KR100294709B1 - Method and apparatus for digital modulation in Transceiver of Digital Television - Google Patents

Abstract

The present invention provides a digital modulation method in a digital TV transmitter suitable for directly modulating a video and audio MPEG-II ((MPEG-II) transport stream received by a digital TV transmitter without being converted into analog. In the digital TV transmitter according to the present invention, a digital modulation method includes delaying an input digital signal to generate a first signal and a second signal having different phases, and generating the first signal. And multiplying the second signal by the digital value of the carrier frequency to adjust the frequency of the band to be transmitted, and converting the adjusted first signal and the second signal into analog signals and sequentially outputting the same. Generated by surrounding noise of modulator or environmental noise such as signal line during analog modulation It is to minimize phase distortion it is possible to transmit a clear image and an audio signal, and can reduce the influence of the adjacent channels caused by the phase distortion that occurs when the analog modulation.

Description

Method and apparatus for digital modulation in digital TV transmitter {Method and apparatus for digital modulation in Transceiver of Digital Television}

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to digital TV, and in particular, a video and audio MPEG-II (Moving Picture Experts Group, hereinafter abbreviated as MPEG-II) received after being compressed by a digital TV transmitter, without converting a transport stream into analog A method and apparatus for digital modulation in a digital television transmitter adapted to direct digital modulation.

In general, a digital TV transmitter converts a digital signal of a compressed MPEG-II transport stream into an analog signal, modulates the converted analog signal into a frequency of a band to be transmitted, and transmits the signal over an air interface.

Modulation that adjusts the baseband frequency to the intermediate frequency band to be transmitted can be performed in various ways depending on the service objectives and requirements of the system.However, in digital TV, 8T-VSB (Vestigial Side Band) is used. Use The VSB method uses a filter that smoothly cuts off sidebands when modulating and transmits transmission signals such as TV video, facsimile, and high-speed data in which the power spectrum is spread to a low frequency region. It is a way to leave. Using the VSB scheme, the frequency occupied band in which only a predetermined extra bandwidth is added to the digital signal width can be used, thereby reducing the required occupied bandwidth in half and efficiently using a transmission frequency.

1 is a block diagram showing a digital TV transmitter according to the prior art.

Referring to FIG. 1, an MPEG-II transport stream compressed and received from a relay station during broadcasting in a digital TV is input to a modulator 100 of a transmitter.

The modulator 100 converts the MPEG-II transport stream having the input baseband frequency into analog, modulates the signal in an 8T-VSB scheme, and adjusts the frequency up to a signal having an intermediate frequency.

The filter 110 converts the signal modulated and outputted through the modulator 100 into airwaves that can be transmitted on the air interface, and the converted signal is amplified by more than 1 kHz by the high power amplifier 120 so that the antenna ( 130).

The configuration diagram of the modulator in the digital TV transmitter configured as described above is shown in FIG. 2.

Referring to FIG. 2, the phase delay unit 200 performs a Hilbert Transform on a received MPEG-II transport stream to generate an I signal and a Q signal having a phase difference of 90 degrees. At this time, the I signal and the Q signal occupy a 12 MHz band, which is twice the frequency occupied by the video signal. Subsequently, I and Q signals, which are digital signals, are converted into analog signals through digital / analog converters 210 and 220, respectively, and are input to the quadrature modulator 230.

The first mixer 231 of the quadrature modulator 230 multiplies the input I signal by the cosine carrier CosWct, and the second mixer 232 multiplies the input Q signal by the sinusoidal carrier SinWct, respectively. That is, the baseband I and Q signals are modulated into the intermediate frequency band by multiplying the cosine waveform having the carrier frequency (Wct) of the band to be modulated by the I signal and multiplying the sine waveform and the Q signal.

Then, the I and Q signals modulated in the intermediate frequency band are added to each other in the adder 234 and transmitted to the antenna (not shown). In this case, the signal output from the adder 232 occupies 6 MHz, such as a frequency band occupied by the transmitted video and audio.

However, the modulator of the conventional digital TV transmitter has the following problems.

First, in the process of converting an MPEG-II transport stream, which is a digital signal, to an analog signal, and modulating the converted analog signal, the modulated signal is phase-distorted and outputted due to noise included in signal lines between elements constituting the modulator.

In other words, the process of generating I and Q signals through Hilbert transform in a phase delay unit, converting baseband digital signals into analog signals, and converting baseband analog signals into intermediate frequency signals However, the phase distortion degree of the transmission signal due to the noise included in the signal lines between the elements constituting the modulator finally affects the I and Q signals, so that the I and Q signals cannot be modulated in synchronization with each other, and thus the signal output from the adder. The VSB waveform of is distorted.

