Improved TDCS Based On Channel Equalization And Estimation In Multi-Path Fading Channel

Transform Domain Communication System (TDCS) is a new communication system which has no carrier modulation, but uses a noise-like basis function to modulate the data, and its waveform is designed in transform domain (frequency or scale) according to the estimation of electromagnetic environments. TDCS processes demonstrated excellent interference avoidance capability under adverse environmental conditions. Because of these advantages, TDCS has been widely applied in military and Cognitive Radio (CR) flied. So it is important to research on it. Till now the research are focused on the Peak-to-Average Power Ratio (PAPR) problem, modulation technologies, synchronization and so on. However, there is another important problem needs to be come over. When TDCS is in a multipath fading channel, its performance decrease dramatically, which is always been existed;so technology against the channel fading should be used in TDCS, such as equalization. Further, since equalization technologies always depend on the channel estimation results, while present blind channel estimation methods need long integration time can't adapt to the time varying channel, and other estimation methods based on pilot frequency have poor accuracy.According to the situations above, the work of the thesis is as follows. First, the basis theory of TDCS is introduced and the principle algorithms about TDCS are analyzed, then a simulation platform is designed. On these bases, the performances of TDCS against the interference and noise are analyzed, and the Bit Error Rates (BER) of different Jam-to-Signals (JS) and different Signal-to-Noises (SNR) are proved. Next, multipath Rayleigh fading channel is established by the Jakes'Model, and the performance of TDCS in multipath fading case is also analyzed. Pre-equalization and post-equalization technologies are introduced to improve the performance of TDCS; bit errors rates of different cases are compared to check the improvement of the equalizations. On these bases, a pre-post-equalization TDCS system is designed in this paper. Finally, a Linear Frequency Modulation (LFM) detecting by Fractional Fourier Transform (FrFT) based channel estimation algorithm is proposed to estimate the parameters of channel effectively for the equalization.