Application Of Adaptive Coding And Modulation In Satellite Communication

In wireless communication filed, due to the open communication channel conditions, communication links of satellite communication systems are susceptible to the impact of the average atmospheric condition. In particular, the high frequency satellite system based on Ka-band are easily influenced by rain attenuation, which Seriously affected the effectiveness and reliability of the system. For digital systems, the reliability can be improved by channel coding and the effectiveness can be assured by modulation. However, when the SNR is relatively high, the scheme employing Low order modulation and large redundancy encoding for reliability will limit the system efficiency, and when the SNR is too low, another method using High order modulation and less redundancy encoding for effectiveness could not guarantee stable and reliable communication in the system. Aiming at the satellite system with limited power and band limited, adaptive coding and modulation(ACM) technology can work better to resistance rain attenuation and other interference to improve the throughputs of system.In this paper, for the Ka-band satellite system, which is easily affected by rain attention, and when it has limited power and limited frequency band, in order to compensate rain attenuation among communication links, it adopts ACM method to changing transmission rate in real time to achieve the satisfactory quality. Firstly, it analyzes the relationship of satellite communication frequency and earth-station geographic position with the rain attention and discusses the influence of rain attention on the system, then gives the attenuation channel model for Ka fixed satellite communication. Secondly, it gives the design of adaptive coding and modulation scheme, it adopts LDPC code and QPSK, 8PSK and 16 APSK forming the coding and modulation map, the receiver estimates the real time signal-noise-ratio to transmit it to the sending side, the sender adjusts the coding and modulation mode according the designed map and transmits the information in the fixed frame format. It demonstrates the ACM scheme through the simulation based on the given channel model, and analyzes the total throughput of the system which adopts the ACM scheme, and discusses the anti rain attenuation performance of the system, then draws the conclusion that there is the necessity and advantage of the employment of the ACM technology. Finally, it shows the generation and combination process of the multi-carrier and multi-rate signal among the ACM transmission, analyzes the whole process of ACM signal, and introduces the composition and functions of the realized system and the whole system scheme. Combined with the design of the monitoring software, it completes the system practice test and gives the test results.As a whole, this paper gives the research significance and the research technique, then realizes the adaptive transmission system through engineering practice. The test result indicates that the realized system can work as the designed target and satisfy the desired map to achieve system performance goal.