Secondly, the components of the digital TV transmitter and the peripheral components of the modulator are degraded, or a slight change in characteristics occurs due to environmental changes such as temperature and humidity, which causes phase distortion of the modulated signal of the MPEG-II transport stream. .

For this reason, the video and audio data broadcast on the digital TV and the video and audio data broadcast on the adjacent channel are distorted and transmitted, thereby providing an unstable broadcasting service to the viewer.

Accordingly, an object of the present invention has been made in view of the above-mentioned problems of the prior art, and digital in a digital TV transmitter that directly modulates an MPEG-II transport stream input to a digital TV transmitter without converting it into an analog signal. To provide a modulation method and apparatus.

According to an aspect of the present invention for achieving the above object, the digital modulation method in the digital TV transmitter, generating a first signal and a second signal having a different phase by delaying the input digital signal; Multiplying the first signal and the second signal by a digital value of a carrier frequency to adjust the frequency of the band to be transmitted, and converting the adjusted first signal and the second signal into an analog signal and sequentially outputting the same. Is done.

Preferably, the frequency adjustment selects, at predetermined intervals, a sampling value for a cosine waveform having the carrier frequency already stored, and multiplies the first signal, and a sampling value for the sine waveform having the carrier frequency already stored. Is selected at predetermined intervals and multiplied by the second signal.

According to another aspect of the present invention for achieving the other object as described above, the digital modulation apparatus in the digital TV transmitter is a channel coding unit for coding and encoding the input digital signal, and the output signal of the channel coding unit phase delayed predetermined A phase delay for generating a first signal and a second signal having a phase difference, a synchronization processor for receiving the first signal and synchronizing with the second signal, a phase synchronization loop for generating a carrier frequency, and the phase synchronization A frequency booster for adjusting the carrier frequency generated in the loop to a carrier frequency of a band to be transmitted, and a sine / cosine calculator for outputting a digital value obtained by sampling a sine / cosine waveform having the carrier frequency stored at predetermined intervals. And a first signal output from the synchronization processor and the sine / cosine. A first multiplier for adjusting the frequency of the first signal by multiplying the digital values output from the calculator and a digital value for outputting the second signal and the digital value output from the sine / cosine calculator to adjust the frequency of the second signal A second multiplier, a first adder that adds the first signal and a second signal that are frequency-adjusted and output from the first multiplier and the second multiplier, and a digital signal that converts the digital signal output from the first adder into an analog signal It consists of an analog converter.

Preferably, a third multiplier multiplying the first signal output from the phase delay unit and a phase error value detected according to the degree of phase distortion of the converted analog signal, and the output signal of the third multiplier and the phase delay unit. And a second adder for compensating for the degree of phase distortion of the sensed analog signal by adding a second signal output from the second signal.

The sine / cosine calculator may further include a memory for storing a digital value of the sine / cosine waveform, a counter for providing a value for selecting a digital value stored in the memory at predetermined intervals, and a value provided with the counter. Accordingly, the decoder is configured to select and output digital values stored in the memory at predetermined intervals.

1 is a block diagram of a digital TV transmitter according to the prior art.

2 is a block diagram of a modulator shown in FIG.

3 is a block diagram of a digital modulator in a digital TV transmitter according to the present invention.

4 is a view for explaining the operation of the cosine operator and the sine calculator shown in FIG.

* Description of the symbols for the main parts of the drawings *

301: channel coding unit 302: symbol frequency generator

303: phase delay unit 304: synchronization processing unit

305, 308, 320: Multiplier 306: Cosine operator

307: Sin calculator 309, 321: Adder

310: frequency uplinker 311: carrier frequency phase locked loop

312: D / A converter 313, 315: filter

314, 316: amplifier 317: log amplifier

318: A / D converter 319: central processing unit

Hereinafter, a configuration and an operation according to an exemplary embodiment of the present invention will be described with reference to the accompanying drawings.

The digital modulation apparatus according to the present invention is to convert the modulated MPEG-II transport stream signal, which is a digital signal input to a conventional digital TV transmitter to an analog signal, and then modulate the digital modulation without converting the analog signal into an analog signal. A clear VSB waveform can be output.

3 is a block diagram illustrating a digital modulator in a digital TV transmitter according to the present invention.

