Research On Multiple Access Interference Suppression And Channel Coding Technology For Tracking And Data Relay Satellite System

Since the 21 st century, Space technology of our country makes great progress. There are more and more spacecrafts in orbit in these years. Space easurement and control system based on ground station and ocean tracking ship costs too much and only has a small orbital coverage, which can no longer meet the demand of China’s space industry. Only a few data relay satellites can cover almost all the low orbit, so it is meaningful to build China’s own tracking and data relay satellite system(TDRSS). Besides, as a data relay station in the space, TDRSS can h elp spacecraft in orbit send messages to the ground twenty four hours a day.In the future, micro and small satellites will paly an importan roll in space. This means there will be many spacecrafts exchange information with ground stations at the same time. Inevitably, interference exists between these spacecrafts. Moreover, transmission power of spacecraft is limited, signals transmit to the ground station from orbit several hundred kilometres or higher. There would be considerable attenuation during the transmission. All these factors mentioned above will threat the integrity and reliability transimitted through the communication link between spacecrafts and ground stations. Therefore, we mainly research multiple access interference suppression and channel coding technology to guarantee the reliability of communication link in TDRSS.Firstly, the communication network model of TDRSS is introduced, significant parameters which can affect the communication quality of TDRSS are introduced. The signal model of forward link and return link in TDRSS is derived.Secondly, forward link mainly transmits telemetry and control command, which need high reliability, and the data rate don’t have to be high. Thus the multiuser detection algorithm based on artificial fish sw arm algorithm is proposed to suppress multiple access interfernce. The proposed algorithm searches the optimal results through artificial fish swarm algorithm. Simulation experiments are conducted to examine the bit error ratio, near far resistance, and us er capacity compared with tradtional multiuser detection algorithms. Because the output of multiuser detection is hard decision results, low-density parity-check(LDPC) code, convolutional code and concatenated coding recommended by CCSDS are tested to get satisfactory bit error ratio performance.Finally, because large amounts of data will be transmitted through the return link of TDRSS, hight data rate is demanded. Multiuser detection and channel decoding can be taken as a whole, then the soft output of m ultiuser detection can be used for soft decision decoding. Next the results of soft decision decoding is fed back to the soft output multiuser to improve the output. After several iterations the performance of this communication system is greatly improved. Simulation results show that the proposed iterative algorithm can achieve low bit error ratio under high code rate.