A couple of days ago I published a blog discussing how I used NRF24L01 radios to implement a point-to-point network between two Raspberry Pi computers. I implemented this as a virtual network device and sent packets between the radios.
Since then, I have made numerous improvements to the software and more than tripled the throughput from ~90kbps to nearly 300kbps. These improvements were through a variety of changes that I will cover in this blog post.
Streaming video from one headless Raspberry Pi to another
Thanks to the higher throughput, I was able to implement streaming video using the h264 HEVC video codec and monaural audio using the Opus codec at 32kbps. The result is great, especially when considering the link.
I recently picked up a set of nRF 2.4GHz radio transceivers. These are low-cost radios with a SPI interface that allow exchanging 32 byte packets across a radio link that can run at up to 2MBit on-air data rates. They are popular among hobbyists who want to introduce wireless to their Arduino-flavored projects. I was able to buy ten of these radios with trace antennas for just $11 and three more with SMA-connected antennas for $18.
NRF24L01 Radios
My first inclination is to try something a bit more extreme with this hardware. There is a GitHub project named RF24Audio that allows transmitting audio data over these radios. I wondered if video could be possible and started brainstorming about how a video transport over this link would look. The further I got into the specifics of streaming video the more convinced I was that an abstract link that could carry any form of data would be more fun.
This led me to build nerfnet: a simple application that allows sending network frames over NRF24L01 radios. This is implemented by exploiting the TUN/TAP virtual network device API under Linux on a Raspberry Pi. The code is available on GitHub for you to review and use.
I was able to demonstrate nearly 90kBit throughput as measured by iperf. I suspect this is the first time that iperf has been used to characterize a link composed of these radios.
andrew@andrew-pi:~/Projects/nerfnet $ iperf -c 192.168.10.2
------------------------------------------------------------
Client connecting to 192.168.10.2, TCP port 5001
TCP window size: 43.8 KByte (default)
------------------------------------------------------------
[ 3] local 192.168.10.1 port 34490 connected with 192.168.10.2 port 5001
[ ID] Interval Transfer Bandwidth
[ 3] 0.0-10.1 sec 110 KBytes 89.4 Kbits/sec
Continue reading or watch the video to learn more about how I pulled this off.
