KR20030094778A - OFDM Transmitter having OFDM signal that inserting pilot and a method inserting pilot signal thereof - Google Patents

Abstract

PURPOSE: An orthogonal frequency division multiplexing(OFDM) transmitter for inserting a pilot signal into an OFDM signal and a method for inserting the pilot signal are provided to easily implement the acquisition of synchronization at a receiving end by inserting at least two pilots over the OFDM symbol and the PN sequence. CONSTITUTION: An orthogonal frequency division multiplexing(OFDM) transmitter for inserting a pilot signal into an OFDM signal includes a pilot insertion unit(300), an IDFT unit(400) and a PN sequence insertion unit(600). The pilot insertion unit(300) inserts at least two pilot data into an effective data. The IDFT unit(400) implements an inverse Fourier transformation of the OFDM symbol inserted thereinto the pilot data. The PN sequence insertion unit(600) inserts the PN sequence and the pilot signal corresponding to the inserted pilot data into the inverse Fourier converted OFDM symbol.

Description

OFDM transmitter for inserting pilot signal into OPM signal and its pilot signal inserting method {OFDM Transmitter having OFDM signal that inserting pilot and a method inserting pilot signal}

The present invention relates to an Orthogonal Frequency Division Multiplexing (OFDM) transmitter, and more particularly, to an OFM transmitter capable of improving reception performance.

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 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 because 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.

1 is a simplified block diagram of a typical OPM transmitter. The input data is encoded by the FEC unit 10 so that an error can be detected and corrected at the receiving end. The encoded data is converted into parallel data by the serial / parallel conversion unit 20 and input to the Inverse Discrete Fourier Transform (IDFT) unit 30. The IDFT unit 30 converts the sample data into the time domain. The IDFT unit 30 outputs N parallel data in the frequency domain as N sample data in the time domain.

The guard interval insertion unit 40 inserts a guard interval GI in units of N sample data outputs, that is, in units of one OFDM symbol. The guard interval (GI) is a copy of some sample data at the end of the OFDM symbol consisting of N sample data, and is inserted at the front end of the OFDM symbol.

The PN sequence inserter 50 inserts a PN sequence for synchronization and channel prediction at the receiver at the front end of the OMD symbol in which the guard interval GI is inserted.

Thereafter, the filter unit 60 filters the predetermined OFDM symbol, and then processes the signal into an RF signal through the RF unit 70 and transmits the RF signal to the receiver through a communication channel.

In this way, by inserting the PN sequence as the synchronization information into the OMD symbol, it is possible to acquire the synchronization signal before performing the Fourier transform (DFT) of the frequency domain, that is, the OMD receiver. However, when the PN sequence, which is the synchronization information, is used for a long time, the amount of data transmitted to the OMD receiver is reduced, resulting in a decrease in data rate.

SUMMARY OF THE INVENTION An object of the present invention for solving the above problems is to provide an OMD transmitter which inserts two or more pilot signals to make receiving side synchronization easier.

1 is a schematic block diagram of a conventional OPM transmitter,

2 is a schematic block diagram of an UFDM transmitter according to an embodiment of the present invention;

3 is a diagram illustrating a structure in which two pilot data are located within valid data by the pilot inserting unit 300 of FIG.

4A to 4B are diagrams illustrating a spectrum in which a pilot signal is inserted into a PN sequence in a frequency domain;

5A through 5B are diagrams illustrating the configuration of the PN sequence insertion unit 600 of FIG. 2 for inserting a pilot signal as shown in FIGS. 4A through 4B.

6 is a diagram illustrating a signal spectrum after pulse shaping by the ODP transmitter of FIG. 2; and

FIG. 7 is a flowchart illustrating a method for inserting two or more pilot signals by the OMD transmitter of FIG. 2.

Explanation of symbols on the main parts of the drawings

100: FEC unit 200: serial / parallel conversion unit

300: pilot insertion unit 400: N-IDFT unit

500: protection section insertion unit 600: PN sequence insertion unit

700: molded filter portion 800: RF portion

In order to achieve the above object, the OMD transmitter according to the present invention includes a pilot insertion unit for inserting two or more pilot data into valid data, and an inverse Fourier transform of the OMD DM with two or more pilot data inserted therein. An IDFT unit and a PN sequence insertion unit for inserting a PN sequence and pilot signals corresponding to two or more pilot data into the inverse Fourier transformed OMD symbols.

Here, if the pilot data is even, the pilot inserting portion inserts the pilot data in a position symmetrical with respect to the center of the OMD die symbol, and when the pilot data is odd, the pilot inserting portion places the center and the center of the OMD die symbol. The pilot data is inserted at positions symmetrically in the.

For example, when two pilot data are inserted, a signal in which the pilot signal is inserted and output from the PN sequence insertion unit is expressed as follows.

Where P (n) is the PN sequence, Is the frequency of the pilot signal.

