are uniformly improved.

The structure of this paper is as follows. In Section \[sec:model\], we present the system model. Section \[policies\] reviews the most relevant relay selection schemes and Section \[sec:minpow\] introduces the $\minpow$ relay selection policy proposed herein. Then, a model of this communication scheme and an outage probability analysis is performed in Section \[sec:outage\], while illustrative examples and numerical results are provided in Sections \[sec:examples\] and \[sec:numerical\], respectively. Finally, conclusions are discussed in Section \[sec:conclusions\].

System model {#sec:model}
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We assume a simple cooperative network consisting of one source $S$, one destination $D$ and a cluster $\mathcal{C}$ with $K$ Decode-and-Forward (DF) relays $R_k \in \mathcal{C}$ ($1 \leq k\leq K$). All nodes are characterized by the half-duplex constraint and therefore they cannot transmit and receive simultaneously. A direct link between the source and the destination does not exist and communication can be established only via relays [@BLE]. Each relay $R_k$ holds a buffer (data queue) $Q_k$ of capacity $L$ (number of data elements) where it can store source data that has been decoded at the relay and can be forwarded to the destination. The parameter $l_k \in \mathbb{Z}_{+}$, $l_k \in[0, L]$ denotes the number of data elements that are 