Some wireless devices are only meant to receive data, and are not able or allowed to send back information to the network using a wireless return channel. In this post we look at how and why OTAcast is a great solution in such cases.
Why is return channel use sometimes restricted?
There are two main groups of devices where a wireless return channel is not allowed or useful:
Devices which need to stay radio silent during operation to avoid being identified by radio triangulation (radio direction finding). This applies to a range of devices used by the military and the intelligence communities to for example receive real-time situational awareness information.
Devices used on networks where a single transmitter serves a big number (100+) of devices. In this case a return channel becomes a scarce resource and allowing devices to compete for access to the return channel, especially for simple packet acknowledgement messages, should be avoided to prevent stalling the network. In fact it is better to avoid using a return channel entirely, especially during file transfers like video clips, images or map transfers. The return channel should instead be reserved for the devices to send critical messages.
OTAcast does not need a return channel
The OTAcast coding library is able to code and decode long messages - like a video clips, images or maps - without being reliant on a return channel for acknowledgements during transmission. This also makes OTAcast coded messages ideal for broadcasting a message to all devices as quickly as possible, while making sure the new information is delivered to all devices without parts missing.
How OTAcast works
OTAcast codes the information to be transmitted in a way that ensures every data packet received by a device has new information and ensures losing data packets does not matter as long as any other data packet will be received. When the device has received a certain number of data packets it will have all it needs to finish decoding the information in its entirety. It does not have to receive a certain sequence or certain set of data packets, only a certain number. This means each device will receive the information as quickly as possible, and a device will never end up waiting for a specific missing packet to be retransmitted. This property allows OTAcast to avoid using a return channel..
OTAcast also functions with intermittent radio connections. Whenever the network is transmitting coded data packets and there is an active connection, the device can collect the data packets, and when the device has received enough data packets, the device decodes the information and presents it to the user.
The extra processing and memory overhead from OTAcast is well within the capabilities of modern embedded microcontrollers and the coded data is just 1-2% more than the original data making it easy and straightforward to integrate OTAcast.