KR100246452B1 - Apparatus and method for frequency synchronization using orthogonal frequency division multiplexing - Google Patents

Abstract

The present invention relates to a frequency synchronization apparatus and method in an OFDM transmission scheme, and by using only pilot carriers continuously input in the OFDM transmission scheme, repetitive symbol transmission is unnecessary, resulting in high efficiency of transmission data and frequency offset. The amount of calculation for the estimation is reduced, so that the hardware can be implemented with simple hardware, and the frequency synchronization device in the OFDM transmission method that enables accurate frequency correction by estimating the frequency offset in accordance with the degree of the frequency offset caused by the radio channel, and The purpose is to provide a method.

According to the frequency synchronization apparatus and method in the OFDM transmission method according to the present invention, unlike in the conventional case that frequency synchronization cannot be secured when the frequency offset caused by the channel is ± 0.5 times or an integer multiple of the frequency interval between subcarriers, By using only pilot carriers that are continuously input in the transmission scheme, repetitive symbol transmission is unnecessary, thereby increasing the efficiency of the transmission data and reducing the amount of calculation for frequency offset estimation, thereby enabling simple hardware implementation. In addition, if the frequency of the received signal exists only within the frequency range of the OFDM transmission scheme due to the frequency offset, it is possible to estimate the width, narrow width, and residual frequency offset step by step quickly and accurately in a short time due to the small amount of calculation, and secure stable frequency synchronization in the future. It is possible to improve the broadcasting quality of the digital TV which the service is expected and greatly improve the user's satisfaction.

Description

Frequency Synchronizer and Method in Orthogonal Frequency Division Multiplexing

The present invention relates to a frequency synchronization apparatus and method in an orthogonal frequency division multiplexing (OFDM) transmission scheme, and by using only pilot carriers continuously input in the OFDM transmission scheme, repetitive symbol transmission is achieved. Since it becomes unnecessary, the efficiency of transmission data is increased and the amount of calculation for frequency offset estimation is reduced, so it is possible to implement with simple hardware, and accurate frequency correction is performed by estimating the frequency offset step by step according to the degree of frequency offset caused by the radio channel. An object of the present invention is to provide a frequency synchronization apparatus and method (Apparatus and Method for Frequency Synchronization Using Orthogonal Frequency Division Multiplexing) in an OFDM transmission scheme.

TV broadcasting, which began in black and white TV half a century ago, is now in a situation where the practical use of digital broadcasting is realized. Digital broadcasting, in which higher broadcasting quality and various functions are added by using the advantages of digital itself, has been decided on various types of standards by country, and research and commercialization technologies for broadcasting equipment and receiving devices are being secured.

First of all, in North America, such as the United States and Canada, a terrestrial broadcasting system employs a transmission method using vestigial sideband modulation, and MPEG-2 (Moving Picture Expert Group II) is selected as a standard for data compression. On the other hand, in Europe, Orthogonal Frequency Division Multiplexing (OFDM) is adopted as a transmission method of digital broadcasting. The OFDM transmission method is a method of improving a transmission speed by using a frequency band by transmitting data in the form of a bit stream in parallel in order to satisfy a high-speed data transmission request like a broadcast signal.

Hereinafter, the apparatus and operation of the OFDM transmission and reception method adopted as a standard of the digital broadcasting transmission method in Europe will be briefly described with reference to FIG. 1.

First, as illustrated in FIG. 1A, the OFDM transmitter 10 includes a data coder 11 for encoding data to be transmitted and data encoded from the data coder 11 in serial units by transmission units. A serial-to-parallel converter 12 for receiving and converting a parallel form, a modulator 13 for receiving a signal input in parallel from the serial-to-parallel converter 12 and modulating subcarriers, and the modulator ( And a multiplex 14 for sequentially transmitting the modulated signals input in parallel from 13).

As illustrated in FIG. 1B, the OFDM receiver 20 includes a demodulator 21 for converting a modulated signal input through a channel into a baseband signal and a parallel input from the demodulator 21. A parallel-serial conversion section 22 for converting the demodulated data into serial and a data decoding section 23 for converting the data input from the parallel-serial conversion section 22 into the original bit stream form.

In the OFDM transmission apparatus configured as described above, the data converted in parallel is multiplied by a subcarrier in the modulator 13, wherein the frequency interval of each subcarrier is in a typical frequency-shift keying (FSK) modulation scheme. Only half of the frequency spacing between each carrier is required. That is, to minimize interference during actual demodulation by adjusting the frequency of the subcarrier when modulating a symbol to be transmitted to a point where the interference signal of the adjacent subcarrier becomes '0'. However, the OFDM transmission apparatus configured as described above has a problem in that the system becomes very complicated as the transmission unit increases. Therefore, a method of Fourier transforming and transmitting data to be transmitted before modulation is commonly adopted.

FIG. 2 illustrates an OFDM transmission apparatus using a Fourier transform as described above, and its operation is similar to that of the general OFDM transmission apparatus illustrated in FIG. 1. As shown in FIG. 2A, the OFDM transmission unit 30 using the Fourier transform includes a data coding unit 31 for encoding data to be transmitted and data encoded from the data coding unit 31 by serial transmission units. A serial-to-parallel converter 32 for receiving inputs in parallel to each other, a Fourier-transformer 33 for receiving a signal input in parallel from the serial-to-parallel converter 32, and Fourier transform, and the Fourier transform It is composed of a modulator 34 for receiving a signal converted to the frequency axis in the unit 33 in series and modulates the carrier wave.

