KR100402798B1 - Equalizer of OFDM signal - Google Patents

Abstract

The OPDM signal equalizer is disclosed. The OPM signal equalizer is an equalizer of the ODM signal that compensates for errors on the transmission channel based on the pilot signal with respect to the OFM signal converted from the OFM receiver. Time interpolator for interpolating the symbols of the OFM signal divided into the imaginary part, the real part and the imaginary part based on the pilot signal, and the symbol for the OFM signal output from the time interpolator. An average value calculating unit that calculates an average value of an F, a frequency interpolator having an average value interpolating a symbol of the OMD signal with respect to the frequency axis, and a real part and an imaginary number of the OFM signal based on the symbol interpolated about the time axis A compensator for compensating for the wealth and a signal synthesizer for synthesizing the real part and the imaginary part of the OMD signal compensated by the compensator Have. By calculating the average value from the input signal and the input signal, the weight of the input signal is variably applied by comparing with the set value with respect to the calculated average value, thereby reducing noise existing in the entire frequency band according to the change of the transmission channel environment. Partial elimination allows accurate frequency interpolation.

Description

Equalizer of OFDM signal

The present invention relates to an equalizer of an Orthogonal Frequency Division Multiplexing (OFDM) receiver. More particularly, the present invention relates to an FM receiver in an OMD receiver for receiving an OMD signal transmitted after being modulated according to the OFM scheme. An equalizer of an OMD receiver which compensates for an error occurring on a transmission channel while a DM signal is transmitted.

In general, a broadcasting system of a high definition television (HDTV) can be roughly divided into an image encoder and a modulator. The video encoding unit compresses digital data of about 1 Gbps obtained from a high quality video source into data of 15 to 18 Mbps. The modulator transmits several tens of Mbps of digital data to the receiver through a limited band channel of 6 to 8 MHz.

In general, digital high-definition television broadcasting adopts a terrestrial simultaneous broadcasting method using a channel of VHF (Very High Frequency) / UHF (Ultra High Frequency) band allocated for conventional television broadcasting. Therefore, the modulation scheme used in the high definition television broadcasting system must satisfy the following conditions due to the environment of terrestrial simultaneous broadcasting.

First, the modulation method used in the high definition television broadcasting system requires high spectrum efficiency in order to transmit digital data of several tens of Mbps to a receiver through a limited band channel of 6 to 8 MHz. Second, the modulation scheme used in the high definition television broadcasting system has multipath fading due to the surrounding buildings or structures, and therefore has a strong characteristic for fading. Third, modulation schemes used in high-definition television broadcasting systems inevitably cause co-channel interference by existing analog television signals, and thus have a strong characteristic against co-channel interference. In addition, digitally modulated signals of high-definition television systems should be able to minimize interference with existing analog television receivers.

Modulation techniques that meet these conditions include quadrature amplitude modulation (QAM) and residual side band (VSB) modulation. In terrestrial broadcasting, the multiplication of QAM and VSB is already limited. have. Here, the transmission rate is determined, and even if the symbol transmission rate is increased in the same multiple dimensions, the transmission rate of the bandwidth is improved. However, when the symbol transmission speeds of 16- / 32-inch quadrature amplitude modulation and 4-valued residual sideband modulation are increased, the interference caused by the interference between the second image and the multipath is severely generated. This is especially true in urban areas where skyscrapers are struggling.

Therefore, in order to solve this problem, the Orthogonal Frequency Division Multiplexing (OFDM) method of digital modulation, which can achieve the double effect of improving the transmission speed per bandwidth and preventing interference, is adopted as the next generation high-definition television terrestrial broadcasting method. Doing.

The OMD method converts a symbol string input in a serial form into parallel data of a predetermined block unit, and then multiplexes the parallelized symbols with different subcarrier frequencies. The OMD system uses a multi-carrier, and has a considerable difference from the conventional single carrier. Multiple carriers have orthogonality with each other. Orthogonality means a property in which the product of two carriers becomes '0', which is a requirement for using multiple carriers. The implementation of the UFDM method is accomplished by the Fast Fourier Transform (FFT) and the Inverse Fast Fourier Transform (IFFT). .

