Abstract
In recent years, more and more wireless communications systems are required to provide also a positioning measurement. In code division multiple access (CDMA) communication systems, the positioning accuracy is significantly degraded by the multiple access interference (MAI) caused by other users in the system. This MAI is commonly managed by a power control mechanism, and yet, MAI has a major effect on positioning accuracy. Probability control is a recently introduced interference management mechanism. In this mechanism, a user with excess power chooses not to transmit some of its symbols. The information in the nontransmitted symbols is recovered by an error-correcting code (ECC), while all other users receive a more reliable data during these quiet periods. Previous research had shown that the implementation of a probability control mechanism can significantly reduce the MAI. In this paper, we show that probability control also improves the positioning accuracy. We focus on time-of-arrival (TOA) based positioning systems. We analyze the TOA estimation performance in a generalized CDMA system, in which the probability control mechanism is employed, where the transmitted signal is noncontinuous with a symbol transmission probability smaller than 1. The accuracy of the TOA estimation is determined using appropriate modifications of the Cramer-Rao bound on the delay estimation. Keeping the average transmission power constant, we show that the TOA accuracy of each user does not depend on its transmission probability, while being a nondecreasing function of the transmission probability of any other user. Therefore, a generalized, noncontinuous CDMA system with a probability control mechanism can always achieve better positioning performance, for all users in the network, than a conventional, continuous, CDMA system.
Highlights
In recent years, more and more wireless communications systems are required to provide a positioning measurement of their mobile users
We focus on timeof-arrival (TOA) positioning techniques for code division multiple access (CDMA) systems
We focused on positioning using TOA and used the asymptotic Cramer-Rao bound for time-delay estimation as the performance measure
Summary
More and more wireless communications systems are required to provide a positioning measurement of their mobile users. One of the main factors that limit the accuracy of TOA estimation in such communication systems is the multiple access interference (MAI). Our derivation will follow the general lines of Botteron et al [13], which derived bounds on the positioning accuracy in asynchronous CDMA systems with known transmitted data. Following [13], we perform an asymptotic analysis (for large observation interval) to produce an asymptotic bound that does not depend on the transmitted data sequences, but only on the data statistics We use this novel bound to show that the TOA estimation mean square error (MSE) for each user does not depend on its transmission probability, while it is a nondecreasing function of the transmission probability of any other user.
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