As shown in FIG. 2B, the OFDM receiver 40 using the Fourier transform estimates a phase of a modulated signal input through a channel to match the phase of the carrier of the receiver, and the phase adder 41. A gain corrector 42 for receiving a signal whose phase has been corrected by the step 41 and converting the magnitude of the signal into the same magnitude, and the phase and magnitude are corrected in the phase corrector 41 and the gain corrector 42. An inverse Fourier transform unit 43 for receiving an input signal and performing inverse Fourier transform, a parallel-to-serial converting unit 44 for converting the signals output in parallel from the inverse Fourier transform unit 43 in series; And a data decoder 45 for reducing the demodulated data output from the parallel-serial converter 44 to the original bit stream.

In the aforementioned OFDM transmission scheme, when the Doppler's effect in which the frequency of a carrier is changed on a wireless channel and a device that acquires frequency synchronization in a receiving device do not operate stably, synchronization of a transmission frequency and a reception frequency cannot be achieved. The difference between the two frequencies is called a frequency offset. When demodulating the received signal, the frequency offset causes a problem that the power of the signal is reduced and the overall performance is degraded. In particular, in the OFDM transmission scheme using the multicarrier, since data is detected for each subcarrier, If a frequency offset of a certain level or more occurs, orthogonality between subcarriers is not maintained, thereby causing interference between adjacent subcarriers. In the OFDM transmission scheme, as the number of subcarriers increases, each subcarrier is densely distributed within a predetermined band, and even a small frequency offset may cause interference among adjacent subcarriers. Therefore, the process of frequency offset correction that accurately matches the received frequency with the transmit frequency is an important problem in determining the performance of the system.

Accordingly, various types of schemes have been proposed for the frequency offset correction, and one of them is a phase locked loop (PLL) based on the frequency offset characteristics obtained by using the periodicity of the guard interval in the OFDM transmission scheme. The second method is to estimate a frequency error by driving a frequency error, and another method is to estimate a frequency offset value by repeatedly transmitting a known symbol string without using a phase locked loop.

Hereinafter, the configuration and operation of the OFDM receiver to which the frequency offset correction method is applied in the OFDM transmission method using the Fourier transform will be described.

As shown in FIG. 3, the frequency offset correction device 50 includes an A / D converter 51 for converting a received analog signal into a digital signal, and the A / D signal using a frequency error estimation signal. A frequency error correcting unit 52 for correcting the frequency of the received signal input from the converting unit 51, and a Fourier transform before transmission by inverse Fourier transforming a signal whose frequency error corrected from the frequency error correcting unit 52 is corrected. The frequency error by inputting a Fourier transform unit 53 for restoring the data in the state before it is received and a symbol demodulated by the inverse Fourier transform unit 53 and calculating a correlation with a previous symbol to estimate a frequency offset A frequency error estimator 54 for feeding back to the correction unit 52 and an equalizer 55 for receiving the demodulated symbols from the Fourier transform unit 53 and removing interference signals and noises other than frequency offsets. It is sex.

first, K A signal transmitted by an OFDM transmission scheme using two subcarriers is received at a receiving end under the influence of a channel represented by fading and fading due to the Doppler effect while passing through a wireless channel. The received signal input to the receiver may be expressed by Equation 1 below.

In Equation 1 H _k Is k Impulse response of the first subcarrier channel, n Is the number of symbols in the transmission unit, Δf Is the frequency offset for which correction is required.

In the frequency offset correction receiving apparatus configured as described above, the frequency error estimator 54 receives the symbols output from the Fourier transform unit, calculates mutual interference with the time delayed signal, and considers the characteristics of the frequency offset to maximize the maximum likelihood estimation. A frequency offset is estimated using a method like Maximum Likelihood Estimation (MLE), and the estimated frequency offset is output to the frequency error correcting unit 52. The frequency error correcting unit 52 may remove the frequency offset by changing the frequency by the estimated frequency error input from the frequency error estimating unit 54.

However, in the conventional OFDM receiver using the frequency offset correction, when a frequency offset of about 0.5 times the frequency interval between subcarriers occurs, it is difficult to distinguish between the frequencies of the adjacent subcarriers and the desired subcarriers. The frequency offset may be adjusted by frequency, and if the frequency offset is an integer multiple of the frequency interval between subcarriers, frequency offset correction may not be possible. In the case of using the conventional frequency offset correction method, the actual amount of data transmission is reduced by repeated transmission of symbols, and the amount of calculation for frequency offset estimation is sharply increased as the number of symbols considered to calculate correlation interference increases. The hardware fabrication is complicated because the memory capacity is excessively increased and the memory capacity is excessively increased.

Accordingly, an object of the present invention is to solve such a problem, and by using only pilot carriers that are continuously input in the OFDM transmission scheme, repetitive symbol transmission is unnecessary, resulting in high efficiency of transmission data. The amount of calculation for frequency offset estimation is reduced, which enables simple hardware implementation, and frequency synchronization in the OFDM transmission scheme that enables accurate frequency correction by estimating the frequency offset in accordance with the degree of frequency offset caused by the radio channel. An apparatus and method are provided.

