KR20030095725A - OFDM transmitter capable of transmitting OFDM symbols stably - Google Patents

Abstract

PURPOSE: An OFDM transmitter capable of stably transmitting OFDM signals is provided to prevent damages of OFDM symbols due to filtering, by inserting a guard band into the OFDM symbols before executing pulse shape filtering. CONSTITUTION: A guard band(GB) insertion unit(140) controls the size of a guard band according to a decided symbol rate, roll-off factors, the point number of multiple subcarriers, and inserts the size-controlled guard band into orthogonal frequency division multiplexing(OFDM) symbols. An inverse discrete fourier transform(IDFT) unit(160) transforms the OFDM symbols through IDFT. A guard interval(GI) insertion unit inserts a guard interval between OFDM symbols to restrain interferences between the OFDM symbols. A pseudo noise sequence(PN) insertion unit(220) inserts pseudo noise sequence information. A pulse shaping unit(240) executes pulse shape filtering to OFDM signals formed of the OFDM symbols according to the roll-off factors.

Description

OFDM transmitter capable of stably transmitting OBDM symbols {OFDM transmitter capable of transmitting OFDM symbols stably}

The present invention relates to an Orthogonal Frequency Division Multiplexing (OFDM) transmitter. More particularly, the present invention relates to Pseudo Noise Sequence (PN) information, which is synchronization information of an OFM signal, and an ODP DM symbol. The present invention relates to an OMD transmitter capable of performing time domain synchronous (TDS) transmission by forming a frame of?.

In general, a broadcasting system of a high definition television (HDTV) can be roughly divided into an image encoder and a modulator. The video encoder 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. Digital high-definition television broadcasting adopts a terrestrial simultaneous broadcasting method using a channel of a very high frequency (VHF) / ultra high frequency (UHF) band allocated for conventional television broadcasting.

In Europe, Orthogonal Frequency Division Multiplexing (OFDM), a digital modulation method that achieves a dual effect of improving transmission speed per bandwidth and preventing interference, is adopted as the next generation high-definition television terrestrial broadcasting method.

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. .

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 advantages of the UF DM method is that the waveform of the UF DM signal is the same as White Gaussian Noise, so the PAL (Phase Alternation by Line) and 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.

In general, an OPM transmitter that transmits an OFM signal using time domain synchronization re-assembles an OFM signal formed on a frequency axis that provides one service allocated to a preset frequency band along a time axis. Arrange. The OPM transmitter inserts a guard interval (GI) for suppressing interference between signals in front of the OFM signal formed along the time axis, and inserts synchronization information before the guard period and transmits it. A method of transmitting an OMD signal using this time domain synchronization is called a TDS-OFDM (Time Domain Synchronous-OFDM).

1 is a block diagram illustrating an OPM transmitter performing general time domain synchronous transmission. The FM transmitter has an inverse discrete fourier transform (IDFT) unit 10, a guard interval (GI) insertion unit 20, a pseudo noise sequence (PN) insertion unit 30, and a pulse shaping filter 40. .

The IDFT unit 10 performs an Inverse Discrete Fourier Transform that rearranges the OFM signal formed based on frequency based on time. The GI insertion unit 20 inserts a guard interval for suppressing interference between neighboring OFM die symbols with respect to the ODP DM signal in which the inverse discrete Fourier transform is performed in the IDFT unit 10. The PN insertion unit 30 inserts Pseudo Noise Sequence (PN) information into the OMD symbol in which the protection interval is inserted. The pseudo-noise string information is synchronization information for predicting synchronization and channel of the OMD signal received by the OMD receiver which receives the transmitted OMD signal. At this time, the synchronization inserter 40 generates a pulse wave corresponding to the OMD signal into which the pseudo noise string information is inserted.

The pulse shaping filter 40 filters the pulse waves so that the pulse waves corresponding to the OFM signals output from the PN inserting unit 30 are formed corresponding to the occupied bands of the assigned OMD signals. The molded filtered OMD signal is a high frequency amplified signal transmitted through the antenna 50.

