KR20040032284A - Single carrier transmission system capable of reducing signal distortion and a method therefore - Google Patents

Abstract

PURPOSE: A single carrier transmitting system capable of reducing distortion of transmission signals and a method thereof are provided to reduce distortion of transmission signals in a channel environment where a burst noise exists, and improve the receipt capability of a receiving side. CONSTITUTION: A scrambler(100) randomizes transmitting data signals. An FEC(Forward Error Correction) unit(110) corrects a bit error of an inputted data stream. A section distinguishing unit(141) distinguishes between a frame synchronous section and a data section of a transmission signal. A modulator(143) modulates the distinguished sections in different single carrier methods. A modulation information transmitting unit(145) transmits information related to the modulation methods to a receiving side through the frame synchronous section.

Description

Single carrier transmission system capable of reducing signal distortion and a method therefore}

The present invention relates to a single carrier transmission system and a transmission method thereof, and more particularly, to a single carrier transmission system and method for reducing distortion of a transmission signal.

As communication, computers, and broadcasting converge to become multimedia, countries around the world are digitizing existing analog broadcasting. In particular, advanced countries such as the United States, Europe, and Japan have already performed some digital broadcasting through satellites. In addition, a standard method for digital broadcasting has been prepared, and this standard method is configured slightly differently in Naramama.

The Federal Communications Commission (FCC) of the United States approved the Digital Television Standard of the Advanced Television Systems Committee (ATSC) as the standard for next generation television broadcasting on December 24, 1996. Under this decision, terrestrial broadcasters must comply with the specifications for video and audio compression, packet data transmission structure, modulation, and transmission system specified in the ATSC standard. The decision was made autonomously.

According to the ATSC standard, video compression adopts the Moving Picture Experts Group (MPEG) -2 video (ISO / IEC IS 13818-2) standard. All digital broadcasts worldwide have adopted this standard. The audio compression scheme adopts the Digital Audio Compression (AC-3) standard proposed by Dolby. The multiplexing method adopts the MPEG-2 system (ISO / IEC IS 13818-1) standard method. This method is used in Europe as well as video compression. The modulation and transmission method adopts 8-VSB (Vestigial Side Band) method. The VSB method is proposed for digital TV broadcasting, and the data rate of 19.39 Mbps can be obtained by using the 6MHz band, and thus the bandwidth efficiency is high and the structure is simple. In addition, it is designed to minimize interference with the existing National Television Standards Committee (NTSC) broadcasting channel and uses a pilot signal, a segment sync signal, and a field sync signal to operate stably even in a noisy situation. In addition, Reed-Solomon (RS) codes and Trellis codes are used to prevent errors.

ATSC digital TV standard uses single-carrier amplitude modulation residual sideband method (VSB) to transmit high-quality video, audio and auxiliary data with 6MHz bandwidth.Two broadcast modes, simultaneous terrestrial broadcast mode and high data rate cable broadcast mode. It is supposed to support. The main feature of this method is that it uses 8-VSB modulation to modify the digital signal by changing the existing analog VSB method.

1 is a block diagram schematically illustrating a digital broadcasting transmission system using an ATSC standard method. Referring to the drawings, the digital broadcasting system includes a scrambler 10, a forward error correction (FEC) unit 20, a mux 30, a pilot inserter 40, a modulator 50, and an RF converter. 60 is provided. The FEC unit 20 also includes an RS encoder (Reed-Solomon encoder) 21, an interleaver 23, and a trellis encoder 25.

The scrambler 10 is also called a data randomizer, and randomizes the transmitted data signal in order to prevent a problem of losing the synchronization signal by repeating the same number such as 00000000b or 11111111b in the synchronous data transmission. The scrambler 10 changes the value of each byte of the data signal according to a predetermined pattern, and this process is reversed at the receiver to restore the correct value.

