Towards Efficient Mobile M2M Communications: Survey and Open Challenges <s> Energy Efficiency <s> It is envisioned that home networks will shift from current machine-to-human communications to the machine-to-machine paradigm with the rapid penetration of embedded devices in home surroundings. In this article, we first identify the fundamental challenges in home M2M networks. Then we present the architecture of home M2M networks decomposed into three subareas depending on the radio service ranges and potential applications. Finally, we focus on QoS management in home M2M networks, considering the increasing number of multimedia devices and growing visual requirements in a home area. Three standards for multimedia sharing and their QoS architectures are outlined. Cross-layer joint admission and rate control design is reported for QoS-aware multimedia sharing. This proposed strategy is aware of the QoS requirements and resilience of multimedia services. Illustrative results indicate that the joint design is able to intelligently allocate radio bandwidth based on QoS demands in resource-constrained home M2M networks. <s> BIB001 </s> Towards Efficient Mobile M2M Communications: Survey and Open Challenges <s> Energy Efficiency <s> Machine-to-machine communications is characterized by involving a large number of intelligent machines sharing information and making collaborative decisions without direct human intervention. Due to its potential to support a large number of ubiquitous characteristics and achieving better cost efficiency, M2M communications has quickly become a market-changing force for a wide variety of real-time monitoring applications, such as remote e-healthcare, smart homes, environmental monitoring, and industrial automation. However, the flourishing of M2M communications still hinges on fully understanding and managing the existing challenges: energy efficiency (green), reliability, and security (GRS). Without guaranteed GRS, M2M communications cannot be widely accepted as a promising communication paradigm. In this article, we explore the emerging M2M communications in terms of the potential GRS issues, and aim to promote an energy-efficient, reliable, and secure M2M communications environment. Specifically, we first formalize M2M communications architecture to incorporate three domains - the M2M, network, and application domains - and accordingly define GRS requirements in a systematic manner. We then introduce a number of GRS enabling techniques by exploring activity scheduling, redundancy utilization, and cooperative security mechanisms. These techniques hold promise in propelling the development and deployment of M2M communications applications. <s> BIB002 </s> Towards Efficient Mobile M2M Communications: Survey and Open Challenges <s> Energy Efficiency <s> A new concept for Machine-to-Machine (M2M) communications infrastructure via airliners is presented. The main principles and resulting challenges are described. A first study on possible coverage within Europe and North America using airliners endorses the concept's feasibility. Furthermore, system dimension aspects are investigated in a proof-of-principle manner to understand its feasibility. All commercial flights during 24 hours were considered on the basis of real global flight data. Paper's goal is stimulating further research activities and ideas in this area. <s> BIB003
Resource usage efficiency is one of the most important requirements for mobile M2M communications when using radio technologies, due to lower available bandwidth, higher link failure, and higher energy consumption. The amount of devices and the requisite that they might have to operate for many years with the same battery, or consuming the least possible energy, demands for energy efficiency in M2M communications BIB001 BIB002 . Lu et al. BIB002 argue that M2M communications cannot be widely accepted as a promising communication technology, if energy efficiency is not met. In Section 7 we illustrate the importance of energy efficiency when using smartphones as mobile M2M gateways. The concept of using a mobile M2M gateway device as an intermediary node to collect and process data from neighbouring sensors is approached by Wu et al.  , who name it a smart M2M device, and Zhang et al. BIB001 , who name it a cognitive gateway. Both works argue that connecting devices through a gateway should be preferred when they are sensitive to cost or power. The use of M2M gateways shall have a direct impact in the reduction of devices accessing and using the channels for communications, reducing interference and contention, and increasing the efficiency. Reducing the number of devices in networks also translates into easier to deploy and less complex transmission scheduling schemes, and eases the problem of the depletion of the pool of unallocated IP addresses. New applications and business opportunities will come along with mobile M2M communications. For example, the innovative idea of using the already existing scheduled airliners as relays between ground devices and satellites, providing a new and complementary M2M infrastructure, is presented in BIB003 . Mobile M2M devices in airplanes can act as M2M gateways by forwarding data received from M2M ground terminals to satellites, and vice versa. With this approach, there is no need for M2M terminals in satellites to have a very powerful amplifier or large dish antennas to send or receive messages, and, thus, the operational costs should be lower. Furthermore, this solution addresses the challenge of connectivity, eventually relieving traffic from cellular networks. However, one should expect important challenges originated from transmission scheduling and mobility.