Higher Spreading Factor Research Articles

Downlink Spreading Factor selection in LoRaWAN

LoRaWAN is one of the most commonly used Internet of Things protocols for applications that require low cost, low power, and long range communications. It has been proved that – mainly due to regional radio duty cycle restrictions – the protocol does not scale well in presence of confirmed (downlink) traffic. To support downlink traffic, LoRaWAN employs two receive windows, RX1 and RX2, whereas a number of channels are assigned to each of those windows. The protocol uses a fixed Spreading Factor (SF) – a LoRa PHY modulation parameter – in RX2, while the SF of the uplink is employed in RX1. Since the SF of RX1 cannot be changed, selecting a low or a high value of SF in RX2 is of critical importance for the duty cycle resources of the gateways. On one hand, selecting high SF values, the time resources of the gateways may get depleted fast leading to low capacity because the transmission time increases with higher SF values. On the other hand, lower SF values reduce reachability due to the worse sensitivity which causes retransmissions, and thus, lower capacity. In this paper, a study of the total theoretical downlink capacity is provided giving useful insights of the protocol behavior as the number of uplinks increases, especially for congested network scenarios. An exhaustive SF selection solution is also presented to compute the maximum downlink capacity. It is shown that the RX2 SF which provides the best capacity may imply fairness compromises for part of the devices. Extensive simulations are employed to confirm the theoretical findings in scenarios with a single and multiple gateways. Experiments conducted on a test-bed for selected scenarios also confirm the theoretical findings.

Performance Evaluation of LoRaWAN SX1276 Radio in Non-Line of Sight conditions

The study presents a comprehensive performance evaluation of the SX1276 radio module within LoRaWAN technology under Non-Line of Sight (NLOS) conditions. LoRaWAN's proliferation in IoT applications demands a thorough understanding of its performance in challenging environments. This study investigates NLOS scenarios, identifying factors influencing signal strength, packet loss, and latency. Finally, the performance of the network under LOS condition was compared to NLOS to shed light on NLOS challenges. Results showed that spreading factor and transmission power are the most critical parameters that influences the performance of the network. Results from the study also shows that in LOS condition the spreading factor 7 has the highest data rate but also the least range. Furthermore, the study revealed that using high spreading factor is more beneficial than high transmission power in non-line of sight conditions. Finally, by comparing both conditions, LoRaWAN nodes under LOS condition was found to have a range of up to 5 km as against 1 km at NLOS which further highlight the importance of LOS in LoRa transmissions.

LoRaHop: Multihop Support for LoRaWAN Uplink and Downlink Messaging

LoRaWAN is one of the most popular protocols to build low-power wide area networks. Unfortunately, it adopts a star topology, which limits network coverage and may also cause an unnecessary decrease in energy efficiency as well as scalability. In fact, end-devices that are deployed far away from a gateway need to increase their transmission power or spreading factor to sustain reliable communications, which increases their energy expenditure as well as the size of the collision domain. The only alternative is the deployment of additional gateways or dedicated relay nodes, which results in higher costs and deployment efforts. In this work, we introduce LoRaHop, an extension of LoRaWAN that enriches end-devices with the ability to form a mesh network and to seamlessly relay packets to/from a gateway, thereby providing LoRaWAN networks with multi-hop support for both uplink and downlink messaging. LoRaHop leverages concurrent transmissions to enable a reliable and efficient data collection or dissemination over the mesh network, as well as to simplify network formation. Furthermore, LoRaHop embeds a mechanism that simplifies rendezvous across devices and that minimizes the impact of mesh operations on existing LoRaWAN transmissions. We implement LoRaHop on off-the-shelf LoRa end-devices (ensuring their interoperability with commercial LoRaWAN gateways and network servers), and evaluate its performance on an outdoor testbed. Our results show that LoRaHop can effectively extend the coverage of a LoRaWAN network while improving reliability by up to 98.33% and reducing energy consumption by up to 48.02%. Our findings further demonstrate that using LoRaHop to create a multi-hop LoRaWAN network that communicates using low spreading factors brings significant benefits in terms of energy efficiency and scalability compared to the use of a single-hop LoRaWAN network using high spreading factors.

