Date of Award

1-1-2012

Document Type

Campus Access Dissertation

Department

Electrical Engineering

First Advisor

Yinchao Chen

Abstract

The co-existence of Global Positioning System services (GPS) with cellular, other services and features in mobile handset, presents challenges to GPS performance. Particularly challenging is the over-the-air (OTA) interface to the GPS receiver that results from carriers like the Global System for Mobile (GSM) and Wideband Code Division Multiple Access (WCDMA), where the transmit (TX) section of the latter can interfere with the performance of the GPS due to TX band noise injected into the GPS band. For the case of WCDMA, the problem is out-of-band interference due to its TX wide band noise, which has a spectrum that overlaps the GPS spectrum; both use spread spectrum technology to encode the data.

Unlike WCDMA, GSM is built on the Time Division Multiple Access (TDMA) technology, where a user occupies one of eight time slots in the multiple access domains. In addition, in WCDMA, the transmission is continuous while in GSM the transmission is pulsed and hence the GPS has to cope with the systems and suffer the degradation due to the pulsed interference in the form of the TX noise. The analysis of the WCDMA and GSM TX noise (based on actual hardware scenarios) and their effects on GPS sensitivity will be introduced in this dissertation. In addition, fundamental line up characterization will be carried out, e.g., the lineup noise figure, insertion and mismatch losses.

This research is to make a cross functional effort between the RF and digital signal processing. Its novelty comes from the fact that rarely published literature is available for mitigating 3G interference to GPS performance in mobile handsets once the interference takes place. It starts with devising the architectural analysis and equations for the 3G TX and GPS RX system along with a novel measurement setup to measure the degradation. The degradation will be in the form of an increase in the total system noise figure (~5.5dB). The total system noise figure will contribute a dB for dB in sensitivity degradation, i.e., ~5.5dB loss in the received signal strength. Loss in the received signal power leads to loss of reliable and accurate service and, most importantly, loss of service in areas where it is needed most. Specifically, the main goal of this work is to use a digital signal processing algorithm to solve an issue that is originated in the RF section of a GPS receiver. Early results show that the 3G interference causes a "de-correlation" with the satellite's locally generated codes. This "de-correlation" is in the form of losing acquisition to the phase/frequency of the carrier signal of the satellite. Detection algorithm and recovery mechanisms were developed in this research to mitigate and offset the effect of the 3G interference.

Share

COinS