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Pre-detection Combining of Small Satellite Downlink’s Replicas
Abstract
This study contributes to the reception quality improvement of small satellites’ signals. Traditionally, the data from a satellite is downloaded through single radio link to the related steerable ground station. This single communication is problematic as it is highly exposed to outages when the channel is deeply affecting the signal or when the steering engine fails. Instead, this paper proposes a terrestrial solution by combining multiple raw replicas of the same downlink received by separate multiple receiving sites. The individual stations are networked to collect multiple raw versions and send them to a virtual ground station for processing and combining. The suggested receive-diversity combining of the raw symbols is promising to improve the performance of the ground stations and reduce the probability of singular site failures. The proposed receive diversity scheme offers the replacement of the conventional expensive steerable antenna by much affordable omnidirectional antenna where the diversity gain compensates the lesser antenna gain. To achieve this diversity payoff, a simple yet efficient pre-detection combining algorithm is also developed in this article. The results show that the diversity mode, under different testing scenarios, can achieve lesser bit error rate (BER) than every other BER in the network. Furthermore, the cooperative reception scheme reduces system outages and exhibits to track more than a satellite at once.
... Not only are errors going to be reduced in the diversity mode, but also the probability of communication outages between the satellite and the GSs will significantly decrease. The results of the prior simulation-based studies are already published in [14][15][16] . ...
... The most likely occurring value at one location in all the signals is taken as the correct bit and hence occupies that same location in the combined stream. More information about the idea of maximum likelihood combining algorithm, the mathematical model derivation, the advantages and disadvantages of this combined method, and the theoretical experimental results can be found in the authors' previous preliminary studies [14][15][16]. ...
Nowadays, countless daily life services are
conveniently provided to the users by connecting billions of
devices through Internet of Things (IoT). However, current IoT
networks are not yet ubiquitous. They are unavailable in the less
inhabited areas such as oceans, forests, and deserts.
Accordingly, for omnipresent coverage of the future generations
of communications, satellites must get integrated into IoT
networks. Because of their low altitude, low earth orbit (LEO)
satellites have attracted attention towards the integration in the
terrestrial IoT networks. Nonetheless, most of the recently
launched LEO satellites are tiny ones designed to provide
affordable space missions. CubeSats, for instance, are popular
LEO satellites with limited size and resources. These limitations
imply low transmitting power and low gain onboard antennas.
As a result, the relevant receiving ground stations (GSs) would
have to utilize high gain antennas with expensive and complex
steering resources to receive such weak signals. This article
suggests a GS-based solution by applying the receive diversity
combining approach. To prove the concept, this work utilized
the GSs community of Satellite Networked Open Ground
Station (SatNOGS) to record real satellite signals. The
combining resulted in an enhanced quality stream in terms of
detection errors compared to each individual GS. Indeed, the
combining gain can compensate the missing gain if the
traditional expensive receiving antenna with its complex
steering mechanism is replaced by cheaper omnidirectional
antenna.
... This keeps the distribution balanced and effective. However, these methods can be more challenging to set up and often have high computational overhead, which makes them impractical for large-scale edge/fog-based systems with limited resources [5], [6], [7], [8]. ...
Edge/fog computing has gained significant popularity as a computing paradigm that facilitates real-time applications, especially in healthcare systems. However, deploying these systems in real-world healthcare scenarios presents technical challenges, among which load balancing is a key concern. Load balancing aims to distribute workloads evenly across multiple nodes in a network to optimize processing and communication efficiency. This article proposes an adaptive load-balancing method that combines the strengths of static and software-defined networking (SDN)-based load balancing algorithms for edge/fog-based healthcare systems. A new algorithm called load balancing of optimal edge-server placement (LB-OESP) is proposed to balance the workload statically in the systems, followed by the presentation of an SDN-based greedy heuristic (SDN-GH) algorithm to manage the data flow dynamically within the network. The LB-OESP algorithm effectively balances workloads while minimizing the number of edge servers required, thereby improving system performance and saving costs. The SDN-GH algorithm leverages the benefits of SDN to dynamically balance the load and provide a more efficient system. Simulation results demonstrate that the proposed method provides an adaptive load-balancing solution that takes into consideration changing network conditions and ensures improved system performance and reliability. Furthermore, the proposed method offers a 12% reduction in system latency and up to 28% lower deployment costs compared to the previous studies. The proposed method is a promising solution for edge/fog-based healthcare systems, providing an efficient and cost-effective approach to managing workloads.
