Fountain-Code Aided File Transfer in 802.11 WLANs

Fountain codes constitute novel erasure codes, which have been standardized for Forward Error Correction (FEC) in broadcast network protocols and by the Third-Generation Partnersonhip Project (3 GPP). The basic operational units of Fountain codes are source packets, which have a particular fixed length. These codes are invoked here in an 802.11 Wireless Local Area Network (WLAN) scenario for protecting file transfers. More specifically, the optimal packet length is selected by considering the 802.11 Media Access Control (MAC) retransmission rate and the properties of the physical layer´s modulation scheme. Naturally, owing to the limited memory of the encoders/decoders, large source files must be decomposed into shorter transport blocks. Therefore, methods for partitioning the file and acknowledging the successful transmission of each block are also proposed here. Compared to the file transfer regime operating without FEC over the classic TCP protocol, the proposed regime requires a lower threshold SNR for accomplishing a successful file transfer and hence enhances the transmission efficiency by about 50%.