• Journal of Satellite, Information and Communications
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• v.12 no.4
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• pp.72-77
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• 2017

The Satellite Based Augmentation System (SBAS) broadcasts to users integrity and correction information for Global Navigation Satellite System (GNSS) such as GPS and GLONASS using geostationary orbit (GEO) satellites. In accordance with the recommendation of the International Civilian Aeronautical Organization (ICAO) to introduce SBAS until 2025, a Korean SBAS system development / construction project is underway with the Ministry of Land, Transport and Maritime Affairs. Korea Augmentation Satellite System (KASS) is a high precision GPS correction system which is composed of KASS Reference Station (KRS), KASS Processing Station (KPS), KASS Uplink Station (KUS), KASS Control Station (KCS) and GEO satellites. In this paper, we provided the conceptual design of the KASS uplink station, which is composed of the Signal Generator Section (SGS) and the Radio-Frequency Section (RFS), and interface between the KASS ground sector and the GEO satellite.

• Journal of Satellite, Information and Communications
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• v.9 no.1
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• pp.107-114
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• 2014

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 uplink in the satellite/terrestrial integrated system and the interference reduction scheme for satellite uplink interfered by terrestrial user equipment.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.2A
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• pp.166-173
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• 2004

Satellite communication system uses a high non-linear HPA(high power amplifiers) in the earth station and satellite transponder. Therefore, it is important to consider the nonlinear effect of HPA on the communication system. In this paper, we find the variation of power spectrum density by nonlinearity HPA and the change of harmonic component according to IBO (input back-off). When the BPSK is used for satellite communication system, we analyze BER performance including the external co-channel interference (CCI) and the adjacent channel interference (ACI) resulting from the HPA nonlinearity. BER degrades as ACI magnitude grows up when the uplink SNR, uplink SIR (signal to co-channel interference power ratio) and downlink SIR are constant at some level. In case there is only non-linear HPA in the satellite, it is shown that BER considerably depends on the ACI magnitude ACI. When there are two non-linear HPAs in the both earth station and satellite, much BER degradation results from the CCI and ACI.

• Proceedings of the KSRS Conference
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• 2004.10a
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• pp.460-463
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• 2004

There is a trend to replace TWTA of SSPA in S-Band uplink application for satellite operation. KARI developed l20W full S-Band SSPA system in early 2004. This paper covers SSPA system design and its test results. Through tests, nominal gain of 57dB, gain stability of +/-1dB over frequency, and gain stability of +/-0.5dB over temperature were shown. IMD value of -16.5dBc, -19dBc were revealed in PI and P3 output operations. With meeting specifications, l20W SSPA is expected to be used in operational S-Band uplink application.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• v.1
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• pp.309-314
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• 2006

In general DGPS system, the correction message is transferred to users by wireless modem. To cover wide area, many DGPS station should be needed. And DGPS users must have a wireless modem that is not necessary in standalone GPS. But SBAS users don't need a wireless modem to receive DGPS corrections because SBAS correction message is transmitted from the GEO satellite by L1 frequency band. SBAS signal is generated in the GUS(Geo Uplink Subsystem) and uplink to the GEO satellite. This uplink transmission process causes two problems that are not existed in GPS. The one is a time delay in the uplink signal. The other is an ionospheric problem on uplink signal, code delay and carrier phase advance. These two problems cause ranging error to user. Another critical ranging error factor is clock synchronization. SBAS reference clock must be synchronized with GPS clock for an accurate ranging service. The time delay can be removed by close loop control. We propose uplink ionospheric error correcting algorithm for C/A code and carrier. As a result, the ranging accuracy increased high. To synchronize SBAS reference clock with GPS clock, I reviewed synchronization algorithm. And I modified it because the algorithm didn't consider doppler that caused by satellites' dynamics. SBAS reference clock synchronized with GPS clock in high accuracy by modified algorithm. We think that this paper will contribute to basic research for constructing satellite based DGPS system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.8B
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• pp.1341-1347
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• 2000