... The proposed system model, the simulated cooperative reception, the developed post-detection combining algorithm, the system resources, and the concept of virtual ground station (VGS) were reported in [20,21]. The authors' third study, presented in [22], modified the algorithm to combine the received undetected symbols as a pre-detection combiner. The same study observed the system performance in engaging 12 sites under five scenarios: Uncorrelated SNRs of (0-11) dB, above average SNRs of (8-9) dB, correlated SNRs of (7) dBs, below average SNRs of (2-3) dB, and severe SNRs of 0 dBs except one site with 8 dB. ...
The popular small satellites already attracted attention towards the integration into the future ubiquitous Internet of Things (IoT) networks. Small satellites can act as IoT base stations to efficiently collect data from sensors in remote areas and offload it to ground stations (GSs). The size constraints of small satellites, however, impose limited power resources and tiny antennas onboard. Consequently, weak signals and outages are more probable at GSs. Therefore, GSs must utilize high gain antennas with complex and expensive steering resources to collect such weak signals through a single radio link. This traditional scheme can track only one satellite at a time with more vulnerability to outages resulting from possible severe signal degradations or from steering engine failures. To contribute to a successful integration of the popular small satellites into the future sixth generation (6G) inclusive IoT networks, this work validates the concept of diversity combining in improving the reception of small satellites signals. Six versions of the small satellite VZLUSAT-2’s beacon were recorded by six simple software defined radio GSs registered at SatNOGS network and then combined. To assess the quality of the combined version, its errors are compared to the errors of the individual versions. According to the findings, if the GSs worked cooperatively in a diversity mode, they could generate a combined version that was always better than any other individually received stream. Furthermore, such a diversity-based scheme reduces the probability of outages and enables the simultaneous tracking of multiple satellites at each GS.
... At the receiver side, the receiving ground terminal will have difficulty retrieving the original data from such received weakened and noisy signals. The ground terminal's operator must then utilize an expensive steerable high gain antenna along with a well-designed low noise amplifier (LNA) [9] . LNAs are vital components of such systems to amplify the received weak signals without adding extra noise [10]. ...
This article presents a power-efficient low noise amplifier (LNA) with high gain and low noise figure (NF) dedicated to satellite communications at a frequency of 435 MHz. LNAs’ gain and NF play a significant role in the designs for satellite ground terminals seeking high amplification and maintaining a high signal-to-noise ratio (SNR). The proposed design utilized the transistor (BFP840ESD) to achieve a low NF of 0.459 dB and a high-power gain of 26.149 dB. The study carries out the LNA design procedure, from biasing the transistor, testing its stability at the operation frequency, and finally terminating the appropriate matching networks. In addition to the achieved high gain and low NF, the proposed LNA consumes as low power as only 2 mW.
Internet of Things (IoT) networks connect billions of devices in endless daily applications. However, the IoT networks lack coverage in less populated areas such as oceans, deserts, forests, and rural, isolated regions. Therefore, future generations of communications must get satellites involved for ubiquitous coverage of IoT networks. The Low Earth Orbit (LEO) satellites are the closest to the earth and hence the best option to get engaged; nevertheless, they are often small satellites with limited resources. Consequently, such satellites create a challenging task at related Ground Stations (GSs) to receive, process, and decode their weak signals. This article presents a receive diversity combining technique as a solution for simple and cheap GS to improve the reception quality of small satellites' weak signals. To validate the suggested technique, the current study combined real small satellite signals from multiple GSs registered at the open-source Satellite Networked Open Ground Station (SatNOGS) global network. The results showed that combining multiple replicas of the satellite signals can significantly improve the link quality.
Popular small satellites host individual sensors or sensor networks in space but require ground stations with directional antennas on rotators to download sensors’ data. Such ground stations can establish a single downlink communication with only one satellite at a time with high vulnerability to system outages when experiencing severe channel impairments or steering engine failures. To contribute to the area of improving the reception quality of small satellites signals, this paper presents a simple receive diversity scheme with proposed processing algorithms to virtually combine satellite downlink streams collected from multiple omnidirectional receivers. These algorithms process multiple received versions of the same signal from multiple geographically separated receiving sites to be combined in one virtual ground station. This virtual ground station helps detect the intended signal more reliably based only on a network of simple and cooperating software-defined radio receivers with omnidirectional antennas. The suggested receive diversity combining techniques can provide significant system performance improvement if compared to the performance of each individual receiving site. In addition, the probability of system outages is decreased even if one or more sites experience severe impairment consequences. Simulation results showed that the bit error rate (BER) of the combined stream is lower than the BER of the best quality receiving site if considered alone. Moreover, virtual ground stations with cooperative omnidirectional reception at geographically separated receivers also allow data to be received from multiple satellites in the same frequency band simultaneously, as software-defined receivers can digitize a wider portion of the frequency band. This can be a significant conceptual advantage as the number of small satellites transmitting data grows, and it is reasonable to avoid the corresponding necessary increase in the number of fully equipped ground stations with rotators.
