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lists the achieved BER of each suggested SP technique versus the raw combin- ing BER values. Excluding the worst stream out of the combined streams reflected slight improvement compared to the original combining BER values. Replacing that worst stream with the best stream improved the performance even more. The best achieved BER values were when always injecting the best stream into the combining matrix which reached zero error at six receiving sites combining. Table 1. BER results from raw receive diversity and proposed SP algorithms.
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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 impa...
Citations
... 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.
... Nevertheless, small satellites are always designed with size and resource restrictions implying low gain transmitting antennas and low power transmitted signal [8]. At the receiver side, the receiving ground terminal will have difficulty retrieving the original data from such received weakened and noisy signals. ...
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.
... In this context, combining multiple small satellite signals and evaluating the system performance will be the main contribution of this paper. In some previous steps to this work, the authors of this article conducted preliminary studies in [14]- [16] where they framed, modeled, and simulated the proposal of applying to receive diversity combining on small satellite downlinks. The previous preliminary studies suggested a network of affordable omnidirectional GSs that could cooperatively receive multiple versions of satellite downlinks. ...
... On the other hand, and as the suggested model implies, the same satellite signal propagates towards N GSs after passing through different N paths. Due to the dependence on multiple propagation paths instead of just one, the probability of outage (Pout) in the proposed scheme becomes the probability of outage in the current system to the power of N, i.e., (Pout) N [14]. ...
... Once the N versions are received, they are stored in a virtual GS with a PC for further processing and combining. More details of the system configuration, mathematical modeling, the combining process, and the simulation results are already provided in [14]- [16]. This work aims to validate the theoretical model by collecting and combining real small satellite signals. ...
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.
... Then, at each column of the square matrix, the algorithm picks the most likely occurring value as the right value and stores it in the corresponding position of the combined stream. 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 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.
... However, free-space optics channels are susceptible to attenuation due to unpredictable weather conditions [11]. Site diversity in ground stations helps alleviate problems due to short contact windows, but installing and maintaining multiple ground stations at several geographical locations involve huge investments [6,12,13]. ...
Satellite communication is inevitable due to the Internet of Everything and the exponential increase in the usage of smart devices. Satellites have been used in many applications to make human life safe, secure, sophisticated, and more productive. The applications that benefit from satellite communication are Earth observation (EO), military missions, disaster management, and 5G/6G integration, to name a few. These applications rely on the timely and accurate delivery of space data to ground stations. However, the channels between satellites and ground stations suffer attenuation caused by uncertain weather conditions and long delays due to line-of-sight constraints, congestion, and physical distance. Though inter-satellite links (ISLs) and inter-orbital links (IOLs) create multiple paths between satellite nodes, both ISLs and IOLs have the same issues. Some essential applications, such as EO, depend on time-sensitive and error-free data delivery, which needs better throughput connections. It is challenging to route space data to ground stations with better QoS by leveraging the ISLs and IOLs. Routing approaches that use the shortest path to optimize latency may cause packet losses and reduced throughput based on the channel conditions, while routing methods that try to avoid packet losses may end up delivering data with long delays. Existing routing algorithms that use multi-optimization goals tend to use priority-based optimization to optimize either of the metrics. However, critical satellite missions that depend on high-throughput and low-latency data delivery need routing approaches that optimize both metrics concurrently. We used a modified version of Kleinrock’s power metric to reduce delay and packet losses and verified it with experimental evaluations. We used a cognitive space routing approach, which uses a reinforcement-learning-based spiking neural network to implement routing strategies in NASA’s High Rate Delay Tolerant Networking (HDTN) project.
... These spectacular features have drawn the attention of many researchers toward the design of circularly polarized antenna with planar and nonplanar structures. Nowadays, CP is utilized for many wireless systems such as WLAN, WiMax, 5G applications, satellite applications [3], etc. As a result, antennas with CP are indispensable in such kinds of applications, so it is essential to propose some original structures that ensure the presence of broadside CP with reasonable bandwidth and compact size. ...
... Ultra-wideband antennas are used in different applications, e.g., in radio systems for communications and in electromagnetic compatibility (EMC) for measurement applications. The evolutions in wireless systems have motivated researchers to develop new communication forms to exploit the spectrum in the best way and enhance the reception quality [2][3][4][5]. Therefore, the cognitive radio technology was the best solution for this matter as it consists of two different antennas, one for sensing with Ultra-wideband of (3.1-10 GHz) to identify the state of the band-idle or active, while the other antenna is a communication antenna (reconfigurable antenna) [6][7][8][9][10][11]. ...
... In Ref. [21], the authors proposed a novel method for optimizing small elliptical planner dipole antenna for ultra-wideband EMC applications. The characteristics of this antennalike wide band (1)(2)(3)(4)(5) and flatness gain enabled it to be a powerful tool for EMC measurements. The LPDA antenna is extensively used because it provides a high directivity and flat gain over the wideband spectrum [22]. ...
This article presents the design, modeling, and fabrication of a printed log-periodic biconical dipole array antenna (PLPBDA) for electromagnetic compatibility (EMC) measurements. The proposed structure used bow tie-shaped dipoles instead of typical dipoles to achieve a size reduction of 50% and bandwidth enhancement of 170% with the help of PCB technology. Furthermore, the balanced feeding method and the modifications in bow tie-shaped dipole dimensions were utilized to obtain broad bandwidth of 5.5 GHz (from 0.5 GHz to 6 GHz). This structure comprises 12 dipole elements with a compact size of 170 × 160 × 1.6 mm, reflecting low fluctuations gain of about (4.6–7) dBi with the help of an extra dipole. Moreover, the achieved frequency and radiation characteristics (simulated and measured) agree with each other and are compatible with the results of classical EMC antennas. The achievements of this structure showed promising results compared to both literature reviews and reference antenna Hyper LOG® 7060 offered for sale.
... The established satellite-to-ground single radio link could be very problematic when the signal is deeply attenuated or when the steering engine unexpectedly fails to rotate. Such scenarios will cause an outage with no options to manage the consequences [4]. Besides the system's high vulnerability to outages and inability to track more than a satellite, another drawback of the related ground stations is the operation frequencies in VHF, UHF, and S bands. ...
A conventional ground station can establish a single downlink with only one satellite at a time through steerable high-gain antenna. In addition to the lack of tracking more than one satellite at once, such single radio communication is highly vulnerable to outages when experiencing severe degrading circumstances or even with steering engine failures. Accordingly, such problematic single radio link would leave the operator with no alternative options to overcome the consequences. This work exhibits a solution to the ground station through networking. Multiple ground stations, with omnidirectional antennas instead of the steerable directive ones, can be engaged in a collaborative network to receive multiple versions of the same transmitted data for processing and combining. The suggested receive diversity combining is performed at a virtual ground station which utilizes a combining algorithm to help detect the original data from the received versions with less errors and hence reflecting more efficient and reliable services. To exploit this aimed diversity gain, a simple combining algorithm is also developed in this article. The simulation results from the proposed scheme have indicated significant performance enhancement over the single site ground station. This cooperative scheme will not only improve the system performance but also offer to track more than one satellite at a time.
... Fig. 3 presents the single radio system flowchart which drives detailed simulation steps for calculating the BER. To verify the results, the MATLAB simulation BERs are plotted along with the theoretical BERs calculated from equations (1) and (2) for the standard BFSK modulation [15]. It is also worth testing the single system versus varying range of data rates and energy per transmitted bits (Eb/N0). ...
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.
