Massive Internet of Things systems, e.g., Low Power Wide Area Networks, aim at connecting very large numbers of low-cost devices with multi-year battery life requirements, a goal that is hard to achieve with current technologies. In this paper, a novel asynchronous spread spectrum technique, called Golden Modulation, is introduced. This modulation provides a vast family of equivalent waveforms with very low cross-correlation even in asynchronous conditions, hence enabling naturally massive multiuser operation without the need for inter-user synchronization or interference cancellation receivers. The basic modulation principles, which rely on spectrum spreading via direct Zadoff-Chu sequences modulation, are presented and the corresponding theoretical bit error rate performance in additive white Gaussian noise and multi-path channels is derived and compared by simulation with realistic receiver performance. The demodulation of the Golden Modulation is described, and its performance in the presence of uncoordinated multiple users is characterized and compared against LoRa in a variety of scenarios. Various higher-layer and backward compatibility issues are also discussed.

LoRaWAN is one of the most employed systems among the Low Power Wide Area Networks. An open problem for the LoRaWAN system is the receiver’s overall synchronization, including the detection of the start of the LoRaWAN packet and the correction of the carrier frequency offset and time offset. The implementation of such a subsystem in currently available chipsets for LoRaWAN is not known. This paper provides a description of a new synchronization subsystem for a LoRaWAN receiver in realistic scenarios, considering the usual operating regions (in terms, for example, of Signal-to-Noise Ratio, maximum carrier frequency offset, and allowed Packet Error Rate). The ambiguity of the effects of the time offset and the carrier frequency offset on the LoRaWAN preamble are established analytically. Different options for the synchronization subsystem are provided, one of which is particularly suited if the requirements on the maximum frequency offset are those set for off–the–shelf chipsets. The performance of the proposed synchronization subsystem and the start of the packet detection algorithm is evaluated through a campaign of simulations. The results confirm that the proposed subsystem meets all of the requirements for successful demodulation and detection of the data part following the preamble.

In this article, we evaluate the performance of a LoRaWAN network in industrial scenarios where different Industrial Internet of Things (IIoT) end nodes communicate to a central controller in order to provide monitoring and sensing information to optimize the efficiency of industrial processes and reduce costs. In particular, we consider confirmed and unconfirmed traffic, multigateway deployments, the usage of different classes of devices, and a nonstandard channel plan. Furthermore, we analyze the higher-layer impact of different models of LoRa PHY layer with industrial channel models. We show that, with proper configuration, LoRaWAN is able to serve IIoT sensing applications with a packet success rate over 90%, providing at the same time limited communication delays.

Uplink ultra-reliable low-latency communication (URLLC) entails dependable and almost instantaneous packet transmissions from industrial Internet of Things terminals to the serving base station. While most of the literature addresses terminals which are always connected to the network, here we focus on terminals which would benefit from a connection-less radio access, because they are employed for low-duty-cycle applications related to industrial safety, while still requiring a URLLC quality of service. Our aim is to investigate the performance of two standard-compliant radio access protocols, i.e., the one-stage approach and the two-stage approach, in supporting uplink URLLC in connection-less mode. We derive a mathematical model of these protocols under the assumption that the base station has multi-user detection capabilities. The model is used to cross-validate our simulator and calibrate the protocols together with the validated simulator, providing well-grounded guidelines for the selection of the parameter values. The simulator is finally exploited to assess the URLLC performance of the proposed protocols. The key outcome of this study is that, when combined with multi-user detection at the base station and after an appropriate system parameters selection, the one-stage approach satisfies the desired URLLC service requirements, thus representing a viable solution to support safety-related industrial applications.