1A is a conceptual diagram of a transmitting end in an OFDM transmission scheme;

1b is a conceptual diagram of a receiving end in an OFDM transmission scheme;

2a is a block diagram of a transmitting end using a Fourier transform in the OFDM transmission scheme,

2b is a block diagram of a receiver using a Fourier transform in the OFDM transmission scheme,

3 is a block diagram of a frequency synchronization device in an OFDM transmission scheme according to the prior art;

4 is a block diagram of a frequency synchronization device in an OFDM transmission scheme according to the present invention;

FIG. 5 is a detailed block diagram of a wide frequency offset estimator in FIG. 4; FIG.

6 is a detailed block diagram of a narrow frequency offset estimator in FIG. 4;

FIG. 7 is a detailed block diagram of a fine frequency offset estimator of FIG. 4; FIG.

8 is a detailed block diagram of a practical example of the implementation of the frequency synchronization device in the OFDM transmission scheme according to the present invention.

<Description of the code | symbol about the principal part of drawing>

100: A / D conversion unit 200: frequency error correction unit

300: Fourier transform unit 400: Frequency error estimation unit

410: wide frequency offset estimator 411: continuous pilot index generator

412: First continuous pilot detector 413: Symbol delay unit

414: second continuous pilot detector 415: correlation detector

416: maximum correlation value setting unit 420: narrow frequency offset estimation unit

421: First narrow pilot detector 423: Second narrow pilot detector

424: narrow correlation detector 425: maximum correlation value detector

426: narrow frequency offset detector 427: test correction frequency generator

430: fine frequency offset estimator 431: first fine pilot detector

433: second fine pilot detector 434: fine phase detector

435: phase locked loop 436: voltage controlled oscillator

500: equalizer

In the OFDM transmission scheme according to the present invention for achieving the above object, the frequency synchronization apparatus and method cannot secure frequency synchronization when the frequency offset caused by the channel is ± 0.5 times or an integer multiple of the frequency interval between subcarriers. Unlike the related art, by using only pilot carriers continuously input in the OFDM transmission scheme, repetitive symbol transmission is unnecessary, thereby increasing efficiency of transmission data and reducing calculation amount for frequency offset estimation. It is possible, and by estimating the frequency offset in accordance with the degree of the frequency offset caused by the radio channel step by step to enable accurate frequency synchronization regardless of the degree of the frequency offset.

Hereinafter, the configuration of the frequency synchronization device in the OFDM transmission method according to the present invention will be described with reference to FIGS.

In the OFDM transmission method according to the present invention, as shown in FIG. 4, the frequency synchronization device uses the A / D converter 100 for converting a received analog signal into a digital form, and using the frequency error estimation signal. Obtain the frequency error correction unit 200 for correcting the frequency of the received signal input from the A / D conversion unit 100 and the frequency-specific characteristics of the signal corrected frequency error input from the frequency error correction unit 200 The Fourier transform unit 300 for Fourier transform and the frequency-dependent characteristics output from the Fourier transform unit 300 are input to calculate the frequency interference by calculating the correlation interference with the previous symbol to the frequency error correction unit 200 A frequency error estimator 400 for feedback and an equalizer 500 for receiving the demodulated symbols from the Fourier transform unit 300 and removing interference signals and noises other than frequency offsets. It is made.

The frequency error estimator 400 receives a signal according to a frequency characteristic from the Fourier transformer 300 to reduce the frequency offset to within an integer multiple of the frequency interval between subcarriers, and after completion, outputs a wide frequency offset signal. The wide frequency offset estimator 410 receives a wide delay signal from the wide frequency offset estimator 410 and uses it as an enable, accurately estimates a frequency offset in which the frequency interval between subcarriers is reduced to within ± 0.5 times, and after completion, a small delay signal. A narrow frequency offset estimator 420 for outputting a small delay delay signal from the narrow frequency offset estimator 420 and used as an enable and tracking the remaining fine frequency offset to ensure accurate frequency synchronization, The fine frequency offset estimator 430 outputs the estimated frequency to the frequency error correcting unit 200. .

As shown in FIG. 5, the wide frequency offset estimator 410 includes a continuous pilot index generator 411 for generating a center frequency of all subcarriers to be applied and a frequency characteristic input from the Fourier transformer 300. A first continuous pilot detector 412 for detecting a pilot signal by receiving a frequency index from the continuous pilot index generator 411, and receiving a signal from the Fourier transform unit 300. A symbol delay unit 413 for delaying time by a time and a signal delayed from the symbol delay unit 413, and a frequency index input from the continuous pilot index generator 411 to detect a pilot signal; The pilot signal output from the continuous pilot detector 414, the first continuous pilot detector 412, and the second continuous pilot detector 414 is received. A correlation detector 415 for calculating the correlation interference between the two signals, a correlation interference amount from the correlation detector 415, and a frequency index from the continuous pilot index generator 411 to receive the maximum correlation interference amount. And a maximum correlation value setting unit 416 for generating a wide frequency estimation frequency offset signal by setting the generated frequency index value.

