[Paper Review] Harnessing NLOS Components for Position and Orientation Estimation in 5G mmWave MIMO

Rico Mendrzik, Henk Wymeersch+2 more|arXiv (Cornell University)|Dec 5, 2017

Indoor and Outdoor Localization Technologies35 references3 citations

TL;DR

This paper proposes leveraging non-line-of-sight (NLOS) multipath components in 5G mmWave MIMO systems for enhanced position and orientation estimation. Using Fisher information theory, it demonstrates that high temporal and spatial resolution enables NLOS components to consistently improve localization accuracy, with information gain dependent on reflector geometry and beamwidth.

ABSTRACT

In the past, NLOS propagation was shown to be a source of distortion for radio-based positioning systems. Every NLOS component was perceived as a perturbation which resulted from the lack of temporal and spatial resolution of previous cellular systems. Even though 5G is not yet standardized, a strong proposal, which has the potential to overcome the problem of limited temporal and spatial resolution, is the massive MIMO millimeter wave technology. Based on this proposal, we reconsider the role of NLOS components for 5G position and orientation estimation purposes. Our analysis is based on the concept of Fisher information. We show that, for sufficiently high temporal and spatial resolution, NLOS components always provide position and orientation information which consequently increases position and orientation estimation accuracy. We show that the information gain of NLOS components depends on the actual location of the reflector or scatter. Our numerical examples suggest that NLOS components are most informative about the position and orientation of a mobile terminal when corresponding reflectors or scatterers are illuminated with narrow beams.

Motivation & Objective

• To re-evaluate the role of NLOS components in 5G mmWave MIMO, traditionally seen as distortions, by assessing their potential for positioning.
• To investigate whether high temporal and spatial resolution in mmWave MIMO enables the extraction of useful information from NLOS components.
• To quantify the contribution of NLOS components to position and orientation estimation accuracy using Fisher information theory.
• To analyze how the geometry of reflectors and beamwidth affects the information gain from NLOS components.

Proposed method

• The authors employ Fisher information matrix (FIM) analysis to model the information content of NLOS components in mmWave MIMO systems.
• They derive the Fisher information contribution of each NLOS component using channel parameters such as angle of departure, delay, and power.
• A rank-one matrix representation is used to model the information contribution of each NLOS path, with eigenvalue analysis determining the dominant information-bearing direction.
• The key equation (39) expresses the total information gain from NLOS components as a function of geometric and signal parameters.
• The analysis accounts for beamforming directivity at both transmitter and receiver via angular variance terms in the Fisher information components.
• The eigenvector corresponding to the non-zero eigenvalue of the NLOS information matrix identifies the dominant direction of position/orientation sensitivity.

Experimental results

Research questions

• RQ1 Can NLOS components in 5G mmWave MIMO provide useful information for position and orientation estimation under high temporal and spatial resolution?
• RQ2 How does the geometry of a reflector (e.g., distance and angle) affect the information content of an NLOS component?
• RQ3 What is the role of beamwidth and directivity in maximizing the information extracted from NLOS components?
• RQ4 How does the Fisher information from NLOS components compare to that from LOS components in terms of localization accuracy?
• RQ5 Under what conditions does the NLOS component contribute more information than the LOS component?

Key findings

• NLOS components always contribute to position and orientation estimation when temporal and spatial resolution are sufficiently high, contrary to traditional assumptions.
• The information gain from NLOS components is maximized when reflectors are illuminated with narrow beams, enhancing angular resolution.
• The Fisher information contribution of each NLOS component is determined by a rank-one matrix with a single non-zero eigenvalue, given by equation (63).
• The dominant direction of position and orientation sensitivity is captured by the eigenvector in equation (64), which depends on the angle of arrival and path loss.
• The total information gain from NLOS components is proportional to the product of signal power, beam directivity, and geometric range terms.
• Numerical results suggest that NLOS components can significantly improve estimation accuracy, especially in dense urban or indoor environments with rich scattering.