A design for the monobit-receiver applicationspecific integrated circuit (ASIC) will be described. The monobit receiver is a wide-band (1-GHz) digital receiver designed for electronic-warfare applications. The receiver can process two simultaneous signals and has the potential for fabrication on a single multichip module (MCM). The receiver consists of three major elements: a nonlinear RF front end, a signal sampler and formatting system (analog-to-digital converter (ADC) and demultiplexers), and a patented "monobit" algorithm implemented as an ASIC for signal detection and frequency measurement. The receiver's front end, ADC, and algorithm experimental performance results were previously presented [1]. The receiver uses a 2-b ADC operating at 2.5 GHz whose outputs are collected and formatted by demultiplexers for presentation to the ASIC. The ASIC has two basic functions: to perform a fast Fourier transform (FFT) and to determine the number of signals and report their frequencies. The ASIC design contains five stages: the input, the FFT, the initial sort, the squaring and addition, and the final sort. The chip will process the ADC outputs in real time, reporting detected signal frequencies every 102.4 ns.Index Terms-Analog-to-digital converter (ADC), fast Fourier transform (FFT), instantaneous frequency measurement (IFM) receivers.

This paper discusses the approaches of software GPS receiver. First, the definition of a software receiver, its difference from a conventional receiver, and the data collection hardware employed is presented. Then the acquisition and tracking algorithm is discussed. The transition from acquisition to tracking for a real time operation is presented. The navigation data decoding, the calculation of satellite position, and user position are discussed briefly. Finally, the advantages of a software receiver is presented.

Abstract---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.

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