CN1929465A - Digital videocast modulating method and device - Google Patents

Abstract

This invention discloses one digital television broadcast signal modulation method, which comprises the following steps: multiplying data signals, pre-generated frequency characters and synchronous wave load and zero wave load distributed symmetrically, wherein, the said guidance characters occupies one part wave load with each load wave not adjacent distributed; the time area signals adds protection isolation with zero filled to form one OFDM character by use of more than one OFDM character and one front frequency signal to generate base band send signals.

Description

A digital TV broadcast modulation method and device

technical field

The invention relates to the field of digital TV broadcasting, in particular to a modulation method and device for digital TV broadcasting.

Background technique

Digital TV broadcasting is a research and application hotspot in the field of broadcasting technology at present, and many countries have launched their own digital TV broadcasting systems one after another. At present, there are various modulation techniques for digital TV broadcasting, among which, the DVB-T standard adopts Orthogonal Frequency Division Multiplexing (OFDM) modulation in terms of transmission, which belongs to the multi-carrier transmission technique.

Referring to FIG. 1 , the modulation structure of the transmitter defined by the DVB-T standard includes an OFDM modulation unit 100 , a guard interval insertion (CP) unit 104 and a framing unit 105 . Wherein, the OFDM modulation unit 100 includes a serial/parallel conversion unit 101 , an inverse fast Fourier transform unit 102 , and a parallel/serial conversion unit 103 . The serial/parallel conversion unit 101 performs serial/parallel conversion on the received data signal and outputs it to the inverse fast Fourier transform unit 102, and the inverse fast Fourier transform unit 102 performs inverse Fourier transform on the received parallel signal and the received pilot symbol After outputting to the parallel/serial conversion unit 103, after the parallel data signal received by the parallel/serial conversion unit 103 is converted into a serial data signal, it is output to the insertion CP unit 104, and the insertion CP unit 104 receives the serial data signal The CP is inserted into the data signal and sent to the framing unit 105, and the framing unit 105 sends the physical frame composed of the received serial data signal as a baseband transmission signal to the radio frequency unit for processing.

From the above modulation system, CP needs to be inserted into the OFDM modulated signal. Because CP and data have certain correlation characteristics, the receiver can complete timing synchronization by relying on CP. However, transmitting CP needs to consume a certain amount of power. However, fading channels, special values of data signals, etc. will deteriorate the correlation between CP and data, thereby greatly reducing the speed and accuracy of timing synchronization.

Moreover, for all digital broadcasting systems based on OFDM modulation, there is a common problem: the peak-to-average power ratio (PAPR) is generally high, which will directly lead to a decrease in the use efficiency of the power amplifier of the transmitter, especially when the number of carriers is small. When it is large, such as 8k mode of DVB-T, the efficiency of the power amplifier of the transmitter is very low. Unfortunately, the existing DVB-T system does not take this issue into consideration.

Contents of the invention

In view of this, the object of the present invention is to provide a digital TV broadcast modulation method and device, which can improve the speed and precision of timing synchronization.

A kind of digital television broadcast modulation method provided by the present invention is realized like this:

a. Multiplexing the data signal, pre-generated pilot symbols and synchronization band symbols in the frequency domain, and performing OFDM modulation on the multiplexed data to obtain a time domain signal;

The synchronization band symbols include subcarriers that transmit synchronization symbols and zero subcarriers that do not transmit any information; the pilot symbols occupy a part of the subcarriers, and the occupied subcarriers are not adjacent to each other;

b. Add a guard interval before the time domain signal, and fill the guard interval with 0 to form an OFDM symbol;

c. Generating a baseband transmission signal using more than one OFDM symbol and a preamble pilot signal.

After step b and between steps c, it further includes: measuring the peak-to-average ratio of the time-domain signal obtained in step a, and judging whether the peak-to-average ratio is greater than a preset threshold, and if it is greater, using a certain algorithm to adjust Synchronous belt sign, return to step a, otherwise, go to step c.

The guard interval is greater than the maximum delay spread of the physical channel.

The baseband transmission signal is a physical frame, and the pre-pilot is located at any position in each physical frame, or the pre-pilot is located before all OFDM symbols in each physical frame.

