KR100852278B1 - OFDM Transmitter capable of preventing the distortion of OFDM signal according to inserting synchronization symbol - Google Patents

Abstract

An OMD transmitter capable of blocking distortion of an OMD signal generated by the insertion of a synchronization symbol is disclosed. The OMD transmitter comprises: an IDFT unit for performing an inverse discrete Fourier transform that rearranges an OFM signal formed based on a frequency based on time, and an ODP DM neighboring to an OFM signal subjected to an inverse discrete Fourier transform The guard section inserts a GI insert that inserts a guard interval to suppress interference between signals, a shaping filter that performs shaping filtering for band limitation of the pseudo noise thermal information on the time axis, and a shaping filtered pseudo noise thermal information. And an additional information insertion unit for inserting into the OMD signal. Occupied spread spectrum of the OMD signal due to the insertion of the pseudo-noise string information, and it is possible to prevent signal distortion of the OMD signal inserted with the guard interval.

Time Domain Synchronization, OSDM, Pseudo-Noise Sequence, Pulse Shaping Filter, Inserting Additional Information

Description

FM transmitter capable of preventing the distortion of the OMD signal generated by the insertion of the synchronization symbol {OFDM Transmitter capable of preventing the distortion of OFDM signal according to inserting synchronization symbol}

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

2 is a diagram illustrating a frame structure of an OMD signal transmitted through a time domain synchronization scheme.

3 is a diagram illustrating a spectrum generated by each block of FIG. 1 with reference to a frequency axis; and

Figure 4 is a block diagram showing a preferred embodiment of the FM transmitter in accordance with the present invention.

Explanation of symbols on the main parts of the drawings

100: FEC coding part 200: IDFT part

300: GI insert 400: molded filter

500: additional information insertion unit 600: RF amplification unit

700: antenna

The present invention relates to an Orthogonal Frequency Division Multiplexing (OFDM) transmitter, and more particularly, to insert a Pseudo Noise Sequence (PN), which is synchronization information of an OFM signal, into an OFM signal. The present invention relates to an OMD transmitter that performs time domain synchronization (TDS) transmission.

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. 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 scheme 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 these problems, Europe adopts Orthogonal Frequency Division Multiplexing (OFDM), a digital modulation method that can achieve the dual effect of improving the transmission speed per bandwidth and preventing interference, as a 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 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.

1 is a block diagram illustrating an OPM transmitter performing general time domain synchronous transmission. The OMD transmitter includes a FEC coding part 10, an inverse discrete fourier transform part ID 20, a guard interval insertion part GI 30, a synchronization information insertion part 40, The pulse shaping filter 50 and the RF amplifier 60 are provided.

The FEC coding unit 10 performs coding for correcting an error occurring in the transmission for each service information of the OMD signal to be transmitted. The IDFT unit 20 performs an Inverse Discrete Fourier Transform that rearranges the OFM signal formed based on frequency based on time. The GI inserting unit 30 inserts a guard interval for suppressing interference between neighboring OSF signals with respect to the OSF signal in which the inverse discrete Fourier transform is performed in the IDFT unit 20. Synchronization information insertion unit 40 is a synchronous information that informs the start of the service according to the stream of the OPM signal to the OPM signal to which the protection interval is inserted in the GI insertion unit 30, Pseudo Noise sequence: Insert PN) information. 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 wave corresponding to the OPM signal into which the pseudo noise string information output from the synchronization inserting unit 40 is inserted occupies a wider band than the OFM signal before the insertion of the pseudo noise string information on the frequency axis.

The pulse shaping filter 50 filters the pulse waves so that the pulse waves corresponding to the OFM signals output from the synchronization information inserting unit 40 are formed corresponding to the occupied bands of the OMD signals assigned thereto. The RF amplification unit 60 amplifies the OPM signal shaping filtered by the pulse shaping filter 50. At this time, the RF signal amplified by the RF amplifier 60 is transmitted from the antenna 70 is transmitted to the receiving end through the transmission channel.

FIG. 2 is a diagram illustrating a frame structure of an OMD signal transmitted through a Time Domain Synchronous (TDS) scheme. The frame of the OMD signal contains pseudo noise string (PN) information, a guard period (GI), and OFM data. The OSDM data is substantially information for reproduction at the receiving end. The guard interval (GI) is an interval allocated to suppress interference between the OMD signals transmitted. The pseudo noise string information is set synchronization information of each of the OFM signals in the stream of the OFM signals.

