Chirp Spread Spectrum Modulation Research Articles

Architecting CubeSat constellations for messaging service, Part I

In today’s modern and globalized world, connectivity is a key factor for businesses, production facilities, sensor networks, and ordinary people. However, there are still populated areas which are not covered by ground-based telecommunications infrastructure. This is where telecommunication satellite constellations come in, as they can provide coverage to remote and uninhabited regions and fill existing connectivity gaps to ensure data transfer.LoRa is one of the technologies designed for data transmissions over long distances with low power consumption. Alongside with other technologies of the Low-Power Wide Area Network family, it is widely used for Internet of Things applications. LoRa chirp spread spectrum modulation is robust against the Doppler frequency shifts encountered in low earth orbits, and it has already been used in IoT satellite communications. Due to the low transmitted signal power, the achieved data rate is not high, making it a suitable technology for telecommunications payloads on CubeSat platforms for messaging services. As compared to existing traditional communication satellite systems, CubeSat constellations are low-cost and may offer an affordable connectivity service to developing regions.This study is divided in two parts. In Part I the demand model is built based on the population distribution not covered by cell towers. The LoRa link performance is analyzed, considering the impact of LoRa channel parameters variation, such as spreading factor and channel bandwidth, while satellite orbital height, transmission antenna beamwidth, and transmitter peak power have a direct impact on the payload mass. Among thousands of possible configurations, 73 feasible payload designs have been downselected. In Part II of the study, the satellite mass and the total system cost are estimated based on the payload parameters obtained. Messages transmission simulation via a constellation is conducted in order to identify optimal constellation architectures for messaging service, as well as the main drivers of the system economic profitability.The presented analysis results provide a deeper understanding of LoRa connectivity advantages and limitations together with the performance drivers, which will support the optimization of future LoRa-based satellite communication systems and other IoT satellite constellations.

A Low-Density Parity-Check Coding Scheme for LoRa Networking

This article presents a novel system, LLDPC , 1 which brings Low-Density Parity-Check (LDPC) codes into Long Range (LoRa) networks to improve Forward Error Correction, a task currently managed by less efficient Hamming codes. Three challenges in achieving this are addressed: First, Chirp Spread Spectrum (CSS) modulation used by LoRa produces only hard demodulation outcomes, whereas LDPC decoding requires Log-Likelihood Ratios (LLR) for each bit. We solve this by developing a CSS-specific LLR extractor. Second, we improve LDPC decoding efficiency by using symbol-level information to fine-tune LLRs of error-prone bits. Finally, to minimize the decoding latency caused by the computationally heavy Soft Belief Propagation (SBP) algorithm typically used in LDPC decoding, we apply graph neural networks to accelerate the process. Our results show that LLDPC extends default LoRa’s lifetime by 86.7% and reduces SBP algorithm decoding latency by 58.09×.

Error mitigation in LPWAN systems: A study on the efficacy of Hamming-coded RPW.

Rotating Polarization Wave (RPW) is a novel Low Power Wide Area Networks (LPWAN) technology for robust connectivity and extended coverage area as compared to other LPWAN technologies such as LoRa and Sigfox when no error detection and correction is employed. Since, IoT and Machine-to-Machine (M2M) communication demand high reliability, RPW with error correction can significantly enhance the communication reliability for critical IoT and M2M applications. Therefore, this study investigates the performance of RPW with single bit error detection and correction using Hamming codes to avoid substantial overhead. Hamming (7,4) coded RPW shows a remarkable improvement of more than 40% in error performance compared to uncoded RPW thereby making it a suitable candidate for IoT and M2M applications. Error performance of coded RPW outperforms coded Chirp Spread Spectrum (CSS) modulation used in LoRa under multipath conditions by 51%, demonstrating superior adaptability and robustness under dynamic channel conditions. These findings provide valuable insights into the ongoing developments in wireless communication systems whilst reporting Q-RPW model as a new and effective method to address the needs of developing LPWAN and IoT ecosystems.

A sub-μs accuracy GPS alternative using electrical transmission grids as precision timing networks.

