CN1319376C - Signal transmission method in digital signal transmission system - Google Patents

Abstract

The present invention discloses a signal transmission method in a digital signal transmission system. The method divides data flow composed of multiple level symbols into continuous data frames to transmit; each data frame comprises three parts which are respectively presetting information, system information and data information; each data frame forms simple single-order circulation by the three parts. The high-efficiency compact data frame structure transmission method designed by the present invention can support the hybrid transmission of multiple kinds of transmission modes of a system in the mode of taking one frame as the minimal independent transmission unit of different transport services; the flexibility of the system selecting different services is increased; the application range of the system is expanded. The signal transmission method of the present invention not only can be applied to single carrier wave time domain transmission systems but also can be applied to multiple carrier wave frequency domain transmission systems, and can also be used for processing frequency domains of the single carrier wave time domain transmission systems, and therefore, the signal transmission method is more flexible. The method can be used for current digital TV ground broadcasting systems.

Description

A Signal Transmission Method in Digital Signal Transmission System

Technical Field The present invention belongs to the field of digital signal transmission, and in particular relates to a data arrangement method for transmission signals in digital terrestrial broadcast transmission.

Background Art As shown in Figure 1, a typical wireless transmission system includes a transmitter and a receiver. In a receiver, if there is a tuner, there is no need for down conversion. Digital modulation technology often encodes digital signals, and then adds necessary auxiliary information, such as: synchronization signals, pilot signals, etc. The coded digital signal forms a baseband signal after channel filtering. The baseband signal is modulated to a corresponding frequency band through an up-converter and then sent. At the receiving end, the tuner converts the high-frequency signal to the baseband to obtain a digital signal through an analog-to-digital converter. After the digital signal is processed, it is restored to the same information as the sending end.

In the digital TV terrestrial broadcast transmission system, it is mainly divided into single-carrier time-domain processing system and multi-carrier frequency-domain processing system. The former is like the American ATSC 8VSB system, and the latter is like the European DVB-TCOFDM system and the Japanese ISDB-T system.

In terms of data transmission at the physical layer, in consideration of countering channel fading and other interference, it is necessary to add some auxiliary data, such as known information and system information, to the data stream at the source, and transmit it together with the data information for Help the receiver recover data. Various transmission standards correspond to their own unique data transmission methods according to their own characteristics. For example, the training sequence in a single-carrier system is known information in the form of preset information, and the pilot frequency in a multi-carrier system is also known information that is known at both ends of the transceiver. At the same time, both systems will transmit system information to help The receiving end determines the system state.

Auxiliary data is harmful to transmission efficiency, but it is very necessary to restore valid data. For example, the cycle of occurrence of certain information can directly affect the ability of the system to track dynamic channel changes; the length of preset information directly affects the ability of channel estimation and the efficiency of channel transmission; the protection of system information is also related to the system mode Can it be reliably identified, etc. These are easy to understand; therefore, how to reasonably arrange the relationship between auxiliary data and effective data information, and determine a reasonable data transmission method, has become another core issue in system design; at the same time, to expand various businesses in the future, The arrangement of the data transmission structure must also leave room for future expansion.

For multi-carrier systems, including the European DVB-T system and the Japanese ISDB-T system, the definite information in the auxiliary data mainly exists in the form of pilots, and is scattered on the corresponding subcarriers in an OFDM symbol at a certain interval . There are two types of pilots: fixed pilots with fixed positions and mobile pilots whose positions change with time. Its system information is also correspondingly transmitted on a dedicated transmission signaling symbol (TPS) subcarrier of the OFDM symbol. Considering that the multi-carrier system needs to perform fast Fourier transform (FFT) and its inverse transform (IFFT), the transmission method of the multi-carrier system is shown in the position where the auxiliary data is distributed in the entire OFDM symbol, see Figure 2. At present, the DMB-T solution of Tsinghua University in China adopts the transmission method of time domain PN (Pseudo-random Noise, pseudo-random noise) sequence plus frequency domain data, see Figure 3. The PN sequence is followed by a piece of frequency domain data used for IFFT to synthesize a basic transmission unit. System information is interspersed in the frequency domain data, still transmitted with subcarriers at specific locations.

