Mobile Fading Environment Research Articles

An Experimental Analysis of Cyclic and Reference Signals of 4G LTE for TOA Estimation and Positioning in Mobile Fading Environments

By design, the 4G LTE signals contain a few patterns that repeat in time and frequency (e.g., various reference signals and the cyclic prefix) to facilitate timing synchronization, frequency error estimation, and channel equalization. For communications, these signal components are considered “overhead” serving the purpose of extracting information-carrying symbols for data decoding. When used as signals of opportunity for navigation, they provide times of arrival (TOA), and changes in TOA estimates can be related to the receiver displacement. Indeed, successful use of LTE signals has been reported for ground vehicles, airborne platforms, and indoor positioning in the literature. Even though LTE signals are well specified in the 3GPP standards, some aspects are left to operators as implementation options that depend on the actual deployment environment and local traffic conditions. To better understand the practical aspects of in-the-air LTE signals, experiments were carried out and an initial study of the cyclic and reference patterns in LTE signals for TOA estimation is presented in this article and in particular the effect of antenna ports on TOA estimation. This article aims at providing essential and insightful information directly useable for developing TOA estimation algorithms and ultimately for navigation with LTE signals.

Performance of adaptive array antennas in mobile fading environment

A performance comparison between uniformly and non-uniformly spaced adaptive array antennas in a mobile fading environment is presented. Here, deterministic and simulation models of the frequency-non-selective mobile fading channels are investigated and used to explain the behaviour of steered beam adaptive arrays in terms of the output signal-to-interference-plus-noise ratio and pointing accuracy. It is found that the non-uniformly spaced arrays give a performance improvement of >25% in comparison with the uniformly spaced arrays.

Characterization of Polarization Diversity at the Mobile

Two new models used to characterize polarization diversity at the mobile are presented and discussed. The first model is built upon existing theoretical models at a base station to demonstrate how those principles apply to the mobile fading environment. Due to limitations of antennas at the mobile, this extended model, although relevant, is not sufficient to characterize polarization diversity of the antennas; therefore, this paper moves on to show how a new approach to polarization diversity at the mobile exists as an inherent feature within an angular diversity system. Results show that, for two polarizations in a fading environment, the best overall output occurs with a plusmn45deg element configuration, although the diversity combiner itself has optimum performance with a plusmn67.5deg configuration due to lower correlation at the input. The second model is also used to demonstrate how differently polarized dipoles are using polarization diversity inherent within an angular diversity system.

Tracking performance of the RLS algorithm applied to an antenna array in a realistic fading environment

In this paper, frequency domain techniques are used to derive the tracking properties of the recursive least squares (RLS) algorithm applied to an adaptive antenna array in a mobile fading environment, expanding the use of such frequency domain approaches for nonstationary RLS tracking to the interference canceling problem that characterizes the use of antenna arrays in mobile wireless communications. The analysis focuses on the effect of the exponential weighting of the correlation estimation filter and its effect on the estimations of the time variant autocorrelation matrix and cross-correlation vector. Specifically, the case of a flat Rayleigh fading desired signal applied to an array in the presence of static interferers is considered with an AR2 fading process approximating the Jakes' fading model. The result is a mean square error (MSE) performance metric parameterized by the fading bandwidth and the RLS exponential weighting factor, allowing optimal parameter selection. The analytic results are verified and demonstrated with a simulation example.

Decision feedback postprocessor for zero-crossing digital FM demodulator

A baseband digital narrow-band FM receiver, called zero-intermediate frequency zero-crossing demodulator (ZIFZCD), has been developed. This demodulator may offer low complexity and simple implementation. However, the bit error rate (BER) performance of the ZIFZCD is inferior to that of the limiter-discriminator-integrate-and-dump (LDI) demodulator. In this paper, a simple decision feedback postprocessor (DFP) is proposed to improve the performance of the ZIFZCD. Analysis and simulation BER results of the ZIFZCD with the DFP are presented for minimum-shift keying (MSK) and Gaussian MSK (GMSK) signals under additive white Gaussian noise (AWGN) and mobile fading environments.

A Novel Anti-Multipath Modulation Technique DSK

This paper describes a new modulation technique called DSK (double phase-shift keying) which shows an interesting antimultipath feature over mobile frequency-selective fading environments. The effect of this technique is shown for various multipath channels by detection waveform and theoretical bit error rate (BER) analyses. A result obtained from a laboratory test is also presented. In the latter part of the paper, a generalized form of DSK is described and extensive investigations are made so as to clarify the anti-multipath effect of DSK in view of the diversity concept and to further explore the possibility of a narrowband scheme. A major result shows that this technique can give a kind of diversity effect which is implicit in the arrival of signals via multiple paths with different delays.