Type of Document Master's Thesis Author Aatique, Muhammad Author's Email Address email@example.com URN etd-82597-03345 Title Evaluation of TDOA Techniques for Position Location in CDMA Systems Degree Master of Science Department Electrical Engineering Advisory Committee
Advisor Name Title Woerner, Brian D. Committee Chair Reed, Jeffrey Hugh Committee Member Tranter, William H. Committee Member Keywords
Date of Defense 1997-08-06 Availability unrestricted AbstractThe Federal Communications Commission (FCC) has adopted regulations requiring
wireless communication service providers to provide position location (PL)
information for a user requesting E-911 service. The Time Difference of Arrival
(TDOA) technique is one of the most promising position location techniques for
cellular-type wireless communication systems. The IS-95 Code Division Multiple
Access (CDMA) system is a popular choice for the companies deploying new
cellular and PCS systems in North America. Hence, the feasibility of TDOA
techniques in CDMA systems is an important issue for position location in the
wireless systems of the future.
This thesis analyzes the performance of TDOA techniques in the CDMA systems. A
comparison and assessment of different algorithms for finding the time
difference estimates and for solving the hyperbolic equations generated by
those estimates has been made. This research also considers a measure of
accuracy for TDOA position location method which is shown to be more suitable
for CDMA systems and more closely matches to the FCC requirements. Among the
other contributions is a proposed method to perform cross-correlations to
identify only the desired user's TDOA in a multiuser environment.
This thesis also evaluates the feasibility and accuracy of TDOA techniques
under varying system conditions that might be encountered in real situations.
This includes varying conditions of Additive White Gaussian Noise (AWGN), Multiple
Access Interference (MAI), power control and loading. The effect of the mobile
position and of different arrangement of base stations on TDOA accuracy is also
studied. Performance comparison in AWGN and Rayleigh fading channels is made.
The feasibility of using increased power levels for the 911 user in combination with interference cancellation
is also studied. The effect of using a single stage of parallel interference
cancellation at neighboring cell sites has also been explored. Non-ideal
situations such as imperfect power control in CDMA operation has also been
investigated in the context of position location. This thesis also suggests amethod to correct TDOA estimation errors in CDMA.
It is shown that this improvement can give greatly improved performance even
under worst-case situations. Performance comparison of results with and without
that modification has also been made under various conditions.
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