As a single-carrier system, the American ATSC system and the ADTB-T system proposed by the applicant arrange transmission signals into frame, field, and segment structures, as shown in FIG. 4 . In the American ATSC system, each frame contains two fields, and each field contains 1 field sync segment and 312 data segments. The segment/field/frame synchronization signal is the preset information predicted by both ends of the transceiver. In the ATSC structure, there are 1/313 frame and field cycle cycles, and 4/832 cycle cycle segments. That is, there are two-order periodic cycles.

Referring to Fig. 5, in the ADTB-T system previously proposed by the applicant, under different modulation modes, the number of fields contained in each frame is different, but each field contains 1 field synchronization segment and 52 data segments. There are also two-order periodic cycles.

In the new digital terrestrial broadcasting system, due to the diversified requirements of broadcasting applications, such as fixed reception of TV signals, mobile reception of TV signals and mobile reception of data signals, etc. As we all know, fixed reception and mobile reception have different requirements on the transmission system due to different reception conditions. Higher data rates are desired for fixed reception, while fast tracking of the channel is required for mobile reception. Existing designs do not fully consider these differences, or the transmission data structure is relatively complex, which is not conducive to optimizing system performance.

SUMMARY OF THE INVENTION The purpose of the present invention is to provide a new digital signal transmission method. The transmission method can be used in a digital terrestrial broadcasting transmission system. The concise data arrangement of the signal transmission method can not only optimize system performance, but also meet the transmission requirements of multiple transmission modes of digital terrestrial broadcasting transmission.

The signal transmission method designed by the present invention is as follows: the data stream composed of multi-level symbols transmitted in the digital transmission system is divided into continuous data frames for transmission; each data frame includes 3 parts, which are respectively preset Configuration information, system information and data information, and thus form a simple first-order cycle. Preset information, system information and data information can be different as the starting position in the data frame, but the order remains unchanged, such as preset information, system information, data information, or system information, data information, preset information, or data information , preset information, system information.

In the mixed transmission mode, the modulation modes of various services are arbitrarily mixed in units of frames, and the modulation mode of each frame is clearly indicated by the system information in the frame.

The preset information can be used for system synchronization, clock recovery, channel estimation and equalizer training. Select an appropriate PN (Pseudo-random Noise, pseudo-random noise) sequence to ensure fast and reliable system synchronization and fast and accurate channel estimation. In the present invention, the preset information may be composed of certain data with a certain number of digits added to the PN sequence, so as to ensure that the length of the preset information is a power of 2 and that the mean value after mapping is zero.

The system information is used to determine the transmission mode of the frame data information and to be used for future function expansion, such as modulation mode, coding method, etc. The system information in the data structure of the sending end is mainly used to identify the transmission mode of the frame at the receiving end for corresponding processing. Especially in mixed mode transmission, the identification of system information is very important. Therefore, when the system information is transmitted, it can be processed to ensure that it can be reliably identified at the receiving end. The present invention adopts spread spectrum protection technology to enhance the robustness of transmission system information, for example, adopts direct sequence spread spectrum method to complete.

The transmitted data information is determined by the system information on its modulation mode, coding mode, etc. The data information can be either time-domain data information or frequency-domain data information, including IFFT or Inverse Discrete Fourier Transform (IDFT). The data can also be a mixture of time domain and frequency domain.

The preset information, system information, and data information may all be time-domain signals, or all may be frequency-domain signals, or may be a mixture of time-domain and frequency-domain signals.

