KR101080671B1

KR101080671B1 - Orthogonal frequency duplex modulation receiver of baseband and method for the same

Info

Publication number: KR101080671B1
Application number: KR1020100041319A
Authority: KR
Inventors: 유수림; 장은석
Original assignee: 주식회사 텔레칩스
Priority date: 2010-05-03
Filing date: 2010-05-03
Publication date: 2011-11-08

Abstract

The present invention relates to a baseband OFDM reception technique. In particular, an OFDM receiver using the same down-conversion clock and sampling clock of an RF block has a cyclic prefix (Cyclic Prefix) correlation that occurs at a distance between a transmitter and a receiver. The present invention relates to a baseband OFDM reception technique for estimating a timing error of a sample clock which is a shift phenomenon and estimating a carrier frequency error based on the estimated information. According to the present invention, a baseband OFDM receiver includes: an analog / digital converter for sampling baseband received signals of RF blocks and outputting baseband sample data; A frequency compensation filter for compensating the carrier frequency component with respect to the baseband sample data with reference to the carrier frequency error value input from the frequency error estimator, and filtering the frequency band corresponding to the bandwidth of the received signal to output sample data; A cyclic estimator for obtaining a sample clock error estimate by calculating a correlation value of a section corresponding to a cyclic prefix from sample data; And a frequency error estimator for providing a frequency compensation filter with a carrier frequency error value generated by multiplying the sample clock error estimate value and the RF center carrier frequency.

Description

Orthogonal Frequency Duplex Modulation Receiver of baseband and method for the same}

The present invention relates to a baseband OFDM reception technique. In particular, an OFDM receiver using the same down-conversion clock and sampling clock of an RF block has a cyclic prefix (Cyclic Prefix) correlation that occurs at a distance between a transmitter and a receiver. The present invention relates to a baseband OFDM reception technique for estimating a timing error of a sample clock which is a shift phenomenon and estimating a carrier frequency error based on the estimated information.

The conventional OFDM transceiver has a configuration of adding a separate OFDM symbol or a subcarrier for frequency estimation for frequency estimation. In the frequency domain estimation method, an FFT is performed to estimate a frequency error using correlation of a corresponding symbol or subcarrier.

When an OFDM symbol for frequency estimation is given, an error of a carrier frequency corresponding to an integer multiple is estimated by finding a position having a high autocorrelation value while changing the order of carriers included in the OFDM symbol. If there is a subcarrier for frequency estimation, the position of the high autocorrelation value for the subcarrier is found to estimate the error of the carrier frequency.

When the OFDM symbol for frequency estimation is used in the frequency domain, a high autocorrelation of the symbol is required, and a high calculation amount is required to calculate a correlation value when estimating a frequency error for the symbol. In addition, in the case of including a frequency error of a multiple of half of the OFDM subcarrier, there is a problem that the probability of estimating an accurate value is lowered due to a decrease in signal correlation when estimating a frequency axis.

In addition, there is a problem in that a frequency estimation subcarrier requires a high autocorrelation, and a frequency estimation probability decreases due to a decrease in correlation, and a data carrier decreases due to the addition of the frequency estimation carrier.

It is an object of the present invention to provide a baseband OFDM reception technique that reconstructs the amount of movement of a cyclic prefix correlation value in the time axis as a separation of carrier frequencies, thereby eliminating errors in carrier frequencies with a relatively small amount of computation.

A baseband OFDM receiver according to the present invention includes an analog / digital converter for sampling baseband received signals of RF blocks and outputting baseband sample data; A frequency compensation filter for compensating the carrier frequency component with respect to the baseband sample data with reference to the carrier frequency error value input from the frequency error estimator, and filtering the frequency band corresponding to the bandwidth of the received signal to output sample data; A cyclic estimator for obtaining a sample clock error estimate by calculating a correlation value of a section corresponding to a cyclic prefix from sample data; And a frequency error estimator for providing a frequency compensation filter with a carrier frequency error value generated by multiplying the sample clock error estimate value and the RF center carrier frequency.