The RS encoder 21 is an FEC structure added to the input data stream. FEC refers to a technique for correcting bit errors that occur during transmission. Atmospheric noise, multipath propagation, signal fading, and nonlinearity of the transmitter all contribute to bit error, and the RS encoder 21 adds 20 bytes after 187 bytes in the case of an MPEG-II transport stream. The 20 additional bytes are called Reed Solomon Parity Bytes. The receiver compares the received 187 bytes with 20 parity bytes to determine accuracy. If an error is detected by the accuracy determination, the receiver locates the error and corrects the distorted byte to recover the original signal. In this way up to 10 bytes of error per stream can be recovered. Any further error is not recoverable, and if not recoverable, the entire stream is discarded.

The interleaver 23 disperses the data on the time axis so as to disturb the order of the data streams so that the transmission signal is less sensitive to interference. Even if noise occurs in any part of the signal band due to the dispersion of the transmission signal, signals in other bands are preserved. The receiver reverses this process and restores the distributed transmission back to the correct value.

The trellis encoder 25 forms an FEC structure that is different from the RS encoder 21. Unlike the RS encoder 21 which handles the entire MPEG-II stream, the trellis encoder 25 encodes in consideration of the influence of time, and this process is also called a convolutional code. Trellis encoder 25 divides an 8-bit byte into four 2-bit words. Here, the 2-bit word is compared with the previous word, and a 3-bit binary code is generated for the purpose of describing the change from the previous word to the current word. This 3-bit code replaces the original 2-bit word and is sent as an 8-level symbol of 8-VSB (3 bits = 8 levels). Thus, the 2-bit word input to the trellis encoder 25 is converted into a 3-bit signal and output. For this reason, an 8-VSB system is sometimes called a 2/3 rate coder. The advantage of trellis coding is that error information can be removed by tracking the passage of the signal over time.

After trellis coding by the trellis encoder 25, the mux 30 inserts a segment sync and a frame sync into the transmission signal. The pilot inserter 40 inserts an ATSC pilot (PILOT: Programmed Inquiry Learning Or Teaching) into the transmission signal into which the segment sync and the frame sync are inserted. Here, a slight DC shift (1.25V) is applied to the 8-VSB baseband signal just before modulation, in which case some residual carrier appears at the zero frequency point of the modulated spectrum. This generated residual carrier is called an ATSC pilot.

The modulator 50 modulates the transmission signal received from the pilot inserter 40 using an 8-VSB modulation scheme. Digital modulation converts any of phase, amplitude, and frequency of a carrier wave into a digital signal. Among these, changing the phase according to a digital value is called phase shift keying (PSK). The most basic is BPSK (Binary Phase Shift Keying), which is a PSK method in which a phase difference of 180 degrees is provided to each carrier when one bit of signal 0 and 1. On the other hand, quadrature phase shift keying (QPSK) is a method of associating four values, that is, two bits, in one symbol with a phase change interval of 90 degrees. Send cos wave multiplied by BPSK signal and sin wave multiplied by BPSK. The 8-PSK sends a 3 bit 8 level signal as a symbol with 45 degrees out of phase. Since 8-PSK transmits three times more information than BPSK over the same bandwidth, the frequency efficiency is higher, but the distance between each phase is closer, making it more susceptible to noise, so more power is needed to achieve the same error rate. Should be used.

In addition, a method of converting the amplitude of the carrier wave is called Amplitude Shift Keying (ASK). The ASK modulated signal is the same as the Amplitude Modulation (AM) except that the modulated wave signal has a predetermined number of amplitude levels rather than a continuous value like an analog signal. For example, when ASK modulation of 3 bits of digital information, the modulation wave has 8 levels, and when modulation of 4 bits, it has 16 levels. This modulated wave signal is a bilateral band signal.

Amplitude Phase Shift Keying (APSK) is a method of transmitting information on both a phase and an amplitude of a carrier wave. QAM (Quadrature Amplitude Modulation) is a method of synthesizing and transmitting two carriers in orthogonal relation to APSK by combining them. For example, 16-QAM can transmit four times the information in the same bandwidth as BPSK, but in this case, since the distance between each code is close, a larger transmission power is required to obtain an equivalent error rate characteristic.