On the other hand, the advantages of the OMD method is as follows. The television terrestrial transmission system has channel characteristics in which reflected waves, co-channel interference, and adjacent channel interference affect transmission quality due to signal transmission, and thus design conditions of the transmission system are very demanding. However, the OS has strong characteristics in the multipath. That is, since multiple carriers are used, symbol transmission time can be increased. This is relatively insensitive to the interference signal due to the multipath, so there is little deterioration in performance even for a long time echo signal. In addition, since the existing signal has a strong property, there is little influence on co-channel interference. Due to this characteristic, a single frequency network (SFN) can be constructed. Here, the single frequency network means that one broadcast broadcasts the whole country on one frequency. As a result, co-channel interference becomes very severe, and since the OMD system is strong in such an environment, it can be used. Thus, using a single frequency network can efficiently use a limited frequency resources.

On the other hand, the FM signal is composed of multiple carriers and each carrier has a very small band. Thus, the overall spectral shape is almost square, resulting in a relatively higher frequency efficiency than a single carrier. In addition, the advantage of the UFDM method is that the waveform of the UFDM signal is the same as White Gaussian Noise, so other broadcast services (PAL (Phase Alternation by Line) or SECAM (Sequential Couleur a) Memoire)) less interference than the method. Accordingly, in the OMD system, the modulation scheme may be different for each carrier, so that hierarchical transmission is possible.

Therefore, recently, in Europe, the digital modulation method of the FM system of such an advantage has been adopted for terrestrial broadcasting of high-definition television. It should be considered at this point that the signal is transmitted on the transmission channel according to the channel condition, and the multipath distortion among the distortions affects the signal and is particularly fatal for digital broadcasting. . Therefore, in order to compensate for this distortion, an equalizer is provided to compensate for errors on the transmission channel when the signal is restored on the receiving side. A conventional equalizer calculates an error on a transmission channel with a neighboring symbol of an OFM signal input by Fourier transform and compensates for an error on a transmission channel of the OFM signal. At this time, the equalizer compensates for the error through a pilot signal which is a synchronization value promised in the transmission and reception period.

However, the conventional equalizer calculates error values individually without considering change values between input symbols. Accordingly, there is a difficulty in calculating an error value of a signal generated by a dynamically changing transmission channel environment. This causes an error value in compensating for distortion occurring on the transmission channel, which in turn causes a deterioration in the performance of the equalizer.

SUMMARY OF THE INVENTION An object of the present invention for solving the above problems is to provide an equalizer of an OFM signal capable of adaptively equalizing a signal transmitted using a pilot signal at a receiving side according to a change of a transmission channel.

1 is a block diagram schematically showing a typical OPM receiver;

Figure 2 is a block diagram showing a preferred embodiment of the equalizer of the FM signal according to the present invention,

3 is a block diagram showing in detail the average value calculation unit of FIG.

FIG. 4 is a detailed block diagram illustrating the operation unit of FIG. 3.

Explanation of symbols on the main parts of the drawings

10: ADC 20: interpolator

30: FFT window adjustment unit 40: FFT unit

50: error detection unit 70: FEC

100: equalization unit 120: signal separation unit

140: time interpolator 160: average value calculation unit

162: delay unit 164: calculation unit

164a: Subtractor 164b: Multiplier

166: output value calculation unit 180: frequency interpolator

220: control unit 240: buffer unit

260: compensation unit 280: signal synthesis unit

According to the present invention, in the equalizer of the FM signal to compensate for the error on the transmission channel based on the pilot signal for the FM signal Fourier transformed by the FM receiver, Signal separation unit divided into real part and imaginary part, time interpolator which interpolates symbols of OSF signal divided into real part and imaginary part based on the time axis based on pilot signal, and OSF signal output from time interpolator An average value calculating unit that calculates an average value of a symbol for a frequency, a frequency interpolator that interpolates a symbol of an OFM signal with an average value, and a real time of the OFM signal based on an interpolated symbol about a time axis and a frequency axis Compensation unit for compensating the negative and imaginary parts, and a new synthesized real and imaginary part of the It is achieved by the equalizer of the OFDM signal including a composite.

