This study investigates the application potential of the SAGE (space-alternating generalized expectation-maximization) algorithm to jointly estimate the relative delay, incidence azimuth, Doppler frequency, and complex amplitude of impinging waves in mobile radio environments The performance, ie, high-resolution ability, accuracy, and convergence rate of the scheme, is assessed in synthetic and real macro- and pico-cellular channels The results indicate that the scheme overcomes the resolution limitation inherent to classical techniques like the Fourier or beam-forming methods In particular, it is shown that waves which exhibit an arbitrarily small difference in azimuth can be easily separated as long as their delays or Doppler frequencies differ by a fraction of the intrinsic resolution of the measurement equipment Two waves are claimed to be separated when the mean-squared estimation errors (MSEEs) of the estimates of their parameters are close to the corresponding Cramer-Rao lower bounds (CRLBs) derived in a scenario where only a single wave is impinging The adverb easily means that the MSEEs rapidly approach the CLRBs, ie, within less than 20 iteration cycles Convergence of the log-likelihood sequence is achieved after approximately ten iteration cycles when the scheme is applied in real channels In this use, the estimated dominant waves can be related to a scatterer/reflector in the propagation environment The investigations demonstrate that the SAGE algorithm is a powerful high-resolution tool that can be successfully applied for parameter extraction from extensive channel measurement data, especially for the purpose of channel modeling

Channel parameter estimation in mobile radio environments using the SAGE algorithm

This paper presents an overview of ultrawideband (UWB) propagation channels. It first demonstrates how the frequency selectivity of propagation processes causes fundamental differences between UWB channels and "conventional" (narrowband) channels. The concept of pathloss has to be modified, and the well-known WSSUS model is not applicable anymore. The paper also describes deterministic and stochastic models for UWB channels, identifies the key parameters for the description of delay dispersion, attenuation, and directional characterization, and surveys the typical parameter values that have been measured. Measurement techniques and methods for extracting model parameters are also different in UWB channels; for example, the concepts of narrowband channel parameter estimation (e.g., maximum-likelihood estimation) have to be modified. Finally, channel models also have an important impact on the performance evaluation of various UWB systems.

Ultrawideband propagation channels-theory, measurement, and modeling

In recent years, indoor positioning has emerged as a critical function in many end-user applications; including military, civilian, disaster relief and peacekeeping missions. In comparison with outdoor environments, sensing location information in indoor environments requires a higher precision and is a more challenging task in part because various objects reflect and disperse signals. Ultra WideBand (UWB) is an emerging technology in the field of indoor positioning that has shown better performance compared to others. In order to set the stage for this work, we provide a survey of the state-of-the-art technologies in indoor positioning, followed by a detailed comparative analysis of UWB positioning technologies. We also provide an analysis of strengths, weaknesses, opportunities, and threats (SWOT) to analyze the present state of UWB positioning technologies. While SWOT is not a quantitative approach, it helps in assessing the real status and in revealing the potential of UWB positioning to effectively address the indoor positioning problem. Unlike previous studies, this paper presents new taxonomies, reviews some major recent advances, and argues for further exploration by the research community of this challenging problem space.

https://www.mdpi.com/1424-8220/16/5/707/pdf

Ultra Wideband Indoor Positioning Technologies: Analysis and Recent Advances.

Pattern recognition

A simple statistical model of azimuthal and temporal dispersion in mobile radio channels is proposed. The model includes the probability density function (PDF) of the delay and azimuth of the impinging waves as well as their expected power conditioned on the delay and azimuth. The statistical properties are extracted from macrocellular measurements conducted in a variety of urban environments. It is found that in typical urban environments the power azimuth spectrum (PAS) is accurately described by a Laplacian function, while a Gaussian PDF matches the azimuth PDF. Moreover, the power delay spectrum (PDS) and the delay PDF are accurately modeled by an exponential decaying function. In bad urban environments, channel dispersion is better characterized by a multicluster model, where the PAS and PDS are modeled as a sum of Laplacian functions and exponential decaying functions, respectively.

