  A network consisting of $n$ source-destination pairs and $m$ relays is
considered. Focusing on the large system limit (large $n$), the throughput
scaling laws of two-hop relaying protocols are studied for Rayleigh fading
channels. It is shown that, under the practical constraints of single-user
encoding-decoding scheme, and partial channel state information (CSI) at the
transmitters (via integer-value feedback from the receivers), the maximal
throughput scales as $\log n$ even if full relay cooperation is allowed.
Furthermore, a novel decentralized opportunistic relaying scheme with receiver
CSI, partial transmitter CSI, and no relay cooperation, is shown to achieve the
optimal throughput scaling law of $\log n$.