Recently, the role of Low-Power Wide Area Networks (LPWANs) as enablers of the Internet of Things (IoT) is emerging. Contrary to what is commonly believed, despite they operate in unlicensed frequency bands, these technologies are subject to stringent spectrum usage regulations, in terms of both channel occupancy and transmission power. In this work, we focus on the LPWAN technology based on the Long-Range™ (LoRa) modulation, proposing a radically new approach with respect to the default Medium Access Control (MAC) procedure in LoRaWAN™, i.e., the protocol stack most widely used on top of LoRa. In particular, we describe and evaluate a new MAC protocol that exploits a novel operation mode called time-power multiplexing, to boost the capacity of LoRa networks. The simulation results show that, with respect to the default LoRaWAN MAC protocol, the proposed solution effectively increases the number of users that the network can sustain.

Low‐Power Wide‐Area Networks (LPWANs) have recently emerged as appealing communication systems in the context of the Internet of Things (IoT). Particularly, they proved effective in typical IoT applications such as environmental monitoring and smart metering. Such networks, however, have a great potential also in the industrial scenario and, hence, in the context of the Industrial Internet of Things (IIoT), which represents a dramatically growing field of application. In this paper we focus on a specific LPWAN, namely, LoRaWAN, and provide an assessment of its performance for typical IIoT employments such as those represented by indoor industrial monitoring applications. In detail, after a general description of LoRaWAN, we discuss how to set some of its parameters in order to achieve the best performance in the considered industrial scenario. Subsequently we present the outcomes of a performance assessment, based on realistic simulations, aimed at evaluating the behavior of LoRaWAN for industrial monitoring applications. Moreover, the paper proposes a comparison with the IEEE 802.15.4 network protocol, which is often adopted in similar application contexts. The obtained results confirm that LoRaWAN can be considered as a strongly viable opportunity, since it is able to provide high reliability and timeliness, while ensuring very low energy consumption.

Low-Power Wide Area Networks (LPWANs) are continuously gaining momentum as fundamental enablers of the Internet of Things (IoT) paradigm. These networks provide longrange coverage to end nodes, exploiting license-free frequency bands. The focus of this work is on one of the most prominent LPWAN technologies: LoRa™. We implemented a new ns-3 module to study the performance of a LoRa-based IoT network in a typical urban scenario. Simulation results show that a LoRa network can scale well, achieving packet success rates above 95% in presence of a number of end devices in the order of 104.

Recently, the role of Low-Power Wide Area Networks (LPWANs) as enablers of the Internet of Things (IoT) is emerging. However, many concerns arise on the performance of LPWANs if higher Quality of Service (QoS) requirements are needed by certain classes of IoT services. In this work, we will focus on one of the most prominent of these technologies, i.e., Long-RangeTM(LoRa). Our aim is to study to what extent a LoRa network is able to support uplink (UL) traffic that requires to be confirmed by the Network Server (NS). The simulation results show that the network performance is severely impacted by the downlink (DL) traffic generated by feedback packets.

Low power wide area networks (LPWAN) are emerging as a new paradigm, especially in the field of Internet of Things (IoT) connectivity. LoRa is one of the LPWAN and it is gaining quite a lot of commercial traction. The modulation underlying LoRa is patented and has never been described theoretically. The aim of this letter is to give the first rigorous mathematical signal processing description of the modulation and demodulation processes. We provide as well a theoretical derivation of the optimum receiver entailing a low-complexity demodulation process, resorting to the Fast Fourier Transform. We compare then the performance of the LoRa modulation and the frequency-shift keying modulation both in an additive white gaussian noise channel and a frequency selective channel, showing the superiority of the LoRa modulation in the frequency selective channel. The results of this letter will enable a further assessment of the LoRa based networks, much more rigorous than what has been done until now.

The fifth-generation (5G) cellular networks will face the challenge of integrating the traditional broadband services with the Internet of Things (IoT), which is characterized by sporadic uplink transmissions of small data packets. Indeed, the access procedure of the previous generation cellular network (4G) is not able to support IoT traffic efficiently, because it requires a large amount of signaling for the connection setup before the actual data transmission. In this context, we introduce two innovative radio access protocols for sporadic transmissions of small data packets, which are suitable for 5G networks, because they provide a resource-efficient packet delivery exploiting a connectionless approach. The core of this paper resides in the derivation of an analytical framework to evaluate the performance of all the aforementioned protocols. The final goal is the comparison between 4G and 5G radio access solutions employing both our analytical framework and computer simulations. The performance evaluation results show the benefits of the protocols envisioned for 5G in terms of signaling overhead and access latency.