Approximate BER Performance of LoRa Modulation With Heavy Multipath Interference

This letter proposes a method to approximate LoRa performance over heavy multipath channels. Firstly, the multipath time delay and LoRa signal duration are combined to analyze the path overlapping interference quantitatively. Then simple BER approximations in coherent and non-coherent detections are derived with Gaussian Q-function and algebraic formulas. With the heavy multipath channel model in 3GPP to mimic the realistic indoor industrial scenarios, the approximate expressions are verified by Monte Carlo simulations. Moreover, performance comparison results show that a high spreading factor leads to severe multipath overlap and may result in BER reduction.

FlyingLoRa: Towards energy efficient data collection in UAV-assisted LoRa networks

Energy efficiency is an increasingly crucial consideration due to the battery-powered end devices in LoRa networks. With the adoption of chirp spread spectrum modulation, end devices far apart from the gateway have to use a high spreading factor and transmit power to send uplink packets, which causes longer transmission time and higher energy consumption compared to the end devices near the gateway, and further causes unfairness issues on energy efficiency. To tackle this problem, we investigate a novel energy-efficient data collection scheme named FlyingLoRa, where an unmanned aerial vehicle carrying one gateway is dispatched to harvest packets from end devices. The goal of FlyingLoRa is to minimize the energy consumption of end devices for packet transmission by jointly optimizing the 3D UAV trajectory, scheduling strategies, and transmission parameters of end devices. We formulate our design as a mixed-integer non-convex optimization problem and propose an efficient iterative algorithm to find a sub-optimal solution. The proposed approach is numerically simulated and the results show that FlyingLoRa improves energy efficiency by 16.13× on average compared with the existing fixed gateway schemes. In addition, we realize FlyingLoRa in real scenarios and evaluate its performance by presenting the actual packet reception rate (PRR) and transmission energy consumption, which shows its effectiveness.

The SF12 Well in LoRaWAN: Problem and End-Device-Based Solutions.

LoRaWAN has become a popular technology for the Internet of Things (IoT) device connectivity. One of the expected properties of LoRaWAN is high network scalability. However, LoRaWAN network performance may be compromised when even a relatively small number of devices use link-layer reliability. After failed frame delivery, such devices typically tend to reduce their physical layer bit rate by increasing their spreading factor (SF). This reaction increases channel utilization, which may further degrade network performance, even into congestion collapse. When this problem arises, all the devices performing reliable frame transmission end up using SF12 (i.e., the highest SF in LoRaWAN). In this paper, we identify and characterize the described network condition, which we call the SF12 Well, in a range of scenarios and by means of extensive simulations. The results show that by using alternative SF-management techniques it is possible to avoid the problem, while achieving a packet delivery ratio increase of up to a factor of 4.7.

M-ary nonlinear sine chirp spread spectrum for underwater acoustic communication based on virtual time-reversal mirror method

Linear chirp spread spectrum technique is widely used in underwater acoustic communication because of their resilience to high multipath and Doppler shift. Linear frequency modulated signal requires a high spreading factor to nearly reach orthogonality between two pairs of signals. On the other hand, nonlinear chirp spread spectrum signals can provide orthogonality at a low spreading factor. As a result, it improves spectral efficiency and is more insensitive to Doppler spread than the linear counterpart. To achieve a higher data rate, we propose two variants (half cycle sine and full cycle sine) of the M-ary nonlinear sine chirp spread spectrum technique based on virtual time-reversal mirror (VTRM). The proposed scheme uses different frequency bands to transmit chirp, and VTRM is used to improve the bit error rate due to high multipath. Its superior Doppler sensitivity makes it suitable for underwater acoustic communication. Furthermore, the proposed method uses a simple, low-power bank of matched filters; thus, it reduces the overall system complexity. Simulations are performed in different underwater acoustic channels to verify the robustness of the proposed scheme.

