ZipTx: Harnessing Partial Packets in 802.11 Networks

Current wireless protocols retransmit any packet that fails the checksum test, even when most of the bits are correctly received. Prior work has recognized this inefficiency, however the proposed solutions (e.g., PPR, HARQ and SOFT) require changes to the hardware and physical layer, and hence are not usable in today's WLANs and mesh networks. They are further tested in channels with fixed modulation and coding, whereas production 802.11 networks adapt their modulation and codes to maximize their ability to correct erroneous bits. This paper makes two key contributions: 1) it introduces ZipTx, a software-only solution that harvests the gains from using correct bits in corrupted packets using existing hardware, and 2) it characterizes the true gains of partially correct packets for the entire range of operation of 802.11 networks, and in the presence of adaptive modulation and error correcting codes. We implement ZipTx as a driver extension and evaluate our implementation in both outdoor and indoor environments, showing that ZipTx significantly improves the throughput.