Referring to FIG. 3, the digital modulator according to the present invention randomizes and codes an input MPEG-II transport stream, and a signal output from the channel coding unit 301. Phase retarder 90 degrees with Hilbert transform to generate an I signal and a Q signal, a synchronization processor 304 for synchronizing the phases of the I signal and the Q signal, and a phase with respect to the carrier frequency Wc. A carrier frequency phase synchronization loop 311 that generates a carrier frequency in synchronization, a frequency upgrader 310 that adjusts the carrier frequency up to a band to be transmitted, and uplinks the carrier frequency to a carrier frequency (Wc) band; A sine calculator 307 for outputting a digital value of a sinusoidal waveform having a carrier frequency at predetermined intervals, and a cosine (Cos) waveform having an upwardly adjusted carrier frequency at a predetermined interval. Multiplying the cosine operator 306 for outputting the hair value, the first multiplier 305 for multiplying the I signal and the digital value output from the cosine operator 306, and the digital value output from the Q signal and the sine operator 307. An adder 309 and an adder 309 that add an I signal and a Q signal which are output after being adjusted to a carrier frequency band through a second multiplier 308, a first multiplier 305, and a second multiplier 308. Digital to analog converter 312 for converting the digital signal output from the analog signal to transmit over the air interface. Here, the filter 313 and the termination output amplifier 314 which are not described here are filtered and amplified and transmitted to an antenna (not shown) so that the analog signal output from the digital-to-analog converter 312 can be transmitted over the air interface.

Further, narrowband filter 315, narrowband amplifier 316, log amplifier 317, anilolog / digital converter 318, central processing unit 319, third multiplier 320, and second adder 321. ) Is a phase compensation circuit for detecting a phase distortion of a modulated output signal and calculating a phase compensation value accordingly.

The operation of the digital modulator configured as described above will be described next.

First, the MPEG-II transport stream, which is a digital signal compressed and transmitted by a broadcasting station, is input to a transmitter of a digital TV. Then, the channel coding unit 301 included in the digital modulator of the transmitter performs channel coding and error correction on the input MPEG-II transport stream to withstand the noise and noise of the wireless environment.

Subsequently, the digital modulator generates I and Q signals, which are digital signals according to the 8T-VSB standard, in order to modulate the channel-coded signals in the 8T-VSB scheme. That is, the signal channel-coded and output through the channel coding unit 301 is input to the phase delay unit 303, and the phase delay unit 303 receives the input signal using a Hilbert transform that phase delays the signal by 90 degrees. It is generated by the in-phase I signal and the Q signal which is phase shifted by 90 degrees.

The digital modulator first adjusts the frequency of the generated I and Q signals to the frequency of the band to be transmitted, that is, to the carrier frequency band (i.e., to modulate), first through the synchronization processor 304. Synchronize the Q signals with each other. This is because the phases of the I and Q signals generated by the phase delay unit 303 may not coincide with each other.

On the other hand, the carrier frequency phase lock loop (PLL) 311 performs phase synchronization with respect to the carrier frequency to generate an accurate carrier frequency, and the frequency uplinker 310 is generated in the carrier frequency phase lock loop 311. The carrier frequency is adjusted to a carrier frequency (ie, 46 MHz), which is a band for transmitting the carrier frequency, and input to the cosine operator 306 and the sine operator 307.

The cosine calculator 306 and the sine calculator 307 respectively output a cosine waveform having an input carrier frequency and a digital value obtained by sampling a sine waveform at predetermined periods.

Then, the first multiplier 305 multiplies the I signal input after synchronization with the Q signal through the synchronization processor 304 and the digital value output from the cosine operator 306, and the second multiplier 308 is in phase. The frequency of the I signal and the Q signal is adjusted upward to the carrier frequency band by multiplying the Q signal outputted by the phase shifter 90 degrees from the delay unit 303 and the digital value output from the sine operator 307.

As described above, the digital modulator according to the present invention uses the cosine operator 306 and the sine operator 307 to digitally modulate the I and Q signals, which are digital signals, in the first multiplier 305 and the second multiplier 308 into a carrier frequency band. ) Is further provided.

The first adder 309 then adds the I and Q signals digitally modulated in the carrier frequency band through the first multiplier 305 and the second multiplier 308. The digital-to-analog converter 312 then converts the modulated digital signal output from the first adder 309 into an analog signal for transmission over the air interface. At this time, the digital-to-analog converter 312 operates in synchronization with the synchronization information of the carrier frequency provided by the frequency uplinker 311.

According to this digital modulation process, the analog signal output from the digital-to-analog converter 312 becomes a VSB waveform which is the final modulated signal.

Meanwhile, the filter 313 filters the analog signal output from the digital-to-analog converter 312, and the terminating output amplifier 314 amplifies the filtered analog signal to have power for transmitting on the air interface, and then the antenna (not shown). Transfer it. In this case, the termination output amplifier 314 amplifies all signals of 38 MHz to 50 MHz, which is twice the channel to be transmitted, to compensate for nonlinear components that may occur after amplifying the analog signal.

