Towards Efficient Mobile M2M Communications: Survey and Open Challenges <s> M2M Support in Cellular Networks <s> In the Internet of Things (IoT) the edge devices often rely on gateways to connect to the Internet, to reduce costs and energy consumption. For those scenarios where the gateway itself does not have a wired Internet connection, LTE is a candidate solution due to its high spectral efficiency, bandwidth, and coverage. In this paper, the suitability of LTE for the interconnection of aggregated edge devices is investigated. The study is carried out under the assumption that the Constrained Application Protocol (CoAP), which is becoming increasingly popular, is used. The performance analysis is carried out through packet-level simulation with the open source simulator ns3. <s> BIB001 </s> Towards Efficient Mobile M2M Communications: Survey and Open Challenges <s> M2M Support in Cellular Networks <s> The Internet of Things (IoT) will see the connection of tens of billions of objects to the Internet over the next 10 years and will lead to improvements in the quality of life for everyone. The density of all the radio-connected IoT objects will place increasing pressure on the available limited spectrum resources. These radio-connected IoT objects will, in addition, often use different radio access technologies (RATs), making service advertising and discovery as well as coordination of radio resources extremely challenging, due to the potentially vast numbers of connected devices. These problems can be addressed both by using centralised co-ordination of radio resources and by distributed intelligent devices that actively manage their own radio resource usage. This paper addresses solutions for centralised co-ordination of the wireless connected IoT devices through a new approach which relies on a shared service-level platform to provide flexible radio spectrum usage. New algorithms for interference mitigation and device co-existence are described which use device management made possible by such a platform, and avoid potential conflicts across heterogeneous systems. Under the assumption that geographically co-located devices are all using a common service platform, the centralised algorithms proposed here have the potential for more efficient solutions than existing inter-RAT interference mitigation solutions. An implementation of our algorithms using the emerging ETSI M2M standard is outlined. <s> BIB002 </s> Towards Efficient Mobile M2M Communications: Survey and Open Challenges <s> M2M Support in Cellular Networks <s> To enable the efficient and low latency machine-type communications (MTC) over long term evolution (LTE), a contention based access (CBA) method is proposed. With CBA, UEs transmit packets on the randomly selected resource without having any UE specific scheduled resources. To address the problem of collision caused by CBA in high traffic load, eNB exploits the MU-MIMO detection technique to decode radio network temporary identifier (RNTI) of the collided UEs and use this information to perform a regular scheduling in subsequent subframe. Detailed low layer signaling enhancement to implement CBA technique in current LTE specification (Rel. 10) is also presented. Simulation results demonstrate that the CBA significanlty outperforms the existing uplink channel access methods. <s> BIB003 </s> Towards Efficient Mobile M2M Communications: Survey and Open Challenges <s> M2M Support in Cellular Networks <s> Supporting trillions of devices is the critical challenge in machine-to-machine (M2M) communications, which results in severe congestions in random access channels of cellular systems that have been recognized as promising scenarios enabling M2M communications. 3GPP thus developed the access class barring (ACB) for individual stabilization in each base station (BS). However, without cooperations among BSs, devices within dense areas suffer severe access delays. To facilitate devices escaping from continuous congestions, we propose the cooperative ACB for global stabilization and access load sharing to eliminate substantial defects in the ordinary ACB, thus significantly improving access delays. <s> BIB004 </s> Towards Efficient Mobile M2M Communications: Survey and Open Challenges <s> M2M Support in Cellular Networks <s> There has been much interest recently in improving power saving and cost efficiency by monitoring the operation status of various facilities over networks. Wireless networks, especially cellular networks, are advantageous in terms of their mobility, coverage, and scalability. However, a weak point is their low reliability due to rapid changes in available bandwidth. We fabricated a prototype of a highly reliable remote energy monitoring system using a cellular network with our proposed transmission control scheme. Experiments were performed in China, where cellular networks are expected to be applied for various applications. We evaluated the effectiveness of our proposed scheme using two different types of cellular network. Results showed that the proposed scheme can achieve the probability that the delay of sensor status over 6 sec is under 10−6 and maintains an 85% throughput compared to a conventional scheme. <s> BIB005 </s> Towards Efficient Mobile M2M Communications: Survey and Open Challenges <s> M2M Support in Cellular Networks <s> Machine-to-Machine (M2M) communication is expected to play a major role within the coming years towards the development of e-healthcare applications. The design of cellular networks, such as Long Term Evolution (LTE), is optimized to serve the data traffic of human-based communication with broadband requirements. E-healthcare traffic has different characteristics such as small packet sizes, narrowband requirements and huge number of devices. The focus of this work is to investigate the impact of e-healthcare traffic on LTE cellular networks. We develop a possible future scenario of electrocardiography (ECG) devices performing remote monitoring of patients with mobility support in our LTE simulation model. Regular LTE traffic is also deployed in the network and the influence of the varying ECG traffic is examined. The simulation results indicate that the e-healthcare related data traffic has a drastic influence on regular LTE traffic. <s> BIB006 </s> Towards Efficient Mobile M2M Communications: Survey and Open Challenges <s> M2M Support in Cellular Networks <s> A machine-to-machine (M2M) communications system is a large-scale network with diverse applications and a massive number of interconnected heterogeneous machines (e.g., sensors, vending machines and vehicles). Cellular wireless technologies will be a potential candidate for providing the last mile M2M connectivity. Thus, the Third Generation Partnership Project (3GPP) and IEEE 802.16p, have both specified an overall cellular M2M reference architecture. The European Telecommunications Standards Institute (ETSI), in contrast, has defined a service- oriented M2M architecture. This article reviews and compares the three architectures. As a result, the 3GPP and 802.16p M2M architectures, which are functionally equivalent, complement the ETSI one. Therefore, we propose to combine the ETSI and 3GPP architectures, yielding a cellular-centric M2M service architecture. Our proposed architecture advocates the use of M2M relay nodes as a data concentrator. The M2M relay implements a tunnel-based aggregation scheme which coalesces data from several machines destined to the same tunnel exit-point. The aggregation scheme is also employed at the M2M gateway and the cellular base station. Numerical results show a significant reduction in protocol overheads as compared to not using aggregation at the expense of packet delay. However, the delay rapidly decreases with increasing machine density. <s> BIB007 </s> Towards Efficient Mobile M2M Communications: Survey and Open Challenges <s> M2M Support in Cellular Networks <s> The field of machine-to-machine (M2M) communications has gained wide popularity and is steadily growing. This paper studies the feasibility of using the Global System for Mobile Communications and in particular the General Packet Radio Service (GPRS) for a low data rate long- lasting battery-powered operation of M2M devices. A model is introduced to estimate the power consumption of a GPRS connection. It allows the identification and evaluation of optimizations of the data transmission procedures. Two M2M modes of GPRS operation are introduced. For applications with frequent transmissions, an Always- on-mode turns out to be most reasonable. For infrequent transmissions, e.g., one transmission every 2 hours, an On/off-mode reduces the power consumption of M2M devices by 93% as compared to the Always-on-mode. With a 3-cell battery providing 25.9 Wh of energy and considering only the power consumption of the communication module, a battery lifetime of up to 5 years is feasible. Measurements show that usually 40% of the energy spent for a short data transmission is wasted by one particular GPRS procedure called non-DRX period. Avoiding this saves up to 35% of total average power, depending on the rate of data transmissions. <s> BIB008
Nowadays cellular networks offer wide coverage areas, high data rate, and decreasing latency, and therefore they are a key enabler of M2M communications. The challenges associated with mass-scale M2M networks can be resumed to the multitude and diversity of devices, the scalable connectivity, and supporting of both legacy and new services and devices  . Marwat et al. BIB006 argue that, even in the presence of regular LTE traffic, mobile M2M traffic can not be considered negligible, and it can have a dramatic impact on the LTE network performance in terms of Quality of Service (QoS) and throughput. Costantino et al. BIB001 evaluate the performance of an LTE gateway using CoAP and representative M2M traffic patterns and network configurations through simulations. The authors argue that traffic patterns depend very much on the single application considered, and, therefore, do not describe or justify their choices. The scenario consists of a single LTE cell where the evolved NodeB (eNB), the only mandatory node in the radio access network (RAN), serves one LTE M2M gateway and a variable number of terminals with traditional Internet traffic, called H2H User Equipments (UEs). The LTE M2M gateway, in turn, serves a variable number of smart objects. The results showed that LTE is sensitive to both intra-UE and inter-UE signal interference, which results in a high delay or packet loss when the number of smart objects served is greater than a few tens or the cell throughput approaches its limits. Tesanovic et al. BIB002 describe algorithms for device management to mitigate interference and device co-existence in LTE. Similar to wireless networks, M2M communications for cellular networks can benefit from improvements on channel access or by introducing data aggregation techniques. A contention based uplink channel access for M2M in an LTE network is proposed by Zhou et al. BIB003 . With contention based access, UEs select resources randomly without indications from eNB, which saves signalling overhead and, hence, latency is reduced. Simulation results showed that a network coordinated random access stabilization scheme used to control the expected number of simultaneous access to a common random access channel (RACH) can effectively improve the access delay in LTE-Advanced BIB004 . Lo et al. BIB007 study the impact of data aggregation in M2M on throughput and delay in a cellular network. They motivate the use of an M2M relay as an M2M data aggregator to improve uplink transmission efficiency in LTE-Advanced due its overheads. They propose a tunnel-based aggregation scheme in which only M2M data units destined to the same tunnel exit point are aggregated at the tunnel's entry point, according to priority classes. The results show a significant reduction in protocol overheads. Furthermore, the results show that aggregation, as expected, increases the delay per unit in the delivery, but the global delay can rapidly decrease with the increase of M2M devices. Transmission scheduling schemes can be introduced in mobile M2M communications to reduce delay or to achieve higher energy consumption efficiency. Yunoki et al. BIB005 achieves a delay reduction in a remote monitoring system by using a transmission scheduling scheme used in an Evolution-Data Optimized (EVDO) and in a Wideband Code Division Multiple Access (W-CDMA) networks. They achieve a probability of sensor status not reaching a monitoring center within a delay of 6 s lower than 10 −6 compared to the probability of 10 −4 for a best-effort effort scheme. This transmission scheduling scheme achieved more than 85% of average throughput compared to the best-effort scheme for the W-CDMA network, while having a similar performance for the EVDO network. Pauls et al. BIB008 study the viability of using the General Packet Radio Service (GPRS) for a low data rate long-lasting battery powered operation of M2M devices. The authors evaluate optimizations of data transmission procedures to reduce the power consumption of GPRS connections, for transmitting small size and latency tolerant user data. For applications that require frequent transmissions, it is better that the devices are always turned on, but, for applications that do not require frequent transmissions, dramatic savings in power consumption (93%) can be obtained if the devices are turned off during the periods that do not transmit.