Fast Finish - New Techniques To Prevent NACK Feedback Implosion In Network Coded Multicast

摘要

We present a new feedback mechanism for wireless broadcast networks that utilize linear network coding. The setup considers transmission of packets from one source to n receivers over a single-hop erasure broadcast channel, but the proposed scheme is applicable to more general lossy networks. Previous feedback protocols can be roughly categorized as systems where all packets use ARQ which requires one feedback message from each receiver upon download completion. Our scheme utilizes a predictive model to ask for feedback only when necessary, i.e. if the probability that all receivers have completed decoding is high. In addition, the proposed NACK-based feedback mechanism enables n receivers to request the number of retransmissions needed for successful decoding within a single time slot. This is in contrast with traditional feedback systems whereby each user will be independently polled and thus the feedback presents a costly challenge to the performance of the network. In particular, we compare the performance of our mechanism with the state of the art negative feedback protocol NORM. We present simulation results that describe the implementation issues concerning the feedback time as well as analytical results that show the scalability of our proposal as the file size, number of receivers, and packet erasure probability increase.