Packet-Level Index Modulation for LoRaWAN

The long range wide area network (LoRaWAN) is one of the enabling technologies for low power wide area (LPWA) networks. In LoRaWAN, a node transmits its packet to a gateway (GW) in an autonomous and decentralized manner. The quantity of data that can be transmitted by each node is limited by the duty cycle (DC). Furthermore, it is not easy for the nodes to perform sophisticated techniques for increasing the data quantity due to their limited functionality, especially when the nodes are battery-powered. If the network size increases, packet collision may occur more frequently. Since the packet transmission drains the LoRaWAN nodes’ battery, the packet collision results in a waste of limited power. Thus, it is necessary to develop a simple but effective transmission strategy that efficiently utilizes limited battery at each LoRaWAN node. This study proposes packet-level index modulation (PLIM), which is suitable for such LPWA networks. PLIM takes advantage of the sparse data packet transmission in time and the selection of a frequency channel among multiple ones by each node. A time slot and frequency channel combination is selected, i.e., the index, to increase the data quantity. For long-range communication, it is necessary to use a higher spreading factor (SF) in LoRaWAN, which results in a lower data rate due to the DC. The proposed PLIM can compensate for such data rate loss by taking advantage of the sparse transmission in time. Numerical evaluation elucidates that the proposed PLIM can increase the data quantity of LoRaWAN system without requiring any modification in the specification. When the SF is 10, the proposed PLIM can increase the data quantity up to 32.5%, compared to the conventional LoRaWAN system.

Performance evaluation of chaotic spreading codes in massive MIMO OFDM system

Background/Objectives: Wireless communication systems are growing towards the implementation of 5G communication systems to satisfy the demand of services in future. OFDMA has some shortcoming like one or more subcarriers of OFDM are completely affected due to the characteristic of the transmission channel. Spreading scheme has been introduced to combat the aforementioned issue. Furthermore, communication channels are affected by multipath fading which changes the amplitude of the received signal. This fading severely affects the communication systems. Therefore, it is essential to develop a more robust technique for higher data transmission and larger throughput. The main objective of this study is to design a massive MIMOOFDM system for secure transmission of data. Chaos based sequence is used to spread the data before transmission which will solve intercell interference and improve the security of data. Methods: This study presents a chaos based massive MIMO-OFDM communication system. The proposed chaos based massive MIMO-OFDM system is implemented and its efficacy is evaluated by computing bit error rate. The effectiveness of the proposed system is investigated by varying the parameters including modulation methods such as PSK and QAM, number of users 10, 20 and 30 and spreading factor of 5, 10 and 15. Findings: Results clearly proved that the proposed system provides exceptional performance with 16QAM modulation scheme, 10 users at high spreading factor value of 15. Novelty: The uniqueness of the proposed system is with enhanced performance and usage of novel modulation scheme by varying the spreading factor value, when compared to its peers. Keywords: Communication system; spreading code; chaotic code; massive MIMO-OFDM; bit error rate

