KR20000010409A - Sending and receiving system of digital television - Google Patents

Abstract

PURPOSE: A sending and receiving system of a digital TV is provided to reduce the distortion of signal and therefore enhancing the performance sending and receiving system by lowering the peak level of the final analog sending signal. CONSTITUTION: The sending and receiving system of a digital TV in which a signal is transmitted in an OFDM signal after the transferring steps of external interleave, inside interleave, mapping, OFDM transition protection interval insertion and analog transferring comprises an interleaver control part which outputs the inside interleaving controlling signal; and an inside interleaver (613) which outputs for mapping after carrying out the interleaving per bit. The system comprises a program multiplying part(601), a splitter(603), an energy dispersing part(604), an external coder(605), internal coder(607), a mapper(613), a frame adapting part(616), an ODFM changing part(617), D/A transferring part(619) and a front end(620).

Description

Digital TV transmission system and reception system

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a transmission method of a European digital TV system. In particular, an Orthogonal Frequency Division Multiplex (OFDM) method using multiple carriers provides a peak to average power for peaks during data transmission. The present invention relates to a digital TV transmission system and a reception system.

Digital TV transmission can be classified into a single carrier modulation method using a single carrier and a multicarrier modulation method for transmitting desired data using a plurality of multiple carriers. . That is, the transmission method of the digital TV is classified into a residual side band (VSB) method using one single carrier and an OFDM method using a plurality of carriers.

Of these, the OFDM method, which is defined as the current terrestrial digital broadcasting system for Europe, is very resistant to ghosts caused by multipath channels and is easy to estimate based on pilot signals. Is the standard for digital broadcasting. The OFDM scheme is further divided into a 2K mode of 1705 carriers and an 8K mode of 6817 carriers according to the number of carriers in an OFDM symbol.

In addition, such OFDM is used to map and transmit data in a manner called quadrature amplitude modulation (QAM). The modulation schemes mainly used are quadrature phase shift keying (QPSK), 16-QAM, and 64-QAM. That is, in order to transmit desired data by the OFDM scheme, first, the data is mapped by one of the three modulation methods described above, followed by an Inverse Fast Fourier Transform (IFFT), and then inserted by a guard interval. Do it. The transmitted data undergoes the reverse process of the transmitting end at the receiving end. First, the FFT is performed and then de-mapped in reverse according to the mapping method of the transmitted data.

FIG. 1 is a block diagram of a conventional digital video broadcasting-terrestrial (DVB-T) transmission system using the OFDM scheme, and its standard is defined in ETS 300 744. FIG.

That is, the program multiplexer 101 multiplexes sources such as video, audio, and data information, and the transport multiplexer 102 multiplexes one or more programs output from one or more program multiplexers to one channel. Usually, three to five programs can be multiplexed within the existing analog channel 6-8 MHz band, depending on the quality of the program.

After the multiplexing process is performed in the transport multiplexer 102, a transport stream (TS) is created in units of 204 bytes, and the splitter 103 is used to generate a high priority and a high priority according to the importance of the signal itself. Processing is divided into two signals of low priority.

At this time, a signal having a large amount of information can be used for moving object reception through a higher priority process, and a signal having a small amount of information can be used for moving object reception through a lower priority process. In this case, two energy dispersing units, two external coders, an external interleaver, and two internal coders are required. However, due to the complexity of the implementation, only non-hierarchical modes without splitters are used in earlier products (now terrestrial digital in the UK).

Therefore, the 204-byte TS output from the transistor multiplexer 602 is input to the energy dissipation unit 104 of the terrestrial channel adapter directly or through a splitter 603. The energy dissipator 104 prevents signal concentration through energy dispersal of the input TS so that the average signal power is zero. In order to prepare for the burst error, the external coder 105 performs external coding and then performs the time base interpolation in the external interleaver 106. The external interleaver 106 interpolates data in units of blocks to prevent the signal from being concentrated in one place even if an error occurs through the channel.

Next, the internal coder 107 performs internal coding to recover the error in units of bits, and then the internal interleaver 108 performs interpolation of the frequency axis. In other words, when data is transmitted by interpolation at the transmitter side, frequency null generated in a specific part of the transmission frequency band is divided into all frequency bands and spread to the frequency null generated in a multipath channel environment. It can improve the performance deterioration.