We consider a cellular Internet of things (CIoT) network where many source nodes aim at exchanging messages with a single concentrator node. To this end, they are assisted by anchor nodes that are trusted and securely connected with the concentrator node. In this context, we aim at providing a message authentication scheme based on the characteristics of the channel between the source nodes and the anchor nodes. According to this approach, the anchor nodes estimate the channel to source nodes in an initially externally authenticated fashion, while forthcoming messages are authenticated by comparing the current channel estimate with the initial estimate. Moreover, assuming that the anchor nodes have a limited energy availability, we derive suitable scheduling policies for the activation of the anchor nodes for authentication purposes. In particular, we aim at maximizing the anchors lifespan while guaranteeing given false alarm and missed detection probabilities of the authentication process. The performance of the proposed authentication protocols is evaluated in a typical CIoT scenario.

In this paper a Bayesian approach to increase the throughput and reduce the latency of the Hybrid-ARQ processes in the Long Term Evolution uplink is proposed. The performance of the enhanced system is evaluated and compared to the standard one using a theoretical framework based on the Accumulated Mutual Information and the theory of Markov chains. The proposed modification is simple to implement in real systems and it is shown to be effective, especially in low mobility scenarios.

The idea that we are moving towards a future networked society is widely accepted. The increase of network access, in particular to the Internet, and the wide heterogeneity of devices and components that access the network, and occasionally communicate with each other, pose great design challenges, but at the same time open unprecedent opportunities. In order to be able to fully exploit the new opportunities, a uniform and standardized software architecture must be adopted. The aim is to regulate and organize the multidisciplinary nature of the Internet-of-Things (IoT) applications. In this article we first introduce the REpresentational State Transfer (REST) architecture style as one of the de-facto standards in a totally-IP-connected world. Then the main focus will move to a new M2M RESTful framework for the IoT, developed following the REST paradigm, but enhancing its interface to introduce new web functionalities that are still accessed via the usual interface of the Internet Web sites.

“Smart City” is a powerful paradigm that applies the most advanced communication technologies to urban environments, with the final aim of enhancing the quality of life in cities and provide a wide set of value-added services to both citizens and administration. A fundamental step towards the practical realization of the Smart City concept consists in the development of a communication infrastructure capable of collecting data from a large variety of different devices in a mostly uniform and seamless manner, according to the Internet of Things (IoT) paradigm. While the scientific and commercial interest in IoT has been constantly growing in the last years, practical experimentation of IoT systems has just begun. In this paper, we present and discuss the Padova Smart City system, an experimental realization of an urban IoT system designed within the Smart City framework and deployed in the city of Padova, Italy. We describe the system architecture and discuss the fundamental technical choices at the base of the project. Then, we analyze the data collected by the system and show how simple data processing techniques can be used to gain insights on the functioning of the monitored system, public traffic lighting in our specific case, as well as other information concerning the urban environment.

Tracking the channel impulse response in systems based on the IEEE 802.11p standard, the most widely accepted standard for the physical layer in Vehicular Area NETworks (VANETs), is still an open research topic. As matter of fact tracking the channel impulse response is the most challenging issue in designing the receiver for VANET devices. In fact, due to high vehicle speeds, the Doppler effect reduces the coherence time and coherence bandwidth of the channel response, making the IEEE802.11p pilot tones not sufficient for channel tracking purposes. In this paper we aim to improve previously proposed techniques by utilizing a channel estimation technique known as “group orthogonal matching pursuit”. Moreover, we propose a novel technique that exploits the data provided by sensors like GPS or speedometer, usually present in vehicles. Simulation results show that both techniques give considerable improvements in terms of bit error rate and packet error rate for a scenario which is particularly stressing the channel estimation, i.e., the highway Road To Vehicle scenario.