The down conversion clock of the RF block and the sampling clock of the analog / digital converter according to the present invention are configured to have the same frequency.

The cyclic estimator may include a pre-correlation value calculator configured to calculate a pre-correlation value between the sample data of the guard interval and the sample data having the guard interval and the N-1 sample interval; A pre-power calculator for calculating a power of the pre-correlation value; A post correlation value calculator configured to calculate a post correlation value between the sample data of the guard period and the sample data having the N + 1 sample interval; A post power calculation unit for calculating a power of a post correlation value; An on correlation value calculator configured to calculate an on correlation value between the sample data of the guard interval and the sample data having the N interval and the guard interval; An on power calculator for calculating power of an on correlation value; And a sample clock error calculator configured to obtain a sample clock error estimate by dividing a value obtained by subtracting the power of the post correlation value from the power of the pre correlation value by the power of the on correlation value.

The cyclic estimator according to the present invention may further include a loop filter that accumulates a sample clock error estimate value and controls a sampling rate of the analog / digital converter based on the accumulated value.

The baseband OFDM reception method according to the present invention comprises the steps of: (a) sampling the baseband received signal of the RF block to obtain baseband sample data; (b) compensating the carrier frequency component for the baseband sample data with reference to the carrier frequency error value calculated in the frequency error estimation step; (c) filtering the frequency band corresponding to the bandwidth of the received signal from the baseband sample data whose carrier frequency component is compensated and outputting the sample data; (d) obtaining a sample clock error estimate by calculating a correlation value for a section corresponding to the cyclic prefix in the sample data; And (e) a frequency error estimation step of providing the carrier frequency error value generated by multiplying the sample clock error estimate value and the RF center carrier frequency to step (b).

Step (a) according to the present invention comprises the step of setting the down conversion clock and the sampling clock of the RF block to the same frequency.

Step (d) according to the present invention includes the steps of calculating a pre-correlation value between the sample data of the guard interval and the sample data having the guard interval and the N-1 sample interval; Calculating a power of the pre-correlation value; Calculating a post correlation value between the sample data of the guard interval and the sample data having an N + 1 sample interval; Calculating the power of the post correlation value; Calculating an on correlation value between the sample data of the guard interval and the sample data having the N guard interval and the guard interval; Calculating a power of an on correlation value; And dividing a value obtained by subtracting the power of the post correlation value from the power of the pre-correlation value by the power of the on-correlation value to obtain a sample clock error estimate value.

Step (d) according to the present invention further comprises the step of accumulating the sample clock error estimate value and controlling the sampling rate of step (a) based on the accumulated value.

According to the present invention, the need for high autocorrelation of an OFDM symbol or a subcarrier for carrier frequency estimation is alleviated. In addition, an OFDM symbol or a subcarrier for carrier frequency estimation is not required.

In addition, according to the present invention, by calculating and estimating the error of the carrier frequency in the time axis, there is an effect of reducing the amount of computation required to calculate the correlation of the carrier frequency in the frequency axis.

1 is a block diagram showing the configuration of a baseband OFDM receiver according to the present invention;
FIG. 2 is an exemplary diagram for describing an operation of compensating for a frequency error of the frequency compensation filter illustrated in FIG. 1. FIG.
3 is a block diagram showing the detailed configuration of the cyclic estimator of FIG.
4 is an exemplary view showing a correlation window with an OFDM symbol for explaining the present invention;
5 is an operation flowchart of a baseband OFDM reception method according to the present invention.

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

1 is a block diagram showing the configuration of a baseband OFDM receiver according to the present invention.

The OFDM receiver calculates the amount of movement of the cyclic prefix correlation value on the time axis to remove the error of the carrier frequency. The clock receiver 100, the RF block 200, the analog / digital converter 300, and the frequency compensation filter 400 ), The cyclic estimator 500 and the frequency error estimator 600 will be described as follows.

