KR20050000262A - TDS-OFDM receiver for using scattered pilots for equalizing and method for equalizing of TDS-OFDM receiver - Google Patents

Abstract

PURPOSE: A TDS-OFDM(Time Domain Synchronous Orthogonal Frequency Division Multiplexing) receiver and a channel equalization method are provided to achieve improved receiving performance by performing a channel equalization on the basis of the channel status estimated by using scattered pilots. CONSTITUTION: A TDS-OFDM receiver comprises a synchronization unit(140) for performing a synchronization on an OFDM broadcast signal which is received through an antenna, down converted to a baseband, and analog-digital converted; a demultiplexer(160) for dividing the signal received from the synchronization unit into a plurality of signals including an OFDM symbol; an FFT(Fast Fourier Transform) unit(300) for performing FFT on the OFDM symbol; a frequency domain equalization unit(500) for performing a channel equalization in a frequency domain, on the basis of the channel status estimated by using the scattered pilots in the OFDM symbol; and a forward error correction unit(600) for detecting and correcting error of the signal received from the frequency domain equalization unit.

Description

TDS-OFDM receiver for performing channel equalization using distributed pilot, and a channel equalization method using the same {TDSS-OFDM receiver for using scattered pilots for equalizing and method for equalizing of TDS-OFDM receiver}

The present invention relates to a TDS-OFDM receiver for performing channel equalization using a distributed pilot and a channel equalization method using the same. More particularly, the channel state estimated by using a distributed pilot in a TDS-OFDM system in which a distributed pilot is inserted The present invention relates to a TDS-OFDM receiver for performing channel equalization based on the same, and a channel equalization method using the same.

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 performed by the Fast Fourier Transform (FFT) and the Inverse Fast Fourier Transform (IFFT), which are simply obtained by the definition of orthogonality and fast Fourier transform between carriers. .

The OMD 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 advantages of the UF DM method is that since the waveform of the UF DM signal is the same as White Gaussian Noise, the PAL (Phase Alternation by Line) and the SECAM (Sequential Couleur a Memoire) methods are used. Has less interference than other broadcasting services. Accordingly, in the OMD system, the modulation scheme may be different for each carrier, so that hierarchical transmission is possible.

Recently, a new terrestrial digital TV transmission standard, DMB-T, has been proposed to improve the speed with respect to the specifications of the terrestrial digital TV transmission system. The transmission system using the DMB-T scheme employs a TDS-OFDM (Time Domain Syncronous Orthogonal Frequency Division Multiplexing) scheme, and an OFDM modulator uses a 3780-point IDFT / DFT processor.

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.

1 is a block diagram of a conventional TDS-OFDM receiver. The TDS-OFDM receiver includes RF RX 10, ADC 12, synchronizer 14, demultiplexer 16, PN correlator 20, first FFT unit 30, second FFT unit 40, frequency It consists of the area equalizing part 50 and the FEC part 60.

The RF RX 10 down-converts the OFDM broadcast signal received through the antenna to baseband, and the analog-to-digital converter (ADC) 12 receives the RF RX ( 10) Convert the analog signal received from the digital signal.

The synchronizer 14 performs symbol timing and frequency synchronization using PN sequence (pseudo noise sequence) information which is transmitted synchronization information. The PN sequence information is synchronization information for predicting synchronization and channel of the OFDM broadcast signal received by the TDS-OFDM receiver receiving the transmitted OFDM broadcast signal, and is inserted in front of a guard interval (GI) to be described later.

The demultiplexer 16 divides the OFDM broadcast signal received from the synchronizer 14 into a PN sequence, a guard interval (GI), and an OFDM symbol (OFDM symbol). A guard interval (GI) is a section inserted between a PN sequence and an OFDM symbol in order to suppress inter symbol interference (ISI) in a multipath environment.

The PN correlator 20 outputs a correlation (PN correlation) between the reference signal sequence and the PN sequence to the first FFT unit 30 to provide information about the channel state, and the first FFT unit 30 provides a correlation. FFT (Fast Fourier Transform) is output to the frequency domain equalizer 50.

The OFDM symbol output from the demultiplexer 16 is output to the second FFT unit 40, and the second FFT unit 40 FFTs the OFDM symbol to output to the frequency domain equalizer 50.