Preferably, the equalizer further has a control unit for controlling the operating time of the time interpolator and the frequency interpolator. In addition, the equalizer further includes a buffer unit for storing the OMD signal output from the time interpolator for a predetermined time and outputting the ODM signal according to the control signal. Accordingly, when the interpolated symbol is output from the frequency interpolator, the controller outputs the ODP DM signal stored in the buffer unit to the compensation unit to compensate the real part and the imaginary part of the OMD signal based on the symbol. To control.

Preferably, the average value calculation unit has a delay unit, a calculation unit, and an output value calculation unit. At this time, the delay unit delays a symbol of the OMD signal for a predetermined time and outputs it. The calculating unit calculates an average value of the symbols of the OMD signals output by the predetermined time delay and the ODM signals output by the time interpolator. The output value calculating unit outputs to the frequency interpolator for adjusting the symbol value of the OMD signal output from the time interpolator based on the average value calculated by the calculating unit.

Preferably, the computing portion has a subtractor and a multiplier. The subtractor calculates a difference between two symbols by subtracting a symbol of the OMD signal output from the time interpolator and a symbol of the OMD signal output with a predetermined time delay. The multiplier calculates the absolute value of the difference value calculated by the subtractor and calculates the square value of the calculated absolute value.

According to the present invention, the average value of the symbols for the OMD signal is calculated, and the weight is set differently for the OMD signal to be output accordingly to compensate for the distortion, thereby adapting the distortion of the OMD signal as the transmission channel changes. Can be equalized.

Hereinafter, the present invention will be described in detail with reference to the drawings. Prior to the description of the present invention, an OPM receiver for receiving an OMD signal to which the present invention is applied will be described.

1 is a block diagram schematically showing an ordinary FM receiver. The OMD receiver is an analog to digital converter (ADC) 10, an interpolator 20, a fast fourier transform (FFT) window adjusting unit 30, an FFT unit 40, an error detector 50, and an equalizer 100. ), And forward error corrector (FEC) 70.

The analog-to-digital converter (ADC) 10 converts the received OMD signal into a digital signal. The interpolator 20 corrects the doubling symbol timing offset of the OMD signal. The FFT window adjustment unit 30 corrects an integer multiple symbol timing offset of the OMD signal. The FFT unit 40 performs Fast Fourier Transform (FFT) on the OMD signal in which the integer multiples and decimal multiple timing offsets are corrected. The error detector 50 detects the symbol timing offset of the OMD signal generated during sampling in order to convert the OMD signal to the digital signal in the ADC 10. In this case, the error detector 50 provides the detected symbol timing offset value to the interpolator 20 and the FFT window adjusting unit 30.

The equalizer 100 compensates for the distortion generated on the transmission channel with respect to the fast Fourier transformed OMD signal output from the FFT unit 40. At this time, the equalizer 100 compensates for the distortion on the transmission channel of the OMD signal by calculating the timing and frequency error values for the symbols of the OMD signal through the pilot signal. The FEC 70 detects an error by the error detection method set for the data of the OMD signal, and corrects the detected error.

Figure 2 is a block diagram showing a preferred embodiment of the equalizer of the FM signal according to the present invention. The equalizer includes a signal separator 120, a time interpolator 140, an average value calculator 160, a frequency interpolator 180, a buffer unit 240, a controller 220, a compensator 260, and a signal. The synthesizer 280 is provided.