The RF block 200 receives the clock from the clock generator 100 and mixes the clock with the received signal to down convert the frequency band of the received signal to the base band. The RF block 200 outputs the baseband received signal obtained through down-conversion of the received signal to the analog / digital converter 300.

The analog / digital converter 300 outputs the baseband sample data obtained by sampling the baseband received signal of the RF block 200 to the frequency compensation filter 400. Here, the down conversion clock of the RF block 200 and the sampling clock of the analog / digital converter 300 are configured to have the same frequency.

The frequency compensation filter 400 compensates the carrier frequency component with respect to the baseband sample data by referring to the carrier frequency error value input from the frequency error estimator 600, and filters the frequency band corresponding to the bandwidth of the received signal. Is output to the cyclic estimator 500.

2 is an exemplary diagram for describing an operation of compensating for a frequency error of the frequency compensation filter illustrated in FIG. 1.

2 (a) is an exemplary diagram illustrating a frequency domain signal of an FFT output in the case of a signal having no frequency error in an OFDM receiver. In contrast, FIG. 2B is an exemplary diagram showing a frequency domain signal when the frequency error is e when there is a frequency error. 2B illustrates an example in which all subcarriers are cyclically shifted by a frequency error in an OFDM received signal.

This frequency error appears in the form of cyclic movement in the frequency domain but in the form of phase rotation in the time domain.

A general OFDM received signal is represented by the following equation 1 by the formula of an inverse discrete Fourier transform.

If a frequency error exists in the OFDM received signal, it is represented by Equation 2 below.

For Equation 2, the phase rotation value in Equation 1

This is the multiplied form. Therefore, if the carrier frequency error value of the frequency error (e) is known, the frequency compensation filter 400 is

The carrier frequency component is compensated for by multiplying the value of with the baseband sample data.

The frequency compensation filter 400 outputs, to the cyclic estimator 500, sample data obtained by filtering a frequency band corresponding to the bandwidth of the received signal with respect to the baseband sample data whose carrier frequency components are compensated.

The cyclic estimator 500 calculates a correlation value for a section corresponding to the cyclic prefix from the sample data output from the frequency compensation filter 400 to obtain a sample clock error estimate.

FIG. 3 is a block diagram showing a detailed configuration of the cyclic estimator of FIG. 1, and FIG. 4 is an exemplary view showing an OFDM symbol and a correlation window for explaining the present invention.

The cyclic estimator 500 includes a pre-correlation value calculator 510, a pre-power calculator 520, a post-correlation value calculator 530, a post-power calculator 540, and an on-correlation value calculator 550. The on power calculator 560 includes a sample clock error calculator 570 and a loop filter 580. Each component constituting the cyclic estimator 500 will be described.

The pre-correlation value calculator 510 pre-correlates between the sample data of the guard interval (GI) 710 and the sample data of the guard interval 710 and the free window interval 730 having an N-1 sample interval. Calculate the value. The free power calculation unit 520 separates the pre-correlation value into a real part and an imaginary part, and adds squares to calculate the power of the pre-correlation value.

The post correlation value calculator 530 calculates a post correlation value between the sample data of the guard period 710 and the sample data of the guard window 710 and the post window period 720 having an N + 1 sample interval. The post power calculator 540 divides the post correlation value into a real part and an imaginary part, and adds squares to calculate the power of the post correlation value.

The on correlation value calculator 550 calculates an on correlation value between the sample data of the guard interval 710 and the sample data of the guard interval 710 and the on window interval 740 having an N sample interval. The on power calculator 560 calculates the power of the on correlation value by squaring the on correlation value.

The sample clock error calculator 570 obtains a sample clock error estimate by dividing the power of the pre-correlation value by subtracting the power of the post-correlation value by the power of the on-correlation value. The sample clock error calculator 570 outputs the obtained sample clock error estimate to the loop filter 580 and the frequency error estimator 600.

The loop filter 580 accumulates the sample clock error estimate and controls the sampling rate of the analog / digital converter 300 based on the accumulated value. The loop filter 580 increases the sampling rate of the analog / digital converter 300 when the accumulated value is a positive value, and decreases the sampling rate of the analog / digital converter 300 when the accumulated value is a positive value.

The frequency error estimator 600 provides the frequency compensation filter 400 with a carrier frequency error value generated by multiplying the sample clock error estimate value received from the sample clock error calculator 570 and the RF center carrier frequency. The frequency compensation filter 400 compensates the carrier frequency component with respect to the baseband sample data by referring to the carrier frequency error value input from the frequency error estimator 600.

5 is an operation flowchart of a baseband OFDM reception method according to the present invention.

The frequency difference between the frequency of the transmitted signal and the signal received by the receiver is caused by the clock used in the receiver. This clock error is represented by the carrier frequency error value of the received signal and the error value of the sampling clock frequency. If the down conversion clock of the RF block and the sampling clock of the analog / digital converter are used identically, the two error values have the same value.

The present invention calculates the correlation value for the interval corresponding to the cyclic prefix on the time axis to find the sample clock error estimate, and then converts the sample clock error estimate to the carrier frequency error value to convert the frequency of the baseband sample data. Eliminate the error. An operation flow for the baseband OFDM reception method will be described.

The RF block receives the clock from the clock generator, mixes the input clock and the received signal, and down-converts the frequency band of the received signal to the base band (S101). The RF block outputs the baseband received signal obtained through down-conversion of the received signal to the OFDM receiver.

The OFDM receiver obtains baseband sample data by sampling the baseband received signal of the RF block (S102). Here, the down conversion clock of the RF block and the sampling clock of the OFDM receiver are configured to have the same frequency.

The OFDM receiver compensates for the carrier frequency component with respect to the baseband sample data by referring to the carrier frequency error value calculated in the frequency error estimation step (S103). The OFDM receiver obtains sample data by filtering a frequency band corresponding to the bandwidth of the received signal with respect to the baseband sample data whose carrier frequency component is compensated.

The OFDM receiver calculates a correlation value for a section corresponding to the cyclic prefix from the obtained sample data to obtain a sample clock error estimate. An operation of obtaining a sample clock error estimate in an OFDM receiver is described as follows.

The OFDM receiver calculates a pre-correlation value between the sample data of the guard period and the sample data of the free window period having the guard period and the N-1 sample interval (S104). The OFDM receiver divides the pre-correlation value into a real part and an imaginary part, and adds squares to calculate a power of the pre-correlation value (S105).

The OFDM receiver calculates a post correlation value between the sample data of the guard interval and the sample data of the guard window and the post window interval having N + 1 sample intervals (S106). The OFDM receiver calculates the power of the post correlation value by dividing the post correlation value into a real part and an imaginary part, and adding the squares to each other (S107).

The OFDM receiver calculates an on correlation value between the sample data of the guard interval and the sample data of the on window interval having the guard interval and the N sample interval (S108). The OFDM receiver calculates the power of the on correlation value by squaring the on correlation value (S109).

The OFDM receiver obtains a sample clock error estimate by dividing the power obtained by subtracting the power of the post correlation value from the power of the precorrelation value by the power of the on correlation value (S110). Here, the sample clock error estimation value means an amount of change in the number of samples of the sample data.

The OFDM receiver accumulates the sample clock error estimate and controls the sampling rate for sampling the baseband received signal of the RF block based on the accumulated value. The OFDM receiver increases the sampling rate if the accumulated value is positive and decreases the sampling rate if the accumulated value is negative.

The OFDM receiver generates a carrier frequency error value by multiplying the sample clock error estimate by the RF center carrier frequency in the frequency error estimation step (S111). The OFDM receiver compensates for the carrier frequency component for the baseband sample data with reference to the carrier frequency error value.