Since the spectrum of the ASK signal is a signal of both side bands, it cannot be said that the channel is efficiently used. Therefore, if this signal is band limited to the residual side band signal, it becomes a VSB signal. For example, three bits of digital information are displayed at eight levels. When the signal is ASK-modulated and then band-limited by a VSB filter, the signal becomes an 8-VSB modulated signal. In other words, the 8-VSB signal is very similar to the analog VSB except that there are eight possible values.

The RF converter 60 converts the modulated transmission signal into a radio frequency (RF) and transmits the converted transmission signal through an antenna.

The ATSC data segment consists of 187 bytes + 20 bytes of the original MPEG-II data stream. After trellis coding, the segment of 207 bytes is converted into 828 (= 207 x 4), 8-level symbol streams.

The segment sync signal is a repeating four symbol (1 byte) pulse added to the head of the data segment and replaces the sync byte of the original MPEG-II transport stream. The receiver can easily identify repeating segment sync signals from completely random data, and can accurately recover the clock even at noise and interference levels that make data recovery impossible. Segments of the transmission signal to which the segment sync signal is assigned are shown in FIG. 2. That is, the segment of the transmission signal is a segment synchronization signal consisting of four symbols, three pseudo noise sequence (PN) information consisting of 63 symbols, a transmission mode consisting of 24 symbols, 92 reserved symbols, and 12 It consists of three precode symbols. Here, the pseudo noise sequence is a synchronization information sequence for predicting synchronization and channel of a transmission signal in a receiver receiving a signal. The pseudo noise string information is generated by the PN information generation unit (not shown) and inserted into the transmission signal by the mux 30.

3 is a diagram illustrating a frame structure of a transmission signal according to the ATSC standard. Referring to the figure, a field of ATSC data consists of 313 consecutive data segments, and ATSC field sync becomes a field data segment. An ATSC data frame consists of two ATSC data fields.

The repetition period of the ATSC data field is 24.2 msec and is similar to the NTSC vertical interval (NTSC period = 16.7 msec). Field sync has a well-known data symbol pattern and is used for ghost cancellation at the receiver. This process is accomplished by comparing the received signal with errors with field synchronization and adjusts the characteristics of the ghost cancellation equalizer using the resulting error vector.

Recently, China's international High Definition Television (Conceptual Group) proposed two standards for independent digital broadcasting in China, one of which is the single-carrier ADTB-T standard.

The ADTB-T standard has a frame structure that combines pseudonoise string information and data similar to the US ATSC standard. However, the ADTB-T standard supports single / hybrid transmission mode and differs from the ATSC standard in that it uses an Offset Quadrate Amplitude Modulation (OQAM) modulation method. More specific differences are presented in the ADTB-T standard.

FIG. 4 is a diagram for comparing constellations of single carrier modulation schemes such as ATSC and ADTB-T. When the sampling frequency (fs) is set to 7.14 MHz, the VSB modulation method separates the digital signal into in-phase components (I) and quadrature components (Q) and equals them with a clock of 2 fs (= 14.28 MHz). Only send data to the components of the phase. In contrast, the QAM modulation system simultaneously transmits data to in-phase and quadrature components with a clock of 1 fs (= 7.14 MHz). In addition, OQAM modulation transmits data alternately between in-phase and quadrature components with a clock of 2 fs (= 14.28 MHz). Sample data according to each modulation scheme is shown in FIG. 5.

However, like a single carrier transmission system according to the ATSC standard or a single carrier transmission system according to the ADTB-T standard, a single carrier transmission system having a frame structure in which pseudo noise string information and data are combined has a pseudo noise of a frame synchronizer or a field synchronizer. Thermal information and data are transmitted in the same modulation method. Such a system can use only one single carrier modulation method, and thus has a problem in that it cannot cope with a change in channel environment due to burst noise.

The present invention was devised to solve the above problems, and provides a single carrier transmission system and a transmission method capable of appropriately responding to changes in the channel environment due to burst noise and enabling the use of various single carrier modulation schemes. The purpose is to provide.