The steps of performing OFDM modulation on the multiplexed data to obtain time-domain signals described in step a include:

a1. Serial/parallel conversion of data signals;

a2, performing inverse Fourier transform on the pilot symbol and the synchronous band symbol and the parallel data signal after serial/parallel conversion;

a3. Convert the signal after the inverse Fourier transform into a serial signal to obtain a time domain signal.

A kind of digital television broadcast modulation device provided by the present invention is realized like this:

A signal modulation device for digital television broadcasting, used for modulating data, and sending the modulated baseband transmission signal to a radio frequency unit, the device includes:

OFDM modulation unit (300), guard interval zero insertion unit (304) and framing unit (305), wherein,

An OFDM modulation unit (300), configured to perform OFDM modulation on received data signals, pilot symbols, and synchronous band symbols through frequency domain multiplexing to obtain time domain signals;

A guard interval zero insertion unit (304), configured to add a guard interval to the time-domain signal, and insert 0 into the guard interval to form an OFDM symbol;

A framing unit (305), configured to use a physical frame composed of more than one OFDM symbol and a preamble pilot as a baseband transmission signal to send to the radio frequency unit.

The device further includes: a peak-to-average ratio measurement unit (606) and an adjustment algorithm unit (607), wherein,

The peak-to-average ratio measurement unit (606), used for measuring the peak-to-average ratio of the frequency domain signal output from the OFDM modulation unit (300) output for measuring, judges whether the peak-to-average ratio is greater than a preset threshold, if greater than, the The peak-to-average ratio is fed back to the adjustment algorithm unit (607), if not greater than, the received frequency domain signal is output to the guard interval zero interpolation unit (304);

An adjustment algorithm unit (607), configured to adjust the timing belt symbol according to the received peak-to-average ratio.

The OFDM modulation unit (300) includes a serial/parallel conversion unit (301), an inverse fast Fourier transform unit (302), and a parallel/serial conversion unit (303), wherein,

A serial/parallel conversion unit (301), configured to send the received data signal to the inverse fast Fourier transform unit (302) after serial/parallel conversion;

An inverse fast Fourier transform unit (302), which is used to perform inverse Fourier transform on the received pilot symbols and synchronous band symbols and the parallel data signals after serial/parallel conversion, and then output to the parallel/serial conversion unit (303) ;

A parallel/serial conversion unit (303), configured to convert the inverse Fourier transformed signal into a serial signal, and output it to the guard interval zero interpolation unit (304).

The present invention does not perform CP insertion processing on the data signal after OFDM modulation, but fills 0 in the guard interval, that is, there is no signal, thus saving power consumption. However, since zero padding cannot improve the speed and accuracy of timing synchronization, the present invention introduces a preamble in each frame. The preamble pilot can be obtained by performing inverse Fourier transform on a series of randomly generated sequences (such as PN sequence). Using the good correlation characteristics of the preamble pilot, the receiver can quickly and accurately time it. Although the introduction of pre-pilots will increase a certain power overhead, this overhead (generally <5%) is far less than the power saved by filling 0 (generally 7% to 25%), so the combined modulation not only saves transmission power , and is conducive to fast and accurate timing synchronization.

Therefore, the present invention has following advantages and characteristics:

(1) Adopt the physical frame structure of pre-pilot + OFDM symbol to solve the problem of fast synchronization of signals in digital TV broadcasting system;

(2) Replace the existing CP or PN sequence method with the 0 insertion method, which not only saves power consumption, but also avoids the introduction of interference like the PN method, so that the complexity of the receiver is lower;

(3) Insert continuous and/or scattered pilot symbols in the time-frequency domain to ensure the accuracy of channel estimation;

(4) Part of the subcarriers are used as the synchronization belt, and the frequency offset can be estimated by using the characteristics of the synchronization belt, and it can also be used to reduce the PAPR.

Description of drawings

FIG. 1 is a block diagram of a modulation structure in the prior art;

Fig. 2 is a schematic flow chart of the modulation method of the present invention;

Fig. 3 is a block diagram of the modulation structure of the present invention;

Fig. 4 is the structure of the basic frame of physical layer, wherein N is the integer greater than 1, represents the included OFDM symbol number;

FIG. 5 is a schematic diagram illustrating the structure of various symbols in the time-frequency domain before modulation in FIG. 4;

Fig. 6 is a block diagram of a specific embodiment for realizing the modulation structure of the present invention.