As shown in FIG. 6, the narrow frequency offset estimator 420 uses the wide frequency offset estimator 410 to correct a frequency offset of a signal with a wide frequency estimation within ± 0.5 times the frequency interval between subcarriers. The first narrow pilot detection unit 421 continuously receives a signal related to the Fourier transform unit 300 and receives a wide delay signal indicating that the wide frequency estimation is completed by the wide frequency offset estimation unit 410. ), A symbol delay unit 422 for receiving a signal relating to a frequency characteristic of a signal whose frequency offset is estimated from the Fourier transform unit 300 and delaying the signal by a characteristic time, and the wide frequency offset estimating unit ( In step 410, a wide delay signal is input and used as an enable, and a pilot signal delayed from the symbol delay unit 422 is received. A narrow pilot detector 423 for detecting a signal and a pilot signal output from the first narrow pilot detector 421 and the second narrow pilot detector 423 for calculating a correlation interference between the two signals. A correlation coefficient detector 424, a maximum correlation value detector 425 for detecting a maximum value by receiving a correlation interference amount from the small correlation coefficient detector 424, and a wide delay signal by the wide frequency offset estimator 410. A narrow frequency offset for generating a small estimated frequency offset signal by receiving a maximum offset value from the maximum correlation detection unit 425 and estimating a frequency offset of ± 0.5 times or less of a frequency interval between subcarriers. The wideband frequency offset estimator 410 receives a wide delay signal from the wideband frequency offset estimator 410 and enables the wideband frequency offset estimator 410. The frequency error correcting unit generates a test correction frequency signal that is input at an estimated frequency within ± 0.5 times the frequency interval between subcarriers and changes from a minimum frequency (-0.5) to a maximum frequency (+0.5) at a predetermined interval as a center frequency. And a test correction frequency generator 427 for outputting to 200.

As shown in FIG. 7, the fine frequency offset estimator 430 outputs a signal related to a frequency characteristic of a signal obtained by correcting the frequency offset estimated by the narrow frequency offset estimator 420. The first fine pilot detector 431 and the Fourier transform unit 300 to continuously receive a small delay signal indicating that the narrow estimation has been completed by the small frequency offset estimator 420 and continuously detect the pilot; A symbol delay unit 432 for receiving a signal relating to a frequency characteristic of the signal having the small frequency offset corrected from the signal delayed by a characteristic time, and a small delay signal received from the small frequency offset estimation unit 420 as an enable A second fine pilot detector 433 for receiving a pilot signal delayed from the symbol delay unit 432 and detecting a pilot signal; The width frequency offset estimator 420 receives a small delay signal for use as an enable, and receives two pilot signals output from the first fine pilot detector 431 and the second fine pilot detector 433. A fine phase detector 434 for detecting a phase difference between the phase and the small frequency offset estimator 420 to receive a small delay signal for use as an enable, and a phase using the phase difference input from the fine phase detector 434 The phase locked loop unit 435 for tracking and outputting the phase difference at a DC voltage level, and the narrow frequency offset estimator 420 receives a small delay signal and uses it as an enable, and the phase locked loop unit 435 And a voltage controlled oscillator 436 for generating a frequency signal corresponding to the DC voltage level input from the input signal.

Hereinafter, the operation of the frequency synchronization device in the OFDM transmission scheme configured as described above will be described in detail with reference to FIGS. 4 to 8.

The wide frequency offset estimator 410 estimates a frequency error within ± 0.5 times the frequency interval between subcarriers by detecting a frequency of a subcarrier to be received when a frequency offset exceeding an integer multiple of the frequency interval between subcarriers occurs.

First, the continuous pilot index generator 411 sequentially generates all frequency index values used in the OFDM transmission scheme. The first continuous pilot detector 412 detects each pilot signal according to the signal output from the Fourier transform unit 300 and the frequency generated by the continuous pilot index generator 411, and the second continuous pilot detector. In 414, the symbol delay unit 413 detects a pilot in a pilot signal delayed in time. Subsequently, the correlation detector 415 detects a correlation between the two pilot signals detected as described above, and the correlation value outputs a maximum value when it matches the frequency index of the continuous pilot index generator 411. Done. Therefore, the maximum correlation value setting unit 416 obtains a frequency index indicating the maximum correlation value, and estimates a frequency error within ± 0.5 times the frequency offset of the frequency interval between subcarriers, and outputs the wide estimated frequency offset. .

The operation of the wide frequency offset estimator 410 as described above may be expressed by Equation 2 below.

From here ΔK Is the frequency index, Z _{n, k} Is the received symbol signal, Y _{n, k} Means continuous pilot data.

As described above, after estimating a frequency error within an integer multiple of ± 0.5 times the frequency interval between subcarriers, the wide delay signal is generated to enable the narrow frequency offset estimator 420.

When enabled by the wide delay signal as described above, the test correction frequency generator 427 sets a frequency estimated by the wide frequency offset estimator 410 as a subcarrier and is maximum at the minimum frequency (−0.5). A frequency signal that varies between frequencies (+0.5) at regular intervals is generated and output to the frequency error correcting unit 200. In addition, the first narrow pilot detection unit 421 and the second narrow pilot detection unit 423 receive the corrected frequency signal through the Fourier transform unit 300 in the same way as the wide frequency offset estimation unit 410. Is detected, and the narrow correlation detector 425 detects and outputs a correlation between the two signals. Subsequently, the maximum correlation value detector 425 receives a correlation value output from the narrow correlation detector 425 to select a test correction frequency signal at which the maximum correlation value is generated.

Accordingly, the narrow frequency offset estimator 420 estimates a frequency offset more than ± 0.5 times the frequency interval between subcarriers in the wide frequency offset estimator 410 by using a test correction frequency signal to more accurately estimate the frequency of the received signal. The frequency offset approaching the offset can be estimated. At this time, the operation of the narrow frequency offset estimator 420 may be expressed as Equation 3 below.