To address the explosive traffic demands, the capacity of the fading channel is increasingly becoming a prime concern in the designing of the wireless communication system. The channel capacity is an extremely important quantity, since it allows the transmission of the data through the channel with an arbitrarily small probability of error. In other words, capacity dictates the maximum rate of information transmission, called as ‘capacity’ of channel, determined by the intrinsic properties of the channel and is independent of the content of the transmitted information. In this paper, we present a comprehensive survey of the existing work related to the channel capacity model over various fading channels. With an elaborated explanation of the theory of channel capacity, definitions of channel capacity based on the channel state information are reviewed. To compliment this, review of the technique to enhance the channel capacity is discussed and reviewed. An effective capacity model to overcome the channel capacity limitation is also explained. Furthermore, as the secure transmission of data is of utmost importance, to address this physical layer security model is also reviewed. We also summarize the work related to channel capacity in various types of wireless networks. We finally cover the future research directions, including less explored aspects of the channel capacity that can be studied to design efficient communication systems.
A wide range of multimedia applications must be supported by the modern fifth generation (5G) wireless communication systems for realizing the diverse applications in smart cities. The diverse applications such as real-time monitoring of roads, smart homes, smart industries, etc., for a sustainable smart city emphasizes a robust and efficient image transmission. In this paper, the influence of maximal ratio combining (MRC) on the reception of images with different orthogonal frequency division multiplexing (OFDM) versions is studied. The different OFDM versions considered here are the fast Fourier transform (FFT) based OFDM and discrete cosine transform (DCT) based OFDM. A comparison between diverse modulation levels for the images transmitted through different OFDM methodologies, along with variation in a number of receiving antennas for MRC, is proposed for additive white gaussian noise (AWGN) and Rayleigh fading channels. The diverse modulation levels used are binary phase shift keying (BPSK), quadrature phase shift keying (QPSK), 8-PSK, and 16-PSK. The parameters that are used to compare different versions of OFDM for MRC antenna configurations are signal-to-noise ratio (SNR) vs. bit error rate (BER) and peak signal-to-noise ratio (PSNR) at the receiver as an estimation parameter for the received image quality.
A distributed single-input multiple-output (SIMO) sonar system is composed of a sound source and multiple underwater receivers. It provides an important framework for underwater target localization. However, underwater hostile environments bring more challenges for underwater target localization than terrestrial target localization, such as the difficulties of synchronizing all the underwater receiver clocks, the varying underwater sound speed and the uncertainties of the locations of the underwater receivers. In this paper, we take the sound speed variation, the time synchronization and the uncertainties of the receiver locations into account, and propose the underwater target localization and synchronization (UTLS) algorithm for the distributed SIMO sonar system. In the distributed SIMO sonar system, the receivers are organized in a star topology, where the information fusion is carried out in the central receiver (CR). All the receivers are not synchronized and their positions are known with uncertainties. Moreover, the underwater sound speed is approximately modeled by a depth-dependent sound speed profile (SSP). We evaluate our proposed UTLS algorithm by comparing it with several benchmark algorithms via numerical simulations. The simulation results reveal the superiority of our proposed UTLS algorithm.
Ambient backscatter communication (AmBC) enables radio-frequency (RF) powered backscatter devices (BDs) (e.g., sensors, tags) to modulate their information bits over ambient RF carriers in an over-the-air manner. This technology also called "modulation in the air", thus has emerged as a promising solution to achieve green communications for future Internet-of-Things. This paper studies an AmBC system by leveraging the ambient orthogonal frequency division multiplexing (OFDM) modulated signals in the air. We first model such AmBC system from a spread-spectrum communication perspective, upon which a novel joint design for BD waveform and receiver detector is proposed. The BD symbol period is designed to be in general an integer multiplication of the OFDM symbol period, and the waveform for BD bit `0' maintains the same state within a BD symbol period, while the waveform for BD bit `1' has a state transition in the middle of each OFDM symbol period within a BD symbol period. In the receiver detector design, we construct the test statistic that cancels out the direct-link interference by exploiting the repeating structure of the ambient OFDM signals due to the use of cyclic prefix. For the system with a single-antenna receiver, the maximum-likelihood detector is proposed to recover the BD bits, for which the optimal threshold is obtained in closed-form expression. For the system with a multi-antenna receiver, we propose a new test statistic, and derive the optimal detector. Moreover, practical timing synchronization algorithms are proposed, and we also analyze the effect of various system parameters on the system performance. Finally, extensive numerical results are provided to verify that the proposed transceiver design can improve the system bit-error-rate (BER) performance and the operating range significantly, and achieve much higher data rate, as compared to the conventional design.