The frequency domain equalizer 50 performs a channel on the FFT OFDM symbol received from the second FFT unit 40 based on the PN correlation of the FFT frequency domain received from the first FFT unit 30. Perform equalization.

The forward error corrector (FEC) 60 detects an error by the error detection method set for the equalized OFDM symbol and corrects the detected error. The FEC unit 60 includes an inner deinterleaver 61, an inner decoder 62, an outer deinterleaver 63, an outer decoder 64, and a decoder. It consists of a scrrambler 65.

The inner interleaver on the sender shuffles the coded data to distribute possible concatenation errors. The inner deinterleaver 61 on the receiving side scrambles the data as opposed to the internal interleaver on the transmitting side, and restores the data string of the state before being input to the internal interleaver on the transmitting side. Therefore, it serves to disperse the concatenation error of the received signal. As the internal deinterleaver 61, a bit deinterleaver and a symbol deinterleaver are generally used.

The internal decoder 62 performs decoding for error correction on the data rearranged by the internal deinterleaver 61. As the internal decoder 62, a convolutional decoder and a turbo decoder are generally used.

The outer interleaver on the transmitting side arranges the encoded data in order according to a predetermined rule. The external deinterleaver 63 on the receiving side transmits the data decoded by the internal decoder 62 to the external interleaver on the transmitting side. Arrange the opposite. Therefore, this process distributes the uncorrected errors in the internal decoder 62, and consequently recovers the signal sequence before input to the external interleaver on the transmitting side. As the external deinterleaver 63, a convolutional deinterleaver is generally used.

The external decoder 64 performs decoding for error correction on the data rearranged by the external deinterleaver 63. As the external decoder 64, an RS decoder (Reed-Solomon decoder) is generally used.

The scrambler on the transmitting side removes the correlation of the input signal by mixing a pseudo random binary sequence with a TS stream of the input MPEG format. On the contrary, the descrambler 65 on the receiving side restores the TS stream of the original MPEG format by removing the pseudo-random binary signal string mixed with the TS stream performed by the scrambler on the transmitting side.

As described above, the conventional TDS-OFDM receiver estimates the state of the channel using the correlation between the reference signal sequence and the PN sequence, and performs equalization of the frequency domain using the estimated channel state. However, when the equalization is performed in the above-described manner, if the information on the channel state estimated using the correlation is not accurate due to the distortion and noise component of the channel, the equalization performance may be degraded.

On the other hand, the present applicant filed on June 20, 2002 for a digital broadcast transmitter inserting a different number of pilot tones according to the reception priority of each region of the data (application number: P2002-0034684).

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to perform a channel equalization based on an estimated channel state using a distributed pilot in a TDS-OFDM system in which a distributed pilot is inserted. An OFDM receiver and a channel equalization method using the same are provided.

1 is a block diagram of a conventional TDS-OFDM receiver;

2 is a block diagram of a TDS-OFDM receiver according to the present invention;

3 is a diagram illustrating the arrangement of distributed pilots for OFDM symbols;

4 is a diagram illustrating an example of interpolation using a distributed pilot for an OFDM symbol;

5A-5C are provided for illustration of a method of compensating for channel distortion, and

6 is a flowchart provided to explain a channel equalization method using a distributed pilot according to the present invention.

Explanation of symbols on the main parts of the drawings

100: RX RF 120: ADC

140: synchronizer 160: demultiplexer

300: FFT unit 500: frequency domain equalizer

600: FEC part

A TDS-OFDM receiver according to the present invention for achieving the above object is a synchronization unit for receiving an antenna, down-converted to baseband and then performing synchronization of an analog-to-digital converted OFDM broadcast signal, received from the synchronization unit A demultiplexer for separating a signal into a plurality of signals including an OFDM symbol, an FFT unit for fast Fourier transform (FFT), and a channel pilot estimated by using a distributed pilot inserted into the OFDM symbol. And a frequency domain equalizer for performing channel equalization in the frequency domain, and a forward error corrector (FEC) for detecting and correcting an error with respect to a signal received from the frequency domain equalizer.

