Galileo/GPS Receiver Fixed-Point Implementation using Conventional and Differential Correlation

摘要

Highly integrated semiconductor solutions for GPS receivers are becoming increasingly important for cellular telephones in order to satisfy the E-911 mandate and the requirements for location based services. Low costs is the most important requirement for successful integrations of GNSS receivers into mobile phones. The cost of microchips can be reduced by shrinking the silicon area, which can be accomplished by optimal choice of the quantization resolutions of the digital baseband section. Since single-shot positioning receivers often host the equivalent of several thousand correlators, the benefit of reducing the bit sizes, is substantial. Another important requirement for single-shot positioning receivers is an enhanced reception sensitivity, which allows moderate indoor operation. Differentially-coherent integration can achieve a sensitivity a gain in the order of 1.5dB over conventional noncoherent integration. This paper therefore compares a fixed-point implementation for GPS and Galileo reception using differential correlation versus noncoherent integration. The quantization loss of each stage is derived in order to allow a good trade-off between the silicon area and the quantization loss. These theoretical derivations are confirmed by the corresponding simulations. A low-pass equivalent model of an RF front-end that allows a combined reception of GPS and Galileo signals is also included. The model accounts for the relevant linear and nonlinear implementation impairments as encountered in integrated CMOS implementation.