Gennaro Boggia

Simulating LTE Cellular Systems: An Open-Source Framework

Long-term evolution (LTE) represents an emerging and promising technology for providing broadband ubiquitous Internet access. For this reason, several research groups are trying to optimize its performance. Unfortunately, at present, to the best of our knowledge, no open-source simulation platforms, which the scientific community can use to evaluate the performance of the entire LTE system, are freely available. The lack of a common reference simulator does not help the work of researchers and poses limitations on the comparison of results claimed by different research groups. To bridge this gap, herein, the open-source framework LTE-Sim is presented to provide a complete performance verification of LTE networks. LTE-Sim has been conceived to simulate uplink and downlink scheduling strategies in multicell/multiuser environments, taking into account user mobility, radio resource optimization, frequency reuse techniques, the adaptive modulation and coding module, and other aspects that are very relevant to the industrial and scientific communities. The effectiveness of the proposed simulator has been tested and verified considering 1) the software scalability test, which analyzes both memory and simulation time requirements; and 2) the performance evaluation of a realistic LTE network providing a comparison among well-known scheduling strategies.

Downlink Packet Scheduling in LTE Cellular Networks: Key Design Issues and a Survey

Future generation cellular networks are expected to provide ubiquitous broadband access to a continuously growing number of mobile users. In this context, LTE systems represent an important milestone towards the so called 4G cellular networks. A key feature of LTE is the adoption of advanced Radio Resource Management procedures in order to increase the system performance up to the Shannon limit. Packet scheduling mechanisms, in particular, play a fundamental role, because they are responsible for choosing, with fine time and frequency resolutions, how to distribute radio resources among different stations, taking into account channel condition and QoS requirements. This goal should be accomplished by providing, at the same time, an optimal trade-off between spectral efficiency and fairness. In this context, this paper provides an overview on the key issues that arise in the design of a resource allocation algorithm for LTE networks. It is intended for a wide range of readers as it covers the topic from basics to advanced aspects. The downlink channel under frequency division duplex configuration is considered as object of our study, but most of the considerations are valid for other configurations as well. Moreover, a survey on the most recent techniques is reported, including a classification of the different approaches presented in literature. Performance comparisons of the most well-known schemes, with particular focus on QoS provisioning capabilities, are also provided for complementing the described concepts. Thus, this survey would be useful for readers interested in learning the basic concepts before going into the details of a particular scheduling strategy, as well as for researchers aiming at deepening more specific aspects.

Standardized Protocol Stack for the Internet of (Important) Things

We have witnessed the Fixed Internet emerging with virtually every computer being connected today; we are currently witnessing the emergence of the Mobile Internet with the exponential explosion of smart phones, tablets and net-books. However, both will be dwarfed by the anticipated emergence of the Internet of Things (IoT), in which everyday objects are able to connect to the Internet, tweet or be queried. Whilst the impact onto economies and societies around the world is undisputed, the technologies facilitating such a ubiquitous connectivity have struggled so far and only recently commenced to take shape. To this end, this paper introduces in a timely manner and for the first time the wireless communications stack the industry believes to meet the important criteria of power-efficiency, reliability and Internet connectivity. Industrial applications have been the early adopters of this stack, which has become the de-facto standard, thereby bootstrapping early IoT developments with already thousands of wireless nodes deployed. Corroborated throughout this paper and by emerging industry alliances, we believe that a standardized approach, using latest developments in the IEEE 802.15.4 and IETF working groups, is the only way forward. We introduce and relate key embodiments of the power-efficient IEEE 802.15.4-2006 PHY layer, the power-saving and reliable IEEE 802.15.4e MAC layer, the IETF 6LoWPAN adaptation layer enabling universal Internet connectivity, the IETF ROLL routing protocol enabling availability, and finally the IETF CoAP enabling seamless transport and support of Internet applications. The protocol stack proposed in the present work converges towards the standardized notations of the ISO/OSI and TCP/IP stacks. What thus seemed impossible some years back, i.e., building a clearly defined, standards-compliant and Internet-compliant stack given the extreme restrictions of IoT networks, is commencing to become reality.

Two-Level Downlink Scheduling for Real-Time Multimedia Services in LTE Networks

Long-term evolution represents an emerging technology that promises a broadband and ubiquitous Internet access. But several aspects have to be considered for providing effective multimedia services to mobile users. In particular, in this work, we consider the design of a quality-of-service (QoS) aware packet scheduler for real-time downlink communications. To this aim, a novel two-level scheduling algorithm is conceived. The upper level exploits an innovative approach based on discrete-time linear control theory. Instead, at the lower level, a proportional fair scheduler has been properly tailored to our purposes. The performance and the complexity of the proposed scheme have been evaluated both theoretically and by using simulations. A comparison with recently proposed scheduling strategies has been also presented, considering several network conditions and real-time multimedia flows. Particular attention has been devoted to the evaluation of the quality-of-experience (QoE) provided to end users. Results have clearly shown that the proposed approach is able to greatly outperform the existing ones especially in the presence of real-time video flows.

