Dual-hop adaptive packet transmission systems with regenerative relaying

We propose and analyze two different approaches for performing adaptive modulation and coding (AMC) in dual-hop transmission systems, where a source node S communicates with a certain destination node D via an intermediate decode-and- forwarding relay station R. In this regard, we consider the most general case, where the AMC on the S-R and R-D links might be performed independently of each other, thus requiring a potential buffering of data packets at the relay station before they can be forwarded to the destination D. With our first approach, AMC is performed solely based on the instantaneous channel realizations, without considering the current buffer level at the relay station, what consequently might result in packet losses due to potential buffer overflows. Our second approach eliminates this problem by taking the current buffer level into account in the AMC transmission over the first hop and reducing the transmission rate accordingly if the buffer would overflow otherwise. Both schemes are analyzed analytically based on a finite-state Markov chain model of our system. Building upon this model, we derive analytical closed-form expressions for a variety of different key performance indicators, which are illustrated for various practical cases by means of selected numerical results.