Call-of-Order 1 Part 2

The performed work and the obtained results can be separated in two parts:

 

Nanosatellite part: a simulation platform has been developed to simulate a Nanosatellite constellation network mimicking a Web Browsing Data Exchange service between hosts located in rural areas and Internet Servers linked to the Internet. The simulator is based on the software Network Simulator 3 (NS3) and includes: a scenario module, to allow arbitrarily setting different parameters related to the network design in order to be able to simulate different scenarios; a nanosatellite movement module, to realistically simulate nanosatellite movement following a defined orbit; a traffic module, to implement a sort of Delay Tolerant Networking (DTN)-HTTP Web Browsing communication; a DTN module, to implement the characteristics of the DTN paradigm needed to realize a communication in this kind of network, such as the store and forward mechanism and the relay action to transmit among heterogeneous portions, and a personalized and light version of the Bundle Protocol. A source routing algorithm based on the Contact Graph Routing (CGR) algorithm has been proposed to guarantee a reliable communication considering the limited available resources. A channel model has been developed to simulate both Nanosatellite/Ground Station and Nanosatellite/Nanosatellite communications, taking into account the local environment effects such as attenuation, fading, Doppler effect. A performance evaluation campaign has been performed in order to test the proposed routing algorithm and to quantify the obtained performance for the considered service in this network. Different scenarios have been simulated changing the number of Nanosatellites and of Ground Stations, defining a proper set of orbital parameters and of satellite link budget parameters. The obtained performance has been collected in terms of Average Delivery Time and Computational Burden on-board nanosatellite. The results show that the proposed network offers a possible solution to give a basic Internet access to rural areas with low performance but an affordable cost especially for remote areas or underdeveloped countries.

 

 

UAV part: a simulation platform based on the software S-NS3, a satellite network extension to NS3 platform, has been developed to simulate a scenario composed of different UAV swarms which deliver data to a Ground Control Station (GCS) through a Geostationary (GEO) satellite. In particular, this scenario involves different swarms delivering M2M traffic to a remote sink application connected to a satellite gateway. Each swarm is composed by a single cluster-head (CH) and multiple UAVs (E) that may possibly also act as routers (R). The CH encapsulates a CoAP proxy module: UAVs gather data through on-board sensors and send it to the “client side” of the proxy. Multiple CHs will compete to contemporarily access the Random Access (RA) satellite channel. A first set of simulations has been performed in order to numerically evaluate and then compare the considered scenario to a MQTT-based one. In particular, the completion time of CoAP and MQTT data exchange has been analyzed for different values of transmission window size (NSTART), obtaining that CoAP provides a lower completion time than MQTT and lower values for larger NSTART values. A second set of simulations has been performed in order to evaluate the average delivery delay. The results show that it is not affected by the NSTART because of the low considered load traffic conditions and the chosen limited number of transmitting nodes. Moreover, mobility slightly affects the delivery delay whereas it tends to increase the packet drops. An alternative ARQ protocol based on a variable-length sliding window mechanism has been proposed. This modified CoAP version outperforms the standard one. Also a congestion control algorithm inspired to the TCP Friendly Rate Control (TFRC) algorithm has been designed. The performance of the proposed solution (CoAP/sb-TFRC) has been compared to the MQTT/TCP solution based on TCP Hybla congestion algorithm. The benefits are evident in terms of average throughput, application-layer goodput, Round Trip Time (RTT), and MAC queue size. Finally, a satellite channel affected by rain fading has been modelled and the obtained results show that the impact of the rain attenuation is non-negligible. The stability of both Hybla and sb-TFRC is preserved, although in the former case the penalty appears to be slightly more evident.

Cryptographic direct-sequence spread spectrum (DSSS) modulation is currently being considered for updating the telecommand standard for space applications. To achieve a better immunity against pulsed jamming scenarios, DSSS can be combined with advanced channel coding schemes. However, an essential prerequisite for reliable channel decoding is accurate synchronization. The first goal of this WI was therefore to develop, analyze and evaluate of symbol and frame synchronization techniques for advanced channel-coded DSSS telecommand links under jamming conditions. The performed work comprises the selection of potential techniques and the identification of the trade-offs in terms of computational complexity, implementation cost and error performance. Computer simulations have been performed, to validate and compare the proposed solutions.