In this case, the internal interleaver 108 is composed of a bit interleaver and a symbol interleaver, and the bit interleaver interpolates digital data to be transmitted in units of bits of a predetermined size. The symbol interpolator interleaves the data interpolated in bit units again in OFDM symbol units.

FIG. 2 is a detailed block diagram of the internal interleaver 108. When the modulation scheme is 16-QAM, since 1 QAM symbol is 4 bits, the internal interleaver 108 includes the demultiplexer 201 and the first to fourth bits. Interpolators 202 to 205 and symbol interpolators 206. Here, one QAM symbol corresponds to one transmission carrier.

Since the demultiplexer 201 has 4 bits when the internal coded data is a 16-QAM symbol, the first bit data of the internal coded data is the first bit interpolator 202, and the second bit data is the second bit. The interpolator 203 outputs the third bit data to the third bit interpolator 204 and the fourth bit data to the fourth bit interpolator 205.

The first to fourth bit interleavers 202 to 205 each have a memory corresponding to one block size (= 126 bits is one block size in an OFDM system). The order is different. That is, the first bit interpolator 202 stores the input data and then moves to the I0 pass, the second bit interpolator 203 to the I1 pass, the third bit interpolator 204 to the I2 pass, and the fourth bit. The interpolator 205 reads the I3 paths and outputs them to the symbol interpolator 206. Each pass has a different order of reading data from the memory.

In this case, the data output order of each bit used for the internal interpolation is fixed for each pass, and the expression of the interpolation method in the non-hierarchical 16-QAM is expressed as Equation 1 below.

Blocksize = 126 bits

Order entered

B (e) = (b _{e, 0} , b _{e, 1} , b _{e, 2} , ..., b _{e, 125} )--e = 0 to 3

Order of output

A (e) = (a _{e, 0} , a _{e, 1} , a _{e, 2} , ..., a _{e, 125} )

a _{e, w} = b _{e, He (w)} , W = 0,1,2, ..., 125

I0: H ₀ (W) = W

I1: H ₁ (W) = (W + 63) mod 126

I2: H ₂ (W) = (W + 105) mod 126

I3: H ₃ (W) = (W + 42) mod 126

First, assuming block size N = 126 bits, H (w) represents when shifted by the relationship of the above equation (1). Here, e varies depending on the QAM method, that is, the constellation number. For 16QAM, e has a value of 0 to 3, and for 64QAM, 0 to 5 has a value.

For example, in order to perform interpolation in the third bit interpolator 204, substituting the w value from 0 to 125 into I2: H ₂ (W) = (W + 105) mod 126 of Equation 1 above,

H ₂ (0) = (0 + 105) mod 126 = 105

H ₂ (1) = (1 + 105) mod 126 = 106

. .

. .

. .

H ₂ (20) = (20 + 105) mod 126 = 125

H ₂ (21) = (21 + 105) mod 126 = 0

H ₂ (22) = (22 + 105) mod 126 = 1

. .

. .

. .

H ₂ (124) = (124 + 105) mod 126 = 103

H ₂ (125) = (125 + 105) mod 126 = 104

Becomes

That is, data inputted in the order of 0, 1, 2, ..., 125 is outputted in the order of 105, 106, 107, ..., 0, 1, ..., 104 on the output side.

Therefore, the first input data is output first in the first bit interpolator 202, the 63rd input data is output first in the second bit interpolator 203, and the third bit interpolator ( In step 204, the 105th input data is output first, and in the fourth bit interpolator 205, the 42nd input data is output first. The bits interleaved by the first to fourth bit interpolators 202 to 205 are output to the symbol interpolator 206 while forming a 4-bit QAM symbol.

The symbol interpolator 206 again interpolates the data input from the first to fourth bit interpolators 202 to 205 in OFDM symbol units. The bit order of the QAM symbol is not changed here.

On the other hand, the internal interleaved data in the internal interpolator 108 is mapped to the frame adaptation unit 110 by mapping the mapper 109 in a method called quadrature amplitude modulation (QAM) in the mapper 109, and a modulation scheme mainly used is QPSK ( Quadrature Phase Shift Keying), 16-QAM, 64-QAM.

