Novel Hilbert Transformer Design Method for Simplified Signal Processing in Navigational Software Radio Receivers

A.J.R.M. Ton Coenen

Abstract:	The paper shows how novel insights from the Telecommunication research can be applied to improve navigational receiver designs. In designing software radio (SWR) receivers for mobile Telecom use as well as for Navigational use (e.g. GPS), the key problem is to remove all redundancy from sampled signals in the earliest stage without affecting the information content. In practice, this boils down to the question of how to apply efficient sample-rate reduction without any signal-quality loss. Here, the addition of a single digital “Hilbert Transformer pair” (HTP) has the potential to enable phase-error-free decimation in current quadrature-bandpass-sampling systems for direct baseband conversion in order to reduce the computational burden. The HTP is also known as a complex half-band (CHB) filter and should be positioned (in our proposed application) between the analog-to- digital-converter (ADC) and the IQ-mixers (IQ: In- phase/Quadrature). The paper depicts how a generalized Fractional-Delay- (FD) filter-design method, that has been patented by Delft University, can be applied successfully to design the required efficient CHB-filters of the best feasible quality. Viz. 1) Flat frequency responses and final perfect phase-linearity to guarantee an exact 90-degrees IQ-phase-shift (in only two possible options) even after quantization of the relatively few CHB-filter coefficients. 2) Avoidance of interference caused by conventional popular decimating quadrature- bandpass-sampling systems. 3) The use of as few as possible multiplier operations for high-speed digital signal processing in (navigational) software radio (SR) applications (e.g., GPS, LORAN-C, EUROFIX). Since one half of an ideal CHB-filter spectrum is inherently empty, the usually required suppression of the upper-band frequencies after IQ-mixing to perform down-conversion will become fully superfluous. In the case of an L-channel SR receiver (e.g. GPS, L¡Ý12), either no traditional amount of twice-L IQ-lowpass-filters is required anymore or filter requirements are drastically relieved.
Published in:	Proceedings of the 13th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2000) September 19 - 22, 2000 Salt Palace Convention Center Salt Lake City, UT
Pages:	835 - 843
Cite this article:	Coenen, A.J.R.M. Ton, "Novel Hilbert Transformer Design Method for Simplified Signal Processing in Navigational Software Radio Receivers," Proceedings of the 13th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2000), Salt Lake City, UT, September 2000, pp. 835-843.
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