CN1722720A - Detect the equipment and the method for the time synchronized of frame and code element - Google Patents

Abstract

An apparatus and method for detecting time synchronization of frames and symbols is provided. The device comprises: a correlation filter for obtaining a correlation value between a local phase reference symbol in a predetermined time domain and a digital signal; a maximum value detector for detecting the position of the maximum value of the output of the correlation filter; from the position of the maximum value a frame synchronizer that searches for a start point of a frame; and a symbol timing synchronizer that synchronizes the symbol timing of the frame from the position of the maximum value.

Description

Device and method for detecting time synchronization of frames and symbols

This application claims the benefit of Korean Patent Application No. 2004-52650 filed with the Korean Intellectual Property Office on Jul. 7, 2004, which is hereby incorporated by reference.

Technical field

The present invention relates to a digital receiving system, and more particularly, the present invention relates to an apparatus and method for detecting synchronization of digital broadcast data frames and synchronization of OFDM symbols received according to an Orthogonal Frequency Division Multiplexing (OFDM) method .

Background technique

The terrestrial digital radio broadcasting systems currently in use are of the European, American and Japanese types, all of which adopt the OFDM method. European Digital Audio Broadcasting (DAB), namely EUREKA-147, is a digital modulation method using coded OFDM (COFDM) with strong resistance to ground multipath attenuation. Digital Multimedia Broadcasting (DMB) in Korea provides compact disc (CD)-level sound quality based on European DAB, various types of data services, and high-quality mobile reception.

FIG. 1 is a diagram showing the structure of a digital data frame using the COFDM method. Referring to Fig. 1, 76 OFDM symbols are located after the empty symbol a, the first OFDM symbol of these 76 OFDM symbols is a phase reference symbol (PRS) b, and the valid data symbol c is located after the PRS b . Null symbol a and PRS b form the synchronization channel of the digital data frame. Each of the above symbols includes a time-domain OFDM subcarrier signal e and a pilot interval (GI) d. Part of the time-domain OFDM subcarrier signal e is inserted into GI d to handle the interruption of ghosting that occurs in the synchronization channel.

PRS b is data known by the transmitter and receiver and provides a phase reference for the differential modulation of the next OFDM symbol. PRS b is also used to detect frame and symbol time synchronization.

A structure of a conventional algorithm used to detect synchronization of OFDM is classified into a structure using a correlation of GI d and a structure using a unit response of a channel.

The symbol time domain synchronization algorithm using GI d has a simple structure, but its stability varies depending on the channel characteristics. The symbol time-domain synchronization algorithm is quite stable on the Gaussian channel, but since the synchronization error occurs in one or more symbols, in channels with multi-path characteristics such as Reilay channel and Riacian channel, the symbol time-domain synchronization Algorithms are unstable.

The structure using the unit response of the channel is more stable than the structure using GI d, but consumes a lot of power. Therefore, the structure using the unit response of the channel is not suitable for developing synchronization detection algorithms that require low power consumption. This is because mobile DBA or DMB requires low power consumption.

Contents of invention

Therefore, the present general inventive concept is made to solve the above-mentioned and/or problems, and an aspect of the present general inventive concept is to provide a method for stably detecting frames and symbols using a PRS depending on low power and characteristics of a channel Devices and methods for time synchronization.

According to an aspect of the present invention, there is provided an apparatus for detecting time synchronization of frames and symbols of a digital signal having a frame structure comprising phase reference symbols and modulated using an OFDM method, which Including: a correlation filter, used to obtain the correlation value between the local phase reference symbol and the digital signal in the predetermined time domain; a maximum value detector, used to detect the position of the maximum value of the output of the correlation filter; a frame synchronizer , for searching the start point of the frame from the position of the maximum value; and a symbol timing synchronizer, for synchronizing the symbol timing of the frame from the position of the maximum value.

The device also includes a frequency error compensator for removing a time-varying frequency component from the digital signal to compensate for the frequency error and outputting the digital signal to the correlation filter.