Detailed ways

The present invention does not perform CP insertion processing on the OFDM modulated data signal, but fills the original guard interval with 0, that is, there is no signal, thus saving power consumption. However, since zero filling cannot improve the speed and accuracy of timing synchronization, the present invention introduces a preamble into each frame, and the preamble can be designed to have good correlation characteristics, so that the receiver can quickly and accurately time the timing.

Referring to shown in Figure 2, realizing the method of the present invention comprises the following steps:

Step 200: Generate and store pre-pilot signals, synchronization band symbols and pilot symbols. Both synchronization symbols and pilot symbols can use PN sequences, that is, generate a series of pseudo-random numbers with values {0, 1}, and then map (0->1, 1->-1) into required symbols through BPSK.

The synchronization band symbol includes two kinds of subcarriers, one is the subcarrier that transmits the synchronization symbol, and the other is the zero subcarrier that does not transmit any information. The zero-setting subcarriers are symmetrically distributed on both sides of the subcarriers transmitting the synchronization symbols. The purpose of using the synchronous band symbols is to estimate the frequency offset, and can also be used to reduce the PAPR of the transmitted signal, such as adaptively adjusting the synchronous symbols through the structure of the feedback loop. The pilot symbols only occupy a part of the subcarriers, and the occupied subcarriers are not adjacent to each other, and the positions of the subcarriers can be changed as the symbols change, or can be fixed.

The timing belt is intended for frequency synchronization of OFDM systems. The symbol structure of the synchronization band, pilot symbols and data is shown in Figure 5a. The synchronization zone includes multiple subcarrier groups, and each subcarrier group contains multiple adjacent subcarriers. Except for one subcarrier that transmits synchronization symbols, this subcarrier is called a synchronization zone symbol subcarrier, and all other subcarriers in the group do not transmit information, which is set to zero. The zero-set subcarriers are distributed symmetrically with respect to the synchronous band symbol subcarriers, as shown in Figure 5b. The meaning of symmetrical distribution includes: if there are 2n zero-set subcarriers, then the number of zero-set subcarriers on both sides of the synchronization symbol subcarrier is n; if there are 2n+1 zero-set subcarriers, then the number of zero-set subcarriers on both sides of the synchronization symbol subcarrier The number of zero-setting subcarriers is n and n+1, or n+1 and n, where n is a positive integer. The synchronous belt symbol can be fixed as time changes during the transmission process, and can also be adjusted appropriately as time changes. If the timing belt symbol is adjusted and changed, the receiving end may not know the value information of the timing belt symbol.

Pilot symbols include continuous pilots and scattered pilots. Continuous pilots occupy some fixed subcarriers and continuously send known sequences in time (symbols); while scattered pilots select certain subcarriers to send known sequences in a certain time (symbols), which is characterized in that the pilots are in Both time (symbols) and frequency (subcarriers) are discontinuous.

Step 201: Data, pilot symbols and synchronization band symbols are multiplexed in the frequency domain.

Step 202: performing OFDM modulation on the data signal obtained through frequency domain multiplexing in step 201 to obtain a time domain signal.

The step of performing OFDM modulation on the data obtained through frequency domain multiplexing to obtain a time domain signal includes: performing serial/parallel conversion on the data signal; Inverse Fourier transform; convert the signal after the inverse Fourier transform into a serial signal to obtain a time domain signal.

Step 203: adding a guard interval before the time-domain signal, and filling the guard interval with 0 to form an OFDM symbol. Also, the guard interval is greater than the maximum delay spread of the channel.

Step 204: Generate a physical frame by using more than one OFDM symbol and a pre-pilot, and use the physical frame as a baseband transmission signal.

Referring to FIG. 4 , the physical frame generated in step 204 includes a preamble and several OFDM symbols, and the preamble in each physical frame occupies one or an integer number of OFDM symbols. Moreover, the preamble pilot can be placed anywhere in the physical frame, but it is generally placed before all OFDM symbols.