FIG. 3 is a diagram illustrating a spectrum generated by each block of FIG. 1. The spectrum shown is a graph formed on the basis of the frequency axis f. In the drawing, the ODP DM spectrum passed through the IDFT unit 20 is 'A', the spectrum of pseudo-noise sequence (PN) information is 'B', and the frequency characteristics of the pulse shaping filter 50 are 'C'. Can be represented graphically. Accordingly, when the OMD signal into which the pseudo-noise string information having a spectrum such as 'B' is inserted passes through the pulse shaping filter 50 having a frequency characteristic such as 'C', it has a spectrum such as 'D'. The OMD signal is output.

However, the OPM signal passing through the pulse shaping filter 50 having a frequency characteristic such as 'C' has a spectrum such as 'A' output from the IDFT unit 20 as 'D' as linear filtering is performed. In contrast, some of the signals are distorted. As described above, the OMD transmitter transmits the OFM signal using the frequency domain, and thus, when the OMD signal is distorted in the frequency domain, the OMD signal cannot be correctly restored.

An object of the present invention for solving the above problems, it is possible to prevent the distortion generated in the FM signal according to the shaping filtering performed to limit the occupied bandwidth of the OMD signal inserted with the pseudo-noise column information The present invention is to provide an FM transmitter.

According to the present invention, in the OMD transmitter for performing time-domain synchronization by inserting pseudo-noise string information, which is the synchronization information of the OFM signal, into the OFM signal, interference between the OFM signals is provided. The GI insertion unit inserts a guard interval into the OPM signal to suppress the noise suppression, a shaping filter which performs shaping filtering for band limiting the pseudo noise thermal information on the time axis, and a shaping filtered pseudo noise thermal information. It is achieved by an OMD transmitter including an additional information insertion unit inserted into an inserted OMD signal.

Preferably, the OMD transmitter of the present embodiment further includes an RF amplifier for amplifying the OFM signal into which the pseudo noise string information is inserted. On the other hand, the pseudo noise string information formed by the shaping filter has an infinite value with respect to the frequency axis. In addition, the pseudo-noise sequence information may be used for symbol timing synchronization and equalization when restoring the OMD signal received at the OMD receiver. Types of shaped filters include RC filters and SRRC filters.

On the other hand, the object as described above, according to the present invention, the IDFT unit for performing an inverse discrete Fourier transform to rearrange the OFM die signal formed on the basis of the frequency, the OFT DM signal subjected to the inverse discrete Fourier transform A GI insertion unit inserting a guard interval to suppress interference between neighboring OFM signals, a shaping filter which performs shaping filtering for band limitation on the time axis of pseudo noise string information, and shaping filtered pseudo noise string It is achieved by an OMD transmitter including an additional information insertion unit for inserting information into an OMD signal inserted with a guard interval.                     

Preferably, the OMD transmitter of the present embodiment further includes an RF amplifier for amplifying the OFM signal into which the pseudo noise string information is inserted. On the other hand, the pseudo-noise train information which is shaped and filtered by the shaping filter forms a pulse wave on the time axis and has an infinite value on the frequency axis. In addition, the pseudo-noise sequence information may be used for symbol timing synchronization and equalization when restoring the OMD signal received at the OMD receiver.

It is preferable that the OMD transmitter of the present embodiment further has an FEC coding unit which performs coding for correcting an error occurring in the transmission on the OMD signal to be transmitted before the IDFT unit. On the other hand, the types of shaping filters for shaping and filtering pseudo noise thermal information include RC filters and SRRC filters.

According to the present invention, before inserting pseudo-noise string information into the OFM signal, the pseudo-noise string information is molded and filtered and inserted into the OPM signal into which the protection interval is inserted, thereby the OPM of the pseudo-noise string information is inserted. It is possible to prevent the spread of the occupied band of the signal, and to prevent signal distortion of the OFM signal in which the guard interval is inserted. Accordingly, the OMD receiver which receives the OMD signal in which the shaped and filtered pseudo-noise string information is inserted may perform more stable reception and restoration of the OMD signal.

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

Figure 4 is a block diagram showing a preferred embodiment of the FM transmitter in accordance with the present invention.

As illustrated, the UFDM transmitter includes a Forward Error Correction coding (FEC) coding unit 100, an Inverse Discrete Fourier Transform (IDFT) unit 200, a Guard Interval (GI) insertion unit 300, and a shaping filter ( 400, an additional information insertion unit 500, and an RF amplifier 600.