For the DRT satellite transponder system, BER and total SNR to be required in the earth terminal are evaluated under the condition of HPA nonlinearity in the FBJ(full-band jamming) or PBJ(partial-band jamming) of uplink and downlink. In case that the satellite Inter bandwidth( Ws) is same to the earth terminal bandwidth($W_r$),in conditions of uplink JSR 10[dB], downlink JSR 10[dB] and processing gain 30[dB], linear transponder system shows that uplink SNR needs to be 14.2[dB] to achieve the total SNR 10[dB] requirement in downlink SNR 14[dB]. However, Nonlinear transponder system with OBO(output backoff) 2[dB] requires 20.1 [dB] uplink SNR. From the above results, the nonlinearity of HPA in the satellite transponder causes the degradation of BER performance so that it is of interest to consider the power increase.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.11
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• pp.5497-5512
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• 2016

An improved optimal weights based on parallel interference cancellation algorithm has been proposed to cancel for interference induced by multi-user access satellite to ground uplink system. Due to differences in elevation relative motion between the user and the satellite, as well as access between users, resulting in multi-user access interference (Multi-user Access Interference, MUI), which significantly degrade system performance when multi-user access. By steepest gradient method, it obtained based on the MMSE criterion, parallel interference cancellation adjust optimal weights to obtain the maximum SINR. Compared to traditional parallel interference cancellation (Parallel Interference Cancellation, PIC) algorithm or serial interference cancellation ( Successive interference Cancellation, SIC), the accuracy of which is not high and too many complex iterations, we establish the multi-user access to the satellite to ground up link system to demonstrate that the improved WPIC algorithm could be provided with high accuracy and relatively low number of iterations.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.6A
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• pp.864-870
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• 1999

A key difference between a tactical military and commercial satcom system is that the military system is expected to provide a service in the presence of ECM threats such as jamming. In this paper, we analyzed the three different type of link system applicable to the military satellite and directly compared to each system in order to find system performance according to the maximum jammer power. For the analysis, we modeled and simulated the SHF satellite system based on uplink jamming. From the results, it is found for each different type of link the maximum jammer power that can be tolerated with link operating at its suggested nominal rate. Also, we studied to the survivability level against the jamming condition through the performance comparison in shipborne and portable terminal consistent with frequency.

• Journal of Satellite, Information and Communications
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• v.5 no.2
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• pp.92-96
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• 2010

We propose a new satellite OFDMA(Orthogonal Frequency Division Multiple Access) scheme with greatly enhanced tolerance of timing offset among the users. In uplink OFDMA systems, timing misalignment among users destroys subcarrier orthogonality and thus, it degrades the performance. In order to avoid this performance degradation, the accurate processing, so called 'ranging', is required to synchronize among users. However, ranging scheme is not available in the satellite systems due to the very long round trip delay. Exploiting the property that PSW(Propoerly Scrambled Walsh-code) code has zero correlation despite ${\pm}1$ chip timing offset, the proposed OFDMA achieves MAI free performance with the timing offset up to ${\pm}1$ OFDM symbol duration for the satellite systems.

• Journal of Satellite, Information and Communications
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• v.12 no.4
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• pp.50-55
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• 2017

In this paper, the design of the RF system monitoring and control system of KUS (KASS: KASS Uplink Station) which constitutes KASS (Korea Augmentation Satellite System) is described. The Korean satellite calibration system is named KASS and aims to develop the SBAS system of the APV-1 level SoL service level and the CAT-1 test operation technology. Software and hardware development environment, function and algorithm of supervisory control device, structure of supervisory control device, and user interface were designed to implement KUS / RFS monitoring control device. We have secured the stability and reliability of the system by using the monitoring and control system design of the COMS (Communication Ocean & Meteorological Satellite) and the Korea Satellite 5A / 7 control system, which has already been used for the design of the surveillance control system. In addition, we have made it possible to provide the user interface according to the actual operator's request more conveniently.