The number of points of multiple subcarriers for inverse discrete Fourier transform is set in the IDFT unit 10 of the OMD transmitter which performs conventional time domain synchronization (TDS) transmission. In general, the number of points of multiple subcarriers for inverse discrete Fourier transform is 3780. That is, the conventional OMD transmitter performs inverse discrete Fourier transform of data for transmission corresponding to 3780 multiple subcarriers through the IDFT unit 10.

FIG. 2 is a diagram illustrating an example of data in which inverse discrete Fourier transform is performed through the IDFT unit 10 of FIG. 1 with reference to a time axis. As shown, the data has an inserted shape corresponding to the totally allocated 3780 multiple subcarriers.

However, when the data having the form of such a frame is filtered by a roll off factor set by the pulse shaping filter 40, there is a problem that data on both sides is damaged. Therefore, the conventional OMD transmitter transmits corrupted data by shaping filtering, and the receiving side receives and restores damaged data. Accordingly, there is a problem in that the receiving side cannot restore the original signal as the damaged signal is restored.

An object of the present invention for solving the above problems is to provide an OMD transmitter for time domain synchronous transmission that can form and transmit a more stable OMD frame without damaging data for transmission.

Another object of the present invention for solving the above problems is, time-domain synchronous transmission that can prevent the loss of data due to shaping filtering by varying the roll-off factor according to the effective band that can be occupied by the data to be transmitted It is to provide an OMD transmitter for.

1 is a block diagram showing an OFM transmitter performing general time domain synchronous transmission;

FIG. 2 is a diagram illustrating an example of data on which inverse discrete Fourier transform is performed through the IDFT unit of FIG. 1 based on a time axis; FIG.

3 is a block diagram showing a preferred embodiment of the OFM transmitter for time domain synchronous transmission according to the present invention;

4 is a diagram illustrating an example of an OMD signal in which a guard band is inserted by the GB insertion unit of FIG. 3;

FIG. 5 is a diagram illustrating a frame example of an OMD signal output from the PN insertion unit of FIG. 3;

FIG. 6 is a diagram illustrating an effective band of an ODP die symbol when the rolloff factor of the pulse forming unit is 0.1 according to the present embodiment;

FIG. 7 is a view showing waveforms formed by pulse shaping filtering of a pulse shaping unit for an ODP DM symbol having a guard band inserted into an effective band according to the present embodiment; and

FIG. 8 is the "symbol ratio" corresponding to the transmission speed of the ODP die symbol determined by FIG. Fig. 9 shows an example of setting the size of the guard band.

Explanation of symbols on the main parts of the drawings

100: FEC unit 120: serial / parallel conversion unit

140: GB insertion unit 160: IDFT unit

180: parallel / serial conversion part 200: GI insertion part

220: PN insertion part 240: pulse molding part

260: RF amplifier 300: antenna

The object as described above, according to the present invention, the GB insertion unit for adjusting the size of the guard band according to the determined symbol rate, the roll-off factor and the number of points of the multiple subcarriers and inserting the sized guard band in the OMD symbol, protection IDFT unit for inverse discrete Fourier transform of band-inserted OMD die symbol, GI insertion portion for inserting a guard interval between OFM die symbol to suppress interference between OFT DM symbols subjected to inverse discrete Fourier transform, protection Pulse shaping filtering is performed according to the roll-off factor of the OPM signal consisting of a PN inserter for inserting pseudo noise string information into an OMD symbol with a section inserted therein, and an OFM symbol with inserted pseudo noise string information. It is achieved by the OMD transmitter including a molding part.

The OMD transmitter of the present embodiment is provided at the front end of the GB insertion unit, and converts the OFM DM symbol from the serial form to the parallel form to provide the GB insertion unit, and between the IDFT unit and the GI insertion unit. And a parallel / serial conversion unit for converting the ODP DM symbol in parallel form, which has been prepared and has undergone inverse discrete Fourier transform in the IDFT unit. As a result, the GI insertion unit inserts a guard interval into each OPM symbol input in series from the parallel / serial conversion unit.

In addition, the OMD transmitter of the present embodiment further includes an FEC unit provided at the front end of the serial / parallel conversion unit and performing coding for correcting an error occurring in transmission with respect to the OFM symbol in series.

Preferably, the OMD transmitter of the present embodiment further includes an RF amplifier for amplifying high frequency to transmit the OFM signal subjected to pulse shaping filtering by the pulse shaping unit through a transmission channel.