1 is a block diagram schematically illustrating a digital broadcasting transmission system using an ATSC standard method;

2 is a diagram illustrating a segment of a transmission signal according to FIG. 1;

3 is a view illustrating a frame structure of a transmission signal according to FIG. 1;

4 is a diagram for comparing the constellations of the single carrier modulation scheme;

5 is a diagram illustrating sample data according to each modulation scheme of FIG. 4;

6 is a block diagram schematically showing a digital broadcasting transmission system according to the present invention;

7 is a flowchart illustrating a single carrier modulation method according to FIG. 6, and

FIG. 8 illustrates sample data according to the single carrier modulation method of FIG. 6.

Explanation of symbols on the main parts of the drawings

10, 100: scrambler 20, 110: FEC part

30, 120: mux 50, 143: modulator

141: section discriminating unit 145: modulation information transmission unit

In the single carrier transmission system according to the present invention for achieving the above object, in the single carrier transmission system for modulating and transmitting the input transmission signal of the frame unit in a single carrier modulation method, the frame synchronization between the transmission signal and the data A section discriminating unit for discriminating a section, a modulator for modulating each section determined by the section discriminating unit using a different single carrier modulation scheme, and information on the modulation scheme of each section, between the frame moving mechanisms; It includes a modulation information transmission unit for transmitting to the receiving side through.

Here, the modulator may be implemented to modulate the frame synchronization mechanism of the transmission signal by VSB modulation, and the data interval is modulated by QAM modulation, and the frame synchronization mechanism of the transmission signal is OQAM modulation. The data section may be implemented to be modulated by a QAM modulation scheme. In addition, the modulator may be implemented to modulate the frame synchronization period of the transmission signal by the VSB modulation method, and the data period is modulated by the OQAM modulation method, the frame synchronization period of the transmission signal is QAM modulation method The data section may be implemented to modulate using an OQAM modulation scheme. In addition, the modulator may be implemented to modulate the frame synchronization period of the transmission signal by the OQAM modulation method, and the data period is modulated by the VSB modulation method, and the frame synchronization period of the transmission signal is the QAM modulation method. The data section may be implemented to be modulated by a VSB modulation scheme.

In the case of modulating a frame movement period and a data period, the modulation unit has the same sampling frequency of the VSB modulation method and the sampling frequency of the OQAM modulation method, and the sampling frequency of the QAM modulation method is the VSB modulation method and the OQAM modulation. It is preferable to modulate such that it is 1/2 of the sampling frequency of the system.

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

6 is a block diagram schematically showing a digital broadcasting transmission system according to the present invention. Referring to the drawings, the digital broadcast transmission system, the scrambler 100, the FEC unit 110, the mux 120, the pilot insertion unit 130, the section discriminating unit 141, the modulator 143, modulation information transmission The unit 145 and the RF converter 150 are provided. In addition, the FEC unit 110 includes an RS encoder (Reed-Solomon encoder) 111, an interleaver (113), and a trellis encoder (115).

The scrambler 100 randomizes the transmitted data signal in order to prevent a problem in which the same number is repeated, such as 00000000b or 11111111b, in the synchronous data transmission, thereby losing the synchronization signal. The scrambler 100 changes the value of each byte of the data signal according to a predetermined pattern, and this process is reversed at the receiver to restore the correct value.

The FEC unit 110 corrects bit errors with respect to the input data stream. Here, the RS encoder (Reed-Solomon enconder) 111, the interleaver (113), and the trellis encoder (115) provided in the FEC unit 110 is provided in the digital broadcast transmission system according to the ATSC standard method. Since the same operation as the same element is performed, the description thereof is omitted.

The PN information generator (not shown) generates pseudo noise string information, which is synchronization information for synchronization between the transmitting side and the receiving side, and transmits the generated pseudo noise string information to the mux 120. Here, the transmitting side refers to a transmitting side having a digital broadcasting transmission system for transmitting digital broadcasting in a single carrier system, and the receiving side refers to a receiving side for receiving digital broadcasting transmitted in a single carrier system. After trellis coding by the trellis encoder 115, the mux 120 inserts segment sync and pseudo noise string information at the head of the transmission signal.

The pilot inserter 130 inserts a pilot into a transmission signal into which segment sync and pseudo noise string information are inserted. Here, the pilot refers to the residual carrier appearing at the zero frequency point of the modulated spectrum.