The plurality of signals may be a guard interval and an OFDM symbol, and the synchronization unit may perform synchronization using the distributed pilot. The plurality of signals may be synchronization information, a guard interval, and an OFDM symbol, and the synchronization unit may perform synchronization using the synchronization information. The synchronization information is preferably a PN sequence (pseudo noise sequence).

The distributed pilot may be inserted in a first subcarrier period with respect to the frequency axis of the OFDM symbol and in a second subcarrier period with respect to the time axis of the OFDM symbol. The first subcarrier period may be 12 subcarriers, and the second subcarrier period may be 4 subcarriers.

The frequency domain equalizer performs channel equalization based on a channel state estimated through interpolation of the scattering pilot with respect to an axis having a small period among the time axis and the frequency axis, and then distributes the distribution with respect to an axis having a large period. The channel equalization is preferably performed based on the channel state estimated through pilot interpolation. In addition, the interpolation may be any one of linear interpolation, zero-order interpolation, zero-order interpolation after linear interpolation, and interpolation using a fractional delay filter.

On the other hand, the channel equalization method of the TDS-OFDM receiver according to the present invention, (a) performing the synchronization of the analog-to-digital OFDM broadcast signal received through the antenna, down-converted to the baseband, (b) Separating the synchronized OFDM broadcast signal into a plurality of signals including an OFDM symbol, (c) fast Fourier transform (FFT) of the OFDM symbol, and (d) a variance inserted into the OFDM symbol Performing channel equalization in the frequency domain based on the channel state estimated using the pilot, and (e) detecting and correcting an error with respect to the equalized signal.

The plurality of signals are a guard interval and an OFDM symbol, and in the step (a), it is preferable to perform synchronization using the distributed pilot. The plurality of signals may be synchronization information, a guard interval, and an OFDM symbol. In step (a), synchronization may be performed using the synchronization information. The synchronization information is preferably a PN sequence (pseudo noise sequence).

The distributed pilot may be inserted in a first subcarrier period with respect to the frequency axis of the OFDM symbol and in a second subcarrier period with respect to the time axis of the OFDM symbol. The first subcarrier period may be 12 subcarriers, and the second subcarrier period may be 4 subcarriers.

In the step (d), the channel equalization is performed based on the channel state estimated through the interpolation of the distributed pilot with respect to the axis having a small period among the time axis and the frequency axis, and then The channel equalization is preferably performed based on the channel state estimated through the interpolation of the distributed pilot. In addition, the interpolation may be any one of linear interpolation, zero-order interpolation, zero-order interpolation after linear interpolation, and interpolation using a fractional delay filter.

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

2 is a block diagram of a TDS-OFDM receiver according to the present invention. Referring to FIG. 2, the TDS-OFDM receiver includes an RF RX 100, an ADC 120, a synchronizer 140, a demultiplexer 160, an FFT unit 300, a frequency domain equalizer 500, and an FEC unit ( 600).

The RF RX 100 down-converts the OFDM broadcast signal received through the antenna to baseband, and the ADC (Analog-to-Digital Converter) 120 converts the RF RX ( Convert the analog signal received from 100) into a digital signal.

The synchronizer 140 performs synchronization of an OFDM broadcast signal, using a distributed pilot inserted into an OFDM symbol. On the other hand, if the PN sequence is inserted into the OFDM broadcast signal, the synchronization unit 140 may perform symbol timing and frequency synchronization using the transmitted PN sequence information.

The demultiplexer 160 divides the OFDM broadcast signal received from the synchronization unit 140 into a guard interval (GI) and an OFDM symbol, and outputs the divided PN sequence separately when the PN sequence is inserted into the OFDM broadcast signal. Separate.

The FFT unit 300 FFTs the OFDM symbols received from the demultiplexer 160 and outputs them to the frequency domain equalizer 500.

The frequency domain equalizer 500 performs channel equalization using a scattered pilot inserted into the FFT OFDM symbol received from the FFT unit 300.

3 is a diagram illustrating the arrangement of distributed pilots for OFDM symbols. As shown, the scatter pilot is represented by a black dot. In Fig. 3, the horizontal axis is the frequency axis f, in which one distributed pilot is inserted for every 12 subcarriers. The vertical axis is the time axis t, and the positions of the distributed pilots are inserted by moving three subcarriers between symbols. The TDS-OFDM receiver receiving the OFDM pilot signal in which the distributed pilot is inserted performs interpolation using the distributed pilot inserted in the OFDM broadcast signal to perform channel estimation on the entire data subcarriers.

