(A) Study on robust synchronization in NOMA-based satellite communication systems

Abstract

This dissertation is about robust synchronization techniques in NOMA-based satellite communication systems. Recently, satellite communication has played an important role in constructing a three-dimensional spatial network that provides a wireless access network to areas where terrestrial networks cannot reach. Efficiency in data transmission can be increased by distributing and connecting large amounts of data through geostationary and nongeostationary orbit satellite communication networks. In these satellite communication transmission technologies, various transmission techniques have been proposed depending on the service type, and this paper also proposes various synchronization technologies depending on each satellite communication frequency, protocol, and channel environment. First, synchronization technologies that are robust to LDM technology to improve data rates in the same band in geostationary satellite broadcasting and communication environments, are proposed. In the case of LDM technology, robust synchronization technology is required because performance degradation occurs when removing interference due to co-channel interference problems due to the use of the same RF and non-linear amplifiers and phase noise. Second, when FTN technology is applied to improve transmission efficiency per bandwidth in a satellite communication environment, inter-symbol interference occurs. Therefore, a symbol synchronization technology that is robust to inter-symbol interference is needed, and this paper proposes a technique close to the maximum likelihood algorithm. Lastly, robust synchronization technology is proposed that is robust to non-geostationary satellite or high-speed mobile terminals in short packet transmissions such as random access channel environments. In particular, the proposed scheme is suitable for timing synchronization in a large Doppler error environment, and its performance evaluation is carried out. In summary, the proposed synchronization techniques presented in this dissertation play a vital role in improving the overall transmission efficiency of satellite communication systems, addressing specific challenges associated with LDM, FTN, and high Doppler effect conditions.