It is widely recognised that over-reliance on GNSS (e.g GPS) for time synchronisation represents an acute threat to modern society, and a diversity of alternatives are required to mitigate the threat of an outage. This paper proposes a GNSS alternative using time dissemination over national scale transmission or distribution networks. The method utilises the same frequency bandwidth and coupling technology as established power line carrier technology in conjunction with modern chirp Spread Spectrum modulation. The basis of the method is the transmission of a time synchronised chirp from a central substation, coupled into the aerial modes of the transmission line. During GNSS operation, all substations can estimate the time of flight by correlating the received chirp with a time-synchronised local copy. During GNSS outage, time sychronisation to the central substation is maintained by correcting for the precalculated time of flight. It is shown that recent advances in chirp spread spectrum allow for a computationally efficient algorithm with the capacity to compute hundreds of thousand of chirp correlations every second, facilitating timing accuracy which satisfies the majority of smart grid applications. ATP-EMTP simulations of the method on large transmission networks demonstrate sub-μs timing accuracy even in the presence of low SNR and impulsive noise. An FPGA prototype demonstrates experimentally sub-μs accuracy for time dissemination over a distance of 700 m. Averaging over time is shown to facilitate satisfactory performance down to , which could extend the range of the system to a national scale and a time dissemination network invulnerable to wireless spoofing and jamming attack vectors.

Image Transmission Analysis using CSS Modulation Scheme

Image transmission through low-speed communication systems has been a challenge to overcome in the last few years. Actual IoT technologies are supported by LPWAN, where power consumption is a primary issue to consider. The image transmission study presented in this paper is based on Chirp Spread Spectrum (CSS) modulation scheme used by LoRa. A simulation model for image transmission is presented, where the communication channel is based on additive white Gaussian noise (AWGN), with a configurable signal-to-noise ratio (SNR). This model allows the modification of several LoRa CSS parameters such as: spreading factor (SF) bandwidth (BW) and code rate (CR). The adopted metrics for the evaluation of the proposed methodology are symbol error rate (SER), bit error rate (BER) and peak signal-to-noise ratio (PSNR). The first two figures of merit allow the study of the transmission quality and with the last one is possible to infer the received image quality. For a SF=8 and SNR=-10 dB the obtained values of SER and BER are 0.001 1e-4, respectively. These values will lead to a PSNR = 21 dB.

An adaptive spreading factor allocation scheme for mobile LoRa networks: Blind ADR with distributed TDMA scheduling

Nowadays, the rapid proliferation of IoT opens up enormous potential for a broad range of applications in every industry. Thanks to the chirp spread spectrum modulation and high receiver sensitivity, LoRa technology has an enormous potential to achieve long range transmission with low power consumption. The most critical bottleneck of the LoRa is the scalability limitations due to ALOHA-based random channel access for uplink packet transmission. When considering the scalability of LoRa networks, ADR (Adaptive Data Rate) is a key mechanism for the LoRaWAN protocol stack which controls the allocation of network resources by appropriately selecting the transmission parameters of end devices. The existing ADR algorithms have been mostly interested for static networks, where both end-devices and gateway(s) are fixed. Unfortunately, these algorithms do not provide the expected performance when it comes to mobility of end devices or gateway(s). This study introduces a clear method for blind ADR implementation, in which the spreading factor assignment made by end devices themselves. The performance of the proposed method has been validated through MATLAB-based computer simulations in urban, suburban, and rural environments. The obtained results show a promising performance in terms of packet reliability and fairness.

LoRa and Rotating Polarization Wave: Physical Layer Principles and Performance Evaluation

Link reliability and enhanced coverage are the primitive concerns of Low-Power Wide-Area Networks (LPWANs) for suitability to critical Internet of Things (IoT) applications. Reliability is limited by the destructive multipath propagation, data rate and sensitivity, that ultimately limits the coverage range. LoRa by far is the predominant LPWAN operating on unlicensed spectrum. Despite its robust Chirp Spread Spectrum (CSS) modulation, there is a severe degradation in its error performance particularly in hostile propagation environments, and an excessive reduction in coverage. Rotating Polarization Wave (RPW) is a potential LPWAN recently emerged to achieve a highly reliable IoT and Machine-to-Machine (M2M) communication. This is the first paper to provide comprehensive error performance comparison between LoRa and RPW. Okumura-Hata model is used for median path loss calculation. Shadowing and fast fading margins of RPW and LoRa are estimated. Effective gain of RPW is computed from error performance. Results have shown that LoRa offers a sensitivity of 23 dB higher than RPW under AWGN conditions. However, under fading conditions, RPW exhibits a sensitivity of 15 dB higher than LoRa. At a reference distance of 100 m, the maximum received signal strength of RPW is -39 dBm, which is 29 dB above LoRa. The maximum coverage distance attained by RPW is 15 km, which is 1.5 times of LoRa.

