"When it comes to image transmission, everyone should be familiar with it. For example, the analog TV service we used a long time ago is a kind of image transmission technology. However, in recent years, with the development of wireless technology, wireless image transmission technology has also developed greatly, especially in some devices that need to transmit pictures on the move. For example, when photographing the magnificent mountains and rivers of the motherland, as well as disaster sites such as fire, earthquake and debris flow, we need to use UAV + wireless image transmission for real-time image transmission. For these application scenarios, we not only need the technology that can simply realize image transmission, but also the clarity and quality of the image, There are extremely strict requirements for the anti-interference ability of signals in transmission, because some scenes are no longer simple entertainment through image transmission, but related to the protection of people's life and property safety. Therefore, the importance of a set of high-quality, anti-interference and wireless image transmission scheme is self-evident.
Sihid COFDM HD digital wireless image transmission development kit
COFDM (coded orthogonal frequency division multiplexing) wireless image transmission is the most advanced and potential modulation technology in the world. Its basic principle is to allocate the high-speed data stream to several subchannels with low transmission rate through serial parallel conversion, that is, a broadband channel in the frequency domain is divided into multiple overlapping subchannel signals for narrowband transmission. In view of the problems mentioned above, COFDM image transmission can effectively solve two problems: one is the multipath interference in moving image transmission, and the other is broadband transmission, which can realize high-quality image. Recently, the author got a COFDM high-definition digital wireless image transmission development kit launched by Shenzhen sihid, which is suitable for some mobile device image transmission fields that currently have requirements for high-definition wireless image transmission.
The sihid COFDM high-definition digital wireless image transmission development kit in hand should not be a formal factory package. What I got is a relatively random combination, including:
One sihid COFDM 2.4GHz dual antenna transmitter
Fc2400a 2.4GHz receiving module
DuPont line, antenna, micro HDMI to micro HDMI line
Sihaida COFDM 2.4GHz dual antenna transmitter and fc2400a 2.4GHz receiving module have been packaged with shell. It must take some effort to see the interior.
COFDM 2.4GHz dual antenna transmitter
Let's take a look at the COFDM 2.4GHz dual antenna transmitter and aluminum body. It looks quite tall, but the white self-adhesive note paper on the front box instantly lowers the grade of this product.
The description page pasted on the box indicates the definition of the front dial switch and expansion interface. It is more practical to paste it directly on the box without reading the description documents. However, there are still insufficient considerations here, such as the interface below, which only shows what interface is on the paper, but the pin to which the signal definition is specific is still unclear, If you want to connect a debugging serial port, but you don't know which is GND, RX and TX.
In addition, the COFDM 2.4GHz dual antenna transmitter also includes a microSD card interface and a micro HDMI interface. The former is used to store compressed encoded data, and the latter can be directly connected to products such as digital cameras and sports cameras to receive HD video data in real time. It can be said to be very convenient and easy to use.
RF development board recommendations:
Usb-kw41z: USB dongle is used as a wireless packet sniffer to monitor wireless communication
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Facing the back of the box interface is the SMA interface base of two antennas, which is also very convenient to connect with the supporting antenna.
The aluminum box of COFDM 2.4GHz dual antenna transmitter is fixed with screws, which is very easy to disassemble. After opening, you can see the internal structure at first sight. Unexpectedly, it adopts the structure of stacking two PCBs.
In addition, on the two built-in PCBs, it can also be found that there is an interface on another PCB. It is speculated that it should be the power supply interface of this board.
From the disassembled COFDM 2.4GHz dual antenna transmitter, its hardware system is still very complex. COFDM 2.4GHz dual antenna transmitter can be divided into sem9363 HD coding modulation board (that is, the board above) and d-pa2400a power amplification board (the board below).
Sem9363 HD encoding modulation board
To realize image transmission, it is preferred to collect video data. Sihid sem9363 wireless digital image transmission coding and modulation board inputs high-definition digital video through microhdmi interface, and then does video compression and coding through on-board Hisilicon hi3516a processor. The compressed video signal is then modulated by COFDM channel through FPGA, which is the most critical step. In terms of the whole scheme, This is the core of sihaida map transmission scheme. The modulated video signal is converted into analog signal through ad9363 RF transceiver and modulated and transmitted. However, what puzzles the author is that at present, only two RF transceivers, ad9361 and ad9364, are officially found in ADI, but ad9363 is not seen.
In addition, sem9363 HD encoding and modulation board concentrates the debugging serial port of hi3516a processor, JTAG debugging port of FPGA, OSD interface, control serial port, power supply and other signals on the external interface of d-pa2400a power amplifier board.
D-pa2400a power amplifier board
The d-pa2400a power amplifier board contains two independent RF power amplifier modules, which look like Avago's mga-22003 power amplifier. These two power amplifier modules power amplify and output the RF signal output by sem9363a, as shown in the figure below.
In addition, as can be seen from the above figure, in fact, the d-pa2400a power amplifier board centrally expands the hi3516a debugging serial port, FPGA JTAG debugging port, OSD interface, control serial port, power supply and other signals on the sem9363 modulation board. The two boards are connected through FPC connector with pin expansion base. At the same time, The two RF outputs of sem9363 board are respectively connected to the two RF input interfaces of d-pa2400a board through IPEX connecting line. The working parameters of each power amplification module on d-pa2400a board are as follows:
Operating frequency: 2.400ghz ~ 2.483ghz
Gain: 34 ± 1dB
Power output 1dB: 31dbm
RF development board recommendations:
Usb-kw41z: USB dongle is used as a wireless packet sniffer to monitor wireless communication
Mrf24j40mc-i / RM: surface mount module conforming to 2.4GHz IEEE 802.15.4 standard
X-nucleus-nfc02a1: a dynamic NFC / RFID tag IC with dual interface EEPROM
Fc2400a 2.4GHz receiving module
After reading COFDM 2.4GHz dual antenna transmitter, let's look at the receiving module. The fc2400a receiving module is protected by a yellow heat shrinkable tube, which can simply prevent dust and splash. Of course, in my opinion, I also want to hide the rough hardware circuit design board.