The signal separator 120 separates the OMD signal output from the FFT unit 40 into a real part and an imaginary part. Here, the real part shows the magnitude of the OFM signal, and the imaginary part shows the phase of the OFM signal. The time interpolator 140 interpolates the symbols of the OMD signals divided into the real part and the imaginary part with respect to the time axis based on the pilot signal.

The average value calculator 160 calculates an average value of symbols for the OMD signal output from the time interpolator 140. In addition, the average value calculator 160 adjusts a symbol for the OMD signal output from the time interpolator 140 according to the calculated average value and provides it to the frequency interpolator 180. The frequency interpolator 180 interpolates the symbols of the OMD signals provided by the average value calculator 160 based on the frequency axis based on the pilot signals.

The buffer unit 240 stores the OFM signal output from the time interpolator 140 for a predetermined time and outputs the control signal according to the control signal. Preferably, the buffer unit 240 stores data of the OMD signal. The controller 220 controls the operating time of the time interpolator 140 and the frequency interpolator 180. In addition, when the interpolated symbol is output from the frequency interpolator 180 to the compensator 260, the controller 220 outputs the buffer FM 240 to the compensator 260 for a predetermined time. To control.

The compensator 260 outputs the OFF output from the buffer unit 240 based on the symbol of the OMD signal output from the frequency interpolator 180, that is, the OMD signal interpolated with respect to the time axis and the frequency axis. The real part and the imaginary part of the DM signal are compensated for. The signal synthesizer 280 synthesizes the real part and the imaginary part of the OMD signal compensated by the compensator 260 to form a form before the ODM signal is separated from the signal separator 120.

Therefore, the average value calculation unit 160 calculates an average value of symbols for the OMD signal and adjusts the symbol of the OMD signal accordingly, thereby dynamically varying the distortion of the OMD signal as the transmission channel changes. Can be calculated. Accordingly, the equalizer can adaptively equalize the OMD signal with respect to the change of the transmission channel.

3 is a detailed block diagram illustrating the average value calculator 160 of FIG. 2. The average value calculator 160 includes a delay unit 162, a calculator 164, and an output value calculator 166.

The delay unit 162 delays a predetermined time without outputting the symbols of the OMD signals output from the time interpolator 140 to the frequency interpolator 180. The calculator 164 calculates an average value of the symbols of the OMD signals delayed by the delay unit 162 and the symbols of the OFM signals output and input from the time interpolator 140. The output value calculator 166 adjusts the value of the symbol of the OMD signal output from the time interpolator 140 based on the average value calculated by the calculator 164 and outputs it to the frequency interpolator 180.

As shown, if the signal input to the average value calculation unit 160 is X (n) and the signal to be output from the output value calculation unit 166 is Y (n), the delay unit 162 is an output value calculation unit ( The output is delayed by 'N' with respect to the signal Y (n) output from 166, and the signal Y (nN) whose output is delayed by 'N' is output to the operation unit 164.

4 is a block diagram illustrating in detail the calculator 164 of FIG. 3. The calculating unit 164 has a subtractor 164a and a multiplier 164b. The subtractor 164a subtracts the signal X (n) input from the time interpolator 140 and the signal Y (nN) output from the delay unit 162 as shown in Equation 1 below. .

The multiplier 164b calculates the absolute value of the value d (n) calculated in Equation 1 above as shown in Equation 2 below, and calculates the square value of the calculated absolute value. At this time, the multiplier 164b provides the calculated square value D (n) to the output value calculator 166.

Accordingly, when the output value calculator 166 receives the square value D (n) output from the multiplier 164b, the output value calculator 166 receives the square value D (n) and the set coefficient 'A as shown in Equation 3 below. Compare 'and set the value to output.

(When D (n)> A) ··········

(When D (n) ≤ A)

The output value calculator 166 sets the weight Γ (n) to '1' when the square value D (n) is greater than the coefficient 'A'. Accordingly, the output value calculator 166 outputs the signal X (n) input from the time interpolator 140 to the frequency interpolator 180 without conversion.

