In the working environment, we are most exposed to wired transmission, but this will be subject to some restrictions due to conversion interface, transmission distance and other reasons, while wireless transmission will not, no wiring is required, no interface restrictions, and the transmission distance is also due to wired transmission. It is also the reason why the Internet of Things uses wireless communication technology extensively.
Key points for WiFi module selection:
1. Communication interface: USB, WAN/LAN, UART, I2S, I2C, SPI, SD, PWM;
2. Power supply mode: 3.3V is more commonly used, and there is also 5V power supply;
3. The processing of the antenna: it is mounted on the PCB; externally connected through the IPEX socket; combined with the main board to design by itself;
4. The specific size of the module is convenient for actual integration;
5. Working frequency band: 2.4-2.5GHz, 5.0-5.8GHz;
6. Platform compatibility, some main control MCUs will have a fixed reference model of wifi chip;
7. Software platform: basically linux and Android, but different kernel versions; some require XP2000, Vista or windows;
8. Module chip manufacturers: the mainstream is Realtek/MTK/Atheros/Broadcom and some domestic RDA/BK, etc.;
Key points of WiFi module selection for video transmission scheme:
Transmission distance: Most drones used for aerial photography will be used in outdoor environments, and in order to better capture distant scenery, the transmission distance of the WiFi module used in drones will become a key reference factor. This is also the main reason why the long-distance image transmission WiFi module SKW77 is recognized by the majority of UAV merchants, and the transmission distance can meet the aerial photography needs of most users;
Data rate: In order to ensure the smoothness of video transmission, the transmission rate of the WiFi module used in the video transmission scheme should preferably be greater than 300Mbps. In the wireless module standard (IEEE802.11), the rate of SKW77 supporting 802.11b/g/n is the highest. It can reach 300Mbps, while the rate of SKW93A supporting 802.11b/g/n/ac in the dual-band WiFi module has reached 733Mbps. Although it is not as good as SKW77 in terms of transmission distance, it can basically meet the rate requirements in short-distance video transmission;
Interface: The communication interface of the WiFi module includes serial port, USB, SD, I²S, I²C, WAN, LAN, SPI, PWM, etc. In the WiFi selection of the video transmission scheme, it is necessary to call the interface according to the actual application function realization process (master-slave device, function, special interface) to choose, such as the USB interface to establish a connection with the 4G module;
The WiFi modules in the UAV video transmission scheme basically appear in pairs, one is built into the UAV, and the other is embedded in a repeater. The WiFi module used in the UAV needs to convert the 4G signal of the 4G module into WiFi Signal, so the selected WiFi module needs to support the function of 4G to WiFi. Both SKW77 and SKW93A have USB interfaces, and both can be connected to the 4G module through the USB interface and perform signal conversion;
Example: Application of SKW77 in UAV wireless video transmission scheme
The overall structure design of the UAV system:
The long-distance WiFi module is applied to the UAV system
The system consists of 4 parts: aircraft end, ground relay end, mobile phone video control end and remote server end.
The main functions of the aircraft-side WIFI module are to establish a WIFI connection with the ground relay terminal; to transmit the camera video to the ground relay terminal; to transmit the control signal transmitted from the ground relay terminal to the control MCU; to transmit the aircraft status information and video through the 4G module to the remote server.
The ground relay terminal is responsible for establishing a relay connection between the aircraft terminal and the mobile terminal.
The mobile terminal is responsible for real-time video viewing and real-time control of various flight states of the aircraft.
The server is responsible for receiving various flight status data and videos of the aircraft. It is convenient to maintain various applications of aircraft.
2. UART serial data transmission:
After the MCU of the serial port device is connected to the SKW77 through the UART interface, data transparent transmission between the serial port and wifi can be realized. The baud rate of the serial port is 115200bps, and the transparent transmission speed can reach 7kByte/s.
3. 4G router:
The SKW77 is connected to the 4G card through the USB interface, and the SKW77 is set to the AP mode. The client can convert the 4G signal into a WiFi signal by establishing a connection with the AP.
4. SD card network storage:
After the SD card storage device and SKW77 module are connected through SDIO, access the SD card by logging in the IP address of SKW77 to realize network data download and upload.
Program reference: http://www.skylab.com.cn/newsview-659.html
The mobile terminal establishes a connection with the WiFi module SKW77 of the ground repeater through WiFi, and the WiFi module SKW77 of the ground repeater communicates with the WiFi module SKW77 of the drone through WiFi, which can send control signals from the ground mobile terminal or pass WiFi transmits the video data of drone aerial photography to the mobile phone for real-time viewing!
The difference between the single-frequency WiFi module and the dual-frequency WiFi module used in the video transmission scheme:
