Nevertheless, most schemes assume deterministic transmission sequences, without considering MAC layer channel access rules. In addition, their performance significantly drops when channel errors are introduced, since high redundancy is required in the sense that more retransmissions must take place in order for the receiver to successfully decode the received encoded packets. As a result, the potential RLNC gain is not fully exploited. These problems can be mitigated by employing a MAC protocol that enables the exchange of information among the relays. However, relay cooperation usually introduces significant overheads and complexity that may not always be supported by low-power WSNs or WBANs. An alternative approach is to adopt a centralized architecture, where all the relays form part of a cloud infrastructure that is controlled by a central entity.

In this paper, we focus on an ambient WSN that acts as a distribution network, connecting one or more WBANs (sources) to a central process unit (destination), and investigate MAC schemes that efficiently handle the flow of information between the two communication ends. Initially, as a reference scheme, we consider baseline MAC (BS-MAC) based on the IEEE 802.15.6 MAC mechanism with slight modifications to support the multi-hop relay topology. In continuation, we apply the RLNC principles to the baseline scenario (NC-MAC), to show the potential gains and to identify significant performance weaknesses in the presence of channel errors.

Finally, we propose a cloud-assisted RLNC-based MAC (CLNC-MAC) that employs centralized control to coordinate transmissions in the relay network, in order to exploit the benefits of RLNC and enhance both performance and reliability.Very few related works can be found in the literature in this context. In [13], a cloud-assisted MAC protocol has been proposed and implemented for wireless local area network (WLAN) deployment. The main idea is to transform the access points into a unified user interface and concentrate MAC layer functions and processing to virtual machines provided by cloud services. Even though the practical contribution of this work is significant, no enhancements are made with respect to the MAC layer mechanism. In particular, the main discussion focuses on implementation issues, i.e., the modification of WLAN cards for virtual interconnection through an OpenFlow switch, whereas the IEEE 802.

11 MAC is employed with no major modifications. The aim of our work is different, since we adopt the cloud architecture as a means to exploit the potential of RLNC in cooperative relay scenarios. Carfilzomib We propose modifications on the IEEE 802.15.6 MAC layer protocol in order to coordinate the request for retransmissions and the data relaying with the help of the cloud, thus enhancing the decoding process of the NC packets at the destination.