A low complexity DSP driven analog impairment mitigation scheme for Low-IF GNSS receivers

Abstract

Due to the increasing demands for location based services within the wireless mass-market; there has been relentless pressure to reduce both the chip area and power dissipation of the user terminal. Low-IF receivers combine the advantages of superheterodyne and direct-conversion architectures offering a highly integrated solution while avoiding the issues associated with DC offsets and flicker noise. The main drawback of the low-IF architecture is its limited image rejection due to analog impairments. In this paper, the sources of the impairments are analyzed for a low-IF receiver operating at the GPS/Galileo L1 band together with a novel low-complexity solution to compensate for them in the DSP domain is proposed. For processing the combined GPS/Galileo L1 signal, a signal simulator we call GNSScope has been developed together with a low-IF receiver model to analyze the influence of the analog impairments. The idea behind our proposed novel adaptive compensator which estimates and compensates for the imbalances and mismatches is that in the absence of these mismatches no correlation exists between the desired and the image channels, which is not the case when impairments are present. Results show that through the deployment of the proposed approach, image-rejection performance can be enhanced by 75 dB. This enhancement in the image-rejection performance subsequently results in relaxed analog front-end specifications leading to high levels of integration making it possible for highly integrated software-defined Global Navigation Satellite Systems (GNSS) receiver to be realistically and economically designed and implemented.