Accumulatively Increasing Sensitivity of Ultrawide Instantaneous Bandwidth Digital Receiver with Fine Time and Frequency Resolution for Weak Signal Detection

Abstract

It is always an interesting research topic for digital receiver (DRX) designers to develop a DRX with (1) ultrawide instantaneous bandwidth (IBW), (2) high sensitivity, (3) fine time-of-arrival-measurement resolution (TMR), and (4) fine frequency-measurement resolution (FMR) for weak signal detection. This is because designers always want their receivers to have the widest possible IBW to detect far away and/or weak signals. As the analog-to-digital converter (ADC) rate increasing, the modern DRX IBW increases continuously. To improve the signal detection based on blocking FFT (BFFT) method, this paper introduces the new concept of accumulatively increasing receiver sensitivity (AIRS) for DRX design. In AIRS, a very large number of frequency-bins can be used for a given IBW in the time-to-frequency transform (TTFT), and the DRX sensitivity is cumulatively increased, when more samples are available from high-speed ADC. Unlike traditional FFT-based TTFT, the AIRS can have both fine TMR and fine FMR simultaneously. It also inherits all the merits of the BFFT, which can be implemented in an embedded system. This study shows that AIRS-based DRX is more efficient than normal FFT-based DRX in terms of using time-domain samples. For example, with a probability of false alarm rate of for frequency-bins with TMR = 50 nSec, FMR = 2.4414 KHz, IBW > 1 GHz and ADC rate at 2.56 GHz, AIRS-based DRX detects narrow-band signals at about −42 dB of input signal-to-noise ratio (Input-SNR), and just uses a little less than real-samples. However, FFT-based DRX have to use all samples. Simulation results also show that AIRS-based DRX can detect frequency-modulated continuous wave signals with 0.1, 1, 10 and 100 MHz bandwidths at about −39.4, −35.1, −30.2, and −25.5 dB of Input-SNR using about 264.6 K, 104.7 K, 40.2 K and 18.3 K real-samples, respectively, in frequency-bins for TTFT.

Very Long-Length FFT Using Multi-Resolution Piecewise-Constant Windows for Hardware-Accelerated Time–Frequency Distribution Calculations in an Ultra-Wideband Digital Receiver

“…The phase rotation factor is determined by the frequency block location and the time step in the overall sampling time series. The details on how to program the BFFT method are given in [ 34 , 35 ] and those on how to implement an FPGA can be found in [ 35 ].…”

“…Since there is no window applied in the AIRS method in [ 34 ], the PCW can also be applied there for weak signal detection in a DRX.…”

“…Among these TFD methods, the FFT-based STFT is still the most widely used method in DRX designs, as it can easily leverage the hardware-based FFT to speed up the spectrogram calculations, and the Fourier spectra are often used for weak signal detection applications [ 18 , 33 , 34 ]. However, the main disadvantages of STFT used in emitter signal feature extractions are that (1) the long signals with slowly changing frequencies can be hardly depicted with narrow analysis window spectrograms and (2) the short pulses and signals with rapidly changing instantaneous frequencies can only be poorly localized in the time domain if wide analysis windows are used.…”

“…A window always has the same length as the long frame and hops with the frame.) Moreover, for a DRX with an ultra-wide instantaneous bandwidth, people have to use a very large number of samples in FFT (e.g., , i.e., long frame) to get a fine frequency resolution and achieve high receiver sensitivity [ 33 , 34 ]. The challenge is that such a long-frame FFT still cannot be directly implemented in today’s field programmable gate array (FPGA) for real-time signal detection and analyses in a DRX.…”

“…Taking advantage of the BFFT processing of time samples in sequential time slots, the accumulatively increasing receiver sensitivity (AIRS) method was introduced in [ 34 ] for ultra-wideband DRX designs. Using AIRS, a DRX can not only cumulatively increase the sensitivity but can also achieve super-high receiver sensitivity when more time samples become available from an ADC.…”