Minimum throughput maximization in LoRa networks powered by ambient energy harvesting

In this paper, we investigate the uplink transmissions in low-power wide-area networks (LPWAN) where the users are self-powered by the energy harvested from the ambient environment. Demonstrating their potential in supporting diverse Internet-of-Things (IoT) applications, we focus on long range (LoRa) networks where the LoRa users are using the harvested energy to transmit data to a gateway via different spreading codes. Precisely, we study the throughput fairness optimization problem for LoRa users by jointly optimizing the spreading factor (SF) assignment, energy harvesting (EH) time duration, and the transmit power of LoRa users. First, through examination of the various permutations of collisions among users, we derive a general expression of the packet collision time between LoRa users, which depends on the SFs and EH duration requirements. Then, after reviewing prior SF allocation work, we develop two types of algorithms that either assure fair SF assignment indeed purposefully `unfair' allocation schemes for the LoRa users. Our results unearth three new findings. Firstly, we demonstrate that, to maximize the minimum rate, the unfair SF allocation algorithm outperforms the other approaches. Secondly, considering the derived expression of packet collision between simultaneous users, we are now able to improve the performance of the minimum rate of LoRa users and show that it is protected from inter-SF interference which occurs between users with different SFs. That is, imperfect SF orthogonality has no impact on minimum rate performance. Finally, we have observed that co-SF interference is the main limitation in the throughput performance, and not the energy scarcity

Recycling cellular downlink energy for overlay self-sustainable IoT networks

This paper investigates the self-sustainability of an overlay Internet of Things (IoT) network that relies on harvest- ing energy from a downlink cellular network. Using stochastic geometry and queueing theory, we develop a spatiotemporal model to derive the steady state distribution of the number of packets in the bu ff ers and energy levels in the batteries of IoT devices given that the IoT and cellular communications are allocated disjoint spectrum. Particularly, each IoT device is modeled via a two-dimensional discrete-time Markov Chain (DTMC) that jointly tracks the evolution of data bu ff er and energy battery. In this context, stochastic geometry is used to derive the energy generation at the batteries and the packet transmission probability from bu ff ers taking into account the mutual interference from other active IoT devices. To this end, we show the Pareto-Frontiers of the sustainability region, which defines the network parameters that ensure stable network operation and finite packet delay. The results provide several insights to design self-sustainable IoT networks. Index Terms —Spatiotemporal models, stochastic geometry, queuing theory, energy harvesting, packet transmission success probability, two-dimensional discrete-time Markov chain, sta- bility conditions

A discriminating microscopy technique for the measurement of ice crystals and air bubbles size distribution in sorbets

24ième Congrès International du Froid ICR 2015, Yokohama, JPN, 16-/08/2015 - 22/08/2015International audienceIn this work, a technique capable to distinguish between ice crystals and air bubbles in sorbets was developed in order to characterize the effect of operating conditions on their size distributions at the exit of the freezer. A pilot freezer was used to crystallize and aerate a commercial lemon sorbet mix. Crystals and bubbles sizes were measured using a light microscope technique under low temperature in a refrigerated glove box developed in the lab for that purpose. Results showed that the developed microscope technique allowed to distinguish them and to quantify their size distributions. Measurements showed that ice crystals size decreases with air flow rate while air bubbles size increases. The latter also increases with the cylinder pressure inside the scraped surface heat exchanger (SSHE)

On the generalization of the hazard rate twisting-based simulation approach

Estimating the probability that a sum of random variables (RVs) exceeds a given threshold is a well-known challenging problem. A naive Monte Carlo simulation is the standard technique for the estimation of this type of probability. However, this approach is computationally expensive, especially when dealing with rare events. An alternative approach is represented by the use of variance reduction techniques, known for their efficiency in requiring less computations for achieving the same accuracy requirement. Most of these methods have thus far been proposed to deal with specific settings under which the RVs belong to particular classes of distributions. In this paper, we propose a generalization of the well-known hazard rate twisting Importance Sampling-based approach that presents the advantage of being logarithmic efficient for arbitrary sums of RVs. The wide scope of applicability of the proposed method is mainly due to our particular way of selecting the twisting parameter. It is worth observing that this interesting feature is rarely satisfied by variance reduction algorithms whose performances were only proven under some restrictive assumptions. It comes along with a good efficiency, illustrated by some selected simulation results comparing the performance of the proposed method with some existing techniques

Application and modeling of GaN FET in 1MHz large signal bandwidth power supply for radio frequency power amplifier

In this paper, implementation and testing of non- commercial GaN HEMT in a simple buck converter for envelope amplifier in ET and EER transmission techn iques has been done. Comparing to the prototypes with commercially available EPC1014 and 1015 GaN HEMTs, experimentally demonstrated power supply provided better thermal management and increased the switching frequency up to 25MHz. 64QAM signal with 1MHz of large signal bandw idth and 10.5dB of Peak to Average Power Ratio was gener ated, using the switching frequency of 20MHz. The obtaine defficiency was 38% including the driving circuit an d the total losses breakdown showed that switching power losses in the HEMT are the dominant ones. In addition to this, some basic physical modeling has been done, in order to provide an insight on the correlation between the electrical characteristics of the GaN HEMT and physical design parameters. This is the first step in the optimization of the HEMT design for this particular application

