1 research outputs found
Compute-and-Forward in Large Relaying Systems: Limitations and Asymptotically Optimal Scheduling
Compute and Forward (CF) is a coding scheme which enables receivers to decode
linear combinations of simultaneously transmitted messages while exploiting the
linear properties of lattice codes and the additive nature of a shared medium.
The scheme was originally designed for relay networks, yet, it was found useful
in other communication problems, such as MIMO communication. Works in the
current literature assume a fixed number of transmitters and receivers in the
system. However, following the increase in communication networks density, it
is interesting to investigate the performance of CF when the number of
transmitters is large.
In this work, we show that as the number of transmitters grows, CF becomes
degenerated, in the sense that a relay prefers to decode only one (strongest)
user instead of any other linear combination of the transmitted codewords,
treating the other users as noise. Moreover, the system's sum-rate tends to
zero as well. This makes scheduling necessary in order to maintain the superior
abilities CF provides. We thus examine the problem of scheduling for CF. We
start with insights on why good scheduling opportunities can be found. Then, we
provide an asymptotically optimal, polynomial-time scheduling algorithm and
analyze its performance. We conclude that with proper scheduling, CF is not
merely non-degenerated, but, in fact, provides a gain for the system sum-rate,
up to the optimal scaling law of