Do not Waste the Waste: Packetized Rateless Algebraic Consistency for IEEE 802.11 Networks

Future communication systems will require low latencies, especially for the small packets used in control applications. In WiFi systems, the main contributors to delays are retransmissions and congestions. Many of the transmitted packets are received with errors at the destination, and they are dropped at the MAC layer. Even if the number of errors is small the packets are discarded. Dropped partial packets are retransmitted, increasing the delays of the system because retransmissions involve new access to a shared medium. We show in our measurement campaign of IEEE 802.11 networks that between 5% and over 50% of the received packets, depending on the Modulation and Coding Scheme (MCS), have errors. However, only a few bits are erroneous (between 2% and 10%). Therefore, we show that a partial packet recovery technique based on network coding can make use of 55% more packets that otherwise would be dropped, which reduces the number of retransmissions and delays. Furthermore, if the length of the packets is short (between 50 and 250 Bytes) the computational overhead is low, which makes the implementation feasible, in such networks, for the short packets typical of applications of control of cyber-physical systems.