From here f (trial) Represents the test calibration frequency.

As described above, when the frequency offset estimation unit 420 completes the frequency offset estimation, a small delay signal is generated to enable the fine frequency offset estimation unit 430. The fine frequency offset estimator 430 tracks and accurately corrects an error remaining in a frequency offset estimated by the test correction frequency signal.

The first fine pilot detector 431 and the second fine pilot detector 433 continuously detect the pilot signal in the same manner as the wide frequency offset estimator 410 and the small frequency offset estimator 420. The fine phase detector 434 detects a phase difference between the two signals. Subsequently, the phase-locked loop unit 435 generates a signal having a DC voltage level capable of compensating for the phase difference detected by the fine phase detector 434, and the voltage-controlled oscillator 436 receiving the input signal is proportional to the voltage level. A frequency offset is generated and output to the frequency error correcting unit 200 to complete the frequency offset estimation. The residual frequency offset estimated by the fine frequency offset estimator 430 may be expressed by Equation 4 below.

From here Δ Is the guard frequency interval between subcarriers, p Means pilot data, Y _1k Is a signal obtained by Fourier transforming the received complex signal, Y _2k Is Y _1k Denotes a time delayed signal.

Hereinafter, a frequency synchronization method in the OFDM transmission method according to the present invention will be described.

In the OFDM transmission method according to the present invention, the frequency synchronization method includes an A / D conversion step of converting a received analog signal into a digital shape, and a reception of the received signal input from the A / D conversion step using a frequency error estimation signal. A frequency error correction step of correcting a frequency, a Fourier transform step of performing Fourier transform to obtain frequency-specific characteristics of a signal from which the frequency error inputted from the frequency error correction step is corrected, and frequency-specific characteristics output from the Fourier transform step A frequency error estimation step of estimating a frequency offset by calculating a correlation with the previous symbol and returning it to the frequency error correction step, and receiving a demodulated symbol from the Fourier transform step, It consists of an equalization step to remove.

The frequency error estimating step includes a wide frequency offset estimation step of receiving a signal according to a frequency characteristic from the Fourier transform step to reduce a frequency offset within an integer multiple of the frequency interval between subcarriers, and outputting a wide delay signal after completion; A narrow frequency offset estimation step of receiving a wide delay signal from the offset estimation step and enabling it, accurately estimating a frequency offset in which the frequency interval between subcarriers is reduced to within ± 0.5 times, and outputting a small delay signal after completion; It is a fine frequency offset estimation step of receiving a small delay signal from the frequency offset estimation step and enabling it, tracking the remaining fine frequency offset to ensure accurate frequency synchronization, and outputting the estimated frequency to the frequency error correction step. It is composed.

The wide frequency offset estimation step includes a continuous pilot index generation step of generating a frequency index of a pilot signal in accordance with a center frequency of a carrier to be received, a signal relating to frequency characteristics input from the Fourier transform step, and the continuous pilot A first continuous pilot detection step of detecting a pilot signal by receiving a frequency index from the index generation step, a symbol delay step of receiving a signal from the Fourier transform step and time delaying by a characteristic time, and a signal delayed from the symbol delay step A second continuous pilot detection step of detecting a pilot signal by receiving a frequency from the continuous pilot index generation step, and receiving a pilot signal output from the first continuous pilot detection step and the second continuous pilot detection step; Two signals A correlation width detecting step for calculating a correlation interference, a correlation index amount is input from the correlation detection step, a frequency index value is input from the continuous pilot index generation step, and a frequency index value for generating a maximum correlation interference amount is set. And a maximum correlation value setting step for generating an estimated frequency offset signal.

In the narrow frequency offset estimating step, the wide frequency offset estimating step receives a signal related to a frequency characteristic of a signal whose frequency offset is corrected within ± 0.5 times the frequency interval between subcarriers, from the Fourier transform step. A first narrow pilot detection step of receiving a wide delay signal indicating that the width estimation has been completed in the frequency offset estimation step and continuously detecting the pilot; and a frequency characteristic of a signal having corrected the frequency offset estimated from the Fourier transform step. A symbol delay step of receiving a signal and time delaying by a characteristic time, and using a wide delay signal in the wide frequency offset estimation step as an enable, and receiving a pilot signal delayed from the symbol delay step to detect a pilot signal. 2nd narrow file A detection step, a narrow correlation detection step of receiving a pilot signal output from the first narrow pilot detection step and the second small pilot detection step and calculating correlation interference between the two signals, and the correlation from the narrow correlation detection step A maximum correlation value detecting step for detecting a maximum value by inputting an interference amount and a wide delay signal in the wide frequency offset estimation step for use as an enable, and receiving a maximum correlation value from the maximum correlation value detecting step for a subcarrier A narrow frequency offset detection step of generating a narrow estimated frequency offset signal by estimating a frequency offset of ± 0.5 times or less of a frequency interval therebetween, and receiving a wide delay signal in the wide frequency offset estimation step and using the enable as an enable, Within ± 0.5 times the frequency interval between subcarriers from the frequency offset estimation step A test correction frequency generation step of generating a test correction frequency signal that varies from a minimum frequency (-0.5) to a maximum frequency (+0.5) at a predetermined interval as a center frequency by receiving a frequency estimated as It consists of.

