Ofdm Radar Waveform Design Methods And Simulation

OFDM (Orthorgonal Frequency Division Multiplexing) radar is a new type of radar system. Recently it is investigated extensively. That's because it exhibits advantages in various aspects, such as large time-bandwidth product, good anti-jamming capability, high spectrum efficiency, simple digital processing and so on. This thesis focuses on the waveform design methods of OFDM signal. The main work and contribution is summarized as follows.Firstly, the basic phase-coded theory is introduced. Then, the autocorrelation characteristics of some phased codes, such as Barker code, Frank code, P3 and P4 codes, complementary code and Huffman code, are discussed in detail. This offeres the theory support for the choice of the phased code in the OFDM radar.Secondly, the waveform and spectrum of the OFDM signal are presented. In addition, its orthogonal spectrum structure is validated, and the main difference from the single carrier phase coded (SCPC) signal is also given. The methods for reducing the PMEPR are summarized. Two methods, i.e., amplitude weighting and the additional phase angle are applied to reduce the PMEPR for the two types of OFDM signal respectively.Thirdly, the wideband ambiguity function of the OFDM signal is derived in detail and the impact of phase-coding on the ambiguity function is discussed in depth. For the IS OFDM signal and the COCS OFDM signal, the influence of the signal's parameters on the sidelobe level and mainlobe width of the autocorrelation function is analyzed. By using the consecutive ordered cyclic shifts for the OFDM signal burst, th recurrent lobes are reduced effectively.Finally, wavelet transform method is applied to the OFDM signal. Specifically, the wavelet packet is employed to modulate the traditional OFDM radar signal. Concretely, we describe the basic principles of wavelet packet modulation, and analyze the time-frequency characteristics of wavelet packet modulated multicarrier. Subsequenctly, the formulation of the wavelet packet modulated OFDM radar signal is presented. In addition, simulations are conducted to demonstrate the time envelope of the wavelet packet modulated OFDM signals, the characteristics of the autocorrelation function, the signal spectrum and the ambiguity function By comparison, it is shown that the wavelet packet modulated OFDM radar signal exhibits more advantageous ambiguity function and higher spectrum utility efficiency.