7 is a flowchart illustrating a single carrier modulation method according to FIG. 6. Referring to the figure, the section discriminating unit 141 determines the frame synchronization section and the data section of the transmission signal output from the pilot inserting unit 130 (S701).

In addition to the ATSC and ADTB-T standards, the CDTB-T (Chinese Digital Television Broadcasting-Terrestrial) standard also has a frame structure that combines the frame synchronization and data sections. In the CDTB-T standard proposed by China's The Academy of Broadcasting Science (ABS) for independent digital broadcasting in China, the frame sync interval consists of three consecutive pseudo-noise information consisting of 511 symbols. Later, the control bits and the remaining bits form a structure that is followed. Three consecutive pseudonoise sequences are called training symbols. Here, the control bit refers to bits used for control purposes, such as parity, start and end bits, among all bits transmitted through a communication line for data transmission in data communication. The spare bit is an area for time axis conversion, bit rate compression, error correction, and the like.

The data section includes payload and tail symbol regions. The payload is an area for information on a higher layer, which is a part that can be used in a communication service. The tail symbol region is a region for additional information for transmission and is called a tail symbol region because it is provided in the last node of the frame.

In the method of discriminating the frame sync section and the data section, the section discriminating unit 141 counts the symbols for the transmission signal in the frame unit, and compares the counted value with the size of the symbol set for each section to compare the frame sync section. And a method for determining a data section may be used.

The modulator 143 modulates each of the frame sync section and the data section determined by the section discriminator 141 by different single carrier modulation schemes (S703). For example, the frame synchronization period of the transmission signal may be set to be modulated by the VSB modulation method, and the data period may be set to be modulated by the QAM modulation method. In this case, the modulator 143 may set the VSB modulation method according to the set modulation method. The data section is modulated by QAM modulation. In addition, the modulator 143 may be configured to adjust the frame sync interval and the data interval according to a preset modulation scheme, respectively, in OQAM modulation scheme-QAM modulation scheme, VSB modulation scheme-OQAM modulation scheme, QAM modulation scheme- OQAM modulation scheme, and OQAM modulation. And a QAM modulation scheme and a VSAM modulation scheme. In this case, the modulator 143 samples the sampling frequency of the VSB modulation method and the sampling frequency of the QAM modulation method so that the sampling frequency of the QB modulation method is the sampling frequency of the VSB modulation method or the sampling frequency of the OQAM modulation method. Sampling is preferably made to be 1/2. This takes into account that the QAM modulation method simultaneously transmits data to in-phase and quadrature components. An example of the sampled data is shown in FIG. 8. Here, although two different modulation schemes are used for the transmission signal in the frame unit, all three modulation schemes may be used by subdividing the data interval into the payload interval and the tail symbol region.

When each section of the transmission signal is modulated by the modulator 143, the modulation information transmitter 145 transmits information on the modulation scheme of each section to the receiver through the frame synchronization section (S705). . As a result, the receiving side can appropriately respond to changes in the modulation scheme of the transmitting side.

The RF converter 150 converts the modulated transmission signal into an RF (radio frequency), and transmits the converted transmission signal through an antenna.

According to the present invention, the single carrier transmission system can not only respond appropriately to changes in the channel environment due to burst noise, but also enable the use of various single carrier modulation schemes. Especially, in case of modulation like OQAM modulation method, QAM modulation method, VSB modulation method, QAM modulation method, etc., the clock of frame synchronization section is operated twice as fast as the data period. It will be possible to improve. In addition, in the case of the VSB modulation method-OQAM modulation method, the transmission signal can reduce distortion in comparison with the conventional VSB modulation method in a channel environment in which burst noise exists in the in-phase component. In addition, in the case of the OQAM modulation method-VSB modulation method, the distortion of the transmission signal can be reduced in comparison with the conventional OQAM modulation method in a channel environment in which short burst noise exists in in-phase and quadrature phase components.

According to the present invention, the single carrier transmission system can not only reduce distortion of a transmission signal in a channel environment in which burst noise exists, but also improve reception performance at a receiving side.