The fine frequency offset estimating step receives a signal relating to a frequency characteristic of a signal corrected by the narrow frequency offset estimating step from the Fourier transform step and completes the narrow estimation in the narrow frequency offset estimating step. A first fine pilot detection step of continuously receiving a pilot delay signal indicating the pilot signal; and a symbol delay for receiving a signal relating to a frequency characteristic of a signal having a small frequency offset corrected from the Fourier transform step and delaying the signal by a characteristic time And a second fine pilot detection step of receiving a wide delay signal for use in enable in the narrow frequency offset estimating step and detecting a pilot signal by receiving a time delayed pilot signal from the symbol delay step; In the offset estimation step A fine phase detection step of receiving a width delay signal and using the enable signal and detecting a phase difference between the two signals by receiving a pilot signal output from the first and second fine pilot detection steps; A phase locked loop step of receiving a wide delay signal in the frequency offset estimating step and using the enable signal and tracking the phase by using the phase difference input from the fine phase detecting step and outputting the phase difference to a DC voltage level; In the offset estimation step, a wide delay signal is input and used as an enable, and a voltage controlled oscillation step of generating a frequency signal corresponding to a DC voltage level input from the phase locked loop step.

Hereinafter, an operation procedure of the frequency synchronization method in the OFDM transmission method according to the present invention will be described in detail.

In the wide frequency offset estimation step, a frequency error is estimated within ± 0.5 times the frequency interval between subcarriers by detecting a frequency of a subcarrier to be received when a frequency offset exceeding an integer multiple of the frequency interval between subcarriers occurs.

First, in the continuous pilot index generation step, all frequency index values used in the OFDM transmission scheme are sequentially generated. In the first continuous pilot detection step, each pilot signal is detected according to the signal output in the Fourier transform step and the frequency generated in the continuous pilot index generation step, and in the symbol delay step in the second continuous pilot detection step. The pilot is detected in the delayed pilot signal. Subsequently, in the correlation detection step, the correlation between the two pilot signals detected as described above is detected. When the correlation matches the frequency index of the continuous pilot index generation step, the maximum value is output. Accordingly, in the maximum correlation value setting step, by obtaining a frequency index indicating the maximum correlation value, the frequency offset is estimated within ± 0.5 times the frequency offset of the frequency interval between the subcarriers and outputs a wide estimated frequency offset.

As described above, after estimating a frequency error within an integer multiple of ± 0.5 times the frequency interval between subcarriers, the wide delay signal is generated to enable the narrow frequency offset estimation step.

When enabled by the wide delay signal as described above, in the test correction frequency generating step, the frequency estimated in the wide frequency offset estimation step is set as a subcarrier, and the minimum frequency (−0.5) to the maximum frequency (+0.5) are used. Generates a frequency signal that changes at regular intervals and outputs the frequency signal to the frequency error correction step. In the first narrow pilot detection step and the second narrow pilot detection step, the pilot is detected by receiving the corrected frequency signal through the Fourier transform step, similarly to the wide frequency offset estimation step, and the narrow correlation detection step. Detects and outputs the correlation between two signals. Subsequently, in the maximum correlation value detection step, a correlation value output in the small correlation detection step is input to select a test correction frequency signal at which the maximum correlation value is generated.

Accordingly, in the narrow frequency offset estimating step, the frequency offset estimated within ± 0.5 times the frequency interval between subcarriers in the wide frequency offset estimating step is more accurately estimated by a test corrected frequency signal, thereby making the frequency offset close to the frequency offset of the received signal. Can be estimated.

In addition, when the frequency offset estimation is completed in the narrow frequency offset estimation step, a narrow delay signal is generated to enable the fine frequency offset estimation step. The fine frequency offset estimating step tracks and accurately corrects an error remaining in the frequency offset estimated by the test correction frequency signal. In the first fine pilot detection step and the second fine pilot detection step, the pilot signal is continuously detected in the same manner as the wide frequency offset estimation step and the narrow frequency offset estimation step, and in the fine phase detection step, the phase difference between the two signals is determined. Detect. Subsequently, in the phase locked loop step, a signal having a DC voltage level capable of compensating for the phase difference detected in the fine phase detection step is generated, and in the voltage controlled oscillation step receiving the input, a frequency signal proportional to the voltage level is generated. Outputting the frequency error correction step completes the frequency offset estimation.

According to the frequency synchronization device and method in the OFDM transmission method according to the present invention described above, by repeatedly estimating the frequency offset of the sub-carrier by using a pilot carrier (pilot carrier) continuously input in the OFDM transmission method, repeated symbol transmission This makes the transmission data more efficient and reduces the amount of computation for frequency offset estimation, making it simple to implement in hardware. In addition, if the frequency of the received signal is only within the frequency range of the OFDM transmission scheme due to the frequency offset, it is possible to estimate the wide, narrow and residual frequency offsets step by step quickly and accurately due to the small amount of calculation. It will be able to improve broadcasting quality and greatly improve user's satisfaction.