In the digital transmission system, by adopting the efficient and concise data frame structure transmission method designed by the present invention, the transmission system can set the system information bit and use the frame as the minimum constituent unit of the transmission data. At the same time, it can also support the mixed transmission of multiple transmission modes of the system by using the frame as the smallest independent transmission unit of different transmission services, which increases the flexibility of the system in selecting different services and expands the application range of the system. By means of preset known sequences, reliable system synchronization and accurate channel estimation can be obtained, so as to recover the transmitted data information better. Since the length of the preset information satisfies the relationship of the power of 2, the Fourier transform can be performed on the preset information, which also satisfies the possibility of realizing single-carrier frequency domain equalization. The system information protected by spread spectrum further ensures the safety and reliability of the transmission system. For different transmission systems, the form of data information can be a time-domain signal or a frequency-domain signal. The signal transmission method of the present invention can be applied to a single-carrier time-domain transmission system, can also be applied to a multi-carrier frequency-domain transmission system, and can also be used for frequency-domain processing of a single-carrier time-domain transmission system, so it is more flexible. This method can be used in the current digital TV terrestrial broadcasting system.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

Figure 1 is a typical system block diagram of digital transmission.

Figure 2 is the data transmission method of European DVB-T, showing the settings of pilot frequency and TPS.

Figure 3 shows the data transmission method of Tsinghua University's DMB-T.

FIG. 4 is a signal transmission method of the data frame field structure of ATSC in the United States.

FIG. 5 is a signal transmission method of the ADTB-T data frame field structure previously applied by the applicant.

FIG. 6 is a first embodiment of the digital signal data frame structure transmission method of the present invention.

FIG. 7 shows preset information composed of multiple PN sequences.

FIG. 8 is a second embodiment of the digital signal data frame structure transmission method of the present invention.

FIG. 9 is a third embodiment of the digital signal data frame structure transmission method of the present invention.

DETAILED DESCRIPTION Referring to Figure 6, the data signal is transmitted according to the frame structure, and the data frame consists of three parts: preset information, system information and data information, which are arranged in the order shown in the figure. In the mixed transmission mode, the modulation modes of various services are arbitrarily mixed in units of frames, and the modulation mode of each frame is clearly indicated by the system information in the frame.

The preset information is used for system synchronization, clock recovery, channel estimation and equalizer training. Select the appropriate PN sequence to ensure the rapid and reliable acquisition of system synchronization and the rapid and accurate channel estimation. Therefore, the selection of preset information will be carried out according to the actual requirements of the system.

In the digital TV terrestrial transmission system, the preset information can choose a PN sequence with good correlation characteristics and flat spectrum to assist system synchronization and channel estimation. It is convenient for FFT operation of frequency domain processing, such as for adaptive frequency domain equalization, the preset information length should be selected as the power of 2. This can be satisfied by adding the appropriate number of known data to the PN sequence. At the same time, in order to keep the spectrum characteristic of the preset information after adding the definite data to be flat, the selected definite data should ensure that the level sum (mean value) after mapping the preset information is zero.

The preset information can be composed of a PN sequence plus a certain number of known data, or multiple PN sequences plus a certain number of known data. For example, to form a preset information with a length of 1024, it can be composed of 2 identical (PN511+'0'); it can also be composed of 2 different (PN511+'0'); it can also be composed of 1 (PN511+'0' ) plus its cyclic extension composition, see Fig. 7.

The PN sequence can be a commonly used two-level sequence, or a three-level PN sequence with better correlation characteristics, or a 4-level PN sequence obtained after 16OQAM mapping of a binary PN sequence. The level of the confirmation signal of a certain number of bits added thereafter depends on the level of the PN sequence.

The length of the preset information affects the ability of the system to track channel characteristics, but also affects the transmission efficiency of the system, so it needs to be set according to the actual use situation, generally can be 64, 256, 512, 1024 or 2048 bits. In the case of wired transmission, the channel conditions are much simpler and better than that of wireless ground, so the length of preset information in wired transmission can be shorter than that in wireless transmission; and in small area transmission of voice services When , the preset information of this transmission mode can also be shorter.

