James B. Y. Tsui

FPGA Frequency Domain Based GPS Coarse Acquisition Processor Using FFT

In this paper we describe the use of the FFT on an FPGA to perform lock on coarse acquisition (C/A) code and carrier frequency in a global positioning system (GPS) receiver. A novel technique of sub-sampling is used in this system to obtain data block sizes that match hardware limitations. The system uses 10 ms of data to perform the lock with 6 ms of processing time and theoretically can operate on signals 20 db below the noise floor

Digital wideband phased array calibration and beamforming using time reversal technique

A 16-channel digital wideband phased array without antenna is characterized using impulse response measurement. A chirp signal is used as probing signal. By careful chirp design, impulse response at sub-band is measured for all the channels. Spectral domain response showing dispersive phase and magnitude reveals significant imbalance among the channels. Based on time reversal technique principle, spectrum-modified time reversal impulse response is calculated. This time reversal response is applied to the chirp probing signal to verify the bandpass characteristics of the sub-band, and the waveform coherent waveform. It is also applied to the CW pilot tone to verify digital beamforming gain.

Wideband signal detection by employing differential sampling rates

A wideband electronic warfare digital receiver design is proposed. The design utilizes the frame-based FFT algorithm commonly implemented in traditional electronic warfare (EW) encoder design [1]. The frequency coverage in traditional digital receiver designs is limited to a single Nyquist zone due to the desire to eliminate aliasing effects from multiple Nyquist zones that generate frequency ambiguities. The proposed design is based on a two-channel structure that allows M Nyquist

Frequency calibration of A/D converter in software GPS receivers

This paper presents a software-based method to calibrate analog-to-digital converter (ADC) sampling frequency in a software GPS receiver. Two front-end systems of a GPS software receiver were used in this study. The sampling frequencies of the ADC were found deviated from the nominal values provided by the manufacturers. Software algorithm was developed to calibrate the sampling frequencies. The algorithm is based on the initial-code-phase velocity and the carrier-phase velocity of the GPS signals at L1 frequency obtained by software receiver measurements. Allan variance analysis of this frequency characterization method is also included in this study