As shown in FIG. 3 , based on the above method, the modulation structure implementing the present invention includes: an OFDM modulation unit 300 , a guard interval zero interpolation unit 304 , and a framing unit 305 . Wherein, the OFDM modulation unit 300 includes a serial/parallel conversion unit 301 , an inverse fast Fourier transform unit 302 , and a parallel/serial conversion unit 303 . The serial/parallel conversion unit 301 is connected with the inverse fast Fourier transform unit 302, the inverse fast Fourier transform unit 302 is connected with the parallel/serial conversion unit 303, the parallel/serial conversion unit 303 is connected with the guard interval zero interpolation unit 304, and the guard interval zero interpolation unit 304 is connected to the framing unit 305 .

The working principle of the modulation structure of the present invention is: after the serial/parallel conversion unit 301 performs serial/parallel conversion on the received data signal, it is sent to the inverse fast Fourier transform unit 302, and the inverse fast Fourier transform unit 302 converts the received pilot symbol After inverse Fourier transform is performed on the parallel data signal with the synchronous band symbol and the serial/parallel conversion, it is output to the parallel/serial conversion unit 303; the parallel/serial conversion unit 303 converts the signal after the inverse Fourier transform into a serial After the signal, it is output to the guard interval zero interpolation unit 304, and the guard interval zero interpolation unit 304 adds a guard interval of a certain length before or after the received serial data signal, and fills all 0s in the guard interval, that is, in the guard interval No signal is sent within the interval, and the data signal after adding the guard interval forms an OFDM symbol. Finally, the data signal with a guard interval of 0 is input to the framing unit 305, and the framing unit 305 multiplexes a basic physical frame formed by multiple OFDM symbols and a preamble pilot in time as a baseband transmission signal sent to the RF unit. Moreover, the preamble pilot can be placed in any position of the basic frame.

Here, since all 0s are filled in the guard interval, the average transmission power of the transmitter is reduced, and generally 5% to 20% of power can be saved.

The present invention can further add a measurement peak-to-average ratio unit and an adjustment algorithm unit, and reduce the transmission signal PAPR by adjusting the synchronous band symbol. Referring to FIG. 6 , the modulation structure of this embodiment includes an OFDM modulation unit 300 , a guard interval zero interpolation unit 304 , a framing unit 305 , a peak-to-average ratio measurement unit 606 and an adjustment algorithm unit 607 . Wherein, the OFDM modulation unit 300 includes a serial/parallel conversion unit 301 , an inverse fast Fourier transform unit 302 , and a parallel/serial conversion unit 303 . The serial/parallel conversion unit 301 is connected with the inverse fast Fourier transform unit 302, the inverse fast Fourier transform unit 302 is connected with the parallel/serial conversion unit 303, the parallel/serial conversion unit 303 is connected with the guard interval zero interpolation unit 304, and the guard interval zero interpolation unit 304 is connected to the framing unit 305 .

The working principle of the modulation structure of this embodiment is: the serial/parallel conversion unit 301 performs serial/parallel conversion on the received data signal, and then sends it to the inverse fast Fourier transform unit 302, and the inverse fast Fourier transform unit 302 converts the received pilot frequency The symbol and synchronous band symbol and the serial/parallel converted parallel data signal are subjected to inverse Fourier transform, and then output to the parallel/serial conversion unit 303; the parallel/serial conversion unit 303 then converts the signal after the inverse Fourier transform into a serial After performing the signal, it is output to the peak-to-average ratio measurement unit 606. After the peak-to-average ratio measurement unit 606 measures the PAPR, it judges whether the PAPR is greater than a preset value. If it is greater, the PAPR is fed back to the adjustment algorithm unit 607; The algorithm unit 607 properly adjusts the timing belt symbol according to the PAPR information, for example, randomly arranges all possible values of the timing belt symbol, and the adjustment algorithm selects the next value according to the order of arrangement each time. Then recirculate OFDM modulation, PAPR measurement, feedback, and adjustment until the PAPR is not greater than the preset threshold, the peak-to-average ratio measurement unit 606 sends the received serial data signal to the guard interval zero interpolation unit 304 to protect Interval zero insertion unit 304 adds a guard interval of a certain length before or after the received serial data signal, and fills all 0s in the guard interval, that is, does not send any signal in the guard interval, and the data after adding the guard interval The signal forms an OFDM symbol. Finally, the data signal with the added guard interval of 0 is input to the framing unit 305 . The framing unit 305 multiplexes a plurality of OFDM symbols and a preamble in time to form a basic physical frame, and sends the physical frame as a baseband transmission signal to the radio frequency unit.