FIG. 4 is a block diagram illustrating the cosine operator and the sine calculator shown in FIG. 3 and illustrates the operations of the cosine operator and the sine operator in more detail.

Referring to FIG. 4, a cosine calculator and a sine calculator are configured to store the digital values stored in the memory 402 and 403, and the digital values stored in the memory 402 and 403. The N bit counter 400 provides a value for selecting at predetermined intervals, and the digital values (ie, sampling values) stored in the memory 402 and 403 according to values provided by the N bit counter 400. It consists of a decoder 401 to select and output.

In the operation of the cosine operator 306 and the sine operator 307 configured as described above, the N-bit counter 400 first adjusts the frequency of the frequency uplinker 310 to 46 MHz and outputs the carrier frequency by 2 ^N periods. In this case, N is a value of 3 or more. In the embodiment of the present invention, assuming that N = 3, since 2 ^N is 8, the N bit counter 400 outputs a sampled value of a cosine waveform having a carrier frequency and a sine waveform at intervals of 8 per period.

In this case, digital values obtained by sampling the sine waveform and the cosine waveform having the carrier frequency are already stored in the memories 402 and 403. Supposing that the sampling values (i.e., digital values of the carrier frequency) are sine 1 to sine 8 and cosine 1 to cosine 8, sine 1 to 8 are stored in the memory 402, and cosine 1 to cosine 8 Is stored in the memory 403.

Then, the decoder 401 selects sampling values stored in the memory 402 and 403 at predetermined intervals (that is, intervals sampled eight times per period) according to the value N provided by the counter 400. In order to synchronize the signal with the Q signal, select and output them in order.

For example, cosine 1 is output at a value corresponding to I1 in the I signal, and sine 1 is output at a value corresponding to Q1 in the Q signal.

As described above, the present invention has the following effects.

First, since digital modulation is directly performed by the modulator of the digital TV transmitter, it is possible to minimize phase distortion caused by environmental noise such as a peripheral element of the modulator or a signal line during analog modulation, so that a clear image and audio signal can be transmitted.

Second, it is possible to reduce the influence of the adjacent channel due to the phase distortion generated during analog modulation.

Third, the number of signal lines and peripheral elements used in the conventional analog modulation can be reduced, thereby reducing the installation and maintenance cost of the modulator and reducing the failure rate.

Claims (5)

Delaying an input digital signal to generate a first signal and a second signal having different phases; Multiplying the first signal and the second signal by a digital value of a carrier frequency to adjust the frequency of the band to be transmitted; And converting the adjusted first signal and the second signal into an analog signal and outputting the analog signal sequentially. The method of claim 1, wherein the frequency adjustment step, Select a sampling value for the cosine waveform having the carrier frequency already stored at a predetermined interval to multiply the first signal, and select a sampling value for the sine waveform having the carrier frequency already stored at a predetermined interval to The digital modulation method in a digital TV transmitter, characterized in that multiplying by the second signal. A channel coding unit for coding and encoding an input digital signal, A phase delay unit configured to delay the output signal of the channel coding unit to generate a first signal and a second signal having a predetermined phase difference; A synchronization processor configured to receive the first signal and synchronize the second signal; A phase locked loop generating a carrier frequency, A frequency booster for adjusting the carrier frequency generated in the phase locked loop to a carrier frequency of a band to be transmitted; A sine / cosine calculator for outputting a digital value sampled at predetermined intervals from a sine / cosine waveform having the carrier frequency already stored; A first multiplier for adjusting the frequency of the first signal by multiplying the first signal output from the synchronization processor and the digital value output from the sine / cosine calculator; A second multiplier for adjusting the frequency of the second signal by multiplying the second signal by a digital value output from the sine / cosine calculator; A first adder for adding the first signal and the second signal which are frequency-adjusted and output by the first multiplier and the second multiplier, And a digital to analog converter for converting the digital signal output from the first adder into an analog signal. The apparatus of claim 3, further comprising: a third multiplier multiplying the first signal output from the phase delay unit and a phase error value detected according to a degree of phase distortion of the converted analog signal; And a second adder for compensating for the amount of phase distortion of the sensed analog signal by adding the output signal of the third multiplier and the second signal output from the phase delay unit. Device. The method of claim 3, wherein the sine / cosine calculator, A memory for storing a digital value of the sine / cosine waveform; A counter for providing a value for selecting digital values stored in the memory at predetermined intervals; And a decoder configured to select and output digital values stored in the memory at predetermined intervals according to values provided by the counter.