Disclosure of Invention
The invention aims to solve the technical problem of providing a reusable wireless video transmission method which can multiplex the existing system module only by setting the required FFT point number without changing the data structure and the system frame, thereby reducing the development cost and shortening the development period.
In order to solve the technical problems, the invention adopts the following technical scheme.
A method for multiplexing wireless video transmission, which is realized based on a system comprising an acquisition transmitting unit with an OFDM modulation module and a receiving display unit with an OFDM demodulation module, the method comprising the steps of: step S1, the acquisition transmitting unit acquires video signals, and packs and multiplexes the video signals after compression processing into TS stream data; step S2, configuring an inner interleaver and an outer interleaver with fixed lengths for an OFDM modulation module, and determining the capacities of the inner interleaver and the outer interleaver according to the number of subcarriers corresponding to the maximum FFT point number which is required to be configured; step S3, the OFDM modulation module sequentially performs RS coding, scrambling, outer interleaving, convolution coding, inner interleaving and framing treatment on TS stream data to form an OFDM data frame; step S4, the OFDM modulation module carries out IFFT transformation on the OFDM data frame, and carries out insertion guard interval GI, up-sampling and low-pass filtering processing on the data after the IFFT transformation in sequence; step S5, the acquisition transmitting unit sequentially carries out DAC conversion, RF carrier modulation and power amplification on the data subjected to the low-pass filtering processing in the step S4 and transmits a wireless signal; step S6, the receiving display unit acquires the wireless signals transmitted by the acquisition transmitting unit, and inputs the wireless signals to the OFDM demodulation module after sequentially performing low-noise amplification, RF carrier demodulation and ADC conversion processing; step S7, the OFDM demodulation module sequentially carries out band-pass filtering, downsampling, synchronous processing and FFT conversion after removing a guard interval GI on the input data; step S8, the OFDM demodulation module takes out pilot frequency from the data after FFT conversion and carries out channel estimation, then carries out channel equalization processing by combining the data except the pilot frequency, and carries out constellation demapping after the channel equalization is completed; step S9, the OFDM demodulation module sequentially carries out inner de-interleaving, convolution decoding, outer de-interleaving, descrambling and RS decoding treatment on the constellation de-mapped data, and then outputs a data TS stream; step S10, the receiving display unit sequentially performs demultiplexing and video decoding processing on the data TS stream and loads the data TS stream on the display and play device.
Preferably, in the step S1, the capturing and transmitting unit captures the HDMI video signal using a CCD camera.
Preferably, in the step S1, the acquisition and transmission unit performs compression processing on the video signal by using a video encoder, and in the step S10, the receiving and display unit performs video decoding processing on the demultiplexed data TS stream by using a video decoder.
Preferably, the video encoder is an H.264/H.265 encoder and the video decoder is an H.264/H.265 decoder.
Preferably, in the step S3, the framing process includes constellation mapping and pilot insertion.
Preferably, in the pilot frequency inserting process, the number and the positions of the pilot frequency are determined according to the FFT point number.
Preferably, in the step S4, the length of the inserted guard interval GI is determined according to the number of FFT points.
Preferably, in the step S5, a 2W power amplifier is used to power amplify the RF carrier modulated signal.
Preferably, in step S7, the synchronization process performed by the OFDM demodulation module includes frequency synchronization, sampling synchronization, and symbol synchronization.
Preferably, in the step S7, the OFDM demodulation module performs band-pass filtering on the input data using a band-pass filter having a bandwidth of 6 MHz.
In the multiplexing wireless video transmission method disclosed by the invention, a video signal is acquired by utilizing an acquisition and transmission unit and is converted into TS stream data, an inner interleaver and an outer interleaver are designed according to the maximum FFT point number which is configured as required, RS coding, scrambling, outer interleaving, convolution coding, inner interleaving and framing are sequentially carried out on the TS stream data, the formed OFDM data frame is subjected to IFFT conversion and then is processed into a wireless radio frequency signal, and a receiving side is provided with video signals for display and play equipment after the receiving and display unit demodulates the wireless radio frequency signal. In the process, when the system needs to be set into a mode of other FFT points, the reuse of the current system can be realized by simply configuring the FFT conversion points without changing a data transmission structure and a system frame.
Detailed Description
The invention is described in more detail below with reference to the drawings and examples.
