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I. 서론 11

1.1. 연구배경 11

1.2. 연구내용 및 범위 18

1.3. 논문 구성 21

II. 위성 채널 간섭 환경 24

2.1. X-밴드 주파수 할당 현황 및 향후 전망 24

2.2. 간섭 방지를 위한 조치 권고 방안 28

2.3. 지상국 안테나 특성 30

2.3.1. 안테나 방사 패턴의 수학적 모델 30

2.3.2. 안테나 크기 별 JPL 첨두 포락선 모델 35

2.3.3. 오프셋 각도에 따른 수신기 성능 열화 39

2.4. 저궤도 위성의 하향링크 시스템 43

III. SISO 49

3.1. SISO 시스템 모델링 49

3.2. SISO 검출 기법 52

3.2.1. 간섭 무시 검출기 52

3.2.2. 연속 간섭 제거 검출기 52

3.2.3. 합동 최소 거리 검출기 54

3.3. 복잡도 58

3.4. 모의실험 60

3.4.1. 모의실험 구성 60

3.4.2. 모의실험 결과 61

IV. SIMO 68

4.1. SIMO 시스템 모델링 68

4.2. 수신 다이버시티 결합 방법 71

4.2.1. 간섭 신호 부재 시 수신 다이버시티 결합 방법 72

4.2.2. 간섭 신호 존재 시 수신 다이버시티 결합 방법 88

4.3. 모의실험 95

4.3.1. 모의실험 구성 95

4.3.2. 모의실험 결과 96

V. MIMO 104

5.1. MIMO 시스템 모델링 104

5.2. 채널 모델링 및 조건수 분석 106

5.2.1. 채널 용량 106

5.2.2. 채널 모델 분석 106

5.2.3. 조건수 분석 108

5.3. MIMO 검출 기법 113

5.3.1. ZF와 MMSE 검출 113

5.3.2. 연속 간섭 제거 검출 115

5.3.3. 최적 순서 적용한 연속 간섭 제거 검출 116

5.3.4. 최대 우도 검출 117

5.4. 모의실험 118

5.4.1. 모의실험 구성 118

5.4.2. 모의실험 결과 118

VI. 결과 및 고찰 125

6.1. SISO 채널에서의 결과 및 고찰 125

6.2. SIMO 채널에서의 결과 및 고찰 126

6.3. MIMO 채널에서의 결과 및 고찰 127

VII. 결론 128

참고문헌 131

ABSTRACT 138

표목차

(Table 2.1.1) Frequency allocation in the ITU-R Radio Regulations (RR) 26

(Table 2.3.1) Offset angles per three antenna diameters 37

(Table 2.3.2) SIR vs. offset angle in degrees per antenna size at 8,260 MHz 38

(Table 3.3.1) Complexity vs. the number of the interference 58

(Table 4.3.1) Simulation parameters in SIMO 95

(Table 5.3.1) SIC for MMSE detection 116

(Table 5.4.1) Simulation parameters in MIMO 118

(Table 6.2.1) Optimal combining selection for various conditions 126

그림목차

(Fig. 1.1.1) Orbit destinations for Nano/Microsatellite 12

(Fig. 1.1.2) Trends in spatial resolution of sensors 13

(Fig. 1.1.3) All kinds of interference signal path 14

(Fig. 1.1.4) Communication schedule of KOMPSAT ground station 15

(Fig. 1.1.5) Histogram for offset angle at KGS and SGS 15

(Fig. 1.3.1) Organization of dissertation 23

(Fig. 2.1.1) Total bandwidth used by all satellites and mean bandwidth per... 25

(Fig. 2.1.2) Bandwidth distribution of operational satellite systems... 27

(Fig. 2.1.3) Bandwidth distribution of operation and planned... 27

(Fig. 2.3.1) Antenna gain pattern of JPL peak envelope model 35

(Fig. 2.3.2) Antenna gain pattern within 0.5 degrees for three antennas 36

(Fig. 2.3.3) Normalized antenna gain for three antennas 38

(Fig. 2.3.4) Offset angle between target satellite and adjacent satellite 39

(Fig. 2.3.5) Performance degradation per antenna size vs. offset angle 41

(Fig. 2.3.6) Performance degradation per elevation angle vs. offset angle 42

(Fig. 2.4.1) Typical LEO satellite interference configuration 43

(Fig. 2.4.2) Fading due to multipath signals for a fixed and mobile... 47

(Fig. 3.1.1) System configuration for SISO 49

(Fig. 3.4.1) BER of II and SIC detectors 61

(Fig. 3.4.2) BER of JMD detector in AWGN 63

(Fig. 3.4.3) BER of JMD detector in Rayleigh fading 63

(Fig. 3.4.4) BER of all detectors @ 0.1567 deg, 2.5 dB for... 65

(Fig. 3.4.5) BER of all detectors @ 0.2428 deg, 6 dB for 7.3 m... 65

(Fig. 3.4.6) BER of JMD detector @ 0.0880 deg for 13 m... 66

(Fig. 3.4.7) BER of JMD detector for 7.3 m antenna, Rayleigh, 16-QAM 67

(Fig. 3.4.8) BER of JMD detector for 7.3 m antenna, Rician, 16-QAM 67

(Fig. 4.1.1) System configuration for SIMO 69

(Fig. 4.2.1) Outage probability of a selection combining method 73

(Fig. 4.2.2) Outage probability of a maximal ratio combining method 79

(Fig. 4.2.3) Outage probability for SC and MRC 80

(Fig. 4.2.4) BER for a maximal ratio combining method 81

(Fig. 4.2.5) BER for a equal gain combining method 85

(Fig. 4.2.6) SNR improvement for SC, EGC and MRC 86

(Fig. 4.2.7) SIMO configuration for L adjacent satellites and M antennas 88

(Fig. 4.3.1) BER for EGC, MRC and OC @ 0.1716 deg, SIR ＝... 96

(Fig. 4.3.2) BER for EGC, MRC and OC @ 0.3433 deg, SIR ＝... 97

(Fig. 4.3.3) BER for EGC, MRC and OC @ 1.3604 deg, SIR ＝... 97

(Fig. 4.3.4) BER for SC, EGC, MRC and OC @ 0.1716 deg,... 98

(Fig. 4.3.5) BER for SC, EGC, MRC and OC @ 1.3604 deg,... 99

(Fig. 4.3.6) BER for MRC and OC @ 0.1716 deg, SIR ＝ 3 dB... 100

(Fig. 4.3.7) BER for EGC, MRC and OC for mixed channel 101

(Fig. 4.3.8) BER for SC, MRC and OC @ 0.3433 deg, SIR ＝ 12... 102

(Fig. 4.3.9) BER for SC, MRC and OC @ 0.3433 deg, SIR ＝ 12... 102

