Recently proposed physical-layer network coding
(PNC) [1] has demonstrated the promise to significantly improve
the throughput of wireless networks whose links can be modeled
as additive white Gaussian noise (AWGN) channels. However,
the extension to multipath channels is problematic, since the
technique would then require both amplitude and phase compensation
at each transmitter. Phase compensation requires accurate
distributed phase tracking, whereas the required amplitude
compensation is even more troubling, as it leads to an inefficient
system that yields no diversity even in the presence of perfect
channel estimates. Here, a system that avoids these limitations is
obtained by reaching up one level higher in the network hierarchy
and performing distributed relay selection with cognizance of the
PNC technique that we will employ at the physical layer. Since
the resulting scheme will achieve a form of selection diversity,
we term it “network coding with diversity” (NCD). To facilitate
performance evaluation, two information-theoretic metrics, the
outage and ergodic capacity, are studied. Our analytical and
simulation results show that the proposed protocol achieves
more robust performance and higher system throughput than
comparable schemes. Finally, the proposed network coding is
extended to the context of cooperative multiple access channels,
which yields a new cooperative protocol with larger outage and
ergodic capacity compared with existing transmission schemes.