Data Fusion For Improved TOA/TDOA Position Determination in Wireless Systems


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Virginia Tech


The Federal Communications Commission (FCC) that regulates all wireless communication service providers has issued modified regulations that all service providers must select a method for providing position location (PL) information of a user, requesting for E-911 service, by October 2000. The wireless 911 rules adopted by the FCC are aimed both for improving the reliability of the wireless 911 services and for providing the enhanced features generally available for wireline calls. From the service providers' perspective, effective position location technologies must be utilized to meet the FCC rules. The Time-of-Arrival (TOA) and the Time-Difference-of-Arrival (TDOA) methods are the technology that can provide accurate PL information without necessitating excessive hardware or software changes to the existing cellular/PCS infrastructure.

The TOA method works well when the mobile station (MS) is located close to the controlling base station. With certain corrections applied, the TOA method can perform reliably even in the presence of Non-Line-of-Sight (NLOS) condition. The TDOA method performs better when the MS is located at a significant distance from the controlling base station. However, under the NLOS environmental condition, the performance of the TDOA method degenerates significantly. The fusion of TOA and the TDOA method exhibits certain advantages that are not evident when only one of the methods is applied.

This thesis investigates the performance of data fusion techniques for a PL system, that are able to merge independent estimates obtained from TOA and TDOA measurements. A channel model is formulated for evaluating PL techniques within a NLOS cellular environment. It is shown that NLOS propagation can introduce a bias into TDOA measurements. A correction method is proposed for removing this bias and new corrected data fusion techniques are compared with previous techniques using simulation method, yielding favorable results.



NLOS, Data Fusion Architecture, TDOA, Position location, TOA