4 illustrates an example of interpolation using a distributed pilot for OFDM symbols. As shown, ① denotes interpolation of the time axis t, and ② denotes interpolation of the frequency axis f. The TDS-OFDM receiver can obtain one channel estimation value for every three subcarriers on the frequency axis f by performing interpolation on the time axis t.

5A to 5C are diagrams for explaining a method of compensating for channel distortion based on an estimated channel state by performing interpolation of a time axis. FIG. 5A is a diagram illustrating the magnitude (M) of the OFDM symbol transmitted from the transmitter based on the time axis. In FIG. 5A, the hatched portion means the size of the distributed pilot, and the hatched portion means the size of the data subcarrier. The distributed pilot has a fixed size, which is also known to the receiving end.

Referring to FIG. 5B, the frequency domain equalizer 500 that receives the OFDM symbol measures the size of the distributed pilot inserted on the same time axis with respect to the received OFDM symbol, and performs interpolation based on the size of the channel. Estimate the state. The channel state estimated in FIG. 5B may be represented by a curve (a). Accordingly, the frequency domain equalizer 500 compensates for the channel distortion by multiplying the received OFDM symbol by the curve b, as shown in FIG. 5C.

Referring to FIG. 4, when the interpolation on the time axis t is completed, the TDS-OFDM receiver performs interpolation on the frequency axis f from the estimated pilot obtained every three subcarriers on the frequency axis f. The channel distortion is compensated based on the channel state estimated by the interpolation. The method of interpolation and the channel distortion compensation method are the same as those performed on the time axis t.

Accordingly, the TDS-OFDM receiver can obtain channel estimation values for the entire subcarrier region and perform channel equalization by compensating data values from the channel estimates for the entire subcarrier region.

On the other hand, in the above embodiment, 12 pilots are inserted in cycles on the frequency axis and 4 cycles in the time axis. However, in the present TDS-OFDM system, each cycle can be arbitrarily changed. Channel estimation through interpolation is preferably performed on an axis with a short pilot period.

In addition, the interpolation used herein may be performed by various methods such as linear interpolation, zero-order interpolation, or zero-order interpolation after linear interpolation, or interpolation using a fractional delay filter. have.

Referring to FIG. 2, the FEC unit 600 detects an error by using an error detection method set for an OFDM symbol received from the frequency domain equalizer 500, and corrects the detected error.

6 is a flowchart provided to explain a channel equalization method using a distributed pilot according to the present invention. Referring to FIG. 6, first, an OFDM broadcast signal received through an antenna is down-converted to baseband by the RF RX 100, converted into a digital signal by the ADC 120, and then synchronized by the synchronizer 140 ( S810).

The demultiplexer 160 separates the OFDM broadcast signal received from the synchronization unit 140 into a guard interval (GI) and an OFDM symbol, and outputs the OFDM symbol to the FFT unit 300 (S820), and the FFT unit 300 The OFDM symbol received from the demultiplexer 160 is FFTed and output to the frequency domain equalizer 500 (S830).

The frequency domain equalizer 500 performs channel equalization using a distributed pilot inserted into an OFDM symbol received from the FFT unit 300 (S840 to S870). In detail, first, the frequency domain equalizer 500 receiving the OFDM symbol measures the size of the distributed pilot inserted in the same time axis with respect to the received OFDM symbol, and performs interpolation based on the size of the channel. The state is estimated (S840) and the channel distortion is compensated based on the estimated channel state (S850). After the interpolation of the time axis t is completed, the frequency domain equalizer 500 performs interpolation on the frequency axis f from the estimated pilot obtained for every three subcarriers on the frequency axis f to determine the state of the channel. In operation S860, the channel distortion is compensated based on the estimated channel state in operation S870.

Finally, the FEC unit 600 detects an error by using an error detection method set for the OFDM symbol received from the frequency domain equalizer 500, and corrects the detected error (S880).

As described above, according to the present invention, in the TDS-OFDM system in which the distributed pilot is inserted, channel equalization can be performed based on the estimated channel state using the distributed pilot, and the reference signal is determined by the distortion and noise component of the channel. By using the correlation between the column and the PN sequence, it is possible to improve the reception performance by preventing the equalization performance from deteriorating when the estimated channel state is not accurate.