A Survey on Scalable LoRaWAN for Massive IoT: Recent Advances, Potentials, and Challenges

Long-range (LoRa) technology is most widely used for enabling low-power wide area networks (WANs) on unlicensed frequency bands. Despite its modest data rates, it provides extensive coverage for low-power devices, making it an ideal communication system for many internet of things (IoT) applications. In general, LoRa is considered as the physical layer, whereas LoRaWAN is the medium access control (MAC) layer of the LoRa stack that adopts a star topology to enable communication between multiple end devices (EDs) and the network gateway. The chirp spread spectrum modulation deals with LoRa signal interference and ensures long-range communication. At the same time, the adaptive data rate mechanism allows EDs to dynamically alter some LoRa features, such as the spreading factor (SF), code rate, and carrier frequency to address the time variance of communication conditions in dense networks. Despite the high LoRa connectivity demand, LoRa signals interference and concurrent transmission collisions are major limitations. Therefore, to enhance LoRaWAN capacity, the LoRa Alliance released many LoRaWAN versions, and the research community has provided numerous solutions to develop scalable LoRaWAN technology. Hence, we thoroughly examine LoRaWAN scalability challenges and state-of-the-art solutions in both the physical and MAC layers. These solutions primarily rely on SF, logical, and frequency channel assignment, whereas others propose new network topologies or implement signal processing schemes to cancel the interference and allow LoRaWAN to connect more EDs efficiently. A summary of the existing solutions in the literature is provided at the end of the paper, describing the advantages and disadvantages of each solution and suggesting possible enhancements as future research directions.

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.

RSSI Analysis on CSS Modulation in the 433 MHz Frequency Band Using Lora in Flood Sensor

Long Range (LoRa) low power is a transmission technology capable of connecting multiple sensors to the Internet of Things in the future. LoRa uses Chirp Spread Spectrum (CSS) frequency modulation which promises to achieve remote connectivity at very low power. More specifically, this paper focuses on the analysis of Receive Signal Strength Indicator (RSSI) on CSS modulation on flood sensors. This paper presents a detailed model of using LoRa on flood sensors, showing that LoRa is capable of transmitting sensor data over long distances with perfect RSSI values. The results showed the potential for a close communication range with a narrow band network at a frequency of 433 MHz and an average RSSI of -50 dB at a maximum distance of 600 meters without obstruction. Although LoRa communication uses CSS modulation and has good RSSI values, in long-distance communication with data in the form of video or large sensor data, this toughness is not sufficient due to long distances and large bandwidth usage, while in this study LoRa type Ai Thinker Ra- 02 SX 1278 can only be set up to 125 KHz according to the datasheet. The disadvantages of using large sensor data over long distances and a larger footprint make CSS vulnerable to other, possibly larger, resources.

A Maximum-Likelihood-Based Two-User Receiver for LoRa Chirp Spread-Spectrum Modulation

Long Range (LoRa) is an emerging low-power wide-area network technology offering long-range wireless connectivity to Internet of Things (IoT) devices. For energy efficiency reasons, LoRa end nodes implement a nonslotted ALOHA multiple access scheme to transmit packets to the gateway. Due to the lack of synchronization between end nodes, collisions between uplink packets have been identified as the main obstacle to the scaling of dense LoRa networks. To tackle this issue, we present in this article a LoRa receiver that is capable of decoding colliding packets from two interfering end nodes. The proposed two-user detector is derived from the maximum-likelihood principle using a detailed model of two colliding LoRa packets. As the complexity of the maximum-likelihood sequence estimation is prohibitive, complexity-reduction techniques are introduced to enable practical implementations of the receiver. An in-depth performance analysis highlights that the proposed two-user detector inherently leverages the differences in received power, time offsets, and frequency offsets between the users to separate and demodulate their respective signals. To demonstrate the practicality of the proposed detector, an interference-robust synchronization algorithm is then designed and evaluated. Simulation results indicate that a LoRa receiver combining the proposed synchronization algorithm and two-user detector is capable of detecting and demodulating two interfering users with satisfactorily error rates.

