Fast image file distribution with Fountain codes via a Wi-Fi ad-hoc network, using low power processors

In this work we propose a system to efficiently broadcast large files at maximum Wi-Fi transmission speed over an ad-hoc network using Fountain codes. With this type of rateless encoding we were able to avoid the feedback channel from the receivers and the need to retransmit the lost packets. This way it is possible to take advantage of the full bandwidth of the channel to transmit useful data. To encode each packet the system has to select n different symbols and since they are chosen randomly from K symbols sized image, the system has to pick a few (symbols) far apart from each other. This makes the CPU cache useless, decreasing the efficiency of the codeword generation process when the message size K is very large, especially on low power processors like ODROID-U3 and RaspberryPI. To overcome this problem we study a Block Angular encoding approach witch divides the message in nb blocks, small enough to be inside the CPU cache. In this paper we compare the encoding results using regular LT codes and the Block Angular codes, discussing its pros and cons in relation to the DETIboot system and other file distributing systems.