Claims (11)

In the frequency synchronization device in the OFDM transmission method, An A / D converter converting the received analog signal into a digital signal; A frequency error correction unit for correcting a frequency of a received signal input from the A / D converter by using a frequency error estimation signal; A Fourier transform unit for Fourier transforming a signal having a frequency error corrected from the frequency error correcting unit; A frequency error estimator which receives a signal for each frequency output from the Fourier transformer, calculates a correlation with a previous symbol, estimates a frequency offset, and outputs the frequency offset to the frequency error corrector; And And an equalizer configured to receive the demodulated symbols from the Fourier transform unit and remove interference signals and noises other than frequency offsets. The method of claim 1, wherein the frequency error estimator A wide frequency offset estimator for receiving a signal according to a frequency characteristic from the Fourier transformer and reducing a frequency offset within an integer multiple of a frequency interval between subcarriers and outputting a wide delay signal indicating completion; A narrow frequency offset estimator that receives a wide delay signal from the wide frequency offset estimator and uses it as an enable, approximates a frequency offset reduced within an integer multiple of the frequency interval between subcarriers, and outputs a narrow delay signal indicating completion. ; And Fine frequency offset estimation for receiving a small delay signal from the narrow frequency offset estimator and enabling it, tracking the remaining fine frequency offset to ensure accurate frequency synchronization, and outputting the estimated frequency to the frequency error correction unit. Frequency synchronization device in the OFDM transmission method, characterized in that consisting of. 3. The wide frequency offset estimation unit of claim 2, wherein A continuous pilot index generator for generating a frequency index corresponding to the center frequencies of all subcarriers in use by the OFDM transmission method; A first continuous pilot detection unit for receiving a Fourier-transformed frequency-specific signal from the Fourier transform unit, receiving a frequency index from the continuous pilot index generator, and detecting a pilot signal; A symbol delay unit receiving a signal from the Fourier transform unit and delaying the signal by a characteristic time; A second continuous pilot detector which receives a time delayed signal from the symbol delay unit, receives a frequency index from the continuous pilot index generator, and detects a pilot signal; A correlation detector for receiving a pilot signal output from the first continuous pilot detector and the second continuous pilot detector and calculating correlation interference between the two signals; And A maximum correlation value setting unit is configured to generate a wide estimated frequency offset signal by inputting a correlation interference amount from the correlation detector and receiving a frequency index from the continuous pilot index generator and setting a frequency index value at which a maximum correlation interference amount is generated. Frequency synchronization device in the OFDM transmission method, characterized in that the. 3. The method of claim 2, wherein the narrow frequency offset estimator The Fourier transform unit receives a Fourier transformed signal from the wide frequency offset estimator within an integer multiple of the frequency interval between subcarriers, and receives a wide delay signal from the wide frequency offset estimator. A first narrow pilot detector for detecting; A symbol delay unit for receiving a signal obtained by correcting a frequency offset within a frequency interval between adjacent subcarriers by the wideband frequency offset estimator and performing a Fourier transform on the Fourier transform unit to delay a time by a characteristic time; A second narrow pilot detector for receiving a wide delay signal from the wide frequency offset estimator and enabling the wide delay signal to detect a pilot signal by receiving a time delayed signal from the symbol delay unit; A narrow correlation detector for receiving a pilot signal detected by the first narrow pilot detector and the second small pilot detector and calculating a correlation interference amount; A maximum correlation value detector for detecting a maximum value by receiving a correlation interference amount from the narrow correlation detector; A narrow frequency offset detector which receives a wide delay signal from the wide frequency offset estimator and uses the enable delay, receives a maximum correlation value from the maximum correlation detector, estimates a frequency offset, and generates a narrow estimated frequency offset signal; ; The wide frequency offset estimator receives a wide delay signal and uses the wide delay signal, and generates a test correction frequency signal, which is a center frequency, at a predetermined interval and outputs the frequency index set from the wide frequency offset estimator to the frequency error correcting unit. Frequency synchronization device in the OFDM transmission method, characterized in that consisting of a test correction frequency generator. The method of claim 2, wherein the fine frequency offset estimator The narrow frequency offset estimator receives a small delay signal and uses the enable signal. The Fourier transform unit receives a signal obtained by correcting the frequency offset estimated by the small frequency offset estimator, and receives a pilot. A first fine pilot detector for detecting; A symbol delay unit for receiving a signal obtained by correcting the frequency offset estimated by the narrow frequency offset estimator and performing a Fourier transform on the Fourier transform unit for delaying the signal by a characteristic time; A second fine pilot detector which receives a small delay signal from the narrow frequency offset estimator and uses the enable delay, and receives a pilot signal delayed from the symbol delay unit to detect a pilot signal; A fine phase detector which receives a small delay signal from the narrow frequency offset estimator and uses the enable delay, and receives a pilot signal detected by the first fine pilot detector and the second fine pilot detector to detect a phase difference between the signals; ; A phase locked loop unit for receiving a small delay signal from the small frequency offset estimator and enabling the small delay signal and tracking a phase using a phase difference input from the fine phase detector to output a phase difference at a DC voltage level; And a voltage controlled oscillator configured to receive a small delay signal from the narrow frequency offset estimator and use it as an enable, and generate a frequency signal corresponding to a DC voltage level input from the phase locked loop. Frequency synchronization device in the scheme. The method of claim 1, wherein the frequency error correction unit A wide delay signal output from the wide frequency offset estimator and a small delay signal are input to the small frequency offset estimator and used as enable, and the wide frequency offset and the small frequency offset are output from the wide frequency offset estimator. OFDM transmission, characterized in that for receiving the sum of the narrow estimated frequency offset from the estimator, the sum of the fine estimated frequency offset from the fine frequency offset estimator, and the test correction frequency signal from the test correction frequency generator Frequency synchronization device in the scheme. In the frequency synchronization method in the OFDM transmission method, An A / D conversion step of converting the received analog form signal into a digital form; A frequency error correction step of correcting a frequency of a received signal input from the A / D conversion step by using a frequency error estimation signal; A Fourier transform step of Fourier transforming the signal having the frequency error corrected from the frequency error correcting step; A frequency error estimation step of receiving a signal for each frequency output from the Fourier transform step, calculating a correlation with a previous symbol, estimating a frequency offset, and outputting the frequency offset to the frequency error correction step; And And an equalization step of receiving the demodulated symbols from the Fourier transform step and removing interference signals and noises other than frequency offsets. 