Research On The Key Technologies Of Generation And Detection Of Multicarrier Communication

With the rapid development of the aviation industry, aeronautical communication is now playing an increasingly important role in both civil and military applications. For an aeronautical wireless communication system working in jamming environments, reliable data transmission is very crucial. In this thesis, the key technologies of waveform generation and signal detection are addressed for aeronautical communication systems. Non-contiguous orthogonal frequency division multiplexing(NC-OFDM), which has been used in the field of Cognitive Radio(CR), is proposed to be applied in aeronautical communication systems.In Chapter 1, the research background of this thesis and the characteristics of multi-carrier communication system are introduced. OFDM is first briefly described. NC-OFDM is then proposed for an anti-jamming aeronautical communication system.In Chapter 2, the aeronautical channel model and the technologies to suppress the high peak-to-average power ratio(PAPR) of NC-OFDM systems are investigated. Noise sharping-clipping factor reduction(NS-CFR) algorithm is first utilized to reduce the PAPR of NC-OFDM systems. And its performance is validated by simulation. A low PAPR pilot waveform is further proposed for a NC-OFDM system with comb pilot pattern, so that the PAPR of the resulting time-domain pilot waveform can be significantly reduced.In Chapter 3, the synchronization techniques are investigated for a NC-OFDM system under jamming scenarios. The system model and the influence of timing synchronization error and frequency offset are first discussed. Subsequently, in order to achieve desirable synchronization performance under the channels with strong narrowband interference(NBI), a novel anti-jamming NC-OFDM synchronization method is proposed. For the proposed method, the training sequence consisting of two repetitive constant amplitude zero auto correlation(CAZAC) sub-sequences are used within one OFDM symbol, which is optimized to reduce the influence of NBI. The relative threshold and several correlation peaks are jointly used to improve the performance of timing synchronization. Meanwhile, the carrier frequency offset is estimated based on the correlation value to reduce the influence of NBI on the frequency synchronization. Simulation results show that this proposed novel method can significantly improve the synchronization accuracy and anti-jamming capability. Therefore, it can work well under the aeronautical channel with strong NBI.In Chapter 4, the anti-jamming signal detection technologies of NC-OFDM system are investigated. Firstly, a receiver window function based method is introduced to suppress the NBI. The results show that this method can improve the anti-jamming capability of the system while keeping the communication link structure unchanged. Then, a channel estimation algorithm based on comb pilot pattern is introduced. A modified interpolation algorithm is proposed to improve the channel estimation performance. The soft detection algorithm of quadrature amplitude modulation(QAM) is also described. Finally, the simulations are performed to verify that the proposed signal detection algorithm can give excellent performance in terms of bit error rate(BER).In Chapter 5, all the proposed algorithms are evaluated by extensive simulations based on the developed link-level aeronautical NC-OFDM communication simulation platform. Firstly, the simulation link structure, system parameters and physical layer frame are described. Then, the performance is verified under various scenarios with different kinds of aeronautical channel and interference. Simulation results show that the proposed algorithms can achieve desirable transmission performance under aeronautical channels with strong interference.In Chapter 6, this thesis is summarized and the possible research topics in the future are also discussed.