Practical Issues in Multi-User Physical Layer Network Coding
The throughput of multiple access systems is limited by the collisions that take place when more than one node accesses the channel in the same time slot. This limitation is particularly problematic in satellite networks with random access, where the long Round-Trip Time (RTT) greatly limits feedback from the receiver, for example to perform load control or to request retransmissions. The authors address several implementation issues related to multi-user physical layer network coding, in which the symbol synchronous collision of an arbitrary number of signals is decoded. In particular, they study the effect of frequency and phase offsets, the imperfect symbol synchronization of the colliding signals and the estimation of frequency and phase offsets and amplitudes in the presence of more than two colliding signals.