Low-Complexity Buffer-Aided Link Selection With Outdated CSI and Feedback Errors

Buffer-aided relays can improve the diversity of multi-hop networks, however, they increase packet delays. Thus, various delay-aware protocols have been developed, but without considering the transmission diversity. Moreover, most works adopt ideal assumptions, such as symmetric links, perfect channel state information (CSI), and error-free feedback channels. So, we propose a low-complexity (LoCo) link selection algorithm, herein called <inline-formula> <tex-math notation="LaTeX">$\mathop {\mathrm {LoCo\!\!-\!\!Link}}$ </tex-math></inline-formula>. The proposed algorithm may experience delays during CSI updates, and hence, by using outdated CSI its performance may deteriorate. To alleviate this issue, we next propose a distributed version of <inline-formula> <tex-math notation="LaTeX">$\mathop {\mathrm {LoCo\!\!-\!\!Link}}$ </tex-math></inline-formula> (<inline-formula> <tex-math notation="LaTeX">$\mathop {\mathrm {d\!\!-\!\!LoCo\!\!-\!\!Link}}$ </tex-math></inline-formula>) dealing with outdated CSI. In both algorithms, the source performs broadcasting toward multiple relays; when the packets are transmitted by a relay to the destination, they are discarded from all other relays. This coordination relies on feedback channels. For non error-free feedback channels, we propose a scheme in which the relays listen to the transmission of the best relay and drop duplicate packets. Results show that <inline-formula> <tex-math notation="LaTeX">$\mathop {\mathrm {LoCo\!\!-\!\!Link}}$ </tex-math></inline-formula> surpasses other algorithms, by decreasing the delay in asymmetric networks. Moreover, <inline-formula> <tex-math notation="LaTeX">$\mathop {\mathrm {d\!\!-\!\!LoCo\!\!-\!\!Link}}$ </tex-math></inline-formula> avoids diversity losses due to outdated CSI, while the effect of non error-free feedback channels is mitigated by taking advantage of the inter-relay channels.