Although the preferred embodiments of the present invention have been illustrated and described above, the present invention is not limited to the specific embodiments described above, and the present invention is not limited to the specific embodiments of the present invention without departing from the spirit of the present invention as claimed in the claims. Anyone skilled in the art can make various modifications, as well as such modifications are within the scope of the claims.

Claims (20)

In a single carrier transmission system for modulating the transmitted transmission signal of the frame unit by a single carrier modulation method for transmission, A section discriminating section for discriminating a frame moving section and a data section of the transmission signal; And And a modulator for modulating each of the sections determined by the section discriminator by different preset single carrier modulation schemes. The method of claim 1, And a modulation information transmission unit for transmitting information on the modulation scheme of each section to the receiving side through the frame synchronization section. The method of claim 2, And the modulator modulates the frame synchronization mechanism of the transmission signal by VSB modulation and modulates the data interval by QAM modulation. The method of claim 2, And the modulator modulates the frame synchronization mechanism of the transmission signal by an OQAM modulation scheme, and modulates the data section by a QAM modulation scheme. The method of claim 2, The modulator modulates the frame synchronization mechanism of the transmission signal by VSB modulation, and modulates the data interval by OQAM modulation. The method of claim 2, The modulator modulates the frame synchronization mechanism of the transmission signal using a QAM modulation scheme, and modulates the data section with an OQAM modulation scheme. The method of claim 2, And the modulator modulates the frame synchronization mechanism of the transmission signal by an OQAM modulation scheme and modulates the data section by a VSB modulation scheme. The method of claim 2, The modulator modulates the frame synchronization mechanism of the transmission signal using a QAM modulation scheme, and modulates the data interval with a VSB modulation scheme. The method according to any one of claims 3 to 8, The modulation unit modulates the sampling frequency of the VSB modulation method and the sampling frequency of the OQAM modulation method to be equal to each other, and the sampling frequency of the QAM modulation method is 1/2 of the sampling frequency of the VSB modulation method and the OQAM modulation method. Single carrier transmission system, characterized in that. The method of claim 9, Wherein the section discriminating unit, the modulating unit, and the modulating information transmitting unit are applicable to the ADTB-T standard and / or the CDTB-T standard of the Chinese single carrier system. In the single carrier transmission method for modulating and transmitting the input frame unit of the transmission signal in a single carrier modulation method, Determining a frame moving period and a data period of the transmission signal; And And modulating each of the sections determined by the section discriminating unit using a predetermined single carrier modulation method. The method of claim 11, And transmitting information on the modulation scheme of each section to the receiving side through the frame synchronization period. The method of claim 12, And wherein the modulation step modulates the frame synchronization period of the transmission signal by VSB modulation, and modulates the data interval by QAM modulation. The method of claim 12, And wherein the modulation step modulates the frame synchronization mechanism of the transmission signal by OQAM modulation, and modulates the data interval by QAM modulation. The method of claim 12, The modulating step is characterized in that the frame synchronization period of the transmission signal is modulated by the VSB modulation method, and the data section is modulated by OQAM modulation method. The method of claim 12, And wherein the modulation step modulates the frame synchronization mechanism of the transmission signal using a QAM modulation scheme and modulates the data interval with an OQAM modulation scheme. The method of claim 12, And wherein the modulation step modulates the frame synchronization mechanism of the transmission signal by OQAM modulation and modulates the data interval by VSB modulation. The method of claim 12, And wherein the modulation step modulates the frame synchronization mechanism of the transmission signal by a QAM modulation scheme and modulates the data interval by a VSB modulation scheme. The method according to any one of claims 13 to 18, In the modulation step, the sampling frequency of the VSB modulation method and the sampling frequency of the OQAM modulation method are the same, and the sampling frequency of the QAM modulation method is 1/2 of the sampling frequency of the VSB modulation method and the OQAM modulation method. Single carrier transmission method characterized in that for modulating. The method of claim 19, Wherein the section discriminating step, the modulating step, and the modulating information transmitting step are applicable to the ADTB-T standard and / or the CDTB-T standard of a Chinese single carrier system.