• Journal of Satellite, Information and Communications
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• v.8 no.4
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• pp.111-116
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• 2013

Because LEO (Low Earth Orbit) satellite has very limited contact time between satellite and ground station, all telemetry data generated on satellite are stored in a mass memory and transmitted to the ground during the contact time. There are two downlink modes, real-time mode and playback mode. Only real-time data frames are transmitted to the ground in real-time mode, real-time and playback data frames stored into mass memory are transmitted to the ground in playback mode. In accordance with the data transmission rate, there are two downlink rates, low downlink rate and high downlink rate. This paper briefly introduces downlink interfaces and flight software of a LEO satellite developed in KARI. And it presents the telemetry storage method, real-time and playback downlink management method, and downlink channel and rate control method.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.11 no.1
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• pp.64-72
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• 1986

The error rate equation fo DS-BPSK(Direct Sequence Binary Phase Shift Keying) signal transmitted through the nonlinear satellite transponder has been derived in the cochannel interference and downlink Gaussian noise environment. The input to the satellite transponder is the superposition of DS-BPSK signal with one interfere which is a cochannel wide-band PN signal. The error rate performance of DS-BPSK system has been evaluated and shown in figures in terms of carrier to interference power ratio(CIR), downlink signal to noise power ratio(downlink SNR) and process gain. In the analysis, it has been shown that the use of a hard limiter in DS-BPSK satellite system leads to the generation of narrow-band intermodulation products which is independent of the process gain. Also it is known that the error rate performance can be improved in the low levels (below 10dB) of CIR as the CIR increase. As the process gain varies from 10 to 100 the curve gives the about 10 dB gain in downlink SNR to maintain a fixed error rate.

• Journal of Satellite, Information and Communications
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• v.8 no.4
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• pp.81-88
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• 2013

The satellite 2.1 GHz frequency bands, 1980-2010 MHz and 2170-2200MHz are allocated for mobile satellite service including satellite IMT, while it does not preclude the use of these bands for mobile services. The concept of an integrated satellite/terrestrial network has been introduced in worldwide because the terrestrial use in these bands adjacent to existing terrestrial IMT bands is attractive to provide mobile broadband services. The integrated satellite/terrestrial infrastructure with a high degree of spectrum utilization efficiency has the ability to provide both multimedia broadband services and public protection and disaster relief solutions. In addition, it is required to consider interference issues between the terrestrial and satellite components in order to reuse the same frequency band to both satellite and terrestrial component. This paper analyzes the interference for satellite downlink in the satellite/terrestrial integrated system and presents the interference mitigation techniques for satellite mobile earth station interfered by terrestrial base stations.

• Journal of information and communication convergence engineering
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• v.3 no.3
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• pp.146-151
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• 2005

This paper represents an attempt to bring together and analyses the measurement data measured by the Satellite Signal Monitoring Center in Korea and the Korea Meteorological Administration/Korea Meteorological Research Institute in close cooperation with this study team. This paper presents the signal characteristic of GEO satellite operating in frequency range 1 to 20GHz associated with Asian Sand Dust (the so-called Yellow Sand Dust). The downlink signal power (dBm) for L-, S-, C-, Ku-, and Ka-band frequencies from GEO satellites were measured in a clear weather and in Asian Sand Dust weather by the Satellite Signal Monitoring Center. The measured signal power(dBm) were compared to the total number concentration and size distribution of Sand Dust that were measured by the Korea Meteorological Administration/Korea Meteorological Research Institute and the possible correlation between these sets data were analyzed. The results demonstrate that the downlink signal level (dBm) of GEO satellite is attenuated by Asian Sand Dust. Hitherto, merger information has been reported as to the influence of sand dust on satellite communications operating in regions affected by sand dust.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.10A
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• pp.1167-1176
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• 2004

This paper presents an adaptive MC-CDMA transmission for downlink in mobile satellite system and simulation results on Ka-band mobile satellite channel. The simulation results show that the proposed scheme support a throughput of several tens of Mbit/s and a spectral efficiency range of 1 bit/s/Hz to 4.7 bit/s/Hz according to channel environments due to the adaptive broadband satellite transmission.

