Abstract-Nyquist folding receiver (NYFR) is a new kind of interception architecture, which can simultaneously intercept wideband signals in multi-Nyquist zones with one or two analog-to-digital converters (ADCs). A parameter estimation algorithm of the linear frequency modulated (LFM) signal intercepted by an improved NYFR is presented. Firstly, the NYFR is improved by introducing a synchronous mechanism, and we denote this structure as a synchronous NYFR (SNYFR). Secondly, taking LFM as an example, the input and output noise distributions of an SNYFR are discussed. Then, a fast parameter estimation algorithm is derived from the frequency spectrum of the output signal, and an advice for the design of local oscillator signal is given. Simulations show that the parameter estimation accuracy is close to the maximum likelihood when the signal to noise ratio (SNR) is above −3 dB.

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Based on the ambiguity function, an approach to intra-pulse modulation recognition is presented. This paper defines the frequency energy accumulation function (FEAF) and time-domain extremum function (TEF) to describe the Doppler frequency shift and time delay properties of signals, respectively. This approach can recognize six types of signals by four characteristic parameters. Simulation results show that the probability of successful recognition (PSR) can reach 90% when the signal to noise ratio (SNR) is above −1 dB.

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