The frequency error compensator may include: a delayer for delaying the digital signal by one sampling time; a conjugate complex unit for obtaining a conjugate complex number of the delayed digital signal; a first multiplier for combining the digital signal with the conjugate complex number Multiply and output the result of the multiplication.

The correlation filter may include: a local phase reference symbol unit, used to obtain the conjugate complex number of the local phase reference symbol; a second multiplier, used to combine the digital signal output from the frequency error compensator with the reference signal by the local phase symbol The conjugate complex numbers obtained by the unit are multiplied; and an integrator is used for accumulating and adding the multiplication results of the second multiplier within a predetermined period of time.

The local phase reference symbol unit can obtain conjugate complex numbers for half of the effective data of the local phase reference symbols, and the integrator can accumulate and add the multiplication results of the second multiplier for half of the effective data of the local phase reference symbols.

The correlation filter may further include: a first sign unit for obtaining a plus sign and a minus sign of the digital signal output from the frequency error compensator and outputting the plus sign and the minus sign to the second multiplier, and a second sign unit , for obtaining the plus and minus signs of the conjugate complex numbers output from the local phase reference symbol unit and outputting the plus and minus signs to the second multiplier.

The first and second sign units may output a positive sign as "1" and a negative sign as "0".

According to another aspect of the present invention, there is provided a method for detecting time synchronization of digital signal frames and symbols having a frame structure comprising phase reference symbols and modulated using an OFDM method, comprising: The correlation value between the local phase reference symbol and the digital signal in the predetermined time domain is obtained, the starting point of the frame is searched from the position of the maximum value, and the symbol timing of the frame is synchronized from the position of the maximum value.

The method may also include removing time-varying frequency components from the digital signal to compensate for frequency errors.

Compensating for the frequency error includes: delaying the digital signal by one sampling time; obtaining a conjugate complex number of the delayed digital signal; and multiplying the digital signal by the conjugate complex number and outputting the multiplied result.

The acquisition of the correlation value includes: obtaining the conjugate complex number of the local phase reference symbol; multiplying the output multiplication result by the conjugate complex number of the local phase reference symbol; and accumulating and adding the phase within a predetermined period of time Multiply the result.

For the effective data half of the local phase reference symbols, complex conjugate numbers are obtained.

The results of the multiplications may be accumulated and added for half of the active data of the local phase reference symbols.

The digital signal can be multiplied with the sign of the complex conjugate of the local phase reference symbol.

Description of drawings

The above-mentioned aspects and features of the present invention will become clearer through the following description of the embodiments in conjunction with the accompanying drawings, wherein:

FIG. 1 is a diagram representing the structure of a digital data frame using the COFDM method;

2 is a block diagram representing an apparatus for detecting time synchronization of frames and symbols according to an embodiment of the present invention;

Figure 3 is a graph representing the output of a correlation filter according to an embodiment of the present invention; and

FIG. 4 is a flowchart of a method for detecting time synchronization of frames and symbols according to an embodiment of the present invention.

Detailed ways

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

In the following description, the same symbols always denote the same components even in different drawings. Matters defined in the description such as detailed structures and components are provided only to help a comprehensive understanding of the present invention. Therefore, it is obvious that things that are not so defined by the present invention can also be implemented. Also, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail.

FIG. 2 is a block diagram of an apparatus for detecting time synchronization of frames and symbols according to an embodiment of the present invention.

The time synchronization detecting device 200 is installed inside a DAB/DMB (Digital Audio Broadcasting/Digital Multimedia Broadcasting) receiver, and receives digital broadcast data modulated according to the OFDM method to compensate for errors in frame synchronization and symbol timing recovery (STR). error.

Before Fast Fourier Transform (FFT), the time synchronization detection device 200 operates in the time domain, so that FFT at a later part of the detection device 200 can be performed based on precise frame synchronization and a precise starting point.

