Research On The Signal Detection Technology Of OFDM In The Aeronautical Channel

Orthogonal frequency division multiplexing(OFDM) technology has been the key technology of mobile broadband communications recently. Compared to traditional aeronautical communication technologies, applying OFDM technology to aviation communication systems can improve the ability of the system to meet the needs of high-capacity and robustness. This paper mainly study signal detection and channel estimation techniques of the OFDM technology used in the broadband wireless communication system.The first chapter of this thesis briefly introduces the background of aeronautical communications, and focuses on the necessity of the application of OFDM technique to aeronautical communications systems.A deep understanding of aviation channel is the premise of research on signal detection and channel estimation techniques. Therefore, the second chapter discusses the basic characteristics of air channel, and describes the characteristics of the channel model under various scenarios. The chapter analyses in detail the advantages and disadvantages of the OFDM technology for aviation communications, as well as the problems caused by high mobility.In OFDM system with high speed, in order to reduce the complexity, existing signal detection algorithms usually consider the frequency domain channel matrix to a banded matrix, so as to ensure the system performance and reduce algorithm complexity. However, most of the detection algorithm does not take soft information output provided by channel coding into account. Therefore, in the third chapter, this thesis proposes an equalization algorithm with soft demodulation, which is based on partial minimum mean-squared error with successive detection, and considers the influence of offset error by residual interference. It can effectively improve the reliability of the output of soft information, and it is easy to implement with a low algorithm complexity. For cruise scenarios in air channel, simulation results show that the algorithm can obtain better performance of the system on the bit error rate.Reliable channel estimation is the precondition of signal detection of OFDM system in aviation communication. The fourth chapter of this thesis studies channel estimation algorithm about aeronautical channel at cruise and landing scenarios. In the cruising scenarios, that aircraft flies at high speed, which leads to strong variability of the aviation channel and the large multipath delay, brings some new challenges to the channel estimation. On the basis of the existing linear model, this paper proposes a channel estimation algorithm suitable for cruise scenarios. This algorithm sets the time domain channel impulse response between the two paths in cruise scenarios channel zero after discretization, so as to reduce the number of the estimator. It lowers algorithm complexity and the cost of pilots. The simulation results show that bit error rate of the channel estimation algorithm is approximately equal to the ideal channel estimation. In landing scenarios, this chapter uses the channel estimation algorithm based on transform domain noise reduction to simulate and study the detection performance of OFDM system in the aviation communications.Finally, the fifth chapter gives a summary of the full text, and points out the next research direction about the application of OFDM transmission technology to aeronautical communications systems.