On the other hand, if the square value D (n) is equal to or less than the coefficient 'A', the output value calculator 166 sets the weight Γ (n) to 'C × D (n)'. In this case, the coefficient 'A' is a constant and serves as an amplitude limiter. Accordingly, the output value calculation unit 166 converts the signal X (n) input from the time interpolator 140 and outputs the frequency interpolator 180 as shown in Equation 4 below.

Where Γ (n) is 'C x D (n)'.

That is, the output value calculator 166 gives a weight of 'Γ (n)' to the signal X (n) currently input and '1' to the delayed signal Y (nN) output from the delay unit 162. A different output value is calculated for each symbol by giving a weight of -Γ (n) '. As a result, the output value calculator 166 multiplies 'X (n)' by 'Γ (n)' (Γ (n) X (n)) to 'Y (nN)' by '1-Γ (n)'. The frequency interpolator 180 provides the value Yn obtained by the addition operation of the value multiplied by ((1-Γ (n)) Y (nN)).

Therefore, by calculating the average value from the input signal and the input signal and variably applying the weight of the input signal through comparison with the set value for the calculated average value, which is present in the entire frequency band according to the change of the transmission channel environment. Partial rejection of noise allows accurate frequency interpolation and further accurate channel estimation.

According to the present invention, by applying the weight of the input signal variably by comparing the set value with respect to the average value calculated by calculating the average value from the input signal and the input signal, the entire frequency band according to the change of the transmission channel environment Partially removes noise present in the circuit allows accurate frequency interpolation. In addition, channel estimation can be made more accurate according to such accurate frequency interpolation.

In the above described and illustrated with respect to the preferred embodiment of the present invention, the present invention is not limited to the specific preferred embodiment described above, without departing from the gist of the invention claimed in the claims in the art Various modifications can be made by those skilled in the art, and such changes are within the scope of the claims.

Claims (5)

In the equalizer of the OMD signal for compensating for errors on the transmission channel based on the pilot signal for the OFM signal converted from the OFM receiver, A signal separator for separating the OFM signal into a real part and an imaginary part; A time interpolator for interpolating symbols of the OMD signal separated by the real part and the imaginary part based on the time axis based on the pilot signal; An average value calculation unit for calculating an average value of the symbols with respect to the OPM signal output from the time interpolator; A frequency interpolator having said average value and interpolating said symbol of said OPM signal based on a frequency axis; A compensator for compensating the real part and the imaginary part of the OFM signal based on the symbols interpolated with respect to the time axis and the frequency axis; And And a signal synthesizer for synthesizing the real part and the imaginary part of the OMD signal compensated by the compensation unit. The method of claim 1, And a controller for controlling an operation time of the time interpolator and the frequency interpolator. The method of claim 2, And a buffer unit configured to store the OSDM signal output from the time interpolator for a predetermined time and output the control signal according to a control signal. The control unit outputs the OMD signal stored in the buffer unit to compensate for the real part and the imaginary part of the OFM signal in the compensation unit based on the symbol when the interpolated symbol is output from the frequency interpolator. And controlling the buffer unit to output a signal to the compensator. The method of claim 3, The average value calculation unit, A delay unit for delaying the symbol of the OFM signal by a predetermined time; An arithmetic unit for calculating an average value of the symbols of the OMD signal and the ODM signal output by the time interpolator; And And an output value calculator for outputting to the frequency interpolator for adjusting a value of the symbol of the OFM signal output from the time interpolator based on the average value calculated by the calculator. Equalizer of DM signal. The method of claim 4, wherein The calculation unit, A subtractor for calculating a difference value between the symbol of the OPM signal output from the time interpolator and the symbol of the OPM signal delayed by a predetermined time; And And a multiplier that calculates an absolute value of the difference value calculated by the subtractor and calculates a square value of the absolute value.