LoRa network reconfiguration with Markov Decision Process and Fuzzy C-Means clustering

Long Range (LoRa) is a proprietary modulation technique that uses Chirp Spread Spectrum (CSS) modulation for low power and wide area communications. Despite the advantages of LoRa technology, the reconfiguration of transmission parameters such as Spreading Factor (SF) and Transmission Power (Ptx), remains limited to maximize the uplink traffic. In this paper, we look upon additional parameters such as the Bandwidth (BW) and the Coding Rate (CR). We apply Fuzzy C-Means (FCM) algorithm to acquire knowledge about the quality of each transmission setting. Then, we use this knowledge in Q-learning and Markov Decision Process (MDP) algorithms as a state transition matrix to converge better and faster to the set of transmission settings that maximize the uplink data rate. As the solution should cope with different scenarios, we vary the number of End Devices (EDs), Base Stations (BSs), Packet Sizes (PSs) and Packet Rates (PRs). In addition, we compare our solution with many algorithms such as EXP3, ADR and EXPLoRaTS. Simulation results show that MDP with FCM clustering preprocessing improves better several Quality of Service (QoS) metrics including the Data Rate (DR), Packet Delivery Ratio (PDR), Time on Air (ToA) and Transmission Energy (Etx). Thus, the PDR and the DR were improved by 25%, the ToA was reduced by 40% and Etx was reduced by 20%.

Dual-Mode Chirp Spread Spectrum Modulation

In this letter, we propose dual-mode chirp spread spectrum (DM-CSS) modulation for low-power wide-area networks. DM-CSS is capable of achieving a higher spectral efficiency (SE) relative to its counterparts, such as Long Range (LoRa) modulation. Considering the same symbol period, the SE in DM-CSS are augmented by: (i) simultaneously multiplexing even and odd chirp signals; (ii) using phase shifts of 0 and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pi $ </tex-math></inline-formula> radians for both even and odd chirp signals; and (iii) using either up-chirp or down-chirp signal. The SE increases by up to 116.66% for the same bandwidth and spreading factor relative to LoRa. We present a complete transceiver architecture along with non-coherent detection process. Simulation results reveal that DM-CSS is not only more spectral efficient but also more energy efficient than most classical counterparts. It is also demonstrated that DM-CSS is robust to phase and frequency offsets.

LoRa Based Framework for Smart Greenhouse Monitoring Systems

Abstract: Agriculture being the largest profession in India depends on various factors like temperature, humidity, soil moisture, and others. LoRa is a long-range, low-power wireless platform framework developed for smart greenhouse monitoring to gain accurate values for dependent factors like temperature, humidity, soil moisture. LoRa is based on chirp spread spectrum modulation, which has low power characteristics like FSK modulation but can be used for long-range communications. LoRa can be used to connect sensors, gateways, machines, devices, animals, people, etc. wirelessly to the cloud. The purpose involves eliminating the traditional methods of the agriculture system and enhancing the crop yield and quality. Automated tools utilization is also being implemented, thereby improving the agricultural conditions, and reducing the human intervention.

The New Era of Long-Range "Zero-Interception" Ambient Backscattering Systems: 130 m with 130 nA Front-End Consumption.

Internet of Things applications based on backscatter radio principles have appeared to address the limitations of high cost and high power consumption. While radio-frequency identification (RFID) sensor nodes are among the most commonly utilized state-of-the-art technologies, their range for passive implementations is typically short and well below 10 m being impractical for “rugged” applications where approaching the tag at such proximity, is not convenient or safe. In this work, we propose a long-range “zero interception” ambient backscatter (LoRAB) communication system relying on low power sensor (tag) deployments. Without employing a dedicated radio transmission, our technology enables the “zero interception” communication of the tags with portable receivers over hundreds of meters. This enables low-cost and low-power communications across a wide range of missions by using chirp spread spectrum (CSS) modulation on ambient FM signals. A laboratory prototype exploiting commercial components (laptops, DAQ, software-defined radios (SDR) platform) have demonstrated the potential by achieving 130 m tag-to-reader distance for a low bit rate of 88 bps with the modulator current consumption at around 103 nA.

Group-Based CSS Modulation: A Novel Enhancement to LoRa Physical Layer

LoRa is a proprietary technology for IoT (Internet of Things) applications and it has attracted widespread interest from both academia and industry in recent years. As the core technique of LoRa physical (PHY) layer, chirp spread spectrum (CSS) modulation is adopted to support long range communications. In this letter, we propose a novel group-based CSS (GCSS) modulation scheme and introduce a new configurable parameter called group number (GN) as an enhancement to LoRa PHY layer with the aim of achieving a more extensive and flexible trade-off between power and spectral efficiency. Moreover, by exploiting the intrinsic properties of GCSS modulation, we prove that the maximum spectral efficiency can reach up to 0.5 bps/Hz. Simulation results of BER (bit error rate) performance in both AWGN and Rayleigh fading channels are presented to verify the feasibility and advantage of this new modulation scheme.