 

As a first candidate frame synchronization scheme we considered the ALG-0 algorithm. It involves a minor modification of the detection procedure currently described in the existing standard. The algorithm is based on hard symbol decisions and has a very low complexity. Compared to the frame synchronization algorithm specified in the current Consultative Committee for Space Data Systems (CCSDS) recommendation, we considered a longer start sequence and relaxed the condition for declaring synchronization. The performance of this algorithm was investigated in the presence of jamming, and it was shown that the frame synchronizer can be designed such that the overall system's robustness against pulsed jamming is limited by the robustness of the code rather than the synchronizer.

 

While the ALG-0 frame synchronizer was chosen with the objective to minimize the impact of the introduction of the new synchronization scheme to the existing standard, a possible way to further improve the frame synchronizer performance is to adopt more involved algorithms. Unfortunately, optimum frame synchronization requires jammer state information (JSI) which is not readily available at the receiver. Two practical frame synchronizers that circumvent this problem without decreasing the performance too much have been proposed. Both these synchronizers have been shown to significantly outperform ALG-0.

 

Finally, we have also studied the performance of symbol timing acquisition procedures under jamming conditions, assuming DSSS with asynchronous BPSK modulation of the PN sequence. Attention has been focused on a first order phase-locked loop (PLL). We have proposed different loop gain selection methods. It was demonstrated that, if JSI is available at the receiver, PLLs with variable loop gains perform better in terms of acquisition speed and tracking accuracy than a conventional PLL with a constant loop gain.

 

The above mentioned DSSS techniques are physical layer security mechanisms of space links that mostly rely on low probability of intercept (LPI) and low probability of detection (LPD) waveforms. In effect, LPI and LPD waveforms along with signal processing and channel coding techniques can be highly effective against jamming attacks and interception. Their anti-jamming performance can be quantized in terms of the power level

and signal at which the protection is broken. As for interception, security performance can be quantized in terms of breaking the pseudo-random sequence spreading the signal. However, novel attacks and computing power evolution could end up breaking their computationally strong security. In this document, we have introduced the information-theoretic approach to the design of keyless physical layer security for space links.  This method exploits physical characteristics of the communication channel to provide unconditionally secure communications. Moreover, the secrecy level of these information theoretical techniques can numerically quantify secrecy according to information-theoretic principles. This allows the design of unconditionally secure cryptographic coding schemes that can lead to practical schemes adapted to channel, system and mission specific constraints and design goals. 

 

Specifically, we have studied the applicability of the concept of wiretap coding to space links. To this aim, we reviewed different secrecy criteria that have been introduced in the literature and can be numerically quantized.

We then focused on cryptographic semantic secrecy for which we introduced wiretap code constructions that are available in the literature. In order to analyze its applicability to space links, we developed a novel signal model that includes the relative geometry of the eavesdropper with respect to the legitimate receiver as well as the respective system-level parameters. In our analysis of the infinite-length regime we obtained the secrecy capacity of typical space Gaussian links for different relative geometries and system parameters. On the other hand, in our analysis of the finite-length regime we presented upper bounds of the semantic secrecy showing how communication with secrecy guarantees can be designed trading o_ reliability and secrecy according to mission-specific needs. Our numerical results confirm the potential of information theoretic physical layer security for space channels. Finally, we identified system layered design options for enabling simultaneous operation with additional information theoretic security protocols. Our final remark is to stress once more that the relevance of this direction of research lies on the fact that off-the-shelf transmission codes can be chosen to ensure reliable transmission over the legitimate channel while a new preprocessing layer is added to ensure secrecy.

 

In a nutshell, the aim of this WI has been to evaluate how the use of multiple simultaneous Spreading Factors can benefit a satellite-based access network system based on E-SSA, and also to design a transmission strategy which can attain maximum performance in the presence of M2M devices powered-up with energy-harvesting devices, thus not having continuous availability of energy.

 

A MATLAB simulator has been implemented to evaluate the performance of the proposed techniques. This document describes the simulator and also shows and discusses the most relevant results that have been obtained. The work conducted in this WI has established a solid base towards an interesting research area.

 

There are two key conclusions which have been obtained throughout the work conducted in this WI:

 

1.     When no Energy Harvesting (EH) is considered at the M2M terminals on the ground, the use of more than one Spreading Factor (SF) is beneficial for the SIC process and improves the overall performance of the E-SSA algorithm. Adding more than one SF in an M2M satellite system based on the E-SSA protocol adds a new source of diversity and improves the overall system throughput.

