complexity, since the integer frequency error estimation and the cell ID detection method are estimated simultaneously, they have the same complexity as 59 · (2D + 1) · 3.

Comparing the complexity of each method, the computational complexity of the integer frequency error estimation and the cell ID detection method according to the embodiment of the present invention is less complex than the prior art because both the complex multiplication operation and the complex addition operation is low complexity of the overall system You lose.

FIG. 7 is a diagram illustrating a failure probability of the integer frequency error estimation according to the conventional and the present invention according to SNR at D = 3 in an OFDMA based downlink system according to an embodiment of the present invention.

It was confirmed that the performance of the integer frequency error estimation scheme of the present invention has similar performance to that of the prior art in the Vehicular B channel which suffers from severe frequency selective fading.

In other words, it can be seen that the performance of the integer multiple frequency error estimation method is related to channel statistics.

In addition, it was confirmed through the simulation results and the above Equation 8 that the channel delay spread should be small in order to increase the performance of the integer frequency error estimation method.

FIG. 8 is a diagram illustrating a failure probability of cell ID index detection according to the prior art and the present invention according to SNR in an OFDMA-based downlink system according to an embodiment of the present invention.

It was confirmed that the cell ID index detection performance of the present invention has almost the same performance as the conventional cell ID index detection performance in the Pedestrian channel and the Vehicular channel.

As shown in FIG. 6, since the cell ID index detection method of the present invention has a lower computational complexity than the prior art, it is possible to effectively reduce the detection time during initial cell search.

The present invention shows a similar performance to that of the prior art in the simulation using the OFDMA-based downlink system environment and can confirm the reduction in complexity.

Therefore, the OFDMA-based downlink system according to the present invention can actually lower the cost of hardware implementation than the prior art.

The embodiments of the present invention described above are not implemented only by the apparatus and / or method, but may be implemented through a program for realizing functions corresponding to the configuration of the embodiment of the present invention, a recording medium on which the program is recorded And such an embodiment can be easily implemented by those skilled in the art from the description of the embodiments described above.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, It belongs to the scope of right.

100: fast Fourier transform unit
110: first correlation value calculator
112: first LS correlator
114: first RS correlator
116: First correlation value multiplier
120: first signal sample adder
130: integer frequency error estimator
140: second correlation value calculator
142: second LS correlator
144: second RS correlator
146: second correlation value multiplier
150: second signal sample adder
160: cell ID detector

Claims (16)

Processing a signal by performing a Fast Fourier Transform (Primary Synchronization) signal received from a transmitter from a time axis to a frequency axis at a receiver;
Calculating a correlation value between left subcarriers and right subcarriers based on a direct current (DC) subcarrier in the fast Fourier transformed PS signal;
Multiplying the correlation values of the calculated left subcarriers and the right subcarriers by correlation values placed at left and right symmetrical positions with respect to the DC subcarrier;
Selecting a real part after summing the multiplied correlation values, estimating an integer multiple frequency error by obtaining a maximum value in the selected real part;
Calculating a correlation value between left subcarriers and right subcarriers based on the DC subcarrier in the signal with the estimated integer frequency error compensated;
Multiplying the correlation values of the calculated left subcarriers and the right subcarriers by correlation values placed at left and right symmetrical positions with respect to the DC subcarrier; And
Selecting a real part after adding the multiplied correlation values, and obtaining a maximum value from the selected real part to detect a cell ID index
Integer frequency error estimation and cell ID index detection method comprising a. The method of claim 1,
A method of estimating integer frequency error and detecting cell ID index, wherein the received PS signal in the frequency domain processed by the fast Fourier transform is represented by Equation 1 below:
[Equation 1]

here,

Is the kth subcarrier signal of the received PS signal in the frequency domain,

Is the kth subcarrier signal of the transmitted PS signal,

Is the guard interval length,

Is an integer frequency error normalized to the subcarrier spacing,

Is the channel response in the frequency domain,

The average is 0 and the variance is

Phosphorus complex additive white Gaussian noise (AWGN). The method of claim 2,
Integer frequency error estimation and cell for calculating a correlation value between the left subcarriers and the right subcarriers based on the DC subcarriers in the received PS signal in the frequency domain processed by the fast Fourier transform using Equation 2 below To detect ID index:
[Equation 2]

here,

Denotes a calculation of a correlation value of the left subcarriers,

Denotes a calculation of a correlation value of the right subcarriers. The method of claim 3,
Multiplying the correlation values of the computed left subcarriers and the right subcarriers by correlation values placed at left and right symmetric positions with respect to the DC subcarrier,

ego,

, An integer multiple frequency error estimation and cell ID index detection method expressed by Equation 3 below:
[Equation 3]

here,

Represented by. 5. The method of claim 4,
The summation of all signal sample values of the multiplied correlation values may include an integer frequency error estimation and a cell ID index detection method represented by Equation 4 below:
[Equation 4]

here,

being. The method of claim 5,
Selecting a real part after summing the multiplied correlation values, and estimating an integer multiple frequency error by obtaining a maximum value in the selected real part,
An integer frequency error estimation and cell ID index detection method for estimating the integer frequency error using Equation 5 below.
[Equation 5]

