Connectivity

ANAFI Ai integrates a 4G radio module (in addition to the Wi-Fi radio) allowing to transmit a video in 1080p with a very low latency (300 ms) without range limit and everywhere in the world.

Compatibility

The ANAFI Ai 4G module supports more than 28 frequency bands, covering more than 98% of the frequencies deployed around the world.

Automatic network switch

The quality and capacity of the 4G and Wi-Fi networks are measured every 100 ms to adapt the streaming to the network conditions. Combined with the routing algorithms, the connection between the drone and its controller is maintained even when the Wi-Fi is strongly disrupted. Thus, when the effective throughput (goodput) of Wi-Fi is lower than 1.5 MBps, the system automatically switches to 4G.

To limit mobile data consumption when the pilot is within range of the drone's Wi-Fi network, the 4G to Wi-Fi transition is also automatically performed, without video stream cut.

The implemented video stream optimization algorithms:

“Congestion control 4G”

The congestion control algorithm allows to:

• Measure packet loss over the entire network loop
• Measure the latency (Round Trip Time)
• Adapt the throughput according to these two parameters

The final objective of the algorithm is to maximize the available throughput while maintaining the lowest possible latency. This algorithm is implemented on each of the interfaces available on the drone, each one having its own parameters optimized according to the network. Thanks to the information provided by this algorithm, the link supervisor decides on the routing and the active interface.

“Remote control drone connection in 4G”

ANAFI Ai connects to the 4G remote control in less than 30 seconds when the drone is not in Wi-Fi range, and in less than 15 seconds when the drone is in Wi-Fi range.

• Discovery and initiation of the connection based on the VOIP SIP protocol
• Use of a relay server to establish the connection on secured networks

Video stream performances

• Latency: 300 ms
• Security: Video and controls secured by SRTP/DTLS in accordance to webRTC
• Antennas: 28 LTE bands between 700 Mhz and 2.6 Ghz

"Omni-directional transmission system“

ANAFI Ai has 4 directional antennas with reflector (gain: 2.5 dBi/antenna). The drone determines the best antenna pair depending on its orientation and position in relation to the pilot's position.

With a recombined gain of 3.5 +/-1.5 dBi in the horizontal plane of the drone, the radio gain of ANAFI Ai is strong homogeneous.

The downward radiation of the antennas has been improved by +4 dB compared to ANAFI.

High Power Radio Front-End Design

The radio front end allows to push the power to the maximum at the foot of the antenna with a very good level of linearity and sensitivity (-94 dBm at 6.5 Mbs), allowing to reach the maximum power of the FCC limit.

Robust Wi-Fi Connection

Parameters 802.11:

A subset of protocol parameters was selected to optimize performance in the drone use cases: relatively low throughput, low latency, variability in reception levels due to drone speed, long range, presence of interferers. These parameters include aggregation, number of retries, MiMo technology (STBC), management frame datarate, and disconnection conditions.

Flow adaptation and monitoring

ANAFI Ai continuously monitors its connection status at 4 Hz and can detect the presence of interference. This allows to dynamically optimize the throughput and the size of the transmitted packets. It also alerts the pilot if he is in a particularly interference-laden environment, or if he is close to losing the signal.

“Smart interference avoidance system“

ANAFI Ai has a channel avoidance algorithm (dual band 2.4 GHz and 5 GHz) in case of interference detection.

Bandwidth reduction

At the limit of its range and if the conditions allow it, ANAFI Ai can switch to 10 MHz bandwidth to improve its sensitivity by 3 dB and gain 40% in range.

The implemented video stream optimization algorithms:

Parrot Gen4 Streaming (4th generation)

“Error concealment”

This algorithm reduces the visual impact of losses on the network and it enables the interoperability of all decoders, while ensuring a syntactically complete stream: missing images parts are reconstructed as skipped portions, identical to those of the reference image.

The glitches are therefore contained within zones impacted by losses, and do not spread to the entire image.

The following graphs illustrate the rate of success in decoding macroblocks, for a network loss rate of 5% - with and without ANAFI Ai’s advanced streaming functions. The algorithm ensures a correct decoding for 75% of the macroblocks. Those enable the user to carry on with his mission without screen freeze or streaming loss.

“Congestion control”

The algorithm estimates the Wi-Fi and radio environment to anticipate and avoid packet loss and congestion on the network, thus helping to reduce latency.

The algorithm is based on an estimate of the link capacity calculated from the data rate and the error rate at the physical level; it then acts on the network encoding and encapsulation parameters.

Metadata

Metadata are transmitted with the video stream. They notably contain drone telemetry elements (position, altitude, speed, battery level, etc.) and video metrics (angle of the camera, exposure value, field of view, etc.).

The synchronization of the images and the metadata open functions as precise map positioning, flight instrument tracing within the HUD or augmented reality elements inclusion.

The inclusion of metadata is using standard methods (RTP header extension); the format of the data, defined by Parrot, is public: it is available within ANAFI Ai’s SDK.