LoRa Beyond ALOHA: An Investigation of Alternative Random Access Protocols

In this article, we present a stochastic geometry-based model to investigate alternative medium access choices for LoRaWAN-a widely adopted low-power wide-area network (LPWAN) technology for the Internet-of-Things. LoRaWAN adoption is driven by its simplified network architecture, air interface, and medium access. The physical layer, known as Long Range (LoRa), provides quasi-orthogonal virtual channels through spreading factors (SFs) and time-power capture gains. However, the adopted pure ALOHA access mechanism suffers, in terms of scalability, under the same-channel same-SF transmissions from a large number of devices. In this article, our objective is to explore access mechanisms beyond-ALOHA for LoRaWAN. Using recent results on time- and power-capture effects of LoRa, we develop a unified model for the comparative study of other choices, i.e., slotted ALOHA and carrier-sense multiple access (CSMA). The model includes the necessary design parameters of these access mechanisms, such as guard time and synchronization accuracy for slotted ALOHA, carrier sensing threshold for CSMA. It also accounts for the spatial interaction of devices in annular shaped regions, characteristic of LoRa, for CSMA. The performance metrics derived from the model in terms of coverage probability, channel throughput, and energy efficiency are validated using Monte-Carlo simulations. Our analysis shows that slotted ALOHA indeed has higher reliability than pure ALOHA but at the cost of lower energy efficiency for low device densities. Whereas, CSMA outperforms slotted ALOHA at smaller SFs in terms of reliability and energy efficiency, with its performance degrading to pure ALOHA at higher SFs.

Performance Analysis of LPWAN Using LoRa Technology for IoT Application

This paper was dedicated to study the performance of an Internet of Things (IoT) application using LoRa Wide Area Network (LoRaWAN). LoRa is a Low Power Wide Area Network (LPWAN) technology developed for IoT applications specifically. Due to the facts that LoRa is a new product, there are questions about its reliability. Hence, a conclusive experiment has been made. The experiment conducted to get an insight to LoRa received signal strength (RSSI) and packet loss. The analysis also includes a measurement of the application Signal to Noise Ratio (SNR) between the transmitter and receiver. The results of the experiment show that with a higher spreading factor, LoRa end device provides more immunity against multi-path and signal fading. The proposed IoT application based on this LoRa technology is for autonomous vehicle status information transmission and intervehicle communications, specifically deployed in UiTM Autonomous Vehicle 1 (UiTM AV1).

Performance Analysis of LPWAN Using LoRa Technology for IoT Application

This paper was dedicated to study the performance of an Internet of Things (IoT) application using LoRa Wide Area Network (LoRaWAN). LoRa is a Low Power Wide Area Network (LPWAN) technology developed for IoT applications specifically. Due to the facts that LoRa is a new product, there are questions about its reliability. Hence, a conclusive experiment has been made. The experiment conducted to get an insight to LoRa received signal strength (RSSI) and packet loss. The analysis also includes a measurement of the application Signal to Noise Ratio (SNR) between the transmitter and receiver. The results of the experiment show that with a higher spreading factor, LoRa end device provides more immunity against multi-path and signal fading. The proposed IoT application based on this LoRa technology is for autonomous vehicle status information transmission and intervehicle communications, specifically deployed in UiTM Autonomous Vehicle 1 (UiTM AV1).

Effect of processing parameters and principal ingredients on quality of sugar snap cookies: a response surface approach.

Effects of processing parameters such as creaming time, dough mixing time, cookie thickness, baking temperature, time and principal ingredients viz. sugar, fat and water on quality of sugar snap cookies were investigated using the Response Surface Methodology. Shorter mixing time (100s) along with higher creaming time (400s) was desirable for producing softer cookies with tender bite and higher spread factor. Cookie baked at 190°C had superior quality in terms of hardness and spread factor as compared with those baked either at lower or at higher temperature. At lower baking temperature, hardness of cookie increased as the baking time was decreased below 14min. Hardness also increased significantly with increase in water content at all levels of sugar concentration in the formula. Optimum cookie quality was obtained with creaming time of 400s and mixing time 100s to make cookie dough containing 59.65% sugar, 46.68% fat and 14% water. Cookie thickness 11mm, baking temperature 190°C and baking time of 16min 30s resulted in best cookies.

