Low Power DTV Transmitter and Receivers for AV Communication in Drones
Drones are connected to their base station via two links – robust, low latency remote control link and a high data rate link for High Definition Audio/Video transmission. Today, the drones (example: Phantom 3 Standard) use 5.8GHz ISM band for the former (remote control and live view) and 2.4GHz band for HD AV Communications. 2.4GHz band suffers from high absorption (through foliage, buildings, etc.) and very high interference. In this short note, we propose use of TV or <1GHz ISM band frequencies for transmission of High Definition Audio/Video from the drone to the base station. Table below lists the frequencies available for HD AV Link in drone applications. We recommend that you consult the local authorities to confirm the frequency availability and limitation on max. transmit power in your locality. In the situation where free ISM band/TV band is not available, licensed channel (<1GHz) may be used.
|ISM Band||TV Band|
|New Zealand||921-929 MHz||510-606 MHz|
|Singapore||866-869 MHz; 920-925 MHz||502 – 806 MHz|
|UK||863-868 MHz||470 – 790 MHz|
|USA||902 – 928 MHz||470-698 MHz|
SL HD Link
We propose the use of TV/ISM band link operating in the < 1GHz frequency spectrum for HD AV Communications. Compared to 2.4GHz radios, for the same transmit power, SL HD link has a higher range, better penetration capability through foliage/buildings and works Non Line of Sight (NLOS).
Saankhya Labs has developed a robust single channel USB based DTV Transmitter (SLM901UU) and Receiver (SLM102UU) for HD AV transmission from the drone to the base station.
Low Power Multi-Standard DTV Transmitter with 0dBm output. It has been tested to work with a receiver as far away as 600m. If the amplifier stage is replaced with a higher gain amplifier, higher range can be obtained. Selection of antenna is also critical – and it has to be omnidirectional, operate in the <1GHz band and be light weight. Selecting a narrow UHF frequency band for transmission will reduce the size/weight of the antenna and thereby improve the battery life.
The Transmit Module interfaces to the HD Camera on board the drone via USB (and derives its power from USB port). The setup diagram if the HD camera on board is an IP based camera is shown below. The IP camera output is connected to Drone mother board, where the software extracts the TS data from the IP stream and routes it over USB to the modulator board.
Multi-Standard HD Receiver for Tablets and other CE devices on the ground. The receiver can be programmed to support reception of ATSC, DVB-T, ISDBT DTV standards from off the air signals. The receiver connects to the Tablet/Smartphone via USB. Android/Linux application needs to be programmed in the smartphone/tablet and paired with the receiver. A simple indoor antenna with built-in amplifier can be used for best reception performance.
The Receive Module interfaces either to the base controller or Tablet used for viewing the HD Video on the ground via USB interface.