Although the present invention has been described in more detail with reference to the examples, the present invention is not necessarily limited to these embodiments, and various modifications can be made without departing from the spirit of the present invention. Therefore, the embodiments disclosed in the present invention are not intended to limit the technical idea of the present invention but to describe the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The protection scope of the present invention should be interpreted by the following claims, and all technical ideas within the equivalent scope should be interpreted as being included in the scope of the present invention.

100: clock generator 200: RF block
300: analog / digital converter 400: frequency compensation filter
500: cyclic estimator 600: frequency error estimator

Claims

An analog / digital converter for sampling the baseband received signal of the RF block and outputting baseband sample data;
A frequency compensation filter for compensating a carrier frequency component with respect to the baseband sample data with reference to a carrier frequency error value input from a frequency error estimator, and filtering a frequency band corresponding to a bandwidth of a received signal to output sample data;
A cyclic estimator for obtaining a sample clock error estimate by calculating a correlation value of a section corresponding to a cyclic prefix in the sample data; And
A frequency error estimator for providing the frequency compensation filter with a carrier frequency error value generated by multiplying the sample clock error estimate by an RF center carrier frequency;
Baseband OFDM receiver configured to include.

The method according to claim 1,
And the down conversion clock of the RF block and the sampling clock of the analog / digital converter are configured to have the same frequency.

The method according to claim 2,
The cyclic estimator,
A pre-correlation value calculator for calculating a pre-correlation value between the sample data of the guard interval and the sample data having the N-1 sample interval, where 'N' represents the number of sample data;
A pre-power calculator for calculating the power of the pre-correlation value;
A post correlation value calculator configured to calculate a post correlation value between the sample data of the guard period and the sample data having the N + 1 sample interval;
A post power calculator configured to calculate power of the post correlation value;
An on correlation value calculator configured to calculate an on correlation value between the sample data of the guard interval and the sample data having the N interval and the guard interval;
An on power calculator for calculating power of the on correlation value; And
A sample clock error calculator configured to obtain a sample clock error estimate by dividing a value obtained by subtracting the power of the post correlation value from the power of the pre correlation value by the power of the on correlation value;
Baseband OFDM receiver, characterized in that configured to include.

The method according to claim 3,
The cyclic estimator,
A loop filter accumulating the sample clock error estimate and controlling a sampling rate of the analog / digital converter based on the accumulated value;
Baseband OFDM receiver, characterized in that further comprises.

(a) sampling the baseband received signal of the RF block to obtain baseband sample data;
(b) compensating a carrier frequency component for the baseband sample data with reference to a carrier frequency error value calculated in the frequency error estimating step;
(c) filtering the frequency band corresponding to the bandwidth of the received signal from the baseband sample data with the carrier frequency component compensated and outputting the sample data;
(d) obtaining a sample clock error estimate by calculating a correlation value for a section corresponding to a cyclic prefix in the sample data; And
(e) a frequency error estimation step of providing the carrier frequency error value generated by multiplying the sample clock error estimate value and the RF center carrier frequency to step (b);
Baseband OFDM reception method comprising a.

The method according to claim 5,
In step (a),
Setting a down conversion clock and a sampling clock of the RF block to the same frequency;
Baseband OFDM reception method, characterized in that configured to include.

The method of claim 6,
In step (d),
Calculating a pre-correlation value between the sample data of the guard interval and the sample data having the N-1 sample interval, where 'N' represents the number of sample data;
Calculating a power of the pre-correlation value;
Calculating a post correlation value between the sample data of the guard interval and the sample data having an N + 1 sample interval;
Calculating the power of the post correlation value;
Calculating an on correlation value between the sample data of the guard interval and the sample data having the N guard interval and the guard interval;
Calculating a power of the on correlation value; And
Obtaining a sample clock error estimate by dividing the power of the pre-correlation value by subtracting the power of the post correlation value by the power of the on correlation value;
Baseband OFDM reception method, characterized in that configured to include.

The method according to claim 7,
In step (d),
Accumulating the sample clock error estimate and controlling the sampling rate of step (a) based on the accumulated value;
The baseband OFDM reception method characterized in that it further comprises.