The invention discloses a multiplexing wireless video transmission method, which is realized based on a system with an acquisition transmitting unit 1 with an OFDM modulation module 10 and a receiving display unit 2 with an OFDM demodulation module 20, and is combined with the figures 1 and 2, and comprises the following steps:
step S1, the acquisition transmitting unit 1 acquires video signals, compresses the video signals, packages and multiplexes the compressed video signals into TS stream data;
step S2, configuring an inner interleaver and an outer interleaver with fixed lengths for the OFDM modulation module 10, and determining the capacities of the inner interleaver and the outer interleaver according to the number of subcarriers corresponding to the maximum FFT point number which is required to be configured;
Step S3, the OFDM modulation module 10 sequentially performs RS coding, scrambling, outer interleaving, convolution coding, inner interleaving and framing treatment on TS stream data to form an OFDM data frame; in the step, the framing process comprises constellation mapping and pilot frequency insertion, and further, in the pilot frequency insertion process, the number and the positions of the pilot frequency are determined according to FFT (fast Fourier transform) points;
Step S4, the OFDM modulation module 10 performs IFFT transformation on the OFDM data frame, and sequentially performs insertion guard interval GI, up-sampling and low-pass filtering on the data after the IFFT transformation, and further, the length of the insertion guard interval GI is determined according to the FFT point number;
Step S5, the acquisition transmitting unit 1 sequentially performs DAC conversion, RF carrier modulation and power amplification on the data subjected to the low-pass filtering processing in step S4 and transmits a wireless signal;
Step S6, the receiving and displaying unit 2 acquires the wireless signal transmitted by the collecting and transmitting unit 1, and inputs the wireless signal to the OFDM demodulation module 20 after sequentially performing low noise amplification, RF carrier demodulation and ADC conversion processing;
Step S7, the OFDM demodulation module 20 sequentially performs band-pass filtering, downsampling, synchronization processing and FFT after removing the guard interval GI, where the synchronization processing of the OFDM demodulation module 20 includes frequency synchronization, sampling synchronization and symbol synchronization;
step S8, the OFDM demodulation module 20 takes out pilot frequency from the data after FFT conversion and carries out channel estimation, then carries out channel equalization processing by combining the data except the pilot frequency, and carries out constellation demapping after the channel equalization is completed;
Step S9, the OFDM demodulation module 20 sequentially performs inner deinterleaving, convolutional decoding, outer deinterleaving, descrambling and RS decoding on the constellation demapped data, and outputs a data TS stream;
step S10, after the receiving display unit 2 sequentially performs demultiplexing and video decoding processing on the data TS stream, the data TS stream is loaded in a display playing device.
In the above multiplexing wireless video transmission method, the acquisition transmitting unit 1 is used to acquire video signals and convert the video signals into TS stream data, and the inner interleaver and the outer interleaver are designed according to the maximum FFT point number configured as required, and after RS encoding, scrambling, outer interleaving, convolutional encoding, inner interleaving and framing processing are sequentially performed on the TS stream data, the formed OFDM data frames are subjected to IFFT transformation and then processed into wireless radio frequency signals, and on the receiving side, the receiving display unit 2 demodulates the wireless radio frequency signals and provides video signals for the display and play device. In the process, when the system needs to be set into a mode of other FFT points, the reuse of the current system can be realized by simply configuring the FFT conversion points without changing a data transmission structure and a system frame.
In the application process, the maximum FFT point number required can be configured according to the actual environment, for example, when the RAM memory size is required to be changed under the limitation of the existing resources, FFT modes with other points can be selected, based on the characteristics, each functional module is not required to be redesigned, the system reuse is convenient, and the transmission format of TS stream has good system environment adaptability and transmission characteristics.
In a preferred manner, in the step S1, the capturing and transmitting unit 1 captures the HDMI video signal using a CCD camera.
Regarding the video encoding and decoding part, in the step S1, the acquisition and transmission unit 1 performs compression processing on the video signal using a video encoder, and in the step S10, the reception and display unit 2 performs video decoding processing on the demultiplexed data TS stream using a video decoder. Further, the video encoder is an H.264/H.265 encoder, and the video decoder is an H.264/H.265 decoder.
Regarding the output portion of the wireless radio frequency signal, the RF carrier modulated signal is power amplified with a 2W power amplifier.
In a preferred manner, in the step S7, the OFDM demodulation module 20 performs band-pass filtering on the input data using a band-pass filter having a bandwidth of 6 MHz.
For better describing the technical solution of the present invention, the reusable wireless video transmission method of the present invention may refer to the following embodiments in practical application.
Example 1
In this embodiment, taking a wireless transmission 1080P30 video source as an example, an h.265 encoder is used to perform encoding compression processing, and an OFDM modem module capable of configuring 512, 1024, 2048-point FFT is designed to implement recycling of a wireless video transmission system.