 

2.     When considering an EH-aware transmission policy, results show that a technique which dynamically adjusts the spreading factor used in each terminal according to its available level of energy achieves a higher throughput and guarantees a reduced outage probability compared to the case of using a single and fixed SF.

 

In addition, the following research lines have been identified for future work:

 

·         When no EH is considered, it would be interesting to find the optimal distribution of SF amongst the population of E-SSA terminals which can provide the highest possible throughput. An analytical study may be carried out in order to determine the optimal distribution of the SFs.

 

·         For the energy harvesting scenario, further studies on this topic involve a detailed tuning of the transmission parameters (e.g., setting the thresholds of the transmission manager), the extension of the system model to consider other inefficiencies, as well as the consideration of other sources of energy harvesting at the transmitter side.

 

 

·         A major area of research would consist in analyzing the performance of the E-SSA protocol in a LEO scenario (with and without EH). Due to their high velocity (of several kilometers per second), LEO satellites introduce a high Doppler effect that leads to a frequency drift. This drift depends on the relative velocity of each single node with respect to the satellite and this fact may have a significant impact on the overall system performance. This frequency drift provokes the next two opposite effects: 1) due to due to different drifts that the gateway observes from each node, the packets transmitted in the same frequency band are no longer completely overlapped, i.e., for packets using the same band, the collisions are less destructive because two interfering burst are rarely completely overlapped, and 2) if guard bands are not properly designed, this frequency drift can provoke collisions with transmissions carried out in the adjacent frequency bands.

The telecommunication companies need to sustain/update the infrastructure, which brings the content from points of presence to the users. However, most of the Internet revenue goes to content providers such as Google and Facebook. At the same time, since some of the links are wireless, the scarce spectrum is another issue. In this WP, we have proposed using mono/multi-beam hybrid satellite-terrestrial networks along with off-line and ICN caching algorithms to substantially off-load the backhaul links.

 

The results showed that the proposed hybrid satellite-terrestrial architecture is able to considerably reduce the required time for file placement while keeping the cache hit ratio very close to the upper bound. In addition, the proposed multi-beam architecture improves the cache hit ratio since cache feeding can be done based on the global popularity of each beam and is closer to BS content popularity distribution. It was revealed that for a long range of values of file popularity parameters, α, the multi-beam architecture outperforms the mono-beam architecture in terms of the cache hit ratio.  This study showed that the hybrid network can improve the cache hit ratio for specific range of file popularity parameter, α, and cache memory. It was shows that coded caching with optimal memory allocation can substantially improve the cache hit ratio. As a future work, it will be interesting to perform online popularity estimation using learning algorithms to perform real time caching.

 

The next part investigated four intelligent ICN caching solutions that jointly exploit the advantages of ICN, which include network layer content-awareness and dynamic multicast group creation, and the wide-area broadcasting capability of satellite networks: 1) Opportunistic multicast for proactively caching future chunks of a requested video, 2) Proactive video caching based on video clustering, 3) Partial video caching, and 4) ICN caching and Network Coding.

 

The first scheme opportunistically exploits the wide-area broadcasting capabilities of satellite networks to proactively cache future chunks of a video that is requested by a user, which has been previously requested by other users and hence is being broadcasted over the satellite network. Validation results were performed for Zipf and non-Zipf popularity distributions (Zipf with exponential cutoff and stretched exponential), showing how the cache hit ratio depends on the aggregate video request rate, the video duration, and the video pool size.

The second scheme considers that videos have been previously clustered into groups, e.g. based on their type and/or user requests, and utilizes information of previous video requests to proactive cache video that has not been seen before at a particular satellite terminal or is new. Results investigated the influence of the cluster popularity and the difference between global and local popularity on the cache performance.

 

Partial video caching extends the previous scheme by treating different parts of a video differently, based on their relative popularity. Validation results illustrated the gains that can be achieved by partial caching and showed that these gains depend on how accurately the video view time is known.

 

The study investigated the gains from combining ICN caching with Network Coding, in terms of the reduced data and signaling traffic over the satellite network and the reduced delay, when Random Linear Network Coding (RLNC) is performed by all caches and when it performed only at the original server that made the video available.