The frame adaptation unit 110 combines a pilot representing a transmission-related information generated by the pilot and the TPS information generator 111 and a transmission parameter signaling (TPS) carrier to the data mapped by the mapper 109. The OFDM modulator 112 outputs the OFDM data to the D / A converter 113 by inserting a guard interval after OFDM modulation on a frame basis. . Here, one frame consists of 68 OFDM symbols.

In addition, the OFDM data inserted with the guard interval is converted into a baseband analog signal by the D / A converter 113, is moved to RF through a front end 114, amplified, and then transmitted.

In this case, when the analog form of the internal OFDM signal is described in detail, the signal input to the OFDM modulator 112 is actually a randomized signal through the energy distributing unit 104 and the interpolators 106 and 108.

In addition, the relationship between the input signal (C _{n, k} ) and the output signal (s (t)) of the OFDM modulator 112 is represented by the following equation (2).

In Equation 2, one symbol in s (t) is added after N C _{n, k} are modulated by g _k (t).

Therefore, when four N-bit QAM symbols (16QAM) are modulated by each carrier and added together, the maximum possible energy and average amplitude energy of the signal can be obtained based on a uniform 16QAM constellation. Equation 3 is as follows.

to be.

In the case of uniform QPSK, the following equation (4) is used.

Becomes

After all, the average power for the peaks at QPSK and 16-QAM is 1.8 times higher at 16-QAM, which indicates that the dynamic range (DR) of the amplifier in the front end 114 of the transmitter must be 1.8 times greater at 16-QAM. Thus, it can be seen that in the case of uniform 64-QAM and non-uniformity, the change in its DR is greater so that the amplifier of the transmitter must have a very high DR in order to achieve the rarest maximum signal power. FIG. 5 shows an almost noise-like form of an OFDM signal viewed from the time axis, and a rare peak signal, for example, a peak signal that is out of threshold, requires an amplifier having a high DR in a digital TV transmitter.

FIG. 3 is a block diagram illustrating a DVB-T receiving system capable of receiving a transmission standard of ETS 300 744. The reverse process of the transmission system is illustrated. That is, the data tuned by the tuner 301 is converted into a digital signal by the A / D converter 302, and after the guard period is deleted by the guard period deleting unit 303, in the frame unit by the OFDM demodulator 304. Demodulated After the OFDM demodulated data is equalized in the equalizer 305 to compensate for the carriers distorted by the channel, the OFDM demodulated data is reversely demapped according to the mapping method of the data transmitted by the demapper 306. 4 is a constellation diagram in a uniform 16-QAM used for demapping. Since one symbol is composed of 4 bits, two bits are divided into a real axis and an imaginary axis, respectively, and then real and imaginary axes are transmitted. An example of the case where a bit value is mapped in accordance with -3, -1,1,3 is shown.

In this case, the data extractor 307 extracts a pilot signal and TPS information from the OFDM demodulated data, so that the tuner 301, the guard interval deletion unit 303, the OFDM demodulator 304, the equalizer 305, And control the operation of the demapper 306. Meanwhile, the demapped data is internally decoded by the internal decoder 309 after deinterpolation is performed in units of symbols and bits in the internal deinterleaver 308. The internal decoded data is externally decoded by the external decoder 311 after the external deinterpolation is performed by the external deinterleaver 310. The externally decoded data is converted into data before the interpolation of the transmitting end in a derandomizer 312. If a splitter is used at the transmitter, an internal decoder 313, an external deinterleaver 314, an external decoder 315, and a derandomizer 316 are separately required at the receiver, and are synthesized by the splitter 317 to transport the stream. It is output as (TS).

Meanwhile, in order to implement an OFDM type digital TV transmission system, it is mentioned that an amplifier having a high dynamic range (DR) is required due to the characteristics of the OFDM signal itself. Therefore, if the RF power amplifier having a small DR is used in the digital TV transmitter as shown in FIG. 1, this causes distortion in the receiver as shown in FIG.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to reduce a large peak power that is randomly required below a threshold, so that distortion in a receiver while using an RF power amplifier having limited DR in a digital TV transmitter is limited. To provide a digital TV transmission system and a reception system that reduce the.