(Fig. 4.3.10) BER for SC, MRC and OC @ 0.3433 deg, SIR ＝... 103

(Fig. 5.1.1) Dual-contact satellite configuration 104

(Fig. 5.2.1) Condition number vs. offset angle 112

(Fig. 5.4.1) BER for single decoding only in AWGN 119

(Fig. 5.4.2) BER for single decoding only in Rayleigh fading 119

(Fig. 5.4.3) Average BER for single decoding in Rayleigh fading 120

(Fig. 5.4.4) MIMO BER for 7.3 m ant., @ θ＝0.15°, K＝0 121

(Fig. 5.4.5) MIMO BER for 13 m ant., @ θ＝0.15°, K＝0 121

(Fig. 5.4.6) MIMO BER for 7.3 m ant., @ θ＝0.3°, K＝0 122

(Fig. 5.4.7) MIMO BER for 13 m ant., @ θ＝0.3°, K＝0 122

(Fig. 5.4.8) MIMO BER for 7.3 m ant., @ θ＝0.05°, K＝1E5 123

(Fig. 5.4.9) MIMO BER for 13 m ant., @ θ＝0.05°, K＝1E5 124

초록보기

As the frequeny allocation of low earth orbit satellites for X-band 8,025-8,400 MHz increases for transmitting the science data with an increase in spatial resolution, this may increase the potential interference risk due to the frequency overlapping between the satellites. When two satellites are closely positioned within the looking angle of the receive antennas the two satellites interfere with each other and this causes the performance degradation of the target satellite unless appropriate measures are taken.

The interference from an adjacent satellites is a function of various parameters, but the most critical factor is the radiation pattern of the receive antenna where the interference is determined by the relative antenna gain corresponding to the offset angle of an adjacent satellite. Accordingly, the three approaches in this paper are proposed where the optimal solutions for single input single output, single input multiple output and multiple input multiple output configuration are applied to reduce the interference risk and enhance the performance.

In single input single output configuration, with assumption of a priori knowledge of the channel state of an adjacent satellite, the joint minimum-distance detector as a reduced complexity maximal likelihood detector is mainly utilized to mitigate the interference where the target signal and the interference are jointly detected. Unlike interference ignorant detector and successive interference cancellation detector, we showed that the joint minimum-distance detector does not experience the error floor. Therefore, the joint minimum-distance detector can significantly reduce the interference thereby improving the performance even under severe interference conditions.

In single input multiple output configuration, various receiver diversity schemes by using additional ground station antennas are addressed. It is clearly confirmed that receive combining schemes can improve the signal-to-noise ratio or signal-to-interference-noise ratio at the output of the combiner compared to the signal-to-noise ratio of a single antenna. Not only optimum combining but also selection combining, maximal-ratio combining and equal-gain combining showed the significant performance enhancement particularly in the presence of interference and fading. In addition, although optimum combining at the expense of complexity outperforms selection combining, maximal-ratio combining, and equal-gain combining, but the appropriate combining selection taking into account the performance and complexity was determined as an optimal method under the different channels and interference conditions.

In multiple input multiple output configuration, various spatial multiplexing techniques using detection schemes such as zero forcing-successive interference cancellation, minimum mean square error-successive interference cancellation, and maximum likelihood were exploited and it turned out that these schemes can enhance the receiver performance through the condition number analysis and thus these schemes can be applicable to dual-contact satellite scenario even under severe interference conditions.

As a result of the various simulations in single input single output, single input multiple output and multiple input multiple output configuration, the proposed schemes in this paper make their use very attractive and sufficient even in the presence of the interference from adjacent satellites and fading in a dual-contact satellite scenario of low earth orbit satellites.

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