Improving Reliability and Scalability of LoRaWANs Through Lightweight Scheduling

Providing low power and long range (LoRa) connectivity is the goal of most Internet of Things networks, e.g., LoRa, but keeping communication reliable is challenging. LoRa networks are vulnerable to the capture effect. Cell-edge nodes have a high chance of losing packets due to collisions, especially when high spreading factors (SFs) are used that increase time on air. Moreover, LoRa networks face the problem of scalability when they connect thousands of nodes that access the shared channels randomly. In this paper, we propose a new MAC layer—RS-LoRa—to improve reliability and scalability of LoRa wide-area networks (LoRaWANs). The key innovation is a two-step lightweight scheduling : 1) a gateway schedules nodes in a coarse-grained manner through dynamically specifying the allowed transmission powers and SFs on each channel and 2) based on the coarse-grained scheduling information, a node determines its own transmission power, SF, and when and on which channel to transmit. Through the proposed lightweight scheduling, nodes are divided into different groups, and within each group, nodes use similar transmission power to alleviate the capture effect. The nodes are also guided to select different SFs to increase the network reliability and scalability. We have implemented RS-LoRa in NS-3 and evaluated its performance through extensive simulations. Our results demonstrate the benefit of RS-LoRa over the legacy LoRaWAN, in terms of packet error ratio, throughput, and fairness. For instance, in a single-cell scenario with 1000 nodes, RS-LoRa can reduce the packet error ratio of the legacy LoRaWAN by nearly 20%.

Blind Channel Estimation Based Linear Precoding using MIMO-OFCDM

MIMO-OFCDM is one of the emerging wireless communication technologies which provide very high data rate transmission with multicarrier modulation technique. OFCDM utilizes spatial diversity method that uses many transmitters and receivers to transmit more than one data in the same frequency at the same time. This paper proposes blind channel estimation based on Linear Precoding (LP) approach for 2 by 2 MIMO-OFCDM broadband communication system. The uniqueness of the proposed method is to estimate the channel response in blind fashion and minimize the BER in MIMO-OFCDM. Linear Precoding based blind channel estimation is implemented to estimate the performance of the MIMO-OFCDM for various parameters including different number of users, three different modulations such as BPSK, QPSK and 16 QAM, two types of Spreading Factors over AWGN and Rayleigh channels. The system performance is then compared with the other existing methods. It is found that the blind channel estimation provides better performance with minimum BER. It also suggests that the LP based blind channel estimation in MIMO OFCDM system outperforms with QPSK modulation with more users and high spreading factor over Rayleigh channel.

Cookies from composite wheat–sesame peels flours: Dough quality and effect of Bacillus subtilis SPB1 biosurfactant addition

Sesame coat is a valuable by-product. The study was carried out on sesame peels flour at different replacing levels of white wheat flour in five cookies dough formulations. The functional properties of composite flours such as swelling capacity, water holding capacity, oil holding capacity, emulsifying capacity, foam capacity, gelatinization temperature, least gelation concentration and bulk density were increased with increase in the sesame peels flour incorporation along with wheat flour. Texture analysis of dough revealed that, the addition of sesame peels flour affected the quality of dough in terms of hardness, cohesion, adhesion and breaking strength. Cookies supplemented with sesame peels flour showed interesting physical properties with lower moisture content and higher spread factor than those made by white wheat flour. But, their hardness increase with the increase of the replacement ratio and their color becomes indesirable. Interestingly, sensory results indicated that cookies supplemented with sesame peels flour were acceptable at a level that not exceeds 30% of incorporation. By the addition of SPB1 biosurfactant at 0.1%, the dough texture profile was significantly improved and the action of this bioemulsifier was more pronounced than a commercial emulsifier known as glycerol monostearate. With the addition of SPB1 biosurfactant on cookies’ dough, we manage to obtain cookies softer and with better overall quality.