The method according to claim 6,
Computing a correlation value between the left subcarriers and the right subcarriers based on the DC subcarrier in the signal compensated for the estimated integer frequency error multiplied by the correlation values placed in the left and right symmetric positions,
Integer frequency error estimation and cell ID index detection method expressed by Equation 6 below:
[Equation 6]

here,

Denotes a calculation of a correlation value of the left subcarriers,

Denotes a calculation of a correlation value of the right subcarriers. The method of claim 7, wherein
Selecting a real part after summing the multiplied correlation values, and obtaining a maximum value from the selected real part to detect a cell ID index,
Integer frequency error estimation and cell ID index detection method expressed by Equation 7 below:
[Equation 7]

here,

Is a signal in which the integer frequency error is compensated for using [Equation 5]. A fast Fourier transform unit for processing a signal by performing a fast Fourier Transform (PS) signal received from a transmitter from a time axis to a frequency axis at a receiver;
A first correlation value calculator configured to calculate a correlation value between left subcarriers and right subcarriers based on a DC (Direct Current) subcarrier in the fast Fourier transformed PS signal and multiply correlation values placed at left and right symmetric positions;
A first signal sample adder for calculating a sum of correlation values multiplied by the first correlation value calculator;
An integer frequency error estimator that selects a real part from an output value of the first signal sample adder, obtains a maximum value thereof, and estimates an integer frequency error;
A second correlation value calculating unit that calculates a correlation value between left subcarriers and right subcarriers based on the DC subcarrier based on the DC subcarrier compensated signal output from the integer frequency error estimator and multiplies correlation values positioned at left and right symmetric positions; ;
A second signal sample adder for calculating a sum of correlation values multiplied by the second correlation value calculator; And
A cell ID detector for detecting a cell ID index by selecting a real part from an output value of the second signal sample adder and obtaining a maximum value among them
Integer frequency error estimation and cell ID index detection apparatus comprising a. 10. The method of claim 9,
Wherein the fast Fourier transform unit comprises:
An integer frequency error estimation and cell ID index detection apparatus for expressing the received PS signal in the frequency domain processed by the fast Fourier transform by Equation 8 below:
[Equation 8]

here,

Is the kth subcarrier signal of the received PS signal in the frequency domain,

Is the kth subcarrier signal of the transmitted PS signal,

Is the guard interval length,

Is an integer frequency error normalized to the subcarrier spacing,

Is the channel response in the frequency domain,

The average is 0 and the variance is

Phosphorus complex additive white Gaussian noise (AWGN). The method of claim 10,
The first correlation calculator calculates a correlation value between the left subcarriers and the right subcarriers based on the DC subcarriers in the received PS signal in the frequency domain processed by the fast Fourier transform unit using Equation 9 below. Compute integer frequency error estimation and cell ID index detection device:
[Equation 9]

here,

Denotes a calculation of a correlation value of the left subcarriers,

Denotes a calculation of a correlation value of the right subcarriers. The method of claim 11,
The first correlation value calculator
Multiplying the correlation values of the computed left subcarriers and the right subcarriers by correlation values placed at left and right symmetric positions with respect to the DC subcarrier,

ego,

, An integer multiple frequency error estimation and cell ID index detection apparatus represented by Equation 10 below:
[Equation 10]

here,

Represented by. The method of claim 12,
The first signal sample adder
An integer frequency error estimation and cell ID index detection apparatus for adding all signal sample values of correlation values multiplied by the first correlation value calculator using Equation 11 below:
[Equation 11]

here,

being. The method of claim 13,
The integer frequency error estimator
An integer multiple frequency error estimation and cell ID index detection apparatus for selecting a real part from a value output from the first signal sample adder, obtaining a maximum value, and estimating an integer frequency error using Equation 12 below:
[Equation 12]

15. The method of claim 14,
The second correlation value calculator
In the signal compensated for the integer frequency error output from the integer frequency error estimator, a correlation value between left and right subcarriers is calculated based on the DC subcarrier and multiplied by correlation values placed at left and right symmetric positions. Integer frequency error estimation and cell ID index detection device represented by
[Equation 13]

here,

Denotes a calculation of a correlation value of the left subcarriers,

Denotes a calculation of a correlation value of the right subcarriers. 16. The method of claim 15,
The cell ID detector is
An integer multiple frequency error estimation and cell ID index detection device for selecting a real part from an output value of the second signal sample adder, obtaining a maximum value, and detecting a cell ID index using Equation 14 below:
[Equation 14]

here,

Is a signal in which the integer frequency error is compensated using the equation (12), u = {25, 29}, u = 34,

being.

Images