 Finally, within the study we extended our testbed that integrates an ICN Publish Subscribe Internet (PSI) prototype implementation and satellite emulation using the OpenSAND tool, with SDN functionality; the testbed was used to validate a subset of the schemes developed within the study.

Precoding for full frequency reuse fixed satellite systems has reached a level of academic maturity and is being considered for implementational studies by operators given the potential gain it offers. Building on some initial works, this study investigated the use of precoding in full frequency reuse mobile interactive multibeam satellite systems. It involved consolidating the channel models for various mobile scenarios - Slow Nomadic, Maritime and Aeronautical - spanning the spectrum of terminal speeds.

 

Based on the channel models, the outdated channel state information at the transmitter which creates impediments to the use of available precoding techniques was investigated.  Due to the fading nature of the satellite communication which equally impacts the desired and interfering signals, it was shown that the precoder matrix is sensitive to the outdated amplitude and not to the phase of the channels. With a focus on unicast scenario, several precoder designs were considered including the traditional Zero-Forcing, MMSE, those based on SLNR reduction as well as optimal precoders derived from various SINR formulations. To cater to different payload architectures, both sum power and per-antenna power constraints were imposed and practical implementation issue of margins for rate allocation were considered. The performance of the various precoders were evaluated on a INMARSAT type of system and it  was shown that the considered scenario does not suffer from a sum-rate reduction in case a perfect rate allocation is performed.  On the contrary, in case the rate allocation is based on a delayed version of the SINR,  a sum-rate degradation was observed. Despite this performance loss, MMSE precoding can increase the sum-rate a 55 % factor given a certain outage target. In addition, it is observed that for the same margin, precoding has smaller outage compared to the benchmark system. 

 

 

Subsequently, a multicast scenario was considered with a geographical scheduling; while MMSE precoding could still achieve gains over the traditional four colour re-use, the gains reduced with the multiplexing order. Finally, the study also discussed different approaches to precoding implementation including on-ground, on-board and hybrid precoding with arguments favouring on-ground precoding if feeder link bandwidth expansion is not an issue.

This project has evaluated the use of Q/V and W bands for future satellite communications. The modelling of the propagation channel, spectrum and regulatory issues are addressed as well as future satellite and earth terminal equipment characteristics. Aeronautical, earth resource down links and point to point professional use applications are evaluated as to their capacity improvements over Ka band. The following are the major conclusions;

·         For operations above Ka band there is no exclusive satellite bands and thus operations will occur in shared bands. At Q/V the portions—(D) 39.5 to 40.5GHz and (U) 48.2 to 50.2GHz and at W band portions-(D) 74 to 76 GHz  and (U) 84 to 86GHz seem most promising for Europe. For Aero systems it is only around airports where co-existence studies would be needed. For larger earth resource gateways these would need coordination in the normal way. For professional terminals if few in number would also need coordination but if uncoordinated operation were required this would need further regulatory decisions. At these Q and W bands it is likely that satellite will receive competition for spectrum from 5G systems in the future.

·         No requirements for Q and W band earth stations on the move are currently in place but these are likely to emerge in the future. It is expected that they will be treated as FSS on the move and need to adhere to FSS regulations.

·         For the Aero application we have shown that the use of Q and W spot beams overlaying Ka can provide increased capacity and are realistic for 2020 and beyond. The use of new flat plate or conformal arrays will enable increases of up to 60% above Ka band and capacities on a 125MHz carrier of 233Mbps per plane which compares with predicted requirements of 175-200Mbps and which could not be attained at Ka band alone.

·         For the earth resource satellite downlink we have evaluated the performance at three locations and shown that Q and W band enable 54% and 132% greater capacity than at Ka band using predicted earth station and satellite equipment. Diversity was also investigated and shown to have the ability to increase availability for smaller antennas or reduced satellite power with all availabilities being in excess of 99.9%. Diversity at W band could especially  combat the effects of clouds but has improvement for rain alone,

·         For the two way Professional mesh links, the use of Q/V band and large antenna size (2-3m) enables an increase in the average throughput with regards to what can be achieved using Ka band. However even using very low SNR modcods the availability is one order of magnitude lower. The use of W band with the assumptions used does not lead to a sufficient availability and does not constitute a viable alternative.