Feedback-based control for providing real-time services with the 802.11e MAC

The 802.11e working group has recently proposed the hybrid coordination function (HCF) to provide service differentiation for supporting real-time transmissions over 802.11 WLANs. The HCF is made of a contention-based channel access, known as enhanced distributed coordination access, and of a HCF controlled channel access (HCCA), which requires a Hybrid Coordinator for bandwidth allocation to nodes hosting applications with QoS requirements. The 802.11e proposal includes a simple scheduler providing a Constant Bit Rate service, which is not well suited for bursty media flows. This paper proposes two feedback-based bandwidth allocation algorithms to be used within the HCCA, which have been referred to as feedback based dynamic scheduler (FBDS) and proportional-integral (PI)-FBDS. These algorithms have been designed with the objective of providing services with bounded delays. Given that the 802.11e standard allows queue lengths to be fed back, a control theoretic approach has been employed to design the FBDS, which exploits a simple proportional controller, and the PI-FBDS, which implements a proportional-integral controller. Proposed algorithms can be easily implemented since their computational complexities scale linearly with the number of traffic streams. Moreover, a call admission control scheme has been proposed as an extension of the one described in the 802.11e draft. Performance of the proposed algorithms have been theoretically analyzed and computer simulations, using the ns-2 simulator, have been carried out to compare their behaviors in realistic scenarios where video, voice, and FTP flows, coexist at various network loads. Simulation results have shown that, unlike the simple scheduler of the 802.11e draft, both FBDS and PI-FBDS are able to provide services with real-time constraints. However, while the FBDS admits a smaller quota of traffic streams than the simple scheduler, PI-FBDS allows the same quota of traffic that would be admitted using the simple scheduler, but still providing delay bound guarantees

On Optimal Scheduling in Duty-Cycled Industrial IoT Applications Using IEEE802.15.4e TSCH

As exposed in a recent report by General Electric, an industrial Internet of Things (IoT) is emerging as a commercially viable embodiment of the IoT where physical sensors gather data readings from the field and deliver the traffic to the Internet. The collected real-time big data, in turn, allow the optimizing of entire industry verticals with enormous return of investments. Although opportunities are ample, it comes along with serious engineering design challenges as industrial applications have stringent requirements on delay, lifetime and standards-compliance. To this end, we advocate the use of an IEEE/IETF standardized IoT architecture along with a recently introduced data-centric scheduling algorithm known as traffic aware scheduling algorithm (TASA). Applying graph theoretical tools to the multi-channel, time-synchronized, and duty-cycled nature of TASA, we rigorously derive optimality and bounds on the minimum number of needed active slots (impacting end-to-end delays) and the network duty-cycle (impacting lifetime). We demonstrate the enormous superiority of TASA over traditional IEEE802.15.4/ZigBee approaches in terms of energy efficiency. The outcome of this paper is currently to lay foundations of the recently formed IETF standardization group 6TSCH with the aim to significantly improve IoT data flows over IEEE802.15.4e TSCH and IETF 6LoWPAN/ROLL enabled technologies.

Traffic Aware Scheduling Algorithm for reliable low-power multi-hop IEEE 802.15.4e networks

The Time Synchronized Channel Hopping (TSCH) protocol is part of the newly defined IEEE 802.15.4e standard and represents the latest generation of highly reliable low-power MAC protocols. With implementation details left open, we conceive here a novel Traffic Aware Scheduling Algorithm (TASA) by extending the theoretically well-established graph theory methods of matching and coloring by means of an innovative approach based on network topology and traffic load. TASA is able to support emerging industrial applications requiring low latency at low duty cycle and power consumption. Preliminary simulation results have also been reported to highlight the effectiveness of the proposed algorithm.

Performance analysis of the RPL Routing Protocol

The IETF Routing Over Low-power and Lossy Networks working group has recently proposed the IPv6 Routing Protocol for Low power and Lossy Networks, i.e., the RPL protocol. It has been designed to face the typical requirements of wireless sensor networks. Given its relevance in the industrial and scientific communities, this paper presents a performance analysis of RPL based on simulations. Our results clearly show that RPL can ensure a very fast network set-up, thus allowing the development of advanced monitoring applications also in critical conditions. On the other hand, we found that further research is required to optimize the RPL signaling in order to decrease the protocol overhead.

Comprehensive Evaluation of the IEEE 802.15.4 MAC Layer Performance With Retransmissions

Supported by IEEE 802.15.4 standardization activities, embedded networks have been gaining popularity in recent years. The focus of this paper is to quantify the behavior of key networking metrics of IEEE 802.15.4 beacon-enabled nodes under typical operating conditions, with the inclusion of packet retransmissions. We corrected and extended previous analyses by scrutinizing the assumptions on which the prevalent Markovian modeling is generally based. By means of a comparative study, we singled out which of the assumptions impact each of the performance metrics (throughput, delay, power consumption, collision probability, and packet-discard probability). In particular, we showed that - unlike what is usually assumed - the probability that a node senses the channel busy is not constant for all the stages of the backoff procedure and that these differences have a noticeable impact on backoff delay, packet-discard probability, and power consumption. Similarly, we showed that - again contrary to common assumption - the probability of obtaining transmission access to the channel depends on the number of nodes that is simultaneously sensing it. We evidenced that ignoring this dependence has a significant impact on the calculated values of throughput and collision probability. Circumventing these and other assumptions, we rigorously characterize, through a semianalytical approach, the key metrics in a beacon-enabled IEEE 802.15.4 system with retransmissions.

Decentralized Traffic Aware Scheduling for multi-hop Low power Lossy Networks in the Internet of Things

The emerging IEEE802.15.4e standard and IETF RPL routing protocol are core to the organization of multi-hop Low-power and Lossy Networks. They provide key functionalities useful for a really viable Internet of Things. However, several open issues still remain and require research efforts to be solved. Among others, the design of effective scheduling schemes in such systems is one of the major problems; in fact, there are no specifications about how schedules should be realized. Trying to fill this gap, this paper presents a new Decentralized Traffic-Aware Scheduling algorithm, which is able to construct optimum multi-hop schedules in a distributed fashion. Its effectiveness has been proved by using simulation results and comparing it with a centralized scheme. The reported performance results encourage the use of the developed scheduling technique, since it allows a very efficient queue management, and thus it minimizes packet discards due to buffer overflows, while at the same time minimizing the network duty cycle.