Abstract
In recent years, a growing interest has been witnessed in the usage of free space optics (FSO) link for satellite communication (SATCOM) scenarios, as it offers much higher data rates up to gigabits per second (Gbps) compared to existing radio frequency (RF) link. However, FSO links are sensitive to beam scintillation and pointing errors. In this paper, we consider a hybrid FSO/RF communication between ground station (GS) and satellite, where the RF link will act as a backup link to improve the reliability of FSO communication. In addition, we also consider high-altitude platform station (HAPS), which will act as a relay station, between GS and satellite to improve the end-to-end system performance. This has led to the development of space-air-ground integrated hybrid FSO/RF SATCOM networks. We analyse the performance of the proposed hybrid network considering an adaptive-combining-based switching scheme for both uplink and downlink scenarios with and without using HAPS as a relay station. In case of adaptive-combining-based switching scheme, the data is continuously transmitted over the FSO link, while maximal-ratio-combining (MRC) of RF and FSO links is performed when the quality of FSO link deteriorates. The performance analysis of adaptive-combining-based switching scheme in terms of outage and average symbol error rate (SER) is carried out and the same is compared with the single-link FSO SATCOM and single-threshold-based switching scheme proposed in the literature for hybrid FSO/RF SATCOM. In addition, the performance gain obtained by the proposed adaptive combining scheme over single-link FSO system for different channel conditions is also reported. Further, the asymptotic analysis is also carried out to obtain the diversity gain of the proposed system.
Highlights
The advancement of space technology together with the sophisticated space-based instruments opened a new chapter for hybrid free space optics (FSO) / radio frequency (RF) satellite communication (SATCOM)
WORKS In this paper, we analyse the performance of adaptivecombining-based switching scheme for uplink and downlink SATCOM scenarios assuming single-hop and dual-hop spaceair-ground integrated network (SAGIN)-based hybrid FSO/RF systems
We inferred that the RF backup link in case of hybrid system is proved to provide a better system performance as compared to single-hop and dual-hop FSO systems
Summary
The advancement of space technology together with the sophisticated space-based instruments opened a new chapter for hybrid free space optics (FSO) / radio frequency (RF) satellite communication (SATCOM). HAPS find various potential applications in disaster monitoring, agricultural observation, atmospheric observation, weather monitoring, and communication relay [1] They can provide better coverage of smaller regions as compared to satellites. VOLUME 9, 2021 analysis of uplink SATCOM system was investigated for different modulation schemes in the presence of atmospheric turbulence and beam-wander induced pointing errors. The performance of HAPS-based relaying with hybrid FSO/RF communication for SATCOM scenario assuming single-threshold-based switching scheme was investigated in [16]. Instead of a hard-switching scheme (i.e. single-threshold-based switching scheme) proposed in [16], we assume adaptive-combining-based switching scheme between FSO and RF links and analyse the performance of single-hop and dual-hop (with HAPS) SATCOM scenarios using outage probability and average symbol error rate (SER). The effect of non-zero boresight pointing or misalignment errors due to misalignment between transmit and receive apertures because of mechanical vibration of HAPS and satellite is taken into consideration in our analysis [25], [26]
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