 

·         A comprehensive evaluation of the receiver ACM loop was performed using Q and W band predicted time series for both one-way and two-way scenarios. It was shown that in all cases, the average spectral efficiency (throughput) could be optimised with ACM margins of 0.8dB or less over the duration of a rain event. These values will reduce further when optimising for transmissions that include a predominant clear sky profile.  The use of variable or adaptive margins could have some advantage at Q band but on the limited data available at W band there was low correlation on the fade slopes which indicate that there would not be much to gain. Further study with measured data is recommended for the future.

The aim of the study was to investigate the use of Ka-/Ku-band  LEO satellites to extend and complement terrestrial networks, so as to provide broadband connectivity to urban or rural areas not served by means of a terrestrial infrastructure. The Team, as jointly agreed with ESA, considered LTE Rel. 13 as a reference for the radio interface and assessed the feasibility of LTE waveforms and PHY/MAC layers procedures, in order to identify which adaptations would be required.

In the first phase of the study, the Team identified the scenario to be analysed and the main channel impairments to be considered, i.e., large Round Trip Time (RTT) delays, large Doppler shifts, and Doppler rate. Based on a thorough review of the allowed architectures in LTE Rel. 13, the Team identified two potential system architectures: i) a satellite Relay Node (Sat-RN) architecture, in which a satellite-enabled RN provides an on-ground LTE cell; and ii) a satellite eNodeB (Sat-eNB) architecture, in which the satellite-enabled entity on-ground is a traditional LTE eNB. It is worthwhile highlighting that in both cases the terrestrial user link (access link) is provided by means of the traditional Uu LTE air interface. Thus, the main difference between the two scenarios resides in the backhaul link, which depends on the type of satellite-enabled entity. In agreement with ESA, the scenario taken into account for the feasibility assessment has been the Sat-RN scenario, in which the on-ground LTE RN is connected to the satellite by means of a Un air interface.

In the second phase, the Team focused on reviewing the Un air interface of LTE Rel. 13. In particular, the main addressed areas have been waveform design and PHY/MAC layer procedures. The Un air interface is almost identical to the traditional Uu interface and, thus, it is based on SC-FDMA in the uplink and OFDM in the downlink. The Team, in agreement with ESA, assumed a FDD framing structure with normal Cyclic Prefix (CP) length as the reference waveform and analysed the impact of the large Doppler shifts (due to the large relative velocity between LEO satellites and fixed RNs) on the subcarrier spacing. By means of geometrical considerations and through mathematical assessment, it has been demonstrated that, in Ku-band, as long as the RNs are capable of estimating their position relative to the satellite with a maximum location error of 4 km, the Doppler shift can be compensated at the gateway and, thus, no modifications would be required.

With respect to the PHY and MAC layers procedures, the Team analysed the impact of the large RTT (approximately 16 ms) on the different timers involved in the procedures. In particular, the focus has been on the backhaul link, since the terrestrial access link is a traditional LTE cell for which no modifications are needed. In particular, the following challenges have been identified:

·         The LTE Random Access procedure is a 4-steps procedure in which two different timers are present: i) the RA response window, which can be as long as 13 ms; and ii) the contention resolution timer, which can be as long as 64 ms. It can be noticed that, while the latter is significantly above the RTT and does not pose any challenge, the former is shorter than the RTT and, thus, proper solutions are needed.

·         The RA procedure with RNs comes into play only during the RN attachment procedure. This is a 2-step procedure in which the RN first connects as a normal user to gather the parameters so as it can operate as a relay and, then, it actually connects as a relay. Although the RA response window is below the RTT, the Team observed that, since the RNs are fixed and the satellites orbits are known, ad-hoc network deployment solutions can be envisaged in order to perform the RN attachment procedure, which only comes into play at network setup.

 

·         In the HARQ procedure, ACK/NACK feedbacks are based on a 4 ms periodicity both in the uplink and in the downlink, which is significantly below the large RTT with LEO constellations. Thus, the HARQ procedure cannot be implemented as is and proper modifications are required.

Call-of-Order 1 Part 1

In this study a MEO system was evaluated considering a constellation of 8 satellites and 7 possible ground station locations at different climatic areas. The outage capacity offered at 5 different scenarios was evaluated keeping the latency less than 150 ms due to round trip and trying to have an availability of 99.9%. The ground terminals were considered with two kinds of antenna classes at 1.8 m and 3.5 m. Four RF scenarios were simulated one at Ka-band (reference) and three at Q band (advanced system) without considering any diversity, one using orbital diversity and one for site diversity. The fifth scenario considered wavelengths at optical range using the site diversity technique.