This paper aims at designing an on-board beam generation process for
multibeam satellite systems with the goal of reducing the traffic at the feeder
link. Full frequency reuse among beams is considered and the beamforming at the
satellite is designed for supporting interference mitigation techniques. In
addition, in order to reduce the payload cost and complexity, this on-board
processing is assumed to be constant and the same for forward and return link
transmissions. To meet all these requirements a novel robust minimum mean
square error (MMSE) optimization is conceived. The benefits of the considered
scheme are evaluated with respect to the current approaches both analytically
and numerically. Indeed, we show that with the DVB-RCS and DVB-S2 standards,
our proposal allows to increase the total throughput within a range between 6\%
and 15\% with respect to other on-board processing techniques in the return and
forward link, respectively. Furthermore, the proposed solution presents an
implicit feeder link bandwidth reduction with respect to the on-ground beam
generation process.
This paper considers large random wireless networks where
transmit-and-receive node pairs communicate within a certain range while
sharing a common spectrum. By modeling the spatial locations of nodes based on
stochastic geometry, analytical expressions for the ergodic spectral efficiency
of a typical node pair are derived as a function of the channel state
information available at a receiver (CSIR) in terms of relevant system
parameters: the density of communication links, the number of receive antennas,
the path loss exponent, and the operating signal-to-noise ratio. One key
finding is that when the receiver only exploits CSIR for the direct link, the
sum of spectral efficiencies linearly improves as the density increases, when
the number of receive antennas increases as a certain super-linear function of
the density. When each receiver exploits CSIR for a set of dominant interfering
links in addition to the direct link, the sum of spectral efficiencies linearly
increases with both the density and the path loss exponent if the number of
antennas is a linear function of the density. This observation demonstrates
that having CSIR for dominant interfering links provides a multiplicative gain
in the scaling law. It is also shown that this linear scaling holds for direct
CSIR when incorporating the effect of the receive antenna correlation, provided
that the rank of the spatial correlation matrix scales super-linearly with the
density. Simulation results back scaling laws derived from stochastic geometry.
Multiple antennas are usually employed to improve the performance of the wireless communication system. To this context, we derive the effective capacity (EC) expressions for Inverse Gamma (I-Gamma) shadowed fading channel, employing maximal ratio combining (MRC) and selection combining (SC) diversity schemes at the receiver (Rx) side. The channels are assumed to be independent and identical distributed (i.i.d.). In addition to this, we also propose the simplified high-power approximation that enables direct interpretation of the system performance concerning system fading parameters. Furthermore, to diminish the effect of shadowing over composite statistics, macroscopic diversity analysis is presented as an application, where Weibull, and I-Gamma models are used to obtain composite statistics. At last, we validate our proposed formulations through the Monte-Carlo simulation.
In order to realize future large-capacity, high-speed and highly advanced multimedia satellite communication and broadcasting systems, utilization of Ka-, Q-, V- and even W-bands radio wave is indispensable. In such radio link, performance degradation due to rain-induced attenuation and noise increase, gaseous attenuation, rain- or ice-induced depolarization and interference from other systems is expected. Above all, rain attenuation is the most significant factor for link performance. This is the reason that attenuation mitigation becomes very important. To cope with such large attenuation events, powerful attenuation mitigation technologies should be developed. Attenuation mitigation methods are roughly classified into the following three categories as shown in Table 1; Static methods such as margin increase in transmitter and receiver system. These are not suitable in the system in which large attenuation is expected. Adaptive methods such as adaptive EIRP allocation toward the area suffered from large attenuation. They are effective in large attenuation case within a limit of total resource capability such as satellite total power. Diversity methods such as site- and time-diversity. They prepare several redundant links which have low attenuation correlation and adopt the best performance link selectively. In this paper, the authors assume adaptive satellite power control method by which satellite transmitting power for relevant area is increased using multi-beams or modified beam pattern. The effect of this method is evaluated by using rain-radar data obtained in Japan. Especially, link performance within a beam is evaluated.