A New LoRa-like Transceiver Suited for LEO Satellite Communications.

LoRa is based on the chirp spread spectrum (CSS) modulation, which has been developed for low power and long-range wireless Internet of Things (IoT) communications. The structure of LoRa signals makes their decoding performance extremely sensitive to synchronization errors. To alleviate this constraint, we propose a modification of the LoRa physical layer, which we refer to as differential CSS (DCSS), associated with an original synchronization algorithm. Based on this modification, we are able to demodulate the received signals without performing a complete frequency synchronization and by tolerating some timing synchronization errors. Hence, our receiver can handle ultra narrow band LoRa-like signals since it has no limitation on the maximum carrier frequency offset, as is actually the case in the deployed LoRa receivers. In addition, in the presence of the Doppler shift varying along the packet duration, DCSS shows better performance than CSS, which makes our proposed receiver a good candidate for communication with a low-Earth orbit (LEO) satellite.

Experimental test and performance of RSSI-based indoor localization in LoRa Networks

LoRa (Long Range) is a wireless communication technology, which has established itself in recent years as one of the most widely used LPWAN (Low-Power Wide-Area Network) technologies in various IoT (Internet of things) applications. It is based on Chirp spread spectrum modulation (CSS) in which the number of bits per symbol depends on the spreading factor used, that varies from 7 to 12. In this paper, we have considered the RSSI (Received Signal Strength Indicator) parameter in the indoor environment. For LoRa, we use the LoRa transceiver based on two HTCC AB01 modules for their ability to modify the spreading factor (SF). In our work, we transmit in the 868MHz frequency band, and we use a bandwidth 125 KHz and three spreading factors SF7, 9 and 12. Subsequently, we tried to measure RSSI in an indoor environment with a short distance under LOS and NLOS conditions for three spreading factors. We sent the temperature measured by the DHT11 sensor from the transmitter to the receiver to measure the RSSI for each distance and for each spreading factor. The experimental results show that LoRa can be used in an indoor context, and that the spreading factor improve the performance of this technology in terms of RSSI. Moreover, the power losses of the received signal are more important in the NLOS conditions compared to those observed in the LOS conditions.

On the LoRa Chirp Spread Spectrum Modulation: Signal Properties and Their Impact on Transmitter and Receiver Architectures

The LoRa modulation scheme is arousing a growing interest in the Internet of Things community as it is adopted by the emerging LoRaWAN technology. In this paper, we firstly analyse the baseband processing for the generation of LoRa signals at the transmitter side, providing a simple algorithm that leverages digital signal processing techniques to reduce the modulator complexity. Secondly, we analytically investigate the signal demodulation technique. Quite surprisingly, we found that its effectiveness depends on the particular choice of the sampling frequency at the receiver side, which purposely does not meet the sampling theorem requirement. Finally, we consider the actual architecture of digital receivers investigating the trade-off between the selectivity of receive digital filters, which impacts on the required computational effort and power consumption, and the receiver performance.

Attack-aware Synchronization-free Data Timestamping in LoRaWAN

Low-power wide-area network technologies such as long-range wide-area network (LoRaWAN) are promising for collecting low-rate monitoring data from geographically distributed sensors, in which timestamping the sensor data is a critical system function. This article considers a synchronization-free approach to timestamping LoRaWAN uplink data based on signal arrival time at the gateway, which well matches LoRaWAN’s one-hop star topology and releases bandwidth from transmitting timestamps and synchronizing end devices’ clocks at all times. However, we show that this approach is susceptible to a frame delay attack consisting of malicious frame collision and delayed replay. Real experiments show that the attack can affect the end devices in large areas up to about 50,000, m 2 . In a broader sense, the attack threatens any system functions requiring timely deliveries of LoRaWAN frames. To address this threat, we propose a LoRaTS gateway design that integrates a commodity LoRaWAN gateway and a low-power software-defined radio receiver to track the inherent frequency biases of the end devices. Based on an analytic model of LoRa’s chirp spread spectrum modulation, we develop signal processing algorithms to estimate the frequency biases with high accuracy beyond that achieved by LoRa’s default demodulation. The accurate frequency bias tracking capability enables the detection of the attack that introduces additional frequency biases. We also investigate and implement a more crafty attack that uses advanced radio apparatuses to eliminate the frequency biases. To address this crafty attack, we propose a pseudorandom interval hopping scheme to enhance our frequency bias tracking approach. Extensive experiments show the effectiveness of our approach in deployments with real affecting factors such as temperature variations.