Therefore, I think it is necessary to "risk the universal condemnation" to take out the receiving board.
In fact, the "peeled" board is not as bad as expected, and the layout design of the circuit board is quite exquisite.
The fc2400a down conversion board converts the received 2.4GHz RF signal into 250MHz signal, then COFDM demodulates and converts it into digital signal through the channel demodulation module, and finally transmits the demodulated digital video signal to the mobile phone (or PC) through USB interface for H.264 decompression and playback.
The RF output of fc2400a board is connected to the RF input of COFDM demodulator module through RF line. In addition, I believe many engineers are also very familiar with the hardware combination of r820t + rtl2832u, which is a very popular TV stick scheme before.
The parameters of the whole fc2400a down converter board are as follows:
Operating frequency: 2.400ghz ~ 2.483ghz
RF interface: SMA antenna interface
Receiving sensitivity: - 96 ± 1dbm at 8MHz, - 97 ± 1dbm at 6mhz
8-bit parameter setting switch (receiving and demodulation parameter setting)
Micro USB interface (USB slave) connects the demodulated video to notebook, tablet, mobile phone and other devices for H.264 decoding and playback.
Power supply voltage: 5V
After reading the transmitting board and receiving board, we basically understand the hardware block diagram of the whole picture transmission development kit, as shown below.
RF development board recommendations:
Usb-kw41z: USB dongle is used as a wireless packet sniffer to monitor wireless communication
Mrf24j40mc-i / RM: surface mount module conforming to 2.4GHz IEEE 802.15.4 standard
X-nucleus-nfc02a1: a dynamic NFC / RFID tag IC with dual interface EEPROM
Power on use
Having said so much, it's better to use it in practice. Sihid COFDM HD digital wireless image transmission development kit is still equipped with very complete things. We basically have everything we need. We only need to prepare another video transmission source and a terminal that can support H.264 decoding and playback.
There are two points to note here: first, from the interface of the development kit itself, it only supports micro HDMI input, so the video source needs to be finally converted to micro HDMI interface output; Second, the terminals supporting H.264 decoding and playback can be mobile tablets or PC terminals. Accordingly, the playback tools installed on different terminals are also different. At present, the official only provides mobile app supporting Android system for mobile phones. In addition, it also needs to be equipped with an additional adapter line between Android mciro USB and the receiving end. Due to the lack of tools at hand, the author chose the second playback terminal PC as the output view, and the PC terminal is more convenient for the existing resources in the author's hand.
Connect the receiver to the PC and you will be prompted to install the driver.
The driver is attached to the official data, so you don't have to find it extra. It's very convenient.
Before drive installation
After installation of the drive
Before starting image transmission, it is also necessary to set the matching settings of the transmitting end and the receiving end
Setting description of transmitter
Setting description of receiving end
What I set here is that the transmitter is set as channel 5, QPSK, 8MHz, dual antenna and real-time priority; The channel set at the receiving end is 5, 8MHz.
The channel bandwidth setting of the receiving end needs to be set together on the software of the PC end, and the player is the splayer provided by sihaida.
The transmitter is connected to Sony's micro single video input source.
After the development board is powered on, the built-in demo will be automatically configured. When the input source is correctly detected and the signal transmission starts, the following LED will flash
If everything goes well, the following image transmission will be realized, which looks good.
However, in the actual experience process, the author is stumbling, but the effect of sihid COFDM HD digital wireless image transmission is very good. Finally, after many tests, it is found that there are some problems:
The heating problem is serious at the transmitter and receiver. The power supply has not been further optimized due to the experimental board
There is a problem with the microhdmi interface at the transmitting end. The connector is too tight and the structure is too compact. It is easy to damage the HDMI cable when plugging in and out the microhdmi connector
After a long experience, excluding the above two problems, the image transmission quality effect of sihid COFDM HD digital wireless image transmission development kit is still very good. If you have a strong demand for wireless HD image transmission, you may not contact sihaida for consultation on related products. After all, the development kit evaluated this time is just the tip of the iceberg of the full version, More software and source code are still in sihaida's own hands. The author has very few resources. In addition, in addition to this development kit, sihaida can also customize Digital HD wireless image transmission products of different specifications according to customer application needs, such as
By designing PA modules of different specifications, it can support other working frequency bands and RF power;
The existing design can be changed to add other video input and output processing interfaces, such as AV input, USB input, SDI input at the transmitting end, HDMI output and SDI output at the receiving end, etc;
IP protocol, low delay, long-distance broadband data transmission, etc.
Engineers who are interested or in need in this area should not miss it. In addition, sihid COFDM HD digital wireless image transmission development kit is also available in aibanwang mall, including 2800rmb function test board and 68000rmb open design board. The open design board contains a full set of development materials. Those who are interested can go and have a look.
Original statement: This article is original by Aiban. Reprint is declined!
RF development board recommendations:
Usb-kw41z: USB dongle is used as a wireless packet sniffer to monitor wireless communication
Mrf24j40mc-i / RM: surface mount module conforming to 2.4GHz IEEE 802.15.4 standard
X-nucleus-nfc02a1: a dynamic NFC / RFID tag IC with dual interface EEPROM“
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