| Traditional phased array radar has some disadvantages. For example, when detecting weak targets, the radar signal is susceptible to be intercepted; when operating in presence of strong clutter, the requirement of dynamic range is very huge; when performing moving target indication (MTI) and moving target detection (MTD), the requirements on frequency stability, phase noise, and system spurs are also very challenging. Applying digital beam forming (DBF) at the receiver end can partially address these problems. In a DBF system, analog-to-digitization (A/D) conversion is performed on each array element, thus the A/D dynamic range requirement is reduced. DBF also facilitates the formation of multiple simultaneous receive beams, which enable faster search rates. However, this type of phased array radar is unable to form multiple simultaneous beams at the transmitter end, since the DBF system still operates as analog beam forming (ABF) system does. Specifically, they scan a narrow sector at one time, and can only perform a single radar function (i.e., search or track) at any given instant.These problems can be resolved by applying multiple-input multiple-output (MIMO) technique to radar. On transmit, the elements (or subarrays) of MIMO radar transmit omnidirectional, orthogonally coded waveforms. On receive, a bank of matched filters are used to separate the echo signals due to different transmitters. Then the DBF is employed to form both receive and effective transmit beams. MIMO radar has many performance improvements, such as the better anti-interception performance, the enhanced capability of weak target detection under clutter, and the advanced ability of low speed target detection under strong clutter.Since MIMO radar transmits orthogonal waveforms, the orthogonal waveform design is crucial for MIMO radar implementation. This dissertation investigates the MIMO radar signal processing and orthogonal waveform design, and the main research focus on the following issues:1. Study and analyze the principles and characteristics of MIMO radar. Based on these, the performance improvements of MIMO radar over the traditional phased array radar counterpart are investigated.2. Analyze the MIMO radar signal processing. First, a MIMO radar signal model is set up, and then the multi-signal matched filter realization and the sequel DBF technology are investigated. Next, the effect of the processing order for matched filter and DBF on the computer complexity is analyzed, and an improved processing architecture is proposed.3. Investigate the design method and performance of the orthogonal linear frequency modulation (LFM) signals. The ambiguity function of a single LFM signal and cross-ambiguity function of orthogonal LFM signals are studied. The positions and levels of cross-correlation peaks (CP) are analyzed, and the design criteria and parameter relationship of LFM signals are presented. The signal processing and wideband resolution performance of MIMO radar based on orthogonal LFM signals are also studied. At last, the designed orthogonal LFM signals are applied to a MIMO radar simulation system.4. Investigate the design method of orthogonal polyphase codes. The design criteria and optimization method of orthogonal polyphase codes are proposed. Genetic algorithm (GA) is employed to optimize the orthogonal polyphase codes, and an improved ambiguity-based design criteria is proposed. The designed orthogonal polyphase codes are also applied to the MIMO radar simulation system.5. Investigate the design and performance of the orthogonal discrete frequency coding waveform (DFCW). Based on the analysis of the ambiguity function of a DFCW signal and the cross-ambiguity function of DFCW signals, the correlation and Doppler performance of the DFCW signals are analyzed. Design criteria and optimization method for DFCW signals are proposed, and the modified GA is applied to optimize the DFCW signals.6. Build a system simulation platform of MIMO radar. The MIMO radar performance and its advantage over the traditional phased radar are investigated. The signal processing algorithm is also analyzed, and some simulations for the MIMO radar system realization are done.
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