According to the present invention, by performing a pulse shaping filtering by inserting a guard band in the OMD symbol, it is possible to prevent the OMD symbol due to filtering. In addition, since the guard band variably sets the size according to the determined symbol rate, the rolloff factor, and the number of points of the multiple subcarriers, it is possible to prevent damage of the OSF symbol included in the effective band due to the pulse shaping filtering. In addition, the guard band is variably set and transmitted without damage to the OSDM symbol by pulse shaping filtering, so that the OS side can be more stably restored.

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

3 is a block diagram illustrating a preferred embodiment of the OFM transmitter for time domain synchronous transmission according to the present invention.

The FM transmitter for time domain synchronous transmission according to the present embodiment includes an FEC unit 100, a serial / parallel conversion unit 120, a guard band (GB) insertion unit 140, and an inverse discrete fourier transform (IDFT) unit ( 160), the parallel / serial conversion unit 180, the GI (Guard Interval) insertion unit 200, the PN (Pseudo Noise Sequence) insertion unit 220, the pulse shaping unit 240, and the RF amplifier 260. Have

The FEC unit 100 performs coding for correcting an error occurring in the transmission on the OMD signal to be transmitted. The serial / parallel conversion unit 120 converts the serial-type OMD signal in which error correction coding is performed into a parallel form.

The GB inserting unit 140 inserts a guard band in the parallel OMD signal. Accordingly, by allocating a predetermined band as a guard band from the number of points allocated to the multiple subcarriers of the OMD signal, it is possible to substantially prevent the loss of the signal in the region where the OFM signal and the multiple subcarriers are inserted.

The IDFT unit 160 performs an Inverse Discrete Fourier Transform on the OMD signal in which the guard band is inserted.

The parallel / serial conversion unit 180 converts the parallel OPM signal in which the inverse discrete Fourier transform is performed into a serial form. The GI insertion unit 200 inserts a guard interval for suppressing interference between neighboring OFM die symbols with respect to the OEP DM signal in series.

The PN insertion unit 220 inserts pseudo noise sequence (PN) information for synchronizing the OMD signal into the OMD signal into which the protection interval is inserted. The pseudo noise string (PN) information is synchronization information for predicting synchronization and channel of the OMD signal received by the OMD receiver receiving the OMD signal transmitted.

The pulse shaping unit 240 performs pulse shaping filtering according to a roll off factor set for the OMD signal into which the pseudo noise string information is inserted. In this case, as a type of filter used for pulse shaping filtering of the pulse shaping unit 240, a SROT filter is used.

The RF amplifier 260 high frequency amplifies the OFM signal subjected to the pulse shaping filtering. The amplified OMD signal is amplified and transmitted along the transmission channel through the antenna 300.

GB inserting unit 140 of the present embodiment is inserted by adjusting the size of the guard band according to the roll-off factor used for pulse shaping filtering in the pulse shaping unit 240, as the pulse shaping filtering by the set roll-off factor is performed Prevent the damage of OSDM symbol.

4 is a diagram illustrating an example of an OMD signal in which a guard band is inserted by the GB insertion unit 140 of FIG. 3. In the drawing, the number of points of multiple subcarriers is set to 3780. However, the number of points of such multiple subcarriers can be applied to this embodiment using any one of 2048, 4096, and 8192 in addition to 3780. As shown in the figure, when the number of points of the multiple subcarriers is set to 3780, the OMD signal data to be transmitted is disposed between 189 to 3591 points of the 3780 points. In this case, it can be seen that the guard band is disposed between 0 points to 189 points, and 3591 points to 3779 points among the 3780 points. Accordingly, the risk of loss of data of the OMD signal for transmission can be reduced.

FIG. 5 is a diagram illustrating an example of a frame of an OMD signal output from the PN insertion unit 220 of FIG. 3.

The frame of the OMD signal is a guard period inserted by the OMD symbol and the GI insertion unit 200 in which the inverse discrete Fourier transform is performed in the IDFT unit 160 with respect to the data frame of FIG. 4 including the guard band. (GI) and pseudo noise string (PN) information inserted by the PN insertion unit 220. FIG.