When three pilot data are inserted, a signal in which the pilot signal is inserted and output from the PN sequence insertion unit is expressed as follows.

Where P (n) is the PN sequence, Is the frequency of the pilot signal and d is a constant.

On the other hand, the method of inserting a pilot signal of the OMD transmitter according to the present invention, the step of inserting two or more pilot data in the valid data of the OMD DM symbols; Inverse Fourier transforming the OMD die symbol into which at least two pilot data are inserted; And inserting a PN sequence and a pilot signal corresponding to two or more pilot data into the PN sequence into the inverse Fourier transformed OMD DM symbol.

Here, if the pilot data is even, the pilot data insertion step inserts the pilot data in a position symmetrical with respect to the center of the OMD die symbol, and when the pilot data is odd, the pilot data insertion method uses the OMD die symbol. Pilot data is inserted into the center and the positions symmetrically to the center.

For example, when two pilot data are inserted, the pilot signal is inserted into the PN sequence and the output signal is expressed as follows.

Where P (n) is the PN sequence, Is the frequency of the pilot signal.

When three pilot data are inserted, a pilot signal is inserted into the PN sequence and the output signal is expressed as follows.

Where P (n) is the PN sequence, Is the frequency of the pilot signal and d is a constant.

Therefore, two or more phase-continuous phases of the OMD DM symbol and the PN sequence can be inserted into the pilot signal, thereby making it easier to acquire synchronization on the receiving side.

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

Figure 2 is a block diagram showing a preferred embodiment of the FM transmitter in accordance with the present invention.

The OPM transmitter is a FEC unit (Forward Error Correction) (100), a serial / parallel conversion unit 200, a pilot insertion unit 300, N-IDFT (Inverse Discrete Fourier Transform) unit 400, the guard interval (Guard Interavl) inserting part 500, PN sequence inserting part 600, shaping filter part 700, RF part 800 and the like.

The FEC unit 100 performs coding on the input data to correct an error that may occur during transmission.

The serial / parallel conversion unit 200 converts the error coded serial data into parallel data and outputs the parallel data.

The pilot inserting unit 300 inserts two or more pilot data P 'into parallel data in order to facilitate synchronization acquisition at the receiving side. For example, if the number of pilot data P 'is odd, one pilot data P' is positioned at the center of the valid data, and the pilot data P 'is positioned so that the remainder is symmetrical. In addition, as shown in FIG. 3, when positioning even-numbered pilot data P ', pilot data P' is inserted so as to be symmetrical at the center of valid data.

The N-IDFT unit 400 performs an Inverse Discrete Fourier Transform that rearranges N parallel data including two or more pilot data P ′ in the frequency domain into N sample data in the time domain. Perform.

The guard interval insertion unit 500 inserts a guard interval GI in units of N sample data with respect to the output serial data. The protection period GI is provided to suppress interference between symbols, for example, and is provided by copying a predetermined number of pieces of sample data of an ODM die symbol end composed of N pieces of sample data to the front end of the OFM die symbol.

The PN sequence inserting unit 600 performs the PN sequence and the receiving side synchronization acquisition for synchronization and channel prediction at the receiving side to the OFM signal in which the guard interval GI is inserted at the guard interval inserting unit 500. To make it even easier, the pilot signal P is inserted. Here, the pilot signal P is preferably equal to the number of two or more pilot data P 'inserted by the pilot insertion unit 300.

Thereafter, the shaping filter unit 700 filters the OFM signal, and the filtered OMD signal is processed by the RF unit 800 as an RF signal and transmitted to the channel.

Hereinafter, a method in which the pilot signal P is inserted into the PN sequence P (n) by the PN sequence insertion unit 600 will be described in detail with reference to FIGS. 4A to 5B.

The PN sequence P (n) is a random signal, and the frequency of the pilot signal P into which the pilot signal P is inserted is If is the pilot tone Has the value of. For example, as shown in FIG. 4A, when an even number, i.e., two pilot signals P are inserted into the PN sequence P (n), the frequency of the pilot signal P Becomes ± 1.89 MHz. This is a frequency value of 1/4 when the symbol rate is 7.56 MHz.

As described above, when two pilot signals P are inserted, as shown in FIG. 5A, an adder A, a multiplexer M, and a counter C are included. The PN sequence and the pilot signal P What is inserted may be expressed as shown in [Equation 1].

On the other hand, as shown in FIG. 4B, when three pilot signals P are inserted into an odd number, that is, three pilot signals P are inserted at the center '0' point, and two pilot signals P are inserted. Frequency when The three pilot signals P are inserted by inserting two pilot signals P at ± 1.89 MHz. here, Is 0, the pilot signal P becomes a value of '1', that is, a constant.