1 is a block diagram of a conventional digital TV transmission system

Figure 2 is a detailed block diagram of the internal interleaver of Figure 1

3 is a block diagram of a conventional digital TV receiving system

4 is a typical uniform 16-QAM constellation

5 is a waveform diagram of an OFDM signal viewed from a time axis

6 is a block diagram of a digital TV transmission system according to the present invention.

7 is a detailed block diagram of the determining unit of FIG. 6.

FIG. 8 is a detailed block diagram of the internal interleaver of FIG. 6.

9 is a block diagram of a digital TV receiving system according to the present invention;

Explanation of symbols for main parts of the drawings

601 program multiplexer 602 transport multiplexer

603: Splitter 604,609: Energy Dispersion

605,610: external coder 606,611: external interleaver

607,612: Internal coder 608,613: Internal interleaver

614: interpolation control unit 614-1: peak detection unit

614-2: discrimination unit 615: pilot and TPS information generation unit

616: frame adaptor 617: OFDM modulator

618: protection interval insertion unit 619: D / A conversion unit

620: Front end

Digital TV transmission system according to the present invention for achieving the above object, through the external interpolation, internal interpolation, mapping, OFDM modulation, guard interval insertion, and analog conversion process for the transport stream multiplexed with one or more programs A digital TV transmission system for transmitting an OFDM signal, comprising: an interpolation control unit for detecting a peak value of the analog signal, comparing whether the peak value is larger than a predetermined threshold value, and outputting an internal interpolation control signal according to a comparison result; When the input of the corresponding data is completed, the interpolation rule is controlled by the interpolation control unit to perform an interpolation for each bit, and includes an internal interleaver for output for mapping.

The interpolation control unit compares a peak detection unit detecting a peak value from the analog signal with a predetermined threshold value and an output of the peak detection unit, increases the index of the internal interpolator according to a comparison result, and transmits the information to the transmission parameter signal TPS. Characterized in that it comprises a determination unit for carrying information.

The internal interpolator repeats the process of performing interpolation again by applying the increased index to one block each time the index provided by the interpolation controller increases, until all OFDM signals within one block are below a threshold. It features.

The internal interleaver is characterized in that the output order of the input data is changed each time the index provided by the interpolator control increases.

The digital TV reception system according to the present invention is a digital TV reception system for demodulating an original signal through an OFDM demodulator, an equalizer, a demapper, an internal deinterleaver, and an external deinterleaver. When the inserter completes input of data corresponding to one block size, the deinterpolation rule is changed according to the interpolation control signal extracted from the TPS information transmitted from the transmitting side, and the deinterpolation is performed for each bit, and then output for external deinterpolation. It is characterized by.

According to such a digital TV transmission system and a reception system, it is possible to reduce distortion in a receiver while using an RF power amplifier having a limited DR in the digital TV transmission end.

Other objects, features and advantages of the present invention will become apparent from the following detailed description of embodiments taken in conjunction with the accompanying drawings.

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

6 is a block diagram of a digital TV transmission system according to the present invention, which includes a program multiplexer 601, a transport multiplexer 602, a splitter 603, an energy dissipator 604, an external coder 605, External Interleaver 606, Internal Coder 607, Internal Interleaver 608, Mapper 613, Interpolator 614, Pilot and TPS Information Generator 615, Frame Adapter 616, OFDM Modulation A unit 617, a guard interval insertion unit 618, a D / A converter 619, and a front end 620 are included.

That is, the difference between the conventional digital TV transmission system and the intermittent control unit 614 is added, the internal interleaver 608 performs the internal interpolation while changing the index value by the control of the intermittent control unit 614, It is different to carry an index on a TPS signal when there is no peak value above a threshold in the OFDM symbol.

To this end, the interpolation control unit 614 is a peak detector 614-1 for detecting the peak of the analog signal output from the D / A converter 619, the peak value detected by the peak detector 614-1 A determination unit 614-2 is configured to compare whether the threshold value is greater than a predetermined threshold value and determine the index value and the TPS signal used in the internal interleaver 608 according to the comparison result.

