建立扩频信号防混叠滤波、采样、量化与解扩输出关系的数学解析模型,推导得到解扩输出信噪比的解析表达式.分析与仿真表明,当量化位数大于等于4 bit,解扩得到总的信噪比损失可以分解为由量化引起的损失和滤波加采样引起损失的乘积,且量化器最优限幅系数只与量化位数相关;当量化位数小于4 bit时,信噪比损失在一定条件下可近似为量化损失和滤波加采样损失的乘积.当量化位数大于4 bit、滤波器带宽大于5倍码率、采样频率大于4倍码率时,再增大上述参数引起的信噪比损失波动小于0.05 dB,对解扩性能提升不明显.该结论可为实用型全球导航卫星系统接收机前端离散化处理优化设计提供理论指导.%The analytical model for the output relations of anti-aliasing filtering,sampling,quantization and de-spreading was established.The formulation of de-spreading output SNR (signal to noise ratio) under the influence of three factors was deduced.Analysis and simulation results show that the total SNR loss can be separated to the product of quantization,filtering and sampling loss when the quantization length up to 4 bit;besides,the optimized clipping level coefficient is only related to quantization length.When the quantization length is less than 4 bit,the total SNR loss approximates to the product of the quantization and sampling plus filtering loss.In the condition of the quantization length up to 4 bit,the filter bandwidth up to 5 times of PN (pseudo-random) code rate,the sample rate up to 4 times of PN code rate,increasing the parameters mentioned above cause the SNR loss less than 0.05 dB,thus the de-spreading performance cannot be increased obviously.Results can be used to optimize the design of the front-end of low-cost global navigation satellite system receiver.
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