Therefore, the OMD symbol for transmission may be included in an OMD frame including pseudo noise string information and a guard interval, thereby preventing loss of the OMD symbol due to pulse shaping filtering.

FIG. 6 is a diagram illustrating an effective band of an ODP die symbol when the rolloff factor of the pulse forming unit 240 is 0.1 according to the present embodiment. When the rolloff factor r is 0.1, it has an effective band of 7.27 MHz with respect to 8 MHz allocated to the broadcast band.

FIG. 7 is a diagram illustrating waveforms formed by pulse shaping filtering of the pulse shaping unit 240 for an OMD DM symbol having a guard band inserted into an effective band according to the present embodiment. At this time, the rolloff factor is 0.1. Accordingly, an effective band of 7.27 MHz is set for 8 MHz, which is an allocated band allocated to the broadcast band. Thus, the ODP DM symbol in the form where the guard band of the predetermined band is inserted at both sides for the effective band of 7.27 MHz is not damaged by the pulse shaping filtering by the rolloff factor.

FIG. 8 shows the "symbol rate" corresponding to the transmission speed of the ODP die symbol determined by FIG. 3, the "rolloff factor", and the "discrete Fourier transform size" which is the number of points of multiple subcarriers for inverse discrete Fourier transform. Fig. 9 shows an example of setting the size of the guard band.

First, if the symbol rate is 7.2727 MHz, the rolloff factor is 0.10, and the discrete Fourier transform size is 3780, the GB inserting unit 140 according to the present embodiment measures 378 points out of 3780 points in the size of the guard band. Set to. At this time, the interval between subcarriers is 1.924KHz.

Further, if the symbol rate is 7.2072 MHz, the rolloff factor is 0.11, and the discrete Fourier transform size is 3780, the GB inserting unit 140 according to the present embodiment uses 416 points of the guard band size as the guard band size. Set to. At this time, the interval between subcarriers is 1.907KHz.

If the symbol rate is 7.17488 MHz, the rolloff factor is 0.115, and the discrete Fourier transform size is 3780, the GB inserter 140 of this embodiment sets the guard band size to 435 points out of the 3780 points as the guard band size. do. At this time, the interval between subcarriers is 1.898 KHz.

On the other hand, if the symbol rate is 7.2727 MHz, the rolloff factor is 0.10, and the discrete Fourier transform size is 4096, then the GB inserting unit 140 of the present embodiment measures the size of the guard band to 410 points among the 4096 points. Set to. At this time, the interval between subcarriers is 1.776 KHz.

Further, if the symbol rate is 7.2072 MHz, the rolloff factor is 0.11, and the discrete Fourier transform size is 4096, the GB inserting unit 140 of this embodiment measures the guard band size to 451 points out of the 4096 points. Set to. At this time, the interval between subcarriers is 1.760KHz.

If the symbol rate is 7.17488 MHz, the rolloff factor is 0.115, and the discrete Fourier transform size is 4096, then the GB inserter 140 of this embodiment sets the guard band size to 472 points among the 4096 points as the guard band size. do. At this time, the interval between subcarriers is 1.752KHz.

On the other hand, if the symbol rate is 7.56 MHz, the rolloff factor is 0.05, and the discrete Fourier transform size is 3780, the GB insertion unit 140 according to the present embodiment measures 189 points out of the 3780 points in the size of the guard band. Set to. At this time, the interval between subcarriers is 2KHz.

If the symbol rate is 7.56 MHz, the rolloff factor is 0.05, and the discrete Fourier transform size is 4096, then the GB inserting unit 140 of this embodiment measures the size of the guard band to 205 points out of the 4096 points. Set to. At this time, the interval between subcarriers is 1.846 KHz.

Accordingly, the guard band is variably sized according to the determined symbol rate, rolloff factor, and the number of points of the multiple subcarriers, and thus, the OSF included in the effective band according to the pulse shaping filtering performed by the pulse shaping unit 240 is performed. This can prevent damage to the symbol. In addition, since the guard band is variably set and transmitted without damage to the ODP die symbol by pulse shaping filtering, the reception side can more efficiently restore the OMD die symbol.

According to the present invention, by performing a pulse shaping filtering by inserting a guard band in the OMD symbol, it is possible to prevent the OMD symbol due to filtering.