• Journal of Satellite, Information and Communications
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• v.2 no.1
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• pp.27-34
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• 2007

A mobile satellite broadcasting service including an ancillary terrestrial component (ATC) takes advantage of the satellite's inherent capability to provide broadcast service over global coverage. We consider the downlink transmission concept using ATC with space=time code (STC) for the mobile satellite communication. We do not regard ATC as simply a repeater but consider it as an antenna for STC. First transmission scenarios for an application of STC are represented. Next, we apply STC in the mobile satellite system including ATC and compare the system performance in the proposed architecture of ATC to that in the conventional structure. The simulation results are compared to the conventional downlink transmission concept for the mobile satellite broadcasting service.

• Proceedings of the KSRS Conference
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• 2007.10a
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• pp.526-529
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• 2007

Due to its inherent feature of high-resolution satellite, there is strong need in some specific area to minimize the processing time required to get a standard image on hand from downlink signal acquisition. However, in general image processing system, it takes considerable time to get image data up to certain level from raw data acquisition because the huge amount of data is dealt sequentially as input data. This paper introduces the high-speed image processing system which generates the image data only for the area selected by user. To achieve the high speed performance, this system includes Quick Look Image display function with sampling, ROI selection function, Image Line Index function, and Distributed processing function. The developed RPS was applied to KOMPSAT-2 320Mbps downlink channel and its effectiveness was successfully demonstrated. This feature to provide the image product very quickly is expected to promote the application of high resolution satellite image.

• Proceedings of the KSRS Conference
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• 2007.10a
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• pp.493-495
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• 2007

Future sub-meter resolution LEO missions require simultaneous dual-polarization downlink and/or multiple channel downlinks in single polarization. Especially, dual-polarization is needed to cope with bandwidth limitation due to high speed data transmission. Current KARI 13m X-Band antenna system needs to be upgraded to cope with such downlink schemes. This paper describes brief discussions on engineering work regarding how to meet the new requirements with minimum impact on current system as well as C&M (Control and Monitoring) software.

• Journal of Satellite, Information and Communications
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• v.4 no.1
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• pp.28-35
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• 2009

We investigate the adaptive channel attenuation compensation of satellite OFDMA downlink users for minimum PAR (Peak to Average power Ratio), which is one of the main challenging issues in satellite OFDMA application. First, we analyze and compare PAR performances of two main different channel attenuation compensation schemes for OFDMA, i.e., PC-OFDMA (power control OFDMA) and AMC-OFDMA (Adaptive Modulation and Coding). While AMC-OFDMA maintains the constant transmission powers through entire user data subcarriers, PC-OFDMA has non-uniform subcarrier transmission powers because subcarrier powers are separately controlled to compensate each user's sub-channel attenuation. We newly found the fact that non-uniform subcarrier power in PC-OFDMA achieves rather reduced PAR compared to AMC-OFDMA and the amount of reduction becomes larger as the power differences among subcarriers increase. Also, there is an additional PAR reduction in PC-OFDMA by optimizing subcarrier grouping scheme for user's sub-channelization.

• Journal of Advanced Navigation Technology
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• v.27 no.3
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• pp.281-286
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• 2023

This paper proposes a design of a wideband array antenna involving the downlink bands of fixed satellite service (FSS) and broadcasting satellite service (BSS) by applying two mixed patch sets. The proposed antenna is implemented on FR4 substrate by arranging rectangular patches in 6 by 2. To design a wideband antenna (10.7~12.75 GHz) covering both FSS downlink bands (10.7~10.95 GHz, 11.2~11.45 GHz) and BSS downlink bands (11.7~12.5 GHz, 12.2~12.75 GHz, 11.7~12.2 GHz), rectangular patches working at 11.5 GHz and 12.5 GHz are arranged alternately, and thus the proposed antenna can obtain a wide bandwidth equivalent to 30.8% of the center frequency. The proposed antenna was fabricated and measured, and the results are well matched with the simulated ones. From the performances, the proposed antenna can be applied to the receiving antenna for FSS and BSS downlinks.