The Internet of Things (IoT) shall be able to incorporate transparently and seamlessly a large number of different and heterogeneous end systems, while providing open access to selected subsets of data for the development of a plethora of digital services. Building a general architecture for the IoT is hence a very complex task, mainly because of the extremely large variety of devices, link layer technologies, and services that may be involved in such a system. In this paper, we focus specifically to an urban IoT system that, while still being quite a broad category, are characterized by their specific application domain. Urban IoTs, in fact, are designed to support the Smart City vision, which aims at exploiting the most advanced communication technologies to support added-value services for the administration of the city and for the citizens. This paper hence provides a comprehensive survey of the enabling technologies, protocols, and architecture for an urban IoT. Furthermore, the paper will present and discuss the technical solutions and best-practice guidelines adopted in the Padova Smart City project, a proof-of-concept deployment of an IoT island in the city of Padova, Italy, performed in collaboration with the city municipality.

In this work, the problem of cross-tier interference in a two-tiered (macro-cell and cognitive small-cells) network, under the complete spectrum sharing paradigm, is studied. A new orthogonal precoder transmit scheme for the small base stations, called multi-user Vandermonde-subspace frequency division multiplexing (MU-VFDM), is proposed. MU-VFDM allows several cognitive small base stations to coexist with legacy macro-cell receivers, by nulling the small- to macro-cell cross-tier interference, without any cooperation between the two tiers. This cleverly designed cascaded precoder structure, not only cancels the cross-tier interference, but avoids the co-tier interference for the small-cell network. The achievable sum-rate of the small-cell network, satisfying the interference cancelation requirements, is evaluated for perfect and imperfect channel state information at the transmitter. Simulation results for the cascaded MU-VFDM precoder show a comparable performance to that of state-of-the-art dirty paper coding technique, for the case of a dense cellular layout. Finally, a comparison between MU-VFDM and a standard complete spectrum separation strategy is proposed. Promising gains in terms of achievable sum-rate are shown for the two-tiered network w.r.t. the traditional bandwidth management approach.

Clock synchronization has become an indispensable requirement in wireless sensor networks due to its central importance in vital network operations such as data fusion and duty cycling, and has attracted considerable research interest recently. Assuming exponentially distributed random delays in a two-way message exchange mechanism, this work proposes a network-wide clock synchronization algorithm using a factor graph representation of the network. Message passing using the max-product algorithm is adopted to derive the update rules for the proposed iterative procedure. A closed form solution is obtained for each node's belief about its clock offset at each iteration. Simulation results show that the application of the proposed message passing-based network-wide clock synchronization algorithm provides convergent estimates for both regular cycle-free and random topologies. Moreover, the mean square error (MSE) performance of the proposed algorithm is also compared with the Cramer-Rao bound (CRB) for small example networks, which further highlights the effectiveness of the proposed algorithm.

The problem of clock offset estimation in a two-way timing exchange regime is considered when the likelihood function of the observation time stamps is exponentially distributed. In order to capture the imperfections in node oscillators, which render a time-varying nature to the clock offset, a novel Bayesian approach to the clock offset estimation is proposed using a factor graph representation of the posterior density. Message passing using the max-product algorithm yields a closed form expression for the Bayesian inference problem.

The general feeling about ecology is changing worldwide. People all around the world are more careful about problems such as energy provisioning and consumption. New ideas, such as the Smart Grid concept, are trying to give solutions to the energy problems by means of a modern power grid with intelligent management capabilities. In such scenarios, networking solutions, e.g., the Internet Protocol version 6 (IPv6), will allow appliances to be remotely coordinated in order to optimize the total power consumption, and balance the power demand. This paper presents an innovative implementation of the IPv6 stack over the 6LoWPAN adaptation layer. Our 6LoWPAN implementation aims to provide a support platform for IPv6 over interoperable constrained-resources devices, such as those embedded in the electrical appliances. Our main goals are to optimize the memory management and to address the portability problems of the stack. In particular we want to develop a stack which is not tied to a particular data-link protocol. Comparison with existing solutions is also provided.