The signal input to the time synchronization detection device 200 has a frame structure with PRS b as shown in Figure 1, the frame structure is modulated according to the OFDM method, sampled at a predetermined time, and passed through the analog-to-digital converter ( ADC) (not shown) is converted into digital data. Digital data, which is a complex number, is decomposed into real numbers and imaginary numbers through an in-phase/quadrature shift (I/Q) unit (not shown), and then input into the time synchronization detection device 200 .

The received digital data frame may have a frame structure as shown in Figure 1, if the received digital data is in transmission mode 1 (Tx1) described in the exemplary embodiment below, then GI includes 504 samples, Effective data e includes 2048 samples.

Referring to FIG. 2 , the time synchronization detection apparatus 200 includes a frequency error compensator 210 , a correlation filter 230 , a maximum value detector 250 , a frame synchronizer 270 , and a symbol timing synchronizer 290 .

The frequency error compensator 210 compensates the carrier frequency error of the digital signal input to the correlation filter 230 . The carrier frequency error of the digital signal prevents the correlation filter 230 from calculating the correlation value.

The frequency error compensator 210 includes a delay 211 , a conjugate complex unit 213 and a first multiplier 215 .

The delayer 211 sequentially delays the OFDM modulated digital signal in units of samples. The delayed digital signal is sent to the complex conjugate unit 213 .

The conjugate complex number unit 213 calculates the conjugate complex number of the digital signal decomposed into real numbers and imaginary numbers.

The first multiplier 215 multiplies the delayed digital signal output from the conjugate complex unit 213 with the received non-delayed digital signal. The multiplied signal is input to the correlation filter 230 . The multiplied result by the first multiplier 215 helps to remove frequency components that change over time.

The correlation filter 230 includes a local PRS unit 233, a second multiplier 237, an integrator 239, a first symbol unit 231, and a second symbol unit 235, and calculates the PRS of the received digital signal frame with the correlation filter 230 known and store the correlation values between the local PRSs in this correlation filter.

The correlation filter 230 multiplies the PRS of the received digital signal frame by the conjugate complex number of the local PRS in the time domain, and accumulates the multiplication result for a predetermined period of time to obtain a correlation value.

The first sign unit 231 obtains the (positive or negative) sign of the sampling value of the frame data input to the correlation filter 230 and outputs the sign to the second multiplier 237 . As a result, only one bit, rather than multiple bits, can be used to use the value of the actual data to obtain the associated value.

The partial PRS unit 233 obtains the conjugate complex number of the partial PRS including real numbers and imaginary numbers in the time domain. In this way, the partial PRS unit 233 performs an inverse FFT (IFFT) on the partial PRS in the frequency domain to convert the PRS in the frequency domain into a PRS in the time domain, and then obtains a conjugate complex number of the partial PRS in the time domain. The local PRS unit 233 obtains the conjugate complex number of the sampling value of the valid data (n=2048) or half of the valid data (n=1024).

The second sign unit 235 obtains the (positive or negative) sign of the conjugate complex number output from the local PRS unit 233 and outputs the sign to the second multiplier 237 .

The first sign unit 231 and the second sign unit 235 may output the positive sign and the negative sign of each sample as '1' and '0', respectively.

The second multiplier 237 multiplies the value output from the first sign unit 231 by the value output from the second sign unit 235 and outputs the multiplied result to the integrator 239 . The second multiplier 237 sequentially multiplies valid data of the PRS or half of the valid data.

If the first and second sign units 231 and 235 output the plus sign and the minus sign as "1" and "0", respectively, the second multiplier 237 can multiply the plus sign "1" by the plus sign "1" to obtain To output the value "1", multiply the plus sign "1" by the minus sign "0" to output the value "0", and multiply the minus sign "0" and the minus sign "0" to output the value "1".