http://www2.elo.utfsm.cl/~ipd465/Papers%20y%20apuntes%20varios/A%20Stochastic%20Model,%20Ped%20Mog%20Fleury.pdf

A stochastic model of the temporal and azimuthal dispersion seen at the base station in outdoor propagation environments

In the last few years, issues concerning the spatial resolution of the received electromagnetic field have attracted a lot of attention in mobile communications. A new method for the high resolution of the electromagnetic field with respect to both the incidence direction and delay is presented. The underlying discrete propagation model relies on the assumption that a finite known number of transverse electromagnetic plane waves characterized by their complex amplitude, propagation delay, and azimuthal incidence direction are impinging in a neighborhood of the receiver position. A space-alternating generalized expectation-maximization (SAGE) algorithm is proposed to replace the high-dimensional optimization procedure necessary to compute the joint maximum-likelihood estimate of the waves parameters by several separate maximization processes which can be performed sequentially. The resolution and the mean convergence rate of the scheme are evaluated by means of Monte-Carlo simulations considering discrete synthetic propagation environments. Finally, the applicability of the SAGE algorithm to real propagation environments is demonstrated.

Wideband angle of arrival estimation using the SAGE algorithm

Multiple-antenna concepts for wireless communication systems promise high spectral efficiencies and improved error rate performance by proper exploitation of the randomness in multipath propagation. In this paper, we investigate the impact of channel uncertainty caused by channel estimation errors on the capacity of Rayleigh and Ricean block-fading channels. We consider a training-based multiple-antenna system that reserves a portion of time to sound the channel. The training symbols are used to estimate the channel state information (CSI) at the receiver by means of an arbitrary linear estimation filter. No CSI is assumed at the transmitter. Our analysis is based on an equivalent system model for training-based multiple-antenna systems which specifies the channel by the estimated (and hence, known) channel coefficients and an uncorrelated, data-dependent, multiplicative noise. This model includes the special cases of perfect CSI and no CSI. We present new upper and lower bounds on the maximum instantaneous mutual information to compute ergodic and outage capacities, and extend previous results to arbitrary (and possibly mismatched) linear channel estimators and to correlated Ricean fading. Several numerical results for single- and multiple-antenna systems with estimated CSI are included as illustration.

Multiple-Antenna Signaling Over Fading Channels With Estimated Channel State Information: Capacity Analysis

We compare channel estimation schemes in the time and frequency domains in terms of the error performance of both the estimated channel impulse response (CIR) and transfer function (TF) as well as the resulting bit-error rate (BER) in an orthogonal frequency-division multiplexing (OFDM) system with a time-multiplexed preamble. If the total number of sub-carriers, K, exceeds the number of taps, L, in the CIR, as is the case in most practical OFDM systems, the TF estimate based on the time domain least squares (LS) scheme is more accurate than the one obtained from direct LS estimation in the frequency domain. An equivalent mean-squared error performance results for the case K=L.

Time versus frequency domain channel estimation for OFDM systems with antenna arrays

We derive power adaptation strategies optimizing the error rates of broadband bit-interleaved coded OFDM systems performing hard-decisions after the demodulation and ideal interleaving. The adaptive subchannel power allocation is based on either perfect or outdated channel state information in a time-division duplex transmission. We find that for an average bit error rate level of 10/sup -6/ a gain of up to 4 dB can be achieved by the proposed adaptation in Rayleigh fading channels.

Dirk Dahlhaus

Papers

Channel parameter estimation in mobile radio environments using the SAGE algorithm

Wideband angle of arrival estimation using the SAGE algorithm

Multiple-Antenna Signaling Over Fading Channels With Estimated Channel State Information: Capacity Analysis

Time versus frequency domain channel estimation for OFDM systems with antenna arrays

Optimal power adaptation for OFDM systems with ideal bit-interleaving and hard-decision decoding