For the system design at Q-band, firstly an identification of available bandwidth at Q-band from ITU regulations was performed. It was found that 5 GHz of available bandwidth exist for satellite downlink. Since there was an available bandwidth of 5 GHz for the downlink keeping the number and size of onboard antennas the same with the Ka-band case, an 833 MHz of bandwidth at user beam was identified. Therefore, for fair comparison, the same mass on satellite and power consumption was considered. Moreover, for the system evaluation at RF, first an optimization on the PHY layer was performed to derive the ModCods at Ka and a second optimization to derive the ModCod table at Q band. More particularly, at Q band for the PHY layer two carriers were considered at each beam to reduce the noise power. For the calculation of capacity, realistic time series generator of attenuation due to atmospheric phenomena was used taking into account the spatial and temporal correlation of the attenuation factors.

From the capacity results it was found that on average there is a 100% increase in system throughput at Q/V band in comparison to reference scenario in clear sky for the same power consumption and mass on board. Moreover, in Q/V band the mean system throughput at clear sky is close to 15 Gbps for the ten user beams. However, in the single link case the 99.9% availability is not always reassured.

Using orbital diversity again the 99.9% availability is not reassured for all the stations but there is an increase in both the availability and capacity. Finally, with site diversity the availability is always on target. Here it must be noted that orbital diversity can be already implemented with the existing O3b system since every ground station has already two antennas.

Finally, for the optical system in most places more than 6 ground stations are required for achieving the target availability of 99.9% and close to 80Gbps can be delivered on ground.

The goal of WI is the design of new advanced signal processing techniques to enhance the throughput of fixed and mobile satellite communications. In more detail, the objective will be driven by two approaches: 
- The use of polarization as an additional degree of freedom has been popularized and has become a realistic new way of MIMO communications. In this WI, more than two polarization planes will be used to increase the overall performance. On the one hand, in fixed links, the long coherence time and the preexisting feedback links can be exploited to provide the Gateway with Channel State Information to adapt the transmission according to the channel magnitudes. On the other hand, the high uncorrelated polarization channels can be used to provide multimedia communications in mobile devices improving the reliability and the latency. 
- Full Duplex has been presented as a new reliable schema to increase the spectral efficiency by transmitting and receiving at the same time at the same frequency. Knowing the transmitted patterns may be used to suppress the interference added to the receiver path. In this WI, new techniques will be presented to outperform the performance of the system by using this approach. 

This work item deals with a literature survey on the adoption of Network Coding (NC), differentiated on the basis of the OSI layer where network coding is adopted. Therefore, this document is divided into three parts, as follows:  Network coding adopted at the application layer (or just below); Network coding applied at the transport layer (or just below);  Network coding applied at the network layer (or just below). The purpose of this document is to survey the different applications of network coding explaining why it is used and how it is used with a particular attention to multipath scenarios and satellite case studies.

The second part of this work contains a detailed description of the selected simulation scenarios by the team and a description of related issues in terms of the layer where NC should be used and NC compatibility issues (ROHC, IPsec). Finally, benchmark techniques are presented and a description of the implementation phase of simulators (3 scenarios) is provided together with some results and comparisons with benchmark schemes.

The third part of this activity contains a survey of currently available simulation tools for network coding and discuss pros and cons.

 

Simulations results and final considerations are also provided that have permitted to highlight the advantages in using network coding.

The objectives of this WI is the design of an end-to-end functional system architecture for an integrated satellite-terrestrial network based on ICN/PSI (Information-Centric Networking/Publish-Subscribe Internet) to support the delivery of M2M/IoT services, investigation of the impact of M2M/IoT traffic on multiple access schemes, test-bed validation of ICN/PSI architectures over enhanced satellite multiple access schemes, and optimization of critical network functions of ICN/PSI architectures over enhanced satellite multiple access schemes.

The investigations will consider various M2M/IoT scenarios where integrated terrestrial-satellite networks offer a significant advantage. The investigations will assess the performance in terms of the reliability, scalability, and signaling overhead, identifying their corresponding tradeoffs and the impact of M2M/IoT traffic characteristics.

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