Firstly, an HDMI video signal is acquired by a high-definition video camera, the image quality is further improved after encoding and compression processing is carried out by an H.265 coder module, and a smaller data volume (with small bandwidth) is beneficial to long-distance wireless transmission, and an H.265 coder module compressed code stream is packed into a 188-byte TS stream by a packing TS stream module according to the ISO/IEC 13818-1 standard and then is sent to an OFDM modulation module for processing.
The OFDM modulation module firstly completes RS coding, scrambling, outer interleaving, convolution coding and inner interleaving treatment. The capacity of the interleaver is used as a reference standard according to the number of subcarriers corresponding to the maximum FFT point number system configured as required, so as to meet the reuse of the interleaver. In this embodiment, the number of maximum FFT points is 2048, and the number of subcarriers is 1656, so the inner and outer interleaver sizes are 1656. In order to make the interleaver store sequences with integer RS code length, the RS code uses the punctured codes RS (207, 187) derived from the original system RS (255, 239, t=8), then the interleaver can store 8 RS codes (207×8=1656), the TS data is scrambled by using the scrambling technique of the DVB-T standard after being encoded by the RS (207, 187), the outer interleaver is set to an interleaving array of 46×36=1656, the inner code uses convolutional coding, and the inner interleaving uses an interleaving array of 72×23=1656. The channel coding and interleaving modules employ this fixed structure regardless of the configuration 512, 1024, 2048-point FFT mode, without redesigning the interleaver size and interleaving depth.
And the framing processing part of the OFDM modulation module completes digital modulation (constellation mapping) and pilot frequency insertion in the framing process, and the number and the positions of the pilot frequency are determined by FFT (fast Fourier transform) points. In this embodiment, for the 2048-point FFT mode, the number of pilots is set to 37, the pilot positions are 0,48,87,121,156,192,231,265,300,333,432,483,525,581,636,714,759,790,834,873,901,939,984,1100,1151,1207,1250,1307,1350,1400,1450,1499,1540,1580,1621,1651,1683; in order for the 1024-point FFT mode, the number of pilots is set to 19, the pilot positions are 0, 48, 87, 121, 156, 192, 231, 265, 300, 333, 432, 483, 525, 581, 636, 714, 759, 790, 834 in order; for 512-point FFT mode, the number of pilots is set to 10, and the pilot positions are set to 0, 48, 87, 121, 156, 231, 265, 300, 333, 402 in sequence, and the pilots can also be set fully with reference to DVB-T standard. The digital modulation mode is QPSK,16QAM,64QAM, and pilot symbols are inserted while modulating. And (3) in order to send the OFDM frames completed by framing into an IFFT conversion module to execute IFFT, and performing 0 setting processing on the rest positions. Taking 2048-point FFT as an example, the subcarrier occupies 1656 positions and the pilot occupies 37 positions, and then the data in the remaining 355 (2048-1656-37) positions is processed by setting 0. Because the channel coding and interleaving module adopts a fixed structure, taking the mode of satisfying the maximum FFT point number as an example, and unifying an interleaver with a size of 1656, for the 2048-point FFT mode, the digital modulation and the pilot frequency insertion, the IFFT, the guard interval insertion and the up-sampling processing can be completed for 1 time; for 1024-point FFT mode, 2 times of 1024 (828 subcarriers+19 pilots+177 zeros) point IFFT operation are needed; for 512-point FFT mode, 4 times of 512 (414 subcarriers+10 pilots+88 zeros) point IFFTs are needed. When the number of the FFT points of the configuration system is 2048, 1024 and 512 respectively, the system automatically circularly executes the digital modulation (constellation mapping), the pilot frequency insertion, the IFFT, the guard interval insertion GI and the up-sampling module respectively for 1,2 and 4 times so as to finish the data in an interleaver with a full storage state, and the setting mode is irrelevant to the transmission data frame structure, can uniformly finish 2048-point data code element operation and does not need to change the transmission mode of the data structure.
In the OFDM modulation module, the IFFT transformation module performs an IFFT operation, and the FFT transformation module performs an FFT operation, requiring that the IFFT/FFT transformation length be large enough to enable a shorter length IFFT/FFT transformation. In this embodiment, if the maximum transform length of the IFFT/FFT is 2048 points, the 1024-point IFFT/FFT can be directly implemented by the 2048-point IFFT/FFT implementation system according to the periodicity of the IFFT/FFT rotation factor, without redesigning the module.