The integrator 239 sequentially adds the values output from the second multiplier 237 for a predetermined period of time to obtain a correlation value. In other words, the integrator 239 may accumulate and add the value output from the second multiplier 237 for one valid data interval (n=2048) or half (n=1024) of the valid data interval.

The correlation filter 230 can obtain the correlation value of each valid data interval (2048 samples) of the PRS. Alternatively, the correlation filter 230 can also obtain the correlation value of half (1024 samples) of the valid data interval. In either case, frame synchronization and symbol timing synchronization can be accurately obtained.

The correlation filter 230 can multiply the actual sampling values without the first symbol unit 231 and the second symbol unit 235 to obtain a correlation value. However, in this case, the sizes of the second multiplier 237 and the integrator 239 may be increased.

The correlation filter 230 may obtain a correlation value by only multiplying, accumulating, and adding the sign of the PRS and the sign of the partial PRS by the first sign unit 231 and the second sign unit 235 . In this way, the correlation filter 230 indicating 1024 or 2048 sample values of the PRS can be reduced to a size sufficient to indicate one symbol. As a result, the size of the second multiplier 237 can be reduced.

The maximum value detector 250 obtains the position of the maximum value of the correlation value output from the correlation filter 230 .

FIG. 3 is a graph showing the output of the correlation filter 230 of the embodiment of the present invention. Referring to FIG. 3, the maximum value f of the correlation value is displayed at the position of half of the effective data. Maximum value detector 250 outputs the position of maximum value f into frame synchronizer 270 and symbol timing synchronizer 290 .

Based on the position of the maximum value f of the correlation value detected by the maximum value detector 250, the frame synchronizer 270 searches for a start point of a frame. The frame synchronizer 270 transmits information on the start point of the frame to an FFT unit (not shown) located at the end of the time synchronization detection device 200 .

The symbol timing synchronizer 290 performs STR based on the position of the maximum value f of the correlation value detected by the maximum value detector 250 to obtain an accurate starting point of the FFT. The output of symbol timing synchronizer 290 is sent to an FFT unit (not shown).

FIG. 4 is a flowchart of a method for detecting frame and symbol time synchronization according to an embodiment of the present invention.

In operation S401, the time synchronization detection apparatus 200 receives an OFDM modulated digital signal. In operation S403, the time synchronization detection apparatus 200 compensates for a carrier frequency error that may occur in the OFDM modulated digital signal. For this purpose, the delayer 211 of the frequency error compensator 200 delays the OFDM modulated digital signal in units of samples, and the complex conjugate unit 213 obtains a complex conjugate of the delayed digital signal. In addition, the first multiplier 215 multiplies the delayed digital signal output by the complex conjugate unit 213 with the received OFDM modulated digital signal, and outputs the multiplied result to the correlation filter 230 .

The correlation filter 230 obtains a correlation value between the input signal and the local PRS. The first sign unit 231 detects the sign of each sample value of the input signal input to the correlation filter 230 . The partial PRS unit 233 obtains the conjugate complex number of half (n=1024) of the effective data of the partial PRS, and the second symbol unit 235 obtains and outputs only the 1024-sample symbols of the conjugate complex number. In operation S405, the second multiplier 237 multiplies the signals output from the first sign unit 231 and the second sign unit 235, and the integrator 239 accumulates half of the effective data (n=1024) and adds the multiplication result to Get the relevant value.

The maximum value detector 250 obtains the position of the maximum value of the correlation value obtained by the correlation filter 230 in operation S407. In operation S409, the frame synchronizer 270 searches for a start point of the frame based on the position of the maximum value, and the symbol timing synchronizer 290 searches for an accurate start point of the FFT based on the position of the maximum value.

The operation of the apparatus for detecting time synchronization of frames and symbols according to the present invention is carried out according to the procedure described above.

As described above, in the apparatus and method for detecting time synchronization of frames and symbols according to the present invention, FFT can be stably performed based on accurate frame synchronization and a starting point of FFT. For symbols using only half of the effective data or only half of the effective data, the correlation value between the digital signal and the local PRS can be obtained. In this way, the size of the device can be considerably reduced. As a result, such devices can be implemented at low power.

