  A two-hop wireless communication link in which a source sends data to a
destination with the aid of an intermediate relay node is studied. It is
assumed that there is no direct link between the source and the destination,
and the relay forwards the information to the destination by employing the
decode-and-forward scheme. Both the source and intermediate relay nodes are
assumed to operate under statistical quality of service (QoS) constraints
imposed as limitations on the buffer overflow probabilities. The maximum
constant arrival rates that can be supported by this two-hop link in the
presence of QoS constraints are characterized by determining the effective
capacity of such links as a function of the QoS parameters and signal-to-noise
ratios at the source and relay, and the fading distributions of the links. The
analysis is performed for both full-duplex and half-duplex relaying. Through
this study, the impact upon the throughput of having buffer constraints at the
source and intermediate relay nodes is identified. The interactions between the
buffer constraints in different nodes and how they affect the performance are
studied. The optimal time-sharing parameter in half-duplex relaying is
determined, and performance with half-duplex relaying is investigated.
