| The work of thesis is as follows. Firstly, a new communication system------transform domain communication system (TDCS) is researched. It is different from traditional communication systems at two points: 1) the communication waveform is designed in transform domain (frequency or scale) according to the estimation of electromagnetic environment, 2) no carrier modulation but a noise-like basis function is used to modulate the data. So, TDCS provides preferable performance for restraining narrowband interference and Low-Probability-of-Intercept/Low-Probability-of-Detection (LPI/LPD).Secondly, the basic theory of narrowband interference suppression in TDCS based on FFT is introduced and the principal algorithms about basis function generation are analyzed. Because AR estimation can bring to false spectrum peaks and fission of spectrum regions, a new algorithm based on adaptive multi-threshold is proposed and applied to TDCS. Utilizing the new algorithm, threshold can be generated without the influence of interference's power. Through simulation, the results show preferable performance for advoiding narrowband interference. Compared with the primal algorithm, it not only has better capability, but also stronger adaptability.Finally, the basic theory of narrowband interference suppression in TDCS based on wavelet packet transformation is introduced. To improve the performance of estimation for interference and the percentage of basis function's bandwidth taking account of system's in TDCS , a new method for generating basis function is proposed based on wavelet packet transformation. Using tree structure algorithms (TSA) calculation to decompose signals can estimate the position of interference accurately and reduce the loss of the avail bandwidth. Through theoretical analysis and simulation, TDCS based on wavelet packet transformation has better interference avoidance capability and adaptive performance, compared with the system based on DWT. |
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