The foregoing embodiments and advantages are merely exemplary and are not to be construed as limiting the invention. The present teachings can be readily applied to other types of devices. In addition, the description of the embodiments of the present invention is intended to be illustrative rather than limiting the scope of the claims, and many alternatives, modifications and changes will be apparent to those skilled in the art.

Claims (14)

1. A device for detecting time synchronization of frames and symbols of a digital signal having a frame structure comprising phase reference symbols and modulated using an OFDM method, comprising: A correlation filter, used to obtain a correlation value between a local phase reference symbol in a predetermined time domain and a digital signal; a maximum value detector for detecting the position of the maximum value of the output of the correlation filter; a frame synchronizer for searching the start of a frame from the position of the maximum value; and The symbol timing synchronizer is used to synchronize the symbol timing of the frame from the position of the maximum value. 2. The device of claim 1, further comprising: A frequency error compensator for removing time-varying frequency components from the digital signal to compensate for frequency errors and outputting the digital signal to a correlation filter. 3. The apparatus of claim 2, wherein the frequency error compensator comprises: a delayer for delaying the digital signal by one sampling time; a complex conjugate unit for obtaining the complex conjugate of the delayed digital signal; and The first multiplier is used for multiplying the digital signal by the conjugate complex number and outputting the multiplication result. 4. The apparatus of claim 2, wherein the correlation filter comprises: A local phase reference symbol unit, used to obtain the complex conjugate of the local phase reference symbol; a second multiplier for multiplying the digital signal output from the frequency error compensator with the conjugate complex number obtained by the local phase symbol reference unit; and An integrator that accumulates and adds up the multiplication results of the second multiplier for a predetermined period of time. 5. The apparatus of claim 4, wherein: The local phase reference symbol unit obtains a conjugate complex number for half of the effective data of the local phase reference symbol; and The integrator accumulates and adds the multiplication result of the second multiplier to half of the effective data of the local phase reference symbol. 6. The apparatus of claim 4, wherein the correlation filter further comprises: The first sign unit is used to obtain the positive sign and the negative sign of the digital signal output from the frequency error compensator, and output the positive sign and the negative sign to the second multiplier; and The second sign unit is used to obtain the positive sign and negative sign of the conjugate complex number output from the local phase reference symbol unit and output the positive sign and negative sign to the second multiplier. 7. The apparatus of claim 6, wherein the first and second sign units output a positive sign as '1' and a negative sign as '0'. 8. A method for detecting time synchronization of frames and symbols of a digital signal having a frame structure comprising phase reference symbols and modulated using an Orthogonal Frequency Division Multiplexing method, comprising: obtaining a correlation value between a local phase reference symbol in a predetermined time domain and a digital signal; search for the start of the frame from the location of the maximum value; and The symbol timing of the frame is synchronized from the position of the maximum value. 9. The method of claim 8, further comprising: Removes time-varying frequency components from digital signals to compensate for frequency errors. 10. The method of claim 9, wherein the step of compensating for frequency error comprises: Delay the digital signal by one sampling time; obtaining the complex conjugate of the delayed digital signal; and Multiplies a digital signal by a complex conjugate number and outputs the result of the multiplication. 11. The method of claim 10, wherein the step of obtaining the correlation value comprises: obtaining the complex conjugate of the local phase reference symbol; multiplying the output multiplication result by the complex conjugate of the local phase reference symbol; and The results of multiplication are accumulated and added over a predetermined period of time. 12. The method of claim 11, wherein the conjugate complex number is obtained for half of the effective data of the local phase reference symbol. 13. The method of claim 12, wherein the multiplication result is accumulated and added for half of valid data of the local phase reference symbol. 14. The method of claim 11, wherein the digital signal is multiplied with the sign of the complex conjugate of the local phase reference symbol.

Images