An analysis of speeding multicast by acknowledgment reduction technique (SMART) with homogeneous and heterogeneous links - a method of types approach

We present a novel feedback protocol for wireless broadcast networks that use linear network coding. We consider transmission of packets from a single source to many receivers over a single-hop broadcast erasure channel with heterogeneous links. We propose a predictive model to minimize feedback as well as extraneous data transmissions by the source. The predictive model will schedule feedbacks only when there is a significant probability that all receivers have completed the download. We demonstrate analytically as well as empirically that reliable multicast can provide a good completion time characteristic for all users, if the initial feedback is delayed until the expected download completion time. We show that with SMART, counter to conventional wisdom the average user's download completion time improves slightly as the number of users increases. Furthermore, we show that completion time of the worst user in a multicast session is not very sensitive to the number of users; however it is very sensitive to imbalanced effective rate and heterogeneity among users. Moreover, we show that SMART performs nearly as well as an omniscient transmitter that requires no feedback.