In addition, although the preferred embodiment of the present invention has been shown and described above, the present invention is not limited to the specific embodiments described above, but the technical field to which the invention belongs without departing from the spirit of the invention claimed in the claims. Of course, various modifications can be made by those skilled in the art, and these modifications should not be individually understood from the technical spirit or the prospect of the present invention.

Claims (16)

A synchronization unit configured to perform synchronization of an OFDM broadcast signal received through an antenna, downconverted to baseband, and then analog-digital converted; A demultiplexer for separating the signal received from the synchronizer into a plurality of signals including OFDM symbols; An FFT unit for performing fast Fourier transform (FFT) on the OFDM symbol; A frequency domain equalizer for performing channel equalization in the frequency domain based on a channel state estimated by using a distributed pilot inserted into the OFDM symbol; And And a forward error corrector (FEC) unit for detecting and correcting an error with respect to the signal received from the frequency domain equalizer. The method of claim 1, The plurality of signals are guard intervals and OFDM symbols, The synchronization unit, TDS-OFDM receiver, characterized in that for performing synchronization using the distributed pilot. The method of claim 1, The plurality of signals are synchronization information, a guard interval, and an OFDM symbol. And the synchronization unit performs synchronization using the synchronization information. The method of claim 3, wherein And the synchronization information is a PN sequence (pseudo noise sequence). The method of claim 1, The distributed pilot is inserted into a first subcarrier period with respect to the frequency axis of the OFDM symbol, and a TDS-OFDM receiver with a second subcarrier period inserted into the time axis of the OFDM symbol. The method of claim 5, The first subcarrier period is 12 subcarriers, And the second subcarrier period is 4 subcarriers. The method of claim 5, The frequency domain equalizer performs channel equalization based on a channel state estimated through interpolation of the distributed pilot with respect to an axis having a small period among the time axis and a frequency axis, and then performs a distribution of the distributed pilot with respect to an axis having a large period. And performing channel equalization based on the channel state estimated through interpolation. The method of claim 7, wherein The interpolation is any one of linear interpolation, zero-order interpolation, zero-order interpolation after linear interpolation, and interpolation using a fractional delay filter. (a) performing synchronization of an OFDM broadcast signal received through an antenna, downconverted to baseband, and then analog-digital converted; (b) dividing the synchronized OFDM broadcast signal into a plurality of signals including an OFDM symbol; (c) fast Fourier transform (FFT) of the OFDM symbol; (d) performing channel equalization in the frequency domain based on a channel state estimated by using a distributed pilot inserted in the OFDM symbol; And (e) detecting and correcting an error with respect to the equalized signal; channel equalization method of a TDS-OFDM receiver. The method of claim 9, The plurality of signals are guard intervals and OFDM symbols, Step (a), the channel equalization method of the TDS-OFDM receiver, characterized in that for performing synchronization using the distributed pilot. The method of claim 9, The plurality of signals are synchronization information, a guard interval, and an OFDM symbol. Step (a), the channel equalization method of the TDS-OFDM receiver, characterized in that for performing synchronization using the synchronization information. The method of claim 11, The synchronization information is a PN sequence (pseudo noise sequence), the channel equalization method of the TDS-OFDM receiver. The method of claim 9, The distributed pilot is inserted into the first subcarrier period with respect to the frequency axis of the OFDM symbol, and the channel equalization method of the TDS-OFDM receiver, characterized in that inserted into the second subcarrier period with respect to the time axis of the OFDM symbol. The method of claim 13, The first subcarrier period is 12 subcarriers, And said second subcarrier period is four subcarriers. The method of claim 13, In the step (d), the channel equalization is performed based on the channel state estimated through the interpolation of the distributed pilot with respect to the axis having a small period among the time axis and the frequency axis, and then the distributed pilot with respect to the axis having a large period. And performing channel equalization on the basis of the channel state estimated through interpolation of the TDS-OFDM receiver. The method of claim 15, The interpolation may be any one of linear interpolation, zero-order interpolation, zero-order interpolation after linear interpolation, and interpolation using a fractional delay filter.