Research On Nonuniform Sampling Technique In Broadband Receiver

With the continuous development of electronic technology,the frequency of signals that need to be processed increases dramatically in the actual radar and electronic warfare systems.The development of the electromagnetic signal frequency toward the GHz,the receiver based on the Nyquist sampling is getting more and more restricted when processing the signal.Since the Nyquist sampling theorem limits the sampling rate,the ADC needs to have a high sampling rate when processing the wideband signal and the amount of data sampled is also great.The theory of compressed sensing and nonuniform sampling break the limitation of sampling rate,and provide the theoretical basis for sampling the signal with a sampling rate which lower than Nyquist rate.Based on compressive sensing theory and the nonuniform sampling theory,this thesis studies the hardware implementation of a nonuniform sampling platform to realizes the direct compression sampling for the frequency domain sparse signal,and the signal reconstruction is carried out by using the OMP algorithm.The main research contents as follows:1.It analyzes the mathematical model of compressive sensing,including signal sparse representation,observation matrix design and signal reconstruction,and combines with the theory of nonuniform sampling to construct nonuniform sampling hardware model.2.The nonuniform sampling platform is designed with the nonuniform sampler(NUS)model as the core.Using the sampling rate of 400 MHz ADC chip to sample sparse signals which frequency is within the 2 GHz,so as to achieve 10 times compression of the Nyquist sampling rate.First,using the sample-and-hold(S/H)to sample the signal nonuniformly,the sample times of the S/H are controlled by nonuniform clock.And let S/H output the signal which amplitude is the current sampling value in the ADC sampling times.Then the ADC chip is used to sample the output signal of S/H,so as to realize the nonuniform sampling of the signal.3.The design of nonuniform clocks is the key to this thesis.In order to ensure that the S/H has the above output characteristics,the nonuniform clock and the ADC sampling clock must have a specific timing relationship.Since the ADC sampling clock can be regarded as fixed,the ADC sampling clock can be used as the reference when designing the nonuniform clock.At the same time,in order to use the OMP algorithm to complete the signal reconstruction,It is necessary to make sure that the nonuniform spaced sample are integer multiples of underlying Nyquist rate.According to the GTH output characteristics of FPGA,we use GTH to output high-speed pseudo-random bit stream to produce nonuniform clock,which will convert the design of nonuniform clock into designing the pseudo-random sequence.By designing the pseudo-random sequence,so that the non-uniform sample times can fall between the adjacent two sample times of the ADC.4.According to the hardware design,complete the hardware platform.Then tested the nonuniform sampling platform under the existing laboratory conditions,and giving the concrete test results.