8. The method of claim 7, wherein the frequency error estimating step is A wide frequency offset estimation step of receiving a Fourier transformed signal from the Fourier transform step to reduce a frequency offset within a frequency interval between adjacent subcarriers and output a wide delay signal; A narrow frequency offset estimating step of receiving a wide delay signal from the wide frequency offset estimating step, using the enable delay, approximating a frequency offset reduced within a frequency interval between adjacent subcarriers, and outputting a narrow delay signal; And Fine frequency offset estimation for receiving a small delay signal from the narrow frequency offset estimation step and enabling it, tracking the remaining fine frequency offset to ensure accurate frequency synchronization, and outputting the estimated frequency to the frequency error correction step. Frequency synchronization method in the OFDM transmission method, characterized in that consisting of steps. 9. The method of claim 8, wherein the step of estimating the wide frequency offset A continuous pilot index generation step of generating a frequency index corresponding to the center frequencies of all subcarriers in use in the OFDM transmission scheme; A first continuous pilot detection step of receiving a Fourier transformed frequency-specific signal from the Fourier transform step, a frequency index received from the continuous pilot index generation step, and detecting a pilot signal; A symbol delay step of receiving a signal from the Fourier transform step and delaying the signal by a characteristic time; A second continuous pilot detection step of receiving a time delayed signal from the symbol delay step, a frequency index from the continuous pilot index generation step, and detecting a pilot signal; A correlation detection step of receiving a pilot signal output from the first continuous pilot detection step and the second continuous pilot detection step and calculating correlation interference between the two signals; And A maximum correlation value setting step of generating a wide estimated frequency offset signal by receiving a correlation interference amount from the correlation detection step, a frequency index value from the continuous pilot index generation step, and setting a frequency index value at which a maximum correlation interference amount is generated. Frequency synchronization method in the OFDM transmission method, characterized in that consisting of. 9. The method of claim 8, wherein the narrow frequency offset estimating step In the wide frequency offset estimation step, a wide delay signal is input and used as an enable, and in the wide frequency offset estimating step, a Fourier transform signal is inputted in a frequency interval between adjacent subcarriers in the Fourier transform step to continuously receive the signal. A first narrow pilot detection step of detecting a pilot; A symbol delay step of receiving a signal obtained by correcting a frequency offset within a frequency interval between adjacent subcarriers in the wide frequency offset estimation step by performing a Fourier transform in the Fourier transform step and delaying the signal by a characteristic time; A second narrow pilot detection step of receiving a wide delay signal from the wide frequency offset estimation step and using the wide delay signal and detecting a pilot signal by receiving a time delayed signal from the symbol delay step; A narrow correlation detection step of receiving a pilot signal detected from the first narrow pilot detection step and the second narrow pilot detection step and calculating a correlation interference amount; A maximum correlation value detection step of detecting a maximum value by receiving a correlation interference amount from the small correlation detection step; In the wide frequency offset estimation step, a wide frequency delay signal is input and used as an enable, and a small frequency offset is detected by generating a small estimated frequency offset signal by estimating a frequency offset by receiving a maximum correlation value from the maximum correlation value detection step. step; And In the wide frequency offset estimating step, a wide delay signal is input and used as an enable, and a test correction frequency signal, which is a center frequency, is generated at regular intervals at a frequency index set from the wide frequency offset estimating step, and is output to the frequency error correcting step. Frequency synchronization method in the OFDM transmission method, characterized in that consisting of a test correction frequency generation step. 9. The method of claim 8, wherein the fine frequency offset estimating step In the narrow frequency offset estimating step, a small delay signal is input and used as an enable, and a signal obtained by correcting the frequency offset estimated by the small frequency offset estimating step is Fourier-transformed in the Fourier transform step to continuously receive a pilot. Detecting the first fine pilot; A symbol delay step of receiving a signal obtained by correcting the frequency offset estimated by the narrow frequency offset estimating step and performing a Fourier transform on the Fourier transform step to delay the signal by a characteristic time; A second fine pilot detection step of receiving a small delay signal in the small frequency offset estimation step and enabling the small delay signal and receiving a pilot signal delayed from the symbol delay step to detect a pilot signal; In the narrow frequency offset estimating step, a small delay signal is input and used as an enable, and a fine phase for receiving a pilot signal detected from the first fine pilot detection step and the second fine pilot detection step to detect a phase difference between the signals A detecting step; A phase locked loop step of receiving a small delay signal in the narrow frequency offset estimating step and enabling the small delay signal and tracking the phase using the phase difference input from the fine phase detection step to output the phase difference as a DC voltage level; And a voltage controlled oscillation step of receiving a small delay signal in the narrow frequency offset estimating step and enabling the signal and generating a frequency signal corresponding to the DC voltage level input from the phase locked loop step. Frequency synchronization device in transmission mode.

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