The system information in the data structure is used to determine the transmission mode of the frame data information, including modulation mode, coding mode, etc., so that the receiving end can make corresponding processing. Especially in mixed mode transmission, the identification of system information is very important. Therefore, when the system information is transmitted, it can be processed to ensure that it can be reliably identified at the receiving end. The invention adopts the spread spectrum protection technology to enhance the robustness of the transmission system information, and adopts the direct sequence spread spectrum method to complete it, and is used to fight against the bad channel fading in the digital TV ground transmission.

Like the preset information, the selection of system information is also determined according to different business requirements, and is automatically recognized at the receiving end. In wired transmission mode, the system information can be 32 or 64 bits long, while in wireless transmission mode, 64 or 128 bits long can be selected. This is also determined according to the degree of protection required for the system in different transmission environments.

The transmitted data information is determined by the system information on its modulation mode, coding mode, etc. The data information can be either time-domain data information or frequency-domain data information, including data processed by IFFT or IDFT, or it can be A mix of time domain and frequency domain. Therefore, this digital signal transmission method can be applied to a single-carrier time-domain transmission system, can also be used in a multi-carrier frequency-domain transmission system, and can also be used in frequency-domain processing of a single-carrier time-domain transmission system.

The data information in each frame can be two-level data or multi-level data.

The preset information, system information, and data information may all be time-domain signals, or all may be frequency-domain signals, or may be a mixture of time-domain and frequency-domain signals.

The signal transmission method designed in the present invention does not require the preset information, system information and data information to be in the first, second and third positions respectively in the data frame, that is to say, the starting points of the frames can be different. But the order of the three parts remains unchanged: the data frame can start with preset information, followed by system information and data information; it can also start with system information, followed by data information and preset information, see Figure 8; it can also start with data information , followed by preset information and system information, see Figure 9.

Claims (10)

1. A signal transmission method in a digital signal transmission system, the data stream is divided into a continuous data frame for transmission, characterized in that: each data frame contains information that can be used for system synchronization, clock recovery, channel estimation and equalization The preset information for device training, the transmission mode that can be used to represent the data information of this frame, and the system information and data information for future function expansion; The order of preset information, system information and data information in the data frame remains unchanged, but the starting point of the frame can be different, and thus form a simple first-order cycle; a frame can start with preset information, followed by system information and data Information; or start with system information, followed by data information and preset information; or start with data information, followed by preset information and system information; The preset information, the system information and the data information are all time-domain signals, or all are frequency-domain signals, or are a mixture of time-domain and frequency-domain signals. 2. The signal transmission method according to claim 1, characterized in that: in the mixed transmission mode, the respective modulation modes of various services are arbitrarily mixed in units of frames, and the modulation mode of each frame is specified by the system information in the frame pointed out. 3. The signal transmission method according to claim 1, characterized in that: the preset information is composed of at least one time-domain pseudo-random noise sequence plus a certain number of definite signals, or is composed of frequency-domain sweep signals , whose length is a power of 2. 4. The signal transmission method according to claim 3, characterized in that: The pseudo-random noise sequence that constitutes the preset information is a two-level pseudo-random noise sequence or a multi-level pseudo-random noise sequence; Level. 5. The signal transmission method according to claim 4, characterized in that: The multi-level pseudo-random noise sequence is a three-level pseudo-random noise sequence, or a 4-level pseudo-random noise sequence obtained after performing 16OQAM mapping on a binary pseudo-random noise sequence. 6. The signal transmission method according to claim 3 or 4, characterized in that: the selected known data ensures that the level sum after mapping the preset information is zero. 7. The signal transmission method according to claim 3, 4 or 5, wherein the length of the preset information is one of 64 bits, 256 bits, 512 bits, 1024 bits or 2048 bits. 8. The signal transmission method according to claim 7, characterized in that: the level sum after mapping the preset information is zero. 9. The signal transmission method according to any one of claims 1 to 5, characterized in that: the direct sequence spread spectrum method is used to spread the protection system information. 10. The signal transmission method according to claim 9, characterized in that: in the wired transmission mode, the length of the system information is 32 or 64 bits; in the wireless transmission mode, the length of the system information is 64 or 128 bits.

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