The four transports of Remote ID

The Remote ID standard precisely prescribes what a drone must broadcast, but leaves open how. The manufacturer chooses from four radio transports. That is convenient for the manufacturer, who uses the chip already in the drone, and awkward for anyone who wants to receive. A receiver that only listens to one transport does not see part of the drones. Below are the four transports and what they mean in practice.

Bluetooth 4: Legacy Advertising

The oldest transport uses the advertising packets of Bluetooth Low Energy, the same technique a fitness tracker uses to announce itself. An advertising packet has room for 25 bytes of Remote ID data. That is too little for the complete message, so the drone alternates between a packet with the identity, one with the position and one with the pilot’s position.

The advantage is that every Bluetooth chip can do it, including older ones. The disadvantage is range. Bluetooth 4 transmits with limited power on 2.4 GHz and the packets are short, so a receiver needs a good antenna and a line of sight to pick them up at a distance.

Bluetooth 5: Long Range

Bluetooth 5 added the Coded PHY, a modulation that encodes each bit several times (S2 or S8). This makes the signal resistant to more noise and lets a receiver decode it from further away, at the cost of data rate. The standard uses S8 and extended advertising, so the full Remote ID message fits in a single packet.

Newer drones often broadcast both Bluetooth 4 and Bluetooth 5 so that old and new receivers see them. A receiver that supports Long Range therefore usually picks up a drone earlier than over Bluetooth 4.

WiFi Beacon

Many drones keep a WiFi link with the controller or the pilot’s phone. For those drones it makes sense to put Remote ID in the WiFi beacon: the frame every access point uses to announce its network name. The Remote ID data sits in a vendor-specific element in that frame, on 2.4 or 5 GHz.

WiFi transmits with more power than Bluetooth, so the range is greater under favourable conditions. The disadvantage is that a receiver has to scan all channels, because the drone itself chooses the channel it broadcasts on.

WiFi NaN

Neighbor Awareness Networking, also known as WiFi Aware, is an extension of WiFi that lets devices find each other without a connection or access point. The Remote ID message sits in service discovery frames broadcast at fixed moments. The European standard EN 4709-002 requires receivers to support this transport, and it is the transport Android phones receive most reliably.

What does this mean for range?

The quoted range of a receiver is always a combination of three factors: the transmit power of the drone, the antenna and height of the receiver and what stands between the two. Rain and buildings attenuate the signal on 2.4 and 5 GHz considerably. A building between drone and receiver can reduce the range from kilometres to hundreds of metres.

That is why the AEROTECT DRID listens on all four at once, with omni antennas covering 360 degrees. That gives 7.5 kilometres in urban areas and 15 kilometres in rural areas. We quote those figures together with the conditions, because a receiver at eye level behind a grandstand will never reach them and a directional antenna goes well past them.

What to look for in a receiver

• Does it support all four transports, or only Bluetooth?
• Can it be mounted at height, outdoors, in the rain?
• How does the data reach your team: over a cable, over 4G, in a platform that merges several receivers?
• What happens with duplicate observations when two receivers see the same drone?