In this case, as shown in FIG. 5B, by adding a constant d to the configuration diagram of FIG. 5A, two pilot signals P inserted symmetrically and a pilot signal P are inserted in the center. do. That is, the insertion of three pilot signals P into the PN sequence may be expressed as shown in [Equation 2].

In this way, by adding the pilot signal P inside the OMD symbol, it is possible to give the gain of the synchronization acquisition at the reception side as well as the synchronization information.

Of course, when the length of the PN sequence (2 ^N -1) is 255 or 511, the PN sequence has a complete period, so that the continuity of the phase and the pilot signal P inserted in the OMD symbol can be maintained.

As described above, the PN sequence into which the pilot signal P is inserted is shaped by the shaping filter 700 as shown in FIG. 6.

Therefore, it is possible to gain reception synchronization acquisition by inserting a pilot signal P whose phase is continuous throughout the OMD DM symbol and the PN sequence.

FIG. 7 is a flowchart illustrating a method for inserting a pilot signal P into an OMD symbol and a PN sequence by an OMD transmitter according to an embodiment of the present invention.

First, in order to correct an error that may occur during transmission with respect to the input data, the FEC unit 100 codes the data (S10), converts the error coded data into parallel data, and outputs the converted data (S20).

Next, in order to more easily acquire the synchronization on the receiving side, the inserting unit 300 inserts two or more pilot data P 'into the N parallel data (S30). For example, if the number of pilot data P 'is odd, the odd pilot data P' is inserted so as to be symmetrical in the center of the valid data. In the case of an even number, pilot data P 'is inserted so as to be symmetrical at the center of the valid data.

An inverse discrete Fourier transform (IDFT) is performed to rearrange N parallel data including two or more pilot data P ′ in the frequency domain to N sample data in the time domain (S40).

A guard interval GI is inserted in units of N sample data transformed by inverse Fourier (S50).

Thereafter, the PN sequence inserting unit 600 pilots the PN sequence for the synchronization and channel prediction at the receiving side to the OPM signal with the guard interval GI inserted therein, and makes it easier to acquire the synchronization at the receiving side. The signal P is inserted (S60). Here, the pilot signal P is preferably equal to the number of two or more pilot data P 'inserted in step S30.

Thereafter, the OMD signal is filtered and RF signal processed and transmitted to the transmission channel.

In this way, it is possible to more easily acquire the synchronization on the receiving side by inserting a pilot signal P whose phases are continuous throughout the ODM symbol and the PN sequence.

According to the present invention, two or more phases in which the phases are continuous throughout the OMD die symbol and the PN sequence can be inserted into the pilot to facilitate the acquisition of synchronization on the receiving side.

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 (10)

A pilot insertion unit for inserting at least two pilot data into valid data; An IDFT unit for inverse Fourier transforming the OMD DM inserted with the pilot data; And And a PN sequence inserting unit inserting a PN sequence and a pilot signal corresponding to the inserted pilot data into the inverse Fourier transformed OMD DM symbol. The method of claim 1, If the pilot data is even, And the pilot inserting unit inserts the pilot data at positions symmetrical with respect to the center of the OSDM symbol. The method of claim 1, If the pilot data is odd, And the pilot insertion unit inserts the pilot data into a center of the OSDM symbol and symmetrical positions in the center. The method of claim 1, When two pilot data are inserted, The OMD transmitter characterized in that the signal is inserted and output from the PN sequence insertion unit as shown in the following equation: Where P (n) is the PN sequence, Is the frequency of the pilot signal. The method of claim 1, When three pilot data are inserted, The OMD transmitter characterized in that the signal is inserted and output from the PN sequence insertion unit as shown in the following equation: Where P (n) is the PN sequence, Is the frequency of the pilot signal and d is a constant. Inserting at least two pilot data into valid data among the OMD symbols; Inverse Fourier transforming the OMD DM inserted with the pilot data; And And inserting a PN sequence and a pilot signal corresponding to the inserted pilot data into the PN sequence into the inverse Fourier transformed OMD DM symbol. The method of claim 6, If the pilot data is even, In the pilot data insertion step, the pilot data insertion method of the FM transmitter, characterized in that for inserting the pilot data in a position symmetrical with respect to the center of the FM symbol. The method of claim 6, If the pilot data is odd, And the pilot data insertion method inserts the pilot data into a center of the OSDM symbol and symmetrical positions in the center of the OSDM symbol. The method of claim 6, When two pilot data are inserted, The pilot signal is inserted into the PN sequence, the output signal is a pilot signal insertion method of the FM transmitter, characterized in that represented by the following equation: Where P (n) is the PN sequence, Is the frequency of the pilot signal. The method of claim 6, When three pilot data are inserted, The pilot signal is inserted into the PN sequence, the output signal is a pilot signal insertion method of the FM transmitter, characterized in that represented by the following equation: Where P (n) is the PN sequence, Is the frequency of the pilot signal and d is a constant.