Abstract
This paper presents a joint time-delay and channel estimator to assess the achievable positioning performance of the Long Term Evolution (LTE) system in multipath channels. LTE is a promising technology for localization in urban and indoor scenarios, but its performance is degraded due to the effect of multipath. In those challenging environments, LTE pilot signals are of special interest because they can be used to estimate the multipath channel and counteract its effect. For this purpose, a channel estimation model based on equi-spaced taps is combined with the time-delay estimation, leading to a low-complexity estimator. This model is enhanced with a novel channel parameterization able to characterize close-in multipath, by introducing an arbitrary tap with variable position between the first two equi-spaced taps. This new hybrid approach is adopted in the joint maximum likelihood (JML) time-delay estimator to improve the ranging performance in the presence of short-delay multipath. The JML estimator is then compared with the conventional correlation-based estimator in usual LTE conditions. These conditions are characterized by the extended typical urban (ETU) multipath channel model, additive white Gaussian noise (AWGN) and LTE signal bandwidths equal to 1.4, 5 and 10 MHz. The resulting time-delay estimation performance is assessed by computing the cumulative density function (CDF) of the errors in the absence of noise and the root-mean-square error (RMSE) and bias for signal-to-noise ratio (SNR) values between −20 and 30 dB.
Highlights
Navigation and positioning technologies are every day more important in civil applications, demanding enhancements on accuracy, availability and reliability
6 Conclusions A new technique for joint time-delay and channel estimation is presented in this paper to improve the ranging performance in channels with close-in multipath
The proposed algorithm is a joint maximum likelihood (JML) time-delay and channel estimator based on a new hybrid channel estimation model, defined by equi-spaced or periodic taps and an arbitrary tap between the first two
Summary
Navigation and positioning technologies are every day more important in civil applications, demanding enhancements on accuracy, availability and reliability. There are still some contributions that propose the joint maximum likelihood (JML) estimation of the time delay and channel response in OFDM systems, considering a model based on equi-spaced or periodic taps, but few of them deal with the specific case of ranging applications. Multipath appears close to the line-on-sight ray in urban and indoor environments, producing a critical degradation in ranging applications This multipath, which is ignored in communications, significantly affects the performance of the periodic-tap estimation model for lowsampling rates, because short-delay multipath may not be properly modelled between samples. Approach, is studied in this paper and used to assess the achievable positioning performance of LTE, considering a low-complexity time-delay estimation that exploits the structure of the LTE OFDM signals This estimation is analyzed for usual working conditions, represented by typical LTE signal bandwidths with the ETU standard channel model. The ETU model defines a harsh environment, where the performance of the conventional estimator is relatively poor
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