Study of the Effect of Surface Roughness on Droplet Spreading Behavior Using CFD Modeling

Water droplet spreading has been simulated at impact velocity of 3.0 m/s, 1.5 m/s and 0.5 m/s on surfaces with texture of ‘triangle’, ‘square’, ‘curve’ as well as smooth surface of aluminum. Higher impact velocity induced the droplet to spread faster and has a bigger diameter. At high impact velocity, spreading factor cannot be determined due to splashing and droplet break ups. In addition, at 1.5 m/s the phenomenon of splashing was found to be almost absent except on the surface with ‘square’ texture. ‘Square’ surface tends to splash earlier compared to other surfaces and is followed by ‘triangle’, ‘curve’ and smooth surface. At low impact velocity, the smooth surface has the highest spreading factor and followed by ‘triangle’, ‘square’ and ‘curve’ surface.

Utilization of germinated and heat-moisture treated brown rices in sugar-snap cookies

Utilization of germinated brown rice (GBR) in sugar-snap cookies and effect of heat-moisture treatment of the GBR were investigated. Brown rice was germinated at 30 °C for 48 h and then a heat-moisture treatment was conducted for the moistened GBR (17 g/100 g moisture content) at 100 °C for 4 h. Sugar-snap cookies were prepared with white rice, brown rice, GBR and the treated GBR flours, as substitutes for wheat flour (30–100 g/100 g). All cookies containing rice flours, regardless of germination and heat-moisture treatment, required significantly less force to compress than did the wheat flour cookie, and this softening effect was increased as the level of rice flour substitution increased. The cookies made with the GBR flour displayed inferior physical characteristics compared to those with wheat flour, but the cookies containing the treated GBR flour showed improved physical properties with lower moisture content and higher spread factor than those containing untreated GBR flour. The cookies containing the treated GBR flours showed relatively a low degree of firming during the ambient storage. The overall results showed that the cookies with acceptable quality and improved nutrition could be prepared by partial or complete replacement of wheat flour with the heat-moisture treated GBR flour.

Effect of chamber pressure on spreading and splashing of liquid drops upon impact on a dry smooth stationary surface

Liquid drop impacts on a smooth surface were studied at elevated chamber pressures to characterize the effect of gas pressure on drop spreading and splashing. Five common liquids were tested at impact speeds between 1.0 and 3.5 m/s and pressure up to 12 bars. Based on experiments at atmospheric pressure, a modification to the “free spreading” model (Scheller and Bousfield in AIChE Paper 41(6):1357–1367, 1995) has been proposed that improves the prediction accuracy of maximum spread factors from an error of 15–5%. At high chamber pressures, drop spreading and maximum spread factor were found to be independent of pressure. The splash ratio (Xu et al. in Phys Rev Lett 94:184505, 2005) showed a non-constant behavior, and a power-law model was demonstrated to predict the increase in splash ratio with decreasing impact speed in the low impact speed regime. Also, drop shape was found to affect splash promotion or suppression for an asymmetry greater than 7–8% of the equivalent drop diameter. The observations of the current work could be especially useful for the study of formation of deposits and wall combustion in engine cylinders.

The Study of Droplet Impact Behavior on Flat Surface with Different Surface Properties

The impact behavior of a liquid droplet on solid surface is a complex phenomenon and yet is a basic component of various industrial processes particularly in the pharmaceutical industry. In this industry, film coating technique is used in tablet coating, in which coating uniformity is important especially if the coating is for functional purposes. Coating uniformity on a tablet could be affected by several factors, one of which is the impingements of droplets on its surface. In this work, the maximum spreading diameter and the initial impact behavior of a single droplet on pharmaceutical tablet surfaces and metal surfaces having different surface properties are investigated. A Charged-Coupled-Device (CCD) high-speed camera with framing rate of 2,000, attached to a 10X microscope, was used to capture the phenomena. The results show that the initial impact behavior of a droplet is not affected by the porosity of a surface. The results on the pharmaceutical tablets, stainless steel and etched silicon surfaces show that the rougher the surface the lower the spreading factor. The droplets on all surfaces demonstrate that a droplet that produces higher spreading factor gives a lower bouncing factor.