In a previous work, we introduced a spectrum sharing technique called Multi-User Vandermonde-subspace Frequency Division Multiplexing (MU-VFDM). This overlay technique allows the coexistence of a downlink Orthogonal Frequency Division Multiple Access (OFDMA) macro-cell and a cognitive multi-user small-cell system in time division duplex mode. In that work, MU-VFDM was shown to be able to completely cancel the interference towards a macro-cell system at the price of perfect channel state information (CSI) at the opportunistic small-cells. In this work we relax the perfect CSI constraint by introducing a channel estimation protocol that does not require cooperation between the two systems, but still provides harmless coexistence between them. The impact of this protocol is evaluated in terms of interference at the legacy and sum-rates at the opportunistic system. Simulation results show that, even with imperfect CSI estimation, MU-VFDM is able to achieve promising rates for the small-cells while incurring a small rate loss at the macro-cell due to interference.

The problem of clock offset estimation in a two-way timing message exchange regime is considered when the likelihood function of the observation time stamps is Gaussian, exponential, or log-normally distributed. A parameterized solution to the maximum likelihood (ML) estimation of clock offset is analytically obtained, which differs from the earlier approaches where the likelihood function is maximized graphically. In order to capture the imperfections in node oscillators, which may render a time-varying nature to the clock offset, a novel Bayesian approach to the clock offset estimation is proposed by using a factor graph representation of the posterior density. Message passing using the max-product algorithm yields an exact expression for the Bayesian inference problem. Several lower bounds on the variance of an estimator are derived for arbitrary exponential family distributed likelihood functions which, while serving as stepping stones to benchmark the performance of the proposed clock offset estimators, can be useful in their own right in classical as well Bayesian parameter estimation theory. To corroborate the theoretical findings, extensive simulation results are discussed for classical as well as Bayesian estimators in various scenarios. It is observed that the performance of the proposed estimators is fairly close to the fundamental limits established by the lower bounds.

In this paper, a consensus-based clock synchronization algorithm is presented and its resilience to frequency displacement estimation errors as well as communication noise is analyzed. The synchronization-enforcing control that is to be applied to clock periods is derived upon re-casting the consensus problem into a convex optimization problem and solving it in a distributed fashion via alternating direction method of multipliers. Conversely, plain consensus is used for reaching agreement on clock values. The proposed algorithm achieves higher convergence rates and equivalent noise resilience with respect to algorithmic solutions based on the only plain average consensus. The superior clock synchronization performance is corroborated via numerical tests.

In a cooperative multi-cell network the uplink signal coming from each mobile terminal (MT) is simultaneously demodulated by multiple base stations (BSs). Both backhaul capacity and BS processing capabilities limit the number of demodulating BSs. In order to fit the information exchange among BSs to backhaul resources we minimize the average number of demodulating BSs, under a constraint on the average outage probability. The BS selection problem becomes more complicated when error control configurations as automatic repeat request (ARQ) and hybrid ARQ (HARQ) with chase combining or incremental redundancy are considered. Multi-cell processing is implemented both by decoding the packet at each BS and by a joint decoding among BSs. We first derive the outage probability as a function of the number of cooperating BSs and the error control strategy. A heuristic approach for BS selection is then developed, to find at each frame which BSs perform demodulation and share the information in the backhaul. Lastly, we show that backhaul usage can be reduced up to 64% with respect to an unoptimized solution.

In orthogonal frequency division multiplexing (OFDM) communication systems mobility results in time-variations of the channel, which yield intercarrier interference (ICI), especially when large OFDM blocks are employed in order to achieve a high spectral efficiency. In this letter we focus on systems with very long OFDM blocks, where many of the existing ICI mitigation techniques can not be applied due to complexity constraints. To mitigate ICI we propose a pre-equalizer, operating on sub-blocks of the received OFDM block, whose aim is to force all sub-blocks to have almost the same equivalent channel. In other words, the pre-equalizer combats only time variations of the channel. Next, after OFDM demodulation, the classical equalizer compensates frequency selectivity of the target channel. Performance of the proposed scheme, together with a suitable channel estimate implemented on a per sub-block basis, is evaluated for a digital video broadcasting scenario, according to the DVB-T2 standard, where the OFDM block size may be 32k, and its possible extension to hand-held devices in a next-generation DVB-H.