The adjustment algorithm unit 607 may use various algorithms for calculation, such as full search algorithm and partial search algorithm.

Claims (8)

1, a kind of signal modulating method of digital television broadcasting is characterized in that, this method may further comprise the steps:

A. the frequency pilot sign that generates with data-signal, in advance and tape symbol is multiplexing on frequency domain synchronously, and multiplex data is carried out modulating in OFDM obtain time-domain signal,

Described synchronous tape symbol comprises subcarrier that transmits synchronizing symbol and the zero setting subcarrier that does not pass any information; Described frequency pilot sign takies a part of subcarrier, and non-conterminous mutually between shared subcarrier;

B. before time-domain signal, increase protection at interval, and protect at interval and fill out 0, form an OFDM symbol;

C. utilize an above OFDM symbol and a pre-pilot signal to generate baseband transmit signals.

2, method according to claim 1, it is characterized in that, after step b and between the step c, further comprise: the peak-to-average ratio of the described time-domain signal that obtains among the measuring process a, and judge that whether this peak-to-average ratio is greater than the threshold value that sets in advance, if greater than, then utilize certain synchronous tape symbol of algorithm adjustment, return step a, otherwise, execution in step c.

3, method according to claim 1 is characterized in that, described protection is expanded greater than the maximum delay of physical channel at interval.

4, method according to claim 1 is characterized in that, described baseband transmit signals is a physical frame, and pre-pilot is arranged in any position of each physical frame, or pre-pilot is arranged in before all OFDM symbols of each physical frame.

5, method according to claim 1 is characterized in that, described in the step a multiplex data is carried out the step that OFDM modulation obtains time-domain signal and comprises:

A1, data-signal is carried out serial/parallel conversion;

A2, with frequency pilot sign and synchronous tape symbol and carry out inverse-Fourier transform through the parallel data-signal after the serial/parallel conversion;

A3, will be that serial signal obtains time-domain signal through the conversion of signals behind the inverse-Fourier transform.

6, a kind of modulating apparatus of digital television broadcasting is used for modulating data, and the baseband transmit signals of modulation is sent to radio frequency unit, it is characterized in that this device comprises:

OFDM modulating unit (300), protection be zero insertion unit (304) and become frame unit (305) at interval, wherein,

OFDM modulating unit (300), the data-signal through frequency domain multiplexing that is used for receiving, frequency pilot sign, synchronous tape symbol carry out the OFDM modulation and obtain time-domain signal;

Protection is zero insertion unit (304) at interval, and being used for increases the protection interval at described time-domain signal, and inserts 0 back formation OFDM symbol in protection at interval;

Become frame unit (305), the physical frame that is used to utilize an above OFDM symbol and pre-pilot to constitute sends to radio frequency unit as baseband transmit signals.

7, device according to claim 6 is characterized in that, this device further comprises: peak-to-average ratio measuring unit (606) and adjustment algorithm unit (607), wherein,

Peak-to-average ratio measuring unit (606), be used to measure the peak-to-average ratio that receives from the frequency-region signal of OFDM modulating unit (300) output, judge that whether peak-to-average ratio is greater than pre-set threshold, if greater than, then this peak-to-average ratio is fed back to adjustment algorithm unit (607), if be not more than, then the frequency-region signal that receives is exported to protection zero insertion unit (304) at interval;

Adjustment algorithm unit (607) is used for according to the synchronous tape symbol of peak-to-average ratio adjustment that receives.

8, device according to claim 6 is characterized in that, OFDM modulating unit (300) comprises serial (301), anti-fast Fourier transform unit (302), parallel/serial converting unit (303), wherein,

Serial (301) is used for sending to anti-fast Fourier transform unit (302) to receiving after data-signal carries out serial/parallel conversion;

Anti-fast Fourier transform unit (302) after the frequency pilot sign that is used for receiving carries out inverse-Fourier transform with synchronous tape symbol and through the parallel data-signal after the serial/parallel conversion, exports parallel/serial converting unit (303) to;

Parallel/serial converting unit (303) is used for exporting to protection zero insertion unit (304) at interval with after being serial signal through the conversion of signals behind the inverse-Fourier transform.

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