In the OFDM modulation module, a guard interval GI (cyclic prefix) operation is inserted, and the length of the guard interval GI added after the IFFT is performed is determined by the number of FFT points. In this embodiment, the GI length is set to 1/32 of the FFT length. Thus, if configured in 2048, 1024, 512-point FFT modes, the corresponding GI lengths are 64, 32, 16, respectively. The up-sampling module completes the signal up-sampling function, the data is up-sampled by 3 times in the embodiment, and then the data is sent out through the DAC module, so that the sending end completes all functions of OFDM modulation.
The DAC conversion module is utilized to complete the digital-to-analog conversion function, the conversion precision is 10bits, then the radio frequency RF module is used for carrier modulation, the baseband signal is modulated at 490MHz working frequency, the output power is improved by the power amplification PA module, and then the output power is transmitted through the antenna, in the embodiment, the PA device with the power of 2W is adopted.
The receiving end firstly amplifies the received weak signal through the low noise amplifier LNA module, then the radio frequency RF module demodulates the received weak signal, the 490MHz working frequency is recovered to the baseband signal, the ADC conversion module executes the analog-to-digital conversion function after the down conversion, the conversion precision is 10bits, and the conversion is completed and then the baseband signal is sent to the OFDM demodulation module to complete the baseband signal processing.
In the OFDM demodulation module, band-pass filtering and downsampling are performed first, and in this embodiment, the band-pass filter uses a bandwidth of 6MHz, and downsampling correspondingly performs downsampling by 3. And then, synchronizing the signals, including frequency synchronization, sampling synchronization and symbol synchronization, and executing the operation of removing the guard interval GI on the data with the synchronization function. The signal is then FFT transformed, here inversely with the IFFT transformation. In addition, pilot frequency is taken out from the data after FFT conversion to be used for channel estimation, channel equalization processing is carried out by combining channel estimation parameters with the rest data (without pilot frequency) after FFT conversion, and the data is sent to a constellation demapping module to execute digital demodulation operation after channel equalization is completed.
In the OFDM demodulation module, channel decoding and de-interleaving processing are carried out on the transmission data subjected to constellation de-mapping, and inner de-interleaving, convolution decoding, outer de-interleaving, descrambling and RS decoding processing are finished. In this embodiment, the interleaver size with 2048-point FFT as the reference is adopted, so that when the constellation demapping module outputs data to fill up one interleaver, the processing such as deinterleaving and decoding can be performed. So for 2048-point FFT mode, the entire interleaver can be filled 1 time; for 1024-point FFT mode, 2 times of FFT transform data are needed to fill the entire interleaver; for 512-point FFT mode, 4 times of FFT transform data are needed to fill the entire interleaver. Equally, for OFDM modem modules in 2048, 1024, 512-point FFT modes, the inner deinterleave, convolutional decode, outer deinterleave, descramble, RS decode module will cycle 1,2, 4 times respectively to ensure that the received data fills 1656-sized interleaver for subsequent processing without redesigning these modules according to the required FFT point number. In response to the channel coding and interleaving module, a corresponding de-interleaving and decoding mode is adopted, and in this embodiment, viterbi decoding (convolutional decoding) and RS decoding are adopted.
And performing demultiplexing operation on the TS stream data output by the OFDM demodulation module by using the TS stream demultiplexing module to remove TS header information and the like, sending the H.265 compressed bare code stream subjected to the TS demodulation operation to a corresponding decoder module to perform H.265 decoding operation, recovering reconstructed original video image data, and displaying the played video data on a display device. The wireless video transmission system takes 2048-point FFT mode as an example, if the prior resource limitation is received, and RAM memory size is required to be reduced, the 1024,512-point FFT mode and the like are adopted, so that the wireless video transmission system can be simply multiplexed, each functional module is not required to be redesigned, the system reuse is convenient, and the transmission format of TS stream has good system application environment adaptability and transmission characteristics.
The multiplexing wireless video transmission method disclosed by the invention reuses and designs the modules such as a data transmission structure, RS coding (decoding), scrambling, outer (de) interleaving, convolution coding (decoding), inner (de) interleaving, pilot frequency, IFFT/FFT, guard interval, channel estimation and the like of an OFDM communication scheme, and can efficiently multiplex the system modules by simply setting the required FFT point number on the premise of not changing the data structure and the system frame, thereby fully playing the roles of the existing system modules without redesigning and reducing the development cost and the design period. Based on the characteristics, the method is suitable for being applied to the fields of wireless communication, mobile communication, digital Video Broadcasting (DVB), high Definition Television (HDTV) and the like, and has good application prospect.
The above embodiments are only preferred embodiments of the present invention, and are not intended to limit the present invention, and modifications, equivalent substitutions or improvements made within the technical scope of the present invention should be included in the scope of the present invention.