Accurate location service for 3G cellular networks

Advances in wireless and positioning technologies have given rise to Location Based Services (LBSs) that provide information with geographic relevance. Improvement in the quality of LBSs can be achieved through an increase in the accessibility of the corresponding positioning technology. This increase is achieved though improvements in the coverage and accuracy of the positioning technology. The inherent qualities of the Global Positioning System (GPS) and its broad range of applications and accuracies make it a clear choice for providing the basis of the positioning technology for LBSs. A highly accurate and advanced implementation of the GPS technology that is not currently utilised with LBSs is the Virtual Reference Station (VRS) network concept. The VRS network concept utilises differential GPS techniques to approximate and remove systematic errors within the positioning fix of a GPS rover station and results in centimetre-level accuracies. Specifically, the VRS network simulates a GPS reference station in close proximity to a GPS rover station whereby positioning corrections are derived and transmitted to the GPS rover station. The VRS however suffers from a number of limitations that hamper its use with LBSs. These limitations are bi-directional communications, high costs and limited coverage. The requirement for bi-directional communications is a critical disadvantage of VRS. The high costs and coverage limitations are largely due to the types of communications technologies that are employed with VRS (i.e. UHF, GSM and GPRS). These limitations can be reduced through application of the Virtual Reference Cell (VRC) concept within the VRS system. However, this VRC implementation shows significantly reduced location accuracy. This thesis proposes utlilising abovementioned limitations of VRS, whilst retaining Real Time Kinematic (RTK) level accuracy. The outcome is a positioning technology with RTK level accuracy dedicated to LBSs for WCDMA user equipment. Here VRS corrections are computed for fixed WCDMA cellular regions that are managed by WCDMA base stations (Node Bs). These corrections are broadcast to UE that are attached to the GPS rover stations. This proposed technology is known as the RTK-VRC system. Field experiments were performed as part of this research to investigate the degradation in positioning accuracy for VRS baselines of up to 2 km. These experiments were necessary to validate the use of WCDMA cellular regions that have a coverage radius of up 2 km. The results from these experiments clearly show that VRS-level accuracy is achievable for baselines of up to 2 km. The thesis also proposes the design of a novel broadcast channel that utilises the WCDMA pilot channel to provide a dedicated communications link for VRS corrections from Node Bs to UE. This novel channel is known as the Common Pilot Broadcast Channel (CPBCH). CPBCH utilises varying Quasi-Orthogonal Sequences (QOSs) for the channelisation process to transfer data over the existing pilot channel. This is achieved while maintaining the functionality of the pilot channel. The implementation of CPBCH will however require modifications to the WCDMA protocol architecture. Matlab simulations were performed to compare the performance of the pilot channel with and without CPBCH implementation. Analysis of the results from the simulations indicates that CPBCH implementation will have no impact on the functionality of the pilot channel for normal conditions. However, for low signal-to-noise ratios (SNRs) the channel estimation process is degraded. The main conclusions from this research are that the RTK-VRC concept together with the CPBCH is capable of providing a ten-fold improvement in the positioning accuracy for LBSs. This is however at the expense of higher and more complex processing. The preliminary design results are extremely promising and warrant the further research and development of the proposed concept.