Monday, November 30, 2020

nerfnet: Streaming Video over nRF24L01

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.

Continue reading to learn more!

Friday, November 27, 2020

nerfnet: Wireless Networking over nRF24L01 2.4GHz Radios

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.