As illustrated in FIG. 7, the determination unit 614-2 receives a peak value detected from an analog signal through a + terminal, and compares a predetermined threshold with a-terminal. The determination unit 702 determines whether the comparison result (a) is greater than zero, and if it is greater than zero, the peak value is larger than the threshold value, so that the index is increased by one and outputted to the internal interleaver 608, which is greater than zero. If it is small, since the peak value is smaller than the threshold value, it is composed of an index output unit 703 that outputs the index value at that time to the pilot and TPS information generator 615.

In the present invention configured as described above, the program multiplexer 601 multiplexes sources such as video, audio, data information, etc., the transport multiplexer 602 multiplexes one or more programs into one channel, and the multiplexed transport stream The energy is dispersed into the energy dissipation unit 604.

In this case, the splitter 603 may be divided into two signals, a high priority and a low priority, according to the importance of the signal itself. In this case, an energy disperser, an external coder, an external interleaver, Two internal coders are required.

On the other hand, the external coder 605 performs an external coding on the energy-dispersed data in the energy dispersing unit 604 and then outputs it to the external interpolator 606 to perform time-base interpolation. The external interleaver 606 interpolates data in units of blocks to prevent the signal from being concentrated in one place even if an error occurs through a channel. Next, the inner coder 607 performs internal coding to recover an error in units of bits and outputs the internal coder 608.

Up to now, the same operation as that of the conventional digital TV transmission system shown in FIG.

In this case, as shown in FIG. 8, when the modulation scheme is 16-QAM, the internal interpolator 608 may include a demultiplexer 801, first to fourth bit interpolators 802 to 805, and a symbol interpolator ( 806, wherein the first to fourth bit interpolators 802 to 805 change each time according to the index i to which the data output order is input.

That is, since the demultiplexer 801 has 4 bits when the internal coded data is a 16-QAM symbol, the first bit data of the 4 bits is the first bit interpolator 802, and the second bit data is the second bit. The interpolator 803 outputs the third bit data to the third bit interpolator 804 and the fourth bit data to the fourth bit interpolator 805.

In this case, the first to fourth bit interpolators 202 to 205 each have a memory corresponding to one block size (= 126 bits is one block size in an OFDM system), and are output from each interleaver. The order of the data depends on the bit interpolation rule and the index i provided by the interpolation control unit 614 as shown in Equation 5 below.

Blocksize = 126 bits

Order entered

B (e) = (b _{e, 0} , b _{e, 1} , b _{e, 2} , ..., b _{e, 125} )--e = 0 to 3

Order of output

A (e) = (a _{e, 0} , a _{e, 1} , a _{e, 2} , ..., a _{e, 125} )

a _{e, w} = b _{e, He (w)} , W = i = 0,1,2, ..., 125

I0: H ₀ (W) = W + i

I1: H ₁ (W) = (W + 63 + i) mod 126

I2: H ₂ (W) = (W + 105 + i) mod 126

I3: H ₃ (W) = (W + 42 + i) mod 126

That is, in the case of the I2 pass, if the input data order is 0,1,2, ..., 125, the data output order is fixed to 105,106,107, ..., 0,1, ..., 104, but the present invention Changes depending on the value of index (i).

For example, if i is 2, the data output order of the I2 pass is 107,108,109, ..., 0,1, ..., 106. That is, the 107th incoming data is output first.

The index (i) value is provided by the interpolation control unit 614.

To this end, the peak detector 614-1 of the interpolation controller 614 detects the peak value of the analog signal output from the D / A converter 619 and outputs the peak value to the discriminator 614-2. 614-2 compares whether the input peak value is larger than a predetermined threshold.

If it is determined by the comparator 701 and the determiner 702 of the discriminating unit 614-2 that the peak value is larger than the threshold value, the index output unit 703 intersects the first to fourth bits of the internal interleaver 608. The index i provided to the inserters 802 to 805 is increased by one (i + 1), and the first to fourth bit interpolators 802 to 805 substitute the increased index i with the above equation (5) for bit interpolation. Do it again.

This process is repeated until all OFDM signals within one block are below the threshold. That is, whenever the peak value exceeds the threshold, bit interpolation is repeatedly performed for one block while increasing the value of i starting from 0 to 125, and then the index i at the moment when all OFDM signals in one block fall below the threshold value is determined by TPS. Is transmitted and received by the receiving system and applied to the internal interleaver. This is because the data order output from the first to fourth bit interpolators 802 to 805 varies depending on the index i, so that the receiver can know the information to accurately perform the interpolation.