Antisense pre-treatment increases gene therapy efficacy in dystrophic muscles

In preclinical models for Duchenne muscular dystrophy, dystrophin restoration during adeno-associated virus (AAV)-U7-mediated exon-skipping therapy was shown to decrease drastically after six months in treated muscles. This decline in efficacy is strongly correlated with the loss of the therapeutic AAV genomes, probably due to alterations of the dystrophic myofiber membranes. To improve the membrane integrity of the dystrophic myofibers at the time of AAV-U7 injection, mdx muscles were pre-treated with a single dose of the peptide-phosphorodiamidate morpholino (PPMO) antisense oligonucleotides that induced temporary dystrophin expression at the sarcolemma. The PPMO pre-treatment allowed efficient maintenance of AAV genomes in mdx muscles and enhanced the AAV-U7 therapy effect with a ten-fold increase of the protein level after 6 months. PPMO pre-treatment was also beneficial to AAV-mediated gene therapy with transfer of micro-dystrophin cDNA into muscles. Therefore, avoiding vector genome loss after AAV injection by PPMO pre-treatment would allow efficient long-term restoration of dystrophin and the use of lower and thus safer vector doses for Duchenne patients

Practical nonlinear energy harvesting model in MIMO DF relay system with channel uncertainty

In this paper, we aim to maximize the end-to- end achievable rate of multiple-input multiple-output (MI MO) decode-and-forward (DF) where the relay is an energy harves t- ing (EH) node using the time switching (TS) scheme. The relay first harvests the energy from the source, then uses its harve sted energy to forward the information carrying signal from the source to the destination. The EH model at the relay is a nonlinear model. Also, we assume that the channel knowledge is imperfect at the relay and destination. We propose the struc ture of the optimal covariance matrices at the source (during EH a nd information decoding periods), the optimal covariance mat rix at the relay and the optimal EH time ratio. Through the simulati on results, we compare between di ff erent linear / nonlinear EH models and we show the gain / loss performance of the linear model compared to other nonlinear EH model

Analysis of power allocation for NOMA-based D2D communications using GADIA

The new era of IoT brings the necessity of smart synergy for diverse communication and computation entities. The two extremes are, on the one hand, the 5G Ultra-Reliable Low-Latency Communications (URLLC) required for Industrial IoT (IIoT) and Vehicle Communications (V2V, V2I, V2X). While on the other hand, the Ultra-Low Power, Wide-Range, Low Bit-rate Communications, such as Sigfox, LoRa/LoRaWAN, NB-IoT, Cat-M1, etc.; used for smart metering, smart logistics, monitoring, alarms, tracking applications. This extreme variety and diversity must work in synergy, all inter-operating/inter-working with the Internet. The communication solutions must mutually cooperate, but there must be a synergy in a broader sense that includes the various communication solutions and all the processing and storage capabilities from the edge cloud to the deep-cloud. In this paper, we consider a non-orthogonal multiple access (NOMA)-based device to device (D2D) communication system coexisting with a cellular network and utilize Greedy Asynchronous Distributed Interference Avoidance Algorithm (GADIA) for dynamic frequency allocation strategy. We analyze a max–min fairness optimization problem with energy budget constraints to provide a reasonable boundary rate for the downlink to all devices and cellular users in the network for a given total transmit power. A comprehensive simulation and numerical evaluation is performed. Further, we compare the performance of maximum achievable rate and energy efficiency (EE) at a given spectral efficiency (SE) while employing NOMA and orthogonal frequency-division multiple access (OFDMA)

How orthogonal is LoRa modulation?

In this paper, we provide, for the first time, a comprehensive understanding of LoRa waveform theory in order to quantify its orthogonality. We present LoRa waveform expressions in continuous and discrete time domains, and analyze measures of orthogonality between different LoRa spreading factors (SFs) through cross-correlation functions. The crosscorrelation functions are analytically expressed in a general form and they account for diverse configuration parameters (bandwidth, SF, etc.) and different cases of signal displacements (time delay shift, frequency shift, etc.). We quantify their mean and maximum in all time domains. We highlight the impact of the temporal displacement and different bandwidths. The general result is that LoRa modulation is non-orthogonal. Firstly, we observe that for same bandwidths the largest maximum crosscorrelation happens for same SF and is equal to 100% due to same symbols; whereas for different bandwidths, the largest maximum cross-correlation is no longer observed at the same SF. Secondly, the maximum cross-correlation is less than 26% between different SFs, is higher for closer SFs and decreases as the difference between SFs increases. After downchirping, the maximum crosscorrelation increases and the mean decreases compared to those before downchirping. Moreover, the maximum cross-correlation is insignificantly impacted by the temporal delay which makes it valid to adopt for the performance analysis of both synchronous and asynchronous systems. Finally, we analyze by simulation the bit error probability statistics for different bandwidth ratios and highlight their correlated behaviour with the insights obtained from the maximum cross-correlation expressions

Resource allocation for non-orthogonal multiple access (NOMA) enabled LPWA networks

In this paper, we investigate the resource allocation for uplink non-orthogonal multiple access (NOMA) enabled low-power wide-area (LPWA) networks to support the massive connectivity of users/nodes. Here, LPWA nodes communicate with a central gateway through resource blocks like channels, transmission times, bandwidths, etc. The nodes sharing the same resource blocks suffer from intra-cluster interference and possibly inter-cluster interference, which makes current LPWA networks unable to support the massive connectivity. Using the minimum transmission rate metric to highlight the interference reduction that results from the addition of NOMA, and while assuring user throughput fairness, we decompose the minimum rate maximization optimization problem into three sub- problems. First, a low-complexity sub-optimal nodes clustering scheme is proposed assigning nodes to channels based on their normalized channel gains. Then, two types of transmission time allocation algorithms are proposed that either assure fair or unfair transmission time allocation between LPWA nodes sharing the same channel. For a given channel and transmission time allocation, we further propose an optimal power allocation scheme. Simulation evaluations demonstrate approximately 100dB improvement of the selected metric for a single network with 4000 active nodes