The FEC coding unit 100 performs coding for correcting an error occurring in the transmission for each service information of the OMD signal to be transmitted. The IDFT unit 200 performs an Inverse Discrete Fourier Transform that rearranges the OFM signal formed based on frequency based on time. The GI inserting unit 300 inserts a guard interval for suppressing interference between neighboring OSF signals with respect to the OSF signal in which the inverse discrete Fourier transform is performed in the IDFT unit 200.

The pulse shaping filter 400 shaping and filtering the band of pseudo noise sequence (PN) information to be inserted into the OPM signal in which the protection interval is inserted in the GI insertion unit 300. At this time, the pseudo noise string information is synchronization information for notifying the start of the OMD signal in accordance with the OMD stream. Pseudo-noise string information forms a pulse wave on the time axis and has an infinite value on the frequency axis. In addition, the pseudo-noise sequence information may be used for symbol timing synchronization and equalization when restoring the OMD signal received at the OMD receiver.

Examples of the pulse shaping filter 400 include a Raised Cosine (RC) filter and a Square Root Raised Cosine (SRRC) filter.

The additional information insertion unit 500 inserts the pseudo-noise sequence information filtered by the shaping filter 400 into the OPM signal in which the protection interval is inserted in the GI insertion unit 300. At this time, the additional information inserting unit 500 generates a pulse wave corresponding to the OMD signal in which the molded-filtered pseudo-noise string information is inserted. The pseudo-noise sequence information filtered by the additional information insertion unit 500 does not affect the spread of the frequency band allocated to the OSDM signal when it is inserted into the OSDM signal to which the protection interval is inserted.

Therefore, before inserting pseudo-noise string information into the OMD signal, the pseudo-noise string information is molded and filtered and inserted into the OFM signal with the protection section inserted therein, thereby occupying the OPM signal according to the insertion of the pseudo-noise string information. It is possible to block spread spectrum and distortion of the OMD signal. Accordingly, in the FM receiver, more stable reception and restoration of the FM signal is possible.

The RF amplifier 600 amplifies the OFM signal into which the pseudo-noise sequence information filtered by the side information inserter 500 is inserted. At this time, the RF signal amplified by the RF amplifier 600 is transmitted through the antenna 700 is transmitted to the receiving end along the transmission channel.

According to the present invention, before inserting pseudo-noise string information into the OFM signal, the pseudo-noise string information is molded and filtered and inserted into the OPM signal into which the protection interval is inserted, thereby the OPM of the pseudo-noise string information is inserted. It is possible to prevent the spread of the occupied band of the signal, and to prevent signal distortion of the OFM signal in which the guard interval is inserted. Accordingly, the OMD receiver which receives the OMD signal in which the shaped and filtered pseudo-noise string information is inserted may perform more stable reception and restoration of the OMD signal.

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 (9)

In the OMD transmitter which performs time domain synchronous transmission by inserting pseudo noise string information, which is synchronization information of the OFM signal, into the OFM signal, A GI insertion unit for inserting a guard interval into the OSF signal to suppress interference between the OSF signals; A shaping filter for shaping the pseudo-noise train information for time-limiting on the time axis; And And an additional information inserting unit inserting the shape-filtered pseudo-noise string information into the OPM signal into which the protection interval is inserted. The method of claim 1, And an RF amplifier for amplifying the RF signal in which the pseudo-noise string information is inserted into the RF signal. The method of claim 2, The pseudo-noise sequence information OPM transmitter characterized in that it has an infinite value with respect to the frequency axis. The method of claim 3, wherein The shaping filter is an UF DM transmitter, characterized in that any one of the RC filter and SRRC filter. An IDFT unit for performing an inverse discrete Fourier transform for rearranging the OFM signal formed based on frequency based on time; A GI insertion unit for inserting a guard interval to suppress interference between the OFM signals adjacent to the OFM signals subjected to the inverse discrete Fourier transform; A shaping filter for shaping the pseudo-noise train information for time-limiting on the time axis; And And an additional information inserting unit inserting the shape-filtered pseudo-noise string information into the OPM signal into which the protection interval is inserted. The method of claim 5, And an RF amplifier for amplifying the OFM signal into which the pseudo-noise string information is inserted at a high frequency. The method of claim 6, The pseudo-noise sequence information OPM transmitter characterized in that it has an infinite value with respect to the frequency axis. The method of claim 7, wherein And an FEC coding unit configured to perform coding for correcting an error occurring in transmission with respect to the OMD signal to be transmitted before the IDFT unit. The method of claim 8, The molded filter is an OMD transmitter, characterized in that any one of the RC filter and SRRC filter.

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