As described above, the internal interleaved data in the internal interleaver 608 is mapped by the mapper 613 in a QAM manner and output to the frame adaptation unit 616, and the frame adaptation unit 616 uses the mapper 613. ) Combines the pilot and the TPS information indicating the transmission-related information generated by the pilot and TPS information generator 615 to the data mapped by the outputted data, and outputs the combined data to the OFDM modulator 617. In this case, the TPS information of the pilot and the TPS information generator 615 includes an index i at the moment when all OFDM signals in one block are below a threshold.

The OFDM modulator 617 performs OFDM modulation on the data output from the frame adaptor 616 in units of frames, and then inserts a guard interval in the guard interval inserter 618 to perform a D / A converter 619. Will output The baseband analog signal converted by the D / A converter 618 is moved to RF through the front end 620, amplified and transmitted, and is output to the interpolation controller 614 for peak detection.

9 is a block diagram illustrating a digital TV receiving system according to the present invention capable of receiving a transmission standard of ETS 300 744. The reverse process of the transmission system is performed. At this time, the pilot and TPS information extraction unit 905 is the same as the digital TV reception system of FIG. 3 except that the index i value transmitted from the transmitter is controlled to control the internal deinterleaver 908.

For example, in the pattern I2, when the index i is 2, the internal deinterleaver 908 determines that the 105th input data is first output from the internal interleaver on the transmitting side when there is no information on the index i. The 21st data entered into the internal deinterleaver 908 will be output first. This will cause an error. That is, since the 107th input data is output first on the actual transmitting side, the internal reverse interleaver 908 outputs the 19th data first to become the original order. The pilot and TPS information extraction unit 905 extracts and controls the information on the index i.

On the other hand, the present invention can be applied to the part implementing the system as an amplifier having a small DR by properly combining the signal itself in the amplifier requiring a high DR.

As described above, according to the digital TV transmission system and the reception system according to the present invention, if the peak value of the analog signal in the digital TV transmitter is larger than a predetermined threshold, the process of changing the application method of the internal interleaver performed during channel coding is repeated. By reducing the peak level of the final analog transmission signal below a certain threshold, the distortion of the signal can be reduced while using an amplifier having a small DR, thereby improving the performance of the digital TV transmission system and the reception system. .

Claims (5)

In a digital TV transmission system in which one or more programs are transmitted as an OFDM signal through external interpolation, internal interpolation, mapping, OFDM modulation, guard interval insertion, and analog conversion for a multiplexed transport stream, An interpolation control unit for detecting a peak value of the analog signal and comparing whether the peak value is larger than a predetermined threshold value and outputting an internal interpolation control signal according to a comparison result; When the input of the external interleaved data corresponding to one block size is completed, the interpolation rule is changed by the control of the interpolation control unit to perform interpolation for each bit, and then includes an internal interleaver for output for mapping. Digital TV Transmission System. The method of claim 1, wherein the intermittent control unit A peak detector for detecting peak values from the analog signal, And a discriminating unit comparing the output of the peak detector with a predetermined threshold, increasing the index of the internal interleaver according to a comparison result, and sending index information to transmission parameter signal (TPS) information. The method of claim 2, wherein the determining unit And if it is determined that the peak value detected by the peak detector is larger than a predetermined threshold, the index of the internal interleaver is increased, and if it is determined that the peak value is smaller, the index value of the internal TV is transmitted to the TPS information. The method of claim 1, wherein the internal interleaver Each time the index provided by the interpolation controller increases, the process of bit interpolation for one block according to the interpolation rule to which the increased index is applied is repeated until all OFDM signals within one block are below a threshold. Digital TV Transmission System. In the digital TV receiving system for demodulating the received OFDM signal to the original signal through an OFDM demodulator, equalizer, demapper, internal deinterleaver, external deinterleaver When the internal deinterleaver has completed input of data corresponding to a block size from the demapper, the deinterleaving rule is changed according to the interpolation control signal extracted from the TPS information transmitted from the transmitting side, and then deinterpolation is performed for each bit. Digital TV receiving system characterized by outputting for external deintercalation.