In addition, since the guard band variably sets the size according to the determined symbol rate, the rolloff factor, and the number of points of the multiple subcarriers, it is possible to prevent damage of the OSF symbol included in the effective band due to the pulse shaping filtering.

In addition, the guard band is variably set and transmitted without damage to the OSDM symbol by pulse shaping filtering, so that the OS side can be more stably restored.

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 (12)

In the OMD transmitter for transmitting the OMD symbol, A GB insertion unit for adjusting the size of the guard band according to the determined symbol rate, the rolloff factor, and the number of points of the multiple subcarriers, and inserting the adjusted guard band into the OSDM symbol; An IDFT unit for inverse discrete Fourier transform of the OMD symbol inserted with the guard band; A GI insertion unit for inserting a guard interval between the OSF DM symbols to suppress interference between the OSF symbols where the inverse discrete Fourier transform has been performed; A PN insertion unit inserting pseudo-noise string information into the OMD DM inserted with the guard interval; And And a pulse shaping unit configured to perform pulse shaping filtering of the OFM signal formed of the OMD DM symbol into which the pseudo-noise string information is inserted, according to the rolloff factor. The method of claim 1, A serial / parallel conversion unit provided at a front end of the GB insertion unit, and converting the OSF symbol from a serial form to a parallel form and providing the GB insertion unit; And And a parallel / serial conversion unit provided between the IDFT unit and the GI insertion unit, and converting the parallel-type OSDM symbol in which the inverse discrete Fourier transform is performed in the IDFT unit into a serial form. , And the GI insertion unit inserts the guard period into each of the OMD symbols inputted in series from the parallel / serial conversion unit. The method of claim 2, An FEC unit provided at a front end of the serial / parallel conversion unit and performing coding for correcting an error occurring in transmission with respect to the ODP die symbol in the serial form. . The method of claim 3, And an RF amplifier for amplifying high frequency amplified RF signals through which the pulse shaping filtering has been performed by the pulse shaping unit through a transmission channel. The method of claim 1, The GB insertion unit, when the determined symbol rate is 7.56 MHz, the rolloff factor is 0.05, and the number of points of the multiple subcarriers is 3780, the size of the guard band is adjusted to any one of 184 to 194 points. The OMD transmitter is inserted into the OMD symbol. The method of claim 1, The GB inserter adjusts the guard band size to any one of 195 to 210 when the determined symbol rate is 7.56 MHz, the rolloff factor is 0.05, and the number of points of the multiple subcarriers is 4096. The OMD transmitter is inserted into the OMD symbol. The method of claim 1, The GB inserter adjusts the guard band size to any one of 373 to 383 when the determined symbol rate is 7.2727 MHz, the rolloff factor is 0.1, and the number of points of the multiple subcarriers is 3780. The OMD transmitter is inserted into the OMD symbol. The method of claim 1, The GB inserter adjusts the guard band size to any one of 405 to 415 when the determined symbol rate is 7.2727 MHz, the rolloff factor is 0.1, and the number of points of the multiple subcarriers is 4096. The OMD transmitter is inserted into the OMD symbol. The method of claim 1, The GB inserter adjusts the guard band size to any one of 411 to 421 when the determined symbol rate is 7.2072 MHz, the rolloff factor is 0.11, and the number of points of the multiple subcarriers is 3780. The OMD transmitter is inserted into the OMD symbol. The method of claim 1, The GB inserter adjusts the guard band size to any one of 446 to 456 when the determined symbol rate is 7.2072 MHz, the rolloff factor is 0.11, and the number of points of the multiple subcarriers is 4096. The OMD transmitter is inserted into the OMD symbol. The method of claim 1, The GB inserter adjusts the guard band size to any one of 430 to 440 when the determined symbol rate is 7.17488 MHz, the rolloff factor is 0.115, and the number of points of the multiple subcarriers is 3780. The OMD transmitter is inserted into the OMD symbol. The method of claim 1, The GB inserting unit adjusts the size of the guard band to any one of 467 to 477 when the determined symbol rate is 7.17488 MHz, the rolloff factor is 0.115, and the number of points of the multiple subcarriers is 4096. The OMD transmitter is inserted into the OMD symbol.