AAL technologies constitute a new paradigm that promises quality of life enhancements in chronic care patients and elderly people. From a communication perspective, they involve heterogeneous deployments of body and ambient sensors in complex multihop topologies. Such networks can significantly benefit from the application of cooperative schemes based on network coding, where random linear combinations of the original data packets are transmitted in order to exploit diversity. Nevertheless, network coordination is sometimes required to obtain the full potential of these schemes, especially in the presence of channel errors, requiring the design of efficient, reliable, and versatile MAC protocols. Motivated by the recent advances in cloud computing, we investigate the possibility of transferring the network coordination to the cloud while maintaining the data exchange and storage at a local data plane. Hence, we design a general framework for the development of cloudassisted protocols for AAL applications and propose a high-performance and error-resilient MAC scheme with cloud capabilities.  AMBIENT ASSISTED LIVING COMMUNICATIONS From a communication perspective, an AAL system usually requires the joint deployment of mobile wireless body area networks (WBANs), formed by sensors deployed in the vicinity of or within the body of moving users, and static ambient wireless sensor networks (WSNs). In this heterogeneous scenario, the low-power shortrange wireless technologies specified within the standards IEEE 802.15.6 and IEEE 802.15.4 for WBANs and WSNs, respectively, are usually employed for sensor interconnection [8] . Although these standards define the basic mechanisms for channel access and transmissions, there are still many open challenges in order to ensure energy-efficient and reliable communication. Given the dense deployment of multiple sensors within a specific area, it is possible to achieve significant enhancements by exploiting diversity through node cooperation. The key idea of cooperative schemes is to encourage nodes to act as relays and forward information overheard by neighboring transmissions. Furthermore, with the introduction of network coding, intermediate nodes can combine and process different received information flows in order to achieve performance improvements even in resource constrained networks such as WBANs [9] . However, the benefits of network coding cannot be fully exploited in the presence of channel errors, and under hostile indoor and body area propagation environments the amount of redundancy required to ensure successful decoding can be prohibitive. An effective way to drastically reduce redundant retransmissions without compromising performance is by enabling the exchange of information among the relays, allowing them to act in a coordinated manner. Hence, novel medium access control (MAC) protocols must be envisioned to handle data transmissions and relay cooperation in such dynamic and multihop topologies. Nevertheless, as deployments tend to grow in complexity, the network coordination becomes overwhelming due to the high number of nodes and the large amount of collected data. Furthermore, distributed approaches may require the nodes to have increasing processing power and storage capabilities. Recent advances in cloud computing offer an alternative solution to mitigate these challenges. This new paradigm, which is revolutionizing the way information systems are designed, is based on a shared pool of hardware and software resources that are easily accessible via the Internet and often managed by third-party providers. Current research on cloud-based pervasive healthcare is still in its initial steps [10], but it seems that there are tremendous opportunities to be seized through the seamless integration of cloud technology and WBANs [11] . Typical cloud services include data storage, processing, and hosting of medical application services and interfaces [12, 13] . A less investigated but equally intriguing topic is to employ cloud resources at lower communication layers, to design innovative MAC protocols and routing schemes with increased flexibility and reconfigurability. In one of the few existing works in this context [14] , a cloud-assisted MAC protocol has been proposed and implemented for a WLAN deployment. The main idea is to transform the access points into a unified user interface and concentrate MAC layer functions to virtual machines provided by cloud services. This novel concept is rather focused on implementation issues, thus offering a significant practical contribution. Another interesting work in [15] gives some preliminary insights on the use of network coding in complex large-scale networks where multiple relay nodes interacting with each other form a wireless cloud. The presented results show the potential gains of different transmission strategies in a very simple topology. The authors also indicate the need for some level of inter-cloud cooperation in order to ensure the best strategy selection by the relays, which can be a challenging task in large-scale networks. Summarizing, these works show that cloud-based solutions for the MAC layer can yield promising results; however, there is a need to establish solid frameworks for the implementation of these schemes. In this article, we present a novel cloud-based architecture conceived for AAL environments where medical and ambient sensors are densely deployed. We envision a scenario where part of the sensor infrastructure is connected to the cloud, forming a network of cloud-enabled relays that can significantly enhance the flow of information within the system. An innovative feature of our framework is that we transfer the network coordination to a central controller, which is located at the cloud and communicates with the nodes through a cloud-assisted control plane, whereas we maintain the exchange and storage of data packets to a local data plane. The remainder of this article is organized as follows. Initially, we describe the proposed cloud-assisted framework, defining the different operation planes and the key architecture components. We then present a specific case study on the application of network coding in cooperative relay networks to illustrate the significant potential of the proposed framework. After identifying a major performance weakness of network coding schemes in the presence of link failures, we propose a novel cloud-assisted MAC scheme that employs cloud resources to achieve relay coordination and demonstrate, through simulation-based performance evaluation, the significant performance gains that can be obtained. Then we provide some suggestions for future lines of research, stemming from the application of the proposed framework to a wide range of applications for AAL environments. Finally, we close the article with some general conclusions. The proposed technology agnostic cloud-based framework defines two planes of operation, as shown in Fig. 1 . The Cloud-Assisted Control Plane -responsible for the network control and coordination. Control signaling has the form of very short
In REF , the authors proposed a framework for designing efficient cloud-assisted protocols in ambient assisted living environments.
Reliable MAC design for ambient assisted living: moving the coordination to the cloud
IEEE Communications Magazine
IEEE Communications Magazine
Computer Science