Hybrid coding and subcarrier modulation scheme in soft-switching links
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摘要: 为了提高自由空间光/射频（FSO/RF）混合通信链路的性能，采用混合低密度奇偶校验（LDPC）编码与副载波相移键控/正交振幅调制（PSK/QAM）联合调制的方法，对不同传输比例下混合系统的误比特率性能进行了仿真分析，取得了不同信道条件下单链路和混合链路传输方案的误比特率数据。结果表明，在弱中强湍流条件下采用副载波二进制相移键控（BPSK）调制，相比开关键控（OOK）调制可获得大约4.4dB~5.2dB的增益。采用软切换的混合LDPC编码与副载波BPSK/16QAM调制方案，依据链路状态调整比例为1：1和3：1时，不同湍流强度下可获得大约0.3dB~7.4dB的性能增益。这一研究结果对于提高FSO/RF混合通信系统的全天候高效可靠传输性能具有重要的参考价值。
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关键词:
- 光通信 /
- 自由空间光/射频链路 /
- 混合低密度奇偶校验编码 /
- 副载波调制 /
- 混合调制
Abstract: In order to improve the performance of free space optical/radio frequency(FSO/RF) hybrid communication links, one modulation method combining hybrid low density parity check (LDPC) coding with subcarrier phase shift keying/quadrature amplitude modulation(PSK/QAM) was adopted. Bit error ratio(BER) performance of hybrid systems with different transmission ratios was simulated and analyzed. BER data of single link and mixed link transmission schemes under different channel conditions were obtained. The results show that subcarrier binary phase shift keying (BPSK) modulation used in weak, moderate and strong turbulence can obtain gain about 4.4dB to 5.2dB compared with on-off keying (OOK) modulation. One soft-switching modulation scheme of hybrid LDPC coding and subcarrier BPSK/16QAM is adopted. When the ratio is adjusted to 1:1 and 3:1 according to link state, performance gains about 0.3dB to 7.4dB can be obtained under different turbulence intensities. This research result has important reference value for improving all-weather efficient and reliable transmission performance of FSO/RF hybrid communication systems. -
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Figure 4. Hybrid system BER performance under various channel conditions
a—comparison between subcarrier BPSK modulation and OOK modulation b—σR2=0.209 in weak turbulence c—σR2=0.677 under moderate turbulence d—σR2=41.87 in strong turbulence
Table 1 SFSO with BER of 10-6 for hybrid subcarrier BPSK/16QAM modulation scheme
σR2 SRF/dB SFSO/dB(when RBER=10-6) BFSO:BRF=1:1 BFSO:BRF=3:1 0.209 5.0 7.60 5.20 11.0 3.50 3.80 0.677 5.0 11.20 7.60 11.0 5.10 5.60 41.87 5.0 19.20 11.80 11.0 8.40 8.80 
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