Given a synchronous wireless network with N nodes uniformly located at random on a finite plane, we consider the problem of distributed peer discovery: all nodes want to discover as many other nodes as possible. We assume that there are a total of K physical resources dedicated for the discovery purpose. Each node can pick one resource to transmit its node identifier on, and can receive on the remaining K-1 resources. We assume that node identifiers are broadcast via coded transmission on one single physical resource. This paper addresses link level strategies to increase the average number of discovered devices when N ≅ aK, where a is the degree of density of the network. A classical strategy of discovering one node per resource would lead to a maximum of K-1 nodes being discovered. We focus on a multiple-access channel (MAC) scernario where multiple interferer users are jointly decoded. We propose a scheme to improve the performance. The method, based on iterative belief propagation on factor graph, is called joint iterative decoding (JID). It is shown, through system simulations, that JID may gain by significantly more than 100% over the classical single-user decoding, and by 20-25% over the successive interference cancellation (SIC).

In a cooperative multi-cell network we propose to simultaneously demodulate the uplink signal coming from mobile terminals (MTs) with multiple base stations (BSs) for a joint decoding of the data packets. However, limited backhaul capacity and BS demodulation capabilities limits the number of cooperating BSs. In this paper we consider MTs using a hybrid automatic repeat request (HARQ) protocol for error control, as in 3G and 4G cellular systems. In order to limit the exchange of information among BSs we aim at minimizing the number of demodulating BSs at each HARQ retransmission, under a constraint on the outage probability after a pre-set number of retransmissions. A greedy approach is developed for the system using HARQ, which determines at each retransmission which BSs must perform demodulation and share the information in the backhaul. Numerical results compare the performance of the proposed algorithm with existing solutions, showing that backhaul usage can be reduced up to 38% in a usual 3G scenario.

A multipath channel length estimation algorithm is proposed. It consists basically of estimating all path delays using a threshold comparison-based criterion. The threshold is obtained by imposing a fixed false alarm probability on the detection of each path delay. Assuming that the shortest delay is normalized to be equal to zero, the longest one is then selected to provide the desired length estimate. The threshold is analytically derived under the hypothesis that the channel impulse response (channel IR) estimate is corrupted by additive white Gaussian noise. Simulation results are presented for Universal Mobile Telecommunication System-time division duplex; they show that the proposed algorithm affords a detector performance very close to the case when the channel IR length is a priori known.

We derive new implementations for baseband and passband orthogonal frequency-division multiplexing based on offset QAM (OFDM-OQAM), which nearly halve the number of arithmetic operations required every symbol period by exploiting the symmetries in the transmitted sequences. We also propose a novel scheme, named conjugate, that employs two different filters being the time-reversed version of each other: one in the modulator for the even subchannels and in the demodulator for the odd ones, and the other in the modulator for the odd subchannels and in the demodulator for the even ones. We formulate both baseband and passband versions of this scheme in which the constraints for the filter design are loosened, requiring only amplitude tailoring of its frequency response. We derive efficient implementations for the conjugate scheme, which exhibit a significantly lower complexity than previous implementations of the traditional OFDM-OQAM scheme.

This paper presents a closed-form spectral evaluation of the family of digital pulse interval modulation (DPIM) schemes, where the information is contained in the relative distance between successive pulses. The framework for spectral evaluation is that of stationary symbol sequences derived from variable-length word sequences, which considers the issue of stationarization, a preliminary task to spectral analysis. For all the considered modulation schemes, the spectrum turns out to be a rational function of exp(j2/spl pi/fT), where T is the slot duration. Moreover, spectral lines occur at integer multiples of 1/T, but occasionally may also occur at submultiples of 1/T.